JP5870654B2 - Liquid developer - Google Patents

Description

  The present invention relates to a liquid developer used for developing an electrostatic latent image in an electronic copying machine, a printer, an on-demand printing machine or the like in which an image is formed using an electrophotographic method, an electrostatic recording method, or the like. . More preferably, the present invention relates to a liquid developer having excellent cleaning properties.

  An image forming apparatus using a liquid developer can be miniaturized because it is finely pulverized and dispersed under a wet condition as compared with a dry powder toner, and an insulating liquid carrier liquid is used as a carrier. A feature is that high-definition images can be formed without causing problems due to scattering of toner particles in the machine.

  In an electrophotographic image forming apparatus using a liquid developer, a developer in which fine toner particles are dispersed in a carrier liquid is used, and an electrostatic latent image formed by exposure on a photoconductor is used. Development is performed using toner particles in the carrier liquid. After development, the resulting image is transferred, dried and fixed on a recording medium such as paper to form an image.

  In these development and transfer processes, toner particles that have not been developed and transferred remain on the roller. Therefore, it is necessary to clean the toner particles using a roller or a blade.

  If the toner particles cannot be removed well in the above cleaning process, the residual toner after transfer is transferred onto the paper surface, which causes a problem. Therefore, toner particle cleaning is an important issue. .

  Especially for liquid developers, the particle size is small, so it is easy to slip through the blade, and in order to obtain good transferability, it is necessary to increase the charge amount per particle. The electrostatic adhesion with the toner becomes stronger, and cleaning becomes more difficult.

In order to improve this cleaning property, conventionally, studies have been made on control of characteristics of the liquid developer. (Patent Documents 1 and 2)
However, Patent Document 1 is based on control of the toner particle diameter and particle shape, and the effect is insufficient. In Patent Document 2, the charge control is performed by the amount of the dispersant in the carrier liquid. However, an increase in the amount of the dispersant causes a deterioration in fixing properties.

JP 2008-209655 A JP 2008-134507 A

  As described above, with respect to the improvement of the cleaning property of the transfer residual toner of the liquid developer, the control of the toner particle diameter and particle shape and the charge control based on the amount of the dispersant in the carrier liquid are insufficient, and there is a lot of room for improvement. .

  An object of the present invention is to provide a liquid developer having excellent cleaning properties, developability, and hot offset resistance.

  As a result of intensive studies, the present inventors have reached the invention of a liquid developer having the following characteristics.

A liquid developer in which toner particles comprising at least a binder resin (A), a colorant (B), and an inorganic oxide (C) are dispersed in a carrier liquid (D) , the inorganic oxide (C) Is a liquid developer containing talc .
The liquid developer as described above, wherein the inorganic oxide (C) has a surface potential V ₁₀ of 0.8 kV or less. V ₁₀ is the surface potential after 10 seconds of corona charging.

The liquid developer according to claim ₁ , wherein the inorganic oxide (C) has a surface potential V1 of 0.2 kV to 1.6 kV. However V ₁ was a surface potential after corona charging one second.
The liquid developer as described above, further comprising 0.1 to 10% by weight of the inorganic oxide (C) in the toner particles.
The liquid developer, wherein the binder resin (A) contains at least a polyester resin.

  As described above, the toner particles in which the inorganic oxide (C) is internally added together with the binder resin (A) and the colorant (B) and the surface characteristics and chargeability are controlled are dispersed in the carrier liquid (D). By doing so, it is possible to provide a liquid developer having good cleaning properties, developability, and hot offset resistance.

Hereinafter, the present invention will be described in more detail.
The liquid developer of the present invention is greatly characterized in that an inorganic oxide (C) is internally added to the toner particles. By selecting the type and amount of inorganic oxide (C) optimally and controlling the surface characteristics and charging characteristics of the toner particles, the cleaning properties are improved, and the developability and hot offset resistance are excellent. .

  Hereinafter, the binder resin (A), the colorant (B), the toner particles composed of the inorganic oxide (C), the carrier liquid (D) and the like constituting the liquid developer of the present invention will be described in detail.

(Toner particles)
The toner particles used in the liquid developer of the present invention are composed of at least a binder resin (A), a colorant (B) and an inorganic oxide (C), in addition to pigment dispersants, plasticizers, waxes and the like. It is also preferable to use an additive.

(Binder resin (A))
In general, the binder resin has a function of uniformly dispersing a colorant such as a pigment or a dye in the resin and a function as a binder when fixing to a substrate such as paper.
Examples of binder resins that can be used include homopolymers of styrene such as polystyrene, poly-p-chlorostyrene, and polyvinyltoluene, and substituted products thereof; styrene-p-chlorostyrene copolymer, styrene-vinyltoluene copolymer Polymer, styrene-vinyl naphthalene copolymer, styrene-acrylic acid ester copolymer, styrene-methacrylic acid ester copolymer, styrene-α-chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl Styrenes such as methyl ether copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-acrylonitrile-indene copolymer Copolymer or cross-linked Tylene copolymer; polyvinyl chloride, phenol resin, natural modified phenol resin, natural resin modified maleic acid resin, acrylic resin, methacrylic resin, polyvinyl acetate, silicone resin, polyester resin, polyurethane resin, polyamide resin, furan resin, Examples thereof include epoxy resins, xylene resins, polyvinyl butyral resins, terpene resins, coumarone indene resins, and petroleum resins.
A polyester resin is particularly preferable in terms of excellent pigment dispersibility and fixability.

  The polyester resin is preferably a thermoplastic polyester, and is obtained by polycondensation of a divalent or trivalent or higher alcohol component and an acid component such as carboxylic acid.

Examples of the alcohol component include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,4-butenediol, Diethylene glycol, triethylene glycol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, 2-ethyl-1,3-hexanediol, bisphenol A, hydrogenated bisphenol A, 1,4-bis (hydroxy Methyl) cyclohexane, divalent alcohols such as bisphenol derivatives represented by the following general formula (1),
Examples of trihydric or higher alcohols such as glycerol, diglycerol, sorbit, sorbitan, butanetriol, trimethylolethane, trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol, and the like, may be used alone or in combination Used in combination.

(In the formula, R is an ethylene or propylene group, x and y are each an integer of 1 or more, and the average value of x + y is 2 to 10.)

As the acid component, divalent carboxylic acids such as benzene dicarboxylic acids such as phthalic acid, terephthalic acid, isophthalic acid and phthalic anhydride or anhydrides thereof; alkyl dicarboxylic acids such as succinic acid, adipic acid, sebacic acid and azelaic acid Or its anhydride;
And a succinic acid or anhydride thereof further substituted with an alkyl group having 16 to 18 carbon atoms;
Unsaturated dicarboxylic acids such as fumaric acid, maleic acid, citraconic acid, itaconic acid, glutaconic acid or anhydrides thereof;
Cyclohexanedicarboxylic acid; naphthalenedicarboxylic acid; diphenoxyethane-2,6-dicarboxylic acid, and the like.
Trivalent or higher carboxylic acids that serve as crosslinking components include trimellitic acid, pyromellitic acid, naphthalenetricarboxylic acid, butanetricarboxylic acid, hexanetricarboxylic acid, tetra (methylenecarboxyl) methane, octanetetracarboxylic acid, benzophenonetetracarboxylic acid and An anhydride etc. are mentioned, These are used individually or in combination of 2 or more types.

  Preferred alcohol components are those obtained by adding 2 to 3 moles of alkylene oxide to bisphenol A, ethylene glycol, neopentyl glycol, etc., and preferred acid components are phthalic acid, terephthalic acid, isophthalic acid or its anhydride, succinic acid, n-dodecenyl succinic acid or its anhydride, dicarboxylic acids such as fumaric acid, maleic acid and maleic anhydride, and tricarboxylic acids such as trimellitic acid or its anhydride.

  As the polycondensation method, a known bulk polymerization method can be used. To control the molecular weight and softening temperature of the polyester resin, the kind and molar ratio of the alcohol component and carboxylic acid to be reacted, as well as the reaction temperature and reaction time. The reaction pressure, catalyst, etc. may be adjusted. Furthermore, it is also possible to use a commercial item as a polyester resin. For example, there are Diacron ER-502 and Diacron ER-508 (both manufactured by Mitsubishi Rayon Co., Ltd.).

Furthermore, it is preferable to use a hybrid resin of a polyester resin and a styrene-acrylic resin in order to improve fixability, dispersibility, and grindability.

A hybrid resin of a polyester resin and a styrene-acrylic resin is synthesized by a known method such as Japanese Patent No. 3531980 and Japanese Patent Application Laid-Open No. 2006-178296.

  The mass ratio of the polyester resin and the styrene-acrylic resin [polyester resin / styrene-acrylic copolymer resin] contained in the binder resin (A) is preferably 1-20. When the mass ratio exceeds 20, the effect of improving fixability, dispersibility, and grindability cannot be obtained, and when the mass ratio is less than 1, the hot offset resistance tends to deteriorate. More preferably, the mass ratio is 3-20.

(Softening temperature (T4))
The softening temperature of the binder resin (A) used in the present invention is preferably in the range of 70 to 140 ° C, more preferably in the range of 80 to 130 ° C. The softening temperature in the present invention is as follows. Using a flow tester CFT-500D manufactured by Shimadzu Corporation, a starting temperature of 40 ° C., a heating rate of 6.0 ° C./min, a test load of 20 kg, a preheating time of 300 seconds, and a die hole diameter of 0.5 mm. The temperature when 4 mm of 1.0 g of the sample flows out under the condition of the die length of 1.0 mm is measured as the softening temperature (T4).
When the softening temperature of the binder resin (A) is lower than 70 ° C., the binder resin (A) is excessively softened during kneading, the dispersibility of the colorant (B) is deteriorated, and a necessary image density as a liquid developer cannot be obtained. Further, the offset resistance is deteriorated, and the dispersion stability of the liquid developer is also deteriorated. On the other hand, if the softening temperature is higher than 140 ° C., good fixability cannot be obtained.

(Average molecular weight)
The binder resin (A) preferably has a weight average molecular weight (Mw) of 2,000 to 100,000, more preferably 3,000 to 30,000, from the viewpoint of offset resistance, fixability and image quality characteristics. More preferred. When the weight average molecular weight (Mw) of the binder resin (A) is smaller than 2,000, offset resistance, color reproducibility and dispersion stability tend to be lowered, and when it is larger than 100,000, the fixing property is deteriorated. There is a tendency.
In addition, the binder resin (A) used in the present invention is a type having a molecular weight distribution curve of two peaks composed of a specific low molecular weight condensation polymer component and a specific high molecular weight condensation polymer component, or one peak. Any of the types having a single molecular weight distribution curve may be used.
The weight average molecular weight was measured by gel permeation chromatography (HLC-8220) manufactured by Tosoh Corporation. A calibration curve was prepared with a standard polystyrene sample. Tetrahydrofuran was used as the eluent, and three TSKgel SuperHM-M (manufactured by Tosoh Corporation) were used as the column. The measurement was performed at a flow rate of 0.6 ml / min, an injection volume of 10 μl, and a column temperature of 40 ° C.

  Furthermore, it is preferable that the ratio of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the binder resin (A), and Mw / Mn is in the range of 2-15. When Mw / Mn is less than 2, the offset resistance is deteriorated, the non-offset region is narrowed, and the low temperature fixability tends to be deteriorated. When Mw / Mn exceeds 15, the pulverizability of the toner particles deteriorates, and the image characteristics as a liquid developer tend to deteriorate.

(Colorant (B))
As the colorant (B) used in the liquid developer of the present invention, the following yellow, magenta, cyan, and black organic pigments, organic dyes, particularly salt-forming compounds thereof, carbon black, and magnetic materials are preferably used. . These can be used alone or in admixture of two or more. Further, it is preferably insoluble in the carrier liquid.

As the yellow colorant, it is preferable to use a yellow organic pigment or a salt forming compound of a yellow dye.
As the yellow organic pigment, compounds represented by benzimidazolone compounds, condensed azo compounds, isoindolinone compounds, anthraquinone compounds, quinophthalone compounds, azo metal complex compounds, methine compounds, and allylamide compounds are used. Specifically, C.I. I. Pigment Yellow 12, 13, 14, 15, 17, 62, 74, 83, 93, 94, 95, 97, 109, 110, 111, 120, 127, 128, 129, 138, 139, 147, 150, 168, 174, 176, 180, 181, 191 and the like are preferably used. Of these, quinophthalone compounds, condensed azo compounds, and benzimidazolone compounds are preferably used.
As the yellow dye salt-forming compound, an acid dye salt-forming compound and a basic dye salt-forming compound are used. Examples of the salt forming compound of the acid dye include C.I. I. It is preferable to use a salt-forming compound composed of Acid Yellow 11, 23 (tartrazine) and a quaternary ammonium salt compound. By constituting the quaternary ammonium salt, the toner particles can maintain a stable positive charge.

As the magenta colorant, it is preferable to use a magenta organic pigment or a salt forming compound of a magenta dye.
As magenta organic pigments, condensed azo compounds, diketopyrrolopyrrole compounds, anthraquinones, quinacridone compounds, lake compounds of basic dyes such as rhodamine lakes, naphthol compounds, benzimidazolone compounds, thioindigo compounds, and perylene compounds are used. Specifically, C.I. I. Pigment Red 2, 3, 5, 6, 7, 23, 48: 2, 48: 3, 48: 4, 57: 1, 81, 81: 1, 81: 2, 81: 3, 81: 4, 122, 144, 146, 166, 169, 177, 184, 185, 202, 206, 209, 220, 221, 254, 255, 268, 269, etc., C.I. I. Pigment violet 1, 19 and the like are preferably used. Among them, it is preferable to use a quinacridone compound, a rhodamine lake pigment, a naphthol pigment, or the like. Specifically, naphthol AS (CI Pigment Red 269 etc.), rhodamine lake (CI Pigment Red 81, 81: 1, 81: 2, 81: 3, 81: 4, 169 etc.), quinacridone (C.I. Pigment Red 122 etc.) Carmine 6B (C.I. Pigment Red 57: 1) is a preferred material.
A combination of a quinacridone pigment and a monoazo pigment, Carmine 6B (CI Pigment Red 57: 1), is preferable because it exhibits a good magenta color and red color.
Further, as a salt-forming compound of a magenta dye, a salt-forming compound of a rhodamine-based acidic dye or a salt-forming compound of a rhodamine-based basic dye is preferably used. Examples of the salt forming compound of the basic dye include C.I. I. It is preferable to use a salt-forming compound consisting of Basic Red 1 and Basic Violet 10 and colorless organic sulfonic acid or organic carboxylic acid (which does not inhibit coloring of the pigment). Since the basic dye exhibits a good positive charge, the toner particles can maintain a stable positive charge. As the organic sulfonic acid, naphthalenesulfonic acid, naphtholsulfonic acid, naphthylaminesulfonic acid and the like are preferably used. As the organic carboxylic acid, a salicylic acid derivative or a higher fatty acid is used.

As the cyan colorant, it is preferable to use cyan, blue organic pigments, cyan, salt forming compounds of blue dyes, and oil-soluble dyes of cyan and blue dyes.
As the cyan organic pigment, copper phthalocyanine compounds and derivatives thereof, anthraquinone compounds, basic dye lake compounds, and the like can be used. Specifically, C.I. I. Pigment Blue 1, 7, 15, 15: 1, 15: 2, 15: 3, 15: 4, 15: 6, 60, 62, 66 and the like are preferably used. Among them, C.I. I. It is preferable to use a copper phthalocyanine compound such as CI Pigment Blue 15: 3.
It is also preferable to use a compound derived from a triarylmethane dye in a form used in combination with the organic pigment. Triarylmethane dyes are effective materials from the viewpoints of both chargeability control and colorability because they have good positive chargeability. In particular, C.I. I. Triarylmethane-based oil-soluble dyes such as Solvent Blue 124 and salt-forming compounds of triarylmethane-based basic dyes are good. C. I. As the solvent blue 124, specifically, COPY BLUE PR manufactured by Clariant is a preferable material. This is C.I. I. It was obtained by condensing Basic Red 9 (paramagenta) and aniline.
Further, in addition to the cyan and blue organic pigments, cyan and blue dye salt forming compounds, and cyan and blue dye oil-soluble dyes, a green pigment can be used as a complementary color for the purpose of adjusting the hue. Specific examples of the green pigment include C.I. I. Halogenated phthalocyanine compounds such as CI Pigment Green 7 and 36 are preferred.

As the black colorant, it is preferable to use organic black pigments such as carbon black and perylene black and organic black dyes such as nigrosine dye and azo metal complex dye from the viewpoint of cost and handling.
As carbon black, various types such as furnace black, channel black, acetylene black, and carbon black derived from biomass can be used, but furnace black carbon and biomass carbon reduce fog (stain on the white background) in image characteristics. This is preferable.
As the nigrosine dye, it is preferable to use a nigrosine base that is refined by wet pulverization or the like and has a volume average particle size of 0.5 to 2 μm. This refined nigrosine dye has a gloss, and a glossy black color can be obtained. Nigrosine refinement can be obtained by the method described in JP-A-2006-171501.
Further, as the black colorant, black can be obtained using the above three colorants of yellow, magenta, and cyan.

Furthermore, in order to obtain black with good image density and contrast, it is preferable to add 1 to 10 parts by mass of a blue dye as a black colorant with respect to 100 parts by mass of the black dye. As the blue pigment, it is preferable to use a halogen-free metal phthalocyanine blue compound, a triarylmethane compound, a dioxazine violet pigment, or the like. In addition, the phthalocyanine blue compound and the triarylmethane compound have a stable positive charging property, which is effective in obtaining good black toner particles. Specifically, C.I. I. Pigment Blue 15: 3, Victoria Pure Blue Lake Pigment (CI Pigment Blue 1), C.I. I. Pigment violet 23, C.I. I. Pigment Violet 19, a salt-forming compound composed of a triarylmethane-based basic dye and a substantially colorless organic acid (a salt-forming compound of CI Basic Blue 7 and an organic acid), a triarylmethane-based oil-soluble dye Is preferably used.
Triarylmethane dyes are effective in controlling the chargeability of toner particles by exhibiting good positive charge, and among them, triarylmethane oil-soluble dyes having excellent dispersibility are preferred.

  The content of the colorant (B) contained in the toner particles used in the present invention varies depending on the type of the binder resin (A) used, but is usually 5 to 30 parts by mass with respect to 100 parts by mass of the toner particles. Preferably it is 5-20 mass parts.

(Inorganic oxide (C))
As the inorganic oxide (C), oxides such as silicon, aluminum, magnesium, calcium, potassium, tin, sodium, boron, titanium, zinc, zirconium and yttrium can be used. In addition, compounds derived from natural minerals such as talc and kaolin clay can also be suitably used. These can be used alone or in combination of two or more.

  Since these inorganic oxides serve as a pulverization interface, they are considered to be present in large amounts on the surface of the toner particles. Due to the effect as a lubricant, the adhesion between the toner particles and the roller is reduced and the cleaning property is improved. Similarly, the contact with the fixing roller is considered to improve the hot offset resistance in order to reduce the adhesion force. In particular, talc is excellent because of its excellent effect as a lubricant.

Talc is a finely pulverized ore called talc, and the composition formula is represented by Mg ₃ Si ₄ O ₁₀ (OH) ₂ (hydrous magnesium silicate). The average particle size is preferably 10 μm or less, and if it is larger than this, dispersion is likely to be poor, resulting in poor developability and transferability.

The inorganic oxide (C) is corona-charged, and the surface potential value (V ₁₀ ) after 10 seconds is preferably 0.8 kV or less. Furthermore, 0.5 kV or less is more preferable. If V ₁₀ is 0.8kV or less, charge of the toner particles is attenuated, electrostatic adhesion between the development roller and the photosensitive member is reduced, the cleaning performance is improved. And V ₁₀ is greater than 0.8 kV, charge decay of the toner particles is small, the developing roller and the photosensitive member, tends strong electrostatic adhesion between the residual toner, thus inferior in cleaning property.
Furthermore, the surface potential (V ₁ ) 1 second after corona charging is preferably 0.2 kV or more and 1.6 kV or less. When V ₁ is less than 0.2 kV, the toner particles are insufficiently charged, resulting in poor developability and transferability. When V ₁ is greater than 1.6 kV, the charge is too large and the electrostatic adhesion force Tends to be strong and has poor cleaning properties.

  The surface potential of the inorganic oxide (C) was measured as follows. In other words, the inorganic oxide sample was put in a black alumite-treated aluminum container (a cylinder with a diameter of 40 mm and a height of 10 mm), placed on a grounded metal plate, a corona discharge site, a surface potential meter, and the top surface of the sample. Set the distance to 10 mm. Particle charging by corona discharge from a 6 kV needle electrode was performed for 10 seconds under an atmospheric condition of 24 ° C. (± 2 ° C.) 45% (± 5%), and measurement was performed with a surface potentiometer immediately thereafter. The above measurement is performed using an electrostatic diffusivity measuring device NS-D100 (manufactured by Nano Seeds Co., Ltd.), and the measuring method is based on JIS C 61340-2-1.

The inorganic oxide surface potential V ₁₀ is equal to or less than 0.8 kV, as an example, aluminum oxide, magnesium oxide, titanium oxide, zinc oxide, zirconium oxide, talc, kaolin and the like. Moreover, following the surface potential _{V 10} is 0.8kV and the inorganic oxide surface potential _{V 1} is equal to or less than 1.6kV than 0.2 kV, talc, and kaolin, and the like, two or more inorganic oxides In combination, for example, an inorganic oxide having a large V ₁ such as silicon dioxide and an inorganic oxide with fast charge decay such as aluminum oxide or magnesium oxide may be combined at an arbitrary ratio to adjust the surface potential. .

  The inorganic oxide (C) is added to the toner particles in the range of 0.1 wt% to 10 wt%. Preferably it is 0.5 weight%-7 weight%, Furthermore, 1-5 weight% is more preferable. If the amount is less than 0.1% by weight, the effect is not recognized. If the amount exceeds 10% by weight, the inorganic oxide in the toner particles becomes poorly dispersed, which tends to cause development failure.

  The average primary particle size of the inorganic oxide (C) is preferably 10 μm or less. When it exceeds 10 μm, it becomes difficult to disperse in the resin, and developability and fixability deteriorate. The particle diameter can be measured with an electron microscope, for example.

(Carrier liquid (D))
The carrier liquid (D) used in the liquid developer of the present invention is preferably an aliphatic hydrocarbon. Examples of the aliphatic hydrocarbons include linear paraffin hydrocarbons, isoparaffin hydrocarbons, and naphthene hydrocarbons. Among these, aliphatic hydrocarbons that have very little residual aromatic hydrocarbon are preferable in terms of the global environment and work environment. Further, those having lipophilic properties, chemically stable and insulating properties are preferred. In addition, the carrier liquid needs to be chemically inert with respect to materials or apparatuses used in the image forming apparatus, particularly members around the development process such as a photoreceptor.

The dry point in the distillation range of the carrier liquid (D) is preferably in the range of 190 to 360 ° C. When the temperature is lower than 190 ° C., the drying is fast, and the regulation blade around the development is fixed, causing image contamination. On the other hand, when the temperature is higher than 360 ° C., it becomes difficult to remove the carrier liquid and the fixability is deteriorated.
Here, the dry point in the distillation range is based on the method defined by ASTM D 86, ASTM D 1078, and JIS K2254.

  The aniline point (JIS K 2256) of the carrier liquid (D) is preferably in the range of 60 to 105 ° C. Moreover, it is preferable to use a Kauri butanol numerical value (KB value: ASTM D 1133) of 30 or less. More preferably, it is the range of 20-30. When the aniline point is lower than 60 ° C. or the Kauri-butanol value exceeds 30, the solubility as a solvent is high, and the carrier liquid dissolves the toner particles, so the toner particle stability is deteriorated, and the color reproducibility. This causes problems such as worsening of the quality of the carrier liquid and staining of the substrate such as paper. If the aniline point exceeds 105 ° C, the compatibility with the dispersant / additives added when dispersing the toner particles in the carrier liquid is poor, resulting in problems such as poor dispersion and insufficient image density. To do.

Specifically describing the insulating property of the carrier liquid (D), the dielectric constant is 5 or less, preferably 1 to 5, and more preferably 1 to 3.
At the same time, the electric resistivity of the carrier liquid (D) is 10 ⁹ Ω · cm or more, preferably 10 ¹⁰ Ω · cm or more, and particularly preferably 10 ¹⁰ to 10 ¹⁶ Ω · cm. Here, the electrical resistivity was measured by combining a universal electrometer MMA-II-17D manufactured by Kawaguchi Electric Manufacturing Co., Ltd. and a liquid electrode LP-05. When the electrical resistivity is 10 ⁹ Ω · cm or less, the chargeability of the toner particles is deteriorated, a sufficient image density cannot be obtained, and the color reproducibility and color developability are deteriorated.

Further, the density (JIS K 2249) at 15 ° C. of the carrier liquid (D) is preferably in the range of 0.67 to 0.9 g / cm ³ . More preferably, it is in the range of 0.70 to 0.85 g / cm ³ . In this range, the toner particles and the dispersant can exist stably, so that excellent fixability and image density can be obtained.
The carrier liquid (D) preferably has a kinematic viscosity (ASTM D445) in the range of 1 to ²⁰ mm ² / s. Especially preferably, it is the range of 1-10. In this range, charged particles can be moved during the phenomenon.
When the kinematic viscosity is less than 1, the viscosity of the liquid developer becomes low, so the transferability to the developing roller is poor, and a sufficient image density cannot be obtained. Furthermore, since the toner particles after development are easy to move, the fineness of the image is easily lost, which is not preferable. On the other hand, if the kinematic viscosity is greater than 20, the fluidity of the toner particles cannot be obtained, electrophoresis is difficult to occur, and a sufficient image density cannot be obtained. Further, the permeability to a substrate such as paper is poor, and it becomes difficult to remove the carrier liquid when the toner particles are fixed, and sufficient fixability cannot be obtained. In particular, the fixability in a superimposed image is greatly deteriorated.

Specifically preferred carrier liquids (D) are especially branched paraffin solvent mixtures such as the trade name “Isopar ^™ M” (Exxon Corporation), in particular isoparaffinic hydrocarbons or “Exol D80”. It is preferably a naphthenic hydrocarbon such as “Exol D110”, “Exol D130” (Exxsol ^™ ).

(Other additives)
(Polymer dispersant)
The polymer dispersant has an effect of favorably dispersing toner particles in a carrier liquid and improving storage stability and development characteristics, and is preferably used in the present invention. Although not specifically limited, titanate cups of fatty acid metal salts such as cobalt naphthenate, zinc naphthenate, copper naphthenate, manganese naphthenate, cobalt octylate, zirconium octylate, and organic titanates such as lecithin and titanium chelate Examples include a ring agent, an alkoxy titanium polymer, a polyhydroxy titanium carboxylate compound, a titanium alkoxide, a succinimide compound, a polyimine compound, a fluorine-containing silane compound, and a pyrrolidone compound. In particular, a polymer dispersant having a pyrrolidone ring is suitable. The polymer dispersant can be added to the carrier liquid or used by adding it to the toner particles during the kneading of the toner.

  The polymer dispersant having a pyrrolidone ring is obtained from a polymerization monomer that can be copolymerized or graft-polymerized with N-vinyl-2-pyrrolidone. The monomer polymerizable with N-vinyl-2-pyrrolidone is not particularly limited, but (meth) acrylic acid esters such as (meth) acrylic acid alkyl ester, (meth) acrylamide derivatives, bases Unsaturated unsaturated monomers and salts or quaternized compounds thereof, vinyl amides, carboxyl group-containing unsaturated monomers and salts thereof, vinyl esters, vinyl ethylene carbonate and derivatives thereof, and α-olefins. As a commercial item, Antaron V-216, Antaron V-220 (made by ISP) etc. are mentioned, for example.

  The polymer dispersant can be added in an amount of about 0.1 to 10 parts by mass with respect to 100 parts by mass of the liquid developer. More preferably, it is the range of 0.1-5 mass parts. When the amount is less than 0.1 parts by mass, the dispersibility of the toner particles is deteriorated. When the amount is more than 10 parts by mass, the dispersibility of the toner particles is good, but the fixability to the substrate tends to deteriorate.

(Pigment dispersant)
As the form of the pigment dispersant internally added to the toner particles, polyamine-based resin type dispersant Solsperse 24000SC, Solspers 32000 (manufactured by Abyssia), Azisper PB821 (manufactured by Ajinomoto Fine Techno Co., Ltd.), acrylic copolymer An agent BYK-116 (manufactured by Big Chemie) or the like can be used. In particular, in the case of producing through a conc that is a colored masterbatch, it is preferably added during the production of the masterbatch.
The addition amount of the pigment dispersant is preferably 3 to 40 parts by mass, more preferably 5 to 30 parts by mass with respect to 100 parts by mass of the colorant (B). When the amount is less than 3 parts by mass, the dispersion effect cannot be obtained, and when the amount is more than 40 parts by mass, the grindability deteriorates.

(Dye derivative)
In the toner particles used in the present invention, it is also possible to use a dye derivative as long as the color developability of the colorant (B) is not impaired.
Examples of the pigment derivative include a compound in which a basic substituent, an acidic substituent, or a phthalimidomethyl group which may have a substituent is introduced into an organic pigment (organic pigment, organic dye), anthraquinone, acridone or triazine. It is done.
In the present invention, a pigment derivative is particularly preferable, and the structure thereof is a compound represented by the following general formula (2).
P-Ln Formula (2)
(However,
P: organic pigment residue, anthraquinone residue, acridone residue or triazine residue L: basic substituent, acidic substituent, or optionally substituted phthalimidomethyl group n: an integer of 1 to 4 is there)
Examples of the organic pigment constituting the organic pigment residue of P include, for example, diketopyrrolopyrrole pigments; azo pigments such as azo, disazo and polyazo; phthalocyanine pigments such as copper phthalocyanine, halogenated copper phthalocyanine and metal-free phthalocyanine Anthraquinone pigments such as aminoanthraquinone, diaminodianthraquinone, anthrapyrimidine, flavantron, anthanthrone, indanthrone, pyranthrone, violanthrone; quinacridone pigments; dioxazine pigments; perinone pigments; perylene pigments; thioindigo pigments; Indoline pigments; isoindolinone pigments; quinophthalone pigments; selenium pigments; metal complex pigments.

  Examples of the dye derivative are described in JP-A-63-305173, JP-B-57-15620, JP-B-59-40172, JP-B-63-17102, JP-B-5-9469, and the like. What is currently used can be used, These can be used individually or in mixture of 2 or more types.

  In the liquid developer of the present invention, the appropriate addition amount of the dye derivative varies depending on the type of the colorant (B) to be used. It is preferable to use in. When the amount is less than 0.1 parts by mass, the effect of improving dispersibility cannot be obtained, and when the amount is more than 30 parts by mass, good charging stability is hardly obtained.

(Charge control agent)
The toner particles in the liquid developer of the present invention may contain a colorless or light-colored charge control agent as long as the hue does not hinder the hue. As the charge control agent, a positive charge control agent or a negative charge control agent is used according to the polarity of the electrostatic image on the electrostatic latent image carrier to be developed.
In the present invention, the toner particles preferably exhibit a positive charge, and a positive charge control agent is usually used.

  As the positive charge control agent, quaternary ammonium salt compounds (for example, tributylbenzylammonium-1-hydroxy-4-naphthosulfonate, tetrabutylbenzylammonium tetrafluoroborate), quaternary ammonium salt organic tin oxide (for example, dibutyltin) Oxide, dioctyltin oxide, dicyclohexyltin oxide), diorganotin borate (dibutyltin borate, dioctyltin borate, dicyclohexyltin borate), electron donating substances such as polymers having amino groups, etc. are used alone or in combination of two or more. be able to.

Further, instead of using the charge control agent, a resin charge control agent can be used.
For positive charging,
Formula _{- {CH 2 -CH (C 6} H 5) a} - {CH 2 -CH (COOC 4 H 9)} b- {CH 2 -C (CH 3) COOC 2 H 4 N + CH 3 (C 2 H ₅ ) ₂ } cCH ₃ (C ₆ H ₄ ) SO ₃ −
(Of these, the quaternary ammonium salt part is 3 to 35 parts by mass, the styrene / acryl part is 97 to 65 parts by mass, thereby determining the values of a, b, and c), Examples of functional groups include styrene / acrylic polymers copolymerized with styrene / acrylic resins.
Specifically, 2-ethylhexyl acrylate / acryloylamino-2-methyl-1-propanesulfonic acid / styrene copolymer, butyl acrylate / N, N-diethyl-N-methyl-2- (methacryloyloxy) ethyl Ammonium = p-toluenesulfonate / styrene copolymer and the like. Since these are colorless and transparent, they are suitable for use in color toners. Further, the resin charge control agent is usually added in an amount of 1.0 to 20 parts by mass, preferably 2.0 to 8.0 parts by mass with respect to 100 parts by mass of the binder resin (A).

(Production method)
A method for producing the liquid developer of the present invention will be described.
The liquid developer of the present invention is preferably obtained through the following six processes.

(1) Preparation of colored master batch for toner particles The binder resin (A), the colorant (B), and the inorganic oxide (C) are heated at a colorant concentration of 10 to 60 parts by mass in the master batch. Kneading is performed using a roll or the like, and after cooling, coarse crushing is performed to obtain a colored master batch. A pigment dispersant and a pigment derivative can also be added.

(2) Preparation of toner particle chips (dilution of colored master batch)
The colored master batch obtained in (1) and the binder resin (A) are preliminarily dispersed by a mixer such as a super mixer. Next, by performing melt-kneading, the colored master batch is diluted to obtain a chip for toner particles having an arbitrary colorant concentration. Further, a polymer dispersant, wax or the like may be added. The chip for toner particles is preferably set to 5 mm or less by a hammer mill, a sample mill or the like.
In addition, the steps (1) and (2) can be unified. In this case, all the materials are charged at the time of preliminary dispersion without going through the coloring masterbatch process of (1). What is necessary is just to produce the chip for use. As the melt-kneading, a known kneader such as a pressure kneader, a Banbury mixer, a uniaxial or biaxial extruder can be used.

(3) Dry pulverization of toner particles The toner particle chip obtained in (2) is pulverized to an average particle size of 10 μm or less. For fine pulverization, it is usually preferable to use a jet airflow pulverizer such as a jet mill or a mechanical pulverizer such as a turbo mill or a kryptron.

(4) Wet grinding (dispersion) of toner particles
The toner particles obtained in (3), the carrier liquid (D), and the polymer dispersant are preliminarily mixed, and then, using a wet pulverizer (disperser), the average particle diameter is 0.5 to 4 μm, preferably 1 to Wet pulverization is performed so as to be in the range of 3 μm. The wet pulverization is preferably performed in a toner particle concentration range of 10% to 50%. It is preferable in terms of production efficiency to perform wet pulverization at a high concentration and then dilute to a desired concentration with a carrier liquid to obtain a liquid developer.

As a wet pulverizer that can be used for wet pulverization of toner particles, a pulverization medium is used, and examples thereof include a container drive medium mill and a medium agitation mill. Examples of the container-driven medium mill include a rolling ball mill, a vibrating ball mill, a planetary ball mill, and a centrifugal fluidizing mill, and examples of the medium agitating mill include a tower pulverizer, a stirring tank mill, a flow tank mill (horizontal type, Vertical type), annular mill and the like.
In any of the above-mentioned apparatuses, refinement by wet pulverization is possible, but among these, it is preferable to use a medium stirring mill from the viewpoint of productivity, pulverization ability, control of particle size distribution, etc. It is preferable to use a wet pulverizer classified as a horizontal distribution tank mill, which is filled with molds and horizontal microbeads and used as a medium.
Specific examples include WAB (Shinmaru Enterprises), DYNO-MILL, and sand mill.

  In the wet pulverizer used in the present invention, the major factors that determine the pulverization properties include the type of pulverizing media, the particle size of the pulverizing media, the filling rate of the dispersion media in the pulverizer, the type of agitator disk, and the solution concentration of the sample to be pulverized. And the type of solvent. Among these, the type of pulverized media and the particle size of the media greatly contribute to pulverization.

The types of grinding media include glass beads (SiO ₂ 70 to 80%, NaO 12 to 16%, etc.), zircon beads (ZrO ₂ 69%, etc.) depending on the viscosity, specific gravity and grinding and dispersion required particle size of the toner particles. SiO ₂ 31%), zirconia beads (ZrO ₂ 95% or more), alumina (Al ₂ O ₃ 90% or more), titania _{(TiO 2 77.7%, Al 2} O 3 17.4%), steel balls or the like Although it can be used, it is preferable to use zirconia beads or zircon beads in order to obtain good grindability.
The particle diameter (diameter) of the pulverization media can be used in the range of 0.1 mm to 3.0 mm, and in particular, the range of 0.3 to 1.4 mm is preferable. If it is smaller than 0.1 mm, the load in the pulverizer increases, and the toner particles melt due to heat generation, making it difficult to pulverize. If it is larger than 3.0 mm, sufficient pulverization cannot be performed. .

(Toner physical properties)
The toner particles used in the present invention preferably have an average particle diameter (D50) of 0.5 to 4 μm, more preferably 1 to 3 μm. When the average particle diameter (D50) is smaller than 0.5 μm, a sufficient image density can be obtained, but the cleaning blade is easily slipped through and the cleaning property is deteriorated. When the average particle diameter (D50) is larger than 4 μm, a sufficient image density cannot be obtained and the color developability is lowered.
The particle size in the present invention is measured using a Nikkiso Co., Ltd. laser diffraction / scattering particle size analyzer Microtrac HRA, and the average particle size (D50) is a cumulative 50 percent diameter value.

  In the present invention, the concentration of toner particles in the liquid developer is preferably 5 to 40% by mass with respect to 100% by mass of the liquid developer. More preferably, it is 10-30 mass%. If the amount is less than 5% by mass, it is difficult to remove the carrier liquid, and the toner particles have poor fixing properties. When the amount is more than 40% by mass, the mobility of the toner particles is deteriorated and a sufficient image density cannot be obtained.

Further, the viscosity of the liquid developer of the present invention is preferably 5 to 180 mPa · s, and the volume specific resistance of the liquid developer is preferably 10 ¹⁰ to 10 ¹⁵ Ω · cm.
The viscosity of the liquid developer can be measured using, for example, an E-type viscometer TV-22 manufactured by Toki Sangyo. The solid content in the liquid developer was adjusted to 25% and fully adjusted to 25 ° C. Then, a 1 ° 34 'cone was set on the TV-22 type viscosity shape, and the viscosity after 1 minute at 20 rpm was measured. . If the viscosity is less than 5 mPa · s, the fineness of the image after development is insufficient, and if it exceeds 180 mPa · s, the mobility of toner particles during development is inferior and high-speed development cannot be performed, and the image density in superposition cannot be obtained. Problems occur.
The volume resistivity can be measured in the same manner as the carrier liquid measuring method described above. If it is 10 ¹⁰ Ω · cm or less, the electrostatic latent image on the photoreceptor cannot be retained, which is not preferable.

  In the use of the liquid developer of the present invention, a development process that can be preferably used is that a liquid developer is supplied to a developing roller made of conductive rubber, and an amorphous silicon photoconductor exposed to LED is used to eliminate static electricity before transfer, intermediate Development is preferably performed via a transfer member. The photoreceptor preferably has a surface potential of +450 to 550 V, a residual potential of +50 V or less, and the bias applied to the developing roller is preferably in the range of +250 to 450 V.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the embodiment of the present invention is not limited to these examples. In the following, all parts represent parts by mass.
Moreover, in the Example, it carried out using the material described below.

(Synthesis of binder resin)
Example of polyester resin production (binder resins A to C)
Into a flask equipped with a reflux condenser, a nitrogen gas inlet tube, a thermometer, and a stirrer, 2 parts of dibutyltin oxide as a polyhydric alcohol and polybasic acid shown in Table 1 were introduced, and nitrogen gas was introduced while stirring. The reaction was performed at 220 ° C. for 6 hours. Further, the reaction was carried out under reduced pressure, and when the desired softening point was reached, the pressure was returned to normal pressure, the temperature was lowered to 100 ° C. or less, and polycondensation was stopped to obtain binder resins A to C.

Example of hybrid resin production (resins D and E)
A polyester resin monomer shown in Table 1 and 2 parts of dibutyltin oxide as a catalyst were introduced into the same apparatus as in the polyester resin production example, nitrogen gas was introduced with stirring, and the reaction was carried out at 220 ° C. for 6 hours. Thereafter, the temperature was lowered to 160 ° C., and a mixture of a vinyl resin monomer shown in Table 1 and a polymerization initiator di-t-butyl peroxide was dropped using a dropping funnel over 1 hour. After further reacting at 160 ° C. for 2 hours, the temperature was raised to 220 ° C., and the reaction was further performed under reduced pressure until the desired softening point was reached, whereby binder resins D and E were obtained.

(Coloring agent)
Cyan colorant C.I. I. Pigment Blue 15: 3 (copper phthalocyanine blue)
Lionol Blue FG7919 (manufactured by Toyochem Co., Ltd.)

(Inorganic oxide)
talc
High filler # 5000PJ (Matsumura Sangyo Co., Ltd.)
FG-15 (Nippon Talc Co., Ltd.)
NANO ACE D-600 (manufactured by Nippon Talc Co., Ltd.)
Kaolin
Glomax LL (manufactured by Takehara Chemical Industry Co., Ltd.)
silica
Aerosil 130 (Nippon Aerosil Co., Ltd.)
alumina
AluminumOxide C (Nippon Aerosil Co., Ltd.)

  Table 2 shows the surface potential measurement results after 1 second and 10 seconds after corona charging of the inorganic oxide.

(Pigment dispersant)
Pigment dispersant 1 Basic resin type dispersant (polyamine resin)
Solspers 24000SC Acid value: 25 mgKOH / g

(Dispersant)
Dispersant 1 Polymer compound having pyrrolidone ring Antaron V216 (α-olefin / vinylpyrrolidone copolymer)
Average molecular weight: 7300 Melting point: about 10 ° C
Dispersant 2 Polymer compound having pyrrolidone ring Antaron V220 (α-olefin / vinylpyrrolidone copolymer)
Average molecular weight: 8600 Melting point: about 80 ° C

(Carrier liquid)
Exol D110 Naphthenic hydrocarbon dry point: 267 ° C. Aniline point: 83 ° C. Kinematic viscosity: 3.50 mm ² / s
Density: 0.810 g / cm ³

[Example 1]
Powder toner 1
Lionol Blue FG7919 15 parts by weight Binder Resin A 79 parts by weight Pigment Dispersant 1 (Solspers 24000SC) 2 parts by weight High Filler # 5000PJ 3 parts by weight Sun Wax 161P (Sanyo Kasei Co., Ltd. polyethylene wax) 1 part by weight After mixing (5 kg in total) with a Henschel mixer having a volume of 20 L (3000 rpm, 3 minutes), melt-kneading with a twin-screw kneading extruder (PCM30) at a supply rate of 4 kg / hr and a discharge temperature of 145 ° C. Kneading was performed with three rolls at a temperature of 140 ° C. After cooling and solidifying, coarsely pulverized with a hammer mill and then finely pulverized with an I-type jet mill (IDS-2 type) to obtain a cyan toner pulverized product 1 having an average particle diameter of about 7.0 μm.
Then
Cyan toner pulverized product 1 25 parts by mass Exol D110 73 parts by mass Dispersant 1 2 parts by mass were weighed, sufficiently stirred and mixed to disperse cyan toner pulverized product 1 in the Exol D110 solution.
The slurry in which the cyan toner pulverized product 1 is dispersed is subjected to a circulation operation for 60 minutes using a wet pulverizer that is a medium agitating mill, Dino Mill Multilab (Shinmaru Enterprises Co., Ltd., capacity 1.4 L), and wet pulverized. Went.
The wet pulverization conditions at this time were as follows.

Agitator disk (material: zirconia) peripheral speed 10m / s, cylinder ZTA, media (material: zirconia) diameter 1.25mm, filling rate 70%
Solution flow rate 45 kg / h, cooling water 5 l / min. , Pressure 0.1 kg / cm ²
After performing wet pulverization for 60 minutes, the slurry was taken out and passed through a mesh having a mesh size of 33 μm (manufactured by SUS304) to obtain liquid developer 1. When the particle size distribution was confirmed, the average particle size (D50) was 2.5 μm.

[Examples 2-9, Comparative Examples 1-2]
Using the raw materials shown in Table 3 and Table 4 in the same manner as in Example 1, powder toner and liquid developer were prepared, respectively.

Printing evaluation The live-action test was conducted using an amorphous silicon photoconductor under an environmental condition of 23 ° C./50% RH using a modification of a commercially available liquid developing copier (Savin 870: manufactured by Sabin). Was set to +450 to 500 V, the residual potential was +50 V or less, the bias of the developing roller was set to +250 to 450 V, and 1000 image tests were performed from the beginning. At this time, the image was produced in a single color for each color, the paper was OK topcoat made by Oji Paper, and the thermocompression bonding was performed at a speed of 30 m / min and 160 ° C.

Regarding the evaluation of the cleaning property, the photosensitive member and the developing roller inside the apparatus were observed after printing 1000 sheets, and evaluated as follows.
○: Residual toner particles are not confirmed on the photoreceptor and the developing roller.
Δ: Some residual toner particles are observed on the photoconductor and the developing roller.
X: Many residual toner particles are confirmed on the photoreceptor and the developing roller.

For evaluation of developability and transferability, the print density after 1000 sheets was measured.
○: Print density 1.6 or more Δ: Print density 1.4 to 1.6
X: Printing density 1.4 or less The image density was measured with a Gretag Macbeth densitometer (D-196).

In addition, fogging refers to dirt on the non-image area, but fogging was performed by measuring the reflectance with a photobolt. 1.0% or less is a good value.

Further, the fixing rate was evaluated as follows. First, an image density ID (ID ₁ ) at the time of output was measured using a printed image obtained by outputting a solid portion of 1 cm × 1 cm after 1000 sheets. Then, a mending tape (3M Scotch 810) was attached to the printed matter, and a 1 kg cylindrical brass weight was rolled and reciprocated five times. Thereafter, the mending tape was removed, the image density ID (ID ₂ ) was measured again, (ID ₂ ) / (ID ₁ ) × 100 was calculated, and the fixing rate (%) was obtained. Here, if the fixing rate is 80% or more, it is preferable for practical use, and if it is 90% or more, it is more preferable.

In addition, with respect to offset resistance, after being output by the above liquid development copying machine, thermocompression bonding is performed at a speed of 15 m / min and a nip thickness of 6 mm by an external fixing machine, and toner particles adhere to the surface of the roll to be thermocompression bonded. The starting temperature was evaluated by the following three ranks. Here, if the thermocompression-bonding roll temperature is 140 ° C. or higher, it is practically preferable.
○: Thermocompression roll temperature is 140 ° C. or higher Δ: Thermocompression roll temperature is 120 ° C. or higher and less than 140 ° C. x: Thermocompression roll temperature is less than 120 ° C.

Table 5 shows the print evaluation results.
In Examples 1 to 9 to which the inorganic oxide was added, the cleaning performance and the hot offset resistance were clearly better than those of Comparative Examples 1 and 2. Also, with regard to fogging, Examples 1 to 9 show good results, whereas in Comparative Examples 1 and 2, the entire surface of the paper is stained due to poor cleaning properties.

  The liquid developer of the present invention is excellent in cleaning properties, developability, offset resistance, and is capable of forming an image using an electrophotographic method, an electrostatic recording method, or the like. It can be preferably used as a liquid developer used for developing the electrostatic latent image.

Claims (5)

A liquid developer comprising at least toner particles comprising a binder resin (A), a colorant (B), an inorganic oxide (C), and a carrier liquid (D) ,
A liquid developer in which the inorganic oxide (C) contains talc . It characterized that, the liquid developer according to claim 1 that the surface potential V ₁₀ is equal to or less than 0.8kV inorganic oxide (C). (Where V ₁₀ is the surface potential after 10 seconds was subjected to corona charging.) Features to claim 1 or 2 liquid developer according the surface potential V ₁ is equal to or less than 1.6kV or 0.2kV inorganic oxide (C). (However, V ₁ is the surface potential one second after corona charging.) The liquid developer according to any one of claims 1 to 3, wherein the inorganic oxide (C) is contained in the toner particles in an amount of 0.1 to 10% by weight. The liquid developer according to any one of claims 1 to 4, wherein the binder resin (A) contains at least a polyester resin.