JPH0421870A - Electrophotographic image forming device - Google Patents

Abstract

PURPOSE:To secure the efficiency of transfer which is close to that at a normal humidity time even it is under a high humidity environment by heating a transfer paper fed from a paper feeding part before it is carried to a transfer part according to humidity and adjusting the moisture content thereof. CONSTITUTION:A temperature sensor 32 which detects temperature and a humid ity sensor 33 which detects humidity are fitted near a tray loading port 31 where a paper feeding tray 11 is loaded and on the outside surface of the cover 10a of a printer main body 10. The outputs of the sensors 32 and 33 are sent to a control circuit on an engine board 34 in the printer main body 10 and a paper heater 30 is controlled according to the detected temperature and the detected humidity. For example, the transfer paper placed within a high humid ity area shown by a hutching is heated by the heater 30 in a short time while the paper is passed and the moisture content thereof is adjusted to nearly 5% which is proper for the transfer. Besides, the heating set line thereof is set to L - L. Thus, the efficiency of the transfer is prevented from being lowered caused by the increase of the moisture content of the transfer paper under the high humidity environment and the fall of the resistance value of the area in accordance with it.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to image forming apparatuses such as printers, facsimile machines, and copying machines that form images using an electrophotographic method.

Conventional technology In an electrophotographic image forming apparatus, in the transfer process, an electric field is applied by corona discharge or the like from the back side of the transfer paper while the transfer paper is in close contact with the surface of the drum or bell-shaped photoreceptor. , an electrostatic transfer method is often used in which a toner image adhering to the surface of a photoreceptor is transferred to transfer paper.

To explain the principle in detail, electrostatic transfer uses a corona discharge from the back side of the transfer paper to charge the toner with a charge of the opposite polarity.This creates an electric field in the gap between the transfer paper and the toner layer on the photoreceptor. Generate density E. The toner is transferred when the Coulomb force F=q-E between the electric field density E and the charge q of the toner overcomes the adhesion force between the toner and the photoreceptor.

The transfer efficiency η (%) is calculated by assuming that the thickness of the toner layer actually transferred is d and x, and the electric field applied from the transfer paper is 0 for the thickness dt of all the layers on the photoreceptor. Since it is thought that it extends to the position where , it is generally expressed by the following formula.

η=d x/d t= (εo・E)/ (6□'
d) = 1/Q2 However, O≦E< (61・dt)/ε.

ε here. is the permittivity of vacuum, E is the electric field density of the air gap, 6□
is the volumetric charge density of one layer of henna, Ql is the surface charge density given to the transfer paper, Q2 is the surface charge density of the entire layer of one henna,
dt is a total thickness of 1 to 1 layer.

That is, the transfer efficiency η is proportional to the charge density E in the gap or the charge density Q1 of the transfer paper.

Now, even if the same transfer paper is subjected to the same corona discharge, the charge density Q on the transfer paper differs depending on the moisture content α (%) and volume resistivity R (Ω cm) of the transfer paper at that time. It is strongly dependent on the temperature and humidity of the surroundings in which the transfer paper is placed.

FIG. 7 shows a characteristic graph of temperature and humidity versus moisture content α (%) and volume resistivity R (Ω·cm) of the transfer paper.

Transfer paper used in electrophotographic image forming apparatuses is often so-called copy paper or pound paper, and since there are many types of these, the range of variation in common types is shown in a band-like manner.

Figure 8 shows the moisture content α (%) of the transfer paper versus the transfer efficiency η (%).
shows the characteristic graph of If the moisture content α is large (7 to 8% or more) and the volume resistivity is low (at high humidity), the charge on the transfer paper due to corona discharge will be decomposed within the transfer paper, so the photoreceptor The charge density Q1 of the transfer paper facing the upper toner layer becomes smaller, and the transfer efficiency η decreases.

In addition, on the contrary, the moisture content α of the transfer paper is extremely small (3~
2% or less) and the volume resistance value is high (at low humidity)
In this case, since the charge caused by the corona discharge remains charged on the back side of the transfer paper and does not move to the surface of the photoreceptor, the charge density Q on the transfer paper similarly decreases, and the transfer efficiency η decreases.

Such a decrease in the transfer efficiency η causes the transfer of the first to third layers on the photoreceptor to the transfer paper to become worse, and the amount of toner remaining on the photoreceptor increases, resulting in the following problems.

■ The image density of letters, numbers, and graphics decreases, causing printing to become unclear or, in extreme cases, to poor transfer (missing print).

(2) Residual toner on the photoreceptor is removed by a cleaning blade and returned to the cleaning unit once, so the cleaning unit fills up quickly and its lifespan is shortened. As a result, the end user will have to replace the battery sooner, increasing running costs.

■ After printing, the background of the transfer paper becomes stained. The toner contains toners of opposite polarity to varying degrees, and these toners adhere uniformly little by little over the entire non-image area of the photoreceptor. The transfer paper is also charged with the opposite polarity due to corona discharge, so normally (at room temperature and humidity), the toner with the opposite polarity receives repulsion and does not transfer to the transfer paper, so it remains on the photoreceptor and causes the above-mentioned It ends up being collected by the cleaning unit.

However, when the transfer efficiency deteriorates, the repulsive force weakens, and when the transfer paper comes into contact with the photoreceptor, it is transferred due to its own weight and adhesive force, and the background of the non-image area of the transfer paper becomes light gray. This results in "skin stains" that make the skin look dirty.

2. Description of the Related Art Conventionally, in order to prevent fixing failure at low temperatures, a technique is known in which a heating device is built into a paper feed stack to warm the transfer paper in the paper stack at low temperatures.

However, the purpose of this is to prevent poor fixing, and the moisture content of the transfer paper cannot be adjusted, and the transfer paper must be warmed up in the paper stack, so you have to wait several minutes after turning on the power. Moreover, it is effective only at low temperatures and cannot control the humidity of transfer paper at high humidity.

Problems to be Solved by the Invention An object of the present invention is to prevent a decrease in transfer efficiency due to an increase in the moisture content of transfer paper in a high-humidity environment and an accompanying decrease in volume resistivity, and to solve the above-mentioned problems. be.

Means for Solving the Problems The present invention visualizes a latent image formed on a photoconductor using a developing device, and transfers the latent image onto a transfer sheet conveyed from a paper feed section via a paper feed conveyance path. In an electrophotographic image forming apparatus that performs image transfer, a paper heater for heating the transfer paper is disposed in the paper feeding and conveying path, and a humidity sensor is provided inside or on the outer periphery of the apparatus main body, and the image forming apparatus according to the output of the humidity sensor and a control circuit for controlling the paper heater.

The paper heater can be built into a roller that conveys the transfer paper.

A humidity sensor detects the humidity inside or around the device body, controls the paper heater according to the detected humidity, and heats the transfer paper fed from the paper feed section according to the humidity before entering the transfer section. It can be heated to adjust its moisture content.

Loss-givement example Next, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a schematic configuration of a laser printer according to the present invention. In the figure, 10 is a printer main body, and 1] is a paper feed tray that is detachably loaded into the printer main body 10.

The transfer paper 13 fed from the lay 11 to the paper feed 1 by the paper feed roller 12 is conveyed to the lower side of the drum-shaped photoreceptor 15 with timing set by a pair of registration rollers 14 .

That is, the registration roller pair 14 consists of two upper and lower rollers, which are pressed against each other by a spring (not shown), and transfer the transfer paper 13 fed by the paper feed roller 12 to the toner image on the photoreceptor 15''. It has both a registration function to match the timing of the transfer paper 13 and a pressure function to apply pressure as it is conveyed. The photoreceptor 15 is rotated clockwise,
At this time, the surface of the photoconductor 1- is charged by the charger 16 and irradiated with laser light from the laser optical system 17.
An electrostatic latent image is formed on 5. This latent image is produced by the developing device 1-
8, the toner forms a visible image, and this visible image is transferred by the transfer charger 20 to two sides of the transfer paper 13, which has been conveyed to the transfer section 19 below the photoreceptor 15. The transfer paper 13 on which the image has been transferred is conveyed to a fixing device 21 and the visible image is fixed thereon. And the fixing device 21
The transfer paper 13 that has come out is discharged to a paper discharge section 24 by paper discharge rollers 22 and 23. On the other hand, the photoreceptor 15 after visible image transfer
After being neutralized by a static eliminating lamp 25, residual toner is removed by a cleaning unit 27 having a cleaning blade 2G, and the removed toner is collected in a 1 henna collection tank 28.

In such a laser printer, in the first embodiment of the present invention, a paper heating heater 30 made of an infrared lamp or a nichrome wire is installed in the middle of the paper feed conveyance path 29 from the paper feed roller 12 to the transfer section 19. Deploy. In the figure, the paper heater 30 is disposed upstream of the pair of registration rollers 14 and above the paper feed conveyance path 29, but it may be placed downstream of the pair of registration rollers 14 or below the paper feed conveyance path 29.

When placed on the lower side, it is advantageous to take out the transfer paper 30 if it jams during transportation, and there is also less risk of the operator touching the paper heater 30 when the cover is opened. In addition, in both the upper and lower cases, prevention of temperature rise inside the machine by adding a paper heater 3o can be done without increasing costs by devising the installation location of the cleaning fan motor of the machine or the ventilation path. .

On the other hand, on the outer surface of the cover 1-0a of the printer main body 10 near the 1-ray loading port 31 into which the paper feed tray 11 is loaded,
A temperature sensor 32 for detecting temperature and a humidity sensor 33 for detecting humidity are attached. In addition, these sensors 32.3
3 may be installed inside the printer main body 10. The outputs of these sensors 32 and 33 are sent to a control circuit on an engine board 34 in the printer main body 10, and the paper heater 30 is controlled according to the detected temperature and humidity.

FIG. 2 shows an environmental characteristic graph of an electrophotographic image forming apparatus such as a laser printer as described above.

Range of thick broken line (170℃~30℃, 20% R1 (~80℃)
%RH) is an example of a range of guaranteed operation. Transfer paper placed in the high temperature area shown by hatching within this range (moisture content of approximately 7% or more and volume resistivity of 1011 to 1
In the present invention, the paper is heated with the paper heating heater 30 for a short time while the paper is passing, and the moisture content is adjusted to around 5% (volume resistance value of 10"1), which is appropriate for transfer. ~10″2Ω・(
7) Adjust the humidity in the vicinity. Let the heating setting line be L-L,
A sequence example of the control method is shown in FIG.

In the example shown in FIG. 3, the temperature detected by the temperature sensor 32 is T (℃
), the detected humidity of the humidity sensor 33 is W (%R11), the correction coefficient a = -10 (%RH) /10 ('C) = -
1(%R)l/℃), and set the paper heater 3o to low, medium,
Adjust to 3 levels of strength. That is, 10≦T≦30 (°
Under the conditions of C), α・T+90>W2C・T+8.0(%
), set the paper heater 30 to "weak", α・T+100>
When W2C・T+90 (%), “medium”, W2C・T+1
When it is 00 (%), it is set as "strong", and at other times, the paper heating heater 30 is turned off.

It should be noted that it is possible to achieve a more appropriate value through finer control in three or more stages, and it goes without saying that even if it is impossible to achieve an optimum value with one stage control, it is still very effective.

The appropriate value for the output of the paper heater 30, that is, the intensity of the heating temperature, will vary depending on the printing/copying speed of the image forming apparatus (number of sheets: 7 minutes) and the size of the transfer paper (A4, A3, etc.). The temperature range is from 100'C (weak) to 300'C (strong).

Placing the paper heater 30 before the pair of registration rollers 14 has the following advantages. In other words, in addition to the moisture content (body resistance value), the effects on transfer paper in high-temperature environments include:
When transfer paper absorbs moisture, wrinkles may appear depending on the type of paper. In such a state, there will be many locations where the transfer paper cannot be brought into close contact with the photoreceptor during transfer, and these locations will not be transferred, resulting in missing prints due to poor transfer. Therefore, if the transfer paper is heated by the paper heater 30 and then pressed by the registration roller pair 14, ironing can be expected to be effective.

FIG. 4 shows an overview of a second embodiment of the invention.

In this example, as shown in detail in FIG. 5, one of the two upper and lower rollers 14a and 4b of the pair of registration rollers 14 is made of a metal pipe with good thermal conductivity such as aluminum, and the inside thereof is The roller 14b has a built-in heater 35, while the other roller 14b is made of heat-resistant rubber and is pressed against the roller 14a by a pressure spring 36. That is, one roller 14a is a hot roller, and the other roller 1
4b is a pressure roller. Similarly to the fixing device 21, the surface temperature of the roller 14a is measured by a thermistor 37.
The temperature is detected by the temperature fuse 38, and the temperature rise above a predetermined value is limited. Further, in addition to installing a temperature sensor 32 and a humidity sensor 33 as in the first embodiment, the developing device 1.
A separate temperature sensor 39 is installed outside or around the temperature sensor 8 .

In the first embodiment described above, heating by the paper heater 30 only needs to be performed when the transfer paper 13 is conveyed, but in the second embodiment, the heating by the heater 35 is performed only when the roller 14 made of a metal pipe is heated.
Since the cleaning is carried out via the air filter A, it is necessary to constantly heat the cleaning fan to an appropriate temperature, and even if the installation location of the cleaning fan and the ventilation path are devised, there is still concern that the temperature inside the machine will rise. The rise in temperature inside the machine may cause the developing device 18 and cleaning unit 2 to
There is a big problem of solidification of the developer in the 7.

In FIG. 2, general toner solidification risk areas are shown by grid lines.

Therefore, in the second embodiment, the temperature T1 ('c) detected by the temperature sensor 32 and the humidity W detected by the humidity sensor 33 are
(%RH) as well as the temperature T2 detected by the temperature sensor 39.
('C) is also sent to the control circuit, and the heater 35 is controlled according to these three elements.

FIG. 6 shows an example of the control sequence, and 10≦T1≦
Under the condition that T2≦50(%), the heater 35 is adjusted in three stages as in the first embodiment. In the case of the second embodiment, the effect of ironing is better than that of the first embodiment.

Effects of the Invention According to the present invention, the transfer paper fed from the paper feed section is heated according to the humidity before entering the transfer section, and its moisture content can be adjusted. It is possible to ensure transfer efficiency close to that when wet. Therefore, ■ Preventing a decrease in image density ■ Extending the life of the cleaning unit ■ Preventing the background from becoming dirty in high humidity ■ Ironing has the effect of preventing transfer defects (missing prints) due to wrinkles.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram of a laser printer according to a first embodiment of the present invention, Fig. 2 is a graph of its environmental characteristics, Fig. 3 is a flowchart of an example control sequence of the paper heating heater, and Fig. 4 is a diagram of a second embodiment of the laser printer. Schematic configuration diagram of example laser printer, No. 5
The figure is an enlarged view of the main part, and FIG. 6 is a flowchart of an example of the heater control sequence. Figure 7 is a characteristic graph of temperature and humidity versus moisture content and volume resistivity of transfer paper.
The figure is a characteristic graph of transfer paper moisture content versus transfer efficiency. 10...Printer body, 13...
... Transfer paper, 14 ... Registration roller pair, 14
a...Hora 1~Lola, 14b...
... Pressure roller, 15 ... Photoreceptor, 18 ...
...Developing device, 19...Transfer section, 29.
・ ...Paper feed conveyance path, 30...Paper heating heater, 33...Humidity sensor, 35...
···heater.

Claims (1)

[Scope of Claims] 1. The latent image formed on the photoreceptor is visualized by a developing device, and transferred by a transfer section to a transfer paper conveyed from a paper feed section via a paper feed conveyance path. In an electrophotographic image forming apparatus, a paper heater for heating the transfer paper is disposed in the paper feed conveyance path, and a humidity sensor is provided inside or on the outer periphery of the apparatus main body, and the paper is heated according to the output of the humidity sensor. An electrophotographic image forming apparatus comprising a control circuit for controlling a heater. 2. The electrophotographic image forming apparatus according to claim 1, wherein the paper heater is built into a roller that conveys the transfer paper in the paper feed conveyance path.