JPH1184920A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of efficiently and effectively performing reduction of curling on a recording member caused when passing through the heat fixing device. SOLUTION: This device is constituted so as to be provided with fixing means capable of fixing the image by colorant T formed on a recording material S provided with hysterisis of the size change at the time of moistening/ dehydrating in insert-transporting the recording material S between the fixing member 131 and the pressure member 132, and moisture feeding means 200 applying the satisfactory moisture capable of causing the hysterisis of the recording material restraining deformation derived from the difference between the volume change of the colorant T and the recording material S, during the time of fixing or after fixing, provided in the vicinity of the fixing means.

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 an image on a recording medium, and more particularly to an image recording apparatus such as electrophotography and electrostatic recording, and more particularly to a method for forming a toner image comprising resin, carbon, a pigment or a dye on the surface. The present invention relates to an image forming apparatus provided with a heat fixing device for applying heat to a recording member such as paper formed on a recording member to fix the toner image on the recording member.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus of this type uses a fixing device to apply a large amount of heat to toner to melt the toner and fix it on a recording member. At this time, if a large amount of toner is applied to one surface of the recording member (for example, 0.5 g / A4), the toner melted once at the time of fixing cools and shrinks, so that the surface on which the toner is applied is markedly curled. (Hereinafter referred to as positive curl).

The occurrence of the normal curl does not cause a serious problem in a normal image forming mode. However, for example, when a sorter is connected to an image forming apparatus to automatically align recording members, a problem may occur. When performing automatic double-sided printing that transfers the toner image to the front and back, the transportability of the recording member,
When the toner image is transferred from the image forming member to the recording member, and then the recording member is electrostatically separated from the image forming member, the transfer to the second side of the recording member may occur. There is a problem that inconvenience is caused in the later separation.

[0004]

Therefore, in order to solve the above-mentioned problem, as described in Japanese Patent Application Laid-Open No. 60-182449, a phenomenon in which a recording member expands when moisture is supplied is used. There is something. The curling occurs because one surface of the recording member shrinks, and if water is applied to the surface, the curling can be reduced.

However, this does not take into account the dimensional change hysteresis when the recording member absorbs moisture. The curl can be reduced at the moment when water is given, but if it is left for a while, the water given to the recording member evaporates,
Further, the curl will be worsened by the hysteresis of the dimensional change of the recording member.

An object of the invention of the present application has been made in view of the above-mentioned point of view, and an image forming method capable of efficiently and reliably reducing curling of a recording member caused by passing through a heat fixing device. It is intended to provide a device.

In particular, in double-sided printing in which images are formed on both sides of a recording member, the present invention improves the transportability of the recording member, reduces the occurrence of jamming, and separates the recording member from the image forming member after the second side printing. Since the characteristics are improved and the water content in the paper which is lost during the first-side fixing is supplied during or after the fixing, the transfer efficiency at the second-side transfer is improved, and this type of use is particularly preferable.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is directed to a recording apparatus in which a recording material passes through a heat fixing device for fixing a toner image on the recording member by applying heat, and thereafter, the recording is performed. It was configured to provide moisture to the member.

In the above-mentioned image forming apparatus, the input image signal and the set image processing method are used.
The setting is made so that the amount of applied water is changed according to the image density average value.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment] FIG. 2 shows a first embodiment of the present invention. FIG. 2 shows a schematic configuration of a color electrophotographic apparatus,
A recording material transport system I provided from the right side of the apparatus main body 1 to a substantially central part of the apparatus main body, and a transfer drum 15 constituting the recording material transport system I at a substantially central part of the apparatus main body 1
And a developing means disposed in close proximity to the latent image forming unit II, that is, a rotary developing device III.

The recording material transport system I has the following configuration. First, an opening is formed in the right wall of the apparatus main body 1, and a detachable recording material supply tray 2,
3 are provided so as to protrude partially outside the machine. Tray 2, 3
The paper feed rollers 4 and 5 are disposed almost directly above, and communicate with the paper feed rollers 4 and 5 and a transfer drum 15 which is a transfer means rotatable in the direction of arrow A disposed on the left. As described above, the paper feed roller 6 and the paper feed guides 7 and 8 are provided.

In the vicinity of the outer peripheral surface of the transfer drum 15, a contact roller 9, a gripper 10, a recording material separating charger 11, and a separating claw 12 are sequentially arranged from the upstream side to the downstream side in the rotation direction. . On the inner peripheral side of the transfer drum 15, a transfer charger 13 and a recording material separating charger 14 are provided.
The transfer drum 15 has a transfer sheet (not shown) made of polyvinylidene fluoride or the like affixed to a portion around which the recording material is wound, so that the recording material is electrostatically adhered onto the transfer sheet. Has become.

A separating claw 12 is provided on the upper right side of the transfer drum 15.
And a fixing device 18 at the end (right) end of the conveying belt means 16 in the recording material conveying direction.
Are arranged. 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 downstream of the fixing device 18 in the transport direction.

Next, the configuration of the latent image forming section II will be described. First, a photosensitive drum 19 serving as a latent image carrier rotatable in the direction of arrow B in FIG. 2 is provided with its outer peripheral surface in contact with the outer peripheral surface of the transfer drum 15. Above the photosensitive drum 19 and in the vicinity of its outer peripheral surface, a charge removing charger 20, a cleaning means 21, and a primary charger 23 are sequentially arranged from the upstream side to the downstream side in the rotation direction of the photosensitive drum 19, and furthermore, Drum 1
An image exposure means 24 such as a laser beam scanner and an image exposure reflection means 25 such as a mirror for forming an electrostatic latent image on the outer peripheral surface of the lens 9 are provided.

Finally, the structure of the rotary developing device III is as follows. A rotatable housing (hereinafter referred to as a “rotating body”) 26 is disposed at a position facing the outer peripheral surface of the photosensitive drum 19, and four types of developing devices are provided in the rotating body 26 at four positions in the circumferential direction. The electrostatic latent image formed on the outer peripheral surface of the photosensitive drum 19 is visualized (that is, developed). The four types of developing devices are a yellow developing device 27Y, a magenta developing device 27M, a cyan developing device 27C, and a black developing device 27BK, respectively.

First, the sequence of the entire image forming apparatus having the above-described configuration will be briefly described by taking a full-color mode as an example. When the above-described photosensitive drum 19 rotates in the direction of arrow B in FIG. 2, the photoconductor on the photosensitive drum 19 is uniformly charged by the primary charger 23. In addition,
In the apparatus shown in FIG. 1, the operation speed of each unit (hereinafter referred to as process speed) is 160 mm / sec. When the photosensitive member is uniformly charged by the primary charger 23, image exposure is performed by the laser light E modulated by the yellow image signal of the document 28, and an electrostatic latent image is formed on the photosensitive drum 19, By the rotation of the rotating body 26, the electrostatic latent image is developed by the yellow developing device 27Y fixed at the developing position in advance.

On the other hand, the recording material conveyed via the paper feed guide 7, the paper feed roller 6, and the paper feed guide 8 is held by the gripper 10 at a predetermined timing, and is brought into contact with the contact roller 9 at the corresponding timing. The transfer roller 15 is electrostatically wound around the transfer roller 15 by the use roller 9 and the electrode facing the same. The transfer drum 15 rotates in the direction of the arrow A in FIG. 2 in synchronization with the photosensitive drum 19, and the developed image developed by the yellow developing device 27 </ b> Y has the outer peripheral surface of the photosensitive drum 19 and the outer peripheral surface of the transfer drum 15. Is transferred by the transfer charger 13 at a portion where the contact is made. The transfer drum 15 continues to rotate as it is, and prepares for the transfer of the next color (magenta in FIG. 2).

On the other hand, the photosensitive drum 19 is provided with a charging device 20 for static elimination.
After being cleaned by the cleaning means 21 using a conventionally known blade method, it is charged again by the primary charger 23 and receives image exposure as shown by the next magenta image signal. The rotary developing device rotates while an electrostatic latent image based on a magenta image signal is formed on the photosensitive drum 19 by image exposure, and places the magenta developing device 27M at the above-described predetermined developing position to thereby perform predetermined magenta developing. I do.

Subsequently, the above-described process is performed for the cyan and black colors, respectively, and when the transfer of the four colors is completed, the four-color image formed on the recording material is transferred to each charger 20, 14, and the gripper 10
With the release of the gripping of the recording material by the
The sheet is separated from the transfer drum 15 by the separation claw 12, sent to the fixing device 18 by the conveyor belt 16, fixed by heat and pressure, and a series of full-color print sequences is completed.
A required full-color print image is formed.

At this time, the fixing operation speed of the fixing device 18 is 90 mm / sec, which is lower than the process speed of the main body, 160 mm / sec. This is because a sufficient amount of heat must be applied to the toner when melting and mixing unfixed images on which two to four layers of toner are stacked as described below. As a result, the amount of heat applied to the toner is increased.

As described above, since a multicolor toner forms two to four layers of a color image, a color image forming electrophotographic apparatus has two points for black-and-white printing in the following two points. It has different features from the device.

The first characteristic relates to the toner used.

Since the toner is required to have good meltability and color mixing upon application of heat, a sharp melt toner having a low softening point and a low melt viscosity is used. By using a sharp melt toner, the color reproduction range of a copy can be widened and a color copy faithful to a multicolor or full-color image of a document can be obtained.

Such a sharp melt toner includes, for example, a binder resin such as a polyester resin or a styrene-acryl ester resin, a coloring agent (a dye, a sublimable dye),
It is manufactured by melt-kneading, pulverizing, and classifying a toner-forming material such as a charge control agent. If necessary, an external addition step of adding various external additives (for example, hydrophobic colloidal silica) to the toner may be added. As such a color toner, a toner using a polyester resin as the binder resin is particularly preferable in consideration of the fixing property and the sharp melt property. Examples of the sharp-melt polyester resin include a polymer compound having an ester bond in the main chain of a molecule synthesized from a diol compound and a dicarboxylic acid. In particular,

[0025]

Embedded image

(Wherein R is an ethylene or propylene group, x and y are each a positive integer of 1 or more, and the average value of x + y is 2 to 10) or a bisphenol derivative represented by the formula: A carboxylic acid component comprising a diol component as a substituent and a divalent or higher carboxylic acid or an acid anhydride thereof or a lower alkyl ester thereof (for example, fumaric acid, maleic acid, maleic anhydride, phthalic acid, terephthalic acid, trimellitic acid) , Pyromellitic acid, etc.) are more preferred because they have sharp melting properties.

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

FIG. 3 shows an example of softening characteristics of a sharp melt toner containing the polyester resin as a binder resin. The measurement conditions are as follows.

Using a flow tester CFT-500A type (manufactured by Shimadzu Corporation), a die (nozzle) diameter of 0.2 m
m, a thickness of 1.0 mm, an extrusion load of 20 kg, and an initial setting temperature of 70 ° C., a preheating time of 300 seconds, and a temperature of 6 ° C. /
A plunger descent amount-temperature curve (hereinafter referred to as a softening S-shaped curve) of the toner drawn when the temperature was raised 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 . Softening S
The character curve becomes a curve 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), the plunger descent stops, and the process ends (D → E).

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

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

The toner or binder resin having such a sharp melt property is defined as T1 when the apparent melt viscosity is 10 ³ poise and T2 when the apparent melt viscosity is 5 × 10 ² poise. T1 = 90 to 150 ° C. | ΔT | = | T1−T2 | = 5 to 20 ° C.

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

Such a sharp-melting color toner also has a property of having a high affinity and being easily offset to the fixing roller.

Therefore, in the fixing device of the image forming apparatus using the color toner as described above, it is necessary to exhibit high releasability over a long period of time. Hereinafter, an important fixing device 130 in the present embodiment will be described with reference to FIG.

In FIG. 1, a fixing device 130 includes a fixing roller 131 having a halogen heater 131a as a heating source inside, and a halogen heater 132 as a heating source inside.
a, and a silicone oil as a release agent is applied to the surface of the fixing roller 131 and the pressure roller 132 rotatably pressed against the fixing roller (there may be no halogen heater 132a inside). Oil application device 133
Cleaning devices 134 and 135 for removing toner adhering to the surfaces of the fixing roller 131 and the pressure roller 132
And

Fixing roller 131 and pressure roller 132
Is a lower layer made of HTV (high temperature vulcanization type) silicone rubber on an aluminum core, an intermediate layer made of fluoro rubber to prevent oil from entering on the outside, and a silicone oil used as a release agent on the outside. It consists of a surface layer made of a good LTV (low temperature vulcanization type) or RTV (room temperature vulcanization type) silicone rubber. In particular, the surface layers of the fixing roller 131 and the pressure roller 132 are made of the same material in order to ensure releasability. Are preferred. The fixing roller 131 and the pressure roller 132 are arranged so as to cooperate with each other to form a nip portion for nipping and conveying the recording material.

Further, each of the halogen heaters 131a, 132
The heating operation of a is controlled by temperature control means (not shown). In other words, the temperature control means is a thermistor 136a,
136b detects the fixing roller 131 and the pressure roller 1
32 based on the surface temperature of each halogen heater 131a, 1
The ON / OFF state of 32a is controlled.

Further, the oil application device 133 can be brought into contact with and separated from the fixing roller 131, and the oil reservoir 133a
Roller 133b, 13 for pumping up the silicone oil inside
It is moved toward the application roller 133d by 3c, and silicone oil is applied to the surface of the fixing roller 131 by the application roller 133d. The oil application device 1
The contact and separation of the fixing roller 131 and the fixing roller 131 are controlled by ON / OFF of a solenoid (not shown).
3e. In the apparatus shown in FIG. 1, an amount of 0.08 g / A4 is applied as a coating amount by a measuring method described later.

The oil application device 133 and the amount of silicone oil applied by the oil application device 133 are determined as follows.

First, the weight of 50 sheets of A4 size white paper is set to A1.
(G), without transferring the image onto the white paper and without applying silicone oil to the rubber layer of the fixing roller, 50 sheets of white paper after passing between the fixing roller and the pressure roller. The weight is defined as B (g).

Next, similarly, the weight of another 50 sheets of A4 size paper is set to A2 (g), and the image is not transferred onto this white paper, but the silicone oil is applied to the rubber layer of the fixing roller. The weight of 50 blank sheets after passing between the fixing roller and the pressure roller is defined as C (g). A above
When 1, B, A2, and C are used, the coating amount X (g) of the silicone oil per sheet of A4 size white paper can be obtained by the following equation.

X = (C + A1-BA2) / 50 Further, in the fixing device shown in FIG.
Reference numerals 34 and 135 denote heat-resistant nonwoven fabric Nomex (trade name) or webs 134a and 135a obtained by plating nickel on the Nomex by an electroless plating method, and the cleaning webs 134a and 135a by using the fixing roller 1 as a fixing roller.
31, a roller 134 pressing against the pressure roller 132
b, 135b and cleaning webs 134a, 135
Unwinding rollers 134c and 135c that unwind a
And take-up rollers 134d and 135d for sequentially winding the cleaning webs 134a and 135a.

In such an apparatus, when the recording material is conveyed to the fixing device 130, the fixing roller 131 and the pressure roller 132 rotate at a constant speed, and the recording material
At the time of passing between the sections 1 and 132, the unfixed toner carried by being pressed and heated from both sides is melted and fixed. At this time, the fixing roller 131 and the pressure roller 13
The toner adhering to the cleaning devices 2 and 3
5 is cleaned.

This apparatus is provided with a re-feed roller 50 and a conveyance path 51 as a conveyance mechanism for forming a two-sided image.

Below the discharge roller 52, a re-feed roller 50 for feeding the recording material once placed on the discharge tray 17 to the latent image forming section II again is provided, and behind the re-feed roller 50. A transport path 51 for transporting the recording material is provided.

Next, the operation of the above-described apparatus when performing double-sided copying of a color image will be described.

The recording material developed in the developing device III and carrying the unfixed toner image on the surface thereof is conveyed by the conveying belt means 16 and fixed by the fixing roller 29 and the pressure roller 30 and then discharged by the discharge roller 52. Tray 17
Brought to you. Thereafter, the sheet is again fed by the sheet re-feed roller 50, passes through the conveyance path 51, is again conveyed to the latent image forming section II, and forms a color image on the back side in the same manner as the front side. In this way, the recording material having the color image already fixed on the front surface and carrying the unfixed color toner image transferred on the rear surface is conveyed to the fixing roller 29 and the pressure roller 30 by the transport belt means 16.

Further, in this embodiment, as shown in FIG. 1, a water application device 200 is arranged so that water can be applied from the back surface of the recording member after passing through the fixing roller and the pressure roller. The water application device 200 utilizes an ink jet head used in an ink jet printer, and jets water instead of ink. For example, a water direction perpendicular to the recording material passing direction (fixing roller 29 axial directions). The ink jet (water jet) head is held by a transfer means (not shown) and can move in the thrust direction, and the interval between the nozzles of the water discharge section is about 100 μm.

When the recording member having the toner image fixed on the first side is conveyed to the location where the water application device 200 is disposed, water is supplied from the back side. As a method of applying the water, for example, there is a method of applying the ink to the entire surface or applying a band to both ends of the recording member.

Generally, a recording member such as paper has a hysteresis of a dimensional change when absorbing moisture. FIG. 4 shows a dimensional change of a wood single fiber due to a humidity change. As can be seen from this figure, the dimensional change between moisture absorption and moisture release is different, and the dimensional change during moisture release is large. This is also the case for paper made of wood fibers. For example, the dimensions of the paper that has been left in a place where the humidity is 50% and the dimensions of the paper that has been left in a place with a high humidity of 50% or more and then returned to a place where the humidity is 50% shrink from the initial stage (hysteresis). This hysteresis is present in any paper. The present invention utilizes this hysteresis.

Next, the flow of why curling can be reduced by applying water will be described. The toner image is transferred onto the recording member by the image forming apparatus.
The toner image is heated and melted by the fixing roller 131 and the pressure roller 132 of the fixing device in FIG. 1, and is fixed on the recording member. At this time, the toner melts and is in an expanded state, but the recording member receives heat, so that moisture evaporates and shrinks. In particular, when the amount of toner applied to the front surface is large, water flows out only from the back surface of the recording member. Thus, when passing through the fixing device, it also depends on the environment outside the image forming apparatus,
The surface toner cools and contracts, and the recording member expands by absorbing moisture from the back surface. Due to the combination of these two factors, as shown in FIG. 6A, if the amount of applied toner is large, remarkable curl is caused and the toner is rounded into a cylindrical shape.

Therefore, the present embodiment is characterized in that moisture is applied from the back of the image after fixing by using the hysteresis of the formed paper, thereby suppressing the expansion of the paper after fixing and curling.

A case where high quality paper is used as an example of a recording member will be described. FIG. 5 shows data on the dependence of the curl amount on the amount of water applied. This is a case where the amount of toner applied is 0.5 g / A4. The curl is 4 when no water is applied as shown in the figure.
Although it was about 0 mm, when water of about 150 mg / A4 was given, the curl dropped to almost zero, paper conveyance,
The level has reached no problem with the sorter loading. Although the water application was performed on the entire surface of A4 paper, there are various methods such as applying only to both ends of the paper. However, in the latter case, it was more effective to apply water in a belt shape perpendicular to the direction of the paper gap.

During the above-mentioned water application, the paper absorbs water,
Once the curl gets worse. However, as shown in FIG. 6 (b), curling is alleviated when left to release moisture, and curling is better than when water is not applied. In order to suppress the curl deterioration during the water application, it is more effective to suppress the curl from the surface.

In addition to the ink jet method, water can be applied to felts, sponges, rollers, etc. by applying water and bringing them into contact with the back surface of the image.
The same effect was obtained for curls that were given the same water as in ink jet.

If the amount of applied toner is 1.0 g / A4 or more, the curl can be reduced to almost zero by applying water, although a curl is generated in the image surface and the curl is cylindrical. Was.

[Second Embodiment] The second embodiment is different from the first embodiment in that curling is reduced by applying water, and is performed by using water vapor.

For example, a humidifier is provided instead of the ink jet head type water application device 200 provided on the discharge side of the fixing device after image formation and image fixing as in the first embodiment. When about 0.2 g of water vapor was applied from the back of an A4 size recording member on which 0.5 g of toner was loaded with this apparatus, the inkjet ink of the first embodiment was applied.
The same effect as that of the head type water application device 200 was obtained, and curling could be reduced.

As a means for applying steam, in addition to the humidifier described above, for example, steam generated from paper of a fixing device can be used. The amount of the water vapor was about 0.14 g / A4 when the amount of water coming out of the paper by heat was measured by the same measurement method as the measurement of the amount of applied oil.
For this reason, for example, the fixing device itself is surrounded by a box, and the steam generated therein can be applied from behind the recording member through a pipe connected to the box. Also in this case, there was an effect of curling reduction as in the case of the humidifier. This method does not require water to be replenished, and therefore has an excellent curl reduction effect in terms of cost.

[Third Embodiment] As described above, at the time of fixing, paper releases moisture from the back surface and contracts. After fixing, the paper absorbs moisture and swells to worsen the curl. The purpose of the third embodiment is to reduce the shrinkage and expansion. By applying water from the back of the paper during the fixing of the toner, the shrinkage and expansion of the paper are suppressed, and the curl is reduced. ing.

FIG. 11 shows a fixing device and a water application device. This fixing device has a fixing roller 131 and a transport belt 201.

The fixing roller 131 has the same configuration as that of the first embodiment, and includes a cleaning device and an oil application device (not shown) as shown in FIG.
The transport belt 201 is formed of, for example, a porous sheet made of silicone rubber or a resin having a high toner release property,
Holes of m to several mm are provided everywhere.

When the transfer paper passes through the nip between the fixing roller 131 and the belt 201, water is applied to the back surface of the paper by the water (steam) coating device 200 through these many holes. This heats the transfer paper,
Although the water flies, since the water is supplied to the paper, the contraction and expansion of the paper are suppressed, and the curl can be reduced efficiently.

For example, when an A4 transfer sheet having an image with a toner application amount of 0.5 g / A4 passes through a nip portion between the fixing roller 131 and the belt 201 in FIG.
When g of water vapor was applied, the curl could be reduced from 50 mm to 8 mm, and the paper transporting sorter loadability could be significantly increased.

[Fourth Embodiment] The configuration of the image forming apparatus of the present embodiment is the same as that of the first embodiment shown in FIG. The description of the common part is omitted.

The object of the present embodiment is to prevent the transfer efficiency on the second side from being lowered because water is taken from the paper at the time of fixing the first side. In the above-described second and third embodiments, it has been described that application of water or water vapor after and during fixing has a great effect on curling reduction. Here, it is described that the transferability of the second surface is improved simultaneously with the curl reduction.

In this embodiment, the diameter of the photosensitive drum 19 is, for example, 80 mm, and the diameter of the transfer drum 15 is 160 mm (twice the diameter of the photosensitive drum 19).

The photosensitive drum 19 is set at 160 mm / sec.
At c, as shown in FIG. 2, the surface of the photosensitive drum 19 is driven to rotate in the direction of arrow B by
It is charged to 500 to -800V. Each developing unit of the developing device 2 has magenta, cyan, yellow, and black toners having negative charges, and visualizes the latent image formed on the photosensitive drum 19 by an inversion phenomenon.

In this embodiment, the transfer drum 15 has the same structure as that shown in FIG. 7, is formed in a cylindrical shape, and is rotatably supported by a shaft. The transfer drum 15 is connected to the cylinder unit 1 connected by the connection unit 10c.
A recording material holding sheet 110 in the form of a film is stretched over a base portion composed of Oa and 10b, and a recording material gripper (not shown) for gripping the leading end of the recording material S fed via the registration roller 6 or the like. ). Further, the transfer drum 1
5, a transfer charger 13 and an inner static eliminator 14 are arranged outside, and an outer static eliminator 150 and a separation charger 11 are arranged outside.

The recording material supporting sheet 110 has, for example, a thickness of 100 to 175 μm and a volume resistivity of 10 ¹⁴ to 10 ¹⁵ Ω ·.
cm polyvinylidene fluoride resin film or the like is used. The transfer charger 13 is, for example, a corona discharger, to which a voltage of +6 to +9 kV is applied and the transfer current is +2.
5 to +500 μA. The static eliminator for neutralizing the recording material S to which the toner image has been transferred is a DC bias (−0.7 kV to −3.7 kV, −50 μA to −265) during AC oscillation.
μA) can be applied to an AC charger (12 kV _PP , 800 μ
A) a corona discharge-type inner static elimination charger 14 comprising:
A corona discharge type external static elimination charger 150 comprising an AC charger (12 kV _PP , 800 μA),
The phases of the AC components of the outer static elimination charger 20 and the inner static eliminator 14 are controlled to be opposite phases. Also,
The separation charger 11 is an AC charger (10 kV _PP , 600 μ
m).

FIG. 9 shows an example of the relationship between the water content in paper and the transfer efficiency. When the transfer current is 200 μA, the transfer efficiency is significantly reduced when the water content in the paper is less than 5%.

For example, 0.4 g in a high-quality paper weighing 5 g
(8%) about water (at 50% humidity).
When this paper is passed through a conventional fixing device, about 0.2 g of water is lost, and transfer failure occurs at the time of second-side transfer. However, when about 0.2 g of water was applied after fixing by the fixing device of the first embodiment, the paper had enough moisture to prevent transfer failure, and transferability was significantly improved. As a result, the image on the second side became very good.

[Fifth Embodiment] In this embodiment, a reflection image density average value of an output image is converted by an input signal and a set image processing method, and water is calculated based on the reflection density average value. It controls the amount of application. The average value of the reflection image density in the present embodiment is defined as follows. In the case of a full-color image, the density of each pixel is magenta D
_M, cyan D _C, is represented by three yellow D _Y. Here, the average density Di of each pixel (= (D _M + D _C + D _Y ))
/ 3). From this, the reflection image density average value D _AVE.

[0075]

(Equation 1)

Is defined.

FIG. 10 shows an example of the relationship between the average value of the reflection image density D _AVE. And the amount of water applied to reduce curling. However, the reflection density was measured by Macbeth reflection densitometer RD1151P-B manufactured by Sakata Inx.

The experimental apparatus used in the first embodiment was used, and the amount of water applied was controlled according to the value of D _{AVE. As} shown in FIG.
Curling was reduced to almost zero.

[0079]

As described above, claims 1, 2, and 4
According to the invention according to the present invention, by applying water or steam to the back of the first image surface during and after the fixing of the first surface when forming a single-sided or double-sided image, respectively.
Severe curl unique to full color can be remarkably reduced, so that the sorter stacking property and the paper transport property at the time of forming the second side image can be improved. Further, the transferability of the toner at the time of forming the second side image is remarkably improved, and a good second side image can be provided.

According to the third and fourth aspects of the present invention,
By controlling the water application amount according to the image information,
Regardless of the image, curling can be efficiently reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a schematic configuration of a first embodiment of the present invention.

FIG. 2 is a sectional view showing a schematic configuration of the first embodiment of the present invention.

FIG. 3 is a diagram illustrating softening characteristics of a sharp melt toner used in the first embodiment.

FIG. 4 is a diagram showing hysteresis of a dimensional change with respect to a humidity change of a single wood fiber.

FIG. 5 is a diagram illustrating an example of a relationship between a curl amount and a water application amount.

FIG. 6 is a diagram illustrating curl behavior in the case of full color.

FIG. 7 is a perspective view illustrating a schematic configuration of the transfer device of FIG. 2;

FIG. 8 is a cross-sectional view illustrating a schematic configuration of the transfer device of FIG. 2;

FIG. 9 is a diagram illustrating an example of a relationship between transfer efficiency and water content in paper according to a fourth embodiment.

FIG. 10 is a diagram illustrating an example of a relationship between a water application amount and an average reflection density according to the fifth embodiment.

FIG. 11 is a sectional view showing a schematic configuration of a third embodiment.

[Explanation of symbols]

 Reference Signs List I Recording material transport system II Latent image forming unit III Rotary developing device 1 Main unit 2, 3 Tray 4, 5, 6 Feed roller 7, 8 Feed guide 9 Contact roller 10 Gripper 11 Recording material separating charger REFERENCE SIGNS LIST 12 separation claw 13 transfer charger 14 separation charger 15 transfer drum 16 transport belt means 17 discharge tray 18 fixing device 19 photosensitive drum 20 charge removing charger 21 cleaning means 23 primary charger 24 image exposure means 25 image exposure reflection means

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tatsuo Takeuchi 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc.

Claims (11)

[Claims] A fixing unit for fixing an image formed of a coloring material formed on a recording material having hysteresis of dimensional change when moisture is absorbed by nipping and conveying the recording material between a fixing member and a pressing member; A water supply means provided in the vicinity of the fixing means for supplying a sufficient amount of water to cause hysteresis of the recording material during or after fixing to suppress deformation due to a difference in volume change between the coloring material and the recording material; An image forming apparatus comprising: 2. A fixing unit for fixing an image formed of a coloring material on a recording material by sandwiching and conveying the recording material between a fixing member and a pressing member; and forming an image on the first surface and fixing the image on the first surface. In an image forming apparatus having a double-sided image forming function of forming an image on both sides of a recording material by causing the recording material to be conveyed again to an image forming unit and a fixing unit and performing image formation and fixing on the second surface, Characterized in that it has a water supply means on the back side of the image surface of the recording material which has been completed or is fixed, for supplying a sufficient amount of water to cause hysteresis of the recording material to suppress deformation due to a difference in volume change between the coloring material and the recording material. Image forming apparatus. 3. An image forming apparatus, wherein the supply of a sufficient amount of water to cause hysteresis to a recording material having a hysteresis due to a dimensional change due to moisture absorption during image formation is controlled by image information. 4. A fixing unit for fixing an image formed on a recording material by nipping and conveying the recording material between a fixing member and a pressing member, and a recording material having an image formed and fixed on the first surface. In an image forming apparatus having a double-sided image forming function of forming an image on both sides of a recording material by performing image formation and fixing on the second surface by conveying the image to the image forming unit and the fixing unit again, An image forming apparatus, wherein the amount of water applied to the back of an image surface is controlled in accordance with the amount of water. 5. The image forming apparatus according to claim 1, wherein the recording material is paper having hysteresis in absorbing and removing moisture. 6. An image forming apparatus according to claim 1, wherein said water supply means is of an ink jet type. 7. The image forming apparatus according to claim 1, wherein said water supply means is an application roller. 8. An image forming apparatus according to claim 1, wherein said water supply means is a sponge. 9. The image forming apparatus according to claim 1, wherein said water supply means is a humidifier. 10. The image forming apparatus according to claim 1, wherein the water is water vapor generated during fixing. 11. The image forming apparatus according to claim 4, wherein the image information is a value obtained by averaging the density of each pixel for all pixels.