JPH11174873A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device capable of easily obtaining light transmissivity with nonoffset type color toner and preventing the occurrence of fixing offset. SOLUTION: A paper sheet P after a full color toner image is transferred in an image forming/transferring part is fed into a fixing device 35 as shown by an arrow B. The toner image on the paper P is melted in such a manner that heat and pressure are applied by a part where a heat generating roller 48 faces a press-contact roller 44, through belts 42 and 45. When the paper P is of a plain paper, a matting tone image is formed at a proper temp. for fixing as the middle temp. between temperatures A and B. When the paper P is an OHP one, the toner image exceeds an offset limit at the temp. B or above and is melted, to form a smooth surface without melting unevenness inside, so that an image extremely excellent in the light transmissivity is formed. The melted toner image is carried in a state where it is closely struck to the carrying surface of the belt 42 and forcibly cooled by the part where a rotary roller 43 faces a rotary roller 46. Even if not only the plain paper, but also the OHP sheet is used, an offset limit temp. or below is obtained and peeling from the belt 42 and further, ejection outside a machine are attained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device which sufficiently melts a toner on a recording member to a viscosity at which a fixing offset occurs, and then cools the toner to a viscosity at which a fixing offset does not occur before fixing and peeling. .

[0002]

2. Description of the Related Art Conventionally, there is an electrophotographic image forming apparatus. This type of image forming apparatus forms an electrostatic latent image on one or a plurality of photoconductors by optical writing, converts the electrostatic latent image into a toner image (development), transfers the developed toner image to paper, The sheet is sent to a fixing device, and the transferred image is fixed on the sheet by applying heat and pressure.

FIG. 4 is a side view schematically showing the above fixing device. The fixing device shown in FIG.
A pressure roller 2 for pressing against the heat roller 1, a temperature sensor 3 for contacting the peripheral surface of the heat roller 1 and measuring the temperature thereof;
Further, a cleaning member 4 is provided which abuts on the peripheral surface of the heat generating roller 1 to clean the same. Usually, these are assembled in a heat-insulating housing (not shown). The heating roller 1 includes a fluororesin layer 1-1, a core metal 1-2, and a heater 1-3. The pressing roller 2 includes a silicon rubber 2-1 and a core metal 2-2.
Comprises a felt member 4-1 and its supporting member 4-2.

A heat roller 1 and a pressure roller 2 transfer a toner image from an image forming / transferring unit on the left side of the drawing, and the paper 5 is fed into the fixing device as shown by an arrow A.
The toner image is discharged to the downstream side (right side in the figure) while applying heat and pressure while rotating to fix the toner image on the paper surface.

In recent years, not only monochrome image forming apparatuses but also image forming apparatuses capable of performing full color printing have been put to practical use. For full color printing,
At least three color toners of Y (yellow: yellow), M (magenta: red dye) and C (cyan: greenish blue), which are the three primary colors of the subtractive color mixture, are used. , The transparency of the secondary and tertiary colors is particularly taken into consideration in order to ensure the color developability after overpainting.

Further, full-color images are most suitable for so-called presentations in offices, lecture halls, various shelters, and the like, and are often used. In this case, a projection device (OHP: overhead projector) is used as a device that can be viewed by a large number of people at the same time. The toner image to be formed is also required to have good light transmittance after fixing, that is, good transparency.
Generally, the transparency of the toner after image fixing is achieved by the fact that the surface thereof is smooth and free from irregular reflection, and the degree of melting is good and there is no turbidity inside.

FIG. 5A is a view for explaining the light transmittance of a toner image. As shown in FIG. 3A, the toner image (toner layer) fused and fixed to the OHP film in the same manner as in the case of fixing to normal paper has the same color tone as that of plain paper when viewed as a reflection image. Can be However, when viewed as a transmission image, light is scattered and irregularly reflected by fine irregularities on the toner image surface, and only an insufficient transmission image is obtained. Therefore, the toner is sufficiently melted in the fixing unit so that irregularities are not generated on the surface of the consolidated toner portion after fixing due to incomplete melting and the smoothness is not lost. It is necessary to prevent turbidity due to unmelted components of the toner from occurring inside the consolidated toner after fixing, and to smooth the surface by sufficient melting.

As a method for smoothing the surface, there is a method of performing a laminating process as shown in FIG. This is because the melted hot-melt resin layer adheres and adheres to the fine irregularities on the surface of the toner image and solidifies, thereby integrating the toner layer and the hot-melt resin layer having the same light transmittance. When integrated, the interface of the OHP film is smooth on both the surface in contact with air and the surface on which the toner layer is fused. One of the interfaces of the hot melt resin layer is integrated with the toner layer, and the other is in close contact with the laminate film substrate (PET). As described above, the interface of the laminate film substrate (PET) is in close contact with the hot melt resin layer on one side, and the other interface is also formed in smooth contact with air. In other words, the OHP image after the lamination process has smooth front and back surfaces that are in contact with air as a whole, and also has a smooth internal interface or is integrated under almost the same light transmittance. As a result, the transmitted light travels straight along the incident optical path without scattering or irregular reflection.

[0009] However, the above-mentioned laminating method has the disadvantage that it is troublesome and expensive and is not common. Therefore, usually, as a simple and low-cost method of realizing transparency, a method using a resin that melts quickly at a relatively low temperature as a toner material is often adopted.

[0010]

By the way, such a low-temperature melting type toner melts almost instantaneously at the time of fixing and becomes in a very low viscosity state. The compatibility between the secondary color toner and the tertiary color toner becomes good, and good color developability as a color image is obtained. Further, since the melt viscosity is low and the pseudo-collecting force of the toner is small, the image surface after fixing, that is, after toner consolidation, becomes smooth. Therefore, on the one hand, a glossy image is obtained as an image for plain paper, and on the other hand, an image with good light transmittance is obtained as an image for OHP paper.

However, in this type of toner, the melt viscosity at the time of fixing is sharply reduced to a low viscosity. Therefore, in a contact-type fixing device using the heat generating roller 1 as shown in FIG. There is a property that a part of the toner is easily transferred to the surface of the heat generating roller 1 (offset is easily generated) (such toner is generally called an offset type toner). For this reason, when using this offset type toner, a large amount of oil is applied to the heat roller 1 in order to prevent the occurrence of offset, that is, to improve the releasability of the toner and the heat roller. Measures have been taken.

[0012] In this case, a large amount of the oil adheres to the paper 5, causing a problem that the user feels uncomfortable or uncomfortable. Further, since this type of toner has a gloss on the surface of the image as described above, it is unsuitable when a matte image without gloss is desired.

On the other hand, there is a non-offset type toner having a higher melt viscosity than such an offset type toner. This non-offset type toner has been conventionally used in a monochrome image copying machine or a monochrome printer. In recent years, this non-offset type toner has been proposed and commercialized as a color toner.

The non-offset type toner for color is designed to start melting from a lower temperature and to rapidly have a lower viscosity than the toner for black and white. As a result, good color developability is exhibited even for secondary colors and tertiary colors of a color image.

Further, an image using a non-offset type toner has a low gloss on the surface and becomes a matte image, and is therefore widely preferred for use in business documents and the like. However, since the image surface has no smoothness, the light transmittance is inferior. Therefore, it cannot be used as it is as a toner for OHP paper which is required to have good light transmittance for an image. That is, the fixing device of the conventional image forming apparatus, which mainly focuses on forming matte-tone images on plain paper, cannot stably obtain images on OHP paper having good light transmittance. is there.

FIG. 6A is a diagram conceptually showing a characteristic showing a relationship between a melting temperature and a light transmittance at the time of fixing in a non-offset type color toner. In FIG. 5A, the horizontal axis indicates the melting temperature, and the vertical axis indicates the light transmittance. Figure (a)
As shown in (2), as the melting temperature increases from temperature A to temperature B, the light transmittance increases from transmittance T1 to transmittance T2. Accordingly, it can be seen that even with a non-offset type color toner, good light transmittance can be obtained if a sufficient amount of heat is applied.

FIG. 6B is a diagram conceptually showing characteristics showing a relationship between a melting temperature and a melt viscosity at the time of fixing in a non-offset type color toner. In FIG. 3B, the horizontal axis indicates the melting temperature, and the vertical axis indicates the melt viscosity. Figure (b)
As shown in (2), as the melting temperature rises from temperature A to temperature B, the melt viscosity decreases from viscosity N2 to viscosity N1. The viscosity in the range of the above-mentioned viscosities N1 to N2 is a viscosity suitable for fixing (the viscosity is in a fixing region). If the viscosity is equal to or higher than the initial viscosity N2 of the melting, the viscosity is too high and is unsuitable for fixing (a region where the viscosity is not fixed). When the melting temperature becomes high and the viscosity is equal to or lower than N1, a high-temperature offset occurs (viscosity is in an offset region).

As can be seen from FIGS. 6A and 6B, a non-offset type color toner is used.
It can be seen that in order to obtain a sufficient light transmittance T2 shown in FIG. 6 (a), it is necessary to raise the temperature to the boundary temperature B just before the occurrence of the high-temperature offset as shown in FIG. 6 (b).

On the other hand, in the fixing device shown in FIG.
Is transferred from left to right as indicated by an arrow A in the figure, and the toner on the paper surface has the highest melting temperature when leaving the heating roller 1. If the setting is made, an offset easily occurs when the sheet 5 separates from the heat roller 1.

There are offsets that occur in the image transfer process and those that occur in the above-described image fixing process, and both are simply referred to as offset phenomena. The offset phenomenon that occurs is referred to as a fixing offset in the following description.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional circumstances,
An object of the present invention is to provide a fixing device which can easily obtain light transmittance using a non-offset type color toner and does not cause fixing offset.

[0022]

The construction of the fixing device of the present invention will be described below. First, the fixing device according to the first aspect of the present invention is an electrophotographic fixing device that records an image on a recording member using a non-offset type toner, wherein the toner to be fixed on the recording member is transferred via a fixing member. And a heating unit that melts the toner to a viscosity equal to or higher than a viscosity at which a fixing offset occurs due to heat and pressure, and cools the toner melted by the heating unit until the recording member is peeled from the fixing member until the viscosity does not cause a fixing offset. And a cooling unit.

Next, the fixing device according to the second aspect of the present invention
An electrophotographic fixing device that records an image on a recording member using a non-offset type toner, wherein the heating unit melts the toner to be fixed on the recording member to a viscosity or more that causes a fixing offset by heat and pressure. A cooling unit that cools the recording member until the toner melted by the heating unit has a viscosity that does not cause fixing offset; and a heating unit that stretches the recording member between the cooling unit and the heating unit. A first conveyor belt circulating to convey from the first to the cooling unit;
The heat and pressure of the heating unit are stretched between the heating unit and the cooling unit so that the heating unit and the cooling unit are circulated in the circulation direction of the conveyance surface while being in contact with the conveyance surface of the first conveyance belt. A second conveyance belt that relays to the recording member and conveys the recording member to the cooling unit in cooperation with the first conveyance belt.
A fixing device, wherein the recording member is separated from the second conveyor belt and discharged after passing through the cooling unit.

[0024]

Embodiments of the present invention will be described below with reference to the drawings. In the following description, the recording member is made of, for example, plain paper or OHP paper.
The fixing member includes, for example, a belt 42, the heating unit includes, for example, the heat roller 41, the pressing roller 44, and the like, the cooling unit includes, for example, rotating rollers 43 and 46, and the first transport belt includes, for example, the belt 45, The second conveyor belt is, for example, a belt 42 or the like.

FIG. 1A is a perspective view of an image forming apparatus according to an embodiment, and FIG. 1B is a side sectional view showing an internal configuration thereof. The image forming apparatus shown in FIGS. 1A and 1B is a tandem type color image forming apparatus as an example. 1A and 1B, the color image forming apparatus 10
Is, for example, a small color image forming apparatus large enough to be mounted on a desktop type personal computer rack,
An opening / closing tray 12 is provided on the front surface (left side in the figure) of the main body base 11, and a paper cassette 13 is detachably provided at a lower portion.

A paper discharge tray 15 is formed on an upper surface of the upper lid 14, and sheets on which an image is discharged from the upper paper discharge port 17 are stacked. Body base 1
An upper lid opening / closing switch 18 is provided on the upper surface of the upper side of the upper lid 14 in front of the upper lid 14.
An operation panel 19 including a plurality of data input keys and the like is provided.

In the inside of the main body base portion 11, a paper transporter is disposed approximately flat at the center in the front-rear direction, stretched and held between the driving roller 21 and the driven roller 22, and circulates clockwise in the drawing. A belt 23 is provided. An image forming unit 24 (24
a, 24b, 24c, 24d) are juxtaposed in a multi-stage manner in the sheet conveying direction.

The image forming section 24 (hereinafter referred to as the image forming section 2)
4d), a photoreceptor drum 25 and a cleaner 26, an initialization charger 27, and a write head 2 in contact with or close to the peripheral surface of the photoreceptor drum 25.
8. The developing device 29 is arranged. A developing roller 31 is rotatably supported in the lower opening of the developing device 29 in contact with the photosensitive drum 25.

The photosensitive drum 25, the cleaner 26,
Although not shown, the initialization charger 27, the developing device 29, and the like are assembled to a unit frame as an image forming unit, and the image forming unit is detachably provided on the main body base 11.

Further, the image forming section 24 downstream of the developing unit 29 of the image forming section 24a upstream (left side in the drawing) in the sheet conveying direction.
Each of the four developing units 29 up to the developing unit 29 of d includes Y (yellow: yellow) toner, M (magenta: red dye) toner and C (cyan: greenish blue) toner, which are three subtractive primary colors. , And Bk (black: black) toner exclusively used for printing characters, black portions of images, and the like.

Each of these color toners is composed of a non-offset type toner. The non-offset type toner is composed of, for example, a resin having a relatively high melting temperature and a dye or pigment obtained by appropriately setting the degree of polymerization of the molecular arrangement with a cross-linkable resin such as polyethylene.

The write head 28 is supported on the back surface of the upper cover 14 via a support member (not shown).
4 moves up and down in an arc with the opening and closing of the upper cover 14.
Is lowered by the closing of the initialization charger 27 and the developing roller 3
1 is positioned. The photosensitive drum 25 is
A transfer unit (not shown), which is in contact with the paper transport belt 23 and is disposed to face the photosensitive drum 25 from the back surface of the paper transport belt 23, is provided.

A standby roll pair 32 is disposed on the upstream side of the paper transport belt 23 in the paper transport direction, and the upstream side is branched laterally (front of the apparatus) and downward. The sheet feed roller 33 and the above-mentioned opening / closing tray 12 are disposed upstream of the sheet feeding roller 33. A paper feed path b composed of two guide plates (not shown) is formed below the branch, and the paper feed end of the paper cassette 13 is located at the beginning of the paper feed path b. . Feed roller 3 above the feed end
4 are provided.

On the other hand, a separation claw (not shown), a fixing device 35, a pair of paper discharge rollers 36, a switching lever (not shown) and the like are provided downstream of the paper conveyance belt 23 in the paper conveyance direction. The fixing device 35 includes upper and lower heat-insulating housings 35a and 35a.
In b, a fixing / conveying mechanism, which will be described in detail later, is provided. The downstream from the above-mentioned switching lever branches sideways and upwards. A rear discharge port 37 is formed in the lateral direction, and a discharge path c that is inverted from the top to the front is formed in the upward direction, and communicates with the upper discharge roller 17. A discharge roller pair 38 is provided in the upper paper discharge roller 17.

An electrical unit 39 on which a predetermined number of circuit boards can be mounted is provided between the paper transport belt 23 and the paper cassette 13. A control device including a plurality of electronic components is mounted on a circuit board provided in the electrical component unit 39.

Although not shown, the above-mentioned control device comprises a controller and an engine. The controller unit includes a CPU (central processing unit), a ROM (read only memory), an EEPROM (rewritable read memory), a frame memory, an image data transfer circuit, and the like, and print data input from a host computer or the like. Is analyzed, and print data is created and transferred to the engine unit.

The engine unit includes a CPU, a ROM, and the like.
The input side receives data and command signals from the controller unit, the output of a temperature sensor (not shown), the output of a paper detection sensor, and the like.The output side is a motor driver that drives a motor (not shown). A clutch driver for switching a drive system to be transmitted to each unit, a print driver for driving the write head 28 based on the print data, a bias power supply for supplying a predetermined bias current to the initialization charger 27, the developing roller 31, a transfer unit, and the like. A driver or the like is connected. The engine unit controls the driving of each unit based on data and command signals from the controller unit, the output of the temperature sensor, the output of the sheet detection sensor, and the like.

Next, the basic operation of image formation in the above configuration will be described again with reference to FIGS. 1 (a) and 1 (b). First, when the power is turned on to the apparatus main body 10 and the type of paper to be used, the number of sheets, the print mode, and other designations are input as keys or signals from a host device to be connected,
The apparatus main body 10 starts printing (printing).

First, the feed roller 34 makes one rotation to take out one sheet of the uppermost sheet P stored in the sheet cassette 13 and feeds the sheet P to the standby roller pair 32 via the sheet feed path b. I do. Alternatively, the paper feed roller 33 feeds the uppermost sheet of paper (usually special paper such as OHP paper) placed on the open / close tray 12 to the standby roller pair 32.

The standby roller pair 32 temporarily stops rotating,
The advance of the sheet is stopped by abutting the leading end of the sheet against the holding portion, the skew of the sheet is corrected, and the transfer timing is waited. The drive roller 21 rotates clockwise to start the circulating movement of the paper transport belt 23. Each image forming unit 24 is sequentially driven in accordance with the printing timing, and the photosensitive drum 25 rotates counterclockwise.

The initialization charger 27 applies a uniform high negative charge while sliding on the peripheral surface of the photosensitive drum 25 to initialize the photosensitive drum 25. The write head 28 is disposed facing the photosensitive drum 25 at a predetermined distance, and performs exposure corresponding to an image signal on the peripheral surface of the photosensitive drum 25 to initialize a high negative potential portion by initialization and the above exposure. An electrostatic latent image composed of a low negative potential portion is formed. The developing roller 31 is pressed against the photosensitive drum 25 to transfer the toner in the developing device 28 to a low potential portion of the electrostatic latent image to form a toner image on the peripheral surface of the photosensitive drum 25 (reversal development). .

At the timing when the leading end of the magenta toner image on the peripheral surface of the photosensitive drum 25 of the image forming portion 24a in the most upstream direction in the sheet conveying direction is rotated and conveyed to the opposing portion with the sheet conveying belt 23, the opposing portion is formed. The standby roller pair 32 starts rotating and feeds the paper P toward the paper transport belt 23 so that the print start position of the paper P coincides with the above. Paper P
Is electrostatically attracted to the paper transport belt 23 and transported downstream.

The sheet P is first conveyed to the first image transfer section formed by the photosensitive drum 25 of the image forming section 24a and the transfer device. The transfer unit transfers a transfer current output from a transfer bias power supply (not shown) to the sheet conveying belt 2.
3 to the sheet P. As a result, the magenta toner image on the photosensitive drum 25 is transferred to the paper P. Subsequently, the second image forming unit 24b from the upstream in the paper transport direction
The cyan toner image is transferred by the photoconductor drum 25 and the transfer device, and the yellow toner image by the photoconductor drum 25 of the third image forming unit 24c and the transfer device is further transferred.
Then, the photosensitive drum 25 of the most downstream image forming unit 24d
The black toner image is transferred by the transfer device.

The sheet on which the toner images of the four colors are superimposed and transferred is separated from the sheet conveying belt 23 by sheet separating claws, and is carried into a fixing device 35 described later in detail. The sheet P, to which heat and pressure are applied by the fixing device 35 to fix the toner image on the sheet surface, is carried out by being sandwiched by the pair of sheet ejection rollers 36.

Then, the paper is guided laterally by the switching lever and is discharged out of the apparatus from the rear paper outlet 37 with the image surface facing upward. Alternatively, the sheet is guided upward by the switching lever, reversed from the top to the front, and discharged onto the discharge tray 15 with the image surface facing downward from the upper discharge roller 17.

FIGS. 2A and 2B are diagrams for further explaining the operation of the fixing device 35 in the color image forming apparatus 10 operating as described above, and FIG. FIG. 4B is an enlarged view of FIG. 3, and FIG. 4B is a view showing a state where the melting temperature of the fixing toner changes. In addition, FIG.
The illustration of the heat insulating housings 35a and 35b shown in FIG. 1 is omitted.

As shown in FIG. 2A, the fixing device 35
An upper conveying mechanism including a heat roller 41, a belt 42 circulating in a counterclockwise direction, a rotating roller 43 extending and supporting the belt 42 together with the heat roller 41, a pressing roller 44, a belt circulating in a clockwise direction; 45, and a lower transport mechanism comprising a rotating roller 46 that stretches and supports the belt 45 together with the pressing roller 44.

The above-described heat roller 41 is provided as a whole in FIG.
Has a configuration similar to that of the heat generating roller 1 shown in FIG. 1, a heater 47 is disposed inside, and a temperature sensor 48 is disposed in contact with the peripheral surface. The press roller 44 has the same configuration as the press roller 2 shown in FIG. 4 as a whole. In the present embodiment, the heating roller 48 and the pressure roller 44 are opposed to each other via a lower circulating portion of the belt 42 and an upper circulating portion of the belt 45 so as to be in pressure contact with each other to form a heating portion.

On the other hand, the rotating rollers 43 and 46, which support the belts 42 and 45 on the other side with the heating roller 48 and the pressure roller 44, are forcibly forced out of the roller cylinder by an air cooling mechanism (not shown). Cooled to near room temperature.

A full-color toner image is formed on the sheet P by each image forming unit 24 in FIG.
Is transported to the fixing device 35 as shown by an arrow B in FIG. 2A, the toner image on the sheet P is first heated by a heating unit at a portion where the heat roller 48 and the pressure roller 44 are opposed to each other. Then, heat and pressure are applied between the heat generating roller 48 and the pressing roller 44 via the belts 42 and 45, and the heat is applied thereto.
As shown in the figure, the temperature of the toner on the sheet starts to rise from the start point of the sections S1 and S2,
Reaches the highest temperature at the end point of the sections S1 and S2 immediately after the release of the pressure bonding. The fused state (melt viscosity) at this time determines the fixed state (matte or translucent gloss).

When the melting temperature is close to the temperature A, the toner image becomes a matte image without gloss, and when the melting temperature exceeds the temperature B, good translucency can be expected, but offset does not occur. As described above.

The melting temperature is determined based on the temperature of the surface of the heat roller 48 detected by the temperature sensor 48.
It can be changed by controlling the output of the heater 47 inside. Also, the melting temperature can be changed by controlling the output of the heater 47 so as to maintain the surface temperature of the heat generating roller 48 constant, and changing the heating time by changing the conveying speed of the belts 42 and 45.

In the present embodiment, in the case of forming an image on plain paper, the control unit controls the melting temperature of the toner image to fall within a range between the temperature A and the temperature B. The temperature A and the temperature B are shown in FIG.
(b) The same setting as the melting temperature A and the melting temperature B shown in (b), and the temperature within the range of the temperature A and the temperature B is the melting temperature at which the optimal fixability of matte tone on plain paper is obtained. It is.

In the case of plain paper as described above, after being heated by the heating unit, it is sandwiched between the upper transport mechanism and the lower transport mechanism, and the toner image surface is transferred to the paper transport surface (downward circulation) of the belt 42 of the upper transport mechanism. 2) while being in close contact with
As shown in the figure, in the section S3 which is slightly naturally cooled between the sections S2 and S3 and passes through the facing portion of the rotating rollers 43 and 46,
Is forced to cool to or below the temperature A, and is separated from the conveyance surface of the belt 42 without causing an offset, and is discharged out of the apparatus by the discharge roller pair 36 shown in FIG.

In the case of forming an image on an OHP sheet, a drive system (not shown) is controlled by a control unit so that the sheet is conveyed at 1/6 the speed of the plain sheet while the surface temperature of the heat roller 48 is kept constant. Controlled. This transfer speed is a transfer speed at which the melting temperature becomes equal to or higher than the offset limit temperature B.

As a result, the toner image on the OHP sheet is sufficiently melted at a temperature equal to or higher than the temperature B as shown in sections S1 to S2 in FIG. As a result, as shown in FIG. 6 (a), an image having an extremely good light transmittance of a transmittance T2 or more is formed.

After being heated in the heating section, the OHP
The sheet is sandwiched between the upper and lower transport mechanisms, and is transported while the smooth formed image surface is in close contact with the paper transport surface (lower circulating portion) of the belt 42 of the upper transport mechanism. As shown in (b), the cooling is slightly spontaneously performed between the sections S2 and S3, and the cooling is forcibly performed between the sections S3 and S4 passing through the opposing portions of the rotating rollers 43 and 46. Is cooled to an intermediate temperature.

The viscosity characteristic of the toner in this temperature range is a characteristic region where no high-temperature offset (fixing offset) occurs, as shown in FIG. by this,
The OHP sheet is peeled off from the conveying surface of the belt 42 without causing an offset, and is discharged outside the apparatus by the discharge roller pair 36 shown in FIG.

As described above, by using a non-offset type color toner to apply heat to a melt viscosity equal to or higher than the fixing viscosity and to cool to a temperature at which no offset occurs before fixing and peeling, a matte tone image and light transmission can be obtained. Any of good images can be formed arbitrarily, and the occurrence of fixing offset can be prevented.

In the above embodiment, plain paper and OHP
The control unit determines (determines) whether to use the paper (designation of the type of paper to be used) by a key input from the operation panel 19 or a signal from a host device to be connected. , Without being limited to this
It may be detected by a paper sensor or the like.

FIG. 3A is a diagram showing an example of the arrangement of paper sensors for detecting the type of paper, and FIG. 3B is a table showing the reflection efficiency of OHP paper and plain paper. As shown in FIG. 1A, a reflection type photo sensor 51 is disposed above the sheet feeding path between the sheet feeding roller 33 and the standby roller pair 32 of the opening / closing tray 12 shown in FIG. You. This photo sensor 51
A black non-reflective plate 52 is arranged below the sheet feeding path facing the image forming apparatus. The paper P fed from the open / close tray 12 to the standby roller pair 32 by the paper feed roller 33 is
1 and the non-reflection plate 52.

As shown in FIG. 3B, assuming that the light reflectance of plain paper is 100%, the light reflectance of OHP paper as compared with this is extremely low at 30%. The remaining 70% of the light transmitted through the OHP sheet is absorbed by the non-reflective plate 52 and is not reflected. Therefore, the output of the reflection type photosensor 51 automatically determines whether the sheet P is plain paper or OHP sheet. Can be easily determined. Based on this determination, the control unit may control the conveying speed of the fixing device 35 to the normal speed or 1/6 speed.

[0063]

As described in detail above, according to the present invention, a normal amount of heat and a higher amount of heat are freely applied to sufficiently cool before fixing and peeling, so that a non-offset type color toner can be obtained. Heat can be applied to the melt viscosity equal to or higher than the fixing viscosity, and it can be cooled to a temperature at which no offset occurs before the fixing is peeled off. It is possible to provide a fixing device that does not generate any heat.

[Brief description of the drawings]

FIG. 1A is a perspective view of a color image forming apparatus according to an embodiment, and FIG. 1B is a side sectional view showing an internal configuration thereof.

FIGS. 2A and 2B further illustrate the operation of the fixing device in the color image forming apparatus. FIG. 2A is an enlarged view of the configuration of the fixing device, and FIG. FIG.

FIG. 3A is a diagram showing an example of the arrangement of a paper sensor for detecting the type of paper, and FIG. 3B is a table showing the reflection efficiency of OHP paper and plain paper.

FIG. 4 is a side view schematically showing a conventional fixing device.

FIG. 5 (a) is a view for explaining light transmittance of a toner image,
(b) is a diagram illustrating surface smoothing by lamination.

6A is a characteristic conceptual diagram showing a relationship between a fixing melting temperature of a non-offset type color toner and light transmittance, and FIG.
3 is a characteristic conceptual diagram showing a relationship between a fixing melting temperature and a melt viscosity of a non-offset type color toner.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heat generation roller 1-1 Fluororesin layer 1-2 Core metal 1-3 Heater 2 Pressure contact roller 2-1 Silicon rubber 2-2 Core metal 3 Temperature sensor 4 Cleaning member 4-1 Felt member 4-2 Support member 10 Color image Forming device 11 Main body base 12 Opening / closing tray 13 Paper cassette 14 Top cover 15 Paper discharge tray 17 Upper paper discharge port 18 Top cover opening / closing switch 19 Operation panel 21 Drive roller 22 Follower roller 23 Paper transport belt 24 (24a, 24b, 24c, 24d) Image Forming Unit 25 Photoconductor Drum 26 Cleaner 27 Initializing Charger 28 Write Head 29 Developing Unit 31 Developing Roller 32 Standing Roller Pair 33 Feeding Roller 34 Feeding Roller 35 Fixing Device 35a, 35b Heat Insulating Housing 36 Paper Delivery Roller Pair 37 Rear paper exit 38 Discharge roller pair 39 Electrical unit 41 Heat generation low La 42, 45 Belt 43, 46 Rotating roller 44 Pressure contact roller 47 Heater 48 Temperature sensor 51 Reflective photo sensor 52 Black non-reflective plate

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasushi Nakamura 2-229 Sakuragaoka, Higashiyamato-shi, Tokyo Inside Casio Electronics Co., Ltd. (72) Inventor Kenji Takano 2-229 Sakuragaoka, Higashiyamato-shi, Tokyo Casio Electronics Industries Inside the corporation

Claims (2)

[Claims] 1. An electrophotographic fixing device for recording an image on a recording member using a non-offset type toner, wherein the toner to be fixed on the recording member is fixed by heat and pressure through a fixing member. And a cooling unit that cools the toner melted by the heating unit to a viscosity that does not cause a fixing offset before peeling the recording member from the fixing member. Characteristic fixing device. 2. An electrophotographic fixing device for recording an image on a recording member using a non-offset type toner, wherein the toner to be fixed on the recording member has a viscosity higher than a viscosity at which a fixing offset is caused by heat and pressure. A heating unit for melting; a cooling unit for cooling the recording member until the toner melted by the heating unit has a viscosity that does not cause a fixing offset; and the recording unit stretched between the cooling unit and the heating unit. A first transport belt that circulates and transports the member from the heating unit to the cooling unit; and a first transport belt that contacts the transport surface of the first transport belt and circulates in a circulating direction of the transport surface. A second member that is stretched between a heating unit and the cooling unit, relays heat and pressure of the heating unit to the recording member, and conveys the recording member to the cooling unit in cooperation with the first conveyance belt. With a conveyor belt Fixing apparatus characterized by discharging the recording member was peeled off from the second conveyor belt after said cooling section passing through.