JP4838010B2 - Toner for electrophotography and method for producing the same - Google Patents

Description

  The present invention relates to an electrophotographic toner suitable for adding an inorganic external additive and a method for producing the same.

  Generally, an external additive is externally added to the electrophotographic toner in order to impart fluidity and the like. Examples of the external additive include inorganic external additives such as silicon dioxide (silica) having a primary particle diameter of about 5 to 20 nm.

  However, if the toner stays in the developing machine due to long-term printing durability, there is a problem that the (inorganic) external additive is buried in the toner due to agitation stress in the machine. In order to solve this, there is a method in which inorganic fine powders such as silica and titanium oxide having a particle size of 20 to 300 nm or more are used in combination as a so-called large particle size external additive.

  On the other hand, in Patent Document 1, the wax component present on the toner surface (particularly the pulverized toner) is considered to be a cause of deterioration in toner fluidity and buried external additive. Toners have been proposed. Patent Document 2 proposes a toner in which an outer shell (shell) is formed of a resin having a Tg higher than the glass transition temperature (Tg) of the resin forming the core material in the capsule toner.

  However, in the case of using the above-mentioned large particle size external additive and the methods described in Patent Document 1 and Patent Document 2, although there is a certain suppression effect on the burying of the external additive, the effect is not sufficient. . For this reason, when long-term running or printing with a low printing rate is performed continuously, burying of external additives cannot be avoided, resulting in a decrease in developability (ID decrease), a decrease in transfer efficiency, developer blocking, toner There is a problem that aggregation occurs.

Japanese Patent No. 3141784 JP 2000-147829 A

  The object of the present invention is to prevent the external additive from being buried in the toner even when long-term running or printing with a low printing rate is continuously performed, thereby reducing developability, transfer efficiency, and developer. An object of the present invention is to provide an electrophotographic toner capable of preventing the occurrence of blocking and toner aggregation and a method for producing the same.

As a result of intensive studies to solve the above problems, the present inventors have obtained the following knowledge. That is, the reason why the external additive is buried in the toner is that the hardness of the resin constituting the toner is insufficient with respect to the inorganic fine powder constituting the external additive. For this reason, even if the shell of the capsule is made of a resin having a high Tg, the external additive is finally buried although there is a difference in degree.
Accordingly, it has been found that if an anti-embedding layer having a hardness equivalent to that of silica is provided on the toner surface, the external additive can be prevented from being buried.

That is, the electrophotographic toner and the method for producing the electrophotographic toner of the present invention have the following configurations.
(1) An electrophotographic toner in which inorganic fine powder is externally added to toner particles. The toner particles include core particles containing at least a resin, a colorant and a wax, and inorganic particles formed on the surface of the core particles. An electrophotographic toner comprising: a first shell layer for preventing burying of fine powder; and a second shell layer for holding fine inorganic powder formed on the surface of the first shell layer.
(2) The toner for electrophotography according to (1), wherein the particle diameter of the inorganic fine powder is larger than the average layer thickness of the second shell layer.
(3) The toner for electrophotography according to (1) or (2), wherein the core particles further contain a charge control agent or a charge control resin.
(4) The electrophotographic toner according to any one of (1) to (3), wherein the first shell layer contains silicon dioxide as a main component.
(5) The electrophotographic toner according to any one of (1) to (4), wherein the average thickness of the first shell layer is 10 nm or more.
(6) The electrophotographic toner according to any one of (1) to (5), wherein the second shell layer contains a resin as a main component.
(7) The toner for electrophotography according to any one of (1) to (6), wherein an average layer thickness of the second shell layer is 20 nm or more.
(8) The electrophotographic toner according to any one of (1) to (7), wherein the inorganic fine powder is at least one selected from silicon dioxide, titanium oxide, aluminum oxide, and magnetic powder.
(9) The toner for electrophotography according to any one of (1) to (8), wherein a particle diameter of the inorganic fine powder is larger than 20 nm.
(10) The electrophotographic toner according to any one of (1) to (9), wherein the inorganic fine powder is composed of two or more kinds.
(11) The electrophotographic toner according to (10), wherein the particle diameter of at least one inorganic fine powder is larger than the average layer thickness of the second shell layer.

(12) a first shell layer forming step of forming a first shell layer containing silicon dioxide as a main component by using silicon dioxide and a solvent on the surface of core particles containing at least a resin, a colorant and a wax; A second shell layer forming step of forming a second shell layer containing a resin as a main component on the surface of the first shell layer by adding a solvent containing A second shell layer fixing step in which toner particles are obtained by heating to a temperature equal to or higher than the glass transition temperature of the resin contained in the layer to fix the second shell layer to the surface of the first shell layer; And an inorganic fine powder external addition step of externally adding an inorganic fine powder larger than the average layer thickness of the second shell layer to the toner particles.
(13) The step of forming the first shell layer includes dispersing the core particles and silicon dioxide particles in a solvent, and then attaching the silicon dioxide particles to the surface of the core particles with a flocculant; The step of fixing the silica particles to the core particles by heating above the glass transition temperature, the step of making the dispersion alkaline by adjusting the pH and fixing the silica particles to each other, and making the dispersion neutral by adjusting the pH The method for producing an electrophotographic toner according to (12), further comprising a returning step.
(14) The second shell layer forming step includes a step of preparing a resin fine particle dispersion, and the resin fine particle dispersion is added to the core particle dispersion on which the first shell layer is formed. The method for producing an electrophotographic toner according to the above (12) or (13), comprising the step of adhering resin fine particles to the surface of the first shell layer.
(15) The toner for electrophotography according to any one of (12) to (14), wherein the core particles are obtained by a method selected from a suspension polymerization method, an emulsion polymerization aggregation method, and a pulverization method. Production method.

  According to the present invention, the first shell layer becomes the burying prevention layer of the inorganic fine powder. Furthermore, the second shell layer becomes a holding layer for the inorganic fine powder for holding the inorganic fine powder. As a result, even when long-term running or printing with a low printing rate is performed continuously, the first shell layer prevents the inorganic fine powder from being embedded in the toner particles, and the inorganic fine powder is fixed on the toner particle surface. And can be retained. In addition, it is possible to prevent the developability, transfer efficiency, developer blocking, and toner aggregation from occurring.

<Toner for electrophotography>
In the electrophotographic toner of the present invention, inorganic fine powder is externally added to the toner particles. The toner particles include predetermined core particles, an inorganic fine powder embedding prevention first shell layer formed on the surface of the core particles, and an inorganic fine powder holding surface formed on the surface of the first shell layer. And a second shell layer.

  One embodiment of the electrophotographic toner of the present invention as described above will be described with reference to the drawings. FIG. 1 shows the structure of an electrophotographic toner according to an embodiment of the present invention. As shown in FIG. 1, this electrophotographic toner 10 is composed of toner particles 20 and inorganic fine powder 4. The toner particle 20 has a core particle 1, a first shell layer 2 formed on the surface of the core particle 1, and a second shell layer 3 formed on the surface of the first shell layer 2. ing. Therefore, the toner particle 20 has a two-layer coat structure of the first shell layer 2 and the second shell layer 3. The externally added inorganic fine powder 4 is held by the second shell layer 3.

  The core particle 1 is a particle containing at least a resin, a colorant, and a wax, and preferably further contains a charge control agent or a charge control resin. The core particle 1 can be produced by a method such as a suspension polymerization method, an emulsion polymerization aggregation method, or a pulverization method described later.

  As shown in FIG. 1, the first shell layer 2 is formed on the surface of the core particle 1 and covers the core particle 1. The first shell layer 2 plays a role of preventing the externally added inorganic fine powder 4 from being buried. In other words, even if an external force is applied to the externally added inorganic fine powder 4, the burying prevention layer of the inorganic fine powder 4 prevents the inorganic fine powder 4 from being buried in the first shell layer 2. For this reason, the first shell layer 2 is preferably composed mainly of silicon dioxide. Thereby, since the 1st shell layer 2 has substantially the same hardness as the inorganic fine powder 4 which is an external additive, the burying of the inorganic fine powder 4 can be prevented reliably.

  The second shell layer 3 is formed on the surface of the first shell layer 2 and covers the first shell layer 2. In the second shell layer 3, when an external force is applied to the externally added inorganic fine powder 4, a part of the inorganic fine powder 4 is buried in the second shell layer 3. That is, the second shell layer 3 plays a role of burying and holding the inorganic fine powder 4. For this reason, it is preferable that the 2nd shell layer 3 has resin as a main component.

  The inorganic fine powder 4 is fine particles used as an external additive of the electrophotographic toner 10, and examples thereof include silicon dioxide (silica), titanium oxide, aluminum oxide, and magnetic powder. Examples of the magnetic powder include metals exhibiting ferromagnetism such as iron, cobalt and nickel including ferrite and magnetite. In particular, the inorganic fine powder 4 is preferably at least one selected from silicon dioxide, titanium oxide, aluminum oxide and magnetic powder.

  Here, FIG. 2 is a schematic diagram showing the first shell layer 2 and the second shell layer 3 in an enlarged manner. 2, t1 is the layer thickness (average layer thickness) of the first shell layer 2, t2 is the layer thickness (average layer thickness) of the second shell layer 3, and d1 is the particle diameter (diameter) of the inorganic fine powder 4. Respectively.

  As shown in FIG. 2, in this embodiment, the particle diameter d1 of the inorganic fine powder 4 to be externally added is larger than the layer thickness t2 of the second shell layer 3. This is because the inorganic fine powder 4 may be completely buried inside the second shell layer 3 when the particle diameter d1 is not larger than the layer thickness t2.

  In the toner 10, the inorganic fine powder may be composed of two or more kinds. In this case, it is preferable that at least one particle diameter d1 of the externally added inorganic fine powder is larger than the layer thickness t2 of the second shell layer 3. That is, in the present invention, the external additive (inorganic fine powder) having a particle size smaller than t2 and the inorganic fine powder 4 having a particle size d1 larger than t2 may be used in combination. Use of an external additive (inorganic fine powder) having a particle diameter smaller than t2 is preferable in that the fluidity of the toner is improved by the external additive (inorganic fine powder) not embedded in the first shell layer 2. . Two or more types of inorganic fine powder 4 having a particle diameter d1 larger than t2 may be used.

  The particle size d1 of the inorganic fine powder 4 should be larger than 20 nm, preferably an inorganic fine powder (large particle size external additive) having a particle size of more than 20 nm and not more than 300 nm, more preferably 30 to 200 nm. Specific examples include silica particles having high fluidity improving effect and d1 of 30 nm or more, silica having high burying prevention effect and d1 of 40 nm or more, and titanium oxide. The “particle diameter” of the inorganic fine powder 4 means an average particle diameter, and can be obtained by measuring a photograph taken with a scanning electron microscope (SEM) and magnified 100,000 times.

  The layer thickness t1 of the first shell layer 2 is not particularly limited. However, when the first shell layer 2 is too thin, the first shell layer 2 cannot withstand the burying stress of the external additive, and a hole is formed. The agent will be buried. In order to prevent such burial, t1 is 10 nm or more, preferably 20 nm or more. Further, when t1 is increased, it is necessary to increase the amount of silica added to the toner weight. However, if the amount added is too large, there is a possibility that the fixing characteristics may be adversely affected. Therefore, even when the amount of silica added is increased in order to increase t1, the silica weight is preferably 10% or less with respect to the total amount of toner.

  The layer thickness t2 of the second shell layer is 20 nm or more, preferably 20 to 200 nm in order to fix the inorganic fine powder 4 on the toner surface. Thereby, even if an external additive having a particle size larger than 20 nm (large particle size external additive) is added, the external additive can be effectively fixed and retained. On the other hand, when t2 is smaller than 20 nm, the ability to immobilize and hold the inorganic fine powder 4 having a large particle diameter is reduced, and the inorganic fine powder 4 is detached, resulting in a decrease in transfer efficiency and desorption. In-machine contamination with the inorganic fine powder 4 may occur. On the other hand, the upper limit of the layer thickness t2 of the second shell layer is preferably 200 nm, more preferably about 2/3 of the average particle size of the large particle size external additive used. This is because if the thickness is increased beyond this, the external additive is buried, resulting in a decrease in fluidity, developability, and transfer efficiency.

  As for the layer thickness t1 of the first shell layer 2 and the layer thickness t2 of the second shell layer, the thicknesses of the cross sections of the toner particles 20 are measured using a scanning electron microscope (SEM), and the average value is calculated. This is the value obtained.

<Method for producing electrophotographic toner>
Next, a method for manufacturing the electrophotographic toner 10 described above will be described. The method for producing the toner 10 includes a first shell layer forming step in which a first shell layer 2 mainly composed of silicon dioxide is formed on the surface of the core particle 1 using a solvent such as silicon dioxide and an aqueous medium, A solvent such as an aqueous medium containing a resin is added to the core particle 1 on which the first shell layer 2 is formed, and a layer containing the resin as a main component (second shell layer 3) is added to the first shell layer. A second shell layer forming step to be formed on the surface of the resin, and heating to a temperature not lower than the glass transition temperature of the resin contained in the second shell layer 3 to fix the resin (second shell layer 3), and A second shell layer fixing step for obtaining particles, and an inorganic fine powder external addition step for externally adding inorganic fine powder having a predetermined particle diameter to the toner particles.

(1) Core particle As described above, the core particle 1 preferably contains at least a resin, a colorant, and a wax, and further contains a charge control agent, a charge control resin, and the like. Examples of the resin, colorant, wax, charge control agent, and charge control resin that can be used for the production of the core particle 1 include the following.

(resin)
The type of resin that can be used for producing the core particle 1 is not particularly limited. For example, polystyrene resin, polyacrylic resin, styrene-acrylic copolymer, polyethylene resin, polypropylene resin, Examples thereof include thermoplastic resins such as vinyl chloride resin, polyester resin, polyamide resin, polyurethane resin, polyvinyl alcohol resin, vinyl ether resin, N-vinyl resin, and styrene-butadiene resin.

  The polystyrene resin may be a styrene homopolymer or a copolymer with another copolymerizable monomer copolymerizable with styrene. As copolymerizable monomers, p-chlorostyrene; vinyl naphthalene; ethylene unsaturated monoolefins such as ethylene, propylene, butylene, and isobutylene; vinyl halides such as vinyl chloride, vinyl bromide, and vinyl fluoride; vinyl acetate, propion Vinyl esters such as vinyl acrylate, vinyl benzoate, vinyl butyrate; methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, dodecyl acrylate, n-octyl acrylate, 2-chloroethyl acrylate, acrylic (Meth) acrylic acid esters such as phenyl acid, methyl α-chloroacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate; other acrylic acid derivatives such as acrylonitrile, methacrylonitrile, acrylamide; Vinyl ethers such as nylmethyl ether and vinyl isobutyl ether; Vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone and methyl isopropenyl ketone; N-vinyl pyrrole, N-vinyl carbazole, N-vinyl indole, N-vinyl pyrrolidene, etc. N-vinyl compounds of

  One of these copolymerization monomers can be copolymerized alone with the styrene monomer, or two or more of these copolymerization monomers can be copolymerized with the styrene monomer. The polystyrene resin preferably has two weight average molecular weight peaks (low molecular weight peak and high molecular weight peak). Specifically, the low molecular weight peak is preferably in the range of 3000 to 20000, and the other high molecular weight peak is preferably in the range of 300000 to 1500,000. Furthermore, it is preferable that Mw / Mn is 10 or more for the weight average molecular weight (Mw) and the number average molecular weight (Mn). If the weight average molecular weight peak is within such a range, the toner can be easily fixed, and offset resistance can be improved.

  Examples of the polyester-based resin include resins obtained by condensation polymerization or co-condensation polymerization of an alcohol component and a carboxylic acid component. Examples of the alcohol component include divalent or trivalent or higher alcohol components, and specific examples include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4- Butanediol, neopentyl glycol, 1,4-butenediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol Diols such as bisphenol A, hydrogenated bisphenol A, bisphenols such as polyoxyethylenated bisphenol A, polyoxypropylenated bisphenol A; sorbitol, 1,2,3,6- Xanthetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, diglycerol, 2-methylpropanetriol, Examples include trivalent or higher alcohols such as 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, 1,3,5, -trihydroxymethylbenzene.

  Examples of the carboxylic acid component include divalent or trivalent carboxylic acids, acid anhydrides or lower alkyl esters thereof, and include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid. Acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, malonic acid, or n-butyl succinic acid, n-butenyl succinic acid, isobutyl succinic acid, isobutenyl succinic acid, n-octyl succinic acid, n- Divalent carboxylic acids such as alkyl succinic acid or alkenyl succinic acid such as octenyl succinic acid, n-dodecyl succinic acid, n-dodecenyl succinic acid, isododecyl succinic acid and isododecenyl succinic acid; 1,2,4-benzenetricarboxylic acid (Trimellitic acid), 1,2,5-benzene Carboxylic acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl- 2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra (methylenecarboxyl) methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, empole trimer acid, etc. And trivalent or higher carboxylic acids.

  The resin is preferably a thermoplastic resin from the viewpoint of good fixability, but the amount of cross-linked portion (gel amount) measured using a Soxhlet extractor is 10% by weight or less, more preferably 0.1 to 10% by weight. If it is a value within the range of%, a thermosetting resin may be used. By introducing a partially crosslinked structure in this way, it is possible to further improve the storage stability, form retention, and durability of the toner without deteriorating the fixability. Therefore, it is not necessary to use 100% by weight of the thermoplastic resin as the toner resin, and a crosslinking agent may be added or a part of the thermosetting resin may be used. As the thermosetting resin, for example, an epoxy resin or a cyanate resin can be used. More specifically, one or more of bisphenol A type epoxy resin, hydrogenated bisphenol A type epoxy resin, novolac type epoxy resin, polyalkylene ether type epoxy resin, cycloaliphatic type epoxy resin, cyanate resin, etc. Combinations are listed.

  In the resin, the glass transition temperature (Tg) is preferably set to a value within the range of 55 to 70 ° C. When the Tg of the resin is less than 55 ° C., the obtained toners are fused with each other and the storage stability tends to be lowered. On the other hand, when the Tg of the resin exceeds 70 ° C., the fixability of the toner tends to be poor. In addition, Tg of resin can be calculated | required from the change point of specific heat using a differential scanning calorimeter (DSC).

(Coloring agent)
The colorant that can be used for producing the core particle 1 is not particularly limited, and examples thereof include magenta, cyan, yellow, and black colorants.

  As the magenta colorant, for example, C.I. I. Pigment red 81, C.I. I. Pigment red 122, C.I. I. Pigment red 57, C.I. Pigment Red 49, C.I. I. Solvent Red 49, C.I. I. Solvent Red 19, C.I. I. Solvent Red 52, C.I. I. Basic Red 10, C.I. I. Disperse Red 15 etc. are mentioned.

  As the cyan colorant, for example, C.I. I. Pigment blue 15, C.I. I. Pigment blue 15-1, C.I. Pigment blue 16, C.I. I. Solvent Blue 55, C.I. I. Solvent Blue 70, C.I. I. Direct Blue 86, C.I. I. Direct Blue 25 etc. are mentioned.

  Examples of the yellow colorant include nitro pigments such as naphthol yellow S, azo pigments such as Hansa Yellow 5G, Hansa Yellow 3G, Hansa Yellow G, Benzidine Yellow G, and Vulcan Fast Yellow 5G, or yellow iron oxide and ocher. And inorganic pigments. In addition, C.C. I. Pigment yellow 12, C.I. I. Pigment yellow 180, C.I. I. Solvent Yellow 2, C.I. I. Solvent Yellow 6, C.I. I. Solvent Yellow 14, C.I. I. Solvent Yellow 15, C.I. I. Solvent Yellow 16, C.I. I. Solvent Yellow 19, C.I. I. Solvent yellow 21 etc. are mentioned.

  Examples of the black colorant include carbon black such as furnace black, channel black, acetylene black, run black, and aniline black. Moreover, you may add the metal (magnetic powder) which shows ferromagnetism, such as iron, cobalt, nickel, such as ferrite and magnetite, as a black type | system | group coloring agent.

(wax)
Examples of waxes that can be used to produce the core particles 1 include plant waxes such as carnauba wax, sugar wax, and wood wax; animal waxes such as beeswax, insect wax, whale wax, and wool wax; and ester side chains. And synthetic hydrocarbon waxes such as Fischer-Tropsch wax, polyethylene wax, and polypropylene wax. The wax preferably has an endothermic main peak in a range of 70 to 135 ° C. in an endothermic curve obtained by a differential scanning calorimeter. This is because when the endothermic main peak is less than 70 ° C., toner blocking and hot offset may occur, and when the endothermic main peak exceeds 135 ° C., low-temperature fixability may not be obtained. The amount of the wax added is preferably in the range of 0.1 to 20 parts by weight with respect to 100 parts by weight of the resin. If the addition amount of the wax is less than 0.1 parts by weight, it is difficult to obtain a sufficient effect of the wax. On the other hand, if the addition amount is more than 20 parts by weight, the anti-blocking property is lowered and the toner may be detached. is there.

(Charge control agent / Charge control resin)
Examples of the charge control agent include positively chargeable charge control agents, and specific examples thereof include pyridazine, pyrimidine, pyrazine, orthooxazine, metaoxazine, paraoxazine, orthothiazine, metathiazine, parathiazine, 1,2,3-triazine. 1,2,4-triazine, 1,3,5-triazine, 1,2,4-oxadiazine, 1,3,4-oxadiazine, 1,2,6-oxadiazine, 1,3,4-thiadiazine, , 3,5-thiadiazine, 1,2,3,4-tetrazine, 1,2,4,5-tetrazine, 1,2,3,5-tetrazine, 1,2,4,6-oxatriazine, 1, Azine compounds such as 3,4,5-oxatriazine, phthalazine, quinazoline, quinoxaline; azine fast red FC, azine fast red 12 Direct dyes composed of azine compounds such as K, azine violet BO, azine brown 3G, azine light brown GR, azinda kugreen BH / C, azine dip black EW and azine black 3RL; nigrosine, nigrosine salt, nigrosine derivative Nigrosine compounds such as: nigrosine BK, nigrosine NB, nigrosine compounds such as nigrosine Z; acid dyes; metal salts of naphthenic acid or higher fatty acids; alkoxylated amines; alkylamides; benzylmethylhexyldecylammonium, decyltrimethylammonium chloride, etc. Quaternary ammonium salts can be exemplified, and these can be used alone or in combination of two or more.

  Further, a quaternary ammonium salt, a carboxylate, a resin having a carboxyl group as a functional group, an oligomer, or the like can also be used as a positively chargeable charge control agent / charge control resin. More specifically, a styrene resin having a quaternary ammonium salt, an acrylic resin having a quaternary ammonium salt, a styrene-acrylic resin having a quaternary ammonium salt, a polyester resin having a quaternary ammonium salt, a carboxylic acid Styrene resin with salt, acrylic resin with carboxylate, styrene-acrylic resin with carboxylate, polyester resin with carboxylate, polystyrene resin with carboxyl group, acrylic with carboxyl group 1 type, or 2 or more types, such as resin, the styrene-acrylic resin which has a carboxyl group, and the polyester-type resin which has a carboxyl group, are mentioned.

  As the charge control agent exhibiting negative chargeability, for example, organometallic complexes and chelate compounds are effective. Examples thereof include aluminum acetylacetonate, iron (II) acetylacetonate, and 3,5-di-tert-butylsalicylate chromium. In particular, acetylacetone metal complexes, salicylic acid metal complexes or salts are preferable, and salicylic acid metal complexes or salicylic acid metal salts are particularly preferable.

  The production method of the core particle 1 having the composition exemplified above is not particularly limited, but in the present invention, a method selected from a suspension polymerization method, an emulsion polymerization aggregation method and a pulverization method is adopted. preferable. Thereby, since the core particle 1 can be obtained efficiently, the productivity of the electrophotographic toner 10 is improved.

(Suspension polymerization method)
When employing the suspension polymerization method, for example, the core particles 1 can be obtained as follows. That is, a composition containing a polymerizable monomer, a colorant, a polymerization initiator, a charge control agent and the like is added to an aqueous phase with stirring, and granulated. After the polymerization reaction, the particles are filtered and dried. The core particle 1 can be obtained.

  Examples of the polymerizable monomer include a monovinyl aromatic monomer, an acrylic monomer, a vinyl ester monomer, a vinyl ether monomer, a diolefin monomer, and a monoolefin monomer. Can be mentioned.

  As the colorant, the same colorant as exemplified above can be used. The added amount of the colorant is 2 to 20 parts by weight, preferably 4 to 15 parts by weight, based on 100 parts by weight of the resin.

  Examples of the polymerization initiator include benzoyl peroxide, lauroyl peroxide, isopropyl peroxycarbonate, cumene hydroperoxide, 2,4-dichloroylbenzoyl peroxide, methyl ethyl ketone peroxide, and the like.

  As the charge control agent, the same charge control agent as exemplified above can be used, and the addition amount thereof is 1 to 15.0 parts by weight, preferably 1.5 to 8 parts per 100 parts by weight of the resin. 0.0 part by weight is preferable. If the addition amount of the charge control agent is less than the above range, it may be difficult to stably charge the toner, and the electrostatic latent image was developed using the toner to form an image. In some cases, a decrease in image density may occur. On the other hand, if the amount of the charge control agent is larger than the above range, environmental resistance, particularly charging failure or image failure under high temperature and high humidity may occur, and the photoreceptor may be contaminated.

(Emulsion polymerization aggregation method)
When employing the emulsion polymerization aggregation method, the core particle 1 can be obtained, for example, as follows. That is, a core particle 1 may be obtained by adding a colorant, a charge control agent, and the like to a dispersion containing a polymer obtained by emulsion polymerization, followed by aggregation and aging.

  In the case of obtaining a polymer in a method different from the above method, for example, emulsion polymerization, a colorant may be added together with the wax. As the colorant, the same colorant as exemplified above may be used, and it is preferable to add 3 to 20 parts by weight with respect to 100 parts by weight of the resin. The charge control agent may be the same charge control agent as exemplified above. In particular, a quaternary ammonium salt compound is used as the positive charge control agent, and a salicylic acid metal is used as the negative charge control agent. It is preferable to use a salt or the like. The amount of use may be determined by the desired charge amount for the toner, but is 0.01 to 15 parts by weight, preferably 0.1 to 10 parts by weight, based on 100 parts by weight of the resin.

(Crushing method)
When employing the pulverization method, the core particles 1 can be obtained, for example, as follows. That is, a predetermined amount of resin, wax, charge control agent, colorant and the like are added, and these are stirred and mixed by a mixing device such as a Henschel mixer. Next, the mixture is melt-kneaded with a twin screw extruder or the like, cooled, and then pulverized with a pulverizer such as a hammer mill or a jet mill. Furthermore, if a classifier such as an air classifier is used, the core particle 1 having a predetermined particle size can be produced.

(2) First shell layer forming step In the first shell layer forming step, the core particles 1 and the silica particles as the raw material of the first shell layer 2 are dispersed in a solvent (for example, an aqueous medium), and then aggregated. An agent (for example, sodium chloride (NaCl)) is added to cause silica particles to adhere to the surface of the core particles 1 to form a shell. Furthermore, it is preferable that the silica particles are fixed to the core particles 1 by heating to a temperature higher than the glass transition temperature (Tg) of the core particles 1. Thereafter, the dispersion is made alkaline (pH = 9 to 13) by adjusting the pH, thereby fixing the silica particles to form the first shell layer 2. Further, the dispersion system is returned to neutral, and the process proceeds to the next second shell layer forming step.

(3) Second Shell Layer Forming Step In the second shell layer forming step, the second shell layer 3 is formed on the first shell layer 2. When forming the second shell layer 3, first, a resin fine particle dispersion is prepared using fine particles of a raw material resin and a solvent (for example, an aqueous medium). Although it does not restrict | limit especially as raw material resin, For example, a polystyrene-type resin, a polyacrylic-type resin, a styrene-acrylic-type copolymer, a polyester-type resin etc. are mentioned. Examples of the fine particles of the raw material resin include fine particles of about 10 nm to 50 nm synthesized by an emulsion polymerization method, and resins obtained by pulverizing a resin synthesized by another polymerization method with a wet mill such as an attritor.

  After preparing the resin fine particle dispersion, a predetermined amount of the resin fine particle dispersion is added to the core particle dispersion on which the first shell layer is formed, and then a flocculant (for example, NaCl) is added, and the resin fine particles are added to the first. The second shell layer 3 (resin coat layer) can be formed on the surface of the first shell layer 2 by adhering to the surface of the shell layer.

(4) Second shell layer fixing step Further, if the temperature is raised to Tg or more of the resin contained in the second shell layer, the second shell layer 3 can be fixed to the surface of the first shell layer 2, After filtration, washing and drying, toner particles 20 are obtained.

(5) Inorganic fine powder external addition step Thereafter, a normal external addition process is performed in a dry manner, whereby the electrophotographic toner 10 can be obtained. In this step, the inorganic fine powder 4 having a particle diameter larger than the average layer thickness of the second shell layer 3 is externally added to the toner particles 20. Examples of the external addition method include a method in which the toner particles 20 and the external additive (inorganic fine powder 4) are mixed using a Henschel mixer or the like.

  Hereinafter, the toner for electrophotography of the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited only to the following Examples.

[Examples 1 to 9 and Comparative Example 1]
<Production Example of Core Particle 1: Suspension Polymerization Method>
80 parts by weight of styrene, 20 parts by weight of 2-ethylhexyl methacrylate, 5 parts by weight of carbon black, 3 parts by weight of low molecular weight polypropylene, 2 parts by weight of a charge control agent (“Bontron P-51” manufactured by Orient Chemical Co., Ltd.) and divinylbenzene (crosslinking) Agent) After 1 part by weight of the mixed solution is sufficiently dispersed by a ball mill, 2 parts by weight of a polymerization initiator 2,2-azobis (2,4-dimethylvaleronitrile) is added, and 400 parts by weight of ion-exchanged water is added. In addition, 5 parts by weight of tribasic calcium phosphate and 0.1 part by weight of sodium dodecylbenzenesulfonate are added as a suspension stabilizer and TK homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) is used for 20 minutes at a rotational speed of 7000 rpm. The mixture was stirred and polymerized at 70 ° C. and 100 rpm for 10 hours under a nitrogen atmosphere. Thereafter, acid washing was performed to remove tricalcium phosphate, and a dispersion liquid (dispersion liquid 1) containing core particles having a volume average particle diameter of 8 μm was obtained. In addition, Tg of the obtained core particle was 62 degreeC.

<Production Example of Core Particle 2: Emulsion Polymerization Aggregation Method>
(1) Emulsion polymerization of binder 20 parts by weight of styrene, 3.5 parts by weight of butyl acrylate, 0.2 parts by weight of divinylbenzene, 0.7 parts by weight of potassium persulfate as a water-soluble polymerization initiator, 200 parts by weight of ion-exchanged water Was put into a round bottom flask and subjected to emulsion polymerization at 100 rpm and 70 ° C. for 8 hours with an anchor-type stirring blade to obtain a dispersion liquid (dispersion liquid 2) containing styrene acrylic having an average particle diameter of 0.3 μm.

(2) Preparation of additive dispersion 5 parts by weight of Carnauba wax No. 1 (manufactured by Kato Hiroyuki), 2 parts by weight of Bontron P-51 (manufactured by Orient Chemical Co., Ltd.), 4 parts by weight of CIPigment Red 122 (manufactured by Dainippon Ink and Company) And 0.1 part by weight of sodium dodecylbenzenesulfonate in 200 parts by weight of ion-exchanged water, dispersed and mixed for 3 hours by a ball mill, and a dispersion containing an additive having an average particle size of 0.3 μm (dispersion 3) was obtained.

(3) Formation of core particles The above dispersions 2 and 3 were mixed, and agglomerates were grown in a round bottom flask with an anchor type stirring blade at 100 rpm and 40 ° C for 1 hour. During the above 1 hour period, 50 parts by weight of ion-exchanged water in which 0.5 part by weight of NaCl was dissolved as a flocculant was continuously added for 50 minutes at a rate of 1 part by weight per minute. After the cohesive growth, the temperature was raised to 70 ° C., and fusion was carried out at 100 rpm for 30 minutes to obtain a dispersion liquid (dispersion liquid 4) containing core particles having a volume average particle diameter of 8 μm. In addition, Tg of the obtained core particle was 63 degreeC.

<Production Example 3 of Core Particle: Kneading and Crushing Method>
100 parts by weight of a binder resin (“Toughton NE-410” manufactured by Kao), 5 parts by weight of carbon black (“MA-100” manufactured by Mitsubishi Kasei), and a charge control agent (“Bontron P manufactured by Orient Chemical Co., Ltd.”) -51 ") 5 parts by weight and 4 parts by weight of Carnauba Wax No. 1 (manufactured by Kato Yoko Co., Ltd.) were charged into a Henschel mixer, mixed, melt-kneaded with a twin screw extruder, cooled with a drum flaker, Coarsely pulverized with a hammer mill. Next, the mixture was finely pulverized with a mechanical mill and classified using an air classifier to prepare core particles having a volume average particle diameter of 8 μm. Thereafter, 1.0 part by weight of a surfactant (sodium dodecylbenzenesulfonate) was added and dispersed in 500 parts by weight of ion-exchanged water to obtain a core particle dispersion (dispersion 5). In addition, Tg of the obtained core particle was 62 degreeC.

<Emulsion polymerization of second shell layer forming particles>
20 parts by weight of styrene, 2 parts by weight of butyl acrylate, 0.2 parts by weight of divinylbenzene, 0.5 parts by weight of a water-soluble polymerization initiator (potassium persulfate), 0.4 parts by weight of a surfactant (sodium dodecylbenzenesulfonate) Part and 200 parts by weight of ion-exchanged water are put into a round bottom flask and subjected to emulsion polymerization at 100 rpm and 70 ° C. for 8 hours with an anchor-type stirring blade to obtain a dispersion of styrene acrylic resin particles (Dispersion 6). Obtained. The resulting styrene acrylic resin particles had a Tg of 75 ° C., a softening point of 140 ° C., and an average particle size of 0.01 μm.

<First shell layer forming step>
Addition amount of silicon dioxide powder (silica particles, “RA200HS” manufactured by Nippon Aerosil Co., Ltd.) shown in Table 1 is added to dispersion 1, dispersion 4 or dispersion 5 containing core particles, and a surfactant (dodecylbenzene) is added. 2 parts by weight (sodium sulfonate) (relative to the weight of silica particles) was used and sufficiently dispersed in the aqueous system. Thereafter, 0.5 part by weight of a flocculant (NaCl) (weight of silica particles) was added, and the silica particles were fixed in the round bottom flask with an anchor-type stirring blade at 100 rpm and 70 ° C. for 30 minutes. . Thereafter, 10 ml of a 2N NaOH aqueous solution was further dropped to fuse the silica, and then the aqueous pH was returned to neutral with a 2N hydrochloric acid aqueous solution to prepare a dispersion of particles on which the first shell layer was formed. .

<Second shell layer forming step>
To the dispersion prepared in the first shell layer forming step, the second shell layer forming particles (dispersion 6) are added at various addition amounts shown in Table 1, and then 0.5 parts by weight of a flocculant (NaCl). (Particle weight for forming the second shell layer) was added to form particles for forming the second shell layer on the surface of the first shell layer.

<Second shell layer fixing step>
Thereafter, the second shell layer forming particles were fixed in a round bottom flask with an anchor type stirring blade at 100 rpm and 75 ° C. for 30 minutes to obtain a composition. Thereafter, the obtained composition was filtered, washed, and dried to obtain a raw powder (toner particles).

<Inorganic fine powder external addition step (preparation of toner)>
100 parts by weight of raw powder, 0.8 parts by weight of silica RA200HS (manufactured by Nippon Aerosil Co., Ltd., average particle size 12 nm) and inorganic fine powder (large particle size external additive) are mixed for 2 minutes using a Henschel mixer, and toner is added. Obtained. Table 1 shows toner prescriptions such as the type and amount of inorganic fine powder (large particle size external additive) and the type of core particles (dispersion 1, 4, or 5) used. In Table 1, “particle diameter” of the large particle size external additive means an average particle diameter. Furthermore, each average layer thickness of the first shell layer and the second shell layer was obtained by measuring each layer thickness using a scanning electron microscope (SEM) and calculating an average value thereof at three cross sections of the toner particles. .

<Preparation of developer for evaluation>
35 g of various toners prepared according to the formulation shown in Table 1 above and 700 g of Kyocera Mita FS-8008C carrier were placed in a 500 ml polypropylene container and mixed at 100 rpm for 30 minutes to prepare a developer for evaluation.

<Evaluation test>
Using the developer and an image forming apparatus (FS-8008C manufactured by Kyocera Mita Co., Ltd.), an evaluation test was performed on 5000 sheets after continuous printing with an initial performance (first sheet) and a printing rate of 1%. The image density was measured with a Gretag Macbeth densitometer on a solid image. The transfer efficiency was determined by measuring the amount of developed toner on the drum of the solid printing portion and the amount of residual toner on the drum after transfer, and obtaining the transfer efficiency by the following formula. The results are shown in Table 2.

The criteria for comprehensive judgment in Table 2 are shown below.
◯: When the image density is 1.30 or more and the transfer efficiency is 85% or more Δ: When the image density is 1.25 to 1.29 or the transfer efficiency is 80 to 84% ×: The image density is 1.24 Or when the transfer efficiency is 79% or less

  According to Tables 1 and 2, when the first shell layer and the second shell layer are formed, and the average layer thickness of the second shell layer is larger than the particle diameter of the inorganic fine powder (large particle size external additive), That is, in Examples 1 to 9, the overall determination is “◯” or “Δ”, indicating a good result.

  In particular, in Examples 1 to 7 in which the average thickness of the second shell layer is 20 nm or more, the overall judgment is “◯”, and it can be seen that extremely good results were obtained. This is presumably because the ability to fix the large particle size external additive on the surface of the toner particles was increased by setting the average thickness of the second shell layer to 20 nm or more.

  On the other hand, in Comparative Example 1 in which the first shell layer was not formed, the image density and the transfer efficiency were lowered due to the embedding of the large particle size external additive.

FIG. 3 is a schematic diagram illustrating a structure of an electrophotographic toner according to an embodiment of the present invention. FIG. 3 is a schematic diagram illustrating a surface of an electrophotographic toner according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Core particle 2 1st shell layer 3 2nd shell layer 4 Inorganic fine powder 10 Toner for electrophotography 20 Toner particle

Claims (14)

An electrophotographic toner in which inorganic fine powder is externally added to toner particles, the toner particles mainly comprising core particles containing at least a resin, a colorant and a wax, and silicon dioxide formed on the surface of the core particles. An inorganic fine powder embedding prevention first shell layer as a component and an inorganic fine powder retaining second shell layer mainly composed of a resin formed on the surface of the first shell layer are provided. Toner for electrophotography.   The electrophotographic toner according to claim 1, wherein a particle diameter of the inorganic fine powder is larger than an average layer thickness of the second shell layer.   The toner for electrophotography according to claim 1, wherein the core particles further contain a charge control agent or a charge control resin. The toner for electrophotography according to any one of claims 1 to 3 average layer thickness of the first shell layer is 10nm or more. The toner for electrophotography according to any one of claims 1 to 4 wherein said second shell layer is composed mainly of resin. The toner for electrophotography according to any one of claims 1 to 5 average layer thickness of the second shell layer is 20nm or more. The inorganic fine powder is silicon dioxide, titanium oxide, toner for electrophotography according to any one of claims 1 to 6 at least one selected from aluminum oxide and magnetic powder. The toner for electrophotography according to any one of the particle diameter of the inorganic fine powder is 20nm greater claims 1-7. The toner for electrophotography according to any one of claims 1 to 8, wherein said inorganic fine powder is composed of two or more. The toner for electrophotography according to claim 9 , wherein the particle diameter of at least one inorganic fine powder is larger than the average layer thickness of the second shell layer. A first shell layer forming step of forming a first shell layer mainly composed of silicon dioxide using silicon dioxide and a solvent on the surface of core particles containing at least a resin, a colorant and a wax;
A second shell layer forming step of adding a solvent containing a resin to the core particles on which the first shell layer is formed, and forming a second shell layer containing the resin as a main component on the surface of the first shell layer;
A second shell layer fixing step in which toner particles are obtained by heating to a temperature equal to or higher than the glass transition temperature of the resin contained in the second shell layer to fix the second shell layer to the surface of the first shell layer; ,
A method for producing an electrophotographic toner, comprising: adding an inorganic fine powder having a particle diameter larger than an average layer thickness of the second shell layer to the toner particles. In the first shell layer forming step, after the core particles and silicon dioxide particles are dispersed in a solvent, the silicon dioxide particles are adhered to the surface of the core particles with a flocculant, and the glass transition of the core particles A step of heating above the temperature to fix the silica particles to the core particles, a step of making the dispersion alkaline by pH adjustment, fixing the silica particles to each other, and a step of returning the dispersion to neutrality by pH adjustment The method for producing an electrophotographic toner according to claim 11 , comprising: The second shell layer forming step includes a step of preparing a resin fine particle dispersion, and the resin fine particle dispersion is added to the core particle dispersion on which the first shell layer is formed. method for producing a toner for electrophotography according to claim 11 or 12, wherein and the step of attaching to the surface of the first shell layer. The method for producing an electrophotographic toner according to any one of claims 11 to 13 , wherein the core particles are obtained by a method selected from a suspension polymerization method, an emulsion polymerization aggregation method, and a pulverization method.

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