JP7686966B2 - Toner for developing electrostatic images and method for producing same - Google Patents

Description

The present invention relates to a toner for developing electrostatic images and a method for producing a toner for developing electrostatic images, and in particular to a toner for developing electrostatic images that satisfies offset resistance, suppresses in-machine contamination, and has excellent image quality.

In the printing field where images are formed by electrophotography, there has been a demand in recent years for a toner for developing electrostatic images (hereinafter also simply referred to as "toner") that can meet the needs of reduced power consumption, faster printing speeds, diversified image forming media, higher image quality, and reduced environmental impact.
The characteristics required for such a toner include low-temperature fixability, which allows a toner image to be fixed at a lower temperature than before, and improved fixing strength. Furthermore, with the expansion of the market to light printing, in addition to the traditional office market, there is a demand for improved stability in the image quality of printed matter, which is a commercial product.

Toners usually contain a binder resin having a binder function (hereinafter, also referred to as a "toner binder"), and it is known to use hybrid resins such as styrene-acrylic resin, polyester resin, and polyester resin having a grafted acrylic polymerized segment as the binder resin. In response to the above-mentioned requirements, techniques are known for improving low-temperature fixability by improving these toner binders, etc. (see, for example, Patent Documents 1 to 3).
However, particularly at high temperatures such as during toner fixing, the internal cohesive force of the toner decreases significantly, resulting in the problem of a hot offset phenomenon in which the fixing member is contaminated when the toner comes into contact with a heating member such as a fixing roller during fixing.

To address this problem, a release agent such as a fatty acid ester wax having a low melt viscosity that seeps out to the interface between the fixing member and the fixed image during fixing and suppresses adhesion has been added in order to suppress adhesion between the fixing member and the toner (see, for example, Patent Document 4).
Although the addition of a low melt viscosity release agent made it possible to ensure releasability, when the newly melted release agent came into contact with the image transport rollers in the printing machine, the release agent could cause problems by contaminating the transport members. The contaminants accumulated and reattached to the image, inducing image defects, which not only reduced the value of the printed matter, but also often forced the printed matter to be disposed of.

JP 2007-279714 A JP 2008-287229 A JP 2010-15159 A Japanese Patent Application Publication No. 8-50368

The present invention was made in consideration of the above problems and circumstances, and the problem to be solved is to provide a toner for developing electrostatic images that satisfies offset resistance, suppresses in-machine contamination, and has excellent image quality, and a method for producing the same.

In the course of investigating the causes of the above problems in order to solve the above problems, the present inventors discovered that it is possible to provide a toner for developing electrostatic images, which has excellent image quality while satisfying offset resistance and suppressing in-machine contamination, by containing a polymer having a specific structural unit as a binder resin and a fatty acid ester as a release agent, and thus arrived at the present invention.
That is, the above-mentioned problems of the present invention are solved by the following means.

［前記一般式（１）中、Ｒ_１及びＲ_２は、それぞれ独立して、メチル基、ｎ－プロピル基、ｉｓｏ－ブチル基、２－エチルヘキシル基のいずれかを表す。］

［一般式（２）中、Ｒ_１及びＲ_２は、それぞれ独立して、メチル基、ｎ－プロピル基、ｉｓｏ－ブチル基、２－エチルヘキシル基のいずれかを表す。］ 1. A toner for developing an electrostatic image, comprising toner base particles containing a binder resin and a release agent,
The binder resin contains a polymer having a structural unit represented by the following general formula (1):
The polymer having a structural unit represented by the general formula (1) is a copolymer of a first polymerizable monomer having a structure represented by the following general formula (2) and a second polymerizable monomer copolymerizable with the first polymerizable monomer,
The release agent contains a fatty acid ester,
The fatty acid ester is at least one of behenyl behenate and pentaerythritol tetrabehenate.
2. A toner for developing electrostatic images.

[In the general formula (1), R ₁ and R ₂ each independently represent any one of a methyl group, an n-propyl group, an iso-butyl group, and a 2-ethylhexyl group.]

[In general formula (2), R ₁ and R ₂ each independently represent a methyl group, an n-propyl group, an iso-butyl group, or a 2-ethylhexyl group.]

2. The toner for developing electrostatic images according to item 1, characterized in that the content of the structural unit derived from the first polymerizable monomer is within a range of 5 to 40% by mass, based on 100% by mass of the polymer having the structural unit represented by the general formula ( 1 ).

3. The toner for developing electrostatic images according to item 1 or 2 , wherein the second polymerizable monomer is selected from the group consisting of at least styrenes, acrylic acid esters, and methacrylic acid esters.

4. The toner for developing electrostatic images according to item 3, wherein the second polymerizable monomer is at least one selected from the group consisting of styrene, acrylic acid, n-butyl acrylate, iso-butyl acrylate, 2-ethylhexyl acrylate, methacrylic acid, and methyl methacrylate.

5. The toner for developing electrostatic images according to any one of items 1 to 4, characterized in that the content of the release agent is within a range of 5 to 20% by mass based on 100% by mass of the polymer having the structural unit represented by the general formula ( 1 ).

6. A method for producing the toner for developing an electrostatic image according to any one of items 1 to 5 , comprising the steps of:
A method for producing a toner for developing an electrostatic image, comprising the steps of: polymerizing a first polymerizable monomer having a structure represented by the general formula (2) to synthesize a polymer having a structural unit represented by the general formula (1) to prepare a binder resin particle dispersion liquid.

According to the above-mentioned means of the present invention, it is possible to provide a toner for developing electrostatic images, which is excellent in image quality, and which can suppress contamination inside a machine caused by a release agent while satisfying offset resistance, and a method for producing the same.
Although the mechanism by which the effects of the present invention are expressed or the mechanism of action has not been clarified, it is speculated as follows. Note that the following mechanism is based on speculation, and the present invention is not limited to the following mechanism in any way.
In the following description, the polymer having a structural unit represented by the general formula (1) is also simply referred to as the "polymer according to the present invention."

Conventional toners containing styrene-acrylic resins are composed of structural units derived from styrene, methyl methacrylate, and n-butyl acrylate as their main components, and in order to reduce power consumption during printing, efforts are being made to lower the Tg (glass transition temperature) and reduce the molecular weight, thereby achieving so-called low-temperature fixing.
On the other hand, as the toner is fixed at a lower temperature, the release agent used is required to melt at a lower temperature (lower melting point) and have a low melt viscosity (lower melt viscosity). Specifically, fatty acid esters such as behenyl behenate are widely used. By lowering the melting point and melt viscosity of such a release agent, it becomes easier to melt during fixing and to easily seep out to the image-fixing roller interface, so that offset generation can be suppressed even when the toner is fixed at a low temperature.
However, as the melting point of the release agent becomes lower, the crystallization temperature at which the release agent solidifies also becomes lower, so it takes a long time to solidify. If the release agent comes into contact with the image transport roller before solidifying, the release agent will migrate to the image transport roller and cause contamination, which may result in contamination of the image and a significant loss of image quality. The release agent is also required to solidify (crystallize) quickly.

The reason why the toner of the present invention is able to achieve both hot offset resistance and good image quality by suppressing contamination of the image transport roller is presumably due to the interaction between the toner binder and the fatty acid ester, which is a release agent.
By introducing the polymer having the structural unit represented by the general formula (1) according to the present invention into a toner binder, it is possible to enhance the dipole interaction with a fatty acid ester, which is a release agent having the same structure.
By increasing the dipole interaction, when the fatty acid ester solidifies (crystallizes), the polymer having the structural unit represented by the general formula (1) according to the present invention functions as a scaffold for the crystallization, so that the crystal nucleus can be formed quickly. As a result, it is considered that the time required for solidification can be shortened. Therefore, it can be inferred that even if the image is brought into contact with the image conveying roller, the solidification proceeds and contamination can be suppressed.

The toner for developing electrostatic images of the present invention is a toner for developing electrostatic images comprising toner base particles containing a binder resin and a release agent, characterized in that the binder resin contains a polymer having a structural unit represented by the general formula (1) and the release agent contains a fatty acid ester.
This feature is a technical feature common to or corresponding to each of the following embodiments.

As an embodiment of the present invention, it is preferable that R ₁ and R ₂ in the general formula (1) each independently represent an alkyl group having 1 to 4 carbon atoms, in terms of further suppressing contamination inside an aircraft.

In addition, it is preferable that the polymer having the structural unit represented by the general formula (1) is a copolymer of a first polymerizable monomer having a structure represented by the general formula (2) and a second polymerizable monomer copolymerizable with the first polymerizable monomer, in that the effects of the present invention can be exhibited more efficiently.

It is preferable that the content of the structural unit derived from the first polymerizable monomer is within the range of 5 to 40% by mass relative to 100% by mass of the polymer having the structural unit represented by the general formula (1), in that good offset performance can be achieved while suppressing roller contamination.

In addition, it is preferable that the second polymerizable monomer is selected from the group consisting of at least styrenes, acrylic acid esters, and methacrylic acid esters, and in particular that the second polymerizable monomer is selected from one or more of styrene, acrylic acid, n-butyl acrylate, iso-butyl acrylate, 2-ethylhexyl acrylate, methacrylic acid, and methyl methacrylate, in that this makes it easier to adjust the glass transition temperature of the polymer according to the present invention.

In terms of interaction with the polymer of the present invention, it is preferable that the fatty acid ester contains a fatty acid ester having 18 to 24 carbon atoms, and it is particularly preferable that the fatty acid ester having 18 to 24 carbon atoms is at least one of behenyl behenate and pentaerythritol tetrabehenate.

In terms of the balance between fixability and offset resistance, it is preferable that the content of the release agent is within the range of 5 to 20% by mass relative to 100% by mass of the polymer having the structural unit represented by the general formula (1).

The method for producing a toner for developing electrostatic images of the present invention is characterized by comprising a step of polymerizing a first polymerizable monomer having a structure represented by the general formula (2) to synthesize a polymer having a structural unit represented by the general formula (1) and preparing a binder resin particle dispersion. This makes it possible to produce a toner that has good offset resistance, can suppress in-machine contamination caused by a release agent, and has excellent image quality.

The present invention, its components, and the form and mode for implementing the present invention are described below. Note that in this application, "~" is used to mean that the numerical values before and after it are included as the lower and upper limits.

[Toner for developing electrostatic images of the present invention]
The toner for developing electrostatic images of the present invention (hereinafter, also simply referred to as "toner") is a toner for developing electrostatic images comprising toner base particles containing a binder resin and a release agent, characterized in that the binder resin contains a polymer having a structural unit represented by the following general formula (1), and the release agent contains a fatty acid ester.

In this specification, "toner base particles" are those that constitute the base of "toner particles." "Toner base particles" contain at least a binder resin and a release agent, and may contain other components such as a colorant and a charge control agent as necessary. "Toner base particles" are called "toner particles" when an external additive is added. "Toner" refers to an aggregate of "toner particles."

<Binder resin>
The binder resin according to the present invention contains a polymer having a structural unit represented by the following general formula (1).

［前記一般式（１）中、Ｒ_１及びＲ_２は、それぞれ独立して、炭素数１～８のアルキル基を表す。］

[In the general formula (1), R ₁ and R ₂ each independently represent an alkyl group having 1 to 8 carbon atoms.]

(Polymer having a structural unit represented by general formula (1))
In the general formula (1), R ₁ and R ₂ are each independently an alkyl group having 1 to 8 carbon atoms. Specific examples thereof include a methyl group, an n-butyl group, an iso-butyl group, and a 2-ethylhexyl group. From the viewpoint of further suppressing contamination of the image transport roller, R ₁ and R ₂ are preferably an alkyl group having 1 to 4 carbon atoms.

A polymer having a structural unit represented by the general formula (1) can be synthesized by polymerizing a monomer having a structure represented by the following general formula (2) (hereinafter also referred to as the "first polymerizable monomer").

［一般式（２）中、Ｒ_１及びＲ_２は、それぞれ独立して、炭素数１～８のアルキル基を表す。］

[In general formula (2), R ₁ and R ₂ each independently represent an alkyl group having 1 to 8 carbon atoms.]

_R1 and _R2 have the same meanings as _R1 and _R2 in formula (1).
The first polymerizable monomer may be used alone or in combination of two or more kinds.
Specific examples of the first polymerizable monomer include the following exemplary compounds M1 to M7, but are not limited thereto.

The first polymerizable monomer may be a commercially available product or a synthetic product.
As an example of the synthesis method, the first polymerizable monomer can be obtained by a condensation reaction between itaconic acid as a starting material and a specific alcohol.

In addition, the content of the structural unit derived from the first polymerizable monomer is preferably within a range of 5 to 50% by mass, and more preferably within a range of 5 to 40% by mass, relative to 100% by mass of the polymer having the structural unit represented by the general formula (1).

The polymerization method for the first polymerizable monomer is not particularly limited, but from the viewpoint of easy synthesis, a method of radically polymerizing the monomer using a known oil-soluble or water-soluble radical polymerization initiator is preferred.

That is, a toner manufacturing method according to a preferred embodiment of the present invention is a method for manufacturing a toner for developing electrostatic images, which includes a binder resin containing a polymer having a structural unit represented by the general formula (1) and a release agent containing a fatty acid ester, and includes a step of (radical) polymerizing a polymerizable monomer having a structure represented by the general formula (2) to synthesize a polymer having a structural unit represented by the general formula (1) and preparing a binder resin particle dispersion liquid. It is also preferable that the method further includes a step of preparing a release agent particle dispersion liquid containing a release agent, and includes a step of mixing the binder resin particle dispersion liquid and the release agent particle dispersion liquid.

Specific examples of oil-soluble polymerization initiators used in radical polymerization include the azo or diazo polymerization initiators and peroxide polymerization initiators shown below. If necessary, known chain transfer agents such as n-octyl mercaptan and n-octyl-3-mercaptopropionate may be used.

Examples of azo or diazo polymerization initiators include 2,2'-azobis-(2,4-dimethylvaleronitrile), 2,2'-azobisisobutyronitrile, 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis-4-methoxy-2,4-dimethylvaleronitrile, and azobisisobutyronitrile.

Examples of peroxide polymerization initiators include benzoyl peroxide, methyl ethyl ketone peroxide, diisopropyl peroxycarbonate, cumene hydroperoxide, t-butyl hydroperoxide, di-t-butyl peroxide, dicumyl peroxide, 2,4-dichlorobenzoyl peroxide, lauroyl peroxide, 2,2-bis-(4,4-t-butylperoxycyclohexyl)propane, and tris-(t-butylperoxy)triazine.

When the polymer having the structural unit represented by the general formula (1) according to the present invention is formed by emulsion polymerization, a water-soluble radical polymerization initiator can be used.
Examples of the water-soluble radical polymerization initiator include persulfates such as potassium persulfate and ammonium persulfate, azobisaminodipropane acetate, azobiscyanovaleric acid and its salts, and hydrogen peroxide.
The polymerization temperature varies depending on the types of monomers and polymerization initiators used, but is preferably within a range of 50 to 100° C., and more preferably within a range of 55 to 90° C. The polymerization time varies depending on the types of monomers and polymerization initiators used, but is preferably, for example, 1 to 12 hours.

(Polymers having other structural units)
The polymer having a structural unit represented by the general formula (1) according to the present invention may be a polymer obtained only from a polymerizable monomer having a structure represented by the general formula (2) (first polymerizable monomer). However, from the viewpoint of more efficiently exerting the effects of the present invention, it is preferable that the polymer is a copolymer of the first polymerizable monomer and another polymerizable monomer copolymerizable with the first polymerizable monomer (also referred to as a "second polymerizable monomer") as described below.

Examples of the second polymerizable monomer include styrene-based monomers (styrenes) such as styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, o-ethylstyrene, m-ethylstyrene, p-ethylstyrene, o-acetoxystyrene, m-acetoxystyrene, and p-acetoxystyrene; methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, tert-butyl acrylate, isobutyl acrylate (iso-butyl acrylate), n-octyl acrylate, and acrylic acid. Examples of the methacrylic acid esters include 2-ethylhexyl, stearyl acrylate, lauryl acrylate, and phenyl acrylate; and methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, lauryl methacrylate, phenyl methacrylate, dimethylaminoethyl methacrylate, and diethylaminoethyl methacrylate.
Among these, from the viewpoint of facilitating adjustment of the glass transition temperature of the polymer, at least one selected from styrenes and acrylic acid esters is preferred, at least one selected from the group consisting of styrene, acrylic acid, n-butyl acrylate, iso-butyl acrylate, 2-ethylhexyl acrylate, methacrylic acid, and methyl methacrylate is more preferred, and at least one of styrene and n-butyl acrylate is even more preferred.

Furthermore, as the second polymerizable monomer, a polymerizable monomer having an ionically dissociable group may be used.
The polymerizable monomer having an ionic dissociation group is, for example, one having a group such as a carboxy group, a sulfonic acid group, or a phosphoric acid group. Specific examples include acrylic acid, methacrylic acid, maleic acid, itaconic acid, and fumaric acid. Among these, acrylic acid or methacrylic acid is preferred.
These second polymerizable monomers may be used alone or in combination of two or more kinds.

In the polymer according to the present invention, the content of the structural unit derived from the second polymerizable monomer is not particularly limited, and can be appropriately adjusted depending on the type of the structural unit.
For example, when the second polymerizable monomer is the above-mentioned styrene-based monomer, the content of the structural units derived from the styrene-based monomer in the polymer is preferably in the range of 20 to 80 mass%, and more preferably in the range of 30 to 70 mass%, based on 100 mass% of all structural units of the polymer.

When the second polymerizable monomer is an acrylic acid ester or a methacrylic acid ester, the content of structural units derived from the acrylic acid ester or methacrylic acid ester in the polymer is preferably within the range of 5 to 50% by mass, and more preferably within the range of 10 to 40% by mass, with the total structural units of the polymer being 100% by mass.

When a polymerizable monomer having an ionic dissociation group is used, the content of the structural unit is preferably within the range of 3 to 8% by mass, with the total structural units of the polymer according to the present invention being 100% by mass.

The method for synthesizing the polymer of the present invention using the first polymerizable monomer and the second polymerizable monomer is similar to the polymerization method of the first polymerizable monomer described above, so a description thereof will be omitted here.

The polymer according to the present invention preferably has a peak molecular weight in the range of 3,500 to 35,000, more preferably 10,000 to 30,000, obtained from the molecular weight distribution in terms of polystyrene measured by gel permeation chromatography (GPC). A peak molecular weight in this range is preferable because the polymer has an appropriate melt viscosity during fixing, and can achieve both good fixing properties and offset resistance.

The peak molecular weight is the molecular weight that corresponds to the elution time of the peak top in the molecular weight distribution. When there are multiple peaks in the molecular weight distribution, it refers to the molecular weight that corresponds to the elution time of the peak top with the largest peak area ratio.

The peak molecular weight of the polymer can be measured by the following method. Specifically, using an apparatus "HLC-8220" (manufactured by Tosoh Corporation) and a column "TSKguard column + TSKgel Super HZM-M triple column" (manufactured by Tosoh Corporation), the column temperature is maintained at 40°C, tetrahydrofuran (THF) is passed as a carrier solvent at a flow rate of 0.2 ml/min, and the measurement sample is dissolved in tetrahydrofuran to a concentration of 1 mg/ml under dissolution conditions in which the sample is treated for 5 minutes at room temperature (25°C) using an ultrasonic disperser.
Next, the sample solution is obtained by processing it with a membrane filter having a pore size of 0.2 μm, and 10 μl of this sample solution is injected into the device together with the above-mentioned carrier solvent, and detected using a refractive index detector (RI detector). The molecular weight distribution of the measurement sample is measured.

From the viewpoint of a balance between fixability and offset resistance, the content of the polymer according to the present invention is preferably in the range of 65 to 99% by mass, more preferably in the range of 70 to 97% by mass, and even more preferably in the range of 75 to 95% by mass, with the total mass of the binder resin being 100% by mass.

The binder resin according to the present invention may contain a resin other than the polymer according to the present invention, and any resin generally used as a binder resin constituting a toner can be used without any restrictions.
Specific examples of the resin include polyester resin, silicone resin, polyolefin resin, polyamide resin, and epoxy resin. These other resins may be used alone or in combination of two or more kinds.

The polyester resin that can be used as the binder resin will be described below.
(Polyester resin)
The polyester resin is a known polyester resin obtained by a polycondensation reaction between a divalent or higher carboxylic acid (a polyvalent carboxylic acid component) and a divalent or higher alcohol (a polyhydric alcohol component). The polyester resin may be amorphous or crystalline.

The valence of each of the polyvalent carboxylic acid component and the polyhydric alcohol component is preferably 2 to 3, and is particularly preferably 2. Therefore, the particularly preferred embodiment will be described below in which the valence is 2 (i.e., the dicarboxylic acid component and the diol component).

Examples of the dicarboxylic acid component include saturated aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1,9-nonanedicarboxylic acid, 1,10-decanedicarboxylic acid (dodecanedioic acid), 1,11-undecanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, 1,13-tridecanedicarboxylic acid, 1,14-tetradecanedicarboxylic acid, 1,16-hexadecanedicarboxylic acid, and 1,18-octadecanedicarboxylic acid; methylenesuccinic acid, Examples of the dicarboxylic acid component include unsaturated aliphatic dicarboxylic acids such as fumaric acid, maleic acid, 3-hexenedioic acid, 3-octenedioic acid, and dodecenylsuccinic acid; unsaturated aromatic dicarboxylic acids such as phthalic acid, terephthalic acid, isophthalic acid, t-butylisophthalic acid, tetrachlorophthalic acid, chlorophthalic acid, nitrophthalic acid, p-phenylenediacetic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, and anthracenedicarboxylic acid; and lower alkyl esters and acid anhydrides of these compounds can also be used. The dicarboxylic acid component can be used alone or in combination of two or more kinds.
In addition, trivalent or higher polyvalent carboxylic acids such as trimellitic acid and pyromellitic acid, anhydrides of the above carboxylic acid compounds, or alkyl esters having 1 to 3 carbon atoms can also be used.

Examples of diol components include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, 1,14-tetradecanediol, 1,18-octadecanediol, 1,20-eicosanediol, and neopentane. Examples of the diol include saturated aliphatic diols such as ethyl glycol; unsaturated aliphatic diols such as 2-butene-1,4-diol, 3-butene-1,4-diol, 2-butyne-1,4-diol, 3-butyne-1,4-diol, and 9-octadecene-7,12-diol; and aromatic diols such as bisphenols such as bisphenol A and bisphenol F, and alkylene oxide adducts of bisphenols such as ethylene oxide adducts and propylene oxide adducts of these. These derivatives can also be used. The diol component may be used alone or in a mixture of two or more types.

There are no particular limitations on the method for producing the polyester resin, and it can be produced by polycondensing (esterifying) the polyvalent carboxylic acid component and the polyhydric alcohol component using a known esterification catalyst.

Catalysts that can be used in the production of polyester resins include alkali metal compounds such as sodium and lithium; compounds containing Group 2 elements such as magnesium and calcium; compounds of metals such as aluminum, zinc, manganese, antimony, titanium, tin, zirconium, and germanium; phosphorous compounds; phosphoric acid compounds; and amine compounds. Specific examples of tin compounds include dibutyltin oxide (dibutyltin oxide), tin octoate, tin dioctoate, and salts of these.

Examples of titanium compounds include titanium alkoxides such as tetra-normal-butyl titanate (Ti(On-Bu) ₄ ), tetraisopropyl titanate, tetramethyl titanate, and tetrastearyl titanate; titanium acylates such as polyhydroxytitanium stearate; and titanium chelates such as titanium tetraacetylacetonate, titanium lactate, and titanium triethanolamine.
The germanium compound may include germanium dioxide.
Further, examples of the aluminum compound include polyaluminum hydroxide, aluminum alkoxide, tributylaluminate, etc. These may be used alone or in combination of two or more.

The polymerization temperature is not particularly limited, but is preferably within the range of 70 to 250°C. The polymerization time is also not particularly limited, but is preferably 0.5 to 10 hours. During polymerization, the reaction system may be depressurized as necessary.

The polyester resin may be a hybrid polyester resin having a graft copolymer structure of a polyester polymerized segment and a styrene-acrylic polymerized segment graft.

<Release Agent>
The toner base particles according to the present invention contain a release agent, and the release agent contains a fatty acid ester.
Examples of fatty acid esters contained in the release agent include, for example, behenyl behenate (behenyl behenate), stearyl stearate (stearyl stearate), behenyl stearate, stearyl behenate, butyl stearate, propyl oleate, hexadecyl palmitate (hexadecyl palmitate), methyl lignocerate (methyl lignocerate), glycerin monostearate (glyceryl stearate), diglyceryl distearate (diglyceryl distearate), pentaerythritol, glyceryl stearate ... Examples of the fatty acid ester include pentaerythritol tetrabehenate (pentaerythritol tetrabehenate ester), diethylene glycol monostearate, dipropylene glycol distearate, sorbitan monostearate, cholesteryl stearate, trimethylolpropane tribehenate, pentaerythritol diacetate dibehenate, glycerin tribehenate, tristearyl trimellitate (tristearyl trimellitate), distearyl maleate, methyl triacontanate (methyl triacontanate), etc. These fatty acid esters can be used alone or in combination of two or more.
Moreover, these fatty acid esters may be commercially available products or synthetic products.

From the viewpoint of interaction with the polymer according to the present invention, the fatty acid ester preferably contains a fatty acid ester having a carbon number in the range of 18 to 24. Examples of such fatty acids include stearic acid, arachidic acid, behenic acid, and lignoceric acid.
A more preferred release agent is at least one of behenyl behenate (behenyl behenate) and pentaerythritol tetrabehenate (pentaerythritol tetrabehenic acid ester).

As long as the release agent contains a fatty acid ester, it may contain a wax other than the fatty acid ester.
Examples of such other waxes include polyolefin waxes such as low molecular weight polyethylene and low molecular weight polypropylene, branched chain hydrocarbon waxes such as microcrystalline wax, long chain hydrocarbon waxes such as paraffin wax and sazol wax, dialkyl ketone waxes such as distearyl ketone, fatty acid amide waxes such as ethylenediamine behenylamide and trimellitic acid tristearylamide, and the like.

From the viewpoint of the balance between fixability and offset resistance, the content of the release agent is preferably within the range of 1 to 25% by mass, and more preferably within the range of 5 to 20% by mass, with the total mass of the polymer according to the present invention being 100% by mass.

The toner base particles used in the present invention may contain a colorant and a charge control agent as necessary.

<Coloring Agent>
The toner base particles according to the present invention may contain a colorant. As the colorant, generally known dyes and pigments can be used.

Colorants for obtaining black toner include carbon black, magnetic materials, iron-titanium composite oxide black, etc. Examples of carbon black include channel black, furnace black, acetylene black, thermal black, lamp black, etc. Also, examples of magnetic materials include ferrite, magnetite, etc.

Colorants for obtaining yellow toner include dyes such as C.I. Solvent Yellow 19, 44, 77, 79, 81, 82, 93, 98, 103, 104, 112, and 162; and pigments such as C.I. Pigment Yellow 14, 17, 74, 93, 94, 138, 155, 180, and 185.

Colorants for obtaining magenta toner include dyes such as C.I. Solvent Red 1, 49, 52, 58, 63, 111, and 122; and pigments such as C.I. Pigment Red 5, 48:1, 53:1, 57:1, 122, 139, 144, 149, 166, 177, 178, and 222.

Colorants for obtaining cyan toner include dyes such as C.I. Solvent Blue 25, 36, 60, 70, 93, and 95; and pigments such as C.I. Pigment Blue 1, 7, 15, 60, 62, 66, and 76.

The colorants for obtaining the toner of each color may be used alone or in combination of two or more kinds for each color.
The content of the colorant is preferably within a range of 0.5 to 20% by mass, and more preferably within a range of 2 to 10% by mass, with the total mass of the toner base particles being 100% by mass.

<Charge Control Agent>
The toner base particles according to the present invention may contain a charge control agent.
The charge control agent used is not particularly limited as long as it is a substance capable of imparting a positive or negative charge through frictional charging and is colorless, and various known positively charged charge control agents and negatively charged charge control agents can be used.

Specific examples of positively charged charge control agents include nigrosine dyes such as "Nigrosine Base EX" (manufactured by Orient Chemical Industry Co., Ltd.), quaternary ammonium salts such as "Quaternary Ammonium Salt P-51" (manufactured by Orient Chemical Industry Co., Ltd.) and "Copy Charge PX VP435" (manufactured by Hoechst Japan KK), alkoxylated amines, alkylamides, molybdic acid chelate pigments, and imidazole compounds such as "PLZ1001" (manufactured by Shikoku Chemical Industry Co., Ltd.).

Examples of negatively charged charge control agents include metal complexes such as "Bontron (registered trademark) S-22," "Bontron (registered trademark) S-34," "Bontron (registered trademark) E-81," and "Bontron (registered trademark) E-84" (all manufactured by Orient Chemical Industry Co., Ltd.), and "Spiron Black TRH" (manufactured by Hodogaya Chemical Co., Ltd.), thioindigo pigments, quaternary ammonium salts such as "Copy Charge NX VP434" (manufactured by Hoechst Japan KK), calixarene compounds such as "Bontron (registered trademark) E-89" (manufactured by Orient Chemical Industry Co., Ltd.), boron compounds such as "LR147" (manufactured by Nippon Carlit Co., Ltd.), and fluorine compounds such as magnesium fluoride and carbon fluoride.

In addition to the above, metal complexes that can be used as negatively charged charge control agents include those having various structures such as oxycarboxylic acid metal complexes, dicarboxylic acid metal complexes, amino acid metal complexes, diketone metal complexes, diamine metal complexes, azo group-containing benzene-benzene derivative skeleton metal complexes, and azo group-containing benzene-naphthalene derivative skeleton metal complexes.

By forming the toner base particles to contain a charge control agent in this manner, the chargeability of the toner is improved.
The content of the charge control agent in the toner base particles is preferably within a range of 0.01 to 30% by weight, and more preferably within a range of 0.1 to 10% by weight.

The form of the toner base particles according to the present invention is not particularly limited, and can be, for example, a so-called single-layer structure (a homogeneous structure that is not a core-shell type), a core-shell structure, a multi-layer structure of three or more layers, a domain-matrix structure, etc.

<External Additives>
In order to improve the fluidity, chargeability, cleaning properties, etc. of the toner, external additives such as a fluidizing agent, a cleaning aid, etc., which are so-called post-treatment agents, may be added to the toner base particles to form the toner of the present invention.

Examples of the external additive include inorganic particles such as inorganic oxide particles, such as silica particles, alumina particles, and titanium oxide particles, inorganic stearic acid compound particles, such as aluminum stearate particles and zinc stearate particles, and inorganic titanic acid compound particles, such as strontium titanate particles and zinc titanate particles. These may be used alone or in combination of two or more kinds.
These inorganic particles may be surface-treated with a silane coupling agent, a titanium coupling agent, a higher fatty acid, a silicone oil, or the like in order to improve heat resistance, storage stability, and environmental stability.

The amount of external additive added is preferably within the range of 0.05 to 5 parts by weight, and more preferably within the range of 0.1 to 3 parts by weight, per 100 parts by weight of the toner base particles.

<Average particle size of toner>
The toner has an average particle size, in terms of volumetric median diameter ( _D50 ), preferably in the range of 4 to 10 μm, and more preferably in the range of 5 to 9 μm. By having the volumetric median diameter ( _D50 ) in the above range, the transfer efficiency is increased, and the image quality of halftones is improved, as well as the image quality of fine lines, dots, etc. is improved.

In the present invention, the volume-based median diameter ( _D50 ) of the toner is measured and calculated using a measuring device consisting of a "Coulter Counter 3" (manufactured by Beckman Coulter, Inc.) connected to a computer system (manufactured by Beckman Coulter, Inc.) equipped with data processing software "Software V3.51."
Specifically, 0.02 g of a measurement sample (toner) is added to 20 mL of a surfactant solution (for example, a surfactant solution prepared by diluting a neutral detergent containing a surfactant component 10 times with pure water for the purpose of dispersing toner particles) and allowed to mix, and then ultrasonic dispersion is performed for 1 minute to prepare a toner dispersion liquid. This toner dispersion liquid is then injected with a pipette into a beaker containing an "ISOTON II" (manufactured by Beckman Coulter, Inc.) in a sample stand until the concentration indicated by the measuring device reaches 8%.
By setting the concentration range here, reproducible measurement values can be obtained. In the measurement device, the number of particles to be measured is set to 25,000, the aperture diameter is set to 50 μm, the measurement range of 1 to 30 μm is divided into 256 parts to calculate the frequency value, and the particle diameter of 50% from the largest volume cumulative fraction is set as the volume-based median diameter (D ₅₀ ).

[Toner manufacturing method]
The toner manufacturing method of the present invention is characterized by having a step of polymerizing a first polymerizable monomer having a structure represented by the general formula (2) to synthesize a polymer having a structural unit represented by the general formula (1) and preparing a binder resin particle dispersion. The toner manufacturing method of the present invention is not particularly limited as long as it has a step of preparing the binder resin particle dispersion. For example, the polymer according to the present invention, a release agent, and if necessary, a colorant, etc. are melt-kneaded, and then pulverized, classified, etc. to obtain a toner.
Alternatively, a toner can be obtained by an emulsion aggregation method in which polymer particles are prepared by emulsion polymerization, mini-emulsion polymerization, or the like of a polymerizable monomer in an aqueous medium, and the polymer particles, release agent particles, and, if necessary, dispersed particles such as colorant particles are aggregated and fused.
As the emulsion aggregation method, the methods described in JP-A-5-265252, JP-A-6-329947, JP-A-9-15904, etc. can be adopted.
Furthermore, a production method using a suspension polymerization method described in JP-A-2010-191043 may also be used.

Among these, a production method utilizing an emulsion aggregation method is preferred from the viewpoints of ease of controlling the particle size and shape and reduction of energy costs during production.
The production method using such an emulsion aggregation method is as follows:
(1A) A binder resin particle dispersion liquid preparation step for preparing a binder resin particle dispersion liquid, (1B) A colorant particle dispersion liquid preparation step for preparing a colorant particle dispersion liquid, (1C) A release agent particle dispersion liquid preparation step for preparing a release agent particle dispersion liquid, (2) An association step for forming associated particles by adding an aggregating agent to an aqueous medium in which binder resin particles, colorant particles, and release agent particles exist, and simultaneously carrying out salting out and aggregation and fusion, (3) An aging step for forming toner particles by controlling the shape of the associated particles, (4) A filtration and washing step for filtering out toner particles from the aqueous medium and removing surfactants and the like from the toner particles, (5) A drying step for drying the washed toner particles, and (6) An external additive addition step for adding an external additive to the dried toner particles. The steps (1A) to (1C) will be described below.

(1A) Binder Resin Particle Dispersion Preparation Step In this step, resin particles are formed by a conventional emulsion polymerization or the like, and the resin particles are aggregated and fused to form binder resin particles. As an example, polymerizable monomers (the first polymerizable monomer and the second polymerizable monomer) constituting the binder resin are introduced into an aqueous medium and dispersed, and the polymerizable monomers are polymerized by a polymerization initiator to synthesize a polymer having a structural unit represented by the general formula (1) according to the present invention, and a binder resin particle dispersion is prepared.

As a method for obtaining a binder resin particle dispersion, in addition to the above-mentioned method of polymerizing a polymerizable monomer in an aqueous medium by a polymerization initiator, for example, a method of performing a dispersion treatment in an aqueous medium without using a solvent, or a method of dissolving a polymer in an organic solvent such as ethyl acetate to prepare a solution, emulsifying and dispersing the solution in an aqueous medium using a disperser, and then performing a solvent removal treatment, can be mentioned.
In this case, if necessary, a release agent may be added to the binder resin in advance. For dispersion, it is also preferable to carry out the polymerization in the presence of a known surfactant (e.g., anionic surfactants such as polyoxyethylene (2) dodecyl ether sodium sulfate, sodium dodecyl sulfate, and sodium dodecylbenzenesulfonate).
The volume-based median diameter of the binder resin particles in the dispersion is preferably within a range of 50 to 300 nm. The volume-based median diameter of the binder resin particles in the dispersion can be measured by a dynamic light scattering method using a "Microtrac UPA-150" (manufactured by Nikkiso Co., Ltd.).

(1B) Colorant Particle Dispersion Preparation Step This colorant particle dispersion preparation step is a step of dispersing a colorant in the form of fine particles in an aqueous medium to prepare a colorant particle dispersion.
The colorant can be dispersed by utilizing mechanical energy. The volume-based median diameter of the colorant particles in the dispersion is preferably within a range of 10 to 300 nm, and more preferably within a range of 50 to 200 nm.
The volume-based median diameter of the colorant particles in the dispersion can be measured by dynamic light scattering using "Microtrac UPA-150" (manufactured by Nikkiso Co., Ltd.) in the same manner as above.

(1C) Release Agent Particle Dispersion Preparation Step This release agent particle dispersion preparation step is a step of preparing a dispersion of release agent particles by dispersing the release agent according to the present invention, which contains a fatty acid ester, in the form of fine particles in an aqueous medium.
The release agent can be dispersed by utilizing mechanical energy. The volume-based median diameter of the release agent particles in the dispersion is preferably within a range of 100 to 1000 nm, and more preferably within a range of 200 to 700 nm.
The volume-based median diameter of the release agent particles in the dispersion liquid can be measured, for example, by a laser diffraction particle size distribution measuring instrument LA-750 (manufactured by Horiba, Ltd.).

(aqueous medium)
The aqueous medium used in steps (1A) to (1C) may be water, or an aqueous medium containing water as the main component (50% by mass or more) and water-soluble solvents such as alcohols and glycols, and optional components such as surfactants and dispersants. The aqueous medium used is preferably a mixture of water and a surfactant.

Examples of the water-soluble solvent include methanol, ethanol, isopropanol, butanol, acetone, methyl ethyl ketone, and tetrahydrofuran. Among these, alcohols such as methanol, ethanol, isopropanol, and butanol, which are organic solvents that do not dissolve the polymer, are preferred.

Examples of the surfactant include cationic surfactants, anionic surfactants, and nonionic surfactants. Examples of the cationic surfactant include dodecyl ammonium chloride, dodecyl ammonium bromide, dodecyl trimethyl ammonium bromide, dodecyl pyridinium chloride, dodecyl pyridinium bromide, and hexadecyl trimethyl ammonium bromide. Examples of the anionic surfactant include fatty acid soaps such as sodium stearate and sodium dodecanoate, sodium dodecyl benzene sulfonate, and sodium dodecyl sulfate. Examples of the nonionic surfactant include polyoxyethylene dodecyl ether, polyoxyethylene hexadecyl ether, polyoxyethylene nonyl phenyl ether, polyoxyethylene lauryl ether, polyoxyethylene sorbitan monooleate ether, and monodecanoyl sucrose.
Such surfactants may be used alone or in combination of two or more. Among the surfactants, anionic surfactants are preferred, and sodium dodecylbenzenesulfonate and sodium dodecyl sulfate are more preferred.
The amount of the surfactant added is preferably within a range of 0.01 to 10 parts by mass, and more preferably within a range of 0.04 to 2 parts by mass, based on 100 parts by mass of the aqueous medium.

The steps from (2) the association step to (6) the external additive addition step can be carried out according to various conventionally known methods.
The flocculant used in the association step (2) is not particularly limited, but is preferably selected from metal salts.

Examples of metal salts include monovalent metal salts such as salts of alkali metals such as sodium, potassium, and lithium; divalent metal salts such as calcium, magnesium, manganese, and copper; and trivalent metal salts such as iron and aluminum.
Specific examples of metal salts include sodium chloride, potassium chloride, lithium chloride, calcium chloride, magnesium chloride, zinc chloride, copper sulfate, magnesium sulfate, manganese sulfate, polyaluminum chloride, etc. Among these, it is particularly preferable to use divalent or trivalent metal salts, since they can promote aggregation with a smaller amount. These can be used alone or in combination of two or more kinds.

[Developer]
The toner of the present invention may be used, for example, as a one-component magnetic toner by incorporating a magnetic material, as a two-component developer by mixing with a so-called carrier, or as a non-magnetic toner alone, and any of these may be suitably used.
As the magnetic material, for example, magnetite, γ-hematite, or various ferrites can be used.

The carrier that constitutes the two-component developer can be magnetic particles made of conventionally known materials such as metals such as iron, steel, nickel, cobalt, ferrite, and magnetite, and alloys of these metals with metals such as aluminum and lead.

As the carrier, it is preferable to use a coated carrier in which the surface of magnetic particles is coated with a coating agent such as resin, or a so-called resin dispersion type carrier in which magnetic powder is dispersed in a binder resin.
The resin for coating is not particularly limited, but examples thereof include olefin resin, styrene resin, styrene-acrylic resin, silicone resin, polyester resin, and fluororesin.
The resin for constituting the resin dispersion type carrier is not particularly limited and any known resin can be used, such as acrylic resin, styrene-acrylic resin, polyester resin, fluororesin, and phenol resin.

The volume-based median diameter of the carrier is preferably within a range of 20 to 100 μm, and more preferably within a range of 25 to 60 μm.
The volume-based median diameter of the carrier can be measured typically by a laser diffraction particle size distribution measuring device "HELOS" (manufactured by SYMPATEC) equipped with a wet disperser.

The amount of toner mixed with the carrier is preferably within the range of 2 to 10% by mass, with the total mass of the toner and carrier being 100% by mass.

[Image forming method]
The toner of the present invention can be suitably used in an image forming method including a fixing step by a heat pressure fixing method in which pressure can be applied and heating can be performed. In particular, the toner can be suitably used in an image forming method in which the fixing step is performed at a relatively low fixing temperature in which the surface temperature of the heating member in the fixing nip is within a range of 80 to 110°C, preferably 80 to 95°C.
Furthermore, the toner can be suitably used in an image forming method in which the fixing linear speed is within the range of 200 to 600 mm/sec.

In this image forming method, specifically, the toner of the present invention as described above is used to develop, for example, an electrostatic image formed on a photoreceptor to obtain a toner image, and this toner image is then transferred to an image support. Thereafter, the toner image transferred to the image support is fixed to the image support by a fixing process using a heat and pressure fixing method, thereby obtaining a printed matter on which a visible image is formed.

The toner of the present invention can be used in a monochrome image forming method and a full-color image forming method.
In the full-color image forming method, any image forming method can be applied, such as a four-cycle image forming method consisting of four types of color developing devices for yellow, magenta, cyan, and black, and one photosensitive body, or a tandem image forming method in which image forming units having color developing devices and photosensitive bodies for each color are installed, one for each color.

The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these. In the following examples, unless otherwise specified, operations were performed at room temperature (25°C). Furthermore, unless otherwise specified, "%" and "parts" mean "% by mass" and "parts by mass", respectively.

The peak molecular weight of the polymer contained in the binder resin was measured as follows. The measurement results are shown in Table I below.
Using an apparatus "HLC-8220" (manufactured by Tosoh Corporation) and a column "TSKguard column + TSKgel Super HZM-M triple column" (manufactured by Tosoh Corporation), the column temperature was maintained at 40°C, and tetrahydrofuran (THF) was passed as a carrier solvent at a flow rate of 0.2 ml/min. The measurement sample was dissolved in tetrahydrofuran to a concentration of 1 mg/ml under dissolution conditions in which the sample was treated for 5 minutes at room temperature (25°C) using an ultrasonic disperser.
Next, the sample solution was obtained by processing with a membrane filter having a pore size of 0.2 μm, and 10 μl of this sample solution was injected into the device together with the above-mentioned carrier solvent, and detected using a refractive index detector (RI detector), and the molecular weight distribution of the measurement sample was obtained.

[Production of Toner 1]
<Preparation of Binder Resin Particle Dispersion 1>
A surfactant solution prepared by dissolving 8 g of sodium dodecyl sulfate in 3 L of ion-exchanged water was charged into a 5 L stainless steel kettle (SUS kettle) equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introducing device, and the liquid temperature was raised to 80° C. while stirring at a stirring speed of 230 rpm under a nitrogen stream.
To this surfactant solution, an initiator solution prepared by dissolving 10 g of potassium persulfate in 200 g of ion-exchanged water was added, and the temperature was raised to 80° C., after which the following monomer mixture was added dropwise over 100 minutes, and the system was heated and stirred at 80° C. for 2 hours to carry out polymerization, thereby preparing binder resin particle dispersion 1:
- Monomer mixture -
Exemplary compound M1 (see the above exemplary compound, in which R ₁ and R ₂ in the general formula (2) are methyl groups (represented as "Me" in Table I below))
161g
Styrene (St) 411g
n-Butyl acrylate (nBA) 177g
Methacrylic acid (MAA) 40g
Acrylic acid (AA) 16g
n-Octyl-3-mercaptopropionate 5.5g
The volume-based median diameter of the binder resin particles in the obtained binder resin particle dispersion 1 was measured by dynamic light scattering using "Microtrac UPA-150" (manufactured by Nikkiso Co., Ltd.) and was found to be 125 nm.

<Preparation of Colorant Particle Dispersion 1>
Colorant: Carbon black (Mogul (registered trademark) L, manufactured by Cabot Corporation)
10 parts by mass
Anionic surfactant (20% aqueous solution of sodium dodecylbenzenesulfonate)
The above components were mixed and dispersed in an SC mill to obtain colorant particle dispersion 1. The volume-based median diameter of the colorant particles in the dispersion was measured by dynamic light scattering using "Microtrac UPA-150" (manufactured by Nikkiso Co., Ltd.) and was found to be 155 nm.

<Preparation of Release Agent Particle Dispersion 1>
Behenyl behenate 100 parts by weight Sodium dodecyl sulfate 5 parts by weight Ion-exchanged water 240 parts by weight The above components were dispersed in a round stainless steel flask using a homogenizer "Ultra-Turrax (registered trademark) T50" (manufactured by IKA Corporation) for 10 minutes, and then dispersed using a pressure discharge type homogenizer to obtain a release agent particle dispersion 1. The volume-based median diameter of the release agent particles in the dispersion was measured using a laser diffraction type particle size distribution measuring instrument LA-750 (manufactured by Horiba, Ltd.) and was found to be 530 nm.

<Preparation of Toner Base Particle Dispersion 1>
Binder resin particle dispersion 1 237 parts by weight Colorant particle dispersion 1 42 parts by weight Release agent particle dispersion 1 18 parts by weight Polyaluminum chloride 1.8 parts by weight Ion-exchanged water 600 parts by weight The above components were mixed and dispersed in a round stainless steel flask using a homogenizer "Ultra Turrax (registered trademark) T50" (manufactured by IKA Corporation), and then heated to 55° C. in a heating oil bath while stirring the contents of the flask. After maintaining at 55° C. for 30 minutes, it was confirmed that aggregated particles having a volume-based median diameter (D50) of 4.8 μm were generated in the solution.
When the temperature of the heating oil bath was further increased to 56° C. and held for 2 hours, the median diameter (D50) on a volume basis became 5.9 μm.
Thereafter, 1 mol/L of sodium hydroxide was added to the system to adjust the pH of the system to 5.0, and the stainless steel flask was then sealed using a magnetic seal and heated to 98° C. with continued stirring. Stirring was continued for 6 hours to complete fusion (fusion) between the binder resin particles, thereby preparing toner base particle dispersion 1. The volume-based median diameter (D50) of the toner base particles in the dispersion was 6.0 μm.

<Cleaning and drying process>
The toner base particle dispersion 1 was subjected to solid-liquid separation using a basket-type centrifuge "MARKIII Model No. 60x40" (manufactured by Matsumoto Kikai Hanbai Co., Ltd.) to form a wet cake of toner base particles.
The wet cake was washed with ion-exchanged water at 45° C. in the basket centrifuge until the electrical conductivity of the filtrate reached 5 μS/cm, and then transferred to a “Flash Jet Dryer” (manufactured by Seishin Enterprise Co., Ltd.) and dried until the moisture content reached 0.5% by mass, thereby obtaining toner base particles.

<Treatment of Toner Base Particles with External Additives>
To 100 parts by mass of the toner base particles obtained above, 1 part by mass of hydrophobic silica (number average primary particle diameter = 12 nm) and 0.3 parts by mass of hydrophobic titania (number average primary particle diameter = 20 nm) were added, and mixed using a Henschel mixer (registered trademark) to perform external additive treatment, thereby producing toner 1.

[Production of Toners 2 to 22]
Toners 2 to 22 were produced in the same manner as in the production of Toner 1, except that each binder resin particle dispersion was prepared using the combination and addition amount of monomers shown in Table I below, each release agent particle dispersion was prepared using the release agent shown in Table I below, and toner base particles were produced using the binder resin particle dispersion and the release agent particle dispersion so as to have the content shown in Table I below.

The volume-based median diameter of the binder resin particles in each of the binder resin particle dispersions prepared using the combinations and amounts of monomers shown in Table I below was all 125 nm.
Furthermore, the volume-based median diameter of the release agent particles in each release agent particle dispersion liquid prepared using the release agent shown in Table I below was as follows:
Pentaerythritol tetrabehenate: 490 nm
Stearyl stearate: 460 nm
Methyl lignocerate: 430 nm
Hexadecyl palmitate: 450 nm
Methyl triacontanoate: 450 nm
Paraffin (paraffin wax, HNP-51, manufactured by Nippon Seiro Co., Ltd.): 600 nm

The composition of each toner is shown in the following Table I. In the following Table I, St represents styrene, MMA represents methyl methacrylate, nBA represents n-butyl acrylate, iBA represents iso-butyl acrylate, 2EHA represents 2-ethylhexyl acrylate, MAA represents methacrylic acid, and AA represents acrylic acid.
In Table I, the amount of the itaconic acid derivative (first polymerizable monomer) and the amount of the second polymerizable monomer represent the amount added when the total amount of the itaconic acid derivative and the second monomer is taken as 100% by mass. The amount of the release agent represents the amount added when the amount of the polymer composed of the itaconic acid derivative and the second monomer is taken as 100% by mass.

[Preparation of Two-Component Developer]
100 parts by mass of ferrite particles (volume-based median diameter: 50 μm (manufactured by Powder Tech Co., Ltd.)) and 4 parts by mass of methyl methacrylate-cyclohexyl methacrylate copolymer resin (volume-based median diameter of primary particles: 85 nm) were placed in a horizontal stirring blade type high-speed stirring device and mixed for 15 minutes under conditions of a stirring blade peripheral speed of 8 m/s and a temperature of 30° C., and then the temperature was raised to 120° C. and stirring was continued for 4 hours. Thereafter, the mixture was cooled and fragments of the methyl methacrylate-cyclohexyl methacrylate copolymer resin were removed using a 200 mesh sieve to produce a resin-coated carrier.
This resin-coated carrier was mixed with each of the above toners 1 to 22 so that the toner concentration was 7% by mass based on the total mass of the toner and carrier, to prepare two-component developers 1 to 22.

[evaluation]
Using the two-component developers 1 to 22, evaluation was performed on the following evaluation items (1) and (2), and the evaluation results are shown in the following Table II.

(1) Hot offset resistance A commercially available multifunction machine "bizhub PRO (registered trademark) C6500" (manufactured by Konica Minolta, Inc.) was used as an image forming apparatus, and the above-mentioned two-component developer was loaded on this apparatus as a developer. The surface temperature of the fixing heating member in the fixing means of the heat roll fixing method was set to 175°C, and an image was formed using cardboard with a weight of 350 g/ ^m2 as an image support under an environment of normal temperature and normal humidity (temperature 20°C, relative humidity 50% RH), and a solid image with 5 g/ ^m3 of toner fixed thereon was obtained as a visible image. After the solid image was formed, a plain cardboard with a weight of 350 g/ ^m2 on which no image was formed was passed through the fixing device again, and the amount of toner offset to the roller was visually determined. Rank 3 or higher is acceptable.
(Evaluation Criteria)
Rank 5: No offset at all Rank 4: Slight offset occurs in some areas Rank 3: Slight offset occurs Rank 2: Clear offset occurs in some areas Rank 1: Clear offset occurs over the entire surface

(2) Roller Contamination Resistance A commercially available multifunction machine "bizhub PRO C6500" (manufactured by Konica Minolta Business Technologies, Inc.) was used as the image forming apparatus, the above-mentioned two-component developer was loaded into this apparatus as the developer, and 1000 solid images with an image density of 0.8 were printed as visible images. Thereafter, the degree of contamination of the transport roller in the multifunction machine that came into contact with the image surface was visually observed, and a four-level evaluation was performed.
(Evaluation Criteria)
Rank 4: No contamination on the transport roller Rank 3: Faint contamination on parts of the transport roller Rank 2: Faint contamination on the transport roller overall Rank 1: Contamination on the transport roller is clearly visible

As is clear from the results shown in Table II above, it was found that toners 1 to 20 of the present invention, which contain a polymer having a structural unit represented by the general formula (1) and use a fatty acid ester wax as a release agent, exhibit excellent performance in both hot offset resistance and roller contamination resistance.
On the other hand, it was found that toner 21 using paraffin wax instead of fatty acid ester wax and toner 22 using a resin that does not contain a polymer having a structural unit represented by the general formula (1) were unable to satisfy both the hot offset resistance and the roller contamination resistance.

Claims (6)

A toner for developing an electrostatic image, comprising toner base particles containing a binder resin and a release agent,
The binder resin contains a polymer having a structural unit represented by the following general formula (1):
The polymer having a structural unit represented by the general formula (1) is a copolymer of a first polymerizable monomer having a structure represented by the following general formula (2) and a second polymerizable monomer copolymerizable with the first polymerizable monomer,
The release agent contains a fatty acid ester,
The fatty acid ester is at least one of behenyl behenate and pentaerythritol tetrabehenate.
2. A toner for developing electrostatic images.

[In the general formula (1), R ₁ and R ₂ each independently represent any one of a methyl group, an n-propyl group, an iso-butyl group, and a 2-ethylhexyl group.]

[In general formula (2), R ₁ and R ₂ each independently represent a methyl group, an n-propyl group, an iso-butyl group, or a 2-ethylhexyl group.] The toner for developing electrostatic images according to claim 1, characterized in that the content of the structural unit derived from the first polymerizable monomer is within the range of 5 to 40% by mass relative to 100% by mass of the polymer having the structural unit represented by the general formula (1). The toner for developing electrostatic images according to claim 1 or 2, characterized in that the second polymerizable monomer is selected from the group consisting of at least styrenes, acrylic acid esters, and methacrylic acid esters. The toner for developing electrostatic images according to claim 3, characterized in that the second polymerizable monomer is at least one selected from styrene, acrylic acid, n-butyl acrylate, iso-butyl acrylate, 2-ethylhexyl acrylate, methacrylic acid, and methyl methacrylate. The toner for developing electrostatic images according to any one of claims 1 to 4, characterized in that the content of the release agent is within the range of 5 to 20% by mass relative to 100% by mass of the polymer having the structural unit represented by the general formula (1). A method for producing the toner for developing an electrostatic image according to any one of claims 1 to 5, comprising the steps of:
A method for producing a toner for developing an electrostatic image, comprising the steps of: polymerizing a first polymerizable monomer having a structure represented by the general formula (2) to synthesize a polymer having a structural unit represented by the general formula (1) to prepare a binder resin particle dispersion liquid.