JP2005316306A - Electrophotographic two-component developer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a two-component developer having a charge amount at a satisfactory level and no fog and capable of stably forming an image of high picture quality although the developer contains toner particles having a high colorant content. <P>SOLUTION: The following two-component developer is used in an image forming apparatus 100 including an image forming unit 1, a recording material supply unit 2, an image fixing unit 3 and a controlling unit 4. The two-component developer comprises: toner particles containing a binder resin, a colorant and a charge controlling agent, wherein the colorant content is ≥10 wt.%; and a silicon resin coated ferrite-based carrier. The toner particles have the resistance in the range of 20×10<SP>9</SP>to 85×10<SP>9</SP>Ωcm. The ferrite-based carrier has the resistance in the range of 2.0×10<SP>10</SP>to 1.0×10<SP>12</SP>Ω when a 500-V DC electric field is applied by a bridge method at 6.5 mm distance. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a two-component developer for electrophotography.

  In an image forming apparatus using electrophotographic technology such as a copying machine, a laser printer, and a fax machine, an electrostatic latent image is formed in a developing area on a photosensitive member by various image forming processes, and then supplied from the developing apparatus. The toner contained in the developer is used to develop the electrostatic latent image in the development area on the photoreceptor, and the resulting toner image is transferred to a recording material. To be recorded.

  In the electrophotographic image forming apparatus, the developer contains a binder resin and a colorant, and the toner particles for developing the electrostatic latent image are rotated together with the toner particles in the developing device. Two-component developers containing a magnetic carrier that stirs, frictionally charges and conveys and adheres toner particles to an electrostatic latent image on the photoreceptor are widely used. Compared to a one-component developer containing toner particles alone, the two-component developer has functions of stirring, transporting and charging the toner particles by the carrier, so that the toner particles do not need to have the function of a carrier, The functions are separated and controllability is improved.

  The environment in which the image forming apparatus is used, the image density of a document used for image formation (for example, copying), and the like vary, and it is necessary to maintain optimum image quality in any state. However, in a high-temperature and high-humidity environment, the charge on the toner particles decreases due to the charge on the surface of the toner particles being released into moisture in the atmosphere. In addition, when copying a document having a high printing rate such that the image density exceeds 35%, a larger amount of toner is required than usual, so that the amount of developer supplied to the developing device increases, The stirring ability is insufficient and the developer is not sufficiently stirred, resulting in poor charging of the toner. As a result, the developing bias potential applied to the toner is lowered. If the toner has a normal development bias potential, it adheres selectively to the electrostatic latent image portion having a particularly high potential in the development area on the photoconductor. However, if the toner has a low development bias potential, Occurrence of a fogging phenomenon in which the toner adheres to the developing region is also remarkable. When fogging occurs, the image quality of the obtained image is impaired, and the toner consumption increases more than necessary.

  In view of such problems of the prior art, proposals have been made regarding the resistance value of the magnetic carrier in the two-component developer.

For example, in a two-component developer containing a toner and a magnetic carrier and developing an electrostatic latent image by a magnetic brush developing method, the volume resistance value measured under an electric field of 1000 V / cm in the form of a magnetic brush is Examples of the two-component developer include 1 × 10 ^{7 to} 3 × 10 ⁹ Ω · cm (for example, Patent Document 1).

Further, it is a carrier in which a core is coated with a resin, for a two-component developer having a static electric resistance value of 1 × 10 ^{8 to} 5 × 10 ⁹ Ω · cm and a dynamic current value of 0.2 to 1.0 μA. A carrier is mentioned (for example, refer patent document 2).

Further, it is a carrier in which a core material is coated with a cured product of silicon resin, the average particle diameter is 60 to 110 μm, the average film thickness of the resin coating is 0.1 to 0.3 μm, and the volume resistance is 1.5 × 10 ^8. Examples include carriers for two-component developers having a viscosity of ˜1.5 × 10 ¹¹ Ω · cm and a triboelectric charge amount of −10 to −20 μC / g (for example, see Patent Document 3).

  Further, the toner comprises a toner containing a binder resin and a colorant and a carrier whose core material surface is coated with a resin layer containing a resistance control agent, and the resin layer of the carrier has a resistance control agent concentration gradient in its thickness direction. In the vicinity of the core of the carrier, there is a two-component developer having the highest resistance control agent concentration, which decreases toward the surface of the resin layer, and the resistance control agent is also present on the surface of the resin layer (for example, Patent Documents). 4).

  Any of these conventional techniques is effective in suppressing the occurrence of fogging. Recently, however, the functions of electrophotographic image forming apparatuses have been diversified, and the basic performance has been enhanced, for example, higher definition and higher image quality of images. Cannot be fully satisfied.

  In order to achieve high definition and high image quality of an image, for example, it is effective to reduce the toner particle size and increase the colorant content in the toner particle. The use of toner particles having such a configuration also has an advantage that toner consumption can be reduced. However, since the colorant contained in the toner is generally conductive, the higher the colorant content, the lower the resistance value as a toner and thus the charging performance, and the lower the resistance value of the two-component developer. As a result, the electric charge due to the developing bias potential applied to the two-component developer easily moves to the surface of the photoreceptor, and the potential of the entire developing area including the portion other than the electrostatic latent image on the surface of the photoreceptor is increased. The occurrence of fog that adheres to portions other than the electrostatic latent image increases. Therefore, even if a developing bias potential is applied to the toner particles having a high colorant content, sufficient charge cannot be imparted, so that the occurrence of fog cannot be avoided. For this measure, even if the resistance value of the carrier is simply increased, minute unevenness of the surface potential in the background portion other than the electrostatic latent image, which is a problem peculiar to the photoconductor, is developed by the edge effect and becomes fogged. appear. Although this can be improved by increasing the developing bias potential, it causes a new problem of a decrease in image density due to a decrease in developing contrast at the same time.

  Further, even when such a toner particle is used in combination with a carrier proposed in the prior art, the occurrence of fog cannot be sufficiently prevented.

  Further, the conventional carrier has low durability and has a drawback that the resin coating layer of the carrier is peeled off when used repeatedly for a long time. When the resin coating layer is peeled off, additives contained in the layer are lost, and the charging performance of the toner is further reduced. In addition, due to the peeling of the resin coating layer, a phenomenon that adversely affects the image quality, such as spent, where the carrier surface is exposed and the toner adheres thereto, is likely to occur.

Japanese Patent Laid-Open No. 5-66615 JP 9-106111 A JP 2001-183873 A JP 2001-350295 A

  An object of the present invention is a two-component developer containing a carrier capable of imparting a sufficiently satisfactory level of charge to toner particles having a high colorant content, and adversely affects the image quality of the formed image. An object of the present invention is to provide a two-component developer for electrophotography capable of forming a high-quality image stably without causing moderate fogging.

The present invention relates to a two-component developer for electrophotography comprising toner particles containing a binder resin, a colorant and a charge control agent and a ferrite carrier coated with a silicon resin.
The colorant content of the toner particles is 10% by weight or more of the total amount of the toner particles,
The resistance value of the toner particles is 20 × 10 ^{9 to} 85 × 10 ⁹ Ωcm (20 × 10 ⁹ Ω or more, 85 × 10 ⁹ Ω or less), and a 500 V DC current of a ferrite-based carrier by a bridge method with an interval of 6.5 mm is used. The resistance value at the time of application of a field is 2.0 × 10 ^{10 to} 1.0 × 10 ¹² Ωcm (2.0 × ¹⁰ Ωcm or more, 1.0 × 10 ¹² Ωcm or less). Component developer.

  The electrophotographic two-component developer of the present invention is characterized in that the above-mentioned silicone resin contains a non-conductive additive.

  Furthermore, the electrophotographic two-component developer of the present invention is characterized in that the coverage of the above-mentioned ferrite carrier coated with a silicone resin with toner particles is 30 to 55% (30% or more and 55% or less). And

According to the present invention, a two-component developer comprising toner particles containing a binder resin, a colorant, and a charge control agent and having a colorant content of 10% by weight or more and a ferrite carrier coated with a silicon resin The resistance value of the toner particles is adjusted to the range of 20 × 10 ^{9 to} 85 × 10 ⁹ Ωcm, and the resistance value of the ferrite-based carrier when the 500 V DC electric field is applied by the bridge method with a spacing of 6.5 mm is set to 2.0. By adjusting to the range of × 10 ^{10 to} 1.0 × 10 ¹² Ωcm, image formation in a high-temperature and high-humidity environment, image formation using a document with a high printing rate such that the image density exceeds 35%, etc. Since the toner particles are given a sufficient charge amount, a high quality image can be stably formed.

  That is, a toner containing 10% by weight or more of a colorant and having low charging performance is coated with a silicon resin and used in combination with a ferrite carrier having a specific resistance value, so that the toner can be used even under high temperature and high humidity. In any case, the charging performance of the particles is not affected by moisture in the air, and even if the supply amount of the two-component developer into the developing device is increased, the stirring ability of the developing device is not impaired. Since a sufficient amount of charge can be imparted to the toner particles, a two-component developer capable of stably forming a high-quality and high-definition image in any situation can be obtained.

  According to the present invention, it is preferable that the silicon resin covering the surface of the ferrite carrier contains a non-conductive additive. As a result, the resistance value of the ferrite carrier is increased moderately, the movement of charges to the surface of the photoreceptor due to the developing bias potential applied to the two-component developer is reduced, and the occurrence of fog is further reduced.

  Further, according to the present invention, it is preferable that the coverage of the above-mentioned ferrite carrier coated with a silicon resin with toner particles is 30 to 55%. As a result, the occurrence of fogging can be further prevented and a high-quality image with a high image density can be formed.

  The two-component developer of the present invention includes toner particles containing a binder resin, a colorant and a charge control agent, and a ferrite carrier coated with a silicon resin.

[Toner particles]
Toner particles, the content of the colorant is not less than 10% by weight of the toner particles the total amount, and the resistance value is in the range of ^{20 × 10 9 Ωcm~85 × 10 9} Ωcm.

  Although there is no particular inconvenience even when the content of the colorant is less than 10% by weight, it is defined as 10% by weight or more in consideration of forming an image with high image density, high definition and high image quality.

When the resistance value of the toner particles is less than 20 × 10 ⁹ Ωcm, the resistance value of the two-component developer is lowered even when the specific ferrite carrier of the present invention is combined, and the occurrence of fog may increase. If it exceeds 85 × 10 ⁹ Ωcm, the image density of the formed image may be lowered.

In the present specification, the resistance value R of the toner particles is obtained as follows.
A measurement sample having a diameter of about 1.5 mm is prepared by tableting 1.00 g of toner with a tablet molding machine. This measurement sample is mounted inside a solid electrode, and the electrode is plugged into a constant temperature bath of a dielectric loss measuring device (trade name: TRS-10T type, manufactured by Ando Electric Co., Ltd.). The measurement mode of the measuring device is set to zero balance mode (ZERO BAL), the PATIO value is determined according to the measurement frequency, and the balance operation is performed. The measurement frequency is 1 kHz, and the PATIO value corresponding to the measurement frequency is 1 × 10 ⁻⁹ . The conductance measured at this time is R ₀ .

  Further, the measurement mode of the measuring device is switched to the major mode (MEAS), and a neutral operation is performed in the same manner as zero neutralization. The capacitance measured at this time is Cx, and the conductance is R ′.

The resistance value R is obtained from the following equation.
R = 10A / (Tx · Gx) (1)
Here, A is an effective electrode area of the dielectric loss measuring apparatus, and is 2.83 cm ² here. Tx is an average value of the thickness of one central point and four peripheral points of the measurement sample. Gx is conductance and is obtained from the following equation.
Gx = PATIO value × (R′−R ₀ ) (2)

  The toner particles may contain general toner additives such as wax and fluidity improver in addition to the binder resin, the colorant, and the charge control agent.

(Binder resin)
As the binder resin, those commonly used in this field can be used. For example, styrene polymer, polyvinyl chloride, phenol resin, naturally modified phenol resin, naturally modified maleic acid resin, acrylic resin, methacrylic resin, polyvinyl acetate. , Silicon resin, polyester, polyurethane, polyamide resin, furan resin, epoxy resin, xylene resin, polyvinyl butyral, terpene resin, coumarone indene resin, petroleum resin, and the like.

  Among these, a styrene polymer is preferable. Styrene polymers include styrene homopolymers and styrene copolymers. Examples of the styrene homopolymer include homopolymers of styrene-substituted products such as polystyrene, poly-p-chlorostyrene, and polyvinyltoluene. On the other hand, in the styrene copolymer, a known vinyl monomer can be used as a comonomer used together with styrene, such as acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, acrylic acid. (Meth) acrylic acid esters such as octyl, 2-ethylhexyl acrylate, phenyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, and substituted products thereof, maleic acid, maleic acid Dicarboxylic acids having a double bond such as butyl, methyl maleate and dimethyl maleate and substituted products thereof, vinyl esters such as vinyl chloride, vinyl acetate and vinyl benzoate, ethylene-based olefins such as ethylene, propylene and butylene, Bini Methyl ketone, vinyl ketones such as vinyl hexyl ketone, vinyl methyl ether, vinyl ethyl ether, vinyl ethers such as vinyl isobutyl ether, acrylonitrile, methacrylonitrile, acrylamide and the like. A vinyl monomer can be used individually by 1 type, or can use 2 or more types together. Specific examples of the styrene copolymer containing such a vinyl monomer include, for example, a styrene-p-chlorostyrene copolymer, a styrene-vinyltoluene copolymer, a styrene-vinylnaphthalene copolymer, and styrene. -Acrylate ester copolymer, styrene-methacrylate copolymer, styrene-α-chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer Examples thereof include a polymer, a styrene-vinyl methyl ketone copolymer, a styrene-butadiene copolymer, a styrene-isoprene copolymer, and a styrene-acrylonitrile-indene copolymer.

  Among these, styrene polymers crosslinked with a crosslinking agent are preferable. As the crosslinking agent, a compound having two or more polymerizable double bonds is mainly used. For example, aromatic divinyl compounds such as divinylbenzene and divinylnaphthalene; carboxylic acid esters having two double bonds such as ethylene glycol diacrylate, ethylene glycol dimethacrylate, and 1,3-butanediol dimethacrylate, divinylaniline, divinyl And divinyl compounds such as vinyl ether, divinyl sulfide and divinyl sulfone, and compounds having three or more vinyl groups. A crosslinking agent can be used individually by 1 type, or can use 2 or more types together.

Furthermore, among these, the weight average molecular weight (Mw) in gel permeation chromatography (GPC) is 15 × 10 ^{4 to} 25 × 10 ⁴ , and the number average molecular weight (Mn) is 2 × 10 ³ to 4 × 10 ^3. Are preferred. Further, it is particularly preferable that the softening point is 145 ° C. to 165 ° C. and the loss elastic modulus G ″ at 140 ° C. is 1 × 10 ⁴ dyn / cm ² to 2 × 10 ⁴ dyn / cm ² .

(Coloring agent)
Dyes and pigments commonly used in this field can be used as the colorant. For example, nigrosine dyes, carmine dyes, various basic dyes, acid dyes, oily dyes, anthraquinone dyes, benzidine yellow organic pigments, quinanthrin organic pigments And carbon blacks such as rhodamine organic pigments, phthalocyanine organic pigments, zinc oxide, titanium oxide, furnace black, acetylene black, and thermal black. Among these, carbon black is preferable. Further, among carbon blacks, those having a primary particle diameter of 15 to 30 nm excellent in dispersibility in the binder resin are preferable, and acidic (pH 7 or less) without impairing other raw material characteristics during production. Those are preferred. A coloring agent can be used individually by 1 type, or can use 2 or more types together. The content of the colorant is 10% by weight or more, preferably 10 to 20% by weight, based on the total amount of toner particles. If it exceeds 20% by weight, the resistance value of the toner becomes too low and the dispersibility of the colorant in the binder resin may be lowered.

(Charge control agent)
As the charge control agent, those commonly used in this field can be used, and examples thereof include nigrosine dyes, metal azo compounds, salicylic acid metal salts, quaternary ammonium salts and the like. A charge control agent can be used individually by 1 type, or can use 2 or more types together as needed. The use amount of the charge control agent is not particularly limited and can be appropriately selected from a wide range, but is preferably 0.5 to 3 parts by weight with respect to 100 parts by weight of the binder resin.

(wax)
As the wax, those commonly used in this field can be used. For example, paraffin wax and derivatives thereof, microcrystalline wax and derivatives thereof, Fischer-Tropsch wax and derivatives thereof, polyolefin wax and derivatives thereof, carnauba wax and derivatives thereof, long chain Examples thereof include carboxylic acids and derivatives thereof, long-chain alcohols and derivatives thereof. The derivatives include oxides, block copolymers of vinyl monomers and waxes, graft modified products of vinyl monomers and waxes, and the like. The amount of the wax used is not particularly limited and can be appropriately selected from a wide range, but is preferably 0.2 to 20 parts by weight with respect to 100 parts by weight of the binder resin.

(Fluidity improver)
The fluidity improver is used as an external additive, and its effect is exhibited, for example, by adhering to the toner surface. As the fluidity improver, those commonly used in this field can be used, and examples thereof include silicon oxide, titanium oxide, silicon carbide, aluminum oxide, and barium titanate. A fluidity improver can be used individually by 1 type, or can use 2 or more types together. The amount of the fluidity improver used is not particularly limited, but is preferably 0.1 to 3.0 parts by weight with respect to 100 parts by weight of the toner particles.

  The toner particles used in the two-component developer of the present invention can be produced according to a known method. For example, a binder resin, a colorant, a charge control agent, and other additives are mixed by a mixer such as a Henschel mixer, a super mixer, a mechano mill, or a Q-type mixer, and the resulting raw material mixture is mixed with a two-screw kneader, one screw Melting and kneading at a temperature of about 70 to 180 ° C. with a kneader such as a kneader, cooling and solidifying the obtained kneaded material, pulverizing the solidified material with an air-type pulverizer such as a jet mill, and classifying as necessary By adjusting the particle size, toner particles having an average particle diameter of preferably 3 to 15 μm, more preferably an average particle diameter of 6.0 to 7.5 μm are obtained.

  In the present invention, since 10% by weight or more of the colorant of the total amount of the toner particles is contained in the toner particles, the colorant and other additives are uniformly dispersed in the binder resin, so that the physical properties of the binder resin are improved. Considering efficient production of toner without damage, it is preferable to employ a master batch method in producing toner particles.

  According to the masterbatch method, a binder resin less than a predetermined amount and a predetermined amount of colorant are mixed with a mixer in the same manner as described above, and the resulting raw material mixture is mixed with a continuous two-roll kneader. Kneading while applying shear force. The obtained kneaded product is cooled and solidified, and further coarsely crushed to obtain a kneaded crushed product. The remaining kneaded resin and other additives are mixed with the kneaded crushed material, diluted and kneaded with an extruder, and the resulting kneaded material is cooled and solidified in the same manner as above, pulverized, and the particle size is adjusted as necessary. Thus, toner particles can be obtained.

  FIG. 1A is a side view schematically showing the configuration of a continuous two-roll kneader 150. FIG.1 (b) is sectional drawing seen from the cut surface line A-A 'of the continuous 2 roll type kneader 150 shown to Fig.1 (a).

  The continuous two-roll kneader 200 includes a raw material supply unit 211, a kneaded product discharge unit 212, a front roll 213, a rear roll 214, heating and cooling medium supply / discharge units 215 and 216, and a roll driving motor. 217, 218.

  A raw material mixture containing a binder resin and a colorant is supplied to the raw material supply unit 211. The front roll 213 and the rear roll 214 are provided so as to be rotationally driven in the axial direction by roll driving motors 217 and 218, respectively. In addition, inside the front roll 213 and the rear roll 214, piping (not shown) for allowing the heating and cooling medium to flow is provided, and by adjusting the temperature of the medium, the surface temperature of the front roll 213 and the rear roll 214, as a result The kneading temperature can be adjusted. The heating and cooling medium is supplied from the heating and cooling medium supply / discharge sections 15 and 16 to the front roll 213 and the rear roll 214, and is circulated through the inside and then discharged. The kneaded material discharge unit 212 discharges the kneaded material to the outside of the apparatus 200.

  According to the continuous two-roll kneader 200, the raw material mixture is supplied from the raw material supply unit 211 between the front roll 213 and the rear roll 214, where it is heated at the surface temperature of the front roll 213 and the rear roll 214. In addition to being subjected to shearing force due to these rotations, they are kneaded while gradually moving in the direction of the kneaded product discharge portion 212. The kneaded material obtained in this manner is discharged from the kneaded material discharge unit 212 to the outside of the kneader 200.

[Ferrite carrier]
The ferrite carrier used in the two-component developer of the present invention is a ferrite particle coated with a silicon resin.

This ferrite carrier is characterized by having a resistance value in the range of 2.0 × 10 ^{10 to} 1.0 × 10 ¹² Ωcm.

If the resistance value of the ferrite carrier is less than 2.0 × 10 ¹⁰ Ωcm, the resistance value of the two-component developer is lowered, and the occurrence of fog may increase. If it exceeds 1.0 × 10 ¹² Ωcm, the image density of the obtained image may be lowered.

  In this specification, the resistance value of the ferrite carrier is a resistance value when a 500 V DC electric field is applied by a bridge method with an interval of 6.5 mm. The circuit 220 shown in FIG. It is obtained from a current value and a voltage value actually measured at the time of placing a ferrite carrier. FIG. 2 is a drawing schematically showing a circuit for measuring the resistance value of a ferrite carrier.

  The circuit 220 is provided on the surface of the acrylic resin substrate 221 so as to face the surface of the acrylic resin substrate 221 with a gap D therebetween, and the electrodes 222a and 222b in which the magnets 223a and 223b are disposed, and the acrylic resin substrate 221. The electrodes 222a and 222b are sandwiched between the terminals 222a and 222b and electrically connected to the electrodes 222a and 222b, a voltmeter 225, and an ammeter 226. A circuit 220 is formed by connecting a voltmeter 225 and an ammeter 226 in series in a conductive path 228 connecting the terminals 224a and 224b. In this circuit 220, the distance D between the electrodes 222a and 222b is set to 6.5 mm. The measurement is performed by filling a ferrite carrier 227 as a sample between the electrodes 222a and 222b and applying a DC electric field of 500 V, and the resistance is obtained from the measured current value and voltage value. The filling amount of the ferrite carrier 227 at this time is 0.200 g.

Next, each component contained in the ferrite carrier will be described.
(Ferrite particles)
Known ferrite particles can be used, such as zinc ferrite, nickel ferrite, copper ferrite, nickel-zinc ferrite, manganese-magnesium ferrite, copper-magnesium ferrite, manganese-zinc ferrite, Manganese-copper-zinc ferrite can be used. These ferrite-based particles are obtained by mixing raw materials, calcining and pulverizing, and then calcining. By changing the calcining temperature, the surface shape of the particles can be changed. Ferrite particles can be used alone or in combination of two or more.

(Silicon resin)
As the silicon resin, those commonly used in this field can be used. For example, silicon varnish (trade names: TSR115, TSR114, TSR102, TSR103, YR3061, TSR110, TSR116, TSR117, TSR108, TSR109, TSR180, TSR181, TSR187, TSR144 , TSR165, manufactured by Shin-Etsu Silicon Co., Ltd .: KR271, KR272, KR275, KR280, KR282, KR267, KR269, KR211, KR212, etc., manufactured by Toshiba Corporation, alkyd modified silicon varnish Manufactured by Toshiba), epoxy-modified silicon varnish (trade names: TSR194, YS54, etc., manufactured by Toshiba Corporation), polyester-modified silicon varnish (trade name: TSR187) , Manufactured by Toshiba Corporation), acrylic modified silicon varnish (trade name: TSR170, TSR171 etc., manufactured by Toshiba Corporation), urethane modified silicon varnish (trade name: TSR175 etc., manufactured by Toshiba Corporation), reactive silicon resin (Trade names: KA1008, KBE1003, KBC1003, KBM303, KBM403, KBM503, KBM602, KBM603, etc., manufactured by Shin-Etsu Silicon Co., Ltd.). A silicon resin can be used individually by 1 type, or can use 2 or more types together as needed.

The silicon resin can contain various additives in order to control the resistance value of the ferrite carrier. Examples of the additive include silicon oxide, alumina, carbon black, graphite, zinc oxide, titanium black, iron oxide, titanium oxide, tin oxide, potassium titanate, calcium titanate, aluminum borate, magnesium oxide, and barium sulfate. And calcium carbonate. Among these, non-conductive additives are preferable. The conductivity value of the non-conductive additive is preferably in the range of 1.0 × 10 ^{1 to} 1.0 × 10 ⁶ Ωcm. An additive can be used individually by 1 type, or can use 2 or more types together. Although there is no restriction | limiting in particular in the usage-amount of an additive, Preferably it is 0.1-20 weight part with respect to 100 weight part of silicone resins.

  A known method can be employed to coat the ferrite-based particles with the silicon resin. For example, a method in which ferrite particles are immersed in a silicon resin solution, a spray method in which the silicon resin solution is sprayed onto the ferrite particles, a fluid bed method in which the silicon resin solution is sprayed in a state where the ferrite particles are suspended by flowing air, Examples thereof include a kneader coater method in which ferrite particles and a silicon resin solution are mixed in a kneader coater to remove the solvent. At this time, the silicon resin solution may contain the additive for controlling the resistance value together with the silicon resin.

  Although the amount of silicon resin used is not particularly limited, it is preferable that the silicon resin coating layer formed on the surface of the ferrite-based particles be used in a thickness of 0.1 to 3 μm.

  The average particle diameter of the ferrite carrier thus obtained is not particularly limited, but is preferably 50 to 90 μm.

  The two-component developer of the present invention can be produced by mixing the toner particles and a ferrite carrier. At that time, the usage amount of the toner particles and the ferrite carrier is not particularly limited, the colorant content in the toner particles, the resistance value of the toner particles and the ferrite carrier, the ferrite particles and the silicon resin contained in the ferrite carrier. Although it can be appropriately selected from a wide range according to various conditions such as the type, the presence or absence of an additive contained in the silicon resin, and the type, the coverage of the ferrite carrier with the toner particles is 30 to 55%, preferably 30% or more to 55. It is preferable to use both in an amount of less than%, more preferably 30% to 51%, particularly preferably 30% to 50%.

The toner coverage is a percentage of the total area of the toner particle surface with respect to the total area of the ferrite carrier surface. That is, the toner coverage (%) is obtained by the following equation (3).
Toner coverage (%) = (S _Ton / S _Car ) × 100 (3)
[ _Wherein S _Ton is the total surface area of all toner particles contained in the two-component developer. S _Car is the sum of the surface areas of all carriers contained in the two-component developer. ]

  If the coverage is less than 30%, the amount of toner contained in the two-component developer decreases, the charge amount per toner increases, and the image density of the resulting image may decrease. If it exceeds 55%, the toner content in the two-component developer is excessively increased, the stirring of the two-component developing device in the developing device becomes insufficient, and there is a risk that toner charging failure and fogging will occur.

  FIG. 3 is a cross-sectional view schematically showing a configuration of a main part of the image forming apparatus 100 in which the two-component developer for electrophotography of the present invention can be used.

  The image forming apparatus 100 records and outputs an image read by the image reading apparatus and data (image information) from a device (for example, an image processing apparatus such as a personal computer) externally connected to the image forming apparatus 100 as an image. Is.

  The image forming apparatus 100 includes an image forming unit 1, a recording material supply unit 2, an image fixing unit 3, and a control unit 4.

  The image forming unit 1 includes a photosensitive drum 5, a charging unit 6, an exposure unit 7, a developing unit 8, a transfer unit 9, a cleaning unit 10, and a charge removing unit 11 provided so as to face the circumferential surface of the photosensitive drum 5. including.

  The photosensitive drum 5 includes a cylindrical or columnar conductive substrate (not shown) and a photoconductive layer formed on the surface of the conductive substrate.

  The charging unit 6 includes a contact type or non-contact type charger such as a charging roller or a charging charger, and charges the peripheral surface of the photosensitive drum 5 to a predetermined polarity and potential.

  The exposure unit 7 is constituted by a laser unit such as a semiconductor laser, and exposes the peripheral surface of the photosensitive drum 5 in a charged state by the charging unit 6 based on image information transmitted from the control unit 4. Write an electrostatic latent image on

  The developing unit 8 supplies the two-component developer replenished from the developer replenishing container 13 to the electrostatic latent image written on the peripheral surface of the photosensitive drum 5 to visualize the electrostatic latent image. As a result, a toner image is formed on the circumferential surface of the photosensitive drum 5.

  The greatest feature of the transfer means 9 is that it is a contact type. For example, the transfer means 9 includes a transfer roller 12 and a voltage applying means (not shown), and recording is performed by applying a voltage from the transfer roller 12 side of the recording material. By charging the material and further applying pressure by the transfer roller 12, the toner image on the circumferential surface of the photosensitive drum 5 is transferred to the recording material. The recording material is supplied to the transfer means 9 by the recording material supply unit 2 described later in synchronization with the exposure by the exposure unit 7. The transfer unit 9 may be a contact method using a transfer belt (not shown) instead of the transfer roller 12.

  The cleaning unit 10 includes a cleaning blade made of an elastic material, and removes toner remaining on the peripheral surface of the photosensitive drum 5 after transferring the toner image to the recording material.

  The neutralizing unit 11 is constituted by a neutralizing lamp or the like, and removes electric charges on the circumferential surface of the photosensitive drum 5 after cleaning.

  In the image forming unit 1, the peripheral surface of the photosensitive drum 5 is uniformly charged by the charging unit 6, and exposure is performed from the exposure unit 7 to write an electrostatic latent image. The electrostatic latent image is visualized by the two-component developer supplied from the developing unit 8, and a toner image is formed on the circumferential surface of the photosensitive drum 5. This toner image is transferred to the recording material by the transfer means 9. After the transfer, the photosensitive drum 5 is cleaned by being subjected to removal of residual toner by the cleaning unit 10 and charge removal by the charge removing means 11. By repeating this series of operations, a plurality of images can be formed.

  The recording material supply unit 2 includes a recording material storage tray 20, a pickup roller 21, and a registration roller 22. The recording material storage tray 20 is a tray for storing recording materials such as plain paper, color copy paper, and OHP film. The recording material supply to the recording material storage tray 20 is performed by pulling out the recording material storage tray 20 to the front side (operation side) of the image forming apparatus 100. The pickup roller 21 separates the recording materials in the recording material storage tray 20 one by one and feeds them to the registration rollers 22. The registration roller 22 sequentially feeds the recording material between the photosensitive drum 5 and the transfer unit 9 in synchronization with the exposure of the exposure unit 7 on the circumferential surface of the photosensitive drum 5 in the image forming unit 1.

  According to the recording material supply unit 2, the recording material stored in the recording material storage tray 20 is supplied to the image forming unit 1 via the pickup roller 21 and the registration roller 22.

  The image fixing unit 3 includes a fixing device 30, a conveyance roller 31, a switching gate 32, a reverse roller 33, and a stacking tray 34. The fixing device 30 includes a fixing roller 35 and a pressure roller 36. In the fixing device 30, the recording material on which the toner image is transferred by the transfer unit 9 of the image forming unit 1 is passed between the fixing roller 35 and the pressure roller 36, and the toner image is applied to the recording material by heat and pressure. Let it settle. As a result, an image is formed (recorded) on the recording material. The conveyance roller 31 feeds the recording material on which the image is formed by the fixing device 30 to the switching gate 32. The switching gate 32 switches the feeding path of the image-recorded recording material.

  When the discharge tray for the image-recorded recording material is set to the stacking tray 34 provided outside the image recording apparatus 100, the switching gate 32 feeds the image-recorded recording material to the reverse roller 33, The recording material is discharged to the stacking tray 34 via the reverse roller 33. The stacking tray 34 is a tray that is provided outside the image forming apparatus 100 and discharges and stores the image-recorded recording material outside the image forming apparatus 100.

  On the other hand, when double-sided image formation or post-processing is designated, the image-recorded recording material is fed to the reverse roller 33 by the switching gate 32. The reversing roller 33 does not pass the recording material as it is, and in a state of sandwiching the recording material, a part of the recording material is discharged in the direction of the stacking tray 34 and then reversely rotated to switch the recording material. Anti-transfer pay towards. At this time, since the switching gate 32 is switched from a solid line state to a broken line state, the image-recorded recording material is mounted outside the image forming apparatus 100 for double-sided image formation or post-processing. It is fed to the material refeeding and conveying device. In the case of forming a double-sided image, the image-recorded recording material is supplied again to the image forming apparatus 100 via the recording material re-supply / conveyance device. When post-processing is performed, the image-formed recording material is fed from the recording material re-feeding and conveying apparatus to another post-processing apparatus via another switching gate (not shown) and further via the relay conveying apparatus.

  According to the image fixing unit 3, the toner image is fixed by the fixing device 30, and the recording material on which the image is recorded is conveyed to the reversing roller 33 via the conveying roller 31 and the switching gate 32, and is loaded according to the setting. The sheet is discharged to 34, or reversely conveyed to a relay conveyance device or a recording material re-feed conveyance device (not shown) via the switching gate 32 again.

  The control unit 4 is provided in the upper and lower space portions of the exposure unit 7 inside the image forming apparatus 100, and includes a circuit board that controls the image forming process, an interface board that receives image data from an external device, and a power supply unit (not shown). Consists of. The power supply device supplies power not only to the circuit board and the interface board but also to each device in the image forming unit 1, the recording material supply unit 2, and the image fixing unit 3.

  Note that conveyance paths 37, 38, and 39 are provided on the lower and side surfaces of the image forming apparatus 100. The conveyance paths 37, 38, and 39 are used for conveying a recording material to the inside or outside of the image forming apparatus 100 when an external apparatus is connected to the image forming apparatus 100. The external device has one or a plurality of recording material storage trays in addition to the above-described recording material re-feed conveyance device, relay conveyance device, and post-processing device, and can accommodate a large number of recording materials of the same size or a plurality of recording materials. There is a recording material supply device that can accommodate a recording material of the size.

  The two-component developer for electrophotography of the present invention is not limited to the image forming apparatus 100 and can be used for a known electrophotographic image forming apparatus using a two-component developer.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.
In addition, the physical property measurement in a present Example was implemented as follows.

[Toner particle resistance]
Using a dielectric loss measuring device (trade name: TRS-10T, manufactured by Ando Electric Co., Ltd.), the loss was calculated from the measured values based on the formulas (1) and (2).

[Resistance value of ferrite carrier]
Using the circuit 220 shown in FIG. 2, the distance D between the electrodes 222a and 222b is 6.5 mm, a ferrite carrier of 0.200 g is filled between the electrodes 222a and 222b, a DC electric field of 500 V is applied, and the measured value is used. The resistance value (Ωcm) of the ferrite carrier was determined.

[Coating ratio of ferrite carrier with toner particles]
Based on the average particle diameter of the toner and the carrier, the total toner surface area and the total surface area of the carrier were obtained and calculated based on the above formula (3).

[Cover]
The developing device was idled for 10 seconds with a potential of 500 V applied, and then the image on the photoreceptor was collected with a mending tape (CAT. No. 810-3-24, manufactured by Scotch), and A3 Affixed to size white paper. About this thing, the reflection density (test value) was measured using the reflection densitometer (brand name: X-Rite504, the product made by USAX-Rite).

  As a blank, the original mending tape from which images were not collected was pasted on A3 size white paper, and the reflection density (blank value) was measured in the same manner as described above.

The difference between the test value and the blank value was determined, and the occurrence of toner fog on the photoreceptor was determined according to the following criteria.
○: Less than 0.05 No fogging occurred Δ: 0.05 or more to less than 0.10 Slight occurrence of fogging ×: 0.10 or more Many fogging occurred.

(Example 1)
[Production of toner]
10 kg of raw material consisting of 90 parts by weight of a synthetic resin (trade name: EPA501, manufactured by Sanyo Chemical Co., Ltd.) and 10 parts by weight of carbon black (colorant, # 44, particle size 24 nm, manufactured by Mitsubishi Chemical Corporation) is used as a Henschel mixer. The mixture was mixed for 3 minutes at a blade rotation speed of 700 rpm. The obtained mixture was quantitatively supplied to a continuous two-roll kneader shown in FIG. 1 with a table feeder, and kneaded to obtain a kneaded product. The kneaded product was cooled and then roughly crushed using a 2 m / m screen with a hammer type pulverizer to obtain a kneaded crushed product.

The operating conditions of the continuous two-roll kneader are as follows.
Roll outer diameter: 0.12m
Effective roll length: 0.8m
Front roll speed: 75rpm
Rear roll rotation speed: 55rpm
Rear roll rotational speed / front roll rotational speed: about 0.7
Front / rear roll gap: 0.1 mm
Heating / cooling medium temperature in roll:
Front roll Raw material mixture supply side: 90 ° C, kneaded product discharge side: 75 ° C
Rear roll Raw material mixture supply side: 15 ° C., kneaded product discharge side: 15 ° C.
Residence time of raw material mixture: about 6 minutes

  With respect to 100 parts by weight of a synthetic resin (trade name: EPB602, manufactured by Sanyo Chemical Co., Ltd.), 10 kg is weighed at a ratio of 4 parts by weight of the kneaded crushed material and the charge control agent (chromium salicylate complex) obtained above. The mixture was mixed for 2 minutes with a Henschel mixer (blade rotation speed 850 rpm) to obtain a raw material mixture. The resistance value of the toner was adjusted by the amount of kneaded crushed material.

  This raw material mixture was kneaded using an extruder (trade name: PCM-30, manufactured by Ikekai Co., Ltd.). The operating conditions were a cylinder set temperature of 100 ° C., a barrel rotation speed of 300 rpm, and a raw material mixture supply speed of 20 kg / h. The obtained toner kneaded product was cooled with a cooling belt and then coarsely pulverized with a speed mill having a φ2 mm screen. Next, the coarsely pulverized product was pulverized with a type I jet mill, and further, fine powder and coarse powder were removed with an elbow jet classifier to produce toner particles having an average particle diameter (D50) of 6.7 μm. The average particle size (D50) was measured with a Coulter counter (TA-II).

[Manufacture of ferrite carriers]
Mn-Mg-based ferrite was added to 500 g of a treatment solution containing 2.0% by weight of silicon resin in terms of solid content and 10% by weight of titanium oxide in 100% by weight of solid content of silicon resin in toluene. After adding 5.0 kg and mixing well, the solvent was removed by heating, and the mixture was treated with a mill for 90 minutes to produce a silicon resin-coated ferrite carrier. The average particle diameter (D50) was 50 μm.

[Manufacture of two-component developer]
Using the toner particles and silicon resin-coated ferrite carrier obtained above, the two are mixed at a ratio such that the coverage of the silicon resin-coated ferrite carrier with the toner particles is 35%. Manufactured.

(Examples 2 to 5)
Toner particles and a silicon resin-coated ferrite carrier were produced in the same manner as in Example 1 while adjusting to a predetermined resistance value, and then the two-component developer of the present invention was produced.

(Comparative Examples 1-5)
The toner particles and the silicon resin-coated ferrite carrier were produced in the same manner as in Example 1 after adjusting to a predetermined resistance value, and then the two-component developer of the present invention was produced.

  Table 1 shows the colorant content (% by weight), the average particle diameter (D50, μm), and the resistance value (Ωcm) of the toner particles obtained in Examples 1 to 5 and Comparative Examples 1 to 5.

  Table 1 shows the types of ferrite particles that are core materials, the average particle diameter (D50, μm), and the resistance value (Ωcm) for the ferrite carriers obtained in Examples 1 to 5 and Comparative Examples 1 to 5. Show.

  Table 1 shows the toner coverage and the fog test results for the two-component developers obtained in Examples 1 to 5 and Comparative Examples 1 to 5. The image forming apparatus used in the fog test is a commercially available copying machine (trade name: AR-620, manufactured by Sharp Corporation) including a contact transfer type transfer unit.

  Further, visual determination results of image density for images obtained by image formation with a commercial copying machine (AR-620) using the two-component developers obtained in Examples 1 to 5 and Comparative Examples 1 to 5 Is also shown in Table 1. “Good” indicates that the image density is high and the image quality is high. “Decrease” means that the image density is clearly lower than “good” and the image quality is insufficient.

  In Table 1, “Mn—Mg” in the section of the core material (ferrite particles) of the ferrite carrier means Mn—Mg ferrite particles.

  From Table 1, it can be seen that by setting the resistance values of the toner particles and the ferrite carrier within the range specified in the present invention, an image having a sufficient image density can be obtained while reducing the toner fog on the photoreceptor. . Further, from the comparison between Example 1 and Comparative Example 1, it is possible to reduce the toner fog on the photosensitive member by not including the conductive additive.

(Examples 6-7 and Comparative Examples 6-7)
A two-component developer was produced in the same manner as in Example 1 except that the toner coverage was changed to the value shown in Table 3.

  The obtained two-component developer was subjected to a fog test and image density determination. The results are shown in Table 2.

  From Table 2, it is possible to further reduce the toner fog on the photoreceptor and to form an image having a sufficient image density by setting the coverage of the ferrite carrier with the toner in the range of 30 to 51%. .

(Example 8 and Comparative Example 8)
The two-component developer of Example 1 and Comparative Example 1 was used, and the fog test and image density were measured with a non-contact transfer type image forming apparatus (trade name: AR-L501, manufactured by Sharp Corporation) using corona discharge. Judgment was made. The results are shown in Table 4. For comparison, the results of the fog test and the image density by the contact transfer type image forming apparatus of Example 1 and Comparative Example 1 are also shown.

  From Table 3, the two-component developer of the present invention is not only an image forming apparatus using a contact transfer system, but also an image forming apparatus using a non-contact transfer system, without increasing the toner fog on the photoreceptor. It can be seen that high-quality and stable images can be provided.

1 is a side view schematically showing a configuration of a continuous two-roll kneader and a cross-sectional view of a portion A-A ′ in the side view. It is drawing which shows roughly the circuit for measuring the resistance value of a ferrite type carrier. 1 is a cross-sectional view schematically showing a configuration of a main part of an image forming apparatus according to a first embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image formation part 2 Recording material supply part 3 Image fixing part 4 Control part 5 Photosensitive drum 6 Charging means 7 Exposure unit 8 Development unit 9 Transfer means 10 Cleaning unit 11 Neutralization means 12 Transfer belt 20 Recording material accommodation tray 21 Pickup roller 22 Registration roller 30 Fixing device 31 Conveying roller 32 Switching gate 33 Reversing roller 34 Loading tray 35 Fixing roller 36 Pressure roller 37, 38, 39 Conveying path 100 Image forming apparatus 200 Continuous two-roll kneader 211 Raw material supply unit 212 Kneading Object discharge unit 213 Front roll 214 Rear roll 215, 216 Heating and cooling medium supply / discharge unit 217, 218 Roll drive motors 217, 218
220 Circuit 221 Acrylic resin substrate 222a, 222b Electrode 223a, 223b Magnet 224a, 224b Terminal 225 Voltmeter 226 Ammeter 227 Ferrite carrier 228 Conductive path

Claims (3)

In a two-component developer for electrophotography comprising toner particles containing a binder resin, a colorant and a charge control agent, and a ferrite carrier coated with a silicon resin,
The colorant content of the toner particles is 10% by weight or more of the total amount of the toner particles,
The resistance value of the toner particles is 20 × 10 ^{9 to} 85 × 10 ⁹ Ωcm, and the resistance value of the ferrite carrier when the 500 V DC electric field is applied by the bridge method with an interval of 6.5 mm is 2.0 × 10 ¹⁰ to 1 A two-component developer for electrophotography, which is 0.0 × 10 ¹² Ωcm.   2. The two-component developer for electrophotography according to claim 1, wherein the silicone resin contains a non-conductive additive.   The two-component developer for electrophotography according to claim 1 or 2, wherein a coverage of the ferrite carrier coated with silicon resin with toner particles is 30 to 55%.

Images