JPH05297625A - Powdery toner - Google Patents

Abstract

PURPOSE:To maintain high transfer efficiency and to prevent the deterioration of an image in a transfer process even in the case of a toner having a small particle diameter. CONSTITUTION:This powdery toner has <=8mum average particle diameter and consists essentially of a resin binder, an electric conductive colorant and fine hydrophobic silica particles. The average particle diameter of the primary particles of the electric conductive colorant is 40-60nm and the average paticle diameter of the primary particles of the fine hydrophobic silica particles is <=13nm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder toner used in electrophotography and the like. More specifically, even in a toner having a small particle diameter, the amount of untransferred toner is reduced, and the transfer efficiency is high and good. The present invention relates to a powder toner that can maintain excellent transfer characteristics.

[0002]

2. Description of the Related Art The electrophotographic copying method is a system for obtaining a hard copy by forming an image by utilizing a photoconductive phenomenon. The process includes charging, exposing, developing, transferring, fixing and cleaning steps. There is. Among them, the transfer process is
The toner developed on the electrostatic latent image is transferred to the recording medium by applying a voltage having a polarity opposite to that of the toner. The transfer process is a process that has a strong influence on the finally obtained copy image together with the developing process.

On the other hand, a toner contains a binder resin and a colorant as essential components, and organic or inorganic materials such as a charge control agent, a conductivity control agent, and a release agent are dispersed and mixed in the binder resin as required. In the production, the resin particles are mixed with each other, and the above-mentioned toner materials are mixed, and the mixture is melt-kneaded to uniformly disperse various constituent materials, followed by cooling, pulverizing,
Toner particles are obtained by classification and, if necessary, spherical treatment.

Recently, there is a strong demand for high-quality images,
Toner particles are becoming smaller. For the resolution of images and the reproducibility of fine lines, it is not necessary to say that the toner has a small particle size. However, when the toner has a small particle size, the following problems occur: the charge amount per toner decreases.

Reverse polarity toner is likely to be generated due to deterioration of fluidity. The adhesion to the photoconductor is increased. Occurs. For this reason, even if a transfer voltage is applied from the back side of the recording medium in the transfer step, the toner is not sufficiently transferred by the Coulomb force, the transfer efficiency is remarkably reduced, and the image is deteriorated contrary to the original purpose.

Conventionally, in order to solve such a problem, by making the particle size distribution of the toner sharper, the charge of the toner is made uniform, and the charge amount of one toner is made equal. Since the colorant has the effect of adjusting the toner resistance in addition to the effect of coloring the toner, finer colorant particles than before are used for the purpose of uniformly dispersing the colorant in the toner particles.

A large amount of hydrophobic silica fine particles are blended for the purpose of reducing the contact area between the toner particles and the photosensitive member and reducing the adhesive force with the photosensitive member. Such measures were taken.

[0008]

[Problems to be Solved by the Invention] However, the following new problems occur in such a measure. As a classification method, an air classifier such as an air flow classifier is generally used, but it is very difficult to make the particle diameters of the particles small. No matter how much the particle size is made uniform, it cannot be said to be very effective because the particle size of the toner itself is small.

Colorants generally have a large tendency to aggregate,
Even if the primary particle size is fine, these primary particles exist in the form of relatively coarse secondary particles in which they are strongly aggregated. Such an aggregation tendency is more remarkable as the primary particles are finer, and in the conventionally used coloring agent, the aggregation particles are significantly fine because the primary particles are considerably fine. It has become a thing.

Among the constituent materials, particularly when the colorant is poorly dispersed, the charge amount and the resistance are lowered. Even though the charge is small, it becomes more difficult to hold the charge, and the transfer efficiency is improved. Bring about a decline. The amount of the hydrophobic silica fine particles liberated from the toner surface increases, and the liberated hydrophobic silica fine particles adversely affect the process means in the copying machine. That is, the liberated hydrophobic silica fine particles adhere to the carrier, resulting in poor charging and poor image density. Furthermore, the toner adheres to the photoconductor and cannot be removed in the cleaning step, so-called filming occurs, black streaks, white streaks and the like occur, and toner cleaning failure occurs.

The inventors of the present invention have found that even for small particle size toners,
By keeping the particle size of the colorant within a certain range, it is possible to uniformly disperse in the toner and maximize the toner charge amount. Also, select hydrophobic silica as the surface treatment agent and keep it below a certain particle size. It was found that the adhesive force with the drum is reduced without being released from the toner surface. That is, it is an object of the present invention to provide a toner capable of maintaining a high transfer efficiency and preventing image deterioration in the transfer process even with a small particle size toner.

[0012]

According to the present invention, in a powder toner having an average particle size of 8 μm or less composed of at least a binder resin, a colorant and hydrophobic silica fine particles, the average particle size of the colorant primary particles is 40 to 40 μm. A powder toner having a particle size of 60 nm and an average particle diameter of primary particles of hydrophobic silica fine particles of 13 nm or less is provided.

In the present invention, the aggregated particles of the colorant preferably have an area ratio of aggregated particles of 1 μm or more of 2% or less in the toner cross section, and the hydrophobic silica fine particles have a projected area coverage of 10 to 30 on the toner particle surface. % Is preferable.

[0014]

The action of the colorant as a resistance adjusting agent is performed through the interface between the colorant particles dispersed in the toner and the binder resin. Therefore, the colorant is small and uniform in the actual toner. It can be easily understood that the dispersed state is electrically stable. Further, it is generally considered that the smaller the toner particle size, the smaller the colorant.

Therefore, it seems seemingly contradictory to select a colorant used in the present invention for the small particle size toner that is larger than the conventional colorant. However, it has already been pointed out that the conventional colorant having a small particle diameter causes agglomeration of primary particles, resulting in poor efficiency of mixing and stirring and incapable of uniform dispersion. On the other hand, when a colorant having a particle size within a certain range is used, good dispersibility can be obtained in the toner particles without agglomeration of temporary particles. As a result, it is possible to increase the charge amount of one toner and improve the charge retention, and it is possible to increase the Coulomb force due to the transfer voltage even in the case of small toner particles having a particle diameter of 8 μm or less. .. The lower limit of the fixed range is 40 nm. This is because when the particle size is less than this, aggregation of primary particles occurs. The primary particles are 6
If the thickness is 0 nm or more, the colorant may not be uniformly contained in each toner particle in toner production.

In the present specification, the average particle size of the primary particles of the colorant is determined as the number average particle size from the particle size and number of the particles by an electron micrograph. In the toner of the present invention, it is preferable that the area ratio of the colorant agglomerated particles of 1 μm or more in the toner particles and the kneaded material is 2% or less.
That is, if this value exceeds the above range, the charge retention of the toner particles tends to deteriorate, and the transfer efficiency tends to decrease.

In the present specification, the area ratio of the colorant agglomerated particles of 1 μm or more means that the toner particles or the toner kneaded material is cut into a section with a microtome, and this cross section is photographed with an optical microscope to obtain the colorant particles. It is obtained by measuring the cross-sectional area and calculating the cross-sectional area ratio. Further, in the present invention, the average particle diameter of the primary particles of the hydrophobic silica fine particles is 1
It is a remarkable feature that it is in the range of 3 nm or less. This is because when the primary particle diameter of the hydrophobic silica fine particles is 13 nm or less, even if the same weight as that of the hydrophobic silica fine particles having a large particle diameter is added, the particles are small and the contact area between the toner particles and the photoconductor is reduced. This is because the van der Waals force, that is, the adhesive force can be reduced even for toner particles having a small particle diameter of 8 μm or less.

By simultaneously satisfying the two requirements of increasing the Coulomb force of the toner particles by the transfer voltage and reducing the van der Waals force with the photoconductor,
High transfer efficiency and image deterioration in the transfer process can be prevented. Further, in the toner of the present invention, it is desirable that the hydrophobic silica fine particles have a projected area coverage of 10 to 30%, preferably 15 to 25% on the toner surface. That is, when this value exceeds the above range, free hydrophobic silica fine particles are liable to be generated, image defects occur due to adhesion to the carrier, and black streaks, white streaks, and toner are caused by filming on the photoconductor. Poor cleaning occurs. If this value is less than the above range, the contact area between the photoconductor and the toner particles increases, which may reduce the transfer efficiency.

In the present specification, the projected area coverage of the hydrophobic silica fine particles on the toner surface means the area coverage of the toner present on the toner surface by taking a scanning electron micrograph of the toner surface and analyzing the image. Ask for. The area coverage means the ratio (%) of the total surface area of the toner particles, which is covered with the additive. In particular,
It is calculated by the following formula.

[0020]

[Equation 1]

In the formula, C is the projected area coverage, S is the projected area of the toner, Si is the projected area of the hydrophobic silica fine particles, and m is the area.
The number of particles of Si is shown. The particle size of the toner particles is a value measured by a Coulter counter.

[0022]

Preferred Embodiment of the Invention The toner particles have an average particle size of 8
Fine particles of less than μm, especially 5 to 7 μm are used. This is a colored toner particle having a sensible property and a fixing property. Generally speaking, the composition thereof is a fine particle in which a colorant, a charge control agent, a release agent and the like are dispersed in a binder resin. It consists of a granular composition.

As the binder resin which is the toner component, styrene resin, acrylic resin, styrene-acrylic resin, polyester resin, polyurethane resin, silicone resin, polyamide, modified rosin or the like is used. As the colorant, a conventionally known colorant can be used. For example, as in Mitsubishi Kasei Carbon Black # 25 (registered trademark), the average primary particle size is 4
Particles of 0 to 60 nm are preferred. In addition, the following coloring agents having 40 to 60 nm can be preferably used.

Black carbon black such as furnace black, channel black, gas black, oil black, acetylene black, lamp black, aniline black, white zinc white, titanium oxide, antimony white, zinc sulfide red red iron oxide, cadmium red, red lead red , Mercury sulfide, cadmium, permanent red 4R, resole red,
Pyrazolone red, watching red calcium salt,
Lake Red D, Brilliant Carmine 6B, Eosin Lake, Rhodamine Lake B, Alizarin Lake, Brilliant Carmine 3B Orange Red Lead Yellow, Molybdenum Orange, Permanent Orange GTR, Pyrazolone Orange, Vulcan Orange, Indanthrene Brilliant Orange RK, Benzidine Orange G, Indanthrene Brilliant Orange GK Yellow Yellow Lead, Zinc Flower, Cadmium Yellow, Yellow Iron Oxide, Mineral Fast Yellow, Nickel Titanium Yellow, Navels Yellow, Naphthol Yellow S, Hansar Yellow G, Hansar Yellow 10G, Benzidine Yellow G, Benzidine Yellow GR, Quinoline Yellow Lake, Permanent Yellow NCG, Tartrazine Lake Green Chromium Green, Chromium Oxide, Pigme Togulin B, Malachite Green Lake, Final Yellow Green Blue Navy Blue, Cobalt Blue, Alkali Blue Lake, Victoria Blue Lake, Phthalocyanine Blue Partial Chloride, Farnest Sky Blue, Indanthrene Blue BC, Metal-free Phthalocyanine Blue Purple Manganese Purple, Fast Violet B, methyl violet lake extender pigments include, for example, perlite powder, barium carbonate,
Examples include clay, silica, white carbon, talc, and alumina white.

Examples of the conductive pigment include conductive carbon black and various metal powders such as aluminum powder. Examples of magnetic pigments include iron trioxide (magnetite iron black); iron sesquioxide (γ-Fe2O3), zinc iron oxide (ZnFe2O4), yttrium iron oxide (Y3Fe5O1).
2), iron cadmium oxide (CdFe2O4), iron oxide gatorium (Gd3Fe5O4), iron oxide copper (CuFe2O)
4), iron oxide lead (PbFe12O19), iron oxide nickel (NiFe2O4), iron oxide neodymium (NdFeO3),
Iron oxide barium (BaFe12O19), iron oxide magnesium (MgFe2O4), iron manganese oxide (MnFe2O)
4), various ferrites such as lanthanum iron oxide (LaFeO3); iron powder, cobalt powder, nickel powder and the like.

Examples of the photoconductive pigment include zinc oxide,
Examples thereof include selenium, cadmium sulfide, selenium, cadmium sulfide, and cadmium selenide. Examples of the release agent include any known release agent, for example, an aliphatic resin, an aliphatic metal salt, an aliphatic compound such as higher fatty acids, fatty acid esters, or partially saponified products thereof. ..
Among them, particularly low molecular weight (weight average molecular weight of 1000 to 1
0000) aliphatic resins are effective. Specifically, for example, low molecular weight polypropylene, high molecular weight polyethylene,
One kind or a combination of two or more kinds of paraffin wax, a low molecular weight olefin polymer composed of a simple olefin having 4 or more carbon atoms, and the like are suitable. Besides, for example, silicone oil and various waxes can be used.

The charge control agent may be any charge control agent known per se, for example, nigrosine base (CI 504).
15), oil black (CI 26150), oil-soluble dyes such as spirone black, metal-containing azo dyes, metal salts of naphthenic acid, metal salts of alkylsalicylic acid, fatty acids, soaps, resin acid soaps and the like are used. The hydrophobic silica-based additive used in the present invention is a gas-phase process silica, that is, fine silica obtained from a high temperature (fire) hydrolysis process of silicon chloride, is treated with silanes such as dimethyldichlorosilane, It is obtained by blocking silanol with an organosilane. Manufacture of Toner A binder resin, a colorant, a charge control agent, a release agent and the like are mixed and stirred. The mixing and stirring should be performed under the condition that a low load and a low shearing force act, and generally, it can be performed by various mixing and stirring devices such as a conical blender, a ribbon blender, a V-type blender, a Nauta mixer, a Henschel mixer, and a ball mill. The mixing and stirring temperature is preferably lower than the glass transition point (Tg) of the binder resin.
The required mixing / stirring time varies depending on the type of equipment and the input amount, but is generally in the range of 10 to 300 minutes.

The pre-mixture thus obtained is melt-kneaded by a conventional method, and the kneaded product is crushed and classified to obtain a toner. The obtained toner is, for example, Aerosil R974
(Registered trademark), the average particle diameter of primary particles is 13 nm.
The following hydrophobic silica fine particles are blended so that the projected area coverage is 10 to 30%, preferably 15 to 25%, and the mixture is sprinkled in the mixing stirrer to obtain the final toner.

The toner according to the present invention is mixed with a magnetic carrier such as ferrite or iron powder to obtain an electrostatic latent image as a two-component developer or as a one-component developer containing a magnetic pigment and a non-magnetic pigment. It is advantageously used for image development.

[0030]

【Example】

Example 1 (Toner compounding component) Styrene-acrylic resin 100 parts by weight Carbon black (average particle size of primary particles: 40 nm) 8.5 parts by weight Chromium complex salt dye (charge control agent) 1.5 parts by weight Low molecular weight polypropylene ( Release Agent) 3 parts by weight The above toner compounding ingredients were mixed for 60 minutes by a V-type mixer to prepare a pre-mixture.

The pre-mixture was melt-kneaded using a twin-screw extruder, cooled, pulverized with a jet mill, and air-classified with an Alpine classifier to obtain a toner having an average particle size of 8.0 μm. To this toner, 0.15 parts by weight of hydrophobic silica fine particles (average particle diameter of primary particles: 13 nm) was added and mixed with a Henschel mixer, and a dusting treatment was performed to obtain a final toner.

The area ratio of aggregated particles of carbon black of 1 μm or more in this final toner was measured to be 2.0%, and the projected area coverage of the hydrophobic silica fine particles present on the surface was measured to be 10%. Met.
Further, a ferrite carrier was mixed with this toner to prepare a developer having a toner concentration of 3.5% by weight. Using this developer, an electrophotographic copying machine (manufactured by Mita Kogyo Co., Ltd .; DC458
Copying was performed according to 5), and image density, resolution, and transfer efficiency were evaluated. The image density is measured with a reflection densitometer (manufactured by Tokyo Denshoku Co., Ltd.), and the transfer efficiency is calculated as a ratio of the weight of the toner transferred onto the transfer paper to the weight of the toner developed on the photoconductor in% by weight. It was The results are shown in Table 1.
Shown in. Example 2 The same as Example 1 except that the addition amount of the hydrophobic silica fine particles was changed to 0.6 part by weight. Comparative Example 1 Instead of a colorant having an average particle diameter of primary particles of 25 nm, instead of hydrophobic silica fine particles having an average particle diameter of 16 nm of primary particles,
Same as Example 1 except that the addition amount was 0.3 parts by weight. Comparative Example 2 The procedure of Example 1 was repeated, except that the primary particles had an average particle diameter of 16 nm instead of the hydrophobic silica fine particles and the addition amount was 0.6 part by weight. Comparative Example 3 The procedure of Example 1 was repeated except that the colorant having an average primary particle diameter of 25 nm was used. Comparative Example 4 The procedure of Example 1 was repeated, except that the amount of hydrophobic silica particles added was changed to 0.8 part by weight. Comparative Example 5 The procedure of Example 1 was repeated except that the amount of the hydrophobic silica fine particles added was changed to 0.08 part by weight.

Table 1 shows the experimental results. The toners of Examples 1 and 2 obtained by the production method of the present invention have the average particle diameter of the primary particles of the coloring agent and the average particle diameter of the primary particles of the hydrophobic silica fine particles within the range of the present invention, The aggregation area ratio of the agent and the projected area coverage of the hydrophobic silica fine particles are also within the range of the present invention, and clear images with good image characteristics and high transfer efficiency were obtained.

On the other hand, even if one of the average particle diameter of the primary particles of the colorant and the average particle diameter of the primary particles of the hydrophobic silica fine particles are lacking as in Comparative Examples 1, 2, and 3, respectively. However, the image quality and the transfer efficiency also decreased. Further, when the aggregation area ratio of the colorant and the projected area coverage of the hydrophobic silica fine particles are outside the scope of the present invention as in Comparative Examples 4 and 5, both the image quality and the transfer efficiency are decreased, and the area is decreased. When the coverage exceeded, white streaks occurred.

[0035]

[Table 1]

[0036]

According to the present invention, by setting the average particle size of the primary particles of the colorant, which is a toner component, within a certain range, the colorant can be uniformly dispersed even in a small particle size toner. By dusting the surface of the toner with hydrophobic silica fine particles having a small diameter, it is possible to reduce the adhesive force with the photoconductor, and it is possible to obtain high image quality and high transfer characteristics by mixing an appropriate amount by a proper method.

Claims (3)

[Claims] 1. A powder toner having an average particle size of 8 μm or less, which is composed of at least a binder resin, a conductive colorant and hydrophobic silica fine particles, wherein the average particle size of primary particles of the conductive colorant is 40 to 60 nm.
And the average particle size of the primary particles of the hydrophobic silica fine particles is 13
A powder toner having a particle size of not more than nm. 2. The powder toner according to claim 1, wherein the area ratio of the conductive colorant aggregate particles having a size of 1 μm or more in the toner cross section is 2% or less. 3. The powder toner according to claim 1, wherein the projected area coverage of the hydrophobic silica fine particles on the surface of the toner particles is 10 to 30%.