JPH10133426A - Carrier for developing electrostatic charge image, developer, and developing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably impart a proper quantity of electric charges to a toner independently of various changes of the environment and to form a high density and high definition image by incorporating an alkaline earth metal oxide, of which specified reduction of weight under specified conditions in the air is within a specified range, into each resin coating layer. SOLUTION: When resin coating layers are formed on the surfaces of particles of a magnetic substance to obtain a resin coated carrier, an alkaline earth metal oxide having 2-30wt.% reduction of weight in the temp. range of 200-500 deg.C at the time of heating at 5 deg.C/min rate in the air is incorporated into the resin coating layers. The alkaline earth metal oxide is produced by a wet method. In the case of <2wt.% reduction of weight, triboelectric charge imparting property varies largely owing to an environmental change and the environmental stability of developing performance is inferior. In the case of >30wt.%, the electric conductivity of the oxide increases and the stability of the charged state of a toner and the developing performance especially in an environment at high humidity are inferior.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier, a developer and a developing method for developing an electrostatic image, and more particularly, to a carrier and a developer which are stable against environmental changes and provide a high density and high definition image. Is provided.

[0002]

2. Description of the Related Art In general, as a two-component developer used in an image forming method such as a copying machine or a printer using an electrophotographic system, a negatively charged toner and a positively charged toner are usually used. And a mixture of these carriers.
The carrier is used for imparting an appropriate amount of negative triboelectric charge to the toner.

[0003] However, recently, image forming apparatuses to which the electrophotographic method such as a laser printer is applied tend to be miniaturized, and accordingly, the image forming apparatus itself,
In particular, a developing device including a developing device has also been reduced in size.

Accordingly, in a small-sized developing device, the amount of developer used for developing an electrostatic latent image is inevitably reduced.

For this reason, in the above-described two-component type negatively chargeable developer, an appropriate amount of negative friction is required in a short time until the replenished toner is transported to the development area of the electrostatic latent image. It is necessary to impart a charged charge to the toner, that is, to improve the charge rising characteristic.

Under these circumstances, as means for improving the charge rising characteristic of a negatively chargeable developer, for example, Japanese Patent Application Laid-Open No. Hei 2-8860 discloses a method for controlling the chargeability of a positively chargeable resin coating layer on a resin-coated carrier. Techniques for adding and containing agents are introduced.

Here, as the positively chargeable charge control agent,
Quaternary ammonium compounds disclosed in JP-A-49-51951 and JP-A-52-10141;
Alkylpyridinium compounds and alkylpicolium compounds (for example, nigrosine SO, nigrosine EX) disclosed in JP-A-6-11461 and JP-A-54-158932.
Etc.) are known.

However, conventionally known positively chargeable charge control agents are organic compounds having a large cohesive force and are inferior in dispersibility and mixing with the coating resin. For this reason, the above-mentioned positively-chargeable charge control agent cannot be uniformly dispersed and contained in the resin coating layer of the carrier, and an appropriate amount of negative triboelectric charge cannot be given to the toner, There is a problem that toner scattering and image fogging occur due to poor charging.

As means for solving this problem, Japanese Patent Laid-Open No.
No. 301245 discloses a method of dispersing and containing a magnesium compound having a single crystal structure grown by a gas phase reaction in a resin coating layer of a carrier. However, when the environment fluctuates variously, an appropriate amount of negative triboelectric charge cannot be stably applied to the toner.

[0010]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, a first object of the present invention is to provide a carrier capable of stably giving a proper amount of charge to toner even when the environment fluctuates variously. Is to provide. A second object is to provide a developer whose development characteristics are always constant even when the environment fluctuates variously. Further, a third object is to provide a high-definition and high-definition developing method even when the environment fluctuates variously.

[0011]

The above object of the present invention is achieved by the following means.

In a resin-coated carrier having a resin coating layer formed on at least the surface of magnetic particles, a temperature of 200 to 500 ° C. when the resin coating layer is heated at a rate of 5 ° C./min in air. A carrier for developing an electrostatic image, comprising an alkaline earth metal oxide having a weight reduction ratio in the range of 2 to 30% by weight.

[0013] The carrier for developing an electrostatic image according to the above item, wherein the alkaline earth metal oxide is produced by a wet method.

[0014] In a developer for developing an electrostatic image comprising at least a carrier having a resin coated on the surface of magnetic particles and a toner containing at least a binder resin and a colorant, the carrier described in the above item or the item is used. A developer for developing an electrostatic charge image.

[0015] Using a developer for electrostatic image development consisting of a carrier in which at least the surface of magnetic particles is coated with a resin and a toner containing at least a binder resin and a colorant, the developer is developed on a developer carrier. A developing method for developing an electrostatic charge image on an electrostatic charge image carrier by forming an agent layer, wherein the developer described in the above item is used.

Hereinafter, the present invention will be described specifically.

(Carrier of the Present Invention) The carrier of the present invention is a resin-coated carrier in which a resin coating layer is formed on at least the surface of magnetic particles.
200 when heated at a rate of 5 ° C./min in the atmosphere
It is characterized in that it contains an oxide of an alkaline earth metal whose weight loss rate in a temperature range of up to 500 ° C. is in a range of 2 to 30% by weight.

The alkaline earth metal oxide has the property of reacting with water contained in the atmosphere and hydrating on its surface through a hydration bond. Has been found to react with water contained in the air to hydrate and change its triboelectricity. Furthermore, they have found that the behavior fluctuates significantly at the beginning of hydration.

As a result of diligent studies, it was found that the temperature was 5 ° C.
/ Min in the temperature range of 200 to 500 ° C. when heated at a rate of / min (hereinafter “W (loss)”)
Also called. ) Is in the range of 2 to 30% by weight,
It has been found that the triboelectrification imparting property can be stably exhibited even with environmental fluctuations.

When the W (loss) is less than 2% by weight, the frictional charge imparting property varies greatly due to environmental fluctuations, and the environmental stability of developing characteristics is poor.

On the other hand, when W (loss) exceeds 30% by weight, the conductivity of the alkaline earth metal oxide increases, and the charge stability and developing characteristics of the toner in a high humidity environment are particularly poor. Will be.

Here, the measurement of the weight loss rate "W (loss)" was measured using a thermal balance analyzer "TGA-5" manufactured by Shimadzu Corporation.
It was measured under atmospheric pressure using a "0" type.

(Constituent Material of Carrier for the Present Invention) As the magnetic particles constituting the carrier, a substance which is strongly magnetized in the direction by a magnetic field, for example, iron, ferrite, magnetite or other iron, nickel, cobalt, etc. Metals or alloys exhibiting magnetism or compounds containing these elements, alloys which do not contain ferromagnetic elements but which exhibit ferromagnetism by appropriate heat treatment, such as manganese-copper-
An alloy of a type called a Heusler alloy such as aluminum or manganese-copper-tin, or magnetic particles such as particles made of chromium dioxide can be used.

The shape of the magnetic particles is not particularly limited.
It is preferably spherical. The specific gravity of the magnetic particles is preferably in the range of ³ to 7 g / cm ³ from the viewpoint of preventing the resin coating layer from being broken during the stirring of the mixture in the developing device and the fusion of the toner constituents to the carrier surface. preferable.

The carrier of the present invention takes into consideration the stability of charge application to the toner, the ability to supply the toner to the electrostatic latent image portion, the transfer of the carrier to the electrostatic latent image portion (carrier adhesion), and the like. Those having a volume average particle size of 15 to 80 μm can be preferably used. The measurement of the volume average particle diameter of the carrier is performed by a laser diffraction particle size distribution analyzer “HELOS”.
(Manufactured by JEOL Ltd.).
However, the dispersion of the carrier particles is as follows: after a measurement sample, a surfactant, and water as a dispersion medium are put into a 50 ml beaker,
This was performed for 120 seconds using an ultrasonic homogenizer having a power of 150 W.

As the alkaline earth metal oxide used in the carrier of the present invention, various kinds of alkaline earth metal elements constituting the oxide can be selected. From the viewpoint, each element of magnesium and calcium is preferable, and magnesium is particularly preferable.

An alkaline earth metal oxide having a preferable range of W (loss) can be easily produced by a wet method. The wet method refers to a method of obtaining an alkaline earth metal oxide by burning an alkaline earth metal hydroxide as a starting material. The alkaline earth metal oxide produced by such a method can be produced in a state where the inside and / or the surface of the alkaline earth metal oxide is appropriately hydrated.

The content of the alkaline earth metal atom in the surface portion of the alkaline earth metal oxide can be measured using an X-ray photoelectron spectrometer (XPS). Specifically, an X-ray photoelectron spectrometer “ESCA-
Using "1000" (manufactured by Shimadzu Corporation), the quantitative analysis of each element is performed under the following analysis conditions, and the content of alkaline earth metal atoms is calculated from the atomic peak area by the following formula.

(Analysis conditions) X-ray: Mg anode type (1253.6 eV) Acceleration: 10 kV, 30 mA Resolution: 31.5 eV Measurement elements: carbon, oxygen, iron, silicon, alkaline earth metal elements (beryllium, magnesium, calcium) , Strontium, barium, and radium) in total 5 kinds of elements Alkaline earth metal atom content (%) = (atomic peak area of alkaline earth metal atom / C, O, Fe, Si, Alkaline earth metal atoms, sum of atomic peak areas of 5 elements in total) ×
100 (%) The BET specific surface area of the magnesium atom-containing material is preferably in the range of 20 to 300 m ² / g, and the number average particle diameter is preferably in the range of 10 nm to 3 μm.
When the BET specific surface area and the number average particle diameter are in these ranges, the magnesium atom-containing material can be uniformly dispersed and contained in the resin coating layer. Here, the measurement of the BET specific surface area of the magnesium atom-containing material is performed by using Micromeritics Flow Soap manufactured by Micromeritics Co., Ltd.
It was measured by Model II2300. Further, the number average particle diameter here refers to the number average particle diameter of primary particles (particles separated into individual unit particles) of a magnesium atom-containing material present in the form of fine particles. Microscope (TEM) "JEM-2000FX"
A photographic image observed and photographed by (JEOL Ltd.) image analysis device "SPICCA" (Nippon Avionics Co., Ltd.)
Means the number average particle diameter measured.

As the coating resin constituting the carrier,
The material is not particularly limited as long as it can impart a negative triboelectric charge to the toner by friction with the toner. Examples thereof include a styrene resin, an acrylic resin, a styrene-acrylic copolymer resin, and a blend thereof. Resins and the like are preferable from the viewpoints of charge-imparting property and ability to form a coating layer (film-forming property).

The glass transition point (Tg) of the coating resin is 50
~ 200 ° C and softening point (Tsp) is 80 ~
Those having a temperature of 300 ° C. are preferred because they have high fixability to the surface of the core material particles and can improve durability. The glass transition point (Tg) and softening point (Tsp) of the coating resin can be controlled by selecting the composition and molecular weight of the resin.

Here, the glass transition point (Tg) is determined by DSC
A value measured by "506S" (manufactured by Seiko Denshi Co., Ltd.) (the same applies hereinafter), and the softening point (Tsp) is a Koka type flow tester "Flow Tester".
(Manufactured by Shimadzu Corporation) (the same applies hereinafter).

The resin for coating is preferably in the form of spherical fine particles.
It is preferably from 1 to 10 μm. Such a particulate resin can be prepared by suspension polymerization, emulsion polymerization, soap-free emulsion polymerization, or the like. Here, the number-average primary particle size of the coating resin is measured by a particle size distribution analyzer “LPA-3”.
000/3100 "(manufactured by Otsuka Electronics Co., Ltd.) (the same applies hereinafter).

(Method of Manufacturing Carrier of the Present Invention) The method of manufacturing the carrier of the present invention can be manufactured by using various conventionally known methods. For example, iron, ferrite,
A resin-coated magnetic carrier using magnetic particles such as magnetite as a core is prepared by dissolving the coating resin in an appropriate organic solvent, and then mixing and dispersing the alkaline earth metal oxide there to prepare a coating solution. Using this coating solution, a coating layer is formed on the surface of the magnetic particles by a method such as immersion method, dry spray method, fluidized bed method, etc. It can be produced by a so-called method, or a method generally called a dry method which does not use a solvent in forming a coating layer.

The coating amount of the coating resin is usually in the range of 0.05 to 6.0% by weight based on core material particles such as ferrite particles. Further, an intermediate layer made of a resin or other material may be provided between the coating resin and the core material particles for controlling a carrier resistance value or for various other purposes.

(Developer of the Present Invention) The developer of the present invention is a resin-coated carrier in which the content of an oxide of an alkaline earth metal, particularly magnesium oxide, in the surface portion of the resin-coated carrier is in a specific range. It is characterized by comprising a carrier and a toner in which organic fine particles having at least nitrogen atoms are added to colored particles containing at least a binder resin and a colorant.

The binder resin constituting the toner includes a styrene resin, an acrylic resin, a styrene-acrylic copolymer resin, a styrene-butadiene copolymer resin, an epoxy resin, a polyester resin, and other conventionally known binder resins. An adhesive resin can be used. (Developing Method of the Present Invention) [Developing Apparatus] As a developing apparatus used in the present invention, a large number of N,
Aluminum containing a magnet roll with S
A layer of the developer is formed on a developer carrier made of a non-magnetic material such as SUS, and the developer layer is moved to the electrostatic latent image portion on the electrostatic image carrier while rotating the developer carrier. Can be brought into contact with or in close proximity to each other to visualize the latent image portion using colored particles (toner).

As a method for regulating the developer layer formed on the developer carrier for developing the electrostatic latent image on the electrostatic charge image carrier, a metal having rigidity on the developer carrier is used. This can be achieved by placing a rod or a metal plate in parallel with the developer carrying member, or by pressing the rod or metal plate onto the developer carrying member. In addition, SUS, aluminum, and other conventionally known metals can be used for the metal bar or metal plate.
The metal rod or metal plate may be either magnetic or non-magnetic.

Further, in the case of using a developing method in which the developer layer formed on the developer carrier is brought into close contact with the latent image portion in a non-contact state to visualize the latent image with toner, the thickness of the developer layer is determined. Is the distance between the developer carrier and the electrostatic image carrier (Dsd)
Although it cannot be said unconditionally depending on the case, it is 1/5 to Dsd.
It is preferable to set it in the range of 4/5.

For example, when Dsd is set to 500 μm, it can be said that it is preferable to set the thickness of the developer layer in the range of 100 to 400 μm. The thickness of the developer layer is less than 1/5 of the set Dsd (Dsd = 500 μm
When the developer layer thickness is less than 100 μm), the electrostatic latent image must be sufficiently developed because the ability to supply the developer to the electrostatic latent image portion on the electrostatic image carrier is too small. Can not.

When the thickness of the developer layer is less than 4/5 of the set Dsd (the thickness of the developer layer is less than 400 μm with respect to Dsd = 500 μm), it is closest to the electrostatic image carrier. Carriers in the developer are transferred to the electrostatic image carrier, and the electrostatic image carrier is damaged, which is not preferable.

For other components, a conventionally known device can be used.

[0043]

【Example】

(Production Example 1 of Carrier) Magnetite composition magnetic substance particles having a volume average particle diameter of 45 μm (specific gravity 5.2 g / c
m ³ ) is 100 parts by weight, and the number average particle diameter is 2.5 μm
Cyclohexyl methacrylate-methyl methacrylate copolymer resin (Tg = 111 ° C., Tsp = 270
C) is 2.8 parts by weight, the number average particle diameter is 0.8 μm, the BET specific surface area is 76 m ² / g, and it is manufactured by a wet method at a rate of 5 ° C./min in the atmosphere. 1.2 parts by weight of magnesium oxide having a weight reduction rate of 9.8% by weight in a temperature range of 200 to 500 ° C. when heated was mixed in a high-speed stirring type mixer at a material temperature of 30 ° C. and a stirring blade. After stirring and mixing at a peripheral speed of 10 m / sec for 20 minutes to prepare a mixture in which the coating resin and the magnesium atom-containing material are adhered to the surfaces of the magnetic particles, the mixture is heated to a material temperature of 120 ° C. Similarly, while heating, in a high-speed stirring type mixer, the peripheral speed of the stirring blade is 10 m / sec.
Carrier 1 in which a resin coating layer containing magnesium oxide dispersed and contained on the surfaces of magnetite magnetic particles was formed by repeatedly applying mechanical impact force by stirring and mixing for 0 minutes.

(Preparation Example 2 of Carrier) In Preparation Example 1 of the carrier, 5 ° C./mo.
Dispersion / containment of magnesium oxide on the surface of magnetite magnetic particles in the same manner except that magnesium oxide having a weight reduction rate of 17.7% by weight in a temperature range of 200 to 500 ° C. when heated at a speed of min is used. The carrier 2 on which the resin coating layer formed was formed.

(Carrier Production Example 3) In Carrier Production Example 1, 5 ° C. /
Dispersion / containment of magnesium oxide on the surface of magnetite magnetic particles in the same manner except that magnesium oxide having a weight reduction rate of 2.8% by weight in a temperature range of 200 to 500 ° C. when heated at a speed of min is used. The carrier 3 having the resin coating layer formed thereon was produced.

(Preparation Example 4 of Carrier) In Preparation Example 1 of the carrier, 5 ° C./mo.
Dispersion / containment of magnesium oxide on the surface of magnetite magnetic particles in the same manner except that magnesium oxide having a weight reduction rate of 29.8% by weight in a temperature range of 200 to 500 ° C. when heated at a speed of min is used. The carrier 4 on which the resin coating layer formed was formed.

(Comparative Carrier Production Example 1) In Carrier Production Example 1, a metal magnesium vapor was oxidized in an oxygen atmosphere to grow a single crystal, and synthesized at a rate of 5 ° C./min in air. 200-500 when heated at
Comparative carrier 1 was prepared in the same manner except that magnesium oxide having a weight reduction ratio of 1.6% by weight in a temperature range of ° C was used.

(Comparative Carrier Production Example 2) In Carrier Production Example 1, 5
After immersing magnesium oxide having a weight reduction rate of 9.8% by weight in a temperature range of 200 to 500 ° C. when heated at a rate of 200 ° C./min into pure water at 90 ° C. for 5 hours, 1
Synthesized by drying sufficiently at 10 ° C, 5 ° C /
Comparative carrier 2 was prepared in the same manner except that 1.2 parts by weight of magnesium oxide having a weight reduction ratio of 37.6% by weight in a temperature range of 200 to 500 ° C. when heated at a rate of min was used.

These carriers 1 to 4 and comparative carrier 1
Table 2 shows the weight loss rate “W (loss)” in the temperature range of 200 to 500 ° C. when each of No. 2 to 2 was heated at a rate of 5 ° C./min in the atmosphere.

[0050]

[Table 1]

(Production Example of Toner) Polyester resin 100 parts by weight Carbon black 10 parts by weight Polypropylene 4 parts by weight The above compounds were mixed, kneaded, pulverized, and classified to produce colored particles having a volume average particle size of 8.5 μm. . Here, the volume average particle diameter of the colored particles is expressed by a Coulter counter TA-
This is a value measured by a type II (manufactured by Coulter, Inc.).

To 100 parts by weight of the colored particles, 0.6 parts by weight of hydrophobic silica fine particles (particle diameter: 12 nm) was added and mixed using a Henschel mixer to prepare a toner.

(Examples 1-4 and Comparative Examples 1-2) 93 parts by weight of each of Carriers 1-4 and Comparative Carriers 1-2 were mixed with 3 parts by weight of the toner using a V-type mixer. As a result, Developers 1 to 4 of the present invention and Comparative Developers 1 and 2 were produced.

<Actual Photographic Test> An electrophotographic copying machine “Konica 7050” was used for each of the developers 1 to 3 and comparative developers 1 and 2 of the present invention produced as described above.
Using a remodeled machine (manufactured by Konica Corporation), 100,000 actual shooting tests were performed under the following conditions, and changes in image density, in-machine contamination due to toner scattering, occurrence of image fogging, and the presence or absence of image fogging were evaluated. .

The evaluation method of the above two items is as follows.

Image Density Transition The relative density of the 2 cm × 5 cm patch portion was measured with an image density measuring device “RD-918” (manufactured by Macbeth) with respect to the output image after the actual shooting test was performed every 10,000 times.

In-machine contamination due to toner scattering After the actual copying test was performed every 10,000 times, the inside of the copying machine was visually inspected. (○) when contamination inside the machine (near the sleeve) is observed, “△” when contamination inside the machine is observed on the entire top cover of the developing unit, almost all of the inside of the copier is contaminated by toner scattering, which is a practical problem. The case was marked "x".

Image Fogging Occurrence The relative density of the white background portion of each output image after the actual shooting test was performed every 10,000 times was measured using an image density measuring device “RD-
918 "(manufactured by Macbeth). If the measured value exceeds 0.1, there is a practical problem.

The modified points and image forming conditions used for image formation are as follows.

"Remodeling point and image forming conditions" VH = -750 V, VL = -50 V DC component of developing bias: -650 V AC component of developing bias: frequency 8 kHz, 2.6 kV Distance between photosensitive member and sleeve: 550 μm Developer Layer thickness: 250 μm The developer layer regulating portion inside the developing device was modified so that the developer layer thickness became a set value.

Material of developer carrier: aluminum Metal bar regulated by developer layer: non-magnetic SUS, 6φ round bar.

Combination of image output environment and original blackening ratio: See Table 2 below.

[0063]

[Table 2]

Table 3 shows the results of the image density transition, Table 4 shows the results of in-machine contamination due to toner scattering, and Tables 5 and 6 show the results of measurement of the relative image density of the white background.

[0065]

[Table 3]

[0066]

[Table 4]

[0067]

[Table 5]

[0068]

[Table 6]

In Comparative Example 1, the actual photographing test was stopped at 30,000 times because the image density decreased and toner scattering and image fogging occurred remarkably. Also in Comparative Example 2, toner scattering and image fogging significantly occurred.
The live-action test was stopped at 10,000 times.

As is clear from Tables 2 to 6, when the developers 1 to 4 of the present invention are used, good charging start-up characteristics can be stably exhibited over a long period of time, and the performance is improved. Since it is not affected by the environment, even if a total of 100,000 actual shooting tests are performed, a good image can be output without causing toner scattering or image fogging.

[0071]

According to the present invention, there is provided a carrier capable of stably giving an appropriate amount of electric charge to a toner even when the environment changes variously. It was possible to provide a high-definition and high-definition developing method even if the supply of the agent and the environment varied.

Continued on the front page (72) Inventor Ryuji Kitani 2970 Ishikawacho, Hachioji-shi, Tokyo Konica Corporation

Claims (4)

[Claims] 1. A resin-coated carrier having a resin coating layer formed on at least the surface of magnetic particles, wherein the resin coating layer has a temperature of 200 to 500 ° C. when heated at a rate of 5 ° C./min in air. A carrier for developing an electrostatic image, comprising an oxide of an alkaline earth metal having a weight reduction ratio in the temperature range of 2 to 30% by weight. 2. The electrostatic image developing carrier according to claim 1, wherein the alkaline earth metal oxide is produced by a wet method. 3. A developer for developing an electrostatic charge image comprising a carrier having a resin coated on at least the surface of magnetic particles and a toner containing at least a binder resin and a colorant, wherein the carrier is according to claim 1 or 2. And a developer for developing an electrostatic image. 4. Using a developer for developing an electrostatic charge image comprising a carrier having at least a surface of magnetic particles coated with a resin and a toner containing at least a binder resin and a colorant, the developer is coated on a developer carrier. A developing method for forming an electrostatic charge image on an electrostatic charge image carrier by forming the developer layer, wherein the developer according to claim 3 is used.