JPH08179566A - Carrier for developing electrostatic charge image - Google Patents

Abstract

PURPOSE: To make a carrier excellent in spent resistance, environmental resistance and durability by carrying out coating with a resin contg. a copolymer of specified organopolysiloxane with a radical-polymerizable monomer. CONSTITUTION: The surfaces of magnetic particles are coated with a resin contg. a copolymer of organopolysiloxane represented by the formula (where R1 is H or methyl) with a radical-polymerizable monomer. Since the organopolysiloxane as a constituent of each coating layer of the resultant carrier has a vinyl group at a terminal, it can be graft-polymerized on the chain of a polymer of the radical-polymerizable monomer by copolymn. with the monomer. When the core material of a carrier is coated with the resultant copolymer, the outside of the carrier is rich in silicon and the inside of the carrier is rich in a part made from the monomer and having affinity for the core material. The adhesiveness of the core material to the coating layer is satisfactory and superior releasability can be imparted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic carrier, and more particularly to a coated carrier having excellent spent resistance and environment resistance.

[0002]

2. Description of the Related Art A developer for a two-component dry copying machine is composed of two components, that is, a fine toner and a carrier larger than the toner, and the toner and the carrier have opposite signs due to friction generated by mixing and stirring the two. It is charged electrostatically. The toner thus charged is electrostatically adhered to the electrostatic latent image formed on the photoconductor to form a visible image, and this image is transferred to a transfer sheet.
By fixing, copying is achieved.

In this case, iron oxide or unoxidized iron powder is usually used as the carrier, but when it is used as it is mixed with the toner, the triboelectrification characteristic for the toner is insufficient. , The toner adheres to the carrier surface during use to form a toner film (spent phenomenon)
Therefore, there is a drawback that the charging characteristics of the carrier change with time, and eventually the life of the developer is shortened.

Further, there is a drawback that there is a large difference between the charging characteristics of the carrier when it is dry and when it is wet. As a method of preventing such a defect, it has been mainstream to coat the surface of the carrier with a resin.

On the other hand, in the case of fluororesins and silicone resins, the surface energy of these resins is small, so that the spent phenomenon can be reduced (Japanese Patent Application Laid-Open No. 54-21730). Publication, JP-A-58-405
57, JP-B-59-26945, JP-A-59-131944, etc.). In particular, in the case of a silicone resin, various molecular structures can be formed by selecting a monomer, and therefore, there is an advantage that a carrier having various charge amount levels can be formed by selecting the monomer, and further, it can be dissolved in various solvents. It has many operational advantages such as being easy to apply uniformly on the surface of the carrier and being capable of curing even at a relatively low temperature. However, although the fluorine-based resin and the silicone-based resin have excellent releasability, they have a drawback that they have poor adhesiveness with the core agent. Further, since the fluorine-based resin has a strong negative polarity, it is difficult to use it for negatively charged toner.

[0006] As a technique of using a copolymer resin containing a siloxane structure as a coating material for a carrier, Japanese Patent Publication No. 59-882.
No. 7 discloses silicon having two or more functional groups and dehydration.
A carrier coated with a resin containing at least a resin-modified silicone resin obtained by condensation by dealcoholization reaction is disclosed, and JP-A-5-224466 discloses a specific organopolysiloxane and another polymerizable monomer. There is disclosed a carrier coated with a resin containing the copolymer as a main component.
However, in both cases, the resin forming the coating layer is different from that of the carrier of the present invention.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrophotographic carrier excellent in spent resistance, environment resistance and durability.

[0008]

The present invention is characterized in that the surface of magnetic particles is coated with a resin containing a copolymer of an organopolysiloxane represented by the formula (I) and a radical-polymerizable monomer. Electrostatic charge development carrier:

Embedded image (Wherein R ₁ is a hydrogen atom or a methyl group).

The organopolysiloxane constituting the coating layer of the carrier of the present invention has a vinyl group at the terminal as represented by the formula (I), and thus copolymerizes with other radically polymerizable monomers. As a result, it is possible to perform graft polymerization on the polymer chain consisting of other radically polymerizable monomers, and when the obtained copolymer is coated on the carrier core material, the silicon component is abundant on the outside of the carrier. The structure exists in. In addition, since there will be abundant portions consisting of monomers with affinity for the carrier on the carrier side,
Adhesion between the carrier and the coating layer is good, and excellent releasability can be imparted to the surface of the coated carrier. Thereby, the coated carrier of the present invention can be made to have excellent spent resistance, environment resistance and durability. Also, one of the features of the coated carrier of the present invention is good flowability, which is brought about by the relatively short backbone of the organopolysiloxane.

The radical-polymerizable monomer forming the copolymer with the organopolysiloxane of the formula (I) has an affinity for the core material of the coated carrier and can be copolymerized with the above-mentioned organopolysiloxane. Well, acrylic acid ester monomers such as methyl acrylate, ethyl acrylate, butyl acrylate, β-hydroxypropyl acrylate, β-hydroxyethyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, methacrylic acid Acid-2-hydroxyethyl, methacrylic acid ester-based monomers such as glycidyl methacrylate, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, methacrylic acid dimethylaminoethyl ester, methacrylic acid diethylaminoethyl ester, dimethyl acrylate Amino group-containing vinyl monomers such as ethyl ester and dimethylaminopropyl methacrylic acid amide, vinyl monomers such as styrene, α-methylstyrene, vinyltoluene, p-ethylstyrene, vinyl acetate and vinyl chloride, N-lauryl maleimide, Maleimide-based monomers such as N-phenylmaleimide and N-cyclohexylmaleimide, ethylene and propylene can be used. Preferred are methyl acrylate, ethyl acrylate, methyl methacrylate, and ethyl methacrylate. These radically polymerizable monomers may be used alone or in combination of two or more. The proportion of the radically polymerizable monomer and the organopolysiloxane of the formula (I) used is 5 to 80% by weight, preferably 20 to 60% by weight, based on the total amount of the organopolysiloxane of the formula (I). If the amount is less than 5% by weight, the effect of siloxane on releasability and environment resistance is impaired, and if it is more than 80% by weight, the adhesion to magnetic particles is reduced.

As a method for radically copolymerizing the above-mentioned radical-polymerizable monomer and organopolysiloxane in order to obtain a coating material for a coated carrier, known suspension polymerization methods and emulsion polymerization methods which are generally used, A solution polymerization method, a bulk polymerization method and the like can be used as appropriate, but from the viewpoint of productivity, the solution polymerization method is preferable. As the solvent and polymerization initiator used in the solution polymerization method, any of those conventionally used can be used.

As the core material of the coated carrier of the present invention, one having a size of at least 20 μm (average particle diameter) is used from the viewpoint of preventing carrier adhesion (scattering) to the electrostatic latent image carrier,
From the viewpoint of preventing deterioration of image quality such as occurrence of carrier stripes, a film having a thickness of at most 100 μm is used. Specific materials include those known as two-component carriers for electrophotography, for example, metals such as ferrite, magnetite, iron, nickel, and cobalt, these metals and zinc, antimony, aluminum, lead, tin, bismuth, beryllium, manganese. ,
With alloys or mixtures with metals such as selenium, tungsten, zirconium, vanadium, metal oxides such as iron oxide, titanium oxide and magnesium oxide, nitrides such as chromium nitride and vanadium nitride, carbides such as silicon carbide and tungsten carbide Mixtures and ferromagnetic ferrites, and mixtures of these can be applied.

The amount of the coating material for coating the core material is 0.3 to 5% by weight, preferably 0.5 to 3% by weight, based on the core material.
Is. This is because if the amount is less than 0.3% by weight, the core material cannot be uniformly coated and the environmental resistance is deteriorated.
Even if it is coated in an amount of more than 5% by weight, it is meaningless because it is already sufficiently coated, and it is economically disadvantageous, and the original action of the carrier is weakened.

In order to coat the carrier core material with the coating material, for example, the obtained copolymer is dissolved in a suitable solvent such as methyl ethyl ketone, methyl isobutyl ketone, dioxane and the like, and the spray drying method and rolling fluidization are used. It may be processed by the method or the like so as to obtain the above-mentioned coating amount. Others It is also possible to coat by dipping the carrier core material in the coating resin solution and drying.

[0015]

EXAMPLES The present invention will be described in more detail below with reference to examples. Synthesis of coating resin The starting monomers, polymerization initiators and polymerization solvents used in the synthesis examples are as follows, and parts are parts by weight. MMA: methyl methacrylate, MPTS: 3-methacryloxypropyltris (trimethylsiloxy) silane, V-40: 1,1'-azobis (cyclohexane-1-carbonitrile) MEK: methyl ethyl ketone

Synthesis Example 1 MEK 100 was placed in a flask having a capacity of 500 ml equipped with a stirrer, a condenser, a thermometer, a nitrogen introducing tube, and a dropping device.
Parts, and kept at 80 ° C. under a nitrogen atmosphere, while stirring, MMA 50.0 parts, MPTS 50.0 parts, V
-40 2 parts of a homogeneous solution of 1 part MEK in 100 parts
The mixture was dropped into the reaction vessel over a period of time, copolymerized, and aged for 5 hours.

Synthesis Example 2 MEK 100 was placed in a 500 ml flask equipped with a stirrer, a condenser, a thermometer, a nitrogen introducing tube, and a dropping device.
Parts, and kept at 80 ° C. under a nitrogen atmosphere, while stirring, MMA 40.0 parts, MPTS 60.0 parts, V
-40 2 parts of a homogeneous solution of 1 part MEK in 100 parts
The mixture was dropped into the reaction vessel over a period of time, copolymerized, and aged for 5 hours.

Synthetic Example 3 In Synthetic Example 1, MMA2 was used in place of 50.0 parts of MMA.
A coating resin was prepared in the same manner except that 5.0 parts and 25.0 parts of styrene were used.

[Production of Toner] To evaluate the performance of the coated carrier of the present invention, a toner was synthesized and used as follows. The following materials: Thermoplastic styrene acrylic resin 100 parts by weight Mn: 4,500 Mw: 197,800 Tg: 60.5 ° C Softening point: 121 ° C Acid value: 24.3 ・ Carbon black 8 parts by weight MA # 8 ( Mitsubishi Kasei Kogyo Co., Ltd.) Additive for offset prevention 4 parts by weight Viscole 660P (manufactured by Sanyo Kasei Kogyo; low molecular weight polypropylene) ・ Bontron S-34 3 parts by weight Orient Chemical Co., Ltd. Put in a 10 liter Henschel mixer, 2000
After mixing for 2 minutes at rpm, extruder PCM30 (L
/D:32.5) was continuously kneaded by extrusion. Next, after cooling the kneaded material, coarsely pulverized with a 2 mm mesh feather mill, finely pulverized with a jet pulverizer, cut coarse powder / fine powder with an airflow classifier, and particles with an average diameter of 11.2 μm. Got Hydrophobic silica based on 100 parts by weight of these particles
(H-2000; manufactured by Nippon Hoechst Co., Ltd.) (0.2 parts by weight) was added and mixed with a Henschel mixer to obtain a toner.

Example 1 The resin obtained in Synthesis Example 1 was diluted with MEK to prepare a coating resin solution having a solid content of 3% by weight. As the core material, calcined ferrite F-300 (average particle diameter: 50 μm, bulk density; 2.53 g / cm ³ ; manufactured by Powder Tech Co., Ltd.) was used.
The above coating resin solution was applied by a Spira coater (made by Okada Seiko Co., Ltd.) so that the amount of the coating resin with respect to the core material was 1.5% by weight, dried, and then classified with a screen mesh having an opening of 75 μm to obtain a resin-coated carrier. Obtained.

[0021] In Example 1, except to use a synthetic Example 2 as the coating resin Then the procedure of Example 1, to obtain a resin-coated carrier.

[0022] In Example 3 Example 1, except to use a synthetic Example 3 as a coating resin Then the procedure of Example 1, to obtain a resin-coated carrier.

Comparative Example 1 A resin-coated carrier was obtained in the same manner as in Example 1 except that acrylic resin BR-83 (manufactured by Mitsubishi Rayon Co., Ltd.) was used as the coating resin.

[Evaluation of Carrier] 5 parts by weight of the toner prepared as described above and 95 parts by weight of each carrier prepared in Examples 1, 2, 3 and Comparative Example 1 were mixed to prepare a developer. This developer was used in a copying machine D: 30 (manufactured by Minolta Co., Ltd.) to copy 20,000 sheets under the environment of 25 ° C. and 55%, and the printing durability was evaluated for the following items. Shown in 1. In addition, the carrier itself was evaluated for the environmental fluctuation of the charge amount and the environmental resistance, and is shown in Table 1.

[0025]

[Table 1]

Evaluation items and method ◇ Charge amount A film charge measuring method was used (toner concentration: 6% by weight). Fog on Image As described above, images were printed using the above copying machine in combination of various toners and carriers. For fogging on the image, evaluate the toner fogging on the white background image,
It was ranked. It can be practically used in a rank or more, but is preferably in a rank or more. ◇ Texture on the image Regarding texture on the image, the texture on the half image was evaluated and ranked. It can be practically used in a rank or more, but is preferably in a rank or more.

◇ Environmental fluctuation of charge amount Charge amount (Q _LL ) after the developer was stored in an environment of 10 ° C. and 15% for 24 hours, and charge amount after being stored in an environment of 25 ° C. and 55% for 24 hours ( Q _NN ) and 24 at 30 ° C and 85%
The charge amount (Q _HH ) after storage for a period of time was measured. ◇ Environmental resistance Environmental change of the above charge amount ○: △ Q ≦ 10μC / g and Q _HH ≧ 15μC / g and Q _LL ≦
35 μC / g △: ΔQ ≦ 15 μC / g and Q _HH ≧ 10 μC / g and Q _LL ≦
40 μC / g ×: ΔQ> 15 μC / g or Q _HH <10 μC / g or Q _LL ＞
40 μC / g However, ΔQ = | Q _LL −Q _HH |, and the image quality of the image printed using the above copying machine under each environment was evaluated and ranked. Practical use is possible with a rank or above, but a rank or above is desirable.

[0028]

As is apparent from the above examples, the carrier of the present invention is excellent in environment resistance and durability and has good printing durability.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Mitsutoshi Nakamura 2-3-13 Azuchi-cho, Chuo-ku, Osaka-shi, Osaka Within Minolta Co., Ltd. (72) Inventor Hiroki Nagai Azuchi-cho, Chuo-ku, Osaka-shi, Osaka 2-chome 3-13 Osaka International Building Minolta Co., Ltd.

Claims (1)

[Claims] 1. A carrier for developing an electrostatic charge image, characterized in that the surface of magnetic particles is coated with a resin containing a copolymer of an organopolysiloxane represented by formula (I) and a radical-polymerizable monomer: [Chemical 1] (In the formula, R ₁ is a hydrogen atom or a methyl group).