JP2009020343A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image forming apparatus and an image forming method with which the smoothness of the surface of a toner image is improved to enhance gloss without causing the deterioration of an image. <P>SOLUTION: The image forming apparatus includes a fixing means 8 heating a toner image formed on a recording medium 22 to temperature higher than a softening point of toner to fix the toner image, and a cooling means 9 rapidly cooling the fixed toner image from a higher temperature side than the softening point of the toner to a lower temperature side than the softening point. In the image forming method, the toner image formed on the recording medium is heated to the temperature higher than the softening point of the toner to fix the toner image, and then the fixed toner image is rapidly cooled from the higher temperature side than the softening point of the toner to the lower temperature side than the softening point. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and an image forming method for forming a toner image on a recording medium by, for example, electrophotography and fixing the toner to form an image.

In an image forming apparatus based on electrophotography, for example, a toner image formed on a photosensitive member is transferred to an intermediate transfer member, and then transferred to a sheet (recording medium) passed between the intermediate transfer member and a transfer roller. Further, the toner image transferred by heating and melting the toner is heated and fixed on the recording medium.
Methods for heat-fixing a toner image on a recording medium are roughly classified into a contact method and a non-contact method. Heating roller fixing, belt fixing, film fixing and the like are known as contact methods. On the other hand, flash fixing and oven fixing are known as non-contact methods. Among them, the contact method using heating roller fixing is most generalized because the toner image and the heating roller are in direct contact with each other so that the thermal efficiency is high and the apparatus can be miniaturized.

However, in the contact method using heating roller fixing, an offset phenomenon is likely to occur in which molten toner remains on the heating roller when the recording medium passes through the heating roller.
Therefore, as a method of suppressing the offset phenomenon, a method of applying a release agent such as silicone oil having high releasability to the surface of the heating roller, or a method of kneading (dispersing) wax inside the toner and melting the wax during heating. A method for ensuring releasability by covering the toner surface has been proposed. In particular, it is possible to reduce the size of the device and reduce maintenance, and in recent years, the wax dispersion technology has been greatly improved in the production of toner by the polymerization method, so the oilless fixing method in which the wax is dispersed in the toner has become the mainstream. .

By the way, with the widespread use of color images, the demands on image quality for image forming apparatuses are diversified. For example, when creating posters and high-quality magazines, high-quality image quality (which has been difficult with conventional electrophotographic images ( For example, a highly glossy image is required.
However, when the heated toner (molten toner) is cooled to about room temperature, the resin contained in the toner contracts during the cooling process, and shrinkage marks may be formed on the surface of the image. When shrinkage marks are formed, the smoothness of the image surface is lowered, so that an image with low gloss can be obtained.

In recent years, since a highly glossy image can be obtained, there is an increasing demand for papers with reduced surface irregularities and coated papers coated with a material that has high thermal conductivity and fills the surface irregularities and smoothes them.
As a method for obtaining a highly glossy image, for example, in Patent Document 1, in the heating belt fixing method, a non-gloss mode for fixing at a fixing temperature and a gloss mode for fixing at a higher temperature than the non-gloss mode are selected and controlled. A possible image forming apparatus is disclosed.
Further, Patent Document 2 discloses an image forming apparatus including a wax melting point vicinity cooling unit that rapidly cools a toner image in the vicinity of the melting point of the wax included in the toner image. In the image forming apparatus, for example, the toner image is brought into contact with a cooling roller (metal roller) when the surface temperature of the toner image is 88 ° C. with a wax melting point of 80 to 85 ° C. as a reference, and the temperature is rapidly increased from 88 ° C. to 76 ° C. By cooling, the crystallization of the wax is suppressed, the white turbidity of the wax layer covering the image surface is suppressed, and the gloss is improved.
Patent Document 3 discloses an image forming method for rapidly cooling a toner image using a cooling device including a heat pipe, a driven roller, and a heat insulating material. According to the image forming method, the change in volume and area after fixing of the toner image is suppressed, and the roughness (graininess) of the image is improved.
Further, Patent Document 4 discloses an image forming apparatus including a toner image cooling blower having a plurality of air blowing holes between a fixing device and a conveyance roller. According to the image forming apparatus, air is blown to cool the toner image and the recording medium, thereby preventing the occurrence of a low gloss portion.
JP-A-4-195079 JP 2005-250335 A JP 2003-208047 A Japanese Patent Laid-Open No. 2003-21978

However, the image forming apparatus described in Patent Document 1 switches the gloss depending on whether the toner is completely melted or leaves the particle shape, and it is difficult to further increase the gloss after completely melting the toner. Met.
Also, the wax has a function of making the surface of the molten toner a mirror surface by coating it with a very thin surface, thereby improving the gloss. Since the gloss depends on the reflectance of the surface, even if the whitening of the wax layer is suppressed as described in Patent Document 2, it is not always sufficient to improve the gloss.

The image forming method described in Patent Document 3 is a method for preventing the dot image and the line image from being crushed when being nipped by a conveyance roller or the like with a high toner temperature. It was difficult to obtain a sufficient effect. Further, the volume change rate after fixing the toner image is defined as 30% and the area change rate as 20%. These values change depending on heating conditions, fixing pressure, toner loading amount, etc. It is not due to characteristics. Therefore, even if the volume change rate and the surface property change rate are defined, it is difficult to improve the surface properties of the toner such as gloss and gloss of the image.
In the image forming apparatus described in Patent Document 4, the fixing device adjacent to the air blower for cooling the toner image is also easily cooled by air, which increases power consumption or varies in the temperature in the axial direction of the heating roller provided in the fixing device. Sometimes occurred. Further, there is a possibility that warm air around the fixing device is scattered in the image forming apparatus, which may cause image deterioration due to a change in the sensitivity of the photosensitive member or a change in the charge amount of the developer.

  The present invention has been made in view of the above circumstances, and an object thereof is to realize an image forming apparatus and an image forming method that improve the smoothness of the image surface and increase the gloss without causing image deterioration.

The image forming apparatus of the present invention includes a fixing unit that heats and fixes a toner image formed on a recording medium to a temperature higher than the softening point of the toner, and the fixed toner image on the higher temperature side than the softening point of the toner. And a cooling means for rapidly cooling on the lower temperature side than the softening point.
Moreover, it is preferable that the cooling rate in the said cooling means is 150-250 degreeC / sec.

Further, the image forming method of the present invention heats and fixes the toner image formed on the recording medium at a temperature higher than the softening point of the toner, and then fixes the fixed toner image at a temperature higher than the softening point of the toner. It is characterized by rapid cooling from the side to a lower temperature side than the softening point.
Furthermore, the cooling rate is preferably 150 to 250 ° C./second.

According to the image forming apparatus and the image forming method of the present invention, the smoothness of the image surface can be improved and the gloss can be increased without causing image deterioration, and a high-quality image can be obtained.
In addition, according to the present invention, a deep color material original vivid hue can be obtained, which is particularly suitable for forming a color image.
Further, when the toner image is rapidly cooled, the recording medium is also cooled, so that the temperature of the discharged paper can be lowered.

Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus of the present invention. In the image forming apparatus 100 of this example, the image forming unit 10 is provided substantially at the center. The image forming unit 10 includes a photosensitive drum 1, and includes a charging unit 2, an exposing unit 3, a developing unit 4, a transfer unit 5, a cleaning blade 6, and a roller 7 disposed around the photosensitive drum 1. I have. A fixing unit 8 is disposed downstream of the photosensitive drum 1 in the recording medium (paper) conveyance direction, and a cooling unit 9 is disposed downstream of the fixing unit to cool the toner image. A sheet feeding unit 20 is provided at the lower part of the image forming apparatus 100, and a sheet feeding roller 21 is disposed downstream of the sheet feeding unit 20 in the sheet feeding direction. Further, a paper discharge unit 30 for discharging the recording medium 22 after image formation is provided.

The photosensitive drum 1 has an electrostatic latent image formed on the surface. As the photosensitive drum 1, it is preferable to use an amorphous silicon photosensitive member, and the constitution thereof is a carrier injection blocking layer made of Si: H: B: O or the like on a conductive substrate, and carrier excitation / transport made of Si: H or the like. A layer (photoconductive layer) and a surface protective layer made of SiC: H or the like are sequentially stacked.
The charging unit 2 is installed above the photosensitive drum 1 and uniformly charges the photosensitive drum 1.
The exposure unit 3 forms an electrostatic latent image on the photosensitive drum 1 based on a document image read from an image data input unit (not shown).

  The developing means 4 supplies toner to the surface of the photosensitive drum 1 on which the electrostatic latent image is formed to form a toner image. Here, the developing means 4 includes a rotary rack 40 and a plurality of developing devices 4Y, 4M, 4C, 4K. The rotary rack 40 rotates the plurality of developing devices 4Y, 4M, 4C, and 4K sequentially to the developing positions facing the photosensitive drum while performing rotation by rotating means (not shown) around the rotation shaft 41. Is. Among the plurality of developing devices, the yellow developing device 4Y, the magenta developing device 4M, the cyan developing device 4C, and the black developing device 4K are held side by side in the circumferential direction of the rotary rack 40 in the order of 4Y, 4M, 4C, and 4K. The developing devices are arranged at intervals of about 90 degrees in the circumferential direction.

  The transfer unit 5 transfers the toner image on the photosensitive drum 1 to a recording medium, and includes an intermediate transfer belt 51, primary transfer rollers 52 and 53, a driving roller 55, a secondary transfer counter roller 54, and a secondary transfer roller 56. It has. The intermediate transfer belt 51 is wound endlessly around the primary transfer rollers 52 and 53, the drive roller 55, and the secondary transfer counter roller 54, and is driven by the drive roller 55, and the toner image formed on the photosensitive drum 1. Plays the role of a transcript that is transferred and temporarily held. The secondary transfer roller 56 is disposed at a position facing the secondary transfer counter roller 54 on the outer peripheral surface of the intermediate transfer belt 51, and plays a role of secondary transfer of the toner image to the recording medium.

The cleaning blade 6 is for cleaning deposits such as residual developer remaining on the photosensitive drum 1, and for example, urethane rubber having a hardness of 77 ° is pressed against the photosensitive drum.
The roller 7 is in contact with the surface of the photosensitive drum 1 and has a buffer function for collecting and discharging toner. The roller 7 has a configuration in which a metal shaft is covered with foamed rubber, and is biased to the photosensitive drum 1 by a spring (not shown) at 9.8 N (one side: 4.9 N). Further, the roller 7 rotates with respect to the photosensitive drum 1 at a surface speed at the contact portion that is 1.2 times faster than the surface speed of the drum.

  As shown in FIG. 2, the fixing unit 8 includes a fixing roller (heating roller) 81 that is a rotatable fixing member, and a pressure roller 82 that is a pressure member that rotates while being in pressure contact with the fixing roller 81. Has been. A heater 83 such as a halogen lamp is disposed inside the fixing roller 81. A thermistor 84 is disposed in contact with the fixing roller 81, and the temperature of the surface of the fixing roller 81 is adjusted by controlling the voltage to the heater 83 through a temperature adjustment circuit. In this state, when the recording medium 22 is conveyed, the fixing roller 81 and the pressure roller 82 rotate at a constant speed, and the recording medium 22 passes through between the fixing roller 81 and the pressure roller 82. The unfixed toner image on the surface of the recording medium is melted and fixed by pressing and heating at a constant pressure and temperature from both sides, and a full-color image is formed on the recording medium 22. The recording medium 22 on which the image is fixed is separated 81 from the fixing roller by a separation claw (not shown) and is discharged outside the apparatus.

As the fixing roller 81 used in the fixing unit 8 as described above, for example, a surface of a metal tube such as an aluminum tube has a good releasability such as a fluorine-based resin, and has excellent heat resistance and wear resistance. Are preferably coated to form the outer layer. In the case where the image forming apparatus emphasizes image quality especially like an electrophotographic color copier, it is preferable to use a fixing roller 81 having silicone rubber as an outer layer of the roller. However, silicone rubber is slightly inferior to fluororesin, so it is desirable to apply silicone oil as a release agent to the surface of silicone rubber. In addition, you may use what wound the fluororesin sheet | seat around the silicone rubber.
On the other hand, the pressure roller 82 is not particularly limited. For example, it is preferable to use a silicone rubber roller having a solid iron bar or the like as a core.

As shown in FIG. 2, the cooling unit 9 includes a cooling roller 91 that is a rotatably disposed cooling body, and a conveying roller 92 that is a conveying body that rotates while being pressed against the cooling roller 91 and conveys the recording medium 22. It has.
The cooling unit 9 rapidly cools the toner image heated by the fixing unit 8 from the high temperature side of the toner to the low temperature side of the softening point (that is, in the vicinity of the softening point of the toner).

When the heated toner image is cooled, the resin contained in the toner shrinks during the cooling process, and shrinkage marks are easily formed on the surface of the image. Particularly, in the vicinity of the softening point of the toner, the volume change is remarkable and the resin is most likely to shrink. Further, when the toner image is gradually cooled (slowly cooled) near the softening point of the toner, the resin tends to shrink. When the shrinkage marks are formed, the smoothness of the image surface is lowered, so that it is difficult to obtain a high gloss image.
However, in the present invention, the shrinkage of the resin contained in the toner can be suppressed by rapidly cooling the toner image in the vicinity of the softening point of the toner. Therefore, the smoothness of the image surface is improved, and a high gloss image can be obtained.

The cooling rate of the toner image in the vicinity of the softening point of the toner is preferably 150 to 250 ° C./second, and more preferably 150 to 230 ° C./second. When the cooling rate is less than 150 ° C./second, the cooling is insufficient and the shrinkage of the resin tends to be difficult to suppress. On the other hand, if the cooling rate exceeds 250 ° C./second, cracks may occur on the image surface.
The surface temperature of the toner image after passing through the cooling roller 91 is preferably 10 to 35 ° C. lower than the softening point of the toner.

  As the cooling roller 91, for example, a heat pipe (made of copper) is preferably used. Since the heat pipe is excellent in heat transfer, the toner can be rapidly cooled by directly touching the toner image. However, since the adhesiveness with the toner is lowered, the cooling rate varies, and a non-uniform image is likely to occur. Therefore, for the purpose of ensuring releasability from the molten toner, a PFA (tetrafluoroethylene and perfluoroalkoxyethylene copolymer) sheet adhered to the surface of the heat pipe via a primer may be used. Good. The thickness of the PFA sheet is preferably about 30 μm when the outer diameter φ of the heat pipe is 20 mm. Furthermore, you may use what adhered the silicone rubber instead of the PFA sheet.

The heat pipe is preferably used by injecting a refrigerant. Examples of the refrigerant include alternative chlorofluorocarbons; ammonia refrigerants; hydrocarbons such as isobutane-based, methanol and ethanol; water and the like.
In the present invention, since the toner image can be cooled without using air or the like by using the cooling roller 91 as described above, the adjacent fixing unit 8 is hardly cooled. Therefore, power consumption can be increased, and variations in the axial temperature of the fixing roller 81 provided in the fixing unit 8 can be reduced. Further, since warm air around the fixing unit 8 is hardly scattered in the image forming apparatus, image deterioration due to a change in sensitivity of the photosensitive drum 1 or a change in the charge amount of the developer is less likely to occur.

  Further, as shown in FIG. 3, the end of the cooling roller 91 is extended to the outside of the sheet passing area and is connected to the heat radiation fin 93. A fan 94 is provided directly below the radiating fin 93, and the refrigerant injected into the cooling roller 91 is cooled in the radiating fin 93. Accordingly, even when continuous paper is passed, the surface temperature of the cooling roller 91 can be maintained at the ambient temperature + 3 ° C.

On the other hand, as the conveyance roller 92, for example, a silicone rubber roller can be used. The conveying roller 92 is in pressure contact with the cooling roller 91 with a pressing force of 29.4 (one side).
Note that the conveyance roller 92 is deprived of heat by the cooling roller 91 via the recording medium 22 and therefore does not need to be actively cooled.

The location of the cooling roller 91 and the conveying roller 92 is not particularly limited as long as the toner temperature after fixing does not fall to the vicinity of the softening point due to natural cooling. For example, from the outlet of the fixing nip portion to the inlet of the cooling nip portion. The distance d is preferably 10 to 50 mm.
Here, as shown in FIG. 2, the fixing nip portion is a contact portion between the fixing roller 81 and the pressure roller 82 in the conveyance direction of the recording medium 22, and the outlet of the fixing nip portion is fixing. It is the end portion 85 on the cooling means 9 side of the nip portion. On the other hand, the cooling nip portion is a contact portion between the cooling roller 91 and the conveyance roller 92 in the conveyance direction of the recording medium 22 as shown in FIG. 2, and the inlet of the cooling nip portion is the cooling nip portion. This is an end portion 96 on the fixing unit 8 side.

In addition, as shown in FIG. 2, the cooling means 9 includes a temperature sensor 95 before and after the cooling roller 91 so that the surface temperature of the toner image on the recording medium 22 can be measured before and after passing through the cooling roller 91. It may be provided.
As the temperature sensor 95, for example, a non-contact type thermometer can be used.

Next, the image forming method of the present invention will be described using the image forming apparatus 100 of FIG.
First, after the photosensitive drum 1 is charged by the charging unit 2, the rotary rack 40 rotates around the rotary shaft 41 provided at the center thereof. Then, the rotary rack 40 stops at the developing position where the developing device 4K corresponding to the first color, black, faces the photosensitive drum 1. In this state, exposure corresponding to black is performed by the exposure unit 3, and an electrostatic latent image corresponding to black is formed on the surface of the photosensitive drum 1. The electrostatic latent image is converted into a toner image by the developing device 4K, and the toner image formed on the surface of the photosensitive drum 1 is transferred onto the transfer belt 51 by a transfer bias applied to the primary transfer rollers 52 and 53. .
When the formation of the black toner image on the transfer belt 51 is completed in this way, the rotary rack 40 rotates around the rotation shaft 41 provided at the center thereof, and the developing device 4C corresponding to cyan develops. Positioned to position. Such an operation is also performed for other colors, cyan, magenta, and yellow, and a full-color toner image is formed on the transfer belt 51.

  As described above, the secondary transfer roller 56 is separated from the transfer belt 51 in the process of primary transfer of the toner image to the intermediate transfer belt 51. On the other hand, when a full-color toner image is formed on the transfer belt 51, the secondary transfer roller 56 is brought into contact with the transfer belt 51. At this time, the transfer belt 51 is formed on the recording medium 22 conveyed from the paper supply unit 20 to the transfer position by the paper supply roller 21 or the like at the same timing by the secondary transfer bias applied to the secondary transfer roller 56. A full color toner image is transferred.

Next, the full-color toner image transferred to the recording medium is fixed to the recording medium 22 by heating and pressing by the fixing unit 8 as shown in FIG. The heating temperature of the toner may be higher than the softening point of the toner, but is preferably 25 to 40 ° C. higher than the softening point of the toner.
The toner image heated by the fixing unit 8 is rapidly cooled by the cooling unit 9 from the high temperature side of the toner to the low temperature side of the softening point (that is, near the softening point of the toner). The cooling rate is preferably 150 to 250 ° C./second, and more preferably 150 to 230 ° C./second.
Thereafter, the recording medium 22 is discharged to the paper discharge unit 30 shown in FIG.

  On the other hand, the residual developer remaining on the photosensitive drum 1 is cleaned by the cleaning blade 6 and discarded in a waste toner container (not shown). The toner remaining on the transfer belt 51 is cleaned by bringing a cleaning device (not shown) of the transfer belt 51 into contact with the transfer belt 51 after the secondary transfer, and is discarded in a waste toner container (not shown). The cleaning device for the transfer belt 51 is separated from the transfer belt 51 after cleaning the entire circumference of the transfer belt 51.

As described above, according to the present invention, the toner image is rapidly cooled in the vicinity of the softening point of the toner, thereby suppressing the shrinkage of the resin contained in the toner and improving the smoothness of the image surface. And a high gloss image can be obtained.
In addition, according to the present invention, a deep color material original vivid hue can be obtained, which is particularly suitable for forming a color image.
Furthermore, since the recording medium (paper) is also cooled when the toner image is rapidly cooled, the temperature of the discharged paper can be lowered.
Further, since the smoothness of the image surface is improved, the stacking property of the discharged paper is also improved.

  In the present invention, since air is used for the cooling means, the fixing means adjacent to the cooling means is not easily cooled. Therefore, there is little increase in power consumption or variation in the axial temperature of the fixing roller provided in the fixing unit. Further, since the warm air around the fixing unit is hardly scattered in the image forming apparatus, image deterioration due to a change in the sensitivity of the photosensitive drum and a change in the charge amount of the developer hardly occurs.

Hereinafter, the present invention will be specifically described with reference to examples.
[Production of Toner A]
80 parts by mass of styrene, 20 parts by mass of 2-ethylhexyl methacrylate, 5 parts by mass of a cyan pigment (CI Pigment Blue 15: 3) as a colorant, 3 parts by mass of low molecular weight polypropylene, and a quaternary ammonium salt compound ( 2 parts by mass of “P-51” manufactured by Orient Chemical Industries Co., Ltd. and 2 parts by mass of a polymerization initiator 2,2-azobis (2,4-dimethylvaleronitrile) are added to a mixed solution of 1 part by mass of divinylbenzene as a crosslinking agent. These are added to 400 parts by mass of purified water, and 5 parts by mass of tribasic calcium phosphate and 0.1 part by mass of sodium dodecylbenzenesulfonate are added as suspension stabilizers, and a TK homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) is used. And stirred for 20 minutes at a rotational speed of 7000 rpm, and further subjected to a polymerization reaction in a nitrogen atmosphere at 70 ° C. and 100 rpm for 10 hours. To obtain a powder having an average particle diameter of 6.3 [mu] m. To this powder, 1.5 parts by mass of hydrophobic silica powder was added and mixed with a Henschel mixer (manufactured by Mitsui Mining) to obtain toner A (cyan toner) having a volume average particle size of 6.3 μm. The volume average particle size was measured with Multimizer III (Colestar Counter).
The charge amount of the obtained toner A was measured by a suction-type charge amount measuring device (Trek) and found to be 33 μC / g.

(Measurement of softening point)
The softening point of the obtained toner A was measured by a flow tester (manufactured by Shimadzu Corporation, “CFT-500A”) and found to be 117 ° C.
The softening point was measured using a measurement sample obtained by compressing 1.5 g of toner A into a cylindrical column having a diameter of 1 cm at a pressure of 16 MPa, extrusion pressure: 1.2732 MPa, temperature increase rate: 6 ° C./min, Under the conditions of die diameter: 1.0 mm and die length: 1.0 mm, the temperature when the measurement sample half-flowed was defined as the softening temperature.

[Manufacture of two-component developer]
<Manufacture of binder resin>
A monomer solution composed of 70 parts by mass of styrene and 30 parts by mass of butyl acrylate was used as a polymerization initiator, and 2,2′-azobis- (2,4-dimethylvaleronitrile) (“V-65” manufactured by Wako Pure Chemical Industries, Ltd.) 6 parts by mass and a solution containing 200 parts by mass of toluene as a solvent (having a condenser and refluxing toluene) were added dropwise over 3 hours. After the dropwise addition, polymerization was carried out for 12 hours while maintaining the temperature at 60 ° C., and then toluene was removed by distillation under reduced pressure. 1 was obtained.
<Manufacture of toner B>
Binder resin no. 1, 3 parts by mass of a quaternary ammonium salt compound (“P-51”, manufactured by Orient Chemical Co., Ltd.) as a charge control material, 4 parts by mass of a cyan pigment (“PB15-3”, manufactured by Ciba-Gaykey, Inc.) as a colorant, and A resin composition for toner was prepared by mixing 5 parts by mass of polyethylene wax (“155 microwax”, manufactured by Nippon Oil Co., Ltd.) as a release agent with a Henschel mixer, and then melt-kneading with a twin screw extruder.
The obtained resin composition for toner was finely pulverized with an airflow pulverizer and classified with an air classifier to obtain toner particles having an average particle diameter of 8 μm on a volume basis.
With respect to 100 parts by mass of the toner particles, 0.5 part by mass of hydrophobic silica (manufactured by Cabot, “TG820”) as a surface treatment agent, and 0 by titanium oxide (manufactured by Titanium Industry Co., “EC-100T”) .8 parts by mass was added and mixed with high agitation with a Henschel mixer to obtain toner B (cyan toner).
<Manufacture of two-component developer>
Toner B is blended with a ferrite carrier (“PF-60B” manufactured by Powder Tech Co., Ltd.) having an average particle diameter of 80 μm whose surface is coated with a silicone resin so that the toner concentration becomes 5% by mass, and the mixture is uniformly stirred and mixed. A component developer was obtained.

(Measurement of softening point)
It was 110 degreeC when the softening point of the obtained toner B was measured with the flow tester (Shimadzu Corporation make, "CFT-500A").
The softening point was measured in the same manner as toner A.

[Examples 1 to 4]
<Configuration of image forming apparatus>
The image forming apparatus having the configuration shown in FIGS. 1 and 2 was appropriately modified according to the developer. Further, the toner A (cyan toner) obtained previously was used as a developer, and the developer was stored in a developing container. The configurations of the fixing unit 8 and the cooling unit 9 are as follows.
(Fixing means)
As the fixing roller 81, the surface of an aluminum tube having an outer diameter of 30 mm and a wall thickness of 1.0 mm is coated with a silicone rubber having a hardness of 5 degrees (JIS-A) and a thickness of 200 μm, and a PFA having a thickness of 30 μm is applied to the surface. (Ethylene fluoride and perfluoroalkoxyethylene copolymer) tube bonded with a primer was used. A halogen heater lamp 83 is arranged inside the fixing roller 81, and the lamp lighting is controlled by a thermistor 84 in contact with the surface of the fixing roller 81 so that the surface temperature of the fixing roller is always 170 ° C.
As the pressure roller 82, a solid iron rod having a core metal having an outer diameter of 18 mm was used on a silicone rubber core having an outer diameter of 30 mm, a hardness of 5 degrees (JIS-A), and a thickness of 6 mm.

(Cooling means)
The cooling roller 91 and the conveying roller 92 opposed to the cooling roller 91 have a distance d from the outlet of the fixing nip portion to the inlet of the cooling nip portion of 30 mm (that is, since the recording medium conveying speed is 150 mm / sec. Was placed 0.2 seconds downstream).
As the conveying roller 92, a silicone rubber roller having an outer diameter of 20 mm and a hardness of 5 degrees (JIS-A) was used.
As the cooling roller 91, cooling rollers A to D were used in which alternative chlorofluorocarbon (refrigerant) was injected into a heat pipe having an outer diameter φ of 20 mm. In addition, the injection amount of the alternative chlorofluorocarbon to be injected into each heat pipe was adjusted so that the surface temperature of the toner image after passing through the cooling roller became the value shown in Table 1.

<Evaluation>
Each cooling roller was attached to the image forming apparatus, and an image sample was taken while recording the surface temperature of the toner image before and after passing through the cooling roller (38 mm = 0.25 seconds later). The measurement interval was 19 mm upstream and downstream in the transport direction with the intersection of the straight line connecting the rotation center of the cooling roller 91 and the rotation center of the transport roller 92 and the transport path of the recording medium as the center. Further, “Color Copy paper, basis weight 90 g / m ² ” manufactured by mondi was used as a recording medium. The toner amount on the recording medium was 1.5 mg / cm ² , and the surface temperature of the toner image before passing through the cooling roller was 140 ° C.
Table 1 shows the surface temperature of the toner image after passing through the cooling roller, the cooling speed in the cooling means, and the glossiness of the image surface of the image sample when the number of printed sheets is 200. However, the cooling rate and the glossiness were determined as follows.

(Cooling rate)
The cooling rate was calculated from the following formula (1).
Cooling rate [° C./second]={(surface temperature of toner image before passing through cooling roller) − (surface temperature of toner image after passing through cooling roller)} / 0.25 (1)
(Glossiness)
The glossiness of the image surface of the image sample was measured with a gloss meter (manufactured by HORIBA, Ltd., “Handy Gloss Checker IG-331”, incident angle: 60 °), and evaluated from the gloss value according to the following evaluation criteria. did. ◎ and ○ are acceptable.
A: The glossiness is 41 or more.
○: Glossiness is 31 or more and less than 40.
X: Glossiness is less than 30.

[Example 5]
Evaluation was performed in the same manner as in Example 2 except that a two-component developer produced from toner B was used as the developer. The results are shown in Table 1.

[Example 6]
Evaluation was performed in the same manner as in Example 3 except that a two-component developer produced from toner B was used as the developer. The results are shown in Table 1.

[Comparative Example 1]
As the cooling roller, a cooling roller E was used in which an alternative chlorofluorocarbon was injected into the heat pipe while adjusting the injection amount of the alternative chlorofluorocarbon so that the surface temperature of the toner image after passing through the cooling roller became the value shown in Table 1. Except for the above, evaluation was performed in the same manner as in Examples 1 to 4. The results are shown in Table 1.

[Comparative Example 2]
Evaluation was performed in the same manner as in Examples 1 to 4, except that no cooling roller was attached. The results are shown in Table 1.

As apparent from Table 1, the glossiness of the images obtained in each example was higher than that of the comparative example. Moreover, it was clear that it was highly glossy visually, and a high-quality image that could only be obtained with coated paper was obtained. In Examples 1 to 6, the toner image was rapidly cooled from the higher temperature side to the lower temperature side than the softening point (117 ° C. or 110 ° C.) of the cyan toner (toner A or toner B) used in this example. It can be presumed that the shrinkage of the resin contained in is effectively suppressed, and as a result, the smoothness of the image surface is improved and the glossiness is increased. However, in the case of Example 1, since the cooling rate was higher than that of Examples 2 and 3 (that is, the temperature was lowered to 40 ° C. or more below the softening point of the cyan toner), the image surface was cracked. It was. Therefore, the gloss value was lower than those in Examples 2 and 3.
On the other hand, in Comparative Example 1, since the toner image was not rapidly cooled in the vicinity of the softening point of the cyan toner, the glossiness was inferior to that of the Example.
In Comparative Example 2, since the cooling roller was not used, the toner image was hardly cooled and the glossiness was further inferior.

In addition, as a result of observing the image surface of the image sample obtained by each Example and the comparative example with the digital microscope (the Keyence Corporation make, "VHX-600", 1000-2000 times), in each Example, it is slightly As the glossiness increased, the size of the spots became smaller, the interval was narrower, and the depth became shallower.
On the other hand, in each comparative example, spots larger than those of the example, wide in intervals, and large indentations were confirmed.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus of the present invention. It is a schematic block diagram which shows an example of a fixing means and a cooling means. It is a side view of the cooling means shown in FIG.

Explanation of symbols

  2: charging means, 3: exposure means, 4: developing means, 5: transfer means, 8: fixing means, 81: fixing roller, 82: pressure roller, 9: cooling means, 91: cooling roller, 92: transport roller , 100: Image forming apparatus

Claims (4)

  Fixing means for fixing the toner image formed on the recording medium by heating to a temperature higher than the softening point of the toner, and fixing the toner image from the high temperature side to the lower temperature side than the softening point of the toner, An image forming apparatus comprising: a cooling unit that rapidly cools the image forming apparatus.   The image forming apparatus according to claim 1, wherein a cooling rate in the cooling unit is 150 to 250 ° C./second.   After the toner image formed on the recording medium is heated and fixed at a temperature higher than the softening point of the toner, the fixed toner image is rapidly moved from the high temperature side to the low temperature side from the softening point. And an image forming method.   The image forming method according to claim 3, wherein the cooling rate is 150 to 250 ° C./second.

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