JP4972537B2 - Carrier manufacturing method - Google Patents

Description

  The present invention relates to a carrier and an image forming apparatus using the carrier. The carrier of the present invention can be suitably used for an image forming apparatus having an electrophotographic printing function such as a copying machine, a printer, and a facsimile machine.

  In general, an image forming apparatus using an electrophotographic system forms an image through charging, exposure, development, transfer, cleaning, static elimination, and fixing processes. Specifically, for example, the surface of a rotating photoconductor is uniformly charged by a charging device, and an electrostatic latent image is formed by irradiating the charged photoconductor surface with laser light according to image information by an exposure device. Is done. Subsequently, the electrostatic latent image on the photoconductor is developed by a developing device to form a toner image on the surface of the photoconductor. The toner image on the photoreceptor is transferred onto the transfer material by the transfer device, and the toner image on the transfer material is heated and fixed by the fixing device. The transfer residual toner remaining on the surface of the photoreceptor is removed by a cleaning device and collected in a predetermined collection unit. In order to prepare for the next image formation, the residual charge is removed from the surface of the photoreceptor after the cleaning by the static eliminator.

As the developer for developing the electrostatic latent image on the photoreceptor, a one-component developer composed of only toner or a two-component developer composed of toner and carrier is generally used.
Since the one-component developer does not use a carrier, a stirring mechanism or the like for uniformly mixing the toner and the carrier is not required. Therefore, there is an advantage that the developing device is simplified. However, there is a drawback that the charge amount of the toner is difficult to stabilize.
Since the two-component developer requires a stirring mechanism for uniformly mixing the toner and the carrier, there is a disadvantage that the developing device becomes complicated. However, it has excellent charging stability and compatibility with high-speed machines. Therefore, it is often used in high-speed image forming apparatuses and color image forming apparatuses.

  As the carrier used in the two-component developer, magnetic particles made of ferrite or the like having a particle diameter of 20 to 100 μm are used. In order to prevent humidity dependency and toner component fusion, the magnetic particle is known as a carrier having a magnetic particle as a core particle and a coating layer made of an acrylic resin or a silicone resin on the surface thereof. .

  The carrier whose core particle surface is coated with resin is excellent in durability, but the two-component developer using this carrier has a marked increase in toner charge amount in the initial stage of use (development of about 1K to 5K sheets), and the image density is increased. It will decline. This increase in toner charge amount was difficult to suppress even when a charge control agent having the same polarity as the toner was added to the resin.

  It has been found that the toner charge amount in the initial use (development of about 1K to 5K sheets) is related to the charge control agent concentration of the carrier surface layer.

Therefore, the present invention comprises a core particle and a resin layer containing a charge control agent and covering the core particle , and the charge control agent is added to the surface layer region of the resin layer with respect to the total weight of the carrier. 02 a method of manufacturing a presence to Ruki Yaria in an amount by weight percent 0.08 wt% or less, the resin constituting the charge control agent and the resin layer, the low polarity chosen from toluene, acetone and ether It is obtained by dissolving in a mixed solvent of a solvent, a high polar low boiling point solvent selected from methanol, ethanol and acetonitrile, and a high polar high boiling point solvent selected from propanol, i-propanol, n-butanol and t-butanol. A resin layer is formed on the core particles by using the coating liquid to be coated .

The present invention also provides a two-component developer comprising a toner and a carrier produced by the above method .

According to the present invention , the amount of the charge control agent on the surface of the coated resin layer can be adjusted, so that the charge control agent is 0.02% by weight or more and 0.02% by weight or more in the surface layer region of the resin layer. Production of the carrier present in an amount of 08% by weight or less is facilitated .

(式中、Ｒ₁及びＲ₄はそれぞれ独立して水素原子、アルキル基、又は置換若しくは非置換の芳香環(縮合環も含む)を示し、Ｒ₂及びＲ₃はそれぞれ独立して置換又は非置換の芳香環(縮合環も含む)を示し、Ｘ⁺はカチオンを示す。)で示すホウ素化合物である。
本実施形態によれば、トナー帯電量の上昇を抑え、トナーに安定した帯電量を与えることができる。 In one embodiment of the carrier of the present invention, the charge control agent is represented by the following general formula (1):

(Wherein R ₁ and R ₄ each independently represent a hydrogen atom, an alkyl group, or a substituted or unsubstituted aromatic ring (including a condensed ring), and R ₂ and R ₃ each independently represent a substituted or non-substituted group. Represents a substituted aromatic ring (including a condensed ring), and X ⁺ represents a cation).
According to this embodiment, it is possible to suppress an increase in the toner charge amount and to give a stable charge amount to the toner.

In another embodiment, the charge control agent is present in the resin layer at 5 wt% or more and 20 wt% or less with respect to the resin weight.
According to the present embodiment, it is possible to suppress an initial increase in toner charge amount and to prevent a decrease in toner charge amount due to long-term use.

In another embodiment, the resin constituting the resin layer is a dimethyl silicone resin.
According to the present embodiment, filming of the toner binder resin hardly occurs on the carrier surface, and stable chargeability can be obtained over a long period of time.

In another embodiment, the core particle includes a ferrite component.
According to the present embodiment, carriers with high saturation magnetization and low density are obtained, so that carrier adhesion to the photoconductor hardly occurs. As a result, it is possible to obtain an image with high dot reproducibility due to the soft spike formation.

Hereinafter, the present invention will be described in more detail.
<Career>
The carrier of the present invention is a carrier comprising core particles and a resin layer containing a charge control agent and covering the core particles. Here, the charge control agent is present in the surface layer region of the resin layer in an amount of 0.02 wt% or more and 0.08 wt% or less based on the total weight of the carrier.

In the present invention, the surface layer region of the resin layer refers to a region in the resin layer from which the charge control agent dissolves in methanol when immersed in methanol at 30 ° C. for 10 minutes.
Therefore, the weight of the charge control agent present in the surface region of the resin layer can be determined by quantifying the charge control agent extracted into methanol during the immersion in methanol at 30 ° C. for 10 minutes. More specifically, 100 g of carrier and 100 ml of methanol are put in a Soxhlet extractor, and methanol is stirred for 10 minutes in an oil bath at 30 ° C., and then the charge control agent extracted in methanol can be quantified by absorbance analysis.

The entire resin layer covering the core particles may contain a charge control agent.
Alternatively, the resin layer may have a configuration in which the outer region includes a charge control agent and the inner region does not include the charge control agent.

In the present invention, the presence of the charge control agent in the surface region of the resin layer is controlled within a predetermined range, so that a sufficient charge control effect is exhibited and the toner charge amount at the start (initial use) is remarkably increased. The rise can be suppressed. Furthermore, the remarkable fall of carrier resistance in a high-humidity environment can be suppressed.
Further, since the inner region of the resin layer does not contain a charge control agent, even if the core particles are exposed due to wear during life (during long-term use), it is possible to prevent the toner charge amount from decreasing.

  FIG. 1 is a conceptual diagram illustrating a covering state in an embodiment of the carrier of the present invention. The surface of the core particle 40 having unevenness on the surface is covered with a resin layer 41 containing a charge control agent. FIG. 2 is a conceptual diagram illustrating the distribution of the charge control agent in the resin layer 41. It shows that the concentration of the charge control agent is high in the resin layer surface layer portion 41a.

Any charge control agent made of a known ionic compound can be used as the charge control agent contained in the resin layer.
The charge control agent preferably has the same polarity as the toner used together. If the toner includes the charge control agent, the same type of toner can prevent the occurrence of reversely charged toner, and better charge control. Since an effect is acquired, it is preferable.

  Examples of the charge control agent imparting negative charge include chromium azo complex dye, iron azo complex dye, cobalt azo complex dye, salicylic acid or its derivative chromium / zinc / aluminum / boron complex or salt compound, naphtholic acid or its derivative chromium / Examples include zinc / aluminum / boron complexes or salt compounds, chromium / zinc / aluminum / boron complexes or salt compounds of benzylic acid or its derivatives, long-chain alkyl carboxylates, and long-chain alkyl sulfonates. (In the above, “chromium / zinc / aluminum / boron complex or salt compound” means a chromium complex or chromium salt compound, zinc complex or zinc salt compound, aluminum complex or aluminum salt compound, or boron complex or boron salt compound. .same as below.)

(式中、Ｒ₁及びＲ₄はそれぞれ独立して水素原子、アルキル基、又は置換若しくは非置換の芳香環(縮合環も含む)を示し、Ｒ₂及びＲ₃はそれぞれ独立して置換又は非置換の芳香環(縮合環も含む)を示し、Ｘ⁺はカチオンを示す。)で示されるホウ素化合物は、帯電量の上昇が起こり難く、帯電安定性に優れているので好ましい。
Ｒ₁及び／又はＲ₄のアルキル基は、好ましくは炭素数１〜６、より好ましくは炭素数１〜２のアルキル基である。 In particular, the following general formula (1):

(Wherein R ₁ and R ₄ each independently represent a hydrogen atom, an alkyl group, or a substituted or unsubstituted aromatic ring (including a condensed ring), and R ₂ and R ₃ each independently represent a substituted or non-substituted group. A boron compound represented by a substituted aromatic ring (including a condensed ring, and X ⁺ represents a cation) is preferable because the charge amount hardly increases and the charge stability is excellent.
The alkyl group of R ₁ and / or R ₄ is preferably an alkyl group having 1 to 6 carbon atoms, more preferably 1 to 2 carbon atoms.

  Examples of charge control agents that impart positive chargeability include nigrosine dyes or derivatives thereof, triphenylmethane derivatives, quaternary ammonium salts, quaternary phosphonium salts, quaternary pyridinium salts, guanidine salts, amidine salts, and the like. Can do.

  The charge control agent is preferably present in the resin layer at 5% by weight or more and 20% by weight or less based on the weight of the resin. When the charge control agent exists in this range in the resin layer, an increase in the toner charge amount at the initial use can be suppressed, and a decrease in the toner charge amount in the life can be suppressed.

<Other carrier configurations>
Next, another configuration of the carrier of the present invention will be described.
The volume average particle diameter of the carrier is not particularly limited, but is preferably 20 to 100 μm, and more preferably 30 to 60 μm. If the volume average particle diameter is too small, the carrier easily moves from the developing roller to the photosensitive drum during development, and white spots may occur in the obtained image. On the other hand, if it is too large, the dot reproducibility may deteriorate and the image may become rough. The volume average particle diameter of the carrier means the total particle diameter of the core particles and the resin layer that covers the core particles. The specific definition of the volume average particle diameter is described below.

  The lower the saturation magnetization of the carrier, the softer the magnetic brush in contact with the photosensitive drum, so that an image faithful to the electrostatic latent image can be obtained. However, if the saturation magnetization is too low, carriers adhere to the surface of the photosensitive drum and white spots are likely to occur. On the other hand, if the saturation magnetization is too high, it becomes difficult to obtain an image faithful to the electrostatic latent image due to the stiffening of the magnetic brush. Therefore, the saturation magnetization of the carrier is preferably in the range of 30 to 100 emu / g, and more preferably in the range of 50 to 80 emu / g. The definition of saturation magnetization is described below.

The carrier provided with the coating layer may adhere to the photoreceptor when the volume resistivity is low, and the toner charge amount is likely to increase when the volume resistivity is high. Therefore, the volume resistivity of the carrier is preferably in the range of 1 × 10 ^{8 to} 5 × 10 ¹² Ω · cm, and more preferably in the range of 1 × 10 ⁹ to 2 × 10 ¹² Ω · cm. The definition of volume resistivity is described below.

<Core particles>
Known magnetic particles can be used for the core particles, but particles containing ferrite components (ferrite particles) are preferred. Ferrite-based particles have high saturation magnetization and can provide carriers with low density. For this reason, carrier adhesion to the photoconductor hardly occurs, and an image with high dot reproducibility can be obtained by forming soft spikes.

  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, Examples of the particles include manganese-copper-zinc ferrite.

The volume average particle diameter of the core particles is preferably 20 to 80 μm, and more preferably 30 to 60 μm. The definition of the volume average particle diameter is described below.
The core particles preferably have a volume resistivity of 1 × 10 ⁶ to 1 × 10 ¹¹ Ω · cm. Ferrite particles having a volume resistivity in this range are generally used because they are inexpensive. If the volume resistivity is low, the toner image may be fogged due to poor electrical insulation. On the other hand, when the volume resistivity is high, the counter charge remaining on the carrier surface tends to cause an edge effect at the periphery of the solid image and a decrease in image density. The volume resistivity is more preferably in the range of 1 × 10 ^{8 to} 5 × 10 ¹⁰ Ω · cm. The definition of volume resistivity is described below.

Ferrite particles can be produced by a known method. For example, ferrite raw materials such as Fe ₂ O ₃ and Mg (OH) ₂ are mixed, and this mixed powder is heated in a heating furnace and calcined. After cooling the obtained calcined product, it is pulverized by a vibration mill so as to become particles of about 1 μm, and a dispersant and water are added to the pulverized powder to prepare a slurry. This slurry is wet pulverized with a wet ball mill, and the resulting suspension is granulated and dried with a spray dryer to obtain ferrite-based particles.

<Resin layer>
The resin to be coated is not particularly limited, and any layer made of a known resin can be used. For example, a layer made of an acrylic resin or a silicone resin can be used.
Examples of the acrylic resin include polyacrylate, polymethyl methacrylate, polyethyl methacrylate, poly-n-butyl methacrylate, polyglycidyl methacrylate, polyfluorinated acrylate, styrene-methacrylate copolymer, styrene-butyl methacrylate copolymer, and styrene. -Ethyl acrylate copolymer etc. are illustrated.

  Commercially available product names are manufactured by Mitsubishi Rayon Co., Ltd .: Dianar SE-5437, SE-5102, SE-5377, SE-5649, SE-5466, SE-5482, HR-169, HR-124, HR-1127 , HR-116, HR-113, HR-148, HR-131, HR-470, HR-634, HR-606, HR-607, LR-1065, LR-574, LR-143, LR-396, LR -637, LR-162, LR-469, LR-216, BR-50, BR-52, BR-60, BR-64, BR-73, BR-75, BR-77, BR-79, BR-80 , BR-83, BR-85, BR-87, BR-88, BR-90, BR-93, BR-95, BR-100, BR-101, BR-102, BR-105, B -106, BR-107, BR-108, BR-112, BR-113, BR-115, BR-116, BR-117, manufactured by Sekisui Chemical Co., Ltd .: ESREC PSE-0020, SE-0040, SE- 0070, SE-0100, SE-1010, SE-1035, Sanyo Chemical Industries, Ltd .: Hymer ST95, ST120, Mitsui Chemicals, Inc .: FM601, and the like.

  Examples of the silicone resin include silicone varnish (manufactured by Toshiba Corporation: TSR115, TSR114, TSR102, TSR103, YR3061, TSR110, TSR116, TSR117, TSR108, TSR109, TSR180, TSR181, TSR187, TSR144, TSR165, Shin-Etsu Chemical ( Co., Ltd .: KR271, KR272, KR275, KR280, KR282, KR267, KR269, KR211, KR212), alkyd modified silicone varnish (Toshiba Corp .: TSR184, TSR185), epoxy modified silicone varnish (Toshiba Corp .: TSR194) YS54), polyester-modified silicone varnish (manufactured by Toshiba Corporation: TSR187), acrylic-modified silicone varnish (manufactured by Toshiba Corporation: TSR170, TSR171), urethane Modified silicone varnish (manufactured by Toshiba Corporation: TSR175), reactive silicone resin (manufactured by Shin-Etsu Chemical Co., Ltd .: KA1008, KBE1003, KBC1003, KBM303, KBM403, KBM503, KBM602, KBM603) and the like.

In particular, a carrier having a layer of straight silicone resin (alkyl-substituted silicone resin) is hard to adhere (filming) to the toner component (binder resin) on its surface, and can maintain the toner charge imparting ability for a long time. preferable.
The straight silicone resin is not particularly limited, and a silicone resin commonly used in this field can be used, but a crosslinkable silicone resin is preferable. As shown below, the crosslinkable silicone resin is a known silicone resin that is cured by crosslinking between hydroxyl groups bonded to Si atoms or a hydroxyl group and a group -OX by a heat dehydration reaction, a room temperature curing reaction, or the like.

〔式中、複数のＲは同一又は異なって１価の有機基を示す。基−ＯＸはアセトキシ基、アミノキシ基、アルコキシ基、オキシム基などである。〕

[Wherein, a plurality of R are the same or different and each represents a monovalent organic group. The group -OX is an acetoxy group, an aminoxy group, an alkoxy group, an oxime group, and the like. ]

  As the crosslinkable silicone resin, either a heat curable silicone resin or a room temperature curable silicone resin can be used. In order to crosslink the thermosetting silicone resin, it is necessary to heat the resin to about 200 to 250 ° C. Although heating is not required to cure the room temperature curable silicone resin, it is preferably heated at 150 to 280 ° C. in order to shorten the curing time.

  Among the crosslinkable silicone resins, dimethyl silicone in which the monovalent organic group represented by R is a methyl group is preferable. Since the crosslinkable silicone resin in which R is a methyl group has a dense crosslink structure, when the resin coating layer of the carrier is formed using the crosslinkable silicone resin, a good carrier such as water repellency and moisture resistance can be obtained. . However, if the cross-linked structure becomes too dense, the resin coating layer tends to become brittle, so selection of the molecular weight of the cross-linkable silicone resin is important.

  The weight ratio of silicon to carbon (Si / C) in the crosslinkable silicone resin is preferably 0.3 to 2.2. If Si / C is less than 0.3, the hardness of the resin coating layer is lowered, and the carrier life and the like may be lowered. When Si / C exceeds 2.2, the charge imparting property of the carrier to the toner is easily affected by the temperature change, and the resin coating layer may be embrittled.

In the present invention, a commercially available cross-linkable silicone resin can be used. For example, SR2400, SR2410, SR2411, SR2510, SR2405, 840RESIN, 804RESIN (all trade names, manufactured by Toray Dow Corning Co., Ltd.), KR271, KR272, KR274, KR216 , KR280, KR282, KR261, KR260, KR255, KR266, KR251, KR155, KR152, KR214, KR220, X-4040-171, KR201, KR5202, and KR3093 (all manufactured by Shin-Etsu Chemical Co., Ltd.) Can be mentioned.
A crosslinkable silicone resin can be used individually by 1 type, or can use 2 or more types together.

A conductive agent may be added to the coating resin layer in order to reduce the resistance. Preferably, the conductive agent is added to a region including the charge control agent in the resin layer, for example, the outer region.
The conductive agent is not particularly limited as long as the volume resistivity value of the carrier can be controlled. For example, silicon oxide, alumina, carbon black, graphite, zinc oxide, titanium black, iron oxide, titanium oxide, tin oxide, Examples of the conductive agent include potassium titanate, calcium titanate, aluminum borate, magnesium oxide, barium sulfate, and calcium carbonate.
A conductive agent can be used individually by 1 type, or can use 2 or more types together.

Among the above conductive agents, carbon black is preferable from the viewpoint of production stability, cost, and low electrical resistance.
The type of carbon black is not particularly limited, but those having a DBP (dibutyl phthalate) oil absorption in the range of 90 to 170 ml / 100 g are preferred from the viewpoint of excellent production stability. A primary particle size of 50 nm or less is particularly preferable because of excellent dispersibility.

  As a content rate of a electrically conductive agent, 0.1-20 weight part is preferable with respect to 100 weight part of resin which comprises a coating layer. If it is less than 0.1 part by weight, conductivity may not be obtained. On the other hand, when the amount exceeds 20 parts by weight, there is a possibility that charge leakage occurs due to excessive conductivity. When silicone resin is used as the coating resin, the content of the conductive agent is preferably 3.0 to 10.0 parts by weight, and more preferably 3.0 to 7.0 parts by weight. Carrier content phenomenon can be improved because a content rate is this range.

  The coverage by the resin layer on the core particle surface is preferably 50 to 100%. If it is less than 50%, the exposed amount of the core particles is excessively increased due to wear, and the carrier resistance may be lowered. For this reason, carrier adhesion and roughness are likely to occur. The definition of the coverage by the resin layer on the core particle surface will be described below.

A known method can be adopted as a method for forming the coating resin layer. For example, there is an immersion method in which a raw material is dissolved or dispersed in a solvent (for example, an organic solvent such as toluene or acetone) to prepare a coating liquid for coating, and core particles are immersed in the obtained coating liquid.
When the coating resin layer is composed of an outer region containing a charge control agent and an inner region not containing a charge control agent, the core particles are first immersed in a coating solution containing no charge control agent to form a resin layer. An inner region can be formed and then immersed in a coating liquid containing a charge control agent to form an outer region on the inner region.

  When an ionic compound such as a quaternary ammonium salt or a quaternary boron compound is used as the charge control agent, generally a charge control agent is used together with a low polarity solvent such as toluene that dissolves the resin for forming the coating layer. A mixed solvent in which a highly polar solvent such as methanol to be dissolved is mixed is used. However, when solvents having different polarities are used, methanol having a low boiling point tends to evaporate, and therefore the ratio of toluene tends to increase. As a result, the charge control agent is deposited and adheres to the core particles at the initial stage of the coating process. For this reason, it is difficult to increase the amount of the charge control agent on the surface of the coating resin layer.

  Therefore, together with a low-polarity solvent for dissolving the resin (for example, toluene, acetone, ether) and a high-polarity, low-boiling-point solvent (for example, methanol, ethanol, acetonitrile) for dissolving the ionic compound charge control agent, By using a high-boiling solvent (for example, propanol, i-propanol, n-butanol, t-butanol, etc.), the charge control agent can be used even after the low-boiling solvent such as methanol evaporates. The amount of the charge control agent can be adjusted on the surface of the coating resin layer without precipitation.

<Two-component developer>
The developer will be described below.
The developer of the present invention is a two-component developer composed of a toner and a carrier, and the carrier according to the present invention described above is used as the carrier.
The mixing ratio of the carrier and the toner is generally 3 to 15 parts by weight of the toner with respect to 100 parts by weight of the carrier. Examples of the method for mixing the carrier and the toner include a method of stirring with a mixer such as a Nauta mixer.

The toner is not particularly limited, and any known toner can be used. For example, the toner described below can be used.
The toner includes colored resin particles (toner particles) and, if necessary, an external additive attached to the surface of the colored resin particles. The external additive is preferably contained in the toner from the viewpoint of preventing the toner from agglomerating and preventing the transfer efficiency when transferring from the photosensitive drum to the recording medium.

  The volume average particle diameter of the colored resin particles is preferably in the range of 4 to 7 μm. Within this range, a high-quality image with excellent dot reproducibility and less fog and toner scattering can be obtained. The definition of the volume average particle diameter is described below.

The BET specific surface area of the colored resin particles is preferably 1.5 to 1.9 m ² / g. When the BET specific surface area is 1.9 m ² / g or less, the external additive can be more easily attached to the surface without excessively entering the recess. As a result, the roller effect (effect of improving fluidity) and the spacer effect (preventing charge leakage) of the external additive are more fully exhibited, and fog and toner scattering are less likely to occur. When it is 1.5 m ² / g or more, the surface of the colored resin particles is not too smooth, the occurrence of poor cleaning is reduced, and as a result, the occurrence of fog is further reduced.

  As a method for controlling the BET specific surface area, a known method can be used. For example, a colored resin particle is rotated at a high speed in a cylindrical pipe to take a corner, or a toner is instantaneously melted in a hot air stream. There is a method such as a sufusion system. The definition of the BET specific surface area is described below.

  The colored resin particles can be produced by a known method such as a kneading and pulverizing method or a polymerization method. As an example, in the kneading and pulverizing method, a binder resin and a colorant, and optionally a charge control agent, a release 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. The obtained raw material mixture is melt-kneaded at a temperature of about 100 to 180 ° C. by a kneader such as a biaxial kneader or a uniaxial kneader. The obtained kneaded product is cooled and solidified, and the solidified product is pulverized by an air pulverizer such as a jet mill. Colored resin particles can be produced by adjusting the particle size such as classification of the obtained pulverized product as necessary.

  As the binder resin, various known styrene resins, acrylic resins, polyester resins and the like can be used. A linear or non-linear polyester resin is particularly preferable. The polyester resin is excellent in that it can satisfy the mechanical strength (hard to generate fine powder), the fixability (hard to peel off from the paper after fixing), and the hot offset resistance at the same time.

The polyester resin can be obtained by polymerizing a monomer composition composed of a polyhydric alcohol having two or more valences and a polybasic acid.
Examples of the divalent alcohol used for polymerization of the polyester resin include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1 Diols such as 1,4-butenediol, 1,5-pentanediol, 1,6-hexanediol, bisphenol A alkylene such as bisphenol A, hydrogenated bisphenol A, polyoxyethylenated bisphenol A, polyoxypropylenated bisphenol A Examples thereof include oxide adducts and the like.

  Examples of the divalent polybasic acid 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, Examples thereof include malonic acid, anhydrides and lower alkyl esters of these acids, alkenyl succinic acids such as n-dodecenyl succinic acid and n-dodecyl succinic acid, and alkyl succinic acids.

  If necessary, a trihydric or higher polyhydric alcohol and / or a polybasic acid may be added to the monomer composition. Examples of the trihydric or higher polyhydric alcohol include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, sucrose, 1,2,4- Butanetriol, 1,2,5-pentanetriol, glycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, 1,3,5-trihydroxymethyl Benzene and others can be mentioned.

  Examples of the tribasic or higher polybasic acid include 1,2,4-benzenetricarboxylic acid, 1,2,5-benzenetricarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, and 2,5,7-naphthalenetricarboxylic acid. 1,2,4-naphthalenetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, tetra (methylenecarboxyl) methane, 1,2,7 , 8-octanetetracarboxylic acid, and anhydrides thereof.

As the colorant, known pigments and dyes generally used for toners can be used.
Specifically, for black toner, carbon black and magnetite can be exemplified.

  For yellow toner, CI pigment yellow 1, 1, 3, 74, 97, 98, etc. acetoacetic acid arylamide monoazo yellow pigments, CI pigment yellow 12, 13, 13, etc. 14 and 17 acetoacetate arylamide disazo yellow pigments, CI pigment yellow 93, condensed monoazo yellow pigments such as 155; CI pigment yellow 180, 150 and 185, etc. Other examples include yellow pigments, yellow dyes such as CI Solvent Yellow 19, 77, 79, and CI Disperse Yellow 164.

  For magenta toner, CI Pigment Red 48, 49: 1, 53: 1, 57, 57: 1, 81, 122, 5, 146, 184, 238 Red pigments such as CI Pigment Violet 19; red dyes such as CI Solvent Red 49, 52, 58, and 8;

For cyan toners, CI pigment blue 15: 3, 15: 4, copper phthalocyanine and its blue dyes and derivatives thereof; CI pigment green 7, 36 (phthalocyanine green) Examples thereof include green pigments and the like.
As content of a coloring agent, it is preferable that it is about 1-15 weight part with respect to 100 weight part of binder resin, More preferably, it is the range of 2-10 weight part.

As the charge control agent that can be used for the toner, known charge control agents can be used.
Specifically, as a charge control agent imparting negative chargeability, chromium azo complex dye, iron azo complex dye, cobalt azo complex dye, salicylic acid or its derivative chromium / zinc / aluminum / boron complex or salt compound, naphtholic acid or Chromium / zinc / aluminum / boron complex or salt compound of its derivative, chromium / zinc / aluminum / boron complex or salt compound of benzylic acid or its derivative, long chain alkyl carboxylate, long chain alkyl sulfonate, etc. Can do.

  Examples of charge control agents that impart positive chargeability include nigrosine dyes or derivatives thereof, triphenylmethane derivatives, quaternary ammonium salts, quaternary phosphonium salts, quaternary pyridinium salts, guanidine salts, amidine salts, and the like. Can do.

The charge control agent is preferably of the same polarity as the charge control agent in the carrier. If the same type of charge control agent is used, the generation of reversely charged toner can be prevented and a better charge control effect can be obtained. More preferable.
The content of the charge control agent is more preferably in the range of 0.1 to 20 parts by weight, and still more preferably in the range of 0.5 to 10 parts by weight with respect to 100 parts by weight of the binder resin.

  Release agents that can be used for the toner include synthetic waxes such as polypropylene and polyethylene, paraffin wax and derivatives thereof, petroleum waxes such as microcrystalline wax and derivatives thereof, and modified waxes thereof, carnauba wax, rice wax, and candelilla wax. And plant waxes. By including these release agents in the toner, the releasability of the toner with respect to the fixing roller or the fixing belt can be improved, and high temperature / low temperature offset during fixing can be prevented. The amount of the release agent added is not particularly limited, but is generally 1 to 5 parts by weight with respect to 100 parts by weight of the binder resin.

  As the external additive, inorganic particles made of silica, titanium oxide, alumina or the like having a number average particle diameter of 7 nm to 100 nm can be used. The definition of the number average particle diameter is described below. Moreover, the inorganic particle to which hydrophobicity was provided by surface-treating with a silane coupling agent, a titanium coupling agent, and silicone oil may be sufficient. Inorganic particles to which hydrophobicity is imparted are preferable because the decrease in electrical resistance and charge amount is reduced under high humidity. In particular, silica particles using hexamethyldisilazane (hereinafter sometimes referred to as HMDS) as a silane coupling agent and having a trimethylsilyl group introduced on the surface are excellent in hydrophobicity and insulating properties. The toner to which the silica particles are externally added can provide excellent chargeability even in a high humidity environment.

  Specific external additives include Aerosil 50 (number average particle size: about 30 nm), Aerosil 90 (number average particle size: about 30 nm), Aerosil 130 (number average particle size: about 16 nm) manufactured by Nippon Aerosil Co., Ltd. ), Aerosil 200 (number average particle size: about 12 nm), Aerosil 300 (number average particle size: about 7 nm), Aerosil 380 (Number average particle size: about 7 nm) (all of which are silica), Degussa (Germany) Aluminum oxide C (alumina; number average particle size: about 13 nm) manufactured by Degussa (Germany), titanium oxide P-25 (titanium oxide; number average particle size: about 21 nm), MOX170 (silica-alumina mixture; number) (Average particle size: about 15 nm), Ishihara Sangyo Co., Ltd. TTO-51 (titanium oxide; number average particle size: about 20 nm), TTO-55 (titanium oxide; number average particle size) : About 40 nm).

The external additive is externally added to the colored resin particles by mixing the colored resin particles with an airflow mixer such as a Henschel mixer.
The amount of the external additive added is preferably 0.2 to 3% by weight. If it is less than 0.2% by weight, the toner may not be sufficiently or fluidly provided. On the other hand, if it exceeds 3% by weight, the toner fixability may be lowered.

  According to the two-component developer of the present invention, the initial charge amount increase of the toner can be suppressed, and the adhesion of the carrier to the photoreceptor and the decrease in the toner charge amount can be suppressed over a long period. Therefore, a stable image can be formed over a long period of time by using the developer of the present invention.

<Image forming apparatus>
Next, the electrophotographic image forming apparatus of the present invention will be described.
As long as the two-component developer according to the present invention is used as a developer, the image forming apparatus according to the present invention is not limited to a specific one with respect to other configurations, and an electrophotographic image forming apparatus using a two-component developer. Any known structure can be employed.

For example, the image forming apparatus of the present invention includes a photosensitive member on which an electrostatic latent image is formed, a charging device that charges the surface of the photosensitive member, an exposure device that forms an electrostatic latent image on the surface of the photosensitive member, and the aforementioned A developing device that contains the two-component developer according to the present invention and supplies toner to the electrostatic latent image on the surface of the photoreceptor to form a toner image, and a transfer device that transfers the toner image on the surface of the photoreceptor to a recording medium And a cleaning device that cleans the surface of the photoreceptor, and a fixing device that fixes the toner image on the recording medium.
The image forming apparatus of the present invention can be, for example, an electrophotographic copying machine, a printer, a facsimile machine, or a complex machine of these.

The image forming apparatus of the present invention will be specifically described below with reference to the drawings.
FIG. 3 is an explanatory diagram showing a configuration of an embodiment of the image forming apparatus according to the present invention. The illustrated image forming apparatus is a tandem color image forming apparatus including four image forming units 1 to 4. Among these, reference numeral 1 indicates a first image forming unit for forming a black toner image, and reference numeral 2 indicates a second image forming unit for forming a cyan toner image. Reference numeral 3 indicates a third image forming unit for forming a magenta toner image, and reference numeral 4 indicates a fourth image forming unit for forming a yellow toner image.

  Above these four image forming units 1 to 4, an intermediate transfer belt (endless belt) 5 is disposed. The intermediate transfer belt 5 is stretched between two support rolls 6 and rotates in the direction indicated by the arrow R. Hereinafter, upstream and downstream are expressed with reference to the secondary transfer position (transfer position of the image to the recording medium) where the secondary transfer roller 8 is disposed with respect to the rotation direction of the intermediate transfer belt 5. As a material for the intermediate transfer belt 5, a material in which an appropriate amount of an electron conductive conductive agent is contained in a resin such as polyimide or polyamide can be used.

The four image forming units 1 to 4 are, from the upstream side, the first image forming unit 1 (black), the second image forming unit 2 (cyan), the third image forming unit 3 (magenta), and the fourth image forming unit 4. They are arranged in the order of (yellow).
Inside the intermediate transfer belt 5, primary transfer rollers 7 for transferring the single color toner images formed by the image forming units 1 to 4 onto the intermediate transfer belt 5 are respectively photosensitive drums of the image forming units 1 to 4. It is provided so as to oppose. The single color toner images formed by the image forming units 1 to 4 are transferred so as to overlap on the intermediate transfer belt 5 to form one color image.

On the downstream side of the fourth image forming unit 4 (yellow) in the rotation direction R of the intermediate transfer belt 5, a secondary transfer roller 8 that transfers the color image formed on the intermediate transfer belt 5 to a sheet (recording medium). It is arranged.
A belt cleaning unit 10 for cleaning the surface of the intermediate transfer belt 5 is provided downstream of the secondary transfer roller 8 in the rotation direction R of the intermediate transfer belt 5 and upstream of the first image forming unit 1. ing. The belt cleaning unit 10 includes a belt cleaning brush 11 disposed in contact with the intermediate transfer belt 5 and a belt cleaning blade 12. The belt cleaning blade 12 is disposed on the downstream side of the belt cleaning brush 11.

Below the image forming units 1 to 4, a tray 14 for storing paper is disposed. The paper in the tray 14 is conveyed by a plurality of paper feed rollers 13 to a secondary transfer position where the secondary transfer roller 8 faces the intermediate transfer belt 5. An arrow P indicates the sheet conveyance direction.
On the downstream side of the secondary transfer roller 8 in the paper transport direction P, a fixing unit 15 for fixing the color image transferred onto the paper on the paper is provided. On the further downstream side of the fixing unit 15, a paper discharge roller 13 a that discharges the paper on which the color image is fixed from the image forming apparatus is provided.

  In the above-described configuration, each single color toner image formed by the image forming units 1 to 4 is sequentially transferred onto the intermediate transfer belt 5, and one color image is formed on the intermediate transfer belt 5. The color image on the intermediate transfer belt 5 is secondarily transferred to the paper conveyed by the paper feed roller 13 at the secondary transfer position, and then fixed on the paper by the fixing unit 15. The sheet on which the color image is fixed is discharged from the image forming apparatus by the discharge roller 13a. On the other hand, after the secondary transfer, the toner remaining on the intermediate transfer belt 5 without being transferred onto the sheet is removed by the belt cleaning unit 10.

  FIG. 4 shows the first image forming unit 1 shown in FIG. The configurations of the second image forming unit 2, the third image forming unit 3, and the fourth image forming unit 4 are substantially the same. Therefore, a detailed description of the configuration of the second image forming unit 2, the third image forming unit 3, and the fourth image forming unit 4 is omitted.

  Around the photosensitive drum 16, a charger 17 for charging the photosensitive drum 16, an exposure unit 18 for writing an electrostatic latent image on the photosensitive drum 16, and a development for visualizing the electrostatic latent image on the photosensitive drum 16 An apparatus 19 is provided with a photosensitive drum cleaner 20 that removes a residue including toner remaining on the photosensitive drum 16 after the primary transfer.

The charger 17 is composed of, for example, a scorotron charger, and performs corona discharge on the photosensitive drum 16 to charge the photosensitive drum 16 to a predetermined potential. In addition, it can also be comprised from the contact-type charger using a corotron charger, a charging roller, or a charging brush.
The exposure device 18 is composed of, for example, a laser exposure device, performs exposure by laser scanning according to an image signal, and changes the surface potential of the photosensitive drum 16 charged by the charger 17, thereby changing the static potential according to the image information. An electrostatic latent image is formed. An LED array device or the like can also be used as the exposure device.

The developing device 19 accommodates the two-component developer according to the present invention in the developing tank 27 and develops the electrostatic latent image on the surface of the photosensitive drum 16 with toner contained in the developer.
The photosensitive drum cleaner 20 includes a cleaning blade 21, a cleaner housing 22, and a seal 23.

  The cleaning blade 21 is disposed in pressure contact with the rotation direction Rd of the photosensitive drum 16 in the counter direction, and scrapes off the residue on the surface of the photosensitive drum 16. The cleaner housing 22 stores the scraped residue, and the cleaning blade 21 is attached to the cleaner housing 22. The seal 23 seals the inside of the cleaner housing 22. One end of the seal 23 is fixed to the cleaner housing 22 on the upstream side of the cleaning blade 21 in the rotation direction Rd of the photosensitive drum 16, and the other end is connected to the photosensitive drum 16. Arranged in contact.

FIG. 5 is a diagram for explaining the developing device 19 shown in FIG. 4 in more detail.
The developing device 19 includes a developing tank 27 in which the two-component developer 31 according to the present invention is accommodated. The developing tank 27 is provided with an opening 30 at a position facing the outer peripheral surface of the photosensitive drum 16. Yes.

  The two-component developer is supplied to the photosensitive drum 16 by carrying the two-component developer on the outer peripheral surface at a position facing the open portion 30 inside the developing tank 27, and an electrostatic latent image is formed. A developing roller 24 for developing is provided. The developing roller 24 is disposed with a predetermined gap from the outer peripheral surface of the photosensitive drum 16.

  The developing roller 24 is a multipolar magnetized member of multipolar magnetization in which magnetic poles N1, N2, and N3 and magnetic poles S1 and S2 made of bar magnets having a rectangular cross-sectional shape are radially spaced apart at a plurality of circumferential positions. 25 and a nonmagnetic sleeve 26 that is rotatably fitted to the multipolar magnetized member 25.

  Both ends of the multipolar magnetized member 25 are supported non-rotatably on both side walls of the developing tank 27, and the magnetic pole N1 (peak value 110 mT) is located at a position toward the rotation center of the photosensitive drum 16, and the magnetic pole S1 (peak value). = −78 mT) is upstream from the magnetic pole N1, for example, at a position of 59 °, the magnetic pole N2 (peak value = 56 mT) is upstream from the magnetic pole N1, for example, at a position of 117 °, and the magnetic pole N3 (peak value = 42 mT) is The magnetic pole S2 (peak value = −80 mT) is disposed upstream from the magnetic pole N1, for example, at a position of 282 °, for example.

  On the upstream side of the position where the sleeve 26 is closest to the outer peripheral surface of the photosensitive drum 16 in the developer transport direction (sleeve rotation direction), the thickness of the developer layer carried on the sleeve 26 is regulated, and the electrostatic charge of the developer is controlled. A regulating member 28 that regulates the transport amount to the latent image is provided. The regulating member 28 is arranged at a predetermined interval with respect to the surface of the sleeve 26.

An agitating member 29 that agitates the developer 31 inside the developing tank 27 and supplies the developer 31 to the developing roller 24 is rotatably provided in the developing tank 27 at a position facing the developing roller 24.
In the image forming apparatus of the present invention, since the toner charge amount is stable over a long period of time, a stable image quality can be obtained over a long period of time.

(Definition)
Definitions of the terms “volume average particle diameter”, “saturation magnetization”, “volume resistivity”, “number average molecular weight”, “coverage”, “BET specific surface area”, “number average particle diameter” used in the present specification Is described.

`` Volume average particle diameter '' of carrier (core particle)
In the present specification, the volume average particle diameter of the carrier (and core particles) is determined by using a dry dispersion apparatus RODOS (manufactured by SYMPATEC) and a dispersion pressure of 3.0 bar in a laser diffraction particle size distribution measuring apparatus HELOS (manufactured by SYMPATEC). Means a value measured under the conditions of

"Volume average particle diameter" of colored resin particles
In the present specification, the volume average particle diameter of the colored resin particles means a value measured with a Coulter Multisizer II (manufactured by Beckman Coulter, Inc.) using a 100 μm aperture.
Specifically, a Coulter Counter TA-II type or Coulter Multisizer II (manufactured by Coulter, Inc.) is used as a measuring device. As the electrolytic solution, a 1% NaCl aqueous solution is prepared using primary sodium chloride. For example, ISOTON R-II (manufactured by Coulter Scientific Japan) can be used.

  As a measuring method, 0.1 to 5 ml of a surfactant, preferably alkylbenzene sulfonate, is added as a dispersant to 100 to 150 ml of the aqueous electrolyte solution, and 2 to 20 mg of a measurement sample is further added. The electrolyte in which the sample is suspended is subjected to a dispersion process for about 1 to 3 minutes with an ultrasonic disperser, and the measuring device is used to measure the volume and number of the toner by measuring the volume and number of toner using a 100 μm aperture as the aperture. Is calculated. The volume average particle diameter is obtained from the volume distribution.

"Saturation magnetization"
In this specification, saturation magnetization refers to a value measured by VSMP-1 manufactured by Toei Kogyo Co., Ltd.

"Volume resistivity"
In this specification, the measurement of the volume resistivity of a core particle and a carrier means the value according to the following procedure. First, 0.2 g of core particles or carriers are filled between two copper plate electrodes having a width of 30 mm and a height of 10 mm, which are installed with a gap of 6.5 mm under an environmental condition of an air temperature of 20 ° C. and a humidity of 65%. . Next, a bridge made of core particles or carriers is formed by the magnetic lines of force of two magnets (100 mT) arranged outside each copper plate electrode so that the N pole and the S pole face each other. In this state, measurement is performed 15 seconds after the application of a voltage of 500V. This measured value is the volume resistivity.

"Coverage"
In this specification, the coverage with the resin layer on the core particle surface means a value calculated by the following method. That is, an electron beam with an acceleration voltage of 2.0 eV is observed using a scanning electron microscope (SEM) without depositing a conductive agent such as gold on the carrier surface. In the carrier, the resin coating layer is observed white by charge-up. On the electron microscope image, the ratio of the white area to the total carrier area is calculated. This calculation is performed for 100 carriers, and the average value obtained is the coverage.

"BET specific surface area"
In this specification, the BET specific surface area means a measurement value obtained by a three-point measurement method using a BET specific surface area measuring device Gemini 2360 (manufactured by Shimadzu Corporation).

"Number average particle size"
In this specification, the number average particle size of the external additive is measured by measuring the particle size of 100 external additives from the obtained image by photographing the external additive using a scanning electron microscope (SEM). And the average value of the obtained particle diameters.

Examples of the present invention will be described below, but the present invention is not limited to the examples.
<Career>
The carriers of Examples and Comparative Examples were produced by the following method.
After mixing the ferrite raw material (manufactured by KDK) in a ball mill, calcining at 900 ° C. in a rotary kiln, the resulting calcined powder has an average particle diameter of about 30 mm by a wet pulverizer (using steel balls as the grinding media). Finely pulverized to 1 μm. The obtained ferrite powder was granulated by a spray drying method, and the granulated product was fired at 1300 ° C. After firing, core particles made of a ferrite component having a volume average particle diameter of about 45 μm and a volume resistivity of 1 × 10 ⁹ Ω · cm were obtained by crushing using a crusher.

  The coating liquid for forming the thermosetting silicone resin layer for coating the core particles is 100 parts by weight of dimethyl silicone resin (manufactured by Toshiba Silicone Co., Ltd.) and boron represented by the following formula (2) as a charge control agent. Prepared by dissolving 10 parts by weight of a compound (LR-147; manufactured by Nippon Carlit Co., Ltd.) and 5 parts by weight of octylic acid as a curing agent in a mixed solvent of toluene: methanol: n-butanol (10: 1: 2). did. In the dip coating apparatus, the core particles were coated by immersing the core particles in the coating liquid. After completely evaporating and removing the solvent, heating was performed at 175 ° C. for 30 minutes to perform thermosetting, and carrier C1 was produced.

Carrier C1 has a charge control agent concentration of 0.05% by weight, a volume average particle diameter of 46 μm, a coverage of 100%, a volume resistivity of 1 × 10 ¹² Ω · cm, and a saturation magnetization at the surface layer of the resin coating layer. It was 65 emu / g.
As shown in Table 1, carriers C2 to C6 were prepared in the same manner as the carrier C1, except that the addition amount of the charge control agent or the mixing ratio of toluene: methanol: n-butanol was different.

<Toner>
A toner was prepared by the following method.
The toner material is described below.
Binder resin (polyester resin obtained by polycondensation using bisphenol A propylene oxide, terephthalic acid or trimellitic anhydride as a monomer: glass transition temperature 60 ° C., softening temperature 115 ° C .; manufactured by Fujikura Kasei Kogyo Co., Ltd.) 100 Part by weight-Colorant (CI Pigment Blue 15: 3) 5 parts by weight-Charge control agent (LR-147: Boron compound; manufactured by Nippon Carlit Co., Ltd.) 2 parts by weight-Release agent (HNP-9) : Microcrystalline wax; Nippon Seiwa Co., Ltd.) 3 parts by weight

The toner material was mixed with a Henschel mixer for 10 minutes, and then melt-kneaded and dispersed at 150 ° C. with a kneading and dispersing apparatus (KNIX MOS140-800; manufactured by Mitsui Mining Co., Ltd.). The kneaded product was cooled and solidified, and then roughly pulverized by a cutting mill and finely pulverized by a jet pulverizer (IDS-2 type; manufactured by Nippon Pneumatic Industry Co., Ltd.). By classifying the finely pulverized product using an air classifier (MP-250 type; manufactured by Nippon Pneumatic Industry Co., Ltd.), the volume average particle size is 6.5 ± 0.1 μm and the BET specific surface area is 1. Colored resin particles of 8 ± 0.1 m ² / g were obtained.

  1 part by weight of silica particles (R8200; manufactured by Evonik) whose surface was treated with hexamethyldisilazane having a number average particle diameter of 12 nm was added to 100 parts by weight of the obtained colored resin particles, and the tip speed of the stirring blade was 15 m. A negatively chargeable toner T1 was produced by stirring for 2 minutes with an airflow mixer (Henschel mixer; manufactured by Mitsui Mining Co., Ltd.) set to 1 sec.

<Two-component developer>
The two-component developers of Examples and Comparative Examples were produced by mixing the carriers C1 to C6 with the toner T1. The mixing of the two components was performed by charging 6 parts by weight of toner and 94 parts by weight of carrier into a Nauta mixer (trade name: VL-0; manufactured by Hosokawa Micron Corporation) and stirring and mixing for 20 minutes.

<Image evaluation>
The produced two-component developer was subjected to a continuous print test using an image forming apparatus (aging tester) as shown in FIG. For the continuous print test, only the image forming unit 1 of the four image forming units of the image forming apparatus was used. As the development conditions of the image forming apparatus, the peripheral speed of the photosensitive member is 400 mm / second, the peripheral speed of the developing roller is 560 mm / second, the gap between the photosensitive member and the developing roller is 0.42 mm, and the gap between the developing roller and the regulating blade is 0.5 mm. The surface potential of the photoconductor and the developing bias are adjusted so that the toner adhesion amount on paper in a solid image (100% density) is 0.5 mg / cm ² and the toner adhesion amount in the non-image area is minimized. did. A4 size electrophotographic paper (multi receiver; manufactured by Sharp Document System Co., Ltd.) was used as a test paper.

  A print test of 50K (50,000) sheets was performed with a text image in which the coverage of the print image recorded on the paper was 6%. Initially, after printing 2K sheets, after 50K printing, the toner charge amount was measured, and the image density and fog density were measured. The measurement method and evaluation method for these values are described below.

The toner charge amount was measured using a suction type small charge amount measuring device (210HS-2A; manufactured by Trek Japan Co., Ltd.).
Regarding the image density, a solid image (100% density) having a side of 3 cm was printed, and the image density of the printed part was measured using a reflection densitometer (RD918; manufactured by Macbeth Co.). The image density is 1.3 or more (paper fiber is completely covered with toner), 1.2 to less than 1.3 is slightly poor, and less than 1.2 (paper fiber is insufficient with toner) The state covered only by

As for the fog density, the density of the non-image area (0% density) was calculated by the following procedure.
Using a whiteness meter (Z-Σ90 COLOR MEASURING SYSTEM; manufactured by Nippon Denshoku Industries Co., Ltd.), the whiteness of the paper before printing and the whiteness in the non-image area of the paper after printing are measured. Was determined as the fog density.
The fog density is less than 0.6 (a state in which the fog is hardly visible to the naked eye), and 0.6 to less than 1.0 is a little poor, and 1.0 or more (a state in which the fog is clearly visible to the naked eye) is bad. .

<Result>
Table 2 shows the results of the continuous print test.

In the developer of Comparative Example 1 in which the charge control agent concentration on the surface layer of the carrier resin layer is less than 0.02% by weight, the charge control agent concentration is too low, so that the effect of the charge control agent cannot be obtained sufficiently. In the initial stage (2K image), an increase in charge amount was observed. The 2K image showed a decrease in image density, and the image quality was not stable.
In the developer of Comparative Example 2 in which the charge control agent concentration on the surface layer of the carrier resin layer exceeds 0.08% by weight, no increase in charge amount was observed in the initial use (2K image), but the charge amount was low. It was not stable. For this reason, fog occurred in the obtained image.

  On the other hand, in the developers of Examples 1 to 4 in which the charge control agent concentration in the surface layer portion of the carrier is 0.02% by weight or more and 0.08% by weight or less, no increase in the charge amount in the initial use is observed. The toner charge amount was stable over a long period of time. The obtained image had a high image density and no fogging occurred. Further, it was satisfactory without white spots due to roughness and carrier adhesion to the photoreceptor.

It is the schematic explaining the covering state by the resin layer of the core particle surface in the carrier of this invention. It is the schematic explaining the distribution of the charge control agent in the resin coating layer in the carrier of FIG. 1 is a schematic diagram illustrating an embodiment of an image forming apparatus of the present invention. FIG. 3 is a schematic enlarged view illustrating one embodiment of a developing unit <image forming unit> in the image forming apparatus of the present invention. In the image forming apparatus of the present invention, a process section <? It is a general | schematic enlarged view explaining the one aspect | mode.

Explanation of symbols

N1, N2, N3, S1, S2 Magnetic pole, P Paper transport direction, R, Rd Rotation direction, 1-4 First to fourth image forming units, 5 Intermediate transfer belt, 6 Support roll, 7 Primary transfer roller, 8 2 Next transfer roller, 10 Belt cleaning unit, 11 Belt cleaning brush, 12 Belt cleaning blade, 13 Paper feed roller, 13a Paper discharge roller, 14 Tray, 15 Fixing unit, 16 Photosensitive drum, 17 Charger, 18 Exposure unit, 19 Developing device, 20 photosensitive drum cleaner, 21 cleaning blade, 22 cleaner housing, 23 seal, 24 developing roller, 25 multipolar magnetized member, 26 sleeve, 27 developing tank, 28 regulating member, 29 stirring member, 30 opening part, 31 Two-component developer, 40 core particles, 41 resin layer, 41 Resin layer surface portion

Claims (6)

A core layer and a resin layer containing a charge control agent and covering the core particle , and the charge control agent is 0.02% by weight or more in the surface layer region of the resin layer with respect to the total weight of the carrier. 08 a method of manufacturing a presence to Ruki Yaria in an amount by weight percent, the resin constituting the charge control agent and the resin layer, and a low polar solvent selected from toluene, acetone and ether, methanol, ethanol And a coating liquid obtained by dissolving in a mixed solvent of a high polarity low boiling point solvent selected from acetonitrile and a high polarity high boiling point solvent selected from propanol, i-propanol, n-butanol and t-butanol And forming a resin layer on the core particles . The charge control agent is represented by the following general formula (1):

(Wherein R ₁ and R ₄ each independently represent a hydrogen atom, an alkyl group, or a substituted or unsubstituted aromatic ring (including a condensed ring), and R ₂ and R ₃ each independently represent a substituted or non-substituted group. The method according to claim 1, which is a boron compound represented by a substituted aromatic ring (including a condensed ring, and X ⁺ represents a cation). The method according to claim 1 or 2, wherein the charge control agent is present in the resin layer in an amount of 5 wt% to 20 wt% with respect to the resin weight. The method according to any one of claims 1 to 3, wherein the resin constituting the resin layer is a dimethyl silicone resin. The method according to claim 1, wherein the core particle includes a ferrite component. A two-component developer comprising a toner and a carrier produced by the method according to claim 1.

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