JP5369788B2 - Transfer fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transfer fixing device which has low energy consumption and is excellent in fixability and capable of forming a high quality image by stably heating a recording medium just before a transfer fixing step by a heating means, for instance, even when the recording medium different in thickness is passed through or even when the surrounding environmental temperature is changed; and to provide an image forming apparatus. <P>SOLUTION: The transfer fixing device includes: the heating member 87 which heats the transfer fixing surface of the recording medium P conveyed toward a nip portion formed by a transfer fixing member 27 and a pressure member 68 and guides the recording medium P conveyed toward the nip portion; an biasing member 91 which biases the recording medium P guided by the heating member 87 toward the heating member 87; and variable means 92 to 94 which vary an biasing force to the recording medium P biased toward the heating member 87 by the biasing member 91. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a transfer fixing device for transferring and fixing a toner image on a recording medium, and an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile, or a composite machine including the same. , About.

2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, a technique using a transfer fixing device that simultaneously performs a transfer process and a fixing process is known (see, for example, Patent Document 1 to Patent Document 3).
An image forming apparatus provided with such a transfer fixing device is less likely to cause a decrease in image quality even when a recording medium having a rough surface is used, compared to an image forming apparatus that performs a transfer process and a fixing process separately. There are advantages.

Specifically, in an image forming apparatus that performs a transfer process and a fixing process separately, when a recording medium with a rough surface is used, an intermediate transfer body such as an intermediate transfer belt cannot follow the surface characteristics of the recording medium. A small gap is formed between the recording medium and the recording medium. For this reason, abnormal discharge occurs in the portion where the minute gap is formed, and the image carried on the intermediate transfer member is not normally transferred onto the recording medium, and the image becomes rough as a whole.
On the other hand, in an image forming apparatus provided with a transfer and fixing device, heat is applied to a toner image simultaneously with transfer, so that the toner is softened and melted to form a block-like lump having viscoelasticity. Therefore, even if a minute gap is formed between the fixing member and the recording medium using a recording medium having a rough surface, the image is transferred as a lump to that portion. Therefore, the image is good and has a high image quality without being distorted.

  Further, the image forming apparatus provided with the transfer fixing device has unfixed toner on the recording medium conveyed to the nip portion (the contact position between the transfer fixing member and the pressure member) where the transfer fixing process is performed. Since the image is not carried, restrictions on the conveyance path of the recording medium are reduced as compared with an image forming apparatus that performs the transfer process and the fixing process separately. That is, an image forming apparatus that performs a transfer process and a fixing process separately is not fixed on a recording medium conveyed to a nip portion (a contact position between a fixing member and a pressure member) in which the fixing process is performed. Since the toner image is carried, restrictions are imposed on the conveyance path from the transfer unit to the fixing unit so as not to contact the unfixed toner image. Therefore, the image forming apparatus including the transfer fixing device has a high degree of design freedom with respect to the recording medium conveyance path, and can improve the conveyance of the recording medium.

In the conventional transfer fixing apparatus described above, the transfer fixing member carrying the toner image is heated to heat and melt the toner image, so that the transfer fixing belt (transfer fixing member) becomes thicker in order to extend the life. When the circumference of the transfer / fixing belt becomes longer due to installation in a large tandem type image forming apparatus, the thermal efficiency of the transfer / fixing belt has been lowered. For this reason, the energy consumption in the transfer fixing apparatus has been increased.
Furthermore, in addition to the above-described heating process of the transfer fixing belt, the conventional transfer fixing apparatus includes a cooling process for cooling the transfer fixing belt after the transfer fixing process in order to reduce thermal damage of the image forming unit. There were many cases. Since such a heating / cooling cycle is repeated, energy consumption in the transfer and fixing device is large.

The inventor of the present application has conducted research to solve such problems, and as a result, the heat of the transfer fixing belt (transfer fixing member) is minimized, and the amount of heat necessary for heating and melting the toner is reduced to the nip portion. We have learned a supplementary measure by efficiently heating the recording medium immediately before being transported to the printer. In order to realize such a measure, it is conceivable to provide a heating member that heats the transfer fixing surface of the recording medium on the upstream side of the nip portion in the conveyance direction of the recording medium and in the vicinity of the nip portion. .
However, in this case, even when a recording medium having a different thickness (paper thickness) is passed or the ambient environmental temperature changes, the heating medium stably heats the recording medium immediately before the transfer fixing process. It becomes important.

  The present invention has been made to solve the above-described problems. Even when a recording medium having a low energy consumption and a different thickness is passed or the ambient environmental temperature changes, the present invention can be used. It is an object of the present invention to provide a transfer fixing device and an image forming apparatus in which a recording medium immediately before the transfer and fixing step is stably heated by a heating member, and a high-quality image with good fixability can be formed.

The transfer fixing device according to the first aspect of the present invention is a transfer fixing device that transfers and fixes a toner image onto a transfer fixing surface of a recording medium, and carries the toner image and travels in a predetermined direction. A transfer fixing member; a pressure member that forms a nip portion that is pressed against the transfer fixing member to convey a recording medium; and the transfer fixing member at a position upstream of the nip portion in the running direction of the transfer fixing member. A heater that heats the fixing member and heats the surface temperature of the toner image immediately before the nip portion carried on the fixing member at a temperature that is equal to or lower than a toner outflow start temperature, and the recording medium that is conveyed toward the nip portion. A heating member that heats the transfer fixing surface and guides the recording medium conveyed toward the nip portion, and an urging member that urges the recording medium guided by the heating member toward the heating member , And a varying means for varying a biasing force to the recording medium is urged toward the heating member by the biasing member, the temperature of the transfer-fixing surface of the nip portion of the recording medium is heated by the heating member Is higher than the surface temperature at the nip portion of the transfer and fixing member heated by the heater.

  According to a second aspect of the present invention, in the transfer fixing device according to the first aspect, the variable means changes a relative position of the urging member with respect to the heating member.

  According to a third aspect of the present invention, there is provided the transfer fixing device according to the first or second aspect, wherein the variable means has a thick recording medium guided by the heating member. The biasing force is controlled to be larger than when the recording medium is thin.

  According to a fourth aspect of the present invention, there is provided the transfer fixing device according to any one of the first to third aspects, wherein the variable means is configured to change the heating member when the temperature of the heating member is low. The urging force is controlled to be greater than when the temperature of is high.

  According to a fifth aspect of the present invention, in the transfer fixing device according to any one of the first to fourth aspects, the ambient temperature is high when the ambient temperature is low. The urging force is controlled to be larger than the time.

  According to a sixth aspect of the present invention, in the transfer fixing device according to any one of the first to fifth aspects, the variable means is controlled so that the biasing force increases with time. Is.

  A transfer fixing device according to a seventh aspect of the present invention is the transfer fixing device according to any one of the first to sixth aspects, further comprising a second variable means for varying the temperature of the heating member. It is.

  According to an eighth aspect of the present invention, in the transfer fixing device according to any of the first to seventh aspects, the recording medium does not pass between the heating member and the biasing member. The urging member is relatively separated from the heating member.

  According to a ninth aspect of the present invention, in the transfer fixing device according to the first aspect, the recording medium stops transporting between the heating member and the biasing member. Sometimes, the heating member is separated in a direction away from the recording medium.

  A transfer fixing device according to a tenth aspect of the present invention is the transfer fixing device according to any one of the first to ninth aspects, wherein the urging member is a heat-resistant brush roller. .

  The transfer fixing device according to an eleventh aspect of the present invention is the transfer fixing device according to any one of the first to tenth aspects, wherein the heating member is a plate-like member formed of copper or aluminum. It is.

  An image forming apparatus according to a twelfth aspect of the present invention includes the transfer fixing apparatus according to any one of the first to eleventh aspects.

  The present invention relates to a heating member that heats a transfer fixing surface while guiding a recording medium conveyed to a nip portion between a transfer fixing member and a pressure member, and an urging member that urges the recording medium toward the heating member. And the urging force by the urging member can be varied. As a result, even when a recording medium with low energy consumption and different thickness is passed or the ambient environmental temperature changes, the recording medium immediately before the transfer fixing process is stably heated by the heating member. Thus, it is possible to provide a transfer fixing device and an image forming apparatus in which a high-quality image with good fixability is formed.

1 is an overall configuration diagram illustrating an image forming apparatus according to Embodiment 1 of the present invention. It is an enlarged view showing a part of the transfer fixing device. It is an enlarged view showing a contact mechanism of the brush-like roller in the transfer fixing device. It is an enlarged view which shows the state which the heating plate left | separated. It is a graph which shows the relationship between the idling distance from a heating plate to a nip part, and the surface temperature of a recording medium. It is a graph which shows an experimental result. FIG. 6 is an enlarged view showing the vicinity of a transfer fixing device according to Embodiment 2 of the present invention. It is a block diagram which shows a part of image forming apparatus in Embodiment 3 of this invention.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

Embodiment 1 FIG.
The first embodiment of the present invention will be described in detail with reference to FIGS.
First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
In FIG. 1, 1 is an apparatus main body of a color copying machine as an image forming apparatus, 2 is a writing section (exposure section) that emits laser light based on input image information, and 20Y, 20M, 20C, and 20BK are colors (yellow, magenta). , Cyan, black), 21 is a photosensitive drum (image carrier) accommodated in each of the process cartridges 20Y, 20M, 20C, and 20BK, 22 is a charging unit that charges the photosensitive drum 21, 23Y, 23M, 23C, and 23BK are developing devices that develop the electrostatic latent image formed on the photosensitive drum 21, and 24 is a transfer bias that transfers the toner image formed on the photosensitive drum 21 to the transfer fixing belt 27. A roller 25 indicates a cleaning device that collects untransferred toner on the photosensitive drum 21.

  Reference numeral 27 denotes a transfer fixing belt as a transfer fixing member onto which a plurality of color toner images are transferred, 29 denotes a cleaning device (belt cleaning device) for cleaning the transfer fixing belt 27 after the transfer fixing step, 32Y, 32M, 32C and 32BK are toner replenishing units for replenishing each color toner to the developing devices 23Y, 23M, 23C and 23BK, 51 is a document conveying unit for conveying the document D to the document reading unit 55, and 55 is for reading image information of the document D. An original reading unit, 61 is a paper feeding unit for storing a recording medium P such as transfer paper, 66 is a transfer fixing device for transferring and fixing a toner image on the recording medium P, and 68 is pressed against the transfer fixing belt 27 to nip. A pressure roller as a pressure member for forming the portion; 70 a heater for heating the transfer fixing belt 27; 85 a uniform temperature distribution in the width direction of the transfer fixing belt 27; A leveling roller as a cooling means for cooling the transfer fixing belt 27, a heating plate 87 as a heating member for heating the recording medium P immediately before the transfer fixing process while guiding it to the nip portion, and 91 a heating plate for the recording medium P A brush-like roller as an urging member that urges toward 87 is shown.

Here, the transfer fixing device 66 includes a transfer fixing belt 27 as a transfer fixing member, heating devices 87 and 88, a pressure roller 68 as a pressure member, a brush roller 91 as an urging member, a heater 70, a leveling member. The roller 85 is configured.
The process cartridges 20Y, 20M, 20C, and 20BK are obtained by integrating the photosensitive drum 21, the charging unit 22, and the cleaning device 25, respectively. Then, image formation of each color (yellow, magenta, cyan, black) is performed on the photosensitive drum 21 in each of the process cartridges 20Y, 20M, 20C, and 20BK.

Hereinafter, an operation during normal color image formation in the image forming apparatus will be described.
First, the document D is transported from the document table in the direction of the arrow in the drawing by the transport roller of the document transport unit 51 and placed on the contact glass 53 of the document reading unit 55. Then, the document reading unit 55 optically reads the image information of the document D placed on the contact glass 53.

  Specifically, the document reading unit 55 scans the image of the document D on the contact glass 53 while irradiating light emitted from the illumination lamp. Then, the light reflected by the document D is imaged on the color sensor via the mirror group and the lens. The color image information of the document D is read for each RGB (red, green, blue) color separation light by the color sensor, and then converted into an electrical image signal. Further, an image processing unit (not shown) performs color conversion processing, color correction processing, spatial frequency correction processing, and the like on the basis of RGB color separation image signals, so that yellow, magenta, cyan, and black are processed. Get color image information.

  Then, the image information of each color of yellow, magenta, cyan, and black is transmitted to the writing unit 2. Then, laser light (exposure light) based on the image information of each color is emitted from the writing unit 2 toward the photosensitive drums 21 of the corresponding process cartridges 20Y, 20M, 20C, and 20BK.

On the other hand, the four photosensitive drums 21 rotate in the clockwise direction in FIG. First, the surface of the photosensitive drum 21 is uniformly charged at a position facing the charging unit 22 (a charging process). Thus, a charged potential is formed on the photosensitive drum 21. Thereafter, the surface of the charged photosensitive drum 21 reaches the irradiation position of each laser beam.
In the writing unit 2, laser light corresponding to the image signal is emitted from the light source corresponding to each color. The laser light is incident on the polygon mirror 3 and reflected, and then passes through the lenses 4 and 5. The laser light after passing through the lenses 4 and 5 passes through different optical paths for each of the yellow, magenta, cyan, and black color components (this is an exposure process).

  The laser beam corresponding to the yellow component is reflected by the mirrors 6 to 8 and then irradiated onto the surface of the photosensitive drum 21 of the first process cartridge 20Y from the left side of the drawing. At this time, the yellow component laser light is scanned in the rotation axis direction (main scanning direction) of the photosensitive drum 21 by the polygon mirror 3 that rotates at high speed. Thus, an electrostatic latent image corresponding to the yellow component is formed on the photosensitive drum 21 charged by the charging unit 22.

  Similarly, the laser beam corresponding to the magenta component is reflected by the mirrors 9 to 11 and then irradiated to the surface of the photosensitive drum 21 of the second process cartridge 20M from the left side of the paper, thereby causing an electrostatic latent image corresponding to the magenta component. An image is formed. The cyan component laser light is reflected by the mirrors 12 to 14 and then irradiated onto the surface of the photosensitive drum 212 of the third process cartridge 20C from the left side of the drawing to form a cyan component electrostatic latent image. The black component laser light is reflected by the mirror 15 and then irradiated on the surface of the photosensitive drum 21 of the fourth process cartridge 20BK from the left side of the paper, thereby forming an electrostatic latent image of black component.

Thereafter, the surface of the photosensitive drum 21 on which the electrostatic latent images of the respective colors are formed reaches positions facing the developing devices 23Y, 23M, 23C, and 23BK, respectively. Then, the respective color toners are supplied from the developing devices 23Y, 23M, 23C, and 23BK onto the photosensitive drum 21, and the latent image on the photosensitive drum 21 is developed (this is a developing step).
Thereafter, the surface of the photosensitive drum 21 after the development process reaches a position facing the transfer and fixing belt 27 stretched and supported by the plurality of roller members 28A to 28C and 85, respectively. Here, a transfer bias roller 24 is installed at each facing position so as to contact the inner peripheral surface of the transfer fixing belt 27. Then, at the position of the transfer bias roller 24, the images (toner images) of the respective colors formed on the photosensitive drum 21 are sequentially superimposed and transferred onto the transfer fixing belt 27 (transfer fixing member) (first transfer). Process.)

Then, the surface of the photosensitive drum 21 after the first transfer process reaches a position facing the cleaning device 25. Then, the untransferred toner remaining on the photosensitive drum 21 is collected by the cleaning device 25 (this is a cleaning process).
Thereafter, the surface of the photosensitive drum 21 passes through a static elimination unit (not shown), and a series of image forming processes on the photosensitive drum 21 is completed.

On the other hand, the surface of the transfer and fixing belt 27 on which the toner images of the respective colors on the photosensitive drum 21 are transferred and carried are run in the direction of the arrow in the figure and contacted with the pressure roller 68 (pressure member). The contact position (the nip part) is reached. Here, the transfer fixing device 66 according to the first exemplary embodiment is provided with a heater 70 that heats the transfer fixing belt 27 (or the toner image carried on the transfer fixing belt 27) on the upstream side of the nip portion. However, the heating amount by the heater 70 is set to be considerably smaller than the conventional one.
The toner image carried on the transfer fixing belt 27 is transferred and fixed to the transfer fixing surface (front surface) of the recording medium P at the nip portion between the transfer fixing belt 27 and the pressure roller 68 ( Transfer / fixing process). Specifically, the transfer fixing surface of the recording medium P is heated by a heating plate 87 (heating member) immediately before the nip portion, and the transfer fixing surface is heated preliminarily by the heater 70 at the nip portion. The toner image is heated and melted by the heat of the fixing belt 27, and the toner image is fixed to the transfer and fixing surface by the pressure of the nip portion. The configuration and operation of the transfer fixing device 66 will be described in more detail later with reference to FIGS.
Thereafter, the surface of the transfer fixing belt 27 reaches the position of the belt cleaning unit 29. Then, deposits such as residual toner on the transfer fixing belt 27 are collected by the belt cleaning device 29, and a series of transfer fixing processes on the transfer fixing belt 27 is completed.

  A toner detection sensor or a transfer fixing belt is positioned at a position facing the transfer fixing belt 27 and downstream of the yellow photosensitive drum 21 at the most downstream position and upstream of the nip portion. It is also possible to install a cleaning mechanism configured so as to be able to contact with and separate from 27. Then, a pattern image for image adjustment formed on the transfer fixing belt 27 through the image forming process described above is detected by a toner detection sensor, and density correction or color misregistration correction of each color is performed based on the detection result. Can do. In this case, the pattern image for image adjustment formed on the transfer fixing belt 27 is removed by the cleaning mechanism before reaching the nip portion with the pressure roller 68.

Here, the recording medium P transported to the nip portion of the transfer fixing device 66 is transported from the paper feeding section 61 via the transport guide 63, the registration roller 64, the heating plate 87, and the like.
Specifically, the transfer paper P fed by the paper feed roller 62 from the paper feed unit 61 that stores the recording medium P passes through the conveyance guide 63 and is guided to the registration roller 64. The recording medium P that has reached the registration roller 64 is conveyed toward the nip portion between the transfer fixing belt 27 and the pressure roller 68 in synchronization with the toner image on the transfer fixing belt 27. At this time, the recording medium P conveyed toward the nip portion is guided to a heating plate 87 (see FIG. 2) as a heating member and is urged toward the heating plate 87 by a brush-like roller 91. However, only the transfer fixing surface of the recording medium P is heated by the heating plate 87.
Thereafter, the recording medium P on which the full-color image has been transferred and fixed passes through the paper discharge conveyance path, and is discharged as an output image outside the apparatus main body 1 by the paper discharge roller 80, and a series of image forming processes is completed. In the image forming apparatus according to the first embodiment, the conveyance speed (or process linear speed) of the recording medium P is set to about 300 mm / second.

The toner used in Embodiment 1 is preferably suitable for low-temperature fixing. Specifically, the softening point (1/2 outflow temperature) of the toner is preferably about 100 ° C.
As the toner binder resin, one having the following composition can be used.
For example, homopolymers of styrene such as polyester, polystyrene, poly p-chlorostyrene, polyvinyltoluene and the like; and styrene-p-chlorostyrene copolymers, styrene-propylene copolymers, styrene-vinyltoluene copolymers. Styrene-vinyl naphthalene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, 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 acid ester copolymer Examples thereof include styrenic copolymers such as polymers.
Moreover, the following resin can also be mixed and used. 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 fat Examples thereof include cyclic hydrocarbon resins, aromatic petroleum resins, chlorinated paraffin, and paraffin wax. Among these, those containing a polyester resin are preferred in order to obtain sufficient fixing properties. In particular, the crystalline polyester resin is sufficiently softened and melted at the time of paper contact, and an image can be formed 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 to be used as a binder resin, it is also preferable to use not only a polymer with only the above bifunctional monomer but also a polymer containing a component with a trifunctional or higher polyfunctional 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.

Further, the toner used in the first exemplary embodiment can contain a release agent for the purpose of improving the release property of the toner on the surface of the transfer fixing belt 27 in the transfer fixing step. As the release agent, all known ones can be used, and in particular, defree fatty acid type carnauba wax, montan wax, oxidized rice wax, and ester wax can be used alone or in combination. As the carnauba wax, those having fine crystallinity, an acid value of 5 or less, and a particle diameter of 1 μm or less when dispersed in a toner binder are preferable. 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. On the other hand, if the amount exceeds 15 parts by weight, problems such as significant spent on the carrier occur.
Further, as an external additive, for the purpose of improving the fluidity of the toner, silica, titanium oxide, alumina, and the like, and if necessary, fatty acid metal salts, polyvinylidene fluoride, and the like may be added.
In particular, since the transfer fixing device 66 can sufficiently heat the toner, even if a relatively large amount of an additive such as submicron large particle size silica is used, the fixing property and the fixing temperature are not affected. Therefore, an external additive prescription considering fluidity and transferability is possible.

Next, the characteristic transfer fixing device 66 in the first embodiment will be described in detail with reference to FIGS.
FIG. 2 is an enlarged view showing a part of the transfer fixing device 66. FIG. 3 is an enlarged view showing contact / separation mechanisms 92 to 94 of the brush roller 91 in the transfer fixing device 66. FIG. 4 is an enlarged view showing a state where the heating plate 87 is separated.
2 and 3, the transfer fixing device 66 includes a transfer fixing belt 27 as a transfer fixing member, heating devices 87 to 89, a pressure roller 68 as a pressure member, and a brush roller as a biasing member. 91, contact / separation mechanisms 92 to 94 as variable means, a cylindrical guide plate 86, a heater 70, a leveling roller 85, and the like.

  Here, the transfer fixing belt 27 as a transfer fixing member is an endless belt having a multilayer structure in which an elastic layer and a surface layer (release layer) are sequentially formed on a base material layer formed on the inner peripheral surface side. . In the first embodiment, a polyimide resin having a layer thickness of about 80 μm is used as the base layer, a silicone rubber having a layer thickness of about 160 μm is used as the elastic layer, and a fluororubber (layer thickness of about 7 μm is used as the surface layer). Or a fluororesin) is used. The elastic layer is for following the irregularities on the surface of the recording medium P, and the surface layer is for ensuring releasability from the toner. Further, the transfer and fixing belt 27 in the first embodiment has a length in the width direction (in the direction perpendicular to the paper surface in FIG. 2) of about 300 mm and a circumferential length (a length in the running direction) of about 1150 mm. Is set to

  The pressure roller 68 as a pressure member has a surface layer (release layer) formed on a cylindrical metal core made of aluminum or the like, and rotates in the clockwise direction in FIG. The pressure roller 68 is in pressure contact with the roller member 28A via the transfer fixing belt 27 by a pressure mechanism (not shown). In this way, a desired nip portion is formed between the pressure roller 68 and the transfer fixing belt 27.

The heating devices 87 to 89 are disposed in the vicinity of the entrance side of the nip portion in the transfer fixing device 66. The heating device includes a heating plate 87 as a heating member, a heating element 88 that heats the heating plate 87, a thermocouple 89 (temperature detection means) for detecting the temperature of the heating plate 87, and the like.
The heating plate 87 as a heating member is a plate-like member made of copper or aluminum having a thickness of about 0.2 to 1.5 mm. The heating plate 87 extends from the vicinity of the registration roller 64 to the vicinity of the nip portion, and functions as a guide plate (guide plate) that guides the recording medium P conveyed toward the nip portion. The heating plate 87 is in contact with the transfer fixing surface (front surface) of the recording medium P conveyed toward the nip portion, and heat generated by the heating element 88 is applied to the recording medium P (transfer fixing surface). It also functions as a heat transfer plate that conducts heat.
The heating element 88 is a heating element having PTC characteristics, and is attached to the surface opposite to the conveying surface of the heating plate 87 (the surface facing the recording medium P). Since the heating element having the PTC characteristic is a resistance heating element whose resistance rapidly increases when a predetermined Curie point is reached, the self-temperature control function can suppress a problem that the heating plate 87 is abnormally heated. it can. Specifically, in the first embodiment, the temperature of the heating plate 87 is controlled in the range of 180 to 220 ° C.
In the first embodiment, since heating plate 87 is formed of copper or aluminum having high thermal conductivity and relatively low cost, heating devices 87 to 89 having high heating efficiency and relatively low cost are provided. Can do.

  As described above, the heating device configured in this way heats only the transfer fixing surface (front surface) of the recording medium P immediately before the transfer / fixing step. In other words, the heating device moves the recording medium P to the nip portion before the temperature of the back surface of the recording medium P (the back surface with respect to the transfer fixing surface) rises (before heat is transferred from the front surface to the back surface). The transfer fixing surface is heated so as to be conveyed to the surface.

The inventor of the present application made a recording when the recording medium P (thick paper 300 g paper) was brought into contact with a copper plate (thickness 1 mm) heated to 160 ° C. for 60 msec and then conveyed (running) in the air at an ambient temperature of 40 ° C. The temperature fluctuation of the transfer fixing surface of the medium P was simulated. As a result, the recording medium P heated to about 140 ° C. by the copper plate is only 110 m. For 10 msec (corresponding to a conveying distance of 3 mm when the conveying speed is 300 mm / sec.) In the air at an atmospheric temperature of 40 ° C. It was found that the temperature decreased until. Therefore, in order to increase the heating efficiency of the recording medium P before the transfer and fixing step, it is necessary to bring the heating member (heating plate 87) for heating the recording medium as close to the nip as possible.
In the first embodiment, the heating plate 87 is formed in a plate shape, the tip thereof is as close as possible to the nip portion, and the length in the transport direction is set as long as possible. The heating efficiency of the recording medium P can be improved.

Here, in the heating plate 87 in the first embodiment, a nickel plating containing fluororesin particles is covered on a guide surface that guides the recording medium P (a surface that contacts the recording medium P). . Specifically, 30 vol% PTFE (polytetrafluoroethylene) is dispersed in a nickel plating film. Such a coating has a hardness in a precipitated state of about Hv300, is harder than a normal resin coating, and is excellent in slipping property, wear resistance, and releasability. Therefore, it is possible to reduce the problem of toner and paper powder adhering to the heating plate 87 and improve the durability of the heating plate 87.
The guide surface of the heating plate 87 (the surface that contacts the recording medium P) can be covered with diamond-like carbon (DLC) or graphite-like carbon (GLC) having high wear resistance.

The heating devices 87 to 89 in Embodiment 1 heat the transfer fixing surface so that the temperature of the transfer fixing surface of the recording medium P is higher than the surface temperature of the transfer fixing belt 27. That is, the toner image T carried on the transfer fixing belt 27 is heated and melted by heat mainly received from the recording medium P at the nip portion.
In the first embodiment, the transfer fixing surface of the recording medium P is heated, and the temperature for obtaining a sufficient gloss on the output image can be set independently. Therefore, the heater 70 (with a halogen heater or a carbon heater) can be set. The temperature (fixing set temperature) of the transfer fixing belt 27 heated by the above can be lowered. Further, since the recording medium P is heated immediately before the transfer / fixing process, the adhesion between the toner T and the recording medium P is not increased more than necessary without being heated excessively.
That is, according to the configuration of the first embodiment, it is possible to perform low-temperature fixing, reduce the warm-up time of the apparatus, and improve energy saving. In addition, since heat transfer to the transfer fixing belt 27 can be suppressed, durability of the transfer fixing belt 27 can be improved. Furthermore, since the heating temperature of the transfer fixing belt 27 is reduced, thermal deterioration of the transfer fixing belt 27 can be suppressed.

  Further, the transfer fixing device 66 according to the first embodiment presses (biases) the recording medium P guided to the nip portion by the heating plate 87 against the heating plate 87 by the brush-like roller 91 (biasing member). It is configured. With this configuration, in order to improve the adhesion force and adhesion time of the recording medium P to the heating plate 87, the temperature of the surface of the recording medium P is reliably raised to the target temperature by the heating plate 87, and fixing failure is prevented. It becomes possible to suppress.

Here, with reference to FIG.2 and FIG.3, the brush-shaped roller 91 as an urging | biasing member is heat-resistant that the brush cloth in which the polyimide fiber, the aramid fiber, etc. were planted on the core metal was wound helically. 2 is a roller member having the property of rotating at the same speed as the conveyance speed of the recording medium P in the clockwise direction of FIG. Then, the recording medium P that has passed the position of the registration roller 64 is heated by the heating plate 87 while being urged by the brush-like roller 91 and pressed against the heating plate 87 immediately before the nip portion. Will be sent to. By imparting heat resistance to the brush-like roller 91, it is possible to reduce a problem that the brush bristles of the brush-like roller 91 are thermally deteriorated by the heat of the heating plate 87.
Here, in the first embodiment, the distance from the registration roller 64 to the nip portion (the nip portion between the transfer fixing belt 27 and the pressure roller 68) is the minimum size that can be passed by the image forming apparatus 1. Therefore, the conveying force applied to the recording medium P between the registration roller 64 and the nip portion is mainly the registration roller 64 and the pressure roller 68 (transferring). Provided by the fixing belt 27).

Further, the brush-like roller 91 as an urging member is in point contact or line contact with the recording medium P guided by the heating plate 87 at a plurality of locations. By making the contact area with the recording medium P as small as possible and pressing the recording medium P against the heating plate 87, the heat is transferred to the brush-like roller 91 side to suppress the problem that the heating efficiency of the recording medium P decreases. In addition, it is possible to suppress a problem that the transportability of the recording medium P is lowered.
In the first embodiment, the pressure width N (nip width) of the brush-like roller 91 in pressure contact with the heating plate 87 is set to be 3 to 12 mm (corresponding to a pressing force of about 3 to 5 kgf). ). The transfer and fixing device 66 according to the first embodiment includes contact / separation mechanisms 92 to 94 as variable means for changing the urging force against the recording medium P urged toward the heating plate 87 by the brush roller 91. This will be explained in detail later.
In the first embodiment, the brush-like roller 91 is used as the urging member. However, a roller member having a surface layer formed of foamed urethane, felt, or the like can also be used as the urging member.

In the transfer fixing device 66 according to the first embodiment, a cylindrical guide plate 86 that covers the pressure roller 68 is provided between the pressure roller 68 and the brush-like roller 91. The cylindrical guide plate 86 is installed with a gap so as not to contact the pressure roller 68, and prevents the brush roller 91 from contacting the pressure roller 68. By providing the cylindrical guide plate 86, even if the brush roller 91 is placed close to the pressure roller 68, the side effect of the brush hair of the brush roller 91 being caught by the pressure roller 68 can be suppressed. Therefore, the distance between the pressure contact position of the heating plate 87 and the brush-like roller 91 and the nip portion of the transfer fixing belt 27 and the pressure roller 68 (idle distance) can be reduced, and there is no side effect. The heating efficiency of the recording medium P before the process can be increased.
In order to reduce the sliding resistance between the cylindrical guide plate 86 and the brush-like roller 91, the outer peripheral surface of the cylindrical guide plate 86 is subjected to a low wear surface treatment such as a fluororesin coating, or the durability of the cylindrical guide plate 86 is improved. In order to increase the thickness, a material with high wear resistance such as diamond-like carbon (DLC) can be covered on the outer peripheral surface of the cylindrical guide plate 86.

As described above, the transfer fixing device 66 according to the first embodiment minimizes the heating of the transfer fixing belt 27, and the recording medium immediately before the amount of heat necessary for heating and melting the toner is conveyed to the nip portion. It supplements by heating P efficiently. However, in this case, the transfer and fixing belt 27 receives a large amount of heat from the heated recording medium P and has a non-uniform distribution, and is the width direction of the transfer and fixing belt 27 (the direction perpendicular to the conveyance direction of the recording medium). ) Causes temperature unevenness, and it becomes easy to generate defective fixing images such as uneven fixing and offset.
In contrast, in the first embodiment, as shown in FIG. 2, the temperature distribution in the width direction of the surface of the transfer and fixing belt 27 after passing through the nip portion is made uniform, and the transfer after the transfer and fixing step is performed. A leveling roller 85 is installed as a cooling means for cooling the fixing belt 27.
The leveling roller 85 is a roller member disposed on the downstream side in the running direction of the transfer fixing belt 27 with respect to the nip portion, and stretches and supports the transfer fixing belt 27 together with the three roller members 28A to 28C. The leveling roller 85 as a cooling means is a heat pipe, and cools the transfer fixing belt 27 and efficiently distributes the temperature distribution in the width direction of the surface of the transfer fixing belt 27 by efficiently convection heat inside the heat pipe. Turn into. As a result, even when the recording medium P immediately before being conveyed to the nip portion is heated by the heating plate 87 with the heating of the transfer fixing belt 27 being minimized, fixing defects such as uneven fixing and offset occur. Can be suppressed.

Here, in the transfer fixing device 66 according to the first embodiment, the urging force with respect to the recording medium P urged toward the heating plate 87 (heating member) by the brush roller 91 (biasing member) is variable. Contact / separation mechanisms 92 to 94 as means are installed. The contact / separation mechanisms 92 to 94 as variable means are configured to change the relative position of the brush-like roller 91 with respect to the heating plate 87.
Specifically, referring to FIG. 3, the contact / separation mechanism includes a lever 92, a cam 93, a tension spring 94, a drive motor (not shown), and the like. The lever 92 is held on the side plate of the apparatus main body so as to be rotatable about the support shaft 92a. A brush-like roller 91 is rotatably held on one end side of the lever 92, and one hook portion of a tension spring 94 is connected to the other end side. The other hook portion of the tension spring 94 is connected to the side plate of the apparatus main body. A cam 93 connected to a drive motor (not shown) is engaged with the center portion of the lever 92. With this configuration, when the cam 93 is rotationally driven by a drive motor (not shown) and the posture of the cam 93 in the rotational direction is determined, the lever 92 is rotated about the support shaft 92a by the spring force of the tension spring 94. (The lever 92 rotates while being in contact with the cam 93), and the position of the brush-like roller 91 is varied in the vertical direction.

Specifically, FIG. 3A shows a state where the brush roller 91 is in contact with the heating plate 87 with a predetermined pressure width (nip width) N. In this state, by changing the posture of the cam 93 in the rotational direction by a predetermined angle, the pressure width N (the urging force against the recording medium P) is increased or decreased. The contact / separation mechanisms 92 to 94 (pressure width variable mechanism) have a thickness (paper thickness) of the recording medium P when the thickness (paper thickness) of the recording medium P guided by the heating plate 87 is thick. The biasing force (pressurizing width N) described above is controlled to be larger than when it is thin.
With a thick recording medium (thick paper), the heat of the transfer fixing surface (front surface) heated by the heating plate 87 is transferred to the back side as time passes, compared to a thin recording medium (thin paper). Therefore, the degree of temperature decrease on the transfer and fixing surface until reaching the nip portion is large. On the other hand, in the case of thin paper, the heating efficiency by the heating plate 87 is higher than that of thick paper. Therefore, if the temperature control of the heating plate 87 based on thick paper is performed, the thin paper will overheat. Or curl due to temperature rise.
Therefore, by performing the above-described control, even when a recording medium P having a different thickness (paper thickness) is passed, the temperature of the recording medium P immediately before the transfer fixing process heated by the heating plate 87 is maintained. A stable transfer-fixed image can be formed without variation. This is based on the fact that the pressure width N (biasing force) of the brush roller 91 with respect to the heating plate 87 affects the amount of heat applied from the heating plate 87 to the recording medium P.

FIG. 5 shows the free running distance from the heating plate 87 to the nip portion (the contact position between the transfer fixing belt 27 and the pressure roller 68), the surface temperature of the recording medium P (the temperature of the transfer fixing surface), and the like. , And is an analysis result of a one-dimensional heat transfer analysis simulation using an implicit method.
In FIG. 5, “300 g paper” indicates thick paper, “45K paper” indicates thin paper, and “nip” indicates the pressure width N of the brush roller 91 against the heating plate 87. In FIG. 5, the temperature of the heating plate 87 is swung to 240 ° C. and 180 ° C., the type of the recording medium P is swung to 300 g paper (thick paper) and 45K paper (thin paper), and the pressure width N is 6 mm and 12 mm. Thus, for each combination, it is analyzed how the temperature of the transfer fixing surface decreases as the free running distance from the heating plate 87 (heating position) increases.

From the analysis result of FIG. 5, 300g paper (thick paper) has a greater degree of heat transfer from the front surface toward the lower temperature back surface than 45K paper (thin paper). It can be seen that the degree of temperature decrease on the transfer and fixing surface increases with the increase in the temperature. Further, as the pressurization width N (heating width) is larger, the heating plate 87 is heated to the vicinity of the center of the recording medium, and the temperature difference between the front surface and the back surface becomes smaller, so the idle running distance becomes longer. However, it can be seen that the degree of temperature drop on the transfer fixing surface is reduced. Further, when the set temperature of the heating plate 87 is high, the amount of heat given to the front surface of the recording medium P also increases, so that the temperature of the transfer fixing surface after reaching a predetermined idle travel distance naturally increases. I understand.
If the surface temperature of the recording medium P is to be maintained at 120 ° C. at a position where the free running distance is 9 mm, when 300 g paper (thick paper) is used, the set temperature of the heating plate 87 is set to 240 ° C. and the pressurization width N is increased. It is necessary to set it to about 12 mm (refer to the position of point A in FIG. 5). On the other hand, when 45K paper (thin paper) is used, the surface temperature of the recording medium P is maintained at 120 ° C. at a position where the free running distance is 9 mm even if the set temperature of the heating plate 87 is 180 ° C. (The position of point B in FIG. 5 can be referred to.). Further, when 45K paper (thin paper) is used, if the set temperature of the heating plate 87 is 240 ° C., the surface of the recording medium P is at a position where the free running distance is 9 mm even if the pressure width N is smaller than 6 mm. The temperature can be maintained at 120 ° C. (see the position of point C in FIG. 5). Therefore, if the 45K paper (thin paper) is heated under the optimum conditions (setting temperature of the heating plate 87: 240 ° C., pressure width N: 12 mm) when 300 g paper (thick paper) is used, The temperature of the transfer fixing surface rises to 160 ° C., and the temperature difference from the thick paper spreads to around 40 ° C. In this way, even if the heating conditions are set so as to give the necessary minimum amount of heat in the thick paper, if the same heating conditions are applied to the thin paper, the temperature becomes higher than the appropriate temperature, and the amount of heat more than the necessary minimum is required. Energy is wasted by giving to the recording medium. Further, excessive heat is transmitted to the transfer fixing belt 27 via the front surface (or back surface) of the recording medium, so that the temperature of the transfer fixing belt 27 rises and problems such as hot offset are likely to occur. Become. Further, the back surface temperature of the recording medium P during double-sided printing becomes higher than necessary, and image degradation and heat cycle problems occur due to remelting of toner.

On the other hand, in the first embodiment, the pressure width N of the brush-like roller 91 against the heating plate 87 is varied according to the thickness of the recording medium P. Therefore, regardless of the thickness of the recording medium P. First, the temperature of the transfer and fixing surface of the recording medium P when fed into the nip portion in the transfer and fixing step can be optimized. Further, since the recording medium P can be heated with a minimum amount of heat necessary for obtaining a good transfer-fixed image, the energy efficiency of the entire apparatus can be improved. Furthermore, since the sheet is heated with the minimum amount of heat when passing the thin paper, it is possible to prevent a problem that the thin paper is curled after the heating.
Note that the paper thickness of the recording medium P to be passed can be detected by installing a paper thickness sensor in the conveyance path of the recording medium P, or input to the operation unit of the apparatus main body 1 by the user. You may judge based on the information regarding the recording medium P. FIG. The contact / separation mechanisms 92 to 94 are variably controlled based on the information about the paper thickness of the recording medium P acquired in this way.

Here, in the first embodiment, the pressing width N is optimized by controlling the contact / separation mechanisms 92 to 94 (variable means) according to the paper thickness of the recording medium P.
On the other hand, the pressurization width N is optimized by controlling the contact / separation mechanisms 92 to 94 (variable means) according to the ambient temperature (atmosphere temperature), the accumulated operating time, the temperature of the heating plate 87, and the like. You can also
Specifically, when the ambient temperature (atmosphere temperature) is low, the contact / separation mechanisms 92 to 94 (variable means) so that the pressurization width N (or urging force) becomes larger than when the ambient temperature is high. Can also be controlled. When the ambient temperature is low, it becomes difficult to heat the recording medium P by the heating plate 87. Therefore, by performing such control, when the sheet is fed into the nip portion in the transfer fixing step, regardless of the environmental temperature. The temperature of the transfer and fixing surface of the recording medium P can be optimized. The environmental temperature can be detected by a temperature sensor installed in the apparatus main body 1.
Also, the contact / separation mechanisms 92 to 94 (variable means) can be controlled so that the pressurization width N (or urging force) increases with time. The restoring force (repulsive force) of the bristles of the brush-like roller 91 decreases with time compared to the initial time, and the pressing width N changes even if the position of the brush-like roller 91 relative to the pressing plate 87 does not change. Since it becomes difficult to heat the recording medium P by the heating plate 87, the temperature of the transfer fixing surface of the recording medium P can be optimized over time by performing such control. The passage of time can be determined by the value of the accumulated print sheet counter provided in the apparatus main body 1.
Further, when the temperature of the heating plate 87 is low, the contact / separation mechanisms 92 to 94 (variable means) are controlled so that the pressurization width N (or urging force) becomes larger than when the temperature of the heating plate 87 is high. You can also When the temperature of the pressure plate 87 is low including the change in the environmental temperature described above, it becomes difficult to heat the recording medium P by the heating plate 87. By performing such control, the recording medium P is placed in the nip portion in the transfer fixing process. The temperature of the transfer and fixing surface of the recording medium P at the time of feeding can be optimized. The temperature of the heating plate 87 can be detected by a thermocouple 89 attached to the heating plate 87.

In the first embodiment, the pressing width N is optimized by controlling the contact / separation mechanisms 92 to 94 (variable means) according to the paper thickness of the recording medium P or the like. On the other hand, a second variable means for changing the temperature of the heating plate 87 is further provided to control and press the contact / separation mechanisms 92 to 94 (variable means) according to the paper thickness of the recording medium P or the like. The width N can be optimized, and the temperature of the heating plate 87 can be optimized.
As described above with reference to FIG. 5, in addition to the pressurization width N, the set temperature of the heating plate 87 has a great influence in order to optimize the temperature of the transfer and fixing surface of the recording medium P. Accordingly, the temperature of the heating plate 87 is also variably controlled according to the paper thickness of the recording medium P, so that the temperature of the transfer fixing surface of the recording medium P when fed into the nip portion in the transfer fixing process is optimized. can do. Specifically, the temperature of the heating plate 87 is controlled by controlling the temperature of the heating element 88 based on the temperature detected by the thermocouple 89 by using a ceramic heater or a plate heater that can easily adjust the temperature as the heating element 88. Can be controlled to an optimum temperature according to the paper thickness of the recording medium P or the like.
In this case, in addition to the paper thickness of the recording medium P, the temperature of the heating plate 87 may be variably controlled according to the ambient temperature, the accumulated operation time, and the like.

Here, FIG. 3B shows a state in which the brush roller 91 is completely separated from the heating plate 87 by the operation of the separation mechanisms 92 to 94 described above.
In the first embodiment, at the time of non-sheet passing (when the recording medium P does not pass between the heating plate 87 and the brush-like roller 91), the brush-like roller 91 is made relative to the heating plate 87. Is controlled to be separated (the state shown in FIG. 3B).
As a result, the brush-like roller 91 comes into contact with the heating plate 87 only at the minimum necessary timing, so that heat is transmitted from the heating plate 87 to the brush-like roller 91 and the brush-like roller 91 is thermally deteriorated. Reduced.

Further, referring to FIG. 4, in the first embodiment, when a jam occurs in the vicinity of the heating plate 87 (when the recording medium P stops being conveyed between the heating plate 87 and the brush-like roller 91). )), The heating plate 87 is controlled to be separated in the direction away from the recording medium P (conveyance path). Specifically, the heating plate 87 is configured to be moved to the position shown in FIG. 4 (rotation about the tip portion) by a drive mechanism (not shown) (not shown). ing. When a jam detection sensor (not shown) detects a jam of the recording medium P in the vicinity of the heating plate 87, the heating by the heating element 88 is cut off and the heating plate 87 is moved away (to the position shown in FIG. 4). Is performed).
This prevents the problem that the recording medium P continues to contact the heating plate 87 and overheats when a jam occurs (in particular, the possibility of overheating to the ignition point is reliably prevented). Since the restraining force of the heating plate 87 on the jammed recording medium P is reduced, the workability of the jam processing (removal processing of the jammed recording medium to the outside of the apparatus main body) is improved.
Further, in addition to such control when a jam occurs, the contact / separation mechanisms 92 to 94 are operated when a jam occurs to move the brush roller 91 away from the conveyance path (by moving to the position shown in FIG. 3B). ) Also improves the workability of the jam processing.

Here, in the transfer fixing device 66 according to the first embodiment, the temperature of the transfer fixing surface of the recording medium P is higher than the surface temperature of the transfer fixing belt 27 (or the toner image T carried on the transfer fixing belt 27). Thus, it is preferable to heat the recording medium P and the transfer fixing belt 27. In such a case, the toner image T carried on the transfer and fixing belt 27 is heated and melted by heat received mainly from the recording medium P at the nip portion.
As described above, the heating devices 87 to 89 and the heater 70 are heated so that the temperature of the recording medium P (transfer fixing surface) is higher than the surface temperature of the transfer fixing belt 27, and thereby the interface with each toner. Hot offset can be prevented by the difference in viscoelasticity. That is, by increasing the temperature on the recording medium P side and lowering the temperature on the transfer fixing belt 27 side in the toner layer, the adhesion force between the recording medium P and the toner is greater than the adhesion force between the transfer fixing belt 27 and the toner. Is increased to improve the releasability of the toner with respect to the transfer-fixing belt 27, whereby a good image free from offset to the transfer-fixing belt 27 can be obtained. Furthermore, the improvement in hot offset resistance can reduce (or eliminate) the amount of wax added to the toner in order to increase the releasability, so that color reproducibility, developability, An improvement in chargeability is expected. In addition, by setting the temperature of the transfer fixing belt 27 low, the transfer fixing belt 27 can be easily cooled, and problems such as thermal deterioration of the photosensitive drum 21 in contact with the transfer fixing belt 27 are reduced. can do.

Specifically, in order not to cause an offset, the surface temperature of the toner image immediately before the nip portion heated by the heater 70 (the toner image carried on the transfer fixing belt 27) is Tt, and the heating devices 87 to 87 are used. 89, Tp is the surface temperature of the recording medium P (transfer fixing surface) immediately before the nip heated by 89, Tb is the temperature of the pressure roller 68, Tfb is the toner outflow start temperature, and Ts is the softening point temperature of the toner. And when
(Tt + Tp) / 2> Tfb (1)
Tt <Tfb (2)
(Preferably Tt <Tfb-20 ° C., more preferably Tt <Tfb-30 ° C.)
Tb <Ts (3)
It is preferable to satisfy the following three conditional expressions.
Here, the softening temperature and the outflow start temperature of the toner can be measured using a “Koka type flow tester CFT500D type” (manufactured by Shimadzu Corporation). A flow tester is a capillary rheometer that measures the viscous resistance when a melt (toner) passes through a capillary. In the measurement method, first, a sample (toner) filled in a cylinder is melted by heating from the surroundings, and a certain pressure is applied from above by a piston. Thereafter, the melted toner is extruded through a die having a narrow hole, and the fluidity (melt viscosity) of the sample is obtained from the flow rate. Measurement conditions are a load: 5 kgf / cm ² , a temperature rising rate: 3.0 ° C./min, a die diameter: 1.00 mm, and a die length: 10.0 mm.

FIG. 6 is a graph showing experimental results that serve as the basis for the above three conditional expressions.
In the experiment, the surface temperature of the toner image (transfer fixing belt 27) immediately before the nip heated by the heater is Tt (corresponding to the horizontal axis in FIG. 6) and the recording medium immediately before the nip heated by the heating device. The surface temperature of P is varied with Tp (corresponding to the vertical axis in FIG. 6), and the fixability (presence of offset) of the output fixed image is observed. FIG. 6A shows the experimental results when using toner whose outflow start temperature Tfb is 90 ° C., and FIG. 6B shows the experimental results when using toner whose outflow start temperature Tfb is 110 ° C. It is. In the experiment, coated paper “Casablanca X” (manufactured by Oji Paper Co., Ltd., basis weight 100 g / m ² ) was used as the recording medium P to be passed, the nip time at the nip portion was 50 ms, and the surface pressure at the nip portion was 2 kgf. / Cm ² . In FIG. 6, “◯” indicates a state where the fixing property is good, “◇” indicates a state where a very small hot offset occurs, and “△” indicates a state where a minute hot offset occurs. “×” indicates a state in which an unacceptable level of hot offset has occurred, and “□” indicates a state in which a cold offset has occurred. In FIG. 6, the sloped line indicated by the broken line indicates the lower limit fixing temperature at which good fixability can be secured, and the range above this broken line is the range at which good fixability can be secured.
6A and 6B, when the temperature Tt of the toner image immediately before the nip portion is higher than the fixing lower limit temperature and higher than the toner outflow start temperature Tfb (Tfb <Tt), the hot offset is detected. It can be seen that a good image cannot be obtained. Therefore, a satisfactory image with almost no offset can be obtained by configuring the heating device and performing appropriate temperature control so as to satisfy the conditional expressions (1) and (2). 6A and 6B, when the condition (Tfb−Tt ≧ 20 ° C.) is satisfied, the amount of hot offset is further reduced, and the condition (Tfb−Tt ≧ 30 ° C.) is satisfied. It can be seen that sometimes the hot offset is almost completely eliminated.
The conditional expression (3) defines the temperature of the pressure roller 68 that forms the nip portion with the transfer fixing belt 27 to be equal to or lower than the toner softening point temperature. The image gloss difference between the front and back surfaces (the first surface and the second surface) can be reduced.

  As described above, according to the first embodiment, the recording medium P conveyed to the nip portion between the transfer fixing belt 27 (transfer fixing member) and the pressure roller 68 (pressure member) is guided and guided. A heating plate 87 (heating member) that heats the transfer fixing surface and a brush-like roller 91 (biasing member) that urges the recording medium P toward the heating plate 87 are provided, and an urging force by the brush-like roller 91 is provided. (Pressure width N) is configured to be variable. As a result, even when a recording medium P with low energy consumption and different thickness is passed or the ambient environmental temperature changes, the recording medium P immediately before the transfer and fixing process is stabilized by the heating plate 87. Heat, the image can be formed with good fixability and high image quality.

In the first embodiment, the transfer and fixing belt 27 is used as the transfer and fixing member. However, a transfer and fixing roller (for example, see Patent Document 3) can also be used as the transfer and fixing member.
In the first embodiment, the leveling roller 85 is used as a cooling means for cooling the transfer fixing belt 27 after the transfer fixing process, but a cooling fan facing the surface of the transfer fixing belt may be used as the cooling means. it can.
Even in these cases, the same effects as those of the first embodiment can be obtained.

Embodiment 2. FIG.
A second embodiment of the present invention will be described in detail with reference to FIG.
FIG. 7 is an enlarged view showing the vicinity of the transfer fixing device in the second embodiment, and corresponds to FIG. 2 in the first embodiment. In the transfer fixing apparatus according to the second embodiment, the toner images formed on the photosensitive drums 21 of the respective colors are primarily transferred to the intermediate transfer belt 95 and then secondarily transferred to the transfer fixing belt 27 and then onto the recording medium P. The third transfer is different from that of the first embodiment in which the toner image formed on the photosensitive drum 21 of each color is primarily transferred to the transfer fixing belt 27 and secondarily transferred to the recording medium P. To do.

In the image forming apparatus according to the second embodiment, the toner images formed on the photosensitive drums for each color (not shown, but arranged in parallel so as to face the intermediate transfer belt 95) are intermediate transfer belts 95. Then, the toner image is secondarily transferred to the transfer and fixing belt 27 between the intermediate transfer belt 95 and the transfer and fixing belt 27. Further, the toner image T transferred to the transfer fixing belt 27 is tertiary transferred and fixed (transfer-fixed) to the recording medium P at the position of the nip portion with the pressure roller 68.
Here, also in the second embodiment, heating devices 87 to 89 for heating the recording medium P immediately before the transfer fixing process are installed in the vicinity of the nip portion between the transfer fixing belt 27 and the pressure roller 68. A brush-like roller 91 (biasing member) that urges the recording medium P immediately before the transfer fixing process toward the heating plate 87 (heating member) is installed so that the contact force to the heating plate 87 can be varied. Yes.

  As described above, also in the second embodiment, similarly to the first embodiment, the sheet is conveyed to the nip portion between the transfer fixing belt 27 (transfer fixing member) and the pressure roller 68 (pressure member). A heating plate 87 (heating member) that heats the transfer fixing surface while guiding the recording medium P, and a brush roller 91 (biasing member) that urges the recording medium P toward the heating plate 87 are provided. The urging force (pressing width N) by the brush roller 91 can be varied. As a result, even when a recording medium P with low energy consumption and different thickness is passed or the ambient environmental temperature changes, the recording medium P immediately before the transfer and fixing process is stabilized by the heating plate 87. Heat, the image can be formed with good fixability and high image quality.

Embodiment 3 FIG.
A third embodiment of the present invention will be described in detail with reference to FIG.
FIG. 8 is a configuration diagram illustrating a part of the image forming apparatus according to the third embodiment. The image forming apparatus according to the third embodiment is different from that of the first embodiment in which four photosensitive drums 21 are installed in that one photosensitive drum 21 is installed.

As shown in FIG. 8, the image forming apparatus according to the third embodiment has a writing unit (not shown) corresponding to each color (yellow, magenta, cyan, black) around one photosensitive drum 21. , A charging unit (not shown), developing devices 23Y, 23M, 23C, 23BK, a cleaning device 25, and the like are disposed. Then, images (toner images) of the respective colors are formed on the photosensitive drum 21 so as to overlap each other, and the color image is transferred onto the transfer fixing belt 27 at a position facing the transfer bias roller 24.
Thereafter, the toner image T carried on the transfer fixing belt 27 is transferred to the recording medium P heated by the heating device at the position of the nip portion with the pressure roller 68 in the same manner as in the above embodiments. It is fixed.

  The transfer fixing device 66 according to the third embodiment also has a recording medium P just before the transfer fixing step in the vicinity of the nip portion between the transfer fixing belt 27 and the pressure roller 68, as in the above embodiments. Heating devices 87 to 89 for heating the are installed. A brush-like roller 91 (biasing member) that urges the recording medium P immediately before the transfer fixing process toward the heating plate 87 (heating member) is installed so that the contact force to the heating plate 87 can be varied. Yes.

  As described above, also in the third embodiment, as in the above embodiments, the sheet is conveyed to the nip portion between the transfer fixing belt 27 (transfer fixing member) and the pressure roller 68 (pressure member). A heating plate 87 (heating member) that heats the transfer fixing surface while guiding the recording medium P, and a brush roller 91 (biasing member) that urges the recording medium P toward the heating plate 87 are provided. The urging force (pressing width N) by the brush roller 91 can be varied. As a result, even when a recording medium P with low energy consumption and different thickness is passed or the ambient environmental temperature changes, the recording medium P immediately before the transfer and fixing process is stabilized by the heating plate 87. Heat, the image can be formed with good fixability and high image quality.

  It should be noted that the present invention is not limited to the above-described embodiments, and within the scope of the technical idea of the present invention, the embodiments can be modified as appropriate in addition to those suggested in the embodiments. Is clear. In addition, the number, position, shape, and the like of the constituent members are not limited to the above embodiments, and can be set to a number, position, shape, and the like that are suitable for carrying out the present invention.

1 image forming apparatus body (apparatus body),
27 transfer fixing belt (transfer fixing member),
66 transfer fixing device,
68 Pressure roller (pressure member),
70 heater,
86 Cylindrical guide plate,
87 Heating plate (heating member),
88 heating element,
89 thermocouple,
91 brush-like roller (biasing member),
92 lever (variable means),
93 cam (variable means),
95 Intermediate transfer belt, P recording medium.

JP-A-2005-37879 JP 2002-99159 A JP 2004-145260 A

Claims (12)

A transfer fixing device for transferring and fixing a toner image to a transfer fixing surface of a recording medium,
A transfer fixing member that carries a toner image and travels in a predetermined direction;
A pressure member that forms a nip portion to which the recording medium is conveyed in pressure contact with the transfer fixing member;
The transfer fixing member is heated at a position upstream of the nip portion in the running direction of the transfer fixing member, and the surface temperature of the toner image immediately before the nip portion carried on the nip portion is set to be equal to or lower than the toner outflow start temperature. A heater for heating at a temperature;
A heating member that heats the transfer and fixing surface of the recording medium conveyed toward the nip portion and guides the recording medium conveyed toward the nip portion;
A biasing member that biases the recording medium guided by the heating member toward the heating member;
Variable means for varying the urging force on the recording medium urged toward the heating member by the urging member;
With
The transfer characterized in that the temperature of the transfer fixing surface at the nip portion of the recording medium heated by the heating member is higher than the surface temperature at the nip portion of the transfer fixing member heated by the heater. Fixing device.   The transfer fixing device according to claim 1, wherein the variable unit varies a relative position of the biasing member with respect to the heating member.   The variable means is controlled so that the biasing force is greater when the recording medium guided by the heating member is thicker than when the recording medium is thin. The transfer fixing apparatus according to claim 1 or 2.   The variable means is controlled so that the urging force becomes larger when the temperature of the heating member is lower than when the temperature of the heating member is high. The transfer fixing device according to any one of the above.   5. The variable means according to claim 1, wherein the biasing force is controlled to be larger when the ambient temperature is low than when the ambient temperature is high. Transfer fixing device.   6. The transfer fixing device according to claim 1, wherein the variable unit is controlled so that the urging force increases with time.   The transfer fixing device according to claim 1, further comprising a second variable unit configured to change a temperature of the heating member.   8. The urging member is separated from the heating member when the recording medium does not pass between the heating member and the urging member. The transfer fixing device according to 1.   9. The recording medium according to claim 1, wherein when the recording medium stops transporting between the heating member and the biasing member, the heating member is separated in a direction away from the recording medium. Transfer fixing device.   The transfer fixing device according to claim 1, wherein the biasing member is a brush-like roller having heat resistance.   The transfer fixing device according to claim 1, wherein the heating member is a plate-like member formed of copper or aluminum.   An image forming apparatus comprising the transfer fixing device according to claim 1.

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