JP2009210809A - Developer for liquid magnetography, process cartridge, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developer for liquid magnetography, the developer having good dispersibility and dispersion stability of magnetic polymer particles and suppressing fog, bleed and disturbance in an image, and to provide a process cartridge and an image forming apparatus using the developer. <P>SOLUTION: The developer for liquid magnetography comprises magnetic polymer particles containing magnetic polymer base particles containing a magnetic powder and a polymer compound, and a dispersion medium dispersing the magnetic polymer particles therein. The dispersion medium is a liquid containing water and the developer as a whole has a surface tension ranging from 27 mN/m to 42 mN/m and a viscosity ranging from 1.0 mPa s to 10.0 mPa s. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a developer for liquid magnetography, a process cartridge, and an image forming apparatus.

2. Description of the Related Art Conventionally, printing technology using magnetic ink is often used for printed matter such as securities, which emphasizes the purpose of security. As a representative example of this magnetic printing, magnetic ink printed characters are described in JIS X9002 for the purpose of character reading.
A magnetic printing technique using magnetic ink for magnetic bar codes is also well known. In this magnetic printing, magnetic ink is printed on various media by offset printing, screen printing, gravure printing, or the like. In this case, in order to obtain optimum printing characteristics, a black magnetic pigment having a particle size of 0.5 μm to several μm is used in the magnetic ink.

  Due to the rapid spread of inexpensive printers, a technique for performing magnetic printing by a method such as ink jet or bubble jet (registered trademark) has been reported (for example, see Patent Documents 1 and 2).

In addition, as an image forming method using a magnetic material, a magnetic latent image is formed on a magnetic recording medium having a magnetic material on the surface by operating a magnetic head, and the magnetic latent image is developed with magnetic toner and then applied to a transfer medium. There is so-called magnetography in which printing is performed by heating or electrostatic transfer, fixing, and a technique using magnetic ink has been reported for this technique.
JP 2000-2111924 A JP 2000-212498 A JP-A-3-29961 Japanese Patent Laid-Open No. 3-59678

  The present invention provides a developer for liquid magnetography in which dispersibility and dispersion stability of magnetic polymer particles are good and image fogging, bleeding, and disturbance are suppressed, and a process cartridge and an image forming apparatus using the developer. The purpose is to do.

The above-mentioned subject is achieved by the following present invention.
That is, the invention according to claim 1
Magnetic polymer particles containing magnetic polymer mother particles containing a magnetic component and a polymer compound, and a dispersion medium for dispersing the magnetic polymer particles,
The dispersion medium is a liquid containing water,
The surface tension of the entire developer is 27 mN / m or more and 42 mN / m or less,
The developer for liquid magnetography is characterized in that the viscosity of the whole developer is 1.0 mPa · s or more and 10.0 mPa · s or less.

The invention according to claim 2
2. The developer for liquid magnetography according to claim 1, wherein the magnetic polymer particles have a zeta potential of −200 mV to −20 mV.

The invention according to claim 3
The magnetic polymer particles are externally added magnetic polymer particles including the magnetic polymer mother particles and external additive particles externally added to the surface of the magnetic polymer mother particles,
The liquid magnetography developer according to claim 1 or 2, wherein the number average primary particle diameter of the external additive particles is 15 nm or more and 500 nm or less.

The invention according to claim 4
The number average particle size of the magnetic polymer base particles is 0.5 μm or more and 10.0 μm or less, and the coefficient of variation of the number average particle size is 0% or more and 30% or less. The developer for liquid magnetography according to any one of claims 1 to 3.

The invention according to claim 5
A magnetic latent image carrier;
A developer storage means for storing the developer according to any one of claims 1 to 4,
Developer supplying means for supplying the developer to the magnetic latent image holding member on which the magnetic latent image is formed;
It is a process cartridge characterized by having.

The invention according to claim 6
A magnetic latent image carrier;
Magnetic latent image forming means for forming a magnetic latent image on the magnetic latent image holding member;
A developer storage means for storing the developer according to any one of claims 1 to 4,
Developer supplying means for supplying the developer to the magnetic latent image holding body on which the magnetic latent image is formed in order to visualize the magnetic latent image as a toner image;
Transfer means for transferring the toner image to a recording medium;
A demagnetizing means for demagnetizing the magnetic latent image on the magnetic latent image holder;
An image forming apparatus comprising:

  According to the first aspect of the invention, the dispersibility and dispersion stability of the magnetic polymer particles are good, and image fogging, blurring, and disturbance are suppressed.

  According to the second aspect of the invention, the dispersibility and dispersion stability of the magnetic polymer particles are more excellent, and fogging, blurring, and disturbance of the image are suppressed.

  According to the third aspect of the present invention, the dispersibility and dispersion stability of the magnetic polymer particles are more excellent, and fogging, blurring, and disturbance of the image are suppressed.

  According to the fourth aspect of the invention, fogging, blurring and disturbance of the image are suppressed, and a higher quality image is formed.

  According to the invention of claim 5, the dispersibility and dispersion stability of the magnetic polymer particles are good, and the fogging, blurring and disturbance of the image are suppressed.

  According to the sixth aspect of the invention, the dispersibility and dispersion stability of the magnetic polymer particles are good, and image fogging, blurring, and disturbance are suppressed.

Hereinafter, embodiments of the present invention will be described in detail.
<Developer for liquid magnetography>
The developer for liquid magnetography of the present embodiment (hereinafter sometimes simply referred to as “developer”) includes magnetic polymer particles containing magnetic polymer mother particles containing a magnetic component and a polymer compound, and magnetic A dispersion medium for dispersing the polymer particles, and the dispersant is a liquid containing water. Further, the developer according to the exemplary embodiment is characterized in that the entire surface tension is 27 mN / m or more and 42 mN / m or less, and the entire viscosity is 1.0 mPa · s or more and 10.0 mPa · s or less.

When the developer has the above configuration, the dispersibility and dispersion stability of the magnetic polymer particles in the developer are good.
In addition, since the developer has the above-described configuration, fogging, bleeding, and disturbance of the formed image are suppressed. As a result, the contrast between the image portion and the non-image portion is also good.

The reason is not clear, but is presumed as follows.
Since the surface tension of the developer is in the above range, local aggregation of the magnetic polymer particles due to the surface tension being too high is suppressed. Furthermore, since the viscosity of the developer is within the above range, the mobility of the magnetic polymer particles in the dispersion medium is increased. Therefore, it is presumed that the dispersibility of the magnetic polymer particles in the developer is good and the dispersion stability with time is also good.

  Further, since the surface tension of the developer is within the above range, development to a region where a magnetic latent image on the surface such as a magnetic latent image holding member is not formed (hereinafter may be referred to as “non-magnetic latent image region”). Adhesion of the agent is suppressed. Further, as described above, since the mobility of the magnetic polymer particles is high, the magnetic polymer particles are easily moved to the magnetic latent image region by magnetophoresis, and the adhesion of the developer to the non-magnetic latent image region is further suppressed. . Therefore, it is estimated that the fog (surface fog) over the entire non-image portion is suppressed. Further, as described above, the local aggregation of the magnetic polymer particles is suppressed, and the mobility of the magnetic polymer particles is high, so it is estimated that fogging around the image area, blurring of the image, and disturbance are suppressed. Is done.

  Further, since the developer has the above structure, the mobility of the magnetic polymer particles is high, and a good image can be formed even if high-speed development is performed. Furthermore, since the developer has the above-described configuration, even if magnetic polymer particles adhere to the surface of the magnetic latent image holding member, it easily peels off, improving the cleaning property of the magnetic latent image holding member and suppressing contamination in the image forming apparatus. Is done.

  Hereinafter, the developer in the embodiment of the present invention will be described in detail along the configuration.

―Magnetic polymer particles―
As described above, the magnetic polymer particles contain magnetic polymer mother particles containing a magnetic component and a polymer compound.
As the form of the magnetic polymer particles, the form in which the magnetic polymer mother particles are used as they are as the magnetic polymer particles, and the externally added magnetic polymer particles including the magnetic polymer mother particles and the external additive particles are used as the magnetic polymer particles. Form.
Hereinafter, the magnetic polymer mother particles will be described.

--Magnetic polymer mother particle--
As described above, the magnetic polymer mother particles include a magnetic component and a polymer compound, and may include other components as necessary.

(Magnetic component)
Examples of the magnetic component include magnetic powder and magnetic fluid.

[Magnetic powder]
As the magnetic powder, magnetite, ferrite or the like represented by the general formula of MO · Fe ₂ O ₃ or M · Fe ₂ O ₄ exhibiting magnetism is preferably used. Here, M is a divalent or monovalent metal ion (specifically, for example, Mn, Fe, Ni, Co, Cu, Mg, Zn, Cd, Li, etc.). Metal is used. Examples thereof include iron-based oxides such as magnetite, γ-iron oxide, Mn—Zn-based ferrite, Ni—Zn-based ferrite, Mn—Mg-based ferrite, Li-based ferrite, and Cu—Zn-based ferrite. Among these, inexpensive magnetite is more preferably used.

Further, the magnetic powder may include other metal oxides in addition to the above-described oxide exhibiting magnetism. Examples of other metal oxides include Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Nonmagnetic metal oxides using a single metal or a plurality of metals such as Sn, Ba, and Pb, and metal oxides exhibiting the above-described magnetism are used. Specifically, for example, as non-magnetic metal oxides, Al ₂ O ₃ , SiO ₂ , CaO, TiO ₂ , V ₂ O ₅ , CrO ₂ , MnO ₂ , Fe ₂ O ₃ , CoO, NiO, CuO, ZnO, SrO, Y ₂ O ₃ , ZrO _{2 and the} like are used.

  The number average primary particle size of the magnetic powder is preferably in the range of 0.02 μm to 2.0 μm. When the number average primary particle diameter of the magnetic powder is out of the above range, the magnetic powder tends to aggregate and it may be difficult to uniformly disperse it in the polymer compound.

  The content of the magnetic powder in the magnetic polymer mother particles is preferably in the range of 2.5% by mass to 50% by mass, and more preferably in the range of 3.0% by mass to 40% by mass. More preferably, it is in the range of 5.0% by mass or more and 30% by mass or less. By setting the content of the magnetic powder in the above range, a sufficient magnetic force can be obtained, and dispersion stability with respect to an aqueous medium as polymer particles can be improved.

In the present embodiment, it is desirable that the magnetic powder is uniformly dispersed in the magnetic polymer mother particles. Here, “uniform” with respect to dispersion means that there are no aggregates having a size of about 10 primary particles of magnetic powder gathered in the system. The same applies to the following.
In this case, it is preferable that the particle size dependence of the magnetic powder content is small (the magnetic powder content does not vary greatly depending on the particle size). Specifically, the ratio of the magnetic powder content (P mass%) of the magnetic polymer mother particles having a number average particle diameter of 2 μm to the magnetic powder content (Q mass%) of the magnetic polymer mother particles of 5 μm. (P / Q) is preferably 0.5 or more, and more preferably in the range of 0.6 or more and 1.0 or less. Regardless of the particle size, the content of the magnetic powder is in the above-mentioned range, so that, for example, when magnetic polymer mother particles are used as magnetic polymer particles in magnetography, it becomes easier to control developability. There are benefits.

  In addition, the presence state of the magnetic powder on the surface of the magnetic polymer mother particle can be confirmed by observing the surface with an electron microscope, and no magnetic powder protruding on the surface of all the observed magnetic polymer mother particles can be seen. desirable.

As for magnetic powder, it is desirable that the surface is hydrophobized. The surface of the magnetic powder that has not been hydrophobized is basically hydrophilic, and the monomer of the polymer compound described later is hydrophobic. Affinity with the monomer is increased. Therefore, the dispersion uniformity and content of the magnetic powder in the magnetic polymer mother particle are also increased.
The method for the hydrophobizing treatment is not particularly limited, and examples thereof include a method in which the surface of the magnetic powder is coated with a hydrophobizing agent such as various coupling agents, silicone oils, and resins. It is preferable to perform a surface coating treatment with a ring agent.

[Magnetic fluid]
A magnetic fluid is a dispersion in which a superparamagnetic material having a single magnetic domain structure having a particle size of 5 nm to 50 nm as magnetic particles is dispersed in a solvent without agglomeration by addition of a surfactant or the like as necessary. That is, the magnetic particles in the magnetic fluid can be easily rotated.

  Examples of superparamagnetic materials that can be used as the magnetic particles include magnetite, iron such as ferrite, cobalt, nickel, manganese and other metals exhibiting ferromagnetism, or alloys or compounds containing these elements. It is not limited to these.

  The saturation magnetization of the magnetic particles is preferably 200 gauss or more and 1000 gauss or less, and more preferably 300 gauss or more and 1000 gauss or less. In addition, it is possible to increase the saturation magnetization by adding particles of rare earth metal, cobalt alloy or the like to the magnetic fluid in this embodiment. Examples of the additive metal include La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, and Er in addition to Co.

The solvent that can be used for the magnetic fluid is preferably a liquid at room temperature (20 to 25 ° C.) in terms of fluidity, but may be a solid at room temperature when used by heating. Examples of such solvents include, but are not limited to, water, organic solvents, silicone solvents, fluorine solvents, and the like.
Specifically, fatty acid hydrocarbons such as n-heptane, n-hexane, n-octane, isooctane, n-decane, 1-decene, cyclohexane, cyclooctane, methylcyclohexane, benzene, toluene, xylene, mesitylene, ethylbenzene, Aromatic hydrocarbons such as tetralin, diethyl ether, di-n-propyl ether, diisopropyl ether, di-n-butyl ether, tetrahydrofuran, dioxane, alkyl diphenyl ether, dialkyl tetraphenyl ether, alkyl diphenyl ether, oligophenylene oxide and other ethers, ethyl acetate , Ester oils such as butyl phthalate, butyl sebacate and fatty acid ester oils, halogen compounds such as chloroform, dichloromethane and dichloroethane, 4-methyl- -Butanol, 1-butanol, acetone, ethanol, methanol, acetonitrile), alcohols such as glycerin, white oil (liquid paraffin), kerosene, decalin, pyridine, mineral oil, spindle oil, kerosene, light oil, poly α-olefin oil system Alkylnaphthalenes, higher alkylbenzenes, higher alkylnaphthalenes, polybutenes (molecular weight of about 300 to 2000), polyalkylene glycols, petroleum solvents such as Isopar H, L and M manufactured by Exxon, silicone oils such as dimethylpolysiloxane, Fluorine oil dispersion medium such as perfluoropolyether can be used.

  Examples of solids at room temperature include alkyl naphthalenes such as octadecanylnaphthalene, nonadecanylnaphthalene, and eicosylnaphthalene; n-undecane, n-dodecane, n-tridecane, n-tetradecane, n-pentadecane, n-hexadecane, Hydrocarbons such as n-heptadecane, n-octadecane, and n-nonadecane and their halides; silicone oils; modified silicones; commercially available products include linear aliphatic carbonization such as Norper 14, 15 and 16 manufactured by Exxon Hydrogen can be mentioned.

  Moreover, a dispersing agent can be used for magnetic fluid as needed. As the dispersant, for example, higher fatty acids are effective, and examples of the higher fatty acids include lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, behenic acid, and salts thereof. These addition amounts are preferably 0.001% by mass or more and 50% by mass or less, and more preferably 0.01% by mass or more and 10% by mass or less with respect to the magnetic particles. When the addition amount is in the above range, the sedimentation of the magnetic particles in the dispersion medium can be suppressed without increasing the viscosity.

The content of the magnetic particles in the magnetic fluid is preferably 5% by mass or more and 80% by mass or less, and more preferably 10% by mass or more and 50% by mass or less. When the content is in the above range, the fluidity of the fluid is good, the magnetic domain directions are easily aligned, and suitable magnetic properties including magnetic responsiveness can be exhibited.
The boiling point of the magnetic fluid is desirably 80 ° C. or higher.

  Examples of the magnetic fluid include product numbers M-300, N-304, N-504, A-200, A-300, A-400, A-500, p-206, P manufactured by Sigma High Chemical Co., Ltd. -306, F-210, F-310, etc., but are not limited thereto.

In order for the ferrofluid to be present in the particles independently in a liquid state, it is desirable that the ferrofluid is enclosed in a capsule. This is because encapsulating in a capsule can avoid mixing with other components during the production of the magnetic polymer mother particles. However, if the magnetic fluid can be held in a liquid state, the encapsulation is not particularly required.
The number average particle size of the capsules is desirably 0.05 μm or more and 2.0 μm or less, and more preferably 0.07 μm or more and 1.2 μm or less. When the number average particle diameter is in this range, the particles can be easily handled and high image quality can be obtained when used as an image forming material. The particle diameter referred to here indicates the number average particle diameter of the particles, and is confirmed by microscopic observation at the time of capsule production or by cross-sectional observation of the particles after production of magnetic polymer particles. Specifically, the average particle diameter of 100 capsules measured.

  There are various methods for producing capsules, and examples thereof include a coacervation method using gelatin, an in-situ polymerization method using an acrylic monomer, and an in-situ polymerization method using melamine as a main raw material. The magnetic fluid capsules in the particles may be prepared separately in advance or may be prepared during polymer polymerization of the magnetic polymer mother particles.

The content of the magnetic fluid in the magnetic polymer mother particles in this embodiment is preferably 1% by mass or more and 60% by mass or less, more preferably 2.0% by mass or more and 40% by mass or less. It is more desirable that the content be 0.0 mass% or more and 25 mass% or less.
When the content is in the above range, it is possible to obtain dispersion without dispersion in the particles of the magnetic fluid capsule and the stability of the polymer particles while ensuring the necessary magnetic force.

  The content of magnetic fluid in the magnetic polymer mother particles is determined by measuring the rate of change of the weight with the combustion temperature using a thermogravimetric measuring device or by using a vibrating sample magnetometer (VSM). It can be obtained by comparing the magnetization and the saturation magnetization of the magnetic polymer particles.

(Polymer compound)
As the polymer compound, a resin conventionally used in a magnetic recording apparatus is used. Specifically, homopolymers of styrene and its substituted products and copolymer resins thereof, copolymer resins of styrene and (meth) acrylate, styrene and (meth) acrylate and other vinyl series Multi-component copolymer resins with monomers, styrene copolymer resins of styrene and other vinyl monomers, and those obtained by crosslinking a part of each of the above resins are used. Furthermore, polymethyl methacrylate, polybutyl methacrylate, polyvinyl acetate resin, polyester resin, epoxy resin, polyamide resin, polyolefin resin, silicone resin, polybutyral resin, polyvinyl alcohol resin, polyacrylic acid resin, phenol resin, aliphatic or finger ring Examples thereof include aromatic hydrocarbon resins, petroleum resins, styrene-vinyl acetate copolymer resins, ethylene-vinyl acetate copolymer resins, wax resins, and the like, or a mixture thereof.

As the polymer compound, a thermoplastic resin is desirable.
Among the above polymer compounds, specific examples of the thermoplastic resin include a polymer obtained by polymerizing at least one of a (meth) acrylate monomer and a styrene monomer.

In the (meth) acrylate monomer, the alcohol residue of the (meth) acrylic acid ester is preferably a substituted or unsubstituted alkyl group having 1 to 18 carbon atoms. Examples of the alkyl group include a methyl group and an ethyl group. Group, n-propyl group, isopropyl group, n-butyl group, t-butyl group, pentyl group, isopentyl group, neopentyl group, hexyl group, heptyl group, n-octyl group, nonyl group, decyl group, undecyl group, dodecyl group Groups and the like. In addition to the alkyl group, the alcohol residue may be a benzyl group, a hydroxyethyl group, a hydroxyethyl group in which a hydroxyl group is protected with a hydrophobic protecting group such as dihydropyran, a polyoxyethylene group, or the like.
In consideration of the dispersibility of the magnetic polymer particles in the dispersion medium, a polymer containing hydroxyethyl methacrylate is used as the polymer compound, or the (meth) acrylate polymer is further modified with (poly) ethylene glycol. It is desirable to let them.

As the styrenic monomer, a vinyl group-containing monomer having a substituted or unsubstituted aryl group having 6 to 12 carbon atoms is desirable. Examples of the aryl group include a phenyl group, a naphthyl group, a tolyl group, pn- Although an octyloxyphenyl group etc. are mentioned, a phenyl group is desirable.

Examples of the substituent in the alkyl group of the (meth) acrylate monomer and the aryl group of the styrene monomer include an alkyl group, an alkoxy group, a halogen atom, and an aryl group.
Examples of the alkyl group include those exemplified for the aforementioned alkyl group. Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, and a butoxy group. Among these, a methoxy group and an ethoxy group are preferable. In addition, examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, and a fluorine atom and a chlorine atom are preferable. Examples of the aryl group include those exemplified for the aforementioned aryl group.

  When both a (meth) acrylate monomer and a styrene monomer are used as the monomer, the ratio of the content of (meth) acrylate and styrene monomer in the mixture is the molar ratio ((meth) acrylate monomer / styrene monomer) ) Is preferably in the range of 95/10 to 5/95, more preferably in the range of 90/10 to 10/90.

  The polymer compound preferably has at least one selected from a hydroxyl group, a carboxyl group, and an alkyl ester group thereof. This greatly improves the water dispersibility of the magnetic polymer particles. In order for the polymer compound to have the functional group, it can be performed by selecting a monomer constituting the polymer compound.

Examples of the monomer having a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, glycerin di (meth) acrylate, and 1,6-bis. (3-acryloxy-2-hydroxypropyl) -hexyl ether, pentaerythritol tri (meth) acrylate, tris- (2-hydroxyethyl) isocyanuric acid ester (meth) acrylate, polyethylene glycol (meth) acrylate and the like.
In addition, the said (meth) acrylate is an expression showing an acrylate or a methacrylate here, and applies to this in the following.

  Examples of the monomer having a carboxyl group include acrylic acid, methacrylic acid, methacryloyloxyethyl monophthalate, methacryloyloxyethyl monohexahydrophthalate, methacryloyloxyethyl monomaleate, and methacryloyloxyethyl monosuccinate.

The presence of each functional group can be confirmed by measuring the infrared absorption spectrum of the magnetic polymer particles, but it is desirable to carry out the following method because it is affected by the magnetic component, etc. Since the hydroxyl group and carboxyl group in the magnetic polymer particles differ depending on the magnetic component, it is desirable to confirm the hydroxyl group and the like of the polymer compound by determining the hydroxyl group amount and carboxy group amount of the polymer component excluding the magnetic component. .

In this case, when the polymer compound has only a hydroxyl group, the amount of the hydroxyl group is preferably in the range of 0.1 to 5.0 mmol / g. If the amount of hydroxyl groups is within this range, good dispersibility in an aqueous medium can be obtained without swelling of the polymer particles.
The amount of hydroxyl groups is desirably in the range of 0.2 to 4.0 mmol / g, and more preferably in the range of 0.3 to 3.0 mmol / g.

On the other hand, when the polymer compound has a carboxyl group, the carboxyl group amount is desirably in the range of 0.005 to 0.5 mmol / g. When the amount of carboxyl groups is in the above range, even if the number of functional groups is smaller than that of hydroxyl groups, good dispersibility in an aqueous medium and swelling suppression effect can be obtained, with respect to fluctuations when other functional groups are present. Can maintain these characteristics.
The amount of carboxyl groups is more preferably in the range of 0.008 to 0.3 mmol / g, and still more preferably in the range of 0.01 to 0.1 mmol / g. In this case, when it also has a hydroxyl group, the amount of the hydroxyl group is more preferably in the range of 0.2 to 4.0 mmol / g, and further preferably in the range of 0.3 to 3.0 mmol / g. is there.

  The hydroxyl group amount can be determined by a general titration method. For example, a reagent such as pyridine solution of acetic anhydride is added to the above polymer compound, heated, hydrolyzed by adding water, separated into particles and supernatant by a centrifuge, and the supernatant is used as an indicator such as phenolphthalein. The amount of hydroxyl groups can be determined by titrating with an ethanolic potassium hydroxide solution or the like.

On the other hand, the amount of carboxyl groups can also be determined by a general titration method. For example, a neutralization reaction is carried out by adding a reagent such as an ethanol solution of potassium hydroxide to the above polymer compound, and the supernatant containing excess potassium hydroxide is automatically titrated by separating it into particles and supernatant using a centrifuge. The amount of the carboxyl group can be determined by titrating with an isopropanol hydrochloric acid solution or the like.
In addition, when the carboxyl group forms a salt structure described later (-COO-Y +: where Y + represents an alkali metal ion, an alkaline earth metal ion, or an organic cation such as ammonium), an acid such as hydrochloric acid is used. After converting the salt into carboxylic acid, the above titration can be performed to determine the amount of carboxyl groups.
That is, the amount of carboxyl groups in this embodiment refers to the amount of carboxyl groups including carboxyl groups contributing to the salt structure when the carboxyl group forms a salt structure.

The polymer compound in this embodiment may be a copolymer obtained by further copolymerizing a monomer having a crosslinkability (crosslinking agent) as necessary. Specifically, divinylbenzene, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, glycidyl (meth) acrylate, 2-([1′-methylpropylideneamino] carboxyamino) ethyl (meth) acrylate, and the like In the polymerization, a crosslinking structure may be used, or the polymer particles may be crosslinked after polymerization.
The content of the crosslinking agent in the monomer mixture is preferably in the range of 0.05 to 20 parts by mass with respect to 100 parts by mass of the total amount of (meth) acrylate monomer and / or styrene monomer, and 0.5 to 10 parts by mass. The range of the part is more suitable.

  Further, the polymer compound may contain a non-crosslinked resin from the viewpoint of improving the fixability. The non-crosslinked resin is not particularly limited as long as it is a polymer that fixes particles on a medium to be fixed such as paper, film by external energy such as heat, ultraviolet rays, and electron beams, solvent vapor, solvent volatilization from the polymer, and the like. .

  Specifically, for example, styrenes such as styrene and chlorostyrene; monoolefins such as ethylene, propylene, butylene, and isoprene; vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate, and vinyl acetate; methyl acrylate , Α-methylene aliphatic monocarboxylic acid esters such as ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, dodecyl methacrylate; vinyl Homopolymers or copolymers of vinyl ethers such as methyl ether, vinyl ethyl ether, and vinyl butyl ether; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, and vinyl isopropenyl ketone;

When the polymer compound contains a non-crosslinked polymer, the molecular weight (number average molecular weight) of the non-crosslinked polymer is preferably in the range of 5000 to 1000000, and more preferably in the range of 10,000 to 500000.
In addition, the said number average molecular weight is measured using a gel permeation chromatography (GPC) about the component which melt | dissolved the high molecular compound in THF and isolate | separated as a dissolved part.

(Other ingredients)
The magnetic polymer mother particles may further contain a dye, a pigment, carbon black and the like for the purpose of coloring the polymer compound. In that case, in the production process of the magnetic polymer mother particles, each additive may be included in a mixture of monomers and the like in which the magnetic component is dispersed, or together with the magnetic component and the monomer and the like in advance. Mixing may be performed simultaneously with the dispersion treatment of the magnetic component and the dispersion treatment of the respective additives.

(Method for producing magnetic polymer mother particles)
In order to obtain the magnetic polymer particles in the present invention, a known method is used. For example, a suspension polymerization method, an emulsion polymerization method, a dispersion polymerization method, a seed polymerization method and the like are preferably used. Furthermore, suspension polymerization may be performed using an emulsification method known as a membrane emulsification method.
Specifically, for example, when magnetic polymer particles are prepared by the suspension polymerization method, first, a mixture in which a desired amount of monomers, magnetic components, a crosslinking agent, a polymerization initiator and the like constituting the polymer compound are added. To prepare.

  As the crosslinking agent, a known crosslinking agent can be selected and used. Examples of suitable crosslinking agents include divinylbenzene, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, methylenebis (meth) acrylamide, and glycidyl. (Meth) acrylate, 2-([1′-methylpropylideneamino] carboxyamino) ethyl methacrylate and the like can be mentioned. Among these, divinylbenzene, ethylene glycol di (meth) acrylate, and diethylene glycol di (meth) acrylate are more preferable, and divinylbenzene is particularly preferable. Examples of suitable polymerization initiators include azo polymerization initiators and peroxide initiators, among which oil-soluble initiators are desirable.

Further, the mixture may further contain a dye for coloring the polymer, an organic pigment, carbon black, titanium oxide, and the like, and further magnetic powder as a magnetic component.
As the magnetic powder, magnetite represented by the general formula MO · _Fe 2 _{O 3} or M · _Fe 2 _{O 4} exhibiting magnetism is suitably used a ferrite.

As a method for preparing a mixture containing the above monomers and the like, for example, first, the monomer, a polymerization initiator, and other necessary components are mixed to prepare a mixed liquid of monomers and the like. The mixing method is not particularly limited.
Next, the magnetic component is dispersed in this. A known method is applied to the dispersion of the magnetic component in the mixed solution. That is, for example, a dispersing machine such as a ball mill, a sand mill, an attritor, or a roll mill is used. In the case where the monomer component is separately polymerized in advance and the magnetic component is dispersed in the obtained polymer, a kneader such as a roll mill, a kneader, a Banbury mixer, or an extruder is used.
The method for preparing the mixture is not limited to the above. For example, a magnetic component may be added at this stage using a mixture of magnetic components at the time of preparing the mixed solution, or the monomer, Magnetic components and the like may be mixed at a time to form a mixture.

Next, the mixture containing the monomer and the like is suspended in an aqueous medium. The suspension is performed, for example, as follows.
That is, the mixture is charged and suspended in an aqueous medium in which a salt such as an inorganic salt is dissolved and a dispersion stabilizer is present. As a suspension method, a known suspension method is used. For example, like a mixer, a special stirring blade is rotated at a high speed to suspend monomers and the like in an aqueous medium, a method of suspending with a rotor-stator shear force known as a homogenizer, and suspension by ultrasonic waves. And mechanical suspension methods such as

Next, magnetic polymer particles are obtained by suspension polymerization of the suspended monomer and particles containing the magnetic component. The polymerization reaction can be carried out not only in the air but also under pressure, but these other reaction conditions are applied as necessary and are not particularly limited.
As the reaction conditions, for example, it is possible to react at a reaction temperature of 40 to 100 ° C. for 1 to 24 hours while stirring the suspension in which the suspended particles are dispersed at an atmospheric pressure of about 80% or more. From the standpoint of obtaining polymer particles at a high rate.

(Characteristics of magnetic polymer mother particles)
The number average particle diameter (primary particle diameter) of the magnetic polymer mother particles is preferably in the range of 0.5 μm to 10.0 μm, more preferably in the range of 0.5 μm to 5.0 μm. More preferably, it is in the range of not less than 0.0 μm and not more than 4.0 μm.
The magnetic polymer base particles preferably have a coefficient of variation in number average particle diameter in the range of 0% to 30%, more preferably 0% to 20%.

  When the number average particle diameter of the magnetic polymer mother particles is in the above range, the particles can be easily handled and high image quality can be obtained when used as an image forming material. Further, when the variation coefficient is in the above range, the variation in size between particles is suppressed within the range of actual production conditions, and a high-quality image is created.

The number average particle size is measured by taking a photograph of dried magnetic polymer mother particles with an optical microscope or an electron microscope, and measuring the particle size of 100 to 200 particles randomly selected from them. The total of these values is divided by the number.
The coefficient of variation is obtained by calculating a standard deviation (μm) as an index of particle size distribution based on the particle size data obtained by the above measurement, and then dividing the standard deviation by the number average particle size to be 100 times. The dimensionless coefficient of variation (%) calculated by

--Externally added magnetic polymer particles--
The magnetic polymer particles may be composed of the above magnetic polymer mother particles alone (a form in which the magnetic polymer mother particles are used as magnetic polymer particles as they are), but the magnetic polymer mother particles and the external additive may be used. The externally added magnetic polymer particles including the agent particles are desirable.
Hereinafter, the externally added magnetic polymer particles will be described.

  The externally added magnetic polymer particles include the above magnetic polymer mother particles and external additive particles that are externally added to the surface of the magnetic polymer mother particles, and the number average primary particle diameter of the external additive particles is 15 nm. It is characterized by being not less than 500 nm.

When the externally added magnetic polymer particles have the above-described configuration, the dispersibility and dispersion stability of the magnetic polymer particles are further improved, and image fogging, bleeding, and disturbance are suppressed.
The reason is not clear, but is presumed as follows.

Since the surface of the magnetic polymer mother particle is externally added by the external additive particles as described above, nonuniformity occurs on the surface of the magnetic polymer particle and irregularities are formed. It is suppressed. Therefore, it is presumed that a good dispersion state and dispersion stability can be obtained despite the fact that the externally added magnetic polymer particles contain a magnetic substance and thus have a large specific gravity.
In addition, since the externally added magnetic polymer particles have the above-described configuration, the contact area between the surface of the magnetic latent image holding member in the image forming apparatus and the externally added magnetic polymer particles is reduced, and the externally added magnetic polymer particles are exposed to the nonmagnetic latent image region. Adsorption of the additive magnetic polymer particles is suppressed. Therefore, it is presumed that image fogging and the like are suppressed.

  In addition, since the externally added magnetic polymer particles have the above-described configuration, even if the externally added magnetic polymer particles adhere to the surface of the magnetic latent image holding member, they are easily peeled off, and the cleaning properties of the magnetic latent image holding member are improved. Contamination in the image forming apparatus is suppressed.

(External additive particles)
The external additive particles mean particles that are added to and adhered to the surface of the magnetic polymer mother particles after preparation.
Specific examples of the external additive particles include inorganic particles and polymer particles.
Examples of inorganic particles include silica, alumina, titania, and other known particles.
Examples of the polymer particles include those obtained by polymerizing a known monomer such as a (meth) acrylate monomer and a styrene monomer by an emulsion polymerization method. ) May be further copolymerized.

As described above, the number average primary particle diameter of the external additive particles is from 15 nm to 500 nm, preferably from 15 nm to 300 nm, and more preferably from 20 nm to 200 nm.
If the number average primary particle diameter of the external additive particles is smaller than the above range, the external additive particles uniformly adhere to the surface of the magnetic polymer mother particles, making it difficult to form a non-uniform state on the surface of the magnetic polymer particles. It may be difficult to obtain the above-mentioned aggregation suppressing effect of the polymer particles.
On the other hand, if the number average primary particle diameter of the external additive particles is larger than the above range, the adsorptivity of the external additive particles on the surface of the magnetic polymer mother particles is lowered, so that it is difficult to create a non-uniform state on the surface of the magnetic polymer particles. In addition, image quality defects may occur due to the peeled external additive particles.

  The addition amount of the external additive particles is preferably 0.5 to 15% by mass, more preferably 0.5 to 7% by mass with respect to the entire externally added magnetic polymer particle.

(External method)
Examples of the method of externally adding the external additive particles to the surface of the magnetic polymer mother particle include a method using a high speed mixer. Specifically, for example, magnetic polymer mother particles and external additive particles may be mixed using a Henschel mixer, a V-type blender, or the like.

--Characteristics of magnetic polymer particles--
The concentration of the magnetic polymer particles in the developer is preferably in the range of 0.5% by mass to 40% by mass, and more preferably in the range of 1% by mass to 20% by mass.
When the concentration of the magnetic polymer particles is within the above range, the liquid viscosity is appropriate and handling is easy, and a sufficient image density is obtained by the magnetic polymer particles formed as an image on the recording medium.

―Dispersion medium―
The dispersion medium is a liquid containing water, and if necessary, a surfactant or dispersant for the purpose of maintaining the dispersion stability of the magnetic polymer particles, or a water solution for the purpose of controlling evaporation or interface characteristics. An organic solvent, other additives, and the like.
Here, “water” means purified water such as distilled water, ion-exchanged water, or ultrapure water.

(Surfactant)
As the surfactant, any known surfactant such as an anionic surfactant, a nonionic surfactant, and a cationic surfactant can be used.

  Examples of the anionic surfactant include alkylbenzene sulfonate, alkylphenyl sulfonate, alkylnaphthalene sulfonate, higher fatty acid salt, sulfate of higher fatty acid ester, sulfonate of higher fatty acid ester, higher alcohol ether. Sulfate salts and sulfonate salts of the above, higher alkyl sulfosuccinate salts, higher alkyl phosphate ester salts, phosphate ester salts of higher alcohol ethylene oxide adducts, and the like.

  Nonionic surfactants include, for example, polypropylene glycol ethylene oxide adducts, polyoxyethylene alkyl phenyl ethers (polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene dodecyl phenyl ether, etc.), polyoxyethylene Alkyl ether (polyoxyethylene oleyl ether, polyoxyethylene cetyl ether, polyoxyethylene lauryl ether, etc.), polyoxyethylene fatty acid ester, polyoxyethylene sorbitan fatty acid ester, fatty acid alkylolamide, oxyethylene adduct of acetylene glycol, etc. Can be mentioned.

  Examples of the cationic surfactant include tetraalkylammonium salts, alkylamine salts, benzalkonium salts, alkylpyridium salts, imidazolium salts, and the like.

  As the surfactant, in addition to the above, for example, silicone surfactants such as polysiloxane oxyethylene adducts; fluorine-based compounds such as perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, oxyethylene perfluoroalkyl ethers Surfactants; biosurfactants such as splicrispolic acid, rhamnolipid, and lysolecithin;

(Dispersant)
As the dispersant, any polymer having a hydrophilic structure portion and a hydrophobic structure portion can be effectively used. For example, styrene-styrene sulfonic acid copolymer, styrene-maleic acid copolymer, styrene-methacrylic acid copolymer, styrene-acrylic acid copolymer, vinyl naphthalene-maleic acid copolymer, vinyl naphthalene-methacrylic acid copolymer. Polymer, vinyl naphthalene-acrylic acid copolymer, acrylic acid alkyl ester-acrylic acid copolymer, methacrylic acid alkyl ester-methacrylic acid, styrene-methacrylic acid alkyl ester-methacrylic acid copolymer, styrene-acrylic acid alkyl ester -Acrylic acid copolymer, styrene-methacrylic acid phenyl ester-methacrylic acid copolymer, styrene-methacrylic acid cyclohexyl ester-methacrylic acid copolymer, etc., and these copolymers are random, block and graft copolymer Coalescence It may be in any of the structure.

  These polymers may be copolymerized with a polyoxyethylene group, a monomer having a hydroxyl group, or a monomer having a cationic functional group in order to improve dispersibility or water solubility, and the hydrophilic group is acidic. The polymer as the group may have a salt structure with a basic compound.

(Water-soluble organic solvent)
The water-soluble organic solvent refers to an organic solvent that does not separate into two phases when added to water, and specifically includes, for example, monovalent or polyhydric alcohols, nitrogen-containing solvents, sulfur-containing solvents, and the like. Derivatives and the like.

Examples of the polyhydric alcohols include ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,5-pentanediol, 1,2,6-hexanetriol, and glycerin.
Examples of the polyhydric alcohol derivative include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, diethylene glycol Examples thereof include ethylene oxide adducts of glycerin.
Examples of monovalent alcohols include ethanol, isopropyl alcohol, butyl alcohol, and benzyl alcohol.

Examples of the nitrogen-containing solvent include pyrrolidone, N-methyl-2-pyrrolidone, cyclohexyl pyrrolidone, triethanolamine and the like.
Examples of the sulfur solvent include thiodiethanol, thiodiglycerol, sulfolane, dimethyl sulfoxide and the like.
Examples of the water-soluble organic solvent include propylene carbonate and ethylene carbonate in addition to those mentioned above.
When the water-soluble organic solvent is added, the amount added is preferably 30% by mass or less, and more preferably 10% by mass or less, based on the entire dispersion medium.

(Other additives)
The dispersion medium is an alkali metal compound such as potassium hydroxide, sodium hydroxide or lithium hydroxide for the purpose of adjusting conductivity, pH of ink, etc .; ammonium hydroxide, triethanolamine, diethanolamine, ethanolamine, 2 -Nitrogen-containing compounds such as amino-2-methyl-1-propanol; compounds of alkaline earth metals such as calcium hydroxide; acids such as sulfuric acid, hydrochloric acid and nitric acid; strong acid and weak alkali salts such as ammonium sulfate; Addition is possible.

  In addition, benzoic acid, dichlorophen, hexachlorophene, sorbic acid, and the like may be added as necessary for the purpose of mold prevention, antiseptic, rust prevention, and the like. Moreover, you may add antioxidant, a viscosity modifier, a electrically conductive agent, a ultraviolet absorber, a chelating agent, etc.

―Developer production method―
Production of the developer in the present embodiment is performed by the following procedure, but is not limited thereto.
First, a dispersion medium containing water as a main solvent and the above additives is prepared with a magnetic stirrer or the like, and the magnetic polymer particles are dispersed in the dispersion medium. A known method is applied to the dispersion. That is, a dispersing machine such as a ball mill, a sand mill, an attritor, or a roll mill is used. Further, as a mixer, a method of rotating a special stirring blade at high speed to disperse, a method of dispersing by the shearing force of a rotor / stator known as a homogenizer, a method of dispersing by ultrasonic waves, and the like can be mentioned.

  It is confirmed by microscopic observation of the dispersed liquid that the magnetic polymer particles are in a single dispersed state in the liquid, and then it is completely dissolved by adding additives such as preservatives. After confirmation, the obtained dispersion liquid is filtered using, for example, a membrane filter having a pore diameter of 100 μm to remove dust and coarse particles, whereby an image forming recording liquid is obtained.

-Developer characteristics-
(Surface tension of developer)
As described above, the surface tension of the developer is from 27 mN / m to 42 mN / m, preferably from 28 mN / m to 41 mN / m, and more preferably from 30 mN / m to 39 mN / m.

  When the surface tension of the developer is within the above range, the fogging of the image is reduced as described above, and the image is improved. If the surface tension of the developer is smaller than the above range, the developer is likely to adhere to the non-magnetic latent image area on the surface of the magnetic latent image holding member, so that the image quality deteriorates due to fogging on the entire non-image area. There is a case. If the surface tension of the developer is larger than the above range, the magnetic polymer particles contained in the developer are likely to be partially aggregated, and the image quality may be deteriorated due to fogging around the image area.

  Since the surface tension of the developer depends on the composition of the developer, the surface tension of the developer is controlled by adjusting the composition of the developer. Specifically, for example, a method of controlling the surface tension of the developer by adjusting the type and concentration of the surfactant according to the characteristics of the magnetic polymer particles can be mentioned.

Suitable surfactants for controlling the surface tension of the developer within the above range include, for example, alkylbenzene sulfonates, alkylphenyl sulfonates, higher fatty acid salts, polyoxy acids among the above surfactants. Examples thereof include ethylene alkyl ether, polyoxyethylene alkylphenyl ether, etc. Among them, higher fatty acid salts, polyoxyethylene alkyl ether, and polyoxyethylene alkylphenyl ether are more preferable.
Further, examples of the amount of the surfactant that is suitable for controlling the surface tension of the developer within the above range include a range of 0.001% by mass or more and 15% by mass or less with respect to the entire developer. The range of 0.01 mass% to 8 mass% is more desirable, and 0.05 mass% to 3 mass% is more desirable.

(Viscosity of developer)
As described above, the viscosity of the developer is 1.0 mPa · s to 10.0 mPa · s, preferably 1.0 mPa · s to 5 mPa · s, and more preferably 1.0 mPa · s to 4 mPa · s. desirable.
When the viscosity of the developer is within the above range, the magnetophoretic property of the magnetic polymer particles in the developer becomes good. When the viscosity of the developer is smaller than the above range, the dispersion medium is likely to evaporate. For example, when the developer is heated, the amount of the dispersion medium may decrease. On the other hand, when the viscosity of the developer is larger than the above range, the image quality may be deteriorated due to the slow speed at which the magnetic polymer particles move toward the magnetic latent image region.

  Since the viscosity of the developer depends on the composition of the developer, the viscosity of the developer is controlled by adjusting the composition of the developer. Specific examples include a method of controlling the viscosity of the developer by controlling the type of surfactant, controlling the concentration of the surfactant, and adding a viscosity modifier.

(Dispersion state of magnetic polymer particles)
The magnetic polymer particles in the developer are desirably in a single dispersed state. Therefore, the dispersion average particle diameter of the magnetic polymer particles in the developer is ideally closer to the number average particle diameter of the magnetic polymer particles. From this viewpoint, when the ratio (A / B) of the dispersion average particle diameter A (μm) of the magnetic polymer particles to the number average particle diameter B (μm) is used as an index of liquid dispersibility, A / B is It is preferably 1.0 or more and 3.0 or less, and more preferably 1.0 or more and 2.5 or less.

When A / B is in the above range, the dispersibility of the magnetic polymer particles is good and high-quality image formation is performed.
The dispersion average particle size of the magnetic polymer particles is a volume average particle size determined by Coulter Counter Multisizer 3 (Beckman Coulter, Inc.).

(Zeta potential of magnetic polymer particles)
The zeta potential of the magnetic polymer particles in the developer is preferably −200 mV to −20 mV, more preferably −150 mV to −20 mV, and further preferably −100 mV to −20 mV. .
Here, the zeta potential is an index indicating the surface potential of the solid surface during liquid dispersion. To be precise, the liquid flow in the electric double layer formed around the fine particles in the solution begins to flow. Defined as potential. As this approaches zero, the repulsive forces of the fine particles weaken and eventually aggregate.

When the zeta potential is in the above range, the dispersibility and dispersion stability of the magnetic polymer particles are more excellent, and image fogging, blurring, and disturbance are suppressed.
The reason is not clear, but is presumed as follows.

When the zeta potential is in the above range, it is considered that an electrostatic repulsive force is generated between the particles because a good surface potential exists on the particle surface. Therefore, it is presumed that a good dispersion state and dispersion stability can be obtained even though the magnetic polymer particles contain a magnetic substance and thus have a large specific gravity.
Further, if the zeta potential is in the above range, the magnetic polymer particles have a surface potential, so that the adsorption of the magnetic polymer particles to the non-magnetic latent image region on the surface of the magnetic latent image holding member is suppressed, and the image fogging is performed. Etc. are presumed to be suppressed.

  In addition, when the zeta potential is in the above range, even if the magnetic polymer particles adhere to the surface of the magnetic latent image, the zeta potential is easily peeled off, the cleaning property of the magnetic latent image holding member is improved, and contamination in the image forming apparatus is suppressed. Is done.

If the zeta potential is larger than the above range and a negative value, the surface potential on the surface of the magnetic polymer particles is insufficient, and the dispersibility of the magnetic polymer particles may be lowered.
Further, if the zeta potential is a positive value, the surface of the magnetic polymer particles has a positive charge. Then, since most of the materials used for the members constituting the recording apparatus are plastics having a negative charge on the surface, contamination due to adsorption of magnetic polymer particles into the apparatus may progress.

  On the other hand, if the zeta potential is lower than the above range, the surface potential on the surface of the magnetic polymer particles is too large, so that when the magnetic polymer particles touch a positively charged material at the time of handling, In some cases, the dispersibility of the magnetic polymer particles becomes unstable, or the amount of the surfactant added needs to be increased to cause foaming.

  The zeta potential is measured using a commercially available zeta electrometer. As a zeta electrometer, for example, Nikkiso Co., Ltd. zeta potential measuring device zeta pulse, zeta potential measuring device zeta plus, Otsuka Electronics ELS-8000, ELS-6000, ELS-Z1, ELS-Z2, ZEECOM (TM) ZC2000 of the company, Zetasizer Nano of Malvern, ESA-8000, ESA-9800 of Shokotsu Trading Co., Ltd. (manufactured by Matec Applied Science), and the like. Among these, it is preferable to measure with a high-concentration type apparatus that can measure the dispersion as it is without diluting.

  The zeta potential of the magnetic polymer particles in the dispersant was measured using the measurement probe by using ESA-8000 (manufactured by Matec Applied Science) as a measurement device, filling the measurement cell with 400 ml of developer and using it as a measurement sample. The measurement was performed in a state where the sample was immersed in a specified amount.

Specifically, at a temperature of 22.0 ° C., an AC electric field is applied to the measurement sample, the pressure generated by electrophoresis of the particles (magnetic polymer particles) is measured with a piezoelectric element, and the zeta potential is determined according to the following formula: Ask.
Formula: Zeta potential = [ESA × η × G (α) ⁻¹ ] / [ε × c × Δρ × V]
Here, ESA is a value obtained by measurement and indicates a pressure per unit electric field. η is the viscosity of the solvent (dispersion medium), G (α) ⁻¹ is a correction term for the action due to inertial force, ε is the dielectric constant of the solvent (dispersion medium), c is the speed of sound in the solvent (dispersion medium), and Δρ is the solvent The density difference between the (dispersion medium) and the particles (magnetic polymer particles), and V represents the volume fraction of the particles (magnetic polymer particles).

  Since the zeta potential depends on the composition of the developer, the zeta potential is controlled by adjusting the composition of the developer. Specifically, for example, a method of using an anionic surfactant as the surfactant, a method of including a salt structure in the polymer compound of the magnetic polymer particles, and the like can be mentioned.

  Examples of the surfactant suitably used for controlling the zeta potential in the above method include the above-mentioned anionic surfactants. Among them, for example, alkylbenzene sulfonate, alkylphenyl sulfonate, higher Fatty acid salts and the like are desirable, and alkylbenzene sulfonates and higher fatty acid salts are more desirable.

  In order to control the zeta potential to the above method, as a method of including a salt structure in the polymer compound of the magnetic polymer particles, for example, a monomer having a carboxyl group is used as the monomer of the polymer compound. And a method of neutralizing the produced magnetic polymer particles with an alkali solution such as an aqueous sodium hydroxide solution. In addition, the above-mentioned thing is used for the monomer which has a carboxyl group.

<Process cartridge, image forming apparatus>
The image forming apparatus of the present embodiment is a magnetography type image forming apparatus. Here, the magnetography method is a method in which a patterned magnetic latent image such as characters and images is formed and visualized with a magnetic toner (magnetic polymer particles) to obtain a hard copy.

  Specifically, the image forming apparatus of the present embodiment includes a magnetic latent image holder (hereinafter sometimes referred to as “image holder”) and a magnetic latent image that forms a magnetic latent image on the magnetic latent image holder. An image forming unit, a developer storing unit that stores the developer in the above-described embodiment, and the developer on a magnetic latent image holding body on which a magnetic latent image is formed to visualize the magnetic latent image as a toner image Developer supplying means for supplying the toner, transfer means for transferring the toner image to a recording medium, and demagnetizing means for demagnetizing the magnetic latent image on the magnetic latent image holding member.

  By applying the developer of the above-described embodiment to an image forming apparatus employing such a magnetography method, not only a high-quality image can be obtained, but also contamination of the work environment by a non-aqueous solvent is suppressed.

  In the present embodiment, it is desirable that the surface of the image carrier has water repellency. As described above, the developer used in this embodiment uses a dispersion medium containing water. Therefore, since the surface of the image carrier has water repellency, even when the developer contacts the image carrier during development, the dispersion medium hardly transfers to the image carrier, and the dispersion medium remains on the image carrier. The toner image is transferred to the recording medium in the absence. Accordingly, a squeeze roller or the like for removing the residual solvent on the image holding member is unnecessary, and the recording medium on which the toner image is transferred hardly needs to be dried.

  Further, since the developer has the above-described configuration, the dispersion medium does not wet and spread on the surface of the image carrier during development, and the magnetic polymerizable particles are only in the magnetic latent image area simultaneously with the contact with the image carrier. Therefore, a development environment in which image fog is hardly generated is created.

FIG. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to the present exemplary embodiment. The image forming apparatus 100 includes a magnetic drum (magnetic latent image holder) 10, a magnetic head (magnetic latent image forming means) 12, a developing device (developer storage means and developer supply means) 14, and an intermediate transfer body (transfer means). 16, a cleaner 18, a demagnetizer (demagnetizer) 20, and a transfer fixing roller (transferr) 28. The magnetic drum 10 has a cylindrical shape, and a magnetic head 12, a developing device 14, an intermediate transfer member 16, a cleaner 18 and a demagnetizing device 20 are sequentially provided on the outer periphery of the magnetic drum 10.
The operation of the image forming apparatus 100 will be briefly described below.

First, the magnetic head 12 is connected to an information device (not shown), for example, and receives binarized image data sent from the information device. The magnetic head 12 forms a magnetic latent image 22 on the magnetic drum 10 by emitting lines of magnetic force while scanning the side surface of the magnetic drum 10. In FIG. 1, the magnetic latent image 22 is indicated by a hatched portion in the magnetic drum 10.
The developing device 14 includes a developing roller (developer supply means) 14a and a developer storage container (developer storage means) 14b. The developing roller 14a is provided so that a part thereof is immersed in the liquid developer (developer) 24 stored in the developer storage container 14b.

  Since the liquid developer 24 is a developer in the above embodiment and has the above-described configuration, the dispersibility of the magnetic polymer particles in the liquid developer 24 is high, and the magnetic polymer particles in the liquid developer 24 have a high dispersibility. Density positional variation is reduced. Therefore, the liquid developer 24 with reduced toner particle density variation is supplied to the developing roller 14a rotating in the direction of arrow A in the figure. Further, if necessary, for example, the liquid developer 24 is continuously stirred at a predetermined rotational speed by a stirring member provided in the developer storage container 14b, whereby the magnetic polymer particles are dispersed in the liquid developer 24. The nature may be further improved.

  The liquid developer 24 supplied to the developing roller 14a is transported to the magnetic drum 10 in a state where the liquid developer 24 is limited to a constant supply amount by a regulating member described later, and the developing roller 14a and the magnetic drum 10 come close (or contact). The magnetic latent image 22 is supplied at the position. As a result, the magnetic latent image 22 is visualized and becomes a toner image 26.

  The developed toner image 26 is transported to a magnetic drum 10 that rotates in the direction of arrow B in the figure and transferred to a paper (recording medium) 30. In this embodiment, before transferring to the paper 30, the magnetic drum 26 is transferred to the magnetic drum 10. The toner image is temporarily transferred to the intermediate transfer member 16 in order to improve the transfer efficiency to the recording medium including the separation efficiency of the toner image from the toner 10, and to perform fixing simultaneously with the transfer to the recording medium. In this embodiment, the intermediate transfer member 16 is used. However, the toner image may be directly transferred from the magnetic drum 10 to the paper 30 without using the intermediate transfer member 16.

  Transfer to the intermediate transfer member 16 is preferably performed by shearing transfer (non-electric field transfer) because the magnetic polymer particles have almost no charge. Specifically, the magnetic drum 10 rotating in the direction of arrow B and the intermediate transfer member 16 rotating in the direction of arrow C are brought into contact with each other with a certain contact portion (contact surface having a contact width in the moving direction), and the toner image. The toner image 26 is transferred onto the intermediate transfer member by an attractive force that is greater than the magnetic force with the magnetic drum 10 relative to the magnetic drum 10. At this time, a peripheral speed difference may be provided between the magnetic drum 10 and the intermediate transfer member 16.

Next, the toner image 26 conveyed in the direction of arrow C by the intermediate transfer body 16 is transferred to the sheet 30 at the contact position between the intermediate transfer body 16 and the transfer fixing roller 28 and is simultaneously fixed. Specifically, the sheet 30 is sandwiched between the transfer fixing roller 28 and the intermediate transfer body 16, and the toner image 26 on the intermediate transfer body 16 is brought into close contact with the sheet 30 to be fixed at the same time as being transferred.
The fixing of the toner image may be performed only by pressing depending on the characteristics of the toner, or may be performed by pressing and heating by providing a heat generating body on the transfer fixing roller 28.

On the other hand, in the magnetic drum 10 in which the toner image 26 is transferred to the intermediate transfer member 16, the transfer residual toner is conveyed to a contact position with the cleaner 18 and collected by the cleaner 18. After cleaning, the magnetic drum 10 rotates and moves to the demagnetization position while holding the magnetic latent image 22.
The degaussing device 20 erases the magnetic latent image 22 formed on the magnetic drum 10. The cleaner 18 and the degaussing device 20 return the magnetic drum 10 to a state in which there is no variation in the magnetization state of the magnetic layer before image formation. By repeating the above operation, images successively sent from the information device are continuously formed in a short time. The magnetic head 12, the developing device 14, the intermediate transfer member 16, the transfer fixing roller 28, the cleaner 18, and the demagnetizing device 20 provided in the image forming apparatus 100 are all operated in synchronization with the rotation speed of the magnetic drum 10. ing.

Next, each configuration of the image forming apparatus of the present embodiment will be described sequentially.
(Magnetic latent image holder)
The configuration of the magnetic drum (magnetic latent image holder) 10 is such that a base layer such as Ni or Ni-P is formed on a drum made of a metal such as aluminum with a thickness of about 1 to 30 μm, and is formed thereon. A magnetic recording layer such as Co-Ni, Co-P, Co-Ni-P, Co-Zn-P, Co-Ni-Zn-P is formed to a thickness of about 0.1 to 10 μm, and Ni, A protective layer of Ni—P or the like is formed with a thickness of about 0.1 μm to 5 μm. If there is a defect such as a pinhole in the plating of the underlayer, a defect is also formed in the magnetic recording layer. Therefore, it is preferable to carry out fine and uniform plating. In addition to plating, there are also methods such as sputtering and vapor deposition. Furthermore, the underlayer and the protective layer are preferably nonmagnetic. Maintaining the surface accuracy of the surface of each layer by tape polishing or the like is suitable for maintaining the gap with the magnetic head 12 forming the magnetic latent image with high accuracy.

The film thickness of the magnetic recording layer is preferably in the range of 0.1 μm to 10 μm, and the magnetic characteristics of the magnetic recording layer are such that the coercive force is 16000 A / m or more and 80000 A / m or less (200 Oersted or more and 1000 Oersted (Oe) or less. The residual magnetic flux density is preferably about 100 mT to 200 mT (1000 gauss to 2000 gauss (G)).
The above is the configuration of the magnetic drum 10 in the case of the horizontal magnetic recording type, but in the case of the vertical magnetic recording type, a configuration in which a recording layer such as Co—Ni—P is provided on the nonmagnetic layer, A configuration in which a soft magnetic layer having a high magnetic permeability is provided below the recording layer may be employed, and the present invention is not limited to any one. Further, the magnetic latent image holding member is not limited to the drum shape in the present embodiment, but may be a belt shape.

In the present embodiment, it is desirable to use the magnetic drum 10 having water repellency. Here, water repellency means the property of repelling water, and specifically means that the contact angle with pure water is 70 degrees or more.
In the present embodiment, the contact angle of the magnetic drum 10 with respect to pure water is desirably 70 degrees or more, and more desirably 100 degrees or more. If the contact angle is less than 70 degrees, liquid may remain on the magnetic drum or image fog may occur even after development with a liquid developer using an aqueous medium described later.

  The contact angle of the surface of the magnetic drum 10 was measured using a contact angle meter (manufactured by Kyowa Interface Science Co., Ltd .: CA-X) and pure water was applied to the surface of the magnetic drum in an environment of 25 ° C. and 50% RH. 3.1 μl was dropped and the contact angle after 15 seconds was determined. The measurement was performed at four points in the circumferential direction at the end and center, and the average value of these was taken as the contact angle.

In order to make the surface of the magnetic drum 10 have a suitable contact angle, it is desirable to coat the surface of the magnetic drum configured as described above.
Examples of the surface coat include fluorine lubrication plating and coating using a polymer containing fluorine atoms or silicon atoms. Fluorine lubrication plating is a functional plating in which fluorine resin (polytetrafluoroethylene: PTFE) is combined and co-deposited with electroless nickel plating, and PTFE particles are uniformly deposited in the formed film. Combines the characteristics of electroless nickel plating and PTFE resin.
Examples of the coating using a polymer containing a fluorine atom or a silicon atom include, for example, a polymer having a fluorine-containing cyclic structure, a copolymer of fluoroolefin and vinyl ether, a photopolymerizable fluororesin composition, and the like. It may be applied to the surface of the layer, or may be coated on the entire surface by sputtering a fluorine atom-containing polymer on the surface of the protective layer.

Of these, fluorine lubrication plating is preferable from the viewpoint of adhesion to the lower plating layer, durability, and the like. The fluorine lubrication plating or fluororesin coating may be performed after forming the protective layer, or a layer formed by fluorine lubrication plating or the like may be used as it is.
The film thickness of the surface layer formed by the surface coating is preferably 0.1 μm or more and 5 μm or less, and more preferably 0.3 μm or more and 3 μm or less.

(Magnetic latent image forming means)
The magnetic latent image forming apparatus (magnetic latent image forming means) basically comprises a magnetic head 12 and its drive circuit. The magnetic head 12 mainly includes a full-line type magnetic head and a multi-channel type magnetic head. In the case of a full-line type magnetic head, it is not necessary to scan the magnetic head 12, but in the case of a multi-channel type magnetic head, It is necessary to scan the magnetic head 12 with respect to the magnetic drum 10. Scanning methods include serial scanning and helical scanning. In the case of helical scanning, the recording speed can be increased by changing the rotational speed of the magnetic drum 12 specially only in the latent image forming step.

  On the other hand, in the case of a full-line magnetic head, for example, if the resolution is 600 dpi, a head of about 500 channels is required to cover the recording width in the width direction of A4 size paper. If they are arranged side by side to form a full line, it is not necessary to scan the head, and extremely high-speed recording becomes possible. In order to achieve the above full line, it is necessary to superimpose the head core and the head core. However, as the resolution is increased, the track pitch becomes narrower. A sheet coil is used.

  Leakage magnetic flux is generated from the tip of the magnetic pole when current is passed through the coil of each channel of the magnetic head 12, thereby magnetizing the magnetic recording medium to form a magnetic latent image. The output from the magnetic head 12 needs to be two to three times the coercivity of the magnetic recording layer in the magnetic drum 10. The magnetic latent image formed here does not disappear unless erased by the demagnetizer 20, and has a multi-copy function by repeating the steps of development, transfer, fixing, and cleaning. In addition, since the magnetic latent image is less susceptible to humidity, it has better environmental stability than the electrostatic type.

(Developer storage means, developer supply means)
FIG. 2 shows a schematic diagram in which the development area in FIG. 1 is enlarged.
The developing device (developer supply means) 14 magnetically develops the developer storage container 14b and the liquid developer 24 stored in the developer storage container 14b in a toner supply area (hereinafter sometimes referred to as “supply area”). And a developing roller 14a to be supplied to the drum 10. As shown in FIG. 2, the developing roller 14a holds a layered liquid developer 24 on its peripheral surface, and is disposed at a position separated from the magnetic drum 10 (for example, a process cartridge is formed by the magnetic drum and the developing device). Is configured). Further, a regulating member 13 that maintains the layer thickness of the liquid developer 24 at a predetermined thickness is disposed upstream of the supply region. The regulating member 13 is a plate-like member extending over the entire width in the axial direction of the developing roller 14a, and one edge portion thereof is arranged so as to be separated from the peripheral surface of the developing roller 14a by a predetermined distance corresponding to a desired toner layer thickness. Yes.

In the developing device 14, a liquid developer 24 containing toner particles (magnetic polymer particles) 26a and an aqueous medium (dispersion medium) is stored in a developer storage container 14b. As described above, the liquid developer 24 is the developer in the above-described embodiment, and the toner particles 26a are highly dispersible in the liquid developer 24. Therefore, the liquid development in which the variation in the toner particle concentration is reduced on the developing roller 14a. Agent 24 is supplied. In addition, as described above, if necessary, for example, a stirring member is provided in the developer storage container 14b, and stirring is continued at a predetermined rotation speed, so that variation in the position of the concentration of the toner particles 26a in the liquid developer 24 can be achieved. It may be further reduced.
Although not shown in FIG. 2, in order to supply the liquid developer to the developing roller 14a, a supply roller that rotates in contact with or close to the developing roller 14a may be provided.

The developing roller 14a includes, for example, a plurality of magnetic poles including an S-pole magnetic pole and an N-pole magnetic pole in the circumferential direction, and these magnetic poles are fixed so as not to rotate together with the developing roller 14a. One of these magnetic poles is in particular arranged between the regulating member 13 and the supply area. Therefore, the liquid developer 24 containing the magnetic toner held on the developing roller 14a is held by the magnetic lines of force (developing magnetic field) of these magnetic poles and conveyed toward the magnetic drum 10.
The developing roller 14a need not be a magnetic roller if the roller surface itself has a liquid developer conveying force, and an anilox roller, a sponge roller, or the like may be used.

  The restricting member 13 is provided at a position from when the developing roller 14 a holds the liquid developer 14 in the developer storage container 14 b until it is supplied to the magnetic drum 10 as described above. The amount of the liquid developer 24 supplied to the magnetic latent image 22 is determined by the gap formed by the regulating member 13 and the developing roller 14a. The material is preferably rubber or phosphor bronze. The liquid developer 24 limited to a constant supply amount by the regulating member 13 is conveyed to the magnetic drum 10 and supplied to the magnetic latent image 22. As a result, the magnetic latent image 22 is visualized and becomes a toner image 26.

  In the development, since the toner particles are magnetic toner, the development can be performed without applying a magnetic field to the developing roller 14a. However, the magnetic field is applied to the developing roller 14a for more efficient development. May be applied.

(Transfer means, fixing means)
The toner image visualized by the developing device 14 is transferred onto the paper 30 by a transfer unit. As described above, in this embodiment, a toner image is not directly transferred from the magnetic drum 10 onto the paper, but is transferred to the intermediate transfer body 16 and then transferred and fixed onto the paper 30. First, transfer to the intermediate transfer member 16 will be described.

  The intermediate transfer member 16 contacts the magnetic drum 10 and transfers the toner image. As the transfer method, there are generally an electrostatic transfer method, a pressure transfer method, and an electrostatic pressure method using both of them. However, as described above, in this embodiment, the toner particles do not have an electric charge. The transfer method and electrostatic pressure method cannot be used. On the other hand, the pressure transfer method is a method in which the toner image is attached to the surface of the transfer medium while being plastically deformed by the pressure between the magnetic drum 10 and the transfer medium, and may be used in combination with shearing transfer.

  In the present embodiment, as described above, the toner image 26 is transferred onto the intermediate transfer member by the attraction force greater than the magnetic force with the magnetic drum 10 with respect to the toner image 26 on the magnetic drum 10. It is preferable to perform adhesive transfer by imparting adhesiveness to the adhesive. For this reason, it is desirable to form, for example, a low hardness silicone rubber layer on the surface of the intermediate transfer member 16.

Next, the toner image 26 transferred to the intermediate transfer body 16 is transferred to a sheet.
A transfer fixing roller 28 is disposed on the opposite side of the magnetic drum 10 across the intermediate transfer member 16 in FIG. 1 so as to form a contact portion with respect to the intermediate transfer member 16, and the toner on the intermediate transfer member 16. The sheet 30 is fed to the contact portion between the intermediate transfer member 16 and the transfer fixing roller 28 in time with the image 26. The transfer fixing roller 28 is constituted by, for example, a stainless steel base, a silicone rubber layer, and a fluororubber layer. By pressing the paper 30 passing through the contact portion against the intermediate transfer body 16, a toner image on the intermediate transfer body 16 is obtained. Is transferred to the paper 30.

  In the present embodiment, the toner image 26 is transferred from the intermediate transfer body 16 to the paper 30 and the toner image 26 is fixed to the paper 30 at the same time. Specifically, if the intermediate transfer body 16 has a roller shape as shown in FIG. 1, the intermediate transfer body 16 and the transfer fixing roller 28 are each a fixing roller in the fixing device because they constitute a roller pair with the transfer fixing roller 28. The fixing function is exhibited with a configuration according to the pressing roller. That is, when the paper 30 passes through the contact portion, the toner image 26 is transferred and simultaneously pressed against the intermediate transfer body 16 by the transfer fixing roller 28, whereby the toner particles constituting the toner image 26 are softened. At the same time, the fixed image 29 is formed by infiltrating into the fibers of the paper 30.

  As described above, for example, a heat generating member is provided on the transfer fixing roller 28, and the toner image is heated by the heat generating member, whereby the toner image melts and enters into the fibers of the paper 30 to be fixed to form a fixed image 29. May be. In this state, the fixed image 29 does not peel off even if the paper 30 is bent or peeled off after the adhesive tape is applied.

  In this embodiment, the fixing is performed simultaneously with the transfer to the paper 30. However, the transfer process and the fixing process may be separately performed, and the fixing may be performed after the transfer. In this case, the transfer roller for transferring the toner image from the magnetic drum 10 has a function according to the intermediate transfer body 16.

(Cleaner)
On the other hand, when the transfer efficiency of the toner image from the magnetic drum 10 to the intermediate transfer member 16 does not reach 100%, a part of the toner image 26 remains on the magnetic drum 10 after transfer. The cleaner 18 removes this, and basically comprises a cleaning blade such as rubber and a container of residual magnetic toner.
If the transfer efficiency is close to 100% and residual toner does not cause a problem, the cleaner 18 need not be provided.

(Demagnetizing means)
When a new image is formed again, it is necessary to erase the magnetic latent image before forming the magnetic latent image with the magnetic head 12. There are two types of demagnetizers, a permanent magnet type and an electromagnet type. In the case of the permanent magnet type, it is magnetized in the circumferential direction of the magnetic drum 10 so that the magnetic flux does not leak locally, and energy such as electric power is unnecessary and inexpensive. However, when the magnetic latent image is not erased, it is necessary to move the degaussing device 20 relative to the magnetic drum 10 to increase the magnetic distance and weaken the erasing magnetic field. On the other hand, the electromagnet type is composed of a yoke and a coil, and it is necessary to pass a current. However, when it is not necessary to erase the magnetic latent image, the erasing magnetic field becomes zero by turning off the current, so that the control is relatively Be free.
In the present embodiment, both the permanent magnet type and the electromagnet type are used.

  In the image forming apparatus 100 in the present embodiment exemplified above, the developer having the above-described configuration is used as the liquid developer 24. Therefore, fogging, blurring, and disturbance of the image are suppressed, and contamination in the image forming apparatus is suppressed. Is done. In particular, when the magnetic drum 10 has water repellency, image fogging, bleeding, and disturbance, and contamination in the image forming apparatus are further suppressed.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but these are illustrative examples, and the present invention is not limited in any way by the following examples. In the examples, “parts” and “%” represent “parts by mass” and “mass%”, respectively, unless otherwise specified.

[Example A]
<Preparation of surface-treated magnetic powder A-1>
To 600 parts of magnetic powder MTS-010 (manufactured by Toda Kogyo Co., Ltd.), 400 parts of styrene acrylic resin (S-LEC P-SE-0020, manufactured by Sekisui Chemical Co., Ltd.) is added and kneaded with a pressure kneader. A surface-treated magnetic powder A-1 (magnetic powder content: 60%) subjected to resin coating treatment was obtained.

<Manufacture of magnetic polymer particles>
(Production of magnetic polymer particles A-1)
After mixing 17 parts of hydroxyethyl methacrylate (manufactured by Wako Pure Chemical Industries, Ltd.), 57 parts of styrene monomer (manufactured by Wako Pure Chemical Industries, Ltd.) and 1 part of divinylbenzene (manufactured by Wako Pure Chemical Industries, Ltd.), To this, 40 parts of the surface-treated magnetic powder A-1 was added and dispersed with a ball mill for 48 hours. To 90 parts of the magnetic powder dispersion, 5 parts of azobisisobutyronitrile (manufactured by Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was added to prepare a mixture containing the monomer and the magnetic powder.

In an aqueous solution obtained by dissolving 28 parts of sodium chloride (manufactured by Wako Pure Chemical Industries, Ltd.) in 160 parts of ion-exchanged water, 30 parts of calcium carbonate (manufactured by Maruo Calcium Co., Ltd., Luminous) as a dispersion stabilizer, carboxymethyl cellulose (first 3.5 parts of Kogyo Seiyaku Co., Ltd., Serogen) was added and dispersed for 24 hours with a ball mill to obtain a dispersion medium.
The mixture was charged into 200 parts of this dispersion medium, and emulsified at 8000 rpm for 3 minutes with an emulsifying device (manufactured by SMT Co., Ltd., HIGH-FLEX HOMOGENIZER) to obtain a suspension. The number average particle diameter of the suspended particles at this time was about 2.5 μm.

On the other hand, nitrogen was introduced into the separable flask equipped with a stirrer, a thermometer, a cooling pipe, and a nitrogen introduction pipe from the nitrogen introduction pipe, and the inside of the flask was made a nitrogen atmosphere. The above suspension was placed therein, reacted at 65 ° C. for 3 hours, further heated at 70 ° C. for 10 hours and cooled. The reaction solution was a dispersion, and no agglomerates could be confirmed during polymerization.
A 10% aqueous hydrochloric acid solution was added to the reaction solution to decompose calcium carbonate, and solid-liquid separation was performed by centrifugation. The obtained particles were washed with 1 L of ion exchange water, and then washed by repeating ultrasonic dispersion and centrifugation in 500 ml of ethanol for 30 minutes three times to obtain magnetic polymer particles.

  The magnetic polymer particles are dried in an oven at 60 ° C., coarse particles are separated through a mesh having a pore size of 5 μm, and further separated using a nylon mesh having a pore size of 1 μm, and the magnetic polymer having a number average particle size of 2.7 μm. Particle A-1 was obtained.

(Characteristic evaluation of magnetic polymer particle A-1)
In thermogravimetric analysis (TGA), the content of magnetic powder in the magnetic polymer particles A-1 was calculated from the amount of weight loss due to heating, and found to be 15%.

Moreover, the amount of hydroxyl groups of magnetic polymer particle A-1 was 0.6 mmol / g. The measurement of the amount of hydroxyl groups was performed as follows.
First, magnetic polymer particles are weighed and placed in a capped test tube, and a pyridine solution (manufactured by Wako Pure Chemical Industries, Ltd.) in acetic anhydride (manufactured by Wako Pure Chemical Industries, Ltd.) prepared in advance is added. Heated under conditions for 24 hours. Further, distilled water was added to hydrolyze acetic anhydride in the test tube, and then centrifuged at 3000 rpm for 5 minutes to separate into particles and supernatant. The separated particles were further washed with ethanol (manufactured by Wako Pure Chemical Industries, Ltd.) by repeated ultrasonic dispersion and centrifugation, and the supernatant and the washing solution were collected in a conical beaker, and phenolphthalein (Wako Pure Chemical Industries, Ltd.) was used as an indicator. The product was titrated with a 0.1M ethanolic potassium hydroxide solution (manufactured by Wako Pure Chemical Industries, Ltd.).

A blank experiment without using magnetic polymer particles was also performed, and the hydroxyl amount (mmol / g) was calculated from the difference according to the following formula (1). Here, the blank experiment means an experiment in which the same operation as the measurement of the hydroxyl group amount is performed except that the magnetic polymer particles are not used.
Hydroxyl group amount = ((BC) × 0.1 × f) / (w− (w × D / 100)): Formula (1)
In the above formula (1), B is the dripping amount (ml) in the blank experiment, C is the dripping amount (ml) of the sample, f is the factor of the potassium hydroxide solution, w is the mass (g) of the magnetic polymer particles, D is the magnetic powder content (%) in the magnetic polymer particles.

(Production of magnetic polymer particles A-2)
6 parts of hydroxyethyl methacrylate (manufactured by Wako Pure Chemical Industries, Ltd.), 1 part of polyethylene glycol methacrylate (manufactured by NOF Corporation, Bremer PE200), 0.5 part of methacrylooxyethyl monophthalate (manufactured by Sigma Aldrich Co., Ltd.) Styrene monomer (manufactured by Wako Pure Chemical Industries, Ltd.) 15 parts, n-butyl methacrylate 20 parts, styrene acrylic resin (manufactured by Sekisui Chemical Co., Ltd., trade name: ESREC P-SE-0020), cyclohexanone 30 parts, After mixing 1 part of divinylbenzene (manufactured by Wako Pure Chemical Industries, Ltd.), 33 parts (magnetic powder content: 60%) of the surface-treated magnetic powder A-1 was added and dispersed for 24 hours with a ball mill. To 90 parts of the magnetic powder dispersion, 1 part of azobisisobutyronitrile (manufactured by Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was added to prepare a mixture containing the monomer and the magnetic powder.

In an aqueous solution obtained by dissolving 28 parts of sodium chloride in 132 parts of ion-exchanged water, 48 parts of calcium carbonate (manufactured by Maruo Calcium Co., Ltd., trade name: Luminous) and carboxymethylcellulose (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) (Product name: Serogen) (2.0 parts) was added and dispersed with a ball mill for 24 hours to obtain a dispersion medium.
The mixture was put into 200 parts of this dispersion medium, and emulsified at 8000 rpm for 3 minutes with an emulsifying apparatus (manufactured by IKA, Ultra Tarrax) to obtain a suspension. The number average particle diameter of the suspended particles at this time was 2.0 μm.

On the other hand, nitrogen was introduced into the separable flask equipped with a stirrer, a thermometer, a cooling pipe, and a nitrogen introduction pipe from the nitrogen introduction pipe, and the inside of the flask was made a nitrogen atmosphere. The above suspension was placed therein, reacted at 65 ° C. for 3 hours, further heated at 70 ° C. for 10 hours and cooled. The reaction solution was a dispersion, and no agglomerates could be confirmed during polymerization.
A 10% aqueous hydrochloric acid solution was added to the reaction solution to decompose calcium carbonate, and solid-liquid separation was performed by centrifugation. The obtained particles were washed with 1000 parts of ion exchange water, then repeatedly washed with 1000 parts of ethanol, and then replaced with 1000 parts of ion exchange water again. The pH was adjusted to 12 with 0.5N sodium hydroxide, and the mixture was stirred at room temperature for 1 hour. After the treatment, it was washed with 1000 parts of ion exchange water, and further washed with 500 parts of ethanol and ion exchange water to obtain magnetic polymer particles.

The magnetic polymer particles were oven-dried at 60 ° C., and the yield of the magnetic polymer particles was measured and found to be 59 parts and the yield was 82%.
The polymer particles were separated from coarse particles through a mesh having a pore diameter of 5 μm, and further separated using a nylon mesh having a pore diameter of 1 μm to obtain magnetic polymer particles A-2 having an average particle diameter of 2.1 μm.

(Characteristic evaluation of magnetic polymer particle A-2)
When the magnetic powder content was calculated in the same manner as the magnetic polymer particle A-1, the magnetic powder content of the magnetic polymer particle A-2 was 15% by mass.
It was 0.33 mmol / g when the amount of hydroxyl groups of magnetic polymer particle A-2 was measured by the same method as magnetic polymer particle A-1.

The amount of carboxyl groups in the magnetic polymer particle A-2 was 0.01 mmol / g. The measurement of the carboxyl group amount was performed as follows.
First, the magnetic polymer particles were weighed and placed in a capped test tube, and dispersed and stirred in N, N-dimethylformamide (manufactured by Wako Pure Chemical Industries, Ltd.) for 1 hour. All of this dispersion was collected in a conical beaker and titrated with a 0.1 M ethanolic potassium hydroxide solution (Wako Pure Chemical Industries, Ltd.) using phenolphthalein (Wako Pure Chemical Industries, Ltd.) as an indicator.

A blank experiment without using magnetic polymer particles was also performed, and the carboxyl group amount (mmol / g) was calculated from the difference according to the following formula (2). Here, the blank experiment means an experiment in which the same operation as the measurement of the carboxyl group amount is performed except that the magnetic polymer particles are not used.
Amount of carboxyl group = ((C−B) × 0.1 × f) / (w− (w × D / 100)): Formula (2)
In the above formula (2), B is a dripping amount (ml) in a blank experiment, C is a dripping amount (ml) of a sample, f is a factor of a potassium hydroxide solution, w is a mass (g) of magnetic polymer particles, D is the magnetic powder content (%) in the magnetic polymer particles.

(Production of magnetic polymer particles A-3)
After mixing 75 parts of styrene monomer (Wako Pure Chemical Industries, Ltd.) and 1 part of divinylbenzene (Wako Pure Chemical Industries, Ltd.), 40 parts of the surface-treated magnetic powder A-1 was added and dispersed for 48 hours with a ball mill. did. To 90 parts of this magnetic powder dispersion, 5 parts of azobisisobutyronitrile (Wako Pure Chemical Industries, Ltd.) was added as a polymerization initiator to prepare a mixture containing the monomer and magnetic powder.

In an aqueous solution in which 28 parts of sodium chloride (Wako Pure Chemical Industries, Ltd.) is dissolved in 160 parts of ion-exchanged water, 30 parts of calcium carbonate (manufactured by Maruo Calcium Co., Ltd., trade name: Luminous) as a dispersion stabilizer, carboxymethylcellulose (1st 3.5 parts of Kogyo Seiyaku Co., Ltd., trade name: Serogen) was added and dispersed with a ball mill for 24 hours to obtain a dispersion medium.
The mixture was charged into 200 parts of this dispersion medium, and emulsified at 8000 rpm for 3 minutes with an emulsifying device (manufactured by SMT Co., Ltd., HIGH-FLEX HOMOGENIZER) to obtain a suspension. The number average particle diameter of the suspended particles at this time was about 2.5 μm.

On the other hand, nitrogen was introduced into the separable flask equipped with a stirrer, a thermometer, a cooling pipe, and a nitrogen introduction pipe from the nitrogen introduction pipe, and the inside of the flask was made a nitrogen atmosphere. The above suspension was placed therein, reacted at 65 ° C. for 3 hours, further heated at 70 ° C. for 10 hours and cooled. The reaction solution was a dispersion, and no agglomerates could be confirmed during polymerization.
A 10% aqueous hydrochloric acid solution was added to the reaction solution to decompose calcium carbonate, and solid-liquid separation was performed by centrifugation. The obtained particles were washed with 1 L of ion exchange water, and then washed by repeating ultrasonic dispersion and centrifugation in 500 ml of ethanol for 30 minutes three times to obtain magnetic polymer particles.

  The magnetic polymer particles are dried in an oven at 60 ° C., coarse particles are separated through a mesh having a pore size of 5 μm, and further separated by using a nylon mesh having a pore size of 1 μm, and the magnetic polymer particles having an average particle size of 2.7 μm. A-3 was obtained.

(Characteristic evaluation of magnetic polymer particle A-3)
When the magnetic powder content was calculated in the same manner as the magnetic polymer particle A-1, the magnetic powder content of the magnetic polymer particle A-3 was 18% by mass.

<Example A-1>
(Preparation of developer A-1)
-Magnetic polymer particles A-1 5 parts-Polyoxyethylene (5) lauryl ether (Emalex 705: manufactured by Nippon Emulsion Co., Ltd.) 1 part-Ion-exchanged water 94 parts Developer A-1 was obtained.
The viscosity at 23 ° C. was measured with a cone rotor type viscometer TVE-22L (manufactured by Toki Sangyo Co., Ltd.). The results are shown in Table 1.
Further, the surface tension was measured at room temperature (23 ° C.) with a pendant drop type contact angle surface tension meter (manufactured by Kyowa Interface Science Co., Ltd.). The results are shown in Table 1.

<Example A-2>
(Preparation of developer A-2)
Magnetic polymer particles A-2 5 parts Polyoxyethylene (10) lauryl ether (Emarex 710: manufactured by Nippon Emulsion Co., Ltd.) 1 part Ion-exchanged water 94 parts The above composition, others are Example A- Developer A-2 was obtained in the same manner as in Example 1. Viscosity and surface tension were measured in the same manner as in Example A-1. The results are shown in Table 1. The numbers shown in the above “polyoxyethylene (10) lauryl ether” indicate the number of polyoxyethylene groups, and so on.

<Example A-3>
(Preparation of developer A-3)
・ 5 parts of magnetic polymer particles A-3 ・ Sodium dodecyl sulfate (manufactured by Wako Pure Chemical Industries, Ltd.) 1 part ・ 94 parts of ion-exchanged water With the above composition, the other components were developed in the same manner as in Example A-1. A-3 was obtained. Viscosity and surface tension were measured in the same manner as in Example A-1. The results are shown in Table 1.

<Example A-4>
(Preparation of developer A-4)
Magnetic polymer particles A-1 5 parts Triton X100 (surfactant) (Wako Pure Chemical Industries, Ltd.) 1 part Glycerin (Wako Pure Chemical Industries, Ltd.) 34 parts Ion-exchanged water 60 parts Other than the above, developer A-4 was obtained in the same manner as in Example A-1. Viscosity and surface tension were measured in the same manner as in Example A-1. The results are shown in Table 1.

<Comparative Example A-1>
(Preparation of developer A-5)
・ Magnetic polymer particles A-1 5 parts ・ Triton X100 (manufactured by Wako Pure Chemical Industries, Ltd.) 1 part ・ Glycerin (manufactured by Wako Pure Chemical Industries, Ltd.) 50 parts ・ Ion-exchanged water 44 parts Developer A-5 was obtained in the same manner as in Example A-1. Viscosity and surface tension were measured in the same manner as in Example A-1. The results are shown in Table 1.

<Comparative Example A-2>
(Preparation of developer A-6)
Magnetic polymer particles A-2 5 parts Polyoxyethylene (20) stearyl ether (Elemax 620: manufactured by Nippon Emulsion Co., Ltd.) 1 part Ion-exchanged water 94 parts The above composition, the others are Example A- Developer A-6 was obtained in the same manner as in Example 1. Viscosity and surface tension were measured in the same manner as in Example A-1. The results are shown in Table 1.

<Comparative Example A-3>
(Preparation of developer A-7)
Magnetic polymer particles A-3 5 parts Aerosol OT (manufactured by Wako Pure Chemical Industries, Ltd.) 1 part Ion-exchanged water 94 parts Developer A in the same manner as in Example A-1 except for the above composition -7 was obtained. Viscosity and surface tension were measured in the same manner as in Example A-1. The results are shown in Table 1.

<Evaluation of developer>
-Evaluation of number average particle diameter (primary particle diameter) of magnetic polymer particles and coefficient of variation thereof-
After freezing the developer at −20 ° C., it was dried in a room temperature vacuum environment to obtain dried magnetic polymer particles. The obtained magnetic polymer particles were photographed with a scanning electron microscope (VE-7800 manufactured by Keyence), the primary particle diameters of 400 randomly selected particles were measured, and the value obtained by dividing the total by the number Was determined as the number average particle size. The results are shown in Table 2. The standard deviation (μm) was determined from the distribution of 400 primary particle sizes (μm), and the coefficient of variation (%) was determined by dividing the number by the number average particle size and multiplying by 100. The results are shown in Table 2.

-Evaluation of dispersibility of magnetic polymer particles in developer-
0.1 ml of developer is taken and dispersed in 100 ml of measurement liquid Isoton (manufactured by Beckman Coulter, Inc.) by shaking and stirred, and volume average using Coulter Counter Multisizer 3 (manufactured by Beckman Coulter, Inc.) The particle diameter (dispersion average particle diameter) was measured. This measurement was performed at the initial stage of developer preparation and after being left for 30 days.
In this measurement, since the presence state of the particles in the solution is maintained, a result equivalent to the particle size distribution in the developer can be obtained even by dilution with the measurement solution. The results are shown in Table 2.

-Magnetophoretic evaluation-
Take 0.5 ml of developer in a 3.5 ml screw-cap test tube (manufactured by AS ONE) and remove the developer with a vortex mixer (manufactured by AS ONE) for 1 minute with an ultrasonic disperser (AS ONE). And then placed on a neodymium magnet (manufactured by As One Co., Ltd.) having a surface magnetic flux density of 0.18 T, and the time until the particles completely moved and the supernatant became transparent was measured. The degree of transparency of the supernatant was judged visually. The results are shown in Table 3.

-Image evaluation-
An image forming apparatus 100 having the configuration shown in FIG. 1 is prepared, a magnetic drum of a commercially available magnetic printer (manufactured by Iwasaki Tsushinki Co., Ltd.) is used as the magnetic drum 10, and the developer A-1 to the developer are used as developers. A-7 was used. The printing conditions were set as follows, and the developability of solid patches and fine lines was evaluated. Specifically, solid images (solid images) and thin line images were developed, and the presence or absence of fogging in the non-image area and the image quality in the image area were visually evaluated in the image after being transferred to the recording paper. The results are shown in Table 3.

Magnetic drum linear velocity: 100 mm / second.
Developing roller peripheral speed / magnetic drum peripheral speed ratio: 1.2.
Transfer conditions (intermediate transfer): The pressing force of the intermediate transfer member to the magnetic drum is set to 0.147 MPa (1.5 kgf / cm ² ).
Transfer fixing condition: The pressing force of the transfer fixing roller against the intermediate transfer member is set to 0.245 MPa (2.5 kgf / cm ² ).

As shown in Table 3, the developers in Example A-1 to Example A-4 had a faster moving speed of the magnetic polymer particles than the developer in Comparative Example A-1.
Further, the developers of Example A-1 to Example A-4 are better than the developers of Comparative Example A-1 to Comparative Example A-3, with no fogging and fine lines on the magnetic latent image on the magnetic drum. To be developed.

[Example B]
(Magnetic polymer particle B-1, magnetic polymer particle B-2)
In Example B, the magnetic polymer particles A-1 and magnetic polymer particles A-2 produced in Example A were used as they were in Example B as magnetic polymer particles B-1 and magnetic polymer particles B-2, respectively.

(Magnetic polymer particle B-3)
The magnetic polymer particle A-2 produced in Example A was neutralized with 1 mol / l sodium hydroxide to obtain magnetic polymer particle B-3 in which the carboxyl group was sodium chlorided. The amount of carboxyl groups in the particles was 0.0 mmol / g, and it was confirmed that all carboxyl groups were neutralized.

<Example B-1>
(Preparation of developer B-1)
-Magnetic polymer particles B-1 5 parts-Sodium dodecyl sulfate (manufactured by Wako Pure Chemical Industries, Ltd.) 1 part-Ion-exchanged water 94 parts With the above composition, dispersed in a ball mill for 3 hours to obtain developer B-1 It was. Viscosity and surface tension were measured as in Example A-1. The results are shown in Table 4.

<Example B-2>
(Preparation of developer B-2)
A developer B-2 was obtained in the same manner as in Example B-1, except that the magnetic polymer particle B-2 was used instead of the magnetic polymer particle B-1. Viscosity and surface tension were measured as in Example A-1. The results are shown in Table 4.

<Example B-3>
(Preparation of developer B-3)
-Magnetic polymer particles B-3 5 parts-Triton X100 (manufactured by Wako Pure Chemical Industries, Ltd.) 1 part-Ion-exchanged water 94 parts Other than the above, the developer B- in the same manner as in Example B-1 3 was obtained. Viscosity and surface tension were measured as in Example A-1. The results are shown in Table 4.

<Comparative Example B-1>
(Preparation of developer B-4)
-Magnetic polymer particle B-1 5 parts-Ion exchange water 95 parts Other than the above composition, a developer B-4 was obtained in the same manner as in Example B-1. Viscosity and surface tension were measured as in Example A-1. The results are shown in Table 4.

<Example B-4>
(Preparation of developer B-5)
Magnetic polymer particle B-2 5 parts BL-4.2 (polyoxyethylene (4.2) lauryl ether)
(Manufactured by Nikko Chemicals Co., Ltd.) 1 part / ion-exchanged water 94 parts Developer B-5 was obtained in the same manner as in Example B-1 except for the above composition. Viscosity and surface tension were measured as in Example A-1. The results are shown in Table 4.

<Evaluation of developer>
-Evaluation of zeta potential-
The zeta potential was measured using ESA-8000 (Matec Applied Science) as a measuring device. Specifically, the measurement cell was filled with 400 ml of developer, and a zeta potential measurement was performed according to a predetermined measurement method in a state where a predetermined amount of measurement probe was immersed. The results are shown in Table 4.

-Evaluation of number average particle diameter (primary particle diameter) of magnetic polymer particles and coefficient of variation thereof-
In the same manner as the evaluation of the number average particle diameter of the magnetic polymer particles in Example A and the coefficient of variation thereof, the number average particle diameter of the magnetic polymer particles in Example B and the coefficient of variation thereof were evaluated. The results are shown in Table 5.

-Evaluation of particle size distribution of magnetic polymer particles-
The particle size distribution of the magnetic polymer particles in the developer of Example B was evaluated in the same manner as the particle size distribution of the magnetic polymer particles in the developer of Example A. The results are shown in Table 5.

-Image evaluation-
The image evaluation of Example B was performed in the same manner as the image evaluation of Example A. The results are shown in Table 6.

  As shown in Table 6, the developers in Examples B-1 to B-3 have better dispersion stability than the developers in Comparative Example B-1, and Example B-4 and Comparative Example B-1 Compared with the developer in No. 1, the fog was further suppressed and the developability of the fine line was good.

[Example C]
(Magnetic polymer mother particle C-1, magnetic polymer mother particle C-2)
The magnetic polymer particles A-3 and magnetic polymer particles A-1 produced in Example A were used as they were in Example C as magnetic polymer mother particles C-1 and magnetic polymer mother particles C-2, respectively. It was.

<Example C-1>
(Preparation of externally added magnetic polymer particles C-1)
· _SiO 2 in (OX50, manufactured by Nippon Aerosil Co., Ltd., number-average primary particle size 40 nm) 5 parts Magnetic polymer mother particles C-1 95 parts of the above composition, and mixed for 2 minutes at a blender mixer (AS ONE Corporation), Externally added magnetic polymer particles C-1 were prepared.

(Preparation of developer C-1)
-Externally added magnetic polymer particles C-1 5 parts-BL-4.2 (polyoxyethylene (4.2) lauryl ether) 1 part-ion-exchanged water 94 parts With the above composition, dispersed for 3 hours by a ball mill, Developer C-1 was obtained. The viscosity, surface tension, and zeta potential of the developer were measured in the same manner as in Example B-1. The results are shown in Table 7.

<Example C-2>
(Preparation of externally added magnetic polymer particles C-2 and developer C-2)
Externally added magnetic polymer particles C-2 and developer C-2 are the same as Example C-1, except that magnetic polymer mother particles C-2 are used instead of magnetic polymer mother particles C-1. Got. The viscosity, surface tension, and zeta potential of the developer were measured in the same manner as in Example B-1. The results are shown in Table 7.

<Example C-3>
(Preparation of externally added magnetic polymer particles C-3 and developer C-3)
The magnetic polymer mother particle C-2 is used instead of the magnetic polymer mother particle C-1, and the polystyrene particle “Stadex number” is used instead of “SiO ₂ (OX50, manufactured by Nippon Aerosil Co., Ltd., number average primary particle diameter 40 nm)”. The average primary particle size: 200 nm (manufactured by JSR, manufactured by drying and pulverizing a dispersion) ”was used in the same manner as in Example C-1, and externally added magnetic polymer particles C-3 and developer C- 3 was obtained. The viscosity, surface tension, and zeta potential of the developer were measured in the same manner as in Example B-1. The results are shown in Table 7.

<Example C-4>
(Preparation of developer C-4)
A developer C-4 was obtained in the same manner as in Example C-1, except that the magnetic polymer mother particle C-1 was used as it was instead of the externally added magnetic polymer particle C-1. The viscosity, surface tension, and zeta potential of the developer were measured in the same manner as in Example B-1. The results are shown in Table 7.

<Example C-5>
(Preparation of externally added magnetic polymer particles C-5 and developer C-5)
Magnetic polymer mother particle C-2 was used instead of magnetic polymer mother particle C-1, and instead of “SiO ₂ (OX50, manufactured by Nippon Aerosil Co., Ltd., number average primary particle diameter 40 nm)”, “SiO ₂ (A200, Externally added magnetic polymer particles C-5 and developer C-5 were obtained in the same manner as in Example C-1 except that “Nippon Aerosil Co., Ltd., number average primary particle diameter 12 nm)” was used. The viscosity, surface tension, and zeta potential of the developer were measured in the same manner as in Example B-1. The results are shown in Table 7.

<Example C-6>
(Preparation of externally added magnetic polymer particles C-6 and developer C-6)
The magnetic polymer mother particle C-2 is used instead of the magnetic polymer mother particle C-1, and the polystyrene particle “STADEX number average” is used instead of “SiO ₂ (OX50, Nippon Aerosil Co., Ltd., number average primary particle 40 nm)”. Externally added magnetic polymer particles C-6 and developer C-6 were obtained in the same manner as in Example C-1, except that “primary particle diameter: 600 nm (manufactured by JSR)” was used. The viscosity, surface tension, and zeta potential of the developer were measured in the same manner as in Example B-1. The results are shown in Table 7.

-Evaluation of number average particle diameter (primary particle diameter) of magnetic polymer mother particles and coefficient of variation thereof-
The developer is placed in a 1% by weight aqueous solution of Triton X100, ultrasonic dispersion and centrifugation are repeated to remove excess external additives and dried to obtain magnetic polymer mother particles to which a minimum amount of external additives are attached. It was. The obtained magnetic polymer mother particles were photographed with a scanning electron microscope (VE-7800 manufactured by Keyence Corporation), and 400 particles randomly selected were primary particles along the outer shell of the mother particles. The diameters were measured, and a value obtained by dividing the total by the number was determined to obtain the number average particle diameter. The results are shown in Table 8.
Further, the standard deviation (μm) is obtained from the distribution of 400 primary particle diameters (μm) obtained by the above measurement, and the coefficient of variation (%) is obtained by dividing by the number average particle diameter and multiplying by 100. It was. The results are shown in Table 8.

-Evaluation of particle size distribution of externally added magnetic polymer particles-
In the same manner as the particle size distribution evaluation of the magnetic polymer particles in the developer of Example A, the particle size distribution evaluation of the externally added magnetic polymer particles in the developer of Example C was performed. The results are shown in Table 8.

-Image evaluation-
The image evaluation of Example C was performed in the same manner as the image evaluation of Example A. The results are shown in Table 9.

As shown in Table 9, the developers in Example C-1 to Example C-3 have better dispersibility and dispersion stability than the developers in Example C-4 and Example C-6. The particle size reproduced the primary particle size.
Further, in the developers in Examples C-1 to C-3, the fog was further suppressed and the developability of fine lines was good as compared with the developers in Examples C-4 to C-6.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus of the present invention. FIG. 3 is an enlarged schematic diagram of a development area in an example of the image forming apparatus of the present invention.

Explanation of symbols

10 Magnetic drum (magnetic latent image holder)
12 Magnetic head (magnetic latent image forming means)
13 Restricting member 14 Developing device (developer supply means)
16 Intermediate transfer member 18 Cleaner 20 Demagnetizing device (demagnetizing means)
22 Magnetic latent image 24 Liquid developer (developer)
26 toner image 26a toner particles (magnetic polymer particles)
28 Transfer fixing roller (transfer means)
29 fixed image 30 paper (recording medium)
100 Image forming apparatus

Claims (6)

Magnetic polymer particles containing magnetic polymer mother particles containing a magnetic component and a polymer compound, and a dispersion medium for dispersing the magnetic polymer particles,
The dispersion medium is a liquid containing water,
The surface tension of the entire developer is 27 mN / m or more and 42 mN / m or less,
A developer for liquid magnetography, wherein the viscosity of the entire developer is 1.0 mPa · s to 10.0 mPa · s.   2. The developer for liquid magnetography according to claim 1, wherein the magnetic polymer particles have a zeta potential of −200 mV to −20 mV. The magnetic polymer particles are externally added magnetic polymer particles including the magnetic polymer mother particles and external additive particles externally added to the surface of the magnetic polymer mother particles,
3. The developer for liquid magnetography according to claim 1, wherein the number average primary particle size of the external additive particles is 15 nm or more and 500 nm or less.   The number average particle size of the magnetic polymer base particles is 0.5 μm or more and 10.0 μm or less, and the coefficient of variation of the number average particle size is 0% or more and 30% or less. The developer for liquid magnetography according to any one of claims 1 to 3. A magnetic latent image carrier;
A developer storage means for storing the developer according to any one of claims 1 to 4,
Developer supplying means for supplying the developer to the magnetic latent image holding member on which the magnetic latent image is formed;
A process cartridge comprising: A magnetic latent image carrier;
Magnetic latent image forming means for forming a magnetic latent image on the magnetic latent image holding member;
A developer storage means for storing the developer according to any one of claims 1 to 4,
Developer supplying means for supplying the developer to the magnetic latent image holding body on which the magnetic latent image is formed in order to visualize the magnetic latent image as a toner image;
Transfer means for transferring the toner image to a recording medium;
A demagnetizing means for demagnetizing the magnetic latent image on the magnetic latent image holder;
An image forming apparatus comprising:

Images