JP3463840B2 - Carrier for electrostatic image development - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic image developing method used for developing an electrostatic image in, for example, electrophotography, electrostatic recording, electrostatic printing, and the like. It is about a career. 2. Description of the Related Art At present, as an electrostatic image developing system, a so-called two-component developer composed of a toner and a carrier, which are colored particles, is used to form a magnetic brush, thereby forming an electrostatic latent image. A two-component developing system for performing development is known. As a carrier in such a two-component development system, generally, a resin-coated carrier obtained by forming a coating resin layer of an appropriate resin on the surface of core particles made of iron powder or ferrite has been awarded. This is because, by the coating resin layer, suitable chargeability can be exhibited, and the generation of a so-called spent toner in which a part of the toner is fused to the surface of the carrier particles can be effectively prevented.
This is because a great durability can be obtained in the developer. On the other hand, in response to the downsizing of the developing device accompanying the recent downsizing of the image forming apparatus, the developer is supplied in a short time from when the toner is supplied to the developing sleeve to when the toner reaches the actual developing area. It has become necessary to be able to attain a sufficiently charged state beforehand. Conventionally, in order to improve the charge rise characteristics of the toner, it is usual that the toner contains, for example, a charge control agent having a negative charge. It is not enough to only include the charge control agent, and the distribution of the charge amount in the entire toner becomes broad because the proportion of the weakly charged toner having the insufficient charge amount increases, and as a result,
There is a problem that remarkable fogging occurs in a formed image and toner scattering increases in the apparatus. Japanese Patent Laid-Open No. Hei 6-301 discloses a method for improving the charge-starting characteristics of a toner having a negative charge by making the carrier particles contain a magnesium compound having a large positive charge.
No. 245 has proposed this. On the other hand, in order to improve the transportability or fluidity of the toner, means for adding and mixing various inorganic fine particles to the toner powder is widely used. However, in a high humidity environment, the inorganic fine particles may absorb moisture. As a result, the charging performance fluctuates, so that the actual charge amount of the toner is environmentally dependent. As means for suppressing such a tendency, means for adding fine silica particles to the coating resin layer of the carrier so that the same moisture absorption state as in the toner also occurs in the carrier is disclosed in, for example, JP-A-6-308.
777, JP-A-6-266169, JP-A-7-56395, and the like. However, in such means, when the film thickness of the coating resin layer is small, the absolute amount of the silica fine particles contained is limited, and therefore, the desired effect is sufficiently obtained because the amount of absorbed moisture is also limited. On the other hand, if the thickness of the coating resin layer is increased to increase the content of the inorganic fine particles, the strength of the coating resin layer is reduced, so that the developer cannot have high durability. [0005] The present invention has been made based on the above-mentioned circumstances, and its object is to provide:
To provide a carrier for developing an electrostatic image having a coating resin layer, which has a good charge rising property, has a small environment dependency of developing property, has excellent durability, and exhibits stable performance. is there. According to the present invention, there is provided a carrier for developing an electrostatic image, comprising a coating resin layer containing inorganic fine particles on the surface of core particles obtained by sintering a plurality of magnetic grains. Is formed, and in the core material particles, the average particle size of the magnetic grains is 1/100 to 1/100 of the volume average particle size of the core material particles.
/ 10, and the apparent density of the core material particles is 1.50 to 3.
100 g / cm ³ . The carrier for developing an electrostatic image of the present invention has a core resin particle provided with a coating resin layer on the surface thereof, and the core particle has a specific physical property obtained by sintering specific magnetic grains. And the coating resin layer contains inorganic fine particles. Therefore, since the surface of the core material particles of the carrier is porous, the coating resin layer is in a state where it is attached to the core material particles with a large adhesive strength, and as a result, a large proportion of the coating resin layer is formed on the coating resin layer. Inorganic fine particles can be contained, and the action of the inorganic fine particles is sufficiently exhibited. As a result, a good charge start-up property is obtained in the toner, and the environment dependency of the developing property is small, and even in a high humidity environment. Stable development can be achieved. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [Core Particles of Carrier] In the present invention, core particles constituting a carrier are particles obtained by sintering a specific magnetic grain. Examples of the material of the core material particles, that is, the magnetic material constituting the magnetic material grains include iron, ferrite, iron and other metals such as magnetite, nickel, cobalt, copper, zinc, and alloys or compounds containing these metals. Can be. Specifically, from the viewpoint that the volume resistivity is small and the environmental compatibility is good,
Particularly, it is preferably magnetite. The magnetite mentioned here is not limited to one having a complete spinel structure as Fe ₃ O ₄ but may be one having a partially broken spinel structure. Further, a magnetic material having a specific gravity of 3 to 7 is preferable because the stress applied to the developer during stirring and mixing in the developing device is reduced, and the saturation magnetization of the magnetic material is preferably 15 to 7.
What is 80-emu / g is preferable. The core material particles have a volume average particle size of 15 to 1
It is preferably 50 μm, especially 20 to 100 μm
It is preferable that The volume average particle size can be measured by “Microtrac SRA MK-II” (manufactured by Nikkiso Co., Ltd.). The core particles need to be substantially spherical. Here, “spherical” means that the value of the ratio of the minor axis / major axis of the particle is 0.7 to 1.0. When the value of this ratio is less than 0.7, the so-called irregularity becomes excessive and causes carrier scattering, and the stress due to agitation and mixing in the developing device increases, so that the coating resin layer of the carrier peels off. And the carrier is liable to be crushed, thereby lowering the durability and causing an image defect.
The ratio of the minor axis / major axis is determined by, for example, using an electron microscope to determine the ratio of the sample
It can be obtained by actually measuring the ratio of the minor axis / major axis for each of the 00 pieces and calculating the simple average value thereof. The core particles have a volume resistivity value of 1 × 1.
0 it or preferably ^{4 ~1 × 10 15 Ω · cm} , preferably a further ^{1 × 10 5 ~1 × 10 10} Ω · cm. This volume resistivity value is obtained by filling 1.0 g of sample particles in an insulating cylindrical container having a cross-sectional area of 1.0 cm ² and
In addition to obtaining the sample height under a load of g, a current value flowing by applying a DC electric field (for example, 100 V) is measured, and the magnitude (unit: V) of the applied electric field and the current value I
From the numerical values of (unit: A) and the sample height d (unit: cm), the volume resistivity R can be obtained by the following equation. R = V / (I × d) The average particle size of the magnetic grains constituting the core material particles is 1/10 of the volume average particle size of the core material particles.
0 to 1/10, especially 1/75 to
It is preferably within the range of 1/20. When the average particle size of the magnetic grains is smaller than 1/100 of the volume average particle size of the core particles, the mechanical strength of the core particles themselves becomes too small. Is crushed. On the other hand, when it is larger than 1/10, a large adhesive force to a coating resin layer described later cannot be obtained, so that the durability of the carrier is low. The average particle diameter of the magnetic material grains of the core material particles can be shown by taking an image of 100 core material particles with an electron microscope, obtaining the circle-equivalent area diameter of the magnetic material grains themselves, and expressing the number average thereof. . The core particles have an apparent density of 1.50 to 1.50.
It is preferably 3.00 g / cm ³ , especially 1.8 g / cm ^3.
It is preferably from 0 to 2.60 g / cm ³ . The apparent density of the core particles depends on the sintered density of the magnetic grains. The apparent density of the core particles is 1.50 g /
When the particle size is less than cm ³ , the carrier is crushed by stirring in the developing device because the bonding strength between unit grains is too small. On the other hand, when the apparent density exceeds 3.00 g / cm ³ , the degree of porosity in the core particles becomes too small, so that the adhesive strength of the coating resin layer cannot be increased, and the carrier has a high durability. It will be low. In addition, the apparent density of the particles can be measured by the method described in JIS Z-2504. In order to produce the core particles as described above, for example, the following method can be used. First, the raw material α-Fe ₂ O ₃ or the like is pulverized to a particle size
m, and then reduced by heating to 500 to 700 ° C. for several hours under a reducing atmosphere such as hydrogen gas, and the obtained iron oxide was mixed with water to prepare a slurry, and this slurry was sprayed with a spray dryer. After sintering, a sintering process is performed. The sintering process is performed under an atmosphere of an inert gas such as a nitrogen gas or a reducing gas, for example, at a sintering temperature of 1050 to 1200 ° C. and a sintering time of 2 to 6 hours. Thereafter, the obtained sintered body may be crushed and classified to collect required particles. In such a sintering process, the particle size of the magnetic grains constituting the core material particles can be controlled by, for example, selecting the crushed particle size of the raw material, the sintering temperature and the sintering time. In addition, the sintering density can be controlled by adjusting the raw material concentration and spray drying conditions when preparing a slurry by mixing the raw material and water. If the phosphate is added to the raw material at a ratio of 0.01 to 5.0% by weight before the raw material α-Fe ₂ O ₃ is pulverized, a uniform sintered state can be obtained. Obtainable. Here, as the phosphate, for example, calcium phosphate, manganese phosphate, zinc phosphate, potassium phosphate, magnesium phosphate, and other dihydrate phosphates can be used. [Coating resin layer] A coating resin layer is formed on the surface of the core material particles. This coating resin layer contains inorganic fine particles in the resin layer. As the resin constituting the coating resin layer, use of a styrene resin, an acrylic resin, a styrene-acryl resin body, a vinyl resin, an ethylene resin, a rosin modified resin, a polyamide resin, a polyester resin, a silicone resin, and others. Can be. These may be used in combination. The coating amount of the coating resin layer is 0.5 to 10.0% by weight based on the core material particles in a state where the inorganic fine particles are contained.
And particularly in the range of 1.0 to 8.0% by weight. If this proportion is less than 0.5% by weight, the thickness of the coating resin layer becomes too small, and a part of the surface of the core material particles is exposed. As a result, stable charging performance can be obtained. On the other hand, if it exceeds 10.0% by weight, the thickness of the coating resin layer becomes excessively large, the adhesive force to the core material particles becomes relatively low, and the phenomenon of peeling of the coating resin layer easily occurs. . The inorganic fine particles contained in the coating resin layer are:
Although not particularly limited, for example, silica, titania, alumina, a magnesium compound and the like can be mentioned, and those having a small hydrophobicity are preferable. Here, the “degree of hydrophobicity” is based on methanol wettability. In the present invention, when the inorganic fine particles are magnesium oxide, magnesium carbonate, magnesium hydroxide, or a magnesium compound having a surface subjected to a hydroxylation treatment, particularly excellent charge rising in a developer is provided. It is preferable because characteristics can be obtained. Particularly preferred magnesium compounds are single crystal magnesium compounds. Furthermore, it is preferable that these magnesium compounds are obtained by adding an alkali to an aqueous solution of a magnesium salt and heating and / or pressurizing the magnesium compound. In addition, a single crystal magnesium compound useful as inorganic fine particles can be easily obtained by reacting a metal magnesium vapor in a water vapor atmosphere containing no carbon dioxide to generate a single crystal. These inorganic fine particles have an average particle size of 1
２００200 nm, and the BET specific surface area is 500
It is preferably in the range of 10 to 10 m ² / g. In particular,
Average particle size is 5 to 100 nm, BET specific surface area is 200 to
Those having a range of 20 m ² / g are preferable because they have good dispersibility in the coating resin layer. The average particle diameter of the inorganic fine particles is less than 1 nm or the BET specific surface area is 500 m ² / g
When the value exceeds, the inorganic fine particles are likely to be completely buried in the coating resin layer, and it is difficult to sufficiently obtain the effect. On the other hand, when the average particle size exceeds 200 nm or when the BET specific surface area is less than 10 m ² / g, it becomes difficult to uniformly disperse the inorganic fine particles in the coating resin layer, and the ratio of the inorganic fine particles that are present in a free state is reduced. , Good charging characteristics are likely to be impaired. The value of the above average particle diameter can be the value of the number average primary particle diameter measured by a transmission electron microscope “LPA-3000 / 3100” (manufactured by Otsuka Electronics Co., Ltd.). In addition, the value of the BET specific surface area can be a value measured by a one-point method using a “BET specific surface area measuring apparatus Flow Sorb II 2300” (manufactured by Shimadzu Corporation). The inorganic fine particles used in the present invention preferably have an electric resistance of 10 ⁶ to 10 ¹⁰ Ω · cm. As the electric resistance value, a resistance value measured in a state where a constant pressure is applied can be used. In this specification, a volume specific resistance of a volume specific resistance measured at a temperature of 20 ° C. and a relative humidity of 50% is used. The value is adopted. The ratio of the inorganic fine particles in the coating resin layer is as follows:
Preferably from 0.5 to 70% by weight, more preferably from 1 to 6% by weight.
0% by weight. When the proportion is less than 0.5% by weight, the effect of the inorganic fine particles is insufficient. On the other hand, when the proportion exceeds 70% by weight, it becomes difficult to form a good coating resin layer, and sufficient adhesiveness is obtained. , The durability is low. [Formation of Coating Resin Layer] In the present invention, the method of forming the coating resin layer on the surface of the core material particles is not particularly limited, but may be a general dip coating method, a spray coating method, a fluidized bed. Although a coating method or the like may be used, in particular, resin fine particles are used as a material for forming a resin phase for the coating resin layer, and inorganic fine particles are adhered to the core material particles by a mechanical impact force. Preference is given to the dry mechanical impact method of filming. According to this dry mechanical impact method,
Since a coating resin layer having a large adhesive force to the core material particles is formed, a carrier having excellent durability is obtained, and it is easy to uniformly disperse a relatively large amount of inorganic fine particles in the coating resin layer, Further, there is an advantage that use of a liquid such as an organic solvent and water is unnecessary. In the first step of the dry mechanical impact method, the core particles, the resin fine particles for forming the resin layer, and the inorganic fine particles are mixed and stirred by an ordinary stirring device or the like to thereby form the core. The inorganic fine particles are uniformly adhered to the surface of the material particles by physical adhesion and electrostatic adhesion. This first step can be performed without heating or while heating to a temperature at which the resin fine particles slightly soften.
Various mixing and stirring devices can be used to perform the first step, but in practice, it is preferable to use one that can continuously perform the second step that follows. In the second step, the mixture obtained in the first step is mechanically agitated without heating or under heating to repeatedly apply a stronger impact force to the mixture than in the first step, whereby On the surface of the core material particles, a coating resin layer in a state where inorganic fine particles are uniformly dispersed in a resin phase of resin fine particles is formed. In the second step, the temperature of the mixture usually rises to about 30 to 60 ° C. due to spontaneous heat generation due to friction of the mixture even when the heating is not performed, and the heat softens the resin fine particles to form the core material particles. The particles spread and adhere to the surface, and the inorganic fine particles are contained in a dispersed state in the resin layer formed as described above. As a result, a coating resin layer is formed. In the case where the second step is performed under heating, the temperature is preferably set to about 60 to 140 ° C. If the temperature is too high, aggregation of the core material particles is likely to occur. [Toner] The toner constituting the developer together with the carrier according to the present invention is not particularly limited, but is constituted by colored particles containing at least a binder resin and a coloring material. And, in particular, those obtained by adding and mixing an inorganic fine powder to a toner powder. The binder resin of the toner is not particularly limited, but polyester resin is preferably used because good negative charging property can be obtained. Further, in order to further improve the charge rising characteristics, a negatively chargeable charge control agent such as a chromium-containing metal complex such as an azo-based chromium metal complex can be added. As the coloring material used for the toner, for example, carbon black, nigrosine dye, etc. are used for black toner, and pigments necessary for yellow, magenta, and cyan toners include C.I. I. Pigment Blue 1
5: 3, C.I. I. Pigment Blue 15, C.I. I. Pigment Blue 15: 6, C.I. I. Pigment Blue 6
8, C.I. I. Pigment Red 48-3, C.I. I. Pigment Red 122, C.I. I. Pigment Red 21
2, C.I. I. Pigment Red 57-1, C.I. I. Pigment Yellow 17, C.I. I. Pigment Yellow 8
1, C.I. I. Pigment Yellow 154 and the like can be suitably used. Examples of the inorganic fine powder to be added to the toner powder include silica fine powder whose surface has been subjected to a hydrophobic treatment with a silane coupling agent or a titanium coupling agent in view of the ability to impart negative chargeability and fluidity. Titania fine powder is preferably used. The inorganic fine powder preferably has a number average primary particle size of 5 to 100 nm. The electrostatic latent image to be developed with the two-component developer composed of the toner and the carrier described above may be formed on any medium. Usually, a selenium photoconductor, an amorphous silicon photoconductor, an organic semiconductor photoconductor, and the like are widely used for forming an electrostatic latent image. Hereinafter, embodiments of the present invention will be described.
The present invention is not limited to these examples. “Parts” indicates parts by weight. [Production of Toner] A toner powder having a volume average particle diameter of 8 μm was obtained by kneading, kneading, pulverizing and classifying the ingredients shown in the following Table 1, and 100 parts of each toner powder was used. On the other hand, 2.0 parts of hydrophobic silica fine powder having a number average primary particle size of 16 nm was mixed with a Henschel mixer to produce toners TA to TD. [Table 1] [Preparation of Carrier] α-Fe ₂ O ₃ crushed into powder having an average particle diameter of about 1 μm is heated and reduced in a hydrogen atmosphere for several hours, and the obtained iron oxide is mixed with water. A slurry was prepared, and this slurry was sprayed with a spray drier and granulated, and then subjected to a sintering treatment at a sintering temperature of about 1100 ° C. and a sintering time of about 20 hours. The obtained sintered body was crushed and classified to produce core particles MK1 to MK3 for a carrier of the present invention and comparative core particles HK1 to HK3 having the physical properties shown in Table 2 below. [Table 2] A set of resin fine particles and inorganic fine particles shown in Table 3 below was added to 100 parts of each of the core particles obtained as described above, and 100 parts of the core particles shown in Table 4 below.
The mixture was further premixed at the ratio shown in (1), and the mixture was further stirred and mixed using a rotary blade type stirrer, whereby the average film thickness of the layer was about 1.
A coating resin layer having a thickness of 0 μm is formed on the surface of the core material particles, whereby the carriers C1 to C9 of the present invention and the carriers HC1 to H for comparison are formed.
C3 was produced. [Table 3] The average particle size of the resin fine particles in Table 3 is about 0.1 μm.
m, CHMA is cyclohexyl methacrylate, MM
A represents methyl methacrylate and St represents styrene.
The particle size of the inorganic fine particles means an average primary particle size. As silica (SiO ₂ ), hydrophilic silica fine particles having a hydrophobicity of 10 were used, and as the magnesium compound, a single crystal was used. . [Developer] As shown in Table 4 below, the above carriers C1 to C9 and comparative carriers HC1 to HC3 were used.
Were mixed with four types of single-color toners TA to TD to prepare four-component two-color developers of black, yellow, magenta, and cyan with each carrier. Here, the mixing of the toner and the carrier was performed under a condition that the toner concentration was 7% by weight by performing a mixing process for 20 minutes in an environment of a temperature of 30 ° C. and a relative humidity of 80% using a V-type mixer. The set of the developer obtained in this manner is used as a carrier C1 to C9 and a carrier H for comparison.
According to C1 to HC3, developers D1 to D9 and comparative developers HD1 to HD3 are used. [Table 4] [Actual photo test A] A modified machine of an electronic copying machine "U-BIX 3035" (manufactured by Konica) equipped with a negatively chargeable organic photoreceptor was used.
9 and Comparative Developers HD1 to HD3. Here, the remodeling point of the electronic copier is that the charging polarity of the photoconductor is positive, the photoconductor potential of the image portion is changed to 750 V, and the photoconductor potential of the non-image portion is changed to 50 V.
And that the developing bias potential in the developing section is changed to -150V. The image density is 1.3 and the area is 10c.
Using a patch of m ² as a manuscript, under a high-temperature high-humidity atmosphere (denoted as “environment H” in the table) at a temperature of 33 ° C. and a relative humidity of 90%, and a low-temperature low-humidity atmosphere at a temperature of 10 ° C. and a relative humidity of 10% ( In the table, "Environment L" is described.) Each of the lower parts was subjected to 10,000 actual shooting tests, and the developability at the beginning and end of the test and the state of toner scattering after the test were examined. Regarding the developability, the amount of toner adhered per 1 cm ^{2 of} the copied image was determined in mg. Regarding the situation of toner scattering, a particle counter was installed in the electronic copying machine, and the count at the end of the test was examined. [Actual Test B] Non-contact reversal development type multicolor image forming apparatus (color electronic copying machine) "Konica 9"
No. 028 "(manufactured by Konica Corporation) was filled with developers D1 to D9 and developers of respective colors related to comparative developers HD1 to HD3. The developing method of this apparatus is such that the developer adhered on the developing sleeve is thinned by a round bar-shaped magnetic stainless steel developer layer thickness regulating rod provided so as to be in contact with the developing sleeve, and the organic semiconductor is removed. The electrostatic latent image formed on the photosensitive member is developed, and the developing conditions are as follows. Photoconductor surface potential: -700 V DC bias potential: -500 V AC bias potential: 2.2 kV (peak-peak value) Developing sleeve rotation speed: 400 rpm Developing layer thickness: 300 μm Developing layer thickness regulating rod sleeve Pressing force: 5 gf /
mm The diameter of the developer layer thickness regulating rod: 6 mm. Then, an original having a pixel ratio of 5% in a portion to be developed with yellow, magenta, cyan and black toners was used, and the same as in the actual test A. The actual photographing test was carried out 10,000 times under each atmosphere condition, and the developability at the beginning and end of the test and the state of toner scattering after the test were examined. Regarding the developability, the total amount of the four types of toner adhered was determined according to the actual test A. The toner scattering state was the same as in the actual test A. In order to check the durability of the carrier,
After the test, the developer was washed with water to remove the toner, leaving only the carrier.After drying, the coating resin layer of the carrier was dissolved in methyl ethyl ketone, and the weight of the remaining core material particles was measured. The coverage of the carrier was determined by the following equation, and the amount of change in the coverage was further determined. Coverage (% by weight) = {(ab) / b} Here, a is the carrier weight after drying, and b is the weight of the core material particles after dissolving the coating resin layer. Further, after the test is completed, the developer in the developing device is sampled, and the carrier 10
The surface of 0 pieces was observed with an electron microscope, and the number of those having a damaged coating resin layer was examined. The above results are as shown in Tables 5 to 7 below. [Table 5] [Table 6] [Table 7] According to the carrier for developing an electrostatic image of the present invention, the surface of the core particles of the carrier is suitably porous, so that the coating resin layer is in contact with the core particles. Is adhered with a large adhesive strength.As a result, it is possible to make the coating resin layer contain a large proportion of the inorganic fine particles, and the action of the inorganic fine particles is sufficiently exhibited, and as a result, the toner is charged well. As a result, stable development can be achieved even in a high humidity environment, since the rising characteristics can be obtained and the environment dependency of the developing property is small.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Meisho Shirase 2970 Ishikawa-cho, Hachioji-shi, Tokyo Konica Corporation (56) References JP-A-59-228664 (JP, A) JP-A-60-134249 (JP, A) JP-A-5-173372 (JP, A) JP-A-7-261465 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 9/107 G03G 9 / 113

Claims (1)

(57) [Claims 1] A coating resin layer containing inorganic fine particles is formed on the surface of core particles obtained by sintering a plurality of magnetic grains, Wherein the average particle size of the magnetic grains is 1/100 to 1/10 of the volume average particle size of the core material particles,
The apparent density of the core particles is 1.50 to 3.00 g / cm ³
A carrier for developing an electrostatic image.