JPS6266269A - Carrier for developing electrostatic image - Google Patents

Abstract

PURPOSE:To maintain stable performance even after repeated use for a long period by forming a coating layer of silicone resin on the surface of the core material of a carrier and incorporating tin into the coating layer. CONSTITUTION:A coating layer of silicone resin contg. tin is formed on the surface of the core material of a carrier. The tin content in the coating layer is 0.6-5.0wt%, preferably 1.2-5.0wt%. In case of <0.6wt%, the effect of tin is not well produced. In case of >5.0wt%, a toner is electrostatically charged to the utmost extent, so the amount of the toner stuck to a latent image is reduced to lower the image density. In order to incorporate tin into a coating layer of silicone resin, tin in a state enabling bonding to silicone resin, e.g., an organotin compound acting as a curing agent for silicone resin is preferably used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrostatic method used together with a toner to develop an electrostatic latent image formed in electrophotography, electrostatic printing, electrostatic recording, etc. The present invention relates to a carrier for electrostatic image development, and particularly relates to a resin-coated carrier for electrostatic image development having a coating layer made of silicone resin.

[Background of the invention]

In recent image forming methods, a method using a static 1i latent image is widely used. In electrophotography, for example, an electrostatic latent image is formed by imparting a uniform electrostatic charge to a photoconductive photoreceptor and then performing imagewise exposure. Such an electrostatic latent image is developed with a developer, and the resulting toner image is transferred to transfer paper or fixed as it is to form a visible image.

As a method for developing an electrostatic latent image, a two-component developer consisting of toner and a carrier containing a magnetic material is used, and the developer is made to stand on the surface of a developer carrier by magnetic force to form a magnetic brush. However, a method is widely used in which the magnetic brush rubs the surface of the latent image carrier to electrostatically adhere the toner particles in the magnetic brush to the electrostatic latent image on the latent image carrier.

As carriers used in such development methods, carriers made of particles of ferromagnetic materials such as iron, ferrite, and magnetite have conventionally been known, but when such carriers are used, the developer During use, toner components may transfer and adhere to the surface of the carrier, reducing the triboelectric charging properties between the toner and the carrier, or the ferromagnetic particles described above are highly hygroscopic and may cause the toner to adhere to the surface of the carrier in a humid environment. There are problems such as early deterioration of triboelectrification between the carrier and the carrier.

[Problems to be solved by the invention]

In order to eliminate these problems, a carrier has been developed in which the surfaces of the above-mentioned ferromagnetic particles are coated with a resin. This resin-coated carrier has superior durability in repeated use compared to conventional carriers, and in particular, carriers whose surface is coated with silicone resin are superior to carriers whose surface is coated with other resins. The surface has better slipperiness than that of the carrier particles, and can effectively prevent toner substances from adhering to the carrier particles.

However, such silicone resin-coated carriers generally have low triboelectric charging ability, and therefore, in order to properly charge the toner through friction with the carrier, it is necessary to provide the toner with a considerable degree of triboelectric charging ability. It is necessary to include a significant amount of fit control agent in the toner particles. Dyes are usually used as this charge control agent, but dyes generally have high hygroscopicity, and therefore the toner's Fi! There is a problem in that the triboelectric charging ability changes greatly and it is difficult to obtain a stable triboelectrical charging ability. Furthermore, the mechanical strength of the silicone resin coating layer is not necessarily sufficient, and if used repeatedly over a long period of time,
There is a problem that the performance of the carrier deteriorates due to wear of the coating layer.

[Purpose of the invention]

The present invention has been made based on the above-mentioned circumstances, and its purpose is to provide a material that has excellent triboelectric charging ability, has excellent mechanical durability, and can withstand repeated use over a long period of time. It is an object of the present invention to provide a carrier for electrostatic image development, which can provide stable performance even in various cases.

[Means for solving problems]

The carrier for electrostatic image development of the present invention has a coating layer made of a silicone resin on its surface.
The coating layer is characterized in that it contains tin.

According to this structure, since the coating layer is made of silicone resin and contains tin, the mechanical strength of the coated layer is significantly improved, and the tin provides excellent positive triboelectric charging ability. As a result, the triboelectric charging properties become stable over a long period of time, and it becomes possible to stably form fog-free images of good quality over a long period of time. Since the carrier has excellent positive triboelectric charging ability, it is not necessary to specifically include an f7 charge control agent in the toner, or even if it is necessary, the content ratio can be kept extremely small. Therefore, the problem of deterioration in moisture resistance that occurs when a toner contains a considerable amount of charge control agent does not occur.

The present invention will be explained in detail below.

In the present invention, a carrier for electrostatic image development is constructed by providing a coating layer made of a silicone resin containing tin on the surface of a carrier core material.

The content of tin in the coating layer is 0.6 to 5.0% by weight, preferably 1.2 to 5.0% by weight. If this content ratio is too small, the effect of tin will not be sufficiently obtained, while if this content ratio is too large, the toner charge amount will become too high and the toner adhesion layer to the latent image will decrease, resulting in concentration becomes lower.

In the present invention, the means for incorporating tin into the coating layer made of silicone resin is not particularly limited, but it is preferable to use tin in a state that can be bonded to silicone resin, such as an organic tin compound that acts as a curing agent for silicone resin. In other words, when using a specific organic tin compound that also acts as a curing agent for silicone resin, after the silicone resin is cured, tin will not be liberated and will reliably exist in the coating layer due to chemical bonding force. As a result, the effects of tin, that is, great mechanical durability and excellent triboelectric charging ability, can be reliably obtained.

In a preferred specific example, for example, a coating liquid is prepared by mixing a silicone resin and a specific organic tin compound that also serves as a curing agent for the silicone resin in a solvent together with other additives added as necessary. This coating liquid is applied to the surface of the carrier core material, and then dried and cured to form a coating layer on the surface of the carrier core material, thereby obtaining the carrier of the present invention.

As such an organic tin compound, for example, the following general formula (A
) can be particularly preferably used.

General formula (A) (R+)xsn(OCORz)v In the formula, R9 represents an alkyl group having 1 to 10 carbon atoms, R2 represents an alkyl group having 1 to 15 carbon atoms, and X represents an integer of 1 to 4,
X+Y=2 or 4.

Specific substances represented by the general formula (A) include, for example, tin dioctoate, diethyltin diacetate,
Examples include dibutyltin diacetate, dibutyltin dilaurate, dioctyltin diacetate, dioctyltin dilaurate, and among these, dibutyltin diacetate and tin dioctoate are particularly preferred.

In the present invention, the silicone resin used for forming the coating layer is not particularly limited, but for example, condensation reaction type silicone resins that are cured by the reactions shown in (1) and (2) below can be particularly preferably used.

■Heating dehydration condensation reaction R3R.

-O-5i-OH+ HO-5i-0-Heating
11 ■ Room temperature humidity curing reaction R, R4] I -O-5i-OX + XO-5i-0-128O
In the formula X l 1, OX represents an alkoxy group, a ketoxime group, an acetoxy group, an aminoxy group, or the like.

Particularly preferred among such condensation reaction type silicone resins are those in which the substituent is a methyl group. A coating layer obtained from a condensation reaction type silicone resin in which the substituent is a methyl group has a dense structure, has a fairly good IΩ aqueous property, and can be used as a carrier with extremely good moisture resistance.

In the present invention, as the silicone resin, either a heat-curable silicone resin or a room-temperature-curable silicone resin can be used. When using a room-temperature-curable silicone resin, heating to a particularly high temperature is recommended for curing. Since this is not necessary, the carrier of the present invention can be easily manufactured.

Room temperature curable silicone resin is a silicone resin that cures at a temperature of about 20 to 25 degrees Celsius or slightly higher than this in a normal atmosphere.
It does not require temperatures exceeding ℃.

In forming the coating layer, a mixture of silicone resin and other resins may be used. Examples of such other resins include acrylic resins, styrene resins, epoxy resins, urethane resins, polyamide resins, and polyester resins. , acetal resin, polycarbonate resin, phenol resin, vinyl chloride resin, vinyl acetate resin, cellulose resin, polyolefin resin, copolymer resins thereof, blended resins, and the like.

As the carrier core material, for example, magnetic metals such as iron, steel, nickel, and cobalt, magnetic oxides such as ferrite and magnetite, copper, carporundum, glass beads, and others can be used. When the carrier core material is a magnetic material, it is possible to obtain a carrier that provides a developer suitable for magnetic brush development. As such carrier core material, those having a weight average particle diameter of 1 to 1000 m are usually used, and those having a weight average particle diameter of 5 to 500 microns are particularly preferred.

The carrier of the present invention is produced by coating the surface of a carrier core material with a coating liquid made by dissolving silicone resin J resin and an organic tin compound as described above in a solvent, and then usually heating and drying to remove the solvent. It can be produced by volatilizing off and curing the coated layer during or after drying.

Specific application methods include a dipping method in which powder of the carrier core material is immersed in a coating solution, a spray method in which the coating solution is sprayed onto the carrier core material, and a method in which the carrier core material is suspended using fluidized air. Examples include the fluidized bed method in which the coating liquid is sprayed onto the core material, and the method in which the carrier core material is transferred onto the surface where the coating liquid is present. In particular, when using the fluidized bed method, the carrier core material A uniform coating film can be formed on the surface, and a coating layer can be stably formed. This fluidized bed coating method is described in, for example, Japanese Patent Application Laid-open No. 155049/1983.

Other additives may be added to the coating solution for forming the coating layer as necessary.The solvent is not particularly limited as long as it dissolves the silicone resin and the organic tin compound, but examples include toluene, Aromatic hydrocarbons such as xylene; Ketones such as acetone and methyl ethyl ketone; tetrahydrofuran, dioxane, higher alcohols,
Alternatively, a mixed solvent of these can be used.

The temperature when curing the coating layer is, for example, 150 to 280
℃, preferably 250°C or less.

When using a room temperature curable silicone resin as the silicone resin, heating is not particularly required when curing, but heating may be performed as necessary to increase the mechanical strength of the coating layer. Furthermore, during drying, metal soaps such as lead, iron, cobalt, manganese, and zinc such as octylic acid and naphthenic acid may be used as drying accelerators, and organic amines such as ethanolamine are also effective as drying accelerators. Can be used.

The thickness of the coating layer thus obtained is usually 0.1 to 10μ.
recommended, preferably 0.3 to 5μ.

Further, the average particle size of the carrier of the present invention is, for example, 1 to 1000.
μ, preferably about 5 to 200n.

The toner constituting the developer together with the carrier of the present invention is not particularly limited, and any known toner can be used.

〔Example〕

Examples of the present invention will be described below, but the present invention is not limited thereto.

(Preparation of silicone resin liquid for coating) A solution of 470 g of dimethyldichlorosilane and 340 g of methyltrichlorosilane dissolved in 1.41 g of toluene was added dropwise to 2.4 g of water preheated to 70° C. using a dropping funnel to dissolve the chlorosilane. Hydrolyze.

The active silanol groups thus generated are polymerized by a dehydration condensation reaction, and the separated water layer retained in the toluene layer formed by dropping is removed, and the toluene layer is washed with water to further proceed with the dehydration condensation reaction. , toluene of siloxane oligomers with hydroxyl groups was obtained. Tri-(methyl ethyl ketoxime) is added to this toluene solution.
- A silicone resin solution for coating was prepared by adding 470 g of methoxysilane.

Example 1 (Manufacture of carrier) 3.4 g of dibutyltin diacetate was added to 240 g of the above-mentioned coating silicone resin liquid, and this was mixed into spherical ferrite particles (with an average particle size of 100 μm) at a temperature of 80° C. using a fluidized bed apparatus. (manufactured by Nippon Iron Powder Co., Ltd.) and further heat-treated at 200° C. for 1 hour to obtain a silicone resin-coated carrier having a tin content of 1.8% by weight in the coating layer. This carrier will be referred to as "carrier 1."

(Manufacture of toner) Styrene-acrylic copolymer with a weight average molecular weight of 12 x 10' (styrene/n-butyl acrylate = 75
/25) 100 parts by weight of carbon black "Mogull-LJ" (manufactured by Cabot Corporation) and 3 parts by weight of low molecular weight polypropylene "Viscol 660PJ (manufactured by Sanyo Chemical Industries, Ltd.) were mixed, and after melting and kneading, The powder was pulverized and classified to obtain toner powder with an average particle size of 12 μl, and fine silica powder “Aerosil R'-972J (manufactured by Nippon Aerosil Co., Ltd.) was mixed therein at a ratio of 0.8% by weight to produce a toner. This toner is referred to as "toner 1".

(Actual photocopying test) A developer was prepared by mixing the carrier 1 and toner I at a ratio of 3.5% by weight of the toner to the carrier.
Copy images were repeatedly formed using a modified machine J (manufactured by Konishiroku Photo Industry Co., Ltd.). As a result, all of the obtained copied images were of excellent image quality with no fogging, and even after the number of copying images exceeded 60,000, the obtained copied images were still of excellent quality without fogging. . In addition, the amount of charge of the toner at the initial stage of the developer is 21 μC/g, which is 6
The amount of charge after 10,000 copies was 20 μC/g, with almost no fluctuation. Further, when the carrier after 60,000 copies was observed under an electron microscope, no adhesion of toner substances to the surface of the carrier particles was observed, nor was any exposure of the carrier core material due to peeling off of the coating resin.

Example 2 (Production of carrier) In the production of the carrier in Example 1, the tin content ratio in the coating layer was set to 4.
．． A silicone resin coated carrier of 5% by weight was obtained.

This carrier will be referred to as "carrier 2."

(Photography test) A developer was prepared using this carrier 2 and the toner 1 used in Example 1 in the same manner as in Example 1, and a real photography test was conducted. All of the resulting copied images were of excellent quality with no fog, and the number of times the copied images were formed was 6.
Even after more than 10,000 repetitions, a copy image of excellent image quality without fogging was still obtained. Further, the charge amount of the toner at the initial stage of the developer was 18 μC/g, and the charge amount after 60,000 copies was 17 μC/g, with almost no fluctuation.

Further, when the carrier after 60,000 copies was observed under an electron microscope, no adhesion of toner substances to the surface of the carrier particles was observed, nor was any exposure of the carrier core material due to peeling off of the coating resin.

Example 3 (Production of carrier) A silicone resin was prepared in the same manner as in Example 1, except that the amount of dibutyltin diacetate was changed to 1.7 g, and the tin content in the coating layer was 0.9% by weight. A coated carrier was obtained. This carrier will be referred to as "carrier 3."

(Photography test) A developer was prepared using this carrier 3 and the toner 1 used in Example 1 in the same manner as in Example 1, and a real photography test was conducted. All of the resulting copied images were of excellent quality with no fog, and the number of times the copied images were formed was 6.
Even after more than 10,000 repetitions, a copy image of excellent quality without fogging was still obtained. In addition, the charge amount of the developer is somewhat low, at 15 μC/g at the initial stage and 12 μC/g after 60,000 copies.
However, there was no practical problem. Further, when the carrier after 60,000 copies was observed under an electron microscope, no adhesion of toner substances to the surface of the carrier particles was observed, nor was any exposure of the carrier core material due to peeling off of the coating resin.

Example 4 (Manufacture of carrier) Silicone having a tin content of 5.5% by weight in the coating layer was prepared in the same manner as in Example 1 except that the amount of dibutyltin diacetate was changed to 10.5 g. A resin-coated carrier was obtained. This carrier will be referred to as "carrier 4."

(Photography test) A developer was prepared using this carrier 4 and the toner 1 used in Example 1 in the same manner as in Example 1, and a real photography test was conducted. The amount of charge of the toner in this developer is 40 μC/g
Although the initial copy image had a slightly low density, it was free of fog.

The amount of charge after 45,000 copies was 13 .mu.C/g, and the resulting copied image had a high density, and although some fogging occurred, it did not pose a practical problem. Further, when the carrier after 45,000 copies was observed under an electron microscope, some adhesion of toner substance to the surface of the carrier particles was observed, but no exposure of the carrier core material due to peeling of the coating resin was observed.

Comparative Example 1 (Production of carrier) In the production of the carrier of Example 1, 2.8 g of isopropyl titanate was used instead of dibutyltin diacetate.
A silicone resin-coated carrier was obtained in the same manner except that . This carrier will be referred to as "comparison carrier 1."

(Photography Test) A developer was prepared in the same manner as in Example 1 using Comparative Carrier 1 and Toner 1 used in Example 1, and a real photography test was conducted. In the resulting copied image, capri was generated from the beginning and the image quality was poor. Also, the interior of the copying machine was so dirty due to toner scattering that the actual copying test was stopped after 2,000 copies.

In addition, the amount of charge of the toner at the initial stage of the developer is 8 μC/g.
The amount of charge after 2,000 copies was as low as 2 μC/g. Further, when the carrier was observed after 2,000 copies using an electron microscope, adhesion of toner substances to the surface of the carrier particles was observed at L2, and exposure of the carrier core material due to separation of ff1l+ of the coating resin was also observed.

〔Effect of the invention〕

As explained in detail above, the carrier of the present invention has a coating layer provided on its surface made of silicone resin and further contains tin, so that it is not coated! 'The mechanical strength of the IN is significantly superior, and the tin provides excellent positive triboelectric charging ability.As a result, the triboelectric charging properties are stable over a long period of time, resulting in good image quality without capri. It becomes possible to form images stably over a long period of time.・Specific organic tin compounds are also effective as curing agents for silicone resins, so by using such compounds, it is possible to incorporate tin into the coating layer without using special means. In this case, tin is not liberated and is reliably present in the coating layer due to chemical bonding force, and the effective portion of tin can reliably provide large mechanical strength and good triboelectric charging ability.

Since the carrier has such excellent triboelectric charging ability, it is not necessary to specifically include a charge control agent in the toner, or even if it is necessary, the content ratio is reduced. Therefore, the problem of deterioration in moisture resistance that occurs when toner contains a considerable amount of charge control agent does not occur.

Since such a coating layer improves the slipperiness of the surface of the carrier particles, the release properties of the surfaces of the carrier particles are excellent, preventing toner substances from adhering to the surfaces of the carrier particles, and from this point of view as well. The triboelectric charging ability becomes stable over a long period of time, and it becomes possible to stably form images of good quality without capri over a long period of time.

Claims (1)

[Scope of Claims] 1) A carrier for electrostatic image development, which has a coating layer made of silicone resin on its surface, wherein the coating layer contains tin. 2) The carrier for electrostatic image development according to claim 1, wherein the content of tin in the coating layer is 0.6 to 5.0% by weight. 3) The carrier for electrostatic image development according to claim 1 or 2, wherein the coating layer is formed by curing a silicone resin with a curing agent containing tin.