JP3548406B2 - Image forming device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine and a laser beam printer.
[0002]
[Prior art]
2. Description of the Related Art In an electrophotographic color image forming apparatus such as a four-color full-color copying machine or a laser beam printer, four color toner images of yellow, magenta, cyan, and black are formed on the surface of a transfer material such as paper in an image forming unit. Transcribe. Subsequently, the transfer material carrying these four unfixed toner images 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 toner images of the four colors are fused and fixed on the surface of the transfer material to finally obtain a color image.
[0003]
[Problems to be solved by the invention]
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.
[0004]
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, and the toner flowing at the place where the fiber mesh is uniform is used. While the resin components are combined with each other to form a flat surface, in a portion where the fiber mesh is not uniform, 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 gloss unevenness described above becomes more conspicuous as the toner is blacker, the fibers of the paper (transfer material) are coarser, the release agent is smaller, and the total amount of toner is smaller. Since the black toner has a large contrast, a slight difference in gloss becomes 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, the gloss unevenness is visually inconspicuous. In addition, the gloss unevenness worsens as the transfer material of the paper has a coarser fiber, especially when the amount of the release agent applied at the time of fixing is 0.02 g / A4 or less. This is because, when the coating amount of the release agent is large, fine irregularities are formed on the entire surface of the image 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 gloss unevenness. 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 no gloss unevenness occurs.
[0006]
As described above, the problem of uneven gloss is likely to occur 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. I can say.
[0007]
SUMMARY OF THE INVENTION An object of the present invention is to solve the problem of gloss unevenness that tends to occur in a general color image forming apparatus, and an object of the present invention is to generate an image with a single color of black toner in a color image forming apparatus. It is an object of the present invention to provide an image forming apparatus which can eliminate gloss unevenness that tends to occur.
[0008]
[Means for Solving the Problems]
The invention according to claim 1 is an image forming unit capable of forming a black toner monochromatic image and a color image, a fixing member that is in contact with an unfixed toner image on a transfer material and is fixed by heat, and press-contacts the fixing member. A pressure member that forms a nip portion for nipping and transferring the transfer material, a release agent application unit that applies a release agent to the fixing member, and a release agent that switches an application amount of the release agent per unit number. In the image forming apparatus having the application switching means, when the image forming signal is a black toner single color image, the amount of the release agent applied per unit number is switched to an application amount larger than the application amount of the color image. And the amount of heat applied to the toner image is reduced.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0019]
<Embodiment 1>
FIG. 6 shows an example of the 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.
[0020]
The image forming apparatus shown in FIG. 1 includes an original reading system I provided at an upper portion, a latent image forming unit II provided below the original reading system I, and an image forming apparatus arranged close to the latent image forming unit II. The developing unit is roughly divided into a developing unit, that is, 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.
[0021]
As shown in FIG. 7, the document reading system I includes a platen 102 on which a document 101 is placed. 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 The light passes through an infrared cut filter 105 and is formed as an original image on a CCD (contact CCD color sensor) 106.
[0022]
As shown in FIG. 8, red (R), green (G), and blue (B) filters are regularly attached to the CCD 106 as shown in FIG. When a document image is formed, an electric signal is output from the CCD 106, and the electric signal is processed by a signal processing circuit shown in FIG.
[0023]
In FIG. 9, reference numerals 106B, 106G, and 106R represent electric signals from the B, G, and R elements on the CCD 106 shown in FIG. The signals 106B, 106G, and 106R are converted into digital signals B, G, and R by an A / D conversion circuit 111, and a density signal Y in the form of a digital signal is generated by a density conversion circuit 112.₁  , M₁  , C₁  Is converted to
[0024]
This Y₁  , M₁  , C₁  The signal is input to a circuit 113 that performs black extraction and UCR (under color removal) processing, and is subjected to arithmetic processing as shown in the following equation to perform Y processing.₂  , M₂  , C₂  , Bk₂  Generated as a signal.
[0025]
Y₂    = Y₁  -K₃  min (Y₁  , M₁  , C₁  )
M₂    = M₁  -K₃  min (Y₁  , M₁  , C₁  )
C₂    = C₁  -K₃  min (Y₁  , M₁  , C₁  )
Bk₂  = K₁  min (Y₁  , M₁  , C₁  ) + K₂
Here, min (Y₁  , M₁  , C₁  ) Is Y₁  , M₁  , C₁  Is the smallest of the signals of₁  , K₂  , K₃  Is a predetermined coefficient.
[0026]
Next, this Y₂  , M₂  , C₂  , Bk₂  The signal is input to a color correction circuit 114 for correcting the spectral distribution of the color material used by the color separation filter of the CCD 106 and the image forming means, and is subjected to arithmetic processing by the equation shown in FIG.
[0027]
Where a₁₁~ A₄₄Are masking coefficients for color correction.
[0028]
Then, the calculation result Y₃  , M₃  , C₃  , Bk₃  Based on the signal, laser beam irradiation of the latent image forming section II described below is performed. Hereinafter, the latent image forming unit II will be described with reference to FIG.
[0029]
As shown in FIG. 6, a drum type electrophotographic photosensitive member (hereinafter, referred to as “photosensitive drum”) 19 as an image carrier is disposed in the latent image forming section II so as to be rotatable in an arrow B direction. Above the photosensitive drum 19 and in the vicinity of its outer peripheral surface, a charge removing charger 20, a cleaning means 21, and a primary charger 23 are sequentially arranged from upstream to downstream in the rotation direction of the photosensitive drum 19. Further, above the outer peripheral surface of the photosensitive drum 19, an image exposure unit 24 such as a laser beam scanner for forming an electrostatic latent image and an image exposure reflection unit 25 such as a mirror are provided.
[0030]
Therefore, the image exposure means 24 determines that the Y₃  , M₃  , C₃  , Bk₃  When the laser beam E is irradiated based on the signal, the laser beam E is irradiated onto the photosensitive drum 19 via the image exposure / reflection means 25, and is uniformly charged in advance by the primary charger 23. An electrostatic latent image is formed thereon, and is visualized as a toner image by the following rotary developing device III. Hereinafter, the rotary developing device III will be described.
[0031]
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 developing devices in a rotatable housing (hereinafter referred to as a “rotating body”) 26. The rotating body 26 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.₃  , M₃  , C₃  , Bk₃  The development is performed with toner of each color corresponding to the electrostatic latent image based on each of the signals. 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.
[0032]
The transfer material transport system IV has the following configuration. First, an opening is formed in the right wall of the above-described apparatus main body 1, and a detachable transfer material supply tray 2, 3 is formed in the opening so that a part thereof projects outside the apparatus main body 1. 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 and 8 are provided so as to communicate with each other. In the vicinity of the outer peripheral surface of the transfer drum 15, a contact roller 9, a gripper 10, a transfer material separating charger 11, and a separating claw 12 are sequentially arranged from the upstream side to the downstream side in the rotation direction (the direction of arrow A). I have. On the inner peripheral side of the transfer drum 15, a transfer charger 13 and a transfer material separating charger 14 are provided. The transfer drum 15 has a transfer sheet (not shown) formed of polyvinylidene fluoride or the like adhered to a portion where the transfer material is wound, and the transfer material is electrostatically adhered onto the transfer sheet. Has become. At the upper right side of the transfer drum 15, a conveyor belt 16 is provided adjacent to the separation claw 12, and at the end (right end) of the conveyor belt 16 in the transfer material conveying direction, a fixing device 18 is provided. I have. 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. .
[0033]
The sequence of the entire image forming apparatus having the above-described configuration will be briefly described by taking a full color mode as an example.
[0034]
When the above-described photosensitive drum 19 rotates in the direction of arrow B in FIG. 6, the surface of the photosensitive drum 19 is uniformly charged to a predetermined polarity and a predetermined potential by the primary charger 23. 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, the yellow image signal Y₃  An image is exposed by the laser beam E modulated by the above, an electrostatic latent image is formed on the photosensitive drum 19, and the yellow developing unit 27 </ b> Y previously set at the developing position by the rotation of the rotating body 26 on the photosensitive drum 1. Is developed with yellow toner attached to the electrostatic latent image.
[0035]
On the other hand, the transfer material conveyed via the paper feed rollers 6, 6,..., The paper feed guide 7, and the paper feed guide 8 is held by the gripper 10 at a predetermined timing, and is brought into contact with the contact roller 9 by the gripper 10. The transfer roller 15 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 rotates in the direction of arrow A in FIG. 6 in synchronization with the photosensitive drum 19, and the toner image developed by the yellow developing device 27 </ b> Y is applied to the outer peripheral surface of the photosensitive drum 19 and the outer peripheral surface of the transfer drum 15. Is transferred by the transfer charger 13 at a portion (transfer nip portion) where it contacts. The transfer drum 15 continues to rotate as it is to prepare for the transfer of the next color (magenta in FIG. 6).
[0036]
The photosensitive drum 19 is neutralized by a neutralizing charger 20 and is cleaned by a cleaning means 21 using a conventionally known blade method. Thereafter, the photosensitive drum 19 is charged again by a primary charger 23, and when the above-described yellow color is obtained by the next magenta image signal. Receives image exposure in the same manner as 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 thereby perform predetermined magenta developing. I do. Subsequently, the same process as described above is performed for cyan and black, respectively, and when the 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, The charge is removed by 14, 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 claw 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.
[0037]
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 has a different toner characteristic from a monochrome apparatus. Have.
[0038]
That is, since the toner is required to have good meltability and color mixing upon application of heat, 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, those using a polyester resin as the binder resin are 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.
[0039]
In particular, it is represented by 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). 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, phthalic acid, A polyester resin obtained by at least co-condensation polymerization with terephthalic acid, trimellitic acid, pyromellitic acid, etc. is more preferable because it has sharp melting characteristics.
[0040]
The softening point of the polyester resin is 75 to 150 ° C, preferably 80 to 120 ° C.
[0041]
FIG. 10 shows an example of softening characteristics of a sharp melt toner containing the polyester resin as a binder resin. The measurement conditions are as follows.
[0042]
Using a flow tester CFT-500A type (manufactured by Shimadzu Corporation), a die (nozzle) having a diameter of 0.2 mm and a thickness of 1.0 mm was applied with an extrusion load of 20 kg, and after an initial setting temperature of 70 ° C. and a preheating time of 300 seconds, , A plunger drop-temperature curve (hereinafter referred to as a “softening S-shaped curve”) of the toner drawn when the temperature was increased at a constant speed of 6 ° C./min. The toner used as the sample is a fine powder weighed 1 to 3 g, and the cross-sectional area of the plunger is 1.0 cm.²  And 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), and the plunger descent stops and ends (D → E).
[0043]
The height H of the softening S-shaped curve indicates the total outflow, and the temperature T corresponding to the point C of H / 2.₀  Indicates the softening point of the toner.
[0044]
Whether or not the toner and the binder resin have a sharp melt property can be determined by measuring the apparent melt viscosity of the toner or the binder resin.
[0045]
The toner or the binder resin having such a sharp melt property has an apparent melt viscosity of 10³  The temperature when showing poise is T₁  , 5 × 10²  The temperature when showing poise is T₂  And when
T₁  = 90-150 ° C
| ΔT | = | T₁  −T₂  | = 5-20 ° C
That satisfy the conditions of
[0046]
The sharp-melt resin having these temperature-melt viscosity characteristics is characterized in that the viscosity is reduced very sharply when heated. Such a decrease in viscosity causes an appropriate mixing of the uppermost toner layer and the lowermost toner layer, and further sharply increases the transparency of the toner layer itself, thereby causing good color reduction mixing.
[0047]
As shown in detail in FIG. 11, the fixing device 18 includes a fixing roller 51 rotatably disposed, a pressure roller 52 that rotates while being in pressure contact with the fixing roller 51, and a releasing agent supply and application unit. The configuration includes a release agent application device 53 and roller cleaning devices 54 and 55. Heaters 56 and 57 such as halogen lamps are disposed inside the fixing roller 51 and the pressure roller 52, respectively. Further, the thermistors 58 and 59 are disposed so as to be in contact with the fixing roller 51 and the pressure roller 52, respectively, and 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.
[0048]
The fixing roller 51 includes, for example, an HTV (high temperature vulcanization type) silicone rubber layer as an elastic layer on an aluminum core metal, a fluorine rubber layer as an oil-resistant layer outside thereof, and an LTV (low temperature low temperature) as a release layer outside thereof. It has a vulcanization type) silicone rubber layer or an RTV (room temperature vulcanization type) silicone rubber layer and is formed to a thickness of 2 mm and a diameter of 60 mm. The pressure roller 52 has the same configuration and a thickness of 1 mm and a diameter of 60 mm.
[0049]
Further, a cleaning device 54 and a release agent applying device 53 are attached to the fixing roller 51, and the cleaning device 54 cleans the toner and the like offset on the fixing roller 51, and also releases the release agent applying device 53. As a result, a release agent such as silicone oil or the like is applied to the fixing roller 51, thereby facilitating separation of the transfer paper from the fixing roller 51 and preventing offset of the toner.
[0050]
The release agent applying device 53 is composed of an oil tank 53a in which a release agent such as silicone oil is stored, and a metal or the like that pumps oil as a release agent from the oil tank 53a with a pump or the like and supplies the oil to the fixing roller 51. It comprises a release agent supply pipe 53b, 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 heat-resistant felt or the like, and makes the release agent dropped on the fixing roller 51 uniform.
[0051]
By applying the release agent in this manner, an amount of 0.02 g / A4 or less is applied.
[0052]
The amount of silicone oil applied by the above-described oil application device 53 is determined as follows.
[0053]
First, superimposition of 50 sheets of A4 size blank paper₁  g, without transferring the image onto the white paper, without applying silicone oil to the rubber layer of the fixing roller 51, and after passing 50 sheets of white paper between the fixing roller 51 and the pressure roller 52. Is assumed to be Bg. Next, similarly, another 50 sheets of A4 size blank paper are superimposed on each other.₂  g, the image is not transferred onto the white paper, but the silicone oil is applied to the rubber layer of the fixing roller 51, and the white paper 50 after passing between the fixing roller 51 and the pressure roller 52. The superposition of the sheets is Cg. A above₁  , B, A₂  , C, the coating amount Xg of silicone oil per sheet of A4 size white paper can be obtained by the following equation.
[0054]
X = ｛(A₁  -B)-(A₂  −C)｝ / 50
The cleaning device 54 includes a cleaning web 54a made of a belt-shaped heat-resistant nonwoven fabric, a pressing roller 54b that presses the cleaning web 54a against the fixing roller 51, an unwind roller 54c that unwinds a new cleaning web 54a, and toner and the like. The take-up roller 54d, etc., which gradually takes up the cleaning web 54a having a reduced cleaning capability, is used to prevent the offset toner from adhering to the thermistor 58 and causing the detection error of the thermistor 58. The cleaning device 54 is provided upstream of the thermistor 58 in the rotation direction of the fixing roller 51.
[0055]
Further, a cleaning device 55 including a cleaning web 55a, a pressing roller 55b, an unwinding roller 55c, a take-up roller 55d, and the like similar to the cleaning device 54 of the fixing roller 51 is attached to the pressing roller 52, and the fixing roller 51 is interposed therebetween. Thus, the toner adhered to the pressure roller 52 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.
[0056]
In this state, when the transfer material (paper) is conveyed, the fixing roller 51 and the pressure roller 52 rotate at a constant speed, and silicone oil is applied to the surface of the fixing roller 51 as a release agent. When the toner passes through the fixing nip N between the fixing roller 51 and the pressure roller 52, the unfixed toner image on the surface of the transfer material is melted and fixed by applying pressure and heat from the front and back surfaces at substantially constant pressure and temperature. Is done. 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).
[0057]
FIG. 1 shows a flowchart of the first embodiment of the present invention. In the first embodiment, the fixing device 18 shown in FIG. 11 is provided with a pressing force variable unit 71 as an applied heat amount changing unit, and when forming an image with a single color of black toner, the pressing force is reduced to reduce the heating amount. By reducing the number, gloss unevenness is eliminated. 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 distal end toward the fixing roller 51. And a pressing member that presses the base end side of the urging member toward the fixing roller 51. The pressing force of the pressing roller 52 against the fixing roller 51 can be changed by appropriately moving the pressing member.
[0058]
That is, when the image is formed with a single color of black toner after the copy button is turned on (S1) (S2), the width of the fixing nip portion N between the fixing roller 51 and the pressing roller 52 is reduced by reducing the pressing force. (Width along the rotation direction of the fixing roller 51 or the pressure roller 52) n is reduced (S5), thereby reducing 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, if the copy is not a black toner single color copy, the pressing force is set to a normal setting (S3).
[0059]
More specifically, in the present embodiment, during full-color fixing, the pressing force is set to 50 kgf and the width n of the fixing nip portion N is set to 7 mm, whereas when the black toner is fixed, the pressing force is set to 40 kgf. As a result, the width n of the fixing nip N is reduced to 6.5 mm. As a result, gloss unevenness did not occur even in the monochrome mode of the black toner having the release agent application amount of 0.01 g / A4, and a good image was obtained.
[0060]
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 not limited to these values. Instead, it can be appropriately set according to the outer diameter, material, hardness, and the like of the fixing roller 51 and the pressure roller 52.
[0061]
<Embodiment 2>
FIG. 2 shows a flowchart according to the second embodiment of the present invention. In the present embodiment, when an image is formed with a single color of black toner in the fixing device 18 shown in FIG. 11, unevenness in gloss is eliminated by increasing the fixing speed. The fixing speed is determined by, for example, changing the rotation speed of the fixing roller 51 by a motor 72 connected to the fixing roller 51 and serving as a rotation speed varying unit. That is, when an image is formed with a single color of black toner after the copy button is turned on (S11) (S12), the amount of heat applied to the toner is reduced by increasing the fixing speed (S15). Then, since the surface of the toner after fixing is not completely melted and becomes an uneven surface, uneven gloss is not generated. If it is determined in step S12 that the copy is not a black toner single color copy, the fixing speed is set to a normal setting (S13), and after the copy is completed, the fixing roller 51 is stopped (S14).
[0062]
More specifically, in this embodiment, the speed at the time of full-color fixing is set to 120 mm / sec, and the speed at the time of black toner single-color fixing is set to 150 mm / sec. Even in the toner single color mode, glossy unevenness did not occur and a good image was obtained.
[0063]
Note that the fixing speed of 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.
[0064]
<Embodiment 3>
FIG. 3 shows a flowchart of the second embodiment of the present invention. In the present embodiment, when an image is formed with a single color of black toner in the fixing device 18 shown in FIG. 11, the unevenness in gloss is eliminated by lowering the fixing temperature. 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, the surface of the toner after fixing is not completely melted and is an uneven surface, so that uneven gloss does not occur. After copying, the fixing temperature is returned to normal (S34). If it is determined in step S32 that the image is not a black toner single color copy, the fixing temperature is set to a normal setting (S33).
[0065]
More specifically, in the present embodiment, by setting the temperature at the time of full-color fixing to 170 ° C. and the temperature at the time of black toner single-color fixing to 150 ° C., the release amount of the release agent is 0.01 g / A4. Even in the mode, gloss unevenness did not occur and a good image was obtained.
[0066]
Note that 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 differs depending on the configuration of the main body.
[0067]
<Embodiment 4>
FIG. 4 shows a flowchart according to the fourth 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, gloss unevenness is eliminated by increasing the release agent application amount. 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 release agent application amount (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 becomes thicker, so that the amount of heat transferred from the fixing roller 51 to the transfer material also decreases. As a result, the image surface after fixing becomes uneven, so that uneven gloss does not occur. If 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 (S44). In S42, if it is not a black toner single color copy, the release agent application amount is set to be small (S43).
[0068]
In the fourth embodiment, as means for changing the release agent application amount, means for changing the contact angle of the release agent regulating blade 53d with the fixing roller 51 shown in FIGS. 5A and 5B, That is, the cam 74 is provided. That is, at the time of full-color copy image formation, as shown in FIG. 5A, the cam 74 is rotated clockwise in FIG. 5 so that the contact angle of the release agent regulating blade 53 d with respect to the fixing roller 51. By increasing the size, the regulation is performed at the edge of the release agent regulating blade 53d, and the amount of the release agent applied is reduced. 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, and the amount of the release agent applied 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 reduce consumption and to form a good image without gloss unevenness when forming a black image.
[0069]
Note that the amount of the release agent applied in the fourth embodiment is not necessarily limited to this value since it differs depending on the configuration and the material of the main body.
[0070]
Also, as the release agent application amount variable means, the contact pressure of the release agent regulating blade 53d can be varied, a plurality of release agent regulating blades can be brought into contact, and so on. The present invention is not limited to the release agent application amount variable means.
[0071]
<Embodiment 5>
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 is increased, the fixing property of the toner is reduced, so that the image surface after the 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.
[0072]
<Embodiment 6>
In the sixth embodiment, the softening point of the black toner is set higher than the softening points of the other color toners, so that gloss unevenness when forming an image with a single color of the black toner is eliminated. In the present embodiment, when an image is formed using a single color of black toner, since the softening point of the black toner is higher than the softening points of the other color toners, the image surface after fixing is not completely melted and has an uneven surface. . As a result, even in the black toner single color mode in which the coating amount of the release agent was 0.01 g / A4, glossy unevenness did not occur and a good image was obtained.
[0073]
【The invention's effect】
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 made smaller than that of a case other than the single color of black toner, so that the toner image is fixed after the fixing. The surface of the toner is not completely melted but is entirely uneven, so that uneven gloss does not occur. The means for varying the amount of applied heat includes means for changing the pressure 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.
[0074]
In addition, when the toner image is a single color of the black toner, the entire image surface after fixing becomes uneven by increasing the amount of the release agent applied compared to the case where the toner image is not a single color of the black toner. Can be reduced.
[0075]
Further, when the toner image is a single color of the black toner, the maximum amount of 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 as compared with the case where the toner image is not a single color of the black toner. The same effect can be obtained by using
[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 according to the third embodiment.
FIG. 4 is a flowchart of 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 showing 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 diagram illustrating 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 calorie variable means (Pressure force variable means)
72 Applied calorie variable means (rotation speed variable means)
73 Applied heat variable means (fixing temperature variable means)
74 Release agent application amount variable means (cam)

Claims (1)

An image forming means capable of forming a black toner single-color image and a color image; a fixing member which is in contact with an unfixed toner image on the transfer material and is fixed by heat; An image comprising: a pressure member forming a nip portion; a release agent application unit for applying a release agent to the fixing member; and a release agent application switching unit for switching an amount of the release agent applied per unit number. In the forming device,
When the image forming signal is a black toner single color image, the amount of release agent applied per unit number is switched to a larger amount than the color image to reduce the amount of heat applied to the toner image. Characteristic image forming apparatus.

Images