JPH07152196A - Electrophotographic toner - Google Patents

Abstract

PURPOSE:To surely polish and remove the oxidized surface layer of an amorphous silicon photoreceptor, to prevent image blurring and to form a satisfactory image by adding alumina particles having a specified average particle diameter and magnetite particles having a specified average particle diameter to toner particles. CONSTITUTION:Alumina particles having 0.1-2mum average particle diameter and magnetite particles having 0.1-2mum average particle diameter are added to toner particles preferably by 1-5 pts.wt., in total, per 100 pts.wt. of the toner particles so that the weight ratio between the alumina particles and the magnetite particles in the resulting electrophotographic toner is preferably regulated to 1:5 to 5:1. Known magnetite particles such as a natural product which is obtd. naturally as magnetite or a synthetic product synthesized from iron, iron (III) oxide, etc., as starting materials may be used as the magnetite particles blended with the alumina particles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic toner, and more particularly to an electrophotographic toner suitable for use in an image forming apparatus using an amorphous silicon photoconductor.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electrostatic copying machine or a laser beam printer, the surface of a photoconductor is first uniformly charged (charging step) and then exposed to expose the surface of the photoconductor. An electrostatic latent image is formed on the surface (exposure step). Next, a developer is brought into contact with the surface of the photoconductor by a developing device. Then, the toner contained in the developer electrostatically adheres to the electrostatic latent image, and the electrostatic latent image is visualized as a toner image (developing step). Next, when this toner image is transferred from the surface of the photoconductor onto the paper (transfer step) and fixed (fixing step), an image corresponding to the electrostatic latent image is formed on the surface of the paper.
Further, after the toner image is transferred onto the paper, the toner remaining on the surface of the photoconductor is removed by a cleaning blade or the like pressed against the surface to prepare for the next image formation (cleaning step). .

As the photoconductor used in the above image forming apparatus, those made of various photoconductive materials have been conventionally used. Among them, the photoconductor using amorphous silicon has a surface hardness of Vickers hardness ( Hv) 200
Since it is extremely hard at about 0, a highly reliable and long-life photoreceptor can be formed, and the amorphous silicon-based material is a non-polluting substance, which is industrially excellent.

However, the surface of the amorphous silicon photoconductor is oxidized by ozone generated during the charging process to form a surface oxide layer, and the surface oxide layer adsorbs moisture in the air, thereby exposing the charge. Leakage tends to occur in the surface direction of the body, and as a result, so-called image deletion occurs in the formed image and the image quality deteriorates, and in particular, the characters and the like of the formed image become difficult to read.

Therefore, by utilizing the fact that the surface hardness of the amorphous silicon photoconductor is extremely hard as described above and is not greatly damaged by a little polishing, the toner and the
Abrasive particles are externally added to the toner of a two-component developer containing a carrier that circulates in the developing device while adsorbing the toner, and the surface oxide layer is polished in, for example, a developing process or a cleaning process. Attempts have been made to polish and remove with agent particles.

Further, as the abrasive particles, alumina,
It has been reported to use particles of magnetite, cerium oxide, strontium titanate or the like.

[0007]

However, among the above, the alumina (α-alumina) particles have a high Vickers hardness (Hv) of about 2000, so that the cleaning blade made of, for example, rubber is easily damaged. There is a problem that toner with poor cleaning is brought into pressure contact with and adheres to the surface of the photoconductor to generate image black spots. The alumina particles have a volume resistivity value of 10 ¹⁵ Ω.
Since it is as large as cm, there is a problem that the charge amount of the toner is increased and the image density of the formed image is lowered.

Further, since the magnetite particles have a Vickers hardness (Hv) of about 500, which is low, it is necessary to add a large amount of them externally in order to obtain a sufficient polishing effect, but the volume resistivity thereof is 10 ³ Ω. Since the size is as small as cm, there is a problem that at the time of development, the toner flows forward in the rotation direction of the photosensitive member, and so-called front pulling occurs in the formed image. Further, the cause of the toner using magnetite particles as the abrasive particles is unknown, but there is a problem that the charge amount is reduced particularly in a low temperature environment of 15 ° C. or less, and defects such as toner scattering and fog occur. .

Further, the cerium oxide particles have an insufficient polishing effect when used on a photoreceptor which has been used for a long period of time, so that the image deletion cannot be sufficiently prevented, and the strontium titanate particles can be removed from the toner surface. There is a problem that the photoconductor is easily detached and remains on the surface of the photoconductor even after the transfer, so that the photoconductor is easily damaged. The present invention has been made in view of the above circumstances, and in particular, the surface oxide layer of an amorphous silicon photoconductor can be surely polished and removed to sufficiently prevent image deletion and cause various image defects. It is an object of the present invention to provide an electrophotographic toner capable of forming a good image without the need.

[0010]

In order to solve the above problems, the present inventors have studied blending alumina particles and magnetite particles among the conventional abrasive particles. That is, the alumina particles have the above disadvantages because the hardness is too high and the volume resistivity is too large, while the magnetite particles have the hardness too low and the volume resistivity is too small. Therefore, if both are blended and the appropriate hardness, that is, the polishing force, and the appropriate electric resistance, that is, the charging property of the toner are adjusted, the disadvantages of both are eliminated. He thought that he could bring out only the strengths.

Therefore, the electrophotographic toner of the present invention is
Alumina particles having an average particle size of 0.1 to 2 μm and magnetite particles having an average particle size of 0.1 to 2 μm are externally added to the toner particles. In the electrophotographic toner of the present invention, the weight ratio of alumina particles to magnetite particles is preferably within the range of 1: 5 to 5: 1. The total amount of externally added alumina particles and magnetite particles is preferably 1 to 5 parts by weight with respect to 100 parts by weight of the toner particles.

The present invention will be described below. In the present invention, both the alumina particles and the magnetite particles used as the abrasive particles have a particle size limited to the range of 0.1 to 2 μm as described above. If the particle size of both abrasive particles is less than 0.1 μm even on the one hand, the polishing effect of the small abrasive particles decreases,
Image deletion cannot be prevented.

On the other hand, if the particle size of both abrasive particles exceeds 2 μm even on the one hand, the abrasive particles are likely to separate from the toner particles, the charging characteristics of the toner deteriorate, and the transfer efficiency decreases. And image fogging, and toner scattering causes dust inside the image forming apparatus. As the alumina particles of the both abrasive particles, α-type, β-type and γ-type crystal type, each can be used, but in particular, the surface oxide layer of the amorphous silicon photoreceptor is surely polished, In order to ensure sufficient hardness for removal, α-type alumina particles are mainly used.

Alumina is also included in the fine particles externally added to the conventional electrophotographic toner as a fluidizing agent and a charge control agent, and the externally added alumina is externally added as abrasive particles in the present invention. The particle size is remarkably smaller than that of the alumina particles, for example, those manufactured by a vapor phase method (such as those manufactured by Nippon Aerosil Co., Ltd.), and the particle size is 0.
Since it corresponds to a particle size of less than 1 μm, it is distinguished from the alumina particles having a particle size of 0.1 to 2 μm in the present invention. It should be noted that the electrophotographic toner of the present invention may be externally added with fine particles such as the externally added alumina as a fluidizing agent or a charge adjusting agent, as described below.

As the magnetite particles to be blended with the above-mentioned alumina particles, there are various conventionally known magnetite particles such as natural products produced naturally as ditite or synthetic products synthesized from iron, iron (III) oxide and the like as raw materials. Magnetite particles can be used. The ratio of the alumina particles and the magnetite particles is not particularly limited in the present invention, but in order to obtain the combined effect of the two abrasive particles, as described above, the weight ratio is 1: 5 to 5: 1.
It is preferably within the range.

If the proportion of the alumina particles is smaller than the above range, the disadvantages of the magnetite particles will be more pronounced, and the formed image may be pre-cured, or toner scattering and fog may occur particularly in a low temperature environment. On the other hand, if the proportion of magnetite particles is small, the disadvantages of alumina particles will appear more strongly, and image black spots may occur in the formed image, or the image density of the formed image may decrease.

The ratio of both abrasive particles is more preferably within the above range, and more preferably within the range of 1: 3 to 3: 1 by weight. Further, the total amount of external addition of both the abrasive particles is preferably 1 to 5 parts by weight with respect to 100 parts by weight of the toner particles. If the total amount of external addition of both abrasive particles is less than the above range, the effect of addition is not sufficiently obtained, and the surface oxide layer of the amorphous silicon photoreceptor cannot be sufficiently polished and removed, so that a flow occurs in the formed image. There is a risk.
On the other hand, when the total amount of external addition of both abrasive particles exceeds the above range, the amount of abrasive particles separated from the toner particles increases, and the toner charging characteristics deteriorate, so the transfer efficiency decreases. In addition, there is a possibility that the toner may scatter and stain the inside of the machine.

As the toner particles to which the above-mentioned abrasive particles are externally added, any known toner conventionally used in the dry developing method can be used. Such a toner is usually manufactured by dispersing additives such as a colorant in a fixing resin. Examples of the fixing resin include styrene polymers, acrylic polymers, styrene-acrylic polymers, chlorinated polystyrene, olefin polymers such as polypropylene and ionomers, polyvinyl chloride, polyesters, polyamides, polyurethanes, and epoxies. Examples thereof include resins, diallyl phthalate resins, silicone resins, ketone resins, polyvinyl butyral resins, phenol resins, rosin-modified phenol resins, xylene resins, rosin-modified maleic acid resins and rosin esters. Among these, an acrylic polymer or a styrene-acrylic polymer is preferable, and a styrene-acrylic polymer is particularly preferable, from the viewpoint of easy pulverization and control of the molecular weight distribution.

As the colorant dispersed in the fixing resin, for example, carbon black, lamp black, chrome yellow, hansa yellow, benzidine yellow, bethlen yellow, quinoline yellow, permanent orange GTR, pyrazolone orange, vulcan orange,
Watchtang Red, Permanent Red, Brilliant Carmine 3B, Brilliant Carmine 6B, DuPont Oil Red Pyrazolone Red, Resor Red, Rhodamine B Lake, Lake Red C, Rose Bengal,
Aniline Blue, Ultramarine Blue, Calco Oil Blue, Methylene Blue Chloride, Phthalocyanine Blue, Phthalocyanine Green, Malachite Green Oxalate, etc. or CI Solvent Yellow 60, CI Solv
Examples include oil-soluble dyes such as ent Red 27 and CI Solvent Blue 35. The amount of these colorants added is 1 to 30 parts by weight, preferably 2 to 100 parts by weight of the fixing resin.
20 parts by weight.

Typical additives other than the colorant include a charge control agent and an offset preventive agent. The charge control agent is blended to control the triboelectric chargeability of the toner, and there are two types, one for controlling the positive charge and one for controlling the negative charge. As the charge control agent for controlling the positive charge, an organic compound having a basic nitrogen atom, such as a basic dye, an aminopyrine, a pyrimidine compound, a polynuclear polyamino compound, an aminosilane, or the like, a filler surface-treated with each of the above compounds, or the like Can be given.

As the charge control agent for controlling the negative charge, nigrosine base (CI5045) and oil black (CI26150) are used.
), An oil-soluble dye such as Bontron S or Spiron Black; a charge control resin such as a styrene-styrene sulfonic acid copolymer; a compound containing a carboxy group (for example, a metal chelate of alkylsalicylic acid), a metal complex dye, a fatty acid metal Examples thereof include soap, resin acid soap, and metal salt of naphthenic acid.

The amount of charge control agent added is 100% for the fixing resin.
0.1 to 10 parts by weight, preferably 0.5
~ 8 parts by weight. The offset preventing agent is blended in order to impart an offset preventing effect to the toner. Examples of the anti-offset agent include aliphatic hydrocarbons, aliphatic metal salts, higher fatty acids, fatty acid esters or partially saponified products thereof, silicone oil, and various waxes. Above all, the weight average molecular weight is 1,000 to 10,000.
Moderate aliphatic hydrocarbons are preferred. Specifically, one or a combination of two or more of low molecular weight polypropylene, low molecular weight polyethylene, paraffin wax, a low molecular weight olefin polymer composed of olefin units having 4 or more carbon atoms, silicone oil and the like is suitable.

The amount of the anti-offset agent added is 0.1 to 10 parts by weight, preferably 0.5 to 8 parts by weight, based on 100 parts by weight of the fixing resin. 1 when magnetic powder is added
A magnetic toner as a component type developer is obtained. The magnetic substance is a substance that is strongly magnetized in that direction by a magnetic field, and is preferably chemically stable, and is preferably a fine powder having a particle size of 1 μm or less, particularly about 0.01 to 1 μm. Typical magnetic materials include iron oxides such as magnetite, hematite and ferrite, as well as metals such as iron, cobalt and nickel, or these metals and aluminum, cobalt, copper, lead, magnesium, tin, zinc and antimony. , Beryllium, bismuth, cadmium, calcium, manganese, selenium, titanium, tungsten, alloys with vanadium, and mixtures thereof.

The amount of the magnetic powder added is 100% for the fixing resin.
20 to 300 parts by weight, preferably 50 to 300 parts by weight
It is 150 parts by weight. In addition, various additives such as a stabilizer may be blended in an appropriate ratio. The toner particles are
In order to treat with the above-mentioned two kinds of abrasive particles, all necessary amounts of toner particles and abrasive particles and other external additives are put into a mixer and surface treatment is carried out at once.

As the external additive other than the abrasive particles, fine particles (particles of silica, titanium oxide or alumina, which are used as a fluidizing agent or a charge control agent in the conventional electrophotographic toner as described above. (Diameter considerably smaller than 0.1 μm) can be used. The particle size of these external additives is not particularly limited, but is 20 to 400 m ² / g, preferably 50 to 200, expressed by BET specific surface area.
m ² / g. The addition amount of these external additives is 0.05 to 2 parts by weight, preferably 0.1 to 1 part by weight, based on 100 parts by weight of the toner. If the addition amount exceeds 2 parts by weight, filming and charger stain will occur, and if it is less than 0.05 parts by weight, the fluidity of the toner will be insufficient, and thus neither is preferable.

The electrophotographic toner of the present invention thus obtained is suitably used for both a one-component developer and a two-component developer. When used as a one-component developer, the electrophotographic toner of the present invention in which the toner particles containing or not containing a magnetic material are surface-treated as described above may be used as it is.

On the other hand, in order to obtain a two-component developer, the electrophotographic toner of the present invention surface-treated as described above may be mixed with a carrier. Examples of the carrier include glass beads, oxidized or unoxidized iron powder, ferrite,
Magnetic particles such as cobalt, or those whose surface is coated with a synthetic resin (acryl-based, fluorine-based, silicone-based, polyester-based resin, etc.) are used. Such carriers generally have a particle size of 50 to 2000 μm. When using a two-component developer, the toner concentration is preferably 2 to 15% by weight.

[0028]

EXAMPLES The present invention will be described below based on Examples and Comparative Examples. Examples 1 to 5, Comparative Examples 3 and 4 <Production of Toner Particles> 85 parts by weight of a styrene-acrylic copolymer as a fixing resin, 10 parts by weight of carbon black, and an offset inhibitor (release agent) 3 parts by weight of low molecular weight polypropylene as a) and 2 parts by weight of a chromium-containing azo dye as a charge control agent are melted, kneaded, pulverized, and then classified to produce toner particles having an average particle diameter of 10 μm. . <Production of Toner for Electrophotography> 100 parts by weight of the toner particles obtained in the production of the above toner particles, 0.5 parts by weight of hydrophobic silica as a fluidizing agent, and alumina particles having the compounding amounts shown in Table 1 below. (Average particle size of 0.6 μm) and magnetite particles (average particle size of 0.6 μm) were sufficiently stirred, mixed and dispersed by a Henschel mixer to obtain an electrophotographic toner.

[0029]

[Table 1]

Examples 6 and 7, Comparative Examples 1 and 2, 1.25 parts by weight of alumina particles having an average particle size shown in Table 2 below, and magnetite were used instead of the alumina particles and the magnetite particles having an average particle size of 0.6 μm. 1.25 of particles
An electrophotographic toner was obtained in the same manner as in Examples 1 to 5 except that parts by weight were externally added.

[0031]

[Table 2]

Comparative Example 5 In place of the alumina particles having an average particle diameter of 0.6 μm, 1. Alumina fine particles having a particle diameter of 0.02 μm (trade name: Alumina-C manufactured by Nippon Aerosil Co., Ltd.) produced by a gas phase method were used. Two
5 parts by weight of magnetite particles (average particle size 0.6 μm)
Example 1 except that 1.25 parts by weight of
In the same manner as in # 1 to # 5, electrophotographic toners were obtained.

The electrophotographic toners of the above Examples and Comparative Examples were mixed with a ferrite carrier having an average particle size of 70 μm to prepare a two-component developer having a toner concentration of 5% by weight. Using the two-component developer, the following tests were conducted to evaluate the characteristics of the electrophotographic toner. Image Evaluation Electrostatic copying machine (DC70 manufactured by Mita Kogyo Co., Ltd.) in which the above two-component developer is replaced with a photoreceptor made of amorphous silicon.
85 remodeling machine) and using the electrophotographic toners of the same Example and Comparative Example as replenishing toners, image deletion, black spots and The presence or absence of pre-drawing was visually observed.

Image Density Measurement The image density (ID) of the 100,000th copy image was measured using a reflection densitometer (TC-6D manufactured by Tokyo Denshoku Co., Ltd.). Blow-off charge amount measurement The blow-off charge amount (μC / g) of the developer after continuous copying of 100,000 sheets was measured using a blow-off charge amount measuring device manufactured by Toshiba Chemical Co.

Fog Density Measurement at Low Temperature When continuous copying of 100,000 sheets was performed in a low temperature environment of 10 ° C., the fog density (FD) of the blank area of the 100,000th copy image was calculated as the reflection density. Total (TC-6D made by Tokyo Denshoku Co., Ltd.)
Was measured using. The above results are shown in Table 3.

[0036]

[Table 3]

From the results shown in Table 3 above, the particle diameters of the externally added alumina particles and magnetite particles are both 0.1 μm.
The electrophotographic toner of Comparative Example 1 having a particle size of less than m generated image deletion. In addition, the image density slightly decreased. Further, in the electrophotographic toner of Comparative Example 2 in which the particle diameters of the alumina particles and the magnetite particles were both more than 2.0 μm, image black spots and fronting occurred, and the fogging density at low temperature increased. In addition, the amount of charge decreased slightly.

In the electrophotographic toner of Comparative Example 3 containing no alumina particles, the pre-printing occurred and the fog density at a low temperature significantly increased. In the electrophotographic toner of Comparative Example 4 containing no magnetite particles, image black spots were generated and the image density was significantly reduced. In addition, the amount of charge increased significantly.

Further, in the electrophotographic toner of Comparative Example 5 in which fine particles of alumina used as a fluidizing agent and a charge adjusting agent in the conventional toner were added instead of the alumina particles, image deletion and pre-cursion occurred. The fogging density at low temperature increased as the temperature increased. In addition, the charge amount decreased.
On the other hand, all of the electrophotographic toners of Examples 1 to 7 do not cause image defects such as image deletion, black spots, and front pulling, and obtain good images with high image density and low fog density at low temperature. It was possible to obtain a sufficient amount of charge.

[0040]

As described in detail above, the toner for electrophotography of the present invention has two types of toner particles: alumina particles having an average particle size of 0.1 to 2 μm and magnetite particles having an average particle size of 0.1 to 2 μm. Since the abrasive particles of various kinds are added externally, the surface oxide layer of the amorphous silicon photoconductor can be surely polished and removed to prevent image deletion and form a good image.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ken Arakawa 1-2-2 Tamatsukuri, Chuo-ku, Osaka City, Osaka Prefecture Mita Kogyo Co., Ltd. (72) Hiroaki Yamaguchi 1-2-2 Tamatsukuri, Chuo-ku, Osaka City, Osaka Prefecture No. 28 In Mita Industry Co., Ltd. (72) Inventor Koji Kuramasu 1-22 Tazumazo, Chuo-ku, Osaka City, Osaka Prefecture Mita Industry Co., Ltd.

Claims (2)

[Claims] 1. An electrophotographic toner comprising externally added alumina particles having an average particle diameter of 0.1 to 2 .mu.m and magnetite particles having an average particle diameter of 0.1 to 2 .mu.m. 2. The ratio of alumina particles to magnetite particles is within a range of 1: 5 to 5: 1 by weight, and the total amount of external addition of both is 1 to 5 with respect to 100 parts by weight of toner particles.
The toner for electrophotography according to claim 1, which is part by weight.