JP2006317620A - Carrier powder for electrophotographic development and developer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carrier powder for electrophotographic development which is free from Mn, so that it is not harmful to the environment, and which excels in peeling resistance (durability) and charge maintaining property of a resin coating layer and excels also in image properties. <P>SOLUTION: The carrier powder for electrophotographic development has ferrite particles, as a core material, obtained as follows; a mixed slurry whose composition is regulated so that Fe and Mg contents satisfy the formula (1): (MgO)<SB>X</SB>(Fe<SB>2</SB>O<SB>3</SB>)<SB>100-X</SB>(where X is 5-35 (mol%)) is prepared using Fe<SB>2</SB>O<SB>3</SB>as an Fe source and an Mg(OH)<SB>2</SB>-containing material as an Mg source, and a dried material of the slurry is calcined and size-controlled. The core material preferably has dimples having an average of shape ratio A of 0.03-0.09 formed on the surface thereof, wherein the shape ratio A is defined by the formula (2): shape ratio A=(dimple depth)/(dimple diameter). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a carrier powder for electrophotographic development used in an electrophotographic dry development method, and a developer using the carrier powder.

  The electrophotographic dry development method is a method in which powder toner as a developer is attached to an electrostatic latent image on a photosensitive member, and the attached toner is transferred to a predetermined paper or the like for development. Here, as the developer, a two-component development method using a two-component developer containing toner and a carrier powder for electrophotographic developer (hereinafter simply referred to as “carrier powder”), and a one-component system containing only toner. It is divided into a one-component development method using a developer. In recent years, toner charge control is easy, stable image quality can be obtained, and high-speed development is possible. In most cases, a two-component development method is used.

  In recent years, carriers using soft ferrites such as Ni—Zn ferrite, Cu—Zn ferrite, or Cu—Zn—Mg ferrite have been used to obtain high quality images in a two-component development method. These soft ferrite carriers have many advantageous properties for obtaining high-quality images as compared with conventionally used iron powder carriers. However, recently, environmental regulations have become stricter, and the use of metals such as Ni, Cu, and Zn has been avoided. In addition, Mn-Mg based ferrite as disclosed in Patent Documents 1 and 2 has also been proposed in consideration of the environment, but in recent years, since Mn has been designated as a PRTR material, there is a movement to refrain from using Mn. Mn-free ferrite powder has been desired.

  Patent Document 3 discloses a carrier containing iron, oxygen, and magnesium as main constituents as a carrier using environment-friendly Mn-free ferrite powder. However, no particular consideration is given to the adhesion to the insulating resin covering the carrier surface and the charge retention, and further improvements are desired.

  On the other hand, Patent Document 4 discloses a carrier powder using a core material (core material) having dimples formed on the surface thereof. It is said that the core material on which dimples are formed has good wear resistance and durability of the resin coating layer, and little changes with time in charging characteristics and resistance value characteristics. However, even those having such dimples exhibited a decrease in adhesion to the resin, durability, and charge retention when Mn-free.

JP 58-123552 A JP 59-111159 A JP 2001-154416 A Japanese Patent No. 2933780

  The present invention intends to develop and provide an environment-friendly Mn-free carrier powder that is excellent in peeling resistance (durability) and charge maintenance of a resin coating layer and excellent in image characteristics.

The above object is a carrier powder having substantially spherical particles of Mg ferrite in the core, and in particular, Fe ₂ O ₃ is used as the Fe source, and Mg (OH) ₂ containing material is used as the Mg source. An electrophotographic developer carrier having a ferrite particle obtained by adjusting the particle size after making a mixed slurry whose composition is adjusted so that the content of the composition satisfies the following formula (1), firing a dried product of the slurry, and adjusting the particle size Achieved with powder.
(MgO) _X (Fe ₂ O ₃ ) _100-X where X is 5 to 35 (mol%) (1)

Here, examples of the Mg (OH) ₂ -containing material include magnesium hydroxide Mg (OH) ₂ and magnesium hydrate, such as 3MgCO ₃ .Mg (OH) ₂ .3H ₂ O. In addition, a mixture of these or a mixture of magnesium oxide may be mentioned. A mixed slurry to which a C-containing material for adjusting sinterability is added is a suitable target. The particle size can be adjusted by pulverization (that is, pulverization) to obtain primary particles, and sieving or classification.

The ferrite particles as the core material have, for example, a composition satisfying the above formula (1), and dimples having an average shape ratio A defined by the following formula (2) of 0.03 to 0.09. It has a structure with a surface.
Shape ratio A = Dimple depth / Dimple diameter (2)

Here, the “dimple diameter” in equation (2) is the long diameter of the dimple, and the “dimple depth” is a cross section including the long axis of the dimple and the center of the particle (the center of gravity when it is assumed to be homogeneous). In this case, the depth is the deepest position in the dimple shape appearing in the cross section. The average of the shape ratio A is an average value of A values measured for individual dimples. Actually, in microscope observation, 10 or more dimples appearing in the field of view for a certain particle are selected at random, and the A value is calculated. The operation of obtaining an average value can be performed on 10 or more randomly selected particles, and the total average value can be calculated and represented by the obtained value. Whether the composition satisfies the formula (1) can be determined by whether X falls within the range defined by the formula (1) in the ratio of Fe to Mg expressed in atomic%. However, it is necessary to support that the particles have a ferrite structure having a composition represented by (MgO) _X (Fe ₂ O ₃ ) _100-X by X-ray diffraction or the like. In general, since composition analysis includes measurement errors, it is rare that the analysis values (atomic ratio) of the three of Fe, Mg, and O strictly satisfy the formula (1). Adopted.

  A carrier powder for electrophotographic development is constructed by forming a resin coating layer on the surface of the core material. Then, a two-component electrophotographic developer comprising a toner and this carrier powder is provided.

  According to the present invention, an environmentally friendly carrier powder having a simple composition Mg ferrite not containing substances subject to environmental regulations such as Ni, Cu, Zn, and Mn is formed on the surface of the core material. Fine dimples have provided significantly improved durability and charge retention, which have not been solved in the past. That is, the resin coated on the particle surface is difficult to peel off from the core material even when subjected to mechanical stress, and can maintain excellent properties in repeated use over a long period of time. This carrier powder is also excellent in terms of image characteristics. Further, since the dimples on the surface of the core material are mainly formed in the firing process, it is not necessary to perform a pulverization process or a surface modification process under special conditions control after the firing, and the productivity is excellent. Therefore, the present invention responds to the recent needs for carrier powders that are becoming increasingly strict in environmental protection.

  As described above, when dimples are formed on the surface of the core material of the carrier powder, it is generally considered that the durability and charge retention of the resin coating layer are improved. In Patent Document 4, physical treatment and chemical treatment are cited as means for forming dimples on the surface of the core material (paragraphs 0009 and 0010). The physical treatment uses mechanical compression, shearing, impact, and friction by a ball mill or the like. The chemical treatment uses sintering, agglomeration, dipping, heating, or electrolysis by a powder production process or a surface modification treatment. However, Patent Document 4 does not show a specific method for forming a desired dimple at the time of firing. Basically, physical treatment (paragraph 0014) or chemical treatment (paragraph) is performed on the fired particles. The dimples are formed by applying 0017).

  As a result of various studies, Mn ferrite, Mn—Mg ferrite, and Cu—Zn ferrite are inherently good in sinterability, and volatile components are easily removed during firing. For this reason, it was found that dimples were not formed or very difficult to form during firing. The ferrite used in Patent Document 4 described above is also considered to be of this type.

  In the present invention, Mg ferrite is employed as the Mn-free ferrite. Mg ferrite has poor sinterability compared with the above-mentioned various ferrites. For this reason, it was considered that the gas component was not easily removed by firing, and that dimples were easily formed on the primary particle surface during firing. If dimples are formed during firing, it is expected that treatment for forming dimples after firing is unnecessary. However, it has been found that it is not always easy to obtain a dimple formed so as to improve the desired characteristics.

As a result of detailed investigations, the inventors have found that when the following requirements are satisfied, a core material of Mg ferrite particles that provides improved durability and charge retention can be obtained.
[1] Use Fe ₂ O ₃ as the Fe source and Mg (OH) ₂ containing material as the Mg source in the starting material before firing.
[2] The composition is adjusted so that the contents of Fe and Mg satisfy the following formula (1).
(MgO) _X (Fe ₂ O ₃ ) _100-X where X is 5 to 35 (mol%) (1)
The mechanism by which a good one can be obtained under such conditions is not yet elucidated, but the volatile component removal during the firing process may be a suitable state for obtaining the desired dimple shape. Inferred.

Further, in the case of Mg ferrite, it has been clarified that dimples having a desired shape necessary for improving the above characteristics are finer than those disclosed in Patent Document 4. Specifically, dimples having an average shape ratio A defined by the following formula (2) of 0.03 to 0.09 are preferable.
Shape ratio A = Dimple depth / Dimple diameter (2)
Focusing on the size of the dimples and ferrite particles, it is preferable that the dimples have an average size ratio B defined by the following formula (3) of 0.002 to 0.05.
Size ratio B = dimple diameter / particle diameter (3)
Also in this case, the long diameter is adopted as the dimple diameter. The particle diameter means the long diameter of the ferrite particle. As for the average of the size ratio B, as in the case of the shape ratio A described above, in the microscopic observation, ten or more dimples appearing in the field of view for a certain particle are randomly selected to obtain the average value of the B values. It can be represented by a value obtained by calculating a total average value for 10 or more randomly selected particles. Specifically, for example, a value obtained by collecting a small amount of sample powder sample, setting it on an observation table so that the particles do not overlap, and randomly selecting the particles to be measured at a magnification of 6000 times can be adopted. At that time, the dimple depth can be measured based on the depth data at the respective positions of the dimple bottom portion and the core surface layer portion. What is necessary is just to calculate the average of A value and the average of B value based on the measurement data about a total of 100 dimples obtained by measuring 10 dimples of each particle for 10 particles.

The carrier powder of the present invention can be obtained as follows.
[Preparation of raw material powder]
In preparing the raw materials for each component constituting the Mg ferrite, Fe ₂ O ₃ (hematite) may be used as the Fe source. A Mg (OH) ₂ containing material is used as the Mg source. Specific examples include magnesium hydroxide Mg (OH) ₂ and 3MgCO ₃ .Mg (OH) ₂ .3H ₂ O which is a kind of magnesium hydrate. These raw materials are weighed so that the composition ratio of Mg and Fe in the soft ferrite satisfies the formula (1). Further, it is desirable to use a substance that becomes a C source in order to adjust the sinterability. For example, carbon black, polyvinyl alcohol (PVA), graphite, polyacrylamide, acetylene, etc. can be used. The C source is preferably added in an amount of 0.5 to 2.0 parts by mass in terms of C element with respect to 100 parts by mass of the total amount of the Fe source and Mg source. If the amount is less than 0.5 parts by mass, the sinterability tends to be insufficiently improved, and if the amount exceeds 2.0 parts by mass, the sintering proceeds so much that it is difficult to maintain the spherical shape of the particles. More preferably, it is 1.0 mass part or less. These raw materials are mixed thoroughly and prepared. This mixed powder is mixed with water, and if necessary, a dispersing agent such as polycarboxylic acid is added and mixed, and a slurry of about 60 to 90% by mass with the mixing ratio of raw materials (each mixed substance other than water) To do. The mixing method may be ordinary mixing using a mortar or the like. Thereafter, it is desirable to wet pulverize this slurry with a ball mill or the like. The slurry in which the raw materials are sufficiently finely mixed in this manner is referred to herein as “mixed slurry”.

[Dry]
The mixed slurry is spray-dried with a spray dryer or the like, or granulated with a pelletizer and then dried with, for example, a rotary kiln to obtain a “dried mixture slurry”. As the dried product, for example, spherical pellets having a diameter of about 10 to 500 μm are preferable.

[Baking]
Next, the dried product (pellet) is fired to form Mg ferrite. For example, baking can be performed at a temperature of 1000 to 1500 ° C. in a nitrogen gas atmosphere in an electric furnace. By using pellets obtained by adjusting the kind and blending amount of the raw material powder as described above, it is considered that fine dimples are formed on the surface of the primary particles in this firing, and a special post-treatment is performed. Thus, a core material of Mg ferrite particles that can improve durability and charge maintenance can be obtained. C added to the raw material is considered to control sinterability and escape as CO ₂ .

(Granularity adjustment)
The Mg ferrite obtained by firing is made into a primary particle state (i.e., pulverized) by being pulverized by a pulverizer. Since fine dimples are already formed on the surface, no special pulverization step or surface modification step is required. There are no particular restrictions on the means for the pulverization treatment as long as the primary particles can be separated. In the pulverization process, the primary particles themselves may be partially pulverized, but such pulverized fine powder may be removed by an air classifier or the like. The pulverized powder is classified or sieved, and a powder having a predetermined particle size is collected and used as a core material for obtaining carrier powder.

[Resin coating]
Next, a resin powder is applied to the particle surface of the core material obtained as described above to construct a carrier powder. The resin coating amount is preferably 0.5 to 5.0 parts by mass with respect to 100 parts by mass of the core material. Various resins can be applied as coating resins, such as acrylic resins, styrene resins, styrene-acrylic resins, olefin resins (polyethylene, chlorinated polyethylene, polypropylene, etc.), polyester resins (polyethylene terephthalate, polycarbonate, etc.). , Unsaturated polyester resins, vinyl chloride resins, polyamide resins, polyurethane resins, epoxy resins, silicone resins, fluorine resins (polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, etc.), Examples include phenol resins, xylene resins, diallyl phthalate resins, and the like.

  In order to perform resin coating, it is common to dilute the predetermined resin in a solvent and coat the surface of the core material. Any solvent may be used as long as the predetermined resin is soluble. When the predetermined resin is soluble in an organic solvent, toluene, xylene, methyl ethyl ketone, methyl isobutyl ketone, methanol or the like can be used. If the predetermined resin is a water-soluble resin or an emulsion type resin, water is used. be able to. As a method for coating the surface of the core material particles, a dipping method, a spray method, a brush coating method, or the like can be applied. In such a wet method, the resin layer is dried after coating. On the other hand, in addition to the wet method, the resin coating can be performed by a dry method in which a predetermined resin powder is adhered to the surface of the core material.

  Regardless of the wet method or the dry method, it is preferable to bake a predetermined resin adhered to the surface of the core material. The baking process can be performed by an external heating method or an internal heating method using a fixed or fluid electric furnace, a rotary electric furnace, a burner furnace, or the like. Baking with microwaves is also possible. The baking temperature varies depending on the predetermined resin, but a temperature higher than the melting point or higher than the glass transition point is required. When the predetermined resin is a thermosetting resin or a condensation type resin, it is necessary to raise the temperature to a temperature at which the curing proceeds sufficiently.

Specifically, for example, when a silicone resin is selected as the predetermined resin and this is coated on the core material, the following may be performed.
First, the silicone resin is diluted with toluene. In that case, with respect to 100 mass parts of core materials used for a process, a silicone resin is mix | blended so that it may become 3 mass parts, for example, and the dilution liquid of a silicone resin is made. This liquid and the core material powder are put into a stirrer, and a curing agent is also added and stirred as necessary. When the stirring and mixing is completed, the solvent is dried and removed by subjecting the core material coated with the resin liquid to a heat treatment of 190 ° C. × 30 minutes, for example. Next, using an oven or a tunnel furnace, the silicon resin is baked by, for example, heating at 169 to 280 ° C. for 3 hours. Thereby, carrier powder is obtained.

[Example 1]
Fe ₂ O ₃ was prepared as the Fe raw material, and Mg (OH) ₂ was prepared as the Mg raw material. These raw materials were prepared so that the composition ratio of MgO: Fe ₂ O ₃ = 20: 80 (molar ratio) as the soft ferrite composition ratio after firing, that is, X in the formula (1) was 20 (mol%). A mixed powder was obtained. To 100 parts by mass of the mixed powder, 0.7 parts by mass of carbon black, 1.5 parts by mass of a dispersant and water were added and stirred to obtain a slurry having a slurry concentration of about 83% by mass. Further, this slurry was wet pulverized by a wet ball mill to obtain a mixed slurry. Next, the mixed slurry was dried with a spray dryer and granulated, and then sieved using a 45 μm and 25 μm sieve to obtain a dried product (pellet) having an average particle size of about 35 μm. The pellets were charged into a firing furnace and fired at 1180 ° C. for 4 hours in a nitrogen gas atmosphere to obtain a massive fired product. The obtained fired product is pulverized with a hammer mill, and the pulverized product is applied to an air classifier to classify and remove the fine powder portion. Then, the non-magnetic portion is separated by magnetic field separation, and the average particle size is about 30 μm through a 38 μm sieve. Core material powder was obtained. As a result of X-ray diffraction, this core material powder was confirmed to have a ferrite structure (the same applies in the following examples).

About the obtained core material powder, the shape ratio A and the size ratio B of the dimple were obtained. In addition, static resistance and magnetic characteristics (saturation magnetization, residual magnetization, coercive force) were examined.
The dimple shape ratio A and size ratio B were determined by measuring the particle diameter, dimple diameter, and dimple depth with an ultra-deep color 3D shape measurement microscope VK-9500 (manufactured by Keyence Corporation). Specifically, a small sample of the sample powder was collected and set on the observation table so that the particles did not overlap, and the particles to be measured were randomly selected at a magnification of 6000 and measured. The dimple depth was measured based on the depth data at the respective positions of the dimple bottom and the core surface layer. The average of the A values and the average of the B values were calculated based on measurement data for a total of 100 dimples obtained by measuring 10 dimples for each particle.
The static resistance is a superinsulator (5g) filled in an insulating pipe with a diameter of 12.9mmφ and a pressure applied with a weight of 265g and connected to electrodes installed above and below the pipe. Measured using Toa Denpa Kogyo Co., Ltd.
The magnetic properties were measured with a room temperature dedicated vibration sample magnetometer (VSM) (manufactured by Toei Kogyo Co., Ltd.).

  Next, a treatment liquid in which the silicone resin was diluted with toluene was prepared. At that time, the silicone resin was adjusted to 3 parts by mass with respect to 100 parts by mass of the core material as the material to be treated. This liquid and the carrier core material were put into a stirrer and stirred. After stirring and mixing, a heat treatment at 190 ° C. for 30 minutes was performed to remove the solvent by drying. Subsequently, it was subjected to a heat treatment at 250 ° C. for 3 hours using an oven, and a silicone resin was baked to prepare a carrier powder.

The obtained carrier powder was examined for static resistance, durability of the resin coating layer, and charge retention.
Static resistance was measured by the method described above.
The durability of the resin coating layer was examined as follows. That is, 75.0 g of carrier powder and 25.0 g of SiC (297 to 1400 μm) were placed in a plastic bottle (100 cc) with an inner lid, and a magnet was wound around the side surface of the plastic bottle. This was set on a shaking machine (Red Devil Equipment Co.) and stirred for 16 hours. The state of coating of the carrier powder after stirring was observed with an electron microscope. Good (excellent) when resin peeling was not observed, and good (allowable) when resin peeling was slight, and resin Those that could not be used due to a lot of peeling were evaluated as x (defect).

The charge maintenance property was examined as follows. That is, 92 parts by mass of a carrier and 8 parts by mass of a toner containing polyester as a main component are agitated and mixed in a ball mill for a maximum of 120 minutes, sampling is performed every hour, and the charge amount at that time is measured using a suction method charge amount measurement device And measured. Then, the difference ΔQ _120-30 between the charge amount of 120 minutes and the charge amount of 30 minutes is obtained, and when the ΔQ _120-30 value becomes zero or positive, ○ (good), and negative one X (defect) was evaluated.

Next, the electrophotographic developer using the carrier powder is used in a 40 sheet machine adopting the digital reversal development method, and the image density, fog density, and carrier jump are examined in the initial image, and ○ (good), Δ (somewhat) (Defect) and x (defect) were evaluated in three stages.
The results are shown in Table 1 (same in the following examples).
Further, the graph of FIG. 1 shows the charge maintenance property (the same applies to the following examples).
For reference, an electron micrograph of the core powder obtained in Example 1 is shown in FIG.

[Example 2]
Experiments were performed in the same manner as in Example 1 except that MgO: Fe ₂ O ₃ = 10: 90, that is, X in the formula (1) was set to 10 (mol%).

Example 3
Experiments were performed in the same manner as in Example 1 except that MgO: Fe ₂ O ₃ = 30: 70, that is, X in the formula (1) was set to 30 (mol%).

[Comparative Example 1]
Experiments were performed in the same manner as in Example 1 except that MgO: Fe ₂ O ₃ = 40: 60, that is, X in the formula (1) was set to 40 (mol%).

[Comparative Example 2]
Experiments were performed in the same manner as in Example 1 except that MgO: Fe ₂ O ₃ = 3: 97, that is, X in the formula (1) was set to 3 (mol%).
For reference, an electron micrograph of the core powder obtained in Comparative Example 2 is shown in FIG.

[Comparative Example 3]
An experiment was performed in the same manner as in Example 1 except that MnO was used instead of the raw material Mg (OH) ₂ and MnO: Fe ₂ O ₃ = 20: 80.

[About the results]
As can be seen from Table 1, the core materials of Examples 1 to 3 made of Mg ferrite obtained by blending the raw materials so as to satisfy the formula (1) have the magnetic properties required for the core material of the carrier powder. Further, the surface had fine dimples having an average shape ratio A of 0.03 to 0.09 and an average size ratio B of 0.002 to 0.05. And in the carrier powder after coat | covering resin, sufficiently high static resistance was shown and the durability of the resin coating layer was also fully improved. Further, the charge amount tended to increase with time (FIG. 1), no decrease was observed, and excellent charge retention was exhibited. Furthermore, the image characteristics were also good.

  On the other hand, in Comparative Example 1, since the X value in the formula (1) was too large, the dimples were too deep for the diameter. Inferior in image quality and image characteristics. In Comparative Example 2, since the X value of the formula (1) was too small, the dimples became too fine, and as a result, the carrier powder was inferior in the durability, charge maintenance and image characteristics of the resin coating layer. In Comparative Example 3, Mn ferrite was used as a core material, and formation of dimples was not recognized. Therefore, the carrier powder is inferior in the durability, charge maintenance and image characteristics of the resin coating layer.

The graph which shows transition of the charge amount about each carrier powder. 4 is an electron micrograph showing the appearance of a core powder made of Mg ferrite obtained in Example 1. FIG. 4 is an electron micrograph showing the appearance of a core powder made of Mg ferrite obtained in Comparative Example 2. FIG.

Claims (4)

Using Fe ₂ O ₃ as the Fe source and Mg (OH) ₂ -containing material as the Mg source, a mixed slurry whose composition was adjusted so that the Fe and Mg contents satisfy the following formula (1) was prepared. After firing the dried slurry, ferrite particles obtained by adjusting the particle size,
A carrier powder for electrophotographic development with a core material.
(MgO) _X (Fe ₂ O ₃ ) _100-X where X is 5 to 35 (mol%) (1) Ferrite particles having a composition satisfying the following formula (1), and dimples having an average shape ratio A defined by the following formula (2) of 0.03 to 0.09 formed on the surface,
A carrier powder for electrophotographic development with a core material.
(MgO) _X (Fe ₂ O ₃ ) _100-X where X is 5 to 35 (mol%) (1)
Shape ratio A = Dimple depth / Dimple diameter (2)   The carrier powder for electrophotographic development according to claim 1 or 2, further comprising a resin coating layer on the surface of the core material.   A two-component electrophotographic developer comprising a toner and the carrier powder according to claim 1.