JP2009003380A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device which heats a recording medium with required sufficient heat capacity and at high speed and performs the transfer and fixation in the succeeding process. <P>SOLUTION: This image forming device is equipped with a transfer/fixing belt 1 consisting of a non-end belt on which image transfer is made, and a pressing member 24 to form the transfer/fixing belt 1 and a nip N. An image is transferred onto the recording medium P which passes through the nip N. A fine gap is formed with the pressing member 24 on the upstream side of the nip N as a reference position, where a heating means 101 is provided so as to contact the surface of the recording medium P. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus including a transfer fixing device applied to electrophotography, electrostatic recording, and electrostatic printing.

Conventionally, an image is formed on an image carrier (photoreceptor) by a developing unit, the image is transferred to an intermediate transfer member by a primary transfer unit, and an image on the intermediate transfer member is transferred by a secondary transfer unit. 2. Description of the Related Art Image forming apparatuses having a configuration in which an image on a transfer material is fixed to an image on a transfer material by a fixing unit are widely known.
In addition, an image forming apparatus configured to perform the above steps step by step is also widely used. In addition, a so-called transfer fixing step that enables the transfer step and the fixing step to be performed simultaneously is performed. An image forming apparatus has also been proposed (for example, see Patent Documents 1 and 2 below). Patent Document 1 shows an image forming apparatus configured to perform secondary transfer fixing from an intermediate transfer member to a transfer material. Patent Document 2 discloses a method after secondary transfer fixing from an intermediate transfer member to a transfer fixing member. An image forming apparatus configured to perform third transfer fixing from a transfer fixing member to a transfer material is shown.

In image forming technology, toner (chargeable powder mainly composed of resin) is generally used.
In such image formation, a process that tends to cause a decrease in image quality is a transfer process.
As a recording medium for forming an image, paper is mainly used, but there are various thicknesses from plain paper to cardboard. Also, the surface properties vary from fine to rough.
In particular, when paper with rough surface properties is applied, a minute gap is formed without following the surface property of the paper, abnormal discharge occurs in the minute gap portion, and the image is not transferred normally, There is a problem that the image tends to be blurred.

On the other hand, an image forming apparatus having a function in which a transfer process and a fixing process are performed at the same time has an advantage that image quality is hardly deteriorated even when a recording medium (paper) having a rough surface is used. ing.
This is because in the transfer process, heating is performed simultaneously with pressurization, so that the toner is softened and melted into a block-like lump having viscoelasticity, and can be transferred even at a position corresponding to a minute gap portion on the surface of the paper. This is because
From the above, it can be said that the image forming apparatus including the transfer fixing unit has a configuration to which a unit optimal for achieving high image quality is applied.

  Furthermore, in the transfer fixing method, since the recording medium does not travel with powder on it, a conveyance guide having a configuration in which the sheet passing direction is narrowly limited to just before the transfer fixing unit can be installed. Further, there is an advantage that it is possible to perform conveyance corresponding to various conditions such as other paper types from thin paper to thick paper. As described above, when the degree of freedom corresponding to the paper type is high, it is possible to effectively reduce the occurrence rate of the paper jam.

By the way, in order to sufficiently increase the thermal efficiency in the transfer and fixing process, it is necessary to increase the temperature at which the recording medium (paper) and the toner are fused, that is, the interface between the paper and the toner.
Conventionally, a method in which toner is sufficiently heated and softened and pressed against paper has been applied.
However, in order to obtain a sufficient effect in this system, not only the toner but also the transfer fixing member is heated. Therefore, when the transfer fixing member is as thick as 300 μm, for example, quadruple tandem imaging is performed. When a method or the like is employed and the circumference is long, sufficient thermal efficiency may not be ensured.
Furthermore, since the same member must be cooled on the one hand and cooled on the other hand in the subsequent process, it is a very disadvantageous structure from the viewpoint of energy efficiency. .

In view of the problems as described above, there has also been proposed a technique for selectively heating the recording medium (paper) itself immediately before the toner contacts (for example, see Patent Document 3 below).
However, this method still has a problem that temperature unevenness occurs, and in particular, there is a drawback that so-called scumming tends to adhere in printing a large number of sheets.

Japanese Patent Laid-Open No. 10-63121 JP 2004-145260 A JP-A-2005-37879

Therefore, in the present invention, in view of the above-mentioned problems of the prior art, when an image is formed by adopting the transfer fixing method, the paper is heated to a temperature at which there is no risk of ignition or the like at a position immediately before the transfer fixing. Furthermore, the present invention provides an image forming apparatus that secures a sufficient heat capacity while heating paper at a low heat capacity and at a high speed.
According to the idea of the image forming apparatus of the present invention, the so-called apparatus warm-up time can be significantly shortened.

  According to the first aspect of the present invention, the image forming apparatus includes a transfer fixing belt formed of an endless belt on which an image is transferred, and a pressure member that forms a nip with the transfer fixing belt, and the recording medium passes through the nip. An image is transferred, and heating means is provided on the upstream side with respect to the nip as a reference position so as to form a minute gap with the pressing member and to come into contact with the surface of the recording medium. An image forming apparatus is provided.

  According to a second aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein a minute gap between the pressure member and the heating unit is equal to or smaller than a minimum thickness of the recording medium.

  According to a third aspect of the present invention, there is provided the image forming apparatus according to the first or second aspect, wherein the distance of the minute gap between the pressure member and the heating means is variable.

  According to a fourth aspect of the present invention, there is provided the image forming apparatus according to any one of the first to third aspects, wherein the heating means is a roller-like rotating member.

  In the invention of claim 5, the heating means is constituted by a plate-like body and a roller-like rotating member, the plate-like body has a heat source, and heat is transferred from the plate-like body to the roller-like rotating member. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured as described above.

  In a sixth aspect of the present invention, the gap between the roller-like rotating member constituting the heating unit and the transfer fixing belt is larger than the gap between the roller-like rotating member constituting the heating unit and the pressure member. The image forming apparatus according to claim 4, wherein the image forming apparatus is provided.

  In a seventh aspect of the present invention, a photosensitive member is disposed on the peripheral surface of the transfer and fixing belt and upstream of the nip as a reference position, and a plurality of color toners are placed on the photosensitive member. The image forming apparatus according to claim 1, wherein a color image is formed by an overlapping method.

  The image forming apparatus according to any one of claims 1 to 7, wherein a toner having a Wadel practical sphericity φ of 0.8 or more is used as a developer. provide.

According to the first aspect of the present invention, the image can be thermally fused efficiently, and at the same time, the surface temperature of the toner can be lowered, and hot offset can be effectively prevented.
According to the second aspect of the present invention, heat transfer to the pressure member and heat transfer to the image forming unit are effectively prevented, so that deterioration of image quality due to heat can be effectively avoided.
According to the invention of claim 3, it is possible to give the degree of freedom of selection to the type and thickness of the recording medium, and it is possible to heat while ensuring a good contact state. When a particularly thick recording medium is used In addition, high-quality images could be formed.
According to the fourth aspect of the present invention, since the heating means has a roller shape, it is possible to reliably avoid the adverse effects caused by friction with the recording medium, and in particular, it is possible to prevent image quality deterioration due to paper dust or the like.
According to the invention of claim 5, since the heating means is composed of the plate-like body and the roller-like rotating member, the heating performance is high and the high-speed response can be improved.
According to the sixth aspect of the present invention, heat transfer to the image forming section can be reliably avoided structurally, and deterioration of image quality can be effectively prevented.
According to the seventh aspect of the present invention, the image forming apparatus can be reduced in size by adopting a configuration in which a color image is formed by superimposing a plurality of color toners on a photoconductor disposed on a transfer fixing belt. did it.
According to the eighth aspect of the present invention, the transferability is improved and the image quality can be improved by applying the toner having the practical value of the Wadel practical sphericity φ of 0.8 or more.

Hereinafter, specific embodiments of the present invention will be described, but the present invention is not limited to the following examples.
(First embodiment)
FIG. 1 shows a schematic configuration diagram of a tandem type color copying machine as an example of an image forming apparatus according to the present invention.
The color copying machine 1 has an image forming unit 1A located at the center of the main body, a paper feeding unit 1B located below the image forming unit 1A, and an image reading unit located above the image forming unit 1A. .
The image forming apparatus in this example is capable of forming an image at a linear velocity of 200 mm / s.
In the image forming unit 1A, a transfer fixing belt 2 as an intermediate transfer member having a transfer surface extending in the horizontal direction is disposed.
On the upper surface of the transfer and fixing belt 2, a configuration for forming an image having a color complementary to the color separation color is provided. Specifically, photoconductors 3Y, 3M, 3C, and 3B as image carriers capable of carrying an image of toners of complementary colors (yellow, magenta, cyan, and black) are formed on the transfer surface of the transfer fixing belt 2. Are juxtaposed along.

The transfer fixing belt 2 has a multilayer structure, and specifically, has a configuration of a polyimide resin (film thickness: 40 μm), rubber (film thickness: 60 μm), and fluororesin (film thickness: 6 μm) serving as a base material. What has is mentioned as a suitable example.
The rubber layer is necessary for reliably following the surface of the recording medium for image formation, and the surface fluororesin layer contributes to releasability from toner and paper powder. Is.

Each of the photoreceptors 3Y, 3M, 3C, and 3B has a drum structure that can rotate in the same direction. Around each of the photoreceptors, charging devices 4Y, 4M, 4C, and 4B that perform image forming processing in a rotating process, writing devices 5Y, 5M, 5C, and 5B as optical writing units, and color toners for each color are accommodated. Developing devices 6Y, 6M, 6C and 6B, primary transfer devices 7Y, 7M, 7C and 7B, and cleaning devices 8Y, 8M, 8C and 8B are arranged.
The alphabets attached to the respective symbols correspond to the colors of the toner as in the photosensitive member 3.

The transfer and fixing belt 2 is wound around a driving roller 11 and rollers 9 and 10 having a driven function, and has a configuration capable of moving in the same direction at a position facing the photoreceptors 3Y, 3M, 3C, and 3B. ing.
A cleaning device 13 for cleaning the surface of the transfer fixing belt 2 is provided at a position facing the driving roller 11.

Next, the actual image forming process will be described with the photoconductor identified.
First, the surface of the photoreceptor 3Y is uniformly charged by the charging device 4Y, and an electrostatic latent image is formed on the photoreceptor 3Y based on image information from the image reading unit.
The electrostatic latent image is visualized as a toner image by a developing device 6Y containing yellow toner, and the toner image is primary-transferred onto the transfer fixing belt 2 by a primary transfer device 7Y to which a predetermined bias is applied. Transcribed.
The other photoconductors 3M, 3C, and 3B are similarly formed with images, and the toner images of the respective colors are sequentially transferred and superimposed on the transfer and fixing belt 2.

  After the image transfer, the toner remaining on each photoconductor 3 is removed by each cleaning device 8. Thereafter, the potential of each photoconductor 3 is initialized by a static elimination lamp (not shown), and is prepared for the next image forming step.

A pressure member (hereinafter also referred to as a pressure roller) 24 is provided at a position facing the roller 9.
The pressure roller 24 has a function of forming a nip N (hereinafter also referred to as a nip or a transfer nip) with the transfer fixing belt 2.
The pressure roller 24 has a metal pipe-like structure made of, for example, aluminum, and the surface is coated with a release layer.

A heating means having a function of heating the surface of the recording medium (paper) P, for example, a roller heater, is provided on the pressure roller 24 side and immediately before the transfer and fixing to the recording medium (paper) P. It has been.
A contact surface of the heating unit 101 with the recording medium (paper) P may be provided with a low friction material layer made of fluororesin or the like for smooth sliding with the recording medium. The thickness of the low friction material layer is preferably about several μm. The heating means 101 is controlled at about 140 to 200 ° C. to heat the surface of the recording medium (paper).
In the process of heating the paper, a measurement was performed with a thermocouple having a diameter of 20 μm fixed to the back side of the paper. After the contact with the heating means 101, the temperature change on the back side of the paper was within 5 ° C. within 0 to 20 ms. It was confirmed. The paper used was generally used copy paper (Ricoh copy paper 6200).
Further, as the contact time between the transfer fixing belt 2 and the pressure roller 24 is shortened, efficient transfer fixing can be performed without taking heat away from the pressure roller.

  The paper feed unit 1B includes a paper feed tray 14 that stacks and stores paper P as a recording medium, and a paper feed roller 16 that feeds paper P in the paper feed tray 14 one by one in order from the top. A pair of transport rollers 17 for transporting the fed paper P, and after the paper P is temporarily stopped and the oblique shift is corrected, the leading edge of the image on the transfer fixing belt 2 coincides with a predetermined position in the transport direction. And a registration roller pair 18 fed toward the nip N at timing.

  By the way, the toner image T (hereinafter also simply referred to as “toner”) primarily transferred from the above-described photoreceptors 3Y, 3M, 3C, and 3B onto the transfer fixing belt 2 is biased by a predetermined bias applying means (on the driven roller 11). The image is transferred to the transfer fixing belt 2 by electrostatic force by an applied bias (including superposition of AC, pulse, etc.).

In the image forming apparatus shown in FIG. 1, a leveling roller 210 for equalizing the temperature of the transfer and fixing belt 2 between the transfer portion for the transfer and fixing belt 2 and the transfer portion for the most upstream photoconductor 3B. Is provided.
The leveling roller 210 is made of a material such as a heat pipe or graphite having a high thermal conductivity, and rotates while being in contact with the transfer fixing belt 2.
The leveling roller 210 may have a function of a heat pipe applied to the driving roller 11 and may be used in combination.

The toner image T transferred to the transfer fixing belt 2 is heated by the amount of heat from the paper until it is fixed to the recording medium (paper) P at the nip N.
In a conventionally known color image forming apparatus, it is necessary to apply a heat amount 1.5 times that of a black and white image forming apparatus in consideration of a temperature drop due to a recording medium (paper). For this reason, the recording medium (paper) is heated more than necessary, and the adhesion to the toner tends to be too high.
In the present embodiment, since the temperature can be controlled by the heating means 101 and the leveling roller 210, it is possible to set a temperature suitable for forming an image having sufficient gloss.
That is, in consideration of the temperature drop due to the recording medium (paper), it is possible to avoid heating more than necessary, and not only can prevent the recording medium (paper) from overheating but also the temperature of the transfer fixing belt 2. (Fixing set temperature) can be kept low.

According to the image forming apparatus of this embodiment, since it is configured to be able to fix at a relatively low temperature, the so-called warm-up time during image formation can be shortened and energy saving is also excellent.
Further, since heat transfer to the image forming unit is also avoided, deterioration of the parts due to heat can be prevented, and durability of the apparatus can be improved.

  As described above, the image forming apparatus of the present invention is positioned as a “transfer fixing apparatus” with respect to a conventional fixing apparatus that simply heats and presses a sheet holding an unfixed toner image.

Next, a second embodiment of the image forming apparatus of the present invention will be described with reference to FIG.
The image forming apparatus of FIG. 2 is an example of a so-called IOI type color copying machine that performs color superposition on a single photoconductor.
In the image forming apparatus of FIG. 2, the same reference numerals are given to the same portions as those of the image forming apparatus of FIG.

In the color superimposing method on the photoconductor, as the image forming operation on the photoconductor, the steps from charging, exposure (writing), and development to one color toner are performed, and a series of steps are also performed for a multicolor toner. Do it on the body.
As shown in FIG. 1, an image forming process is performed on one photoconductor for each color and a photoconductor for each color is provided in a quadruple tandem system. Compared with the quadruple tandem system, it is excellent in high-speed compatibility, and space saving and cost reduction of the entire apparatus can be achieved.

Next, the image forming apparatus of the present invention will be described with specific examples.
[Example 1]
This example is an example in which a minute gap is formed with the transfer fixing roller 2 using a roller-shaped rotating body as a pressure member.
1, 2, 4, and 5 can be applied.
FIG. 4 is a schematic configuration diagram of another example of the image forming apparatus according to the present invention, in which the heating unit includes a plate-like body 103 and a roller-like rotating member 101. Details will be described later.
When the heating means is constituted only by the roller-like rotating member 101, it may be simply expressed as the heating means 101.

FIG. 5 is an enlarged view of the vicinity of the pressure member (pressure roller) 24 of the image forming apparatus common to FIGS.
In these, stoppers are provided so as to form a constant minute gap while pressing the compression springs 102 on both ends of the shaft of the roller-like rotating member 101 so as to be pressed against the pressure roller 24 side.
That is, as shown in FIG. 5, a minute gap A is formed, and on the other hand, the roller-shaped rotating member 101 is movable in the direction of expanding the gap A by the function of the compression spring 102. This makes it possible to handle all types of paper.
The gap A is preferably about 50 μm. This is smaller than the minimum thickness of the recording medium (paper) used for printing. For example, 45k paper assumed as the thinnest general-purpose paper has a thickness of about 70 μm.
In addition, Ricoh's copy paper, type 6200, generally called plain paper, has a thickness of about 90 μm. The thickness of recommended paper 70W for full color made by Ricoh is about 95 μm. Furthermore, the thickness of the 220 k paper assumed as the thickest paper is about 220 μm.
Furthermore, there is a printing paper with a thickness of about 300 μm that is assumed as a special application.
By controlling the spring pressure so that such a thick sheet can also pass through the gap A, it becomes possible to travel from a thin sheet to a thick sheet by always contacting the heating means.

[Example 2]
In this example, it is assumed that the roller-like rotating member 101 has a heating function.
As shown in the schematic configuration diagram of the main part of FIG. 5, the roller-shaped rotating member 101 having a heating function includes a metal roller shaft 101a, a metal roller outer periphery 101b, and a semiconductor 101c as an inside.
As a material of the semiconductor 101c, a known material can be used as appropriate, and the semiconductor 101c functions as a heater.
Specifically, a material such as a thermistor or a magnetic shunt alloy made of a barium titanate semiconductor magnetic element can be applied.

Example 3
In this example, the heating means is composed of a plate-like body and a roller-like rotating member, the plate-like body has a heat source, and heat is transferred from the plate-like body to the roller-like rotating member. To do.
A plate-like body 103 shown in FIG. 4 is a heating element, and is configured to conduct heat by being brought into contact with the roller-like rotating member 101.
In the configuration in which only the roller-like rotating member 101 is provided with a heating function as in the above-described example, a desired heating capacity may not be obtained depending on the size of the roller. A sufficient heating capacity can be secured by providing a heat source in the shape body. Thereby, it can be set as the structure especially adapted to the apparatus which requires many heating capacities, such as a high-speed machine.

  In addition, a plate-shaped heating member can also be used as the recording medium conveying guide member 111 that is clearly shown in FIGS.

Next, image formation was actually performed using the image forming apparatus described with reference to FIGS.
<Experiment 1>
FIG. 3A shows a schematic configuration diagram of the heating means (heater). FIG. 3B shows an enlarged view of the heating means when viewed from the paper supply side.
As the heating means (heater) 21, one having 10 positive characteristic thermistors 212 made of a barium titanate-based semiconductor ceramic body in parallel was applied.
The weight of the heating means (heater) 21 is about 25 g, and a SUS plate having a thickness of 0.2 mm was used for the electrode 213 that also functions as a heat transfer plate.
AC100V was applied between these two electrodes to heat them.
The semiconductor has a Curie point of 200 ° C., and when this temperature is exceeded, the resistance between the electrodes rapidly increases. For example, the current was 1/2 at 210 ° C. and 1/4 at 220 ° C.
When the temperature was raised for 6 seconds with a power input of 1200 W, the temperature reached 190 to 200 ° C., and it was safe without exceeding 210 ° C.
Moreover, since it has the structure connected in parallel, according to the said power-on conditions, each thermistor is controlled to 200 degreeC, and the temperature nonuniformity in the paper passing width direction can also be suppressed to about 10 degreeC or less.
Further, when the contact time of the heater with the recording medium was set to 10 to 20 ms and the pressure was applied by the nip after 2 to 5 ms, sufficient fixability and color developability could be obtained.
For the toner, Xerox EA-HG toner and Ricoh PxP toner were used.
<Experiment 2>
In this example, a magnetic shunt alloy was used as the heating means (heater) 21 in FIG. This is an alloy of Ni and iron, and those containing about 40% of Ni are known to have a drastic decrease in permeability near the Curie point of 200 ° C. This was formed into a leaf spring shape having a thickness of 0.3 mm, and induction heating was performed with a high frequency of 20 kHz by an induction coil (not shown).
When the temperature was raised in 3 seconds with a power input of 1200 W, the temperature became 190 ° C. to 200 ° C., and it was safe without exceeding 210 ° C.
Regarding temperature uniformity, each part was self-controlled at 200 ° C., and thus temperature unevenness in the paper passing width direction could be suppressed to 10 ° C. or less.
By setting the contact time of the heater to the recording medium to 10 to 20 ms and setting the pressure to be applied by the nip after 2 to 5 ms, it was possible to obtain sufficient fixability and color development.
As the toner, Xerox EA-HG toner and Ricoh PxP toner were applied.

Example 4
In this embodiment, as shown in FIG. 5, the gap B between the roller-like rotating member 101 constituting the heating means and the transfer fixing belt 2 is such that the roller-like rotating member 101 constituting the heating means and the pressure member 24. A configuration that is larger than the gap A will be described.
In this example, toner is transferred to the transfer and fixing belt 2 by an image forming process. The toner particle size is 5 to 8 μm, and assuming that the four colors for full color formation are superimposed, the thickness of the toner layer is theoretically 3 to 4 times the toner particle size. It becomes. It is assumed that the maximum is 40 μm. When the display color is increased, the thickness of the toner layer further increases.
Therefore, the gap B between the roller-shaped rotating member 101 and the transfer fixing belt 2 must be larger than the assumed maximum thickness.
Further, the toner on the transfer and fixing belt 2 may be unstable in reproducing the image quality if the transfer and fixing conditions change due to the influence of heat.
Further, considering that the fine positional relationship varies depending on the running state of the transfer and fixing belt 2, the gap B in FIG. 5 needs to be set larger than the assumed maximum thickness of the toner layer.
From this viewpoint, the gap B is set larger than the gap A. For example, the gap B is desirably set to 2 mm or more.

Example 5
In this embodiment, a case will be described in which image formation is performed by a method in which toners of a plurality of colors are superimposed on a single photoconductor.
As shown in FIG. 2, in the image forming apparatus of the present invention, since the recording medium is heated by the heating unit 101, the adverse effect of heat on the image forming unit such as a photoconductor can be effectively prevented. It has a configuration.
By taking advantage of such structural features, a further advantage can be obtained in the so-called upper color superposition method in which a single photoconductor as shown in FIG. 2 is applied.
In this method, as an image forming operation on the photosensitive member, steps from charging, exposure (writing), and development are performed on one photosensitive member as a series of steps for multicolor toner.
Compared with the quadruple tandem system shown in FIG. 1, it has excellent high-speed compatibility, and further has the advantage that the entire apparatus can be reduced in size and space.

In the configuration of each of the embodiments described above, the pressure member constituting the nip in the transfer fixing unit has been described as a roller, but the present invention is not limited to this example.
Other examples include, for example, a belt-shaped one.
Further, the conveyance direction of the recording medium (paper) is not limited to the arrow direction shown in the drawing.
For example, in the case where the image forming and transfer body rotation direction and the image forming position are located below the transfer body, the conveyance is in the direction opposite to the arrow direction shown in the figure.

Next, an embodiment of a spherical toner will be described.
It is known that toner transferability (transfer efficiency, fidelity) affects the image quality of a target image, and this toner transferability is related to the shape of the toner.
As a result of studies for optimizing the toner shape in order to achieve high image quality, it was confirmed that toner having a Wadel practical sphericity φ of 0.8 or more has good transferability.
The Wardel practical sphericity φ is expressed by the following equation.
φ = (diameter of circle equal to particle projection area) / (diameter of circle circumscribing particle projection image)
Specifically, it can be easily calculated by taking an appropriate amount of toner on a slide glass, enlarging (500 times) with a microscope, and measuring 100 arbitrary toners.
By applying a toner that satisfies such conditions, the secondary transfer efficiency can be increased and high image quality can be achieved.

Any conventionally known material can be used as the material constituting the toner.
As the binder resin, for example, styrene such as polyester, polystyrene, poly-p-chlorostyrene, polyvinyltoluene, and the like, a homopolymer of a substituted product thereof, a styrene-p-chlorostyrene copolymer, a styrene-propylene copolymer, Styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer Polymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-α-chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene- Vinyl methyl ether copolymer, styrene Vinyl ethyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-acrylonitrile-indene copolymer, styrene-maleic acid copolymer, styrene-maleic Any styrenic copolymer such as an acid ester copolymer can be applied.
Moreover, you may mix and use the following resin.
That is, for example, polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyurethane, polyamide, epoxy resin, polyvinyl butyral, polyacrylic acid resin, rosin, modified rosin, terpene resin, phenol resin, Aliphatic or alicyclic hydrocarbon resins, aromatic petroleum resins, chlorinated paraffins and paraffin waxes may be mentioned. When a polyester resin is contained, it is suitable for obtaining sufficient fixability.
In particular, the crystalline polyester resin is suitable because it is sufficiently softened and melted at the time of paper contact and can form an image with high color reproducibility as well as fixing strength.
The polyester resin is obtained by condensation polymerization of alcohol and carboxylic acid, and the alcohol used is polyethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butane. Diols such as diol, neopentyl glycol, 1,4-butenediol, 1,4-bis (hydroxymethyl) cyclohexane, bisphenol A, hydrogenated bisphenol A, polyexethylenated bisphenol A, polyoxypropylenated bisphenol A, etc. And a divalent alcohol simple substance obtained by substituting these with a saturated or unsaturated hydrocarbon group having 3 to 22 carbon atoms, and other divalent alcohol simple substance.
Examples of the carboxylic acid used to obtain the polyester resin include maleic acid, fumaric acid, mesaconic acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, Adipic acid, sebacic acid, malonic acid, divalent organic acid monomers in which these are substituted with a saturated or unsaturated hydrocarbon group having 3 to 22 carbon atoms, acid anhydrides thereof, lower alkyl esters and linolenic acid Dimers and other divalent organic acid monomers can be mentioned.

In order to obtain a polyester resin which is a binder resin, it is also preferable to use not only a polymer based on the above bifunctional monomer but also a polymer containing a component based on a trifunctional or higher functional monomer. It is.
Examples of the polyhydric alcohol monomer having three or more valences that are such polyfunctional monomers include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sarbitane, pentaesitol, dipenta. Esitol, tripentaerythritol, sucrose, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol , Trimethylolethane, trimethylolpropane, 1.3.5-trihydroxymethylbenzene, and others.
Examples of the trivalent or higher polyvalent carboxylic acid monomer include 1,2,4-benzenetricarboxylic acid, 1,2,5-benzenetricarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, 5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2 -Methylenecarboxypropane, tetra (methylenecarboxyl) methane, 1,2,7,8-octanetetracarboxylic acid, embol trimer acid, acid anhydrides thereof, and the like.

The toner preferably contains a release agent for the purpose of improving the releasability of the toner on the surface of the transfer fixing member during transfer fixing.
As the mold release agent, conventionally known ones can be applied. For example, de-free fatty acid type carnauba wax, montan wax, oxidized rice wax, and ester wax can be used alone or in combination.
The carnauba wax is preferably a microcrystalline one, having an acid value of 5 or less and a particle size of 1 μm or less when dispersed in a toner binder.
The montan wax generally refers to a montan wax refined from minerals, and like a carnauba wax, it is microcrystalline and preferably has an acid value of 5 to 14.
The oxidized rice wax is obtained by air-oxidizing rice bran wax, and the acid value is preferably 10-30.
When the acid value of each wax is less than the respective range, the low temperature fixing temperature rises and the low temperature fixing becomes insufficient. On the contrary, when the acid value exceeds each range, the cold offset temperature rises and the low-temperature fixing becomes insufficient.
The added amount of the wax is 1 to 15 parts by weight, preferably 3 to 10 parts by weight with respect to 100 parts by weight of the binder resin. If it is less than 1 part by weight, the releasing effect is thin and the desired effect is difficult to obtain. In addition, when the amount exceeds 15 parts by weight, it has been confirmed that problems such as significant spent on the carrier occur.

As other external additives, for the purpose of improving the fluidity of the toner, silica, titanium oxide, alumina, and the like, and if necessary, fatty acid metal salts and polyvinylidene fluoride may be added.
In particular, since transfer fixing can sufficiently heat the toner, even if a relatively large amount of an additive such as a submicron large particle size silica is used, the fixing property and fixing temperature are not affected. It is possible to prescribe external additives in consideration of transferability.

1 is a schematic configuration diagram of an image forming apparatus of the present invention. FIG. 3 is a schematic configuration diagram of another example of the image forming apparatus of the present invention. (A) The schematic block diagram of the heater which comprises a heating means is shown. (B) The enlarged block diagram of a heater is shown. FIG. 3 is a schematic configuration diagram of another example of the image forming apparatus of the present invention. 1 is a schematic configuration diagram of a main part of an image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Color copier 2 Transfer fixing belt 3Y, 3M, 3C, 3B Photoconductor 4Y, 4M, 4C, 4B Charging device 5Y, 5M, 5C, 5B Writing device 6Y, 6M, 6C, 6B Developing device 7Y, 7M, 7C, 7B Primary transfer device 8Y, 8M, 8C, 8B Cleaning device 9, 10 Roller 11 Drive roller 13 Cleaning device 14 Paper feed tray 16 Paper feed roller 17 Transport roller pair 18 Registration roller pair 21 Heating means 24 Pressure member (Pressure) roller)
101 roller-like rotating member 101a metal roller shaft 101b metal roller outer periphery 101c semiconductor 102 compression spring 103 plate-like body 212 positive temperature coefficient thermistor 213 electrode

Claims (8)

A transfer fixing belt composed of an endless belt on which image transfer is performed;
The transfer fixing belt and a pressure member that forms a nip,
An image is transferred onto a recording medium passing through the nip;
An image forming apparatus comprising: a heating unit that forms a minute gap with the pressure member and is in contact with the surface of the recording medium on the upstream side with respect to the nip as a reference position. .   The image forming apparatus according to claim 1, wherein a minute gap between the pressure member and the heating unit is equal to or less than a minimum thickness of the recording medium.   The image forming apparatus according to claim 1, wherein a distance of a minute gap between the pressure member and the heating unit is variable.   The image forming apparatus according to claim 1, wherein the heating unit is a roller-like rotating member. The heating means is composed of a plate-like body and a roller-like rotating member,
4. The image forming apparatus according to claim 1, wherein the plate-like body has a heat source, and heat is transferred from the plate-like body to the roller-like rotating member. 5. .   The gap between the roller-like rotating member constituting the heating unit and the transfer fixing belt is larger than the gap between the roller-like rotating member constituting the heating unit and the pressure member. Item 6. The image forming apparatus according to Item 4 or 5. A photoconductor is disposed on the circumferential surface of the transfer fixing belt and upstream of the nip as a reference position,
7. The image forming apparatus according to claim 1, wherein a color image is formed by a method of superimposing a plurality of colors of toner on the photoconductor.   8. The image forming apparatus according to claim 1, wherein toner having a Wadel practical sphericity φ of 0.8 or more is used as a developer. 9.

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