JPH0643696A - Electrophotographic developer - Google Patents

Abstract

PURPOSE:To obtain a developer excellent in the rising property of toner electrification and hardly causing toner spent by mixing a carrier having a rugged surface structure, a carrier having no rugged surface structure, and an electrophotographic toner. CONSTITUTION:Two kinds of carriers having a rugged surface structure and having no rugged surface structure are mixed with a specified amt. of toner. By using the carrier having a rugged surface, the rising property of the toner electrification is improved but toner spent is also caused. Thereby, by mixing a proper amt. of the carrier having no rugged surface, the disadvantage of the carrier having rugged surface is suppressed as small as possible, while the advantage of the carrier is maintained. The rugged surface of the carrier is defined according to the following formula: alpha=[circumference of the projected image of the carrier (measured value)]/[circumference of the carrier having the medium particle size (calculated value)]. The carrier having no rugged surface satisfies alpha<=1.2, while the carrier having rugged surface satisfies alpha>1.2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developer for electrophotography, and more particularly to a developer for electrophotography used for image formation by applying a so-called Carlson process such as electrostatic copying machines and laser beam printers. It is a thing.

[0002]

2. Description of the Related Art A magnetic brush developing method using a two-component developer containing a toner and a carrier forms an image in the following steps. (A) First, a developer containing an electrophotographic toner is held on the outer periphery of a developing sleeve having a magnetic pole inside to form a so-called magnetic brush.

(B) This magnetic brush is brought into sliding contact with a photosensitive member having an electrostatic latent image formed on the surface thereof, and the electrophotographic toner is electrostatically adhered to the electrostatic latent image to form a toner image. Make it visible. (C) The toner image is transferred from the surface of the photoconductor onto paper,
Further, the image is formed by fixing it on the paper with a fixing roller.

As the electrophotographic developer used for the image formation, a two-component dry developer composed of a magnetic carrier and an electrophotographic toner is widely used. The toner particles are triboelectrically charged by mixing with the carrier. In the triboelectrification of the carrier and the toner, the time for the charge to reach saturation, that is, the rise of the toner charge is an important characteristic in the electrophotographic developer. Toner is consumed during development and toner is replenished from the hopper to the developing machine. However, if the toner charge rise is poor, the saturated charge amount cannot be reached in a short time and uncharged toner is generated, causing fog and toner scattering.

In order to solve this problem, it has been attempted to coat the carrier surface with various resins. The resin-coated carrier surface is smooth and has no surface irregularities.

[0006]

The rise of toner charging depends on the shape of the carrier surface. That is, the larger the specific surface area of the carrier is, the more the contact probability between the toner and the carrier is increased, so that the charging rise is improved. Therefore, in the case of a resin-coated carrier whose surface is not in a concavo-convex state, the toner charging rise becomes worse. On the other hand, in the case of a carrier having an uneven surface, the toner charging rises better, but when the number of copies increases, toner spent occurs due to contact between the toner and the carrier.

In recent years, high image quality has been demanded, and the particle size of toner has been reduced. The smaller the particle size of the toner, the more particularly the improvement of the charging rise of the toner is required. That is, when the toner has a small particle size, the fluidity of the toner is lowered, and the frictional electrification between the toner and the carrier is deteriorated in the developing machine, so that the toner charging rise is deteriorated.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrophotographic developer which has a good toner charge build-up and which hardly causes toner spent. Another object of the present invention is to provide a developer having a good charge buildup even when a small particle size toner is used.

[0009]

According to the present invention, an electrophotographic developer obtained by mixing a carrier having an uneven surface structure and a carrier having a non-uneven surface structure with an electrophotographic toner. Will be provided. The ratio of the carrier having an uneven structure to the entire carrier is 20 to 40 wt%
Is preferred. The carrier particle size is 50 to 7
It is preferably 0 μm.

According to the present invention, by mixing a predetermined amount of two kinds of carrier, a carrier having an uneven surface structure and a carrier having a non-convex surface structure, with a predetermined amount of toner, the toner charging start-up is improved and no toner spent is generated. It was made on the basis of what we should know. The mechanism by which the toner charging rise and toner spent are improved by using the above two types of carriers has not been clarified so far, but is presumed to be due to the following mechanism.

[0012] When the carrier alone has an uneven surface,
Toner charging rises well, but toner spent occurs. By mixing an appropriate amount of the uneven carrier into the non-uneven carrier, the advantages of the uneven carrier can be utilized and the drawbacks thereof can be minimized. Here, the unevenness of the carrier is defined as follows.

[0012]

[Equation 1] The carrier having no uneven structure means that the α is 1.2 or less, and the carrier having the uneven structure means that that α is larger than 1.2.

Generally, the unevenness of the carrier surface is caused by a change in the baking temperature of the magnetic material. The lower the baking temperature is, the more uneven the carrier surface is formed and the lower the apparent density is. When the carrier particle size in combination with the small particle size toner is less than 50 μm, the toner covering area with respect to the carrier becomes large and the fluidity as a developer tends to deteriorate. Further, since the number of contact between the toner and the carrier is increased, the spent is increased and the opposite polarity toner is generated.
This causes problems such as fogging and toner scattering.

When the carrier particle size is 70 μm or more, the charge rise becomes poor and the saturated charge amount becomes low, so that fog and toner scattering are likely to occur. Carrier particle size is 50
In the case of .about.70 .mu.m, problems may occur depending on the compounding ratio of the surface condition of the carrier to the one having unevenness and the one having no unevenness. When the proportion of carriers that are not in a concavo-convex state is 20 wt% or less with respect to the whole, there are many concavo-convex portions of the carrier, so that the toner and the carrier are likely to be triboelectrically charged and the charging rise is improved, but there are many concavo-convex portions. Spent is generated and the life of the developer tends to be shortened. On the other hand, if the proportion of carriers that are not in a concavo-convex state is 40 wt% or more with respect to the whole, the rise of toner charging is not improved.

The electrophotographic developer of the present invention will be described in detail below. Toner Particles The binder resin in the present invention is not particularly limited, and examples thereof include epoxy resin, polyester resin, styrene resin, acrylic resin, polyamide resin, petroleum resin, silicone resin, diene resin, olefin. Resins, vinyl acetate polymers, polyethers, polyurethanes, paraffin waxes and copolymers thereof may be used alone or in combination. Of these resins, it is preferable to use a styrene resin, particularly a styrene-acrylic copolymer.

Examples of the colorant include various color pigments, extender pigments, conductive pigments, magnetic pigments and photoelectric pigments. These may be used alone or in combination of two or more depending on the purpose. As the color pigment, the following pigments are preferably used. Black Furnace Black. , Channel black, thermal, gas black, oil black, carbon black such as acetylene black, lamp black, aniline black.

White zinc white, titanium oxide, antimony white, zinc sulfide. Red red iron oxide, cadmium red, red lead, mercury sulfide, permanent red 4R, resole red, pyrazolone red, watching red calcium salt, lake red D, brilliankamine 6B, eosin lake, rhodamine lake B, alizarin lake, brilliant carmine 3B orange red mouth Yellow lead, molybden orange, permanent orange GTR, pyrazolo orange, vulcan orange, indanthrene brilliant orange RK, benzidine orange G, indanthrene brilliant orange GK.

Yellow yellow lead, zinc white, cadmium yellow, yellow iron oxide, mineral fast yellow, nickel titanium yellow, navels yellow, naphthol yellow S, Hansa yellow G, Hansa yellow 10G, benzidine yellow G, benzidine yellow GR, Quinoline yellow rake, permanent yellow NCG, tartrazine rake.

Green chrome green, chrome oxide, pigment green B,
Malachite Green Rake, Fanal Yellow Green G. Blue Navy Blue, Cobalt Blue, Alkali Blue Lake, Victoria Blue Lake, Phthalocyanine Blue Partial Chloride, Fast Sky Blue, Indanthrene Blue B
C.

Purple Manganese purple, fast violet B, methyl violet lake. Examples of extender pigments include perlite powder, barium carbonate, clay, silica, white carbon, talc, and alumina white. Examples of the conductive pigment include conductive carbon black and aluminum powder.

As magnetic materials, various ferrites such as iron trioxide (Fe3O4), iron sesquioxide (γ-Fe2O3), zinc oxide (ZnFe2O4), yttrium iron oxide (Y3Fe5O13), cadmium iron oxide (CdFe2O4), Gatrinium oxide (Gd3Fe5O
4), iron oxide copper (CuFe2O4), iron oxide lead (PdFe12O19), iron neodymium oxide (NdFeO3), iron manganese oxide (MnFe2O4), iron oxide lanthanum (LaFeO3), iron powder, cobalt powder, nickel powder, etc. .

Examples of the photoconductive pigment include zinc oxide, selenium, cadmium sulfide and cadmium selenide. The colorant is 1 to 30 with respect to 100 parts by weight of the binder resin.
It is used in a proportion of parts by weight, preferably 2 to 20 parts by weight. As the charge control agent, two types of charge control agents for positive charge control and negative charge control are used depending on the polarity of the toner.

As the charge control agent of the positive charge control agent, organic compounds having a basic nitrogen atom such as basic dyes, aminopyrine, pyrimidine compounds, polynuclear polyamino compounds, aminosilanes and the like, and surface-filled with the above compounds are used. Agents and the like. Examples of the charge control agent for controlling the negative charge include a compound containing a carboxy group (for example, metal chelate of alkylsalicylate), metal complex salt dye, fatty acid soap, metal salt of naphthenic acid and the like.

The charge control agent is used in an amount of 0.1 to 10 parts by weight, preferably 0.5 to 8 parts by weight, based on 100 parts by weight of the binder resin. Examples of the release agent (anti-offset agent) include aliphatic hydrocarbons, aliphatic metal salts, higher aliphatics, fatty acid esters or partially saponified products thereof, silicone oil, and various waxes. Above all,
Aliphatic hydrocarbons having a weight average molecular weight of about 1,000 to 10,000 are preferable. 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 is suitable.

The release agent is used in an amount of 0.1 to 10 parts by weight, preferably 0.5 to 8 parts by weight, based on 100 parts by weight of the binder resin. The toner particles are obtained by uniformly preliminarily kneading the above components in a dry blender, a Henschel mixer, a ball mill, etc., and kneading the mixture with, for example, a Banbury mixer, a roll, a uniaxial or biaxial extrusion kneading device, etc. After being melt-kneaded uniformly using an apparatus, the obtained kneaded product is cooled and pulverized, and if necessary, classified, or in addition, it may be manufactured by a suspension polymerization method or the like.

The particle size of the toner particles is suitably 3 to 35 μm, preferably 5 to 25 μm, and in the case of small particle size toner, the particle size is about 4 to 10 μm. Carrier The carrier core material in the present invention includes particles of iron, oxidized iron, reduced iron, magnetite, copper, silicon steel, ferrite, nickel, cobalt and the like, and alloys of these materials with manganese, zinc, aluminum and the like. Particles, particles of iron-nickel alloy, iron-cobalt alloy, etc., particles obtained by dispersing the various particles in a binder resin, titanium oxide, aluminum oxide, copper oxide, magnesium oxide, lead oxide, zirconium oxide, silicon carbide, Conventionally, particles of ceramics such as barium titanate, lithium titanate, lead titanate, lead zirconate and lithium niobate, particles of high dielectric constant substances such as ammonium dihydrogen phosphate, potassium dihydrogen phosphate, Rochelle salt, etc. There are various known carrier core materials.

As the coating resin for the carrier, methyl silicone resin, methylated melanin resin, (meth) acrylic polymer, styrene- (meth) acrylic copolymer, olefin polymer (polyethylene, chlorinated polyethylene, Polypropylene, etc.), polyvinyl chloride, polyvinyl acetate, polycarbonate, cellulose resin, polyester resin, unsaturated polyester resin, polyamide resin, polyurethane resin, epoxy resin, silicone resin other than methyl silicone resin, fluorine resin (polytetrafluoroethylene, Polychlorotrifluoroethylene,
Polyvinylidene fluoride, etc.), phenol resin, xylene resin, dilyl phthalate resin, polyacetal resin, amino resins other than methylated melamine resin, and various resins conventionally known for use as coating carriers. These may be used alone or in combination of two or more. In addition, the resin coat layer may contain additives such as silica, alumina, carbon black, and fatty acid metal salts for adjusting the characteristics of the resin coat layer, if necessary.

[0028]

EXAMPLES The present invention will be described below based on Examples and Comparative Examples. Toners used in Examples and Comparative Examples are shown below. Toner fixing resin (styrene-acrylic resin) 100 parts by weight carbon black (trade name MA-100 manufactured by Mitsubishi Kasei) 10 parts by weight Charge control agent (chromium-containing dye) 1.5 parts by weight and as a surface treatment agent 0.3 part by weight of silica is added to 100 parts by weight of the toner. The central particle diameter of the toner is 8 μm. Example 1 A carrier having a concavo-convex structure having a particle size of 50 μm and a carrier having a non-convex structure having a particle size of 50 μm were mixed at 20% with respect to the whole, and were mixed and stirred with a toner in a Nauta mixer, and an electrostatic copying machine as a developer ( Model number DC-120 manufactured by Mita Kogyo Co., Ltd.
In 5), continuous copying of 20000 m was performed, and image density, fog, charge amount, spent amount, toner scattering, fluidity, charge buildup, and carrier jump were measured and confirmed. The results are shown in Table 1.

The image density was high, a good image free from fog was obtained, and toner scattering did not occur. Example 2 A carrier having a particle size of 50 μm having an uneven structure and a carrier having a particle size of 50 μm having no uneven structure were mixed in an amount of 40% with respect to the whole. In the following, a developer was prepared in the same manner as in Example 1 and the same measurement and confirmation were performed. went. The results are shown in Table 1.

A high image density and a good image free from fog were obtained. Example 3 20% of a carrier having an uneven structure and a particle size of 70 μm and a carrier having a uneven structure of 70 μm were mixed in an amount of 20%, and a developer was prepared in the same manner as in Example 1 and the same measurement and confirmation were performed. went. The results are shown in Table 1.

A high image density and a good image free from fog were obtained. Example 4 A carrier having a particle size of 70 μm having an uneven structure and a carrier having a particle size of 70 μm having no uneven structure were mixed in an amount of 40% with respect to the whole. In the following, a developer was prepared in the same manner as in Example 1 and the same measurement and confirmation were performed. went. The results are shown in Table 1.

A high image density and a good image free from fog were obtained. Comparative Example 1 A carrier having an uneven structure having a particle size of 40 μm and a carrier having a non-uneven structure having a particle size of 40 μm were mixed in an amount of 30%, and a developer was prepared in the same manner as in Example 1 and the same measurement and confirmation were performed. went. The results are shown in Table 1.

Since the particle size of the carrier was small, the fluidity deteriorated. In addition, carrier jumps also occurred. Comparative Example 2 A carrier having a concavo-convex structure having a particle size of 50 μm and a carrier having a concavo-convex structure having a particle size of 50 μm were mixed in an amount of 15% with respect to the whole. went. The results are shown in Table 1.

Since the proportion of the carrier having the concavo-convex structure is high, the rising of the charge is good, but the spent is generated and the toner is scattered. Comparative Example 3 A carrier having a concavo-convex structure having a particle size of 50 μm and a carrier having a non-convex structure having a particle size of 50 μm were mixed by 45% with respect to the whole. went. The results are shown in Table 1.

Since the proportion of the carrier having the concavo-convex structure is small, the rise of charging is deteriorated, the amount of uncharged toner increases, and toner scattering occurs. Comparative Example 4 A carrier having a concavo-convex structure having a particle size of 70 μm and a carrier having a concavo-convex structure having a particle size of 70 μm were mixed in an amount of 15%, and a developer was prepared in the same manner as in Example 1 and the same measurement and confirmation were performed. went. The results are shown in Table 1.

Since the proportion of the carrier having the concavo-convex structure is small, the rise of charging is deteriorated, the amount of uncharged toner is increased, and toner scattering is slightly generated. Comparative Example 5 A carrier having an uneven structure having a particle size of 70 μm and a carrier having a non-uneven structure having a particle size of 70 μm were mixed in an amount of 45% with respect to the whole. In the following, a developer was prepared in the same manner as in Example 1 and the same measurement and confirmation were performed. went. The results are shown in Table 1.

Since the ratio of the carrier having the concavo-convex structure is large, the spent is generated and the toner is scattered. Comparative Example 6 A carrier having a concavo-convex structure having a particle size of 80 μm and a carrier having a concavo-convex structure having a particle size of 80 μm were mixed in an amount of 30% with respect to the whole. went. The results are shown in Table 1.

Since the carrier particle size is larger than the toner particle size, the rise of charging is deteriorated and toner scattering occurs. Comparative Example 7 A carrier having an uneven structure and a particle size of 60 μm was used to prepare a developer in the same manner as in Example 1, and the same measurement and confirmation were performed. The results are shown in Table 1.

Since only the uneven structure is provided, the charge rise is good, but the spent is generated, and the fog and the toner are scattered. Comparative Example 8 A carrier having a particle size of 60 μm, which does not have a concavo-convex structure, was used to prepare a developer in the same manner as in Example 1, and the same measurement and confirmation were performed. The results are shown in Table 1.

Charging rises poorly, causing fog and toner scattering.

[0041]

[Table 1]

Each test method is as follows. (1) Measurement of image density It was measured using a reflection densitometer (TC-6D manufactured by Tokyo Denshoku Co., Ltd.). (2) Measurement of Fog Density Using the same reflection densitometer as described above, the density of the blank area of the copied image was measured to obtain the fog density.

(3) Charge Amount The blow-off charge (μC / g) of the developer was measured using a blow-off manufactured by Toshiba Chemical Co. (4) Spent Rate The developer after printing 20,000 sheets was washed with a surfactant to remove the toner, and 100 g was weighed. Then, the weighed carrier was washed with toluene to remove the spent toner adhering to the carrier. The carrier from which the spent toner was removed was dried and weighed (this is Ag).

[0044]

[Equation 2] (5) Toner Scattering The condition inside the copying machine and the surface of the copy were visually judged and evaluated according to the following criteria.

◯: No toner scattering Δ: Slight toner scattering X: Toner scattering (6) Charge rising Time until the charge amount is saturated when the carrier and toner are mixed ○: Saturation takes a short time △: Slightly slow ×: Slow (7) Carrier jump Visual inspection by looking at the image ○: No carrier jump △: Slightly bad ×: Yes

[0046]

The effect of the present invention is that a high image density is obtained by specifying the particle size of the carrier and the concavo-convex structure, a good image without fog is obtained, and the occurrence of problems such as toner scattering is suppressed. There is.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Seijiro Ishimaru 1-2-2 Tamatsukuri, Chuo-ku, Osaka Mita Industrial Co., Ltd. (72) Takeshi Higuchi 1-2-2 Takumazo, Chuo-ku, Osaka Within Mita Engineering Co., Ltd.

Claims (3)

[Claims] 1. A developer for electrophotography, which is obtained by mixing a carrier having an uneven surface structure and a carrier having a uneven surface structure with an electrophotographic toner. 2. The developer for electrophotography according to claim 1, wherein the ratio of the carrier having a concavo-convex structure to the entire carrier is 20 to 40 wt%. 3. The electrophotographic developer according to claim 1, wherein the carrier particle size is 50 to 70 μm.