JP2002215004A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus which can efficiently solve both the problem of temperature rise in the apparatus main body and the problem of 'sticking of OHT sheets with each other'. SOLUTION: The image forming apparatus is provided with: photoreceptor drums (image carriers) 4Y, 4M, 4C, and 4K; a transfer belt 8 (transfer means) which transfers a toner image formed on the photoreceptor drums 4Y, 4M, 4C, and 4K to a transfer material S; a fixing device 20 (fixing means) which heats and pressurizes the transfer material S where the toner image has been transferred and which fixes the toner image on the transfer material; and at least one cooling fan 50 installed in the device main body. The rotating direction of the cooling fan 50 is changed according to the type of transfer material S. In this way, a more proper air flow can be realized, and the problem of the temperature rise in the device main body which has been a problem of conventional apparatuses and the problem of 'the sticking of OHT sheets with each other' can be efficiently solved with a more inexpensive constitution.

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 such as a copying machine or a printer employing an electrophotographic system or an electrostatic recording system.

[0002]

2. Description of the Related Art A conventional color image forming apparatus will be described with reference to FIG.

FIG. 4 is a sectional view of a conventional color image forming apparatus. In the color image forming apparatus, first, laser scanner units 1Y, 1M, 1C, and 1K corresponding to yellow, magenta, cyan, and black, respectively. From the laser light 2Y, 2M, 2 according to the image data of each color.
C, 2K are emitted, and the charging rollers 3Y, 3M, 3C, 3
Photosensitive drum 4 of each color whose surface is uniformly charged by K
Latent images corresponding to the image data of each color are formed on Y, 4M, 4C, and 4K. Then, the developing device 5 corresponding to each color
The latent images on the photosensitive drums 4Y, 4M, 4C, and 4K are respectively formed of yellow, magenta, cyan, and cyan by the toners of the respective colors contained in the Y, 5M, 5C, and 5K via the developing sleeves 6Y, 6M, 6C, and 6K of the respective colors. Each is developed as a black toner image.

On the other hand, a sheet feeding roller 1 is
1 is transported by the pair of transport rollers 12a,
12b and 13a, 13b and belt drive rollers 7a, 7
b, 7c, are conveyed in the direction of the arrow by the transfer belt 8 which is driven to rotate in the counterclockwise direction.
Y, 4M, 4C, 4K and the transfer belt 8 are nipped and transported by backup rollers 8Y, 8M, 8C, 8K, and the photosensitive drums 4Y, 4Y, 4M, 4
The toner images of each color are sequentially transferred from C and 4K.

The sheet S on which the toner image has been transferred by the transfer process is conveyed to the fixing device 20. The fixing device 20 includes a fixing roller 2 including a halogen heater 23.
1 and a pressure roller 22 that rotates while being pressed against the fixing roller 21 at a predetermined pressure, and the paper S passes through a nip N that is a contact point between the fixing roller 21 and the pressure roller 22 of the fixing device 20. As a result, the toner image is fixed on the sheet S by heat and pressure, and the sheet S on which the toner image has been fixed is discharged onto the sheet discharge tray 25.

By the way, a cooling fan 50 for preventing a rise in the temperature inside the apparatus main body is arranged near the fixing device 20. The cooling fan 50 is held by the fan duct 40 and rotates so as to efficiently discharge the heat generated from the fixing device 20 to the outside of the apparatus main body (that is, so that the air flow is in the direction of the arrow). , Developing device 5
Heated air is prevented from flowing into the image forming section where Y, 5M, 5C, 5K and the like are arranged.

[0007]

Recently, it has been strongly desired in image forming apparatuses to increase the printing speed and to enable high-quality image printing on various transfer materials.
In such an image forming apparatus, how to efficiently and appropriately fix a toner image to various kinds of transfer materials becomes a problem.

For example, there is a very high need for printing color images on an OHT film for presentation.
Regarding image quality, there is a demand for sufficient light transmittance when a projector is used. Such an OH
In order to achieve both high image speed and high image quality in a T film, various technical problems related to the fixing device are often encountered.

As one example, there is a problem of "sticking between sheets" between OHT films stacked and discharged. This problem may occur when the heating performance of the fixing device is increased and the pressing force is increased in order to maintain the transparency of the image on the OHT film, and the printing speed of the apparatus body is also increased. That is, in the case of face-up discharge, before the toner image of the previous page discharged onto the discharge tray is sufficiently dried, the next page is discharged thereon, so that the toner image of the previous page is formed. This is a problem that occurs due to sticking to the non-image side of the next page.

When "sticking between sheets" occurs, a trace remains on the image itself even if the user peels off the sticked sheet, and the trace appears as a difference in shading when projected by a projector. In most cases, the toner image itself becomes unusable, such as peeling off.

As described above, the problem of "sticking between sheets" has been a major problem to be solved in OHT printing.

Further, if the heating performance of the fixing device is improved, there is a high possibility that various problems are caused even by a rise in the temperature inside the main body of the fixing device. A typical example is not only the thermal deterioration of each plastic part in the apparatus main body but also, for example, the deterioration of the toner held in the developing apparatus due to heating.

As described above, in order to solve the problems relating to the fixing device accompanying the improvement of image quality and the printing speed, a cooling fan is installed in the vicinity of the fixing device in the main body of the apparatus, and heat generated from the fixing device is sucked. An in-machine cooling method of discharging this out of the apparatus main body is widely and generally employed.

However, no countermeasure has been established to more efficiently solve both the in-machine cooling method and the problem of "sticking between sheets" of the OHT sheet. For example, in order to solve these problems, a cooling fan for discharging heated air in the vicinity of the fixing device to the outside of the apparatus main body and cooling air discharged directly to the toner image surface of the OHT sheet downstream of the fixing device. It is conceivable to install another cooling fan for the purpose of promoting cooling and drying. However, adding a new fan for OHT sheet printing increases the cost of the apparatus body.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to efficiently solve both the problem of temperature rise in the apparatus main body and the problem of "sticking between sheets" of an OHT sheet. It is an object of the present invention to provide an image forming apparatus capable of performing the above.

[0016]

According to one aspect of the present invention, there is provided an image carrier, a transfer unit configured to transfer a toner image formed on the image carrier to a transfer material, and
An image forming apparatus, comprising: a fixing unit that heats and pressurizes a transfer material onto which a toner image has been transferred to fix the toner image on the transfer material; and at least one cooling fan installed in an apparatus body. The rotation direction of the cooling fan is switched according to the type of the transfer material.

According to a second aspect of the present invention, in the first aspect of the present invention, an air flow path is formed so as to connect the cooling fan and a transfer material conveying path located downstream of the fixing unit. And

According to a third aspect of the present invention, in the first or second aspect of the present invention, a means for determining whether or not the transfer material is an OHT sheet is provided. The cooling fan is rotated in a direction in which the air is taken in and discharged to the transfer material transporting path downstream of the fixing means, and when the transfer material is other than the OHT sheet, the air in the downstream area of the fixing means is sucked and removed. The cooling fan is rotated in a direction of discharging the cooling fan out of the image forming apparatus.

According to the present invention, the rotation direction of the cooling fan is switched between when the apparatus main body is in a standby state or when printing plain paper and when printing an OHT sheet. The problem of temperature rise in the main body of the device, which has been a problem in the past, and the "sticking between sheets" in the OHT sheet
Can be efficiently solved by a cheaper configuration.

[0020]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIGS. 1 to 3 are sectional views of an image forming apparatus according to the present invention. In these figures, the same elements as those shown in FIG. 4 are denoted by the same reference numerals. Is omitted.

In the image forming apparatus according to the present embodiment, timing sensors 30a and 30b, which are optical sensors, are installed immediately before the pair of registration rollers 13a and 13b. The timing sensors 30a and 30b are a pair of optical sensors on the light emitting side and the light receiving side, respectively, and detect that the leading end St of the sheet S reaches the registration roller pair 13a and 13b. This timing sensor 30a,
30b pre-feeds the leading end St of the paper to the registration roller pair 13a, 13b before printing the paper S, and temporarily feeds the paper S until a print signal is input and the apparatus main body can print. It is installed to make it stand by.

At the same time that the paper S is pre-fed to the standby position, the image forming apparatus
OHT detection sensors 31a and 31 which are another pair of optical sensors installed in the paper passing area to determine whether the sheet is a sheet or not.
b. That is, if the light emitted from the OHT detection sensor 31a on the light emitting unit side is received by the OHT detection sensor 31b on the light receiving side, the paper S can be regarded as an OHT sheet as a transparent film.

Conversely, if the light emitted from the OHT detection sensor 31a is blocked, it can be determined that the pre-fed sheet S is not a transparent OHT sheet but another opaque sheet.

On the other hand, a cooling fan 50 is provided in the vicinity of the fixing device 20 of the present image forming apparatus for the purpose of preventing a temperature rise in the apparatus main body. And this cooling fan 50
Is formed between the upper area immediately after the fixing device 20 and the outer wall of the apparatus main body.

In the image forming apparatus having the above-described configuration, normally, when the sheet S is a standby state where printing is not performed or the pre-fed sheet S is a sheet Sp other than the OHT sheet, cooling is performed in the same manner as in the conventional image forming apparatus. Fan 5
Reference numeral 0 denotes a rotation of the developing device 5Y, 5M, 5C, 5 so as to efficiently discharge the heat generated from the fixing device 20 to the outside of the apparatus main body (that is, so that the flow of air is in the direction of the arrow).
Heated air is prevented from flowing into the image forming section where K and the like are arranged.

However, the pre-fed paper S
Is determined by the OHT detection sensors 31a and 31b to be the OHT sheet So, and thereafter, when a print signal is input, the polarity of the power supply voltage is immediately switched as shown in FIG. Is reversed, and the airflow is switched in a direction opposite to the normal direction. That is, after that, when printing and paper passing of the OHT sheet So are started, the flow of air around the cooling fan 50 becomes as shown in FIG. That is, outside air outside the apparatus main body is taken in, and the outside air is blown to the toner image surface of the OHT sheet So passing through the fixing device 20 downstream of the fixing device 20. As a result, the toner image on the surface of the OHT sheet So is immediately cooled, and the toner image changes from a liquid state to a fixed state at once.

Therefore, even if the printing operation is performed continuously,
Since the next OHT sheet So is discharged after the toner image of the OHT sheet So previously discharged onto the discharge tray 25 is sufficiently fixed, the problem of "sticking between sheets" is solved.

Such a flow of air actually disperses the heat generated from the fixing device 20 into the main body of the apparatus, and the heated air generates more heat than in the normal rotation direction of the cooling fan 50. It is likely to flow into the area.

However, in view of the general use condition of OHT sheets, a print job for a long time, such as printing several hundred sheets at a time, is very unlikely, and may cause a problem due to a rise in temperature in the apparatus body. It can be determined that there is no sex.

As described above, the rotation direction of the cooling fan 50 is switched between the case where the apparatus main body is in the standby state or the case where the printing operation of the plain paper Sp is performed and the case where the OHT sheet So is printed. By realizing the air flow, the problem of temperature rise in the apparatus main body and the problem of "sticking between sheets" in the OHT sheet So, which have been problems in the past, can be solved with a less expensive configuration.

[0032]

As is apparent from the above description, according to the present invention, the image carrier, the transfer means for transferring the toner image formed on the image carrier to the transfer material, and the transfer of the toner image An image forming apparatus comprising: fixing means for heating and pressing the transferred transfer material to fix the toner image on the transfer material; and at least one cooling fan installed in the apparatus main body.
Since the rotation direction of the cooling fan is switched according to the type of the transfer material, a more appropriate air flow can be realized. The effect that the problem of "sticking" can be efficiently solved by a cheaper configuration can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a cross-sectional view of the image forming apparatus when an OHT sheet is passed according to the present invention.

FIG. 3 is a cross-sectional view of the image forming apparatus when plain paper is passed according to the present invention.

FIG. 4 is a sectional view of a conventional color image forming apparatus.

[Explanation of symbols]

 4Y, 4M, 4C, 4K Photosensitive drum (image carrier) 8 Transfer belt (transfer unit) 20 Fixing device (fixing unit) 25 Discharge tray 30a, 30b Timing sensor 31a, 31b OHT detection sensor 40 Fan duct 50 Cooling fan S , Sp paper (transfer material) So OHT sheet (transfer material)

Claims (3)

[Claims] An image carrier, a transfer unit for transferring a toner image formed on the image carrier to a transfer material, and a transfer material on which the toner image has been transferred is heated and pressed to transfer the toner image to the transfer material. In an image forming apparatus having a fixing unit for fixing on the upper side and at least one cooling fan installed in the apparatus main body, a rotation direction of the cooling fan is switched according to a type of a transfer material. Image forming apparatus. 2. The image forming apparatus according to claim 1, wherein an air flow path is formed so as to connect the cooling fan and a transfer material conveying path located downstream of the fixing unit. 3. A means for determining whether or not the transfer material is an OHT sheet is provided. If the transfer material is an OHT sheet, air outside the apparatus main body is taken in and is fed downstream of the fixing means to a transfer material conveyance path. When the transfer material is other than an OHT sheet, the cooling fan is rotated in a direction in which air in a downstream area of the fixing unit is sucked and discharged out of the image forming apparatus. The image forming apparatus according to claim 1, wherein: