JP2000019785A - Resin-coated carrier for electrophotographic developer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resin-coated carrier in which a coating layer is stably adhered to the surface of a core material. Provided is an electrophotographic carrier having high durability, and capable of providing an image having excellent image quality without causing image defects such as image deletion. SOLUTION: This resin-coated carrier for an electrophotographic developer has a coating layer made of a silicone resin or a modified silicone resin containing an imidazole compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin-coated carrier for an electrophotographic developer constituting a two-component developer used for developing an electrostatic latent image such as electrophotography, electrostatic recording and electrostatic printing. About.

[0002]

2. Description of the Related Art Electrostatography, in which an electric latent image is formed on the surface of a photoconductive material by electrostatic means and the latent image is developed to form an image, is well known in the art. For example, U.S. Pat.
Numerous methods are known as described in JP-B-97,691, JP-B-42-23910, JP-B-43-24748 and the like. That is, in electrostatography
Generally utilizing a photoconductive material, to form an electrostatic latent image on a photosensitive member by various means, then, on the latent image,
A toner image corresponding to an electrostatic latent image is formed by attaching a very finely grounded electro-detection material called toner carried and conveyed by a developer carrier, and, if necessary, an image support such as paper. After transferring the toner image to the body surface,
A copy is obtained by fixing the toner image by heating, pressurizing or solvent vapor. At this time, when a step of transferring a toner image is provided, a step for removing residual toner on the developer carrier is usually provided.

As a developing method for visualizing an electric latent image using toner, for example, US Pat.
776, the cascade development method described in U.S. Pat. No. 2,618,552, and the magnetic method described in U.S. Pat. No. 2,874,063. Brush method and US Pat. No. 3,90
A method using a conductive magnetic toner described in Japanese Patent No. 9,258 is known. In addition to the above, a bias electric field composed of an alternating current component and a direct current component is applied between a developer carrying member (developing sleeve) and a photoconductive layer, which is disclosed in JP-A-62-63970. A so-called J / B development method for performing development is known. As a typical development method, there is a magnetic brush method. In the magnetic brush method, a two-component developer composed of a toner and a magnetic carrier is used. By using magnetic particles such as steel and ferrite as a carrier, the developer is carried on a developer carrier having a built-in magnet. A developer containing a magnetic carrier is held therein, and the developer is arranged in a brush on the developer carrier by the magnetic field of the magnet. When the magnetic brush contacts the electrostatic latent image surface on the photoconductive layer, only the toner in the developer is attracted from the brush to the electrostatic latent image,
The development of the electrostatic latent image is performed.

[0004] Carriers constituting the two-component developer applied to the above-mentioned developing method are roughly classified into conductive carriers and insulating carriers. As the conductive carriers, oxidized or unoxidized iron powder is usually used. Used. However, in the developer containing the iron powder carrier as a component, there is a problem that the triboelectric charging property with respect to the toner is unstable, and further, a fog is generated in a visible image formed by the developer. That is, with the use of the developer, toner particles adhere and accumulate on the surface of the iron powder carrier particles (called "spent toner"), so that the electric resistance of the carrier particles increases, the bias current decreases, and the frictional friction decreases. As a result of the instability of the charging property, the image density of the visible image developed by the developer decreases, and the fog increases. Therefore, when continuous copying is performed by an electronic copying apparatus using a developer containing an iron powder carrier, the developer deteriorates in a small number of times, and thus it is necessary to replace the developer early, which ultimately increases costs. Become.

On the other hand, as an insulating carrier, generally,
A typical example is a resin-coated carrier in which the surface of a carrier core material made of a ferromagnetic material such as iron, nickel, or ferrite is uniformly coated with an insulating resin. In the developer using such an insulating resin-coated carrier, toner particles are less likely to be fused to the surface of the carrier than in the case of the above-described conductive carrier. It is easy to control the properties, has excellent durability and has a long service life, and is particularly suitable for a high-speed electronic copying machine.

Here, there are various characteristics required for the insulating carrier, but particularly important characteristics are appropriate chargeability, impact resistance, abrasion resistance, and good adhesion between the core and the coating material. And uniformity of charge distribution.
In view of these required characteristics, there are still problems to be improved in conventionally used insulating carriers, and the perfect ones are not known at present. For example, a proposal has been made to improve the durability of a developer by using a resin having a small surface energy as a material for a coating layer in order to prevent the spent of a carrier such as toner fusion. That is, it is said that a carrier coated with a silicone resin, a fluorine resin, or the like hardly causes spent, and has a long life as a developer. However, on the contrary, in this case, the charging ability between the toner and the carrier is weakened.
Toner scattering increases, causing the inside of the machine to be contaminated.
This leads to an image defect and the overall life is short.

In order to overcome the above problems, various studies have been made on the carrier constituting the developer, but no satisfactory carrier has yet been obtained. For example, as described in Japanese Patent Application Laid-Open No. 62-112462, the resin layer was improved by adding various silane coupling agents to the condensation reaction type silicone resin, but it was sufficiently satisfactory. It was not something.

[0008]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an electrophotographic carrier which solves the above-mentioned problems of the prior art. That is, it is a resin-coated carrier in which the coating layer is stably adhered to the surface of the core material. In addition to sufficient charge-imparting properties, it has excellent environmental stability, has sufficient durability, and has a high image quality. It is an object of the present invention to provide an electrophotographic carrier capable of giving an image of excellent image quality without causing any problem.

[0009]

The above objects are achieved by the present invention described below. That is, the present invention is a resin-coated carrier for an electrophotographic developer, which has a coating layer made of a silicone resin or a modified silicone resin containing an imidazole compound.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be further described below with reference to preferred embodiments. The present inventors have conducted intensive studies to solve the above-mentioned problems of the prior art, and as a result, if the imidazole compound is contained in the silicone resin and the modified silicone resin that coat the carrier core material, the durability and environmental performance are improved. Sufficient charge can be given to the toner regardless of the image quality.Furthermore, it is possible to obtain an excellent image quality with no image deletion at all, even with respect to the image deletion that tends to occur remarkably under high humidity. The inventors have found that the present invention can be performed, and have reached the present invention. Although the reason for this is not clear, such an effect appears because the unpaired electron of nitrogen present in the ring structure of the imidazole compound has a nitrogen-containing ring structure regardless of the conjugation of the ring. I guess it was.

Examples of the imidazole compound used as a constituent material of the resin-coated carrier for an electrophotographic developer of the present invention include compounds represented by the following structural formulas. However, the imidazole compound used in the present invention,
It is not particularly limited to this.

[0012]

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[0013]

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As the silicone resin used for the coating layer of the resin-coated carrier for an electrophotographic developer of the present invention, any straight silicone resin having an organosiloxane bond can be used. Specifically, for example, KR-271 and KR-255 manufactured by Shin-Etsu Chemical Co., Ltd., SR-2410 and SR-24 manufactured by Dow Corning Toray Silicone Co., Ltd.
06, SR-2411, TSR- manufactured by Toshiba Silicone Co., Ltd.
127B, TSR-144 and the like. A catalyst or the like may be added to these straight silicone resins as needed. As the modified silicone resin, a modified silicone resin such as an alkyd resin, a polyester resin, an epoxy resin, a polyurethane resin, and an acrylic resin can be used. As commercially available products, for example, KR-206 (modified alkyd resin) manufactured by Shin-Etsu Chemical Co., Ltd.,
KR-9706 (modified acrylic resin), ES-100
1N (modified with epoxy resin), SR-2101 (modified with alkyd resin) manufactured by Dow Corning Toray Silicone Co., Ltd., and the like. In the present invention, a straight silicone resin is preferable among the above, and a methyl silicone resin is particularly preferable in terms of coating strength when a coating layer is formed.

The resin-coated carrier for an electrophotographic developer of the present invention is constituted by coating a core material with the above-mentioned resin material. The core material used in this case is used as a carrier material. Any of those conventionally known can be used. Examples include ferromagnetic metals such as iron and cobalt, and iron oxides such as magnetite, hematite, and ferrite. Preferably, ferrite or iron whose surface is easily controlled is used, and ferrite is particularly preferable.

The carrier core material used in the present invention includes:
It is preferable to use one having an average particle size of 20 to 100 μm, particularly preferably 30 to 65 μm. That is, when the average particle diameter is less than 20 μm, the number of fine particles in the distribution of carrier particles increases, the magnetization per particle decreases, and carrier scattering easily occurs. On the other hand, when the average particle size of the carrier exceeds 100 μm, the specific surface area is reduced, and the toner tends to be scattered. Also, in this case, in a full-color image having many solid portions, the reproduction of the solid portions in particular tends to be poor.

In the resin-coated carrier for an electrophotographic developer of the present invention, a coating resin layer is formed on the surface of the above-mentioned core material with a silicone resin containing the imidazole compound described on the left. Solvents used in this case include toluene, xylene, methyl ethyl ketone, methyl isobutyl ketone, and cellsol butyl acetate.

The resin coating amount of the resin coating layer on the surface of the core material constituting the resin-coated carrier for an electrophotographic developer according to the present invention is 0.1 to 0.1 with respect to the total amount of the resin-coated carrier.
About 5.0% by weight, preferably 0.15 to 2.0% by weight
Range. The baking device for forming the resin coating layer may be either an external heating system or an internal heating system, for example, a fixed or fluid electric furnace, a rotary electric furnace, a burner furnace, or a microwave. Burning may be used. The baking temperature is 130 to 3
The temperature is preferably set to about 00 ° C.

The resin-coated carrier for an electrophotographic developer of the present invention is used as a two-component developer by mixing with a toner when an image is formed. The toner used at this time is obtained by dispersing various additives such as a colorant and, if necessary, a charge control agent in a binder resin. The binder resin used for the toner is not particularly limited, but includes polystyrene, chloropolystyrene, styrene-chlorostyrene copolymer, styrene-acrylate copolymer, styrene-methacrylic acid copolymer, and Rosin-modified maleic resin, epoxy resin, polyester resin, polyurethane resin and the like can be mentioned. These are used alone or in combination.

As the charge control agent that can be used in preparing the toner, any suitable charge control agent can be used. For example, salicylic acid metal chelates, mixed metal monoazo dyes, nigrosine base and the like can be mentioned.

As the colorant, conventionally known dyes and / or pigments can be used, and any of the conventionally known dyes used for full-color toners can be used. For example, carbon black, phthalocyanine blue, permanent red, permanent yellow and the like can be used. The content of these colorants in the toner is based on 100% by weight of the binder resin.
It is preferable to set it to about 0.5 to 10% by weight. An external additive such as silica fine powder can be appropriately added to the toner in addition to the above-described forming materials.

When preparing the toner used in the present invention, for example, the above-mentioned materials such as the binder resin, the charge control agent, and the colorant are sufficiently mixed with a mixer such as a Henschel mixer.
After kneading with a twin-screw extruder, cooling and coarsely pulverizing the mixture with a pulverizer such as a feather mill, and then using a jet pulverizer, an air classifier or the like to obtain particles of a desired particle size, and further, if necessary, silica. It is obtained by adding an external additive such as fine powder and mixing with a mixer.

[0023]

Next, the present invention will be described more specifically with reference to examples and comparative examples. Hereinafter, imidazole compounds (structures 1 to 4) used in the examples are shown. Structure-
The imidazole compounds of structures 1 and 4 have the following structural formula A, and the imidazole compounds of structures 2 and 3 have the following structural formula B. Further, R _{1 to} R ₁₀ and Z ₁ in these structural formulas are shown in Table 1 below.

[0024]

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[0025]

TABLE 1 Substituents in structural formulas A and B

Example 1 Ferrite particles having an average particle diameter of 35 μm (trade name: F-400, manufactured by Powder Tech) were used as a carrier core material. A mixed solution in which the following components were dissolved in toluene as a coating agent was prepared. Then, using a fluidized bed, the above coating agent is coated so as to have a coating amount of 1% by weight with respect to the carrier core material.
Baking was performed at 80 ° C. for 30 minutes to obtain a resin-coated carrier of this example in which the carrier core material was covered with a resin. (Coating agent) ・ Acrylic modified silicone resin (trade name: KR-9706, manufactured by Shin-Etsu Chemical Co., Ltd.) 100 parts ・ Imidazole compound (Structure-1) 5 parts

For evaluation of the obtained carrier, various cyan, magenta, yellow, and black toners for Canon CLC-700 manufactured by Canon Inc. were used, and the toner of each color was adjusted to 6% by weight based on the carrier. To prepare a two-component developer. For evaluation, CLC
Using -700 (manufactured by Canon Inc.), an image output test was performed and evaluated. At that time, the evaluation was made using, as indices, fluctuations in image density, fog on images after 50,000 sheets, environmental fluctuations in charge amount, and image flow on the photosensitive drum. Table 2 shows the obtained results.

Example 2 An epoxy-modified silicone resin (trade name: SR) was used instead of the acrylic-modified silicone resin.
-2145, manufactured by Dow Corning Toray Silicone Co., Ltd.)
The resin-coated carrier of this example was obtained in the same manner as in Example 1 except for using. Evaluation was performed in the same manner as in Example 1 using the obtained carrier. The results are shown in Table 2.

Example 3 Instead of an acrylic-modified silicone resin, a silicone resin (trade name: SR-241)
1, Dow Corning Toray Silicone Co., Ltd.) was used in the same manner as in Example 1 to obtain a resin-coated carrier of this example. Evaluation was performed in the same manner as in Example 1 using the obtained carrier. The results are shown in Table 2.

Example 4 Structure of imidazole compound
A resin-coated carrier of this example was obtained in the same manner as in Example 1 except for using the two. Evaluation was performed in the same manner as in Example 1 using the obtained carrier. Table 2 shows the results.
It was shown to.

Example 5 Structure of imidazole compound
A resin-coated carrier of this example was obtained in the same manner as in Example 1 except for using the three. Evaluation was performed in the same manner as in Example 1 using the obtained carrier. Table 2 shows the results.
It was shown to.

Example 6 Structure of imidazole compound
A resin-coated carrier of this example was obtained in the same manner as in Example 1 except that the one of Example No. 4 was used. Evaluation was performed in the same manner as in Example 1 using the obtained carrier. Table 2 shows the results.
It was shown to.

Comparative Example 1 A resin-coated carrier was obtained in the same manner as in Example 1 except that no imidazole compound was used. Evaluation was performed in the same manner as in Example 1 using the obtained carrier. The results are shown in Table 2.

Comparative Example 2 A resin-coated carrier was obtained in the same manner as in Example 2 except that the imidazole compound was not used. Evaluation was performed in the same manner as in Example 1 using the obtained carrier. The results are shown in Table 2.

Comparative Example 3 A resin-coated carrier was obtained in the same manner as in Example 3 except that the imidazole compound was not used. Evaluation was performed in the same manner as in Example 1 using the obtained carrier. The results are shown in Table 2.

[0036]

[Table 2] Table 2: Copy evaluation results

<Evaluation> In the evaluation, an image output test of 50,000 sheets was performed, and the image density fluctuation, fogging on the image, the environmental fluctuation of the charge amount, and the image flow on the photosensitive drum occurred at that time. Was evaluated according to the following criteria by the following method. 1. Image density Copy under proper exposure conditions. D. Was evaluated by measuring the image density of the solid portion with a Macbeth densitometer, and evaluated according to the following criteria. ：: Original density is reproduced very well without density unevenness Δ: Original density is reproduced. (Practical level) ▲: Non-uniform and uneven density. (A level that causes a problem in practical use) ×: A large change compared to the original density (a level that is not practical)

2. Fog on the image Toner fog on the white background image is REFLE manufactured by Tokyo Denshoku Co., Ltd.
It was measured using COMETER MODELTC-6DS and ranked according to the following criteria. ：: less than 0.5% Δ: 0.5 or more to less than 1.5% ：: 1.5 or more to less than 2.5% ×: 2.5% or more

3. Environmental variation of charge amount The charge amount Q (LL) after leaving the developer in an environment of 15 ° C. and 10% humidity and the charge amount Q (HH) after leaving the developer in an environment of 30 ° C. and 80% humidity for one day. Is calculated using a method for measuring the amount of charge described later, and then the difference ΔQ (= Q (LL) −
Q (HH)) was determined and ranked according to the following criteria. 〇: ΔQ = less than 10 μC Δ: ΔQ = 10 μC or more and less than 15 μC ▲: ΔQ = 15 μC or more and less than 20 μC ×: ΔQ = 20 μC or more

4. Image Flow on Photosensitive Drum A halftone image was formed using CLC700 in an environment of 30 ° C. and 80% humidity, and the image quality was evaluated according to the following criteria. ：: No image deletion is observed at all. Δ: Level slightly observed but not problematic in practical use. ：: Level that causes problem in practical use.

Hereinafter, a method of measuring the charge amount used for evaluating the environmental fluctuation of the charge amount will be described. FIG. 1 is a schematic perspective view of a charge amount measuring device for measuring a triboelectric charge of a toner. First, a 500 mesh screen 2 at the bottom
3, about 0.5 to 0.9 g of the developer collected from the developing sleeve of the developing device is placed in a metal measuring container 22 having
A metal lid 24 is provided. At this time, the entire weight of the measuring container 22 is weighed, and the measured value is defined as W ₁ (g). Next, suction is performed from the suction port 27 of the suction device 21 (at least the portion in contact with the measurement container 22 is an insulator). At this time, the air flow control valve 26 is adjusted to adjust the pressure of the vacuum gauge 25 to 250 mmA.
q. In this state, suction is sufficiently performed, preferably for about 2 minutes, to remove the toner by suction. Electrometer 29 at this time
Is V (volt). Here, 28 is a capacitor, and its capacitance is C (μF). Further, the weight of the entire measurement container after suction is weighed, and the measured value is defined as W ₂ (g). From these measured values, the triboelectric charge amount (μC
/ G) is calculated as follows.

[0042]

(Equation 1)

[0043]

As described above, according to the present invention,
The resin coating layer is stably adhered to the carrier core material, and in addition to sufficient charge-imparting property to the toner, has excellent environmental stability, has sufficient durability, and is used for image formation. In this case, an electrophotographic carrier having excellent characteristics capable of forming an image with excellent image quality without causing occurrence of image deletion or the like is provided.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an apparatus for measuring a triboelectric charge of a toner.

[Explanation of symbols]

 21: Suction machine 22: Measurement container 23: Conductive screen 24: Lid 25: Vacuum gauge 26: Air flow control valve 27: Suction port 28: Condenser 29: Electrometer

Claims (1)

[Claims] 1. A resin-coated carrier for an electrophotographic developer, comprising a coating layer comprising a silicone resin or a modified silicone resin containing an imidazole compound.