JP4572783B2 - Image forming method - Google Patents

Description

  The present invention relates to an image forming method using a toner containing a wax.

  In recent years, in the field of electrophotographic image forming technology, color image formation using a plurality of color toners has been performed in addition to the conventional monochrome image formation. With the advancement of digital technology, for example, it becomes possible to reproduce a minute dot image at a level of 1200 dpi (dpi; number of dots per inch, 1 inch = 2.54 cm) using toner, thereby achieving high resolution. Entry into the printing industry, which requires rich color reproducibility and high-speed print production, has come to be considered.

  As described above, one of the factors for obtaining a finished toner image that is inferior to that of a printed image is a wax-embedded oil typified by polymerized toner whose particle size and shape can be controlled in the manufacturing process. The presence of less toner can be mentioned (for example, see Patent Document 1).

  In addition, print production by printing has the advantage of creating a large amount of high-quality images, but it is not suitable for ordering small prints with a small number of prints, because it requires time and effort to create prints. Had a face. On the other hand, an electrophotographic image forming method can provide a user with a required number of printed materials on demand without causing a plate like printing, and accepts a small print request with a small number of orders. It is a system that is convenient for contractors with many cases. Then, development of an image forming apparatus capable of creating an on-demand print is in progress. For example, there is a technique for providing a user-friendly device by making it possible to set a cover sheet, an insert sheet, or the like in an output bundle of printed materials, and by reducing the size of the apparatus and the number of parts ( For example, see Patent Document 2).

In addition, toner designs suitable for on-demand print creation are being developed. For example, there is a toner in which the toner image obtained by double-sided printing has a specific range of the dynamic friction coefficient of the toner image or the area occupied by carbon or oxygen by ESCA surface analysis so as not to cause blocking or tacking (for example, (See Patent Document 3). Also, by providing a step of concentrating the resin particle dispersion during the toner manufacturing process, the performance of the toner is improved, odor generation at the time of heat fixing and odor adhesion to printed matter are eliminated, and it is equivalent to an offset print image There is a toner that can obtain a pictorial image (see, for example, Patent Document 4).
Japanese Patent Application Laid-Open No. 2002-214821 (see paragraph 0049, etc.) Japanese Patent Laying-Open No. 2005-15225 (see paragraph 0097 etc.) Japanese Patent Laying-Open No. 2004-157423 (see paragraph 0018) JP 2004-271484 A (see paragraph 0019 and the like)

  By the way, as represented by bookbinding products, printed products are often formed on both sides of a sheet, and as described in Patent Document 2, a good toner image can be obtained even if images are formed on both sides. The toner has been improved so that the toner can be obtained.

  However, in the toner image formed on the back side after image formation on one side, there were problems such as unevenness on the image and low image density compared to the front side. .

  An object of the present invention is to provide an image forming method capable of forming a good toner image free from image defects on the back side when images are formed on both sides of a sheet. In particular, it is an object of the present invention to provide an image forming method applicable to on-demand print creation that requires high image quality for double-sided printed matter.

It has been confirmed that the above problem can be solved by the configuration described below. That is,
(1)
An image forming method for forming a toner image on both sides of a transfer sheet,
The toner that forms the toner image contains at least 10% by mass to 30% by mass of a polyolefin wax,
When the surface resistivity of the toner is ρt and the surface resistivity of the wax is ρw,
ρt / ρw <1
An image forming method having the following relationship:

(2)
The image forming method according to (1), wherein a ratio ρt / ρw of the surface resistivity ρt of the toner and the surface resistivity ρw of the wax is 0.63 or more and 0.98 or less .

(3)
The toner image is formed on both sides of the transfer sheet via an intermediate transfer belt, and the surface resistivity of the toner is higher than the surface resistivity of the intermediate transfer belt. The image forming method according to (1) or (2).

  According to the present invention, it is possible to form a good toner image that does not cause image defects on the back side even when images are formed on both sides of the transfer sheet. That is, it is possible to form a good toner image without density unevenness and image omission without being affected by the toner image portion and the white background portion formed on the front surface.

  Therefore, it is possible to provide an image forming method that can be applied to on-demand print creation that requires high image quality for double-sided printed matter.

  The present invention relates to an image forming method using an oilless toner containing a wax. In the present invention, by making the surface resistivity of the toner smaller than the surface resistivity of the wax alone, it is possible to prevent image defects such as density unevenness on the back side during double-sided printing. This is because the surface resistivity of the wax is made larger than the surface resistivity of the toner, and the charge distribution on the back surface is made uniform by the presence of the wax layer uniformly formed on the front surface, and there is no unevenness. It is estimated that uniform transfer can be performed.

  That is, a uniform wax layer is formed on the front surface via toner or a fixing device after fixing. At this time, a region where the toner layer is present and a region where the toner layer is present are formed on the paper surface, but the resistivity on the paper surface can be increased by making the wax layer higher than the toner layer so that the resistivity is dominant on the paper surface. Make the distribution of. By uniforming the resistivity distribution, a uniform charge distribution is obtained when the charge is applied to the back surface side, so that it is estimated that the transfer performance does not vary.

  Hereinafter, the present invention will be described in detail.

  First, the toner used in the image forming method according to the present invention will be described. The toner used in the present invention contains a wax. When the surface resistivity of the toner is ρt and the surface resistivity of the wax contained in the toner is ρw, ρt / ρw <1. It has a relationship.

  FIG. 1 shows the structure of the toner used in the present invention. The toner shown in FIG. 1 has a so-called sea-island structure in which a wax phase is present as an isolated phase (island) in a continuous resin phase (sea). FIGS. 1A and 1B are schematic views of a toner having a sea-island structure in which a wax phase is present in a continuous phase of a resin.

  The structure of the toner used in the present invention is confirmed by a cross-sectional photograph taken with a transmission electron microscope. That is, it is confirmed by transmission electron microscope (TEM) that the colorant phase having different luminance and the above-described wax phase are present in an island shape in the continuous phase (resin phase) of the resin.

  Examples of the transmission electron microscope apparatus for observing the toner structure include “LEM-2000 type (manufactured by Topcon Corporation)”.

  For example, the toner can be photographed with a transmission electron microscope after the toner is sufficiently dispersed in a room temperature curable epoxy resin, embedded and cured, and then dispersed in a styrene fine powder having a particle size of about 100 nm. Mold. At this time, if necessary, the obtained block can be dyed with ruthenium tetroxide or osmium tetroxide. After the pressure molding, a flaky sample is cut out using a microtome equipped with diamond teeth and loaded into a transmission electron microscope (TEM) to photograph a tomographic form of the toner.

  The toner used in the present invention is a so-called oilless toner containing a wax. The wax is not particularly limited as long as it satisfies the above-described surface resistivity relationship, and a known wax can be used.

  Specifically, polyolefin waxes such as polyethylene wax, polypropylene wax and polybutylene wax, long chain hydrocarbon waxes such as paraffin wax and sazol wax, dialkyl ketone waxes such as distearyl ketone, carnauba wax and montan wax. , Trimethylolpropane tribehenate, pentaerythritol tetramyristate, pentaerythritol tetrastearate, pentaerythritol tetrabehenate, pentaerythritol diacetate dibehenate, glycerin tribehenate, 1,18-octadecanediol distearate , Ester waxes such as tristearyl trimellitic acid and distearyl maleate, ethylenediamine dibehenyl amide, trimellitic acid Such as amide-based waxes such as stearyl amide.

  The melting point of the wax is usually 40 to 160 ° C, preferably 50 to 120 ° C, more preferably 60 to 90 ° C. By setting the melting point within the above range, the heat-resistant storage stability of the toner is ensured, and stable toner image formation can be performed without causing cold offset or the like even when fixing at a low temperature. Further, the wax content in the toner is preferably 10% by mass to 30% by mass.

As shown in the following procedure, the surface resistivity of the toner and wax used in the present invention is measured with a measurement sample prepared by pressurizing the toner or wax to create a measurement sample and molding only with pressure without applying heat. Is done.
(1) A toner or wax is put into a pressure molding machine, and pressure is applied to produce a disk-shaped measurement sample having a diameter of 80 mm and a thickness of 2 mm.
(2) A sample prepared on the counter electrode is placed, and an HR probe (diameter 50 mm) conforming to JIS-K6911 is placed on the sample.
(3) The counter electrode and the probe are connected to a microammeter (using a digital ultrahigh resistance / microammeter “R8340A” (manufactured by Advantest)), and a voltage of 500 V is applied between the counter electrode and the probe. The measurement environment is a temperature of 23 ° C. and a humidity of 45%.

  The pressure molding machine is an apparatus that press-molds a powder sample such as toner or wax into a disk shape, and produces a high-density measurement sample.

  In FIG. 2, the external shape (a) and measurement state (b) of the measurement sample produced with the press molding machine are shown.

  Next, the resin constituting the toner used in the present invention will be described.

  The weight average molecular weight (Mw) of the resin constituting the toner used in the present invention is not particularly limited, and has the same weight average molecular weight (Mw) as the binder resin constituting the known toner. It is.

  The molecular weight of the resin constituting the toner used in the present invention can be measured using, for example, GPC (gel permeation chromatography) using THF (tetrahydrofuran) as a solvent.

  In the method of measuring the molecular weight of a resin by GPC (gel permeation chromatography), first, a measurement sample is dissolved in tetrahydrofuran (THF) so as to have a concentration of 1 mg / ml. The dissolution condition is 5 minutes using an ultrasonic disperser at room temperature.

  Next, after processing with a membrane filter having a pore size of 0.2 μm, 10 μl of sample solution is injected into GPC.

  Examples of specific measurement conditions for GPC are shown below.

Apparatus: HLC-8220 (manufactured by Tosoh Corporation)
Column: TSKguardcolumn + TSKgelSuperHZM-M3 series (manufactured by Tosoh Corporation)
Column temperature: 40 ° C
Solvent: tetrahydrofuran (THF)
Flow rate: 0.2 ml / min
Detector: Refractive index detector (RI detector)
In the measurement of the molecular weight of the sample, the molecular weight distribution of the sample is calculated using a calibration curve measured using monodisperse polystyrene standard particles. Ten polystyrenes for calibration curve measurement were used.

  The toner used in the present invention preferably has a volume-based median diameter (volume D50% diameter) of 3 to 8 μm. The volume-based median diameter can be measured and calculated using a device in which a computer system for data processing (manufactured by Beckman Coulter) is connected to Coulter Multisizer III (manufactured by Beckman Coulter, Inc.).

  As a measurement procedure, 0.02 g of toner is blended with 20 ml of a surfactant solution (for example, a surfactant solution obtained by diluting a neutral detergent containing a surfactant component 10 times with pure water for the purpose of dispersing the toner). After that, ultrasonic dispersion is performed for 1 minute to prepare a toner dispersion. This toner dispersion is injected into a beaker containing ISOTON II (manufactured by Beckman Coulter, Inc.) in a sample stand with a pipette until a measurement concentration of 5 to 10% is reached, and the measuring machine count is set to 2500. To do. The aperture diameter of the Coulter Multisizer was 50 μm.

The softening point of the toner and wax used in the present invention can be calculated by measurement with a flow tester. Specifically, using a flow tester “CFT-500” (manufactured by Shimadzu Corporation), the diameter of the die pores is 1 mm, the length is 1 mm, the load is 20 kg / cm ² , the temperature rising rate is 6 ° C./min, and the temperature rising start temperature. A softening point is defined as a temperature corresponding to one half of the height from the outflow start point to the outflow end point when a 1 cm ³ sample is melted out under a condition of 50 ° C.

  Next, a method for producing the toner used in the present invention will be described.

  The toner containing the wax used in the present invention has a structure in which the wax is not exposed on the surface of the toner in order to develop stable charging performance, and the built-in wax can be efficiently leached out during fixing. Is preferred. That is, the toner having the structure as shown in FIG. 1A is preferable, and such a toner can be manufactured through a process of aggregating resin particles containing wax in an aqueous medium to form particles. Is possible.

As typical methods for agglomerating resin particles containing wax in an aqueous medium to form toner particles, the following two methods may be mentioned.
(1) A method of producing a toner through a step of polymerizing a polymerizable monomer in which wax is dissolved to form resin particles, and aggregating the formed resin particles in an aqueous medium.
(2) A method for producing a toner through a step of aggregating resin particles and wax particles in an aqueous medium.

  Hereinafter, a method for producing the toner used in the present invention will be further described.

  For example, as described in (1) above, the toner used in the present invention is obtained by dissolving or dispersing wax in a polymerizable monomer that forms a resin, and then mechanically dispersing fine particles in an aqueous medium. The polymerizable monomer is polymerized by the mini-emulsion polymerization method to form composite resin particles containing a wax. There is a method of forming toner by aggregating the formed composite resin particles and colorant particles. In this case, when the wax component is dissolved in the polymerizable monomer, the wax component may be dissolved and dissolved or melted and dissolved.

  Further, as described in (2) above, resin particles are formed by polymerizing a polymerizable monomer that is mechanically dispersed in an aqueous medium to form resin particles, and the formed resin particles, colorant particles, and wax particles. There is a method of forming a toner by agglomerating the toner.

  The method for producing resin particles will be further described with the method (1) as the main.

[Dissolution / dispersion process]
In this step, a wax compound is dissolved in the radical polymerizable monomer, and a radical polymerizable monomer solution in which the wax compound is mixed is prepared. In the method (2), a radical polymerizable monomer is prepared without containing wax.

[Polymerization process]
In a preferred example of this polymerization step, a radical polymerizable monomer solution is added to an aqueous medium containing a surfactant having a critical micelle concentration (CMC) or less, and mechanical energy is applied to form droplets. Then, a water-soluble radical polymerization initiator is added, and the polymerization reaction proceeds in the droplet. An oil-soluble polymerization initiator may be contained in the droplets. In such a polymerization process, mechanical energy is imparted and forcedly emulsified (formation of droplets) is essential. Examples of the mechanical energy applying means include means for applying strong stirring or ultrasonic vibration energy such as homomixer, ultrasonic wave, and manton gorin.

  By this polymerization step, in the case of (1), resin particles containing wax are obtained. In the case of (2), resin particles containing no wax are obtained. Here, the produced resin particles may be colored particles. The colored resin particles can be obtained by polymerizing a monomer composition containing a colorant. In addition, when using uncolored resin particles, the dispersion of the colorant particles is added to the dispersion of the resin particles in the aggregation / fusion process described later to melt the resin particles and the colorant particles. Color particles can be obtained by attaching.

  In the case of (2), the colored particles can be formed by adding the colored particle dispersion and the wax particle dispersion to the resin particle dispersion and fusing the resin particles with the colorant particles and the wax particles. It is.

[Aggregation / fusion process]
As a method of aggregation and fusion in the aggregation / fusion process, a salting out / fusion method using resin particles (colored or non-colored resin particles) obtained in the polymerization process is preferable. In the agglomeration / fusion step, fine particles of internal additives such as wax particles and charge control agents can be agglomerated and fused together with the resin particles and the colorant particles.

  The “aqueous medium” in the agglomeration / fusion step is one in which the main component (50% by mass or more) is made of water. Examples of components other than water include organic solvents that dissolve in water, such as methanol, ethanol, isopropanol, butanol, acetone, methyl ethyl ketone, and tetrahydrofuran.

  The colorant particles can be prepared by dispersing the colorant in an aqueous medium. The dispersion treatment of the colorant is performed in a state where the surfactant concentration is set to a critical micelle concentration (CMC) or more in water. The disperser used for the dispersion treatment of the colorant is not particularly limited, but preferably an ultrasonic disperser, a mechanical homogenizer, a pressure disperser such as a manton gorin or a pressure homogenizer, a sand grinder, a Getzmann mill, a diamond fine mill, or the like. A medium type disperser is mentioned. Examples of the surfactant used include the same surfactants as those described above. The colorant (fine particles) may be surface-modified. In the surface modification method of the colorant, the colorant is dispersed in a solvent, the surface modifier is added to the molecular weight solution, and the system is reacted by raising the temperature. After completion of the reaction, the colorant is separated by filtration, washed and filtered with the same solvent, and dried to obtain a colorant (pigment) treated with the surface modifier.

  Also, the wax particle dispersion can be prepared in the same procedure as the colorant particle dispersion.

  The salting out / fusing method, which is a preferred agglomeration and fusing method, is a salting out method comprising an alkali metal salt, an alkaline earth metal salt, a trivalent salt, or the like in water in which resin fine particles and colorant fine particles are present. An agent is added as a coagulant having a critical coagulation concentration or higher, and then salting-out proceeds by heating to a temperature above the glass transition point of the resin fine particles and above the melting peak temperature (° C.) of the mixture. At the same time, it is a process of fusing. Here, the alkali metal salt and the alkaline earth metal salt which are salting-out agents include lithium, potassium, sodium and the like as the alkali metal, and examples of the alkaline earth metal include magnesium, calcium, strontium and barium. Preferably, potassium, sodium, magnesium, calcium, and barium are used.

  When agglomeration and fusion are performed by salting out / fusion, it is preferable to make the time allowed to stand after adding the salting-out agent as short as possible. The reason for this is not clear, but there are problems that the aggregation state of the particles fluctuates depending on the standing time after salting out, the particle size distribution becomes unstable, and the surface property of the fused toner fluctuates. appear. The temperature for adding the salting-out agent needs to be at least the glass transition temperature of the resin fine particles. The reason for this is that if the temperature at which the salting-out agent is added is equal to or higher than the glass transition temperature of the resin fine particles, the salting out / fusion of the resin fine particles proceeds rapidly, but the particle size cannot be controlled. There arises a problem that particles having a particle size are generated. Although the range of this addition temperature should just be below the glass transition temperature of resin, generally it is 5-55 degreeC, Preferably it is 10-45 degreeC.

  Further, the salting-out agent is added at a temperature not higher than the glass transition temperature of the resin fine particles, and then the temperature is raised as quickly as possible to a temperature not lower than the glass transition temperature of the resin fine particles and not lower than the melting peak temperature (° C.) of the mixture. Heat to. The time until this temperature rise is preferably less than 1 hour. Further, although it is necessary to quickly raise the temperature, the rate of temperature rise is preferably 0.25 ° C./min or more. The upper limit is not particularly clear, but if the temperature is increased instantaneously, salting out proceeds rapidly, so there is a problem that particle size control is difficult, and 5 ° C./min or less is preferable. By this fusing step, a dispersion of associated particles obtained by salting out / fusing resin fine particles and arbitrary fine particles is obtained.

[Shelling process]
In the shelling step, the resin particle dispersion for shell is added to the associated particle dispersion, the resin particles are aggregated and fused on the surface of the associated particles, and the surface of the associated particles are coated with the resin particles for shell to give colored particles. Form. As described above, by forming the shell, the coloring agent and the wax are not exposed on the surface of the colored particles, and good charging performance is imparted.

  Specifically, the dispersion resin of shell resin particles is added to the associated particle dispersion while maintaining the temperature in the above-described aggregation / fusion process, and the resin for shell is slowly added over several hours while continuing heating and stirring. The particles are coated on the associated particle surface to form colored particles. The heating and stirring time is preferably 1 hour to 7 hours, particularly preferably 3 hours to 5 hours. To stop the particle growth by adding a terminator such as sodium chloride when the colored particles have reached a predetermined particle size by shelling, and then fuse the resin particles for the shell adhered to the associated particles. Continue to stir for several hours. In the shelling step, a surface layer having a thickness of 10 to 500 nm is formed on the surface of the associated particles. In this way, resin particles can be fixed to the surface of the core particles to form a shell, and colored particles having a uniform shape can be formed.

  In the present invention, it is possible to produce a rounded toner having a uniform shape through the above-described steps.

[Cooling process]
This step is a step of cooling (rapid cooling) the dispersion of colored particles. As a cooling treatment condition, cooling is performed at a cooling rate of 1 to 20 ° C./min. The cooling treatment method is not particularly limited, and examples thereof include a method of cooling by introducing a refrigerant from the outside of the reaction vessel, and a method of cooling by directly introducing cold water into the reaction system.

[Solid-liquid separation and washing process]
In this solid-liquid separation / washing step, a solid-liquid separation process for solid-liquid separation of the colored particles from the dispersion of colored particles cooled to a predetermined temperature in the above-described step, and a solid-liquid separated toner cake (in a wet state) A cleaning treatment for removing deposits such as a surfactant and a salting-out agent from an aggregate obtained by agglomerating certain colored particles into a cake is performed. Here, the filtration method is not particularly limited, such as a centrifugal separation method, a vacuum filtration method using Nutsche or the like, a filtration method using a filter press or the like.

[Drying process]
In this step, the washed toner cake is dried to obtain dried colored particles. Examples of dryers used in this process include spray dryers, vacuum freeze dryers, vacuum dryers, etc., stationary shelf dryers, mobile shelf dryers, fluidized bed dryers, rotary dryers It is preferable to use a stirring dryer or the like. The water content of the dried colored particles is preferably 5% by mass or less, more preferably 2% by mass or less. In addition, when the dried colored particles are aggregated by weak interparticle attractive force, the aggregate may be crushed. Here, as the crushing treatment device, a mechanical crushing device such as a jet mill, a Henschel mixer, a coffee mill, a food processor, or the like can be used.

[External process]
This step is a step of preparing a toner by mixing the dried colored particles with an external additive as necessary. As an external additive mixing device, a mechanical mixing device such as a Henschel mixer or a coffee mill can be used.

  Next, the polymerizable monomer that can be used in the method for producing the toner used in the present invention will be described. The resin constituting the toner that can be used in the present invention contains a polymer obtained by polymerizing at least one polymerizable monomer as a constituent component. Specifically, styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-chlorostyrene, 3,4-dichlorostyrene, p-phenylstyrene, p-ethylstyrene, 2 , 4-dimethylstyrene, p-tert-butylstyrene, pn-hexylstyrene, pn-octylstyrene, pn-nonylstyrene, pn-decylstyrene, pn-dodecylstyrene, etc. Styrene or styrene derivatives, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, methacryl Lauryl acid, methacrylate , Methacrylate derivatives such as diethylaminoethyl methacrylate, dimethylaminoethyl methacrylate, methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, isobutyl acrylate, n-acrylate -Octyl, 2-ethylhexyl acrylate, stearyl acrylate, lauryl acrylate, phenyl acrylate, acrylate derivatives, olefins such as ethylene, propylene, isobutylene, vinyl chloride, vinylidene chloride, vinyl bromide, fluoride Halogenated vinyls such as vinyl and vinylidene fluoride, vinyl esters such as vinyl propionate, vinyl acetate and vinyl benzoate, vinyl ethers such as vinyl methyl ether and vinyl ethyl ether, vinyl methyl Vinyl ketones such as ketone, vinyl ethyl ketone, vinyl hexyl ketone, N-vinyl compounds such as N-vinyl carbazole, N-vinyl indole, N-vinyl pyrrolidone, vinyl compounds such as vinyl naphthalene, vinyl pyridine, acrylonitrile, methacrylo Examples thereof include vinyl monomers such as acrylic acid or methacrylic acid derivatives such as nitrile and acrylamide. These vinyl monomers can be used alone or in combination.

  Moreover, it is also possible to use combining what has an ionic dissociation group as a polymerizable monomer which comprises resin. For example, it has a substituent such as a carboxyl group, a sulfonic acid group, a phosphoric acid group as a constituent group of the monomer, specifically, acrylic acid, methacrylic acid, maleic acid, itaconic acid, cinnamic acid, fumar Acid, maleic acid monoalkyl ester, itaconic acid monoalkyl ester, styrene sulfonic acid, allyl sulfosuccinic acid, 2-acrylamido-2-methylpropane sulfonic acid, acid phosphooxyethyl methacrylate, 3-chloro-2-acid phosphooxy And propyl methacrylate.

  Furthermore, polyfunctionality such as divinylbenzene, ethylene glycol dimethacrylate, ethylene glycol diacrylate, diethylene glycol dimethacrylate, diethylene glycol diacrylate, triethylene glycol dimethacrylate, triethylene glycol diacrylate, neopentyl glycol dimethacrylate, neopentyl glycol diacrylate, etc. It is also possible to use a crosslinkable resin by using a functional vinyl.

  Next, the polymerization initiator, chain transfer agent, and surfactant that can be used in the toner production method used in the present invention will be described.

  The resin constituting the toner used in the present invention is produced by polymerizing the polymerizable monomer described above, and usable radical polymerization initiators include oil-soluble polymerization initiators and water-soluble polymerization initiators. Is mentioned.

  Oil-soluble polymerization initiators include 2,2'-azobis- (2,4-dimethylvaleronitrile), 2,2'-azobisisobutyronitrile, 1,1'-azobis (cyclohexane-1-carbonitrile ), 2,2'-azobis-4-methoxy-2,4-dimethylvaleronitrile, azobisisobutyronitrile and other azo or diazo polymerization initiators, benzoyl peroxide, methyl ethyl ketone peroxide, diisopropyl peroxycarbonate, Cumene hydroperoxide, t-butyl hydroperoxide, di-t-butyl peroxide, dicumyl peroxide, 2,4-dichlorobenzoyl peroxide, lauroyl peroxide, 2,2-bis- (4,4-t -Butylperoxycyclohexyl) propane, tris- (t- Chiruperuokishi) triazine and the like polymeric initiators having a side chain a peroxide-based polymerization initiator or a peroxide, such as.

  Examples of the water-soluble polymerization initiator include persulfates such as potassium persulfate and ammonium persulfate, azobisaminodipropane acetate, azobiscyanovaleric acid and salts thereof, and hydrogen peroxide.

  In addition, a dispersion stabilizer can be used to appropriately disperse the polymerizable monomer and the like in the reaction system. Dispersion stabilizers include tricalcium phosphate, magnesium phosphate, zinc phosphate, aluminum phosphate, calcium carbonate, magnesium carbonate, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, calcium metasilicate, calcium sulfate, barium sulfate , Bentonite, silica, alumina and the like. Furthermore, those generally used as surfactants such as polyvinyl alcohol, gelatin, methylcellulose, sodium dodecylbenzenesulfonate, ethylene oxide adduct, and higher alcohol sodium sulfate can be used as the dispersion stabilizer.

  Moreover, it is also possible to use a generally used chain transfer agent for the purpose of adjusting the molecular weight of the resin. The chain transfer agent is not particularly limited, and examples thereof include mercaptans such as octyl mercaptan, dodecyl mercaptan, tert-dodecyl mercaptan, n-octyl-3-mercaptopropionate, terpinolene, carbon tetrabromide and α-methyl. Styrene dimer or the like is used.

  In addition, in order to perform polymerization using a radical polymerizable monomer, it is necessary to disperse oil droplets in an aqueous medium using a surfactant. Although it does not specifically limit as surfactant which can be used in this case, The following ionic surfactant can be mentioned as an example of a suitable thing.

  Examples of ionic surfactants include sulfonates (sodium dodecylbenzenesulfonate, sodium arylalkylpolyethersulfonate, 3,3-disulfonediphenylurea-4,4-diazo-bis-amino-8-naphthol-6 Sodium sulfonate, ortho-carboxybenzene-azo-dimethylaniline, 2,2,5,5-tetramethyl-triphenylmethane-4,4-diazo-bis-β-naphthol-6-sodium sulfonate, etc.), sulfuric acid Ester salts (sodium dodecyl sulfate, sodium tetradecyl sulfate, sodium pentadecyl sulfate, sodium octyl sulfate, etc.), fatty acid salts (sodium oleate, sodium laurate, sodium caprate, sodium caprylate, sodium caproate, potassium stearate) Beam, calcium oleate and the like).

  Nonionic surfactants can also be used. Specifically, polyethylene oxide, polypropylene oxide, combination of polypropylene oxide and polyethylene oxide, ester of polyethylene glycol and higher fatty acid, alkylphenol polyethylene oxide, ester of higher fatty acid and polyethylene glycol, ester of higher fatty acid and polypropylene oxide, sorbitan ester Etc.

  Next, the colorant used for the toner used in the present invention will be described. As the colorant used in the toner used in the present invention, carbon black, a magnetic material, a dye, a pigment, and the like can be arbitrarily used. Specific colorants are shown below.

  Examples of the black colorant include carbon black such as furnace black, channel black, acetylene black, thermal black, and lamp black, and magnetic powder such as magnetite and ferrite.

  Examples of the colorant for magenta or red include C.I. I. Pigment red 48; 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 154, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. Pigment red 238 and the like.

  Examples of the colorant for orange or yellow include C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 94, C.I. I. Pigment yellow 138, solvent yellow 162, and the like.

  Examples of the colorant for green or cyan include C.I. I. Pigment blue 15, C.I. I. Pigment blue 15; 2, C.I. I. Pigment blue 15; 3, C.I. I. Pigment blue 15; 4, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. Pigment blue 62, C.I. I. And CI Pigment Blue 66.

  These colorants may be used alone or in combination of two or more as required. The addition amount of the colorant is set in the range of 1 to 30% by mass, preferably 2 to 20% by mass with respect to the whole toner.

  As the charge control agent, a known one that can be dispersed in water can be used. Specific examples include nigrosine dyes, naphthenic acid or higher fatty acid metal salts, azo metal complexes, disalicylic acid metal salts, dibenzyl acid salts or metal complexes thereof.

  In addition, it is preferable that these charge control agents and waxes have a number average primary particle diameter of about 200 to 900 nm in a dispersed state.

  Further, the toner used in the present invention may be a suspension as disclosed in, for example, Japanese Patent Application Laid-Open No. 7-152198, in addition to the toner prepared through the above-described particle association process in an aqueous medium. It can also be produced by a polymerization method. That is, a polymerizable monomer composition in which a colorant and a wax are dissolved and dispersed in a polymerizable monomer is put into an aqueous medium, and the polymerizable monomer composition is dispersed and stirred in the aqueous medium. In this method, toner is prepared by polymerization.

  The toner used in the present invention may be either a one-component developer or a two-component developer, but a non-magnetic one-component developer is particularly preferably used for forming a clear full-color pictorial image. Is done.

  Next, an image forming apparatus capable of performing the image forming method according to the present invention will be described. The image forming apparatus that can carry out the image forming method according to the present invention is not particularly limited, but is a monochrome image forming apparatus that forms an image with monochromatic toner, or a toner image on an image carrier as an intermediate transfer belt. A color image forming apparatus that sequentially transfers images to each other, and a plurality of image carriers for each color are arranged in series on the intermediate transfer member, and each color toner image formed on each image carrier is placed on the intermediate transfer member. Examples thereof include a tandem color image forming apparatus that transfers and forms an image.

  FIG. 3 is a cross-sectional configuration diagram showing a color image forming apparatus as an embodiment of the image forming apparatus of the present invention. Note that the image forming apparatus in FIG. 3 can perform so-called double-sided printing, which forms an image on both sides of the transfer sheet P.

  This image forming apparatus is called a tandem color image forming apparatus, and includes a plurality of sets of image forming units 10Y, 10M, 10C, and 10K, an endless belt-shaped intermediate transfer belt unit 7 as a transfer unit, and a transfer sheet P. An endless belt-shaped sheet feeding and conveying means 21 and a belt type fixing device 24 as a fixing means. A document image reading device SC is disposed above the main body A of the image forming apparatus.

  As one of the different color toner images formed on each photoconductor, an image forming unit 10Y that forms a yellow image includes a drum-shaped photoconductor 1Y as a first image carrier, and the photoconductor 1Y. A charging unit 2Y, an exposure unit 3Y, a developing unit 4Y, a primary transfer roller 5Y as a primary transfer unit, and a cleaning unit 6Y are arranged around the periphery. In addition, an image forming unit 10M that forms a magenta image as another different color toner image is a drum-shaped photoconductor 1M as a first image carrier, and is arranged around the photoconductor 1M. The charging unit 2M, the exposure unit 3M, the developing unit 4M, the primary transfer roller 5M as the primary transfer unit, and the cleaning unit 6M are included. In addition, an image forming unit 10C that forms a cyan image as another different color toner image includes a drum-shaped photoconductor 1C as a first image carrier, and around the photoconductor 1C. A charging unit 2C, an exposure unit 3C, a developing unit 4C, a primary transfer roller 5C as a primary transfer unit, and a cleaning unit 6C are disposed. In addition, an image forming unit 10K that forms a black image as one of other different color toner images is disposed around a drum-shaped photoconductor 1K as a first image carrier and the photoconductor 1K. A charging unit 2K, an exposure unit 3K, a developing unit 4K, a primary transfer roller 5K as a primary transfer unit, and a cleaning unit 6K.

  The endless belt-shaped intermediate transfer belt unit 7 includes an endless belt-shaped intermediate transfer body 70 as a second image carrier having a semiconductive endless belt shape that is wound around a plurality of rollers and is rotatably supported.

  The respective color images formed by the image forming units 10Y, 10M, 10C, and 10K are sequentially transferred onto the rotating endless belt-shaped intermediate transfer belt 70 by the primary transfer rollers 5Y, 5M, 5C, and 5K, and are combined. A colored image is formed. A transfer sheet P such as a sheet as a recording medium accommodated in the sheet feeding cassette 20 is fed by a sheet feeding / conveying means 21, passes through a plurality of intermediate rollers 22 A, 22 B, 22 C, 22 D, and a registration roller 23, and is secondary. It is conveyed to a secondary transfer roller 5A as a transfer means, and color images are collectively transferred onto the transfer sheet P. The transfer sheet P to which the color image has been transferred is fixed by the belt-type fixing device 24, is sandwiched between the discharge rollers 25, and is placed on the discharge tray 26 outside the apparatus.

  On the other hand, after the color image is transferred to the transfer sheet P by the secondary transfer roller 5A, the residual toner is removed by the cleaning means 6A from the endless belt-shaped intermediate transfer belt 70 from which the transfer sheet P is separated by curvature.

  During the image forming process, the primary transfer roller 5K is always in pressure contact with the photoreceptor 1K. The other primary transfer rollers 5Y, 5M, and 5C are in pressure contact with the corresponding photoreceptors 1Y, 1M, and 1C, respectively, only during color image formation.

  The secondary transfer roller 5A comes into pressure contact with the endless belt-shaped intermediate transfer belt 70 only when the transfer sheet P passes through the secondary transfer roller 5A.

  Further, the housing 8 can be pulled out from the apparatus main body A through the support rails 82L and 82R.

  The housing 8 includes image forming units 10Y, 10M, 10C, and 10K, and an endless belt-shaped intermediate transfer belt unit 7.

  The image forming units 10Y, 10M, 10C, and 10K are arranged in tandem in the vertical direction. An endless belt-shaped intermediate transfer belt unit 7 is disposed on the left side of the photoreceptors 1Y, 1M, 1C, and 1K in the figure. The endless belt-shaped intermediate transfer belt unit 7 includes an endless belt-shaped intermediate transfer belt 70 that can be rotated by winding rollers 71, 72, 73, 74, and 76, primary transfer rollers 5Y, 5M, 5C, and 5K, and a cleaning unit. 6A.

  The image forming units 10Y, 10M, 10C, and 10K and the endless belt-shaped intermediate transfer belt unit 7 are integrally pulled out from the main body A by the drawer operation of the housing 8.

  In this manner, toner images are formed on the photoreceptors 1Y, 1M, 1C, and 1K by charging, exposure, and development, and the toner images of the respective colors are superimposed on the endless belt-shaped intermediate transfer belt 70, and are collectively applied to the transfer sheet P. The image is transferred and fixed by a belt-type fixing device 24 by pressing and heating. The photoreceptors 1Y, 1M, 1C, and 1K after transferring the toner image to the transfer sheet P are cleaned with the cleaning device 6A to remove the toner remaining on the photoreceptor, and then the above-described charging, exposure, and development cycle. The next image formation is performed.

  An example of the structure of the endless belt-shaped intermediate transfer belt 70 is shown in FIG. 4A shows a two-layer structure having a surface layer 701 and a base material layer 703, and FIG. 4B shows an intermediate layer 704 on the base material layer 703 and a surface on the intermediate layer 704. A three-layer structure including the layer 701 is employed. FIG. 4C illustrates a four-layer structure in which two intermediate layers 704 and 705 are provided outside the base material layer 703 and a surface layer 701 is provided outside the intermediate layer 705.

  The surface layer 701 preferably contains a binder resin having a low surface energy. By reducing the surface energy on the intermediate transfer belt 70, the separation of the toner image from the belt can be promoted. As a result, the transferability of the toner image from the intermediate transfer belt 70 to the transfer sheet P during the secondary transfer is promoted, and a high-quality toner image is obtained on the transfer sheet. Examples of the material having low surface energy include a fluorine-based material, a silicon-based material, or a material mainly composed of these materials, a fluorine resin powder, a silicon resin, and a material obtained by dispersing a silicone oil component.

  Next, the base material layer 703 avoids deformation of the belt due to a load applied to the intermediate transfer belt 70 such as elongation caused by tension generated by tension on the tension roll and contact with the cleaning blade, and affects the transfer portion. It is made of a material having rigidity that reduces Specifically, resin materials such as polyimide, polyester, polyether ether ketone, polyamide, polyphenylene sulfide, polycarbonate, polyvinylidene fluoride (PVDF), polyfluoroethylene-ethylene copolymer (ETFE), and the like are used as main raw materials. Resin material is mentioned. It is also possible to use a material obtained by blending the aforementioned resin material and elastic material. Examples of the elastic material include polyurethane, chlorinated polyisoprene, NBR, chloropyrene rubber, EPDM, hydrogenated polybutadiene, butyl rubber, and silicone rubber. These may be used alone or in combination of two or more.

  Among these, it is preferable to contain a polyimide resin. The polyimide resin is formed by heating polyamic acid that is a precursor of the polyimide resin. The polyamic acid can be obtained by dissolving tetracarboxylic dianhydride or an approximately equimolar mixture of its derivative and diamine in an organic polar solvent and reacting in a solution state.

Further, the surface resistivity of the intermediate transfer belt 70 is preferably lower than the surface resistivity of the toner used in the present invention. In this way, by making the surface resistivity of the intermediate transfer belt lower than the surface resistivity of the toner, the toner image formed on the intermediate transfer belt can be smoothly transferred onto the transfer sheet. Specifically, the surface resistivity of the intermediate transfer belt 70 is preferably 1 × 10 ⁸ to 1 × 10 ¹² Ω / □.

  The surface resistivity of the intermediate transfer belt can be measured based on JIS K6991 by using a circular electrode (for example, HR probe of Hiresta IP manufactured by Mitsubishi Yuka Co., Ltd.). For a specific method for measuring the surface resistivity, reference can be made to, for example, paragraph 0048 of JP-A-2001-242725 and the description of FIG.

  The image forming apparatus capable of performing the image forming method according to the present invention is preferably capable of so-called double-sided printing in which an image is formed on both sides of the transfer sheet P.

  When the duplex printing mode is selected and image formation is performed on the back surface of the transfer sheet P, predetermined image data is applied to the back surface of the transfer sheet P in the same manner as image formation performed on the front surface of the transfer sheet P. Forming a toner image based thereon; At this time, after the transfer sheet P on which the image fixing of the front surface has been completed is conveyed to the refeeding means 9 below by the sorting guide 27 and the rear end portion is nipped by the refeeding reverse roller 91, The transfer sheet P is reversed by reverse feeding. The reversed transfer sheet P is sent out to the refeed conveyance path 92, and the toner image formed on the photoreceptors 1Y, 1M, 1C, and 1K and superimposed on the endless belt-shaped intermediate transfer belt 70 is transferred onto the transfer sheet P. Transfer and fix. In this way, toner images are formed on both sides of the transfer sheet P.

  The transfer sheet P used in the image forming method according to the present invention is a support that holds a toner image, and is usually called an image support, a transfer material, or transfer paper. Specific examples include plain paper from thin paper to thick paper, coated printing paper such as art paper and coated paper, commercially available Japanese paper and postcard paper, OHP plastic film, and various transfer sheets such as cloth. It is done.

  Further, in the image forming method according to the present invention, glossy coated paper and non-glossy paper, which are papers used for offset printing with many opportunities to output pictorial photo-like images, can be used.

  Glossy coated paper used for offset printing is required to have high hydrophilicity on the paper surface in order to promote wetting by dipping water used during printing. In addition, a glossy layer is formed by applying a resin emulsion such as wax or polyacrylamide having a melting point of 100 ° C. to 160 ° C. to the paper substrate so that fibers and fillers do not peel from the paper surface even when the paper is wet. Yes.

  The glossy coated paper produced by the cast method (a method of producing glossy coated paper by pressing the paper against the mirror-finished cylinder surface while the paint applied to the base paper is dry) A structure in which two or more layers are laminated is representative. Such glossy coated paper uses a cured product formed by irradiating an electron beam curable resin composition containing no pigment on the inner resin coating layer, and an electron containing pigment on the outer resin coating layer. A cured product formed by irradiating a beam-curable resin composition with an electron beam is used. Glossy coated paper has high surface whiteness and good cosmetic properties.

  On the other hand, non-glossy paper for offset printing, like glossy coated paper, requires high hydrophilicity on the paper surface in order to promote wetting by dipping water used during printing. In addition, a chemical called a paper strength agent that gives strength to paper is used so that fibers and fillers do not peel from the paper surface even when the paper is wet.

  As the paper strength agent, polyacrylamide is generally used, and there are anionic polyacrylamide, cationic polyacrylamide and amphoteric polyacrylamide depending on its ionicity. The main formulation of the paper strength agent is a single formulation in which cationic polyacrylamide or amphoteric polyacrylamide is added to the pulp slurry as a single product, or a combined formulation in which anionic polyacrylamide and cationic polyacrylamide are added to the pulp slurry, respectively. There is.

  In addition, the strength to break was improved by making paper using a vinyl monomer having an acrylamide monomer and an anionic group, and optionally a vinyl monomer having a cationic group copolymerized. There is also non-glossy paper.

  Furthermore, there are non-glossy papers coated with starch or polyvinyl alcohol as a paper strength agent. When polyvinyl alcohol is used as the paper strength agent, the content of polyvinyl alcohol in the coating solution is set to 50% by mass or more, and a penetrant such as a polyglycol type nonionic surfactant is added to 10 to 10,000 ppm. When the coating solution is used, a good non-glossy paper can be obtained.

The paper weighed is preferably 64 to 150 g / m ² .

Hereinafter, although an example is given and explained concretely, the embodiment of the present invention is not limited to this. In the following description, “part” and “%” all mean “part by mass of solid” and “% by mass of solid” unless otherwise specified.
1. Preparation of toner 1-1. Preparation of Toners 1 to 5 (1) Preparation of Toner Shell Resin Particles s1 The following polymerizable monomers were mixed to prepare a polymerizable monomer solution.

Styrene 322.3g
n-Butyl acrylate 121.9g
Methacrylic acid 35.5g
n-octyl-3-mercaptopropionate 9.55 g
In a separable flask equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introducing device, 7.08 g of anionic surfactant C ₁₂ H ₂₅ OSO ₃ Na was dissolved in 3010 g of ion-exchanged water, and stirred at 230 rpm under a nitrogen stream. While stirring at a speed, the internal temperature was raised to 80 ° C. to prepare a surfactant solution.

An initiator solution in which 9.2 g of a polymerization initiator (potassium persulfate: KPS) is dissolved in 200 g of ion-exchanged water is added to the surfactant solution to bring the temperature to 75 ° C., and then the polymerizable monomer. The solution was added dropwise over 1 hour. After completion of the dropping, polymerization was carried out by heating and stirring at 75 ° C. for 2 hours to prepare toner shell resin particles. The obtained toner particles for toner shell were designated as “toner shell resin particles s1”.
(2) Preparation of Toner Base Resin Particle Dispersion Liquid 1 A polymerizable monomer solution 11 was prepared by mixing the following polymerizable monomers.

72.1 g of styrene
n-Butyl acrylate 20.0g
Methacrylic acid 7.9g
In a separable flask equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introduction device, 7.08 g of anionic surfactant C ₁₂ H ₂₅ OSO ₃ Na was dissolved in 3010 g of ion-exchanged water and stirred under a nitrogen stream. While raising the internal temperature to 80 ° C., a surfactant solution was prepared.

To the surfactant solution, an initiator region in which 9.2 g of a polymerization initiator (potassium persulfate: KPS) was dissolved in 200 g of ion-exchanged water was added to a temperature of 75 ° C. Body solution 11 was added dropwise over 1 hour. After completion of the dropping, the reaction system was heated and stirred at 75 ° C. for 2 hours to perform polymerization (first stage polymerization) to obtain a dispersion of resin particles. This is designated as “toner base resin particles 1”.
(3) Preparation of Colorant Dispersion Liquid (Bk) Anionic surfactant C ₁₀ H ₂₁ (OCH ₂ CH ₂ ) ₂ OSO ₃ Na 90 g was added to 1600 g of ion-exchanged water, dissolved and stirred into a solution of carbon black. (Regal 330R: Cabot Corp.) 400 g was gradually added. Next, a colorant dispersion (K) was prepared by performing a dispersion treatment using a mechanical disperser CLEARMIX (manufactured by M Technique Co., Ltd.). The particle diameter of the colorant particles in this dispersion was measured using an electrophoretic light scattering photometer “ELS-800” (manufactured by Otsuka Electronics Co., Ltd.) and found to be 110 nm.
(4) Preparation of Wax Dispersion 1 A wax dispersion having the following constitution was prepared and used as Wax Dispersion 1.

Wax (polypropylene wax) 20 parts Nonionic surfactant (polyglycerin behenate) 0.7 parts Ion exchange water 100 parts Anionic surfactant (sodium dodecyl sulfate) 0.35 parts (5) Preparation of colored particles 1Bk ( Meeting process)
Toner base resin particle dispersion 1 420.7 g (solid content conversion), ion exchange water 900 g, “colorant dispersion liquid (Bk)” 200 g (solid content conversion), “wax dispersion 1” 80 g (solid content conversion) Were stirred in a reaction vessel (four-necked flask) equipped with a temperature sensor, a cooling tube, a nitrogen introducing device, and a stirring device. After adjusting the temperature in the container to 30 ° C., a 5 mol / liter sodium hydroxide aqueous solution was added to this solution to adjust the pH to 11.0.

  Next, an aqueous solution in which 12.1 g of magnesium chloride hexahydrate was dissolved in 1000 g of ion-exchanged water was added over 10 minutes at 30 ° C. with stirring. After standing for 3 minutes, the temperature of the system was raised to 90 ° C. over 60 minutes to grow the particle size and perform an association reaction. In this state, the particle size of the associated particles was measured with “Coulter Counter TA-III (manufactured by Beckman Coulter)”. When the volume-based median diameter reached 7 μm, 40.2 g of sodium chloride was added to 1000 g of ion-exchanged water. The aqueous solution dissolved in was added to stop particle growth. Subsequently, as the aging treatment, the liquid temperature was set at 98 ° C., and the mixture was heated and stirred for 6 hours to continue the fusion.

Further, 96 g of toner shell resin particles (s1) were added, and the mixture was heated and stirred for 3 hours to be fused to the surface of the associated particles. Thereafter, 40.2 g of sodium chloride was added, the mixture was cooled to 30 ° C. at a cooling rate of 8 ° C./min, hydrochloric acid was added to adjust the pH to 2.0, and stirring was stopped. The generated particles were filtered, repeatedly washed with ion exchange water at 45 ° C., and then dried with hot air at 40 ° C. to obtain “colored particles 1Bk”.
(6) Preparation of Toner 1Bk The obtained “colored particle 1Bk” has 1% by mass of hydrophobic silica having a number average primary particle size of 12 nm and a hydrophobization degree of 68 nm, and a number average primary particle size of 20 nm. Then, hydrophobic titanium oxide having a hydrophobization degree of 63 was added so as to be 1.2% by mass and mixed by a Henschel mixer to obtain “Black Toner 1Bk”. The surface resistivity of the obtained toner was measured with the above-described measuring apparatus and found to be 1.9 × 10 ¹⁷ Ω / □. Moreover, when the surface resistivity of the used wax 1 was measured, it was 2.0 × 10 ¹⁷ Ω / □.
(7) Preparation of toners 1Y, 1M, and 1C In preparation of toner 1Bk, C.I. I. Pigment Yellow 74 was used in the same procedure except that Yellow Yellow 1Y was replaced with C.I. I. Magenta Toner 1M was replaced with C.I. I. A cyan toner 1C was prepared in the same procedure except that Pigment Blue 15: 3 was used. The resulting toner had the same surface resistivity as that of toner 1Bk.
(8) Preparation of Toners 2 to 5 Toners 2 to 5 were prepared in the same procedure except that the addition amount of “wax dispersion 1” in the association step of preparation of toner 1 was changed to 120 g, 240 g, 70 g, and 40 g. The surface resistivity of the produced toner is shown in Table 1 described later.
1-2. Preparation of Toners 6 to 10 (1) Preparation of Toner Shell Resin Particles s1 Shell resin particles s1 were prepared in the same procedure as in the toner 1 to toner 5 preparation steps described above. That is,
Styrene 322.3g
n-Butyl acrylate 121.9g
Methacrylic acid 35.5g
n-octyl-3-mercaptopropionate 9.55 g
In a separable flask equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introducing device, 7.08 g of anionic surfactant C ₁₂ H ₂₅ OSO ₃ Na was dissolved in 3010 g of ion-exchanged water, and stirred at 230 rpm under a nitrogen stream. While stirring at a speed, the internal temperature was raised to 80 ° C. to prepare a surfactant solution.

An initiator solution in which 9.2 g of a polymerization initiator (potassium persulfate: KPS) is dissolved in 200 g of ion-exchanged water is added to the surfactant solution to bring the temperature to 75 ° C., and then the polymerizable monomer. The solution was added dropwise over 1 hour. After completion of the dropping, polymerization was carried out by heating and stirring at 75 ° C. for 2 hours to prepare toner shell resin particles. The obtained toner particles for toner shell were designated as “toner shell resin particles s1”.
(2) Preparation of Toner Base Resin Particle Dispersion 2 7.008 g of anionic surfactant C ₁₂ H ₂₅ OSO ₃ Na was ion exchanged into a separable flask equipped with a stirrer, temperature sensor, cooling tube, and nitrogen introducing device. It was dissolved in 3010 g of water, and the internal temperature was raised to 80 ° C. while stirring at a stirring speed of 230 rpm under a nitrogen stream.

  An initiator solution prepared by dissolving 9.2 g of a polymerization initiator (potassium persulfate: KPS) in 200 g of ion-exchanged water was added to the surfactant solution to bring the temperature to 75 ° C., and then 70.1 g of styrene, n A monomer mixture composed of 19.9 g of butyl acrylate and 10.9 g of methacrylic acid was added dropwise over 1 hour. After completion of the dropwise addition, the system was heated and stirred at 75 ° C. for 2 hours to carry out polymerization (first stage polymerization) to prepare “resin particle dispersion for toner base (2H)”.

  Next, 131.2 g of pentaerythritol tetrabehenate, 105.6 g of styrene, 30.0 g of n-butyl acrylate, 6.2 g of methacrylic acid and n-octyl-3-mercaptopropion were added to a flask equipped with a stirrer. It added to the monomer liquid mixture which consists of 5.6 g of acid ester, heated at 90 degreeC, and it was made to melt | dissolve, and the monomer solution was prepared.

Meanwhile, a surfactant solution in which 1.6 g of an anionic surfactant C ₁₂ H ₂₅ OSO ₃ Na is dissolved in 2700 g of ion-exchanged water is prepared in a flask equipped with a stirrer, and the internal temperature is raised to 98 ° C. 28 g of the above-mentioned “toner base resin particle dispersion (2H)” was added in terms of solid content.

  Next, in a surfactant solution containing “toner base resin particle dispersion (2H)” by a mechanical disperser “CLEARMIX” (manufactured by M Technique Co., Ltd.) having a circulation path, The monomer solution was mixed and dispersed over 8 hours to prepare an emulsion in which emulsion particles (oil droplets) having a uniform dispersed particle size were dispersed.

  Next, an initiator solution prepared by dissolving 5.1 g of a polymerization initiator (potassium persulfate: KPS) in 240 g of ion-exchanged water and 750 g of ion-exchanged water are added to this dispersion (emulsion). Polymerization (second stage polymerization) was performed by heating and stirring at 98 ° C. for 12 hours. By the second-stage polymerization, a dispersion (2HM) of composite resin particles obtained by coating the resin particle surfaces with a resin containing pentaerythritol tetrabehenate ester.

Further, an initiator solution in which 7.4 g of a polymerization initiator (potassium persulfate: KPS) was dissolved in 200 g of ion-exchanged water was added to a flask with a stirrer charged with the entire amount of the composite resin particle dispersion (2HM), and the temperature Was added dropwise over 1 hour with a monomer mixture of 300 g of styrene, 95 g of n-butyl acrylate, 15.3 g of methacrylic acid and 10.4 g of n-octyl-3-mercaptopropionic acid ester. Then, this system was heated and stirred at 80 ° C. for 2 hours to carry out polymerization (third stage polymerization). Thereafter, this system was cooled to 28 ° C. to prepare “toner base resin particle dispersion 2” composed of composite resin particles having a structure in which the surface of the composite resin particles was coated with resin.
(3) Preparation of colored particles 6Bk (association step)
Toner base resin particle dispersion 2 439.2 g (converted to solid content), ion-exchanged water 900 g, “colorant dispersion (Bk)” 200 g, temperature sensor, cooling tube, nitrogen introducing device, stirring device attached reaction It stirred in the container (four necked flask). After adjusting the temperature in the container to 30 ° C., a 5 mol / liter sodium hydroxide aqueous solution was added to this solution to adjust the pH to 11.0.

  Next, an aqueous solution in which 12.1 g of magnesium chloride hexahydrate was dissolved in 1000 g of ion-exchanged water was added over 10 minutes at 30 ° C. with stirring. After standing for 3 minutes, the temperature of the system was raised to 90 ° C. over 60 minutes to grow the particle size and perform an association reaction. In this state, the particle size of the associated particles was measured with “Coulter Counter TA-III (manufactured by Beckman Coulter)”. When the volume-based median diameter reached 6 μm, 40.2 g of sodium chloride was added to 1000 g of ion-exchanged water. The aqueous solution dissolved in was added to stop particle growth. Subsequently, as the aging treatment, the liquid temperature was set at 98 ° C., and the mixture was heated and stirred for 6 hours to continue the fusion.

Further, 96 g of toner shell resin particles (s1) were added, and the mixture was heated and stirred for 3 hours to be fused to the surface of the associated particles. Thereafter, 40.2 g of sodium chloride was added, the mixture was cooled to 30 ° C. at a cooling rate of 8 ° C./min, hydrochloric acid was added to adjust the pH to 2.0, and stirring was stopped. The produced particles were filtered, washed repeatedly with ion exchange water at 45 ° C., and then dried with warm air at 40 ° C. to obtain “colored particles 6Bk”.
(4) Preparation of Toner 6Bk The obtained “colored particles 6Bk” had 1% by mass of hydrophobic silica having a number average primary particle size of 12 nm and a hydrophobization degree of 68 nm, and a number average primary particle size of 20 nm. Then, hydrophobic titanium oxide having a hydrophobization degree of 63 was added so as to be 1.2% by mass and mixed by a Henschel mixer to obtain “Black Toner 2Bk”. Table 1 shows the surface resistivity of the obtained toner 6.
(5) Preparation of toners 6Y, 6M, and 6C In preparation of toner 6Bk, C.I. I. Pigment Yellow 74 was used in the same procedure except that Pigment Yellow 74 was used. I. Magenta Toner 6M was replaced by C.I. I. A cyan toner 6C was prepared in the same procedure except that Pigment Blue 15: 3 was used. The obtained toners 6Y, 6M, and 6C have the same surface resistivity as that of the toner 6Bk.
(6) Preparation of toner 7 In preparation of the toner base resin particle dispersion 2 of toner 6, the amount of pentaerythritol tetrabehenate added was changed to 208.5 g, and the toner base resin particles in the association step Toner 7 was produced in the same procedure except that the amount of dispersion 2 added was changed to 482.4 g.
(7) Preparation of Toner 8 In preparation of toner base resin particle dispersion 2 of toner 6, the amount of pentaerythritol tetrabehenate added was changed to 506.4 g, and toner base resin particles in the association step Toner 8 was produced in the same procedure except that the amount of dispersion 2 added was changed to 649.2 g.
(8) Preparation of toner 9 In preparation of the toner base resin particle dispersion 2 of toner 6, the amount of pentaerythritol tetrabehenate added was changed to 109.8 g, and the toner base resin particles in the association step Toner 9 was prepared in the same procedure except that the amount of dispersion 2 added was changed to 427.2 g.
(9) Preparation of toner 10 In the preparation of the toner base resin particle dispersion 2 of toner 6, the amount of pentaerythritol tetrabehenate added was changed to 62.2 g, and the toner base resin particles in the association step Toner 10 was produced in the same procedure except that the amount of dispersion 2 added was changed to 400.5 g. The surface resistivity of each toner is shown in Table 1 described later.
1-3. Preparation of Toners 11 to 15 (1) Preparation of Toner 11 To 292 parts by mass of ion-exchanged water, 45 parts by mass of a 0.1 mol / liter Na ₃ PO ₄ aqueous solution was added and heated to 60 ° C. The mixture was stirred at 12,500 rpm using a mixer (made by Tokushu Kika Kogyo Co., Ltd.). To this, 68 parts by mass of a 1.0 mol / liter CaCl ₂ aqueous solution was gradually added to obtain a pH 6 aqueous medium containing a calcium phosphate compound.

  Next, a polymerizable monomer composition was prepared using a polymerizable monomer having the following composition.

Styrene 83 parts by mass n-butyl acrylate 32 parts by mass Carbon black (Regal 330R: manufactured by Cabot Corp.) 17 parts by mass Charge control agent (di-t-butyl salicylate) 5 parts by mass Divinylbenzene 1 part by mass After heating, 14 parts by mass of wax 1 (polypropylene) was added and sufficiently dissolved and dispersed to prepare a dispersion composition.

  In this dispersion composition, a mixture of 3.5 parts by mass of an organic peroxide initiator t-butyl peroxypivalate and 1.5 parts by mass of toluene was dissolved to obtain a polymerizable monomer composition. .

  This polymerizable monomer composition was put into the aqueous medium, and granulated for 10 minutes by stirring at a high speed with a high-speed rotary shear stirrer CLEARMIX (manufactured by M Technique Co., Ltd.). This was replaced with a paddle stirrer, and polymerization was continued at an internal temperature of 65 ° C. After 5 hours from the start of the polymerization reaction, 5 parts by mass of anhydrous sodium carbonate was added to the system, and then the polymerization temperature was raised to 80 ° C., and stirring was further continued for 5 hours to complete the polymerization. The pH of the suspension at the completion of the polymerization was 10.6. After cooling, solid-liquid separation is performed by filtration, washing with water, reslurry is performed, further dilute hydrochloric acid is added to dissolve the dispersant, solid-liquid separation, washing with water, filtration, and drying are performed again to obtain colored particles. .

  1% by mass of hydrophobic silica (number average primary particle size 12 nm, hydrophobicity 68) and hydrophobic titanium oxide (number average primary particle size 20 nm, hydrophobicity 63) were added to the obtained colored particles. Toner 11Bk having a volume-based median diameter of 7.0 μm was prepared by adding 2% by mass and mixing with a Henschel mixer.

Instead of carbon black (Regal 330R: manufactured by Cabot Corporation) used in the production of the toner 11Bk, C.I. I. Pigment Yellow 74 is used to replace toner 11Y with C.I. I. Pigment Red 122 is used to add toner 11M to C.I. I. Toner 11C was prepared using Pigment Blue 15: 3.
(2) Preparation of Toner 12 Toner 12 was prepared in the same procedure except that in the toner 11 preparation process, the amount of wax 1 added was changed to 23 parts by mass.
(3) Production of Toner 13 Toner 13 was produced in the same procedure except that the amount of wax 1 added was changed to 56 parts by mass in the production process of toner 11.
(4) Preparation of Toner 14 Toner 14 was prepared in the same procedure except that in the toner 11 preparation process, the amount of wax 1 added was changed to 12 parts by mass.
(5) Preparation of Toner 15 Toner 15 was prepared in the same procedure except that the amount of addition of wax 1 was changed to 7 parts by mass in the toner 11 preparation step.

Toners 1 to 15 produced as described above are shown in Table 1 described later.
3. Manufacture of carriers (Manufacture of ferrite core material)
MnO and 18 mol%, 4 mol% of MgO, Fe ₂ O ₃ 2 hours pulverized 78 mol% in a wet ball mill, after mixed dried, calcined by holding for 2 hours at 900 ° C., 3 it in a ball mill It grind | pulverized for time and was made into the slurry. A dispersant and a binder were added, granulated and dried with a spray dryer, and then subjected to main firing at 1200 ° C. for 3 hours to obtain ferrite core material particles having a resistance value of 4.3 × 10 ⁸ Ω · cm.
[Manufacture of resin for coating]
First, a cyclohexyl methacrylate / methyl methacrylate (copolymerization ratio 5 /) was prepared by an emulsion polymerization method in which the concentration in an aqueous medium using sodium benzenesulfonate having an alkyl group having 12 carbon atoms as a surfactant was 0.3% by mass. 5), a volume average primary particle size of 0.1 μm, a weight average molecular weight (Mw) of 200,000, a number average molecular weight (Mn) of 91,000, Mw / Mn = 2.2, and a softening point temperature. Resin fine particles having (Tsp) 230 ° C. and glass transition temperature (Tg) 110 ° C. were obtained. The resin fine particles azeotroped with water in the emulsified state, and the residual monomer amount was 510 ppm.

Next, 100 parts by mass of ferrite core material particles and 2 parts by mass of the resin fine particles are put into a high-speed agitator / mixer equipped with stirring blades, stirred and mixed at 120 ° C. for 30 minutes, and the mechanical impact force is applied to the volume. A resin-coated carrier having an average particle size of 61 μm was obtained.
4). Production of Developer Each of the toners 1 to 15 described above was mixed with the carrier to prepare a developer of each color having a toner concentration of 6% by mass. Developers 1 to 15 were prepared by combining the developers of the respective colors as shown in Table 1. The configuration of each developer set is shown in Table 1 described later.
5). Evaluation Experiment (1) Evaluation Apparatus The produced developers 1 to 15 are mounted on the image forming apparatus (Konica Minolta 8050 (manufactured by Konica Minolta Business Technology)) shown in FIG. The images output on the 1000th and 2000th sheets were evaluated. Image formation is performed in a high-temperature and high-humidity environment (30 ° C., 80% RH), and the recording paper is a color recording paper “POD gloss coat” (manufactured by Oji Paper Co., Ltd.) 128 g / mm ² (A3 size) for on-demand printing. Using.

The original used for image formation is a character image (3 points, 5 points) with a pixel ratio of 7%, a color human face image (dot image including halftone, with a gray patch with a reflection density of 1.30), Solid white image, solid image using two-color toner (using cyan toner and magenta toner, toner adhesion amount 15 g / m ² (the thickness of the toner layer after fixing is 20 μm)) is published in 1/4 equal parts The two original images (A4 size) were used. At this time, the character image and the color human image printed on the back side are output on the back side of the solid white image output on the front side and the solid image.

The fixing temperature of the image forming apparatus was set so that the surface temperature of the upper roller was 200 ° C. and the surface temperature of the lower roller was 180 ° C.
(2) Evaluation items Evaluation was performed by evaluating the transferability of the images output on the back surfaces of the 1000th and 2000th recording sheets. Specifically, the solid toner image portion omission, the character image portion omission, and the density unevenness on the back surface where the front surface is a solid white image and the two-layer solid toner image portion were evaluated. In the evaluation, ◎ and ○ are acceptable and × is unacceptable.

<Occurrence of solid image part>
In the solid image portion formed on the back surface, the number of omissions having a major axis of 0.4 mm or more was counted and evaluated. The missing part was measured with a microscope with a video printer.

A: White spot frequency of 0.4 mm or more: Both occurrences of missing parts are 3 or less. ○: White spot frequency of 0.4 mm or more: 4 or more and less than 10 occur in the 2000th printed image. Number of print images of 3 sheets or less ×: White spot frequency of 0.4 mm or more: 10 or more images occurred in 1000th print image.

<Missing text image>
The character image formed on the back surface was observed with a magnifying glass to evaluate the occurrence of omission on the character image.

◎: No omission up to the 2000th sheet ○: Occurrence of omission up to the 1000th print and there was no omission that could be finally observed on the 2000th sheet, but no problem in practical use ×: 1000th print Occurrence occurred.

<Uneven density>
At the start, the reflection densitometer evaluated the variation in R density of the gray patch portion provided in the color human face image portion formed on the back surface of the recording paper output on the 2000th sheet.

Density fluctuation = (reflection density at 2000th sheet) − (reflection density at start)
A: Density difference is less than 0.05 B: Density difference is 0.05 or more and less than 0.20 X: Density difference is 0.20 or more The results are shown in Table 1.

As is clear from the results in Table 1, in Examples 1 to 3 and 7 to 9 corresponding to the present invention, even if 2000 double-sided continuous printing is performed or a toner image is formed on the back side, a solid image portion There was no missing or missing character part. On the other hand, in the comparative example, image defects were observed before 2000 sheets were obtained, and the results were clearly different from the examples.

Further, when the finish of the color human face image was visually evaluated using a loupe, it was confirmed that in Examples 1 to 3 and 7 to 9, there was no omission on the face image regardless of the state of the front surface. In the comparative example, when a toner image is formed on the front surface at the 1000th sheet, it was confirmed that a face image was missing even without a loupe.

  As described above, it was confirmed that good toner transfer was also exhibited on the back side when double-sided continuous printing was performed by the image forming method according to the present invention.

It is a schematic diagram which shows the structure of the toner which contains a wax. It is the schematic of the measuring apparatus which measures the surface resistivity of a toner and wax. 1 is a schematic diagram of an image forming apparatus capable of duplex printing. FIG. 3 is a schematic diagram illustrating a structure example of an endless belt-shaped intermediate transfer belt.

Explanation of symbols

1 (1Y, 1M, 1C, 1K) Photoconductor 2 (2Y, 2M, 2C, 2K) Charging unit 3 (3Y, 3M, 3C, 3K) Exposure unit 4 (4Y, 4M, 4C, 4K) Developing unit 5 ( 5Y, 5M, 5C, 5K) Primary transfer means 6 (6Y, 6M, 6C, 6K) Cleaning means 7 Endless belt-like intermediate transfer belt unit 70 Endless belt-like intermediate transfer belt 701 Surface layer 703 Substrate layer P Transfer sheet

Claims (3)

An image forming method for forming a toner image on both sides of a transfer sheet,
The toner that forms the toner image contains at least 10% by mass to 30% by mass of a polyolefin wax,
When the surface resistivity of the toner is ρt and the surface resistivity of the wax is ρw,
ρt / ρw <1
An image forming method having the following relationship: 2. The image forming method according to claim 1, wherein a ratio ρt / ρw of the surface resistivity ρt of the toner and the surface resistivity ρw of the wax is 0.63 or more and 0.98 or less . The toner image is formed on both sides of the transfer sheet via an intermediate transfer belt, and the surface resistivity of the toner is higher than the surface resistivity of the intermediate transfer belt. The image forming method according to claim 1.

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