JP2006071840A - Two-component developer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a two-component developer to be used for image formation by a hybrid developing system, the developer preventing deterioration in a magnetic carrier and stably forming a high-quality image. <P>SOLUTION: The two-component developer is used for an image forming apparatus structured in such a manner that: the two-component developer held on the circumferential surface of a magnetic roller 11 is brought into contact with a developing roller 12 to electrostatically deposit a nonmagnetic toner in the two-component developer onto the circumferential surface of the developing roller 12; and further the nonmagnetic toner on the developing roller 12 is made to jump to the circumferential surface of a photoreceptor drum 13 to develop an electrostatic latent image on the photoreceptor drum into a toner image. The two-component developer comprises a nonmagnetic toner containing color particles and a magnetic carrier, wherein the magnetic carrier has a resin coating layer on the surface of magnetic particles and the resin coating layer has ≤25 dyn/cm critical surface tension. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a two-component developer used for development processing by a hybrid development system.

In an image forming apparatus such as an electrostatic copying machine, a laser beam printer, or a plain paper facsimile, a method of developing an electrostatic latent image on an image carrier such as a photosensitive drum is composed of a magnetic carrier and a nonmagnetic toner. Examples thereof include a two-component development method using a two-component developer and a one-component development method using a one-component developer using only toner.
Among these, in the two-component development system, there is a problem that the carrier moves onto the photosensitive drum to cause a transfer failure, or the carrier further moves onto the transfer paper and causes a flaw on the fixing roller of the fixing device. There's a problem. On the other hand, the one-component developing system often has a problem that toner is charged by friction and image defects such as fog are likely to occur due to toner charging failure.

  Therefore, a so-called hybrid development method has been proposed as a development method for solving these problems. In this hybrid development system, a two-component developer composed of a non-magnetic toner and a magnetic carrier is held on the circumferential surface of the magnetic roller, and the two-component developer is brought into contact with the circumferential surface of the developing roller, so that the developing roller is placed on the developing roller. A developing system that forms a toner layer composed of only non-magnetic toner, and further carries out a development process by flying the toner layer onto an electrostatic latent image on the photosensitive drum. Since the development process is executed in a non-contact state, it is advantageous in that the deterioration of the image quality is suppressed.

  In this hybrid development method, the toner is supplied from the magnetic roller to the developing roller at all times and over the entire peripheral surface of the developing roller regardless of the printing rate of the formed image. The toner remaining on the developing roller without being consumed is usually removed by an electrical method such as applying a reverse bias voltage. Further, in the developing device described in Patent Document 1, the toner remaining on the developing roller (“toner carrier 2” in the same document) without being consumed by the development processing is disposed downstream in the rotation direction of the developing roller. The toner is removed by a physical method using the toner peeling means 5 (for example, a scraper 29 shown in FIG. 5 of the same document).

In Patent Document 2, in the hybrid developing method, the nonmagnetic toner remaining on the developing roller is removed without applying a large mechanical force, and a magnetic device used as a developing device that can suppress the occurrence of a hysteresis phenomenon. A configuration in which the form factor of the carrier is 130 or more is disclosed. The shape factor is a numerical value representing the shape and surface state of the particle, and is calculated by the formula: {(peripheral length of carrier) ² / (projected area of carrier) × (1/4) π × 100}. The The degree of unevenness on the particle surface is represented by this shape factor. For example, a carrier having a shape factor of 130 or more means that the degree of unevenness is large and is a non-spherical carrier.
JP 2000-298396 A Japanese Patent Application Laid-Open No. 07-092813

  In the hybrid development method, as described above, the toner supply from the magnetic roller to the development roller is always performed over the entire peripheral surface of the development roller regardless of the printing rate of the formed image. The toner remaining on the developing roller without being consumed by the toner is removed by an electrical method such as applying a reverse bias voltage. By repeating this removal operation, the magnetic carrier is contaminated with fine powder toner ( There is a problem that the magnetic carrier is contaminated by so-called toner spent) or free external additives, and the charging performance of the magnetic carrier is lowered. Further, such deterioration of the magnetic carrier occurs particularly remarkably when an image with a low printing rate is repeatedly developed, which causes a problem of toner charging failure and low charged toner scattering in the developing device (toner scattering). ).

Further, as in the developing device described in Patent Document 1, when the toner peeling means is pressed against the developing roller to remove the toner remaining after the development processing, the toner peeling means is always pressed, so that the developing roller May wear, and is not suitable for applications where durability of the device is required.
Furthermore, in the hybrid development system, every time image forming processing is executed, a toner layer is formed on the developing roller with a magnetic brush on a magnetic roller composed of a magnetic carrier and a non-magnetic toner. Since the toner layer remaining on the developing roller is removed by the magnetic brush, the chance of contact between the magnetic carrier and the non-magnetic toner is greatly increased compared to the case of the normal two-component developing method, and the magnetic layer The replacement of the nonmagnetic toner held on the carrier is frequently performed. Therefore, in the hybrid development, problems such as an increase in the amount of toner spent as described above and peeling of the coat layer from the surface of the magnetic carrier are likely to occur.

  Further, as in the invention described in Patent Document 2, when a non-spherical carrier having a large surface irregularity is used as the magnetic carrier in the two-component developer, the contact ratio between the magnetic carriers increases, and the magnetic carrier Since sufficient charge can be injected into the magnetic carrier at the tip of the brush, a large electric field for transferring non-magnetic toner can be applied between the developing roller and the magnetic roller, preventing hysteresis. It becomes possible to do. However, when the magnetic carrier is non-spherical and the surface is uneven, the fluidity of the two-component developer is reduced, and the amount of toner spent increases or the magnetic carrier is increased by repeating the image forming process. New problems occur, such as the exfoliation of the coating layer being promoted.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a two-component developer that can be used for image formation by a hybrid development system and that can stably form a high-quality image by preventing deterioration of a magnetic carrier. Is to provide.

In order to achieve the above object, the present invention provides
(1) A magnetic roller, a developing roller, and a photosensitive drum carrying an electrostatic latent image on the peripheral surface thereof, and holding a two-component developer composed of nonmagnetic toner and a magnetic carrier on the peripheral surface of the magnetic roller. The two-component developer held on the magnetic roller is brought into contact with the developing roller so that the nonmagnetic toner is electrostatically attached to the peripheral surface of the developing roller, and the nonmagnetic toner on the developing roller is further removed. A two-component developer used in an image forming apparatus configured to fly to the peripheral surface of the photosensitive drum and visualize the electrostatic latent image on the photosensitive drum as a toner image;
The non-magnetic toner has colored particles and a surface treatment agent, and the magnetic carrier has magnetic particles and a resin coat layer provided on the surface thereof, and a critical surface of the resin coat layer. A two-component developer characterized by having a tension of 25 dyn / cm or less,
(2) The said resin coat layer contains at least 1 sort (s) of resin chosen from the group which consists of a silicone type resin, a fluorine-type resin, and a polyamide-type resin, The said (1) characterized by the above-mentioned. Two-component developer,
(3) The nonmagnetic toner has colored particles and a surface treatment agent, and the content ratio of the colored particles having a particle size of 2.0 μm or less is based on the number of the colored particles. The two-component developer according to (1) or (2) above, wherein the colored particles have an average circularity of 0.925 or more,
Is to provide.

  In the present invention, the critical surface tension of the resin coat layer on the surface of the magnetic carrier is a value specific to the resin material forming the resin coat layer. The critical surface tension (dyn / cm) is obtained by applying a resin material to be measured on a flat plate and treating it under the same conditions as in the production of the magnetic carrier to form a resin film. Each contact angle of pure water, methylene iodide and α-bromonaphthalene is measured on the resin coating, and can be calculated by the Zisman method based on the measurement result of the contact angle.

  In the present invention, the particle size of the colored particles is calculated based on an image analysis result by an image analysis means such as a flow type particle image analyzer, and indicates a circle-equivalent diameter for each colored particle. . Specifically, the particle size of the colored particles is obtained by obtaining a circle having the same area as the projection surface of one colored particle shown on the analysis image and calculating the diameter of the circle. The content ratio (number basis) of the colored particles having a particle size of 2.0 μm or less with respect to the total number of the colored particles is calculated based on the analysis result of the particle size (equivalent circle diameter) for each colored particle. be able to.

  In the present invention, the circularity of the colored particles is calculated based on the analysis result of the image of each colored particle by image analysis means such as a flow type particle image analyzer. Specifically, the circularity of the colored particles is obtained by obtaining a circle having the same area as the projection surface of one colored particle appearing on the analysis image and dividing the circumference of the circle by the circumference of the projection surface. Sought by. As the circularity of the colored particles approaches 1, the shape of the colored particles approaches a true sphere. Conversely, as the circularity becomes smaller than 1, the degree of flatness of the colored particles increases. Is shown. The average circularity of the colored particles is an arithmetic average of the circularity calculated for arbitrarily extracted samples (500 to 3000) of colored particles.

  In addition, the value of the said particle size is the value measured in the range of particle size 0.6-400 micrometers with the flow type particle image analyzer (FPIA-2000, Sysmex Co., Ltd. product). Since the measurable range of the particle size distribution by the measuring device is in the range of 0.6 to 400 μm, the present invention targets colored particles in the range of 0.6 to 400 μm. The same applies to the average circularity of the colored particles.

  According to the two-component developer of the present invention, since the adhesion of colored particles to the carrier surface is reduced, the charging performance of the carrier can be prevented from being lowered and the occurrence of toner scattering can be prevented.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
The two-component developer of the present invention comprises a nonmagnetic toner containing colored particles and a magnetic carrier.
In the two-component developer of the present invention, the colored particles constituting the nonmagnetic toner include, for example, a binder resin and, if necessary, a charge control agent, an offset preventing agent, a stabilizer, and the like. Then, after melting, kneading, pulverization (coarse pulverization, fine pulverization), and classification. The colored particles are not limited to those produced by the above pulverization method, and may be those formed by a suspension polymerization method.

  The pulverizer used for finely pulverizing the coarsely pulverized colored particles is not limited to this. For example, the trade name “Turbomill” manufactured by Turbomill Industry Co., Ltd., Nippon Pneumatic Industry Co., Ltd. ) Product name "Fine Mill", Hosokawa Micron Co., Ltd. product name "Inomizer", Nippon Engineering Co., Ltd. product name "Super Rotor", Kawasaki Heavy Industries Ltd. product name "Sebros", The brand name “Kryptron” can be mentioned. Further, after the pulverization process is performed on the colored particles, the pulverization process can also be performed by processing for a certain period of time with a high-speed stirring type mixer such as a Henschel mixer (manufactured by Mitsui Mining Co., Ltd.). it can.

The particle diameter of the colored particles is not limited to this, but is preferably 4 to 12 μm, more preferably 6 to 10 μm as the volume-based center particle diameter.
In the hybrid developing method, particularly when an image with a low printing rate is repeatedly developed, only the portion of the peripheral surface of the developing roller where toner is consumed by the developing process is difficult to be removed by the above-described electrical method or the like. In addition, highly charged toner that hardly migrates to the photosensitive drum may remain and accumulate. In such a case, at the time of the next development process, there is a possibility that the image density of the previously developed image portion may be lowered, and there is a problem of causing a so-called ghost phenomenon in which the history of the previous development process appears as an afterimage.

  Therefore, in order to prevent the occurrence of the ghost phenomenon, it is preferable to reduce the content ratio of the small particle size toner in order to prevent the generation of the highly charged toner. Specifically, in the two-component developer of the present invention, the content ratio of the colored particles having a particle size of 2.0 μm or less is set to be 10% or less on the number basis with respect to the total number of the colored particles. Is preferred. The content ratio based on the number is more preferably 8% or less.

  Fine colored particles having a particle size of less than 2.0 μm have a large surface area per weight, so that they are highly charged and easily have an increased electric adhesion force. Adhesion is also great. Therefore, such fine colored particles are unlikely to be separated from the surface of the developing sleeve or the magnetic carrier, and if the content ratio in the colored particles is high, the effect of removing the toner on the developing roller after the development processing is ineffective. There is a possibility that the above-described ghost phenomenon may occur due to a sufficient density or a decrease in the density of the toner layer formed on the developing roller. However, in the two-component developer of the present invention, since the content ratio of fine colored particles having a particle size of less than 2.0 μm is set low, the non-magnetic toner is prevented from being highly charged, Electrical and physical adhesion can be reduced. Therefore, the two-component developer of the present invention can prevent the ghost phenomenon from occurring.

  The minimum value of the particle size of the colored particles required by the flow type particle image analyzer is about 0.6 μm at present. Therefore, in the present invention, among colored particles having a particle size of 2.0 μm or less, the number-based content ratio is calculated only for those having a particle size of 0.6 μm or more. For the purpose, it is preferable that the content ratio of the colored particles having a particle size of less than 0.6 μm is also low.

  In the present invention, in order to calculate the content ratio of colored particles having a particle size of 2.0 μm or less, taking into consideration the maximum value of the particle size of the colored particles obtained by image analysis means such as the flow type particle image analyzer. As the standard, the total number of colored particles having a particle diameter in the range of 0.6 to 400 μm is used. However, since the colored particles having a large particle size are causative substances that deteriorate the image quality of the formed image, the colored particles having a particle size exceeding 20 μm are usually not included at all, or the particle size is 0. It is preferable that the content ratio with respect to the total number of colored particles in the range of 6 to 400 μm is 1% by number or less.

In order to set the content ratio (number basis) of the colored particles having a particle size of 2.0 μm or less so that the above range is satisfied, the colored particles are classified and colored with a particle size of 2.0 μm. What is necessary is just to implement operation which removes particle | grains.
In the two-component developer of the present invention, it is preferable that the average circularity of the colored particles is set to 0.925 or more. The average circularity of the colored particles is more preferably 0.940 or more.

When the average circularity of the colored particles is 0.925 or more, since the shape of the colored particles is almost spherical, the flowability of the nonmagnetic toner is improved, and a toner layer having a uniform thickness is formed on the developing roller. Since it becomes easy, the image quality of a formed image can be improved.
Further, by setting the average circularity of the colored particles to 0.925 or more, it is possible to suppress the occurrence of a transfer dropout phenomenon. In other words, when transferring a toner image visualized on a photosensitive drum to an intermediate transfer body or a recording medium, even if a transfer bias voltage is applied and the nonmagnetic toner is electrically attracted, the nonmagnetic When the physical adhesion between the toner and the photosensitive drum exceeds the level, there is a possibility that a sufficient transfer is not achieved and a part of the toner image remains on the photosensitive drum, so-called transfer dropout phenomenon. is there. This transfer dropout phenomenon becomes remarkable when the colored particles of the non-magnetic toner are indefinite (when the circularity is low). In the two-component developer of the present invention, as described above, the average circular shape of the colored particles The degree is set to a high value of 0.925 or more, and the physical adhesion between the nonmagnetic toners or between the nonmagnetic toner and the photosensitive drum is suppressed. it can.

  By the way, when the average circularity of the colored particles is 1 or very close to 1, the unevenness of the surface of the colored particles is reduced, so that the nonmagnetic toner remaining after the transfer process is removed from the photosensitive drum. When doing so, the cleaning blade may slip through. Therefore, when used in an image forming apparatus in which the cleaning means for removing residual toner from the photosensitive drum is a cleaning blade, the average circularity of the colored particles is set to 0.925 to 0.980. Preferably, it is 0.940-0.980.

In order to set the average circularity of the colored particles to 0.925 or more, for example, when the colored particles are pulverized, the pulverization conditions may be appropriately set such as increasing the pulverization time or repeating the pulverization process a plurality of times. .
Examples of the binder resin that forms the colored particles include styrene polymers, acrylic polymers, styrene-acrylic polymers, olefin polymers such as chlorinated polystyrene, polypropylene, and ionomer; polyester resins, polyamide resins. , Polyurethane resins, epoxy resins, diallyl phthalate resins, silicone resins, ketone resins, polyvinyl butyral resins, phenol resins, rosin modified phenol resins, xylene resins, rosin modified maleic resins, rosin esters, and the like. Of these, a styrene polymer, a styrene-acrylic polymer, and a polyester resin are preferable.

  The styrenic polymer includes not only a homopolymer of styrene but also a copolymer of styrene and another monomer. Examples of other monomers copolymerizable with styrene include p-chlorostyrene; vinyl naphthalene; ethylene unsaturated monoolefins such as ethylene, propylene, butylene, and isobutylene; vinyl chloride, vinyl bromide, and vinyl fluoride. Vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate; methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, n-octyl acrylate, Acrylic esters such as dodecyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, methyl α-chloroacrylate; methacrylic esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate; acrylonitrile, methacrylo Nitori , Other acrylic acid derivatives such as acrylamide; vinyl ethers such as vinyl methyl ether and vinyl isobutyl ether; vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone and methyl isopropynyl ketone; N-vinyl pyrrole, N-vinyl carbazole, N -N-vinyl type compounds such as vinylindole and N-vinylpyrrolidene. These monomers can be copolymerized with styrene either alone or in combination of two or more.

Examples of the polyester resin include those obtained by polycondensation of a polyvalent carboxylic acid component and a polyhydric alcohol component.
Examples of the polyvalent carboxylic acid component include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, Divalent carboxylic acids such as malonic acid; n-butyl succinic acid, n-butenyl succinic acid, isobutyl succinic acid, isobutenyl succinic acid, n-octyl succinic acid, n-octenyl succinic acid, n-dodecyl succinic acid, n-dodecenyl succinic acid Alkyl esters or alkenyl esters of divalent carboxylic acids such as isododecyl succinic acid and isododecenyl succinic acid; 1,2,4-benzenetricarboxylic acid (trimellitic acid), 1,2,5-benzenetricarboxylic acid, 2 , 5,7-Naphthalenetricarboxylic acid, 1,2,4-na Talentricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid , Tetra (methylenecarboxyl) methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, emporic trimer acid and other trivalent carboxylic acids. These polyvalent carboxylic acids may be anhydrides.

  Examples of the polyhydric alcohol component include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol, Diols such as 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol; bisphenol A, hydrogenated bisphenol A, poly Bisphenols such as oxyethylenated bisphenol A and polyoxypropylenated bisphenol A; sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentae Trytol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butane Examples include triols and higher polyhydric alcohols such as triol, trimethylolethane, trimethylolpropane, and 1,3,5-trihydroxymethylbenzene.

Examples of the colorant used for producing the colored particles include various pigments.
Examples of the black pigment include carbon black, acetylene black, lamp black, and aniline black.
Examples of yellow pigments include yellow lead, zinc yellow, cadmium yellow, yellow iron oxide, mineral fast yellow, nickel titanium yellow, naples yellow, naphthol yellow S, Hansa Yellow G, Hansa Yellow 10G, Benzidine Yellow G, and Benzidine Yellow. GR, quinoline yellow lake, permanent yellow NCG, tartrazine lake and the like.

Examples of the orange pigment include red lip yellow lead, molybdenum orange, permanent orange GTR, pyrazolone orange, Vulcan orange, and indanthrene brilliant orange GK.
Examples of red pigments include bengara, cadmium red, red lead, mercury cadmium sulfide, permanent red 4R, resol red, pyrazolone red, watching red calcium salt, lake red D, brilliant carmine 6B, eosin lake, rhodamine lake B, alizarin. Rake, brilliant carmine 3B, etc. are mentioned.

Examples of purple pigments include manganese purple, fast violet B, and methyl violet lake.
Examples of blue pigments include bitumen, cobalt blue, alkali blue lake, Victoria blue lake, phthalocyanine blue, metal-free phthalocyanine blue, phthalocyanine blue partially chlorinated, fast sky blue, and induslen blue BC.

Examples of the green pigment include chrome green, chromium oxide, pigment green B, malachite green lake, final yellow green G, and the like.
The colorant can be appropriately selected and used according to the color required for the developer. The colorants exemplified above may be used alone or in admixture of two or more.
The charge control agent used in the production of the colored particles is blended in the binder resin for the purpose of controlling the frictional charge of the toner, and is used for positive charge control and negative charge control depending on the charge polarity of the toner. Either one is selected and used.

Examples of the charge control agent for controlling positive charge include organic compounds having a basic nitrogen atom, such as basic dyes, aminopyrines, pyrimidine compounds, polynuclear polyamino compounds, aminosilane compounds, and the basic compounds exemplified above. Examples thereof include a filler subjected to a surface treatment with an organic compound having a nitrogen atom.
Examples of the charge control agent for controlling the negative charge include oil-soluble dyes such as nigrosine base (CI5045), oil black (CI26150), Bontron S, and spiron black; charge controllability such as styrene-styrenesulfonic acid copolymer. Resin; Compound containing carboxyl group (for example, alkyl salicylic acid metal chelate), metal complex dye, fatty acid metal soap, resin acid soap, naphthenic acid metal salt and the like.

The blending amount of the charge control agent is not particularly limited. For example, it is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 8 parts by weight with respect to 100 parts by weight of the binder resin. Part.
The anti-offset agent used in the production of the colored particles is blended in the binder resin for the purpose of suppressing the occurrence of toner offset phenomenon during the image forming process (particularly the fixing process). Specific examples include aliphatic hydrocarbons, aliphatic metal salts, higher fatty acids, fatty acid esters or partially saponified products thereof, silicone oil, and various waxes. Of these, aliphatic hydrocarbons having a weight average molecular weight of about 1000 to 10,000 are preferable. More specifically, low molecular weight polypropylene, low molecular weight polyethylene, paraffin wax, low molecular weight olefin polymers composed of olefin units having 4 or more carbon atoms, silicone oil, carbana wax, etc. may be mentioned, and these may be used alone or Two or more kinds can be mixed and used.

The compounding amount of the offset inhibitor is not particularly limited. For example, it is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 8 parts by weight with respect to 100 parts by weight of the binder resin. It is.
In the present invention, the non-magnetic toner is used by attaching an external additive to the surface of the colored particles as necessary.

The external additive is not particularly limited, and examples thereof include fine particles (inorganic fine particles) such as silica, alumina, and titanium oxide, and fine particles (resin fine particles) such as acrylic resin and styrene resin. Above all, the silica fine particles are preferably hydrophobic silica fine particles.
The magnetic carrier in the two-component developer of the present invention has a resin coat layer on the surface of the magnetic particles.

The magnetic particles constituting the magnetic carrier are not particularly limited, and examples thereof include ferrite particles, magnetite particles, and iron powder particles. The magnetic carrier may be a so-called magnetic powder dispersion type carrier in which the above exemplified magnetic particles are dispersed in a resin such as an acrylic resin, a styrene resin, a silicone resin, or an epoxy resin.
The resin coat layer formed on the surface of the magnetic particles has a critical surface tension of 25 dyn / cm or less, preferably 22 dyn / cm or less from the viewpoint of preventing fine toner particles from adhering to the surface of the magnetic carrier. is there.

The material for forming the resin coat layer having a critical surface tension of 25 dyn / cm or less is not limited to this, and examples thereof include silicone resins, fluorine resins, and polyamide resins.
The saturation magnetization value of the magnetic carrier is not particularly limited, but is preferably 35 to 50 emu / g.

The volume resistivity of the magnetic carrier is not particularly limited, but is preferably 10 ⁸ to 10 ¹² Ω · cm.
The volume average particle diameter of the magnetic carrier is not particularly limited, but is preferably 35 to 50 μm.
As an image forming apparatus for executing an image forming process using the two-component developer of the present invention, for example, as shown in FIG. 1, a magnetic roller 11, a developing roller 12, and an electrostatic latent image on the peripheral surface A two-component developer of the present invention is held on the peripheral surface of the magnetic roller 11, and the two-component developer held on the magnetic roller 11 is brought into contact with the developing roller 12. The non-magnetic toner in the two-component developer is electrostatically attached to the peripheral surface of the developing roller 12, and the non-magnetic toner on the developing roller 12 is caused to fly to the peripheral surface of the photosensitive drum 15. Examples thereof include an electrostatic latent image on the photosensitive drum 15 that is visualized as a toner image. The two-component developer is accommodated in the housing 14 of the developing device.

In the above image forming apparatus, the developing device includes a housing 14 that can be formed from a suitable synthetic resin. An end surface of the housing 14 facing the photosensitive drum 15 is opened, and the two-component developer of the present invention is accommodated in the housing 14.
In the housing 14, the agitating / conveying means 13 for agitating and conveying the two-component developer contained therein, the magnetic roller 11 for magnetically holding and conveying the two-component developer on the peripheral surface, the magnetic roller 11, and the photosensitive member. A developing roller 12 that is arranged with a predetermined gap with respect to each peripheral surface of the body drum 15 and that has only the nonmagnetic toner in the two-component developer attached to the peripheral surface is rotatably arranged. Has been.

Examples of the magnetic roller 11 include a cylindrical magnetic sleeve made of a nonmagnetic material such as aluminum and a stationary permanent magnet disposed in the magnetic sleeve.
A two-component developer is magnetically attracted and held on the surface of the magnetic roller 11 to form a magnetic brush, and the two-component developer is conveyed by the rotation of the magnetic sleeve.

The magnetic roller 11 is configured such that a predetermined DC bias voltage is applied from a DC power supply device, for example.
The developing roller 12 is configured by, for example, a cylindrical member (sleeve) made of a conductive material. The material of the sleeve may be a uniform conductor, and examples thereof include SUS and a material whose peripheral surface is coated with a conductive resin.

The developing roller 12 is configured such that, for example, a predetermined DC bias voltage is applied from a DC power supply device, and a predetermined AC bias voltage is superimposed and applied from the AC power supply device.
As a means for removing the toner remaining on the developing roller 12 without being consumed by the developing process, a method other than a physical method such as bringing a toner peeling means such as a scraper into contact with the developing roller is excluded. For example, a removing means using an electrical method such as a means for applying a reverse bias voltage can be employed.

The photosensitive material in the photosensitive drum 15 is not particularly limited, and examples thereof include a positively charged organic photosensitive member (positive OPC) and an amorphous silicon (a-Si) photosensitive member.
When positive OPC is used, generation of ozone and the like can be reduced, and charging can be stabilized. In particular, the positive OPC having a single layer structure can be used for a long period of time, and even when the film thickness changes, the change in the photosensitive characteristic is small and the image quality can be stabilized. Is preferred. When normal OPC is used in a long-life image forming system, black spots are generated due to dielectric breakdown as the film thickness decreases, or sensitivity decreases due to a large film thickness. In order to prevent this, it is preferable to set the film thickness of the positive OPC to about 20 to 40 μm.

Examples of the exposure apparatus for the photosensitive drum 13 include a semiconductor laser and an LED head.
When the cleaning blade 16 is used as a means for removing the toner remaining on the peripheral surface of the photosensitive drum 15 (transfer residual toner), the phenomenon that the non-magnetic toner slips through the cleaning blade 16 is prevented. From the viewpoint, the average circularity of the colored particles constituting the non-magnetic toner of the two-component developer is preferably set in the range of 0.925 to 0.980.

  The cleaning blade 16 is not particularly limited, and various blades known as means for removing transfer residual toner, such as an elastic blade, can be used.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.
Example 1
i) Preparation of colored particles For 100 parts by weight of binder resin (polyester resin), 4 parts by weight of colorant (carbon black), 1 part by weight of positively chargeable charge control agent (quaternary ammonium salt), and prevention of offset 5 parts by weight of an agent (carnauba wax) was blended, mixed with a Henschel mixer, and then melt-kneaded with a biaxial roll mill.

Among the above ingredients, the product name “MA-100” manufactured by Mitsubishi Chemical Co., Ltd. is used for the colorant, and the product name “Bontron P-” manufactured by Orient Chemical Industry Co., Ltd. is used for the positive charge control agent. 51 "was used for each.
Next, the melt-kneaded product thus obtained was cooled with a drum flaker, coarsely pulverized using a hammer mill, further finely pulverized, and then the particle size was adjusted by classification to obtain colored particles for black toner. . Note that both a mechanical pulverizer (turbo mill) and a jet pulverizer were used for fine pulverization of the melt-kneaded product.

  On the other hand, in place of 4 parts by weight of carbon black, 4 parts by weight of yellow pigment (CI Pigment Yellow 180), 4 parts by weight of magenta pigment (CI Pigment Red 122), or cyan pigment (C Pigment Blue 15: 1) Colored particles for color toner (yellow, magenta or cyan) were obtained in the same manner as for colored particles for black toner, except that 4 parts by weight of each were used. .

Table 1 shows the content ratio (% by weight) of the colored particles in the range of 0.6 to 2.0 μm and the particle size of 0 to the total number of the colored particles in the range of 0.6 to 400 μm. Average circularity (dimensionless number) of colored particles in the range of 6 to 400 μm.
ii) Preparation of non-magnetic toner To the colored particles of each color obtained in i) above, an external additive is added and mixed with a Henschel mixer, whereby black toner (Bk) and yellow toner (Y ), Magenta toner (M), and cyan toner (C) in total, four non-magnetic toners were obtained.

As the external additive, silicon oxide fine particles (primary particle diameter of 12 nm) and titanium oxide fine particles (primary particle diameter of 44 nm) are used. The amount was adjusted to 6% by weight and 0.8% by weight of titanium fine particles.
iii) Production of two-component developer The non-magnetic toner obtained in ii) above and a magnetic carrier were stirred and mixed with a ball mill to obtain a two-component developer.

As the magnetic carrier, a magnetic particle having an average particle diameter of 50 μm and a saturation magnetization of 40 emu / g and having a coat layer made of a silicone resin is used. The critical surface tension of the carrier is as follows.
I: Silicone resin coat, critical surface tension 22 dyn / cm
The respective content ratios of the two-component developer were adjusted so that the nonmagnetic toner was 5% by weight and the magnetic carrier was 95% by weight.

iv) Performance evaluation Using the two-component developer obtained in iii) above, 100,000 sheets of images were continuously formed on a document with a printing rate of 5%, and the following performance evaluation for the two-component developer was performed. Carried out. The results are shown in Table 2. Further, separately from this, using the two-component developer obtained in iii) above, an image was continuously formed on a 10,000 sheet original with a printing rate of 0.3%, and the two-component developer The following performance evaluation was performed. The results are shown in Table 3.

For image formation, an image forming apparatus (color printer “FS5016” manufactured by Kyocera Mita Co., Ltd.) using a hybrid developing system was used.
The performance evaluation items are as follows.
(A) Image Density When the printing rate of the original is 5%, the image of the formed image for each color toner at the start of the image forming process and after the image forming process of 50,000 sheets and 100,000 sheets. Concentration was measured. On the other hand, when the printing rate of the original is 0.3%, the solid portion of the formed image is formed for each color toner at the start of the image forming process and after the image forming process of 5000 sheets and 10,000 sheets. Image density was measured. Moreover, in any case, the image density was measured using a reflection densitometer (product number “TC-6D” manufactured by Tokyo Denshoku Co., Ltd.), and was measured at 9 positions per one formed image. The average value was used as the measured image density.

The image density is required to be 1.20 or more for any color toner.
(B) Presence or absence of ghost phenomenon After an image is formed using a two-component developer in which the non-magnetic toner is the cyan toner (C), the formed image is visually observed, The occurrence of a ghost phenomenon was evaluated for three times after 10,000 and 100,000 image forming processes. The evaluation criteria are as follows.
A: Generation of a ghost phenomenon was not observed.
B: Some ghost phenomenon occurred.
C: The occurrence of the ghost phenomenon was remarkable.

In the case where the non-magnetic toner is a toner other than the cyan toner (C), the presence or absence of the ghost phenomenon was evaluated in the same manner as in the case of the cyan toner. Since the evaluation results were the same as those for cyan toner, only the results for cyan toner are shown in the table below.
(C) Presence or absence of toner scattering phenomenon The transfer paper used for the image forming process was visually observed to evaluate the presence or absence of toner contamination. The toner contamination is caused by the toner falling from the developing device of the image forming apparatus due to the toner scattering phenomenon. In addition, the above-described toner scattering is caused by a decrease in the charge amount of the colored particles due to a decrease in the charging performance of the carrier due to adhesion of the colored particles to the surface of the carrier.

The evaluation was A when no toner contamination (occurrence of toner scattering phenomenon) was observed. On the other hand, in the case where toner contamination (occurrence of toner scattering phenomenon) occurs, the following table shows the number of images formed (number of repetitions) when toner contamination occurs.
(D) Presence or absence of transfer loss phenomenon After an image is formed using a two-component developer in which the non-magnetic toner is the above-described cyan toner (C), the formed image is visually observed and the image forming process is started. In addition, the presence or absence of occurrence of a transfer loss phenomenon was evaluated twice for the 100,000 sheets after the image forming process. The evaluation criteria are as follows.
A: The occurrence of a transfer dropout phenomenon was not observed.
B: Some ghost phenomenon occurred.
C: The occurrence of the ghost phenomenon was remarkable.

In the case where the non-magnetic toner is a toner other than the cyan toner (C), the presence / absence of a transfer dropout phenomenon was evaluated in the same manner as in the case of the cyan toner. Since the evaluation results were the same as those for cyan toner, only the results for cyan toner are shown in the table below.
Examples 2 and 3, Comparative Examples 1 and 2
For Examples 2 and 3 and Comparative Example 1, the same nonmagnetic toner as used in Example 1 was mixed with a magnetic carrier shown in Table 1 to obtain a two-component developer. In Comparative Example 2, the magnetic carrier shown in the following Table 1 was used, and the nonmagnetic toner colored particles shown in the following Table 1 were used as a two-component developer.

The same evaluations as in Example 1 were performed for the developers of Examples 2 and 3 and Comparative Examples 1 and 2 thus produced.
The above results are shown in Tables 2 and 3. In addition, the kind and surface critical tension of the coating resin of the carrier used for each Example and the comparative example are as follows.
II: Polyamide-based resin coat, critical surface tension 18 dyn / cm
III: Fluorine resin coating, critical surface tension 14 dyn / cm
IV: Epoxy resin coating, critical surface tension 46 dyn / cm

  In Table 1, the values described in the column of “colored particles” are as follows. For the black toner (Bk), the yellow toner (Y), the magenta toner (M), and the cyan toner (C), the upper row indicates that the particle size is 0. The ratio of colored particles having a particle size in the range of 0.6 to 2.0 μm (wt%, wt%) to the total number of colored particles in the range of 6 to 400 μm is shown. Shows the average circularity (dimensionless number) of the colored particles in the range of 0.6 to 400 μm.

As is apparent from the results shown in Tables 2 and 3, in Examples 1 to 3 in which the critical surface tension of the coating layer of the magnetic carrier was 25 dyn / cm or less, the occurrence of toner scattering could be suppressed.
In contrast, Comparative Example 1 in which the critical surface tension of the coating layer of the magnetic carrier is out of the above range is an example in combination with the same toner as in Example 1, but charging of the magnetic carrier due to adhesion of the toner spent or external additive. Although the performance has deteriorated and toner scattering does not occur in normal printing with a normal printing rate of 5%, the printing rate is very low at 0.3%, and the same non-magnetic toner and magnetic carrier are developed for a long time. In the case of stirring in the apparatus, toner scattering occurred relatively early.

  In addition, when the same magnetic carrier as in Comparative Example 1 and a nonmagnetic toner having an average circularity of 0.925 or less are used, the unevenness of the surface of the nonmagnetic toner is large, resulting in that of Comparative Example 1. Toner scattering occurred at an earlier stage than the case. In Comparative Examples 1 and 2, it was confirmed that the image density also decreased with the number of printed sheets as the charging performance of the magnetic carrier decreased. Further, in Comparative Example 2, the occurrence of the ghost phenomenon was also confirmed. .

  The present invention is not limited to the above description, and various design changes can be made within the scope of the matters described in the claims.

1 is a schematic diagram illustrating an embodiment of an image forming apparatus according to the present invention.

Claims (3)

A magnetic roller, a developing roller, and a photosensitive drum that bears an electrostatic latent image on the peripheral surface, and a two-component developer composed of a non-magnetic toner and a magnetic carrier are held on the peripheral surface of the magnetic roller. The two-component developer held on the magnetic roller is brought into contact with the developing roller so that the nonmagnetic toner is electrostatically attached to the peripheral surface of the developing roller. Further, the nonmagnetic toner on the developing roller is attached to the photoreceptor. A two-component developer used in an image forming apparatus configured to fly on a peripheral surface of a drum and visualize an electrostatic latent image on the photosensitive drum as a toner image;
The non-magnetic toner has colored particles and a surface treatment agent, and the magnetic carrier has magnetic particles and a resin coat layer provided on the surface thereof, and a critical surface of the resin coat layer. A two-component developer having a tension of 25 dyn / cm or less.   2. The two-component developer according to claim 1, wherein the resin coat layer contains at least one resin selected from the group consisting of a silicone resin, a fluorine resin, and a polyamide resin. . The non-magnetic toner has colored particles and a surface treatment agent, and the content ratio of the colored particles having a particle size of 2.0 μm or less is 10% based on the number of the colored particles. The two-component developer according to claim 1 or 2, wherein the average circularity of the colored particles is 0.925 or more.

Images