JP2017198831A - Image forming apparatus and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that, even when used for continuous printing, can ensure sufficient stress resistance and fixability of toner to continuously form high quality images.SOLUTION: An image forming apparatus comprises developing parts (developing devices 11) and toner supply parts (supply toner containers 115). The developing parts are configured to store an initial developer containing a first toner and carrier and develop electrostatic latent images with the toner. The toner supply parts are configured to supply a second toner into the developing parts. The thickness Sof a shell layer of a first toner base particle of the first toner (initial toner) and the thickness Sof a shell layer of a second toner base particle of the second toner (supply toner) satisfy the relational expressions (1) and (2) shown below. (1) 18nm≤S<S≤40nm; (2) 1.3<S/S<2.1.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image forming apparatus and an image forming method.

  Patent Document 1 discloses a technique in which a toner having a smaller weight average particle diameter than a toner (initial toner) contained in an initial developer is used as a replenishing toner.

JP 2005-49437 A

  However, it is considered difficult to continuously form high-quality images over a long period of time in continuous printing only with the technique disclosed in Patent Document 1. Specifically, in the technique disclosed in Patent Document 1, since the particle size of the initial toner needs to be larger than the particle size of the toner for replenishment, replenishment fog (specifically, toner replenishment) at the initial use of the image forming apparatus. It is considered that it is difficult to suppress fog generated due to a decrease in toner charge amount) and toner scattering (specifically, toner scattering in the developing unit of the image forming apparatus).

  The present invention has been made in view of the above circumstances, and even when used in continuous printing, sufficient stress resistance and fixing properties of toner are ensured to continuously form high-quality images. An object of the present invention is to provide an image forming apparatus and an image forming method.

The image forming apparatus according to the present invention includes a developing unit and a toner replenishing unit. The developing unit stores an initial developer including a first toner and a carrier, and is configured to develop the electrostatic latent image with the toner. The toner replenishing unit is configured to replenish the second toner into the developing unit. The first toner includes a plurality of first toner particles including first toner base particles and a first external additive attached to the surface of the first toner base particles. The second toner includes a plurality of second toner particles including second toner base particles and a second external additive attached to the surface of the second toner base particles. Each of the first toner base particles and the second toner base particles includes a toner core containing a binder resin and a shell layer that covers the surface of the toner core. The thickness S _{1 of the} shell layer of the first toner base particles and the thickness S _{2 of the} shell layer of the second toner base particles satisfy the following relational expressions (1) and (2).
18 nm ≦ S ₂ <S ₁ ≦ 40 nm (1)
1.3 <S ₁ / S ₂ <2.1 (2)

The image forming method according to the present invention includes a first development for developing an electrostatic latent image with an initial developer in a developing unit, and replenishment of replenishing toner into the developing unit after the start of the first development. Second developing for developing the electrostatic latent image with the developer in the developing section. The initial developer includes an initial toner and a carrier. The initial toner includes a plurality of first toner particles including first toner base particles and a first external additive attached to the surface of the first toner base particles. The replenishment toner includes a plurality of second toner particles including second toner base particles and a second external additive attached to the surface of the second toner base particles. Each of the first toner base particles and the second toner base particles includes a toner core containing a binder resin and a shell layer that covers the surface of the toner core. The thickness S _{1 of the} shell layer of the first toner base particles and the thickness S _{2 of the} shell layer of the second toner base particles satisfy the following relational expressions (1) and (2).
18 nm ≦ S ₂ <S ₁ ≦ 40 nm (1)
1.3 <S ₁ / S ₂ <2.1 (2)

  According to the present invention, even when used for continuous printing, an image forming apparatus and an image forming apparatus that can maintain sufficient toner stress resistance and fixability and can continuously form high-quality images. It becomes possible to provide a method.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a developing unit of the image forming apparatus illustrated in FIG. 1. FIG. 2 is a diagram illustrating a schematic configuration of toner particles (particularly, toner mother particles) used in the image forming apparatus according to the embodiment of the present invention.

  An embodiment of the present invention will be described. Note that the evaluation results (values indicating shape, physical properties, etc.) relating to powder (more specifically, toner core, toner base particles, external additive, toner, carrier, etc.) are not specified unless specified. A considerable number of average particles are selected from the above and the number average of the values measured for each of the average particles.

The number average particle diameter of the powder is the number average value of the equivalent circle diameter of primary particles (diameter of a circle having the same area as the projected area of the particles) measured using a microscope unless otherwise specified. . Moreover, the measured value of the volume median diameter (D ₅₀ ) of the powder is measured using a laser diffraction / scattering particle size distribution measuring device (“LA-750” manufactured by Horiba, Ltd.) unless otherwise specified. It is the value. The glass transition point (Tg) is measured in accordance with “JIS (Japanese Industrial Standard) K7121-2012” using a differential scanning calorimeter (“DSC-6220” manufactured by Seiko Instruments Inc.) unless otherwise specified. It is the value.

  Hereinafter, a compound and its derivatives may be generically named by adding “system” after the compound name. When the name of a polymer is expressed by adding “system” after the compound name, it means that the repeating unit of the polymer is derived from the compound or a derivative thereof. Acrylic and methacrylic are sometimes collectively referred to as “(meth) acrylic”. Further, acrylonitrile and methacrylonitrile may be collectively referred to as “(meth) acrylonitrile”.

  The image forming apparatus according to the present embodiment will be described below with reference to FIGS. 1 and 2.

  An image forming apparatus 100 shown in FIG. 1 is a tandem electrophotographic apparatus. The image forming apparatus 100 includes developing devices 11a to 11d, photosensitive drums 12a to 12d, a transfer device 10, a fixing device 17, and a cleaning device 18. The transfer device 10 includes a transfer belt 13, a drive roller 14a, a driven roller 14b, a tension roller 14c, primary transfer rollers 15a to 15d, and a secondary transfer roller 16. The transfer belt 13 is stretched around a driving roller 14a, a driven roller 14b, and a tension roller 14c. The transfer belt 13 is driven by a driving roller 14a and rotates in a direction indicated by an arrow in FIG. The fixing device 17 is, for example, a nip fixing type fixing device including a heating roller and a pressure roller. The cleaning device 18 removes the toner remaining on the transfer belt 13. When an image is formed using the image forming apparatus 100, a developer containing toner and a carrier (specifically, a magnetic carrier) is set in each of the developing apparatuses 11a to 11d. Each of the developing devices 11 a to 11 d corresponds to a developing unit of the image forming apparatus 100. The image forming apparatus 100 includes a control unit 20 that electronically controls the operation of the image forming apparatus 100 based on outputs from various sensors. The control unit 20 includes, for example, a CPU (Central Processing Unit), a RAM (Random Access Memory), and a storage device that stores a program and rewritable data. The user can give an instruction (electric signal) to the control unit 20 through an input unit (for example, a keyboard, a mouse, or a touch panel) (not shown).

  The image forming apparatus 100 forms an electrostatic latent image on each surface layer (photosensitive material layer) of the photosensitive drums 12a to 12d based on the image data. Next, the formed electrostatic latent image is developed using a developer (toner and carrier) set in each of the developing devices 11a to 11d. Each of the developing devices 11a to 11d has a configuration shown in FIG. Hereinafter, when it is not necessary to distinguish (when common properties are described), each of the developing devices 11a to 11d is described as the developing device 11, and each of the photosensitive drums 12a to 12d is described as the photosensitive drum 12. To do. FIG. 2 is a cross-sectional view showing the internal configuration of the developing device 11.

  As shown in FIG. 2, the developing device 11 includes a developing roller 111, a regulating blade 112, a first stirring shaft 113, and a second stirring shaft 114. Further, the developing device 11 has a housing portion R. The housing part R houses the first stirring shaft 113 and the second stirring shaft 114. The developing roller 111 is disposed in the vicinity of the photosensitive drum 12.

  The developing device 11 (developing unit) is configured to develop an electrostatic latent image with toner. In the initial (unused state) image forming apparatus 100, the storage unit R stores an initial toner (first toner) and an initial developer (first developer) including a carrier. As the developing roller 111 rotates in the direction of the arrow shown in FIG. 2, the developer in the storage portion R is conveyed to the area where the photosensitive drum 12 and the developing roller 111 face each other.

  In contact with the developing device 11, a replenishment toner container 115 is provided as a toner replenishment unit. The replenishment toner container 115 is configured to replenish replenishment toner (second toner) into the developing device 11. The replenishment toner container 115 stores replenishment toner. The replenishment toner in the replenishment toner container 115 is supplied to the developing device 11 (specifically, the storage portion R). The replenishment toner container 115 includes a replenishment amount adjusting member 115a. The replenishment amount of developer (amount supplied from the replenishment toner container 115 to the developing device 11) can be controlled by the replenishment amount adjusting member 115a. The replenishment amount adjusting member 115 a is configured by, for example, a screw shaft whose rotation operation is controlled by the control unit 20. For example, the developer replenishment amount may be changed according to the rotation amount of the screw shaft. The replenishment toner container 115 may include an agitation device for agitating the replenishment toner in the replenishment toner container 115.

  Each of the first stirring shaft 113 and the second stirring shaft 114 has a spiral stirring blade. The first agitation shaft 113 and the second agitation shaft 114 convey the developer in opposite directions while agitating the developer in the developing device 11 (specifically, the accommodating portion R). By stirring the developer, the toner in the developer is triboelectrically charged, and the carrier in the developer carries the toner.

  The developing roller 111 includes a magnet roll and a developing sleeve. The magnet roll has magnetic poles (for example, an N pole and an S pole based on a permanent magnet) at least on the surface layer portion thereof. The developing sleeve is a nonmagnetic cylinder (for example, an aluminum pipe). The magnet roll is located in the developing sleeve (in the cylinder), and the developing sleeve is located in the surface layer portion of the developing roller 111. The shaft of the magnet roll and the developing sleeve are connected via a flange so that the developing sleeve can rotate around the non-rotating magnet roll.

  While the developing roller 111 rotates in the direction of the arrow in FIG. 2, the carrier in the housing portion R is attracted by a magnetic force, and the developer (carrier and toner) is carried on the surface. The carrier particles form a magnetic brush. The magnetic brush is a carrier particle cluster spiked on the surface of the developing roller 111. Toner adheres to the surface of the carrier particles connected in spikes. The thickness (ear height) of the magnetic brush is regulated to a predetermined thickness by the regulation blade 112.

  In order to extend the life of the photosensitive drum, it is preferable to use, for example, an amorphous silicon (a-Si) photosensitive drum as the photosensitive drum 12. The photosensitive drum 12 has a cylindrical outer shape. The photoconductor drum 12 includes a metal cylinder (for example, an aluminum pipe) as a core material, and protects the photoconductor layer (for example, a-Si layer) and the photoconductor layer outside the core material. And a protective layer. The photosensitive drum 12 is supported rotatably. The photosensitive drum 12 is driven by a motor (not shown), for example, and rotates in the direction of the arrow in FIG.

  By applying a bias (voltage) to the developing roller 111 and the photosensitive drum 12, a potential difference is generated between the surface potentials of the two. Due to this potential difference, the toner carried on the developing roller 111 (specifically, the toner charged by friction with the carrier) easily moves to the photosensitive drum 12. Of the developer carried on the developing roller 111, the toner is attracted by an electric force to the exposed portion of the electrostatic latent image formed on the photosensitive drum 12 (for example, the portion whose potential is lower than the surrounding due to exposure). Then, it moves to the photosensitive drum 12. As a result, a toner image is formed on the surface of the photosensitive drum 12. A magnetic brush on the developing roller 111 may come into contact with the photosensitive drum 12 during development of the electrostatic latent image. However, the toner may be ejected from the developing roller 111 toward the photosensitive drum 12 by the above-described electric force without contacting the magnetic brush with the photosensitive drum 12.

  The description will be continued with reference to FIG. As described above, in the image forming apparatus 100, the developing devices 11a, 11b, 11c, and 11d respectively develop the electrostatic latent images formed on the photosensitive drums 12a, 12b, 12c, and 12d (each image carrier). . The image forming apparatus 100 forms a toner image on each photoconductive drum 12 and then applies a bias (voltage) to each of the primary transfer rollers 15a to 15d to adhere the toner adhered to each of the photoconductive drums 12a to 12d. The (toner image) is transferred (primary transfer) to the transfer belt 13 (intermediate transfer member). Further, by applying a bias (voltage) to the secondary transfer roller 16, the toner image on the transfer belt 13 is transferred (secondary transfer) to the recording medium P (transfer object) being conveyed. Thereafter, the fixing device 17 heats the toner to fix the toner on the recording medium P. Thereby, an image is formed on the recording medium P.

  The image forming apparatus 100 includes a plurality of photosensitive drums 12a to 12d. For this reason, the image forming apparatus 100 sequentially transfers the toner images formed on each of the plurality of photosensitive drums 12a to 12d to the transfer belt 13 in the primary transfer step, thereby transferring a plurality of toner images onto the transfer belt 13. Different types of toner images (eg, toner images of different colors) can be superimposed. In the image forming apparatus 100, the toner images superimposed on the transfer belt 13 can be collectively transferred to the recording medium P in the secondary transfer process. For example, a full color image can be formed on the recording medium P by superimposing four color toner images of black, yellow, magenta, and cyan. As the recording medium P, for example, printing paper can be used.

  In an example of an image forming method by the image forming apparatus 100, first, a two-component developer (first toner and carrier) is introduced into the developing device 11 of the image forming apparatus 100, and the toner charged in the developing device 11 is used. The electrostatic latent image (specifically, the electrostatic latent image formed on the surface of the photosensitive drum 12) is developed. By stirring the two-component developer in the developing device 11, a toner charged by friction with the carrier (for example, positively charged in a positively chargeable toner) can be obtained. Initially, the electrostatic latent image is developed with the initial developer (first toner and carrier) in the developing device 11, but thereafter, the replenishment of the replenishing toner (second toner) into the developing device 11 is for replenishment. While performing from the toner container 115, the electrostatic latent image is developed with the developer in the developing device 11. Each time the electrostatic latent image is developed, the toner is consumed, and new toner (second toner) sufficient to supplement the consumed amount is supplied from the supply toner container 115 into the developing device 11. On the other hand, the carrier remains in the developing device 11 without being consumed. In the image forming apparatus 100, the developing device 11 does not include a unit that discharges the carrier in the developing device 11. The carrier in the developing device 11 is replaced with a new carrier, for example, when the image forming apparatus 100 is regularly maintained.

  The image forming apparatus according to the present embodiment has the following configuration (hereinafter referred to as a basic configuration). The application target of the present invention is not limited to the image forming apparatus 100 described above. For example, the present invention may be applied to a touch-down image forming apparatus. In the touch-down image forming apparatus, for example, another developing roller is provided between the developing roller 111 and the photosensitive drum 12.

(Basic configuration of image forming apparatus)
The image forming apparatus includes a developing unit (for example, the developing device 11) and a toner replenishing unit (for example, a replenishing toner container 115). The developing unit contains an initial developer including a first toner (initial toner) and a carrier, and is configured to develop the electrostatic latent image with the toner. The toner replenishing unit is configured to replenish the second toner (replenishment toner) into the developing unit. The first toner includes a plurality of first toner particles including first toner base particles and a first external additive attached to the surface of the first toner base particles. The second toner includes a plurality of second toner particles including second toner mother particles and a second external additive attached to the surface of the second toner mother particles. Each of the first toner base particles and the second toner base particles includes a toner core containing a binder resin and a shell layer that covers the surface of the toner core. The thickness S ₁ of the shell layer of the first toner base particles (hereinafter referred to as the first shell thickness S ₁ ) and the thickness S ₂ of the shell layer of the second toner base particles (hereinafter referred to as the second shell thickness). (Denoted as S ₂ ) satisfies the following relational expressions (1) and (2).
18 nm ≦ S ₂ <S ₁ ≦ 40 nm (1)
1.3 <S ₁ / S ₂ <2.1 (2)

  The initial developer is a developer stored in the developing unit in an unused state (for example, at the time of product sales). The replenishment toner is toner that is replenished into the developing unit after the start of use of the initial developer. The first external additive and the second external additive may be the same external additive or different external additives.

  Of the toner and carrier contained in the developer in the developing unit, the toner is consumed to form an image. On the other hand, among the toner and carrier contained in the developer in the developing unit, the carrier is not consumed for forming an image and remains in the developing unit. The developer in the developing section is used while being stirred. For this reason, when the developer is present in the developing portion for a long period of time, a phenomenon (spent) in which the toner particles adhere to the carrier particles tends to occur. However, according to the inventor's research, the phenomenon that the external additive of the toner particles is detached from the toner particles and adheres to the carrier particles (contamination of the external additive) It is particularly likely to occur at the time). The inventor speculates that this is because there is almost no spent in the initial stage of use, and the surface of the carrier particles is in a state in which the external additive is easily adsorbed.

  When the external additive of the toner particles is detached from the toner particles and adheres to the carrier particles, the stress resistance of the toner tends to decrease. For this reason, in the initial stage of use, the stress resistance of the toner in the developing unit tends to be insufficient particularly in a high temperature and high humidity environment. In addition, when the carrier in the developing unit is contaminated with an external additive, the charge imparting property of the carrier fluctuates, and the charge amount of the toner may become excessive or insufficient.

In the image forming apparatus having the above basic configuration, the first shell thickness S ₁ and the second shell thickness S ₂ satisfy the relational expression (2). For this reason, the first shell thickness S ₁ is not less than 1.3 times and not more than 2.1 times the second shell thickness S ₂ . By increasing the thickness of the shell layer (first shell thickness S ₁ ) in the initial toner (first toner) used at a time when stress resistance tends to be insufficient (initial use of the image forming apparatus). Even in the initial stage of use, it becomes easy to ensure sufficient stress resistance in a high temperature and high humidity environment. In addition, in the replenishing toner (second toner), it is easy to ensure sufficient fixability over a long period of time by making the thickness of the shell layer (second shell thickness S ₂ ) relatively thin. If contamination of the external additive occurs to some extent at the initial stage of use, the external additive contamination is less likely to occur thereafter. For this reason, in the replenishment toner (second toner), if the thickness of the shell layer is too thick, it is considered that the toner fixability tends to deteriorate as the toner replenishment proceeds.

In the image forming apparatus having the above basic configuration, the first shell thickness S ₁ and the second shell thickness S ₂ satisfy the relational expression (1). For this reason, the first shell thickness S ₁ is 40 nm or less, and the second shell thickness S ₂ is 18 nm or more. By not making the first shell thickness S ₁ too thick, it is possible to ensure a sufficient toner fixing property in the initial use. In addition, by making the second shell thickness S ₂ not too thin, it is possible to ensure sufficient toner stress resistance over a long period of time.

  In the above basic configuration, in the first preferred example of the first toner (initial toner) and the second toner (replenishment toner), the shell layer of the first toner base particle and the shell layer of the second toner base particle are respectively And a thermosetting resin (more specifically, a melamine resin or a urea resin).

  In the above basic configuration, in the second preferred example of the first toner (initial toner) and the second toner (replenishment toner), the shell layer of the first toner base particles and the shell layer of the second toner base particles One of them contains a thermosetting resin (more specifically, a melamine resin or a urea resin), and the other contains a thermoplastic resin having a glass transition point of 60 ° C. or more and 80 ° C. or less.

  In order to enhance the functionality of the first toner particles and the second toner particles, two or more kinds of external additive particles (for example, silica particles and titanium oxide particles) are used for each of the first external additive and the second external additive. May be included. When the toner particles include silica particles and titanium oxide particles as external additives, it is considered that fluidity due to the silica particles and abrasiveness due to the titanium oxide particles are imparted to the toner particles, respectively.

  In order to improve the low-temperature fixability of the toner, the toner core of the first toner base particles and the toner core of the second toner base particles preferably each contain a polyester resin as a binder resin. The binder resin contained in the toner core of the first toner base particles and the binder resin contained in the toner core of the second toner base particles may have the same monomer composition or different monomer compositions. You may have. Two resins having the same monomer composition mean that the other contains a monomer that is not in one. For example, in the case where two resins are copolymers of plural types of monomers, if the types of monomers constituting the resin (the plural types of monomers) are the same, even if the ratio of each monomer is different, The two resins will have the same monomer composition.

  In order to continuously form high-quality images by continuous printing, the volume median diameter of each of the initial toner (first toner) and the replenishing toner (second toner) is 4 μm or more and 12 μm or less. The volume median diameter is preferably 25 μm or more and 100 μm or less.

  Hereinafter, preferred examples of the toner particles contained in each of the first toner and the second toner will be described.

  The toner particles include toner base particles and an external additive. The external additive adheres to the surface of the toner base particles. The toner base particles include a toner core and a shell layer (capsule layer) formed on the surface of the toner core. The toner core contains a binder resin. If necessary, an internal additive (for example, at least one of a release agent, a colorant, a charge control agent, and a magnetic powder) may be dispersed in the binder resin of the toner core. The shell layer is substantially composed of a resin. For example, by covering a toner core that melts at a low temperature with a shell layer having excellent heat resistance, it is possible to achieve both heat-resistant storage stability and low-temperature fixability of the toner. Additives may be dispersed in the resin constituting the shell layer. An external additive may be attached to the surface of the shell layer (or the surface region of the toner core not covered with the shell layer). A plurality of shell layers may be laminated on the surface of the toner core. Hereinafter, a material for forming the shell layer is referred to as a shell material.

  A preferred example of the configuration of toner particles (particularly, toner mother particles) will be described below with reference to FIG.

  The toner base particle 30 shown in FIG. 3 has a toner core 31 and a shell layer 32 formed on the surface of the toner core 31. The shell layer 32 is substantially composed of a resin. The shell layer 32 covers the surface of the toner core 31. In the example of FIG. 3, the shell layer 32 completely covers the surface of the toner core 31. That is, the shell layer 32 covers the entire surface of the toner core 31.

  Preferred examples of the resin constituting each of the toner particles and carrier particles are shown below.

<Preferable thermoplastic resin>
Suitable examples of thermoplastic resins include styrene resins, acrylic resins (more specifically, acrylic ester polymers or methacrylic ester polymers), olefin resins (more specifically, polyethylene). Resin or polypropylene resin), vinyl chloride resin, polyvinyl alcohol, vinyl ether resin, N-vinyl resin, polyester resin, polyamide resin, or urethane resin. Further, a copolymer of each of these resins, that is, a copolymer in which an arbitrary repeating unit is introduced into the resin (specifically, a styrene-acrylic acid resin or a styrene-butadiene resin) is used. May be.

  The thermoplastic resin can be obtained by addition polymerization, copolymerization, or condensation polymerization of one or more thermoplastic monomers. The thermoplastic monomer is a monomer that becomes a thermoplastic resin by homopolymerization (more specifically, an acrylic acid monomer or a styrene monomer), or a monomer that becomes a thermoplastic resin by condensation polymerization (for example, by condensation polymerization). A combination of a polyhydric alcohol and a polyhydric carboxylic acid to be a polyester resin.

  The styrene-acrylic acid resin is a copolymer of one or more styrene monomers and one or more acrylic monomers. In order to synthesize a styrene-acrylic acid resin, for example, a styrene monomer and an acrylic acid monomer as shown below can be suitably used.

  Preferable examples of the styrene monomer include styrene, alkyl styrene (more specifically, α-methyl styrene, p-ethyl styrene, 4-tert-butyl styrene, etc.), p-hydroxy styrene, m-hydroxy styrene. , Vinyl toluene, α-chlorostyrene, o-chlorostyrene, m-chlorostyrene, or p-chlorostyrene.

  Preferable examples of the acrylic acid monomer include (meth) acrylic acid, (meth) acrylonitrile, (meth) acrylic acid alkyl ester, or (meth) acrylic acid hydroxyalkyl ester. Suitable examples of the (meth) acrylic acid alkyl ester include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, iso-propyl (meth) acrylate, and (meth) acrylic. Examples include n-butyl acid, iso-butyl (meth) acrylate, or 2-ethylhexyl (meth) acrylate. Suitable examples of the (meth) acrylic acid hydroxyalkyl ester include 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, or (meth) acrylic. The acid 4-hydroxybutyl is mentioned.

  The polyester resin is obtained by polycondensation of one or more polyhydric alcohols and one or more polyhydric carboxylic acids. As the alcohol for synthesizing the polyester resin, for example, dihydric alcohols (more specifically, diols or bisphenols) as shown below or trihydric or higher alcohols can be suitably used. As the carboxylic acid for synthesizing the polyester resin, for example, divalent carboxylic acids or trivalent or higher carboxylic acids as shown below can be suitably used.

  Suitable examples of diols include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol, Examples include 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, di1,2-propanediol, polyethylene glycol, poly1,2-propanediol, or polytetramethylene glycol.

  Preferable examples of the bisphenol include bisphenol A, hydrogenated bisphenol A, bisphenol A ethylene oxide adduct, or bisphenol A propylene oxide adduct.

  Preferable examples of trihydric or higher alcohols include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butane. Triol, 1,2,5-pentanetriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, or 1,3,5- Trihydroxymethylbenzene is mentioned.

  As preferable examples of the divalent carboxylic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, adipic acid, sebacic acid, azelaic acid, malonic acid Succinic acid, alkyl succinic acid (more specifically, n-butyl succinic acid, isobutyl succinic acid, n-octyl succinic acid, n-dodecyl succinic acid, isododecyl succinic acid, etc.), or alkenyl succinic acid (more specific Specifically, n-butenyl succinic acid, isobutenyl succinic acid, n-octenyl succinic acid, n-dodecenyl succinic acid, or isododecenyl succinic acid, etc.) may be mentioned.

  Preferred examples of the trivalent or higher carboxylic acid include 1,2,4-benzenetricarboxylic acid (trimellitic acid), 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra (methylenecarboxyl) Examples include methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, or empole trimer acid.

<Preferable thermosetting resin>
Preferred examples of the thermosetting resin include melamine resin, urea resin, sulfonamide resin, glyoxal resin, guanamine resin, aniline resin, polyimide resin (more specifically, maleimide polymer or bismuth resin). Maleimide polymer, etc.), xylene-based resin, or epoxy resin.

The thermosetting resin can be obtained by crosslinking (polymerizing) one or more thermosetting monomers. Moreover, a thermosetting resin can also be synthesize | combined with a thermoplastic monomer by using a crosslinking agent. The thermosetting monomer is a monomer having crosslinkability. For example, when monomers of the same kind are three-dimensionally connected via “—CH ₂ —” to become a thermosetting resin, the monomer corresponds to a “thermosetting monomer”.

  Preferable examples of the thermosetting monomer include methylol melamine, melamine, methylolated urea (more specifically, dimethylol dihydroxyethylene urea), urea, benzoguanamine, acetoguanamine, or spiroguanamine.

  Next, preferred examples of the configuration of the toner particles and the carrier particles will be described.

[Toner core]
(Binder resin)
In the toner core, the binder resin generally occupies most of the components (for example, 85% by mass or more). For this reason, it is considered that the properties of the binder resin have a great influence on the overall properties of the toner core. In order to achieve both the heat-resistant storage stability and the low-temperature fixability of the toner, the toner core preferably contains the above-mentioned “suitable thermoplastic resin” as the binder resin. The polyester resin and the styrene-acrylic acid resin It is particularly preferable to contain at least one of the following.

(Coloring agent)
The toner core may contain a colorant. As the colorant, a known pigment or dye can be used according to the color of the toner. In order to form a high-quality image using toner, the amount of the colorant is preferably 1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the binder resin.

  The toner core may contain a black colorant. An example of a black colorant is carbon black. The black colorant may be a colorant that is toned to black using a yellow colorant, a magenta colorant, and a cyan colorant.

  The toner core may contain a color colorant such as a yellow colorant, a magenta colorant, or a cyan colorant.

  As the yellow colorant, for example, one or more compounds selected from the group consisting of condensed azo compounds, isoindolinone compounds, anthraquinone compounds, azo metal complexes, methine compounds, and arylamide compounds can be used. Examples of the yellow colorant include C.I. I. Pigment Yellow (3, 12, 13, 14, 15, 17, 62, 74, 83, 93, 94, 95, 97, 109, 110, 111, 120, 127, 128, 129, 147, 151, 154, 155 168, 174, 175, 176, 180, 181, 191, or 194), naphthol yellow S, Hansa yellow G, or C.I. I. Vat yellow can be preferably used.

  The magenta colorant is, for example, selected from the group consisting of condensed azo compounds, diketopyrrolopyrrole compounds, anthraquinone compounds, quinacridone compounds, basic dye lake compounds, naphthol compounds, benzimidazolone compounds, thioindigo compounds, and perylene compounds. One or more compounds can be used. Examples of the magenta colorant include C.I. I. Pigment Red (2, 3, 5, 6, 7, 19, 23, 48: 2, 48: 3, 48: 4, 57: 1, 81: 1, 122, 144, 146, 150, 166, 169, 177 184, 185, 202, 206, 220, 221 or 254) can be preferably used.

  As the cyan colorant, for example, one or more compounds selected from the group consisting of a copper phthalocyanine compound, an anthraquinone compound, and a basic dye lake compound can be used. Examples of cyan colorants include C.I. I. Pigment blue (1, 7, 15, 15: 1, 15: 2, 15: 3, 15: 4, 60, 62, or 66), phthalocyanine blue, C.I. I. Bat Blue, or C.I. I. Acid blue can be preferably used.

(Release agent)
The toner core may contain a release agent. The release agent is used, for example, for the purpose of improving the fixing property or offset resistance of the toner. In order to improve the fixing property or offset resistance of the toner, the amount of the release agent is preferably 1 part by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the binder resin.

  Examples of the release agent include low molecular weight polyethylene, low molecular weight polypropylene, polyolefin copolymer, polyolefin wax, microcrystalline wax, paraffin wax, or aliphatic hydrocarbon wax such as Fischer-Tropsch wax; oxidized polyethylene wax or a block thereof Oxides of aliphatic hydrocarbon waxes such as copolymers; plant waxes such as candelilla wax, carnauba wax, wood wax, jojoba wax, or rice wax; animal properties such as beeswax, lanolin, or whale wax Waxes; mineral waxes such as ozokerite, ceresin, or petrolatum; waxes based on fatty acid esters such as montanate ester wax or castor wax; fats such as deoxidized carnauba wax The wax portion of the ester or the whole was deoxygenated can be suitably used. One type of release agent may be used alone, or multiple types of release agents may be used in combination.

  In order to improve the compatibility between the binder resin and the release agent, a compatibilizer may be added to the toner core.

(Charge control agent)
The toner core may contain a charge control agent. The charge control agent is used, for example, for the purpose of improving the charge stability or charge rising property of the toner. The charge rising characteristic of the toner is an index as to whether or not the toner can be charged to a predetermined charge level in a short time.

  By adding a positively chargeable charge control agent (more specifically, pyridine, nigrosine, quaternary ammonium salt, or the like) to the toner core, the cationic property of the toner core can be increased. However, when sufficient chargeability is ensured in the shell layer, the toner core does not need to contain a charge control agent.

(Magnetic powder)
The toner core may contain magnetic powder. Examples of magnetic powder materials include ferromagnetic metals (more specifically, iron, cobalt, nickel, or alloys thereof), ferromagnetic metal oxides (more specifically, ferrite, magnetite, or dioxide). Chromium or the like) or a material subjected to ferromagnetization treatment (more specifically, a carbon material or the like imparted with ferromagnetism by heat treatment) can be preferably used. In order to suppress elution of metal ions (for example, iron ions) from the magnetic powder, it is preferable to use the surface-treated magnetic particles as the magnetic powder. One type of magnetic powder may be used alone, or a plurality of types of magnetic powder may be used in combination.

[Toner core preparation method]
Preferable examples of the method for producing the toner core include a pulverization method or an aggregation method. These methods tend to favorably disperse the internal additive in the binder resin of the toner core.

  In an example of the pulverization method, first, a binder resin, a colorant, a charge control agent, and a release agent are mixed. Subsequently, the obtained mixture is melt-kneaded using a melt-kneading apparatus (for example, a single-screw or twin-screw extruder). Subsequently, the obtained melt-kneaded product is pulverized and classified. Thereby, a toner core is obtained. When the pulverization method is used, the toner core can often be produced more easily than when the aggregation method is used.

  In an example of the aggregation method, first, these fine particles are aggregated in an aqueous medium containing fine particles of the binder resin, the release agent, and the colorant until a desired particle diameter is obtained. Thereby, aggregated particles containing the binder resin, the release agent, and the colorant are formed. Subsequently, the obtained aggregated particles are heated to unite the components contained in the aggregated particles. Thereby, a toner core having a desired particle diameter is obtained.

[Shell layer]
For example, by chemically reacting the toner core and the shell material in the liquid, the shell layer is bonded (chemically bonded) to the surface of the toner core. The shell layer may be a film without graininess or a film with graininess. When a shell layer is formed in an aqueous medium using a water-soluble material as the shell material, it is considered that a film having no graininess is formed as the shell layer. When resin particles are used as the shell material, it is considered that if the material (resin particles) is completely melted and cured in a film-like form, a film having no graininess is formed as the shell layer. On the other hand, if the material (resin particles) is not completely melted and cured in a film form, a film having a form in which the resin particles are two-dimensionally connected (a film having a granular feeling) is formed as a shell layer. it is conceivable that. For example, the resin particles are adhered to the surface of the toner core in the liquid and the liquid is heated, whereby the resin particles can be dissolved to form a film. However, the resin particles may be formed into a film by being heated in the drying step or receiving a physical impact force in the external addition step. The entire shell layer is not necessarily formed integrally. The shell layer may be a single film or an assembly of a plurality of films (islands) that are separated from each other.

  In order to ensure sufficient heat-resistant storage stability of the toner, the shell layer preferably contains a thermosetting resin (more specifically, a “suitable thermosetting resin” or the like). In order to ensure sufficient heat-resistant storage stability of the positively chargeable toner, it is particularly preferable that the shell layer contains a melamine resin and / or a urea resin. The melamine resin is a condensation polymer of melamine and formaldehyde (or a polymer of methylol melamine). The urea resin is a condensation polymer of urea and formaldehyde (or a polymer of methylolated urea). In order to improve the heat resistant storage stability of the toner, it is preferable that 80% by mass or more of the resin contained in the shell layer is a thermosetting resin, and 90% by mass or more of the resin is thermoset. More preferably, the resin is a thermosetting resin, and more preferably 100% by mass of the resin is a thermosetting resin.

  In order to achieve both heat-resistant storage stability and fixing property of the toner, the shell layer has a glass transition point (Tg) of 60 ° C. or higher and 80 ° C. or lower (more specifically, “preferable thermoplastic resin” or the like) ) Is preferably contained. In order to achieve both heat-resistant storage stability and fixability of the positively chargeable toner, the shell layer particularly preferably contains a styrene-acrylic acid resin having a glass transition point (Tg) of 60 ° C. or higher and 80 ° C. or lower. .

[Method for forming shell layer]
Preferable examples of the method for forming the shell layer include an in-situ polymerization method, a liquid-cured coating method, and a coacervation method. More specifically, after the toner core is placed in an aqueous medium in which a water-soluble shell material is dissolved, the aqueous medium is heated to advance the polymerization reaction of the shell material, thereby forming a shell layer on the surface of the toner core. A forming method (hereinafter referred to as a first shell forming method) is preferable.

  The aqueous medium is a medium containing water as a main component (more specifically, pure water or a mixed liquid of water and a polar medium). As a polar medium in the aqueous medium, for example, alcohol (more specifically, methanol or ethanol) can be used. The boiling point of the aqueous medium is about 100 ° C.

  In order to uniformly adhere the shell material to the surface of the toner core, it is preferable to highly disperse the toner core in a liquid containing the shell material. In order to highly disperse the toner core in the liquid, a dispersant may be included in the liquid. However, the amount of the dispersant contained in the liquid is preferably 75 parts by mass or less with respect to 100 parts by mass of the toner core. Examples of the dispersant include sodium polyacrylate, polyparavinylphenol, partially saponified polyvinyl acetate, isoprenesulfonic acid, polyether, isobutylene-maleic anhydride copolymer, sodium polyaspartate, starch, gum arabic, polyvinyl Pyrrolidone or sodium lignin sulfonate can be preferably used. One type of dispersant may be used alone, or two or more types of dispersants may be used in combination.

  When a shell layer containing a melamine resin and / or a urea resin is formed by the first shell formation method, the temperature of the aqueous medium during shell layer formation is 40 The temperature is preferably from 80 ° C. to 80 ° C., more preferably from 55 ° C. to 70 ° C.

  In forming the shell layer, resin particles (for example, a resin dispersion) may be used as the shell material. More specifically, in the liquid containing the resin particles and the toner core, the resin particles are adhered to the surface of the toner core, and then the temperature of the liquid is heated to a temperature higher than the Tg of the resin particles. A method in which film formation is advanced to form a shell layer on the surface of the toner core (hereinafter referred to as a second shell forming method) is preferable.

  In the second shell forming method, a resin dispersion can be used as the shell material. For example, in the case of forming a shell layer substantially containing a polymer of a vinyl compound, an emulsion polymerization reaction is allowed to proceed in a liquid (for example, an aqueous medium) containing a vinyl compound and an ionic surfactant. A dispersion (shell material) is obtained. When forming a shell layer containing an oily resin (a resin having a relatively low solubility in water), the oily resin is dissolved in a solvent (for example, an organic solvent), and then the resulting solution is used as an ionic surfactant. And a polyelectrolyte together with an aqueous medium, for example, using a homogenizer, the material in the aqueous medium is subjected to a dispersion treatment (specifically, microparticulation by shearing force or impact force) to obtain a resin dispersion ( Shell material) is obtained. The solvent used can be evaporated by heating and / or reduced pressure.

[External additive]
As the first external additive and the second external additive (powder containing a plurality of external additive particles, respectively), the following external additive particles can be used. For example, the toner base particles (powder) and the external additive (powder) are stirred together, so that the external additive adheres (physically bonds) to the surface of the toner base particles with a physical force.

  The external additive particles are preferably inorganic particles such as silica particles or metal oxide particles (more specifically, alumina, titanium oxide, magnesium oxide, zinc oxide, strontium titanate, or barium titanate). Particularly preferred. However, particles of an organic acid compound such as a fatty acid metal salt (more specifically, zinc stearate) or resin particles may be used as the external additive particles. Moreover, you may use the composite particle which is a composite of a multiple types of material as external additive particle | grains. One type of external additive may be used alone, or a plurality of types of external additives may be used in combination.

The external additive particles may be surface-treated. For example, when silica particles are used as the external additive particles, hydrophobicity and / or positive chargeability may be imparted to the surface of the silica particles by the surface treatment agent. Examples of the surface treatment agent include a coupling agent (more specifically, a silane coupling agent, a titanate coupling agent, or an aluminate coupling agent), or silicone oil (more specifically, dimethyl silicone oil). Etc.) can be suitably used. As the silane coupling agent, a silane compound (more specifically, methyltrimethoxysilane, aminosilane or the like) may be used, or a silazane compound (more specifically, HMDS (hexamethyldisilazane) or the like). May be used. When the surface of the silica particles is treated with the surface treatment agent, a large number of hydroxyl groups (—OH) present on the surface of the silica particles are partially or entirely substituted with functional groups derived from the surface treatment agent. As a result, silica particles having a functional group derived from the surface treating agent (specifically, a functional group that is more hydrophobic and / or positively charged than the hydroxyl group) on the surface can be obtained. For example, when the surface of the silica particles is treated with a silane coupling agent having an amino group, the hydroxyl group of the silane coupling agent (for example, a hydroxyl group generated by hydrolysis of the alkoxy group of the silane coupling agent with moisture) A dehydration condensation reaction (“A (silica particle) —OH” + “B (coupling agent) —OH” → “AO—B” + H ₂ O) occurs with a hydroxyl group present on the surface of the silica particle. By such a reaction, the amino group is imparted to the surface of the silica particle by chemically bonding the silane coupling agent having an amino group and the silica particle. More specifically, the hydroxyl group present on the surface of the silica particles is substituted with a functional group having an amino group at the end (more specifically, —O—Si— (CH ₂ ) ₃ —NH ₂ or the like). Silica particles provided with amino groups tend to have a stronger positive charge than untreated silica particles. When a silane coupling agent having an alkyl group is used, a hydroxyl group present on the surface of the silica particle is converted into a functional group having an alkyl group at the end (more specifically, − it can be replaced by O-Si-CH _3, etc.). Thus, the silica particle to which the hydrophobic group (alkyl group) was provided instead of the hydrophilic group (hydroxyl group) tends to have stronger hydrophobicity than the untreated silica particle.

[Carrier particles]
The carrier particles have magnetism. In order to impart magnetism to the carrier particles, at least a part of the carrier particles may be formed of a magnetic material (for example, a ferromagnetic material such as ferrite), or the carrier particles may be formed of a resin in which the magnetic particles are dispersed. You may form at least one part.

  The carrier particles may be carrier particles without a coat layer (for example, ferrite carrier particles), or may be carrier particles with a coat layer (hereinafter referred to as coated carrier particles). In order to form a high-quality image over a long period of time using a developer, it is preferable to use coated carrier particles. The coated carrier particles include a carrier core and a coat layer that covers the surface of the carrier core. The coat layer is substantially composed of a resin. Additives may be dispersed in the resin constituting the coat layer. The coat layer may cover the entire surface of the carrier core, or may partially cover the surface of the carrier core.

  Hereinafter, suitable examples of the coated carrier particles will be described. The coated carrier particle includes a carrier core and a coat layer. In addition, you may use the carrier core which has the following structure as carrier particles as it is, without covering with a coating layer.

(Career core)
The carrier core preferably includes a magnetic material. Examples of the magnetic material contained in the carrier core include magnetite, barium ferrite, maghemite, Mn—Zn ferrite, Ni—Zn ferrite, Mn—Mg ferrite, Ca—Mg ferrite, Li ferrite, or Cu—Zn ferrite. Metal oxides are preferred, and magnetite is particularly preferred. As a material for each carrier core, one type of magnetic material may be used alone, or two or more types of magnetic materials may be used in combination. A commercially available product may be used as the carrier core. Also, the carrier core may be made by pulverizing and firing the magnetic material.

  The entire carrier core may be formed of the magnetic material, or the particles of the magnetic material may be dispersed in the binder resin of the carrier core. As the binder resin for the carrier core, for example, one or more resins selected from the group consisting of the “preferable thermoplastic resin” and the “preferable thermosetting resin” described above can be used.

(Coat layer)
The coat layer is formed on the surface of the carrier core so as to cover the carrier core. Examples of the method for forming the coat layer include a method of immersing the carrier core in a liquid containing a resin (or resin material), or a liquid containing a resin (or resin material) in the carrier core in the fluidized bed. The method of spraying is mentioned.

  The resin constituting the coat layer is preferably an insulating resin. However, in order to reduce the electric resistance of the carrier particles, a conductive material may be added to the resin. By changing the amount of the conductive material in the resin, the electric resistance of the carrier particles can be adjusted. The lower the electrical resistance of the carrier, the lower the charge imparting property of the carrier. Further, the electric resistance of the carrier particles can also be adjusted by changing the amount of the coating layer covering the carrier core (and thus the thickness or the covering rate of the coating layer).

  As the resin constituting the coating layer, a thermoplastic resin (more specifically, the “preferable thermoplastic resin” or fluorine-containing resin described above) may be used, or a thermosetting resin (more specifically, Specifically, the above-mentioned “suitable thermosetting resin” or silicone resin may be used. Moreover, you may provide crosslinking | crosslinked property to a thermoplastic resin by mixing a thermoplastic monomer and a hardening | curing agent. The coat layer may have a sea-island structure.

  In order to improve the durability or fluidity of the carrier, the coating layer preferably contains one or more resins selected from the group consisting of fluorine-containing resins and silicone resins, and preferably contains a silicone resin. Particularly preferred. Examples of the fluorine-containing resin include polyvinyl fluoride, polyvinylidene fluoride, polytetrafluoroethylene (PTFE), polytrifluoroethylene (more specifically, polychlorotrifluoroethylene, etc.), polyhexafluoropropylene, and tetrafluoroethylene. -One or more resins selected from the group consisting of hexafluoropropylene copolymers (FEP) are particularly preferred. As the silicone resin, methyl silicone resin is particularly preferable.

  Examples of the present invention will be described. Tables 1 and 2 show apparatuses DA-1 to DA-14 and DB-1 to DB-14 (image forming apparatuses, respectively) according to examples or comparative examples. Table 3 shows toners T-1 to T-16 used in each apparatus. “Amount” of “shell material” in Table 3 indicates the amount of shell material (unit: parts by mass) when the amount of toner core is 100 parts by mass.

  Hereinafter, a manufacturing method, an evaluation method, and an evaluation result of apparatuses DA-1 to DA-14 and DB-1 to DB-14 will be described in order. In the evaluation in which an error occurs, a considerable number of measurement values with sufficiently small errors are obtained, and the arithmetic average of the obtained measurement values is used as the evaluation value.

[Toner Preparation]
(Production method of toner core A)
Using an FM mixer (manufactured by Nippon Coke Industries Co., Ltd.), 100 parts by mass of a polyester resin (Toughton (registered trademark) NE-410 manufactured by Kao Corporation) and polypropylene wax (manufactured by Sanyo Kasei Kogyo Co., Ltd.) Trademark) 660P ") 5 parts by mass, carbon black (" REGAL (registered trademark) 330R "manufactured by Cabot Corporation) 5 parts by mass, and quaternary ammonium salt (" BONTRON (registered trademark) P-51 manufactured by Orient Chemical Industry Co., Ltd.) " ]) 1 part by mass was mixed.

Subsequently, the obtained mixture was melt-kneaded using a twin-screw extruder (“PCM-30” manufactured by Ikegai Co., Ltd.). Subsequently, the obtained kneaded product was cooled and then pulverized using a pulverizer (“Turbo Mill” manufactured by Freund Turbo). Subsequently, the obtained pulverized product was classified using a classifier (“Elbow Jet EJ-LABO type” manufactured by Nippon Steel Mining Co., Ltd.). As a result, a toner core A having a volume median diameter (D ₅₀ ) of 7 μm was obtained.

(Production method of toner core B)
Toner core B was prepared in the same manner as in toner core A except that 5 parts by mass of microcrystalline wax (“HNP-9” manufactured by Nippon Seiwa Co., Ltd.) was used instead of 5 parts by mass of polypropylene wax (Biscol 660P). Was the same. The obtained toner core B had a volume median diameter (D ₅₀ ) of 7 μm.

(Production method of toner core C)
The production method of the toner core C is the same as the production method of the toner core A except that 100 parts by mass of a polyester resin (“XPE258” manufactured by Mitsui Chemicals, Inc.) is used instead of 100 parts by mass of the polyester resin (Tufton NE-410). Met. The resulting toner core C had a volume median diameter (D ₅₀ ) of 7 μm.

(Production method of toner core D)
Toner core D was prepared by using toner core A except that 100 parts by mass of styrene-acrylic acid resin (“CPR300” manufactured by Mitsui Chemicals, Inc.) was used instead of 100 parts by mass of polyester resin (Tufton NE-410). It was the same as the manufacturing method. The resulting toner core D had a volume median diameter (D ₅₀ ) of 7 μm.

(Method for preparing resin dispersion)
A 1 L three-necked flask equipped with a thermometer and a stirring blade was set in a water bath. Inside the flask, 815 mL of ion-exchanged water having a temperature of 30 ° C. and a cationic surfactant (“Kotamin” (registered trademark) manufactured by Kao Corporation) 24P ", lauryltrimethylammonium chloride 25 mass% aqueous solution) 75mL. Thereafter, the temperature in the flask was raised to 80 ° C. using a water bath. Subsequently, two kinds of liquids (first liquid and second liquid) were dropped into the contents of the flask at 80 ° C. over 5 hours. The first liquid was a mixed liquid of 68 mL of styrene and 12 mL of n-butyl acrylate. The second liquid was a solution in which 0.5 g of potassium persulfate was dissolved in 30 mL of ion exchange water. Subsequently, the temperature in the flask was kept at 80 ° C. for another 2 hours to polymerize the flask contents. As a result, a suspension of resin fine particles (resin dispersion having a solid content concentration of 8% by mass) was obtained. The resin fine particles contained in the obtained resin dispersion had a number average particle size of 31 nm and Tg of 68 ° C.

(Formation of shell layer)
A 1 L three-necked flask equipped with a thermometer and a stirring blade was prepared, and the flask was set in a water bath. Subsequently, 300 mL of ion-exchanged water was put in the flask, and the temperature in the flask was kept at 30 ° C. using a water bath. Subsequently, dilute hydrochloric acid was added to the flask to adjust the pH of the flask contents to 4.

  Subsequently, the shell material shown in Table 3 was added to the flask by the amount shown in Table 3. Regarding “type” of “shell material” in Table 3, “A” is an aqueous solution of urea melamine formaldehyde cocondensate (“Milben (registered trademark) resin SUM-100” manufactured by Showa Denko KK), and “B” is Water-soluble methylol melamine ("Nika Resin (registered trademark) S-260" manufactured by Nippon Carbide Industries Co., Ltd.), "C" is the above resin dispersion (resin dispersion having a solid content concentration of 8% by mass prepared by the above procedure) Respectively. For example, in the production of the toner T-1, an aqueous solution of melamine formaldehyde cocondensate (milben resin SUM-100) was added in an amount corresponding to 1.4 parts by mass with respect to 100 parts by mass of the toner core to be added later. .

  In order to sufficiently disperse the shell material in the liquid, 75 parts by mass of a dispersion stabilizer was added to the liquid with respect to 100 parts by mass of the toner core. When an aqueous solution of urea melamine formaldehyde cocondensate (milben resin SUM-100) is used as the shell material, sodium acrylate (“Julimer (registered trademark) AC-103” manufactured by Toagosei Co., Ltd.) is used as a dispersion stabilizer. It was used. When water-soluble methylol melamine (Nikaresin S-260) is used as a shell material, partially saponified polyvinyl acetate (“GOHSENOL (registered trademark) GM-14L” manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) is used as a dispersion stabilizer. used. However, when the above “C” (resin dispersion) was used as the shell material, no dispersion stabilizer was added.

  Subsequently, 300 g of a toner core (any one of toner cores A to D shown in Table 3 defined for each toner) was added to the flask. For example, in the production of toner T-1, 300 g of toner core A was added to the flask. Thereafter, the flask contents were stirred for 1 hour under the conditions of a rotation speed of 200 rpm and a temperature of 40 ° C.

  Subsequently, 300 mL of ion-exchanged water was added to the flask, and the temperature in the flask was increased to 70 ° C. at a rate of 1.0 ° C./min while stirring the flask contents at a rotation speed of 100 rpm. The flask contents were stirred for 1 hour under the condition of a speed of 100 rpm. As a result, a shell layer was formed on the surface of the toner core, and a dispersion of toner base particles was obtained. Thereafter, the pH of the dispersion of the toner base particles was adjusted to 7 (neutralized) using sodium hydroxide, and the dispersion of the toner base particles was cooled to room temperature (about 25 ° C.).

(Washing process)
The dispersion of toner base particles obtained as described above was filtered (solid-liquid separation) using a Buchner funnel. As a result, toner base particles in the form of wet cake were obtained. Thereafter, the obtained wet cake-like toner base particles were redispersed in ion-exchanged water. Further, dispersion and filtration were repeated 5 times to wash the toner base particles.

(Drying process)
Subsequently, the washed toner base particles (powder) were dispersed in an aqueous ethanol solution having a concentration of 50% by mass to obtain a slurry of toner base particles. Subsequently, the toner base particles in the slurry were removed under the conditions of a hot air temperature of 45 ° C. and a blower air volume of 2 m ³ / min. Dried. As a result, dried toner base particles (powder) were obtained.

(External)
Using an FM mixer (“FM-10B” manufactured by Nippon Coke Kogyo Co., Ltd.), 100 parts by mass of toner base particles (toner base particles prepared by the above procedure) and hydrophobic silica particles (trimethylsilyl group and amino group) Surface-modified silica particles: 0.7 parts by mass of “AEROSIL (registered trademark) RA-200H” manufactured by Nippon Aerosil Co., Ltd.) and conductive titanium oxide particles (“EC-100” manufactured by Titanium Industry Co., Ltd.), base material: TiO ₂ and coating layer: Sb-doped SnO ₂ film) 1.0 part by mass was mixed at a rotational speed of 3500 rpm for 5 minutes. As a result, external additives (silica particles and titanium oxide particles) adhered to the surface of the toner base particles. Thereafter, the obtained powder was sieved using a 200-mesh (aperture 75 μm) sieve. As a result, toners (toners T-1 to T-16) containing a large number of toner particles (capsule toner particles) were obtained.

  In the toners T-1 to T-16 obtained as described above, the shell layer covered the entire surface of the toner core. Regarding the toners T-1 to T-16, the results of measuring the thickness of the shell layer are as shown in Table 3. For example, for toner T-1, the shell layer thickness was 28 nm. The method for measuring the thickness of the shell layer was as follows.

<Method for measuring thickness of shell layer>
A sample (toner) was dispersed in a room temperature curable epoxy resin and cured in an atmosphere at 40 ° C. for 2 days to obtain a cured product. After the obtained cured product is dyed with a predetermined dye (osmium tetroxide or ruthenium tetroxide), it is cut out with an ultramicrotome (“EM UC6” manufactured by Leica Microsystems, Inc.) equipped with a diamond knife. A flake sample was obtained. Then, the cross section of the obtained thin piece sample was image | photographed using the transmission electron microscope (TEM) (The JEOL Co., Ltd. product "JSM-6700F"). The magnification of the microscope was adjusted so that one whole toner particle was in the visual field. Specifically, the magnification of the microscope was about 10,000 times.

  The thickness of the shell layer was measured by analyzing the TEM image using image analysis software ("WinROOF" manufactured by Mitani Corporation). Specifically, in one toner particle to be measured, the thickness of the shell layer where the shell layer is formed thickest (maximum shell thickness) and the shell where the shell layer is formed thinnest The thickness of each layer (minimum shell thickness) was measured, and the arithmetic average value (= (maximum shell thickness + minimum shell thickness) / 2) of the two measured thicknesses was determined as the toner particles. It was set as the thickness of the shell layer of (measurement object). The thickness of the shell layer was measured for each of the 10 toner particles contained in the sample (toner), and the average number of the 10 particles was used as the evaluation value (shell layer thickness) of the sample (toner).

[Career preparation]
30 parts by mass of a silicone resin was dissolved in 200 parts by mass of toluene to obtain 230 parts by mass of a resin solution. Subsequently, using a fluidized bed coating apparatus ("Spiraflow (registered trademark) SFC-5" manufactured by Freund Sangyo Co., Ltd.), 1000 parts by mass of the carrier core (Mn-Mg ferrite core having a number average primary particle size of 35 μm). On the other hand, after the whole amount (230 parts by mass) of the resin solution was applied by spraying, heat treatment was performed at 200 ° C. for 60 minutes to obtain a carrier (powder).

[Preparation of initial developer]
10 parts by mass of initial toner (any one of toners T-1 to T-5 and T-7 to T-10 shown in Table 1 and Table 2 specified for each apparatus) and a carrier (prepared according to the procedure described above) 100 parts by weight of the carrier) was mixed for 30 minutes using a powder mixer (“Rocking Mixer (registered trademark)” manufactured by Aichi Electric Co., Ltd., mixing method: container rotation swinging method), and an initial developer ( A two-component developer) was prepared. For example, in the manufacture of the apparatus DA-1, the carrier prepared in the above-described procedure and the toner T-1 are mixed.

[Manufacture of image forming apparatus]
The initial developer and the replenishing toner were set in a color multifunction machine (“TASKalfa 500ci” manufactured by Kyocera Document Solutions Inc.). More specifically, the color multi-function peripheral includes a developing device configured to develop an electrostatic latent image formed on a photoreceptor with toner, and a replenishing toner configured to replenish replenishing toner into the developing device. And had a container. The initial developer (initial developer prepared in the above-described procedure) is charged into the developing device of the color multifunction peripheral, and the replenishment toner (the toners T-1 to T shown in Tables 1 and 2 defined for each device) -7 or any of T-10 to T-16) was put into a replenishing toner container of the color multifunction peripheral. For example, in the manufacture of device DA-1, a mixture of toner T-1 and carrier (initial developer) is charged into the developing device of the color multifunction device, and toner T-10 is charged into the replenishment toner container of the color multifunction device. did. As a result, apparatuses DA-1 to DA-14 and DB-1 to DB-14 (each image forming apparatus) were obtained.

For each of the devices DA-1 to DA-14 and DB-1 to DB-14 obtained as described above, the initial toner relative to the shell layer thickness (second shell thickness S ₂ ) of the replenishment toner Tables 1 and 2 show the ratio of the thickness of the shell layer (first shell thickness S ₁ ) (shell thickness ratio: S ₁ / S ₂ ). For example, in the device DA-1, the shell thickness ratio was 1.40 (= 28/20) (see Tables 1 and 3).

[Evaluation method]
Evaluation methods for the devices DA-1 to DA-14 and DB-1 to DB-14 (hereinafter referred to as target devices) are as follows.

  A sample image with a printing rate of 5% is recorded using the target device (any one of the devices DA-1 to DA-14 and DB-1 to DB-14) in an environment of a temperature of 32.5 ° C. and a humidity of 80% RH. A press life test was performed in which 50,000 sheets were continuously printed on a medium (printing paper). Specifically, when continuous printing is instructed, the target device first develops the electrostatic latent image on the photosensitive member with the initial developer in the developing device, thereby printing on the recording medium (printing paper) (image formation). ) After that, the target device develops the electrostatic latent image on the photosensitive member with the developer in the developing device while replenishing the replenishing toner into the developing device, thereby printing (recording the image) on the recording medium (printing paper). Formation) continued.

  At the timing when all the continuous printing of 50,000 sheets in the printing durability test was completed, the following stress resistance evaluation and fixing property evaluation were performed.

(Stress resistance)
5 g of the developer taken out from the developing device of the target device was placed on a sieve having a known mass of 200 mesh (aperture 75 μm). Subsequently, the sieve was set on a powder tester (manufactured by Hosokawa Micron Corporation), and the sieve was vibrated for 30 seconds under the condition of the rheostat scale 2 according to the manual of the powder tester, and the developer was sieved. Then, after sieving, the mass of the developer (developer that did not pass through the sieve) remaining on the sieve was determined by measuring the mass of the sieve containing the developer. From the mass of the developer before sieving and the mass of the developer after sieving (the mass of the developer remaining on the sieve after sieving), the aggregation rate (unit: mass%) is calculated based on the following formula: Asked.
Aggregation rate = 100 × mass of developer after sieving / mass of developer before sieving

  When the aggregation rate was 1.00% by mass or less, it was evaluated as “good”, and when the aggregation rate was over 1.00% by mass, it was evaluated as “poor” (not good).

(Fixability)
A solid image having a size of 20 mm × 20 mm was formed on an evaluation paper (“Multi Paper Super Economy + A4” manufactured by Askle Co., Ltd.) using the target apparatus in an environment of a temperature of 32.5 ° C. and a humidity of 80% RH. Thereafter, the paper on which the image was formed was passed through the fixing device of the target device. Subsequently, using a reflection densitometer (“SpectroEye (registered trademark)” manufactured by X-Rite), the image density (hereinafter referred to as pre-rubbing ID) of the image on the paper passed through the fixing device was measured. Subsequently, an image on the evaluation sheet was rubbed 5 times with no weight (using only the weight of the weight) using a 500 g weight coated with a fabric. Subsequently, using a reflection densitometer (SpectroEye), the image density of the image on the evaluation paper (hereinafter referred to as post-rubbing ID) was measured. Subsequently, the fixing rate (unit:%) was determined according to the formula “fixing rate = 100 × ID after rubbing / ID before rubbing”. The fixing rate indicates how much the image density (ID) decreases after rubbing, based on the image density (ID) before rubbing. That is, the fixing rate is an index indicating the ratio of the toner that is sufficiently fixed in the toner constituting the image.

  When the fixing rate was 90% or more, it was evaluated as ◯ (good), and when the fixing rate was less than 90%, it was evaluated as x (not good).

[Evaluation results]
Tables 4 and 5 show the results of evaluating the stress resistance (aggregation degree) and fixing property (fixing rate) of the toner for each of the devices DA-1 to DA-14 and DB-1 to DB-14. “0.00 (mass%)” in the evaluation results of the stress resistance (cohesion degree) indicates that all the developer has passed through the sieve.

The apparatuses DA-1 to DA-14 (image forming apparatuses according to Examples 1 to 14) each had the above-described basic configuration. Specifically, in each of the devices DA-1 to DA-14, the first toner (initial toner) includes a first toner base particle and a first external additive attached to the surface of the first toner base particle. It contained a plurality of toner particles. The second toner (replenishment toner) includes a plurality of second toner particles including second toner base particles and a second external additive attached to the surface of the second toner base particles. Each of the first toner base particles and the second toner base particles was provided with a toner core containing a binder resin and a shell layer covering the surface of the toner core. A first shell thickness S ₁ (thickness of the shell layer of the first toner mother particles S _1), and the second shell thickness S ₂ (thickness of the shell layer of the second toner particles S _2), above (1) and (2) were satisfied (see Table 1).

  As shown in Table 4, regarding the devices DA-1 to DA-14, good results were obtained in the evaluation of the stress resistance and the fixing property of the toner. Further, the devices DA-1 to DA-14 were able to continuously form high-quality images in continuous printing.

  The image forming apparatus and the image forming method according to the present invention can be used to form an image in, for example, a copying machine, a printer, or a multifunction peripheral.

DESCRIPTION OF SYMBOLS 10 Transfer device 11, 11a-11d Developing device 12, 12a-12d Photoconductor drum 13 Transfer belt 14a Drive roller 14b Driven roller 14c Tension roller 15a-15d Primary transfer roller 16 Secondary transfer roller 17 Fixing device 18 Cleaning device 20 Control Part 30 Toner mother particle 31 Toner core 32 Shell layer 100 Image forming apparatus 111 Developing roller 112 Regulating blade 113 First agitation shaft 114 Second agitation shaft 115 Replenishment developer container 115a Replenishment amount adjustment member P Recording medium R Storage part

Claims (9)

A developing unit containing an initial developer including a first toner and a carrier, and configured to develop the electrostatic latent image with the toner;
A toner replenishing portion configured to replenish the second toner into the developing portion;
With
The first toner includes a plurality of first toner particles including first toner base particles and a first external additive attached to the surface of the first toner base particles;
The second toner includes a plurality of second toner particles including second toner base particles and a second external additive attached to the surface of the second toner base particles,
Each of the first toner base particles and the second toner base particles includes a toner core containing a binder resin, and a shell layer covering the surface of the toner core,
The thickness S _{1 of the} shell layer of the first toner base particles and the thickness S _{2 of the} shell layer of the second toner base particles satisfy the following relational expressions (1) and (2): Image forming apparatus.
18 nm ≦ S ₂ <S ₁ ≦ 40 nm (1)
1.3 <S ₁ / S ₂ <2.1 (2)   The image forming apparatus according to claim 1, wherein at least one of the shell layer of the first toner base particles and the shell layer of the second toner base particles contains a thermosetting resin.   The at least one of the shell layer of the first toner base particles and the shell layer of the second toner base particles contains a melamine resin and / or a urea resin as the thermosetting resin. The image forming apparatus described in 1.   Either one of the shell layer of the first toner base particles and the shell layer of the second toner base particles further contains a thermoplastic resin having a glass transition point of 60 ° C or higher and 80 ° C or lower. The image forming apparatus according to 3.   The image formation according to any one of claims 1 to 4, wherein the shell layer of the first toner base particles and the shell layer of the second toner base particles cover the entire surface of the toner core, respectively. apparatus.   The image forming apparatus according to claim 1, wherein each of the first external additive and the second external additive includes two or more kinds of external additive particles.   The image formation according to claim 1, wherein the toner core of the first toner base particle and the toner core of the second toner base particle each contain a polyester resin as the binder resin. apparatus.   The image forming apparatus according to claim 1, wherein the developing unit does not include a unit that discharges a carrier in the developing unit. A first development for developing the electrostatic latent image with an initial developer in the developing unit;
A second development for developing an electrostatic latent image with a developer in the developing unit while supplying toner for replenishment into the developing unit after the start of the first development;
Including
The initial developer includes an initial toner and a carrier,
The initial toner includes a plurality of first toner particles including first toner base particles and a first external additive attached to a surface of the first toner base particles;
The replenishment toner includes a plurality of second toner particles including second toner mother particles and a second external additive attached to the surface of the second toner mother particles,
Each of the first toner base particles and the second toner base particles includes a toner core containing a binder resin, and a shell layer covering the surface of the toner core,
The thickness S _{1 of the} shell layer of the first toner base particles and the thickness S _{2 of the} shell layer of the second toner base particles satisfy the following relational expressions (1) and (2): Image forming method.
18 nm ≦ S ₂ <S ₁ ≦ 40 nm (1)
1.3 <S ₁ / S ₂ <2.1 (2)

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