JPS58117578A - Photosensitive drum - Google Patents

Abstract

PURPOSE:To improve the adaptability and perform vapor condensation preventing and dehumidifying operations, which follow up the variance of the uniformly heated ambient temperature of a photosensitive drum, to prevent the image unevenness, by providing a heating body including a positive characteristic thermistor in the photosensitive drum. CONSTITUTION:A heating body 9 is provided in a drum 8. The heating body 9 consists of a heat conductive material 10, a positive characteristic thermistor 11, and a nichrome heater 12. Almost all of the heat generated in the heating body 9 is used for heating of the drum 8, and the heat utility is improved considerably. The heat conductive material 10 is provided with arc-shaped parts 14 and 15; and since these arc-shaped parts 14 and 15 face most of the inside face of the drum 8, the heat is transmitted from the heat conductive material 10 to the drum 8 throughout all of the surface of the inside face of the drum 8. Air heated in the heating body 10 is charged from a gap G2 into a gap G1 and is brought into contact with the inside face of the drum 8 to heat it.

Description

[Detailed description of the invention] The present invention relates to a photosensitive drum for a copying machine.

The photosensitive drum of a copying machine generally has a structure in which a photoconductor material such as selenium is coated on the surface of a base drum made of aluminum or the like to form a photosensitive layer. It is involved in all copying processes such as transfer, and plays an important role that can be called the heart of the copying machine.

FIGS. 1 to 3 are diagrams showing models of each copying process of charging, exposure, and development. First, as shown in FIG. 1, while rotating the photoreceptor drum l as shown by the arrow a, a discharge wire 3 in the charging electrode 2 provided above the drum l is connected to the discharge wire 3.
When a high voltage of about 00 V is applied, the air near the discharge wire 3 is ionized and becomes electrically charged ions, which are applied to the surface of the photosensitive layer 5 coated on the base drum 41 of the photosensitive drum l. (+) ions are attached, and correspondingly (-) ions are generated on the shite bass drum 4.

This is the charging process.

The photosensitive layer 5 functions as an insulating layer unless exposed to light, but
When exposed to light, the exposed area becomes conductive, and as shown in Figure 2, the (+) ions and (-) ions generated on both sides of the photosensitive layer 5 neutralize each other and the charge disappears. do. Therefore, when the pattern of the original to be copied is projected onto the photosensitive layer 5 as light shading through the optical system of the copying machine, an electrostatic latent image corresponding to the pattern of letters and figures of the original is created on the photosensitive layer 5. is formed.

Next, as shown in FIG. 3, toner having a negative weight (-) opposite to the positive (+) ions on the photosensitive layer 5 is deposited by one step such as a magnetic brush method, thereby creating an electrostatic latent image. Develop. Thereafter, a copy image is obtained by going through the process of transfer and heat fixing (9).

If water droplets are attached, even if the photoreceptor drum 1 is charged, (+) ions will not reach the area where the water droplets are attached, and even if they do, they will disappear in a short time. This may cause unevenness in the copied image.

Further, when the humidity of the atmosphere around the photoreceptor drum 1 is high, after the photoreceptor drum 1 is charged, (+) ions attached to the surface of the photoreceptor drum 1 are absorbed by the moisture. This may cause similar image unevenness to occur. Therefore, measures have been taken to heat the photoreceptor drum l to a temperature slightly higher than the ambient temperature to prevent image unevenness due to dew condensation or humidity.

However, when heating the photoreceptor drum l for the above-mentioned purpose, conventionally the photoreceptor drum l is heated as shown in FIG.
A heating element 6 made of a nichrome heating element, a sheathed heater, or the like is disposed outside the drum, and the heating element 6 heats the photoreceptor drum 1 from the outside. However, in such a structure, of the heat generated in the heating element 6, only one surface facing the photoreceptor drum 1 contributes to the heating of the photoreceptor drum 1, and the heat generated on the other surface is The heat generated is wasted, and the efficiency of heat utilization is poor. Further, it takes time for heat to be conducted from the heating element 6 to the photoreceptor drum l. For this reason,
After turning on the power switch of the heating element 6, it took a long time to start up until copying became possible, and there was a drawback that it lacked quick response. Furthermore, since there is a temperature difference of 71 between the lower part of the photoreceptor drum 1 where the heating element 6 is opposed and the upper part where the heating element 6 is not located, the dehumidification effect on the photoreceptor drum l becomes uneven. There was also a drawback.

As another conventional example, as shown in FIG. 5, a heating element 6 such as a nichrome heating element or a sheathed heater is arranged in the center of the inner diameter of the photosensitive drum 1.

However, in the case of this conventional example, since the heating element 6 is rod-shaped, the distance between the heating element 6 and the base drum of the photoreceptor drum l becomes hot, and the heating element 6 is connected to the photoreceptor drum 1. The disadvantage is that the heat conduction time is long and the response time is poor.

Furthermore, in the conventional devices shown in FIGS. 4 and 5, for example, as shown in FIG. 5, a temperature controller 7 made of a thermostat or the like is connected in series with the heating element 6 to adjust the temperature. . However, this type of temperature controller 7 operates with a preset constant temperature as the target value regardless of fluctuations in the ambient temperature, so when the outside temperature becomes high, etc. It became difficult to maintain a temperature difference, and it was often impossible to dehumidify or prevent condensation. Moreover, since the temperature control is on/off control using a thermostat, temperature fluctuations are unavoidable, the number of parts is large, which is disadvantageous for miniaturization, and the on/off control is performed using contacts, making it reliable. There were also drawbacks, such as a lack of sexuality.

The present invention eliminates the above-mentioned conventional drawbacks, has high heat conduction efficiency from the heating element to the drum, is highly responsive, enables uniform heating of the drum, and can follow fluctuations in ambient temperature to prevent condensation. It is an object of the present invention to provide a highly reliable photoreceptor drum that performs a dehumidifying operation and prevents the occurrence of image unevenness.

1. In order to achieve objective 11, the photosensitive drum 1 according to the invention
, is characterized by a heating element containing a positive temperature coefficient thermistor inside the drum.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings, which are examples.

6 is a front sectional view of the photosensitive drum according to the present invention, FIG. 7 is a sectional view taken along the line B1--B1 in FIG. 6, and FIG. 8 is a sectional view taken along the line B2--B2 in FIG. 6. In the figure, 8 is a drum constituting the photoreceptor drum, and the first
As explained in FIGS. 3 to 3, the structure is such that the outer surface of the base drum made of aluminum or the like is coated with a photosensitive layer made of selenium or the like.

9 is a heating element provided inside the drum 8. The heating element 9 includes a heat transfer element 10, a positive temperature coefficient thermistor 11, and a nichrome heater 12.

The heat transfer body 10 is constructed using a metal material with good thermal conductivity, such as aluminum. In this example,
The heat transfer body 10 has 1 part 11 part 13 in the center part, 2 parts,
The IF characteristic thermistor 11 is attached to the flat part 13, and arcuate parts 14.15 having a slightly smaller diameter curvature than the inner diameter curvature of the drum 8 are connected on both sides of the flat part 13,
It is arranged inside the drum 8 so that a gap Gl is formed between the arcuate portion 14.15 and the inner diameter surface of the drum 8. The dimension of the gap Gl is l-10m
It is desirable to set it to m, preferably around 2 mm.

Further, a heat transfer body 1 is provided between both ends of the arcuate portion 14.15.
A gap G2 is provided to allow the inside and outside of the 0 to communicate with each other.

When installing the positive temperature coefficient thermistor 11, a heat-resistant insulating sheet 16 made of polyester sheet, silicone sheet, mica, or polyimide is interposed between the surface of the flat part 13 and the positive temperature coefficient thermistor. The thermistor is closely fixed by a connecting member 17 such as a screw. Further, the nichrome heater 12 is attached along the inner diameter surface of the arcuate portion 14.15.

1. As mentioned above, when the heating element 9 is provided inside the drum 8, most of the heat generated in the heating element 9 can be used for heating the drum 1.8, so it is more efficient than the conventional one. As a result, heat utilization efficiency is significantly improved.

Moreover, as shown in the embodiment, the heat transfer body IO is provided with an arcuate portion 14.15, and this arcuate portion 14.15 is connected to the drum 8.
Since the inner diameter surface of the drum 8 is opposed to most of the inner diameter surface of the drum 8, heat conduction from the heat transfer body 10 to the drum 8 is carried out over substantially the entire inner diameter surface of the drum 8. Therefore, the drum 8 is heated very quickly, and a photosensitive drum with excellent responsiveness is realized.

Furthermore, since a gap G2 is provided between both ends of the arcuate portions 14 and 15, the air heated inside the heat transfer body 10 passes through this gap G2 and enters the gap G1, so that the air reaches the inner diameter surface of the drum 8. It will heat up when you touch it. For this reason, drum 8
can be heated evenly and efficiently. Moreover, when there is the gap G2 as described above, the heat transfer body 10 becomes elastic, so that the heat transfer body 10 can be easily assembled into the drum 8.

Furthermore, since the heat generating portion of the heat generating element 9 includes the positive temperature coefficient thermistor 11, the following effects can be obtained.

(a) The positive temperature coefficient thermistor 11 is made of barium titanate-based semiconductor porcelain having a positive temperature coefficient of resistance, and any heat generation temperature can be obtained by appropriately selecting the Curie temperature. By replacing a part of Ba in barium titanate with lead PB, strontium, etc., the Curie temperature can be freely controlled to move either to the high temperature side or to the low temperature side based on about 120°C. Therefore, by configuring the heating element 9 including the positive temperature coefficient thermistor 11, it becomes possible to heat the drum 8 at an optimal temperature.

(b) The positive temperature coefficient thermistor 1.1 has a current control function or a self-temperature control function, whose electrical resistance value increases rapidly when a specific temperature is reached, and which automatically controls the current and heat generation temperature. Therefore, by using the positive temperature coefficient thermistor 11 as a heat generation source, it is possible to realize a photosensitive drum that is free from the risk of overheating and does not cause overheating burnout of copy paper. What's more, it is 1/4th the temperature of a conventional thermostatic temperature controller, providing continuous temperature control without 111i degree fluctuations, and does not require any temperature sensor or temperature control circuit, resulting in highly reliable heat generation. body 9 can be realized.

(c) The positive characteristic thermistor 11 follows the amount of heat dissipation, the human power changes, and the heat generating mixed acid changes. For example, when the ambient temperature rises, the heat generation temperature increases accordingly, and the device operates so that the temperature difference between the ambient temperature and the heat generation temperature remains approximately constant despite fluctuations in the ambient temperature. Therefore, unlike conventional thermostatic temperature regulators, it is possible to realize a photoreceptor drum that follows changes in ambient temperature and prevents the formation of dew condensation.

(d) Since the positive temperature coefficient thermistor 11 operates in a high resistance region in the steady state 1 in thermal equilibrium, the power consumption is significantly smaller than that of the conventional nichrome heating element, and the economical efficiency is extremely high. Moreover, since the temperature of the positive temperature coefficient thermistor 11 rises quickly, the start-up time of the machine is shortened, and its responsiveness is improved.

The mounting portion of the positive temperature coefficient thermistor 11 is the flat portion 13, as described above. With this structure, the flat portion 13 where the positive temperature coefficient thermistor 11 is located and which generates a high temperature is located farther from the inner diameter surface of the drum 8 than other portions, so that the heating action on the drum 8 is applied to the entire surface of the heat transfer body 10. This makes uniform heating possible.

The positive temperature coefficient thermistor 11 and the nichrome heater 12 are
As shown in FIG. 9, they are electrically connected in series. With such a series connection structure, when the power is turned on, the positive temperature coefficient thermistor 11 operates as a low resistance, and the nichrome heater 12 quickly enters the normal heating state through the low resistance positive coefficient thermistor 11, and the drum 8 is this nichrome heater 1
It is rapidly heated by the heat generating operation of step 2. This results in extremely high responsiveness. On the other hand, when the positive temperature coefficient thermistor 11 enters a steady state and reaches thermal equilibrium, it operates as a high resistance, so that the current flowing through the nichrome heater 12 is
Limited by the characteristic thermistor 11, the power consumption in steady state becomes very small. That is, positive characteristic thermistor 1
By connecting 1 and the nichrome heater 12 in series, it is possible to simultaneously obtain the improvement in quick response 1 and the effect of reducing power consumption.

The heat transfer body 10 is installed so as not to rotate with respect to the drum 8 which rotates as indicated by arrow a. This is possible because the gap Gl is provided between the inner diameter surface of the drum 8 and the arcuate portion 14.15 constituting the heat transfer body 10. In this way, when the heat transfer body 10 is arranged so as not to rotate relative to the drum 8, when power is supplied to the positive temperature coefficient thermistor 11 and the nichrome heater 12 connected to the heat transfer body 10, the slip ring and brush Since a rotary power supply device consisting of a combination of the above and the like is not required, the power supply structure is simplified and the reliability is improved.

Next, the effects of the present invention will be explained in more detail with reference to the measured data shown in FIGS. 10 to 13. In Figure 1O, the room temperature is 1
Time-current characteristics when the temperature is 0°C, fal1 diagram is the time-current characteristics when the room temperature is 24°C, Figure 12 is the time-temperature characteristics when the room temperature is 10°C, and Figure 13 is the room temperature. The time-temperature characteristics are shown when the temperature is 24°C. The temperatures shown in FIGS. 12 and 13 are the surface temperatures of the drum 8 constituting the photosensitive drum. .

As is clear from the measured data of the time-current characteristics shown in FIGS. 10 and 11, the photosensitive drum according to the present invention includes the positive temperature coefficient thermistor 11 as the heat generation source of the heating element 9. 0 until a certain period of time Ti has passed.
．． A very large inrush current of about 8A flows. For this reason, as shown in FIGS. 12 and 13, the surface temperature of the photoreceptor drum rises by around 5°C in about 3 to 4 minutes after startup.
It will be available for use in a short time.

After the time Ti has elapsed, the positive temperature coefficient thermistor 11 is subjected to self-heating and heating action from the nichrome heater 12, and its resistance value increases rapidly, causing a current limiting action.

As a result, the positive temperature coefficient thermistor 11 and the nichrome heater 1
The current flowing through 2 suddenly decreases from about 0.8 A to about 0.15 A, and thereafter stabilizes at this current value. For this reason,
In the steady state m-, the power consumption decreases to about 175 at startup, making it very economical.

Further, in the steady state region M where the current value is stable, as shown in FIGS. 12 and 13, the surface temperature of the drum 8 becomes approximately constant, resulting in constant temperature heating. Therefore, overheating and burning of the copy paper will not occur.

Moreover, as is clear from the comparison between FIG. 12 and FIG. 13, the surface temperature of the drum 8 was stable at 20'O, which is 10°C higher than the room temperature when the room temperature was 10oC.
If the room temperature rises to 24°C, it will be 10°C higher than this3
Stable at 4°C. In other words, the surface temperature of the drum 8 changes following changes in room temperature. Therefore, unlike conventional thermostatic temperature regulators, it is possible to reliably prevent condensation from occurring even when the outside temperature becomes high.

As described above, the photosensitive drum according to the present invention is characterized by having a heating element containing a positive temperature coefficient thermistor inside the drum. It is possible to provide a highly reliable photosensitive drum that is capable of heating, performs dew condensation prevention and dehumidification operations in accordance with changes in ambient temperature, and does not cause image unevenness.

[Brief explanation of drawings]

Figures 1 to 3 are diagrams showing models of the charging, exposure, and development processes of a copying machine, Figures 4 and 5 are diagrams showing a conventional method of heating a photoreceptor drum, and Figure 6 is A front sectional view of the photoreceptor drum according to the present invention, FIG. 7 is B1-B in FIG.
1 line, FIG. 8 is a sectional view taken along line B2-B2 in FIG. 6, FIG. 9 is an electrical equivalent circuit diagram, and FIG. 10 is a time-current characteristic when the room temperature is lOoC. , Figure 11 shows the time-current characteristics when the room temperature is 24°C, Figure 12 shows the time-temperature characteristics when the room temperature is 10°C, and Figure 13 shows the time-current characteristics when the room temperature is 24°C. FIG. 3 is a diagram showing temperature characteristics. 8... Drum 9... Fist heating element 10... Heat transfer element 11... Positive characteristic thermistor' 12... Nichrome heater Fig. 3 Fig. 4

Claims (6)

[Claims] (1) A photosensitive drum that is rotatably installed inside a copying machine and has a heating element including a positive temperature coefficient thermistor inside the drum. (2) The photosensitive drum according to claim 1, wherein the heating element is provided so as not to rotate. (3) The heating element is configured by electrically connecting the positive temperature coefficient thermistor and a resistance heating element in series.
A photosensitive drum according to claim 1 or 2. (4) The heating element according to claim 1, 2 or 3, wherein the heating element has an arc-shaped heat transfer element facing the inner peripheral surface of the drum at a distance. photosensitive drum. (5) The heat transfer body has the above-mentioned 1 on the flat portion.
5. The photosensitive drum according to claim 4, wherein a one-piece characteristic thermistor is attached. (6) The photosensitive drum according to claim 4 or 5, wherein the heat transfer body has an air JAC hole that communicates between the inside and the outside.