JPH08211658A - Carrier for electrophotographic developer - Google Patents

Abstract

PURPOSE: To provide a carrier having superior durability such as spending resistance by regulating the mol.wt. distribution (wt. average mol.wt./number average mol.wt.) of polyolefin resin coating the surface of a carrier core material to a specified range. CONSTITUTION: In a carrier for an electrophotographic developer consisting of a carrier core material and polyolefin resin coating the surface of the core material, the mol.wt. distribution (wt. average mol.wt./number average mol.wt.) of the polyolefin resin is regulated to >=10. A metal such as ferrite or magnetite is used as the core material. The polyolefin resin is not limited if the mol.wt. distribution is >=10 and it is, e.g. a homo- or copolymer of α-olefin such as ethylene or propylene. The surface of the core material is treated with a catalyst and olefin is directly polymerized on this surface to coat the surface of the core material.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to 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, the adhesiveness between the carrier core material and the resin to be coated is strong, and the image quality deteriorates even after long-term use. It also has excellent spent resistance.

[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]

To achieve the above object, according to the present invention, there is provided a carrier for an electrophotographic developer, which comprises a carrier core material and a polyolefin resin coating the surface of the carrier core material. Provided is a carrier for an electrophotographic developer, characterized in that the polyolefin resin coating the surface of the core material has a molecular weight distribution (weight average molecular weight / number average molecular weight) of 10 or more.

In a preferred embodiment, the surface of the carrier core material is coated with a polyolefin resin by treating the carrier core material with a catalyst, and the olefin monomer is directly added to the surface of the treated carrier core material. Polymerize,
Provided is a carrier for an electrophotographic developer, which comprises coating the surface of a carrier core material with a polyolefin resin.

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 not particularly limited, but for example, metals such as ferrite, magnetite, iron, nickel and cobalt, these metals and zinc, antimony, aluminum, lead, tin, bismuth, Beryllium, manganese, selenium, tungsten, zirconium,
Alloys or mixtures with metals such as vanadium, the above metals such as ferrite, metal oxides such as oxides, iron oxide, titanium oxide and magnesium oxide, nitrides such as chromium nitride and vanadium nitride, silicon carbide, tungsten carbide, etc. And a mixture of these with a carbide, a ferromagnetic ferrite, and a mixture thereof. The particle size is not particularly limited, and those having a particle size of 20 to 100 μm can be preferably used.

2. Polyolefin Resin The molecular weight distribution (weight average molecular weight / number average molecular weight) of the polyolefin resin used in the present invention is 10
If it is above, there is no particular limitation, for example, ethylene,
Examples include homopolymers of α-olefins such as propylene, 1-butene, 1-hexene, 1-octene, and 4-methylpentene-1, copolymers thereof, or a mixture thereof. Among these, ethylene is included. Predominantly polymerized polyethylene is particularly preferred.

The molecular weight distribution of the polyolefin resin used in the present invention is 10 or more, preferably 14 or more, more preferably 20 or more. When the molecular weight distribution is less than 10, it is difficult to obtain a carrier having a well-balanced surface hardness and impact strength and high overall durability. That is, when the molecular weight of the coating resin is low and the molecular weight distribution is narrow, the resin is brittle, and the resin gradually peels off due to mechanical stress such as impact and shear in the developing machine during use. On the contrary, when the molecular weight is high and the molecular weight distribution is narrow, the impact strength becomes strong and the resin does not peel off, but the crystallinity lowers and the surface hardness lowers. Adhesion to surface (Since the coating resin is a polyethylene-based resin, general spent formation has not occurred, but as a result of observation with an electron microscope, it can be seen that the toner is present in a state where the toner has stuck to the surface of the coating resin. ), And the chargeability changes. The molecular weight is preferably 10,000 to 1,000,000, more preferably 50,000 to 500,000.

3. Coating of the polyolefin-based resin resin on the surface of the carrier core material In the present invention, the coating method of the polyolefin-based resin resin on the surface of the carrier core material is not particularly limited,
The surface of the carrier core material may be treated with a catalyst, olefin or the like may be directly polymerized on the surface of the treated carrier core material, and the surface of the carrier core material may be coated with the polymerized polyolefin resin. .

In the present invention, as a method for obtaining a polyethylene resin having a desired molecular weight distribution, for example, after treating the core material with a catalyst, a small amount of water or alcohol is added to the system to modify the catalyst component. , A method of making properties of active sites non-uniform. Regarding the addition of water to this system, there are a method of directly adding water, a method of adding by dispersing in a solvent, and a method of adding as adsorbed water of carbon black as an additive for adjusting physical properties. it can. Also, the resin having the desired molecular weight distribution can be obtained by a method of adding hydrogen to be added as a molecular weight regulator in two stages, a method of continuously adding a small amount of hydrogen, or the like. Furthermore, various organic and / or inorganic materials may be dispersed and / or dissolved in order to improve the charging property and other various developer properties, and those obtained by fixing these materials on the surface of a coated carrier are used. May be.

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

In the present invention, since the resin coating is formed as described above, the thickness can be limited accurately and easily.

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 960 g of sintered ferrite powder (average particle size 50 μm) was placed in an autoclave having an internal volume of 2 liters and purged with argon, heated to 80 ° C. and dried under reduced pressure (10 mmHg) for 1 hour. . After that, the temperature is lowered to 40 ° C. and dehydrated hexane 800
ml was added and stirring was started. Then, 5.0 mmol of diethylaluminum chloride and 0.05 mmol of the titanium-containing catalyst component of the above (1) were added as titanium atoms and reacted 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 3.0 kg / cm
It was ² G. After that, hydrogen is supplied and 3.2 kg / cm
^{When the} pressure was raised to ² G and 5.0 mmol of triethylaluminum was added to start the polymerization, the system internal pressure dropped to 2.3 kg / cm ² G and became stable in about 5 minutes. afterwards,
Carbon black (Mitsubishi Chemical Corporation: MA-100) 4g
Was poured into a slurry form with 100 ml of dehydrated hexane, and then while continuously feeding ethylene so as to maintain the system internal pressure at 4.3 kg / cm ² G, 65 minutes (a total of 40 g of ethylene was introduced into the system. At that point, introduction was stopped) and polymerization was carried out to obtain 1004 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 95.6: 0.4: 4.0 (weight ratio).
The carbon black used (made by Mitsubishi Chemical: MA
The water adsorption amount of 100) was measured and found to be 1.8%.

[Comparative Example 1] The same procedure as in Example 1 was carried out except that the carbon black (MA100 manufactured by Mitsubishi Chemical Co., Ltd.) in Example 1 was thoroughly dried in advance so that the water adsorption amount was 0.4%. In this case, it took 42 minutes for 40 g of ethylene to polymerize.

[Example 2] Carbon black produced in the same manner as in Comparative Example 1 was used and produced in the same manner as in Example 1, but the continuous feeding of ethylene in the latter half was started and 10 after the minute, pressurized to 4.5 kg / cm ² G by the addition of hydrogen, and polymerization was carried out for 40g at continued supply of ethylene so as to maintain the subsequent inner pressure to 4.5 kg / cm ² G total 45 minutes .

Various carriers were adjusted by changing the type of added carbon black, the amount of adsorbed water, the amount of added carbon black and the polymerization method. Table 1 shows the results. In addition, in the column of carbon black type in Table 1, Mitsubishi Chemical Corporation
The case of using MA100 manufactured by K.K. was designated as A, the case of using Ketjen Black EC600JD manufactured by Ketjen International was designated as B, and the case of no addition was designated as C.

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

Measurement of molecular weight distribution <Pretreatment> The coating resin of the resin-coated carrier was dissolved with TCB (trichlorobenzene) (solvent), and the core material was filtered off with a glass filter. <Measurement> Device: Waters ALC / GPC Column: TSK HM + GMH6 × 2 150 ° C Temperature: 135 ° C Solvent: TCB

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 operate continuously. <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 in a ratio of 100: 5 (weight ratio) was charged into the above-described evaluation machine (developing machine), and the developing machine was continuously operated for 250 hours. (Idling) was carried out. This is a registered seal 6
It corresponds to 0 to 700,000 sheets. 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.

[0028]

[Table 1]

[0029]

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.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasushi Hamada 1280, Kamizumi, Sodegaura-shi, Chiba Idemitsu Kosan Co., Ltd.

Claims (2)

[Claims] 1. A carrier for an electrophotographic developer comprising a carrier core material and a polyolefin resin coating the surface of the carrier core material, wherein a molecular weight distribution (weight average molecular weight) of the polyolefin resin coating the surface of the carrier core material. / Number average molecular weight)
A carrier for an electrophotographic developer, which is 10 or more. 2. The coating of a polyolefin resin on the surface of the carrier core material, the carrier core material is treated with a catalyst, and the olefin monomer is directly polymerized on the surface of the treated carrier core material to obtain a polyolefin. The carrier for an electrophotographic developer according to claim 1, wherein the surface of the carrier core material is coated with a system resin.