JPH0766218B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Use of the Invention] The present invention transfers an image carried by an image carrier such as a photosensitive drum or an insulating drum onto a transfer material which is carried while being held by a dielectric. The present invention relates to an image forming apparatus which can be applied to an apparatus for forming an image, such as a color copying machine or a color printer.

[Prior art]

FIG. 3 is an explanatory view of a conventional color electrophotographic copying machine for forming a full-color copied image. In the figure, a corona charger 2, an exposure optical system 3, a developing device 4, a transfer drum 5, and a cleaner 6 are placed around the photosensitive drum 1. The optical system 3 comprises a document scanning section 3a and a color separation filter 3b.

The developing device 4 has four existing organs around the central axis 4b. 4Y is a yellow developing device, 4M is a magenta developing device, 4C is a cyan developing device, and 4B is a black developing device. . Further, the entire developing device is rotated to sequentially develop each of the four colors. Further, the transfer drum 5 is composed of a cylinder 5a, a transfer charger 5b, a transfer material gripper 5c, an inner charger 5d, and an outer charger 5e, and a transfer material-carrying sheet is stretched over the peripheral opening area.

To form a full-color image, first, a blue color-separated electrostatic latent image is formed on the photosensitive drum 1 and developed by the yellow developing device 4Y.
On the other hand, the transfer material is gripped by the gripper 5c of the transfer drum 5 from the transfer material cassette 7 via the transport system. Transfer drum 5
The toner image on the photosensitive drum 1 is transferred onto the transfer material by the transfer material charger 5b as the rotation of the transfer material advances, and at the same time, the transfer material is attracted to the transfer material carrying sheet. This operation is repeated three more times, that is, magenta, cyan, and black, as in the known full-color image forming method. When the transfer of the four color toner images is completed in this way, the toner images are separated from the transfer drum 5 and discharged to the tray 10 via the heat roller fixing device 9.

At the time of transfer, the operation is performed such that the current is sequentially increased each time the transfer of each color is repeated. The reason for this will be described with reference to FIG. 2 below.

First, a current I ₁ is applied during the first transfer. The transfer material carrying sheet 501 is charged to V ₁ by this current, and the toner on the image carrying body is transferred onto the transfer material. Since the transfer material moves in synchronism with the image carrier 1, the transfer material on the transfer drum 5 separates from the image carrier after transfer, but at the time of this separation, the air in the vicinity is ionized. Toner that forms development on the image carrier is
For example, when the charging polarity is negative, the transfer current is positive.

In this state, negatively charged air among the above-mentioned ionized air adheres to the surface of the transfer material, and positively charged air adheres to the surface of the image carrier. The negative charge attached on the transfer material affects the positive charge of transfer on the back surface of the transfer material carrying sheet 501, and acts to weaken the transfer electric field as a whole.

On the other hand, since the transferred toner itself is negative, the transfer electric field is weakened in the same manner as the above-mentioned development. For this reason, it is necessary to increase the transfer current so as to compensate for the next transfer electric field. If transfer relationship transfer current and the charging s-position of the transfer material carrying sheet 501 is positive, the second transfer current, when the charging people position of the transfer material carrying sheet with the respective _{I 2, V 2 I 1 <} I 2 , V ₁ <V ₂
Becomes

In addition, | V ₂ -V ₁ | had better be at least 0.5KV at a minimum.
The same relationship holds for the subsequent transfer. A PET (polyethylene terephthalate) film is used as the transfer material carrying sheet 501.

[Problems to be solved by the invention]

Conventionally, the above-mentioned transfer current value has always been a constant change amount over a predetermined operating temperature range of a color copying machine.

However, in the high temperature and high humidity environment where the humidity is particularly high in the environment in which the copying machine is installed, the volume resistance of the transfer material used is higher than that at room temperature or room temperature (eg 23 ° C, 60%). In the worst case, it drops to 1/100. In addition, the dielectric that carries the transfer material for multiple transfer also adsorbs moisture on the surface, so the surface resistance decreases. For this reason, if the above-mentioned transfer current setting value is left as it is, the phenomenon of the transfer gap, which occurs when the transfer current is too strong, is likely to occur.

On the other hand, in a low temperature and low humidity environment where the humidity is particularly low in the environment where the copying machine is installed, the volume resistance of the transfer material used increases by 100 times in the case of paper as compared with the room temperature and normal humidity environment. Further, also in the above-mentioned dielectric, the moisture adhering to the surface of the dielectric is reduced, so that the surface resistance is increased.

For this reason, the transfer current of the nth color is not discharged by an appropriate amount before the transfer of the (n + 1) th color, so that charges are sequentially accumulated.

Therefore, there is a problem that an image defect is likely to occur due to a decrease in transfer efficiency if the transfer current setting value is left unchanged.

In order to solve the problems described above, a method of changing the transfer current using a humidity sensor has been proposed. However, a humidity sensor such as a crystal humidity sensor, a polymer humidity sensor, or a ceramics humidity sensor generally used as a humidity sensor outputs a relative temperature under a temperature environment in which the humidity sensor is installed. Cannot detect the amount of water in the air.

The reason for this will be described with reference to FIG.

FIG. 8 shows the amount of water contained per unit volume (saturated water content) calculated from the saturated water vapor pressure with respect to temperature at 30 ° C. as 100. For example, at 30 ° C., the humidity sensor outputs a voltage corresponding to 100% when the water content in the air is 100, and outputs a voltage corresponding to 50% when the water content is 50.

On the other hand, the saturated moisture content at 10 ° C is about 31, but the humidity sensor outputs this moisture content as 31% at 30 ° C. But 10
Humidity sensor placed in the environment of ℃ 100% this moisture content
Output as.

As described above, the volume resistance of the paper and the surface resistance of the dielectric sheet depend on the amount of water in the air.Therefore, when controlling only the humidity sensor, the amount of change in the transfer current in a low humidity environment is It was found to be unsuitable for control for the purpose of increasing the amount and reducing the change under high humidity environment.

The present invention is to eliminate the above-mentioned problems, and an object of the present invention is to provide a transfer device capable of preventing a phenomenon in which transfer failure occurs due to a change in environment and always forming a good image.

〔Example〕

An embodiment of the present invention will be described with reference to FIG. 1 and FIGS. 4 to 6.

In FIG. 1, the transfer charger 5b as transfer charging means has an opening width of 22 mm, and the distance between the discharge wire and the photosensitive drum is 11 mm. Further, the transfer material carrying sheet 501 which is a dielectric has a diameter of 1
It is 60 mm and the moving speed is 160 mm / sec. Further, reference numeral 504 is a temperature / humidity sensor as a detection means for detecting temperature and humidity, and is provided in the vicinity of the transfer material carrying sheet at a position where rotation is not hindered.

No. 4 depending on the temperature and humidity detected by the temperature and humidity sensor
According to the figure, which of the areas 1 to 3 is to be recognized is recognized.

FIG. 5 is a block diagram according to the present invention. The T and H signals from the temperature and humidity sensor are converted into digital signals by the A / D converter and sent to the I / O. 2 output from I / O
Areas of the two signals are specified by referring to the table 1 in which area. After the area is designated, it is referred to as Table 2 this time through the CPU. When referred to, the signal relating to the transfer current stored in Table 2 is read and the CPU again receives D / A conversion through I / O. From here, it is sent to the high-voltage power supply device to generate the set output.

Further, the CPU is set so that these series of processing operations are performed prior to the copying operation.

Regions (1) to (4) in FIG. 4 represent equal moisture content curves per unit volume. That is, in the same region, the charging characteristics of the toner,
It is considered that the charging characteristics of the transfer material and the moisture absorption and charging characteristics of the transfer material-carrying sheet are almost the same, and the environment is similar.

In this way, from the humidity sensor output and temperature sensor output, the area where the moisture content in the air is equal is specified, and the transfer current is controlled to adapt to the volume resistance change due to the moisture absorption of the transfer material and the surface resistance change of the dielectric film. The transfer current output can be controlled.

In the above conventional copying apparatus, four colors, that is, yellow (Y), magenta (M), cyan (C), black (B)
It has already been described that the transcription of k) is carried out, and the respective transfer currents have always had a constant change amount with respect to environmental changes, but in the present invention, in the region recognized by the above method,
The current shown in FIG. 6 was decided to flow according to each environment. In addition, regarding the determined value of the proper transfer current in each environment shown in FIG. 6, a representative point (X in FIG. 4) in each environment is shown.
Point) was set, and the current value showing the best transfer rate under that environment was defined as the proper transfer current value.

The values of the representative point temperature, humidity, and proper transfer current in each environment are shown together in FIG. The current values in FIG. 6 are designated in the table 2 in FIG.

The areas (1) to (4) in FIG. 4 used in the present invention may be increased or decreased as necessary without impairing the gist of the present invention.

〔effect〕

As described above, in the present invention, the temperature and humidity are detected by the detection means, and the output of the transfer charging means is controlled based on the amount of water per unit volume with respect to the temperature and humidity. It is possible to control the output of the transfer charging unit in accordance with the change in the charging characteristic of the image carried by the image carrier.

[Brief description of drawings]

FIG. 1 is an enlarged view of the vicinity of a transfer charger of a color electrophotographic copying machine of the present invention, FIG. 2 is an enlarged view of the vicinity of a transfer charger of a conventional color electrophotographic copying machine, and FIG. 3 is a conventional color electrophotographic copying machine. FIG. 4 is a diagram of the area division of environmental conditions, and FIG. 5 is a block diagram showing a control example of the present invention. FIG. 6 is a graph showing proper transfer current values in each environment set by the present invention, and FIG. 7 is an explanatory view summarizing conditions of representative points and proper transfer current values in each environment set by the present invention. FIG. 8 is a graph showing the relationship between temperature and saturated water content. In the figure, 1 ... Photosensitive drum 2 ... 1-time charger 3 ... Exposure optical system 4 ... Developing device 5 ... Transfer drum 5a ... Transfer charger 5d ... Inner charger 501 ... Transfer material carrying sheet 502 …… Transfer drum outer frame 503 …… Transfer charger shield 504 …… Transfer wire 505 …… Temperature and humidity sensor.

Claims (1)

[Claims] 1. An image carrier that carries an image, a dielectric that holds the transfer material and conveys the transfer material to a transfer position of the image carrier, and a dielectric member on the side opposite to the image carrier. Is arranged,
An image forming apparatus comprising: a transfer charging unit that transfers an image of the image carrier to a transfer material held by the dielectric at the transfer position; and a detection unit that detects temperature and humidity. An image forming apparatus characterized in that the output of the transfer charging means is controlled based on the detected amount of water per unit volume with respect to temperature and humidity.