JPH06230687A - Image forming device - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an image forming apparatus capable of using thick letters as a transfer material and increasing the image forming speed particularly when small size plain paper is used as the transfer material. (First invention). An image forming apparatus is provided with a photosensitive drum 3, a transfer drum 9 that supports and rotates the transfer material P, and a transfer unit that transfers a visible image formed on the photosensitive drum 3 onto the transfer material P. In the above, the transfer drum 9 is large enough to carry a plurality of small-sized transfer materials P, and is provided with a plurality of grippers (transfer material gripping means) and transfer sheets (transfer material suction means) (first invention). ). According to the first aspect of the present invention, since the transfer drum 9 includes both the gripper and the transfer sheet, it is possible to use thick letters as the transfer material P, and particularly when small-sized plain paper is used as the transfer material P. A plurality of plain papers can be attracted to the transfer drum 9, and the speed of image forming operation can be increased.

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 which employs an electrophotographic system or an electrostatic recording system.

[0002]

2. Description of the Related Art Conventionally, a gripper method or an electrostatic attraction method has been used as a method for gripping a transfer material in a color image forming apparatus adopting a multiple transfer method.

FIG. 16 is a cutaway perspective view of a transfer drum 9 used in the gripper system. The transfer drum 9 is opened and closed by a connecting plate 9c connecting the ring portions 9a and 9b so as to narrow the leading end of the transfer material. It has individual grippers 91. A transfer sheet (or screen mesh or the like) 93 is wound around the connecting plates 9c along the outer circumference of the ring portions 9a and 9c.

17 and 18 show a transfer drum 9 used in the electrostatic attraction method. The transfer drum 9 is composed of ring portions 9a and 9b and a connecting plate 9c like the gripper method. A transfer sheet 93 is wound around a notched cylindrical frame. Then, as shown in FIG. 18, a corona charger 7 that is an adsorption charging unit that operates to electrostatically attract the transfer material, and the corona charger 7
The grounded metal roller 8 is provided at a position facing the transfer sheet 93 with the transfer sheet 93 sandwiched therebetween, and charges necessary for adsorption are induced in the transfer sheet 93 during the adsorption charging operation.

[0005]

However, each of the above conventional examples has the following problems.

That is, in the gripper system, A4
Even when using small size paper such as landscape or B5 landscape, A3
Even when using a large size paper such as portrait or A4 portrait, the transfer drum 9 can carry only one transfer material (paper), compared to a method of carrying a plurality of small size papers like the electrostatic attraction method. There was a drawback that the copy speed was slow.

Further, in the electrostatic adsorption method, when a thick letter (particularly 160 gr / m ² or more) is used, the thick letter may be peeled off immediately after adsorption charging or peeled off after transfer. There is a problem that the types of transfer materials that can be used are limited.

Therefore, the object of the first aspect of the present invention is to use thick letters as the transfer material and to increase the image forming speed when the small size plain paper is used as the transfer material. To provide a forming apparatus.

FIG. 19 shows the structure of a conventional color copying machine.

In the illustrated color copying machine, a photosensitive drum 3, which is an image carrier, is rotatably supported so as to rotate in the direction of the arrow in the drawing, and an image forming means is arranged around it.

Thus, the photosensitive drum 3 is uniformly charged by the primary charger 4, and is irradiated with the light image color-separated or the light image L corresponding to the color image by the exposing means such as a laser beam exposing device. An electrostatic latent image is formed on the photosensitive drum 3. In the case of this example, the surface of the photosensitive drum 3 is charged to about −700 V by the primary charger 4, but the potential is such an environment where the apparatus is placed, the deterioration degree of the photosensitive drum 3, or the image density. It changes with.

By the way, a place where a toner image corresponding to an image portion on the photosensitive drum 3 is formed is exposed by a laser beam or the like, and a point having the maximum density is exposed by the maximum emission light amount, and the emission amount is changed. Set to FFh level. In addition, the laser beam is not emitted at a place on the photosensitive drum 3 where the toner image is not formed, and the emission amount is set to the OOh level.

Thus, an image having gradation can be formed by causing such an emitted light amount to emit light from the OOh level to the FFh level in accordance with the shading of the image. Then, the electrostatic latent image on the photosensitive drum 3 formed by the above exposure is visualized as a toner image by the developing device 1.

The developing device 1 has four developing devices 1M, 1C, 1Y and 1BK for separately storing four color developers (toners) of magenta, cyan, yellow and black. In the apparatus 1, the desired developing device 1M (1
C, 1Y, 1BK) is attached to and detached from a position facing the outer peripheral surface of the photosensitive drum 3 to develop the electrostatic latent image formed on the photosensitive drum 3.

At this time, the developing device 1M (1C, 1Y, 1B
A developing bias is applied to K) to prevent fog in the white background of the image. In this example, the white background potential is -700 V, FFh
The potential of the image-exposed portion of the device becomes −100 V. At this time, the potential of the developing bias is −550 V and the frequency is 2
Apply KHz and amplitude 2KV _PP . | (-7 at this time
00V)-(-550V) | = 150V is called a fog removal potential, and | (-550V)-(-100V) | = 450V is called a contrast potential. The image density is determined by the magnitude of this contrast potential to form an image. .

That is, when the contrast potential is high, the image density is high, and conversely, when the contrast potential is low, the image density is low.

The maximum image density is adjusted by the primary charger 4
It is adjusted by the charge amount. That is, when the image density is reduced, the amount of charge on the photosensitive drum 3 by the primary charger 4 is reduced, and for example, the surface potential of the photosensitive drum 3 is -500V.
And lower it. At this time, calculation was made from the fog removal potential of 150 V, etc.
The voltage is set to 50V, and a potential of -350V is applied as a developing bias.

Even when other maximum densities are set, the contrast potential is changed by changing the surface potential of the photosensitive drum 3 and the developing bias potential by the primary charger 4 as described above, and the image density is changed.

By the way, the toner image on the photosensitive drum 3 is
The image is transferred onto the transfer material P carried by the transfer separation device 13 and conveyed in the direction of the arrow in the figure.

Next, referring to FIG.
This will be described with reference to FIGS.

The transfer drum 30, which is a part of the transfer separation device 13, has a cylindrical ring 31, 32 arranged at both ends.
And a drum frame 30a composed of a connecting portion 33 for connecting the cylindrical rings 31 and 32, and the drum frame 30a
The transfer sheet 34 is made of polyvinylidene fluoride or the like. The diameter of the transfer drum 30 is set to 180 mm, for example, and the peripheral length thereof is twice or more the length of the A4 lateral size transfer material.

The separating means 40, which is a part of the transfer separation device 13, has a separation claw support 41 provided along the axial direction of the transfer drum 30 and a plurality of separation means fixed to the support 41. A separation pressing roller 42a is integrally provided at the tip of the separation claw 42.

Further, abutting rollers 45 and 46 are provided on both ends of the support 41 via appropriate support plates 43 and 44. The abutting rollers 45 and 46 contact the cylindrical rings 31 and 32 of the transfer drum 30 when the separation claw operation clutch (not shown) is actuated, and the ring 3
Guided by guide grooves 35 and 36 formed in the rollers 1, 32, the tip of the separation claw 42 is moved downward (that is, the transfer drum 30).
(Normal direction of) and rotate.

At the connecting portion 33 of the transfer drum 30, a transfer sheet 34 and a transfer material P adsorbed and carried by the transfer sheet 34 are held.
The cutout 3 is provided to facilitate the insertion of the separation claw 42 between
7 are formed. In addition, at the tip of the transfer sheet 34,
A cut 34a is formed along the cutout 37 of the connecting portion 33 to the non-image area of the transfer material, and the leading end of the transfer sheet 34 is formed by locally increasing the curvature of the shaded portion in FIG. It is fixed to.

The transfer material P is a registration roller 2 shown in FIG.
8 is sent in synchronization with the image, but the transfer separation device 1
There is provided a transfer material adsorbing means for adsorbing and holding the transfer material P fed to the transfer sheet 3 on the transfer sheet 34.

The transfer material attracting means is provided inside the transfer drum 30, and the transfer material attracting means applies a corona charge for attraction to the back surface of the transfer sheet 34, which charges the reverse polarity of the toner image on the photosensitive drum 3. It has a container 23 and a conductive roller 24 provided outside the transfer drum 30. The conductive roller 24 serves as an opposite electrode of the suction corona charger 23 that is grounded and is corona-discharging, and injects charges into the transfer material P to electrostatically attract the transfer material P to the transfer sheet 34. Make up.

When the transfer material P is adsorbed, the conductive roller 24 has a gap of, for example, 0 to 100 μm with the transfer sheet 34.
m, and preferably the transfer material P
Is supplied so that its front end overlaps the cut 34a of the transfer sheet 34 and does not enter the image area.

By the way, when continuous copying is designated by an operation panel (not shown), the length of the transfer material P in the conveying direction is less than half the length of the peripheral length of the transfer drum 30 minus the width of the connecting portion 33. In this case, the second transfer material P is fed subsequently to the first transfer material P, and the second transfer material P is attracted to the transfer sheet 34 at a position symmetrical to the first transfer material P. Let
That is, two transfer materials P are simultaneously adsorbed on the transfer sheet 34 and conveyed. As a result, a copying speed about twice as high as that when the copying operation is performed without adsorbing only one sheet on the transfer sheet 34 is obtained.

In order to transfer the first color toner image (for example, magenta toner image) on the photosensitive drum 3 onto the first transfer material P, the transfer corona charger 1 is provided on the back surface of the transfer sheet 34.
4 is used to give a charge having a polarity opposite to that of the toner. For this reason,
A current of −200 μA is passed through the charger 14.

Next, subsequently, the same latent image is formed on the photosensitive drum 3, the toner of the first color is developed on the photosensitive drum 3, and the toner of the first color is similarly applied to the second transfer material. Transcribe. By the time the first transfer material P reaches the position of the conductive roller 24 for the second time, the conductive roller 24 is released, and is separated from the transfer sheet 34 by a distance of 2 mm or more, for example, so as not to disturb the transferred toner image. Corona charging for transfer of a second color toner image (here, cyan toner image) on the photosensitive drum 3 formed in synchronization with the first transfer material P onto which the first color toner image has been transferred. Transfer using the device 14.

Similarly, the second color toner image is transferred to the second transfer material P. Thereafter, in the same manner, the toner images of four colors are transferred onto the second transfer material P.

The transfer current for the first color is -200.
μA, the second color is -250 μA, the third color is -300 μA,
The fourth color is sequentially increased to -350 μA. This is because the transfer sheet 34 is charged up due to the transfer current, and thus it is necessary to flow a large amount of current in order to cancel it.

After the completion of the transfer process, in order to weaken the attraction of the transfer material P to the transfer sheet 34, the pair of AC corona dischargers 15 and 16 facing each other with the transfer sheet 34 sandwiched therebetween are used to remove the electricity.

In order to separate the first transfer material P from the transfer sheet 34, the grooves 3 of the rings 31 and 32 shown in FIG.
The transfer sheet 34 is provided with an outer separation pressing roller 42a which is driven integrally with the separation claw 42 guided by the rollers 5, 36.
The outer separation pressing roller 42a is moved along the notch 34a of the connecting portion 33 by being pressed against the front end of the first transfer material P at the place where the curvature of the transfer sheet 34 is locally reduced. The separation claw 42 is inserted between the transfer sheet 34 and the transfer sheet 34, and the transfer material P is separated from the transfer sheet 34.

When the second transfer material P is separated from the transfer sheet 34, an inner separation pressing roller 53, which is driven as shown in FIG. 23, is pressed against the transfer sheet 34.
The outer separation pressing roller 42a is also guided by the groove 34a and pressed against the transfer sheet 34 to locally reduce the curvature of the transfer sheet 34 and separate the front end of the transfer material P from the curvature, so that the transfer material P and the transfer material P are separated from each other. Separation is performed by inserting a separation claw 42 between the transfer sheets 34. The transfer material P and the transfer sheet 3
In order to prevent image disturbance due to peeling discharge that occurs when 4 is separated, it is preferable to perform AC corona discharge using the corona discharger 17.

When the length of the transfer material P conveying method is longer than that described above, the front end of the transfer material P is located at the same position as the front end of the first transfer material P regardless of whether the copying is one copy or continuous copying. The transfer sheet 34 is adsorbed to the transfer sheet 34, and the same transfer / separation process as in the case of the first transfer material P is performed. At this time, the inner separation pressing roller 53 is not driven. After the transfer / separation process is completed, the transfer material P is sent to the fixing device 26 via the conveyor belt 25.

Here, the fixing device 26 is shown in FIG.
Will be explained.

The fixing device 26 has a fixing roller 121 and a pressure roller 125, and the rollers 121 and 125 are pressed against each other and are rotationally driven in the direction of the arrow. The fixing roller 121 covers the outer layer of the aluminum cored bar 122 with HTV silicone rubber (high temperature vulcanizing type silicone rubber) 123 with a thickness of 0.8 mm, and further coats the outer layer with LTV silicone rubber (low temperature vulcanization). (Sulfurized type silicone rubber) 124 is coated to a thickness of 200 μm.

In the pressure roller 125, the outer layer of the core metal 126 made of aluminum is coated with the HTV silicone rubber 127 to a predetermined thickness, and the surface layer thereof is coated with the resin film 127 '.
Is covered. It should be noted that the fixing roller 121 and the pressure roller 125 have a halogen heater 12 as a heating source.
8 are arranged respectively.

A thermistor 129 is brought into contact with the pressure roller 125, and the thermistor 129 controls ON / OFF of the supply of current to the halogen heater 128. In this way, the surface temperature of the fixing roller 121 and the pressure roller 125 has a predetermined value suitable for fixing the unfixed toner image on the transfer material P (for example, 170).
℃) is maintained.

On the other hand, in order to improve the releasability of the toner from the fixing roller 121, a releasing agent applying device 132 is provided at a predetermined position of the fixing device 26. In this release agent applying device 132, the silicone oil 133 (manufactured by Shin-Etsu Chemical Co., Ltd .: dimethylsilicone oil KF96, 300 cs) in the oil tank 132a is used for the roller groups 134, 135.
The silicone oil 133 pumped up is regulated to a constant amount by the application amount adjusting blade 140, and then the silicone oil 133 is applied to the fixing roller 121 by an on / off device including a plunger 142 and a spring 143.

The transfer material P is the fixing roller 121 having the above structure.
By passing between the pressure roller 125 and the pressure roller 125, the toner image is fixed by heat and pressure.

An image forming operation of forming and fixing a visible image on both the front surface and the back surface of the transfer material in the color copying apparatus will be described.

The image forming apparatus shown in FIG. 25 is equipped with a re-feeding roller 40 and a conveyance path 41 for double-sided image formation.

That is, below the fixing discharge roller 42, a re-feed roller 40 for feeding the transfer material P once placed on the discharge tray 37 to the transfer separation device 13 again is provided, and the re-feed roller 40 is re-fed. A transport path 41 for transporting the transfer material P is disposed behind the roller 40.

The transfer material P, which has been developed in the developing device 1 and carries an unfixed toner image on its surface, is transported by the transport belt 25, fixed by the fixing roller 121 and the pressure roller 125, and then discharged. The paper is sent to the discharge tray 37 by the paper roller 42. After that, the transfer material P is again fed by the re-feeding roller 40, passes through the conveyance path 41, and is conveyed again to the transfer separation device 13 to form a color image on the back surface like the front surface.

In this way, the transfer material P having the color image already fixed on the front surface and carrying the unfixed color toner image transferred on the back surface is fixed to the fixing roller 1 by the conveyor belt 25.
21 and the pressure roller 125 to carry out fixing, and finally to the discharge tray 37 to complete double-sided color copying.

Here, the developer, that is, the toner, used in such a color electrophotographic copying apparatus will be described.

In forming a multi-color image or a full-color image, by using a sharp melt toner, the color reproduction range of the copy can be widened and a color copy faithful to the original can be satisfactorily obtained.

The toner is produced by melt-kneading, pulverizing and classifying a binder resin such as polyester resin or styrene-acrylic ester resin, a colorant (dye or sublimable dye), a toner forming material such as a charge control agent. It still,
If necessary, various external additives (eg, hydrophobic colloidal silica) are added to the toner.

Considering the fixing property and the sharp melt property, it is particularly preferable to use the polyester resin as the binder resin for the color toner. Examples of the sharp melt polyester resin include polymer compounds having an ether bond in the main chain of a molecule composed of a diol compound and a dicarboxylic acid. In particular,

[0052]

[Chemical 1] (In the formula, R is an ethylene or propylene group, and X, Y
Are positive integers of 1 or more, and the average value of X + Y is 2 to 10. ), A bisphenol derivative represented by the formula (1) or a substituted product thereof is used as a diol component, and a divalent or higher carboxylic acid, its acid anhydride or its lower alkyl esterified carboxylic acid (for example, fumaric acid, maleic acid, maleic anhydride, A polyester resin obtained by at least copolycondensing phthalic acid, terephthalic acid, trimellitic acid, pyromellitic acid, etc.) as a dicarboxylic acid has more sharp melting characteristics, and is therefore more preferable. The softening point of the polyester resin is 75 to 150 ° C., preferably 80 to 120.
℃ is good.

FIG. 26 shows the softening characteristics of the toner containing the polyester resin as the binder resin.

The method of measuring the softening point will be described. Flow tester CFT-500A type (manufactured by Shimadzu Corporation).
Using a die (nozzle) with a diameter of 0.2 mm and a thickness of 1.
When the extrusion load of 20 kg is set to 0 mm, the preset temperature is 70 ° C., the preheating time is 300 seconds, and then the temperature is uniformly increased at a rate of 6 ° C./min. Curve). As the sample toner, fine powder precisely weighed from 1 to 3 g is used, and the cross-sectional area of the plunger is 1.0 cm ² . The softened S-shaped curve becomes a curve as shown in FIG.

According to the results shown in FIG. 26, as the temperature rises at a constant speed, the toner is gradually heated and starts to flow (plunger descending A → B).

Further, when the temperature rises, the toner in the melted state largely flows out (B → C → D), and the plunger descending stops and ends (D → E).

By the way, the height H of the softened S-shaped curve represents the total outflow amount, and the temperature T _{0 with} respect to the C point of H / 2 represents the softening point of the sample (for example, toner or resin).

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.

A toner or a binder resin having a sharp melt property means that the temperature at which the apparent melt viscosity is 10 ³ poise is T ₁ , and the temperature at which the apparent melt viscosity is 5 × 10 ² poise is T _2.
And when

[0060]

[Formula 1] T ₁ = 90 to 150 ° C. | ΔT | = | T ₁ −T ₂ | = 5 to 20 ° C.

The sharp-melting resin having these temperature-melt viscosity characteristics is characterized by extremely sharply decreasing the viscosity when heated.

Such a decrease in viscosity causes the uppermost toner layer and the lowermost toner layer to be appropriately mixed, and the transparency of the toner layer itself is sharply increased, which enables good color-reducing mixing.

However, when a visible image is formed on both surfaces of the transfer material, the transfer material tends to curl to the toner side due to heating by fixing after the first surface image formation. That is, the transfer material is pulled due to contraction of the toner after heating, and the transfer material tends to curl due to evaporation of water contained in the transfer material itself.

In particular, in the case of color copying, since a plurality of layers of toner are placed and more solid images such as photographs and pictures are present than line drawings such as characters, the curling of the transfer material is more remarkable than in the case of black and white copying. Becomes

The curled transfer material becomes unstable when it is re-fed and also causes a problem when it is wound around the transfer drum. That is, the transfer drum electrostatically attracts the transfer material, but since the transfer drum has a curvature of, for example, a diameter of 180 mm, the curled transfer material is peeled off from the transfer drum. Alternatively, as shown in FIG. 27, there arises a problem that the front end and the rear end of the transfer material P float above the transfer sheet 34.

Further, when the transfer material curls, the adsorption of the transfer material to the transfer drum becomes unstable. Therefore, for example, when the cyan, yellow, and black positions are superimposed on the first magenta color position, the transfer material is transferred. The positions of the materials are misaligned and proper color superposition cannot be performed. As a result, image quality defects such as color shift and moire occur.

Further, after the transfer, the curled image on the transfer material comes into contact with the inside of the main body in the conveying path leading to the fixing device or contacts with an upper guide or the like when entering the fixing device. There is a problem that the image is disturbed or the transfer material cannot enter the fixing nip.

Therefore, the object of the second invention is to prevent the curling of the transfer material after fixing and prevent the occurrence of image distortion in the double-sided image formation and to obtain a good double-sided image. To provide a device.

Further, the conventional image forming apparatus has the following problems.

That is, the carrying roller 24 is the developing device 1B.
Due to the scattering of toner from K, 1M, 1C, and 1Y or the scattering of the unfixed toner image carried on the transfer material held on the transfer drum 30, the toner adheres and becomes dirty over time,
This causes unnecessary stains on the transfer material P. That is, since the transfer material P is sandwiched between the transfer sheet 34 of the transfer drum 30 and the carrying roller 24 and passed through, the toner attached to the carrying roller 24 is transferred to the transfer material P and transferred.
Cause stains.

Therefore, conventionally, in order to remove dirt such as toner adhering to the carrying roller 24, a mylar or the like is brought into contact with the carrying roller 24 as a scraper, but the mylar sheet is damaged. However, there is a problem that the toner is melted by the heat of rubbing between the mylar sheet and the transport roller 24, and the melted toner is more firmly attached to the transport roller 24.

Therefore, an object of the third invention is to provide an image forming apparatus capable of preventing the surface of the carrying roller from being soiled and also being soiled by powder of the transfer material.

By the way, in a color electrophotographic apparatus, for example, a toner image of each color formed on an image carrier by an electrophotographic method is transferred onto a transfer material by a transfer apparatus to obtain a color image on the transfer material.

A typical transfer device is equipped with a transfer drum as a transfer material carrier, and the transfer drum has a transfer material carrier sheet (for example, a flexible transfer material carrier member between the cylindrical end frames). , A film-shaped dielectric sheet such as polyethylene terephthalate or polyvinylidene fluoride resin) is wound in a cylindrical shape.

Further, the diameter of the transfer drum is such that the largest one of the transfer materials to be used can be surely subjected to steps such as adsorption and separation.
And it is set so that it is not as large as possible. For example, when the maximum size of the transfer material is A3 size, the diameter is set to about 160 mm.

Thus, the transfer material is supplied to the transfer drum of the transfer device, and its end is mechanically fixed and held by the gripper provided on a part of the peripheral surface of the transfer drum. Alternatively, during winding, for example, corona discharge may be performed from the carrier sheet side or the transfer material side to electrostatically exert an attractive force between the carrier sheet and the transfer material to attract and hold the transfer material on the carrier sheet. (Refer to Japanese Patent Laid-Open No. 55-32079).

In order to attract and hold the transfer material,
A corona discharger is provided as a charge giving means inside the transfer sheet suction position of the carrier sheet (on the back side of the surface opposite to the transfer material holding surface), and if necessary, outside the carrier sheet (transfer material holding surface side). ) Is provided with a conductor roller for transferring to the transfer material, facing the corona discharger, and a charge having a polarity opposite to the triboelectrifying polarity of the toner forming the toner image on the image carrier is applied to the transfer material. .

In the color electrophotographic copying apparatus, the toner image is electrostatically formed on the transfer material, which is adsorbed and held on the carrier sheet as described above, each time a toner image of each color is formed on the image carrier. Is performed on all of the toner images of a plurality of colors by multiple transfer in which the transfer drum is rotated a plurality of times, whereby a toner image of a plurality of colors is superimposed on the transfer material to obtain a color image.

The transfer material on which the toner images of a plurality of colors have been transferred is
After that, the electrostatic attraction force (Coulomb force) generated between the transfer material and the carrying sheet is weakened by using a corona discharger, and the separating member is inserted between the transfer material and the carrying sheet. The transfer material is separated from the carrier sheet.

Further, in such a color electrophotographic copying apparatus, in order to reduce the difference in transferability at the time of the next transfer due to the presence or absence of the transfer material, further, in order to improve the image forming speed, When copying size paper, a configuration is used in which a plurality of transfer materials are continuously arranged on the surface of a transfer drum by a gripper and electrostatic attraction, or only electrostatic attraction.

When a plurality of small size sheets are continuously arranged on the transfer drum in this way, for example, when A4 size sheets are horizontally fed and placed on the transfer drum having a diameter of 160 mm,
The distance between two transfer materials is expressed by the following equation.

[0082]

## EQU00002 ## Distance between two transfer materials = (transfer drum circumference-transfer material length × 2) / 2 = (160π−210 × 2) / 2 ≈41.33 (mm) In a photographic device, light is applied to a document image, and the reflected light is imaged on a photoconductor to form a latent image.
Then, the latent image is developed and the developed image is transferred,
An exposure process for the original image is required every time. The same applies to color electrophotographic copying machines, G (green), R
Exposure is carried out by using the separated color light of (red) and B (blue).

Thus, as described above, when a plurality of transfer materials are placed on the transfer drum at a short distance, the original illuminating device is operated about 4 times after the illumination of the first transfer material is completed.
It is necessary to return to the home position and start the next exposure within the distance between transfer materials of 0 mm.

If the process speed of the entire system is 160 mm / sec, the time that can be spent for the above recovery is 40/160 sec, that is, only about 0.25 seconds. During this 0.25 second, the distance of 210 mm moved by the document illuminating device must be restored.

Actually, in order to reverse what has been moving in a certain direction and move in the original direction again, a margin time is required at each reversing, so that it takes less than 0.25 seconds. You have to go back a length of 210mm. Therefore, it is necessary to move the document illumination device at a speed of about 1000 mm / sec or more. In an electrophotographic apparatus configured to move at such an extremely high speed, an image is adversely affected by the vibration associated with the movement. Therefore, recently, document image information is read using a sensor such as a CCD and once 2. Description of the Related Art Recently, a digital signal is converted, data is compressed and stored, and a laser optical system is driven based on the compressed storage data to form an image.

By the way, the data compression rate is usually 1/5 to
Since it is about 1/10, the image reproducibility is not so problematic in a line image or a monochrome image, but in a high-definition full-color image, image deterioration is unavoidable, and image defects such as moire and rustling occur. There was a problem.

Therefore, an object of the fourth invention is to provide an image forming apparatus capable of obtaining a good image free from moire and roughness regardless of the type of image to be formed.

[0088]

In order to achieve the above object, a first aspect of the present invention is directed to an image carrier, a transfer material carrier which carries and rotates a transfer material, and a transfer material carrier which is formed on the image carrier. In an image forming apparatus comprising a transfer means for transferring a visible image onto a transfer material, the transfer material carrier has a size sufficient to carry a plurality of small-sized transfer materials, and a transfer material gripping means and It is characterized by comprising a plurality of adsorption means.

The second invention is an image forming apparatus capable of forming an image formed on an image bearing member only on the front surface of a transfer material or on both the front surface and the back surface, and fixing the image to obtain a permanent image. It is characterized in that the image amount on each side during double-sided image formation is smaller than the image amount during image formation only on the front side.

A third aspect of the invention is an image forming apparatus provided with a carrying roller for carrying a transfer material, wherein a magnet is provided in the carrying roller.

According to a fourth aspect of the invention, an electrostatic latent image is formed in accordance with a digital image signal corresponding to an original image or a digital image signal subjected to data compression / expansion processing, and the electrostatic latent image is visualized by a developing means. An image carrier that forms an image and carries the visible toner image, and is disposed so as to face the image carrier;
A movable transfer material carrier capable of carrying a plurality of transfer materials according to the size of the transfer material, and a visible toner image carried on the image carrier are successively superposed on the transfer material carried on the transfer material carrier. In a high-speed mode in which a plurality of transfer materials are carried on the transfer material carrier and a digital image signal is subjected to data compression and expansion processing to form an image. , One transfer material is carried on the transfer material carrier, and data is compressed into a digital image signal,
A feature is that a high image quality mode is provided for forming an image without performing expansion processing.

[0092]

According to the first aspect of the present invention, since the transfer material carrier has both the gripping means and the suction means, thick paper can be used as the transfer material, and especially small size plain paper is used as the transfer material. In this case, a plurality of plain papers can be adsorbed on the transfer material carrier, and the speed of the image forming operation can be increased.

According to the second aspect of the present invention, curling of the transfer material after fixing is suppressed, problems such as image distortion and paper jam are eliminated in double-sided image formation, and a good double-sided image can be formed.

According to the third aspect of the invention, since the toner, the carrier, etc., which are scattered and adhered to the surface of the transfer roller, are restrained and retained by the magnet, the surface of the transfer roller is always kept clean, and the transfer material is kept. The problem of dirt is eliminated.

According to the fourth aspect of the invention, a high-speed mode in which a plurality of small-sized transfer materials are carried by the transfer means in accordance with the type of image to be formed and image data is compressed and expanded to form a high-speed image, and a small-size image is formed. Even if only one sheet of the transfer material is carried by the transfer means, and a high image quality mode is provided to output the image data without compressing or expanding it, a good image without moiré or shading can be obtained regardless of the type of image to be formed. Obtainable.

[0096]

【Example】

[First Invention] An embodiment of the first invention will be described below with reference to the accompanying drawings.

<First Embodiment> FIG. 1 is a vertical sectional view of a full-color copying apparatus according to the first embodiment of the present invention.

In FIG. 1, reference numeral 1 is a rotary developing device, and the developing device 1 has a yellow developing device 1 in its rotating body.
It is equipped with Y, magenta developing unit 1M, cyan developing unit 1C and black developing unit 1BK.

Reference numeral 2 is a toner replenishing device for replenishing the developing device 1 with toner as a developer, which has a yellow hopper 2Y, a magenta hopper 2M, a cyan hopper 2C and a black hopper 2BK. There is.

In the full color mode, the photosensitive drum 3, which is an image carrier, rotates in the direction of the arrow in the figure, and the photosensitive drum 3 is rotated.
The upper photoconductor is uniformly charged by the charger 4.

Next, image exposure is performed by the laser light E modulated by the yellow image signal of the original document (not shown),
An electrostatic latent image is formed on the photosensitive drum 3. Then, the electrostatic latent image formed on the photosensitive drum 3 is visualized as a toner image by the yellow developing device 1Y which is previously set at the developing position.

On the other hand, the transfer material P supplied from the transfer material cassette 20a or 20b via the paper feed guide 5a, the paper feed roller 6 and the paper feed guide 5b is transferred to the transfer drum by a method described later in synchronization with a predetermined timing. It is wrapped around 9.

The transfer drum 9 rotates in the direction of the arrow in the figure in synchronization with the photosensitive drum 3, and the toner image developed by the yellow developing device 1Y is transferred to the transfer charger 1 at the transfer portion.
0 is transferred onto the transfer material P. The transfer drum 9 continues to rotate and is ready for transfer of the next color (a magenta toner image in FIG. 1).

Thereafter, the photosensitive drum 3 is cleaned by the cleaning member 12, charged again by the charger 4, and then exposed by the next magenta image signal in the same manner as described above. During this time, the developing device 1 rotates and the magenta developing device 1M is placed at a predetermined developing position.
The magenta developing device 1M visualizes the electrostatic latent image formed on the photosensitive drum 3 as a toner image.

Thereafter, the same steps as described above are performed for cyan and black, respectively, and when the transfer of the toner images of four colors onto the transfer material P is completed, the transfer material P is transferred to each charger 1.
After the charge is removed by 3, 14, it is separated from the transfer drum 9 by the separating claw 15 and sent to the fixing device 17 by the conveyor belt 16, where the toner image is fixed by the fixing device 17 and discharged to the outside of the machine. A series of full-color printing operations are completed, and a full-color print image is formed.

By the way, in the full-color copying apparatus according to the present embodiment, the operation unit (not shown) is provided with a switch (not shown) corresponding to thick paper for the user to set according to the situation.

When the transfer material P to be used for copying is a thick letter, the user turns on the thick paper corresponding switch, and when it is plain paper, does the hand touch the thick paper corresponding switch? Alternatively, when the switch for thick paper is already turned on, the switch is pushed again or the initialization switch (reset button) is pushed to turn off the switch for thick paper.

Here, when the switch for thick paper is turned on, regardless of whether the transfer material P is small size paper (A4 landscape, B5 landscape, etc.) or large size paper (A3 portrait, A4 portrait, etc.),
One transfer material P is a transfer drum 9 by the gripper method.
Is adsorbed on.

That is, the thick letter transfer material P taken out from the transfer material cassette 20a or 20b is sent to the transfer drum 9 along the paper feeding and conveying path, and this is transferred to the gripper 91 (see FIG. 2) of the transfer drum 9. When gripped, the lower guide 5b is raised to a predetermined position by a driving unit (not shown), and the tip of the transfer material P is gripped by the gripper 91. After that, various kinds of toner images of respective colors are transferred onto the transfer material P as described above.

After that, when the transfer drum 9 is rotated to the separation position, the gripper 91 is opened more than when the paper is being fed, and the paper tip pushing member 94 pushes the tip of the transfer material P as shown in FIG. Then, the separation claw 15 enters between the pushed transfer material P and the transfer drum 9, and the transfer material P is separated from the transfer drum 9.

Next, when the transfer material P is plain paper, that is, when the transfer material P is a small size paper when the transfer material P is a normal operation (when the thick paper corresponding button is not pressed), two transfer materials are used. P is electrostatically attracted to the transfer drum 9, and if the transfer material P is a large size paper, one transfer material P is electrostatically attracted to the transfer drum 9.

That is, the transfer material P taken out from the transfer material cassette 20a or 20b is sent to the transfer drum 9 along the paper feeding / conveying path, and at this time, the lower guide 5b and the suction roller 8 are respectively driven (not shown). It is raised to a predetermined position by the means, and the adsorption charger 7 starts discharging almost at the same time. As a result, the transfer material P is electrostatically adsorbed on the transfer sheet 93 of the transfer drum 9. FIG. 3 schematically shows a state where two small-sized transfer materials P are attracted to the transfer drum 9.

After that, various kinds of transfer of each color are performed as described above, and toner images of four colors are transferred onto each transfer material P. When the transfer drum 9 is rotated to the separation position, the separation push-up roller 95 pushes up the transfer sheet 93 of the transfer drum 9 to float the tip of the transfer material P, as shown in FIG. Then, the separation claw 15 enters the gap between the floating transfer material P and the transfer sheet 93, and the transfer material P is separated.

<Second Embodiment> FIG. 5 is a control block diagram showing a second embodiment of the present invention.

In the present embodiment, the paper thickness detection sensor 100 detects whether the transfer material P is thick letter or plain paper, and the CPU 200 determines whether to use the first sequence or the second sequence based on the detection result. Then, the copying operation is performed according to the determination.

The first sequence is similar to the sequence when the cardboard switch is pressed in the first embodiment, and the second sequence is similar to the normal operation sequence in the first embodiment. .

Here, the paper thickness detection sensor 100 will be described.

FIG. 6 is a schematic block diagram of the paper thickness detecting device.
The paper thickness detection sensor 100 is installed in the vicinity of the paper feed guide 5a shown in FIG. 1, and is composed of a laser emitting unit 101 and a CCD light receiving unit 102.

Thus, for example, the optical path of the laser beam from the laser emitting section 101 where the plain paper P ₁ comes to the sensor section is L
It becomes ₁ like, the laser light reaches at point A shown in CCD light receiving portion 102. Further, when the thick letter P ₂ comes to the sensor section, the optical path of the laser light from the laser emitting section 101 becomes like L ₂ , and this laser beam is transmitted to the CCD light receiving section 10.
2 is reached at point B shown.

Therefore, by detecting the arrival position A or B of the laser beam to the CCD light receiving section 102, it is possible to determine whether or not the transfer material is a thick letter.

<Third Embodiment> FIG. 7 is a control block diagram showing a third embodiment of the present invention. In the present embodiment, the result of discrimination by the paper thickness detection sensor 100 between thick letters and plain paper and the user Either the first sequence or the second sequence in the second embodiment is selected according to both ON / OFF states of the thick paper corresponding switch 300 similar to that shown in the first embodiment by the operation, and the selected sequence is set. A copying operation is performed along the line.

That is, if at least one of the determination result of thick letter or plain paper and the ON / OFF state of the thick paper corresponding switch 300 is designated as thick letter, the first sequence (that is, thick sheet correspondence in the first embodiment) When the switch is pressed), the copying operation is performed, and if both are designated as plain paper, the copying operation is performed in the second sequence (that is, the sequence during the normal operation in the first embodiment). Done.

<Fourth Embodiment> In each of the first to third embodiments described above, an image forming apparatus using a transfer drum has been described as an example. However, the present invention forms an image using a transfer belt shown below. It can also be applied to a device.

Each image forming unit A, B, shown in FIG.
C and D respectively have photosensitive drums 3a, 3b, 3c and 3d, around which primary chargers 4a, 4b, 4c and 4 are provided.
d, exposure means 8a, 8b, 8c, 8d, developing devices 1a, 1
b, 1c, 1d, transfer chargers 10a, 10b, 10c,
10d, static eliminators 13a, 13b, 13c, 13d and 14a, 14b, 14c, 14d, cleaner 12a,
12b, 12c, and 12d are arranged, and the photosensitive drums 3a to
An endless transfer belt 9'is arranged below 3d.

After the transfer material P is fed by the paper feed roller, it is transferred by the transfer belt 9'to each image forming unit A.
The transfer chargers 10a to 10d of D to D are conveyed through the transfer unit.

FIG. 9 is a block diagram of the transfer belt 9 '.

A plurality of grippers 9 are attached to the transfer belt 9 '.
1'is provided, and a space (length) between the grippers 91 'is set so that the maximum copy paper size (A3 in this case) can be sufficiently carried.

The operation sequence is as follows:
Similar to the case of the transfer drum 9 in the embodiment, it has two kinds of first sequence and second sequence. The first
The sequence is a thick letter mode, and the second sequence is a normal operation mode (plain paper mode).

The copying operation is the same as that of the above-mentioned embodiment, so its explanation will be omitted. However, as a characteristic of this embodiment, when a thick letter is supported, regardless of whether it is a small size or a large size, one sheet is copied. The transfer material P is gripped by the gripper 91 ′. That is, in this embodiment, it is possible to carry up to three transfer materials P on the transfer belt 9 '. However, in the apparatus shown in FIG. 8, three transfer materials P are not carried at the same time.

On the other hand, at the time of normal operation (corresponding to plain paper), in the case of the small size, it is possible to carry up to six transfer materials P on the transfer belt 9 '. However, FIG.
In the device shown in FIG. 6, six transfer materials P are not simultaneously carried.

In the above-described first to fourth embodiments, the two holding methods of gripper and electrostatic attraction coexist, but, for example, air suction, suction by an adhesive material, and other holding methods are combined. You may use together. Further, although the combination of the corona discharger and the earth roller is used as the electrostatic attraction method, a brush or a roller may be used instead of the corona discharger, and a bias voltage may be applied to both sides of these. Further, the transfer material or the transfer material carrier may be pre-charged so that the transfer material may be adsorbed to the transfer material carrier. [Second Invention] An embodiment of the second invention will be described below with reference to the accompanying drawings.

<First Embodiment> Since the device used in this embodiment is the same as the device shown in FIGS. 19 and 25, its description is omitted.

In the present embodiment, the image forming trust is reduced in order to reduce the image amount in the case where only the front side is copied and when the double sided copy is made.

At the time of single-sided image formation, the image was formed with an image forming contrast of 300 V and a fog removing potential of 150 V.

On the other hand, during double-sided image formation, image formation was performed on both the front and back sides with an image forming contrast of 200 V and a fog removing potential of 150 V.

From the above, the maximum density as the image amount was 1.8 when the front surface image was formed, whereas the maximum density when the double-sided image was formed was 1.2.

As a result, after the image formation on the first side of the double-sided image formation is completed, the curl is almost eliminated, and when forming the image on the second side, the conventional problems such as paper jam and image rubbing do not occur at all.

Further, since the image density on the front surface is reduced, after the double-sided image is formed, the show-through of the front image from the back surface is almost eliminated, and the show-through from the back surface on the front surface is also eliminated. It has become possible to form a good image on both sides.

<Second Embodiment> In the present embodiment, in order to reduce the image amount in comparison with the first embodiment, the laser emission light amount is used up to the maximum FFh at the time of front surface image formation, and at the time of double-sided image formation. Is 80% of the maximum emitted light amount of the laser CC
The image was formed on the front surface and the back surface by using up to h.

As a result, the maximum density in the front surface image formation was 1.8, whereas the maximum density in the double-sided image format was 1.5.

Therefore, also in this embodiment, the same effect as that of the first embodiment could be obtained.

<Third Embodiment> As compared with the conventional example, the transfer current at the time of image formation only on the surface was formed so that the first color was 200 μA, the second color was 250 μA, the third color was 300 μA, and the fourth color was 350 μA.

On the other hand, the transfer current during double-sided image formation is as follows: 1st color: 100 μA 2nd color: 150 μA 3rd color: 200 μA 4th color: 250 μA, 1st color: 150 μA 2nd color: 200 μA Third color: 250 μA Fourth color: 300 μA Low to form a double-sided image.

As a result, the maximum image density during image formation on only the front surface was 1.8, whereas the maximum image density during double-sided image formation was 1.6.

By the above, the same effect as in the first embodiment can be obtained.

In the above description, the image amount is represented by the image density, but the image density is an amount that can be changed depending on the softening point of the toner, the fixing density, the amount of the release agent applied by the fixing device, the smoothness of the transfer material, and the like. is there.

However, the image density is generally preferable as a quantification method because it can be easily measured with a Macbeth (trade name) image densitometer.

Alternatively, the image amount may be evaluated by the toner amount on the transfer material. For example, in the first embodiment, the amount of toner when forming a full-color solid image was 80 mg / cm ² when forming an image only on the surface, whereas the amount of toner when forming a double-sided image was 60 mg / cm ^2. . In this way, it is more preferable to define the image amount and reduce the image amount only when the image is formed on the front surface and when the double-sided image is formed.

By the way, in the conventional example, an invention is disclosed in which the image amount of the first surface is reduced in order to reduce the curl amount of the first surface, but the present invention is greatly different in that the image amount of both surfaces is reduced. Further, reducing the image amount on only one side has a drawback that the apparent image feeling on the front and back sides becomes uncomfortable, but by reducing the image amount on both sides as in the present invention, there is no discomfort on the front and back sides. It has become possible to form various images.

In the above embodiments, the full-color image formation was mainly described, but it goes without saying that the present invention can be applied to general black-and-white image formation. However, the problem of curling is apt to occur particularly in full-color image formation with a large solid image ratio, and the present invention is particularly effective.

When changing the image amount, the transfer current,
Although the contrast and the amount of emitted light are shown as an example, the absolute value is not a problem and may be a value based on each device.

Furthermore, the developing bias frequency and amplitude may be changed in the case of image formation only on the surface and during double-sided image formation, and each value may be lowered during double-sided image formation to reduce the image amount. [Third Invention] An embodiment of the third invention will be described below with reference to the accompanying drawings.

<First Embodiment> In this embodiment, as shown in FIG.
In the full-color electrophotographic copying machine shown in FIG.
As shown in FIG. 3, a magnet 24-3 is arranged in the transport roller 24.

In FIG. 10, reference numeral 24 is a conveying roller and 2 is a conveying roller.
Reference numeral 4-1 is an outer sleeve constituting the transport roller 24, and the sleeve 24-1 is made of a pipe having a thickness of 0.5 mm and a diameter of 20 mm.

Further, 24-2 is a central axis and 24-3 is a magnet. In the magnet 24-3, as shown in FIG.
The N pole is arranged on the pole and the outer peripheral side, and the magnetic force is magnetized to about 1000 G.

In the carrying roller 24, the sleeve 24-1 is grounded.

In the carrying roller 24, the sleeve 24-1 on the outer circumference is rotationally driven by a driving device (not shown) at a speed equivalent to that of the transfer drum 30, and the magnet 2 is moved.
4-3 is fixedly arranged inside.

By using such a transport roller 24, even if the surface of the transport roller 24 is clean in the initial stage of use, toner is gradually scattered and adhered to the surface of the transport roller 24 as it is used. To do. At this time, a small amount of the carrier of the developer component also adheres. This is due to the scattering from the developing device 27 and the transfer drum 30.
This is because the carrier, which is slightly present in the toner on the transfer material held by, drops off from the transfer material and adheres thereto.

As described above, the carrier adheres to the transport roller 24, the carrier is transported to the magnet 24-3 by the rotation of the sleeve 24-1, and is restrained by the magnetic force of the magnet 24-3 (constrained in FIG. 10). The prepared carrier is indicated by 24-4).

The toner adhered on the sleeve 24-1 is removed by the sleeve 2 by the restrained carrier 24-4.
It is trapped in the carrier 24-4 without circulating over 4-1. That is, the toner and the carrier that have been scattered and adhered onto the sleeve 24-1 are naturally restrained by the magnet 24-3 and accumulated, so that the surface on the transport roller 24 is always kept clean.

As described above, it is no longer possible to attach extra stains on the transfer material. Further, since the carrier and the toner, which are sequentially attached onto the conveying roller 24, are attached by being bound by the magnet 24-3, it is necessary to remove them periodically, but since they are not heat-sealed, they are easy. It can be cleaned.

<Second Embodiment> In this embodiment, the first
In contrast to the embodiment, the carrier is previously attached to the transport roller 24, that is, only the carrier is attached to the sleeve 24-1 facing the magnet 24-3.

By doing so, even if a small amount of toner scatters and adheres at the beginning of use, the toner is instantly collected by the carrier that has been restrained in advance, and the surface of the transport roller 24 is always kept clean. It is possible to continue to.

<Third Embodiment> In this embodiment, the present invention is applied to the registration roller 28.

Although the toner and the carrier adhere to the registration roller 28 due to the scattering from the developing device 27 and the transfer drum 30, the registration roller 28 is always kept in a clean state as in the above-described embodiment, and the paper is dirty. The problem of was solved.

In the above embodiments, one magnet 24-3 is provided in the transport roller 24, but a plurality of magnets may be arranged. However, no magnet is arranged on the side of the sleeve 24-1 that contacts the paper. Further, the magnet 24-3 has a rod shape, but a cylindrical magnet may be put in the sleeve 24-1 and magnetized at only one place or a plurality of places. Further, the polarities and magnetic forces of the magnets are not limited to the present embodiment as long as they are effective. [Fourth Invention] An embodiment of the fourth invention will be described below with reference to the accompanying drawings.

<First Embodiment> An image forming apparatus according to the first embodiment of the present invention will be described.

FIG. 12 is a sectional view of a color electrophotographic apparatus which is an image forming apparatus according to the first embodiment. In the color electrophotographic apparatus, a photosensitive drum which is an image carrier rotatably driven in the direction of the arrow in the figure. 3 is uniformly charged by a primary charger 4, and an optical image L corresponding to image information is formed on the photosensitive drum 3 by an exposing means such as a laser beam exposing device.
Is irradiated to form an electrostatic latent image. Then, the electrostatic latent image formed on the photosensitive drum 3 is visualized as a toner image by the movable developing device 1.

By the way, the movable developing device 1 includes four developing devices 1M, which separately store four color developers of magenta color developer, cyan color developer, yellow color developer and black color developer. 1C, 1Y, 1BK, and a guide (not shown) that holds these four developing units 1M, 1C, 1Y, 1BK and can move in the horizontal direction.
The movable developing device 1 is provided with a desired developing device 1M.
(1C, 1Y, 1BK) is conveyed to the developing position facing the outer peripheral surface of the photosensitive drum 3, and the electrostatic latent image on the photosensitive drum 3 is developed.

The toner image on the photosensitive drum 3 is transferred onto the transfer drum 30D in advance by the action of the transfer charger 15 and the attraction charger 51 and the conductive roller 52 in the transfer portion of the transfer device 30. The image is transferred to the transfer material P that is adsorbed and held by.

Each time a toner image of each color is formed on the photosensitive drum 3 on the transfer material P adsorbed and held by the transfer drum 30D, the toner image is electrostatically transferred. All the toner images of a plurality of colors are subjected to multiple transfer by rotating a plurality of times, thereby superimposing the toner images of the plurality of colors on the transfer material P, and then the transfer material P is paired with a pair of static eliminator 16 at the separating portion. , 17 and separate charger 5
4. Further, the image is separated from the transfer drum 30D by the action of the separation roller 53, the transfer material P is conveyed to the fixing device 26, and the toner image transferred onto the transfer material P is thermally fixed to obtain a color image.

On the other hand, after the residual toner on the surface of the photosensitive drum 3 is cleaned by the cleaning device 12, the photosensitive drum 3 is subjected to the color image process again.

Further, in this image forming apparatus, the operation section is provided with a switch for switching between the high image quality mode and the high speed mode.

The flow of processing in the image forming apparatus when the transfer material P is continuously supplied to form an image for each mode will be described below with reference to the flowchart of FIG.

First, when the high speed mode is selected, the length of the transfer material P in the advancing direction is determined by a method such as using the transfer material size determining means of the sheet feeding cassette. It is calculated whether a plurality of transfer materials P can be carried on the transfer drum 30D according to the length in the traveling direction.

For example, in the case of laterally feeding A4 size paper, since the length in the traveling direction is 210 mm, the diameter 1
The main body of the apparatus is controlled so as to carry two sheets on the transfer drum 30D of 60 mm, the original image is read, the image data corresponding to the original image is compressed, and the compressed image data is temporarily taken into the memory section of the main body of the apparatus. . Then, the image data is taken out from the memory unit for each image formation of each color to form the image. When it is not possible to carry a plurality of sheets, image formation is performed in the same flow as in the high image quality mode described below.

On the other hand, when the high image quality mode is selected,
The apparatus main body is controlled so that only one transfer material P is carried on the transfer drum 30D regardless of the length of the transfer material P in the traveling direction. When the original image is read, the image data is used to form the image as it is. The original image is repeatedly read for each color to form a color image.

With the above-described structure, when the continuous image formation of the small size paper capable of carrying a plurality of sheets on the transfer drum 30D is performed, the original image is a high-definition full-color image according to the judgment of the user of the apparatus. When higher image quality is required, the copying speed will be slightly reduced by selecting the high image quality mode, but since image formation can be performed without compressing or expanding the image data, there is no moire or shading. High-quality image formation became possible.

<Second Embodiment> FIG. 14 is a diagram showing a processing flow in the image forming apparatus according to the second embodiment of the present invention.

In this embodiment, in the image signal processing unit in the image forming apparatus, first, whether or not an image to be formed is subjected to multiple transfer, that is, magenta color, cyan color, yellow color and black color, respectively. It is determined whether or not a monochromatic image is formed in which only one color is formed.

When the image is formed by two or more colors of magenta color, cyan color, yellow color and black color, that is, when it is determined that the multiple transfer is performed, the first
The image formation is performed in the high-quality mode described in the embodiment, and the image formation is performed in the high-speed mode when a single-color image is formed and a plurality of transfer materials can be adsorbed on the transfer drum.

With such a configuration, when the image data is compressed and decompressed, the high image quality mode is automatically selected for a color image having two or more colors that are severely deteriorated in image quality. The same effect as in the first embodiment can be obtained more easily.

In the present embodiment, the high image quality mode and the high speed mode are automatically switched, but a combination with the changeover switch which can be mode switched according to the judgment of the user of the apparatus shown in the first embodiment is used. It is more preferable then.

<Third Embodiment> FIG. 15 is a diagram showing a processing flow in the image forming apparatus according to the third embodiment of the present invention.

In the present embodiment, the image signal processing unit in the image forming apparatus first determines whether the image to be formed is a character image or a line image.

If it is determined that the image is not a character or line image, image formation is performed in the high image quality mode described in the first embodiment, and a character or line image is formed on the transfer drum. If multiple sheets can be adsorbed,
The image formation is performed in the high speed mode.

With such a configuration, when the image data is compressed / decompressed, the high image quality mode is automatically selected for a color image other than a character or line image whose image quality is severely deteriorated. Then, the same effect as that of the first embodiment can be obtained more easily.

In this embodiment, the high image quality mode and the high speed mode are automatically switched. However, the structure is combined with the changeover switch shown in the first embodiment capable of mode switching according to the judgment of the user of the apparatus. Further, a more preferable result is obtained by a combination with the structure of automatically switching the mode depending on the judgment as to whether or not two or more color images are formed as shown in the second embodiment, or a combination with both of them. It goes without saying that you can get

[0189]

As is apparent from the above description, according to the first aspect of the invention, since the transfer material carrier has both the holding means and the suction means, thick paper can be used as the transfer material and the transfer material can be transferred. When small-sized plain paper is used as the material, a plurality of plain papers can be adsorbed to the transfer material carrier, and the speed of image forming operation can be increased.

According to the second aspect of the present invention, curling of the transfer material after fixing is suppressed, and problems such as image distortion and paper jam during double-sided image formation are eliminated, and good double-sided images can be formed.

According to the third aspect of the invention, since the toner, the carrier, etc. scattered and adhered to the surface of the transfer roller are restrained by the magnet and stay, the surface of the transfer roller is always kept in a normal state, and the transfer material is kept. The problem of dirt is eliminated.

According to the fourth aspect of the invention, a high-speed mode for forming a high-speed image by compressing and decompressing image data by causing a transfer means to carry a plurality of small-sized transfer materials in accordance with the kind of image paste to be formed, Even if only one transfer material of a size is carried by the transfer means, and a high image quality mode is provided to output without compressing or expanding the image data, a good image without moire or shading can be obtained regardless of the type of image to be formed. Obtainable.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of an image forming apparatus (full color copying machine) according to a first embodiment of the first invention.

FIG. 2 is a diagram showing a state of recording material separation from a gripper type transfer drum in the image forming apparatus according to the first embodiment of the first invention.

FIG. 3 is a cross-sectional view showing a state in which two small-sized recording materials are carried on an electrostatic attraction type transfer drum in the image forming apparatus according to the first embodiment of the first invention.

FIG. 4 is a diagram showing a state of recording material separation from the electrostatic attraction type transfer drum in the image forming apparatus according to the first embodiment of the first invention.

FIG. 5 is a control block diagram showing a second embodiment of the first invention.

FIG. 6 is a schematic configuration diagram of a cardboard detection sensor used in the second embodiment of the first invention.

FIG. 7 is a control block diagram showing a third embodiment of the first invention.

FIG. 8 is a vertical sectional view of a color image forming apparatus according to a fourth embodiment of the first invention.

FIG. 9 is a perspective view of a transfer belt used in a color image forming apparatus according to a fourth embodiment of the first invention.

FIG. 10 is a configuration diagram of a carrying roller according to a third invention.

FIG. 11 is a schematic configuration diagram of an image forming apparatus according to a third invention.

FIG. 12 is a schematic configuration diagram of a main part of an image forming apparatus according to a fourth invention.

FIG. 13 is a flowchart showing a processing flow in the image forming apparatus according to the first embodiment of the fourth invention.

FIG. 14 is a flowchart showing a processing flow in the image forming apparatus according to the second embodiment of the fourth invention.

FIG. 15 is a flowchart showing a processing flow in the image forming apparatus according to the third embodiment of the fourth invention.

FIG. 16 is a cutaway perspective view of a transfer drum adopting a gripper method.

FIG. 17 is a cutaway perspective view of a transfer drum adopting an electrostatic attraction method.

FIG. 18 is a sectional view of a transfer drum adopting an electrostatic attraction method.

FIG. 19 is a schematic configuration diagram of a conventional image forming apparatus.

FIG. 20 is a perspective view of a transfer separation device.

FIG. 21 is a perspective view of a transfer drum frame.

FIG. 22 is a perspective view of a connecting portion between the connecting portion and the transfer sheet of the transfer / separation device.

FIG. 23 is an explanatory view of the operation of transfer material separation.

FIG. 24 is a schematic configuration diagram of a fixing device.

FIG. 25 is a schematic configuration diagram of an image forming apparatus.

FIG. 26 is a softening characteristic diagram of toner.

FIG. 27 is a diagram showing how the transfer material curls.

[Explanation of symbols]

 3 Photosensitive Drum (Image Carrier) 9 Transfer Drum (Recording Material Carrier) 9'Transfer Belt (Recording Material Carrier) 10 Transfer Charger (Transfer Means) 24 Conveying Roller 24-3 Magnet 51 Adsorption Corona Charger 52 Conductive rollers 91, 91 'Gripper (transfer material gripping means) 93 Transfer sheet (transfer material suction means) 100 Thick paper detection sensor (thick paper detection device) P Transfer material

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical indication location G03G 15/01 114 Z (72) Inventor Nobuhiko Takekoshi 3-30-2 Shimomaruko, Ota-ku, Tokyo Kyano (72) Inventor Ken Jojo 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Co., Ltd. (72) Inventor Yasuo Nami 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Co., Ltd. (72) Inventor Nobuatsu Sasana 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Tetsuya Atsumi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Takao Ogata 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (8)

[Claims] 1. An image carrier, a transfer material carrier that carries and rotates a transfer material, and a transfer unit that transfers a visible image formed on the image carrier onto the transfer material. In the image forming apparatus, the transfer material carrier is large enough to carry a plurality of small-sized transfer materials, and is provided with a plurality of transfer material holding means and a plurality of suction means. 2. The image forming apparatus according to claim 1, wherein the transfer material gripping means or the suction means is switched and used according to the type of the transfer material. 3. When a thick letter is used as the transfer material, only the tip of the thick letter is gripped by a clamper-type gripping means provided on the transfer material carrier, and when other transfer material is used, the thick letter is kept static. The image forming apparatus according to claim 2, wherein the transfer material is adsorbed to the transfer material carrier by the electroadsorption means. 4. The electrostatic attraction means is composed of a pair of corona dischargers, or a corona discharger and a grounded conductive member arranged on the opposite side of the transfer material and the transfer material carrier with the transfer material sandwiched therebetween. The image forming apparatus according to claim 3, wherein the image forming apparatus is configured. 5. A paper thickness detection device is provided, and it is determined whether the transfer material is a thick letter or another transfer material based on the detection result from the detection device, and the transfer material holding means or the suction means is switched and used. The image forming apparatus according to claim 2, wherein the image forming apparatus comprises: 6. An image forming apparatus capable of forming an image formed on an image bearing member only on the front surface of a transfer material or on both the front surface and the back surface, and fixing the image to obtain a permanent image. An image forming apparatus characterized in that an image amount of each surface at a time is smaller than an image amount at the time of forming an image of only the surface. 7. An image forming apparatus comprising a carrying roller for carrying a transfer material, wherein the carrying roller is provided with a magnet. 8. A digital image signal corresponding to an original image,
Alternatively, an electrostatic latent image is formed in accordance with a digital image signal subjected to data compression / expansion processing, the electrostatic latent image is converted into a visible toner image by a developing means, and an image bearing member carrying the visible toner image; A movable transfer material carrier which is arranged so as to face the carrier and can carry a plurality of transfer materials according to the size of the transfer material, and a visible toner image carried on the image carrier is a transfer material carrier. In an image forming apparatus having a transfer means capable of sequentially superimposing a transfer material carried on a transfer material, a plurality of transfer materials are carried on the transfer material carrier, and data compression and expansion processing for digital image signals are performed. A high-speed mode in which an image is formed by applying a high-speed mode and a high-quality mode in which one transfer material is carried on a transfer material carrier and an image is formed without performing data compression and expansion processing on a digital image signal are provided. Image forming equipment characterized by .