JP7713362B2 - Method for producing toner for developing electrostatic images - Google Patents

Description

The present invention relates to a method for producing a toner for developing electrostatic images, which is used to develop latent images formed in electrophotography, electrostatic recording, electrostatic printing, etc.

In recent years, as printers and copiers have become faster, more compact, and have higher image quality, there is a growing need for toner that can meet these demands.

In the past, various studies have been conducted on the manufacturing method of toner in order to design any toner. For example, in Patent Document 1, a method of manufacturing toner by melting and kneading a composition consisting of resin and additives, cooling, solidifying, pulverizing, and classifying the composition, in which a mixed raw material having an additive concentration in the resin (hereinafter referred to as the additive concentration in the first half) of 10 to 50% by weight is continuously supplied from at least one raw material supply port provided within 0.3 L from the inlet side of a kneading extruder having a barrel length L and having extrusion flow properties, and the resin alone or the additive concentration in the resin is continuously supplied from one to five raw material supply ports provided 0.3 L to 0.9 L from the inlet side. The document states that a continuous toner production method characterized by continuously supplying raw material with a concentration of 20% by weight or less and lower than the additive concentration in the first half, setting the ratio of the flow rate of the raw material supplied to the raw material supply port within 0.3L to the raw material supplied to the raw material supply port between 0.3L and 0.9L to 10:1 to 1:5 (weight ratio), and continuously removing the kneaded material from the kneading extruder outlet, makes it possible to obtain a high-quality toner with excellent dispersion of additives in the resin and with little molecular cleavage of the resin.

Patent Document 2 also describes a method for producing toner for developing electrostatic images, which involves compounding and mixing at least a resin and a colorant, kneading the mixture, and then pulverizing and classifying the mixture to obtain a toner. The method is characterized in that fine toner powder is supplied during the kneading process, and it describes how even a large amount of fine toner powder can be recycled into the production process with good productivity, and how the recycled fine powder toner has little performance degradation, good fixing performance, stable image and image quality characteristics even during continuous use, and excellent durability.

Japanese Patent Application Publication No. 3-149567 Japanese Patent Application Publication No. 8-95296

However, the toners described in Patent Documents 1 and 2 still do not have sufficient low-temperature fixability and durability, and there is room for improvement.

The present invention relates to a method for producing a toner for developing electrostatic images that has excellent low-temperature fixing properties and durability.

The present invention relates to a method for producing a toner for developing electrostatic images, which includes a step of melt-kneading a mixture of raw materials containing an amorphous resin, a crystalline polyester resin, and a release agent using a twin-screw extruder, and which has one or more raw material supply ports at a position f1 less than 0.3 L from the inlet end of the barrel and at a position f2 between 0.3 L and 0.9 L, where L denotes the length of the barrel of the twin-screw extruder, and which supplies a raw material containing an amorphous resin from the raw material supply port F1 at f1, and supplies a raw material containing a crystalline polyester resin and a release agent from the raw material supply port F2 at f2.

The method of the present invention allows for the production of a toner for developing electrostatic images that has excellent low-temperature fixing properties and durability.

The present invention is a method for producing a toner for developing electrostatic images, which includes a step of melt-kneading a mixture of raw materials containing an amorphous resin, a crystalline polyester resin, and a release agent using a twin-screw extruder. It has been discovered and completed that a toner for developing electrostatic images (hereinafter simply referred to as toner) with excellent low-temperature fixing properties and durability can be obtained by supplying the amorphous resin, the crystalline polyester resin, and the release agent to the twin-screw extruder from respective predetermined positions during melt-kneading of the mixture of raw materials using the twin-screw extruder.

Although the details of why the present invention exhibits its effects are unclear, it is presumed that the effects are due to the following mechanism.
Although crystalline polyester resins have excellent low-temperature fixing properties, when they are melt-kneaded using a twin-screw extruder, which has excellent productivity and versatility, they tend to separate from the amorphous binder resin, which is the main component of the toner, and form coarse domains together with the release agent. As the amount added increases, there is an issue that durability in high-temperature and high-humidity environments tends to decrease.
For example, in Patent Document 1, it is known that in the melt-kneading process of a kneading extruder, the material to be dispersed, such as a pigment, is kneaded for a long time to improve the dispersion state, maintain a suitable dispersion diameter, and knead for a short time to avoid molecular cutting of the resin, so that the raw material supply port is divided. However, the present inventors have found that this is not the case in the dispersion of crystalline polyester resin. In the melt-kneading process of a twin-screw extruder, the raw material mixture is heated by friction with the barrel, and melt kneading proceeds. However, when a crystalline polyester resin is added in addition to a release agent, the release agent and the crystalline polyester resin melt in the barrel before the amorphous binder resin and become low in viscosity, so that the friction with the barrel required for the amorphous binder resin, which is the main component, to melt is insufficient. As a result, it is necessary to disperse the crystalline polyester resin and the release agent in a state where the amorphous binder resin, which is the main component and the dispersion medium, is not sufficiently melted, and the crystalline polyester resin and the release agent are dispersed at a higher concentration than designed. As a result, sufficient kneading strength is not imparted, and coarse domains of the crystalline polyester resin and the release agent are formed.
In contrast, in the present invention, a raw material containing an amorphous resin is supplied from a raw material supply port F1 close to the inlet end of the barrel of a twin-screw extruder, and a raw material containing a crystalline polyester resin and a release agent is supplied from a raw material supply port F2 farther from the inlet end of the barrel than the raw material supply port F1, and melt-kneaded, thereby ensuring sufficient friction between the amorphous binder resin and the barrel. This makes it possible to sufficiently melt the amorphous binder resin that serves as a dispersion medium, create a good dispersion state of the crystalline polyester resin and the release agent, and obtain a toner that can achieve both low-temperature fixability and durability under high-temperature and high-humidity environments.

Examples of amorphous resins include amorphous polyester resins, vinyl resins such as styrene resins, epoxy resins, polycarbonate resins, polyurethane resins, and composite resins having two or more of these resins. Among these, polyester resins are preferred from the viewpoint of low-temperature fixability. Examples of polyester resins include polyester resins and composite resins having polyester resins and styrene resins.

The crystallinity of a resin is represented by a crystallinity index defined as the ratio of the softening point to the maximum endothermic peak temperature measured by a differential scanning calorimeter, i.e., the value of [softening point/maximum endothermic peak temperature]. A crystalline resin is a resin having a crystallinity index of 0.6 or more, preferably 0.7 or more, more preferably 0.9 or more, and 1.4 or less, preferably 1.2 or less, more preferably 1.1 or less.
On the other hand, an amorphous resin is a resin in which no endothermic peak is observed, or if an endothermic peak is observed, the crystallinity index is greater than 1.4, preferably greater than 1.5, more preferably 1.6 or more, or less than 0.6, preferably 0.5 or less.
The crystallinity of the resin can be adjusted by the type and ratio of the raw material monomers, and the production conditions (e.g., reaction temperature, reaction time, cooling rate), etc. The maximum endothermic peak temperature refers to the temperature of the peak with the largest peak area among the observed endothermic peaks. In the case of a crystalline resin, the maximum endothermic peak temperature is the melting point.

As the amorphous polyester resin, a polycondensation product of an alcohol component and a carboxylic acid component, including an alkylene oxide adduct of bisphenol A, is preferred.

The alkylene oxide adduct of bisphenol A is represented by the formula (I):

(In the formula, OR and RO are oxyalkylene groups, R is an ethylene group and/or a propylene group, x and y are the average number of moles of alkylene oxide added, each of which is a positive number, and the sum of x and y is 1 or more, preferably 1.5 or more, and 16 or less, preferably 8 or less, more preferably 6 or less, and even more preferably 4 or less.)
Preferred is a compound represented by the following formula:

From the viewpoint of low-temperature fixability, the content of the alkylene oxide adduct of bisphenol A in the alcohol component is preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, even more preferably 95 mol% or more, and even more preferably 100 mol%.

Other alcohol components include aliphatic diols, bisphenol A, hydrogenated bisphenol A, sorbitol, pentaerythritol, glycerin, trimethylolpropane, and other trihydric or higher alcohols.

Carboxylic acid components include aliphatic dicarboxylic acid compounds, aromatic dicarboxylic acid compounds, trivalent or higher carboxylic acid compounds, etc.

Aliphatic dicarboxylic acid compounds include fumaric acid, maleic acid, succinic acid, succinic acid derivatives substituted with hydrocarbon groups, glutaric acid, adipic acid, sebacic acid, anhydrides of these acids, and alkyl esters of these acids having 1 to 3 carbon atoms.

Examples of aromatic dicarboxylic acid compounds include phthalic acid, isophthalic acid, terephthalic acid, anhydrides of these acids, and alkyl esters of these acids having 1 to 3 carbon atoms.

Examples of trivalent or higher carboxylic acid compounds include trimellitic acid, pyromellitic acid, anhydrides of these acids, and alkyl esters of these acids having 1 to 3 carbon atoms.

In addition, the alcohol component may contain a monohydric alcohol, and the carboxylic acid component may contain a monovalent carboxylic acid compound, as appropriate.

From the viewpoint of adjusting the softening point of the polyester resin, the equivalent ratio of the carboxylic acid component to the alcohol component (COOH group/OH group) is preferably 0.6 or more, more preferably 0.7 or more, even more preferably 0.75 or more, and is preferably 1.2 or less, more preferably 1.16 or less.

The amorphous polyester resin can be produced, for example, by polycondensing an alcohol component and a carboxylic acid component in an inert gas atmosphere, preferably in the presence of an esterification catalyst, and, if necessary, in the presence of an esterification promoter, a polymerization inhibitor, etc., at a temperature of preferably 160°C or higher, more preferably 200°C or higher, and preferably 250°C or lower, more preferably 240°C or lower.

Examples of the esterification catalyst include tin compounds such as dibutyltin oxide and tin(II) 2-ethylhexanoate, and titanium compounds such as titanium diisopropylate bistriethanolamine. The amount of the esterification catalyst used is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, and preferably 1.5 parts by mass or less, and more preferably 1 part by mass or less, relative to 100 parts by mass of the total amount of the alcohol component and the carboxylic acid component. Examples of the esterification promoter include gallic acid. The amount of the esterification promoter used is preferably 0.001 parts by mass or more, more preferably 0.01 parts by mass or more, and preferably 0.5 parts by mass or less, and more preferably 0.1 parts by mass or less, relative to 100 parts by mass of the total amount of the alcohol component and the carboxylic acid component. Examples of the polymerization inhibitor include t-butylcatechol. The amount of the polymerization inhibitor used is preferably 0.001 parts by mass or more, more preferably 0.01 parts by mass or more, and preferably 0.5 parts by mass or less, more preferably 0.1 parts by mass or less, per 100 parts by mass of the total amount of the alcohol component and the carboxylic acid component.

In the present invention, the polyester resin may be modified to such an extent that its properties are not substantially impaired. Examples of modified polyester resins include polyester resins grafted or blocked with phenol, urethane, epoxy, or the like, by the methods described in JP-A-11-133668, JP-A-10-239903, JP-A-8-20636, and the like. Among the modified polyester resins, urethane-modified polyester resins in which polyester resins are urethane-extended with a polyisocyanate compound are preferred.

In the amorphous composite resin having the polyester resin and the styrene-based resin, the polyester resin is the same as the amorphous polyester resin, and the styrene-based resin is an addition polymer of raw material monomers containing at least styrene or a styrene derivative such as α-methylstyrene or vinyltoluene (hereinafter, styrene and styrene derivatives are collectively referred to as "styrene compounds").

The content of the styrene compound, preferably styrene, in the raw material monomer of the styrene-based resin is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more, from the viewpoint of storage stability, and is preferably 95% by mass or less, more preferably 93% by mass or less, and even more preferably 90% by mass or less, from the viewpoint of low-temperature fixability.

The styrene-based resin may also contain, as a raw material monomer, an alkyl (meth)acrylate ester having an alkyl group with 7 or more carbon atoms. Examples of alkyl (meth)acrylate esters include 2-ethylhexyl (meth)acrylate, (iso)octyl (meth)acrylate, (iso)decyl (meth)acrylate, and (iso)stearyl (meth)acrylate. It is preferable to use one or more of these. In this specification, "(iso)" means that both the case where this group is present and the case where it is not present are included, and when these groups are not present, it indicates that it is normal. Furthermore, "(meth)acrylic acid" refers to acrylic acid, methacrylic acid, or both.

The number of carbon atoms in the alkyl group in the (meth)acrylic acid alkyl ester as a raw material monomer for the styrene-based resin is preferably 7 or more, more preferably 8 or more, from the viewpoint of improving the low-temperature fixing property of the toner, and is preferably 12 or less, more preferably 10 or less. The number of carbon atoms in the alkyl ester refers to the number of carbon atoms derived from the alcohol component that constitutes the ester.

The raw material monomers for styrene-based resins may include raw material monomers other than styrene compounds and (meth)acrylic acid alkyl esters, for example, ethylenically unsaturated monoolefins such as ethylene and propylene; diolefins such as butadiene; halovinyls such as vinyl chloride; vinyl esters such as vinyl acetate and vinyl propionate; ethylenically monocarboxylic acid esters such as dimethylaminoethyl (meth)acrylate; vinyl ethers such as methyl vinyl ether; vinylidene halides such as vinylidene chloride; and N-vinyl compounds such as N-vinylpyrrolidone.

The addition polymerization reaction of the raw material monomers for styrene-based resins can be carried out in the presence of a polymerization initiator such as dibutyl peroxide or dicumyl peroxide, a polymerization inhibitor, a crosslinking agent, etc., in the presence of an organic solvent or without a solvent, by a conventional method, and the temperature conditions are preferably 110°C or higher, more preferably 140°C or higher, and preferably 200°C or lower, more preferably 170°C or lower.

When an organic solvent is used in the addition polymerization reaction, xylene, toluene, methyl ethyl ketone, acetone, etc. can be used. The amount of the organic solvent used is preferably 10 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the raw material monomer of the styrene-based resin.

The amorphous composite resin is preferably a resin in which a polyester resin and a styrene-based resin are bonded together, and more preferably a resin in which the resin is chemically bonded together via a bireactive monomer that can react with both the raw material monomers of the polyester resin and the raw material monomers of the styrene-based resin.

The bireactive monomer is preferably a compound having at least one functional group selected from the group consisting of hydroxyl group, carboxyl group, epoxy group, primary amino group, and secondary amino group, preferably a hydroxyl group and/or a carboxyl group, more preferably a carboxyl group, and an ethylenically unsaturated bond in the molecule, more preferably at least one selected from the group consisting of acrylic acid, methacrylic acid, fumaric acid, maleic acid, and maleic anhydride, and from the viewpoint of reactivity of polycondensation reaction and addition polymerization reaction, at least one selected from the group consisting of acrylic acid, methacrylic acid, and fumaric acid is even more preferable. However, when used together with a polymerization inhibitor, a polyvalent carboxylic acid compound having an ethylenically unsaturated bond such as fumaric acid functions as a raw material monomer for polyester resin. In this case, fumaric acid, etc. is not a bireactive monomer, but a raw material monomer for polyester resin.

The amount of the bireactive monomer used is preferably 1 mol or more, and more preferably 2 mol or more, relative to 100 mol of the total of the alcohol components of the polyester resin, from the viewpoint of charging stability under high temperature and high humidity conditions, and is preferably 30 mol or less, more preferably 20 mol or less, and even more preferably 10 mol or less, from the viewpoint of increasing the dispersibility of the styrene resin and the polyester resin and improving the transferability of the toner.
The amount of the bireactive monomer used is preferably 1 part by mass or more, more preferably 2 parts by mass or more, relative to 100 parts by mass of the raw material monomers of the styrene resin in terms of charging stability under high temperature and high humidity conditions, and is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less, in terms of increasing the dispersibility of the styrene resin and the polyester resin and improving the transferability of the toner. Here, the polymerization initiator is included in the total amount of the raw material monomers of the styrene resin.

The amorphous composite resin can be produced, for example, by a method including step (A) of a polycondensation reaction with raw material monomers of a polyester resin and step (B) of an addition polymerization reaction with raw material monomers of a styrene-based resin. (i) Step (B) may be carried out after step (A), (ii) Step (A) may be carried out after step (B), or (iii) Step (A) and Step (B) may be carried out simultaneously. Note that it is preferable to use a bireactive monomer together with the raw material monomers of a styrene-based resin.

In the method (i), after step (B), the reaction temperature may be increased again, and if necessary, a raw material monomer of the amorphous polyester resin having a valence of three or more and serving as a crosslinking agent may be added to the reaction system to further promote the polycondensation reaction of step (A) or the reaction with the bireactive monomer.
Alternatively, instead of carrying out the polycondensation reaction in step (A), a polycondensation resin that has been polymerized in advance may be used. When steps (A) and (B) are carried out in parallel, a mixture containing raw material monomers for a styrene resin may be dropped into a mixture containing raw material monomers for a polyester resin to cause the reaction.

It is preferable that steps (A) and (B) are carried out in the same container.

The mass ratio of polyester resin to styrene resin in the amorphous composite resin (polyester resin/styrene resin) is preferably 98/2 or less, more preferably 95/5 or less, and even more preferably 90/10 or less from the viewpoint of charging stability under high temperature and high humidity, and is preferably 60/40 or more, more preferably 70/30 or more, and even more preferably 75/25 or more from the viewpoint of low temperature fixability. In the above calculation, the mass of polyester resin is the amount obtained by subtracting the amount of reaction water dehydrated by the polycondensation reaction (calculated value) from the mass of the raw material monomer of the polyester resin used, and the amount of bireactive monomer is included in the amount of raw material monomer of the polyester resin. The amount of styrene resin is the total amount of raw material monomer of the styrene resin.

From the viewpoint of storage stability, the softening point of the amorphous resin is preferably 90°C or higher, more preferably 100°C or higher, and from the viewpoint of low-temperature fixability, it is preferably 160°C or lower, more preferably 140°C or lower.

From the viewpoint of low-temperature fixing property and fixing width, the amorphous resin may be made of resins with different softening points. The difference in softening points between the two types of resins is preferably 10°C or more, more preferably 20°C or more, even more preferably 30°C or more, and is preferably 60°C or less, more preferably 50°C or less.

The softening point of the amorphous resin with the higher softening point (resin AH) is preferably 110°C or higher, more preferably 120°C or higher, and even more preferably 140°C or higher, from the viewpoint of fixing width, and is preferably 180°C or lower, and more preferably 160°C or lower, from the viewpoint of low-temperature fixing ability.

The softening point of the amorphous resin with the lower softening point (resin AL) is preferably 70°C or higher, more preferably 90°C or higher, and even more preferably 100°C or higher, from the viewpoint of storage stability, and is preferably 130°C or lower, more preferably 125°C or lower, and even more preferably 120°C or lower, from the viewpoint of low-temperature fixability.

The mass ratio of resin AH to resin AL (resin AH/resin AL) is preferably 10/90 or more, more preferably 20/80 or more, even more preferably 30/70 or more, and is preferably 90/10 or less, more preferably 80/20 or less, even more preferably 70/30 or less.

From the viewpoint of storage stability, the glass transition temperature of the amorphous resin is preferably 40°C or higher, more preferably 50°C or higher, and from the viewpoint of low-temperature fixability, it is preferably 80°C or lower, more preferably 70°C or lower, and even more preferably 65°C or lower.

From the viewpoint of low-temperature fixability, the acid value of the amorphous resin is preferably 1 mgKOH/g or more, more preferably 3 mgKOH/g or more, and from the viewpoint of moisture absorption, it is preferably 20 mgKOH/g or less, more preferably 15 mgKOH/g or less.

The content of the amorphous resin in the total amount of the amorphous resin and the crystalline polyester resin is preferably 55% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and even more preferably 80% by mass or more, from the viewpoint of transfer efficiency, and is preferably 99% by mass or less, more preferably 97% by mass or less, and even more preferably 96% by mass or less, from the viewpoint of low-temperature fixability.

Examples of crystalline polyester resins include crystalline polyester resins and crystalline composite resins having polyester resins and styrene resins.

As a crystalline polyester resin, for example, a polycondensation product of an alcohol component containing an aliphatic diol and a carboxylic acid component containing an aliphatic dicarboxylic acid compound is preferable.

Examples of aliphatic diols include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, neopentyl glycol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, etc., and one or more of them may be used in combination.

From the viewpoint of low-temperature fixing ability, the aliphatic diol is preferably an α,ω-aliphatic diol having a hydroxyl group at the end of the carbon chain, and more preferably an α,ω-straight-chain alkane diol.

The carbon number of the aliphatic diol is preferably 6 or more, more preferably 10 or more, from the viewpoint of dispersibility of the colorant, and is preferably 14 or less, more preferably 12 or less, from the viewpoint of storage stability.

The content of the aliphatic diol in the alcohol component is preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, and even more preferably 95 mol% or more.

Other alcohol components include aromatic diols such as alkylene oxide adducts of bisphenol A, and trihydric or higher alcohols such as sorbitol, pentaerythritol, glycerin, and trimethylolpropane.

Aliphatic dicarboxylic acid compounds include succinic acid (carbon number: 4), fumaric acid (carbon number: 4), adipic acid (carbon number: 6), suberic acid (carbon number: 8), azelaic acid (carbon number: 9), sebacic acid (carbon number: 10), dodecanedioic acid (carbon number: 12), tetradecanedioic acid (carbon number: 14), succinic acid having an alkyl or alkenyl group on the side chain, anhydrides of these acids, and alkyl esters of these acids having 1 to 3 carbon atoms.

The carbon number of the aliphatic dicarboxylic acid compound is preferably 4 or more, more preferably 8 or more, from the viewpoint of low-temperature fixability, and is preferably 14 or less, more preferably 12 or less, from the viewpoint of storage stability.

The content of the aliphatic dicarboxylic acid compound in the carboxylic acid component is preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, and even more preferably 95 mol% or more.

Other carboxylic acid components include aromatic dicarboxylic acid compounds, aliphatic dicarboxylic acid compounds, trivalent or higher carboxylic acid compounds, etc.

In addition, the alcohol component may contain a monohydric alcohol, and the carboxylic acid component may contain a monovalent carboxylic acid compound, as appropriate.

The equivalent ratio of the carboxylic acid component to the alcohol component (COOH group/OH group) is preferably 0.8 or more, more preferably 0.9 or more, from the viewpoint of storage stability, and is preferably 1.2 or less, more preferably 1.1 or less, from the viewpoint of low-temperature fixability.

The polycondensation reaction conditions of the alcohol component and the carboxylic acid component of the crystalline polyester resin are the same as those of the amorphous polyester resin, except for the preferred reaction temperature. The reaction temperature is preferably 120°C or higher, more preferably 180°C or higher, and preferably 230°C or lower, more preferably 220°C or lower.

In the crystalline composite resin having the polyester resin and the styrene-based resin, the polyester resin is the same as the crystalline polyester resin, and the styrene-based resin is an addition polymer of raw material monomers containing at least styrene or a styrene derivative such as α-methylstyrene or vinyltoluene (hereinafter, styrene and styrene derivatives are collectively referred to as "styrene compounds").

The content of the styrene compound, preferably styrene, in the raw material monomer of the styrene-based resin is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 100% by mass, from the viewpoint of storage stability.

The raw material monomers for styrene-based resins may include raw material monomers other than styrene compounds, such as (meth)acrylic acid alkyl esters, ethylenically unsaturated monoolefins such as ethylene and propylene; diolefins such as butadiene; halovinyls such as vinyl chloride; vinyl esters such as vinyl acetate and vinyl propionate; ethylenic monocarboxylates such as dimethylaminoethyl (meth)acrylate; vinyl ethers such as methyl vinyl ether; vinylidene halides such as vinylidene chloride; and N-vinyl compounds such as N-vinylpyrrolidone.

The addition polymerization reaction of the raw material monomers for styrene-based resins can be carried out in the presence of a polymerization initiator such as dibutyl peroxide or dicumyl peroxide, a polymerization inhibitor, a crosslinking agent, etc., in the presence of an organic solvent or without a solvent, by a conventional method, and the temperature conditions are preferably 110°C or higher, more preferably 140°C or higher, and preferably 200°C or lower, more preferably 170°C or lower.

When an organic solvent is used in the addition polymerization reaction, xylene, toluene, methyl ethyl ketone, acetone, etc. can be used. The amount of the organic solvent used is preferably 10 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the raw material monomer of the styrene-based resin.

The crystalline composite resin is preferably a resin in which a polyester resin and a styrene-based resin are bonded together, and more preferably a resin in which the resin is chemically bonded together via a bireactive monomer that can react with both the raw material monomers of the polyester resin and the raw material monomers of the styrene-based resin.

The manufacturing methods for the bireactive monomer and the crystalline composite resin are the same as those for the composite resin described above for the amorphous resin.

The mass ratio of polyester resin to styrene resin in the crystalline composite resin (polyester resin/styrene resin) is preferably 98/2 or less, more preferably 95/5 or less, and even more preferably 90/10 or less, from the viewpoint of charging stability under high temperature and high humidity, and is preferably 60/40 or more, more preferably 70/30 or more, and even more preferably 75/25 or more, from the viewpoint of low temperature fixability. In the above calculation, the mass of polyester resin is the amount obtained by subtracting the amount of reaction water dehydrated by the polycondensation reaction (calculated value) from the mass of the raw material monomer of the polyester resin used, and the amount of bireactive monomer is included in the amount of raw material monomer of the polyester resin. The amount of styrene resin is the total amount of raw material monomer of the styrene resin.

From the viewpoint of storage stability, the softening point of the crystalline polyester resin is preferably 50°C or higher, more preferably 65°C or higher, and even more preferably 70°C or higher, and from the viewpoint of low-temperature fixability, it is preferably 120°C or lower, and more preferably 110°C or lower.

The melting point of the crystalline polyester resin is preferably 60°C or higher, more preferably 70°C or higher, from the viewpoint of storage stability, and is preferably 130°C or lower, more preferably 120°C or lower, from the viewpoint of low-temperature fixability.

The content of the crystalline polyester resin in the total amount of the amorphous resin and the crystalline polyester resin is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 4% by mass or more, from the viewpoint of low-temperature fixability, and is preferably 45% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and even more preferably 20% by mass or less, from the viewpoint of transfer efficiency.

The mass ratio of the amorphous resin to the crystalline polyester resin (amorphous resin/crystalline polyester resin) is preferably 60/40 or more, more preferably 65/35 or more, and even more preferably 70/30 or more, from the viewpoint of low-temperature fixability, and is preferably 99/1 or less, more preferably 97/3 or less, and even more preferably 95/5 or less, from the viewpoint of transfer efficiency.

In the toner, amorphous resin and crystalline polyester resin are contained as binder resins.

The total content of the amorphous resin and the crystalline polyester resin in the binder resin is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 100% by mass.

The content of the binder resin in the toner is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and is preferably less than 100% by mass, more preferably 98% by mass or less, even more preferably 95% by mass or less.

Examples of release agents include hydrocarbon waxes such as polypropylene wax, polyethylene wax, polypropylene-polyethylene copolymer wax, microcrystalline wax, paraffin wax, and Fischer-Tropsch wax, and oxides thereof; ester waxes such as carnauba wax, montan wax, and deacidified waxes thereof, and fatty acid ester wax; fatty acid amides, fatty acids, higher alcohols, and fatty acid metal salts; and the like, which can be used alone or in combination of two or more.

From the viewpoint of transferability, the melting point of the release agent is preferably 60°C or higher, more preferably 70°C or higher, and from the viewpoint of low-temperature fixability, it is preferably 160°C or lower, more preferably 140°C or lower, even more preferably 120°C or lower, and even more preferably 100°C or lower.

The content of the release agent is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 2 parts by mass or more, relative to 100 parts by mass of the binder resin, from the viewpoints of the low-temperature fixing property and transfer property of the toner and the dispersibility in the binder resin, and is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, even more preferably 7 parts by mass or less, and even more preferably 4 parts by mass or less.

The total amount of the crystalline polyester resin and the release agent is, from the viewpoint of low-temperature fixability, preferably 5 parts by mass or more, more preferably 7 parts by mass or more, and even more preferably 9 parts by mass or more, and is preferably 40 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less, per 100 parts by mass of the amorphous resin.

Toner raw materials may include additives such as colorants, charge control agents, magnetic powders, flow improvers, conductivity adjusters, reinforcing fillers such as fibrous substances, antioxidants, and cleaning improvers, in addition to the binder resins, amorphous resins and crystalline polyester resins, and release agents.

As colorants, dyes, pigments, magnetic materials, etc. used as toner colorants can be used. Examples include carbon black, phthalocyanine blue, permanent brown FG, brilliant fast scarlet, pigment red 122, pigment green B, rhodamine B base, solvent red 49, solvent red 146, solvent blue 35, quinacridone, carmine 6B, isoindoline, disazo yellow, etc. In the present invention, the toner may be either a black toner or a color toner.

From the viewpoint of improving the image density and low-temperature fixability of the toner, the content of the colorant is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and preferably 40 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less, per 100 parts by mass of the binder resin.

The charge control agent is not particularly limited, and may contain either a positively charged charge control agent or a negatively charged charge control agent.

Positively charged charge control agents include nigrosine dyes such as "Nigrosine Base EX", "Oil Black BS", "Oil Black SO", "Bontron N-01", "Bontron N-04", "Bontron N-07", "Bontron N-09", and "Bontron N-11" (all manufactured by Orient Chemical Industries Co., Ltd.); triphenylmethane dyes containing a tertiary amine as a side chain; quaternary ammonium salt compounds such as "Bontron P-51" (manufactured by Orient Chemical Industries Co., Ltd.), cetyltrimethylammonium bromide, and "COPY CHARGE PX VP435 (Clariant), etc.; polyamine resins, such as AFP-B (Orient Chemical Industries, Ltd.); imidazole derivatives, such as PLZ-2001 and PLZ-8001 (both manufactured by Shikoku Chemical Industries, Ltd.); styrene-acrylic resins, such as FCA-701PT and FCA-201-PS (Fujikura Chemical Industries, Ltd.), etc.

Examples of negatively chargeable charge control agents include metal-containing azo dyes, such as "Varifast Black 3804", "Bontron S-31", "Bontron S-32", "Bontron S-34", and "Bontron S-36" (all manufactured by Orient Chemical Industry Co., Ltd.), "Aizen Spiron Black TRH", and "T-77" (manufactured by Hodogaya Chemical Co., Ltd.); metal compounds of benzilic acid compounds, such as "LR-147" and "LR-297" (both manufactured by Nippon Carlit Co., Ltd.); metal compounds of salicylic acid compounds, such as "Bontron E-81", "Bontron E-84", "Bontron E-88", and "Bontron E-304" (all manufactured by Orient Chemical Industry Co., Ltd.), and "TN-105" (manufactured by Hodogaya Chemical Co., Ltd.); copper phthalocyanine dyes; and quaternary ammonium salts, such as "COPY CHARGE NX VP434 (Clariant), nitroimidazole derivatives, etc.; organometallic compounds, etc.

From the viewpoint of the charge stability of the toner, the content of the charge control agent is preferably 0.01 parts by mass or more, more preferably 0.2 parts by mass or more, and preferably 10 parts by mass or less, more preferably 5 parts by mass or less, even more preferably 3 parts by mass or less, and even more preferably 2 parts by mass or less, per 100 parts by mass of the binder resin.

In the present invention, the amorphous resin, the crystalline polyester resin, the release agent, and, if necessary, additives such as a colorant and a charge control agent are subjected to a process of melt kneading using a twin-screw kneader.

A twin-screw kneader is a kneader that kneads and extrudes the supplied raw materials in a cylinder (barrel) by rotating two screw shafts, and then discharges them. The twin-screw kneader used in the present invention has two or more raw material supply ports. When the length of the barrel of the twin-screw extruder is L, the kneader has one or more raw material supply ports at a position f1 that is less than 0.3 L from the inlet end of the barrel, and at a position f2 that is 0.3 L to 0.9 L. There is no particular limit to the number of raw material supply ports, but the standard specification for a twin-screw kneader is one raw material supply port. Considering the cost of adding raw material supply ports and the corresponding effects, it is preferable to have two or less ports at each of f1 and f2.

f1 is preferably 0.01 L or more, more preferably 0.02 L or more, even more preferably 0.03 L or more, and is preferably 0.3 L or less, more preferably 0.2 L or less, even more preferably 0.1 L or less.

f2 is preferably 0.3 L or more, more preferably 0.35 L or more, even more preferably 0.4 L or more, and is preferably 0.9 L or less, more preferably 0.8 L or less, even more preferably 0.7 L or less.

The distance between raw material supply port F1 at f1 and raw material supply port F2 at f2 is preferably 0.1 L or more, more preferably 0.2 L or more, even more preferably 0.3 L or more, and preferably 0.9 L or less, more preferably 0.7 L or less, even more preferably 0.5 L or less. When there are multiple raw material supply ports F1 and F2, it is preferable that the distance between the closest raw material supply ports F1 and F2 is within the above range.

Raw material containing amorphous resin is supplied from raw material supply port F1 of f1.

The amount of amorphous resin supplied from raw material supply port F1 is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 100% by mass of the amorphous resin contained in the toner. Here, when raw material supply port F1 has two or more raw material supply ports, the amount of amorphous resin supplied from the raw material supply port F1 means the total amount of amorphous resin supplied from those raw material supply ports.

The content of amorphous resin in the raw material supplied from raw material supply port F1 is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and is 100% by mass or less, preferably 98% by mass or less, more preferably 96% by mass or less.

Raw materials containing crystalline polyester resin and release agent are supplied from raw material supply port F2.

The crystalline polyester resin supplied from the raw material supply port F2 is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 100% by mass of the crystalline polyester resin contained in the toner. Here, when the raw material supply port F2 has two or more raw material supply ports, the amount of the crystalline polyester resin supplied from the raw material supply port F2 means the total amount of the crystalline polyester resin supplied from those raw material supply ports.

The amount of release agent supplied from raw material supply port F2 is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 100% by mass of the release agent contained in the toner. Here, when raw material supply port F2 has two or more raw material supply ports, the amount of release agent supplied from the raw material supply port F2 means the total amount of release agent supplied from those raw material supply ports.

Additives such as colorants and charge control agents may be supplied from either the raw material supply port F1 or F2, or may be supplied in portions, but from the viewpoint of improving dispersibility, it is preferable to supply them from the raw material supply port F1.

The total amount of amorphous resin and crystalline polyester resin supplied from raw material supply port F2 is preferably less than 50% by mass, more preferably 40% by mass or less, even more preferably 30% by mass or less, even more preferably 15% by mass or less, and is preferably 3% by mass or more, more preferably 5% by mass or more, even more preferably 7% by mass or more of the total amount of amorphous resin and crystalline polyester resin contained in the toner.

It is preferable that the raw materials to be supplied to each raw material supply port are mixed in advance using a mixer such as a Henschel mixer or ball mill before being supplied.

The set temperature of the barrel is preferably 70°C or higher, more preferably 80°C or higher, and even more preferably 90°C or higher, from the viewpoint of fixing width, and is preferably 160°C or lower, more preferably 150°C or lower, and even more preferably 140°C or lower, from the viewpoint of durability.

Twin-screw extruders are available in co-rotating and counter-rotating types depending on the direction of rotation of the screw shafts, but in the present invention, the co-rotating type is preferred from the viewpoint of ensuring mixing strength and material dispersion.

After melt kneading using a twin-screw extruder, it is preferable to appropriately cool the kneaded material until it reaches a pulverizable hardness, and then, if necessary, perform a pulverization process and a classification process to obtain toner particles. Here, cooling refers to cooling the kneaded material to a temperature between 0°C and 50°C, or to cooling below the glass transition temperature of the binder resin in the kneaded material.

In the grinding process, the kneaded material may be ground to the desired particle size all at once or in stages, but from the viewpoint of efficient and more uniform grinding, it is preferable to carry out the grinding in two stages: coarse grinding and fine grinding.

Mills used for coarse grinding include hammer mills, cutter mills, atomizers, and rotoplexes.

In coarse pulverization, it is preferable to pulverize until the maximum diameter is 3 mm or less. For example, pulverized material with a maximum diameter of 3 mm or less can be obtained by coarsely pulverizing the kneaded material until the particle size is about 0.05 mm or more and 3 mm or less, and then passing the kneaded material through a sieve with 3 mm openings.

Mills used for fine grinding include jet mills such as fluidized bed jet mills and collision plate jet mills, mechanical mills, etc.

It is preferable to adjust the degree of pulverization appropriately depending on the particle size of the desired toner particles.

Classifiers used in the classification step include airflow classifiers, inertial classifiers, sieve classifiers, etc. During the classification step, the pulverized material that is removed due to insufficient pulverization may be subjected to the pulverization step again, and the pulverization step and classification step may be repeated as necessary.

In the present invention, it is preferable to further include an external addition step in which the obtained toner particles are mixed with an external additive. A mixer such as a Henschel mixer can be used to mix the toner particles with the external additive.

External additives include inorganic fine particles such as silica, alumina, titania, zirconia, tin oxide, and zinc oxide, and organic fine particles such as resin particles such as melamine-based resin fine particles and polytetrafluoroethylene resin fine particles, and two or more types may be used in combination. Among these, silica is preferred, and from the viewpoint of the transferability of the toner, hydrophobic silica that has been hydrophobized is more preferred.

Hydrophobic treatment agents for hydrophobizing the surface of silica particles include hexamethyldisilazane (HMDS), dimethyldichlorosilane (DMDS), cyclic silazane, silicone oil, aminosilane, octyltriethoxysilane (OTES), methyltriethoxysilane, etc.

From the viewpoint of the chargeability, fluidity, and transferability of the toner, the average particle diameter of the external additive is preferably 5 nm or more, more preferably 10 nm or more, and even more preferably 15 nm or more, and is preferably 250 nm or less, more preferably 200 nm or less, and even more preferably 90 nm or less.

From the viewpoint of the chargeability, fluidity, and transferability of the toner, the content of the external additive is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 0.3 parts by mass or more, per 100 parts by mass of the toner particles before treatment with the external additive, and is preferably 5 parts by mass or less, and more preferably 3 parts by mass or less.

The volume median particle diameter ( _D50 ) of the toner obtained by the method of the present invention is preferably 3 μm or more, more preferably 4 μm or more, and preferably 15 μm or less, more preferably 10 μm or less. In this specification, the volume median particle diameter ( _D50 ) means the particle diameter at which the cumulative volume frequency calculated by volume fraction is 50% calculated from the smallest particle diameter. In addition, when the toner is treated with an external additive, the volume median particle diameter of the toner particles before treatment with the external additive is taken as the volume median particle diameter of the toner.

The toner obtained by the method of the present invention can be used as it is as a single-component developing toner, or mixed with a carrier as a two-component developing toner, in image forming devices using a single-component developing method or a two-component developing method, respectively.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. The physical properties of the resins and the like can be measured by the following methods.

[Softening point of resin]
Using a flow tester "CFT-500D" (Shimadzu Corporation), 1g of sample is heated at a temperature increase rate of 6℃/min while applying a load of 1.96MPa with the plunger and extruding it from a nozzle with a diameter of 1mm and a length of 1mm. The plunger descent amount of the flow tester is plotted against the temperature, and the temperature at which half of the sample has flowed out is taken as the softening point.

[Maximum endothermic peak temperature of resin]
Using a differential scanning calorimeter "Q-100" (manufactured by TA Instruments Japan, Inc.), 0.01 to 0.02 g of sample is weighed into an aluminum pan and cooled from room temperature (25°C) to 0°C at a rate of 10°C/min, and maintained at 0°C for 1 minute. Then, measurements are performed at a rate of 10°C/min. The temperature of the peak with the largest peak area among the observed endothermic peaks is regarded as the maximum endothermic peak temperature.

[Glass transition temperature of amorphous resin]
Using a differential scanning calorimeter "Q-100" (TA Instruments Japan, Inc.), 0.01 to 0.02 g of sample is weighed into an aluminum pan, heated to 200°C, and cooled from that temperature to 0°C at a rate of 10°C/min. The sample is then heated at a rate of 10°C/min and the endothermic peak is measured. The glass transition temperature is the temperature at the intersection of an extension of the baseline below the maximum endothermic peak temperature and a tangent line showing the maximum slope from the rising part of the peak to the top of the peak.

[Acid value of resin]
Measurements are performed based on the method of JIS K0070:1992, except that the measurement solvent is changed from the ethanol and ether mixture specified in JIS K0070 to a mixture of acetone and toluene (acetone:toluene = 1:1 (volume ratio)).

[Melting point of release agent]
Using a differential scanning calorimeter "DSC Q20" (manufactured by TA Instruments Japan Co., Ltd.), 0.01 to 0.02 g of the sample is weighed into an aluminum pan, heated to 200°C at a heating rate of 10°C/min, and cooled from that temperature to -10°C at a heating rate of 5°C/min. Next, the sample is heated to 180°C at a heating rate of 10°C/min and measured. The maximum endothermic peak temperature observed from the obtained melting endothermic curve is regarded as the melting point of the release agent.

[Average particle size of external additives]
The average particle size refers to the number-average particle size, and is calculated by measuring the particle sizes (average of major and minor axes) of 500 particles in a scanning electron microscope (SEM) photograph and averaging these by number.

[Volume Median Particle Size ( _D50 ) of Toner]
Measuring device: Coulter Multisizer II (manufactured by Beckman Coulter, Inc.)
Aperture diameter: 100μm
Analysis software: Coulter Multisizer AccuComp version 1.19 (Beckman Coulter, Inc.)
Electrolyte: Isoton II (Beckman Coulter, Inc.)
Dispersion solution: Emulgen 109P (Kao Corporation, polyoxyethylene lauryl ether, HLB (Griffin): 13.6) was dissolved in the electrolyte to adjust the concentration to 5% by mass. Dispersion conditions: 10 mg of a measurement sample was added to 5 mL of the dispersion solution, and the mixture was dispersed for 1 minute using an ultrasonic disperser (machine name: US-1, manufactured by SND Corporation, output: 80 W). Thereafter, 25 mL of the electrolyte solution was added, and the mixture was further dispersed for 1 minute using the ultrasonic disperser to prepare a sample dispersion solution.
Measurement conditions: The sample dispersion is added to 100 mL of the electrolyte so as to reach a concentration at which the particle sizes of 30,000 particles can be measured in 20 seconds, and 30,000 particles are measured, and the volume median particle size (D ₅₀ ) is determined from the particle size distribution.

Resin Production Example 1
The raw material monomers and esterification catalysts of the amorphous polyester resins other than trimellitic anhydride shown in Table 1 were placed in a 10-liter four-neck flask equipped with a nitrogen inlet tube, a dehydration tube, a stirrer, and a thermocouple, and reacted at 230°C for 12 hours, and then reacted at 8.3 kPa for 1 hour. The temperature was lowered to 160°C, and the raw material monomers of the styrene resin, the bireactive monomers, and dicumyl peroxide were dropped over 1 hour using a dropping funnel. After maturing the addition polymerization reaction for 1 hour while maintaining the temperature at 160°C, the temperature was raised to 210°C, and the raw material monomers of the styrene resin were removed at 8.3 kPa for 1 hour. Furthermore, trimellitic anhydride was added at 210°C, and the reaction was continued until the desired softening point was reached, to obtain amorphous composite resins (resins H1 and H2). The physical properties of the obtained resins are shown in Table 1.

Resin Production Example 2
The alcohol components, carboxylic acid components other than trimellitic anhydride, and esterification catalyst shown in Table 2 were placed in a 10-liter four-neck flask equipped with a nitrogen inlet tube, a dehydration tube, a stirrer, and a thermocouple, and the mixture was heated to 200°C under a nitrogen atmosphere and reacted for 6 hours. After further heating to 210°C, trimellitic anhydride was added and the mixture was reacted for 1 hour at normal pressure (101.3 kPa), and further reacted at 40 kPa until the desired softening point was reached, to obtain amorphous polyester resins (resins A1 to A3). The physical properties of the obtained resins are shown in Table 2.

Resin Production Example 3
The alcohol components shown in Table 2, carboxylic acid components other than trimellitic anhydride, esterification catalyst, and polymerization inhibitor were placed in a 10-liter four-neck flask equipped with a nitrogen inlet tube, a dehydration tube, a stirrer, and a thermocouple, and the mixture was heated to 200°C under a nitrogen atmosphere and reacted for 6 hours. After further heating to 210°C, trimellitic anhydride was added and reacted for 1 hour at normal pressure (101.3 kPa), and further reacted at 40 kPa until the desired softening point was reached, to obtain an amorphous polyester resin (resin A4). The physical properties of the obtained resin are shown in Table 2.

Resin Production Example 4
The raw material monomers of the crystalline polyester resin shown in Table 3 and the esterification catalyst were placed in a 10-liter four-neck flask equipped with a nitrogen inlet tube, a dehydration tube, a stirrer and a thermocouple, heated to 160°C and reacted for 6 hours. Then, the raw material monomers of the styrene resin and the bireactive monomers shown in Table 3 were dropped over 1 hour using a dropping funnel. After the addition polymerization reaction was matured for 1 hour while maintaining the temperature at 160°C, the raw material monomers of the styrene resin were removed for 1 hour at 8.3 kPa. Furthermore, the temperature was raised to 200°C over 8 hours and reacted for 2 hours at 8.3 kPa to obtain crystalline composite resins (resins C1 and C2). The physical properties of the obtained resins are shown in Table 3.

Resin Production Example 5
The raw material monomers, esterification catalyst, and polymerization inhibitor for the crystalline polyester resin shown in Table 3 were placed in a 10-liter four-neck flask equipped with a nitrogen inlet tube, a dehydration tube, a stirrer, and a thermocouple, and the temperature was raised from 130°C to 200°C over 10 hours under a nitrogen atmosphere, and the reaction was carried out at 200°C and 8 kPa for 1 hour to obtain a crystalline polyester resin (resin C3). The physical properties of the obtained resin are shown in Table 3.

Examples 1 to 18
The amorphous resin and release agent (only Example 15) supplied from the raw material supply port F1 shown in Tables 4 and 5, 1.0 part by mass of a negative charge control agent "Bontron E-304" (manufactured by Orient Chemical Industries Co., Ltd.) and 6.0 parts by mass of a colorant "REGAL330R" (manufactured by Cabot Specialty Chemicals, Inc.) were mixed for 2 minutes using a Henschel mixer to obtain a raw material mixture to be supplied from the raw material supply port F1.

The amorphous resin (only Example 6), crystalline polyester resin, and release agent supplied from the raw material supply port F2 shown in Tables 4 and 5 were mixed for 2 minutes using a Henschel mixer to obtain a raw material mixture to be supplied from the raw material supply port F2.

The resulting raw material mixture was fed from raw material feed ports F1 and F2 to a co-rotating twin-screw extruder "PCM-43" (manufactured by Ikegai Iron Works, shaft diameter 4.2 cm) and melt-kneaded.
The length L of the barrel of the secondary extruder was 1600 mm, and the raw material supply port F1 was located at a position 75 mm (0.05 L) from the inlet end of the barrel, the raw material supply port F2 was located at a position 695 mm (0.43 L), and the kneaded product discharge port was located at a position 1560 mm (0.98 L).
The operating conditions of the twin-screw extruder were a barrel set temperature of 120°C, a shaft rotation speed of 150 r/min, and the mixture supply rate from the raw material supply ports F1 and F2 was adjusted so that the discharge rate of the kneaded product having the desired composition ratio of the raw materials was 20 kg/h.

The resulting kneaded material was cooled and coarsely pulverized using a pulverizer "Rotoplex" (manufactured by Hosokawa Micron Corporation), and a coarsely pulverized material with a volumetric particle size of 2 mm or less was obtained using a sieve with 2 mm mesh. The resulting coarsely pulverized material was finely pulverized using a DS2 type air classifier (impingement plate type, manufactured by Japan Pneumatic Co., Ltd.) by adjusting the pulverization pressure so that the volumetric median particle size was 7.0 μm. The resulting finely pulverized material was classified using a DSX2 type air classifier (manufactured by Japan Pneumatic Co., Ltd.) by adjusting the static pressure (internal pressure) so that the volumetric median particle size was 7.5 μm, and toner particles were obtained.

100 parts by mass of the obtained toner particles were mixed with 1.0 part by mass of hydrophobic silica "R972" (manufactured by Nippon Aerosil Co., Ltd., hydrophobic treatment agent: DMDS, average particle size: 16 nm) and 1.0 part by mass of hydrophobic silica "RY-50" (manufactured by Nippon Aerosil Co., Ltd., hydrophobic treatment agent: silicone oil, average particle size: 40 nm) as external additives in a Henschel mixer (manufactured by Mitsui Mining Co., Ltd.) at 2100 r/min (circumferential speed: 29 m/sec) for 3 minutes to obtain a toner.

Comparative Examples 1 to 3
A toner was obtained in the same manner as in Example 1, except that the binder resins and release agents shown in Tables 4 and 5 were used, and these were mixed with 1.0 part by mass of a negatively charged charge control agent "Bontron E-304" (manufactured by Orient Chemical Industries Co., Ltd.) and 6.0 parts by mass of a colorant "REGAL330R" (manufactured by Cabot Specialty Chemicals, Inc.) for 2 minutes using a Henschel mixer, and the mixture was supplied to the twin-screw extruder from the raw material supply port F1.

Test Example 1 [Low temperature fixability]
Toner was filled into a printer "OKI MICROLINE 5400" (manufactured by Oki Data Corporation) that had been modified to be able to take unfixed images, and a 2 cm square solid unfixed image was printed. Using an external fixing device modified from a printer "OKI MICROLINE 3010" (manufactured by Oki Data Corporation), the unfixed image was fixed at each temperature while increasing the temperature of the fixing roll from 100°C to 200°C in increments of 5°C at a fixing roll rotation speed of 180 mm/sec, and a fixed image was obtained. The image obtained at each fixing temperature was rubbed five times back and forth with a sand eraser (manufactured by LION, ER-502R) with a load of 500 g, and the image density before and after rubbing was measured using an image densitometer X-Rite eXact (manufactured by X-Rite Corporation). The temperature at which the image density ratio before and after rubbing ([image density after rubbing/image density before rubbing] x 100) first exceeded 85% was taken as the minimum fixing temperature, and was used as an index of low-temperature fixability. The lower the minimum fixing temperature, the better the low-temperature fixing property. The results are shown in Tables 4 and 5.

Test Example 2 [Hot offset (HO) resistance]
In the same manner as in Test Example 1, an unfixed image of a 2 cm square solid image was printed. Using an external fixing device modified from an "OKI MICROLINE 3010" printer (manufactured by OKI Data Corporation), the unfixed image was fixed at each temperature while increasing the temperature of the fixing roll from 100°C to 200°C in increments of 5°C at a fixing roll rotation speed of 90 mm/sec, to obtain a fixed image. The fixed image obtained was visually confirmed, and the maximum fixing temperature was determined as the maximum fixing temperature at which no hot offset was observed. The higher the temperature, the better the hot offset resistance. The results are shown in Tables 4 and 5.

Test Example 3 [Durability]
A durability test was carried out with 120g of toner loaded into a non-magnetic single-component developing device "MICROLINE 5400" (manufactured by Oki Data Corporation) at a print rate of 3% in an environment of 30°C and 80% humidity. A solid image was printed every 500 sheets, and the test was stopped when print defects, specifically white streaks or smudges that reveal the white background of the paper, were observed. The more sheets printed before print defects occurred, the better the durability. The results are shown in Tables 4 and 5.

The above results show that, compared to Comparative Examples 1 to 3, in which all raw materials were fed into the twin-screw kneader at once, the toners of Examples 1 to 18 are superior in low-temperature fixability, hot offset resistance, and durability.

The toner for developing electrostatic images obtained by the method of the present invention is suitable for use in developing latent images formed in electrophotography, electrostatic recording, electrostatic printing, etc.

Claims (4)

1. A method for producing a toner for developing electrostatic images, comprising a step of melt-kneading a mixture of raw materials containing an amorphous resin, a crystalline polyester resin, and a release agent in a twin-screw extruder, the method comprising the steps of: (a) melt-kneading a mixture of raw materials containing an amorphous resin, a crystalline polyester resin, and a release agent in a twin-screw extruder; ( b) kneading the mixture of raw materials containing an amorphous resin, a crystalline polyester resin, and a release agent in a twin-screw extruder; and (c) kneading the mixture of raw materials containing an amorphous resin, a crystalline polyester resin, and a release agent in a twin-screw extruder. 2. The method according to claim 1 , wherein the amount of the release agent supplied from the raw material supply port F2 is 60% by mass or more of the release agent contained in the toner. 3. The method according to claim 1 , wherein the total amount of the amorphous resin and the crystalline polyester resin supplied from the raw material supply port F2 is less than 50% by mass of the total amount of the amorphous resin and the crystalline polyester resin contained in the toner. The method according to any one of claims 1 to 3 , wherein the total amount of the crystalline polyester resin and the release agent is 5 parts by mass or more and 40 parts by mass or less per 100 parts by mass of the amorphous resin.