JPH06103402B2 - Negative charging magnetic developer - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a magnetic developer used in electrophotography, and more particularly to a negatively chargeable magnetic developer excellent in fluidity and charge stability.

(Prior Art) A two-component developer conventionally used as a developer for electrophotography, which is a mixture of Natto powder composed of resin and pigment such as carbon black, and carrier particles composed of magnetic powder such as iron powder or glass beads. A one-component magnetic developer containing a developer and magnetic powder such as magnetite in toner powder is known.

According to the developing method using the two-component phenomenon agent, the toner powder is charged by mutual friction between the toner powder and the carrier particles,
A magnetic brush is formed on a non-magnetic sleeve having a magnet inside, and it is brought into sliding contact with a photoconductor having an electrostatic latent image for development, but only toner powder is consumed, so It is necessary to keep the toner concentration constant, and a stirring means is also required on the apparatus, so that the size tends to increase.

On the other hand, the developing method using a one-component magnetic developer is one in which the developer is charged with each other or by friction with the sleeve surface as described above, is brought into contact with the photoreceptor, and the developer is transferred to perform development. Since it is not necessary to control the toner concentration unlike a two-component system and the apparatus system can be downsized, it is useful for downsizing and cost reduction of the copying machine itself, and therefore, the development thereof is being particularly advanced.

However, since it is necessary to form a uniform thin layer on the sleeve, this one-component developer is required to have excellent predeterminedness in fluidity and chargeability of the developer.

Conventionally, in order to solve these problems, means such as surface-treating the developer with a fluidizing agent such as hydrophobic silica has been used, but it shows excellent properties in the initial stage, but in the long-term use, the fluidizing agent is used. Since the hydrophobic silica itself shows a large negative chargeability on the surface of the developer, the developer is electrostatically aggregated and the surface characteristics of the agent change due to the decrease in fluidity or the drop from the developer surface. The characteristics could not be maintained, and problems such as reduction in image density occurred. In addition, it has been proposed that silica, which has been hydrophobized with silicone oil, is used as a fluidizing agent to improve the fluidity and charge stability of silica produced by the wet method. A developer treated with silica has a difficulty in obtaining a charge amount for obtaining a good image, and is not satisfactory at the initial density.

In addition, recently, a method has been proposed in which a magnetic brush of a one-component developer is held in a non-contact state, and the developer is caused to fly by an electric field or a magnetic field to perform development. According to this method, there is an advantage that background fog, which is a characteristic development in contact development, can be reduced. However, according to this developing method, it is necessary to form an extremely thin developer layer on the sleeve. Therefore, a developer having a particularly excellent fluidity is required, and in repeated copying, environmental changes etc. are caused. On the other hand, it is always necessary to have stable electric resistance and stable layer formation. In the case of using a conventionally known magnetic developer, none of the above-mentioned characteristics is satisfactory, and the density is lowered and the density is changed due to repeated copying of image unevenness.

(Summary of the Invention) As a result of intensive studies in view of the above-mentioned present situation, the present inventors have obtained an excellent result by simultaneously using hydrophobic silica and a metal oxide coated with a modified low silicone oil as a surface treatment agent. It is possible to add liquidity,
It has been found that it becomes possible to maintain the developer electrification current high and stably.

That is, according to the present invention, in a negatively chargeable developer mainly composed of a fixing solvent and magnetic powder, the developer is coated with hydrophobic silica and amino- or mercapto-modified silicone oil as a surface treatment agent. There is provided a negatively chargeable magnetic developer, characterized in that the prepared metal oxide is supported at a weight ratio of 1: 3 to 5: 2.

Further, the metal oxide is preferably composed of wet process silica or alumina alone, more preferably a combination of wet process silica and alimina.

(Example) The present invention will be described in detail below.

The characteristics of the magnetic developer are roughly classified into a magnetic characteristic and a charging characteristic. The magnetic characteristic is determined by the magnetic powder contained and is an almost invariable factor. The charging property is almost determined by the charging property of the fixing medium used, but since this medium has a strong tendency to be determined from the viewpoint of the fixing property, difficult control of the charging property is almost impossible. In addition, since the charging property depends on the surface property of the developer, the surface treatment agent is a major factor for controlling the surface property.

An important feature of the present invention is that hydrophobic silica and a metal oxide coated with an amino- or mercapto-modified silicone oil are simultaneously used as a surface treatment agent. When the hydrophobic silica is used alone, as described above,
Since the hydrophobic silica itself exhibits a large negative charging property, it causes a decrease in fluidity, but the addition of the metal oxide subjected to the above-mentioned predetermined coating treatment can suppress this decrease in fluidity, resulting in a long-term It becomes possible to maintain excellent fluidity. On the other hand, with only the coated metal oxide, although the fluidity is improved, on the contrary, the negative charging property is decreased,
Causes a decrease in concentration.

For the above reason, the hydrophobic silica and the coated metal oxide are supported on the particle surface of the developer in a weight ratio of 1: 5 to 10: 1, particularly 1: 2 to 5: 1. Is preferred.

The hydrophobic silica used in the present invention, which is produced by a dry method, has a silanol group on the surface blocked by dimethylcyclolosilane or the like to be hydrophobized.

As the metal oxide, wet silica (hydrophilic silica) produced by a wet method or alumina produced by a gas phase method can be used alone or in combination.

In the present invention, the amino-modified silicone oil for coating the above-mentioned metal oxide is one in which a part of the methyl group of the side chain among the siloxane bonds of general silicone oil is modified to an organic group containing at least nitrogen. Yes, and is represented by the following general formula (1).

However, m ≧ 1 n ≧ 1 R ₁ : an alkylene group having 5 or less carbon atoms R ₂ , R ₃ : hydrogen, an alkyl group or —R ₄ —NH ₂ (R ₄ : an alkylene group having 5 or less carbon atoms) R ₅ : methyl Group or methoxy group Typical examples include the following [I] and [II].

Further, the mercapto-modified silicone oil is one in which the methyl group of the side chain is substituted with an organic group having at least a sulfur atom, like the amino-modified silicone oil, and is represented by the following general formula (2).

However, m ≧ 1 n ≧ 1 R ₁ : alkylene group having 5 or less carbon atoms R ₂ : hydrogen, alkyl group or —R ₄ —SH (R ₄ : alkylene group having 5 or less carbon atoms) There is.

In the present invention, the coating treatment of the metal oxide is obtained by dissolving the modified silicone oil described above in a solvent such as toluene, dispersing the metal oxide, and then drying by heating or vacuum treatment at 100 to 200 ° C. . The surface treatment agent obtained by such treatment is in a state of being covered with oil, that is, made hydrophobic. When two types of metal oxides are obtained during the coating treatment, the treatments may be performed separately, but when the same oil is used, the two types of metal oxides are simultaneously dispersed in the oil solution. It is also possible to do so.

The amount of surface treatment agent is 100 parts by weight of the developer before treatment,
It is preferably treated at a rate of 0.1 to 5 parts by weight, particularly 0.5 to 2 parts by weight. If the surface treatment agent is less than 0.1 parts by weight,
The effect as a surface treatment agent cannot be exhibited, and the charge amount is insufficient. On the other hand, if the amount exceeds 5 parts by weight, the surface treatment agent carrying capacity per developer particle becomes more than the capacity, so that the surface treatment agent is often desorbed, resulting in adverse effects on the inside of the machine as well as on the photoreceptor.

The magnetic developer of the present invention is basically composed of a magnetic powder such as magnetite in an amount of 30 to 60% by weight with respect to the total amount of the developer in a fixing medium, and a powder pair formed by dispersing a charge control agent if desired. Composed of compositions. These dispersions are in terms of their dispersibility
It is preferred to use those in the range of 0.1 to 5 microns.

The fixing resin used in the present invention is particularly limited to a resin for negative charging, preferably styrene,
Vinyl toluene, α-methylstyrene, α-chlorostyrene, vinyl naphthalene, vinyl aromatic monomers such as vinyl xylene, acrylic acid, methacrylic acid, ethyl acrylate, methyl methacrylate, butyl methacrylate, butyl acrylate, 2-ethylhexyl acrylate, A homopolymer of an acrylic monomer such as 2-ethylhexyl methacrylate or a copolymer thereof is used. Further, as monomers that can be combined with these resins, butadiene, isoprene, conjugated diolefin-based monomers such as chloroprene, fumaric acid, and ethylenically unsaturated carboxylic acids such as maleic anhydride or esters thereof,
Examples thereof include vinyl esters such as vinyl acetate.

Further, as the fixing medium, low molecular weight olefin resins such as low molecular weight polypropylene and low molecular weight polyethylene, and various waxes such as paraffin wax and carnauba wax are added as an anti-offset agent in an amount of 2 to 20% by weight based on the whole medium. Is also possible. At this time,
These offset preventing agents can be simply kneaded with the above-mentioned resins, but can also be coexisted during the polymerization of the fixing medium.

As the charge control agent, it is preferable to use a dispersion type in a fixing medium. Chromium in the negatively chargeable magnetic developer,
Complex salt azo dyes such as iron and cobalt are used.

In the production of the magnetic developer of the present invention, a fixing medium, magnetic powder and the like are mixed at a predetermined ratio and then kneaded by a three-roll, twin-screw extrusion method or the like, and thereafter, pulverization and classification are carried out if desired. A developer having a particle size of 5 to 30 μm is manufactured by performing heat treatment or the like. The surface treatment agent can be supported on the surface of the developer by subjecting this developer to the above-mentioned surface treatment agent and a supermixer, etc., by performing a dusting treatment. When the surface treatment agent is dazzled, the hydrophobic silica and the coated metal oxide may be sprinkled separately, or may be previously mixed as a surface treatment agent and dipped with this mixture. . In addition, in the dusting treatment, the surface treatment agent is carried on the powder surface by electrostatic attraction such as van der Waals force, but if desired, heat treatment after the dusting treatment is carried out to fix it on the powder surface and carry it. It is also possible to let.

The developer of the present invention is particularly suitable for a developing method that requires fluidity and charge stability, for example, the applicant of the present invention has previously filed Japanese Patent Application No. 59-202977.
It is effective for the developing method proposed in. This development method is the first
It will be described with reference to the drawings.

A cylindrical non-magnetic sleeve 2 made of Al or the like is arranged at a position close to the photoconductor 1. Inside the sleeve 2, an N-pole repulsive electrode 3 is provided in a position close to the photoconductor 1, and other magnets 4 having different polarities are alternately provided inside. An ear cutting member 5 made of a magnetic material is arranged above the sleeve. The behavior of the developer will be described below. The hopper 6
The developer 7 contained therein is conveyed to the developing area 8 as the sleeve 2 rotates after being regulated to a predetermined layer pressure by the bristle cutting member 5. In the developing area 8, as shown in the enlarged view of FIG. 2, the developer layer 9 is loosened by the repulsive magnetic field 3 of the magnet 4, and the floating toner 10 is formed between the developer layer 9 and the photoconductor 1. Floating toner
10 is electrostatically and selectively attracted to the electrostatic latent image 11 by its own electric charge, so that the latent image 11 becomes a visible image 12. The developer 7 having passed through the developing area 8 is returned to the inside of the hopper 6 again as the sleeve 2 rotates, and stands by for the next development.

According to such a developing method, it is necessary to bring the photosensitive sleeves close to each other, and it is necessary to set the layer thickness so that the developer layer does not contact the photosensitive body. To a very thin layer of 30 to 200 μm.
In order to form such a thin layer, it is at least necessary that the developer does not aggregate at the bristle cutting position.

In addition, since the transfer to the photosensitive member 1 is governed by the charge amount of each developer in the developing area 8, it is necessary to always maintain a stable charge amount.

According to this developing method, by using the developer of the present invention, it is possible to stably form the above-mentioned layer thickness due to excellent fluidity, that is, non-aggregating property.

Moreover, in the developing area 8, stabilization of the charging characteristics is achieved, and it becomes possible to supply a stable image over a long period of time.

According to the developing method of the present invention, the coercive force of the developer is set in the range of 40 to 3000e in view of the magnetic attraction force by the magnet 4 in the developing area 8 and the transportability on the sleeve 2. Is preferred.

This developing method is not limited to the configuration shown in FIG.
All changes are possible. For example, instead of the bristle cutting member 5, a flexible member such as a film or a metal thin plate may be used to regulate the layer by surface contact with the developer. If desired, for the purpose of improving the reproducibility of fine lines and gradation of the image, the bias applying means 13 applies a direct current or a pulse voltage of the same polarity as the latent image polarity of the photoconductor to the sleeve 2 within a range not higher than the potential of the photoconductor. It is also possible to apply.

The invention is illustrated in the following example.

Example Styrene-butyl acrylate copolymer 55 parts by weight Low molecular weight polypropylene 5 parts by weight Magnetite (coercive force 100 Oersted average particle size 0.2 μ
m) 40 parts by weight Negative charge control agent 0.5 parts by weight The mixture of the above formulation was melt-kneaded by a twin-screw extruder and then pulverized by a jet mill to obtain a developer having a particle size of 5 to 25 μm. The coercive force of the developer was 1000e and the saturation magnetization was 32emu / g.

Then, the obtained developer was treated with a surface treatment agent by a super mixer according to the composition of the surface treatment agent shown in Table 3.

In addition, the oil treatment of the surface-treating agent was carried out by dispersing 10 g of any of the metal oxides shown in Table 2 in a solution prepared by dissolving 0.5 g of oil in 150 ml of toluene using the silicone oil shown in Table 1. Heat dry at 100 ° C. After cooling, the surface treatment agent aggregated with a mixer was pulverized and then the aggregate was removed.

The metal oxides shown in Table 2 were used.

According to the formulation shown in Table 3, the surface-treated developer was subjected to a copy test using the developing device shown in FIG. The development conditions are: developer layer thickness 100 μm, amorphous silicon photoreceptor, maximum surface potential +450 V, repulsive magnetic field (maximum drop height)
The setting was 100 gauss and the distance between the photosensitive member and the sleeve was 200 μm.

As is clear from Table 3, hydrophobic silica alone (No. 11)
The initial concentration was high, but the fluidity decreased and fogging was noticeable. The coated alumina alone (No.14)
However, the charge amount was insufficient and the density was low. In addition, those treated with unmodified silicone oil (No.
6, 10) all had insufficient fluidity and lacked stability. In contrast to these comparative examples, the developer of the present invention is
All of them were excellent in image characteristics and fluidity, and stable images were obtained.

(Effects of the Invention) As described above, the developer of the present invention has a fluidity by using hydrophobic silica and a metal oxide coated with amino-modified or mercapto-modified silicone oil as the surface treatment agent. In addition, since the charging stability is improved and the charging stability is excellent, a stable image can be obtained for a long period of time.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a developing method using the developer of the present invention, and FIG. 2 is an enlarged view of a developing area of the developing method of FIG. 1 ... Photoconductor, 2 ... Sleeve 4 ... Magnet, 7 ... Developer

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-59-143161 (JP, A) JP-A-57-201253 (JP, A) JP-A-59-200265 (JP, A) JP-A-55- 26518 (JP, A) JP-A-60-84546 (JP, A)

Claims (2)

[Claims] 1. A negatively-charged developer containing a fixing medium and magnetic powder as main components, the developer being a surface treatment agent, a metal coated with hydrophobic silica and amino- or mercapto-modified silicone oil. A negatively chargeable magnetic developer, characterized in that an oxide is supported at a weight ratio of 1: 3 to 5: 2. 2. The negatively chargeable magnetic developer according to claim 1, wherein the metal oxide is wet process silica or alumina alone or in combination.