JPH1010775A - Toner for developing electrostatic charge image and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently produce a spherical toner for developing an electrostatic charge image contg. a polymer and a colorant, having satisfactory transferability and uniform in particle diameter. SOLUTION: A polymer is dissolved in a solvent and mixed with a colorant, the resultant mixed soln. is dispersed in an aq. medium in the presence of an inorg. dispersant and then the solvent is removed by freeze-drying the resultant dispersion liq. at -10 to -200 deg.C, preferably -30 to -180 deg.C under <=40Pa, preferably <=13Pa pressure to produce the objective toner for developing an electrostatic charge image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a toner for developing an electrostatic image containing a polymer and a colorant.

[0002]

2. Description of the Related Art An electrophotographic method includes a charging step of imparting chargeability to a photoreceptor, an exposure step of forming an electrostatic latent image on the photoreceptor, a developing step of developing the electrostatic latent image with toner, and a step of developing the developed image. The method includes a transfer step of transferring the image to a support such as paper, a fixing step of fixing the transferred image on the paper, and a cleaning step of removing the toner remaining on the photoconductor. The toner used in this method is usually produced by a kneading and pulverizing method in which a polymer is melt-kneaded together with a pigment and a charge controlling agent, cooled, finely pulverized, and further classified. The shape of the toner obtained by this method is irregular, and the irregular toner has a drawback that the developed toner image is not completely transferred to a support such as paper, that is, there is a so-called reduction in transfer efficiency. Further, in the kneading and pulverizing method, the shape of the toner slightly changes depending on the pulverizability of the material used and the conditions of the pulverizing process, and it is difficult to intentionally control the toner shape.

A method for obtaining a spherical toner is disclosed in
As described in JP-A-3-25664, a polymer solution (a toner composition mixed solution) previously dissolved in a solvent is dispersed in an aqueous medium, and the solvent is removed from the obtained dispersion to form particles. There are known ways to do this.
However, this method basically removes the solvent in a liquid state, and the dispersed particles tend to aggregate during the removal of the solvent, so that spherical particles cannot be efficiently obtained.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances in the prior art.
That is, an object of the present invention is to provide a spherical toner for developing an electrostatic image containing a polymer and a colorant, having a good transferability and a uniform particle size, and a method for efficiently producing the same. .

[0005]

Means for Solving the Problems As a result of diligent studies by the present inventors, a step of dissolving a polymer in a solvent and mixing a colorant, and a step of dispersing the obtained mixed solution in an aqueous medium containing an inorganic dispersant. And a method for producing a toner for developing an electrostatic image, which has a step of removing the solvent from the obtained suspension, if the solvent is removed by freeze-drying, the toner has good transferability and a uniform particle size. The inventors have found that a spherical toner for developing a charge image can be obtained efficiently, and have completed the present invention.

That is, the method for producing a toner for developing an electrostatic image of the present invention comprises a step of dissolving a polymer in a solvent and mixing a colorant, and dispersing the obtained mixed solution in an aqueous medium in the presence of an inorganic dispersant. And a step of removing the solvent by freeze-drying the obtained dispersion. Further, the toner for developing an electrostatic image of the present invention is characterized by being manufactured by the above method.

[0007]

Embodiments of the present invention will be described below in detail. The method for producing the electrostatic image developing toner of the present invention will be described. In the present invention, in the first step, a polymer and a colorant, and if necessary, a compound appropriately mixed with a release agent and a charge control agent, which are usually added to toner particles, are added to a solvent and dissolved and mixed. It is necessary to. In this case, the components may be blended in advance by melting and kneading a polymer with a colorant, a release agent, a charge control agent, and the like, or, after dissolving the polymer in a solvent, a colorant, It may be obtained by dispersing and mixing a release agent, a charge control agent, and the like using a media-containing disperser such as a ball mill or a sand mill, or a high-pressure disperser. In this mixing step, mixing may be performed by any method as long as the method dissolves the polymer in the solvent.

The polymers used in the present invention include styrenes such as styrene and chlorostyrene, monoolefins such as ethylene, propylene, butylene and isoprene, and vinyls such as vinyl acetate, vinyl propionate, vinyl benzoate and vinyl butyrate. Esters, methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, phenyl acrylate,
Α-methylene aliphatic monocarboxylic acid esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, dodecyl methacrylate, vinyl methyl ether,
Examples thereof include homopolymers and copolymers of monomers such as vinyl ethers such as vinyl ethyl ether and vinyl butyl ether, and vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone and vinyl isopropenyl ketone. Examples of suitable polymers include polystyrene, styrene-alkyl acrylate copolymer, styrene-alkyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyethylene, Polypropylene and the like can be given. Further examples include polyester, polyurethane, epoxy resin, silicone resin, polyamide, modified rosin, paraffin wax and the like.

The coloring agents used in the present invention include carbon black, magnetic powder, cyan, magenta, yellow,
Other known coloring agents for the toner particles for electrostatic image development can be used.

[0010] Examples of the release agent include low molecular weight polyolefins such as polyethylene and polypropylene, and others.
A known release agent for the toner particles for developing an electrostatic image can be used. Further, as the charge control agent, a quaternary ammonium salt compound and other known charge control agents for toner particles for electrostatic image development can be used.

[0011] The solvent used in the present invention includes:
Methyl acetate, ester solvents such as propyl acetate, ether solvents such as diethyl ether, methyl ethyl ketone,
Examples include ketone solvents such as methyl isopropyl ketone and methyl isobutyl ketone, hydrocarbon solvents such as toluene and cyclohexane, and halogenated hydrocarbon solvents such as dichloromethane, chloroform and trichloroethylene. These solvents must be capable of dissolving the polymer, and preferably have a water-soluble ratio of about 0 to 30% by weight. Also, when industrializing,
In consideration of safety, cost and productivity, cyclohexane is particularly preferred.

These solvents have a toner composition mixed solution having a viscosity of 1 to 10,000 mPa · s at 20 ° C. or 40 ° C.
s, particularly preferably 1 to 2000
It is blended so as to be in the range of mPa · s.

The second step of the present invention is a dispersion suspension step comprising dispersing the mixed solution obtained in the above mixing step in an aqueous medium in the presence of an inorganic dispersant. This dispersing and suspending step can be performed using an apparatus capable of applying a strong shearing force. As a device that can apply strong shearing force,
There is no particular limitation as long as it is generally commercially available as an emulsifying machine and a dispersing machine. Examples thereof include a homogenizer (manufactured by IKA), a polytron (manufactured by Kinematica),
Batch type emulsifier such as TK Auto Homomixer (manufactured by Tokushu Kika Kogyo), Ebara Milder (manufactured by Ebara Corporation), T
K pipeline homomixer (manufactured by Tokushu Kika Kogyo), colloid mill (manufactured by Shinko Pantech), slasher, trigonal wet pulverizer (manufactured by Mitsui Miike Kakoki), Cavitron (manufactured by Eurotech), fine flow mill (manufactured by Eurotech) Continuous emulsifying machine such as Taiheiyo Kiko Co., Ltd., high-pressure emulsifying machine such as Microfluidizer (manufactured by Mizuho Industries), Nanomizer (manufactured by Nanomizer), APV gourin (manufactured by Goulin), membrane emulsifying machine (cooling industry) ), A vibratory emulsifier such as a vibro mixer (manufactured by Reika Kogyo Co., Ltd.), and an ultrasonic emulsifier such as an ultrasonic homogenizer (manufactured by Branson).

The aqueous medium in the present invention must be used by dispersing an inorganic dispersant in water, and the polymer dispersant can be dissolved as required. The inorganic dispersant may be dispersed in water using a disperser with media such as a ball mill, an ultrasonic disperser, or the like. The polymer dispersant may be uniformly dissolved in water.

The water used in the present invention is generally ion-exchanged water, distilled water or pure water. As the inorganic dispersant, hydrophilic ones are preferable, and specific examples thereof include silica, alumina, titania, calcium carbonate, magnesium carbonate, tricalcium phosphate, clay, diatomaceous earth, bentonite and the like. Particularly, calcium carbonate is preferred. It is preferable that the surface of the inorganic dispersant is coated with a polymer having a carboxyl group, and the coating can stably produce the particle. As the polymer having a carboxyl group, a number average molecular weight of 1000 to 20 by a VPO method or the like is used.
Approximately 0000 can be used. Specific examples of the polymer having a carboxyl group used include acrylic acid resins, methacrylic acid resins, fumaric acid resins, maleic acid resins, and the like. Certain homopolymers of acrylic acid, methacrylic acid, fumaric acid, maleic acid and the like and copolymers thereof with other vinyl monomers can also be used.
Further, the carboxyl group may be a metal salt such as a sodium salt, a potassium salt, and a magnesium salt.

These inorganic dispersants have an average particle diameter of 1 to 1.
Those having a range of 1000 nm are used, and particularly preferably those having a range of 5 to 100 nm. Further, these inorganic dispersants are used in an amount of 1 to 500 parts by weight, preferably 10 to 300 parts by weight, based on 100 parts by weight of the toner.

The polymer dispersant used in the present invention is preferably a hydrophilic one, particularly preferably a polymer dispersant having a carboxyl group, and further has a non-lipophilic group such as a hydroxypropoxy group or a methoxy group. A polymer dispersant can be more preferably used. Specific examples include carboxymethylcellulose and carboxyethylcellulose, and carboxymethylcellulose is particularly preferable. These celluloses have a degree of etherification of 0.1.
Those having an average degree of polymerization of 6 to 1.5 and an average degree of polymerization of 50 to 3000 can be used. The carboxyl group is a sodium salt,
Metal salts such as potassium salts and magnesium salts may be used. These polymer dispersants have an aqueous medium viscosity of 20 ° C.
To 10000 mPa · s, and particularly preferably in the range of 1 to 2000 mPa · s.

The third step of the present invention is a solvent removing step for removing the solvent in the dispersion formed in the second dispersion and suspension step. In the solvent removing step, the solvent in the dispersion is removed by freeze-drying in order to suppress aggregation of the suspended particles in the suspension. Lyophilization is at -10 ° C to -200 ° C
Can be performed in the range of Preferably, it is in the range of −30 ° C. to −180 ° C. In addition, freeze-drying is performed under a pressure of 4
The treatment is performed at 0 Pa or less, and particularly preferably performed at 13 Pa or less.

In the present invention, the following steps can be performed as necessary. First, a washing and dehydrating step of removing, washing, and dehydrating an inorganic dispersant and a polymer dispersant from the fine particle powder generated in the third solvent removing step may be performed.
In the washing and dehydrating step, the fine particle powder generated in the solvent removing step is subjected to an acid treatment to dissolve the inorganic dispersant, followed by washing with water and dehydrating. However, an alkali treatment may be added after the acid treatment.

Further, as a next step, a drying step,
A sieving step and an external addition step can be performed. In these steps, drying of the fine-particle cake generated in the washing and dehydrating step,
By performing sieving and external addition, an electrostatic image developing toner is prepared. In these steps, drying, sieving, and external addition may be performed by any method as long as the method does not cause aggregation and pulverization of the toner.

[0021]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. The shape of toner particles is determined by scanning electron microscope (SEM)
The area (S) and the perimeter (L) of the toner were determined from a micrograph of the toner using an image analyzer Luzex (manufactured by Nireco), and the toner shape was quantified from the following shape factor. Shape factor = (L ² / S) / 4π × 100 The closer this value is to 100, the closer to a true sphere. In the spheroidization according to the present invention, the shape factor is desirably less than 120. A Coulter Multisizer II (manufactured by Coulter Inc.) was used to measure the particle size and distribution of the toner particles. The particle size is the weight average particle size and the measure of the breadth of the distribution is G
SD (Geometric Standard D)
evolution): (weight 50% diameter) / (weight 84%)
(Diameter). As this value approaches 1, the particle size becomes monodisperse. What is generally called monodisperse particles is GSD
The value is around 1.1. The obtained toner and 1
A 00 μm spherical iron carrier was mixed to form a developer, and the transfer efficiency was measured using this developer by a V500 copying machine manufactured by Fuji Xerox Co., Ltd.

Example 1 [Mixing Step] Ethylene-ethyl acrylate copolymer (83:17) (trade name: Evaflex EEA (A7
07), manufactured by Du Pont-Mitsui Chemicals, Inc. 16.35 g, carbon black 20 g and cyclohexane 200 g were stirred by a sand mill at 60 ° C. for 1 hour and then at 40 ° C. for 2 hours (this is referred to as solution A). On the other hand, 35.728 g of ethylene-ethyl acrylate copolymer (83:17) (trade name: Evaflex EEA (A707), manufactured by Du Pont-Mitsui Chemicals), cyclohexane 41
8.52 g was placed in a 1-liter separable flask and stirred at 55 ° C. for 6 hours to prepare a polymer solution (this is referred to as solution B). 6.82 g of Liquid A and 108.72 g of Liquid B were mixed to prepare an oil phase medium (this was referred to as Liquid C).

[Dispersion and Suspension Step] Also, 0.5 g of hydroxymethyl cellulose was dissolved in 149.5 g of ion-exchanged water, and then 40 g of calcium carbonate coated with an acrylic acid-maleic acid copolymer was added, followed by stirring for 1 hour ( This is referred to as liquid D). Add 47.04 g of D solution to 14 ion-exchanged water.
4.65 g was added, and this was used as an aqueous medium (this was referred to as solution E). The solution C was slowly charged while the solution E was stirred with a homogenizer, and stirred at 10,000 rpm for 2 minutes to obtain 307.23 g of a dispersion.

[Solvent Removal Step] The dispersion prepared in the dispersion suspension step was freed of cyclohexane for 2 days at −35 ° C. and 0.1 Pa using a freeze dryer. Agglomerates did not exist in the obtained fine particle powder.

[Washing Dehydration Step] 110.3 g of the fine particle powder obtained in the solvent removing step was washed twice with ion-exchanged water by suction filtration, followed by adding 2.5 kg of 0.6 N hydrochloric acid and washing by suction filtration. Further, 2.5 kg of 0.6 N sodium hydroxide was added, and washing with ion-exchanged water was repeated three times by suction filtration, followed by drying in a drier at 35 ° C. for 24 hours, sieving with a 45 μm mesh, and statically sieving. A toner for developing a charge image was obtained.

[Measurement] The shape of the obtained toner was measured by SEM.
As a result of the photograph, it was spherical and the shape factor was 107.
The average particle size of the toner obtained in the sieving step is 10.9.
μm, GSD was 1.18, and transfer efficiency was 98%.

Example 2 The procedure of Example 1 was repeated, except that in the solvent removal step, the dispersion suspension was treated with a freeze dryer at 0.2 Pa and -23 ° C. for 2 days to remove cyclohexane. . [Measurement] In the fine particle powder obtained after the solvent removing step, a small amount of aggregate was observed. The shape of the obtained toner is
As a result of the SEM photograph, it was spherical, and the shape factor of the toner was 10
Nine. The average particle size of the toner obtained in the sieving step was 10.8 μm, the GSD was 1.21, and the transfer efficiency was 97.
%Met.

Example 3 The polymer used in Example 1 was replaced with an ethylene-vinyl acetate copolymer (trade name: Evaflex EVA55)
0, manufactured by Du Pont-Mitsui Chemicals Co., Ltd.). [Measurement] Agglomerates were not observed in the fine particle powder obtained after the solvent removal step. The shape of the obtained toner was spherical as a result of the SEM photograph, and the shape factor of the toner was 108. The average particle size of the toner obtained in the sieving step was 10.4 μm, the GSD was 1.19, and the transfer efficiency was 98%.

COMPARATIVE EXAMPLE 1 In the solvent removal step, the dispersion was treated with 100 mmHg, 30 mmHg.
The procedure was performed in the same manner as in Example 1 except that the mixture was stirred at 3 ° C. for 3 hours. [Measurement] Agglomerates were observed in the fine particle suspension obtained after the solvent removal step. The shape of the obtained toner is SE
As a result of the M photograph, the surface was uneven, and the shape factor of the toner was 126. The average particle size of the toner obtained in the sieving step was 10.33 μm, the GSD was 1.25, and the transfer efficiency was 84%.

[0030]

According to the present invention, good transferability is obtained,
It is possible to efficiently produce a spherical toner for developing an electrostatic charge image having a uniform particle diameter and containing a polymer and a colorant without classifying the toner.

Claims (2)

[Claims] A step of dissolving a polymer in a solvent and mixing a colorant, a step of dispersing the obtained mixed solution in an aqueous medium in the presence of an inorganic dispersant, and a step of freeze-drying the obtained dispersion. A method for producing a toner for developing an electrostatic image, comprising a step of removing a solvent. 2. A polymer is dissolved in a solvent, a colorant is mixed, the obtained mixed solution is dispersed in an aqueous medium in the presence of an inorganic dispersant, and the obtained dispersion is lyophilized to remove the solvent. And a toner for developing an electrostatic image.