JP2008164771A - Toner for electrophotography - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide toner for electrophotography capable of stably obtaining a high-quality image over a long term. <P>SOLUTION: The toner for electrophotography contains a toner base particle 10 and an external additive and the toner base particle 10 has an elastic modulus of 0.5 to 1.0, determined by a following measurement method. The measurement method comprises a step (1) of putting the tip of a probe on the surface of the toner host particle 10 to set the position of the tip of the probe thereupon as a reference point, a step (2) of forcing the probe into the toner host particle 10 by applying the load of 2.0×10<SP>-6</SP>N to the probe to measure the depth H from the reference point to the tip of the probe, and a step (3) of measuring the depth H<SB>0</SB>from the reference point to the tip of the probe in the state of removing the load to measure the elastic modulus from expression: the elastic modulus=(H-H<SB>0</SB>)/H. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrophotographic toner.

  External additives such as titanium oxide and silica adhere to the surface of the toner base particles for the purpose of controlling the charging ability, fluidity, etc. of the toner for electrophotography (hereinafter also simply referred to as toner). . However, if the external additive falls off from the surface of the toner base particles or is buried in the toner base particles, the charging ability and fluidity of the toner will be reduced, so that the image density may be lowered or image density unevenness may occur. The toner adheres to the non-image area (so-called fogging occurs), and as a result, the image quality deteriorates.

The following methods are known as methods for suppressing a decrease in toner charging ability.
(1) A method of suppressing the burying of the external additive on the surface of the toner base particles by using an external additive having a large particle diameter.
(2) A method in which an external additive is buried in advance on the surface of toner base particles.
However, the methods (1) and (2) cannot give good fluidity to the toner.

The following toner has been proposed as a toner having both charging ability and fluidity.
(3) A toner using hydrophobic silica fine powder and hydrophobic titanium oxide fine powder having an average particle size of 0.02 to 0.5 μm and a hydrophobicity of 20 to 95% as external additives (Patent Document 1).
(4) An electrostatic charge image developer using titanium oxide surface-treated with silica and alumina as an external additive (Patent Document 2).
(5) Toners using silica hydrophobized with silicone oil, silica hydrophobized with alkylsilane, and titanium oxide hydrophobized with silicone oil or alkylsilane as external additives (patented) Reference 3).

The toners (3) to (5) are improved in image quality and long-term stability, but are insufficient from the level required for recent color toners. In particular, at low temperature and low humidity, the charging stability is insufficient, so that the image quality deteriorates, and the image quality deterioration becomes more significant after printing a large number of sheets.
JP 07-043930 A JP 07-281474 A JP 2004-258265 A

  Accordingly, an object of the present invention is to provide an electrophotographic toner capable of stably obtaining a high-quality image over a long period of time.

  The toner for electrophotography of the present invention contains toner mother particles, and the elastic modulus of the toner mother particles determined by the following measurement method is 0.5 to 1.0.

(Measurement method of elastic modulus)
(I) The tip of the probe is applied to the surface of the toner base particle, and the position of the tip of the probe at this time is used as a reference point.
(Ii) A load of 2.0 × 10 ⁻⁶ N is applied to the probe to push the probe into the toner base particles, and the depth H from the reference point to the tip of the probe is measured.
(Iii) The depth H ₀ from the reference point to the tip of the probe is measured with the load removed, and the elastic modulus is obtained from the following equation (1).
Elastic modulus = (H−H ₀ ) / H (1).

  The electrophotographic toner of the present invention is preferably a non-magnetic one-component developer.

  According to the electrophotographic toner of the present invention, a high-quality image can be stably obtained over a long period of time.

<Toner base particles>
The elastic modulus of the toner base particles is 0.5 to 1.0, preferably 0.7 to 1.0. If the elastic modulus of the toner base particles is 0.5 or more, even if the external additive is pressed against the surface of the toner base particles, the external additive is hardly embedded in the toner base particles. As a result, a decrease in toner charging ability and fluidity can be suppressed.

The elastic modulus of the toner base particles is determined by a measuring method having the following procedures (i) to (iii).
(I) The tip of the probe is applied to the surface of the toner base particle, and the position of the tip of the probe at this time is used as a reference point.
(Ii) A load of 2.0 × 10 ⁻⁶ N is applied to the probe to push the probe into the toner base particles, and the depth H from the reference point to the tip of the probe is measured.
(Iii) The depth H ₀ from the reference point to the tip of the probe is measured with the load removed, and the elastic modulus is obtained from the following equation (1).
Elastic modulus = (H−H ₀ ) / H (1).

Procedure (i):
As a measuring device, Nanoindenter (registered trademark) (manufactured by MTS Systems) is used. A method for measuring the mechanical properties (hardness, elastic modulus, etc.) of a minute region using a nanoindenter (registered trademark) is commonly known as a nanoindentation method. According to the nano-indentation method, the elastic modulus of one particle can be measured. Therefore, compared to the conventional measurement method for bulk toner base particles, voids existing between the particles, external additives, and from the measurement container Accurate elastic modulus measurement is possible without being affected.

As the probe, an indenter made of a diamond tip and having a regular triangular pyramid tip is used.
The toner base particles are fixed so as not to move.
The position of the tip of the probe when the tip of the probe is brought into contact with the surface of the toner base particles is recorded as a reference point in the measuring device.

Step (ii):
As shown in FIG. 1, the depth H is the distance from the reference point (the original surface of the toner base particles 10) to the highest point at the tip of the probe when a predetermined load is applied.
The depth H can be measured from the moving distance of the probe.

Step (iii):
When the load on the probe is removed, the surface of the toner base particles pushed by the probe tries to restore to the original position. However, when the elasticity of the toner base particles is low, the surface of the toner base particles cannot be restored to the original position.
Therefore, as shown in FIG. 1, by measuring the depth H ₀ from the reference point to the tip of the probe with the load removed, the amount of restoration of the surface of the toner base particle 10 (H−H ₀ ). The elastic modulus can be obtained by dividing the restoration amount by the depth H.
The depth H ₀ can be measured from the position of the tip of the probe when the load applied to the probe becomes 0 after unloading.

The toner base particles, for example, monovinyl monomer, obtained monomer composition containing a crosslinkable compound and pigment (M _A) was polymerized in a suspension polymerization method or an emulsion polymerization method, a binder toner mother particles containing a resin and a pigment (T _a) can be mentioned.
The monomer composition (M _A ) may contain various additives such as a charge control agent, a mold release agent, a polymerization initiator, a molecular weight modifier, a lubricant, and a dispersion stabilizer as necessary.

(Monovinyl monomer)
A monovinyl monomer is a monomer having one polymerizable carbon-carbon unsaturated double bond. Examples of the polymerizable carbon-carbon unsaturated double bond include a vinyl group, an acryloyl group, and a methacryloyl group.

  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. Derivatives of (meth) acrylic acid; monoolefin monomers such as ethylene, propylene and butylene. (Meth) acrylic acid means acrylic acid or methacrylic acid.

  A monovinyl monomer may be used individually by 1 type, and may be used in combination of 2 or more type. Of these monovinyl monomers, an aromatic vinyl monomer alone or a combination of an aromatic vinyl monomer and a derivative of (meth) acrylic acid is preferable.

(Crosslinkable compound)
The crosslinkable compound is a compound having two or more polymerizable carbon-carbon unsaturated double bonds. Examples of the polymerizable carbon-carbon unsaturated double bond include a vinyl group, an acryloyl group, and a methacryloyl group. By using the crosslinkable compound, the elastic modulus of the toner base particles can be controlled.

  Examples of the crosslinkable compound include macromonomers described later; aromatic divinyl monomers such as divinylbenzene, divinylnaphthalene, and derivatives thereof; ) Esters of acrylic acid and polyhydric alcohols; divinyl monomers such as N, N-divinylaniline and divinyl ether; polyfunctional monomers such as pentaerythritol triallyl ether and trimethylolpropane triacrylate.

(Macromonomer)
By using the macromonomer as the crosslinkable compound, toner base particles having an appropriate elastic modulus can be obtained. The macromonomer is a macromolecule having two or more polymerizable carbon-carbon unsaturated double bonds at the end of the molecular chain, and is usually an oligomer or polymer having a number average molecular weight of 1000 to 30000. When the number average molecular weight is within the above range, the fixability and storability of the 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 a vinyl group, an acryloyl group, a methacryloyl group, and the like, and a methacryloyl group is preferable 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.

  Macromonomer includes styrene, styrene derivative, methacrylic acid ester, acrylic acid ester, acrylonitrile, methacrylonitrile, etc., or a polymer obtained by polymerizing two or more of these; macromonomer having polysiloxane skeleton Etc. Of these, hydrophilic ones are preferable, and a polymer obtained by polymerizing methacrylic acid ester or acrylic acid ester alone or in combination thereof is particularly preferable. Further, by using a macromonomer having a number average molecular weight of 500 to 2,000 having two or more polymerizable carbon-carbon unsaturated double bonds at the end of the molecular chain as a crosslinkable compound, the molecular weight of the toner base particles is increased so much. Without this, a crosslinked structure can be easily formed.

  0.5-5 mass parts is preferable with respect to 100 mass parts of monovinyl monomers, and, as for the quantity of a crosslinkable compound, 0.5-3 mass parts is more preferable. By setting the amount of the macromonomer within the above range, toner base particles having an appropriate elastic modulus can be obtained.

(Pigment)
Examples of the pigment include known pigments used for toner.
Examples of black pigments include carbon black and nigrosine-based pigments; magnetic particles such as cobalt, nickel, iron tetroxide, manganese iron oxide, zinc iron oxide, and nickel iron oxide. Carbon black having an average primary particle diameter of 20 to 40 nm is preferable from the viewpoint of obtaining good image quality and enhancing the safety of the toner to the environment.

Examples of color toner pigments include yellow pigments, magenta pigments, and cyan pigments.
Examples of yellow pigments include condensed azo compounds, isoindolinone compounds, anthraquinone compounds, azo metal complexes, methine compounds, allylamide compounds, and the like. 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; Nephthol Yellow S, Hansa Yellow G, C.I. I. Examples thereof include bat yellow.

  Examples of magenta pigments include condensed azo compounds, diketopyrrolopyrrole compounds, anthraquinone compounds, quinacridone compounds, basic dye lake compounds, naphthol compounds, benzimidazolone compounds, thioindigo compounds, and perylene compounds. , C.I. I. Pigment Red 2, 3, 5, 6, 7, 23, 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, 163, 166, 169, 170, 177, 184, 185, 187, 202, 206, 207, 209, 220, 251, 254, etc .; C.I. I. Pigment violet 19 and the like.

  Examples of cyan pigments include copper phthalocyanine compounds, derivatives thereof, anthraquinone compounds, basic dye lake compounds, and the like. I. Pigment blue 1, 2, 3, 6, 7, 15, 15: 1, 15: 2, 15: 3, 15: 4, 16, 17, 60, 62, 66, etc .; phthalocyanine blue, C.I. I. Bat Blue, C.I. I. Acid blue and the like.

These pigments may be used alone or in combination of two or more.
0.1-50 mass parts is preferable with respect to 100 mass parts of monovinyl monomers, and, as for the quantity of a pigment, 1-20 mass parts is more preferable.

(Charge control agent)
In order to improve the chargeability of the toner, various positively chargeable or negatively chargeable charge control agents may be contained in the monomer composition (M _A ).
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 (made by Orient Chemical Industries), COPY CHARGE NX VP434 (made by Clariant), COPY CHARGENEG VP2036 (made by Clariant), TNS-4-1 (made by Hodogaya Chemical Co., Ltd.), TNS-4-2 (Hodogaya) Chemical Industry), LR-147 (Nippon Carlit), copy Charge control agents such as Lou PR (Clariant); quaternary ammonium (salt) group-containing copolymer, a charge control resins such as sulfonic acid (salt) group-containing copolymers.

  The amount of the charge control agent is preferably 0.01 to 10 parts by mass, and more preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the monovinyl monomer.

(Release agent)
In order to improve the offset resistance of the toner or the releasability at the time of fixing with a hot roll, a release agent may be contained in the monomer composition (M _A ).
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, modified waxes thereof; synthetic waxes such as Fischer-Tropsch wax; polyfunctional ester compounds such as pentaerythritol tetramyristate, pentaerythritol tetrapalmitate, and dipentaerythritol hexamyristate.

These mold release agents may be used individually by 1 type, and may be used in combination of 2 or more type. Of these release agents, synthetic waxes, terminal-modified polyolefin waxes, petroleum waxes, and polyfunctional ester compounds are preferred.
0.1-50 mass parts is preferable with respect to 100 mass parts of monovinyl monomers, and, as for the quantity of a mold release agent, 0.5-20 mass parts is more preferable, and 1-10 mass parts is especially preferable.

(Polymerization initiator)
Examples of the polymerization initiator 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′-azobisisobutyronitrile Azo compounds such as 2,2′-azobis (2-methylpropionate); di-t-butyl peroxide, dicumyl peroxide, lauroyl peroxide, benzoyl peroxide, t-butylperoxy-2-ethyl Hexanoate, t-hexylperoxy-2-ethylhexanoate, t-butylperoxypivalate, di-isopropylperoxydicarbonate, di- Peroxides such as t-butylperoxyisophthalate, 1,1 ′, 3,3′-tetramethylbutylperoxy-2-ethylhexanoate, t-butylperoxyisobutyrate; these polymerization initiators And a redox initiator combined with a reducing agent.

Among these initiators, an oil-soluble polymerization initiator soluble in a monovinyl monomer is preferable, and a water-soluble polymerization initiator may be used in combination as necessary.
The amount of the polymerization initiator is preferably 0.1 to 20 parts by mass, more preferably 0.3 to 15 parts by mass, and particularly preferably 0.5 to 10 parts by mass with respect to 100 parts by mass of the monovinyl monomer.
The polymerization initiator may be added in advance to the monomer composition (M _A ), and in order to suppress premature polymerization, the suspension of the monomer composition (M _A ) before or during the polymerization. Or you may add to an emulsion.

(Molecular weight regulator)
In the polymerization of the monomer composition (M _A ), a molecular weight modifier may be 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.

0.01-10 mass parts is preferable with respect to 100 mass parts of monovinyl monomers, and, as for the quantity of a molecular weight modifier, 0.1-5 mass parts is more preferable.
The molecular weight modifier may be previously added to the monomer composition (M _A), before or during polymerization polymerization may be added to a suspension or emulsion of the monomer composition (M _A) Good.

(Dispersion stabilizer)
As the dispersion stabilizer, a colloid of a poorly water-soluble metal compound is preferable.
Examples of poorly 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 oxides such as aluminum oxide and titanium oxide A metal hydroxide of aluminum hydroxide, magnesium hydroxide, ferric hydroxide or the like. Of these, colloids of poorly water-soluble metal hydroxides are preferred because the particle size distribution of the polymer particles can be narrowed and the sharpness of the image is improved.

As the colloid of the poorly water-soluble metal compound, a colloid of poorly water-soluble metal hydroxide obtained by adjusting the pH of the aqueous solution of the water-soluble polyvalent metal compound to 7 or more is preferable. Particularly preferred are colloids of sparingly water-soluble metal hydroxides produced by reaction in the aqueous phase with alkali metal oxide salts.
The colloid of a poorly water-soluble metal compound preferably has a particle size (D50) of 50% or less when the cumulative number from the small particle size side in the number particle size distribution is 0.5 μm or less. It is more preferable that the particle diameter (D90) of which the cumulative number from 90 is 90% is 1 μm or less.

If necessary, a water-soluble polymer may be used as a dispersion stabilizer. 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, but it may be used for stably performing suspension polymerization within a range in which the charging characteristics do not become environmentally dependent.

  The amount of the dispersion stabilizer is preferably 0.1 to 20 parts by mass with respect to 100 parts by mass of the monovinyl monomer. When the amount of the dispersion stabilizer is too small, it is difficult to obtain sufficient polymerization stability, and polymerized aggregates are easily generated. When there is too much quantity of a dispersion stabilizer, aqueous solution viscosity will become large and superposition | polymerization stability will become low.

(Method for producing toner mother particles)
Toner particles (T _A) is obtained by a monomer composition (M _A) is polymerized by a suspension polymerization method or emulsion polymerization method, obtained by polymerization of monovinyl monomer and the crosslinking compound These are colored polymer particles in which a polymer serves as a binder resin, and pigments and other additives such as a charge control agent and a release agent are dispersed therein.

Specifically, the toner base particles (T _A ) became droplets in the step of forming the monomer composition (M _A ) into fine droplets (droplet forming step) in an aqueous dispersion medium. It is manufactured through a step of polymerizing the monomer composition (M _A ) (polymerization step) and a step of washing and drying the obtained colored polymer particles (recovery step).

Droplet formation process:
Monovinyl monomer, crosslinkable compound including macromonomer and pigment, and other additives are mixed using a mixer if necessary, and a media type wet mill (eg, bead mill) is used as necessary. And wet pulverizing to prepare a monomer composition (M _A ).
Next, the monomer composition (M _A ) is added to an aqueous dispersion medium and dispersed by stirring to obtain uniform droplets of the monomer composition (M _A ) (primary volume average particle diameter of about 50 to 1000 μm). Droplets) are preliminarily formed to obtain a dispersion.
Next, stirring is performed using a high-speed rotary shear type stirrer or the like until the particle size of the droplets becomes a particle size close to the target toner to obtain a suspension (or emulsion).

When a color toner pigment is used as the pigment and a charge control resin is used as the charge control agent, the pigment and the charge control resin are previously kneaded to prepare a pigment master batch, which is then used as the monomer composition (M _A ) may be contained.
As the aqueous dispersion medium, water such as ion exchange water is used. If desired, a hydrophilic solvent such as alcohol may be added.
In order to avoid premature polymerization, the polymerization initiator is preferably added to the dispersion just before stirring using a high-speed rotary shear type stirrer.
The dispersion stabilizer is preferably added to the aqueous dispersion medium before adding the monomer composition (M _A ).

The volume average particle size and particle size distribution of the droplets of the monomer composition (M _A ) in the suspension affect the volume average particle size and particle size distribution of the toner base particles. If the particle size of the droplet is too large, the particle size of the toner base particle becomes too large, and the resolution of the image is lowered. When the particle size distribution of the droplets is wide, the particle size distribution of the toner base particles is widened, causing a variation in fixing temperature, causing problems such as fogging and toner filming. Therefore, it is preferable that the droplets of the monomer composition (M _A ) are formed so as to be approximately the same size as the toner base particles.

As the volume average particle diameter of the droplets of the monomer composition (M _A ), a particle diameter Dv50 (μm) having a cumulative volume of 50% calculated from the small particle diameter side in the particle size distribution is used. The droplet particle size Dv50 (hereinafter referred to as droplet particle size Dv) can be measured, for example, using a SALD particle size distribution measuring instrument (manufactured by Shimadzu Corporation).
The droplet particle diameter Dv of the monomer composition (M _A ) is preferably 3 to 10 μm, more preferably 4 to 9 μm, and particularly preferably 4 to 8 μm. In order to obtain a high-definition image, a toner having a small particle diameter is effective. For this purpose, it is preferable to reduce the droplet particle diameter Dv.
The particle size distribution (volume average particle size / number average particle size) of the droplets of the monomer composition (M _A ) is preferably 1 to 2, and more preferably 1 to 1.5.

Examples of the method for controlling the droplet particle diameter Dv of the monomer composition (M _A ) include a method of adjusting the amount of a dispersion stabilizer such as a colloid of a hardly water-soluble metal hydroxide. However, the droplet particle diameter Dv also varies depending on the stirring condition of the dispersion. Therefore, in order to obtain a substantially desired droplet particle diameter Dv, it is preferable to first adjust the amount of the dispersion stabilizer and control the stirring conditions and the like.

  As the stirrer, for example, (1) a multistage in-line disperser manufactured by IKA in Germany, a disperser represented by Ebara Milder manufactured by Ebara Seisakusho, that is, a rotor that is a comb-shaped concentric ring Disperser having a combination with a stator, rotating the rotor at high speed, allowing the dispersion to flow from the inside of the rotor to the outside of the stator, and stirring the dispersion in the gap between the rotor and the stator (2) The action of shearing force, impact force, pressure fluctuation, cavitation, and potential core generated on the rotor rotating at high speed and the screen surrounding it, represented by Claremix CLM-0.8S manufactured by M Technique Co., Ltd. (3) A liquid film is formed by pressing the dispersion liquid against the inner wall of the tank by centrifugal force, represented by a TK homomixer manufactured by Tokushu Mining Co., Ltd. Stirrer or the like to form droplets by the tip of the stirring device rotating swings at a speed and the like.

Polymerization process:
Hereinafter, the suspension polymerization method will be mainly described.
Suspension polymerization is performed by charging a suspension containing droplets of the monomer composition (M _A ) into a polymerization reactor and heating.
The polymerization temperature is preferably 5 to 120 ° C, and more preferably 35 to 95 ° C. If the polymerization temperature is too low, a highly active polymerization initiator 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 toner base particles, resulting in poor storage stability.

The monovinyl monomer contained in the monomer composition (M _A), from the viewpoint of lowering the fixing temperature of the toner, the glass transition temperature (Tg) of preferably not more than 80 ° C., more preferably 40 to 80 ° C., in particular Preferably, a monovinyl monomer or a combination thereof capable of obtaining a polymer at 50 to 70 ° C. is selected. The Tg of the polymer is a calculated value calculated according to the type and ratio of the monovinyl monomer.

  By the above suspension polymerization, colored polymer particles in which pigments and the like are dispersed in the polymer are obtained. The colored polymer particles may be used as toner base particles. For the purpose of improving the storage stability (blocking resistance), low-temperature fixability, meltability at the time of fixing, etc., on the colored polymer particles, A polymer layer may be formed to form core-shell type polymer particles. By using the core-shell type polymer particles, it is possible to obtain a toner that can cope with high-speed printing (copying, printing, etc.), full color, OHP (overhead projector) permeability, and the like.

The core-shell type polymer particle is produced by using the colored polymer particle as a core particle, further polymerizing a shell monomer in the presence of the core particle, and a polymer layer ( Shell).
As the monomer for shell, the same monomer as the above-mentioned monovinyl monomer can be used.
As the monomer for the shell, one that forms a polymer having a Tg higher than that of the polymer constituting the core particle is preferable from the viewpoint of improving the storage stability of the toner. And since Tg of the polymer which comprises a core particle can be set low, the fixing temperature of a toner can be lowered | hung or a melting characteristic can be improved.

As the core monomer, a monomer capable of forming a polymer having a Tg of preferably 60 ° C. or lower, more preferably 40 to 60 ° C. is selected from the viewpoint of the balance between the fixing temperature and the storage stability. preferable.
As the monomer for the shell, it is preferable to select a monomer that can form a polymer having a Tg of more than 80 ° C., such as styrene and methyl methacrylate.

The Tg of the polymer formed by the shell monomer is preferably more than 50 ° C and 120 ° C or less, more preferably more than 60 ° C and 110 ° C or less, and particularly preferably more than 80 ° C and less than 105 ° C.
The difference in Tg between the polymer formed from the core monomer and the polymer formed from the shell monomer is preferably 10 ° C or higher, more preferably 20 ° C or higher, and particularly preferably 30 ° C or higher.

  The mass ratio of the core monomer to the shell monomer (core monomer / shell monomer) is preferably from 40/60 to 99.9 / 0.1, and from 60/40 to 99.99. 7 / 0.3 is more preferable, and 80/20 to 99.5 / 0.5 is particularly preferable. If the ratio of the monomer for the shell is too small, the effect of improving the storage stability of the toner is small, and if it is excessive, the effect of reducing the fixing temperature is small.

A charge control agent may be added to the shell monomer. Examples of the charge control agent include the above-described charge control agents.
The amount of the charge control agent is preferably 0.01 to 10 parts by mass, and more preferably 0.1 to 5 parts by mass with respect to 100 parts by mass of the shell monomer.

From the viewpoint of efficiently forming the shell, it is preferable to add a water-soluble polymerization initiator when adding the monomer for shell. 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′-azobis- And azo compounds such as [2-methyl-N- [1,1-bis (hydroxymethyl) ethyl] propionamide].
The amount of the water-soluble polymerization initiator is preferably 0.1 to 50 parts by mass, and more preferably 1 to 20 parts by mass with respect to 100 parts by mass of the shell monomer.

  The average thickness of the shell is preferably 0.001 to 1.0 μm, more preferably 0.003 to 0.5 μm, and particularly preferably 0.005 to 0.2 μm. If the shell is too thick, the toner fixability is lowered, and if the shell is too thin, the toner storage stability is lowered. If the core particle diameter and shell thickness can be observed with an electron microscope, the core particle size and shell thickness selected at random from the observation photograph can be measured directly. When it is difficult to observe the shell and the shell, it is calculated from the particle diameter of the core particle and the amount of the monomer for the shell.

Collection process:
By the polymerization step, a dispersion containing colored polymer particles (including core / shell type polymer particles) is obtained. In the recovery process, a filtration / washing process, a drying process, and the like are sequentially performed.
In the filtration / washing step, the dispersion obtained in the polymerization step may be used as it is, or ion exchange water or the like may be added to adjust the concentration of the colored polymer particles.

In the filtration / washing step, in order to solubilize and remove the dispersion stabilizer, for example, acid washing or alkali washing may be performed according to the type of the dispersion stabilizer. For example, when a colloid of a poorly water-soluble metal hydroxide such as magnesium hydroxide is used as the dispersion stabilizer, an acid such as dilute sulfuric acid is added to make the pH of the dispersion acidic, and the colloid is Dissolve in dispersion medium.
Further, the monomer removal treatment may be performed by stripping or the like in the state of the dispersion. Further, in order to adjust the particle diameter of the colored polymer particles, the colored polymer particles may be aggregated or associated.

Examples of the filtration / washing method include a method of simultaneously performing filtration and washing of the colored polymer particles using a vacuum belt filter.
After the washing step, wet colored polymer particles (wet cake) are recovered.
The collected colored polymer particles are dried according to a conventional method. Thus, the dried colored polymer particles, i.e. toner particles (T _A) is obtained.

(GPC measurement)
The toner base particles (T _A ) preferably have an amount of tetrahydrofuran (hereinafter referred to as “THF”) insoluble matter appropriately adjusted so as to have an elastic modulus of 0.5 to 1.0. That is, the toner base particles (T _A ) with respect to the peak area (S _B ) (100%) derived from the binder resin in the GPC chart of the reference toner base particles (T _B ) obtained in the following procedures (i) to (v). peak area derived from the binder resin in the GPC chart in) _{(S a)} is 50 to 95%.

(I) 15 mg of toner base particles (T _A ) are added to 5 mL of THF, and the soluble component is completely dissolved to prepare sample solution A.
(Ii) Using a filter having an area of 4.0 cm ² and a pore size of 0.45 μm, the sample solution A is filtered at a pressure of 0.15 kgf / cm ² to remove THF-insoluble matter that does not pass through the filter.
(Iii) Gel Permeation Chromatography (GPC) measurement is performed on the sample liquid A that has passed through the filter, and the peak area (S of the region between the peak derived from the binder resin and the baseline in the obtained GPC chart (S _A ) is determined.
(Iv) _A monomer composition (M _B ) having the same composition as that of the monomer composition (M _A ) except that the crosslinkable compound is not contained, under the same conditions as the polymerization of the monomer composition (M _A ) Reference toner base particles (T _B ) obtained by polymerization in step 1 are prepared.
(V) The same operation as in the above (i) to (iii) is performed to determine the peak area (S _B ) derived from the binder resin in the GPC chart of the reference toner base particles (T _B ).

  Hereinafter, each procedure will be described in detail.

Procedure (i):
The amount of THF and the amount of toner mother particles _{(T A)} is accurately weighed.
Dissolution of the soluble component of THF contained in the toner base particles (T _A) uses a ball mill or stirrer, sufficiently performed over 1 to 5 hours. At this time, you may heat to room temperature-50 degreeC.

Step (ii):
A commercially available HPLC sample pretreatment filter may be used as the filter.
The pore size is the nominal value of a commercial product.
The pressure applied during filtration is adjusted by a weight attached to pressurize the piston portion of the syringe used during filtration.

Step (iii):
A commercially available GPC apparatus may be used as the GPC apparatus used for GPC measurement. A commercially available column may be used as the column.
As the solvent, THF is used. The flow rate is 1.0 mL / min.
By GPC measurement, for example, the GPC chart shown in FIG. 2 is obtained. The horizontal axis is the elution time (minutes), and the vertical axis is the intensity (mV).

The GPC chart in FIG. 2 is obtained by polymerizing a monomer composition (M _A ) containing a monovinyl monomer (100 parts by mass), a crosslinkable compound (3 parts by mass), a pigment and the like by a suspension polymerization method. 4 is a GPC chart of the obtained toner base particles (T _A ).
The peak area (S _A ) of the region between the peak derived from the binder resin and the baseline in the GPC chart is determined. For GPC chart of FIG. 2, a peak derived from the binder resin, the peak in the vicinity of the elution time of 12.5 minutes ～18.5 min, peak area _{(S A)} is a 8000 (mV · sec) is there.

Step (iv):
The reference toner base particles (T _B ) are obtained by replacing the monomer composition (M _B ) having the same composition as the monomer composition (M _A ) except that it does not contain a crosslinkable compound. It is obtained by polymerization under the same conditions as the polymerization of _A ). When the composition of the monomer composition (M _B ) does not match the composition of the monomer composition (M _A ) excluding the crosslinkable compound (for example, when two or more types of monovinyl monomers are used) their proportion, if the amount of pigment may vary), the concentration of the binder resin contained in the sample liquid B, will be the absorption coefficient of the binder resin or the like is changed, compared with the GPC chart of the toner particles (T _a) Can not be.

Step (v):
The same operation as the above (i) to (iii) is performed, and the area (S _B ) of the GPC chart of the reference toner base particles (T _B ) is obtained.
In order to compare the GPC chart of the toner base particles (T _B ) and the GPC chart of the toner base particles (T _A ), the amount of THF and the amount of the toner base particles (T _B ) are accurately weighed, and the sample It is necessary to completely match the concentration of the reference toner base particles (T _B ) in the liquid _{B with} the concentration of the toner base particles (T _A ) in the sample liquid A.
Filtration needs to be performed under the same conditions using the same filter as in (ii) above.
GPC measurement also needs to be performed under the same conditions using the same GPC apparatus as in (iii) above.

GPC chart of Figure 3, except without the crosslinking compound, the monomer composition (M _A) and the monomer composition having the same composition of (M _B), the monomer composition (M _A) 5 is a GPC chart of reference toner base particles (T _B ) obtained by polymerization under the same conditions as in the polymerization of.
The peak area (S _B ) of the region between the peak derived from the binder resin and the baseline in the GPC chart is determined. For GPC chart of FIG. 3, a peak derived from the binder resin, the peak in the vicinity of elution time 12 min ～18.5 min, peak area _{(S B)} is 11000 (mV · sec).
From the above measurement, the binder resin in the GPC chart of the toner base particles (T _A ) with respect to the peak area (S _B ) (100%) derived from the binder resin in the GPC chart of the reference toner base particles (T _B ). The ratio of the derived peak area (S _A ) is determined. In the case of FIGS. 2 and 3, the ratio of the peak area (S _A ) derived from the binder resin in the GPC chart of the toner base particles (T _A ) is 73%.

(Number average molecular weight)
It is preferable that the number average molecular weight (polystyrene conversion) of the binder resin obtained by performing GPC measurement on the sample liquid A that has passed through the filter is 8000 to 30000. If the number average molecular weight is less than 8000, the melt viscosity of the toner may decrease and hot offset may occur. When the number average molecular weight exceeds 30000, the melt viscosity of the toner increases and the low-temperature fixability may deteriorate.

(Volume average particle diameter)
The volume average particle diameter (Dv) of the toner base particles is preferably 3 to 10 μm, more preferably 4 to 9 μm, and particularly preferably 4 to 8 μm. In order to increase the resolution and obtain a high-definition image, it is preferable to make the volume average particle diameter of the toner small.

The volume average particle diameter (Dv) is measured as follows.
A multisizer type II or type III manufactured by Coulter Co. is used as a measuring device, and an interface for outputting a number average distribution and a volume average distribution and a personal computer are connected thereto. A 1% NaCl aqueous solution is prepared using sodium chloride (reagent grade 1) as an electrolytic solution. In 100 to 150 mL of the electrolytic solution, 0.1 to 5 mL of a surfactant (preferably alkylbenzene sulfonate) is added as a dispersant, and 0.5 to 50 mg of toner mother particles of a measurement sample are added and suspended. The electrolytic solution in which the sample is suspended is dispersed for about 1 to 3 minutes with an ultrasonic disperser, and then the particle size distribution of the toner base particles is measured using the 100 μm aperture with the above measuring device. Find the volume distribution.

<External additive>
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, strontium titanate, and the like.
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.
Of these, inorganic oxide particles are preferred, and silicon dioxide is particularly preferred.
The inorganic particles may be those whose surfaces have been subjected to a hydrophobic treatment, and silicon dioxide that has been subjected to a hydrophobic treatment is particularly preferred.

One type of external additive may be used alone, or two or more types may be used in combination. When the external additives are used in combination, a combination of inorganic particles having different average particle diameters or a combination of inorganic particles and organic resin particles is preferable.
The amount of the external additive is preferably 0.1 to 6 parts by mass with respect to 100 parts by mass of the toner base particles.
Examples of the method for attaching the external additive to the toner base particles include a method in which the toner base particles and the external additive are put in a mixer such as a Henschel mixer and stirred.

<Toner for electrophotography>
The electrophotographic toner of the present invention is a toner containing toner base particles and, if necessary, an external additive.
The electrophotographic toner of the present invention can be used as a toner component of various developers, and is preferably used as a nonmagnetic one-component developer.

  In the electrophotographic toner of the present invention described above, since the elastic modulus of the toner base particles is 0.5 to 1.0, even if the external additive is pressed against the surface of the toner base particles, the external additive Is difficult to be embedded in the toner base particles. As a result, the toner charging ability and fluidity are prevented from being lowered, so that the image density is lowered, the image density is uneven, and the fog is suppressed, and the image quality is improved.

[Example 1]
80 parts by mass of styrene, 20 parts by mass of 2-ethylhexyl methacrylate, 5 parts by mass of carbon black (manufactured by Mitsubishi Chemical Corporation, MA-100), 3 parts by mass of low molecular weight polypropylene (manufactured by Sanyo Chemical Co., Ltd., Viscol 660P) as a release agent , Charge control agent (manufactured by Orient Chemical Co., Ltd., N-07), a macromonomer (number average molecular weight), which is a crosslinkable compound, in which a functional group at a molecular end is substituted with a methacryloyl group as a crosslinkable functional group 1500) After 1.0 parts by mass of the mixed solution is sufficiently dispersed by a ball mill, 2.0 parts by mass of 2,2′-azobis (2,4-dimethylvaleronitrile) as a polymerization initiator, molecular weight regulator A monomer composition was prepared by adding 3.0 parts by mass of t-dodecyl mercaptan. The monomer composition is added to 400 parts by mass of ion-exchanged water, and further 5 parts by mass of tricalcium phosphate and 0.1 part by mass of sodium dodecylbenzenesulfonate are added as a dispersion stabilizer, and TK homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) is added. ) And stirred at a rotational speed of 5000 rpm for 45 minutes to obtain a suspension. The suspension was heated at 70 ° C. for 10 hours under a nitrogen atmosphere while stirring at 100 rpm to polymerize the monomer composition. The dispersion of colored polymer particles was acid washed to remove tricalcium phosphate. The dispersion was filtered, and the collected colored polymer particles were washed and dried to obtain toner mother particles. The volume average particle diameter (Dv) of the toner base particles was 7.5 μm.

  100 parts by weight of toner base particles and 0.8 parts by weight of an external additive (silica RA200HS, manufactured by Nippon Aerosil Co., Ltd.) are mixed at a peripheral speed of 3500 mm / second for 10 minutes using a Henschel mixer, and a non-magnetic one-component developer is mixed. Obtained.

[Examples 2 and 3]
Toner base particles and a non-magnetic one-component developer were obtained in the same manner as in Example 1 except that the amount of macromonomer was changed to the amount shown in Table 1.

Example 4
The toner base particles and the non-magnetic one-component developer were changed in the same manner as in Example 1 except that the macromonomer was changed to the number average molecular weight shown in Table 1, and the amount of the macromonomer was changed to the amount shown in Table 1. Obtained.

Example 5
Toner base particles and a non-magnetic one-component developer were obtained in the same manner as in Example 1 except that the macromonomer was changed to divinylbenzene and the amount of divinylbenzene was changed to the amount shown in Table 1.

[Comparative Example 1]
Except that the macromonomer having a number average molecular weight of 1500 was changed to a macromonomer having a number average molecular weight of 10,000, and the amount of the macromonomer was changed to the amount shown in Table 1, the toner mother particles and A non-magnetic one-component developer was obtained.

[Comparative Example 2]
Toner base particles and a non-magnetic one-component developer were obtained in the same manner as in Example 1 except that the amount of macromonomer was changed to the amount shown in Table 1.
[Reference Example 1]
Toner base particles (reference toner base particles (T _B )) were obtained in the same manner as in Example 1 except that no macromonomer was used.

[Evaluation]
The following evaluation was performed on the toner base particles and the non-magnetic one-component developers of Examples 1 to 5 and Comparative Examples 1 and 2. The results are shown in Table 1.

(Elastic modulus)
One particle was arbitrarily selected from the toner base particles, and the elastic modulus of the particles was determined by the following procedures (i) to (iii). As a measuring device, Nanoindenter (registered trademark) (manufactured by MTS Systems) was used, and as a probe, a tip of a regular triangular pyramid made of a diamond tip was used, and the measurement was performed at 25 ° C. . As the diamond tip, a tip having a tip tip radius of curvature of 10 nm or less and a half cone angle from the tip of the tip to 200 nm of 10 ° or less was used.
(I) The tip of the probe was applied to the surface of the toner base particles, and the position of the tip of the probe at this time was used as a reference point.
(Ii) A load of 2.0 × 10 ⁻⁶ N was applied to the probe to push the probe into the toner base particles, and the depth H from the reference point to the tip of the probe was measured.
(Iii) The depth H ₀ from the reference point to the tip of the probe was measured with the load removed, and the elastic modulus was determined from the following equation (1).
Elastic modulus = (H−H ₀ ) / H (1).

(GPC measurement)
(I) the sealed can container, Examples 1 to 5, the toner base particles of Comparative Example 1 and 2 _{(T A)} accurately 15mg weighed and added THF5mL was accurately weighed a whole pipette. The inside of the container was rotated and stirred at 100 rpm for 24 hours to completely dissolve the soluble matter, thereby preparing sample solution A.

(Ii) The sample solution A is filtered at a pressure of 0.15 kgf / cm ² using a filter having an area of 4.0 cm ² and a pore size of 0.45 μm (manufactured by Toji Field Co., Ltd., Chromatodisc 25N), and does not pass through the filter. The THF insoluble matter was removed.

(Iii) GPC measurement was performed on the sample liquid A that passed through the filter using the following apparatus under the following conditions.
GPC device: manufactured by Tosoh Corporation, HLC-8220GPC, solvent: THF, flow rate: 1.0 ml / min, sample column: TSK-GEL GMH _XL × 2, reference column: TSK-GEL GRCX _LH .
The peak area (S _A ) of the region between the peak derived from the binder resin and the baseline in the obtained GPC chart was determined.

(Iv) The toner of Reference Example 1 was prepared as reference toner base particles (T _B ).
(V) the same activities as the above (i) ~ (iii), the peak area was determined to be derived from the binder resin in the GPC chart of the reference toner particles _{(T B) (S B)} .
From the above measurement, the binder resin in the GPC chart of the toner base particles (T _A ) with respect to the peak area (S _B ) (100%) derived from the binder resin in the GPC chart of the reference toner base particles (T _B ). The ratio of the peak area (S _A ) derived (referred to as area ratio in the table) was determined. The results are shown in Table 1.

(Specific surface area change rate)
The BET specific surface area X of the toner base particles contained in the nonmagnetic one-component developer was measured.
The nonmagnetic one-component developer was aged in a developing device for 60 minutes, and the BET specific surface area Y of the toner base particles contained in the nonmagnetic one-component developer that was forcibly deteriorated was measured.
The specific surface area change rate was calculated from the following formula (2).
Specific surface area change rate (%) = | X−Y | / X × 100 (2).
If the rate of change is within 30%, it is not the degree of toner deterioration that causes image problems such as replenishment fog.

(Fixing characteristic evaluation)
An unfixed image was output using a printer (DP560, manufactured by Mita Kogyo Co., Ltd.) loaded with a non-magnetic one-component developer. As a recording medium, evaluation paper (Colorcopy 90, manufactured by Neusidler) was used, and an image was output at a toner amount of 1.5 mg / cm ² .
Using a fixing jig in which a fixing unit (manufactured by Kyocera Mita, FS-1800) was modified, an unfixed image was fixed under the following conditions, and offset resistance and tape peelability were evaluated. The results are shown in Table 1.
(Fixing conditions)
Evaluation linear velocity: 150 mm / second, evaluation temperature: offset resistance is 210 ° C. ± 5 ° C., and tape peelability is 150 ° C. ± 5 ° C.

(Offset resistance)
The offset resistance was evaluated according to the following criteria. In the table, “Hot” indicates that a hot offset (a phenomenon in which the toner of the image melts and adheres to the heating roller again) has occurred, and “Cold” indicates a cold offset (an image near the interface with the recording medium). This indicates that the toner is not sufficiently melted, and thus the image is not sufficiently fixed and a part of the image is removed by the heating roller.
○: An image pattern does not occur as an offset in the heating roller cycle.
Δ: Image pattern slightly occurs as an offset in the heating roller cycle.
X: The image pattern is clearly generated as an offset in the heating roller cycle.

(Tape peelability)
When a commercially available cellophane tape was affixed on the image fixing surface and peeled off by a vertical method, the peeled state was judged by comparing with a limit sample. In the table, “Hot” indicates that the image surface is rough due to the occurrence of hot offset and the tape peelability is poor, and “Cold” indicates that the toner is sufficiently fixed on the paper due to the occurrence of cold offset. This indicates that the tape peelability has deteriorated due to the absence.
○: No peeling.
Δ: Slightly peeled off.
X: Peeling.

(Fogging density)
The fog density was measured for the evaluation paper output in the fixing characteristic evaluation.
The fog density was measured by measuring the density difference between the non-image portion of the output evaluation paper and the evaluation paper before output using a Gretag Macbeth densitometer: RD-19 type (manufactured by Sakata Inx Corporation). .
○: The fog density is 0.008 or less.
Δ: The fog density exceeds 0.008 and is 0.01 or less.
X: The fog density is greater than 0.01.

(Image density unevenness)
The image output in the fixing characteristic evaluation was subjected to 10-point density measurement using a densitometer and evaluated according to the following criteria.
○: The obtained density difference is 0.1 or less.
(Triangle | delta): Ten-point density | concentration measurement is performed using a densitometer and the obtained density | concentration difference exceeds 0.1, but there is no density | concentration difference visually.
X: Conspicuous unevenness in density visually.

  Since the electrophotographic toner of the present invention can stably obtain a high-quality image over a long period of time, it is useful for full-color printing that requires high image quality.

It is a diagram illustrating a depth H and a depth H ₀ in the measurement of elastic modulus of the toner mother particles. 3 is a GPC chart of toner base particles (T _A ) obtained by polymerizing a monomer composition (M _A ) containing a monovinyl monomer, a crosslinkable monomer, a pigment and the like by suspension polymerization. . 3 is a GPC chart of reference toner base particles (T _B ) obtained by polymerizing a monomer composition (M _B ) that does not contain a crosslinkable monomer by suspension polymerization.

Explanation of symbols

  10 Toner base particles

Claims (2)

Contains toner base particles,
An electrophotographic toner, wherein the toner base particles have an elastic modulus of 0.5 to 1.0, which is determined by the following measurement method.
(Measurement method of elastic modulus)
(I) The tip of the probe is applied to the surface of the toner base particle, and the position of the tip of the probe at this time is used as a reference point.
(Ii) A load of 2.0 × 10 ⁻⁶ N is applied to the probe to push the probe into the toner base particles, and the depth H from the reference point to the tip of the probe is measured.
(Iii) The depth H ₀ from the reference point to the tip of the probe is measured with the load removed, and the elastic modulus is obtained from the following equation (1).
Elastic modulus = (H−H ₀ ) / H (1).   The toner for electrophotography according to claim 1, which is a non-magnetic one-component developer.

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