JP2018185507A - White toner for electrostatic charge image development and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a white toner for electrostatic charge image development that can provide extremely stable, high-quality full-color images for a long period even in a highly stressful environment.SOLUTION: A white toner for electrostatic charge image development of the present invention includes toner particles consisting of toner base particles containing a binder resin, white colorant, and a mold release agent, and an external additive. The toner contains, as the external additive, fatty acid metal salt particles having a median diameter based on volume within a range of 0.5 to 1.5 μm; the toner particles have an average circularity within a range of 0.870 to 0.950.SELECTED DRAWING: None

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a white toner for developing an electrostatic image and an image forming method. More specifically, the present invention relates to a white for developing an electrostatic image that can provide an extremely stable high-quality full-color image for a long time even under high stress conditions. The present invention relates to a toner and an image forming method.

In recent years, toners with small-diameter lubricant (fatty acid metal salt particles) added have been known for the purpose of achieving higher image quality and higher stability of images output by electrophotographic devices such as copiers and printers. (For example, see Patent Documents 1 and 2).
However, along with further miniaturization of these devices, it is necessary to satisfy the image quality with a smaller amount of developer than conventional ones, in particular, as the developing machine is further miniaturized.

In such a process with a small amount of developer, it is necessary to charge the supplied toner in a short time, and therefore, it is necessary to mix it with a carrier with higher stress than in the past.
Under this mixed stress, even with the developer described in the above-mentioned patent document, the lubricant is detached from the surface of the toner particles. For example, the developer is supplied from the back side with respect to the longitudinal direction of the developing sleeve. If it is a machine, the lubricant that is uniformly held by the toner particles must be supplied to every corner of the surface of the photoreceptor, but the lubricant removed from the toner particles immediately transfers to the photoreceptor on the back side. Thus, when the developer moves to the front side of the developing sleeve, the lubricant is depleted, and various image problems that cause cleaning defects (streaked image defects) have occurred.

On the other hand, as a method for forming images on a wide variety of transfer materials, there is a demand for white toner for developing electrostatic images (hereinafter also simply referred to as white toner).
White toner has been whitened using titanium oxide particles, which are inorganic fine particles, for a long time from binder resins, but contains toner particles with a small average circularity (average circularity of 0.950 or less). However, the white toner has a problem that the white colorant is easily exposed on the surface of the toner particles and the fluidity of the toner is deteriorated.

  On the other hand, in batch fixing in which white toner is further added to conventional Y (yellow), M (magenta), C (cyan), and Bk (black) four-color toners, the toner layer becomes thicker. Therefore, it is unavoidable to raise the fixing temperature. However, if the fixing temperature is simply increased, only the interface between the toner layer and the fixing roller is melted, resulting in deterioration of fixing separation property.

Japanese Patent No. 5335330 Japanese Patent No. 5335332

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems and circumstances, and the solution is to develop an electrostatic charge image image that can provide a highly stable high-quality full-color image over a long period of time even under high stress conditions. A white toner and an image forming method are provided.

  In order to solve the above problems, the present inventor contains fatty acid metal salt particles having a volume-based median diameter within a specific range as an external additive in the process of examining the cause of the above problems, and the like. By using white toner for developing electrostatic images with an average circularity within a specific range, it is possible to provide a highly stable, high-quality full-color image over a long period of time even under high stress conditions. The present inventors have found that a toner and an image forming method can be provided, and have reached the present invention.

  That is, the said subject which concerns on this invention is solved by the following means.

1. A white toner for developing an electrostatic charge image, comprising toner particles comprising a binder resin, a white colorant and a release agent, and an external additive,
As the external additive, containing fatty acid metal salt particles having a volume-based median diameter in the range of 0.5 to 1.5 μm,
A white toner for developing an electrostatic charge image, wherein the toner particles have an average circularity in a range of 0.870 to 0.950.

  2. 2. The white toner for developing electrostatic images according to item 1, wherein the fatty acid metal salt is zinc stearate.

  3. Item 1. The image forming method according to the first aspect, wherein the toner is used together with a color toner for developing an electrostatic charge image containing a colorant other than white, and is used for an image forming method in which the image is simultaneously transferred onto a transfer material by an intermediate transfer member and further fixed in a batch. Or the white toner for electrostatic image development of a 2nd term | claim.

4). An image forming method having at least a charging step, a latent image forming step, a developing step, a transfer step, a fixing step, and a cleaning step,
The transfer step includes
The white toner for developing an electrostatic charge image according to any one of items 1 to 3 and the colored toner for developing an electrostatic charge image containing a colorant other than white are primarily transferred to an intermediate transfer member. And a process of
Secondary transfer of the toner image formed on the intermediate transfer member onto a transfer material;
An image forming method comprising:

  5. 5. The image forming method according to claim 4, wherein an average circularity of toner base particles contained in the colored toner for developing an electrostatic charge image is in a range of 0.951 to 0.990.

6). Transferring the white toner for developing an electrostatic charge image to a non-image forming region of the intermediate transfer member corresponding to between the transfer materials continuously conveyed;
6. In the cleaning step, the white toner for developing an electrostatic charge image is collected, and the intermediate transfer member is cleaned using the white toner for developing an electrostatic charge image. Image forming method.

  By the above-mentioned means of the present invention, it is possible to provide a white toner for developing an electrostatic charge image and an image forming method capable of providing a high-quality full-color image that is extremely stable over a long period of time even under high stress conditions.

  The expression mechanism / action mechanism of the effect of the present invention is not clear, but is presumed as follows.

In the white toner for developing an electrostatic charge image of the present invention, in addition to the lubricant capturing effect by the electric field in the vicinity of the surface due to the work function difference between the binder resin on the surface of the toner base particles and the wax (release agent) domain, When the particle size is within a specific range, the lubricant is not electrostatically detached from the toner particles, and the lubricant is supplied more evenly in the longitudinal direction of the developing sleeve, and is transported more stably to the intermediate transfer body and the fixing device. It is.
As a result, even in white toner under high stress conditions, the lubricant is not detached by the developing machine, which has a great effect on the cleaning of the intermediate transfer member, and can eliminate image defects caused by toner spent on the intermediate transfer member. It is considered possible.

Further, in the present invention, the small diameter lubricant adheres to the surface of the white toner base particles by introducing the small diameter lubricant to the problem that the white colorant peculiar to the white toner is exposed and the fluidity is deteriorated. By covering the white colorant that caused the deterioration of the color with a small-diameter lubricant, the fluidity is improved, and the developer reaches the intermediate transfer body and further the fixing process, and the separation property of the fixed image of the white toner is also improved. It is to improve.
In other words, when a small-diameter lubricant is brought into the fixing machine, even when fixing with a large amount of toner including white, the small-diameter lubricant exists at the interface between the surface of the molten toner base particles and the fixing roller (belt). We believe that it can improve the performance.

Furthermore, the white toner for developing an electrostatic charge image of the present invention can be used as a stable cleaning means.
This is because the white toner for developing an electrostatic charge image of the present invention was captured by the cleaning means together with a normal cleaning means (blade) because the lubricant has a small diameter and the average circularity of the toner particles is small. It is considered that the toner spent component on the intermediate transfer member can be scraped off at the edge portion of the toner particle, thereby enabling stable cleaning.

  As described above, by adopting the white toner for developing an electrostatic charge image of the present invention, it is possible to obtain an extremely stable high image quality over a long period of time in addition to white image formation.

Schematic showing a configuration as an example of an image forming apparatus

  The white toner for developing an electrostatic image of the present invention contains fatty acid metal salt particles having a volume-based median diameter in the range of 0.5 to 1.5 μm as an external additive, and the average circularity of the toner particles is It is in the range of 0.870 to 0.950. This feature is a technical feature common to the inventions according to the following embodiments.

  In an embodiment of the present invention, the fatty acid metal salt is preferably zinc stearate from the viewpoint of the performance as a lubricant and the electrostatic toner retention.

  Further, the white toner for developing an electrostatic charge image of the present invention is an image which is collectively transferred onto an image transfer material by an intermediate transfer member together with the colored toner for developing an electrostatic charge image containing a colorant other than white, and further fixed together. It is preferably used in the forming method.

  The present invention is an image forming method having at least a charging step, a latent image forming step, a developing step, a transferring step, a fixing step, and a cleaning step, wherein the transferring step includes the white toner for developing an electrostatic image and a non-white toner. A step of primary-transferring an electrostatic image developing colored toner containing a colored colorant to an intermediate transfer member, and a step of secondary-transferring a toner image formed on the intermediate transfer member onto a transfer material. An image forming method can be provided.

  Further, the average circularity of the toner base particles contained in the colored toner for developing an electrostatic image is preferably in the range of 0.951 to 0.990 from the viewpoint of charging stability and low-temperature fixability. .

  Also, from the viewpoint of long-term cleaning stability, white toner for developing an electrostatic charge image is transferred to a non-image forming region of an intermediate transfer member corresponding to a continuously conveyed transfer material, and the electrostatic charge is transferred in the cleaning process. It is preferable to collect the white toner for image development and clean the intermediate transfer member using the white toner for electrostatic image development.

  Hereinafter, the present invention, its components, and modes and modes for carrying out the present invention will be described in detail. In addition, in this application, "-" showing a numerical range is used by the meaning containing the numerical value described before and behind that as a lower limit and an upper limit.

<White toner for electrostatic image development>
The white toner for developing an electrostatic charge image of the present invention contains toner particles comprising a toner base particle containing a binder resin, a white colorant and a release agent, and an external additive. Fatty acid metal salt particles having a median diameter in the range of 0.5 to 1.5 μm are contained, and the average circularity of the toner particles is in the range of 0.870 to 0.950.

  In the present invention, the toner refers to an aggregate of toner particles.

A white and, in case of transferring only white toner on the transfer material, the surface JIS Z 8781-4: 2013 were measured in accordance with, the lightness ^{L *} in the CIEL ^* a ^* b ^* color system The colors are 80 or more, and a ^* and b ^* satisfy the conditions of −10 ≦ a ^* ≦ 10 and −10 ≦ b ^* ≦ 10, respectively.

(Average circularity of toner particles in white toner for developing electrostatic images)
The average circularity of the toner particles in the white toner for developing an electrostatic charge image is in the range of 0.870 to 0.950. If the average circularity is less than 0.870, sufficient retention of the lubricant cannot be obtained and the toner particles are easily separated from the toner particles, resulting in an image defect with bias. If it is larger than 0.950, the toner particles become more spherical, so that the cleaning effect on the intermediate transfer member cannot be expected.

The method for measuring the average circularity of toner particles (or toner base particles) will be described below.
First, 10 mL of ion-exchanged water from which impure solids are removed in advance is prepared in a container. After adding a surfactant (alkyl benzene sulfonate) as a dispersant, 0.02 g of a measurement sample is further added and dispersed uniformly.
As a means for dispersion, an ultrasonic disperser “Tetora 150 type” (manufactured by Nikka Ki Bios Co., Ltd.) is used, and dispersion treatment is performed for 2 minutes to obtain a dispersion for measurement. In that case, it cools suitably so that the temperature of this dispersion may not be 40 degreeC or more.

In order to suppress variation in circularity, the installation environment of the apparatus is set to 23 ° C. ± 0.5 ° C. so that the in-machine temperature of the flow type particle image analyzer FPIA-2100 (manufactured by Sysmex Corporation) is in the range of 26 to 27 ° C. The autofocusing is performed every 2 hours, preferably every 2 hours using 2 μm latex particles.
To measure the circularity of the toner particles, the above flow-type particle image analyzer is used, the concentration of the dispersion is readjusted so that the toner particle concentration at the time of measurement is 3000 to 10,000 particles / μL, and the toner particles are 1000 Measure more than one. After the measurement, using this data, data having an equivalent circle diameter of less than 2 μm is cut to determine the average circularity of the toner particles.

The degree of circularity of the white toner can be controlled by controlling the brittleness of the binder resin and selecting a kneading and grinding method, particularly a grinding method.
Examples of the pulverization method include a collision plate type airflow pulverizer (I type pulverizer), a high-speed rotating rotor type pulverizer (turbo mill, kryptron), etc. The rotor-type pulverizer is a direction in which the circularity increases. In particular, in a high-speed rotating rotor type pulverizer, the circularity is changed by controlling the temperature of the pulverizing section, and the higher the temperature, the higher the circularity.

<Toner base particles>
The toner base particles according to the present invention contain a binder resin, a white colorant, and a release agent.

(Binder resin)
Examples of the binder resin according to the present invention include homopolymers of styrene such as polystyrene, poly-p-styrene, polyvinyltoluene, and the like, and substituted polymers thereof, styrene / p-chlorostyrene copolymers, and styrene / propylene copolymers. Styrene / vinyl toluene copolymer, styrene / methyl acrylate polymer, styrene / ethyl acrylate copolymer, styrene / butyl acrylate copolymer, styrene / methyl methacrylate copolymer, styrene / ethyl methacrylate copolymer Polymer, styrene / butyl methacrylate copolymer, styrene / α-chloromethyl methacrylate copolymer, styrene / acrylonitrile copolymer, styrene / vinyl methyl ether copolymer, styrene / vinyl methyl ketone copolymer, styrene・ Butadiene copolymer, styrene / isoprene copolymer Styrene copolymer such as styrene / maleic acid copolymer, styrene / maleic acid ester copolymer, polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyester, polyurethane, Polyamide, epoxy resin, polyvinyl butyral, polyacrylic acid resin, rosin, modified rosin, terpene resin, phenol resin, aliphatic hydrocarbon resin, aromatic petroleum resin, chlorinated paraffin, paraffin wax, etc. Alternatively, they can be mixed and used.

(White colorant)
As the white colorant according to the present invention, known ones can be appropriately employed, and examples thereof include titanium oxide, zinc oxide, barium sulfate, alumina, and calcium carbonate.
Moreover, a commercially available thing can also be used, for example, Ishihara Sangyo Co., Ltd. ET-500W and ET-300W are mentioned as a titanium oxide.

(Release agent)
The toner base particles according to the present invention contain a release agent as an essential component.

  As the release agent, wax is preferably used. Examples of the wax include low molecular weight polyethylene wax, low molecular weight polypropylene wax, Fischer-Tropsch wax, microcrystalline wax, hydrocarbon waxes such as paraffin wax, carnauba wax, pentaerythritol behenate, behenyl behenate, Examples thereof include ester waxes such as behenyl acid and fatty acid amides. These can be used alone or in combination of two or more.

  Preferred commercially available hydrocarbon waxes include, for example, “Biscol 660P”, “Biscol 550P” (above, manufactured by Sanyo Chemical Industries), “Polyethylene 6A” (manufactured by Allied Chemical), “High Wax 400P”, “ “High Wax 100P”, “High Wax 200P”, “High Wax 320P”, “High Wax 220P”, “High Wax 2203A”, “High Wax 4202E” (Mitsui Petrochemical Co., Ltd.), “Hoechst Wax PE520”, Examples include “Hoechst wax PE130” and “Hoechst wax PE190” (manufactured by Hoechst Japan).

As the fatty acid amide, an alkylene bis fatty acid amide is preferable, and an alkylene bis fatty acid amide having a melting point in the range of about 100 to 180 ° C. is particularly preferable.
Preferred examples of such commercially available alkylene bis fatty acid amides include “bisamide”, “diamond 200 bis”, “Lublon O” (manufactured by Nippon Hydrogen Industries Co., Ltd.), “Plasto Flow” (manufactured by Nitto Chemical Co., Ltd.), "Alflow H3O5", "Alflow V-60" (Nippon Yushi Co., Ltd.), "Hoechst Wax C" (Hoechst Jaban), "Nobuco Wax-22DS" (Nobuco Chemical), "Adva Wax-28Q" ”(Manufactured by Advance Co., Ltd.),“ Kaoh Wax-EB ”(manufactured by Kao Corporation),“ Varicin-285 ”(manufactured by Baker Custer Oil Co., Ltd.) and the like. In particular, “Hoechst wax C” is preferable.

  The ester wax is preferably a fatty acid ester having a melting point of about 30 to 130 ° C. or a partially saponified product thereof. For example, a fatty acid polyhydric alcohol ester, a fatty acid higher alcohol ester, a fatty acid and a polyhydric alcohol moiety. An ester mixed ester etc. can be mentioned. In particular, higher alcohol esters of fatty acids are preferred.

As the wax, it is preferable to use a wax having a melting point of 50 to 150 ° C. from the viewpoint of reliably obtaining low-temperature fixability and releasability of the toner. The wax content is preferably in the range of 2 to 20% by mass, more preferably in the range of 3 to 18% by mass, and still more preferably in the range of 4 to 15% by mass with respect to the total amount of the binder resin. It is.
In addition, it is preferable to form a domain as the presence state of the wax in the toner particles in order to exert a releasability effect. By forming the domain in the binder resin, each function can be easily performed.
The domain diameter of the wax is preferably in the range of 300 nm to 2 μm. If it is this range, the effect of releasability is fully acquired and the capability to hold | maintain a small diameter lubricant is also securable.

<External additive>
From the viewpoint of improving the charging performance, fluidity, and cleaning properties of the toner, particles such as known inorganic fine particles and organic fine particles and a lubricant can be added as external additives to the surface of the toner base particles. As these external additives, various types may be used in combination.

  The lubricant is used for the purpose of further improving the cleaning property and the transfer property. Examples of the lubricant include zinc stearate, aluminum, copper, magnesium, calcium salts, zinc oleate, manganese, and the like. (Higher) fatty acid metals such as iron, copper, magnesium salts, zinc palmitate, copper, magnesium, calcium salts, zinc linoleate, calcium salts, zinc ricinoleate, calcium salts, etc. Examples include salt particles.

In the present invention, the external additive contains fatty acid metal salt particles (lubricant) having a volume-based median diameter in the range of 0.5 to 1.5 μm. This is because the effects of the present invention can be effectively expressed by using a lubricant having a particle size in the above-described range from the relationship between physical and electrostatic retention with the toner base particles. When the volume-based median diameter of the fatty acid metal salt particles is less than 0.5 μm, it is deformed and fused by the mixing stress of the developing machine and contaminates the surfaces of the carrier and other members. On the other hand, when the volume-based median diameter of the fatty acid metal salt particles is larger than 1.5 μm, the retention property with respect to the toner base particles is lowered and the toner particles are separated immediately, and an image defect with a bias occurs.
The volume-based median diameter (volume average particle diameter) of the fatty acid metal salt particles (lubricant) can be measured using a laser diffraction particle size analyzer SALD-2100 (manufactured by Shimadzu Corporation).

  As the fatty acid metal salt (particle) having a volume-based median diameter, the above-mentioned various (higher) fatty acid metal salts (particles) can be used. Among them, metal stearates are preferable, for example, calcium stearate, stearin Examples thereof include magnesium oxide and zinc stearate, and zinc stearate is particularly preferable from the viewpoint of performance as a lubricant and electrostatic toner retention.

  The content of the volume-based median diameter fatty acid metal salt particles (lubricant) is preferably in the range of 0.05 to 0.60 mass% with respect to the total amount of toner. When the content of the fatty acid metal salt particles (lubricant) is 0.05% by mass or more, the effects of the present invention can be effectively expressed. If the content of the fatty acid metal salt particles (lubricant) is 0.60% by mass or less, charging inhibition between the toner and the carrier due to excessive addition is suppressed, and the effect of the present invention can be effectively exhibited. .

  In the present invention, it is only necessary to use a lubricant having the above-mentioned particle size range (the fatty acid metal salt particles having a volume-based median diameter) as an external additive. Particles may be used in combination.

  Inorganic fine particles include inorganic oxide fine particles such as silica, titania and alumina, inorganic stearic acid compound fine particles such as aluminum stearate fine particles and zinc stearate fine particles, inorganic titanic acid such as calcium titanate, strontium titanate and zinc titanate. Examples thereof include inorganic fine particles such as compound fine particles. Among these, inorganic titanate compound fine particles (metal oxide fine particles) such as strontium titanate and calcium titanate have a high polishing effect. Examples of the silica particles include colloidal silica, hydrolyzate of alkoxysilane (silica prepared by a sol-gel method), silica produced by a wet method such as precipitated silica, fumed silica, fused silica, etc. Silica and the like produced in (1) are used.

  These inorganic fine particles are treated with silane or titanium coupling agents, higher fatty acids, silicone oil, etc. for gloss treatment and hydrophobization, if necessary, to improve heat-resistant storage stability and environmental stability. Processing etc. may be performed. From the viewpoint of improving the fluidity of the external additive, it is preferable to use silica particles that have been subjected to a hydrophobic treatment (surface treatment) with hexamethyldisilazane (HMDS) or the like.

  As these inorganic fine particles, it is preferable to use spherical fine particles having a number average primary particle diameter of about 5 nm to 2 μm, with or without hydrophobic treatment. The number average primary particle diameter of the inorganic fine particles can be calculated using an electron micrograph. Specifically, a 30,000 times photograph of a toner sample is taken with a scanning electron microscope, and this photographic image is taken. Is captured by the scanner. In the image processing analysis device LUZEX (registered trademark) AP (manufactured by Nireco Co., Ltd.), the external additive present on the toner surface of the photographic image is binarized and the horizontal direction of 100 external additives is classified. The ferret diameter is calculated, and the average value is defined as the number average primary particle diameter.

  As the inorganic fine particles, two types of particles (for example, silica particles) having different number average primary particle diameters may be used. For example, the larger number average primary particle diameter is preferably in the range of 60 to 250 nm, and more preferably in the range of 80 to 200 nm. Within such a range, adhesion of particles having a larger particle diameter to the toner base particles can be promoted, and the stability of the charge amount and the cleaning property can be improved. Further, the number average primary particle diameter of the smaller particle diameter is preferably in the range of 5 to 45 nm, and more preferably in the range of 12 to 40 nm. Within such a range, good chargeability of the small-diameter silica particles can be sufficiently obtained, and the initial charge amount in a high-temperature and high-humidity environment can be easily obtained by facilitating uniform adhesion on the surface of the toner base particles. The stability of the charge amount can be improved.

  As the organic fine particles, spherical organic fine particles having a number average primary particle diameter of about 10 nm to 2 μm can be used. Specifically, homopolymers such as styrene and methyl methacrylate and organic fine particles made of these copolymers can be used. The number average primary particle diameter of the organic fine particles can be calculated using an electron micrograph in the same manner as the number average primary particle diameter of the inorganic fine particles.

  The addition amount of the external additive is preferably in the range of 0.1 to 10.0 parts by mass with respect to 100 parts by mass of the toner base particles.

  Examples of the method of adding the external additive include a method of adding using various known mixing apparatuses such as a Turbuler mixer, a Henschel mixer, a Nauter mixer, and a V-type mixer.

<Charge control agent>
The toner particles according to the present invention may contain various additives such as a charge control agent as necessary. The charge control agent is not particularly limited, and various known compounds can be used.

<Toner particle size>
The particle diameter of the toner particles constituting the white toner is preferably in the range of 4 to 12 μm, and more preferably in the range of 5 to 9 μm, for example, in terms of volume-based median diameter.
When the volume-based median diameter is in the above range, the transfer efficiency is increased, the image quality of halftone is improved, and the image quality of fine lines and dots is improved.

The volume-based median diameter of the toner particles is measured and calculated using a measuring apparatus in which a data processing computer system (Beckman Coulter) is connected to “Multisizer 3” (Beckman Coulter, Inc.).
Specifically, 0.02 g of toner is added to 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 toner particles). Then, ultrasonic dispersion treatment was performed for 1 minute to prepare a dispersion of toner particles, and this dispersion of toner particles was put into “ISOTON II” (manufactured by Beckman Coulter) in a sample stand. Inject into a beaker with a pipette until the displayed concentration of the measuring device is 5-10% by mass. Here, a reproducible measurement value can be obtained by setting the concentration range. In the measurement apparatus, the measurement particle count number is 25000, the aperture diameter is 50 μm, the frequency range is calculated by dividing the measurement range of 1 to 30 μm into 256, and the volume integrated fraction is 50 % Is the volume-based median diameter.

<Developer for developing electrostatic image>
The white toner for developing an electrostatic charge image of the present invention can be used as a non-magnetic one-component developer, but may be mixed with a carrier and used as a two-component developer. When white toner is used as a two-component developer, the carrier includes magnetic particles made of a conventionally known material such as a metal such as iron, ferrite, or magnetite, or an alloy of such metal and a metal such as aluminum or lead. In particular, ferrite particles are preferable. Further, as the carrier, a coated carrier in which the surface of magnetic particles is coated with a coating agent such as a resin, a dispersion type carrier in which a magnetic fine powder is dispersed in a binder resin, or the like may be used.

  The volume-based median diameter of the carrier is preferably in the range of 15 to 100 μm, and more preferably in the range of 25 to 60 μm. The volume-based median diameter of the carrier can be typically measured by a laser diffraction particle size distribution measuring apparatus “HELOS” (manufactured by Sympathic) equipped with a wet disperser.

<Method for producing white toner for developing electrostatic image>
The method for producing the white toner for developing an electrostatic image of the present invention is not particularly limited, and examples thereof include a pulverization method, an emulsion polymerization aggregation method, and an emulsion aggregation method. The average circularity of the toner particles is 0.870 to 0.950. From the viewpoint of being within the range, it is preferable to produce by a pulverization method.

An example of using a pulverization method as a method for producing a white toner will be described below.
(1) A step of mixing a binder resin, a white colorant and a release agent, and if necessary, an internal additive with a Henschel mixer or the like (2) a step of kneading the obtained mixture while heating with an extrusion kneader or the like (3) A step of roughly pulverizing the obtained kneaded material with a hammer mill or the like and then further pulverizing with a turbo mill pulverizer or the like. (4) The obtained pulverized material is subjected to, for example, an air classifier utilizing the Coanda effect. (5) A step of adding an external additive to the toner base particles.

  In the emulsion polymerization aggregation method, a dispersion of binder resin fine particles (hereinafter also referred to as “binder resin fine particles”) produced by the emulsion polymerization method is referred to as colorant fine particles (hereinafter also referred to as “colorant fine particles”). .) Mixing with a dispersion liquid of a releasing agent such as a dispersion liquid and wax, agglomerating the toner particles until a desired particle size is achieved, and further fusing the binder resin fine particles to perform shape control, A method for producing toner particles.

  In the emulsion aggregation method, a binder resin solution dissolved in a solvent is dropped into a poor solvent to form a resin particle dispersion, and this resin particle dispersion is mixed with a colorant dispersion and a release agent dispersion such as wax. In this method, toner particles are produced by agglomerating until a desired toner particle diameter is obtained, and further controlling the shape by fusing the binder resin fine particles.

As an example of a method for producing a white toner, an example in which an emulsion polymerization aggregation method is used is shown below.
(1) Step of preparing a dispersion in which fine particles of white colorant are dispersed in an aqueous medium and a dispersion in which a release agent is dispersed (2) An internal additive is added to the aqueous medium as necessary. Step of preparing dispersion in which contained binder resin fine particles are dispersed (3) Step of preparing dispersion of binder resin fine particles by emulsion polymerization (4) Dispersion of fine particles of white colorant and binding Step of forming toner base particles by mixing the dispersion of resin fine particles and aggregating, associating and fusing the fine particles of white colorant and binder resin fine particles (5) Dispersion system of toner base particles (aqueous medium) ) Step of removing toner base particles from the toner and removing the surfactant, etc. (6) Step of drying the toner base particles (7) Step of adding an external additive to the toner base particles

  In the case of producing a white toner by the emulsion polymerization aggregation method, the binder resin fine particles obtained by the emulsion polymerization method may have a multilayer structure of two or more layers made of binder resins having different compositions. For the binder resin fine particles having such a structure, for example, those having a two-layer structure, a dispersion of resin particles is prepared by emulsion polymerization treatment (first-stage polymerization) according to a conventional method, and a polymerization initiator is added to the dispersion. And a polymerizable monomer are added, and this system can be obtained by a polymerization treatment (second stage polymerization).

  In addition, toner particles having a core / shell structure can be obtained by an emulsion polymerization aggregation method. Specifically, the toner particles having a core / shell structure are first formed of a binder resin fine particle for a core particle and a white colorant. The core particles are prepared by agglomerating, associating and fusing the fine particles, and then the binder resin fine particles for the shell layer are added to the core particle dispersion, and the binder resin fine particles for the shell layer are formed on the core particle surface. It can be obtained by agglomerating and fusing to form a shell layer covering the core particle surface.

<Image forming method>
The image forming method of the present invention includes at least a charging step, a latent image forming step, a developing step, a transferring step, a fixing step, and a cleaning step. The white toner for developing an electrostatic image of the present invention and a colored color other than white It is preferable to use an electrostatic image developing colored toner containing an agent (hereinafter also simply referred to as a colored toner). Thereby, it is possible to form an image having concealability, hue, and transferability that can meet the demands of the production print market.

<Colored toner for developing electrostatic image containing colorant other than white>
The color toner for developing an electrostatic image containing a colorant other than white (for example, Y (yellow), M (magenta), C (cyan), Bk (black)) is not particularly limited and is generally not limited. Known toners such as toners containing various colorants can be used.
The average circularity of the toner base particles in the colored toner for developing an electrostatic image is preferably in the range of 0.951 to 0.990. The average circularity of the toner base particles in the colored toner can be obtained in the same manner as the average circularity of the toner particles in the white toner for developing an electrostatic image.
The method for producing the colored toner is not particularly limited, but it is preferably produced by an emulsion polymerization method in order to realize the above average circularity.

(Charging process)
In this step, the electrophotographic photosensitive member is charged. The method for charging is not particularly limited, and for example, a charging means described later can be suitably used.

(Latent image forming process)
In this step, an electrostatic latent image is formed on the electrophotographic photosensitive member (electrostatic latent image carrier).
The electrophotographic photosensitive member is not particularly limited, and examples thereof include a drum-shaped one made of an organic photosensitive member such as polysilane or phthalopolymethine.
As will be described later, the electrostatic latent image is formed by uniformly charging the surface of the electrophotographic photosensitive member with a charging unit and exposing the surface of the electrophotographic photosensitive member imagewise with an exposing unit.
The exposure means is not particularly limited, and those described below can be used.

(Development process)
The development step is a step of developing the electrostatic latent image with a dry developer containing toner to form a toner image.
The toner image is formed using a dry developer containing toner, for example, using a developing unit described later.
Specifically, in the developing unit, for example, the toner and the carrier are mixed and stirred, and the toner is charged by friction at that time, and is held on the surface of the rotating magnet roller, thereby forming a magnetic brush. Since the magnet roller is disposed in the vicinity of the electrophotographic photosensitive member, a part of the toner constituting the magnetic brush formed on the surface of the magnetic roller moves to the surface of the electrophotographic photosensitive member by an electric attractive force. . As a result, the electrostatic latent image is developed with toner, and a toner image is formed on the surface of the electrophotographic photosensitive member.

(Transfer process)
In this step, the toner image is transferred to a transfer material.
Transfer of the toner image to the transfer material is performed by peeling and charging the toner image onto the transfer material.
As the transfer means, for example, a corona transfer device using corona discharge, a transfer belt, a transfer roller, or the like can be used.
In addition, in the transfer process, for example, an intermediate transfer member (intermediate transfer member) is used, and after a toner image is primarily transferred onto the intermediate transfer member, the toner image is secondarily transferred onto a transfer material. The toner image formed on the photographic photosensitive member can be directly transferred onto a transfer material.
The transfer material is not particularly limited, and is a plain paper from thin paper to thick paper, high-quality paper, coated printing paper such as art paper or coated paper, commercially available Japanese paper or postcard paper, a plastic film for OHP, Various types such as cloth can be mentioned.

(Fixing process)
In the fixing step, the toner image transferred to the transfer material is fixed to the transfer material. The fixing method is not particularly limited, and a known fixing unit as described later can be used. Specifically, for example, a heat roller fixing constituted by a heating roller having a heating source therein and a pressure roller provided in pressure contact with the heating roller so as to form a fixing nip portion. One of the methods is mentioned.

(Cleaning process)
In this step, the liquid developer that has not been used for image formation or remains untransferred is removed from the developer carrier such as a developing roller, a photoreceptor, and an intermediate transfer member.
The cleaning method is not particularly limited, but it is preferable to use a blade that is provided with its tip in contact with the photoconductor and scratches the surface of the photoconductor. For example, a cleaning unit as described below is used. Can do.
In the cleaning process, white toner for developing an electrostatic charge image is transferred to a non-image forming area of an intermediate transfer body corresponding to a transfer material that is continuously conveyed, and the electrostatic image development is performed by a cleaning unit such as a blade. It is preferable to collect the white toner and clean the intermediate transfer member using the white toner for developing an electrostatic image.

<Image forming apparatus>
FIG. 1 shows, as an example, an image forming apparatus that can use the white toner for developing an electrostatic charge image of the present invention.
The image forming apparatus includes a charging unit, an electrostatic image forming unit, a developing unit, a transfer unit, a fixing unit, and a cleaning unit, and the developing unit is a white toner for developing an electrostatic image of the present invention. It is preferable that the toner image is formed by developing the electrostatic charge image with a developer for developing an electrostatic charge image containing the toner.
Further, the image forming apparatus has five or more electrostatic charge image forming units and developing units, for example, white (W), yellow (Y), magenta (M), cyan (C) and black. A full-color image that realizes white having concealment, hue, and transferability that can meet the demands of the production print market by having electrostatic charge image forming means and developing means corresponding to the five colors (Bk) for each color. Is preferable.

  This image forming apparatus 100 is called a tandem color image forming apparatus, and includes five sets of image forming units (image forming units) 10W, 10Y, 10M, 10C, and 10Bk, an endless belt-shaped intermediate transfer body unit 7, and the like. The sheet feeding unit 21 and the fixing unit 24 are included. A document image reading device SC is disposed on the upper part of the main body A of the image forming apparatus 100.

The image forming unit 10W for forming a white image includes a drum-shaped photoreceptor 1W, a charging unit 2W, an exposure unit 3W, a developing unit 4W, a primary transfer roller 5W as a primary transfer unit, and a cleaning unit 6W.
An image forming unit 10Y that forms a yellow image includes 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 disposed around a drum-shaped photoreceptor 1Y. Means 6Y are provided.
The image forming unit 10M that forms a magenta image includes a drum-shaped photoreceptor 1M, a charging unit 2M, an exposure unit 3M, a developing unit 4M, a primary transfer roller 5M as a primary transfer unit, and a cleaning unit 6M.
The image forming unit 10C for forming a cyan image includes a drum-shaped photoreceptor 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.
The image forming unit 10Bk for forming a black image includes a drum-shaped photoreceptor 1Bk, a charging unit 2Bk, an exposure unit 3Bk, a developing unit 4Bk, a primary transfer roller 5Bk as a primary transfer unit, and a cleaning unit 6Bk.

  The five sets of image forming units (10W, 10Y, 10M, 10C, and 10Bk) are respectively charged with the charging units 2W, 2Y, 2M, 2C, and 2Bk, and the electrostatic charges around the photoreceptors 1W, 1Y, 1M, 1C, and 1Bk. Image forming means exposure means 3W, 3Y, 3M, 3C and 3Bk, rotating developing means 4W, 4Y, 4M, 4C and 4Bk, and cleaning means 6W for cleaning the photoreceptors 1W, 1Y, 1M, 1C and 1Bk. , 6Y, 6M, 6C and 6Bk.

  The image forming units 10W, 10Y, 10M, 10C, and 10Bk have the same configuration except that the colors of toner images formed on the photoreceptors 1W, 1Y, 1M, 1C, and 1Bk are different. This will be described in detail.

  The image forming unit 10W includes a charging unit 2W, an exposure unit 3W, a developing unit 4W, and a cleaning unit 6W around a photoconductor 1W that is an image forming body, and a white (W) toner image is formed on the photoconductor 1W. Form. In the present embodiment, in the image forming unit 10W, at least the photoreceptor 1W, the charging unit 2W, the developing unit 4W, and the cleaning unit 6W are provided so as to be integrated.

  The charging unit 2W is a unit that applies a uniform potential to the photoreceptor 1W. In the present invention, examples of the charging means include contact or non-contact roller charging methods.

  The exposure means 3W performs exposure based on the image signal (white) on the photoreceptor 1W given a uniform potential by the charging means 2W, and forms an electrostatic latent image corresponding to the white image. As the image forming means, the exposure means 3W is composed of an LED in which light emitting elements are arranged in an array in the axial direction of the photoreceptor 1W and an image forming element, or a laser optical system.

  The developing unit 4W includes, for example, a developing sleeve that contains a magnet and rotates while holding the developer, and a voltage applying device that applies a DC and / or AC bias voltage between the developing sleeve and the photosensitive member. In particular, the developing unit 4W preferably forms a toner image by developing the electrostatic image with the developer for developing an electrostatic image containing the white toner for developing an electrostatic image of the present invention.

  The fixing unit 24 is, for example, a heat roller fixing formed by a heating roller having a heating source therein and a pressure roller provided in pressure contact with the heating roller so as to form a fixing nip portion. One of the methods is mentioned.

  The cleaning unit 6W includes a cleaning blade and a brush roller provided on the upstream side of the cleaning blade.

  The image forming apparatus 100 includes a photosensitive member and components such as a developing unit and a cleaning unit that are integrally coupled as a process cartridge (image forming unit), and the image forming unit is detachable from the apparatus main body. It may be configured. In addition, a process cartridge (image forming unit) is formed by integrally supporting at least one of a charging unit, an exposure unit, a developing unit, a transfer unit, and a cleaning unit together with a photoreceptor, and a single image is formed on the apparatus main body. It is good also as a unit and the structure which can be attached or detached using guide means, such as a rail of an apparatus main body.

  The endless belt-shaped intermediate transfer body unit 7 has 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.

  Each color image formed by the image forming units 10W, 10Y, 10M, 10C and 10Bk is rotated by an endless belt-like intermediate transfer by primary transfer rollers 5W, 5Y, 5M, 5C and 5Bk as primary transfer means. The color image is sequentially transferred onto the body 70 to form a synthesized color image. A transfer material (image support for carrying a final fixed image: for example, plain paper, transparent sheet, etc.) P accommodated in the paper feed cassette 20 is fed by the paper feed means 21, and includes a plurality of intermediate rollers 22A, After passing through 22B, 22C, 22D and the registration roller 23, it is conveyed to the secondary transfer roller 5b as the secondary transfer means, and is secondarily transferred onto the transfer material P, and the color images are collectively transferred. The transfer material P onto which the color image has been transferred is fixed by the fixing means 24, is sandwiched between the paper discharge rollers 25, and is placed on a paper discharge tray 26 outside the apparatus. Here, a toner image transfer support formed on a photosensitive member such as an intermediate transfer member or a transfer material is generically referred to as a transfer medium.

  On the other hand, the endless belt-shaped intermediate transfer body 70 obtained by transferring the color image onto the transfer material P by the secondary transfer roller 5b as the secondary transfer unit and then separating the curvature of the transfer material P has the residual toner removed by the cleaning unit 6b. The

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

Further, the white toner for developing an electrostatic charge image of the present invention may be developed and transferred to the intermediate transfer member 70 by bringing the primary transfer roller 5W into contact with the photosensitive member 1W even when the image is not formed.
Usually, since no image is formed between the transfer materials P that are continuously conveyed, the toner images of the respective colors are not transferred to the non-image forming regions of the intermediate transfer body 70 corresponding to the transfer materials P. The white toner for developing an electrostatic charge image of the present invention is developed and transferred to a non-image forming area of the body 70. The white toner is not transferred to the transfer material P as a matter of course, and thus is not transferred by the secondary transfer roller 5b but is held by the intermediate transfer body 70 and then removed by the cleaning means 6b. Here, since the average circularity of the toner particles in the white toner is in the range of 0.870 to 0.950, the fine toner on the intermediate transfer body 70 at the edge portion of the toner particles collected by the cleaning unit 6b. The spent component can be scraped off, and in addition to the cleaning means 6b, white toner can function as a cleaning means.

  The secondary transfer roller 5b contacts the endless belt-shaped intermediate transfer body 70 only when the transfer material P passes through the secondary transfer roller 5b and secondary transfer is performed.

  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 10W, 10Y, 10M, 10C, and 10Bk, and an endless belt-shaped intermediate transfer body unit 7.

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

In the image forming apparatus 100 shown in FIG. 1, a color laser printer is shown, but the present invention can be similarly applied to a monochrome laser printer and a copy. The exposure light source may also be a light source other than a laser, such as an LED light source.
Further, as described above, the image forming apparatus 100 has five or more electrostatic charge image forming units and developing units, respectively, so that it has excellent concealability, hue, and transferability that can meet the demands of the production print market. It is preferable because a full-color image that realizes a white color can be formed.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

<< Preparation of fatty acid metal salt >>
Fatty acid metal salts S1 to S8 were prepared as follows.

<Preparation of fatty acid metal salt S1>
140 parts by mass of stearic acid was added to 1000 parts by mass of ethanol, and 50 parts by mass of zinc hydroxide was slowly added to the mixture at 75 ° C. and mixed for 1 hour. Then, it cooled to 20 degreeC and took out the product, it was made to dry at 150 degreeC, and ethanol was removed. The obtained solid material of zinc stearate is coarsely pulverized with a hammer mill, then finely pulverized with a jet airflow pulverizer “I-20 Jet Mill” (manufactured by Nippon Pneumatic Co., Ltd.), and a wind classifier “DS- A fatty acid metal salt S1 made of zinc stearate having a volume average particle diameter of 0.72 μm was prepared by classification with a “20 / DS-10 classifier” (manufactured by Nippon Pneumatic Co., Ltd.) at a cut point of 1.1 μm.
In this example, the volume-based median diameter (volume average particle diameter) of the fatty acid metal salt particles was measured using a laser diffraction particle size analyzer SALD-2100 (manufactured by Shimadzu Corporation).

<Preparation of fatty acid metal salt S2>
In the preparation of the fatty acid metal salt S1, a fatty acid metal salt S2 made of zinc stearate having a volume average particle size of 0.51 μm was prepared in the same manner except that the cut point was changed to 0.8 μm.

<Preparation of fatty acid metal salt S3>
In the preparation of fatty acid metal salt S1, fatty acid metal salt S3 made of zinc stearate having a volume average particle diameter of 1.48 μm was prepared in the same manner except that the cut point was changed to 1.9 μm.

<Preparation of fatty acid metal salt S4>
In the preparation of the fatty acid metal salt S1, a fatty acid metal salt S4 made of calcium stearate having a volume average particle diameter of 0.78 μm was prepared in the same manner except that zinc hydroxide was changed to calcium hydroxide.

<Preparation of fatty acid metal salt S5>
In the preparation of fatty acid metal salt S2, fatty acid metal salt S5 made of calcium stearate having a volume average particle size of 0.52 μm was prepared in the same manner except that zinc hydroxide was changed to calcium hydroxide.

<Preparation of fatty acid metal salt S6>
In the preparation of the fatty acid metal salt S3, a fatty acid metal salt S6 made of calcium stearate having a volume average particle size of 1.49 μm was prepared in the same manner except that zinc hydroxide was changed to calcium hydroxide.

<Preparation of fatty acid metal salt S7>
A fatty acid metal salt S7 made of zinc stearate having a volume average particle size of 0.42 μm was prepared in the same manner except that the cut point was changed to 0.5 μm in the preparation of the fatty acid metal salt S1.

<Preparation of fatty acid metal salt S8>
In the preparation of fatty acid metal salt S1, fatty acid metal salt S8 made of zinc stearate having a volume average particle size of 1.67 μm was prepared in the same manner except that the cut point was changed to 2.0 μm.

<Production of toner>
Toners TW1 to TW5 and T1 to T8 were produced as follows.

<Preparation of Toner TW1>
(1) Preparation of toner base particle TW1 Binder resin: Styrene / n-butyl acrylate copolymer (Mw: 111000, Mn: 4000, Mw / Mn: 26) 100 parts by mass White colorant: Titanium oxide ET-500W ( Ishihara Sangyo Co., Ltd.) 50 parts by weight Mold release agent: Polyolefin (Biscol 660P, Sanyo Chemical Industries) 5 parts by weight Mold release agent: alkylene bis fatty acid amide (Hoechst wax C1, Hoechst)
5 parts by mass are mixed, melt-kneaded, cooled, coarsely pulverized, further pulverized using a turbo mill (cooling water temperature: 5 ° C.), and then classified to have a volume average particle size of 7.1 μm, White toner base particles TW1 having an average circularity of 0.878 were prepared.

In this example, the volume average particle diameter of the toner base particles was measured as follows.
The volume average particle diameter of the toner base particles was measured and calculated using a measuring apparatus in which a computer system for data processing (manufactured by Beckman Coulter) was connected to “Multisizer 3” (manufactured by Beckman Coulter).
Specifically, 0.02 g of toner base particles are added to 20 mL of a surfactant solution (for example, a surfactant solution in which a neutral detergent containing a surfactant component is diluted 10 times with pure water for the purpose of dispersing the toner base particles. ), And then subjected to ultrasonic dispersion treatment for 1 minute to prepare a dispersion of toner base particles. This toner base particle dispersion is used as “ISOTONII” (Beckman Coulter, Inc.) in the sample stand. Was poured into the beaker containing the product until the indicated concentration of the measuring device was 5 to 10% by mass. In the measuring device, the measurement particle count number is 25000, the aperture diameter is 50 μm, the frequency value is calculated by dividing the measurement range of 1 to 30 μm into 256, and the volume integrated fraction is 50% from the largest. The particle size was defined as the volume average particle size.

In this example, the average circularity of the toner base particles (and toner particles) was measured as follows.
First, 10 mL of ion-exchanged water from which impure solids are removed in advance is prepared in a container. After adding a surfactant (alkyl benzene sulfonate) as a dispersant, 0.02 g of a measurement sample was further added and dispersed uniformly.
As a means for dispersion, an ultrasonic disperser “Tetora 150 type” (manufactured by Nikka Ki Bios) was used for dispersion treatment for 2 minutes to obtain a dispersion for measurement. In that case, it cooled suitably so that the temperature of this dispersion might not become 40 degreeC or more.
In order to suppress variation in circularity, the installation environment of the apparatus is set to 23 ° C. ± 0.5 ° C. so that the in-machine temperature of the flow type particle image analyzer FPIA-2100 (manufactured by Sysmex Corporation) is in the range of 26 to 27 ° C. The autofocus was adjusted every 2 hours using 2 μm latex particles.
To measure the circularity of the toner base particles, the above-mentioned flow type particle image analyzer is used to readjust the dispersion concentration so that the toner base particle concentration at the time of measurement is 3000 to 10,000 particles / μL, More than 1000 particles were measured. After the measurement, data having an equivalent circle diameter of less than 2 μm was cut using this data, and the average circularity of the toner base particles was determined.

(2) Preparation of Toner Particle TW1 0.75 mass of small-diameter silica fine particles (“RX-200” fumed silica HMDS treatment, number average particle size 12 nm: manufactured by Nippon Aerosil Co., Ltd.) on 100 parts by mass of dried toner base particle TW1. Parts, spherical silica fine particles (silica HMDS treatment by “X-24 9600” sol-gel process, number average particle size 80 nm: manufactured by Shin-Etsu Chemical Co., Ltd.) 1.50 parts by mass, fatty acid metal salt S1 (zinc stearate particles) 0.30 0.5 parts by mass of calcium titanate particles (“TC-110”, silicone oil-treated number average particle size 300 nm: manufactured by Titanium Kogyo Co., Ltd.) as metal oxide fine particles having a high polishing effect are added to a Henschel mixer “FM10B. (Mitsui Miike Chemical Co., Ltd.), mixing with stirring blade peripheral speed of 40 m / sec, treatment temperature of 30 ° C. for 12 minutes , The average degree of circularity was produced white toner TW1 is 0.877.

<Preparation of Toners TW2 to TW5>
In the production of the toner TW1, white toners TW2 to TW5 were produced in the same manner except that the pulverization method and the cooling water temperature in the preparation of the toner base particles were changed as shown in Table I.

<Preparation of Toner T1>
(1) Preparation of toner base particle T1 Binder resin: Styrene / n-butyl acrylate copolymer (Mw: 111000, Mn: 4000, Mw / Mn: 26) 100 parts by mass Colorant: C.I. I. Pig. Yellow 74 10 parts by weight Release agent: Polyolefin (Biscol 660P, manufactured by Sanyo Chemical Industries) 5 parts by weight Release agent: alkylene bis fatty acid amide (Hoechst wax C1, manufactured by Hoechst)
5 parts by mass are mixed, melt-kneaded, cooled, coarsely pulverized, further pulverized using a turbo mill (cooling water temperature: 10 ° C.), and then classified to have a volume average particle diameter of 7.1 μm, Colored toner base particles T1 having an average circularity of 0.891 were prepared.

(2) Preparation of Toner T1 To 100 parts by mass of dried toner base particle T1 is added 2.0 parts by mass of n-butyltrimethoxysilane-treated silica (number average primary particle diameter 30 nm), and a Henschel mixer “FM10B” is added. The peripheral speed of stirring blades (manufactured by Nippon Coke Kogyo Co., Ltd.) was set to 60 m / sec, the treatment temperature was 30 ° C., and the treatment time was 20 minutes, and the external addition treatment was performed. After the external addition process, colored particles T1 were prepared by removing coarse particles using a sieve having an opening of 90 μm.

<Preparation of Toners T2 to T4>
In the production of the toner T1, the colorant is C.I. I. Pig. Red 57: 1, C.I. I. Pig. Colored toners T2 to T4 were prepared in the same manner except that the color was changed to Blue 15: 3 and carbon black (BPL, manufactured by Cabot Corporation).

<Preparation of Toner T5>
(1) Preparation of resin fine particles (preparing step of dispersion of resin fine particles [1] for core part)
Through the first-stage polymerization, second-stage polymerization and third-stage polymerization shown below, resin fine particles [1] for the core part having a multilayer structure were prepared.

(A) First stage polymerization (Preparation of dispersion of resin fine particles [A1])
In a reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introduction device, a surfactant solution in which 4 parts by mass of sodium polyoxyethylene-2-dodecyl ether sulfate was dissolved in 3040 parts by mass of ion-exchanged water was charged. The internal temperature was raised to 80 ° C. while stirring at a stirring speed of 230 rpm under a nitrogen stream. To this surfactant solution, a polymerization initiator solution in which 10 parts by mass of a polymerization initiator (potassium persulfate: KPS) was dissolved in 400 parts by mass of ion-exchanged water was added to a temperature of 75 ° C., and then 532 masses of styrene. A monomer mixture consisting of 1 part by weight, 200 parts by weight of n-butyl acrylate, 68 parts by weight of methacrylic acid, and 16.4 parts by weight of n-octyl mercaptan was dropped over 1 hour, and this system was kept at 75 ° C. for 2 hours. Polymerization (first stage polymerization) was carried out by heating and stirring to prepare a dispersion of resin fine particles [A1].
The weight average molecular weight (Mw) of the resin fine particles [A1] prepared by the first stage polymerization was 16,500.

In this example, the measurement of the weight average molecular weight (Mw) was performed using “HLC-8220” (manufactured by Tosoh Corporation) and the column “TSKguardcolumn + TSKgelSuperHZM-M3 series” (manufactured by Tosoh Corporation) and maintaining the column temperature at 40 ° C. Meanwhile, tetrahydrofuran (THF) as a carrier solvent was allowed to flow at a flow rate of 0.2 ml / min, and the sample to be measured was dissolved in tetrahydrofuran so as to have a concentration of 1 mg / mL under a dissolution condition in which treatment was performed for 5 minutes using an ultrasonic disperser at room temperature. Next, the sample solution is obtained by processing with a membrane filter having a pore size of 0.2 μm, and 10 μL of this sample solution is injected into the apparatus together with the carrier solvent, and detected using a refractive index detector (RI detector). The molecular weight distribution of the sample to be measured using monodisperse polystyrene standard particles It calculated using the calibration curve measured using. As a standard polystyrene sample for calibration curve measurement, the molecular weights manufactured by Pressure Chemical are 6 × 10 ² , 2.1 × 10 ³ , 4 × 10 ³ , 1.75 × 10 ⁴ , 5.1 × 10 ⁴ , 1 .1 × 10 ⁵ , 3.9 × 10 ⁶ , 8.6 × 10 ⁵ , 2 × 10 ⁶ , 4.48 × 10 ⁶ , and at least about 10 standard polystyrene samples were measured, and a calibration curve It was created. A refractive index detector was used as the detector.

(B) Second stage polymerization (preparation of dispersion of resin fine particles [A2]: formation of intermediate layer)
In a flask equipped with a stirrer, a monomer mixture comprising 101.1 parts by mass of styrene, 62.2 parts by mass of n-butyl acrylate, 12.3 parts by mass of methacrylic acid, and 1.75 parts by mass of n-octyl mercaptan As a release agent, 93.8 parts by mass of paraffin wax “HNP-57” (manufactured by Nippon Seiwa Co., Ltd.) was added and heated to 90 ° C. for dissolution.
On the other hand, a surfactant solution in which 3 parts by mass of sodium polyoxyethylene-2-dodecyl ether sulfate was dissolved in 1560 parts by mass of ion-exchanged water was heated to 98 ° C., and the resin fine particles [A1 32.8 parts by mass (in terms of solid content) was added, and the monomer solution containing paraffin wax was added for 8 hours using a mechanical disperser “CLEAMIX” (manufactured by M Technique Co., Ltd.) having a circulation path. A dispersion liquid containing emulsified particles having a dispersed particle diameter of 340 nm was prepared by mixing and dispersing. Next, a polymerization initiator solution in which 6 parts by mass of potassium persulfate was dissolved in 200 parts by mass of ion-exchanged water was added to this emulsified particle dispersion, and the system was polymerized by heating and stirring at 98 ° C. for 12 hours. (Second-stage polymerization) was performed to prepare a dispersion of resin fine particles [A2].
The weight average molecular weight (Mw) of the resin fine particles [A2] prepared by the second stage polymerization was 23000.

(C) Third stage polymerization (preparation of dispersion of resin fine particles [1] for core part: formation of outer layer)
A polymerization initiator solution in which 5.45 parts by mass of potassium persulfate was dissolved in 220 parts by mass of ion-exchanged water was added to the resin particles [A2], and 293.8 parts by mass of styrene under a temperature condition of 80 ° C., A monomer mixed solution consisting of 154.1 parts by mass of n-butyl acrylate and 7.08 parts by mass of n-octyl mercaptan was added dropwise over 1 hour. After completion of the dropping, the mixture was heated and stirred for 2 hours for polymerization (third stage polymerization), and then cooled to 28 ° C. to obtain a dispersion of resin fine particles [1] for the core part.
In addition, the weight average molecular weight (Mw) of the resin fine particles for core [1] was 26800.
The volume average particle diameter of the resin fine particles [1] for core portion was 125 nm. As the volume average particle size, a value measured using a particle size distribution measuring apparatus “Coulter Multisizer 3” (manufactured by Beckman Coulter, Inc.) was adopted.
Furthermore, the glass transition temperature (Tg) of the resin fine particles [1] for the core portion was 30.5 ° C.

In this example, the glass transition temperature (Tg) was measured using a differential scanning calorimeter “Diamond DSC” (manufactured by PerkinElmer).
First, 3.0 mg of a sample was sealed in an aluminum pan and set in a holder. An empty aluminum pan was set as a reference. A first temperature raising process for raising the temperature from 0 ° C. to 200 ° C. at a raising / lowering rate of 10 ° C./min, a cooling process for cooling from 200 ° C. to 0 ° C. at a cooling rate of 10 ° C./min, A DSC curve was obtained for the resin (core resin fine particles) under the measurement conditions (temperature increase / cooling conditions) in this order through the second temperature increase process in which the temperature was increased from 200 to 200 ° C. Based on the DSC curve, an extension of the baseline before the rise of the first endothermic peak in the second temperature rising process and a tangent line indicating the maximum slope between the rising end of the first endothermic peak and the peak apex. And the intersection was defined as the glass transition temperature (Tg).

(Process for preparing dispersion of resin fine particles [1] for shell layer)
In the first stage polymerization of the resin particles for core [1], styrene is changed to 548 parts by mass, 2-ethylhexyl acrylate is changed to 156 parts by mass, methacrylic acid is changed to 96 parts by mass, and n-octyl mercaptan is changed to 16.5 parts by mass. The polymerization reaction and the post-reaction treatment were performed in the same manner except that the monomer mixture solution was used to prepare a dispersion of resin fine particles [1] for shell layer.
The weight average molecular weight (Mw) of the resin particles for shell layer [1] was 26800.
In addition, the glass transition temperature (Tg) of the resin particles for shell layer [1] was 49.8 ° C.

(2) Preparation of Colorant Fine Particle Dispersion [1] 90 parts by mass of sodium dodecyl sulfate was added to 1600 parts by mass of ion-exchanged water. I. Pig. Yellow 74 is gradually added in an amount of 420 parts by mass, and then dispersed using a stirrer “CLEARMIX” (manufactured by M Technique Co., Ltd.), whereby a colorant fine particle dispersion in which colorant fine particles are dispersed [1 Was prepared.
The particle size of the colorant fine particles in this colorant fine particle dispersion [1] was measured using an electrophoretic light scattering photometer “ELS-800” (manufactured by Otsuka Electronics Co., Ltd.), and the volume average particle size was 110 nm. .

(3) Preparation of toner base particle T5 (a) Formation of core part (core particle) 420 parts by mass (in terms of solid content) of dispersion of resin fine particles [1] for core part, 900 parts by mass of ion-exchanged water, and coloring 100 parts by mass of the agent fine particle dispersion [1] was placed in a reaction vessel equipped with a temperature sensor, a cooling tube, a nitrogen introducing device, and a stirring device and stirred. After adjusting the temperature in the reaction vessel to 30 ° C., 5 mol / L sodium hydroxide aqueous solution was added to this solution to adjust the pH to 8-11.

Next, an aqueous solution in which 60 parts by mass of magnesium chloride hexahydrate was dissolved in 60 parts by mass of ion-exchanged water as a flocculant containing Mg element was added at 30 ° C. over 10 minutes with stirring. After standing for 3 minutes, the heating was started, and the system was heated to 80 ° C. (core formation temperature) over 80 minutes. In this state, the particle size of the particles is measured with a flow type particle image analyzer “FPIA2100” (manufactured by Sysmex Corporation), and the volume-based average particle size (also referred to as “target particle size of core particles”) is 5.8 μm. At this point, an aqueous solution in which 40.2 parts by mass of sodium chloride is dissolved in 1000 parts by mass of ion-exchanged water is added to stop the growth of the particle size, and the liquid temperature is 80 ° C. (core aging temperature) as aging treatment. Then, the fusion was continued by heating and stirring for 1 hour to form a core part (core particle) [1].
In addition, when the circularity of the core part (core particle) [1] was measured by a flow type particle image analyzer “FPIA2100” (manufactured by Sysmex Corporation), the average circularity was 0.930.

(B) Formation of Shell Layer Next, at 65 ° C., 46.8 parts by mass (in terms of solid content) of a dispersion of resin fine particles for shell layer [1] (in terms of solid content) is added. An aqueous solution in which 2 parts by mass of a Japanese product was dissolved in 60 parts by mass of ion-exchanged water was added over 10 minutes, and then the temperature was raised to 80 ° C. (shelling temperature) and stirring was continued for 1 hour. After the fine particles of the resin fine particles for shell layer [1] were fused on the surface of the particles [1], the shell layer was formed by aging to a predetermined circularity at 80 ° C. (shell aging temperature). . Here, an aqueous solution in which 40.2 parts by mass of sodium chloride was dissolved in 1000 parts by mass of ion-exchanged water was added, and the mixture was cooled to 30 ° C. at 8 ° C./min. By repeatedly washing with exchange water and then drying with warm air at 40 ° C., the core part (core particle) has a shell layer on the surface, the volume average particle diameter is 7.1 μm, and the average circularity is 0.951. A colored toner base particle T5 was prepared.

(4) Preparation of Toner T5 To 100 parts by mass of dried toner base particle T5, 2.0 parts by mass of n-butyltrimethoxysilane-treated silica (number average primary particle diameter 30 nm) is added, and Henschel mixer “FM10B” is added. The peripheral speed of stirring blades (manufactured by Nippon Coke Kogyo Co., Ltd.) was set to 60 m / sec, the treatment temperature was 30 ° C., and the treatment time was 20 minutes, and the external addition treatment was performed. After the external addition, coarse toner particles were removed using a sieve having an opening of 90 μm to prepare a colored toner T5.

<Preparation of Toners T6 to T8>
In the preparation of the toner T5, the colored colorant is C.I. I. Pig. Red 57: 1, C.I. I. Pig. Toners T6 to T8 were prepared in the same manner except that the color was changed to Blue 15: 3 and carbon black (BPL, manufactured by Cabot).

<Evaluation>
As an evaluation machine, a commercially available digital printing system “bizhub PRESS C1100 5 developing machine remodeling machine (batch transfer with intermediate transfer member + batch fixing, manufactured by Konica Minolta Co., Ltd.)” was used. In this evaluation machine, when the developer amount at the start was 1100 g originally, 1000 g was put in and a real image was taken.
The white toner and the colored toner obtained as described above were put in an appropriate combination as shown in Table III (Experiment No. J1 to J16), and 100,000 sheets were printed in an environment of 20 ° C./50% RH. The following evaluation was performed in the initial state and the state after printing 50,000 sheets and 100,000 sheets.
The evaluation results are shown in Table III.

<Image density>
The initial state and the image density of the solid image portion after printing 50,000 sheets and 100,000 sheets were measured using a reflection densitometer “RD-918” (manufactured by Macbeth) and evaluated according to the following evaluation criteria.
For the measurement of the white image density, first, a high-quality black paper (64 g / m ² ) having an image density of about 1.35 is prepared, and a white solid image portion with white toner is output thereto, and a Macbeth reflection densitometer “RD-918”. Was used to measure the absolute image density at 20 locations, and the white image density was determined from the following formula.

White image density = quality black paper density (average value of image density at 20 locations of 1.35 quality black paper)
-White solid image area measured density (average value of image density at 20 white solid image areas)

  If the white image density is 1.20 or more, there is no practical problem, but if it is less than 0.80, the practical use is severe.

A: 1.30 or more B: 1.20 or more, less than 1.30 C: 0.80 or more, less than 1.20 D: less than 0.80

<Fog density>
The initial state and the fog density after printing 50,000 sheets and 100,000 sheets were measured using a reflection densitometer “RD-918” (manufactured by Macbeth) and evaluated according to the following evaluation criteria. The fog density is a measurement method similar to the above-described white image density measurement, but the density of the non-image portion after printing is measured.

Fog density = quality black paper density (average image density at 20 locations of 1.35 quality black paper)
-Non-image area density (average value of image density at 20 non-image areas)

  If the fog density is less than 0.010, there is no practical problem, but if it is 0.015 or more, the practical use is severe.

A: Less than 0.005 B: 0.005 or more, less than 0.010 C: 0.010 or more, less than 0.015 D: 0.015 or more

<Cleanability of intermediate transfer member>
The initial state and the cleaning property of the intermediate transfer body after printing 50,000 sheets and 100,000 sheets were visually observed and evaluated according to the following evaluation criteria.

A: Good cleaning performance B: Minor spots or streaks due to toner are generated due to toner slipping, but it does not appear in the image and there is no practical problem C: Clear spots caused by toner due to toner slipping, Streaks appear, appear on the image, and have practical problems

<Fixing separation>
After initial printing, and after printing 50,000 and 100,000 sheets, five solid images are overlaid in the order of W, Y, M, C, and Bk on the paper to form an image, and the separation from the fixing device is visually observed. Observed and evaluated according to the following evaluation criteria.

A: The fixing process is good and uniform fixing is possible over the entire fixing area. B: There is no problem in practical use although there is slight separation of the fixing machine in the whole solid image. C: Separation during full solid output. There is a problem in practical use.

<Summary>
As is apparent from Table III, the image formation using the white toner for developing an electrostatic charge image of the present invention was compared with the image formation using the white toner for developing an electrostatic charge image of the comparative example. It was confirmed that the intermediate transfer member was excellent in cleaning property and fixing separation property.
As described above, toner particles including a toner base particle including a binder resin, a white colorant and a release agent and an external additive are contained, and the volume-based median diameter is 0.5 to 1. Using a white toner for developing an electrostatic image containing fatty acid metal salt particles in the range of 5 μm and having an average circularity of the toner particles in the range of 0.870 to 0.950 can be used under high stress conditions. It can be seen that it is useful for providing a high-quality full-color image that is extremely stable over a long period of time.

1W, 1Y, 1M, 1C, 1Bk photoconductor 2W, 2Y, 2M, 2C, 2Bk charging means 3W, 3Y, 3M, 3C, 3Bk exposure means 4W, 4Y, 4M, 4C, 4Bk developing means 5W, 5Y, 5M, 5C, 5Bk Primary transfer roller 6W, 6Y, 6M, 6C, 6Bk Cleaning means 10W, 10Y, 10M, 10C, 10Bk Image forming unit 70 Intermediate transfer body 100 Image forming apparatus

Claims (6)

A white toner for developing an electrostatic charge image, comprising toner particles comprising a binder resin, a white colorant and a release agent, and an external additive,
As the external additive, containing fatty acid metal salt particles having a volume-based median diameter in the range of 0.5 to 1.5 μm,
A white toner for developing an electrostatic charge image, wherein the toner particles have an average circularity in a range of 0.870 to 0.950.   The white toner for developing an electrostatic charge image according to claim 1, wherein the fatty acid metal salt is zinc stearate.   2. The image forming method according to claim 1, wherein the toner is used together with a color toner for developing an electrostatic charge image containing a colorant other than white, and is transferred onto a transfer material by an intermediate transfer member and fixed together. Alternatively, the white toner for developing electrostatic images according to claim 2. An image forming method having at least a charging step, a latent image forming step, a developing step, a transfer step, a fixing step, and a cleaning step,
The transfer step includes
The primary transfer of the white toner for developing an electrostatic charge image according to any one of claims 1 to 3 and the colored toner for developing an electrostatic charge image containing a colorant other than white to an intermediate transfer member. And a process of
Secondary transfer of the toner image formed on the intermediate transfer member onto a transfer material;
An image forming method comprising:   The image forming method according to claim 4, wherein an average circularity of the toner base particles contained in the colored toner for developing an electrostatic charge image is in a range of 0.951 to 0.990. Transferring the white toner for developing an electrostatic charge image to the intermediate transfer member corresponding to a non-image forming region between the transfer materials continuously conveyed;
6. The white toner for developing an electrostatic charge image is collected in the cleaning step, and the intermediate transfer member is cleaned using the white toner for developing an electrostatic charge image. Image forming method.

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