JPH1184941A - Image forming device - Google Patents

Abstract

(57) Abstract: Provided is an image forming apparatus which enables stable fixing even when toners having different softening points are used, and enables low power consumption of a fixing device. An image forming section for forming an unfixed image on a recording material using toners having different softening points, and heating and pressurizing the recording material while nipping and conveying the recording material, the unfixed image is formed on the recording material. In the image forming apparatus, the image forming unit further includes a detecting unit that detects image density information, and the fixing temperature is set according to the image density detected by the detecting unit. Change (S
102-S106).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image forming apparatus such as an electrophotographic apparatus for forming an image.

[0002]

2. Description of the Related Art Generally, an image forming process in an image forming apparatus such as an electrophotographic apparatus includes a step of forming a latent image on a photosensitive drum based on an image signal for a document image, and a step of developing a latent image on the photosensitive drum with a developing device. Visualizing the image as a developing material image, transferring the visible image on the photosensitive drum to the recording material, fixing an unfixed image formed on the recording material by heating and pressing as a permanent image And a step of causing

The images formed on the recording material include a black-and-white image using only black and a color image using a plurality of colors. In a fixing step in an image process for forming a color image, a toner image in which a plurality of colors are stacked is fixed on a recording material. Especially in full color images, yellow,
Sharp melt toners having a low softening point, that is, a low melting point, are used in order to mix each of the magenta, cyan, and black colors by heating and melting a plurality of layers of toner forming a toner image in order to reproduce colors close to the image of the original. Can be
In general, the toners of the respective colors are designed to have the same softening point.

Conventionally, as a method of controlling gloss, a method of changing a fixing temperature or a process speed has been proposed. Further, in a full-color image forming apparatus in which a black toner having a high softening point and a color toner having a low softening point are combined, a method of controlling the glossiness of an image by changing the order of lamination of the black toner and the color toner has also been proposed. ing.

[0005] In addition, for example, when an area for forming an image is small, such as a character original, an excessive amount of heat is applied to fix an unfixed image.

[0006]

The reason that color toners having different softening points for each color could not be used is that the fixing temperature is constant, so that the fixing temperature region (A3 The temperature range in which the size of the recording material can be sufficiently fixed from the leading edge to the trailing edge) is different, so the common fixing temperature range when mixing colors in a full-color image is narrowed, and stable fixing becomes difficult. is there.

Further, when the original has many white backgrounds such as a character original, the amount of heat required for fixing is reduced. However, since the fixing temperature cannot be controlled while checking the image density, the amount of heat is increased more than necessary. It is a situation to give.

An object of the present invention is to provide an image which enables stable fixing even when toners having different softening points are used, enables low power consumption of a fixing unit, and enables control of gloss of a permanent image. It is intended to provide a forming apparatus.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an image forming section for forming an unfixed image on a recording material by using toners having different softening points; A fixing means for fixing the unfixed image on the recording material by heating and pressurizing the recording medium, and a fixing means for changing a fixing temperature, wherein a detecting means for detecting image density information is provided in the image forming section. The fixing temperature is changed according to the image density detected by the detecting means, and the gloss of the image is controlled by changing the order of lamination of the toner.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) FIG. 1 is a sectional view showing a schematic configuration of a digital four-color full-color image forming apparatus showing an image forming apparatus according to a first embodiment of the present invention.

The image forming apparatus shown in FIG. 1 has a lower digital color image printer section (hereinafter simply referred to as "printer section") I and the aforementioned digital color image reader section (hereinafter simply referred to as "reader section") II. For example, based on the image of the document D read by the reader unit II,
An image is formed on the recording material P by the printer unit I.

Hereinafter, the configuration of the printer unit I and then the configuration of the reader unit II will be briefly described.

The printer section I has a photosensitive drum 1 as an image carrier that is driven to rotate in the direction of arrow R1.

Around the photosensitive drum 1, a primary charger (charging means) 2, an exposure means 3,
A developing device (developing means) 4, a transfer device 5, a cleaning device 6, a pre-exposure lamp 7, and the like are arranged.

Below the transfer device 5, ie, the printer unit I
In the lower half portion, a paper feeder 8 for the recording material P is disposed, and further, a separating unit 9 is provided above the transfer device 5, and a downstream side of the separating unit 9 (downstream in the conveying direction of the recording material P). (Side), a fixing device 10 and a paper discharge unit 11 are arranged.

The photosensitive drum 1 has a substrate 1a on an aluminum drum and an OPC (organic optical semiconductor) photosensitive member 1b covering the back side thereof, and is driven in a predetermined direction in the direction of arrow R1 by driving means (not shown). It is configured to be driven to rotate at the process speed (peripheral speed). The photosensitive drum 1 will be described later in detail.

The primary charger 2 includes a shield 2a having an opening at a portion facing the photosensitive drum 1, and a discharge wire 2 arranged inside the shield 2a in parallel with the bus of the photosensitive drum 1.
b and a grid 2c arranged in the opening of the shield 2a to regulate the charging potential. A charging bias is applied to the primary charger 2 by a power supply (not shown), so that the surface of the photosensitive drum 1 is uniformly charged to a predetermined polarity and a predetermined potential.

Exposure means 3 includes a laser output section (not shown) for emitting a laser beam based on an image signal from a reader section II described later, and a polygon mirror 3a for reflecting the laser beam.
, A lens 3b, and a mirror 3c. Exposure means 3
The laser beam irradiates the surface of the photosensitive drum 1 with the laser beam, thereby exposing the photosensitive drum 1 and removing an electric charge of an exposed portion to form an electrostatic latent image. In the present embodiment, the electrostatic latent image formed on the surface of the photosensitive drum 1 is color-separated into four colors of yellow, cyan, magenta, and black based on the image of the original, and a static image corresponding to each color is formed. Electrostatic latent images are sequentially formed.

The developing device 4 has four developing units in order from the upstream side along the rotation direction of the photosensitive drum 1 (direction of arrow R1), that is, each color of yellow, magenta, cyan, and black, each of which is made of resin. Developing devices 4Y, 4C, 4M, and 4Bk containing the toner (developer). Each of the developing units 4Y, 4C, 4M, and 4Bk has a developing sleeve 4a for attaching toner to an electrostatic latent image formed on the surface of the photosensitive drum 1, and has a predetermined color used for developing the electrostatic latent image. The developing device is alternatively arranged at a developing position close to the surface of the photosensitive drum 1 by the eccentric cam 4b,
The toner is attached to the electrostatic latent image via the developing sleeve 4a to form a toner image (visible image) as a visible image. The three color developing units other than the developing unit used for development are retracted from the developing position.

The transfer device 5 includes a transfer drum (recording material carrying pair) 5a that carries the recording material P on the surface, a transfer charger 5b that transfers the toner image on the photosensitive drum 1 to the recording material P, and a recording material P.
Charger 5c for causing the transfer drum 5a to adsorb
And an attraction roller 5d and an inner charger 5e opposed thereto,
A recording material carrying sheet 5g made of a dielectric pair is integrally stretched in a cylindrical shape in a peripheral opening area of a transfer drum 5a having an outer charger 5f and rotatably driven in the direction of arrow R5. Have been. As the recording material supporting sheet 5g, a dielectric sheet such as a polycarbonate film is used. The transfer device 5 is configured to adsorb and carry the recording material P on the surface of the transfer drum 5a.

The cleaning device 6 includes a cleaning blade 6a for scraping off residual toner remaining on the surface of the photosensitive drum 1 without being transferred to the recording material P, and a cleaning container 6b for collecting the scraped toner.

The pre-exposure lamp 7 is arranged adjacent to the upstream side of the primary charger 2 and removes unnecessary charges on the surface of the photosensitive drum 1 cleaned by the cleaner 6.

The paper feeder 8 is provided with recording materials P of different sizes.
Paper feed cassette 8a for stacking and storing paper, a paper feed roller 8b for feeding the recording material P in the paper feed cassette 8a, a number of transport rollers, a registration roller 8c, and the like, and a recording material of a predetermined size. P is supplied to the transfer drum 5a.

The separating means 9 is provided for the recording material P after the transfer of the toner image.
Charger 9a for separating the toner from the transfer drum 5a,
It has a separation claw 9b and a separation push-up roller 9c.

The fixing device 10 is arranged below a fixing roller 10a having a heater inside and a fixing roller 10a.
Pressure roller 1 for pressing recording material P against fixing roller 10a
0b.

The paper discharge unit 11 includes a conveyance path switching guide 11 a and a discharge roller 11 which are disposed downstream of the fixing device 10.
b, a paper discharge tray 11c and the like. Further, below the conveyance path switching guide 11a, a conveyance vertical path 11d, a reversing path 11e, a stacking member 11f, an intermediate tray 11g, and a conveyance roller for forming an image on both sides of one recording material P are formed. 11h, 11i, a reversing roller 11j and the like are arranged.

Between the primary charger 2 and the developing device 4 around the photosensitive drum 1, there is provided a potential sensor S1 for detecting the charged potential on the surface of the photosensitive drum, and between the developing device 4 and the transfer drum 5a. Between them, density sensors S2 for detecting the density of the toner image on the photosensitive drum 1 are arranged.

Next, the reader section II will be described. The reader unit II disposed above the printer unit I includes:
An original table glass 12a on which an original D is placed; an exposure lamp 12b for exposing and scanning the image surface of the original D while moving;
A plurality of mirrors 12c that further reflect the reflected light from
It has a lens 12d for condensing the reflected light, a full color sensor 12e for forming a color separation image signal based on the light from the lens 12d, and the like. The color-separated image signal is processed by a video processing unit (not shown) through an amplifier circuit (not shown).
To be sent.

Next, the operation of the image forming apparatus having the above configuration will be described.
A brief description will be given while adding some components. In the following description, four full-color images are formed in the order of yellow, cyan, magenta, and black.

The image of the original D mounted on the original platen glass 12a of the reader unit II is irradiated by an exposure lamp 12b, color-separated, and the yellow image is first read by a full-color sensor 12e and subjected to predetermined processing. Is sent to the printer unit I as an image signal.

In the printer section I, the photosensitive drum 1 has an arrow R
It is driven to rotate in one direction, and the surface is uniformly charged by the primary charger 2. A laser beam is emitted from a laser output unit of the exposure unit 3 based on the image signal sent from the reader unit II, and the charged photosensitive drum 1 surface is exposed by a light image E via a polygon mirror 3a and the like. I do. The exposed portion of the surface of the photosensitive drum 1 has its charge removed, whereby an electrostatic image corresponding to yellow is formed.

In the developing device 4, the yellow developing device 4Y is arranged at a predetermined developing position, and the other developing devices 4Y are arranged.
C, 4M, and 4Bk are retracted from the developing position. The electrostatic latent image on the photosensitive drum 1 has yellow toner attached thereto by the developing device 4Y and is visualized to be a toner image.

The yellow toner image on the photosensitive drum 1 is transferred to the recording material P carried on the transfer drum 5a. The recording material P is supplied to the transfer drum 5a at a predetermined timing from a predetermined paper feeding cassette 8a having a size suitable for a document image via a paper feeding roller 8b, a conveying roller, a registration roller 8c, and the like. Things.

The recording material P supplied in this manner is adsorbed so as to wind around the surface of the transfer drum 5a, and is fed by an arrow R5.
, And the yellow toner image on the photosensitive drum 1 is transferred by the transfer charger 5b.

On the other hand, the photosensitive drum 1 after the transfer of the toner image
The residual toner on the surface is removed by the cleaning device 6, and unnecessary charges are further removed by the pre-exposure lamp 7 to be used for the next image formation starting from the primary charger.

The processes from the reading of the original image by the reader unit II, the transfer of the toner image to the recording material P on the transfer drum 5a, the cleaning of the photosensitive drum 1, and the neutralization are performed by other processes than yellow. The same applies to the colors, that is, cyan, magenta, and black, and the four color toner images are transferred onto the recording material P on the transfer drum 5a so as to overlap.

Recording material P to which four color toner images have been transferred
Is separated from the transfer drum 5a by a separation charger 9a, a separation claw 9b, and the like, and is conveyed to the fixing device 10 with an unfixed toner image carried on the surface. The recording material P is a fixing device 1
The fixing roller 10a and the pressing roller 10b are heated and pressurized, and the toner image on the surface is fused and fixed.

The recording material P after fixing is discharged onto a discharge tray 11c by a discharge roller 11b. When images are formed on both sides of the recording material P, the fixing device 10 immediately drives the transport path switching guide 11a to transport the discharged recording material P to the reversing path 11e via the transport vertical path 11d. After being guided, the sheet is retreated in a direction opposite to the direction in which the sheet is fed by the reverse rotation of the reversing roller 11j with the rear end thereof as the leading end, and is stored in the intermediate tray 11g. After that, an image is formed on the other surface again by the above-described image forming process, and then discharged onto the discharge tray 11c.

On the transfer drum 5a after the separation of the recording material P, the recording material supporting sheet 5g is used in order to prevent scattering of powder on the recording material supporting sheet 5g, adhesion of oil on the recording material P, and the like. Fur brush 1 facing each other through
Cleaning is performed by 3a and the backup brush 13b, and by the oil removing roller 14a and the backup brush 14b. Such cleaning is performed before or after image formation, and is performed as needed when a jam (paper jam) occurs.

Next, the fixing device 10 will be described with reference to FIG.

In FIG. 2, a fixing roller 10a that comes into contact with the toner image is a hollow iron core metal 31 having a thickness of 0.7 mm.
A 1 mm thick silicone rubber layer 32 on the top, and FE on the outside
It has a P (tetrafluoroethylene-hexafluoropropylene copolymer) coat layer 33 and has a diameter of 40 mm.

On the other hand, the pressure roller 10b has a 5 mm thick silicone rubber layer 35 and a PFA (tetrafluoroethylene-perfluoroalkylvinyl ether copolymer) tube layer 36 on a solid iron core 34. Provided and formed to a diameter of 30 mm.

In the fixing roller 10a, halogen heaters 37 and 38, which are heat generating means, are provided in the metal core 31. The temperature of the fixing roller 10a is detected by a thermistor 39 provided on the fixing roller 10a, and based on the detected temperature, the halogen heaters 36 and 3 are controlled by the control device 40.
7 is controlled so that the temperature of the fixing roller 10a is maintained constant. The fixing roller 10a and the pressing roller 10b are pressed by a pressing mechanism (not shown) with a total pressure of about 30 kg. The fixing roller 10a and the pressure roller 10b have a process speed of 110 mm / sec.
It is rotating at c.

In the fixing device 10 described above, the recording material P carrying the unfixed toner image on its surface is nipped and conveyed to a fixing nip between the fixing roller 10a and the pressure roller 10b, and is heated and pressurized at this time. Is fixed.

Next, referring to FIGS. 3 and 4, a description will be given of the means for detecting the density information of an image according to the present embodiment.

In FIG. 3, an image of a document 51 to be copied is projected by a lens 52 onto an image pickup device 53 such as a CCD. The image sensor 53 decomposes a document image into a number of pixels and generates a photoelectric conversion signal corresponding to the density of each pixel. The analog image signal output from the image sensor 53 is sent to an image signal processing circuit 54, where the analog image signal is converted into a pixel image signal having an output level corresponding to the density of the pixel. Sent.

The pulse width modulation circuit 55 forms and outputs a laser drive pulse having a width (time length) corresponding to the level of each input pixel image signal. That is, as shown in FIG. 4A, a wider drive pulse W is applied to a high-density pixel image signal, and a narrower drive pulse S is applied to a low-density pixel image signal. , A drive pulse I having an intermediate width is formed for a medium-density pixel image signal.

The laser drive pulse output from the pulse width modulation circuit 55 is supplied to the semiconductor laser 56, and causes the semiconductor laser 56 to emit light for a time corresponding to the pulse width. Therefore, the semiconductor laser 56 is driven for a longer period of time for high-density pixels, and is driven for a shorter period of time for low-density pixels.

Therefore, the photosensitive drum 1 is exposed to a high-density pixel in a longer range in the main scanning direction and to a lower-density pixel in a shorter range in the main scanning direction by an optical system described later. Is done. That is, the dot size of the electrostatic latent image differs according to the density of the pixel. In addition, FIG.
, L, M, and H respectively.
Indicated by

The laser beam 56a emitted from the semiconductor laser 56 is swept by a rotary polygon mirror 57, and a lens 58 such as an f / θ lens and a fixed mirror for directing the laser beam 56a toward the photosensitive drum 1 as an image carrier. By 59, a spot image is formed on the photosensitive drum 1. Thus, the laser beam 56a scans the photosensitive drum 1 in a direction substantially parallel to the rotation axis of the photosensitive drum 1 (main scanning direction) to form an electrostatic latent image.

By the formation of the electrostatic latent image, the level of the output signal of the image signal processing circuit 54 is counted for each color. This counting is performed as follows in the embodiment of FIG.

First, the output signal of the pulse width modulation circuit 55 is supplied to one input of an AND gate 60.
The clock pulse shown in FIG. 4B from the clock pulse oscillator 61 is supplied to the other input of the ND gate 60. Accordingly, the AND gate 60 outputs the signal shown in FIG.
As shown in (1), the number of clock pulses corresponding to each pulse width of the laser drive pulses S, I, W, that is, the number of clock pulses corresponding to the density of each pixel are output. The number of clock pulses is integrated by the counter 62 for each pixel, and the video count number is calculated. The video count of each pixel is supplied to the CPU 63.

The ROM 64 stores a single-color fixing temperature (described later) of each color toner. The CPU 63 calculates the ratio of the density of each color per original from the video count number of each pixel and each color, determines the optimal fixing temperature at the time of color mixing, and sends the mixed color fixing temperature to the control device 40 of the fixing device. Output. Then, the control device 40 controls the temperature of the fixing device 10.

Next, a method for determining the mixed color fixing temperature in the present embodiment will be described with reference to FIGS.

FIG. 5 shows a fixing temperature range of the magenta toner used in the present embodiment. The paper type used was Canon recommended paper SK80 (80 g / m ² ), A3, and the amount of applied toner was 1.0 g / A4. Others followed the conditions of the present embodiment.

In the region below the solid line shown in the graph, a low-temperature offset occurs, and in the region above the broken line, a high-temperature offset occurs. Therefore, in FIG.
In the region between the solid line and the broken line, a good fixed image is obtained.

Here, the temperature at the center of the fixing temperature region when the amount of applied toner is 100% (when the entire surface is solid) is defined as a single-color fixing temperature Tm (° C.). For the cyan toner, yellow toner, and black toner, Tc,
ty and Tk (all units are in ° C.).

Further, the ratio of the density of the magenta toner per original is Dm (%). Similarly, let Dc, Dy, and Dk be the percentages of the density of each color toner (all units are%). In addition, in consideration of the non-colored area of the original, that is, the area of the non-image area, the ratio of the area of the non-image area per original is set to Dw (%). Naturally, Dm
+ Dc + Dy + Dk + Dw is 100.

FIG. 6 shows a flowchart for calculating the mixed color fixing temperature T.

First, when the start button is pressed to copy a document, the document is read as described above in block S101, and a photoelectric conversion signal corresponding to the density of each pixel of the document image is generated.

Next, in block S102, the output level of each pixel is counted and integrated to calculate a video count. This pulse integration value is sent to the CPU 63, and the density Dm, Dc, Dy, Dk, Dk,
And Dw are determined.

Next, in block S104, the mixed-color fixing temperature T1 for two colors having a high single-color fixing density among the toners used for copying the document is determined by the following equation.

T1 = (Th−Tl) * Dh / (Dh + Dl) + Tl where Th is the single color fixing temperature of the toner having the higher single color fixing temperature, Tl is the single color fixing temperature of the toner having the lower single color fixing temperature, Dh is the density of the toner having the higher single-color fixing temperature,
Dl indicates the density of the toner having the lower single-color fixing temperature.

Here, if the read original is monochrome, the fixing temperature T1 obtained in block S104 is sent to the control device of the fixing device, and the fixing temperature is controlled in block S105.

If the read original is a multi-color original,
In block S106, the two colors having a high single-color fixing temperature are regarded as a single-color toner having a single-color fixing temperature Tl and a density Dh + Dl. Then, the block S for the toner and the toner having the next highest single-color fixing temperature (of course, this toner has the third highest single-color fixing temperature as a whole).
After the calculation of block 104 is performed for all the toners, the mixed color fixing temperature T1 obtained at that time is output to block S105.

As an example, in the case of a full-color original, the operation of block S104 is repeated four times.

[0067]

【Example】

[Embodiment 1] In this embodiment 1, a total toner amount of two colors is set to 1 using magenta toner (single-color fixing temperature 190 ° C.) and cyan toner (single-color fixing temperature 170 ° C.) having different single-color fixing temperatures. 0 g / A4 and the ratio of magenta toner was 100% (cyan 0%), 70% (30%), 5%.
0% (50%), 30% (70%), 0% (100%)
Was changed. The order of superimposing the toner was such that the lower layer was cyan toner and the upper layer was magenta toner. The paper type used was Canon recommended paper SK80 (80 g / cm ² ) and A3.

In the first embodiment, magenta toner,
For each of the cyan toners, a non-magnetic pulverized toner manufactured by a pulverization method was used.

In the pulverization method, a pigment, an organic dye, or the like is added and mixed as a colorant into a thermoplastic polymer, and a charge adjusting material and other additives are added as necessary. This is a method for producing a toner via

The actual fixable temperature was also measured for each toner density ratio.

In the conventional image forming apparatus, when toners having different fixing temperatures are used as in the first embodiment, the toner having a higher fixing temperature is used as a reference.
Regarding the toner combination of the present embodiment, the fixing temperature at the time of color mixing is 190 ° C. irrespective of the toner concentration.

Table 1 shows the results of Example 1. In each case, good and stable fixing could be performed at a temperature lower than the conventional fixing temperature of 190 ° C.

[0073]

[Table 1]

Example 2 In Example 1, a polymerized toner obtained by a polymerization method was used for both the magenta toner and the cyan toner. The respective single-color fixing temperatures were set the same as in the first embodiment.

In the polymerization method, a colorant and other internal additives are added and dispersed in a monomer, and the resulting mixture is dispersed to droplets of a required particle size, polymerized, washed, filtered, dried and classified. This is a method of manufacturing a toner through a process.

Table 2 shows the results of Example 2. In this case as well, good and stable fixing was achieved at a temperature lower than the conventional fixing temperature of 190 ° C.

[0077]

[Table 2]

Example 3 In Example 2, the order of laminating the magenta toner and the cyan toner was changed, and the glossiness of the obtained permanent image was measured. Gloss is D
Using an IN 75 ° meter, the measurement was performed at the center of the permanent image.

Table 3 shows the measurement results in this case. Glossiness was higher for a permanent image in which the upper layer of the toner layer was a cyan toner having a low single-color fixing temperature. Therefore, the gloss of the permanent image could be increased by providing a toner having a low single-color fixing temperature on the toner layer when mixing colors.

As a comparative example, the same measurement was performed in Example 3 using a conventional magenta toner and a cyan toner having the same softening point. The single color fixing temperature of the toner used here was 180 ° C.

In this case, no change in gloss was observed in any of the results of the comparative examples.

[0082]

[Table 3]

[0083]

As described above, according to the image forming apparatus of the present invention, when toners having different softening points are used, stable fixing can be achieved by adjusting the fixing temperature according to the density of each color of the document. Therefore, the fixing temperature at the time of single color and at the time of mixed color can be lowered, so that the power consumption of the fixing device can be reduced.

Also, by changing the order of lamination of the toner layers, it is possible to control the gloss of the permanent image.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a schematic configuration of a first embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a diagram illustrating a schematic configuration of a fixing device of the image forming apparatus of FIG. 1;

FIG. 3 is a block diagram of the image forming apparatus of FIG. 1;

FIG. 4 is a waveform chart showing a method for counting density information of the image information signal in FIG. 3;

FIG. 5 is a diagram illustrating a relationship between a single-color fixing temperature of a toner used in the present invention and an amount of applied toner.

FIG. 6 is a flowchart for calculating a mixed-color fixing temperature in the control block diagram of FIG. 3;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photosensitive drum 10 fixing device 40 control device 51 document 52 lens 53 imaging element 54 image signal processing circuit 55 pulse width modulation circuit 56 semiconductor laser 57 rotating polygon mirror 58 lens 59 fixed mirror 60 AND circuit 61 clock pulse oscillator 62 counter 63 CPU 64 ROM

Claims (3)

[Claims] An image forming section for forming an unfixed image on a recording material using toners having different softening points, and heating and pressurizing the recording material while nipping and transporting the recording material, the unfixed image is formed on the recording material. An image forming apparatus having a fixing temperature variable fixing unit for fixing the image on the image forming apparatus; An image forming apparatus including a fixing temperature control unit that changes a fixing temperature of the unit. 2. The image forming apparatus according to claim 1, wherein the control unit determines the fixing temperature based on each image density corresponding to each toner having a different softening point and its single-color fixing temperature. . 3. The image forming apparatus according to claim 1, wherein the gloss of the image is controlled by changing the order in which toners having different softening points are stacked.