JP2005156586A - Method for manufacturing polymerized toner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method with which a residual polymerizable monomer can be efficiently removed by stripping treatment and a polymerized toner having excellent toner characteristics can be obtained. <P>SOLUTION: In the method for manufacturing the polymerized toner including a process of obtaining a water dispersion containing colored polymer particles and a process of subjecting the water dispersion containing the colored polymer particles to stripping treatment, the water dispersion is supplied into an evaporator and is subjected to the stripping treatment within the evaporator. At this time, the treatment conditions are so controlled that the ratio L<SB>2</SB>/L<SB>1</SB>of the maximum liquid depth L<SB>2</SB>of the water dispersion by the rise of the liquid level during the stripping treatment to the maximum depth L<SB>1</SB>of the water dispersion before the stripping treatment in the evaporator is confined within a range of 1.1 to 2.0. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a polymerized toner. More specifically, the present invention relates to a method for producing a polymerized toner in which the content of volatile organic substances such as residual polymerizable monomers is efficiently reduced, and which is excellent in storage stability, print density, and image quality. Regarding the method. In the present invention, colored polymer particles obtained by the polymerization method are referred to as “polymerized toner”, and those obtained by adding an external additive to the colored polymer particles are referred to as “developer”. This developer may be conventionally called “electrophotographic toner” or “toner”.

  In image forming apparatuses such as electrophotographic and electrostatic recording copying machines, laser beam printers, and facsimiles, a developer is used to visualize the electrostatic latent image formed on the photoreceptor. . The developer is mainly composed of colored particles in which a colorant, a charge control agent, a release agent and the like are dispersed in a binder resin.

  The colored particles are roughly classified into a pulverized toner obtained by a pulverization method and a polymerized toner obtained by a polymerization method. In the pulverization method, a binder resin, a colorant, and other additive components are melt-kneaded, and then the kneaded product is pulverized and classified to obtain a pulverized toner as a colored resin powder. The binder resin is synthesized in advance by polymerizing a polymerizable monomer.

  In contrast, in the polymerization method, for example, colored polymer particles are obtained by polymerizing a polymerizable monomer composition containing a polymerizable monomer, a colorant, and other additive components in an aqueous medium. As a result, a polymerized toner is obtained. As such a polymerization method, a suspension polymerization method is mainly used, but a dispersion polymerization method and an emulsion polymerization method are also known. In the emulsion polymerization method, for example, a polymerization monomer is emulsion-polymerized in an aqueous medium to produce resin fine particles, and then a colorant dispersed with an emulsifier is chemically aggregated with the resin fine particles to form toner particles. A method is adopted in which particles having a diameter are further heated to form spherical colored polymer particles. The emulsion polymerization method is also called an emulsion polymerization aggregation method because it requires an aggregation step.

  In any method, it is difficult to completely polymerize the polymerizable monomer in the polymerization step, and it is inevitable that the unreacted polymerizable monomer remains in the colored particles and thus in the developer. Even if the amount of unreacted polymerizable monomer remaining in the colored particles is small, (i) it volatilizes by heating at the time of fixing and deteriorates the working environment or generates odors. (Ii) Storage Blocking the toner inside, (iii) deteriorating the fluidity of the toner and lowering the image quality, (iv) facilitating the occurrence of offset, (v) causing toner filming on the members of the image forming apparatus. It causes various problems such as facilitation.

  The problem of residual polymerizable monomer is more serious with polymerized toner than with pulverized toner. In the case of pulverized toner, it is easy to reduce the residual polymerizable monomer by heat treatment, drying treatment or the like at the production stage of the binder resin. On the other hand, in the case of the polymerized toner, the residual polymerizable monomer must be removed from the colored polymer particles containing additive components such as a colorant, a charge control agent, and a release agent. However, since the residual polymerizable monomer is easily absorbed by these additive components, it is difficult to reduce the residual polymerizable monomer as compared with the case of the binder resin alone. In addition, since the polymerized toner easily aggregates, there is a limit to the reduction of the residual polymerizable monomer by the heat treatment. In recent years, there has been an increasing demand for polymerized toners that can be fixed at low temperatures in response to high-speed printing and full-color printing. It is extremely difficult to reduce body weight.

  Conventionally, a method of performing a stripping process has been proposed in order to remove residual polymerizable monomers from the polymerized toner. In the stripping treatment, an aqueous dispersion of colored polymer particles is introduced into an evaporator (container or tank), a gas is blown into the aqueous dispersion (a bubbling method), and a method of heating under reduced pressure (a vacuum stripping). Method) and the like to remove volatile organic substances such as residual polymerizable monomers.

  For example, a method has been proposed in which, after suspension polymerization, the suspension medium is distilled off while a saturated vapor of the suspension medium is blown into a suspension containing polymerized toner particles (colored polymer particles). (For example, refer to Patent Document 1). Also, a method of reducing residual polymerizable monomer by subjecting an aqueous dispersion of colored polymer particles obtained by suspension polymerization to a reduced-pressure stripping treatment at a temperature not lower than the glass transition temperature of the polymer component and lower than 100 ° C. Has been proposed (see, for example, Patent Document 2).

  However, it is known that the stripping treatment method tends to cause foaming or bumping at the gas-liquid interface of the aqueous dispersion of colored polymer particles, and is difficult to operate stably. Therefore, for example, a method has been proposed in which, after the polymerization step, a silicone antifoaming agent is added to the suspension containing the polymerized toner particles, and the aqueous medium is distilled off from the suspension while suppressing foaming and bumping ( For example, see Patent Document 3).

  Further, when removing the residual polymerizable monomer by distilling the aqueous dispersion containing the colored polymer particles, air or an inert gas is injected into the gas phase part from the upper part of the evaporator, A method for suppressing foaming and bumping has been proposed (see, for example, Patent Document 4). Furthermore, the stripping treatment is performed while stirring the aqueous dispersion containing the colored polymer particles, and at this time, a part of the stirring blade used for stirring is protruded from the liquid surface of the aqueous dispersion to suppress foaming. A method has been proposed (see, for example, Patent Document 5).

  However, it has been found that it is difficult to remove the residual polymerizable monomer to an extent that it can be satisfactorily satisfied satisfactorily by the method of suppressing the liquid level fluctuation of the aqueous dispersion due to foaming or bumping during the stripping process. .

Japanese Patent Laid-Open No. 5-100485 JP 2000-321809 A Japanese Patent No. 2923820 JP 2001-92180 A JP 2001-117272 A

  The object of the present invention is to remove the residual polymerizable monomer to an extent that it can be efficiently and sufficiently satisfied in the step of stripping the aqueous dispersion containing the colored polymer particles, and has excellent toner characteristics. Another object of the present invention is to provide a production method capable of obtaining a polymerized toner.

As a result of earnest research to achieve the above-mentioned object, the present inventor supplies an aqueous dispersion containing colored polymer particles into the evaporator to perform a stripping process. At that time, stripping in the evaporator is performed. The ratio L ₂ / L ₁ of the maximum liquid depth L ₂ of the aqueous dispersion due to the rise in the liquid level during the stripping process with respect to the maximum liquid depth L ₁ of the aqueous dispersion before treatment is in the range of 1.1 to 2.0. The present inventors have come up with a method of performing stripping processing while controlling processing conditions.

  The stripping method is generally performed by a method of stripping while blowing a gas such as an inert gas or water vapor into an aqueous dispersion (a bubbling method) or a method of heating under reduced pressure (a vacuum stripping method). Yes. Also, the stripping treatment is often performed while heating or stirring the aqueous dispersion. When the stripping process is performed by such a method, the volume (hold up) of the aqueous dispersion in the evaporator during the stripping process increases. This increase in volume includes foaming.

  In general, in a continuous operation or batch operation in which a different phase system such as gas-liquid, liquid-liquid, solid-liquid or the like is handled, the amount of the dispersed phase accumulated in the process vessel or the tube is called hold-up. When the volume (hold-up) of the aqueous dispersion in the evaporator increases during the stripping process, the liquid level of the aqueous dispersion in the evaporator rises.

  Conventionally, from the viewpoint of avoiding adverse effects on the toner characteristics due to the stripping process, it has been considered necessary to stably perform the stripping process while suppressing an increase in the liquid level including foaming at the liquid level. From the viewpoint of processing efficiency, it has been considered desirable to perform a stripping process by supplying a large amount of aqueous dispersion into the evaporator. For this reason, it has been considered necessary to suppress the rise in liquid level including foaming as much as possible.

  However, the present inventor does not suppress the rise of the liquid level of the aqueous dispersion in the evaporator during the stripping process, but rather performs the stripping process while increasing the level within a predetermined range, so that the residual polymerization. It has been found that the removal rate of volatile organic substances such as a polymerizable monomer is increased, and a polymerized toner in which the content of the residual polymerizable monomer is reduced to a sufficiently satisfactory level in a relatively short time can be obtained. Moreover, it has been found that by controlling the rise in the liquid level during the stripping process within a predetermined range, the characteristics of the obtained polymerized toner are not deteriorated but rather improved. The present invention has been completed based on these findings.

According to the present invention, a polymer obtained by polymerizing a polymerizable monomer in an aqueous medium by a polymerization process or a polymerization process and a subsequent aggregation process is used as a binder resin, and at least a color weight in which a colorant is dispersed therein. Step 1 of obtaining coalescent particles to obtain an aqueous dispersion containing the colored polymer particles, and volatilization contained in the colored polymer particles by stripping the aqueous dispersion containing the colored polymer particles. In the method for producing a polymerized toner including the step 2 for removing the organic substances, an aqueous dispersion containing the colored polymer particles is supplied into the evaporator, and the stripping process in the step 2 is performed in the evaporator. At that time, the ratio L ₂ / L ₁ of the maximum liquid depth L ₂ of the aqueous dispersion due to the rise in the liquid level during the stripping process with respect to the maximum liquid depth L ₁ of the aqueous dispersion before the stripping process in the evaporator is 1. In the range of 1 to 2.0 Method for producing a polymerized toner which is characterized in that the stripping treatment while controlling the process conditions so that there is provided.

  According to the production method of the present invention, the removal efficiency of volatile organic substances such as residual polymerizable monomers from an aqueous dispersion containing colored polymer particles is improved, and the content of residual polymerizable monomers is extremely high. A small amount of polymerized toner can be obtained efficiently. Furthermore, according to the production method of the present invention, a polymerized toner having excellent toner characteristics can be obtained. The polymerized toner obtained by the production method of the present invention is excellent in storability and printing density, and fog is suppressed.

1. Production process 1 of aqueous dispersion containing colored polymer particles 1 :
The method for producing a polymerized toner of the present invention includes Step 1 of obtaining an aqueous dispersion containing colored polymer particles by a polymerization step or a polymerization step followed by an aggregation step. In this step, a polymerization method such as a suspension polymerization method, a dispersion polymerization method, or an emulsion polymerization method is employed. Among these, the suspension polymerization method and the emulsion polymerization method are preferable, and the suspension polymerization method is more preferable.

  The suspension polymerization method includes a step of polymerizing a polymerizable monomer composition containing at least a colorant and a polymerizable monomer in an aqueous medium. As the aqueous medium, an aqueous medium containing a dispersant is generally used. In the suspension polymerization method, first, a polymerizable monomer composition is suspended in an aqueous medium containing a dispersant to form fine droplets, and then suspension polymerization is performed to produce colored polymer particles. Let If necessary, a step of further polymerizing the polymerizable monomer for shell in the presence of the colored polymer particles is added to form colored polymer particles having a core / shell structure (hereinafter referred to as “core / shell type coloring”). May be referred to as “polymer particles”).

  Therefore, in the production method of the present invention, in step 1, a polymerizable monomer composition containing at least a colorant and a polymerizable monomer is polymerized in an aqueous medium to produce colored polymer particles, By further polymerizing the polymerizable monomer for the shell in the presence of the colored polymer particles to produce core-shell type colored polymer particles, the colored polymer particles or the core-shell type colored polymer particles are obtained. A step of producing an aqueous dispersion containing the same.

  In the emulsion polymerization method, a polymerizable monomer composition containing a polymerizable monomer and a colorant is emulsion-polymerized in an aqueous medium containing an emulsifier, and then the resulting colored resin fine particles are aggregated to form a toner. A method of enlarging the particle size can be employed. As another emulsion polymerization method, first, a polymerizable monomer is emulsion-polymerized in an aqueous medium containing an emulsifier to form resin fine particles, and then a colorant dispersed with an emulsifier is used as a chemical compound with resin fine particles. And a method of forming colored polymer particles having a toner particle diameter by agglomeration and then applying heat to spherical colored polymer particles. Toner additives other than the colorant such as a release agent can be dispersed in an emulsifier and added in the aggregation step.

  As the aqueous medium, water such as ion-exchanged water is generally used, but if desired, a water-added hydrophilic solvent such as alcohol may be used. In the polymerization method, generally, a dispersant is contained in an aqueous medium to increase the stability of the droplets of the polymerizable monomer composition dispersed in the aqueous medium. The polymerizable monomer composition may contain various additives such as a charge control agent, a release agent, a crosslinkable monomer, a macromonomer, a molecular weight modifier, a lubricant, and a dispersion aid as necessary. Can do. The polymerizable monomer composition is polymerized in the presence of a polymerization initiator.

  In the suspension polymerization method, a dispersant such as a hardly water-soluble metal hydroxide colloid is used, but a surfactant can also be used in combination. In the emulsion polymerization method, various emulsifiers are added to the aqueous medium in order to stabilize the dispersion of the polymerizable monomer or polymerizable monomer composition. Among these polymerization methods, the suspension polymerization method is preferable in that spherical colored polymer particles having a desired particle diameter are easily obtained and core-shell type colored polymer particles are easily formed. Therefore, the suspension polymerization method will be mainly described below.

(1) Polymerizable monomer:
In the present invention, a monovinyl monomer is used as the main component of the polymerizable monomer. Examples of the monovinyl monomer include aromatic vinyl monomers such as styrene, vinyltoluene, and α-methylstyrene; (meth) acrylic acid; methyl (meth) acrylate, ethyl (meth) acrylate, (meth) Such as propyl acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, (meth) acrylamide, etc. Examples include, but are not limited to, (meth) acrylic acid derivatives; monoolefin monomers such as ethylene, propylene, and butylene.

  Monovinyl monomers may be used alone or in combination of a plurality of monomers. Of these monovinyl monomers, aromatic vinyl monomers alone, combinations of aromatic vinyl monomers and (meth) acrylic acid derivatives, and the like are preferably used.

  When a crosslinkable monomer is used together with a monovinyl monomer, the hot offset property can be improved. The crosslinkable monomers can be used alone or in combination of two or more, and the amount used is usually 10 parts by weight or less, preferably 0.01 to 100 parts by weight with respect to 100 parts by weight of the monovinyl monomer. 7 parts by weight, more preferably 0.05 to 5 parts by weight, particularly preferably 0.1 to 3 parts by weight.

  It is preferable to use a macromonomer together with a monovinyl monomer because the balance between storage stability at high temperature and fixability at low temperature is improved. The macromonomer is a macromolecule having a polymerizable carbon-carbon unsaturated double bond at the end of the molecular chain, and is an oligomer or polymer having a number average molecular weight of usually 1,000 to 30,000. When the number average molecular weight is within the above range, it is preferable because the fixability and storability of the polymerized toner can be maintained without impairing the meltability of the macromonomer.

  Examples of the polymerizable carbon-carbon unsaturated double bond at the molecular chain terminal of the macromonomer include an acryloyl group and a methacryloyl group, and a methacryloyl group is preferred from the viewpoint of ease of copolymerization. The macromonomer is preferably one that gives a polymer having a glass transition temperature higher than that of a polymer obtained by polymerizing a monovinyl monomer.

  Specific examples of macromonomers include polymers obtained by polymerizing styrene, styrene derivatives, methacrylic acid esters, acrylic acid esters, acrylonitrile, methacrylonitrile, etc. alone or in combination of two or more; macromonomers having a polysiloxane skeleton Among these, a hydrophilic one is preferable, and a polymer obtained by polymerizing methacrylic acid ester or acrylic acid ester alone or in combination thereof is particularly preferable.

  When the macromonomer is used, the amount used is usually 0.01 to 10 parts by weight, preferably 0.03 to 5 parts by weight, more preferably 0.05 to 1 part per 100 parts by weight of the monovinyl monomer. Parts by weight. When the amount of the macromonomer is within the above range, it is preferable because the preservability of the polymerized toner is maintained and the fixing property is improved.

(2) Colorant:
As the colorant, various pigments and dyes used in the field of toner such as carbon black and titanium white can be used. Examples of the black colorant include carbon black and nigrosine-based dyes and pigments; magnetic particles such as cobalt, nickel, iron tetroxide, manganese iron oxide, zinc iron oxide, and nickel iron oxide. When carbon black is used, it is preferable to use carbon black having a primary particle size of 20 to 40 nm because good image quality can be obtained and the safety of the toner to the environment is enhanced. As a color toner colorant, a yellow colorant, a magenta colorant, a cyan colorant, or the like can be used.

  As the yellow colorant, condensed azo compounds, isoindolinone compounds, anthraquinone compounds, azo metal complexes, methine compounds, allylamide compounds, and the like are used. Specifically, for example, C.I. I. Pigment Yellow 3, 12, 13, 14, 15, 17, 62, 65, 73, 74, 83, 90, 93, 95, 96, 97, 109, 110, 111, 120, 128, 129, 138, 147, 155, 168, 180, 181 and the like. In addition, Nephthol Yellow S, Hansa Yellow G, C.I. I. Examples thereof include bat yellow.

  Examples of the magenta colorant include condensed azo compounds, diketopyrrolopyrrole compounds, anthraquinone compounds, quinacridone compounds, basic dye lake compounds, naphthol compounds, benzimidazolone compounds, thioindigo compounds, and perylene compounds. Specifically, for example, C.I. I. Pigment Red 2, 3, 5, 6, 7, 23, 31, 48, 48: 2, 48: 3, 48: 4, 57, 57: 1, 58, 60, 63, 64, 68, 81, 81: 1, 83, 87, 88, 89, 90, 112, 114, 122, 123, 144, 146, 149, 150, 163, 166, 169, 170, 177, 184, 185, 187, 202, 206, 207, 209, 220, 251, 254 and the like. In addition, C.I. I. Pigment violet 19 and the like.

  Examples of cyan colorants include copper phthalocyanine compounds and derivatives thereof, anthraquinone compounds, basic dye lake compounds, and the like. Specifically, for example, C.I. I. Pigment Blue 1, 2, 3, 6, 7, 15, 15: 1, 15: 2, 15: 3, 15: 4, 16, 17, 60, 62, 66, and the like. In addition, phthalocyanine blue, C.I. I. Bat Blue, C.I. I. Acid blue and so on.

  These colorants can be used alone or in combination of two or more. The colorant is usually used in a proportion of 0.1 to 50 parts by weight, preferably 1 to 20 parts by weight, based on 100 parts by weight of the polymerizable monomer.

(3) Charge control agent:
In order to improve the chargeability of the polymerized toner, it is preferable to include various positively chargeable or negatively chargeable charge control agents in the polymerizable monomer composition. Examples of the charge control agent include metal complexes of organic compounds having a carboxyl group or a nitrogen-containing group, metal-containing dyes, nigrosine, charge control resins, and the like.

  Specifically, Bontron N-01 (manufactured by Orient Chemical Co., Ltd.), Nigrosine Base EX (manufactured by Orient Chemical Co., Ltd.), Spiron Black TRH (manufactured by Hodogaya Chemical Co., Ltd.), T-77 (manufactured by Hodogaya Chemical Co., Ltd.) Bontron S-34 (made by Orient Chemical Industries), Bontron E-81 (made by Orient Chemical Industries), Bontron E-84 (made by Orient Chemical Industries), Bontron E-89 (made by Orient Chemical Industries), Bontron F-21 (manufactured by Orient Chemical Co., Ltd.), COPY CHARGE NX VP434 (manufactured by Clariant), COPY CHARGE NEG VP2036 (manufactured by Clariant), LR-147 (manufactured by Nippon Carlit), copy blue PR (manufactured by Clariant), etc. Charge control agent; quaternary ammonium (salt) group-containing copolymer , Charge control resins such as sulfonic acid (salt) group-containing copolymers; and the like can be given. The charge control agent is usually used in a proportion of 0.01 to 10 parts by weight, preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the polymerizable monomer.

(4) Release agent:
A release agent can be included in the polymerizable monomer composition for the purpose of preventing offset or improving the releasability at the time of hot roll fixing. Examples of the release agent include polyolefin waxes such as low molecular weight polyethylene, low molecular weight polypropylene, and low molecular weight polybutylene; plant-based natural waxes such as candelilla, carnauba, rice, wood wax, jojoba; paraffin, microcrystalline, petrolactam, and the like. Petroleum waxes and modified waxes thereof; synthetic waxes such as Fischer-Tropsch wax; polyfunctional ester compounds such as pentaerythritol tetramyristate, pentaerythritol tetrapalmitate, dipentaerythritol hexamyristate; and the like. These release agents can be used alone or in combination of two or more.

  Among these release agents, synthetic waxes, terminal-modified polyolefin waxes, petroleum waxes, and polyfunctional ester compounds are preferable. The ratio of the release agent used is usually 0.1 to 50 parts by weight, preferably 0.5 to 20 parts by weight, more preferably 1 to 10 parts by weight with respect to 100 parts by weight of the polymerizable monomer.

(5) Lubricant / dispersion aid:
Lubricants such as fatty acid salts of fatty acids such as oleic acid and stearic acid, fatty acids and metals such as Na, K, Ca, Mg, and Zn; silane-based or titanium-based couplings for the purpose of uniform dispersion of colorants, etc. A dispersing aid such as an agent can be contained in the polymerizable monomer. Such lubricants and dispersants are usually used at a ratio of about 1/1000 to 1/1 based on the weight of the colorant.

(6) Polymerization initiator:
Examples of the polymerization initiator for the polymerizable monomer include persulfates such as potassium persulfate and ammonium persulfate; 4,4′-azobis (4-cyanovaleric acid), 2,2′-azobis [2-methyl -N- (2-hydroxyethyl) propionamide], 2,2'-azobis (2-amidinopropane) dihydrochloride, 2,2'-azobis (2,4-dimethylvaleronitrile), 2,2'- Azo compounds such as azobisisobutyronitrile; di-t-butyl peroxide, dicumyl peroxide, lauroyl peroxide, benzoyl peroxide, t-butylperoxy-2-ethylhexanoate, t-hexylperoxy 2-ethylhexanoate, t-butyl peroxypivalate, di-isopropyl peroxydicarbonate, di-t-butyl peroxyiso Tallates, 1,1 ', 3,3'-tetramethylbutyl peroxy-2-ethylhexanoate, t- butyl peroxides of peroxy isobutyrate and the like; and the like. A redox initiator in which these polymerization initiators and a reducing agent are combined can also be used.

  Among these initiators, it is preferable to select an oil-soluble polymerization initiator that is soluble in the polymerizable monomer, and a water-soluble polymerization initiator can be used in combination as necessary. The polymerization initiator is usually used in a proportion of 0.1 to 20 parts by weight, preferably 0.3 to 15 parts by weight, more preferably 0.5 to 10 parts by weight with respect to 100 parts by weight of the polymerizable monomer. It is done.

  The polymerization initiator can be added in advance to the polymerizable monomer composition, but in order to suppress premature polymerization, after completion of the droplet forming step of the polymerizable monomer composition or during the polymerization reaction It can also be added directly to the suspension.

(7) Molecular weight regulator:
In the polymerization, a molecular weight modifier is preferably used. Examples of the molecular weight modifier include mercaptans such as t-dodecyl mercaptan, n-dodecyl mercaptan, n-octyl mercaptan, 2,2,4,6,6-pentamethylheptane-4-thiol; carbon tetrachloride, four And halogenated hydrocarbons such as carbon bromide; The molecular weight modifier is usually contained in the polymerizable monomer composition before the start of polymerization, but can also be added during the polymerization. The molecular weight modifier is usually used in a proportion of 0.01 to 10 parts by weight, preferably 0.1 to 5 parts by weight, with respect to 100 parts by weight of the polymerizable monomer.

(8) Dispersant:
The dispersant used in the present invention (sometimes referred to as “dispersion stabilizer”) is preferably a colloid of a slightly water-soluble metal compound. Examples of the hardly water-soluble metal compounds include sulfates such as barium sulfate and calcium sulfate; carbonates such as barium carbonate, calcium carbonate and magnesium carbonate; phosphates such as calcium phosphate; metal oxidation such as aluminum oxide and titanium oxide A metal hydroxide of aluminum hydroxide, magnesium hydroxide, ferric hydroxide, and the like. Of these, a colloid of a poorly water-soluble metal hydroxide is preferable because it can narrow the particle size distribution of the polymer particles and improve the sharpness of the image.

  Although the colloid of the hardly water-soluble metal compound is not limited by its production method, the colloid of the hardly water-soluble metal hydroxide obtained by adjusting the pH of the aqueous solution of the water-soluble polyvalent metal compound to 7 or more, particularly water-soluble It is preferable to use a colloid of a poorly water-soluble metal hydroxide produced by a reaction between a polyvalent metal compound and an alkali metal hydroxide in an aqueous phase. The particle diameter of the colloid of the poorly water-soluble metal compound is such that D50 (50% cumulative value of the number particle size distribution) is 0.5 μm or less and D90 (90% cumulative value of the number particle size distribution) is 1 μm or less. preferable.

  A dispersing agent is normally used in the ratio of 0.1-20 weight part with respect to 100 weight part of polymerizable monomers. When this ratio is too small, it is difficult to obtain sufficient polymerization stability, and polymerized aggregates are easily generated. On the other hand, if the ratio is too large, the viscosity of the aqueous solution increases and the polymerization stability decreases.

  In the present invention, a water-soluble polymer can be used as a dispersant as required. Examples of the water-soluble polymer include polyvinyl alcohol, methyl cellulose, gelatin and the like. In the present invention, it is not necessary to use a surfactant for stabilizing the dispersion, but it should be used as necessary for stable suspension polymerization within a range in which the environmental dependence of charging characteristics does not increase. Can do.

(9) Polymerization step:
The polymerized toner is colored polymer particles in which a polymer formed by polymerization of a polymerizable monomer becomes a binder resin, and additive components such as a colorant and a release agent are dispersed therein. If this colored polymer particle is used as a core and a shell composed of a polymer layer is formed thereon, core-shell type colored polymer particles can be obtained.

  Taking the suspension polymerization method as an example, the polymerized toner can be obtained, for example, by the following steps. A polymerizable monomer, a colorant, and other additives are mixed using a mixer, and if necessary, wet-pulverized using a media-type wet pulverizer (for example, a bead mill). A meter composition is prepared. Next, the polymerizable monomer composition is dispersed in an aqueous medium containing a dispersant and stirred to form uniform primary droplets of the polymerizable monomer composition. In general, in this step, primary droplets having a volume average particle size of about 50 to 1000 μm are formed. In order to avoid premature polymerization, the polymerization initiator is preferably added to the aqueous medium after the size of the droplets in the aqueous medium becomes uniform.

  A polymerization initiator is added to and mixed with a suspension in which droplets of the polymerizable monomer composition are dispersed in an aqueous medium, and the particle size of the droplets is targeted using a high-speed rotary shearing stirrer. Stir until small particle size close to polymerized toner particles. In this way, secondary droplets having a minute particle diameter are formed. In general, in this step, secondary droplets having a volume average particle size of about 1 to 12 μm are formed.

  A suspension containing secondary droplets of the polymerizable monomer composition is charged into a polymerization reactor, and suspension polymerization is usually carried out by raising the temperature to a temperature of 5 to 120 ° C, preferably 35 to 95 ° C. If the polymerization temperature is too low, a polymerization initiator having a high catalytic activity must be used, which makes it difficult to manage the polymerization reaction. When the polymerization temperature is too high, when an additive that melts at a low temperature is included, this may bleed on the surface of the polymerized toner, and the storage stability of the polymerized toner may deteriorate.

  The volume average particle size and particle size distribution of the fine droplets of the polymerizable monomer composition affect the volume average particle size and particle size distribution of the polymerized toner. When the particle size of the droplet is too large, the particle size of the generated polymer toner particles (colored polymer particles) becomes too large, and the resolution of the image is lowered. If the particle size distribution of the droplets is wide, the fixing temperature varies, causing problems such as fogging and toner filming. Therefore, it is desirable to form the droplets (secondary droplets) of the polymerizable monomer composition before polymerization so as to be approximately the same size as the generated polymer toner particles.

  The volume average particle diameter of the droplets of the polymerizable monomer composition is usually 1 to 12 μm, preferably 2 to 10 μm, more preferably 3 to 8 μm. In order to obtain a high-definition image, particularly when a polymer toner having a small particle diameter is used, the volume average particle diameter of the droplets is preferably 2 to 9 μm, more preferably 3 to 8 μm. The particle size distribution (volume average particle size / number average particle size) of the droplets of the polymerizable monomer composition is usually 1 to 3, preferably 1 to 2.5, and more preferably 1 to 2. In particular, when forming fine droplets, an aqueous dispersion medium containing a monomer composition is placed in a gap between a rotor that rotates at high speed and a stator that surrounds the rotor and has small holes or comb teeth. A distribution method is preferred.

  One or more of the above-mentioned monovinyl monomers are selected as the polymerizable monomer. To lower the toner fixing temperature, the glass transition temperature Tg is usually 80 ° C. or lower, preferably 40 to 80 ° C. It is preferable to select a polymerizable monomer or a combination of polymerizable monomers that can form a polymer at about 50 to 70 ° C. In the present invention, the Tg of the polymer constituting the binder resin is a calculated value calculated according to the type and use ratio of the polymerizable monomer to be used, that is, “calculated Tg”.

  Suspension polymerization produces colored polymer particles in which an additive component such as a colorant is dispersed in a polymer of a polymerizable monomer. In the present invention, the colored polymer particles are recovered and used as a polymerization toner. A polymer layer is further formed on the colored polymer particles obtained by suspension polymerization for the purpose of improving the storage stability (that is, blocking resistance), low-temperature fixability, and meltability during fixing of the polymerized toner. Thus, colored polymer particles having a core-shell structure can be obtained.

  As a method for forming the core-shell structure, for example, the above colored polymer particles are used as core particles, and a polymerizable monomer for shell is further polymerized in the presence of the core particles, and a polymer is formed on the surface of the core particles. A method of forming a layer (shell) can be employed. When a monomer that forms a polymer having a Tg higher than that of the polymer component constituting the core particle is used as the polymerizable monomer for the shell, the storage stability of the polymerized toner can be improved. On the other hand, by setting the Tg of the polymer component constituting the core particle low, the fixing temperature of the polymerized toner can be lowered or the melting characteristics can be improved. Therefore, by forming colored polymer particles having a core-shell structure in the polymerization step, a polymerized toner that can cope with high speed printing, full color, overhead projector (OHP) permeability, and the like can be obtained.

  As the polymerizable monomer for forming the core and the shell, a preferable monomer can be appropriately selected from the monovinyl monomers described above. The weight ratio of the polymerizable monomer for the core and the polymerizable monomer for the shell is usually 40/60 to 99.9 / 0.1, preferably 60/40 to 99.7 / 0.3, more preferably Is 80 / 20-99.5 / 0.5. If the ratio of the polymerizable monomer for the shell is too small, the effect of improving the storage stability of the polymerized toner is small, and if it is excessive, the effect of reducing the fixing temperature is small.

  The Tg of the polymer formed by the polymerizable monomer for shell is usually more than 50 ° C. and 120 ° C. or less, preferably more than 60 ° C. and less than 110 ° C., more preferably more than 80 ° C. and less than 105 ° C. The difference in Tg between the polymer formed from the core polymerizable monomer and the polymer formed from the shell polymerizable monomer is preferably 10 ° C. or higher, more preferably 20 ° C. or higher, particularly Preferably it is 30 degreeC or more. In many cases, from the viewpoint of the balance between the fixing temperature and the storage stability, a core polymerizable monomer that can form a polymer having a Tg of usually 60 ° C. or lower, preferably 40 to 60 ° C. is selected. Is preferred. On the other hand, as the polymerizable monomer for the shell, it is preferable to use a monomer that forms a polymer having a Tg exceeding 80 ° C. such as styrene or methyl methacrylate, either alone or in combination of two or more. .

  The polymerizable monomer for shell is preferably added to the polymerization reaction system as droplets smaller than the average particle diameter of the core particles. When the particle size of the shell polymerizable monomer droplets is too large, it is difficult to form a polymer layer uniformly around the core particles. In order to make the polymerizable monomer for the shell into small droplets, the mixture of the polymerizable monomer for the shell and the aqueous dispersion medium is finely dispersed using, for example, an ultrasonic emulsifier. What is necessary is just to add the obtained dispersion liquid to a polymerization reaction system.

  When the polymerizable monomer for shell is a relatively water-soluble monomer (for example, methyl methacrylate) having a solubility in water at 20 ° C. of 0.1% by weight or more, It is not necessary to perform the fine dispersion process because it is easy to move quickly, but it is preferable to perform the fine dispersion process in order to form a uniform shell. When the polymerizable monomer for shell is a monomer having a solubility in water at 20 ° C. of less than 0.1% by weight (for example, styrene), it is subjected to fine dispersion treatment or solubility in water at 20 ° C. Is preferably added to the reaction system by adding 5% by weight or more of an organic solvent (for example, alcohols) to the reaction system.

  A charge control agent can be added to the polymerizable monomer for shell. The charge control agent is preferably the same as that used in the core particle production described above. When used, the charge control agent is usually 0.01 to 10 parts by weight with respect to 100 parts by weight of the polymerizable monomer for shell. , Preferably 0.1 to 5 parts by weight.

  To produce a core / shell polymerized toner, the shell polymerizable monomer or its aqueous dispersion is added all at once or continuously or intermittently to the suspension containing the core particles. . When adding the shell polymerizable monomer, it is preferable to add a water-soluble radical initiator in order to efficiently form the shell. If a water-soluble polymerization initiator is added at the time of addition of the shell polymerizable monomer, the water-soluble polymerization initiator enters the vicinity of the outer surface of the core particle to which the shell polymerizable monomer has migrated, and the core monomer surface is overlapped. It is considered that the combined layer is easily formed.

  Examples of the water-soluble polymerization initiator include persulfates such as potassium persulfate and ammonium persulfate; 2,2′-azobis [2-methyl-N- (2-hydroxyethyl) propionamide], 2,2′- An azo initiator such as azobis- [2-methyl-N- [1,1-bis (hydroxymethyl) ethyl] propionamide] can be used. The amount of the water-soluble polymerization initiator used is usually 0.1 to 50% by weight, preferably 1 to 20% by weight, per 100 parts by weight of the shell polymerizable monomer.

  The average thickness of the shell is usually 0.001 to 1.0 μm, preferably 0.003 to 0.5 μm, and more preferably 0.005 to 0.2 μm. When the shell thickness is too large, the fixing property of the polymerized toner is lowered, and when it is too small, the storage property of the polymerized toner is lowered. When the core particle diameter and shell thickness of the polymerized toner can be observed with an electron microscope, it can be obtained by directly measuring the particle size and shell thickness randomly selected from the observation photograph. When it is difficult to observe the core and the shell, it can be calculated from the particle size of the core particle and the amount of the polymerizable monomer that forms the shell.

2. Stripping process step 2 :
By the production process 1, an aqueous medium containing colored polymer particles (including core / shell type colored polymer particles), that is, an aqueous dispersion is obtained. The aqueous dispersion is used as it is or by adding ion exchange water or the like to obtain an aqueous dispersion having a solid content concentration suitable for stripping treatment. Next, the aqueous dispersion is stripped to remove volatile organic substances such as unreacted polymerizable monomers remaining in the colored polymer particles.

  The solid content concentration of the aqueous dispersion containing the colored polymer particles to be supplied to the stripping treatment is preferably in the range of 5 to 45% by weight, more preferably 10 to 40% by weight, particularly preferably 15 to 35% by weight. It is. When an aqueous dispersion containing colored polymer particles at a relatively high concentration is obtained in the production step 1, water such as ion exchange water is added during the stripping treatment to disperse the water in a desired solid content concentration. It is preferable to adjust to a liquid.

  During the stripping treatment, it is preferable to add an antifoaming agent to the aqueous dispersion. As the antifoaming agent, a silicone-based antifoaming agent can be used, but it is preferable to use a non-silicone-based antifoaming agent from the viewpoint of excellent properties of the polymerized toner. Non-silicone-based antifoaming agents include oil-based antifoaming agents, mineral oil-based antifoaming agents, polyether-based antifoaming agents, polyalkylene glycol type nonionic surfactants, fats and polyalkylene glycol type nonionic surfactants, And at least one non-silicone antifoaming agent selected from the group consisting of an emulsion containing mineral oil and a polyalkylene glycol type nonionic surfactant. Among these non-silicone defoamers, from the viewpoint of defoaming effect and toner properties, mineral oil defoamers, polyalkylene glycol type nonionic surfactants, oils and fats and polyalkylene glycol type nonionic surfactants are used. Emulsions containing are preferred.

  These antifoaming agents can be used by appropriately selecting from various commercially available defoaming agents or anti-foaming agents. The mineral oil-based antifoaming agent is a modified hydrocarbon oil based on mineral oil, and examples of commercially available products include trade name “antifoaming agent DF714S” manufactured by Japan PCM Co., Ltd. Examples of the polyalkylene glycol type nonionic surfactant include a polyethylene glycol type nonionic surfactant and a nonionic surfactant made of a polyoxyethylene / polyoxypropylene block copolymer. A trade name “SN deformer 180” (foam suppressor comprising a polyoxyalkylene-type nonionic surfactant) is available. Emulsions containing fats and oils and polyalkylene glycol type nonionic surfactants are obtained by emulsifying fats and oils with polyalkylene glycol type nonionic surfactants. Examples of commercially available products include products manufactured by San Nopco Co., Ltd. The name “SN deformer 1407K” (foam suppressant composed of oils and fats, emulsions such as polyethylene glycol type nonionic surfactants) and the like. Examples of commercially available polyether antifoaming agents include polyether type surfactants such as “Adecanol LG-51” and “Adecanol LG-109” manufactured by Asahi Denka Co., Ltd. Special polyether compounds such as “U-510” can be used.

  The amount of the antifoaming agent used is preferably 0.01 to 1 part by weight, more preferably 0.05 to 0.5 part by weight, based on 100 parts by weight of the polymerizable monomer composition or colored polymer particles. is there. If the amount of the antifoaming agent used is too small, it may be difficult to obtain a sufficient antifoaming effect. If the amount is too large, the antifoaming effect may be saturated and the toner characteristics may be adversely affected. Arise.

  Other methods for suppressing foaming include a method in which a part of the stirring blade of the stirring device protrudes from the liquid surface, and a method in which the liquid is sprayed from the upper part of the evaporator. You may use together these methods and the method of using an antifoamer.

  As a stripping treatment method for an aqueous dispersion, a method of blowing an inert gas (nitrogen, argon, helium, etc.), water vapor, dry air, carbon dioxide or the like (a bubbling method), a method of heating under reduced pressure (a decompression stroke), Ripping method). A method of performing vacuum stripping while blowing a gas into the aqueous dispersion may be adopted. The gas to be blown can be heated to an appropriate temperature of less than 100 ° C. from the viewpoint of improving the efficiency of the stripping process and preventing aggregation of the colored polymer particles. As the gas, an inert gas such as nitrogen gas and water vapor (steam) are preferable.

  The gas is normally blown into the aqueous dispersion from an opening of a gas blowing pipe provided below the evaporator. The installation location of the gas blowing tube is not particularly limited, and the side surface and bottom of the evaporator are arbitrary, and the installation height is also arbitrary, but it is preferably installed at a position slightly away from the center of the bottom of the evaporator. .

  The shape of the opening of the gas blowing tube (sometimes referred to as “gas blowing port”) may be a single tube opening, but it has a structure in which a diffuser plate is connected to the opening of the single tube. preferable. It is preferable to blow gas through the diffuser plate because the removal rate of volatile organic substances by blowing the gas is improved. As the diffuser plate, a synthetic resin hard porous body in which synthetic resin particles such as ABS resin, styrene resin, polymethyl methacrylate, ultrahigh-density polyethylene, high-density polyethylene, low-density polyethylene, and polypropylene are bonded is preferable. . The pore diameter of the diffuser plate is usually selected from the range of 5 to 600 μm, and the porosity is usually selected from the range of 30 to 40%.

  When gas is blown through the diffuser plate, the bubble diameter can be controlled, and the removal rate of volatile organic substances by fine bubbles is increased. In addition, in order to make a bubble diameter fine, the method called a micro bubble, the method of using an ejector and a pressurization dissolution tank, etc. are mentioned. A porous ceramic tube is preferably used for blowing water vapor.

  By heating the aqueous dispersion during the stripping treatment, it is possible to help volatilize volatile organic substances such as the residual polymerizable monomer and increase the recovery efficiency of the residual polymerizable monomer. The temperature of the aqueous dispersion during the stripping treatment is preferably a glass transition temperature Tg of the polymer component constituting the colored polymer particles of not less than 100 ° C., more preferably not less than Tg and not more than 95 ° C., more preferably not less than Tg + 5 ° C. and not less than 90 ° C. It is below ℃. The glass transition temperature is a value measured by a differential scanning calorimeter (DSC). When the polymer component has two or more Tg, the lowest Tg is used as a reference. During the stripping process, it is desirable to control the heating conditions and the like so that the temperature of the aqueous dispersion is maintained substantially constant at a desired temperature within the above range.

  The aqueous dispersion is heated using, for example, an evaporator (container or tank) provided with a heat medium circulation jacket, an evaporator provided with a heat exchanger, an evaporator connected to an external heat exchanger, or the like. . The aqueous dispersion may be heated by blowing heated gas. If the temperature of the aqueous dispersion is too low, evaporation of the aqueous dispersion due to the stripping process becomes insufficient, and the movement of the residual polymerizable monomer in the colored polymer particles becomes slow, and the residual polymerizable single amount The body removal rate decreases. On the other hand, if the temperature of the aqueous dispersion is too high, the dispersion stability of the colored polymer particles decreases, and agglomerates are formed during the stripping process, or the scale adheres to the wall surfaces of the evaporator and the stirrer. .

  Although the pressure in an evaporator can be suitably determined with the specific method of a stripping process, it is normally selected from the range of 5-105 kPa. When the gas blowing method is adopted as the stripping treatment method, it is preferable that the pressure in the evaporator is usually in the range of 70 to 105 kPa. When adopting a vacuum stripping method or a method of vacuum stripping while blowing gas, the pressure in the evaporator is normally controlled within a range of 5 to 70 kPa, preferably 10 to 60 kPa, more preferably 20 to 50 kPa. It is desirable to do.

  The stripping treatment time varies depending on the scale of the treatment apparatus, the treatment amount, the specific treatment method, the level of the desired residual polymerizable monomer amount, etc., but is usually 0.5 to 50 hours, preferably 1 to 30. The time can be selected from the range of 3 to 20 hours, more preferably.

  It is preferable to arrange a stirrer in the evaporator and perform the stripping treatment while stirring the aqueous dispersion. The stirrer is not particularly limited, but for example, a stirrer provided with stirring blades (blades) such as a flat plate paddle, an inclined paddle, a bull margin blade and its deformed blade, a full zone blade, and a wall wetter blade is preferable.

  The peripheral speed of the blade tip of the stirring blade (hereinafter sometimes referred to as “the peripheral speed of the stirring blade”) is not particularly limited, but is preferably 0.1 to 6 m / sec, more preferably 0.3 to 5 m / second. It is desirable to control within a range of sec, more preferably within a range of 0.5 to 4 m / sec.

  Stripping treatment removes part of the aqueous medium of the aqueous dispersion, residual polymerizable monomer contained in the aqueous dispersion, residual polymerizable monomer in the colored polymer particles, and other volatile volatile substances. Is done. As described above, the aqueous dispersion in the evaporator is concentrated by the stripping treatment, but an aqueous medium may be newly added to replenish the evaporated aqueous medium, if desired. However, according to the method of the present invention, the stripping process can be performed efficiently without adding an aqueous medium. Residual polymerizable monomers and aqueous media can be recovered and reused.

  FIG. 1 shows an example of a stripping processing system that can be suitably employed in the method of the present invention. The evaporator 1 is provided with a stirrer 3 having a stirring blade. A heat medium circulation jacket 2 is provided on the outer peripheral wall of the evaporator 1 so that the temperature in the evaporator can be adjusted to a desired temperature. A gas such as nitrogen gas is blown into the evaporator 1 through a gas blowing pipe 5 by a blower 6 from a gas source (not shown).

  While stirring the aqueous dispersion 4 in the evaporator 1 with the stirrer 3, the temperature in the evaporator 1 is raised to a predetermined temperature, and then a gas is blown from the blower 6 into the evaporator 1 through the opening of the pipe 5. Infuse. Part of the aqueous medium of the aqueous dispersion, residual polymerizable monomer, and other volatile substances are led to the condenser 8 through the gas line 7 and then to the condensation tank 9. Liquid components such as water condensed and liquefied in the condensation tank 9 are collected there (recovery line not shown). The gaseous component is guided to the volatile substance removing device 11 through the gas line 10. The volatile substance removing device 11 is, for example, an adsorption tower filled with activated carbon or a bubbling device in which cold water is stored, and the polymerizable monomer and other volatile organic substances are removed there. Thereafter, a gaseous component such as nitrogen gas is circulated and reused by blowing into the evaporator 1 from the opening of the gas blowing pipe 5 through the gas circulation line 12 through the blower 6 and the gas circulation line 13. Can do.

  As shown in FIG. 2, a non-contact type level meter 16 is installed on the top of the evaporator 1. As the non-contact type level meter, a microwave level meter is preferable. The microwave level meter is based on the principle of frequency modulation (FM) -continuous wave (CW) radar, and the time required for the microwave to reciprocate between the reference position of the installed transmitter and the surface of the object to be measured. It is a measuring device that uses the fact that the measurement distance is proportional to determine the level by measuring. The microwave level meter can measure the level with high accuracy without contact with the object to be measured simply by being attached to the installation nozzle on the tank. The present inventor has found that this microwave level meter can be used for accurate measurement of the liquid level including bubbles generated at the gas-liquid interface of an aqueous dispersion containing colored polymer particles.

The flow rate of a gas such as nitrogen gas or water vapor is preferably 0.03 to ³ m ³ / (hr · kg), more preferably 0.05 to ² m ³ / (hr · kg) from the viewpoint of suppressing excessive foaming. It is desirable to control to be within a range of the degree. When vacuum stripping is simply performed without blowing gas, the heated aqueous dispersion is evaporated without increasing the vacuum level within the system without using the blower 6.

In the present invention, an aqueous dispersion containing colored polymer particles is supplied into an evaporator, and stripping is performed in the evaporator. At that time, the aqueous dispersion before stripping in the evaporator The processing conditions are controlled so that the ratio L ₂ / L ₁ of the maximum liquid depth L ₂ of the aqueous dispersion is within the range of 1.1 to 2.0 due to the rise in the liquid level during the stripping process with respect to the maximum liquid depth L ₁ . Stripping process is performed.

As shown in FIG. 2, the maximum liquid depth of the aqueous dispersion 4 supplied into the evaporator 1 before the stripping process (that is, the liquid depth in a stationary state) is the liquid level 14 of the aqueous dispersion and the evaporator 1. the length L ₁ is between the bottom of the deepest portion of the inner. During the stripping process, the liquid level of the aqueous dispersion 4 rises from the liquid level 14 at rest to the liquid level 15 by heating, stirring, blowing of gas, decompression, foaming, and the like. Maximum liquid depth due to the liquid level rise is represented by L ₂ shown in FIG.

Conventionally, for example, when a stripping process is performed by blowing a gas such as nitrogen gas into an aqueous dispersion, the processing conditions are often controlled so that the bubble level at the initial stage of the stripping process shows a maximum value. This foam level is usually kept low and gradually decreases during the stripping process. As described above, in the prior art, the stripping process is performed while suppressing an increase in the liquid level during the stripping process. In the prior art, the liquid level in the evaporator has not been measured during the stripping process. Furthermore, the rise in the liquid dispersion liquid level varies depending on various factors such as the type and flow rate of the blown gas, the number of revolutions of the stirring blade, the pressure in the evaporator, and the foaming suppression means. For these reasons, it is common to employ a means for suppressing the rise in the liquid level during the stripping process as much as possible. The liquid level rise (liquid depth) is positively allowed and the ratio L ₂ / L ₁ until controlling the process conditions to be within a predetermined range, did not envision even a person skilled in the art.

In contrast, in the present invention, the liquid level during the stripping process is detected by a non-contact type level meter, and the ratio L ₂ / L ₁ is 1.1 to 2.0 based on the detected level information. Stripping processing is performed while controlling processing conditions so as to be within the range. The ratio L ₂ / L ₁ is preferably 1.2 to 1.9, more preferably 1.25 to 1.80, and particularly preferably 1.40 to 1.80.

In order to set the ratio L ₂ / L ₁ to such a large value, an evaporator having a large processing volume is used or the amount of aqueous dispersion supplied into the evaporator is reduced. Furthermore, the type and flow rate of the gas blown into the aqueous dispersion, the shape of the gas inlet, the pressure in the evaporator, the temperature of the aqueous dispersion, the peripheral speed of the stirring blade, the type and amount of antifoaming agent, or these Control processing conditions consisting of two or more combinations. Preferred processing conditions can be obtained in advance by experiments, and initial processing conditions can be set based on the experimental results. Further, these processing conditions may be changed during the stripping process. For example, when the liquid level shows a tendency to decrease by measurement with a non-contact type level meter, the ratio L ₂ / L ₁ can be adjusted within a predetermined range by increasing the amount of gas blown.

When the ratio L ₂ / L ₁ is less than 1.1, the removal rate of volatile organic substances such as residual polymerizable monomers is decreased, and it takes a long time to reach a desired residual polymerizable monomer concentration. In short, production efficiency is reduced. On the other hand, if the ratio L ₂ / L ₁ becomes too large, it becomes necessary to increase the capacity of the evaporator or make the amount of the aqueous dispersion charged too small, which is not practical.

  According to the method of the present invention, the treatment conditions can be controlled so as to positively allow the liquid dispersion of the aqueous dispersion to rise, so that the stripping treatment can be performed efficiently. According to the method of the present invention, colored polymer particles having a residual polymerizable monomer content of usually 130 ppm or less, preferably 100 ppm or less, more preferably 95 ppm or less can be obtained by controlling the stripping treatment conditions. . If desired, the content of the residual polymerizable monomer in the colored polymer particles can be reduced to 60 ppm or less, and further to 50 ppm or less.

  In the colored polymer particles (polymerized toner) obtained by the method of the present invention, fog is remarkably suppressed, the image density is high, and there is no variation in image density. Further, the polymerized toner obtained by the method of the present invention is excellent in storage stability, and blocking during storage is suppressed. When the non-silicone antifoaming agent described above is used as an antifoaming agent, a polymerized toner having a high charge amount can be obtained without adversely affecting the chargeability of the polymerized toner.

3. Collection process :
After the stripping step 2, colored polymer particles are recovered from the aqueous dispersion. The collection of the colored polymer particles is performed by dehydration, washing, filtration, and drying processes according to a conventional method, and the dried colored polymer particles are collected. Prior to dehydration, in order to solubilize and remove the used dispersant, treatment such as acid cleaning or alkali cleaning is performed according to the type of the dispersant.

  The volume average particle size of the polymerized toner (including core / shell type polymerized toner) of the present invention is usually 1 to 12 μm, preferably 2 to 11 μm, more preferably 3 to 10 μm. In the case of obtaining a high-definition image by increasing the resolution, it is desirable to reduce the volume average particle diameter of the polymerized toner to preferably 2 to 9 μm, more preferably 3 to 8 μm.

  The particle size distribution represented by the volume average particle size dv / number average particle size dp of the polymerized toner of the present invention is usually 1.7 or less, preferably 1.5 or less, more preferably 1.3 or less. If the volume average particle diameter dv of the polymerized toner is too large, the resolution tends to be lowered. If the particle size distribution dv / dp of the polymerized toner is too large, the ratio of the colored polymer particles having a large particle size increases, and the resolution tends to decrease.

  The polymer toner of the present invention is substantially spherical with a sphericity represented by a ratio dl / ds of the major axis dl to the minor axis ds of preferably 1 to 1.3, more preferably 1 to 1.2. It is preferable. When substantially spherical polymerized toner is used as the non-magnetic one-component developer, the transfer efficiency of the toner image on the photoreceptor to the transfer material is improved.

  The polymerized toner of the present invention can be used as a toner component of various developers, but is preferably used as a nonmagnetic one-component developer. When the polymerized toner of the present invention is a non-magnetic one-component developer, an external additive can be mixed as necessary. Examples of the external additive include inorganic particles and organic resin particles that act as a fluidizing agent and an abrasive.

  Examples of the inorganic particles include silicon dioxide (silica), aluminum oxide (alumina), titanium oxide, zinc oxide, tin oxide, barium titanate, and strontium titanate. As organic resin particles, methacrylic acid ester polymer particles, acrylic acid ester polymer particles, styrene-methacrylic acid ester copolymer particles, styrene-acrylic acid ester copolymer particles, a core is a styrene polymer, and a shell is methacrylic acid. Examples thereof include core / shell type particles formed of an ester copolymer.

  Among these, inorganic oxide particles are preferable, and silicon dioxide is particularly preferable. The surface of the inorganic fine particles can be hydrophobized, and silicon dioxide particles that have been hydrophobized are particularly suitable. Two or more types of external additives may be used in combination. In the case of using a combination of external additives, a method of combining inorganic particles having different average particle sizes or a combination of inorganic particles and organic resin particles is preferable. . The amount of the external additive is not particularly limited, but is usually 0.1 to 6 parts by weight with respect to 100 parts by weight of the polymerized toner. In order to attach the external additive to the polymerized toner, the polymerized toner and the external additive are usually placed in a mixer such as a Henschel mixer and stirred.

  EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. However, the present invention is not limited only to the following examples. Parts and% are based on weight unless otherwise specified. The evaluation methods performed in this example are as follows.

1. Evaluation method in stripping process:
(1) Measurement of liquid depth:
A non-contact type microwave level meter was placed on the top of the evaporator, and the liquid depth was measured by the level meter. The microwave level meter is based on the principle of frequency modulation (FM) -continuous wave (CW) radar, and the time required for the microwave to reciprocate between the reference position of the installed transmitter and the surface to be measured. Is a measuring device that obtains a level using the fact that the measurement distance is proportional to the measurement distance. A microwave level meter can perform high-accuracy level measurement without touching the object to be measured simply by being attached to the installation nozzle above the evaporator. The maximum liquid depth was calculated from the height of the evaporator and the distance between the top of the evaporator and the liquid level.

(2) Measurement of residual polymerizable monomer amount:
2-1. Before stripping process:
The colored polymer particles (3 g) before the stripping treatment are accurately weighed to the nearest 1 mg. After adding 27 g of N, N-dimethylformamide to 3 g of the colored polymer particles and stirring for 15 minutes, 13 g of methanol is added and further stirred for 10 minutes. The solution thus obtained is allowed to stand to precipitate insolubles. The supernatant of this solution is taken as a measurement sample, and 2 μl thereof is injected into a gas chromatograph to quantify the polymerizable monomer.

  The measurement conditions by gas chromatograph are column = TC-WAX (0.25 mm × 30 m), column temperature = 80 ° C., injection temperature = 200 ° C., FID detection side temperature = 200 ° C. As a standard sample for determination, an N, N-dimethylformamide / methanol solution of each monomer is used.

  Since the colored polymer particles before the stripping treatment are in a wet state, the amount of the polymerizable monomer in the colored polymer particles is calculated as a ratio to the pure solid content in the wet colored polymer particles. That is, the amount of the polymerizable monomer is calculated by multiplying the calculated pure solid content ratio by the amount of the polymerizable monomer in the wet colored polymer particles. The pure solid content in the wet colored polymer particles is determined by the following procedure.

  (i) An aqueous dispersion of colored polymer particles before the stripping treatment is collected. (ii) The collected aqueous dispersion is filtered to obtain wet colored polymer particles. (iii) Weigh the wet colored polymer particles to the nearest 1 mg. (iv) The wet colored polymer particles are dried at 105 ° C. for 1 hour, and the weight of the solid content obtained by drying is precisely weighed. (v) The ratio of the pure solid content in the colored polymer particles in a wet state is calculated from the difference in weight before and after drying.

2-2. After stripping process:
After the stripping process, 3 g of the washed and dried colored polymer particles are precisely weighed to the nearest 1 mg. The amount of polymerizable monomer is measured in the same manner as described above except that the colored polymer particles are used. The amount of the polymerizable monomer in the colored polymer particles after washing and drying is calculated as a ratio to the weight of the colored polymer particles. In Examples and Comparative Examples, the type of the residual polymerizable monomer after the stripping treatment / drying was only styrene.

2-3. Removal rate of residual polymerizable monomer:
The removal rate of the remaining polymerizable monomer in the colored polymer particles is expressed as a ratio of the amount of polymerizable monomer removed per unit time based on the amount of polymerizable monomer before stripping. It is the value. That is, during the stripping process, sampling is performed every hour, and the amount of the polymerizable monomer is measured by the above method. Based on this measurement result, “processing time x” vs. “polymerizable monomer amount y” is plotted, and a semilogarithmic graph with y as a logarithm is created. An exponential approximation formula y = a · e ^−bx is created from this graph, and the following formula is used, using this formula ^: Rs = 100 · (1−e ^−b )
To calculate the monomer reduction rate Rs (% / hr). This Rs value is taken as the removal rate of the residual polymerizable monomer.

2. Measurement of particle size and particle size distribution of colored polymer particles:
The particle size distribution represented by the volume average particle diameter dv of the colored polymer particles and the ratio dv / dp of the volume average particle diameter dv and the number average particle diameter dp is measured by Multisizer (manufactured by Beckman Coulter, Inc.). . The measurement conditions with the multisizer are: aperture diameter = 100 μm, medium = Isoton II, concentration = 10%, number of measured particles = 100,000.

3. Evaluation of storage stability:
The developer was put in a sealable container and sealed, and then the container was submerged in a constant temperature water bath maintained at a temperature of 55 ° C. After 8 hours, the container was taken out of the constant temperature water bath, and the developer in the container was transferred onto a 42 mesh sieve. At this time, the developer is gently taken out of the container and carefully transferred onto a sieve so as not to destroy the aggregated structure of the developer. The sieve was vibrated for 30 seconds using a powder measuring machine under conditions of a vibration intensity of 4.5, and the weight of the developer remaining on the sieve was measured to obtain the weight of the aggregate developer. The weight percent of the aggregate developer relative to the weight of the developer initially placed in the container was calculated. Each sample was measured three times, and the average value was used as an index of storage stability.

4). Image evaluation:
(1) Print density:
Copy paper is set in a commercially available non-magnetic one-component developing type printer (printing speed = 24 sheets / min), and developer (toner) to be evaluated is put in the developing device. After standing overnight in an environment (N / N environment) at a temperature of 23 ° C. and a humidity of 50%, continuous printing is performed from the beginning at 5% density, and solid printing is performed at the time of printing the 100th sheet. Using a McBeth transmission image density measuring machine, the solid front end print density and the solid rear end print density were measured.

(2) Fog:
The developer to be evaluated is put in a developing device of a commercially available non-magnetic one-component developing system printer (printing speed = 24 sheets / min), and left for a whole day and night in an environment of 23 ° C. and 50% humidity (N / N environment). Thereafter, continuous printing is performed on the printing paper at a printing density of 5%, solid white printing is performed on the 100th sheet, and printing is stopped halfway. The toner on the photoconductor after development is peeled off with an adhesive tape (trade name “Scotch Mending Tape 810-3-18”, manufactured by Sumitomo 3M Limited), and the toner is pasted on a new printing paper. Next, the whiteness b of the printing paper with the adhesive tape attached is measured with a whiteness meter (Nippon Denshoku Co., Ltd.), and the whiteness a of the printing paper with the adhesive tape alone is measured in the same manner. To do. A difference a−b between the whiteness a and the whiteness b is calculated and set as a fog value.

[Example 1]
(1) Preparation process of polymerizable monomer composition for core:
Styrene 80.5 parts and n-butyl acrylate 19.5 parts, polymethacrylic acid ester macromonomer (manufactured by Toa Gosei Chemical Co., Ltd., trade name “AA6”, Tg = 94 ° C.) 0.3 parts, divinylbenzene 0.5 Parts, 1.2 parts of t-dodecyl mercaptan, 7 parts of carbon black (trade name “# 25” manufactured by Mitsubishi Chemical Corporation), 1 part of charge control agent (trade name “Spiron Black TRH” manufactured by Hodogaya Chemical Co., Ltd.) , And 2 parts of release agent (Fischer-Tropsch wax, manufactured by Sasol, trade name “Paraprint Spray 30”, endothermic peak temperature = 100 ° C.) are supplied to a media-type wet pulverizer to perform wet pulverization. A polymerizable monomer composition was prepared.

(2) Preparation process of aqueous medium:
To an aqueous solution in which 10.2 parts of magnesium chloride is dissolved in 200 parts of ion-exchanged water, an aqueous solution in which 6.2 parts of sodium hydroxide is dissolved in 50 parts of ion-exchanged water is gradually added with stirring to obtain a magnesium hydroxide colloid ( A slightly water-soluble metal hydroxide colloid). When the particle size of the generated colloid was measured with a Microtrac particle size distribution measuring instrument (manufactured by Nikkiso Co., Ltd.), D50 (50% cumulative value of the number particle size distribution) was 0.35 μm, and D90 (90 of the number particle size distribution). % Cumulative value) was 0.84 μm. The measurement conditions in the microtrack particle size distribution measuring instrument were measurement range = 0.12 to 704 μm, measurement time = 30 seconds, and medium = ion exchange water. In this manner, an aqueous medium containing magnesium hydroxide colloid as a dispersant was prepared.

(3) Preparation process of aqueous dispersion of polymerizable monomer for shell:
3 parts of methyl methacrylate and 100 parts of water were finely dispersed with an ultrasonic emulsifier to obtain an aqueous dispersion of a polymerizable monomer for shell. The droplet diameter of the polymerizable monomer for shell was measured by adding the obtained droplet to a 1% sodium hexametaphosphate aqueous solution at a concentration of 3% and measuring with a Microtrac particle size distribution analyzer. It was 1.6 μm.

(4) Droplet formation process:
The core polymerizable monomer composition prepared in the step (1) was added to the aqueous medium containing the magnesium hydroxide colloid obtained in the step (2) and stirred until the droplets were stabilized. Next, 6 parts of t-butyl peroxy-2-ethylhexanoate (manufactured by NOF Corporation, trade name “Perbutyl O”) as a polymerization initiator is added to an aqueous medium, and then an emulsifier / disperser Ebara Milder (Hagiwara) (Made by Seisakusho Co., Ltd.) was used for high shear stirring to form fine droplets of the polymerizable monomer composition in the aqueous medium. In this manner, an aqueous dispersion in which droplets of the polymerizable monomer composition for the core were dispersed was prepared.

(5) Polymerization process:
The aqueous dispersion in which the droplets of the polymerizable monomer composition for core prepared in step (4) were dispersed was placed in a reactor equipped with a stirring blade, and the temperature was raised to 85 ° C. to initiate the polymerization reaction. . The polymerization reaction was carried out until the polymerization conversion reached almost 100%. At that time, the water-soluble initiator [manufactured by Wako Pure Chemical Industries, Ltd., trade name “VA-086”; 2,2′-azobis [2 -Methyl-N- (2-hydroxyethyl) -propionamide]] in an aqueous solution in which 0.3 part was dissolved was added to the reactor. After the polymerization was continued for 4 hours, the reaction was stopped by cooling to obtain an aqueous dispersion containing the produced colored polymer particles having a core / shell structure. The solid content concentration of the aqueous dispersion was 27%. At this point, the amount of residual polymerizable monomer in the colored polymer particles before the stripping treatment was measured.

(6) Stripping process:
A cylindrical container (evaporator) was used for the stripping process. When the inner diameter of the container is D and the height is L, L / D = 1.2. The volume V of the container can be obtained by V = πD ² L / 4 = 0.3πD ³ ). A stirrer having a stirring blade is disposed at the center of the container. The stirring blade is composed of four 45 ° inclined paddle blades having a diameter d (= D / 2) and a width b = (D / 6), and is mounted in two stages on the stirring shaft. The center of the lower stirring blade is located at a height of L / 6 from the bottom of the container, and the center of the upper stirring blade is located at a height of L / 3 from the bottom of the container. Stirring was performed at a rotational speed such that the peripheral speed of the blade tip of the stirring blade (peripheral speed of the stirring blade) was 1 m / sec. The non-contact type microwave level meter was installed at a position of D / 4 from the center at the top of the container. The aqueous dispersion of colored polymer particles obtained in the step (5) was placed in this container so that the volume was V / 2, that is, the maximum liquid depth was L ₁ = L / 2.

For the stripping process, the processing system shown in FIG. 1 was used. That is, the evaporator 1 (container) provided with the temperature control jacket 2 and the stirring device 3 was used for the stripping process. An aqueous dispersion of colored polymer particles was diluted with ion exchange water to a solid content concentration of 20% to prepare an aqueous dispersion for stripping treatment. The aqueous dispersion 4 was supplied into the evaporator 1. Next, 0.1 part of an antifoaming agent (manufactured by San Nopco, trade name “SN Deformer 180”) was added to the aqueous dispersion 4 in the evaporator 1. Nitrogen gas was allowed to flow from the gas blowing pipe 5 at the bottom in the evaporator 1, and the gas phase part of the evaporator 1 was replaced with nitrogen gas. Next, after the aqueous dispersion 4 is heated to 80 ° C. while being stirred with the stirrer 3, the blower 6 is started and the flow rate of nitrogen gas is adjusted to 0.16 m ³ / (hr · kg). Then, nitrogen gas was blown into the aqueous dispersion 4 from the gas blowing pipe 5 having a straight tube shape, and stripping treatment was performed to remove the residual polymerizable monomer from the aqueous dispersion 4. .

  The nitrogen gas after stripping was sequentially led to the condenser 8 and the condensation tank 9 through the line 7. The condensed nitrogen gas was passed through a line 10 to a volatile substance removing device (adsorption tower filled with activated carbon) 11 where volatile substances such as polymerizable monomers contained in the nitrogen gas were removed. The nitrogen gas from which volatile substances were removed passed through the circulation line 12, and was blown again into the evaporator 1 from the blower 6 through the line 13 and the gas blowing pipe 5.

Stripping treatment was performed for 6 hours at a temperature of about 80 ° C. of an aqueous dispersion of colored polymer particles, a pressure of 101 kPa in the evaporator 1, and a nitrogen gas flow rate of 0.6 m ³ / (hr · kg). During the stripping process, sampling was performed every hour, and the amount of residual polymerizable monomer in the colored polymer particles was measured. After 6 hours of treatment, the aqueous dispersion was cooled to 25 ° C.

(7) Post-processing process:
After step (6), sulfuric acid is added to the aqueous dispersion of colored polymer particles in the evaporator 1 while stirring to perform acid cleaning (25 ° C., 10 minutes), and the pH of the aqueous dispersion is 4.5 or less. Adjusted. Next, the aqueous dispersion was dehydrated and washed using a continuous belt filter (trade name “Eagle Filter” manufactured by Sumitomo Heavy Industries, Ltd.), and the solid content was separated by filtration. The solid content was dried with a dryer at 45 ° C. for 10 hours. Thus, colored polymer particles having a volume average particle size dv of 7.5 μm and a particle size distribution dv / dp of 1.19 (colored polymer particles having a core / shell structure) were recovered. The amount of residual polymerizable monomer in the colored polymer particles after drying was measured.

(8) Non-magnetic one-component developer preparation process:
To 100 parts of the colored polymer particles recovered in the step (7), 0.8 part of silica having a hydrophobized average particle diameter of 14 nm (made by Nippon Aerosil Co., Ltd., trade name “RX200”) is added, and a Henschel mixer is added. And mixed to prepare a non-magnetic one-component developer (electrophotographic toner) for developing electrostatic images. Image evaluation was performed about the obtained toner. The results are shown in Table 1.

[Example 2]
A diffuser plate (manufactured by Daisen Membrane Systems Co., Ltd .; BPF-12) is connected to the opening of the gas blowing tube (hereinafter, sometimes referred to as “gas blowing port”), and the peripheral speed of the stirring blade The operation was performed in the same manner as in Example 1 except that 1 was changed from 1 m / sec to 2.0 m / sec. The results are shown in Table 1.

[Example 3]
The nitrogen gas flow rate during the stripping process was changed from 0.16 m ³ / (hr · kg) to 0.08 m ³ / (hr · kg), and the peripheral speed of the stirring blade was changed from 1 m / sec to 2.0 m / The same operation as in Example 1 was performed except that the period was changed to sec. The results are shown in Table 1.

[Example 4]
The nitrogen gas flow rate during the stripping process was changed from 0.16 m ³ / (hr · kg) to 0.08 m ³ / (hr · kg), and a diffuser plate [Daisen Membrane Systems ( The same operation as in Example 1 was carried out except that BPF-12] was used. The results are shown in Table 1.

[Example 5]
The same as in Example 1 except that the blowing of nitrogen gas was stopped, the pressure in the evaporator was reduced to 40 kPa, and the peripheral speed of the stirring blade was changed from 1 m / sec to 2.0 m / sec. Operated. The results are shown in Table 1.

[Example 6]
The same operation as in Example 1 was performed except that steam at 100 ° C. was steamed at a flow rate of 1.5 kg / (hr · kg) instead of nitrogen gas. The results are shown in Table 1.

[Example 7]
Instead of blowing nitrogen gas, steam (steam) at 100 ° C. is blown at a flow rate of 1.5 kg / (hr · kg), and a diffuser plate [Daisen -The same operation as in Example 1 was performed except that MPF manufactured by Membrane Systems Co., Ltd .; BPF-12] was connected. The results are shown in Table 1.

[Comparative Example 1]
The same operation as in Example 1 was performed except that the nitrogen gas flow rate during the stripping treatment was changed from 0.16 m ³ / (hr · kg) to 0.08 m ³ / (hr · kg). The results are shown in Table 1.

[Comparative Example 2]
Without the addition of a defoaming agent, a nitrogen gas flow rate at the stripping process change 0.16 m ³ / from (hr · kg) to ^{0.32m 3 / (hr · kg)} , diffuser plate to the gas blowing inlet [ Daisen Membrane Systems Co., Ltd .; BPF-12] was connected, and the peripheral speed of the stirring blade was changed from 1 m / sec to 2.0 m / sec. did. The aqueous dispersion overflowed and processing could not be continued. The results are shown in Table 1.

[Comparative Example 3]
The same operation as in Example 1 was performed except that the blowing of nitrogen gas was stopped and the pressure in the container was reduced to 80 kPa. The results are shown in Table 1.

[Comparative Example 4]
The operation was performed in the same manner as in Example 6 except that the flow rate of water vapor at 100 ° C. was changed from 1.5 kg / (hr · kg) to 0.3 kg / (hr · kg). The results are shown in Table 1.

  According to the production method of the present invention, a volatile organic substance can be efficiently removed in the stripping process, the content of the residual polymerizable monomer is remarkably reduced, and a polymer toner having excellent toner characteristics is obtained. Provided. The polymerized toner obtained by the method of the present invention can be used as a main component constituting a developer of an image forming apparatus using an electrophotographic system or an electrostatic recording system.

1 is a schematic diagram showing an example of a stripping processing system employed in the present invention. It is sectional drawing which shows the liquid level and maximum liquid depth in an evaporator.

Explanation of symbols

1: evaporator, 2: jacket, 3: stirrer equipped with stirring blades,
4: aqueous dispersion of colored polymer particles, 5: gas blowing tube, 6: blower,
7: gas line, 8: condenser, 9: condensation tank, 10: gas line,
11: Volatile substance removal device, 12: Gas circulation line, 13: Gas circulation line,
14: Liquid level before stripping treatment, 15: Liquid surface during stripping treatment,
16: Non-contact type microwave level meter.

Claims (9)

A polymer formed by polymerizing a polymerizable monomer in an aqueous medium is used as a binder resin by a polymerization step or a polymerization step followed by a coagulation step, and colored polymer particles in which at least a colorant is dispersed therein are generated. Step 1 for obtaining an aqueous dispersion containing the colored polymer particles, and a step of stripping the aqueous dispersion containing the colored polymer particles to remove volatile organic substances contained in the colored polymer particles. In the method for producing a polymerized toner containing 2, an aqueous dispersion containing colored polymer particles is supplied into an evaporator, and the stripping process in step 2 is performed in the evaporator, The ratio L ₂ / L ₁ of the maximum liquid depth L ₂ of the aqueous dispersion due to the rise in the liquid level during the stripping process relative to the maximum liquid depth L ₁ of the aqueous dispersion before the stripping process is 1.1 to 2.0 Processing conditions to be within range Method for producing a polymerized toner which is characterized in that the stripping treatment while controlling the.   The manufacturing method of Claim 1 which performs a stripping process by the method of blowing gas in the water dispersion liquid in an evaporator, or the method of depressurizing the inside of an evaporator.   The production method according to claim 1 or 2, wherein the stripping treatment is performed while stirring the aqueous dispersion in the evaporator with a stirrer equipped with a stirring blade.   4. The stripping treatment is performed while heating the aqueous dispersion in the evaporator to a temperature not lower than 100 ° C. and not lower than the glass transition temperature of the polymer component constituting the colored polymer particles. 5. Manufacturing method.   The production method according to any one of claims 1 to 4, wherein a stripping treatment is performed by adding an antifoaming agent to the aqueous dispersion. During the stripping process, the liquid depth is measured by a non-contact type level meter provided at the top of the evaporator, and the processing conditions are controlled so that the ratio L ₂ / L ₁ is in the range of 1.1 to 2.0. The manufacturing method according to claim 1, wherein the stripping process is performed while performing the stripping process.   The type and flow rate of the gas blown into the aqueous dispersion, the shape of the gas inlet, the pressure in the evaporator, the temperature of the aqueous dispersion, the peripheral speed of the stirring blade, the type and added amount of the antifoaming agent, or these two The manufacturing method of Claim 6 which performs a stripping process, controlling the process conditions consisting of the above.   The manufacturing method according to claim 6, wherein the non-contact type level meter is a non-contact type microwave level meter. The method according to any one of claims 1 to 8 wherein the ratio L _{2 /} L ₁ performs the stripping treatment while controlling the processing conditions to be within the range of 1.2 to 1.9.

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