JPH10333378A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve productivity of both-side printing by minimizing the reduction of fixing speed for an image on a second side of a recording material at the both-side printing time. SOLUTION: The fixing performance of the image on the second side of a recording material is deteriorated when the toner spread quantity on the image of the second side is >=0.4 g/A4 in the case fixing speed is 200 mm/sec, and remains in good conditions until the quantity is <=0.5 g/A4 in the case when the fixing speed is 150 mm/sec. The surface potential on a photosensitive drum after forming the latent image becomes for instance, 500 V by an absolute value, on a section that the maximum quantity toner is mounted, and 0 V on the section that the toner is not mounted, and moreover the proportional relation is present between the total surface potential by integrating surface potential data of the image on the second side in the respective image element for four colors and the toner spread amount of the image on the second side. On determining the whole surface potential based on the surface potential data of the image on the second surface, the fixing speed is kept to 200 mm/sec when the data is <=150 V, and slowed to 150 mm/sec when the data is >150 V.

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 for forming a color image by transferring a plurality of color images to a recording material, and more particularly to an image forming apparatus for transferring a plurality of color images to both sides of a recording material. The present invention relates to an image forming apparatus with an improved fixing method.

[0002]

2. Description of the Related Art Conventionally, various image forming apparatuses are known. Among them, a photosensitive drum as a latent image carrier is subjected to image exposure with a laser beam, and the formed electrostatic latent image is developed to form an image. Is widely used. Such an image forming apparatus has advantages such as high quality of an obtained image and high speed of image formation, and is widely used as an output device such as a color copying machine or a color laser beam printer.

[0003] For example, a color copying machine as shown in FIG. 6 is exemplified. This color copier includes a document feed system O provided on an upper portion of an apparatus main body 1, a document reading system I, a latent image forming section II provided below the document reading system I, and a latent image forming section II. The developing device is substantially constituted by a developing means disposed close to II, that is, a rotary developing device III, and a recording material conveying system IV provided from the right side of the apparatus main body 1 to a substantially central portion of the apparatus main body. The configuration of the image forming apparatus will be described.

First, an original reading system I will be described with reference to FIG. FIG. 7 is a diagram showing a schematic configuration of the document reading system I. In FIG. 7, reference numeral 101 denotes a document, and 102 denotes a platen (document table). The platen 102 is fixedly mounted on the apparatus main body 1, and an irradiation light source 103 and a CCD (contact CCD color sensor) are provided below the platen 102.
An optical system unit 107 including an optical system 106 and the like is provided.

When a copy key of an operation unit (not shown) is pressed, the optical system unit 107 irradiates the original 101 placed on the platen 102 with light from the irradiation light source 103 while moving in the direction of the arrow. Scan sequentially. Then, the reflected light from the original 101 passes through the imaging element array 104 and the infrared cut filter 105,
An image is formed on the CCD 106 as a document image.

As shown in FIG. 8, R, G, and B pixels (elements) provided with red (R), green (G), and blue (B) filters are regularly formed in the CCD 106. , By scanning the original 101 with light irradiation
When a document image is formed on the CD 106, an analog electric signal corresponding to the document image is output from each pixel of the CCD 106,
The electric signal is processed by the signal processing circuit shown in FIG.

In FIG. 9, reference numerals 106B, 106G,
Reference numeral 106R denotes an electric signal from each of the B, G, and R elements on the CCD 106 in FIG. Each analog electric signal 106
B, 106G, and 106R are converted into digital signals B, G, and R by an A / D conversion circuit 111, and then Y ₁ , which is a digital density signal, is converted by a density conversion circuit 112.
The signals are converted into M ₁ and C ₁ signals.

[0008] The density signals Y _1, M _1, C ₁ is input to the circuit 113 that performs black extraction and UFR (background removal) process, the calculation process as shown in the following equation, Y _2, M
It is generated as a _2, C _2, Bk ₂ signals.

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 ): signals Y ₁ , M ₁ , C ₁ means the minimum signal of _{1; k 1, k 2,} k 3: is a predetermined constant.

[0010] Next, the _{Y 2, M 2, C 2} , Bk 2 signals, the color correction circuit 1 in order to correct the spectral distribution of the colorant used in the color separation filter and the image forming means CCD106
14 and is subjected to an arithmetic process represented by the following equation.

[0011]

(Equation 1) Here, a _{11 to} a ₄₄ are masking coefficients for color correction, respectively.

The operation results Y ₃ , M ₃ , C ₃ ,
Based on the Bk ₃ signal, laser beam irradiation of the latent image forming unit II described below is performed. The latent image forming section II will be described with reference to FIG.

As shown in FIG. 6, a photosensitive drum 19, which is a latent image carrier rotatable in the direction of arrow B, is provided on the latent image forming portion II.
Are arranged. In the vicinity of the outer peripheral surface of the photosensitive drum 19, a charge removing charger 20, a cleaning unit 21, and a primary charger 23 are sequentially arranged in this order from upstream to downstream in the rotation direction of the photosensitive drum 19. Above 19, an image exposure means 24 such as a laser beam scanner and a reflection means 25 such as a mirror are provided.

The image exposure means 24 operates as described above for Y ₃ , M ₃ , C
₃ , a laser beam E is emitted based on the Bk ₃ signal, and the laser beam E is
The surface is irradiated. Prior to the irradiation of the laser beam E, the surface of the photosensitive drum 19 is uniformly charged by the primary charger 23, and the charged charge on the surface of the photosensitive drum 19 is attenuated by the irradiation of the laser beam E, so that the electrostatic charge is reduced. A latent image is formed as the charge decay portion. This latent image is rotated by
Developed by III.

The rotary developing device III is disposed at a position intersecting the outer peripheral surface of the photosensitive drum 19, and four types of developing devices are provided at equal intervals in the circumferential direction in a rotating body 26 of a rotatable housing. It is installed. The four types of developing devices are a yellow developing device 27Y, a magenta developing device 27M, and a cyan developing device 27C.
And a black developing device 27Bk, which are used for developing an electrostatic latent image based on the above-described Y ₃ , M ₃ , C ₃ , and Bk ₃ signals, respectively. The electrostatic latent image on the photosensitive drum 19 is visualized as a toner image by development, and this toner image is transferred onto a recording material conveyed by a recording material conveyance system IV. The recording material transport system IV will be described.

The recording material transport system IV has the following configuration. An opening is formed in the right wall of the apparatus main body 1, and recording material supply trays 2 and 3 are detachably disposed in the opening, and a part of the trays 2 and 3 projects outside the apparatus main body 1. I do. Paper feed rollers 4 and 5 are disposed almost directly above the trays 2 and 3, and the paper feed rollers 4 and 5 are connected to a transfer drum 15 disposed below the photosensitive drum 19 so that the paper feed rollers 4 and 5 communicate with each other. A roller 6 and paper feed guides 7 and 8 are arranged. In the vicinity of the outer peripheral surface of the transfer drum 15, a contact roller 9, a charger 11 for recording material separation, and a separation claw 12 are sequentially arranged from the upstream side to the downstream side in the rotation direction.
The transfer charger 13 and the recording material separating charger 4
Are arranged.

The transfer drum 15 is formed by adhering a transfer sheet (not shown) made of polyvinylidene fluoride or the like on the peripheral surface, and the recording material is electrostatically attracted onto the transfer sheet. I have. At the upper right side of the transfer drum 15, a conveying belt unit 16 is installed close to the separation claw 12, and a fixing device 18 is disposed at the end (right end) of the conveying belt unit 16 in the recording material conveying direction. I have. A discharge tray 17 that extends to the outside of the apparatus main body 1 and is detachable from the apparatus main body 1 is provided further downstream of the fixing device 18 in the transport direction.

The sequence of the entire image forming apparatus having the above configuration will be briefly described by taking a full color mode as an example. First, the photosensitive drum 19 rotates in the direction of arrow B in FIG. Charger 23
Is charged uniformly. In this example, the photosensitive drum 19
The operation speed (process speed) of each part of the device is 160
mm / sec. The uniformly charged photosensitive drum 19 described above
Is the yellow image signal Y _{3 of the} original 101 (FIG. 7).
The image exposure is performed by the laser beam E modulated by the above, and an electrostatic latent image is formed on the surface of the photosensitive drum 19. The electrostatic latent image is developed by the rotation of the rotating body 26 by the yellow developing device 27Y previously set at the developing position, and is visualized as a yellow toner image.

On the other hand, the recording material conveyed via the paper feed guide 7, the supply roller 6, and the paper feed guide 8 is gripped by the gripper 10 of the transfer drum 15 at a predetermined timing, and Electrostatically wound around the peripheral surface of the transfer drum 15 by the electrode facing the electrode. The transfer drum 15 rotates in the direction of arrow A in FIG. 6 in synchronization with the photosensitive drum 19, and the yellow toner image formed on the photosensitive drum 19 is transferred when the photosensitive drum 19 and the transfer drum 15 are in contact with each other. At the site, the image is transferred onto the recording material by the action of the transfer charger 13. The transfer drum 15 continues to rotate as it is, and prepares for transfer of the toner image of the next color (magenta in this example).

After the transfer, the photosensitive drum 19 is neutralized by a neutralizing charger 20 and is cleaned by a cleaning means 21 having a blade. Then, the photosensitive drum 19 is charged by a primary charger 23 and is exposed to an image based on the next magenta image signal. Receive. The rotary developing device III rotates while the magenta image is formed on the photosensitive drum 19 by the image signal, and places the magenta developing device 27M at the developing position. Is subjected to magenta development. The obtained magenta toner image is transferred onto the recording material on the transfer drum 15 so as to be superimposed on the yellow toner image.

Subsequently, the same process as described above is carried out for the cyan and black colors, and when the superposition transfer of the four color toner images of yellow, magenta, cyan and black onto the recording material is completed, The recording material is discharged by 20 and 14, the gripping of the recording material by the gripper 10 is released, and the transfer drum 15 is separated by the separation claw 12. The separated recording material is sent to a fixing device 18 by a conveying belt unit 16, where the toner image is mixed and fixed by applying heat and pressure by a roller system, and is formed into a full-color print image. Thus, a series of full-color print sequences is completed, and the recording material is discharged to the tray 17.

The above description is for one-sided printing. When performing double-sided printing, the recording material on which the above-described single-sided printing (first-side printing) has been performed is placed upside down and upside down on the manual feed tray 17, and then placed there. The recording material is inserted into the above-described transport system and transported to the transfer drum 15, and the toner images of the respective colors for the second surface sequentially formed on the photosensitive drum 19 are superimposedly transferred on the second surface of the recording material, and By fixing the toner image on the second side, a double-sided full-color print having full-color images on both sides of the recording material can be obtained.

As another method of double-sided printing, a recording material on which printing on the first side has been completed is temporarily stored in a tray (not shown) in the apparatus main body 1, and then recorded again in a manner inverted upside down and back and forth. In some cases, the material is fed to the transfer drum 15 to perform the transfer of the second side and the subsequent steps.

As described above, in a color copying machine, a color image is formed by superimposing and transferring toner images of four colors. In the image area, toner is laminated in two to four layers. The image toner has different characteristics from the toner of a black-and-white copying machine.

That is, since a toner for a color image is required to have good meltability and color mixing when heat is applied, a sharp melt toner having a low softening point and a low melt viscosity is used. You. By using the sharp melt toner, a color print image having a wide color reproduction range with respect to a document can be obtained.

Such a sharp melt toner is obtained by melt-kneading toner forming materials 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 crushing and classifying. If necessary, a 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 a binder resin is preferable in consideration of fixability and sharp meltability.

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 expression

[0028]

Embedded image (Wherein R is an ethylene group or a propylene group,
x and y are each a positive integer of 1 or more, and x + y
And the carboxylic acid component comprising a divalent or higher carboxylic acid or an acid anhydride thereof or a lower alkyl ester thereof (for example, a bisphenol derivative represented by the formula Fumaric acid, maleic acid, maleic anhydride, phthalic acid,
A polyester resin obtained by at least co-condensation polymerization with terephthalic acid, trimetic acid, pyromellitic acid, etc. is more preferable because it has sharp melting characteristics.

The softening point of the polyester resin is 75 to 150.
C, preferably 80 to 120C. FIG. 10 shows an example of softening characteristics of a sharp melt toner containing this polyester resin as a binder resin. The measurement conditions are as follows.

Using a flow tester CFT-500A type (manufactured by Shimadzu Corporation), die (nozzle) diameter 0.2 m
m, a thickness of 1.0 mm, an extrusion load of 20 kg is applied,
After an initial setting temperature of 70 ° C. and a preheating time of 300 seconds, 6 ° C. /
A plunger drop amount-temperature curve (hereinafter, referred to as a “softening S-shaped curve”) of the toner drawn when the temperature was increased at a constant speed at a speed of one minute was obtained. The toner used as the sample is a fine powder precisely weighed from 1 to 3 g, and the cross-sectional area of the plunger is 1.0 cm ² .

The softening S-shaped curve 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), plunger descent stops and ends (D →
E). The height H of the S-shaped curve indicates the total amount of toner flowing out, and the temperature T ₀ corresponding to the point C of H / 2 indicates the softening point of the toner.

Whether or not the toner and the binder resin have a sharp melt property can be determined by measuring the apparent melt viscosity of the toner or the binder resin. A toner having a sharp melt property or a binder resin is defined as a temperature at which the apparent melt viscosity shows 10 ³ poise is T ₁ , 5 × 10 5
When the temperature at which shows the ² poise was _{T 2, 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 is reduced very sharply when heated. Such a decrease in viscosity causes an appropriate mixing of the uppermost toner layer and the lowermost toner layer of the toner layers stacked in a plurality of layers, and furthermore, the transparency of the toner layer itself is rapidly increased, and good color reduction mixing is performed. Cause

Therefore, as shown in FIG. 11, the fixing device 18 uses a fixing roller 29 of a fixing member having a halogen lamp 36 as a heating means and a pressure roller 30 of a fixing member also having a heater 37. These are pressurized at a total pressure of about 40 kg by a pressing mechanism (not shown) and used. Further, a thermistor 38 contacting the surface of the pressure roller 30 is provided.
The surface temperature of the fixing roller 29 and the pressure roller 30 are controlled to be constant at about 150 ° C. by controlling the heat generated by the halogen lamps 36 and 37 by the controller 39. As described above, the unfixed transfer toner image t by the sharp melt toner on the recording material P conveyed to the fixing device 18 is heated and pressed, and can be favorably fixed on the recording material P.

However, such a sharp-melt color toner also has a property of having a high affinity for the fixing roller 29 and being easily offset, so that the fixing device 18 has a high releasability for a long period of time. It is necessary to show.

Therefore, as shown in FIG. 11, the fixing roller 29 is provided with an oil application device D for cleaning agent and a cleaning device C, and the pressure roller 30 is provided with a cleaning blade C1 for removing oil stains. To improve the performance.

The oil applicator D includes a dimethyl silicone oil 41 (KF96 manufactured by Shin-Etsu Chemical Co., Ltd.) in an oil pan 40.
300 cs) is pumped onto the oil application roller 43 via the oil pump roller 42, the amount of oil pumped onto the application roller 43 is regulated by the application amount adjusting blade 44, and then the oil is applied to the fixing roller 29 by the application roller 43. I do. The oil applying roller 43 is detachable from the fixing roller 29 and abuts on the peripheral surface of the fixing roller 29 from 5 mm before the front end of the recording material to 5 mm after the rear end to apply oil. The amount of application is 0.1 per A4 recording material.
08 g.

The amount of silicone oil applied to the fixing roller 29 by the oil application device D can be measured as follows.

First, in order to obtain a blank, the weight of 50 sheets of A4 size white paper was measured and set as A ₁ (g). The image was not transferred onto this white paper, and the silicone oil was transferred to the fixing roller 29. Without coating, white paper is passed between the fixing roller 29 and the pressure roller 30, and the weight of 50 blank papers after passing is measured and defined as B (g). Next, the same A
The weight of 50 new blank sheets of 4 sizes was measured and this was A ₂
(G), the image is not transferred to the blank paper, but the silicone oil is applied to the fixing roller, and the blank paper is passed between the fixing roller and the pressure roller. Let the weight of the sheet be C (g).

From the above weights A ₁ , B, A ₂ , and C, A4
Silicone oil application amount per blank sheet of size X
(G) is obtained from the following equation.

X (g) = {(CA ₂ − (BA ₁ )}} / 50

In the cleaning device C, a non-woven web 46 made of Nomex (trade name) is applied to a pressing roller 45.
Thus, cleaning is performed by pressing against the fixing roller 29. The web 46 is appropriately wound by a winding device (not shown) so that toner and the like do not accumulate on the contact portion.

Further, the fixing roller 29 and the pressure roller 30 of the fixing device 18 are configured to have high releasability. That is, the fixing roller 29 is formed by placing an HTV (high temperature vulcanization type) silicone rubber layer 32 on an aluminum cored bar 31.
A RTV (room temperature vulcanization type) silicone rubber layer 33 is formed as a heat-resistant elastic layer on the outside of the
mm and a roller having a diameter of 40 mm. The pressure roller 30 is placed on an aluminum cored bar 34 by 1 mm.
An HTV silicone rubber layer 35a having a thickness of 30 nm is formed, and a fluororesin layer 35b is provided on the surface thereof.
m roller. By combining the fixing roller 29 and the pressing roller 30 having such a configuration, the releasability from the sharp melt toner is further improved.

However, with the recent spread of color copiers, color copiers are as fast as black and white copiers.
Convenience: automatic two-sided copying or use of postcard to large size paper, thin to thick paper, and O
It has become necessary to respond to various needs such as HP films and pack print films.

Therefore, in order to meet such needs,
An improvement of the fixing device 18 has 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 are made of RTV or LTV silicone rubber having a high toner releasing effect. . At the same time, in order to satisfy the high-speed color fixing, the roller is enlarged (for example, the outer diameter is 60 mm or 80 mm) to increase the nip. Further, since thick paper is used, the fixing temperature is increased. As a result, the fixing property was improved.

However, the silicone rubber of the surface layer, which is originally used for maintaining the releasability, and the silicone rubber of the lower layer for forming the nip which wraps the sharp melt toner, are both used silicone oil. Since it is very familiar with silicone rubber, a large amount of silicone rubber will enter the rubber over a long period of use, and the bottommost silicone rubber will contain a large amount of silicone oil, and will peel off between the core and the core during heating. May occur.

For this reason, in a copying machine which is required to make a large number of copies at a high speed, in order to prevent the lower silicone rubber from peeling off, both the fixing roller and the pressure roller are connected to the lower silicone rubber. Between the surface silicone rubber, an oil-resistant fluororubber that does not absorb and allow the passage of silicone oil has often been used.

[0048]

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

In the case of the fixing device 18 in a color copying machine,
Since the outer layers of the fixing roller 29 and the pressure roller 30 are made of rubber or resin having poor heat conductivity, if the recording material is continuously passed at a high speed (for example, 200 mm / sec) to perform fixing,
Since the frequency at which the heat of these rollers is taken away by the recording material increases, the temperature of the rollers drops significantly. As a result, the fixability of the image tends to deteriorate. In particular, when the image on the second side of the recording material is fixed at the time of double-sided printing, the fixing capacity is likely to be deteriorated due to the heat capacity of the toner on the first side, and a cold offset is generated depending on conditions.

For example, the gloss (the surface properties and gloss of the image after fixing) of the image depends on the type of recording material and the amount of toner (the amount of lamination), but at the lowest point of the roller temperature shown in FIG. In the image on the second side of the recording material, the gloss is lower than the image on the second side of the first recording material. Further, depending on the length of the recording material, a fixing failure (cold offset) occurs at the rear end of the second surface of the recording material.

As a countermeasure against this, the fixing speed of the second side of the recording material is reduced to, for example, 100 mm / sec, but the production efficiency of double-sided printing is significantly reduced.

An object of the present invention is to provide an image forming apparatus capable of improving the production efficiency of double-sided printing by minimizing the reduction in the fixing speed of the image on the second side of the recording material during double-sided printing. It is.

[0053]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the invention forms an electrostatic latent image on an image carrier, develops with a developer,
By transferring, a recording material on which an image composed of a plurality of color developers is formed is sandwiched between a pair of fixing members having a heat-resistant elastic rubber or resin surface layer, and heated and pressed to form the image. In an image forming apparatus for fixing to a recording material, the image forming apparatus includes means for measuring a developer amount of an image formed on the recording material, and the fixing is performed in accordance with a developer amount of the image measured by the developer amount measuring means. An image forming apparatus that changes a fixing speed of an image by a member.

According to the present invention, images are formed on both the first and second surfaces of the recording material, and the fixing speed of the image to be changed is the fixing speed of the image formed on the second surface of the recording material. Can be. The developer amount of the image to be measured can be the developer amount of the image on the second side of the recording material, and further, the total amount of the developer amount of the image on the first side and the second side of the recording material. Can be. Further, the images of the first and second surfaces of the recording material are the same as those of the same area of the recording material.
It can be the image part of the face and the second face. The developer amount measuring means can estimate and measure the developer amount of an image formed on the recording material based on potential data of an electrostatic latent image formed on the image carrier.

The fixing member may include a pair of rollers pressed against each other, and at least one of the rollers may have a heat source. Means for measuring the temperature of the environment in which the image forming apparatus is placed, wherein the change in the fixing speed according to the amount of the developer of the image corresponds to the fixing speed according to the temperature of the environment measured by the temperature measuring means. Can be taken into account.

[0056]

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

Embodiment 1 The present invention is characterized in that the fixing speed of the image on the second side is controlled so that the reduction in the fixing rate of the image on the second side of the recording material is minimized during double-sided printing. Since the mechanical configuration of the image forming apparatus and its fixing device itself is the same as that of the conventional image forming apparatus and its fixing device shown in FIGS. 6 and 11, FIGS. I will explain with help.

In this embodiment, the fixing speed of the image on the second side is controlled by the amount of toner constituting the image on the second side of the recording material, that is, the amount of toner applied to the image on the second side.

Table 1 shows that the image forming apparatus shown in FIG.
After forming and fixing a full-color image on the first side of the recording material of A4, an image is formed on the second side of the recording material by changing the amount of applied toner, and the image is fixed. It is the experimental result which investigated the dependence on quantity. The recording material passes continuously, and the fixing speed (process speed) is 200
mm / sec and 150 mm / sec. The fixing property is based on the recording material at the lowest temperature of the fixing roller 29 and the pressing roller 30 in FIG.

In Table 1, the symbol is ○: good fixability,
Δ: Immediately before the occurrence of a cold offset, x: Indicates the occurrence of a cold offset.

[0061]

[Table 1]

As can be seen from Table 1, when the image on the second side of the recording material was fixed at a fixing speed of 200 mm / sec, the amount of toner applied was 0.4 g / A4 or more, and the fixability of the image on the second side deteriorated. I do. However, when the fixing speed is reduced to 150 mm / sec, the image on the second surface can be satisfactorily fixed up to a toner application amount of 0.5 g / A4.

Therefore, in this embodiment, based on the above experimental results, the amount of toner applied to the image on the second side of the recording material is
The fixing speed of the image on the second side is changed.

There are various methods such as a dot counter method and a video counter method for measuring the amount of applied toner of an image. In this embodiment, the electrostatic latent image formed on the surface of the photosensitive drum 19 in FIG. From the potential data. The potential data of the electrostatic latent image was obtained by actually measuring the surface potential of the photosensitive drum on which the latent image of each color was formed.

The surface potential after the formation of the latent image on the photosensitive drum 19 depends on the environment.
Absolute value is, for example, 500 V, and the place where no toner is applied is 0
V. The sum of the surface potential data of the image on the second surface for four colors at each pixel (referred to as “total surface potential”) is 2
The amount of applied toner of the face image has a substantially proportional relationship as shown in FIG.

Accordingly, in the present embodiment, the total surface potential is obtained based on the surface potential data of the image on the second surface, and if the total surface potential is 150 V or less, the fixing speed is not reduced and, for example, 200 mm / sec. If the voltage exceeds 150 V, the fixing property deteriorates.
Slow down to 0 mm / sec.

In the above description, it is assumed that the surface potential data of the image is used for each recording material to be passed, and for the entire area of the image formed on the recording material. However, the surface potential data of the image may not be necessary for each recording material to be passed depending on the type of toner and the like. In this case, the rear end of the recording material at which the roller temperature is most reduced, for example, The surface potential data corresponding to the image portion in the area 5 cm from the rear end in the paper passing direction may be used.

As described above, in the present embodiment, the toner amount (toner application amount) of the image formed on the second side of the recording material during double-sided printing is predicted from the surface potential data of the photosensitive drum 19 corresponding to the image. Therefore, the fixing speed of the image on the second side is reduced only when the surface potential data is such that the toner amount exceeds the predetermined amount. Can be established,
Therefore, the production efficiency of double-sided printing can be improved.

Embodiment 2 In Embodiment 1, the fixing speed of the image on the second side of the recording material was controlled by the amount of toner applied to the image on the second side. In addition to being affected not only by the amount of toner applied to the image on the first surface, but also by the amount of toner applied to the image on the first surface, it varies depending on the total amount of applied toner on the first and second images.

FIGS. 2 and 3 show the results of examining the fixability of the image on the second surface with respect to the amount of toner applied to the image on the first surface and the image on the second surface of the recording material. FIG. 2 shows a case where the fixing speed of the image on both the first and second surfaces is 200 mm / sec.
Is a case where the fixing speed of the image on the first side is 200 mm / sec and the fixing speed of the image on the second side is 150 mm / sec.

If the fixing speed of the image on the second side is 200 mm / sec, which is the same as that of the image on the first side, as shown in FIG. 2, the point of the first-side toner applied amount = 1.0 g / A4 and the second-side toner applied amount = The fixing can be performed in the area covered by the mesh inside the line connecting the points of 1.0 g / A4 (the amount of applied toner on the first surface + the amount of applied toner on the second surface = 1.0 g / A4). In other words, in other words, the first-side toner applied amount + the second-side toner applied amount ≦ 1.0
With g / A4, the image on the second side can be fixed at a fixing speed of 200 mm / sec.

If the fixing speed of the image on the second side is set to 150 mm / sec, which is slower than that of the image on the first side, the fixing area is widened, and as shown in FIG. 3, the amount of toner on the first side is 1.3 g / A.
Line connecting the point No. 4 and the point of the second side toner = 1.3 g / A4 (the amount of toner applied on the first side + the amount of toner applied on the second side = 1.3)
g / A4) can be fixed in the area covered with the net.
In other words, 1.0 g / A4 <toner applied amount on first side + 2
When the amount of applied toner on the second side ≦ 1.3 g / A4, the fixing speed of the image on the second side needs to be reduced to 150 mm / sec.

Therefore, in this embodiment, when the sum of the amounts of applied toner on the first side and the second side of the recording material is 1.0 g / A4 or less, the fixing speed of the image on the second side is not reduced and is the same as that on the first side. 2
Fixes at 00 mm / sec and the sum of the amount of applied toner is 1.0 g
/ A4, the fixing speed of the image on the second side is set to 15
The image is fixed to 0 mm. However, in the case of a commonly used document or an image based on computer graphics, there are many images with a small amount of toner, so that the fixing speed of the image on the second side is hardly reduced.

Also in this embodiment, the first and second surfaces of the recording material
The amount of applied toner of the image on the surface is the same as in the first embodiment.
It can be predicted from the surface potential data of the latent image of the first image formed on the photosensitive drum 19 and the latent image of the second image. The predicted toner application amount of the image on the first side is stored in the memory in the copying machine, and is matched with the predicted toner application amount of the image on the second side when forming the image on the second side.
It is determined whether to change the fixing speed of the second side.

As described above, in the present embodiment, one of the recording materials
Since the fixability of the second image is determined based on the total amount of toner applied to the first and second images and the fixing speed of the second image is controlled, unlike the first embodiment, the risk of cold offset is reduced. Can be avoided.

Embodiment 3 In Embodiments 1 and 2, it was assumed that the environment was a normal temperature environment with an air temperature of 20 ° C. However, if the temperature of the environment changes, the fixability changes remarkably.

FIG. 4 shows that the temperature of the environment is 15 ° C. (room temperature),
9 shows the fixability of the image on the second side at 0 ° C. and 25 ° C. FIG.
As shown in (2), when the temperature of the environment decreases, the fixable area becomes narrower.
It is necessary to reduce the fixing speed of the face image.

Therefore, in the present embodiment, for example, the total amount of toner applied to the first and second images of the recording material is calculated by
When controlling the fixing speed of the image on the second side, the data of the fixable area using the fixing speed of the image on the second side as a parameter is obtained in advance in each temperature range of 15 ° C. or lower, 15 to 25 ° C., and 25 ° C. or higher. Are stored in a memory in the copying machine. As an example, FIG. 5 shows a temperature of 15 ° C., a fixing speed of the second side image of 100 mm / sec, 150 mm / sec, and 200 mm / sec.
It shows the fixable area in seconds.

As described above, the data of the fixable area is provided in the copying machine in advance, and at the time of double-sided image formation, the current temperature is measured by a temperature sensor (not shown) installed in the copying machine. If it is measured,
Based on FIG. 5, similarly to the second embodiment, the operation of controlling the fixing speed of the image on the second surface is performed based on the total amount of applied toner of the images on the first and second surfaces of the recording material.

In this embodiment, even if the temperature environment is different, the fixing of the fixing speed of the image on the second side of the recording material can be minimized and the production efficiency of double-sided printing can be improved. .

In this embodiment, the amount of toner applied to the image and the environmental temperature are employed as factors that influence the fixability of the image on the second surface of the recording material. However, the material, thickness, humidity of the environment, and the like of the recording material may be used. The fixability of the image on the second side is affected. Therefore, the data of the fixable area as shown in FIG. 5 is created by using the material of the recording material and the like as parameters, and an appropriate fixing speed of the second image can be determined and controlled according to the data.

In each of the first to third embodiments, the case where the roller type fixing device 18 is used as the fixing means has been described. However, the present invention is not limited to this, and a belt type fixing device or a non-contact type fixing device is used. The present invention can be applied to a case where a fixing device is used.

The amount of toner applied to the image on the recording material is
It was estimated from the surface potential data of the latent image formed on the photosensitive drum 19 and used as a measured value of the amount of applied toner. However, a dot counter that uses a read signal of a reader unit that has read the original and a dot counter that is formed on a recording material It can also be measured by a gloss meter densitometer or the like which measures the amount of toner of the formed image by a reflected light amount method.

[0084]

As described above, according to the present invention,
Depending on the toner amount of the image on the recording material during duplex printing,
Since the fixing speed of the image on the second side of the recording material is controlled, the fixing speed of the image on the second side can be reduced to a minimum and the production efficiency of double-sided printing can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. FIG. 1 is a diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. 6 is a graph showing a relationship between the total surface potential and the total surface potential.

FIG. 2 is a diagram illustrating the relationship between the amount of applied toner of the first image and the second image of the recording material used for controlling the fixing speed of the second image of the recording material according to another embodiment of the present invention. 6 is a graph showing a fixable area.

FIG. 3 is a graph similar to FIG. 2 when the fixing speed of the image on the second side of the recording material is changed.

FIG. 4 shows a recording material 2 according to still another embodiment of the present invention.
9 is a graph showing a fixable area of an image on a second surface at each temperature of an environment when controlling a fixing speed of an image on the second surface.

5 is a graph showing a fixable area of an image on a second surface with respect to an amount of applied toner of an image on a first surface and an image on a second surface of a recording material used in the control of the embodiment in FIG. 4;

FIG. 6 is a configuration diagram illustrating a color copying machine as an example of a conventional image forming apparatus.

FIG. 7 is a diagram showing an original reading system of the copying machine shown in FIG. 6;

8 is a diagram showing a CCD installed in the original reading system of FIG.

FIG. 9 is a diagram showing a signal processing circuit for processing an electric signal from the CCD of FIG. 8;

FIG. 10 is a view showing softening characteristics of a sharp melt toner suitable for use in the copying machine of FIG. 7;

FIG. 11 is a configuration diagram illustrating a fixing device installed in the copying machine of FIG. 7;

12 is an explanatory diagram illustrating a temperature decrease of a fixing roller and a pressure roller when a recording material is continuously passed through the fixing device of FIG. 11 at a high speed.

[Explanation of symbols]

 18 Fixing Unit 19 Photosensitive Drum 29 Fixing Roller 30 Pressure Roller

Claims (8)

[Claims] 1. A recording material, on which an image composed of a plurality of color developers is formed by forming an electrostatic latent image on an image carrier, developing with a developer, and transferring the latent image, is heat-resistant elastic rubber or resin. Means for measuring a developer amount of an image formed on the recording material in an image forming apparatus for fixing the image on the recording material by nipping and heating and pressing with a pair of fixing members having a surface layer of An image forming apparatus that changes a fixing speed of the image by the fixing member according to a developer amount of the image measured by the developer amount measuring unit. 2. An image is formed on both surfaces of a first side and a second side of the recording material, and the fixing speed of the image to be changed is:
The image forming apparatus according to claim 1, wherein the fixing speed is a fixing speed of an image formed on the second surface of the recording material. 3. The image forming apparatus according to claim 2, wherein the developer amount of the image to be measured is the developer amount of the image on the second surface of the recording material. 4. The image forming apparatus according to claim 2, wherein the developer amount of the image to be measured is a total amount of the developer amounts of the images on the first and second sides of the recording material. 5. The image forming apparatus according to claim 4, wherein the images of the first and second surfaces of the recording material are image portions of the first and second surfaces of the same area of the recording material. 6. The developer amount measuring means for predictively measuring a developer amount of an image formed on the recording material based on potential data of an electrostatic latent image formed on the image carrier. 1 image forming apparatus. 7. The image forming apparatus according to claim 1, wherein the fixing member includes a pair of rollers pressed against each other, and at least one of the rollers has a heating source. 8. A device for measuring a temperature of an environment in which the image forming apparatus is placed, wherein a change in the fixing speed according to an amount of a developer of the image corresponds to a temperature of the environment measured by the temperature measuring device. 2. The method according to claim 1, wherein a change in the fixing speed according to the condition is taken into consideration.
Image forming apparatus.