JP2000029250A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a fixing speed for a second side from being reduced and yet to realize excellent fixing performance at the time of forming an image on the both sides of one sheet of a recording material. SOLUTION: As for this image forming device, when both sides print is selected (S1), 'full color only' and 'the case that monochrome color is present' are displayed on a display part (S2) of a device main body. In the meantime, when 'full color only' is selected (S3), 'place an original please' is displayed (S4), in accordance with the display, a full color image is printed on the first side of a recording material and thereafter, the full color image of the original on the other side is printed on the second side. On the other hand, when 'the case that monochrome color is present' is selected in S2 (S5), 'place a monochrome color original please' is displayed (S6), in accordance with the display, the monochrome color image is printed on the first side and then, another monochrome color or full color is printed on the second side. Since the monochrome color whose fixability grows worse on the second side is printed on the first side, the fixing speed drop of the fixing defect can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 In a fixing device of a conventional image forming apparatus, since a rubber or a synthetic resin having poor heat conductivity is generally used for an outer layer between a fixing roller and a pressure roller, if the printing speed is increased, In addition, the temperature of the fixing roller and the pressure roller greatly decreases, and the fixability of the toner to the recording material tends to deteriorate. As a result, for example, when an image is formed on both surfaces of one recording material, fixability is particularly deteriorated when an image is formed on the second surface after the image formation on the first surface is performed first. Although it depends on the weight of the recording material and the toner, when continuous paper is passed, as shown in FIG. 7, the gloss of the image at the lowest point of the roller temperature differs from the gloss of the first image. Further, depending on the length of the recording material, a fixing failure (cold offset) at the rear end of the recording material may occur.

In the double-sided image formation on one recording material, the mode in which the fixing property of the second side is most deteriorated is the case where the first side is full color and the second side is monocolor, as shown in Table 1 below. . This is because the number of prints per minute of monocolor is four times that of full color, and in the case of the monocolor mode, the distance between the recording materials becomes narrower and the roller temperature becomes lower. This is because the sex deteriorates.

Conventionally, as a measure for preventing the fixing property of the second surface from being deteriorated, the fixing speed of the second surface is made lower than the fixing speed of the first surface. For example, on the first side, 1
The fixing speed of 60 mm / s was changed to 100 mm on the second side.
/ S.

[0005]

However, as described above, when the fixing speed of the second side during the double-sided image formation is reduced, there is a problem that the number of images formed per unit time is reduced. . This problem goes against the market trend of increasing the image forming speed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of realizing a good fixing property without lowering a fixing speed of a second side during double-sided image formation.

[0007]

According to a first aspect of the present invention, there is provided an image forming section for forming an image on a recording material by using a developer in which a plurality of colors are melted and mixed; In the image forming apparatus having a fixing unit for applying heat to the image and fixing the image on the recording material, when forming an image on both one surface and the other surface of one recording material, According to the type of the document image to be image-formed on the surface and the type of the document image to be image-formed on the other surface, the image forming order of the one surface and the other surface is determined before and after.
It is characterized by the following.

According to a second aspect of the present invention, in the first aspect of the present invention, the type of the original image formed on the one surface and the other surface is full color or mono color. I do.

According to a third aspect of the present invention, when the original image formed on the one surface is full color and the original image formed on the other surface is monocolor, After forming the full-color image on the first surface, the mono-color image is formed on the second surface.

[0010] The invention of claim 4 is the invention of claim 1, 2, or 3.
The invention according to claim 1, further comprising an automatic document feeder for loading the original into the reading position and unloading the read original from the reading position, wherein the order of forming images on one surface and the other surface of the recording material is determined by the automatic original feeding device. It is determined by the feeding device.

[0011]

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

<Embodiment 1> In this embodiment, the type of a document image formed on one surface of a recording material (hereinafter referred to as "printing" as appropriate) and the document image printed on the other surface are described. When the type is different, the order of the printing order is appropriately set according to the type of the document image. For example, in a case where one side is printed in full color and the other side is printed in mono color, first the first side (the side to be printed first; the same applies hereinafter) is printed in mono color, and thereafter Full color is printed on the second side (the side to be printed later; the same applies hereinafter). Details will be described below.

First, FIG. 1 shows a schematic configuration of an electrophotographic four-color full-color copying machine as an example of an image forming apparatus according to the present invention.

A copying machine shown in FIG.
That. ) Are a document feed system (automatic document feeder) V and a document reading system (document reading device) I provided above, a latent image forming section II provided below the document reading system I, and a latent image forming section II. Developing means disposed close to the image forming unit II, that is, a rotary developing device III, and a right-hand side of an image forming apparatus main body (hereinafter simply referred to as “apparatus main body”) 1 to a substantially central portion of the apparatus main body 1. It is roughly divided into the recording material transport system IV provided.

Hereinafter, the structure of the image forming apparatus will be described. First, the document reading system I will be described with reference to FIGS. 2, 3, and 4. FIG.

FIG. 2 is a schematic configuration diagram of the original reading system I.
In FIG. 1, reference numeral 101 denotes an original, and 102 denotes an original table (platen). The document table 102 is provided immovably with respect to the apparatus main body 1, and the optical system unit 107 provided below the document table 102 moves in the direction of an arrow, thereby sequentially placing the document table 102 on the document table 102. Manuscript 101
Is scanned. That is, when the copy key (not shown) of the operation unit (not shown) is pressed, irradiation from the irradiation light source 103 is performed in accordance with the movement in the above-described arrow direction, and the reflected light from the document 101 is changed to the image forming element. The light passes through the array 104 and the infrared cut filter 105 and is imaged as a document image on a CCD (contact CCD color sensor) 106.

As shown in FIG. 3, red (R), green (G), and blue (B) filters are regularly attached to the CCD 106 for each pixel.
When a document image is formed on the CCD 106 as the document 101 is scanned, an electric signal is output from the CCD 106, and the electric signal is processed by the signal processing circuit shown in FIG.

In FIG. 4, 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.
Y ₂ , M ₂ , C ₂ , B
It is generated as a k 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 the arithmetic processing shown in FIG. 10 is performed. However, a ₁₁ ~a ₄₄ in FIG. 10 is a masking coefficient for each color correction.

Then, 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, and visualization is performed. Hereinafter, the latent image forming section II will be described with reference to FIG.

In the latent image forming section II, a drum type electrophotographic photosensitive member (hereinafter referred to as "photosensitive drum") 1 as an image carrier is provided.
9 is disposed rotatably in the direction of arrow B. 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 the upstream side to the downstream side in the rotation direction of the photosensitive drum 19, and furthermore, A laser beam scanner (image exposure means) 24 and a mirror (image exposure reflection means) 25 for forming an electrostatic latent image are provided on the outer peripheral surface of the photosensitive drum 19.

Therefore, after the surface of the photosensitive drum 19 is neutralized by the neutralizing charger 20 and uniformly charged by the primary charger 23, the above-mentioned Y ₃ , M ₃ , C ₃ , Bk are image-exposure means 24. Irradiation of the laser beam E is performed based on the _three signals, and an electrostatic latent image is formed on the surface.
The electrostatic latent image on the photosensitive drum 19 is developed by the following rotary developing device III. Hereinafter, 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 four types of developing devices are mounted at four positions in a circumferential direction in a rotatable rotary 26. It is configured. These four types of developing units
Each of the yellow developing device 27Y and the magenta developing device 27
M, cyan developing device 27C, and black developing device 27Bk
The toner of each color is applied to the photosensitive drum 1 corresponding to the electrostatic latent image based on each of the above-described Y ₃ , M ₃ , C ₃ , and Bk ₃ signals.
The toner image is developed (visualized) by being attached to the electrostatic latent image on the toner image 9. Then, the toner image on the photosensitive drum 19 after the development is transferred onto a recording material conveyed by the next recording material conveyance system IV. Hereinafter, the recording material transport system IV will be described.

The recording material transport system IV has the following configuration. First, an opening is formed in the right wall of the apparatus main body 1 in the drawing, and detachable recording material supply trays 2 and 3 are provided in the opening so as to protrude partially outside the apparatus. I have. Feed rollers 4 and 5 are disposed almost directly above the trays 2 and 3, and the supply rollers 4 and 5 and a transfer drum 15 serving as a transfer means rotatable in the direction of arrow A disposed to the left. The paper feed roller 6 and the 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, the contact roller 9, gripper 10, recording material separating charger 11,
Separating claws 12 are sequentially arranged. Also, the transfer drum 1
5, the transfer charger 13 and the recording material separating charger 1
4 are provided. The transfer drum 15 has a transfer sheet (not shown) formed of polyvinylidene fluoride or the like affixed to a portion where the recording material is wound, and the recording material is electrostatically adhered onto the transfer sheet. Has become. A conveying belt means 16 is provided on the upper right side of the transfer drum 15 in close proximity to the separation claw 12, and a fixing device (fixing section) 18 is provided at the end (right end) of the conveying belt means 16 in the recording material conveying direction. Have been. Fixing device 18
Includes a fixing roller 29 and a pressure roller 30 having halogen heaters 36 and 37, respectively. The fixing device 18 will be described later in detail. A discharge roller 52 is disposed further downstream of the fixing device 18 in the transport direction, and further downstream, a discharge tray extending outside the apparatus main body 1 and detachably attached to the apparatus main body 1. 17 are provided. Then, between the discharge tray 17 and the above-described paper feed roller 6, the printing is performed on the first side, and the recording material P discharged to the discharge tray 17 is printed on the second side. A transport roller 50 that transports P toward the paper feed roller 6 and a transport guide 51 are provided.

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. When the photosensitive drum 19 rotates in the direction of arrow B in FIG.
The surface of the photosensitive drum 19 is uniformly charged by the primary charger 23. In the apparatus shown in FIG. 1, the operation speed of each unit (hereinafter, referred to as “process speed”) is 1.
60 mm / sec. Photosensitive drum 1 by primary charger 23
9 is uniformly charged, the image is exposed by the laser beam E modulated by the yellow image signal Y ₃ of the original 101, an electrostatic latent image is formed on the photosensitive drum 19, and the rotation of the rotary 26 is performed. Thus, the above-described electrostatic latent image is developed by the yellow developing device 27Y fixed at the developing position in advance to become a yellow toner image.

On the other hand, the recording material conveyed via the paper feed guide 7, the paper feed roller 6, 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 and the contact roller 9. The transfer roller 15 is electrostatically wound around the surface of the transfer drum 15 by the contact roller 9 and the facing electrode. The transfer drum 15 rotates in the direction of arrow A in FIG. 1 in synchronization with the rotation of the photosensitive drum 19 in the direction of arrow B. The toner image developed by the yellow developing device 27Y The image is transferred onto a recording material by the transfer charger 13 at a transfer nip portion where the outer peripheral surface of the transfer drum 15 is in contact. The transfer drum 15 continues to rotate as it is to prepare for the transfer of the next color (magenta in FIG. 1).

After the transfer of the toner image, the photosensitive drum 19 is discharged by the above-described charging device 20 for cleaning, is cleaned by the cleaning means 21 using a conventionally known blade method, and is charged again by the primary charging device 23.
As in the case of yellow by the next magenta image signal,
Receive image exposure. The above-mentioned 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 the magenta developing device 27
M is located at the development position, and a magenta toner is attached to the electrostatic latent image on the photosensitive drum 19 to form a toner image. Subsequently, the same process as described above is performed for cyan and black, respectively, and four color toner images are superimposed on the recording material. When the transfer of the toner images for four colors is completed, the recording material is neutralized by the chargers 11 and 14, and the gripper 10
Is released from the transfer drum 15 by the separation claw 12 and sent to the fixing device 18 by the transport belt 16. Here, the toner image is fixed on the recording material by heat and pressure, a series of full-color print sequences is completed, and a required full-color print image is formed. The recording material discharged to the discharge tray 17 after the printing on the first side is thus conveyed by the conveying rollers 50 to the sheet feeding roller 6 along the conveying guide 51 when printing on the second side. You.

As described above, since a multicolor toner forms two to four layers in a color image, in an electrophotographic image forming apparatus capable of forming a color image, the toner becomes black and white. It has characteristics different from those of the toner of the image forming apparatus.

That is, since a toner for a color image forming apparatus 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 required. Is used. This is because a color copy with a wide color reproduction range of a copy can be obtained by using a 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 (dye, 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. 11 (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, phthalic acid) Acid, terephthalic acid, trimellitic acid,
A polyester resin obtained by at least co-condensation polymerization with a pyromellitic acid) 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. 5 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.

Using a flow tester CFT-500A type (manufactured by Shimadzu Corporation), a die (nozzle) diameter of 0.2 mm,
A plunger descent amount-temperature curve (hereinafter referred to as a drawing) of a toner drawn when a thickness of 1.0 mm is applied, an extrusion load of 20 kg is applied, the preheating time is 300 seconds, the preheating time is 300 seconds, and the temperature is increased at a constant speed of 6 ° C./min. "Softening S-shaped curve"). The toner used as the sample is a fine powder precisely weighed 1 to 3 g, and the cross-sectional area of the plunger is 1.0 cm ² . The softening S-shaped curve is as shown in FIG. As the temperature rises at a constant speed,
The toner is gradually heated and starts to flow (plunger descent A → B). When the temperature is further increased, the toner in the molten state flows out greatly (B → C → D), and the plunger descent stops and ends (D → E).

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

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.

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 an 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.

Therefore, as the fixing device 18, FIG.
As shown in FIG. 2, a fixing roller (fixing member) 29 having a halogen heater 36 as a heat generating means and a pressing roller (fixing member) 30 also having a halogen heater 37 are combined by a pressing mechanism (not shown) to a total pressure of about The temperature of the pressure roller 30 is detected by a thermistor 38 in contact with the pressure roller 30 using a pressurized pressure of 40 kg, and the halogen heaters 36 and 37 are controlled by the control device 39 based on the detected temperature, By controlling both the temperature of the fixing roller 29 and the temperature of the pressure roller 30 so as to be constant at about 150 ° C., the developer t of the sharp melt toner transferred onto the recording material P is satisfactorily heated. It is fixed on P.

However, such a sharp-melt color toner has a high affinity and also has a property that it is easily offset to the fixing roller 29. Therefore, in the above-described fixing device 18, a high releasing property is required for a long time. It is necessary to show sex.

[0042] Therefore, in the fixing device 18 shown in FIG. 6, with the oil application device O as a release agent application means, a cleaning device C, the oil of the pressure roller 30, a cleaning blade C ₁ to remove dirt, even more The release property is improved.

The oil applicator O is a dimethyl silicone oil 41 (KF963 manufactured by Shin-Etsu Chemical Co., Ltd.) in an oil pan 40.
00cs) is passed through an oil pumping roller 42 and an oil application roller 43, and is applied to the fixing roller 29 by regulating an oil application amount by an oil application amount adjusting blade 44. In the apparatus shown in FIG. An amount of 0.08 g / A4 was applied by a measuring method described later.
Note that the oil application roller 43 can be brought into contact with and separated from the fixing roller 29, and the oil application range by this contact and separation is between a position 5 mm from the leading end of the recording material and a position 5 mm from the trailing end.

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

First, the weight 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 29, after passing the paper between the fixing roller 29 and the pressure roller 30. The weight of 50 blank sheets is defined as B (g). Next, similarly, the weight of another 50 blank sheets of A4 size is defined as A ₂ (g),
Although the image is not transferred onto the blank paper, the fixing roller 29
Is applied to the rubber layer, and the white paper 5 after the paper is passed between the fixing roller 29 and the pressure roller 30.
The weight of 0 sheets is defined as C (g). A ₁ , B, A ₂ ,
When C is used, the coating amount X (g) of the silicone oil per A4 size white paper can be obtained by the following equation.

X = (C + A ₁ -BA ₂ ) / 50 On the other hand, in the fixing device 18 shown in FIG. 6, the cleaning device C is a nonwoven fabric web 4 made of Nomex (trade name).
6 is pressed against the fixing roller 29 by the pressing roller 45 for cleaning. The web 46 is appropriately wound by a winding device (not shown) so that toner or the like does not accumulate on the contact portion.

Further, in the fixing device 18 described above, as shown in FIG. 6, an HTV (high temperature vulcanization type) silicone rubber layer 3 is formed on an aluminum cored bar 31 as a fixing roller 29.
2, and an RTV (room temperature vulcanization type) silicone rubber layer 33 as a heat-resistant elastic layer on the outside thereof, a thickness of 3 mm and a diameter of 40 mm.
A 1 mm thick HTV layer 35a was provided on an aluminum cored bar 34, and a fluororesin layer 35b was provided on the surface of the HTV layer 35a as a pressure roller 30. A roller is used, and by combining the fixing roller 29 and the pressure roller 30 having such a configuration, the releasability from the sharp melt toner is further improved.

However, in recent years, with the spread of the color image forming apparatus, the speed and the convenience of the color image forming apparatus are the same as those of the black and white image forming apparatus, that is, the automatic double-sided copying, the use of the recording material from the postcard to the large size, and the use of the thin paper. It has become necessary to respond to various needs such as cardboard, OHP film and pack print film.

Therefore, in order to meet such needs,
Improvements of the above-described fixing device 18 have been proposed. For example, in order to fix a two-sided image, not only the fixing roller 29 but also the surface layer of the pressure roller 30 have an RTV having a high toner release effect.
Alternatively, an LTV (low temperature vulcanization type) silicone rubber is used. At the same time, in order to satisfy the high speed of color fixing, it is necessary to increase the nip between the fixing roller 29 and the pressure roller 30, and the diameter of the roller is increased (for example, a diameter of 60 mm or 80 mm). In addition, since thick paper or the like is used, the fixing performance must be improved, and the fixing temperature must be increased.

However, the silicone rubber of the surface layer, which is originally used for maintaining the mold releasability, and the silicone rubber of the lower layer for forming the nip which wraps the sharp melt toner, are both used in the silicone oil used. Because it is very familiar with silicone oil, a large amount of silicone oil enters the rubber depending on the durability, and the bottommost layer of silicone rubber contains a large amount of silicone oil, and peels off between the core metal interface during heating. Sometimes occurred.

Therefore, in an image forming apparatus which is required to make a large number of copies at a high speed, in order to prevent the peeling, both the fixing roller 29 and the pressure roller 30 are made of the lower silicone rubber and the surface silicone rubber. During this period, the use of an oil-resistant layer of fluororubber which absorbs silicone oil and does not allow the oil to pass through has often been used.

However, the above-described image forming apparatus has the following problems. In the case of a color image forming apparatus, since the outer layers of the fixing roller 29 and the pressure roller 30 are made of rubber or resin having poor heat conductivity, when the speed is increased, the temperature of the fixing roller 29 and the pressure roller 30 may decrease. growing. As a result, there is a possibility that the fixability of the second surface may be deteriorated particularly when images are formed on both the front and back surfaces of the recording material. As shown in FIG. 7, depending on the weight of the recording material and the toner, when a plurality of recording materials are continuously passed, the gloss of the image at the lowest point of the roller temperature differs from the gloss of the first image. Would. Further, depending on the length of the recording material, a fixing failure (cold offset) at the rear end of the paper may occur.

The mode in which the fixability of the second side is most likely to be deteriorated in the double-sided image formation is the case where the first side is full color and the second side is monocolor, as shown in Table 1 below. However,
The number of prints per minute for a mono color is four times that of a full color print. In the case of the mono-color mode, since the space between the recording materials becomes narrow and the roller temperature becomes low, the fixing property at the lowest point of the roller temperature tends to be deteriorated.

[0054]

[Table 1] 1st surface 2nd surface 2nd surface fixability at the lowest temperature of roller 2nd surface fixability (speed 160mm / s) (speed 100mm / s) Full color Full color △ ○ Full color Mono color × ○ Mono color Full color ○ ○ Mono color Full color ○ ○ Maximum full color glue amount 0.8g / A4 However, the maximum amount of toner to be applied is 0.
8 g / A4, and 0.3 g / A4 for monocolor.

In Table 1, ○, ×, and × are subjective evaluations, ○ indicates that the toner is sufficiently fixed on the paper, Δ indicates that the toner does not reach the cold offset, but the fixability is insufficient, and Each state indicates that an image is missing due to a cold offset.

Conventionally, as a countermeasure, the fixing speed of the second side has been reduced (for example, from 160 mm / s to 100 mm / s), but this reduces the productivity of the second side of both sides.

Therefore, in the present invention, defective fixing is prevented without lowering the fixing speed of the second side. Hereinafter, this point will be described in detail.

In this embodiment, as described above, when the type of printing on one side of the recording material is different from the type of printing on the other side, the printing order is changed according to the type of printing. The front and rear are set appropriately. For example, when a full-color print is performed on one side and a mono-color print is performed on the other side, the mono-color is printed on the first side and the full-color is printed on the second side. That is, the order of the printing order in duplex printing is determined according to the type of the original image (in the above description, whether the image is full color or monocolor).

First, the user places two documents 101 on a document table 102 (see FIG. 2). These two originals 1
01 has different original images to be printed on one surface and the other surface of one recording material P, respectively. It is needless to say that one original 101 having two types of original images may be used. And the user
When the double-sided print mode is selected by a button (not shown) on the operation panel, printing is performed so as to avoid the disadvantageous condition of full color on the first side and monocolor on the second side in Table 1 described above.

When double-sided printing is selected, the type of the two originals 101, that is, full-color or mono-color, is identified by the pre-scanner. This identification is performed by electrical processing as in the prior art. Here, when all the original images are full color only or mono color only, normal printing is performed. For example, the process speed of printing the first and second sides of the recording material P is 1
The printing speed is maintained at 60 mm / s, and printing can be performed without changing the throughput of the first side and the second side (see Table 1).

If one original image is full color and the other original image is monocolor, the monocolor image is first printed on the first side at a process speed of 160 mm / s. Thereafter, a full-color image is printed on the second side at a process speed of 160 mm / s (see Table 1).

If printing is performed on the first and second surfaces of the recording material P as described above, the process speeds of the first and second surfaces can be made the same, and the fixing failure can be performed without lowering the throughput. It is possible to fix without using.

In the above, the case where the original 101 is placed on the original plate 102 and the original image is printed has been described. However, the present invention is not limited to this. For example, both sides of one recording material P may be printed by an image signal from a controller. The same applies to the case of printing a document image.

<Embodiment 2> In this embodiment, when the user selects double-sided printing, the user places the original 101 on the original table 10 as instructed by a monitor (not shown) of the apparatus main body 1.
2.

As shown in the flowchart of FIG. 8, when double-sided printing is selected (S1), a message as shown in S2 is displayed on a display unit (not shown) of the apparatus main body 1. The user judges and selects one of the modes.

When "full color only" is selected (S
3) Then, a message "Please place either manuscript" appears. When the user places the document 101 in accordance with the instruction, the first side of the recording material has a process speed of 160 mm /
Printed with s. Later, "Please replace the manuscript"
Is displayed (not shown). User 2nd original 1
01, put 160mm / s on the second side at the same speed as the first side
Printed with. In this mode, the operations on the first side and the second side are the same (as before).

When "when there is a monocolor" is selected (S5), a message "Please put a monocolor original" is displayed (S6). The user places the mono-color original 101 on the platen in accordance therewith, and sets the first side to process speed 1.
Printed at 60 mm / s. On the second side, the most disadvantageous mode (see Table 1) can be avoided for any image, and printing can be performed at the same speed as the first side at 160 mm / s. For this reason, regardless of whether the original image to be printed is full-color or mono-color, double-sided printing can be performed without lowering productivity.

<Embodiment 3> This embodiment combines a conventional automatic document feeder.

As shown in the flowchart of FIG. 9, the user sends two or more originals 101 to the automatic original feeder V (FIG. 1).
(See S1), and when double-sided printing is selected (S1
1) The two originals 101 are placed on an original platen 102 (see FIG. 2).
To determine whether the original 101 is full color or mono color. As in the first embodiment,
The type of the document image of each document 101 is identified based on the signal obtained by the electrical processing.

The most disadvantageous mode of double-sided printing is shown in Table 1.
As shown in FIG. 5, the first surface is full color and the second surface is monocolor. Therefore, double-sided printing is performed so as to avoid this mode.

If the original image of the first original 101 is monocolor (S12), as in the conventional case (S14), the two-sided printing is performed by printing the monocolor image on the first side of the recording material and printing the second original 1
01 without discriminating the original image of the second original 10
One original image is printed on the second side of the recording material. In either case, printing is performed at a process speed of 160 mm / s.

If the original image of the first original 101 is full color, the original image of the second original 101 is identified (S13). If the original image is monocolor, the monocolor image is placed on the first side of the recording material. Printing is started in such a manner (S15). Then, the first document 101 is again conveyed to the document table 102, and the first document image is printed on the second side of the recording material 1 (S17), and the printing is completed (S18). All printings are performed at a process speed of 160 mm / s.

If the original image of the second original 101 is full color in S13, the conventional printing similar to S14 is performed (S16).

As described above, when printing is performed on both sides of the recording material using the automatic document feeder V, the most disadvantageous mode of the fixing property of the two-sided printing can be avoided, so that the productivity is reduced. No fixing failure was also avoided.

In the first to third embodiments, the fixing speed is limited to 160 mm / sec.
It can be appropriately set according to the properties (thickness, type, etc.) of the toner material and the recording material, the roller configuration of the fixing roller 29 and the pressure roller 30, and the like.

Further, the fixing device 18 has been described as having the fixing roller 29 and the pressure roller 30. However, the fixing device 18 is not limited to this. It is also possible to use a contact type or the like.

[0077]

As described above, according to the present invention,
When forming images on both sides of one recording material, it is possible to realize good fixing properties without lowering the fixing speed of the second side.

[Brief description of the drawings]

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

FIG. 2 is a longitudinal sectional view showing a schematic configuration of a reading device.

FIG. 3 is an enlarged view showing a configuration of a CCD.

FIG. 4 is a block diagram illustrating a signal processing circuit.

FIG. 5 is a diagram illustrating softening characteristics of a toner.

FIG. 6 is a longitudinal sectional view illustrating a configuration of a fixing device.

FIG. 7 is a diagram illustrating a relationship between the number of continuous sheets of recording material and a roller temperature.

FIG. 8 is a flowchart showing the operation of the second embodiment.

FIG. 9 is a flowchart showing the operation of the third embodiment.

FIG. 10 is a diagram showing a calculation process in the color correction circuit.

FIG. 11 is a diagram showing a structural formula of a polyester resin.

[Explanation of symbols]

 1 Image Forming Apparatus 15 Transfer Drum 18 Fixing Unit (Fixing Device) 19 Image Carrier (Photosensitive Drum) I Document Reading System II Image Forming Unit (Latent Image Forming Unit) III Image Forming Unit (Rotary Developing Device) IV Recording Material Transport system V Automatic document feeder (document feed system) P Recording material

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H027 EB04 EE03 FA13 FA28 GB14 2H028 BA01 BA06 BB01 BB04 2H030 AD05 AD07 BB24 BB43 2H076 BA14 BA59 BA76 BA83

Claims (4)

[Claims] An image forming section for forming an image on a recording material with a developer in which a plurality of colors melt and mix, and a fixing section for applying heat to the image on the recording material to fix the image on the recording material. In the image forming apparatus, when performing image formation on both one side and the other side of one recording material, a type of a document image to be formed on the one side and an image on the other side An image forming apparatus, wherein the order of forming an image on the one surface and the other surface is determined according to the type of a document image to be formed. 2. The image forming apparatus according to claim 1, wherein the type of the document image formed on the one surface and the other surface is full color or mono color. 3. When the original image formed on one surface is full color and the original image formed on the other surface is monocolor, after forming the full color image on the first surface, The image forming apparatus according to claim 2, wherein an image is formed on a second surface of a monocolor image. 4. An automatic document feeder for carrying in a document to a reading position, and carrying out the read document from the reading position, wherein the image forming order on one surface and the other surface of the recording material is determined by the automatic document feeder. The image forming apparatus according to claim 1, wherein the image forming apparatus is determined by a document feeder.