JP2002169400A - Image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming method that prevents the occurrence of hot offset and ensures satisfactory image formation for a long time, even in image formation using a high processing speed and a heat fixing roll of a small diameter. SOLUTION: The image forming method includes a step of forming an electrostatic latent image on an electrostatic carrier, a step of forming a toner image on the electrostatic carrier by use of developer, a step of transferring the toner image to a transfer body, and a step of fixing the transferred toner image on the transfer body by use of a heat fixing roll and a pressure member pressed to the heat fixing roll. In the image forming method, (1) one-component developer is used as the developer, and an amount of free magnetic powder contained in the developer is <=0.1 vol.%, and (2) the outside diameter of the heat fixing roll is <=40 mm and the processing speed thereof is >=200 mm/s.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a toner image formed by developing an electrostatic latent image formed on an electrostatic carrier using a developer, transferring the toner image to a transfer member, and thermally fixing the toner image. To an image forming method.

[0002]

2. Description of the Related Art Developing systems in image forming apparatuses such as printers and copiers are roughly classified into two-component developing systems and one-component developing systems. A two-component developing method including a toner and a carrier such as iron powder has been widely used, but has a disadvantage that the toner is attached to the carrier surface to deteriorate the developer. In addition, since only toner is consumed in the two-component developing method, an apparatus such as an automatic density controller for maintaining a constant mixing ratio of toner and carrier is required, and the developing apparatus becomes large.

On the other hand, a magnetic one-component developing system using a toner containing a magnetic substance inside without using a carrier,
Since a device such as an automatic density adjusting device such as a two-component developing system is not required, the developing device is compact, and since there is no carrier contamination, maintenance such as carrier replacement becomes unnecessary. For this reason, copiers, printers and multifunction machines using magnetic one-component development methods
It is becoming mainstream in the field of personal copy for small offices and individuals such as SOHO.

In an image forming method for fixing a toner image developed by using the above-mentioned developer on a transfer member by heating and pressing, it is important to enhance the smoothness of the surface of the heat fixing roll. One. That is, if there is a depression on the surface of the heat fixing roll, the toner enters the depression. At this time, when printing a plurality of sheets in succession, the toner that has entered the dent adheres to the subsequent paper and is removed.
In a single-printer, it is not removed.In personal printers and facsimile machines, which use many single-prints, the toner that enters the dents is deformed by the heat of the overshoot when the heating member returns from the standby state, and the volatile components evaporate and dents However, non-visual offsets (hereinafter also referred to as NVOs) occur although they do not directly affect the image.
Then, as the number of fixed images advances, the contamination by NVO progresses, and the ability to separate from the toner image on the surface of the heat fixing roll decreases, resulting in hot offset.

In order to solve the above-mentioned problem, the surface of the heat fixing roll is coated with a special resin, and the surface of the roll is smoothed to such an extent that the toner is not embedded. (JP-A-56-69674).

[0006]

In recent years, there has been an increasing demand for higher speed and smaller size of image forming apparatuses. Accordingly, the process speed has been increased, and image forming using a small diameter heat fixing roll has been performed. . However, in the miniaturized and high-speed image forming process, even when image formation is performed using the above-described conventional technology, the contamination of the heat fixing roll surface progresses as the number of fixed images advances, and There is a problem that the releasability of the resin is reduced and hot offset occurs.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and is intended to increase the process speed and to perform image formation using a small-diameter heat fixing roll. Suppress the occurrence of hot offset,
An object of the present invention is to provide an image forming method capable of forming a good image over a long period of time.

[0008]

Means for Solving the Problems In order to achieve the above object, the inventor has made intensive studies on the cause of the decrease in the releasability on the surface of the heat fixing roll. And it was found that embedding of the free magnetic powder contained in the developer into the small dents still existing even when the surface of the roll was smoothed was a major factor in lowering the releasability. In particular, when increasing the process speed and forming an image using a small-diameter heat-fixing roll, the surface of the heat-fixing roll is severely worn by the free magnetic powder, causing many scratches on the roll surface, or It has been found that when the magnetic powder enters or the flaw is large, the toner is buried in the flaw, and this is the main factor that significantly reduces the releasability.
The present invention has been made based on such findings.

That is, the image forming method according to the present invention comprises:
A step of forming an electrostatic latent image on the electrostatic carrier, a step of forming a toner image on the electrostatic carrier using a developer, a step of transferring the toner image on a transfer body, and a heat fixing roll Fixing the toner image transferred onto the transfer member by using a pressure member pressed against the heat fixing roll, and (1) using a magnetic one-component developer as a developer, (2) The outer diameter of the heat fixing roll is 40 mm or less, and the process speed is 200 mm / s or more.

In this method, since the amount of the free magnetic powder contained in the developer is set to 0.1 vol% or less, it is possible to reduce the possibility that the free magnetic powder is buried in the depression existing on the surface of the heat fixing roll. In particular, if the process speed is 2
Even when image formation is performed at a high speed of not less than 00 mm / s and using a small apparatus in which the outer diameter of the heat fixing roll is 40 mm or less, scratches on the surface of the heat fixing roll due to free magnetic powder. Can be reduced, and the possibility that free magnetic powder can enter the wound on the roll surface or that toner can be embedded in the wound can be reduced.

In the image forming method according to the present invention, the heat fixing roll may have a release resin layer containing inorganic particles in a fluorine resin on the outer peripheral surface. By doing so, the wear resistance of the heat fixing roll surface is improved. When a releasing resin layer containing inorganic particles in a fluorine-based resin is formed on the outer peripheral surface of the heat fixing roll, if the developer contains a large amount of free magnetic powder, the free magnetic powder surrounds the inorganic particles. In some cases, the particles are scraped and worn, and the inorganic particles are detached to form pits on the surface of the heat fixing roll. NVO is generated when toner is buried in the pits, and hot offset occurs when NVO proceeds. On the other hand, in the image forming method according to the present invention, the amount of the free magnetic powder contained in the developer is set to 0.1 vol% or less. This is preferable because the fear that inorganic particles are desorbed due to abrasion to form pits is reduced.

Further, in the image forming method according to the present invention, the heat fixing roll has a perfluoroalkoxy resin (PF
It may be characterized by having a release resin layer composed of A). By doing so, the releasability, durability, and heat resistance of the heat fixing roll surface are improved.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of an image forming method according to the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram schematically showing an image forming section 10 provided in an image forming apparatus such as a printer or a copying machine, which can suitably carry out the image forming method according to the present embodiment. FIG. 2 is a configuration diagram schematically showing the fixing device 16 included in the image forming unit 10.

The image forming section 10 includes a photosensitive member (latent image carrier)
11, a charging device 12 for charging the photoconductor 11, an exposure device 13 for outputting a laser beam modulated based on image data, and a toner image formed on the photoconductor 11 by exposure by the exposure device 13. A transfer device 15 for transferring the toner image formed on the photoconductor 11 onto a transfer member P such as paper; and a fixing device for fixing the toner image 21 transferred onto the transfer member P. Device 16,
And a removing device 17 for removing toner and the like remaining on the photoconductor 11.

As shown in FIG. 2, the fixing device 16 heats and presses the toner image 21 on the transfer member P to fix the toner image 21 thereon. And a temperature sensor 24 for detecting the temperature of the outer peripheral surface of the heat fixing roll 22 provided close to the outer peripheral surface of the heat fixing roll 22.
And a pressure roll 25 arranged opposite to the heat fixing roll 22.

The heat fixing roll 22 includes a core metal 26 and a core metal 2.
6 and a release resin layer 27 for preventing the offset phenomenon of the toner image 21 provided on the surface of the toner image 21. As a material for forming the metal core 26, iron, stainless steel, or aluminum having excellent thermal conductivity is generally used.
Other metals or the like may be used.

The resin constituting the release resin layer 27 includes:
For example, fluorine resins such as silicone rubber, a copolymer of terafluoroethylene and perfluoroalkyl vinyl ether, a copolymer of tetrafluoroethylene and ethylene, and a copolymer of tetrafluoroethylene and hexafluoroethylene are exemplified. Further, at this time, it is preferable to add inorganic particles to the resin in order to harden the surface of the heat fixing roll 22 and suppress abrasion due to paper passing stress. Ceramic particles are preferred as the inorganic particles, and Si particles
C is particularly preferably used. In addition, the particle diameter of the inorganic fine particles is preferably 1 to 3 μm.

In a system in which inorganic particles are not added, the resin constituting the release resin layer 27 is preferably made of a perfluoroalkoxy resin (PFA). If you do this,
The balance between the releasability and the durability of the surface of the heat fixing roll 22 is achieved.

In order to improve the adhesion to the core metal 26, it is preferable to apply a primer treatment or the like to the inner surface of the release resin layer 27. Since the heat fixing roll 22 has the release resin layer 27 as described above, the offset resistance can be improved without using a release agent.

Here, the thickness of the release resin layer 27 is 10 μm.
It is preferably from 50 to 50 μm, and more preferably from 10 to 40 μm. When the thickness of the release resin layer 27 is smaller than 10 μm, the life of the heat fixing roll 22 tends to be shortened due to abrasion. If the thickness of the release resin layer 27 is larger than 50 μm, the thermal conductivity is deteriorated, and a fixing failure due to temperature unevenness on the surface of the heat fixing roll 22 occurs, and a temperature rise during heating is slowed to increase a warm-up time. Tends to be longer.

The heating member 23 is composed of, for example, a Colts lamp or a ceramic heater, and is connected to an electric circuit for controlling a heating state based on the outer peripheral surface temperature of the heat fixing roll 22 detected by the temperature sensor 24. . The temperature sensor 24 is configured by a thermosensitive resistance element such as a thermocouple or a thermistor.

The pressure roll 25 is formed, for example, by covering a metal core roll 28 with a silicone rubber 29 or the like, and is arranged so that the transfer member P can pass between the core roll 28 and the heat fixing roll 22.

In the image forming apparatus provided with the image forming section 10 having such a configuration, as shown in FIG. 1, the photosensitive member 11 can rotate around the support 19 at a predetermined rotational speed in the direction of arrow A. In synchronization with this, the transfer roll 15, the heat fixing roll 22 of the fixing device 16, the pressure roll 2
5 can rotate.

Next, an image forming method according to the present embodiment using an image forming apparatus provided with the image forming section 10 having the above-described configuration will be described.

First, an electrostatic latent image is formed on the photoconductor 11 charged by the charging device 12. For example, if the image forming apparatus is a copying machine, a laser beam modulated based on image data read by a reading unit (not shown) is output from the exposure device 13 onto the photoconductor 11 to form an electrostatic latent image. . If the image forming apparatus is a printer, a laser beam modulated based on image data sent from a personal computer or the like is output from the exposure device 13 onto the photoconductor 11 to form an electrostatic latent image.

Next, the electrostatic latent image is developed by the developing device 14 using a developer to form a toner image on the photoconductor 11. As the developer (toner), a magnetic one-component developer containing at least a binder resin and a magnetic powder is used.

Examples of the binder resin usable in the present embodiment include known synthetic resins and natural resins. For example, one or more vinyl monomers or copolymers can be mentioned. Typical vinyl monomers are styrene,
Propylene, butylene, ethylenically unsaturated monoolefins such as isobutylene, for example, vinyl chloride, vinyl bromide, vinyl fluoride, vinyl acetate, vinyl propionate,
Vinyl benzoate, vinyl formate, vinyl stearate, vinyl esters such as vinyl caproate, for example, methyl acrylate, ethyl acrylate, n-butyl acrylate,
Ethylenic monocarboxylic acids such as isobutyl acrylate, dodecyl acrylate, n-octyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, methyl-α-chloroacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate and Esters thereof, for example, acrylonitrile, methacrylonitrile, acrylamide, etc.
For example, ethylenic carboxylic acids and esters thereof such as dimethyl maleate, diethyl maleate and dibutyl maleate, for example, vinyl methyl ketone, vinyl hexyl ketone, vinyl ketones such as methyl isopropenyl ketone, for example, vinyl methyl ether, vinyl isobutyl ether, Vinyl ethers such as vinyl ethyl ether and the like; vinylidene halides such as vinyl denchloride and vinylidene chlorofluoride; and N-vinyl compounds such as N-vinyl pyrrole, N-vinyl carbazole, N-vinyl indole and N-vinyl pyrrolidone And the like.

The magnetic powder that can be used in the present embodiment includes known magnetic substances, for example, metals such as iron, cobalt and nickel and alloys thereof, Fe ₃ O ₄ , γ-Fe
Examples include metal oxides such as ₂ O ₃ and cobalt-added iron oxide, various ferrites such as MnZn ferrite and NiZn ferrite, magnetite, hematite and the like. Further, those whose surfaces are treated with a silane coupling agent or a titanate coupling agent may be used. Particularly, those coated with a polymer have excellent affinity for a binder resin, etc. It is also desirable from the viewpoint of preventing desorption. The particle size of the magnetic powder is preferably from 50 to 400 nm, more preferably from 100 to 250 nm.

This magnetic powder is preferably contained in an amount of 30 to 70% by weight, more preferably 35 to 65% by weight, based on 100% by weight of the total amount of the developer. If the content of the magnetic powder is less than 30% by weight, the binding force of the magnet on the toner carrier of the developing device 14 is reduced, and a problem of toner scattering occurs. In addition, the content of the magnetic powder is 70% by weight.
When it exceeds, there is a problem that the reproducibility of the concentration is reduced.

In the present embodiment, the developer may contain a release agent. Examples of usable release agents include aliphatic hydrocarbon waxes such as low molecular weight polyethylene, low molecular weight polypropylene, microcrystalline wax and paraffin wax, and fatty acid waxes such as carnauba wax and montanic acid ester wax. These waxes may be used alone or in combination of two or more.

In particular, by using low molecular weight polyethylene wax and low molecular weight polypropylene wax together,
It is possible to obtain a toner-fixed image excellent in rubbing stress, and to improve a phenomenon (smudge phenomenon) in which when a toner image after fixing is rubbed with white paper, a part of the toner image is broken and transferred to rubbed white paper. There are advantages that can be.

In this embodiment, a colorant may be added to the developer to adjust the color tone. The colorant that can be used is not particularly limited, and a known colorant can be used, and can be appropriately selected depending on the purpose. As the colorant, for example, carbon black, organic pigments and dyes can be appropriately used.

The developer may contain various substances for the purpose of charge control, electric resistance control and the like. For example, fluorinated surfactants, salicylic acid, chromium dyes such as chromium complex, polymeric acids such as copolymers containing maleic acid as a monomer component, quaternary ammonium salts, azine dyes such as nigrosine, carbon You may contain black etc.

Further, the developer may contain a petroleum resin in order to satisfy the pulverizability and the heat preservability. The petroleum-based resin is synthesized from diolefins and monoolefins contained in a cracked oil fraction by-produced from an ethylene plant that produces ethylene, propylene, etc. by steam cracking of petroleum.

Further, the developer may contain a fluidity improver. Usable fluidity improvers include PMMA, nylon, melamine, benzoguanamine, fluorine-based spherical particles or various known inorganic compounds as resin powder,
For example, SiO ₂ , TiO ₂ , Al ₂ O ₃ , MgO, Cu
O, ZnO, SnO ₂ , CeO ₂ , Fe ₂ O ₃ , BaO, C
aO, K ₂ O, Na ₂ O, ZrO ₂ , CaO.SiO ₂ , C
aCO ₃ , K ₂ O (TiO ₂ ) n, MgCO ₃ , Al ₂ O _3.
2SiO ₂ , BaSO ₄ , MgSO _{4 and the} like. Among them, it is preferable to use SiO ₂ , TiO ₂ , and Al ₂ O ₃ . These fluidity improvers may be used alone or in combination of two or more. The particle size of the fluidity improver is preferably 0.1 μm or less, and the amount of addition is preferably 0.1 to 20% by weight based on 100% by weight of the total amount of the developer.

In the present embodiment, the particle size of the developer can be arbitrarily set, but it is preferable that the volume average particle size is 4 to 8 μm in view of image quality. If the volume average particle size exceeds 8 μm, it tends to be difficult to obtain high image quality. If the volume average particle size is less than 4 μm, stable charging will be difficult to obtain, and fog tends to occur.

In this embodiment, it is necessary that the amount of free magnetic powder contained in the developer is 0.1 vol% or less. Here, the free magnetic powder refers to a magnetic powder detached from the developer and a magnetic powder that is easily detached by contact between the developer particles due to a flow in the developing device 14 or the like.

In the present embodiment, the developer can be produced by any known method such as a pulverization method and a polymerization method. In the pulverization method, the binder resin, the magnetic powder, the release agent, the colorant, and the like are charged into a heat kneader, melt-kneaded, cooled, and then pulverized and classified. At this time, at the time of melting by the hot kneader, the MI (Melt Index) of the molten raw material is 1
8 g / 10 min or less, preferably 18 to 1 g / 10 m
It is preferable to knead the mixture under such conditions as to make the mixture in. MI is 1
If it exceeds 8 g / 10 min, the stress applied to the resin at the time of kneading is insufficient, and the dispersion of the magnetic powder is not sufficient, so that an aggregate of the magnetic powder is easily generated. When the aggregates of the magnetic powder are generated in the slab in this way, the powder breaks at the interface of the magnetic powder during pulverization from the slab, and the magnetic powder aggregates are easily exposed on the developer surface. The exposed magnetic powder agglomerates are easily detached due to friction with the developer, and even if fine particles are removed at the time of manufacture, a large amount of free magnetic powder is generated in the container of the developing device 14, and The amount of free magnetic powder contained may exceed 0.1 vol%. Here, MI can be measured according to the method prescribed in ASTM D1238 and JIS K6760. The MI itself changes depending on the measurement conditions, but here, the load is 5.0 k.
gf, measured at 150 ° C.

In order to reliably maintain the amount of free magnetic powder contained in the developer at 0.1 vol% or less, resin-coated magnetic powder may be used. Resins usable for resin coating include polyethylene, polypropylene, polystyrene, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether, polyvinyl ketone, and vinyl chloride-vinyl acetate copolymer. Coalesce, styrene-acrylic acid copolymer, straight silicone resin consisting of organosiloxane bond, fluororesin, polyester,
Examples thereof include polyurethane, polycarbonate, phenol resin, amino resin, melamine resin, benzoguanamine resin, urea resin, and epoxy resin.

Here, the description returns to the image forming method according to this embodiment. After developing the electrostatic latent image formed on the photoconductor 11 to form a toner image, the toner image is transferred onto a transfer body P such as paper. The transfer of the toner image is performed by the photoconductor 1
The transfer is performed by transporting the transfer body P between the transfer roll 1 and the transfer roll 15.

Finally, the transfer body P is transported to the Nip portion 30 of the heat fixing roll 22 and the pressure roll 25 pressed against the heat fixing roll 22, and heated and pressed to fix the toner image 21 on the transfer body P. Let it.

Here, the rotation speed of the heat fixing roll 22 (ie, the rotation speed of the photoconductor 11) as the process speed is set to 200 mm / sec or more. As described above, in a medium-high speed image forming process in which the rotation speed of the heat fixing roll 22 is 200 mm / sec or more, the image forming method according to the present embodiment has a remarkable function and effect described later. The rotation speed of the heat fixing roll 22 is 200 to 50.
It is preferably 0 mm / sec. When the rotation speed of the heat fixing roll 22 exceeds 500 mm / sec,
The centrifugal force acting on the upper toner increases, causing the toner to be scattered, and the fixation on the transfer member P is deteriorated, so that the image quality tends to deteriorate. The rotation speed of the heat fixing roll 22 is more preferably 200 to 400 mm / sec, further preferably 200 to 350 mm / sec, and particularly preferably 205 to 300 mm / sec.

The outer diameter of the heat fixing roll 22 is 40 mm.
The following is assumed. If the outer diameter of the heat fixing roll 22 exceeds 40 mm, the heating member 23 having a large heat capacity is required and the fixing device 16 itself becomes large, which is not preferable from the viewpoint of low power consumption and space saving. The heat fixing roll 2
The outer diameter of 2 is preferably 20 to 40 mm. When the outer diameter of the heat fixing roll 22 is less than 20 mm, the mechanical strength of the roll base tube is reduced, which tends to cause blurring in the axial direction, thereby lowering the fixability of the toner image and the Nip portion with the pressure roll 25. For example, a problem may occur in that the area of the toner image 30 cannot be obtained, and sufficient heat cannot be applied to the toner image.

As described above, an image is formed on the transfer body P through the above steps.

Next, the operation and effect of the image forming method according to this embodiment will be described.

In the image forming method according to the present embodiment, since the amount of free magnetic powder contained in the developer is set to 0.1 vol% or less, there is a possibility that the free magnetic powder is buried in the depression existing on the surface of the heat fixing roll 22. Can be reduced. In particular, even when image formation is performed at a high speed such as a process speed of 200 mm / s or more and using a small apparatus in which the outer diameter of the heat fixing roll 22 is 40 mm or less, the free magnetic powder may be used. The occurrence of scratches on the surface of the heat fixing roll 22 can be reduced, and the risk of free magnetic powder entering the scratches formed on the roll surface and the toner being buried in the scratches can be reduced. As a result, it is possible to suppress a remarkable decrease in the releasability of the surface of the heat fixing roll 22, suppress the occurrence of hot offset, and form a good image over a long period of time.

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

[0049]

EXAMPLES The particle size and SiC particle size of the developer (toner) used in this example were measured with a particle size analyzer TA-II manufactured by Coulter Counter Co., Ltd. at an aperture diameter of 100 μm.

The amount of free magnetic powder was measured according to the following procedure. First, place 1.000 toner in a 100cc beaker.
0 g was precisely weighed (about ± 0.0001 g). Next, after adding 25 ml of Triton solution and leaving it for about 10 minutes,
ec stirred. Then, the solution containing the toner was irradiated with ultrasonic waves to disperse the free magnetic powder in the Triton solution. Finally, the amount of free magnetic powder was measured by an ultraviolet-visible spectrophotometer by comparison with a previously prepared calibration curve (500 nm).

Example 1 (1) Formation of developer Binder resin: styrene-butyl acrylate copolymer (composition ratio 75/25, weight average molecular weight Mw: 8000)
0) 46 parts by weight-Magnetic powder: hexahedral magnetite (manufactured by Toda Kogyo Co., Ltd .: MTH009)
F Particle size: 0.2 μm) 50 parts by weight ・ Negative charge control agent: 1 part by weight of (Fe-containing azo dye) ・ Release agent: Low molecular weight polypropylene (softening point: 149 ° C.)
2 parts by weight, low molecular weight polyethylene (softening point 120 ° C) 1
Parts by weight The above-mentioned materials were powder-mixed by a Henschel mixer, and kneaded with an extruder having a set temperature of 140 ° C. (melt viscosity of the materials at the time of kneading: MI 16.5 g / 10 min). After cooling, coarse and finely pulverized, 50% volume diameter D50
Of 6.9 μm. Further, this pulverized product was classified to obtain a classified product having a D50 of 7.1 μm and a particle size of 5 μm or less: 22 pop%. R972 (colloidal silica manufactured by Nippon Aerosil Co., Ltd.) based on 100 parts by weight of the obtained toner classified product
1.0 parts by weight was externally added using a Henschel mixer to obtain a magnetic toner. When the amount of free magnetic powder in the obtained magnetic toner was measured, it was 0.06 vol%.

(2) Image Forming Apparatus A modified model of LaserPress 4161II manufactured by Fuji Xerox Co., Ltd. equipped with a heat fixing roll formed as described below was used. The heat fixing roll forms a release resin layer by applying a perfluoroalkoxy resin (PFA) as a fluorine-based resin to a surface of a core metal having an outer diameter of 35 mm so as to have a thickness of 37 μm. The average particle size of the mold resin layer is 2.
It was formed by adding 4.2% by weight of 4 μm SiC particles.

(3) Image formation and evaluation The temperature was adjusted so that the fixing process speed (namely, the rotation speed of the heat fixing roll) was 220 mm / s.
After printing one sheet at a low temperature and low humidity of 15 ° C. and a humidity of 15 RH%, 5000 sheets of images were formed by intermittent running with waiting for one minute. At this time, the first image density (Initia
l-density) and the image density of the 5000th sheet
4 Measured with a densitometer. After running 5000 sheets, the surface of the heat-fixing roll was visually observed to check the toner adhesion. Furthermore, after running 5000 sheets, the temperature at which hot offset occurs was measured.

[Example 2] (1) Generation of developer Binder resin: polyester resin (Mw45000) 51
Part by weight-Magnetic powder: 45 parts by weight of octahedral magnetite coated with polyester resin (particle size: 0.22 µm)-Release agent: Polypropylene wax (trade name: P200)
3 parts by weight (manufactured by Mitsui Chemicals, Inc.), 1 part by weight of polyethylene wax (trade name: PE130 Client Japan) The above materials were powder-mixed with a Henschel mixer, and extruded at a set temperature of 160 ° C. (melting of materials during kneading). (Viscosity: MI 17.8 g / 10 min). After cooling, coarse and finely pulverized, 50% volume diameter D50
Of 6.3 μm. The pulverized product was further classified to obtain a classified product having a D50 of 6.8 μm and a particle size of 5 μm or less: 29 pop%. TS720 (colloidal silica manufactured by Cabot Corp.)
The parts by weight were externally added using a Henschel mixer to obtain a magnetic toner. When the amount of free magnetic powder in the obtained magnetic toner was measured, it was 0.02 vol%.

(2) Image Forming Apparatus A modified model of LaserPress 4161II manufactured by Fuji Xerox Co., Ltd. equipped with a heat fixing roll formed as described below was used. The heat fixing roll was formed by covering the surface of a core metal having an outer diameter of 35 mm with a PFA tube so as to have a thickness of 35 μm.

(3) Image formation and evaluation Image formation was performed in the same manner as in Example 1 except that the fixing process speed was changed to 280 mm / s, and evaluation was performed in the same manner as in Example 1. Comparative Example 1 (1) Generation of Developer Binder Resin: Polyester Resin (Mw30000) 46
Parts by weight ・ Magnetic powder: hexahedral magnetite (Made by Toda Industries: MTH009
F Particle size: 0.2 μm) 50 parts by weight ・ Release agent: polypropylene wax (trade name: P200)
3 parts by weight (manufactured by Mitsui Chemicals, Inc.), 1 part by weight of polyethylene wax (trade name: PE130 Client Japan) The above materials were powder-mixed with a Henschel mixer, and extruded at a set temperature of 160 ° C. (melting of materials during kneading). (Viscosity: MI 22 g / 10 min). After cooling, coarse pulverization and fine pulverization were performed to obtain a pulverized product having a 50% volume diameter D50 of 6.6 μm. The pulverized product was further classified to obtain a classified product having a D50 of 6.8 μm and a particle size of 5 μm or less: 31 pop%. TS720 (colloidal silica manufactured by Cabot Corp.)
The parts by weight were externally added using a Henschel mixer to obtain a magnetic toner. When the amount of free magnetic powder in the obtained magnetic toner was measured, it was 0.14 vol%.

(2) Image Forming Apparatus Laser Press 416 manufactured by Fuji Xerox Co., Ltd.
A modified model II was used.

(3) Image formation and evaluation Using the above-mentioned developer, the fixing process speed was 26
An image was formed in the same manner as in Example 1 except that the speed was set to 0 mm / s, and the evaluation was performed in the same manner as in Example 1.

Comparative Example 2 (1) Generation of Developer The same developer as that used in Comparative Example 1 was used.

(2) Image Forming Apparatus Laser Press 416 manufactured by Fuji Xerox Co., Ltd.
A modified model II was used.

(3) Image formation and evaluation Using the developer described above, the fixing process speed was 22
An image was formed in the same manner as in Example 1 at 0 mm / s, and the evaluation was performed in the same manner as in Example 1.

Table 1 shows the results obtained in Examples 1 and 2 and Comparative Examples 1 and 2.

[0063]

[Table 1]

[0064]

According to the image forming method of the present invention, since the amount of the free magnetic powder contained in the developer is set to 0.1 vol% or less, the free magnetic powder may be buried in the depression existing on the surface of the heat fixing roll. Can be reduced. In particular, even when image formation is performed at a high speed such as a process speed of 200 mm / s or more and using a small apparatus having an outer diameter of a heat fixing roll of 40 mm or less, the heat generated by the free magnetic powder The generation of scratches on the surface of the fixing roll can be reduced, and the risk of free magnetic powder entering the scratches on the roll surface and the developer being embedded in the scratches can be reduced. As a result, according to the present invention, it is possible to suppress a remarkable decrease in the releasability of the surface of the heat fixing roll, suppress occurrence of hot offset, and form a good image over a long period of time.

[Brief description of the drawings]

FIG. 1 is a configuration diagram schematically showing an image forming unit provided in an image forming apparatus such as a copying machine or a printer, which can suitably execute an image forming method according to an embodiment.

FIG. 2 is a configuration diagram schematically illustrating a fixing device included in an image forming unit.

[Description of References] 10 ... image forming apparatus, 11 ... photoconductor, 12 ... charging device,
13: Exposure device, 14: Developing device, 15: Transfer roll,
16 fixing device, 17 removing device, 19 support, 21
... toner image, 22 ... heat fixing roll, 23 ... heating member, 2
4 temperature sensor, 25 pressure roll, 26 core metal, 2
7 release resin layer, 28 core roll, 29 silicone rubber, 30 Nip part, P transfer body.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Michio Takeo, Fuji Xerox Co., Ltd., 1600 Takematsu, Minami Ashigara, Kanagawa Prefecture (72) Inventor Tomohiro Takeda, 1600 Takematsu, Minami Ashigara City, Kanagawa Prefecture, Inventor Shinpei Takagi 1600 Takematsu, Minamiashigara-shi, Kanagawa Prefecture, Fuji Xerox Co., Ltd. 1600 address Fuji Xerox Co., Ltd. F term (reference) 2H005 CB04 EA10 FA06 FB02 2H033 AA09 AA20 BA58 BB12 BB37 CA40 3J103 AA02 AA85 FA09 FA12 GA57 GA58

Claims (1)

[Claims] 1. A step of forming an electrostatic latent image on an electrostatic carrier, a step of forming a toner image on the electrostatic carrier using a developer, and transferring the toner image on a transfer body And fixing the toner image transferred onto the transfer member by using a heat fixing roll and a pressure member pressed against the heat fixing roll. Using a component developer, the amount of free magnetic powder contained in the developer is 0.1 vol% or less, the outer diameter of the heat fixing roll is 40 mm or less, and the process speed is 200 mm / s or more. Image forming method.