JPH0728278A - Positively charging magnetic one-component toner - Google Patents

Abstract

PURPOSE:To obtain the toner capable of forming a sleeve layer uniform in thickness at all times and consequently capable of forming a stabilized picture without lowering the picture density or the fluidity even after repeated printing in one-component development using the positively charging toner. CONSTITUTION:The one-component toner particle consists of a binder resin, a magnetic powder and a positive charge control agent, and the positively charging magnetic one-component toner contains a dry-process colloidal silica and a wet-process colloidal silica having 1-20mum volume average particle diameter. Since the dry-process colloidal silica and the wet-process colloidal silica are jointly used in the positively charging magnetic toner in one-component development, the defect caused when only the dry-process colloidal silica is used is eliminated, the fluidity is improved, the charge quantity is stabilized, and a high-quality picture is stably obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic toner for visualizing an electrostatic charge image in electrophotography and the like.

[0002]

2. Description of the Related Art The electrophotographic process is a process in which a photoconductive phenomenon is used to form an electrostatic latent image on a photoreceptor and toner is attached to the electrostatic latent image by electrostatic force to form a visible image. There are two types: a method of directly forming a toner image on a photosensitive paper (CPC) and a method of transferring a toner image formed on a photosensitive body to a recording paper (PPC). Electrophotographic developing methods include a dry developing method and a wet developing method, and the main dry developing method is a cascade developing method (US Pat. No. 2,221,776).
No.), two-component magnetic brush development method (US Pat. No. 28740)
63), one-component insulating toner developing method (Japanese Patent Publication No. 41-94)
No. 75), a one-component conductive toner developing method (US Pat.
909258), and so on.

The cascade developing method is a method in which gravity is used to drop a developer onto a photosensitive member to attach toner, but it is rarely used at present. Currently, the mainstream developing methods are the two-component magnetic brush developing method and the one-component insulating toner developing method, but the two-component magnetic brush developing method is a method in which toner particles and carrier particles are mixed with a developer. It is a system in which a developer is conveyed and developed by a developing roller on a magnet roller, which has the advantages of good image quality and colorization. But,
It requires a mechanism to keep the ratio of toner and carrier constant and a stirring mechanism for the developer, which makes the device large and complicated.
Since the charging ability is lowered due to the adhesion of the toner to the carrier surface, the carrier particles deteriorate when used for a long period of time, so that the developer needs to be replaced.

On the other hand, in the one-component insulating toner developing method, since carrier particles are not used, a mechanism for controlling the toner concentration and stirring is unnecessary, and the apparatus can be downsized. Moreover, there is no waste such as waste carriers.
There is also an advantage. As a typical one-component insulating toner developing method, a BMT method using triboelectric charging between toner particles, a jumping developing method of flying magnetic toner charged triboelectrically with a sleeve or a blade, and the like are well known. Among them, in the jumping developing method, a bias voltage is applied to the gap provided between the toner layer and the photoconductor to eject the toner onto the photoconductor to perform the development. There are few stains on the product, and the development speed can be increased.

In the electrophotographic development method, a positive development method in which a toner having a charge having a polarity opposite to that of the latent image charge is attached, and a charge having the same polarity as the charge on the photoconductor is formed at a place where the charge on the photoconductor is removed. There are two types of reversal development methods that deposit charged toner. Plain paper copying machines mainly use the positive development method, but printers and digital copying machines use the reverse development method. For example, a laser beam printer uses a semiconductor laser (light emission wavelength of 760 to 830 nm) as a light source,
The laser light emitted from the light source is scanned on the surface of the photoconductor by a polygon mirror to remove the electric charge in the image area and form an electrostatic latent image. In this system, the light source is very small, so that high resolution can be obtained, and the demand is increasing with the office automation.

The toner applied to the one-component developing method is one in which a dye, a pigment, a magnetic powder and the like are dispersed in a binder resin, melted and kneaded by a twin-screw extruder, and then pulverized and classified to 1 to 30 μm. It is used. Further, dry colloidal silica or the like is used as an external additive of the toner, which greatly contributes to the improvement of fluidity. It is also well known to use wet silica as an external additive for improving fluidity and chargeability. When the fluidity is improved, uniformization of the toner layer on the sleeve during development is promoted, and a stable image can be obtained. However, when the printing is repeated, the toner deteriorates due to collision between the toner particles or between the toner and the sleeve, and pressure is applied to deteriorate the fluidity, and the charging becomes unstable, and a uniform image cannot be obtained. To obtain a stable image, it is also necessary to give a stable charge to the toner. Therefore, it is better to add a metal oxide such as aluminum oxide or zinc oxide, which is a charging aid, to the toner to supplement the charged charge. To be

However, since these conventional metal oxides generally have an indefinite shape, the photosensitive member is damaged by the pressure of the blade or the fur brush in the cleaning section for removing the residual toner. Further, since the volume average particle diameter is often 0.1 μm or less, the physical adhesion force such as van der Waals force is large when it is added to the toner. Therefore, it adheres firmly to the toner surface,
As a result, the toner fluidity is reduced. The decrease in toner fluidity hinders the formation of a good sleeve layer pressure and decreases the image density. Therefore, these metal oxides cannot sufficiently compensate for the adverse effects caused by the addition of dry colloidal silica.

Further, since wet silica itself has hydrophilicity, it deteriorates environmental stability characteristics. Especially high temperature,
It causes fog in high humidity. Therefore, a method of making the silica surface hydrophobic is often used. JP-A-58-
In JP 60754, a method of hydrophobizing the surface of wet silica with silicone oil and mixing it in the toner is disclosed in Japanese Patent Laid-Open No.
Japanese Patent No. 170947 proposes a method in which the surface of wet silica is subjected to a hydrophobic treatment with a dimethylsilane compound or a trimethylsilane compound and mixed in the toner. When wet silica and dry colloidal silica are used in combination, the particle size of wet silica is larger than that of dry colloidal silica, so if a large amount is added to improve the fluidity of the toner, filming may occur on the photoreceptor. . In JP-A-4-80764, in order to solve this problem, dry colloidal silica and a hydrophobicity of 50 to 80%,
A method has been proposed in which wet silica having an average particle size of 0.05 to 5 μm and further containing 10 μm or more of coarse particles is not used and is mixed into the toner.

In this method, however, the purpose of imparting fluidity to the toner is achieved by reducing the average particle size of the wet silica, so that the silica toner, which occurs during repeated printing, is generated. Embedding on the surface cannot be prevented. For this reason, there is a problem that the fluidity of the toner decreases with repeated printing, and the image deteriorates.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a toner in which the image density does not decrease even when repeatedly printed in a one-component developing method using a positively chargeable toner. A further object of the present invention is to provide a toner capable of obtaining a stable image by forming a uniform sleeve layer thickness without causing deterioration in fluidity even when printing is repeated.

[0011]

The first invention is a one-component toner particle containing a binder resin, magnetic powder and a positive charge control agent as main components, wherein dry colloidal silica and a volume average particle diameter of 1 to 20 μm are used. It is a positively chargeable magnetic one-component toner containing wet silica. The second invention is the positively chargeable magnetic one-component toner of the first invention, which is manufactured by a mechanical pulverization method. A third invention is the positively chargeable magnetic one-component toner of the first invention, characterized in that the dry colloidal silica has a positively chargeable property.

A fourth invention is the positively chargeable magnetic one-component toner of the first invention, wherein the wet silica is hydrophobized with dimethylpolysiloxane. As a result of studies to solve the above-mentioned problems, the present inventors have found that the toner has a dry colloidal silica content of 1 to 20 μm and a volume average particle size of 1 to 20 μm.
It has been found that the object can be achieved by adding the wet silica mentioned above together. When dry colloidal silica and wet silica having a volume average particle diameter of 1 to 20 μm are used together in the toner, the dry colloidal silica greatly contributes to the improvement of the fluidity of the toner, and the wet silica contributes to the charging of the toner. Contribute.

The conventional metal oxides, which are charging assistants, have the drawback of imparting charge to the toner but deteriorating the fluidity of the toner. However, the wet silica has a volume average particle diameter of 1 to 1. Since it is 20 μm, the van der Waals force is weak, it does not adhere firmly to the toner surface, and it exists in a state of being separated from the toner. Therefore, even if the wet silica is added, the fluidity of the toner is not impaired, and conversely, an effect of improving the fluidity of the toner can be obtained although it is slight. The method for producing the dry colloidal silica used in the present invention is generally produced by hydrolyzing silicon tetrachloride gas in a flame of hydrogen and oxygen, and is represented by the following formula.

2H ₂ + O ₂ → 2H ₂ O SiCl ₄ + 2H ₂ O → SiO ₂ + 4HCl SiCl ₄ + 2H ₂ + O ₂ → SiO ₂ ↓ + 4HCl ↑ Further, dimethyldichloro for imparting hydrophobicity. It is known to modify with silane and the like. The amount of dry colloidal silica added is 0.01 to 100 parts by weight of the toner.
3 parts by weight is preferable, and 0.1 to 0.5 parts by weight is particularly preferable. If the amount added is 0.01 part by weight or less, sufficient fluidity cannot be obtained, and the effect of the present invention cannot be obtained.

Further, even if it is added in excess of 3 parts by weight, the fluidity does not increase in proportion to the added amount, and conversely the cost increases, which is not suitable. Next, regarding wet silica, various manufacturing methods thereof are known. Currently, it is manufactured by a method of precipitating silica by neutralizing and decomposing sodium silicate with an acid or an alkali metal salt. The reaction formula is as follows. Na ₂ O ・ x SiO ₂ + H ₂ So ₄ ───── ＞ xSiO ₂・ n H ₂ O + Na ₂ SO ₄ Na ₂ O ・ x SiO ₂ + CaCl ₂ + 2HCl ── ＞ xSiO ₂・ n H _{The amount of 2} O + CaCl ₂ wet silica added is 100 parts by weight of the toner,
0.01 to 5 parts by weight is preferable, and 0.1 is particularly preferable.
~ 2 parts by weight.

If the amount of wet silica added is more than 5 parts by weight, the charge imparted to the toner becomes too high and the fog phenomenon occurs, which is not preferable. The volume average particle diameter is preferably 1 to 20 μm, particularly preferably 1 to 1
It is 0 μm. When the above numerical value is 1 μm or less, the van der Waals force becomes large, and when it is added to the toner, it firmly adheres to the toner surface and reduces the toner fluidity, which is not preferable. Further, if it is 20 m or more, the specific surface area is reduced and the charge imparting ability to the toner is lowered, which is not preferable. Here, the volume average particle diameter is a value measured by the Coulter counter method.

As the binder resin used in the present invention, polystyrene type, styrene-acrylic copolymer type, ethylene vinyl acetate copolymer type, vinyl acetate type, acrylic type and the like can be used. Further, as the positive charge control agent, a nigrosine-based oil-soluble dye is the most common, but in addition,
Crystal violet, quaternary ammonium salt and the like can also be used in the present invention. As the magnetic powder, known ferrite powders such as various ferrites, magnetites and hematites can be used. If necessary, wax or the like can be added.

[0018]

EXAMPLES The present invention will be described in more detail below with reference to examples. In addition,% shows weight% and a part shows a weight part. Example 1 Styrene acrylic resin 62 having a number average molecular weight of 12000
%, Magnetite 35% with a volume average particle size of 4 μm, polypropylene wax with a number average molecular weight of 4000 1%, and nigrosine dye 2% were mixed using a Henschel mixer, melt-kneaded with a twin-screw extruder, and then with an atomizer grinder. The powder was pulverized and further classified to 12 μm by an air stream classifier to obtain a base toner. To 100 parts of the obtained base toner, 0.5 parts of dry colloidal silica surface-treated with polysiloxysan and water glass were neutralized with hydrochloric acid, filtered, washed with water, dried, and then pulverized and classified to 6 μm. 2 parts by weight of the wet silica prepared above was added and dry-mixed with a Henschel mixer to obtain a test toner.

The obtained toner was subjected to image formation using a commercially available copying machine (trade name: NP-4330 Canon Inc.) adopting a one-component developing method, and an image density of 1.35 (reflection densitometer Macbeth RD-918 was used) and no fog was observed. When a printing durability test was conducted on 50,000 sheets, an image density of 1.32 equivalent to the initial level was obtained even after printing 50,000 sheets, and similarly, fog was not observed, and stable and high-quality images were obtained. I was able to get Example 2 0.1 part of dry colloidal silica surface-treated with polysiloxysan on the base toner of Example 1, water glass was neutralized with hydrochloric acid, filtered, washed with water, dried, and then pulverized and classified to 6 μm. A test toner was obtained in the same manner by adding 1 part of wet silica.

The obtained toner was subjected to image formation by using a commercially available copying machine (trade name: NP-4330, manufactured by Canon Inc.) adopting the one-component developing method. As a result, an image density of 1.35 was sufficiently obtained. No occurrence of fog was observed. Moreover, when a printing durability test of 50,000 sheets was performed, even after printing 50,000 sheets,
An image density of 1.31 equivalent to that at the initial stage was obtained, and similarly, generation of fog was not observed, and a stable high-quality image could be obtained. Comparative Example 1 To the base toner of Example 1, only 0.3 part of dry colloidal silica surface-treated with polysiloxysan was added to obtain a test toner in the same manner.

The obtained toner was subjected to image formation using a commercially available copying machine (trade name: NP-4330 Canon Inc.) adopting the one-component developing method, and the image density was as low as 1.05.
Some fog also occurred. In addition, a printing durability test of 50,000 sheets was performed, and after printing 50,000 sheets, the image density was 1.
It was as low as 00 at the beginning, the fog was worse than at the beginning, and the image was unbearable for use. Comparative Example 2 0.3 parts of dry colloidal silica surface-treated with polysiloxysan was added to the base toner of Example 1, and the volume average particle size was 0.
A test toner was obtained in the same manner by adding 2 parts by weight of 02 μm tin oxide.

The obtained toner was subjected to image formation using a commercially available copying machine (trade name: NP-4330 Canon Inc.) adopting the one-component developing method, and the image density was as low as 0.90, showing a sufficient image density. Couldn't get

[0023]

When the dry colloidal silica and the wet silica having a volume average particle size of 1 to 20 μm are added to the toner in combination, the dry colloidal silica adheres to the surface of the toner and acts to improve the fluidity. It is considered that the presence of the particles separated between the toner particles causes frictional charging with the toner particles without impairing the fluidity, and acts as a function of imparting charging.

[0024]

In the positively chargeable magnetic toner in the one-component developing method, when wet colloidal silica having a volume average particle diameter of 1 to 20 μm and dry colloidal silica are used in combination, dry colloidal silica is used alone. It is possible to obtain a stable and high-quality image by solving the above-mentioned drawback, improving the fluidity and stabilizing the charge amount.

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display area G03G 9/08 375

Claims (4)

[Claims] 1. A one-component toner particle containing a binder resin, a magnetic powder and a positive charge control agent as main components, which contains dry colloidal silica and wet silica having a volume average particle size of 1 to 20 μm. Positively chargeable magnetic one-component toner. 2. The positively chargeable magnetic one-component toner according to claim 1, which is manufactured by a mechanical grinding method. 3. The positively chargeable magnetic one-component toner according to claim 1, wherein the dry colloidal silica has a positively chargeable property. 4. The positively chargeable magnetic one-component toner according to claim 1, wherein the wet silica is hydrophobized with dimethylpolysiloxane.