JPH08211659A - Carrier for electrophotographic developer - Google Patents

Abstract

PURPOSE: To provide a carrier having superior durability and spending resistance. CONSTITUTION: In a carrier for an electrophotographic developer as an aggregate of carrier particles each consisting of a carrier core material and a thermoplastic resin coating the surface of the core material by direct polymn. on the surface of the core material, the core material is made of an aggregate of crystalline particles and carrier particles whose core material does not contain crystalline particles of >10μm average particle diameter account for >=80% of the aggregate of carrier particles.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a carrier for an electrophotographic developer. More specifically, it relates to a carrier for an electrophotographic developer, which has excellent durability and is suitably used as an electrophotographic two-component developer.

[0002]

2. Description of the Related Art Conventionally, as a method of developing an electrostatic latent image in electrophotography, a two-component developing method using a mixture of insulating non-magnetic toner and magnetic carrier particles is known. In the two-component developing method, the carrier plays a role of triboelectrifying the toner and transporting the toner to the surface of the photoconductor so as to contact with the electrostatic latent image.

The granular carrier used in such a two-component developing system is used for preventing toner spent on the carrier surface, forming a uniform carrier surface, preventing surface oxidation, preventing moisture sensitivity deterioration, and extending the life of the developer. It is customary to coat the photoreceptor with a suitable material for the purpose of protecting the photoreceptor from scratches or friction by the carrier, controlling the charge polarity or adjusting the charge amount, and is called a coating carrier.

However, the conventional coating carrier is not satisfactory in terms of durability because the coating layer is easily peeled off by the impact such as stirring applied during use.

As a method for solving such a problem, the present applicant has developed a technique for directly polymerizing an olefin-based monomer on a carrier core material such as ferrite to form a polyolefin-based resin coating, and reported it previously. (For example, JP-A-2-187771). Since the polyolefin resin-coated carrier obtained by this method has a direct coating formed on the carrier core material, it has strong adhesion between the carrier core material and the polyolefin resin coated, and even after long-term use. The image quality is not deteriorated and the spent resistance is excellent.

[0006]

However, recent technological advances in the field of electrophotography are remarkable, and higher quality images are required, and the demand for longer life is further increasing. There has been a problem that the above technology cannot always be fully satisfied.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a carrier for an electrophotographic developer having excellent durability such as spent resistance.

[0008]

In order to achieve the above object, according to the present invention, a carrier core material and a thermoplastic resin for directly polymerizing on the surface of the carrier core material to coat the surface of the carrier core material are used. In the carrier for an electrophotographic developer, which is an aggregate of carrier particles, the carrier core material is composed of an aggregate of crystal particles and does not contain crystal particles having an average particle size of more than 10 μm. The carrier particles are composed of 8 of carrier particle aggregates.
There is provided a carrier for an electrophotographic developer characterized by occupying 0% or more.

Further, as a preferred embodiment, there is provided a carrier for an electrophotographic developer, wherein the thermoplastic resin contains a polyolefin resin as a main component.

The electrophotographic developer carrier of the present invention will be specifically described below. 1. Carrier Core Material The carrier core material used in the present invention is composed of an aggregate of crystal particles such as ferrite and magnetite obtained by a sintering method. Surface property of these sintered bodies (crystal particles) (specifically, the grain size and grain size distribution of crystal grains existing near the surface)
Is variously adjusted depending on the raw material, its particle size, the type of binder used, the sintering temperature, and other conditions. That is, the surface property can be varied depending on the degree of crystal growth during sintering.

In this case, it has been found that the surface properties of the crystal particles used in the manufacturing process of the carrier have a great influence on the durability and the like of the coated carrier. That is, as a method for producing the carrier of the present invention, for example, the surface of the aggregate of crystal particles constituting the carrier core material is treated with a catalyst, and the monomer is supplied to the catalyst which is treated and adsorbed / supported on the surface. In the case of employing a resin on the surface of which a monomer is directly polymerized to form a thermoplastic resin to be described later, for example, a polyolefin resin, and coating with the resin is adopted, the treatment of the carrier core material by the catalyst will be described in detail. As a result of examination, it was found that the catalyst selectively adsorbed and supported on the crystal grain boundaries (the boundaries between the crystal grains forming the agglomerates).

Further, since the polymerization grows from the adsorbed / supported catalyst, the carrier core material (aggregate of crystal particles) containing the crystal particles having an average particle size exceeding 10 μm is a carrier core material of a thermoplastic resin. Adhesive strength to
It has been found that the ratio of the carrier core material exposed increases with long-term use. That is, as a result of producing a thermoplastic resin-coated carrier using core materials having various surface properties and performing a durability test, carrier particles composed of carrier core materials containing no crystal particles having an average particle size of more than 10 μm. It has been found that the peeling of the coating resin can be prevented by using a carrier which occupies 80% or more of the aggregate (carrier) of carrier particles. 90% or more,
It is more preferably 95% or more, and most preferably 99% or more.

It is to be noted that carrier particles composed of a carrier core material not containing crystal particles having an average particle size of more than 10 μm occupy 80% or more of the aggregate of carrier particles means that the average particle size exceeds 10 μm. This means that the number of carrier particles made of a carrier core material that does not include crystal particles having smooth portions is 80% or more of the number of aggregates of carrier particles. The shape is not particularly limited, and any shape such as a spherical shape or an indeterminate shape can be used. The particle size of the carrier core material is also not particularly limited, and for example, a particle size of 20 to 100 μm can be preferably used.

2. Thermoplastic resin As the thermoplastic resin used in the present invention, for example,
Poly (meth) acrylic resin, polyolefin resin,
There are various thermoplastic resins such as polyamide resins, polyether resins, polysulfonic acid resins, polyester resins, polybutyral resins, urethane / urea resins, Teflon resins and the like, and their mixtures. Polyolefin resins are preferred. As the polyolefin resin, ethylene, propylene, 1-butene,
1-hexene, 1-octene, 4-methylpentene-1
And the like, and those obtained by homopolymerization of α-olefins, copolymers thereof, or a mixture thereof. Of these, polyethylene in which ethylene is mainly polymerized is particularly preferable. Further, various organic and / or inorganic materials may be dispersed and / or dissolved and used in order to improve the charging property and other various developer characteristics, and those obtained by fixing these materials on the surface of a coated carrier are used. May be.

In the present invention, as a method for directly polymerizing the surface of the carrier core material to coat the surface thereof, in addition to the above-mentioned examples, for example, the method described in Japanese Patent Publication No. 62-61272 can be cited. be able to.

The thickness of the resin coating is not particularly limited and may be, for example, 0.1 to 5.0 μm.

The final resistance value of the carrier is not particularly limited, and can be adjusted by, for example, the type of additive such as carbon black and the amount thereof.

[0018]

EXAMPLES The present invention will be described in more detail below with reference to examples. [Example 1] (1) Preparation of titanium-containing catalyst component In a flask having an internal volume of 500 ml replaced with argon, 200 ml of dehydrated n-heptane and 12 in advance at room temperature were added.
15 g (25 mmol) of magnesium stearate dehydrated under reduced pressure (2 mmHg) at 0 ° C. is put into a slurry. 0.44 g (2.3 mmol) of titanium tetrachloride was added dropwise with stirring, and then the temperature was started and the reaction was carried out under reflux for 1 hour to obtain a viscous transparent titanium-containing catalyst (active catalyst) solution. .

(2) Activity Evaluation of Titanium-Containing Catalyst Component In an autoclave having an internal volume of 1 liter replaced with argon, 400 ml of dehydrated hexane and 0.
8 mmol, diethylaluminum chloride 0.8 millimolar, and the titanium-containing catalyst obtained in (1) above were added as 0.004 mmol as titanium atoms.
The temperature was raised to 0 ° C. At this time, the system internal pressure is 1.5 kg / cm
It was ² G. Next, hydrogen was supplied to give 5.5 kg / cm ^2.
After the pressure was increased to G, ethylene was continuously supplied so that the total pressure was maintained at 9.5 kg / cm ² G, and polymerization was performed for 1 hour to obtain 70 g of a polymer. Polymerization activity is 365kg /
g · Ti / Hr, and the MFR (1
Melt flow property at 90 ° C, load 2.16 kg; JIS
K 7210) was 40.

(3) Production of Polyethylene Coated Carrier Sintered ferrite powder 96 having an average particle size of 50 μm and a surface property of 5 was placed in an autoclave having an internal volume of 2 liters, which was replaced with argon.
Add 0 g and raise the temperature to 80 ° C and depressurize for 1 hour (10 mmH
g) It was dried. Then, the temperature was lowered to 40 ° C., 800 ml of dehydrated hexane was added, and stirring was started. Then 5.0 mmol of diethylaluminum chloride and (1) above
The titanium-containing catalyst component of 1 was added as a titanium atom in an amount of 0.05 mmol, and the reaction was carried out for 30 minutes. Then, the temperature was raised to 90 ° C., and 4 g of ethylene was introduced. At this time, the system internal pressure is 3.
It was 0 kg / cm ² G. After that, hydrogen is supplied, and 3.
After increasing the pressure to ² kg / cm ² G and adding 5.0 mmol of triethylaluminum to start the polymerization, the system internal pressure dropped to 2.3 kg / cm ² G and became stable in about 5 minutes. After that, carbon black (Ketjen Black EC600JD manufactured by Ketjen International) 2
40 g of 100 g of dehydrated hexane in a slurry state, and then 40 minutes while continuously supplying ethylene so as to maintain the system internal pressure at 4.3 kg / cm ² G (40 g of ethylene was introduced into the system in total). At that point, introduction was stopped) and polymerization was carried out to obtain a total of 1002 g of carbon black-containing polyethylene resin-coated ferrite. It was observed by an electron microscope that the surface of the ferrite was thinly covered with polyethylene, and the carbon black was uniformly dispersed in the polyethylene. When this composition was measured by TGA (thermobalance), the composition ratio of ferrite, carbon black and polyethylene was 95.8: 0.2: 4.0 by weight.

Hereinafter, various carriers were adjusted by changing the type of carrier core material, surface properties, type of added carbon black, amount of adsorbed water, amount of added, etc. and polymerization method. Table 1 shows the results. In Table 1, in the column of carbon black type, A is used when MA100 manufactured by Mitsubishi Chemical Co. is used, B is used when Ketchen Black EC600JD manufactured by Ketjen International is used, and 4500 manufactured by Tokai Carbon Co., Ltd. is used. The case where there was was set as C.

Evaluation The surface properties and the apparent resistance of the carrier of the obtained carrier were measured and the durability was evaluated. The results are shown in Table 1.

Measurement of surface property At least 100 carrier core materials are observed (photographed) by an electron microscope, and the number of carrier particles composed of carrier core materials containing no crystal particles having an average particle size of more than 10 μm on the surface is determined. It was calculated. The index of surface property is as follows. For example, when the number of carrier particles made of a carrier core material that does not include crystal particles having an average particle size of more than 10 μm accounts for 95% of the number of aggregates of carrier particles:
95 In the case where the number of carrier particles made of a carrier core material which does not include crystal particles having an average particle size of more than 10 μm accounts for 60% of the number of aggregates of carrier particles: 60

Measurement of apparent resistance An electrode area of 5 cm ² and a load of 1 kg were provided with a carrier layer having a thickness of 0.5 cm, a voltage of 1 to 500 V was applied to the upper and lower electrodes, and the current value flowing therethrough was measured. Calculated and calculated.

Evaluation of Durability <Evaluator> A commercially available medium speed copying machine (45 sheets / minute) was modified so that the developing machine could continuously operate independently. <Evaluation> A predetermined amount of a developer obtained by mixing the carrier according to the example and the comparative example and a commercially available polyester-based toner at a ratio of 100: 5 (weight ratio) was added to the above-described evaluation device (developing device), and the developing device was continuously operated for 50 hours. (Idling) was carried out. After that, the developer was taken out of the developing machine, and the following analysis was carried out on the carrier obtained by separating (blowing off) the electrostatically adhered toner with a stainless steel wire net having a mesh size smaller than the carrier particle size. <Analysis> Amount of peeling of coating resin: Measured by thermal analysis (TGA) and electron microscope observation. Toner Spent Amount: Spent toner is THF
It was dissolved in (tetrahydrofuran) and quantified by IR.

[0026]

[Table 1]

[0027]

As described above, according to the present invention, it is possible to provide a carrier for an electrophotographic developer having excellent durability such as spent resistance.

Front Page Continuation (72) Inventor Yasushi Hamada 1280, Kamizumi, Sodegaura, Chiba Idemitsu Kosan Co., Ltd.

Claims (2)

[Claims] 1. A carrier for an electrophotographic developer, which is an aggregate of carrier particles comprising a carrier core material and a thermoplastic resin which is directly polymerized on the surface of the carrier core material to cover the surface of the carrier core material, The carrier core material is composed of an aggregate of crystal particles, and the carrier particles composed of a carrier core material containing no crystal particles having an average particle size of more than 10 μm occupy 80% or more of the aggregate of carrier particles. A carrier for an electrophotographic developer, which is characterized in that 2. The carrier for electrophotographic developer according to claim 1, wherein the thermoplastic resin contains a polyolefin resin as a main component.