JP2003076200A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which can prevent image staining with offset toner and prolong the life of a web. SOLUTION: The image forming device is equipped with an electrostatic charging device which accumulates uniform electric charges on an image carrier, a latent image means which forms a latent image corresponding to image information on the electrostatically charged image carrier through exposure, a developing device which forms a toner image by developing the latent image with toner, a transfer device which transfers the toner image on the image carrier to a transfer material, and a fixing device which heats and fixes the unfixed image on the transfer material by using a roller pair. The image forming device is provided with a roller cleaning device for cleaning the rollers of the fixing devices to change the cleaning efficiency of a roller cleaning device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having a fixing device for heating and fixing an unfixed image on a transfer material by using a roller pair.

[0002]

2. Description of the Related Art In a conventional image forming apparatus of this type, an image of a document or an image corresponding to an input image signal is exposed on the surface of an image carrier uniformly charged by a charging means, and the surface of the image carrier is exposed. An electrostatic latent image is formed on the electrostatic latent image, a developing unit develops the electrostatic latent image into a toner image, the transferring unit transfers the toner image to a transfer material, and a fixing unit transfers the toner image on the transfer material. There are electrophotographic copiers and printers that fix and output on top.

FIG. 2 shows an example of a conventional fixing device.

The fixing device shown in FIG. 2 has a heater 12 inside.
The heating roller 10 provided with and the pressure roller 11 whose surface layer is formed of a rubber layer are pressed against each other and rotated, and the transfer material 6 is nipped and conveyed, and at the same time, the toner on the transfer material 6 is melted at the temperature of the surface of the heating roller 10. And is fixed to the transfer material.

Next, the control of the surface temperature of the heating roller 10 of the conventional fixing device will be described.

The temperature of the surface of the heating roller 10 is detected by the surface temperature detecting device 1 in contact with the heating roller 10 of the fixing device.
It does by 3.

Further, a predetermined control temperature is set in advance in the temperature control device 14 in FIG. The temperature control device 14 compares the surface temperature of the heating roller 10 detected by the surface temperature detection device 13 with the set control temperature, and when the surface temperature is lower, the heater 12 is energized. When the surface temperature is lower, the heater 12 is deenergized.

A web 18 made of a nonwoven fabric impregnated with silicon oil is brought into contact with the heating roller 10 by a web pressure roller 19 as a roller cleaning device.

The unused portion of the web 18 is wound on the side of 18a in the shape of a cloth, and the web drive device 20 for rotating 18b moves the web 18 from the right to the left in the figure at a speed much slower than that of the heating roller 10. Then, after cleaning the residual toner and the like on the heating roller 10 at the nip portion between the web pressure roller 19 and the heating roller 10, silicone oil is applied to the heating roller 10 and is wound like a piece on the 18b side.

The traveling speed of the web 18 is controlled at a constant speed based on signals from the web drive device 20 and the control device 14.

Silicon oil is applied to the heating roller 10 as a release agent, and the toner on the transfer material is applied to the heating roller 10.
It prevents the offset that adheres to the. If the offset of the toner by the web 18 is prevented and the cleaning of the offset toner is incomplete, the toner offset to the heating roller 10 rubs through the web 18 and touches the transfer material again, and the offset toner stains the transfer material, resulting in image stains. Will occur.

As described above, the surface of the heating roller 10 is cleaned by the web 18 and the oil is applied to the surface of the heating roller 10 to prevent the offset and the cleaning with the offset toner, thereby preventing the image contamination due to the offset toner.

The web drive device 20 is configured to be driven only during image formation and not to wind the web 18 during image formation suspension.

[0014]

Generally, it is preferable that the amount of advance (feed amount) of the web 18 per unit time is as small as possible within a range where image stains due to offset do not occur.

When the feed amount of the web 18 is increased, the amount of oil applied per unit time and the amount of progress of the web 18 at the nip portion increase, so that image stains due to the offset toner hardly occur, but the length of the web 18 is constant. Therefore, there is a drawback that the life of the web 18 is shortened.

Now, the life of the web 18 will be described.

The unused portion of the web 18 is used in the nip portion on the side of 18a and is wound on the side of 18b. Web 18
The total length of is limited by factors such as space in the body. The web 18 is generally a consumable item, and it is referred to as the life of the web 18 from the start of use until the entire length is used and the unused portion on the side of 18a disappears.

The unused portion remaining on the web 18a is called the remaining amount, and when the remaining amount of the web 18 is exhausted, it is replaced by a service person or the like. Therefore, prolonging the service life of the web 18 is an important technical issue from the running cost and the troublesomeness of replacement. Although it is improved to some extent by increasing the total length of the web 18, this is not a preferable means because it leads to an increase in the size of the main body. Therefore, it is desired to reduce the feed amount of the web 18, but this may prevent image stains due to offset and may not be able to be completed. Thus, the prevention of image stains due to offset toner and the prolongation of the life of the web are contradictory issues.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of both preventing image stains due to offset toner and extending the service life of the web. It is in.

[0020]

To achieve the above object, the present invention provides a charging device for charging a uniform charge on an image carrier, and a latent image corresponding to image information on the charged image carrier. Image forming means for forming a toner image on the latent image, a developing device for developing the toner on the latent image to form a toner image, a transfer device for transferring the toner image on the image carrier to a transfer material, and an unfixed image on the transfer material. An image forming apparatus having a fixing device for heating and fixing an image using a pair of rollers is characterized in that a roller cleaning device for cleaning the roller of the fixing device is provided and the cleaning efficiency of the roller cleaning device is switched.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Embodiment 1> FIG. 1 is a sectional view of an essential part of an image forming apparatus according to the present invention. In the image forming apparatus shown in the figure, an original illumination lamp 31 illuminates an original 30 in a reader section. The image information is converted into a voltage by the CCD 32, and the voltage is converted into a digital image signal by A / D conversion. Then, the digital image signal is counted in the image amount by a video counter (not shown), and the image information is fed back to the control device 14.

In the printer section, the laser 33 is generated on the surface of the image carrier 1 uniformly charged by the primary charging device 3 based on the digital image signal corresponding to the original image read by the reader section.
More image exposure is applied to form an electrostatic latent image. And
After developing the electrostatic latent image into a toner image by the developing device 4, the toner image is transferred to a transfer material (not shown) by the transfer device 7. The transfer material provided with the toner image has the toner image fixed by the fixing device 9, and is then ejected as an output image. The output speed of the transfer material in this case is 50 sheets per minute, and the process speed is 300 mm / s.

A schematic structure of the fixing device 1 will be described with reference to FIG.

The fixing device 1 has a halogen heater 12 inside.
A heating roller 10 having an outer diameter of 50 mm and a pressure roller 11 having an outer diameter of 50 mm and having a surface layer formed of rubber or the like are pressed against each other and rotated, and the transfer material 6 is nipped and conveyed, and at the same time, the temperature of the surface of the heating roller 10 is increased. Then, the toner on the transfer material 6 is melted to fix the toner image on the transfer material 6.

A web 18 made of a nonwoven fabric impregnated with silicon oil is brought into contact with the heating roller 10 by a web pressure roller 19 made of rubber or the like and having an outer diameter of 15 mm. The contact nip width between the web 18 and the heating roller 10 is about 5 mm.

A thermistor 13 as a heating roller surface temperature detecting element is in contact with the surface of the heating roller 10, and the detected heating roller surface temperature is fed back to the controller 14. The heater 12 is a halogen heater with an output of 750 W, and its output is controlled by the control device 14 so that the surface temperature of the heating roller during image formation becomes 20 ° C.

The unused portion of the web 18 is wound on the side of 18a in the shape of a piece, and is moved from the right side to the left side in FIG. After cleaning the residual toner and the like on the heating roller 10 at the nip portion of the heating roller 10, it is wound into a piece-like shape on the 18b side.

The web driving device 20 can control the traveling speed of the web 18 based on a signal from the control device 14.

Here, the traveling speed (feed amount) of the web 18
An example in which the image is controlled by the image amount will be described as a first embodiment.

The transfer material 6 having the image amount (image area) obtained by counting the traveling speed of the web 18 with a video counter (not shown).
An example is shown in which switching is performed by the ratio (image ratio) with respect to the entire image formable area.

FIG. 3 shows the relationship between the image ratio and the web feed amount.

When forming an image with a high image ratio,
By increasing the feed amount of the web, the amount of toner that accumulates in the nip part between the web and the heating roller is reduced, and the amount of toner that scrapes through the web without being captured by the web is reduced, and it is possible to reduce image stains caused by offset toner. Became. At this time, the image ratio is 4%, 15%, 50%, 100
%, Images were continuously formed on 1000 sheets, but no image stain due to the offset toner was observed in any of the documents.

For the detection of the image amount, it is preferable to count the image images of the entire document.
Even if only a part of the image of the document is counted, such as 0 mm, a great effect can be obtained. Further, as the detecting means, the same effect can be obtained by using a method such as detecting the potential of the electrostatic latent image portion on the image carrier other than counting by the video counter. At this time, the potential measuring element for measuring the potential on the image carrier is preferably provided between the latent image forming section and the developing section.

<Second Embodiment> Next, a second embodiment of the present invention will be described.

The offset level varies not only with the image amount but also with the type of image.

Cold offset is often seen in halftone images having poor fixing properties, printed photographic images, etc., and tends to occur in halftone images and the like.

In the halftone image, the amount of toner per unit area is small, unfixed toner particles are easily isolated, and the toner and the fibers of the transfer material are not easily entangled in the fixing nip. Therefore, the toner or the transfer material is not completely caught and is easily offset to the heating roller side.

In the halftone image, d of the unfixed image
The toner located in the outline portion of ot is also difficult to directly contact the heating roller and is difficult to fix on the paper, so that it is difficult to fix on the transfer material and is offset to the heating roller side.

With regard to hot offset, in a solid image having a high toner density, the higher the toner mounting height, the more likely it is that there will be a lack of separation. This tendency becomes severe especially when the area of a solid image is large.

An example in which the feed amount of the web is switched according to the type of image and the surface temperature of the roller will be described as a second embodiment.

The outline of the configuration of the second embodiment is similar to that of the first embodiment, but only the control of the web feed amount is different. The output image data is subjected to a Fourier analysis by the control device 14 described above, and the frequency of the image data is analyzed. Depending on the frequency obtained,
If the frequency is higher than a predetermined value, consider it as a halftone dot image,
When the roller surface increases the feed amount of the web at low temperature, the image with low frequency is considered as a solid image.By increasing the feed amount of the web when the roller surface is at high temperature, the recovery force of the offset toner and the release agent silicone oil roller The amount of application to the toner is increased to prevent the image from being smeared by the offset toner.

FIG. 4 shows the setting of the feed amount of the web with respect to the frequency of the output image and the surface temperature of the heating roller in the second embodiment.

<Third Embodiment> Next, a third embodiment of the present invention will be described.

The offset toner amount changes depending on the environment. This change occurs at a low temperature of the roller, and becomes large at a low temperature offset. Generally, in a low humidity environment where the amount of water vapor in the air is small, the roller surface is greatly charged with paper,
Since the toner that has not been sufficiently melted is electrostatically attracted to the heating roller side, the offset amount increases, and it becomes difficult to clean the web, which easily causes image contamination.

On the other hand, in a high humidity environment in which a large amount of water vapor is contained in the air, the charge amount of the roller does not increase, so the offset amount of the low temperature offset becomes relatively small.

The amount of water vapor in 1 m ^{3 of} air, that is, the absolute amount of water vapor, is determined from the environmental temperature and humidity obtained from the outputs of the environmental temperature sensor and the environmental humidity sensor for detecting the environment in which the image forming apparatus is placed. An example in which the amount of web is switched depending on the amount of water vapor and the roller temperature will be described as a third embodiment.

FIG. 5 shows the web feed amount with respect to the absolute water vapor amount and the heating roller temperature in Example 3.

The absolute water vapor content was obtained from the following formula.

Absolute water vapor amount = 0.622 × {P / (π−P)} × 10 ³ = 0.622 × {ψPs / (100 × 760−ψ)} × 10 ³ P: vapor pressure (mmHg) ψ : Relative humidity (%) Ps: Saturated vapor pressure (mmHg) π: Atmospheric pressure 760 mmHg ψ = (P / Ps) × 100% → P = ψPs / 100 In Example 3, 15 ° C./10% (1.05 g / 1.05 g / k
g), 23 ° C / 30% (5.26g / kg), 23 ° C /
1,000 sheets were continuously fed in three environments of 60% (10.52 g / kg), but the image was not stained with the offset toner.

<Fourth Embodiment> Next, a fourth embodiment of the present invention will be described.

In an image forming apparatus capable of fixing a plurality of types of toner at the same time, since the thermal characteristics differ depending on the type of each toner, it is difficult to prevent the offset of all the toners at the same time and reduce the feed amount of the web. Is.

In particular, the magnetic properties of the magnetic toner in which the magnetic substance such as metal is contained in the toner and the non-magnetic toner in which the magnetic substance is not contained in the toner are largely different from each other in many cases. In the magnetic toner, the melting point of iron, which is generally used for the magnetic material inside, is around 1500 ° C., and it does not soften in the temperature range of 100 to 200 ° C. which is generally used for fixing toner. Since the viscosity of the toner as a whole does not easily decrease, fixing becomes difficult when the roller surface has a low temperature, which is disadvantageous for low-temperature offset.

On the other hand, the non-magnet toner is often composed of only the resin without containing the metal magnetic material in the toner. Therefore, at a high temperature, the viscosity is likely to drop in a short time, and thus a high temperature offset is likely to occur. .

An example in which the feed amount of the web is switched according to the ratio of the toner to be image-formed and the roller surface temperature will be described as a fourth embodiment.

In Example 4, charging, latent image formation, development, non-magnetic toner A, and magnetic toner B are successively carried out in one rotation of the image carrier, and two types of toner on the image carrier are transferred onto the transfer material. Batch transfer is performed, and two types of toners A and B are simultaneously fixed on the transfer material. The outline of the configuration of the fixing device is the same as that of the first embodiment, and only the control of the web feed amount is different.

FIG. 6 shows the relationship between the ratio of the toners A and B forming an image and the temperature of the heating roller surface and the feed amount of the web in Example 4.

In this way, the web feed amount is changed to the toner A,
By controlling the ratio of B, it is possible to optimally reduce the feed amount of the web while preventing the image from being stained due to the offset of the toner.

[0059]

As is apparent from the above description, according to the present invention, a charging device for charging a uniform charge on an image carrier and a latent image corresponding to image information on the charged image carrier. Image forming means for forming a toner image on the latent image, a developing device for developing the toner on the latent image to form a toner image, a transfer device for transferring the toner image on the image carrier to a transfer material, and an unfixed image on the transfer material. In an image forming apparatus having a fixing device that heats and fixes an image by using a pair of rollers, a roller cleaning device for cleaning the roller of the fixing device is provided, and the cleaning efficiency of the roller cleaning device is switched. It is possible to obtain the effect that both the prevention of image stains due to the above and the longer life of the web can be achieved at the same time.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of an image forming apparatus according to the present invention.

FIG. 2 is a sectional view of a fixing device of the image forming apparatus according to the present invention.

FIG. 3 is a diagram illustrating control of a web feed amount according to the first embodiment.

FIG. 4 is a diagram illustrating control of a web feed amount according to a second embodiment.

FIG. 5 is a diagram illustrating control of a web feed amount according to a third embodiment.

FIG. 6 is a diagram illustrating control of a web feed amount according to a fourth embodiment.

[Explanation of symbols]

1 Image carrier 2 Pre-exposure device 3 charging device 4 Developing device 6 Transfer material 7 Transfer device 8 cleaning device 9 Fixing device 10 heating roller 11 Pressure roller 12 Fixing heater 13 Temperature sensing element 14 Control device 18 Web 19 Web pressure roller 20 Web drive

Claims (5)

[Claims] 1. A charging device for charging a uniform charge on an image carrier, latent image means for forming a latent image corresponding to image information on the charged image carrier by exposure, and toner for the latent image. An image that includes a developing device that develops to form a toner image, a transfer device that transfers the toner image on the image carrier to a transfer material, and a fixing device that heats and fixes an unfixed image on the transfer material using a roller pair. An image forming apparatus, comprising a roller cleaning device for cleaning a roller of the fixing device, and switching cleaning efficiency of the roller cleaning device. 2. The image forming apparatus according to claim 1, wherein the cleaning efficiency of the roller cleaning device is switched based on image information. 3. The temperature detecting means for detecting the temperature of the fixing device is provided, and the cleaning efficiency of the roller cleaning device is changed based on the temperature detected by the temperature detecting means. The image forming apparatus described. 4. A cleaning efficiency of the roller cleaning device is provided based on a temperature / humidity environment detected by the environment detection means, the environment detection means detecting a temperature / humidity environment inside and / or around the image forming apparatus. The image forming apparatus according to claim 1, wherein the image forming apparatus is switched. 5. The image forming apparatus according to claim 1, wherein a fixing device capable of fixing a plurality of types of toners at the same time is provided, and the cleaning efficiency of the roller cleaning means is switched depending on the type and ratio of toners for image formation. apparatus.