JP2006235286A - Electrostatic charge image developer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrostatic charge image developer which prevents the degradation in electrostatic chargeability, is excellent in spending resistance, and can form an image stable for a long period of time without being environmentally affected. <P>SOLUTION: The electrostatic charge image developer comprises an electrostatic charge image developing carrier and toner. The carrier is 1.10 to 1.20 in average sphericity, is 1 to 2 in surface characteristic, and does not have a coating resin layer. The toner contains at least alumina as an additive. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrostatic charge image developer used when developing an electrostatic latent image formed by electrophotography, electrostatic recording, or the like.

  In the electrophotographic method, an electrostatic latent image is formed on a photoconductive photoreceptor by charging and exposure, and the latent image is visualized by using an electrostatic charge image developer composed of a carrier and a toner. The toner image on the photoreceptor is transferred to a transfer material to form an image. However, since the toner having a small particle size has a strong adhesive force with the carrier, it is likely to be fused with the surface of the carrier due to the stress received in the developing device and easily generate toner spent. Further, as the toner spent by repeated use increases, the triboelectric chargeability of the carrier changes, which adversely affects image formation.

  Therefore, in Patent Document 1, the generation of toner spent and the generation of fine particle carriers are suppressed by defining the average sphericity of carriers and the ratio of carriers having a constant sphericity. In Patent Document 2, carrier sphericity and surface roughness are defined, and conductive powder is included in the coating resin to prevent deterioration of the carrier with time and to improve stability against environmental fluctuations.

Patent Documents 1 and 2 describe a carrier provided with a coating resin layer in either case. Regarding the carrier provided with the coating resin layer, there are merits that it is excellent in durability and environmental stability, and charging is easily controlled, and various techniques have been disclosed. However, the carrier provided with the coating resin layer is worn out or peeled off due to contact with the toner or contact between the carriers during long-term use, and the chargeability is lowered and the image density is lowered. There is a problem that the spent resistance is also inferior.
Japanese Patent Laid-Open No. 9-244301 JP 2000-221733 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide an electrostatic charge image developer that can prevent deterioration in chargeability, has excellent spent resistance, and can form a stable image over a long period of time without being influenced by the environment. It is in.

  As a result of intensive studies to solve the above problems, the present inventors have found that the electrostatic charge image developing carrier has no coating resin layer and the sphericity and surface properties are controlled within a predetermined range, and at least an external additive. Discovered the new fact that a developer composed of toner containing alumina as an agent is excellent in spent resistance and can form stable images over a long period of time without being affected by the environment. The present invention has been completed.

That is, the electrostatic charge image developer of the present invention is an electrostatic charge image developer comprising an electrostatic charge image developing carrier and a toner, and the carrier has an average sphericity represented by the following formula (1) of 1. 10 to 1.20, the surface property represented by the following formula (2) is 1 to 2, it does not have a coating resin layer, and the toner contains at least alumina as an external additive. It is characterized by being.

  According to the electrostatic charge image developer of the present invention, a carrier having an average sphericity of 1.10 to 1.20 and a surface property of 1 to 2 and a toner externally added with alumina (aluminum oxide) are used. Even though the coating resin layer is not provided on the carrier, it has excellent durability and spent resistance, and can form a stable image over a long period of time without being influenced by the environment. Since the wear of the coating resin layer seen in the carrier provided with the resin layer does not occur, it is possible to prevent a decrease in chargeability.

  The electrostatic charge image developer of the present invention does not have a coating resin layer, has an average sphericity of 1.10 to 1.20, a surface property of 1 to 2, and at least an external additive. And a toner containing alumina as an agent.

<Carrier for developing electrostatic image>
The carrier used in the present invention is a so-called non-coated carrier that does not include a coating resin layer. The carrier including the coating resin layer is excellent in durability and environmental stability, and charging is easily controlled. Further, if there are many irregularities on the surface of the carrier, it is advantageous to have a coating resin layer because it can be firmly fixed to the carrier core by the anchor effect. However, when the carrier including the coating resin layer is used for a long period of time, the coating resin layer is worn or peeled off due to contact with the toner or contact between the carriers, and the surface property of the carrier changes, and the charging property is decreased. Fog associated with the quantity distribution is likely to occur. Therefore, in the present invention, a carrier for developing an electrostatic charge image is used in which the coating resin layer is not provided and the sphericity and surface properties are controlled within a predetermined range.

(Sphericity)
The average sphericity of the carrier in the present invention is 1.10 to 1.20, preferably 1.12 to 1.17. The closer the sphericity is to 1, the closer the shape is to a true sphere. In the present invention, by adjusting the average sphericity of the carrier to 1.10 to 1.20 so as to be close to a true sphere, the fluidity of the carrier can be improved and the charge rising of the toner can be accelerated. When the sphericity of the carrier is greater than 1.20, uniform charging cannot be obtained, the charge amount distribution is easily disturbed, and there is a problem in durability. On the other hand, when the average sphericity of the carrier is less than 1.10, that is, when the shape is too close to a true sphere, the charge rising of the toner is worsened, and reversely charged toner or weakly charged toner is generated, resulting in fog. Will increase. This is particularly remarkable in a high-temperature and high-humidity environment where the charge amount is low.

  The sphericity and average sphericity of the carrier are obtained using the above formula. Specifically, when the sphericity is obtained, the maximum carrier diameter (L) and the area of the carrier projection image (S) are used, and when the average sphericity is obtained, the number of carriers and the total sphericity are used. . The values for obtaining the sphericity and average sphericity can be measured, for example, by observing the carrier with a scanning electron microscope (SEM) and using a personal image system (LA-525 manufactured by JEOL Ltd.).

(Surface property)
The surface property of the carrier in the present invention is 1 to 2, preferably 1.2 to 1.9. The larger the surface property value, the finer the surface is, and the smaller the surface property value is, the smaller the surface property is. (The smaller the unevenness is, the closer it is to 1 and the larger the unevenness is, the larger it is.) In the present invention, by adjusting the surface property of the carrier to 1 to 2 and reducing the unevenness on the surface of the carrier, it is difficult to spend and uniform. Excellent charging and excellent durability. When the surface property of the carrier is greater than 2, there are many irregularities, and toner fine powder enters the recesses, and the adhesion of the toner is improved, and spent tends to occur. For this reason, the developer is deteriorated, the charging performance is lowered, the reverse polarity toner or the weakly chargeable toner is generated, and the fog increases.

The surface property of the carrier can be determined by the above formula (2). The true spherical equivalent specific surface area (S _A ) in the formula can be measured using, for example, a laser diffraction particle size distribution analyzer HELOS (manufactured by JEOL Ltd.) equipped with a wet disperser. The actual specific surface area (S _B ) of the carrier can be measured with a BET specific surface area meter Flow Soap II 2300 (manufactured by Shimadzu Corporation). The true spherical equivalent surface area (S _A ) is a value obtained by measuring the surface area of a certain number of carriers by measuring the diameter of a random portion from a certain direction and assuming that the carrier is a true sphere having the diameter as a diameter. The actual specific surface area (S _B ) of the carrier is a value obtained based on the BET surface area measurement method for measuring the amount of adsorption of gas molecules adsorbed only on the carrier surface.

Note that, in the carrier of the present invention that does not have a coating resin layer, when the electric resistance is low, the carrier may fly or the carrier may adhere to the photosensitive member. Therefore, in the present invention, it is preferable to use a carrier having a certain resistance value or more. For example, when the value of static resistance by the bridge method is measured using a carrier 0.2 g and a bridge-type electric resistance measuring device, the value when a voltage of 1000 V is applied is 3.5 × 10 ⁸ Ω · cm to 7. It preferably has an electric resistance of 0 × 10 ⁸ Ω · cm. When a voltage of 100 V is applied under the same conditions, it preferably has an electric resistance of 8.0 × 10 ⁹ Ω · cm to 7.0 × 10 ¹⁰ Ω · cm.

  Examples of the carrier that can be used in the present invention include a carrier made of a known magnetic material such as ferrite, magnetite, lithium, manganese, or iron powder.

As the magnetic powder used for the production of the carrier, a known magnetic powder can be used. For example, ferromagnetic iron such as triiron tetroxide (Fe ₃ O ₄ ), diiron trioxide (Fe ₂ O ₃ ), etc. Oxide, zinc iron oxide (ZnFe ₂ O ₄ ), iron yttrium oxide (Y ₃ Fe ₅ O ₁₂ ), cadmium oxide (CdFe ₂ O ₄ ), iron gadolinium oxide (Gd ₃ Fe ₅ O ₁₂ ), copper iron oxide ( CuFe ₂ O ₄ ), lead iron oxide (PbFe ₁₂ O ₁₉ ), neodymium iron oxide (NdFeO ₃ ), barium oxide (BaFe ₁₂ O ₁₉ ), iron manganese oxide (MnFe ₂ O ₄ ), iron lanthanum oxide (LaFeO ₃₎ ), Or a ferrite such as a composite thereof, or a ferromagnetic metal or alloy such as iron (Fe) powder, cobalt (Co) powder, nickel (Ni) powder, or the like can be used alone or in combination. The particle shape of the magnetic material is not particularly limited, and may be any shape such as a spherical shape, a cubic shape, or an indefinite shape. Further, a carrier may be manufactured by adding a metal oxide such as copper oxide (CuO) or zinc oxide (ZnO), phosphorus (P), or the like to the metal or the like.

  The ferrite carrier can be manufactured, for example, by the following method. First, the raw material is temporarily fired and then poured into water and pulverized with a ball mill or the like. Further, polyvinyl alcohol is added as a binder, and an antifoaming agent, a dispersing agent and the like are added to obtain a slurry for granulation. As the binder, the dispersant, and the like, a material that is decomposed or burned during firing and scattered and selected so as not to adversely affect the process and the formation of ferrite is selected. Next, this slurry is granulated while being heated and dried with a spray dryer. The granulated and dried product is spherical and is generally called a granule. The granules are filled in an alumina container and fired. A tunnel electric furnace is usually used for firing the ferrite. The firing temperature is 900 to 1400 ° C., and the firing time is 10 to 30 hours. In order to control electric resistance as a carrier, cooling after firing may be performed in a nitrogen atmosphere. In this firing step, a solid phase chemical reaction occurs and a ferrite carrier is completed.

As a specific example of carrier production, first, phosphorus (P) is added to and mixed with a mixture of ferric trioxide (Fe ₂ O ₃ ), copper oxide (CuO) and zinc oxide (ZnO), and then a heating furnace (Heated). Next, the calcined product is cooled and then pulverized, and a dispersant and water are added to prepare a slurry. Thereafter, the slurry is pulverized, granulated and dried to produce a granulated product. Further, the granulated product is loaded into a firing furnace and fired in a mixed gas of nitrogen gas and oxygen gas to obtain a fired product. The obtained fired product is pulverized with a pulverizer and then sieved to obtain a carrier. Here, in order to produce a carrier having a surface property of 1 to 2, the firing temperature may be 1120 to 1180 ° C. In order to obtain an average sphericity of 1.10 to 1.20, phosphorus (P) may be added and mixed, and then heated (calcined) in a heating furnace. Further, in order to adjust the resistance value of the carrier, the addition amount of phosphorus (P) may be adjusted. In the present invention, the addition amount of P is changed to diiron trioxide (Fe ₂ O ₃ ), copper oxide (CuO), and zinc oxide. It is preferable to set it as 2.0 to 2.5 weight% with respect to the mixture of (ZnO).

<Toner>
The toner used in the present invention contains at least alumina (aluminum oxide) as an external additive. When alumina is contained as an external additive, the charge amount distribution is sharper, stable even when the environment changes and when used for a long time, and the generation of fog can be suppressed. In particular, such an effect is noticeable in the negatively chargeable toner.

  Examples of the alumina that can be used in the present invention include alumina powder having a particle size of 0.1 μm to 0.5 μm, and specific examples thereof include alumina oxide C (manufactured by Nippon Aerosil Co., Ltd.). The amount of alumina added may be determined in consideration of the suppression of fog generation and the like, but is 0.1 to 1.0 part by weight, preferably 0.2 to 0.5 part by weight based on 100 parts by weight of the toner particles. Good part.

  The toner used in the present invention is not particularly limited, and examples thereof include a toner manufactured using a release agent, a charge control agent, a colorant and the like together with a binder resin.

(Binder resin)
The type of the binder resin is not particularly limited. For example, polystyrene resin, polyacrylic resin, styrene-acrylic copolymer, polyethylene resin, polypropylene resin, vinyl chloride resin, polyester resin, polyamide And thermoplastic resins such as styrene resins, polyurethane resins, polyvinyl alcohol resins, vinyl ether resins, N-vinyl resins, and styrene-butadiene resins.

  The polystyrene resin may be a styrene homopolymer or a copolymer with another copolymerizable monomer copolymerizable with styrene. As copolymerizable monomers, p-chlorostyrene; vinyl naphthalene; ethylene unsaturated monoolefins such as ethylene, propylene, butylene, and isobutylene; vinyl halides such as vinyl chloride, vinyl bromide, and vinyl fluoride; vinyl acetate, propion Vinyl esters such as vinyl acrylate, vinyl benzoate, vinyl butyrate; methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, dodecyl acrylate, n-octyl acrylate, 2-chloroethyl acrylate, acrylic (Meth) acrylic acid esters such as phenyl acid, methyl α-chloroacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate; other acrylic acid derivatives such as acrylonitrile, methacrylonitrile, acrylamide; Vinyl ethers such as nyl methyl ether and vinyl isobutyl ether; Vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone and methyl isopropenyl ketone; N-vinyl pyrrole, N-vinyl carbazole, N-vinyl indole, N-vinyl pyrrolidene, etc. N-vinyl compounds of One of these copolymerization monomers can be copolymerized alone with the styrene monomer, or two or more of these copolymerization monomers can be copolymerized with the styrene monomer. The polystyrene resin preferably has two weight average molecular weight peaks (low molecular weight peak and high molecular weight peak). Specifically, the low molecular weight peak is preferably in the range of 3000 to 20000, and the other high molecular weight peak is preferably in the range of 300000 to 1500,000. Furthermore, it is preferable that Mw / Mn is 10 or more for the weight average molecular weight (Mw) and the number average molecular weight (Mn). If the weight average molecular weight peak is within such a range, the toner can be easily fixed, and offset resistance can be improved.

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

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

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

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

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

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

  The addition amount of the charge control agent is 0.1 to 10.0 parts by weight, preferably 0.1 to 5.0 parts by weight with respect to 100 parts by weight of the binder resin. If the amount of the charge control agent added is less than the above range, it may be difficult to stably charge the toner, and the electrostatic latent image was developed using the toner to form an image. In some cases, a decrease in image density may occur. On the other hand, when the amount of the charge control agent is larger than the above range, there may be disadvantages such as environmental resistance, particularly charging failure or image failure under high temperature and high humidity, and contamination of the photoreceptor.

(Coloring agent)
The colorant is not particularly limited, and examples thereof include magenta, cyan and yellow colorants. These colorants are added in an amount of 2 to 20 parts by weight, preferably 4 to 15 parts by weight, based on 100 parts by weight of the binder binder resin.

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

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

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

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

(Production method)
A predetermined amount of a binder resin, a release agent, a charge control agent, and a colorant are added, and the mixture is stirred and mixed by a mixing device such as a Henschel mixer. Next, the mixture is melt-kneaded with a twin screw extruder or the like, cooled, and then pulverized with a pulverizer such as a hammer mill or a jet mill. Next, toner particles having a predetermined particle diameter are obtained using a classifier such as an air classifier.

<Electrostatic image developer>
The electrostatic image developer of the present invention comprises the carrier and the toner. In the present invention, when an electrostatic charge image developer is obtained by mixing a carrier and a toner, the amounts of the carrier and the toner are not particularly limited, and may be determined in consideration of spent resistance and stable image formation. However, the carrier may be contained in an amount of 90 to 97% by weight, preferably 94 to 96% by weight, and the toner is contained in an amount of 3 to 10% by weight, preferably 4 to 6% by weight, based on the total amount of the electrostatic charge image developer. It is good.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further in detail, this invention is not limited to a following example.

[Example]
<Manufacture of carriers>
(Manufacture of carrier A)
First, a mixture composed of ferric trioxide (Fe ₂ O ₃ ), copper oxide (CuO), and zinc oxide (ZnO) was prepared. The content thereof was 53 mol% Fe ₂ O ₃ , 23.5 mol% CuO and 23.5 mol% ZnO with respect to the total mixture. Next, 2.0% by weight of phosphorus (P) was added to the mixture to prepare a raw material.

  The prepared raw materials were mixed well and calcined by heating in an air atmosphere (900 ° C., 3 hours). The obtained calcined product is cooled, pulverized to about 1 μm with a pulverizer, and a dispersant (trade name: San Nopco SN Dispersant 5468) is added with water at a ratio of 1% by weight with respect to the dry powder. A slurry with a concentration of 70% was obtained. This slurry was pulverized with a wet ball mill, and granulated and dried with a spray dryer to obtain a granulated product composed of dried particles having an average particle diameter of 70 μm. Next, this granulated product was loaded into a firing furnace and fired at 1160 ° C. for 3 hours in a mixed gas in which the oxygen concentration in nitrogen gas was adjusted to about 2% by volume. The fired product was pulverized with a pulverizer and then sieved to obtain carrier A (ferrite particles) having an average particle size of 55 μm.

(Manufacture of carrier B)
A carrier B having an average particle size of 55 μm was obtained in the same manner as the carrier A, except that the addition amount of P was changed to 2.5 wt% and the firing temperature was changed to 1180 ° C.

(Manufacture of carrier C)
A carrier C having an average particle size of 55 μm was obtained in the same manner as the carrier A except that the firing temperature was changed to 1120 ° C.

(Manufacture of carrier D)
A carrier D having an average particle size of 55 μm was obtained in the same manner as the carrier A except that the addition amount of P was changed to 2.5 wt% and the firing temperature was changed to 1140 ° C.

(Manufacture of carrier E)
A carrier E having an average particle size of 55 μm was obtained in the same manner as the carrier A except that the addition amount of P was changed to 2.5% by weight, the firing temperature was changed to 1120 ° C., and calcining was not performed. It was.

(Manufacture of carrier F)
A carrier F having an average particle size of 55 μm was obtained in the same manner as the carrier A except that the firing temperature was changed to 1220 ° C.

(Manufacture of carrier G)
A carrier G having an average particle size of 55 μm was obtained in the same manner as the carrier A except that the firing temperature was changed to 1080 ° C.

(Manufacture of carrier H)
Carrier H having an average particle size of 55 μm was obtained in the same manner as Carrier A, except that the addition amount of P was changed to 1.0 wt% and the firing temperature was changed to 1060 ° C.

(Manufacture of Carrier I)
First, a coating resin solution (resin solution of KR9706: manufactured by Shin-Etsu Chemical Co., Ltd.) and melamine resin (370: manufactured by Mitsui Cytec Co., Ltd.) dissolved in toluene at a ratio of 5: 5 (weight ratio). The total amount of the resin was 20% by weight with respect to the total weight), and the carrier A was prepared as a carrier core. Next, the coating resin liquid is added at a ratio of 0.25% by weight with respect to the carrier core, charged into a container of a stirrer, and mixed and stirred while the carrier core is immersed in the resin liquid for a predetermined time. The particles were coated with a coating resin. This coating resin was loaded into a fixed heating apparatus, heated and held at 200 ° C. for 2 hours to cure the resin, sieved, and carrier I having an average particle diameter of 60 μm and a coating resin layer was obtained.

(Manufacture of carrier J)
A carrier J having a coating resin layer with an average particle size of 60 μm was obtained in the same manner as the carrier I except that the coating resin solution was added at a ratio of 0.50% by weight to the carrier core.

(Manufacture of carrier K)
A carrier K having an average particle size of 60 μm and a coating resin layer was obtained in the same manner as the carrier I except that the carrier B was used as the carrier core.

(Manufacture of carrier L)
A carrier L having a coating resin layer with an average particle diameter of 60 μm was obtained in the same manner as the carrier I except that the carrier E was used as the carrier core.

  About the obtained carrier, average sphericity, surface property, and resistance (static resistance) were measured. The average sphericity is observed with a scanning microscope (SEM) at a magnification of 150 times, the maximum diameter of the carrier projection image and the area of the carrier projection image are measured by a personal image system (LA-525 manufactured by JEOL), and Calculated using the formula. In the calculation, the number of carriers was 50. The results are shown in Table 1.

  In the measurement of the surface property of the carrier, first, the actual specific surface area of the carrier is measured using a BET specific surface area meter (Flow Soap II model 2300 manufactured by Shimadzu Corporation), and a laser diffraction particle size distribution measuring instrument equipped with a wet disperser ( The true spherical equivalent specific surface area was measured using HELOS) manufactured by JEOL. The surface property of the carrier was calculated using the measurement result and the above formula. The results are shown in Table 1.

  The carrier resistance (static resistance) was measured by the bridge method. Specifically, 0.2 g of carrier is set in a bridge type electric resistance measuring device (electrode interval 2 mm), and the magnet is moved back and forth five times before and after approaching the electrode terminal. A measuring instrument and a superinsulator were connected, voltages were applied in the order of 1000 V and 100 V, and values indicated by the superinsulator were read 10 seconds after the voltage application. The results are shown in Table 1.

<Manufacture of toner>
Each material shown in the following (a) to (d) was premixed with a Henschel mixer and then melt-kneaded using a twin-screw extruder. Next, the melt-kneaded product was cooled, pulverized with a jet mill, and air-classified with a classifier to obtain toner particles with an average particle size of 8.0 μm.
(A) Resin (70: 28: 2 copolymer by weight ratio of styrene-carboxyl tbutyl methacrylate-acrylic acid, molecular weight 300000, Mw / Mn32) 100 parts by weight (b) Colorant (carbon black [MA-100] (Mitsubishi Chemical Corporation)) 10 parts by weight (c) Magnetic powder (Magnetite [BL-100] (Titanium Industry Co., Ltd.)) 2 parts by weight (d) Charge control agent (Bontron S-34 (Orient) Chemical industry)) 1 part by weight

  The following external additives were added to the toner particles and mixed and dispersed for 2 minutes with a Henschel mixer to obtain toners A and B. In addition, the addition amount shown below was shown by the weight part with respect to 100 weight part of toner particles.

(Toner A)
・ Alumina (alumina oxide C, manufactured by Nippon Aerosil Co., Ltd.) 0.3 part by weight ・ Silica (R972, manufactured by Nippon Aerosil Co., Ltd.) 0.3 part by weight ・ Titanium oxide (STT65C, manufactured by Titanium Industry Co., Ltd.) 0.3 part by weight (toner B)
・ Silica (R972, manufactured by Nippon Aerosil Co., Ltd.) 0.3 part by weight ・ Titanium oxide (STT65C, manufactured by Titanium Industry Co., Ltd.) 0.3 part by weight

[Examples 1 to 3 and Comparative Examples 1 to 12]
<Preparation of electrostatic charge image developer>
45 g of the toner and 955 g of the carrier were placed in a plastic container, and stirred for 120 minutes at 75 rpm of the container using a ball mill to prepare an electrostatic charge image developer. The toner and carrier used are shown in Tables 2-4.

<Evaluation test of electrostatic image developer>
The following evaluation test was performed using the produced electrostatic charge image developer. The evaluation test was performed in three environments: (1) room temperature 23 ° C. relative humidity 50%, (2) room temperature 10 ° C. relative humidity 15%, and (3) room temperature 32 ° C. relative humidity 80%. Tables 2 to 4 show the test results under these circumstances. The test items are as follows.

(Image density test and fog test)
Under each environment, a developer was set in a copying machine (Anessis602 Kyocera Mita Co., Ltd.), and the image density and fogging after initial and after 100,000 copies were measured. In the measurement of image density and fog, a reflection densitometer (TC-6D manufactured by Tokyo Denshoku Co., Ltd.) was used to measure the density of the printer image solid black portion and the non-image portion. Note that the image density was the density of the solid black portion of the copy image, and the fog was (density of the non-image area) − (density of the base paper). The evaluation criteria for image density and fog are as follows.
Image density evaluation criteria ○: 1.3 or more Δ: 1.2 to 1.3
×: Less than 1.2 / Fog evaluation criteria ○: Less than 0.008 ×: 0.008 or more

(Carrier adhesion test)
After copying 100,000 sheets in the image density test and the fog test, the photoreceptor was visually observed to determine the presence or absence of an image in the circumferential direction of the photoreceptor due to carrier adhesion, and the presence or absence of carrier adhesion was determined. The evaluation criteria for carrier adhesion are as follows.
・ Evaluation criteria for carrier adhesion ○: No carrier adhesion ×: Carrier adhesion (level of adhesion causing problems in actual use)

(Measurement of reversely charged toner amount)
The charge amount distribution of the developer was measured with a charge amount distribution measuring device “Espert Analyzer EST-1” (manufactured by Hosokawa Micron Corporation), and the reverse toner amount (count%) was determined.

(Measurement of spent amount)
3 g of the developer obtained above is placed on a 400-mesh sieve, and only the toner in the developer is sucked with a vacuum cleaner. Next, the carbon amount (C amount) of the developer remaining on the sieve was measured with a carbon analyzer (HORIBA, EMIA 110 type), and the spent amount was determined from the difference from the C amount of the new carrier.

  According to Tables 2 to 4, in Examples 1 to 3 using a developer composed of any one of the carriers A, B and C and the toner A containing alumina, the image density is 1.3 or more. It can be seen that good results were obtained without the occurrence of fog and reversely charged toner.

  On the other hand, Comparative Examples 1 to 3 using Toner B containing no alumina, Comparative Examples 4 to 6 using a carrier having an average sphericity outside the range of 1.10 to 1.20, and a surface property of 1 In Comparative Examples 7 to 8 using a carrier outside the range of ~ 2 and Comparative Examples 9 to 12 using a carrier provided with a coating resin layer, fog and reversely charged toner are generated after printing 100,000 sheets Therefore, it is not suitable for printing a large number of sheets.

  In Comparative Example 8, “-” is described in the test result, but the amount of reversely charged toner at the start shows a high numerical value, and furthermore, a large amount of carrier adhesion occurred, so the test was interrupted. This is presumably because the use of a carrier having a large surface property value of 3.76 reduces the chargeability of the carrier, generates reversely chargeable toner, and the carrier adheres to the photoreceptor.

Further, in the carrier provided with the coating resin layer, the spent amount tends to be large. In particular, in Comparative Examples 10 to 12, the spent amount is 0.19 or more under any environment, and good results are obtained. You can see that it wasn't.

Claims (1)

An electrostatic image developer comprising an electrostatic image developing carrier and toner,
The carrier has an average sphericity represented by the following formula (1) of 1.10 to 1.20, a surface property represented by the following formula (2) of 1 to 2, and has a coating resin layer. Not
The electrostatic image developer, wherein the toner contains at least alumina as an external additive.