JPH11174891A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate irregular gloss apt to be caused at the time forming an image with single black toner by providing a fixing device with an applied heating value varying means for varying a heating value applied to a toner image on transfer material through a fixing nip part according to whether the toner image is single black toner image or not. SOLUTION: The fixing device 18 is provided with a pressuring force varying means 71 functioning as the applied heating value varying means, and the irregular gloss is eliminated by decreasing pressuring force and reducing heating amount in the case of forming the image with the single black toner. The means 71 is composed of a bearing rotatably supporting both ends in the longitudinal direction of the shaft center of the pressure roller 52, an energizing member such as a compression spring, etc., for energizing the bearing fixed at the edge part toward a fixing roller 51, and a pressing member for pressing the base end side of the energizing member to the roller 51 side. By properly moving the pressing member, the pressuring force of the roller 52 to the roller 51 is varied.

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 and a laser beam printer.

[0002]

2. Description of the Related Art An electrophotographic color image forming apparatus,
For example, in a four-color full-color copying machine or a laser beam printer, four color toner images of yellow, magenta, cyan, and black are transferred to the surface of a transfer material such as paper in an image forming unit. Subsequently, the transfer material carrying the unfixed toner images of the four colors is heated and pressurized while being nipped and conveyed at a fixing nip portion (pressing portion) between a fixing roller and a pressure roller of the fixing device. As a result, the four color toner images are fused and fixed on the surface of the transfer material to finally obtain a color image.

[0003]

However, in the above-described image forming apparatus, when an image is formed in a single black color, there is a problem that gloss unevenness occurs and the image quality tends to deteriorate. .

At the time of fixing, the toner is melted. At this time, if the toner is melted too much, the fluidity becomes too high, so that the resin component of the toner flows along the fibers of the transfer material,
Where the fiber mesh is uniform, the flowing toner resin components are combined with each other to form a flat surface, while where the fiber mesh is uneven, the toner resin components are not combined with each other, resulting in an uneven surface. In the above-mentioned plane portion, light is specularly reflected and gloss is produced. On the other hand, irregularities are irregularly reflected and gloss is not produced, and the surface looks whitish. For this reason, minute gloss unevenness occurs on the image.

[0005] The above-mentioned gloss unevenness is smaller for black toner.
Further, it becomes more remarkable as the fibers of the paper (transfer material) are coarser, the amount of the release agent is smaller, and the total amount of the toner is smaller. Since the black toner has a large contrast, a slight difference in gloss is noticeable as uneven gloss. On the other hand, in other color toners (yellow, magenta, and cyan toners are collectively referred to as the same hereinafter), since the contrast is not as large as that of the black toner, gloss unevenness is not visually noticeable. In addition, the gloss unevenness is worse for a transfer material having a coarser fiber of the paper.
When the value is less than g / A4, it deteriorates rapidly. This is because when the coating amount of the release agent is large, fine irregularities are formed entirely on the image surface after fixing by the release agent. This is because there is no large difference, and the gloss becomes low and uniform as a whole, so that there is no uneven gloss. Further, when the total amount of the toner is large, the toner covers all the eyes of the fiber even in a portion where the fiber is uneven, so that the surface becomes flat and gloss unevenness does not occur.

As described above, the problem of gloss unevenness occurs when the same image is formed on the same transfer material when the image is formed with a single color of black toner and a small amount of the release agent applied. It is easy to do.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problem of gloss unevenness which tends to occur in a general color image forming apparatus. An object of the present invention is to provide an image forming apparatus capable of eliminating gloss unevenness that tends to occur during formation.

[0008]

According to a first aspect of the present invention, there is provided an image forming apparatus for forming an image on a transfer material using a plurality of color toners including a black toner. A pressure roller is pressed against the fixing roller to form a fixing nip portion. The transfer material carrying the unfixed toner image is heated and pressed to transfer the transfer material while nipping and conveying the transfer material at the fixing nip portion. A fixing device for melting and fixing the toner image on the transfer material, wherein the fixing device changes an amount of heat applied to the toner image on the transfer material through the fixing nip portion depending on whether the toner image is a single color of black toner or not. It is characterized by having a calorie variable means.

In the image forming apparatus according to the present invention, the applied heat amount changing means reduces the applied heat amount when the toner image is a single color of black toner, as compared with a case other than a single color of black toner. And

The image forming apparatus according to a third aspect is characterized in that the applied heat amount changing means is means for changing a pressing force between the fixing roller and the pressure roller.

According to a fourth aspect of the present invention, in the image forming apparatus, the applied heat amount changing means is means for changing a rotation speed of the fixing roller and the pressing roller.

The image forming apparatus according to a fifth aspect is characterized in that the applied heat amount changing means is means for changing a fixing temperature.

According to a sixth aspect of the present invention, there is provided an image forming apparatus for forming an image on a transfer material by using a plurality of color toners including a black toner. A fixing device for fixing the unfixed toner image on the transfer material by heating and pressing the unfixed toner image while nipping and transferring the transfer material carrying the unfixed toner image at the fixing nip portion; The fixing device is
The amount of release agent applied to the image surface when fixing the toner image
The image forming apparatus further includes a release agent application amount changing unit that changes depending on whether the toner image is a single color of black toner.

According to a seventh aspect of the present invention, in the image forming apparatus according to the first aspect, the variable means for applying a release agent includes: an amount of the release agent applied when the toner image is a single color of black toner, compared to a case other than a single color of black toner. And the amount of applied heat is reduced.

According to another aspect of the present invention, there is provided an image forming apparatus for forming an image on a transfer material using toner of a plurality of colors including black toner, wherein the developing device develops a toner image on an image carrier. A transfer means for transferring the toner image on the image carrier to a transfer material, and a pressure roller being pressed against a fixing roller to form a fixing nip portion, and a transfer material carrying an unfixed toner image is transferred to the fixing nip portion. A fixing device that heats and presses the unfixed toner image and melts and fixes the unfixed toner image on the transfer material, wherein the fixing device includes a monochromatic black toner when the toner image is a monochromatic black toner. The present invention is characterized in that the maximum amount of toner on the transfer material is increased as compared with other cases.

According to a ninth aspect of the present invention, in the image forming apparatus for forming an image on a transfer material using a plurality of color toners including black toner, a fixing nip portion is formed by pressing a pressure roller against a fixing roller. And a fixing device that heats and presses the unfixed toner image and melts and fixes the unfixed toner image on the transfer material while nipping and transferring the transfer material carrying the unfixed toner image at the fixing nip portion. A point higher than the softening point of the toner of another color other than the black toner.

An image forming apparatus according to claim 10, further comprising a release agent applying device for applying a release agent to an image surface at the time of fixing the toner image, wherein the release is performed when the toner image is a single color of black toner. The amount of the agent applied is set to 0.02 g / A4 or less.

[0018]

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

<Embodiment 1> FIG. 6 shows an example of an image forming apparatus according to the present invention. FIG. 1 is a longitudinal sectional view showing a schematic configuration of a four-color full-color copying machine.

The image forming apparatus shown in FIG. 1 includes an original reading system I provided at an upper portion, a latent image forming section II provided below the original reading system I, and a vicinity of the latent image forming section II. Developing means, ie, a rotary developing device III, and a transfer material transport system IV provided from the right side of the apparatus main body 1 to a substantially central portion of the apparatus main body 1. Hereinafter, the document reading system I will be described in order.

As shown in FIG. 7, the original reading system I
A platen 102 on which a document 101 is placed is provided.
The platen 102 is fixedly provided on the upper surface of the apparatus main body 1. The optical system unit 107 provided below the platen 102 sequentially scans the document 101 on the platen 102 by moving in the direction of the arrow in FIG. That is, when the copy key (not shown) of the operation unit (not shown) is depressed, irradiation from the irradiation light source 103 is performed along with the movement in the arrow direction, and the reflected light from the document 101 is transmitted to the imaging element array 104 and Infrared cut filter 10
5 passes through the CCD (contact CCD color sensor) 10
6 is formed as an original image.

As shown in FIG. 8, the CCD 106 is provided with red (R), green (G), and blue (B) filters for each pixel regularly. When a document image is formed on the CCD 106, an electric signal is output from the CCD 106, and the electric signal is processed by a signal processing circuit shown in FIG.

In FIG. 9, 106B, 106G, 10
6R represents an electric signal from each of the B, G, and R elements on the CCD 106 shown in FIG. This 106B, 106
The respective signals G and 106R are converted into digital signals B, G and R by an A / D conversion circuit 111, and the density conversion circuit 112
, The density signals Y ₁ , M ₁ ,
It is converted to C _1.

The Y ₁ , M ₁ , and C ₁ signals are input to a circuit 113 for performing black extraction and UCR (under color removal) processing.
By the arithmetic processing as shown in the following equation, Y ₂ , M ₂ , C ₂ ,
It is generated as a Bk ₂ signal.

Y ₂ = Y ₁ -k ₃ min (Y ₁ , M ₁ , C ₁ ) M ₂ = M ₁ -k ₃ min (Y ₁ , M ₁ , C ₁ ) C ₂ = C ₁ -k ₃ min (Y ₁ , M ₁ , C ₁ ) Bk ₂ = K ₁ min (Y ₁ , M ₁ , C ₁ ) + k ₂ where min (Y ₁ , M ₁ , C ₁ ) is Y ₁ , M ₁ ,
A minimum signal among the C _{1 signal, k 1, k 2, k} 3
Is a predetermined coefficient.

Next, the _{Y 2, M 2, C 2} , Bk 2 signals, a color correction circuit for correcting the spectral distribution of the colorant used in the color separation filter and the image forming means CCD 106 11
4 and subjected to arithmetic processing by the formula shown in FIG.

Here, a _{11 to} a ₄₄ are masking coefficients for color correction, respectively.

The operation results Y ₃ , M ₃ , C
₃ , based on the Bk ₃ signal, a latent image forming unit II described below.
Laser beam irradiation is performed. Hereinafter, the latent image forming unit II will be described with reference to FIG.

As shown in FIG. 6, a drum-type electrophotographic photosensitive member (hereinafter, referred to as a "photosensitive drum") 19 as an image carrier is disposed in the latent image forming section II so as to be rotatable in the direction of arrow B. I have. Above the photosensitive drum 19 and near its outer peripheral surface,
From the upstream side to the downstream side in the rotation direction of the photosensitive drum 19, a charge removing charger 20, a cleaning unit 21, and a primary charger 23 are sequentially arranged, and further above the outer peripheral surface of the photosensitive drum 19. Are provided with an image exposure means 24 such as a laser beam scanner for forming an electrostatic latent image, and an image exposure reflection means 25 such as a mirror.

Therefore, the image exposing means 24 makes the aforementioned Y
_When the laser beam E is radiated based on the ₃ , M ₃ , C ₃ , and Bk ₃ signals, the laser beam E is radiated on the photosensitive drum 19 via the image exposure / reflection means 25, and is previously charged by the primary charger 23. An electrostatic latent image is formed on the uniformly charged photosensitive drum 19, and is visualized as a toner image by the following rotary developing device III. Less than,
The rotary developing device III will be described.

The rotary developing device III is disposed at a position facing the outer peripheral surface of the photosensitive drum 19, and includes four types of rotatable housings (hereinafter referred to as "rotating members") 26. The developing device is mounted at a position that divides the rotating body 26 into four equal parts in the circumferential direction. The four types of developing devices are a yellow developing device 27Y, a magenta developing device 27M, a cyan developing device 27C, and a black developing device 27BK, respectively.
Development is performed with toner of each color corresponding to the electrostatic latent image based on each signal of ₃ , M ₃ , C ₃ , and Bk ₃ . Then, the developed toner image on the photosensitive drum 19 is transferred onto a transfer material transported by the next transfer material transport system IV. Hereinafter, the image is transferred onto the transfer material transported by the transfer material transport system IV. Hereinafter, the transfer material transport system IV will be described.

The transfer material transport system IV has the following configuration. First, an opening is formed in the right wall of the apparatus main body 1 described above, and detachable transfer material supply trays 2 and 3 are made to protrude partially outside the apparatus main body 1 through the opening. It is arranged. Paper feed rollers 4 and 5 are disposed above the trays 2 and 3, and a transfer drum 15 as a transfer unit rotatable in the direction of arrow A disposed to the left with the paper feed rollers 4 and 5. , And paper feed guides 7, 8 are provided so as to communicate with each other. In the vicinity of the outer peripheral surface of the transfer drum 15, the rotation direction (arrow A)
Direction) From the upstream side to the downstream side, a contact roller 9, a gripper 10, a transfer material separating charger 11, and a separating claw 12 are sequentially arranged. A transfer charger 13 and a transfer material separating charger 14 are provided on the inner peripheral side of the transfer drum 15. The transfer drum 15 has a transfer sheet (not shown) formed of polyvinylidene fluoride or the like attached to a portion where the transfer material is wound, and the transfer material is electrostatically adhered to the transfer sheet. Has become. In addition, on the upper right side of the transfer drum 15, a conveying belt means 16 is provided in close proximity to the separation claw 12, and
The fixing device 18 is disposed at the end (right end) of the transfer material transport direction. Further, further downstream of the fixing device 18 in the transport direction, a discharge roller 50 and a discharge tray 17 extending outside the apparatus main body 1 and detachably attached to the apparatus main body 1 are provided. .

The sequence of the entire image forming apparatus having the above configuration will be briefly described by taking a case of a full color mode as an example.

When the above-described photosensitive drum 19 rotates in the direction of arrow B in FIG.
Thereby, it is uniformly charged to a predetermined polarity and a predetermined potential.
In the image forming apparatus shown in FIG. 6, the operation speed of each part (hereinafter referred to as “process speed”) is 160 mm /
sec. When the photosensitive drum 1 is uniformly charged by the primary charger 23, image exposure is performed by the laser beam E modulated by the yellow image signal Y ₃ of the original 101, and the electrostatic latent image is formed on the photosensitive drum 19. Is formed,
The yellow toner is adhered to the electrostatic latent image on the photosensitive drum 1 by the yellow developing device 27Y which is fixed at the developing position in advance by the rotation of the rotating body 26, and the developing is performed.

On the other hand, the transfer material conveyed via the paper feed rollers 6, 6,...
It is held by the gripper 10 at a predetermined timing, and is electrostatically wound around the surface of the transfer drum 15 by the contact roller 9 and the electrode facing the contact roller 9. The transfer drum 15 is synchronized with the photosensitive drum 19 in FIG.
The toner image developed by the yellow developing unit 27Y is transferred at a portion (transfer nip portion) where the outer peripheral surface of the photosensitive drum 19 and the outer peripheral surface of the transfer drum 15 are in contact with each other. The image is transferred by the charger 13. The transfer drum 15 continues to rotate as it is to prepare for the transfer of the next color (magenta in FIG. 6).

The photosensitive drum 19 is provided with a charge removing device 20 for discharging.
After being removed by the cleaning means 21 using a conventionally known blade method, the toner is again charged by the primary charger 23 and subjected to image exposure by the next magenta image signal in the same manner as in the case of yellow described above. The rotary developing device III rotates while an electrostatic latent image based on a magenta image signal is formed on the photosensitive drum 19 by image exposure, and places the magenta developing device 27M at a predetermined developing position to perform predetermined magenta developing. I do. Subsequently, the same process as described above is performed for cyan and black, respectively. When transfer of four colors on the transfer material is completed, the toner images of four colors formed on the transfer material are charged to the respective chargers 20, 1
4, the gripping of the transfer material by the gripper 10 is released, and the transfer material is separated from the transfer drum 15 by the separation claws 12, sent to the fixing device 18 by the transport belt 16, and fixed by heat and pressure. A series of full-color print sequences is completed, and a required full-color image is formed.

As described above, since a multicolor toner forms two to four layers in a color image, an electrophotographic apparatus capable of forming a color image differs from a monochrome apparatus in terms of toner. It has features.

That is, since the toner is required to have good meltability and color mixing when heat is applied, a sharp melt toner having a low softening point and a low melt viscosity is used. This is because a color copy having a wide color reproduction range of a copy (copy) can be obtained by using the sharp melt toner. Such a sharp melt toner is prepared by melt-kneading, pulverizing, and classifying a toner-forming material such as a binder resin such as a polyester resin or a styrene-acryl ester resin, a colorant (a dye or a sublimable dye), and a charge control agent. It is manufactured by doing.
If necessary, an external addition step of adding various external additives (for example, hydrophobic colloidal silica) to the toner may be added. As such a color toner, a toner using a polyester resin as the binder resin is particularly preferable in consideration of the fixing property and the sharp melt property. Examples of the sharp melt polyester resin include a polymer compound having an ester bond in the main chain of a molecule synthesized from a diol compound and a dicarboxylic acid.

In particular, the structural formula shown in FIG. 13 (where R is an ethylene or propylene group, x and y are each a positive integer of 1 or more, and the average value of x + y is 2 to 10). And a carboxylic acid component comprising a divalent or higher carboxylic acid or an acid anhydride thereof or a lower alkyl ester thereof (for example, fumaric acid, maleic acid, maleic anhydride, A polyester resin obtained by at least co-condensation polymerization with phthalic acid, terephthalic acid, trimellitic acid, pyromellitic acid, etc. is more preferable because it has sharp melting characteristics.

The softening point of the polyester resin is 75 to 15
0 ° C, preferably 80 to 120 ° C.

FIG. 10 shows an example of the softening characteristics of a sharp melt toner containing this polyester resin as a binder resin. The measurement conditions are as follows.

Using a flow tester CFT-500A type (manufactured by Shimadzu Corporation), a die (nozzle) diameter of 0.2 mm,
A plunger drop-temperature curve of the toner drawn when a temperature of 70 ° C. is applied at an initial set temperature of 70 ° C., a preheating time is 300 seconds, and the temperature is increased at a constant speed of 6 ° C./min. (Hereinafter referred to as “softening S-shaped curve”). The toner used as the sample is a fine powder precisely weighed from 1 to 3 g, and the cross-sectional area of the plunger is 1.0 cm ² . The softening S-shaped curve becomes a curve as shown in FIG. That is, as the temperature rises at a constant speed, the toner is gradually heated and starts flowing out (plunger descent A → B). When the temperature is further increased, the toner in a molten state flows out greatly (B → C → D),
Plunger descent stops and ends (D → E).

The height H of the softening S-shaped curve indicates the total outflow, and the temperature T ₀ corresponding to the point C of H / 2 indicates the softening point of the toner.

Whether or not the toner and the binder resin have sharp melt properties can be determined by measuring the apparent melt viscosity of the toner or the binder resin.

The toner or binder resin having such a sharp melt property is defined as T ₁ when the apparent melt viscosity is 10 ³ poise and T ₂ when the apparent melt viscosity is 5 × 10 ² poise. _{when, T 1 = 90~150 ℃ | ΔT} | = | T 1 -T 2 | = refers to satisfy the condition of 5 to 20 ° C..

The sharp-melt resin having these temperature-melt viscosity characteristics is characterized in that the viscosity decreases sharply when heated. Such a decrease in viscosity causes appropriate mixing of the uppermost toner layer and the lowermost toner layer, and furthermore, sharply increases the transparency of the toner layer itself and causes good color mixing.

As shown in detail in FIG. 11, the fixing device 18 includes a rotatable fixing roller 51, a pressure roller 52 that rotates while being in pressure contact with the fixing roller 51,
The configuration includes a release agent application device 53 as a release agent supply / application device and roller cleaning devices 54 and 55. Inside the fixing roller 51 and the pressure roller 52,
Heaters 56 and 57 such as halogen lamps are provided respectively. The thermistors 58 and 59 are disposed so as to be in contact with the fixing roller 51 and the pressure roller 52, respectively. The voltage to the heaters 56 and 57 is controlled through a temperature control circuit, so that the fixing rollers 51 and The temperature of the surface of the pressure roller 52 is adjusted.

The fixing roller 51 is composed of, for example, an HTV (high temperature vulcanization type) silicone rubber layer as an elastic layer on an aluminum core, a fluorine rubber layer as an oil-resistant layer on the outside thereof,
Further, an LTV (low temperature vulcanization type) silicone rubber layer or an RTV (room temperature vulcanization type) silicone rubber layer is formed as a release layer on the outside thereof, and has a thickness of 2 mm and a diameter of 60 mm.
The pressure roller 52 has the same structure and is formed to have a thickness of 1 mm and a diameter of 60 mm.

Further, a cleaning device 54 and a release agent application device 53 are attached to the fixing roller 51. The cleaning device 54 cleans toner and the like offset on the fixing roller 51, and releases the release agent. The coating device 53 applies a release agent such as silicone oil to the fixing roller 51,
This facilitates separation of the transfer paper from the sheet No. 1 and prevents offset of the toner.

The release agent applying device 53 includes an oil tank 53 a in which a release agent such as silicone oil is stored, and an oil which is a release agent pumped up from the oil tank 53 a by a pump or the like and supplied to the fixing roller 51. It is composed of a release agent supply pipe 53b made of the same, a pressing pad 53c for uniformizing the release agent on the fixing roller 51, and a release agent regulating blade 53d for controlling the amount of the release agent. The release agent supply pipe 53b is arranged along the fixing roller 51 above the fixing roller 51, has a plurality of holes, and drops the release agent onto the surface of the fixing roller 51 from these holes. The pressing pad 53c is made of a heat-resistant felt or the like, and makes the release agent dropped on the fixing roller 51 uniform.

By applying the release agent in this manner, the 0.1%
An amount of 02 g / A4 or less is applied.

The amount of silicone oil applied by the above-described oil application device 53 is determined as follows.

First, the superposition of 50 sheets of A4 size blank paper is
₁ g, without transferring the image onto the blank paper and without applying silicone oil to the rubber layer of the fixing roller 51.
The overlap of 50 blank sheets after passing between the fixing roller 51 and the pressure roller 52 is defined as Bg. Next, another A4
The superimposition of 50 blank sheets of size is A ₂ g, and the image is not transferred onto the blank sheet. However, silicone oil is applied to the rubber layer of the fixing roller 51, and the fixing roller 51 and the pressing roller 52 The superimposition of 50 blank sheets after the sheet is passed is defined as Cg. Using the above A ₁ , B, A ₂ and C, A4
Amount of silicone oil applied per blank sheet of size X
g is obtained as in the following equation.

X = {(A ₁ −B) − (A ₂ −C)} / 50 The cleaning device 54 includes a cleaning web 54 a made of a belt-shaped heat-resistant nonwoven fabric and a cleaning web 5
A pressing roller 54b for pressing the fixing roller 4a against the fixing roller 51;
It comprises an unwinding roller 54c for unwinding a new cleaning web 54a, and a winding roller 54d for gradually winding the cleaning web 54a to which toner or the like has adhered and the cleaning ability has been reduced. The cleaning device 54 is provided upstream of the thermistor 58 in the rotation direction of the fixing roller 51 so that toner does not adhere to the thermistor 58 to cause detection failure.

The pressing roller 52 is also provided with a fixing roller 51.
Cleaning web 5 similar to the cleaning device 54 of FIG.
A cleaning device 55 including a pressing roller 55a, a pressing roller 55b, an unwinding roller 55c, a winding roller 55d, and the like is attached, and the toner adhered to the pressing roller 52 via the fixing roller 51 is cleaned. Further, an oil removing blade 60 made of fluorine rubber or silicone rubber is in contact with the pressure roller 52 in order to remove an excessive release agent remaining on the pressure roller 52.

In this state, when the transfer material (paper) is conveyed, the fixing roller 51 and the pressing roller 52 rotate at a constant speed, and the surface of the fixing roller 51 is coated with silicone oil as a release agent. When the transfer material passes through the fixing nip portion N between the fixing roller 51 and the pressure roller 52, the unfixed toner image on the surface of the transfer material is pressed and heated at a substantially constant pressure and temperature from both sides. Melted and fixed. As a result, a full-color image is formed on the transfer material. The transfer material on which the image is fixed is separated from the pressure roller 52 by the lower separation claw 68, and is discharged to the discharge tray 17 via the above-described discharge roller 50 (see FIG. 6).

FIG. 1 shows a flowchart according to the first embodiment of the present invention. In the first embodiment, the fixing device 18 shown in FIG.
In the case where an image is formed with a single color of black toner, the pressing force is reduced to reduce the amount of heating, thereby eliminating uneven gloss. As the pressing force varying means 71, a general means can be used.
For example, a bearing that rotatably supports both ends in the longitudinal direction of the axis of the pressure roller 52, and a biasing member such as a compression spring that biases the bearing fixed to the tip toward the fixing roller 51. And a pressing member that presses the base end side of the urging member toward the fixing roller 51 side. The pressing force of the pressing roller 52 against the fixing roller 51 can be changed by appropriately moving the pressing member.

That is, after the copy button is turned on (S1), when an image is to be formed with a single color of black toner (S1).
2) The width n of the fixing nip N between the fixing roller 51 and the pressing roller 52 (the width along the rotation direction of the fixing roller 51 or the pressing roller 52) is reduced by reducing the pressing force. (S5) This reduces the amount of heat applied to the toner on the transfer material. Then, the surface of the toner after fixing is not completely melted and becomes an uneven surface, so that gloss is reduced as a whole, but unevenness in gloss is not generated.
After the copy is completed, the pressure is returned to normal (S6), and the copy is terminated (S4). In S2, when the copy is not a black toner single color copy, the pressing force is set to a normal setting (S3).

More specifically, in the present embodiment, the pressing force is set to 50 kgf and the width n of the fixing nip portion N is set to 7 mm during full-color fixing, whereas the pressing force is set during black toner fixing. Is reduced to 40 kgf, thereby reducing the width n of the fixing nip portion N to 6.5 mm.
As a result, even in the single color mode of the black toner having the release agent application amount of 0.01 g / A4, gloss unevenness did not occur, and a good image was obtained.

In the present embodiment, as an example, the pressing force is set as described above to reduce the width n of the fixing nip portion N. However, the present invention is limited to these values. The fixing roller 51 and the pressure roller 5 are not
2 can be set appropriately according to the outer diameter, material, hardness, and the like.

<Embodiment 2> FIG. 2 shows a flowchart of Embodiment 2 of the present invention. In this embodiment, FIG.
In the fixing device 18 shown in FIG. 1, when forming an image with a single color of black toner, the fixing speed is increased to eliminate uneven gloss. The fixing speed is determined, for example, by changing the rotation speed of the fixing roller 51 by a motor 72 connected to the fixing roller 51 as a rotation speed varying unit. That is, copy button ON
After (S11), when an image is formed with a single color of black toner (S12), the fixing speed is increased (S1).
5) The amount of heat applied to the toner is reduced. Then, the surface of the toner after fixing is not completely melted and is an uneven surface, so that uneven gloss does not occur. In S12,
If it is not a black toner single color copy, the fixing speed is set to the normal setting (S13), and after the copy is completed, the fixing roller 51 is stopped (S14).

More specifically, in the present embodiment, by setting the speed at the time of full-color fixing to 120 mm / sec and the speed at the time of black toner single-color fixing to 150 mm / sec, the coating amount of the release agent is 0.01 g / sec. Even in the black toner single color mode of A4, a glossy unevenness did not occur and a good image was obtained.

The fixing speed in the present embodiment is an example, and the fixing speed is not necessarily limited to this value because the fixing speed differs depending on the configuration of the main body.

<Embodiment 3> FIG. 3 shows a flowchart of a second embodiment of the present invention. In the present embodiment, in the case of forming an image with a single color of black toner in the fixing device 18 shown in FIG. 11, the fixing temperature is lowered to eliminate gloss unevenness. The fixing temperature is changed by changing the voltage applied to the heaters 56 and 57 by the control device 73. That is, when an image is formed with a single color of black toner after the copy button is turned on (S31) (S32), the amount of heat applied to the toner is reduced by lowering the fixing temperature (S35). Then, since the surface of the toner after fixing is not completely melted and becomes an uneven surface, uneven gloss does not occur. After copying, the fixing temperature is returned to normal (S34). In S32,
If it is not a black toner single color copy, the fixing temperature is set to the normal setting (S33).

More specifically, in the present embodiment, the temperature at the time of full-color fixing is set to 170 ° C. and the temperature at the time of black toner single-color fixing is set to 150 ° C., so that the amount of the release agent applied is 0.01 g / A4. Even in the black toner single-color mode, gloss unevenness did not occur and a good image was obtained.

The fixing temperature in the present embodiment is an example, and the fixing temperature is not necessarily limited to this value because the fixing temperature varies depending on the configuration of the main body.

<Fourth Embodiment> FIG. 4 shows a flowchart of a fourth embodiment of the present invention. In this embodiment, FIG.
In the case of forming an image with a single color of black toner in the fixing device 18 shown in FIG. 1, unevenness in gloss is eliminated by increasing the amount of release agent applied. That is,
When an image is formed with a single color of black toner after the copy button is turned on (S41) (S42), by increasing the amount of release agent applied (S45), the entire image surface after fixing becomes uneven. At the same time, when the release agent application amount increases, the heat insulating layer of the release agent increases, so that the amount of heat transferred from the fixing roller 51 to the transfer material also decreases. As a result, the surface of the image after fixing becomes uneven, so that gloss unevenness does not occur. When the release agent application amount is increased, after the copy is completed, the release agent application amount is reduced (returned to the original), and the copy is terminated (S
44). In S42, if the copy is not a black toner single color, the release agent application amount is set to a small value (S42).
43).

In the fourth embodiment, as a means for changing the release agent application amount, the contact angle of the release agent regulating blade 53d with the fixing roller 51 shown in FIGS. 5A and 5B is made variable. That is, a cam 74 is provided. That is, at the time of full-color copy image formation, as shown in FIG.
By rotating the cam 74 clockwise in the figure to increase the contact angle of the release agent regulating blade 53d with respect to the fixing roller 51, regulation is performed at the edge of the release agent regulating blade 53d, Reduce the amount of mold agent applied. On the other hand, when an image is formed only with black toner, as shown in FIG. 5B, the cam 74 is rotated counterclockwise in FIG. Is reduced, regulation is performed at the antinode portion of the release agent regulating blade 53d, so that the release agent application amount is increased. By doing so, the release agent application amount during full-color fixing is 0.01 g / A4, and the release agent application amount during black toner single-color fixing is 0.04 g / A4. It is possible to save consumption and to form a good image without gloss unevenness when forming a black image.

The amount of the release agent applied in the fourth embodiment is
The value is not necessarily limited to this value because it differs depending on the main body configuration and the material.

As the means for varying the amount of the release agent applied, the contact pressure of the release agent regulating blade 53d can be varied, and a plurality of release agent regulating blades can be brought into contact. The present invention is not limited to the release agent application amount variable means of the fourth aspect.

<Fifth Embodiment> In the fifth embodiment, when an image is formed with a single color of black toner, unevenness in gloss is eliminated by increasing the image density. In the present embodiment, when an image is formed with a single color of black toner, the image density is increased, that is, the maximum amount of toner that can be transferred onto the transfer material during development by the fixing device 4 is increased. When the amount of the toner on the transfer material increases, the fixability of the toner decreases, so that the image surface after fixing is not completely melted and has an uneven surface. In addition, when the amount of toner applied increases, the toner easily covers the fibers of the transfer material. As a result, even in the black toner single color mode with a release agent application amount of 0.01 g / A4, a good image was obtained without gloss unevenness.

<Embodiment 6> In Embodiment 6, by making the softening point of the black toner higher than the softening points of the other color toners, it is possible to reduce gloss unevenness in the case of forming an image with a single color of the black toner. It is intended to be eliminated. In the present embodiment, when an image is formed with a single color of black toner, the softening point of the black toner is higher than the softening points of the other color toners, so that the image surface after fixing is not completely melted and has an uneven surface. . As a result, the release agent application amount 0.0
Even in the 1 g / A4 black toner single-color mode, gloss unevenness did not occur and a good image was obtained.

[0073]

As described above, according to the present invention,
When the toner image is of a single color of black toner, the amount of heat applied to the toner image on the transfer material is smaller than that of a case other than the single color of black toner, so that the toner surface after fixing is not completely melted. As a result, the entire surface becomes an uneven surface, so that gloss unevenness does not occur. The means for varying the amount of applied heat includes means for changing the pressing force between the fixing roller and the pressure roller, means for changing the rotation speed between the fixing roller and the pressure roller, means for changing the fixing temperature. Etc.

When the toner image is a single color of black toner, the entire image surface after fixing becomes uneven by increasing the coating amount of the release agent as compared with the case where the toner image is not a single color of black toner, so that uneven gloss is caused. Can be reduced.

Further, when the toner image is a single color of the black toner, the maximum amount of the loaded toner is increased and the softening point of the black toner is set higher than the softening points of the toners of other colors. The same effect can be obtained by increasing the height.

[Brief description of the drawings]

FIG. 1 is a flowchart of Embodiment 1.

FIG. 2 is a flowchart according to the second embodiment.

FIG. 3 is a flowchart of the third embodiment.

FIG. 4 is a flowchart according to the fourth embodiment.

FIGS. 5A and 5B are diagrams showing an operation of a release agent application amount varying unit according to a fourth embodiment.

FIG. 6 is a longitudinal sectional view showing a schematic configuration of an image forming apparatus according to the present invention.

FIG. 7 is a diagram illustrating a configuration of a document reading system.

FIG. 8 is a diagram showing a configuration of a CCD in a document reading system.

FIG. 9 is a block diagram of an image processing circuit in a document reading system.

FIG. 10 is a graph showing softening characteristics of a sharp melt toner.

FIG. 11 is a longitudinal sectional view showing a schematic configuration of a fixing device mounted on the image forming apparatus according to the present invention.

FIG. 12 is a diagram showing a calculation process by a color correction circuit.

FIG. 13 is a view showing a structural formula of an example of a sharp-melt polyester resin.

[Explanation of symbols]

 4 Developing Device 13 Transfer Means (Transfer Charger) 15 Transfer Means (Transfer Drum) 18 Fixing Device 51 Fixing Roller 52 Pressure Roller 53, 55 Release Agent Coating Device 71 Applied Heat Amount Variable Means (Pressing Force Variable Means) 72 Applied Heat Amount Variable means (rotation speed variable means) 73 Applied heat amount variable means (fixing temperature variable means) 74 Release agent application amount variable means (cam)

Claims (10)

[Claims] 1. An image forming apparatus for forming an image on a transfer material using a plurality of color toners including a black toner, wherein a pressure roller is pressed against a fixing roller to form a fixing nip portion, and an unfixed toner image is carried. A fixing device for fixing the unfixed toner image on the transfer material by heat and pressure while nipping and transferring the transferred transfer material in the fixing nip portion; and the fixing device is connected to the fixing nip portion through the fixing nip portion. An image forming apparatus comprising: an applied heat amount varying unit that changes an amount of heat applied to the toner image on the transfer material depending on whether the toner image is a single color of black toner. 2. The image according to claim 1, wherein the applied heat amount changing unit reduces the applied heat amount when the toner image is a single color of black toner, as compared with a case other than a single color of black toner. Forming equipment. 3. The image forming apparatus according to claim 1, wherein the applied heat amount changing unit changes a pressing force between the fixing roller and the pressing roller. 4. The image forming apparatus according to claim 1, wherein the applied heat amount changing unit changes a rotation speed of the fixing roller and the pressing roller. 5. The image forming apparatus according to claim 1, wherein the applied heat amount changing unit is a unit that changes a fixing temperature. 6. An image forming apparatus for forming an image on a transfer material using toner of a plurality of colors including black toner, wherein a pressure roller is pressed against a fixing roller to form a fixing nip portion, and an unfixed toner image is carried. A fixing device that heats and presses the unfixed toner image and melts and fixes the unfixed toner image on the transfer material while nipping and transferring the transferred transfer material at the fixing nip portion; An image forming apparatus comprising: a release agent application amount changing unit that changes an application amount of a release agent applied to the toner image according to whether the toner image is a single color of black toner. 7. The release agent applied amount changing means reduces the amount of applied heat for increasing the applied amount of the release agent when the toner image is a single color of the black toner as compared with a case other than the single color of the black toner. The image forming apparatus according to claim 6, wherein: 8. An image forming apparatus for forming an image on a transfer material using a plurality of color toners including a black toner, a developing device for developing a toner image on an image carrier, and a developing device for developing the toner image on the image carrier. A transfer unit and a pressure roller are pressed against the transfer material to form a fixing nip portion. The transfer material carrying the unfixed toner image is nipped and conveyed by the fixing nip portion. A fixing device that melts and fixes the transfer material on the transfer material by heating and pressing the toner image on the transfer material, when the toner image is a single color of black toner, than when the toner image is not a single color of black toner. An image forming apparatus, wherein the maximum riding amount of the vehicle is increased. 9. An image forming apparatus for forming an image on a transfer material using toner of a plurality of colors including black toner, wherein a fixing roller is pressed against a fixing roller to form a fixing nip portion, and an unfixed toner image is carried. A fixing device that heats and presses the unfixed toner image and melts and fixes the unfixed toner image on the transfer material while nipping and transporting the transferred transfer material in the fixing nip portion. An image forming apparatus comprising: 10. A release agent applying device for applying a release agent to an image surface at the time of fixing a toner image, wherein the amount of the release agent applied is 0.02 g / when the toner image is a single color of black toner.
A4 or less, A claim 1, 2, 3, 4, 5, 6, 7,
10. The image forming apparatus according to 8 or 9.