JPH07244396A - One-component magnetic developer and developing method - Google Patents

Abstract

PURPOSE:To obtain a one-component magnetic developer having satisfactory electrostatic charge characteristics and excellent in durability. CONSTITUTION:This one-component magnetic developer contg. at least a resin, magnetic powder and a releasing agent is composed of a magnetic toner and 1X10<-3>-5X10<-2> number% releasing agent-based particles basing on the amt. of the magnetic toner. The vol. average particle diameter (Dp) of the releasing agent-contg. particles and the vol. average particle diameter (Dt) of the magnetic toner satisfy the relation of 0.8<Dp/Dt<1.2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a one-component magnetic developer for developing electrostatic images.

[0002]

2. Description of the Related Art Conventionally, a developing method using a magnetic toner does not require a carrier, and thus has an advantage that the structure of a developing device is simplified. However, in the developing method using this magnetic toner, since charging is imparted to the toner by mutual frictional charging of the toner itself or frictional charging with the developing sleeve, the toner tends to be insufficiently unstable and the charging property of the toner is improved. Various methods have been proposed to achieve this.

For example, a method of improving the charging property by adding an external additive (JP-A-60-32060) has been proposed.
When these inorganic fine particles are added, there is a drawback that scratches are generated due to the adhesion of the inorganic fine particles to the photoreceptor.
Further, a method of adding organic fine particles has also been proposed (JP-A-60-186851, etc.). However, in this case, there is a drawback that the organic fine particles themselves adhere to the fixing roller or the like to cause offset. Further, Japanese Patent Laid-Open No. 1-234858 proposes a developer in which polyethylene particles having a size of 1 μm or more are 10 or less per 100 toner particles. In this case, there is no choice but to increase the amount of addition and mixing, which causes a problem of fusion to the toner particles themselves in addition to imparting the charge, and there is a problem that the image density is lowered in repeated use.
In particular, these problems remarkably occur in an environment where high temperature and high humidity are likely to cause a leak of electrostatic charge.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide a magnetic toner having excellent durability. Further, the magnetic toner of the present invention can be suitably used in a so-called thin layer forming system in which a thin developer layer is conveyed to a developing area. The reason for this is that in the case of the thin layer forming method, the triboelectric charging effect between the toners is relatively small, and the effect of substances other than the triboelectrically charged toner on the toner needs to be more significantly exhibited. is there.

[0005]

As a result of intensive studies to achieve the above object, it was found that the object of the present invention can be achieved by using the following magnetic toner.

Namely, 1) at least a resin and magnetic powder and a release agent at the developer comprising magnetic toner containing, developer is the magnetic toner and 1 × 10 ^-3 ~5 × 10 ^{- 2} % by number of particles containing a release agent as the main component, and the volume average particle diameter (Dp) of the particles containing the release agent as the main component is the volume average particle diameter (Dt) of the magnetic toner. ) Against 0.8 <Dp / Dt <
2. A developer characterized in that it is 1.2, 2) a developer comprising a magnetic toner containing at least a resin, magnetic powder and a release agent is conveyed to a development area in a layer thickness of 20 to 500 μm, and on the photoreceptor. In the developing method for developing an electrostatic latent image, the developer is the magnetic toner and 1 × 10 ^{−3 to} 5 × 10 5.
^-2 % by number of particles containing a release agent as a main component, and the volume average particle diameter (Dp) of the particles containing the release agent as a main component is The object of the present invention was achieved by a development method characterized in that a developer having 0.8 <Dp / Dt <1.2 with respect to Dt) is used.

The particles containing a release agent as a main component are particles in which the release agent is added in an amount of 80% by weight or more in all the constituent components of the existing particles. That is, the characteristics of the present invention are to exert the effect of imparting triboelectric chargeability to the magnetic toner and improve the chargeability of the toner itself by allowing the particles having no magnetism and having different chargeability to be present. For this reason, it is preferable to add and mix particles having different charging characteristics. However, it is not preferable to use a material having a completely different toner composition because it adheres to the non-image portion, and it is preferable to use the same material as the constituent material of the magnetic toner and to control the charging property therein. Further, in terms of particle size, the addition of particles having a particle size approximately equal to that of the magnetic toner has a great effect of imparting triboelectric charging.

The term "particles containing a release agent as a main component" as used herein refers to particles containing 80 to 95% by weight of the release agent, but the release agent itself has different triboelectric charging characteristics from the toner. Is to have. However, in the case of a material which is composed of a pure release agent, since the release agent itself is a soft material, it is likely to cause a problem due to fusion to a developing device or the like under a high temperature and high humidity environment. Further, when the content of the release agent is small, the effect of imparting charge is small. Furthermore, it is preferable that the material forming the particles is the same as the material forming the magnetic toner. The reason for this is that when a material having substantially the same thermal characteristics as the toner itself is used, the fixability is the same as that of the toner, so that problems such as offset do not occur. Further, in the present invention, it is preferable that the particle diameter of the particles containing the release agent as a main component is substantially the same as the volume average particle diameter of the toner. That is, in the case of large particles, it is necessary to add and mix a large amount in order to impart the charging property, and since the particles contain almost no magnetic material, the problem of scattering of the particles themselves occurs. . When the particle size is small, the effect of imparting charge to the toner becomes large, but the effect becomes excessive, the amount of charge of the particles themselves increases, and the adhesive force to the surface of the developing device increases, so that the adhesion to the surface of the developing device increases. Cause problems. Therefore, as the average particle diameter, the volume average particle diameter (Dp) of the particles containing the release agent as a main component is 0.8 <Dp / Dt <1.2 with respect to the volume average particle diameter (Dt) of the magnetic toner. It is preferable.

The addition amount is 1 × 10 with respect to the magnetic toner.
^{-3 to} 5 × 10 ^-2 number% may be added. If the addition amount is too large, a phenomenon in which these particles are released occurs, causing a problem of fogging due to adhesion on the photoconductor or in-machine contamination due to scattered particles. Further, when the added amount is small, the effect of imparting charge cannot be exhibited.

The present invention improves the stability of developed image density, especially in high temperature and high humidity environments.

The magnetic toner is a developer that greatly depends on the charge amount. In a high-temperature and high-humidity environment, leakage of electric charges from the surface of the magnetic toner increases, and the amount of charge decreases. In this case, a phenomenon occurs in which the density decreases as the charge amount decreases. In order to solve this problem, it is necessary to increase the charge imparting effect on the magnetic toner. Heretofore, it has been shown that the chargeability can be made uniform by adjusting the released polyethylene wax particles to a certain amount or less. However, as a result of diligent studies, it was found that the charge amount was improved and the concentration was stabilized under high temperature and high humidity by adding and mixing particles containing a specific amount of a release agent as a main component.

If the amount of addition is too large, the particles may adhere to the surface of the developing device or adhere to the surface of the magnetic toner, resulting in a problem that the image density is lowered. Further, when the addition amount is small, the effect of imparting charge becomes small and the concentration cannot be secured in a high temperature and high humidity environment.

A specific method for producing the particles is as follows. In the same manner as in the case of producing an ordinary toner, the materials constituting the toner are used and the release agent is adjusted to a desired range, and kneading / pulverization / It can be obtained by classifying. Also, at this stage, the required particle size distribution is adjusted.

As a method of adding to the magnetic toner, the required amount may be added and mixed in the same manner as the conventional external additive mixture.

[0015]

[Action]

[Structure of Developer] The magnetic toner of the present invention contains a binder resin, magnetic powder, and additives such as a release agent, a charge control agent, and a coloring agent, which are used as necessary, and the particle size thereof is The volume average particle diameter is usually 1 to 30 μm, preferably 5 to 20 μm. The binder resin that constitutes the magnetic toner is not particularly limited, and various conventionally known resins can be used. For example, styrene resin, acrylic resin, styrene / acrylic resin, polyester resin, etc. may be mentioned. Ferromagnetic particles such as ferrite and magnetite having a number average primary particle diameter of 0.1 to 2.0 μm are used as the magnetic powder, and the addition amount of the magnetic powder is 20 to 70% by weight in the colored particles.

Other additives include colorants, charge control agents, release agents and the like, but the colorants are not particularly limited, and various conventionally known materials are used. For example, carbon black, nigrosine dye, aniline blue, calcoil blue, chrome yellow, ultramarine blue,
Examples include DuPont Oil Red, Quinoline Yellow, Methylene Blue Chloride, Phthalocyanine Blue, Malachite Green Oxalate and Rose Bengal.
Examples of the charge control agent include salicylic acid derivatives and azo metal complexes, and the release agent described below can be used as the release agent.

[Type of Release Agent] Any conventionally used release agent can be used. Specific examples include olefins such as low molecular weight polypropylene / low molecular weight polyethylene / ethylene-propylene copolymer, and microcrystalline wax / carnauba wax / sazol wax / paraffin wax.

The addition amount of these is 1 to 5% by weight in the toner.
It is preferable to add.

Of these, low molecular weight polypropylene and low molecular weight polyethylene can be preferably used. In the particles containing the release agent of the present invention as a main component, 80% or more, preferably 80% or more.
~ 95% by weight.

In the magnetic toner of the present invention, in addition to the particles containing the release agent added in the present invention as a main component, silica and titanium oxide having a number average primary particle diameter of 5 to 500 nm for imparting fluidity. Inorganic fine particles such as strontium titanate and aluminum oxide may be added. These may be used after being subjected to a hydrophobic treatment. Further, a higher fatty acid metal salt such as zinc stearate may be added as a cleaning aid.

[Definition of Thin Layer Formation] The thin layer forming method means a method of forming a toner layer of 20 to 500 μm on the surface of the developing sleeve in the developing region. When forming this thin layer, there is a method of pressing a toner layer regulating rod against the surface of a developing blade or a magnetic blade that uses magnetic force. Furthermore, there is also a method in which a urethane blade, a phosphor bronze plate, or the like is brought into contact with the surface of the developing sleeve to regulate the toner layer.

The gap between the developing sleeve and the surface of the photoreceptor may be larger or smaller than the toner layer. Further, a system in which only the DC component is applied as the developing bias may be used, or AC
Any method of applying a bias may be used.

The pressing force of the pressure regulating member is preferably 1 to 15 gf / mm, and when the pressing force is small, the regulation force is insufficient and the conveyance becomes unstable. On the other hand, when the pressing force is large, the stress on the developer increases, so that the durability of the developer decreases. An even more preferable range is 3 to 10 gf /
mm.

[Measurement Method of Number Percentage] A method of measuring the amount of particles having a release agent as a main component is constant after adjusting a constant concentration dispersion liquid with a Coulter counter (measurement range: 2.00 to 50.8 μm). The time was measured, and the number was calculated. In this case, since the conventional method causes an error in the addition amount measurement, the amount of the particles containing the release agent as the main component after addition to the magnetic toner is determined.

That is, first, 5.0 g of the magnetic toner is sampled, 20 ml of the aqueous surfactant solution is added, and after stirring, ultrasonic waves are irradiated for 90 seconds to disperse. Then, 3.5 m of this dispersion is sampled, added to 150 ml of Isoton solution, and irradiated with ultrasonic waves for 10 to 20 seconds. After that, measurement is performed for 1 minute with a Coulter counter. Here, the area in which the magnetic toner is present in 90% by number or more and the number of the magnetic toner in the area are determined.
Let this number be A.

Next, after adding particles containing a release agent as a main component to the magnetic toner, 5.0 g of the developer was sampled, 20 ml of an aqueous surfactant solution was added, and after stirring, ultrasonic irradiation was performed for 90 seconds. After that, the magnetic toner and the particles containing the release agent as a main component are separated. Then, a magnet is applied to the bottom of the container to deposit the magnetic toner on the bottom of the container. Then, 3.5m of the supernatant
Collect at least l and let stand for at least 6 hours. Prepare 150 ml of Isoton solution in a beaker, collect 3.5 ml of the supernatant liquid, and add to the Isoton solution. Then, after irradiating with ultrasonic waves for 10 to 20 seconds, measurement is carried out for 1 minute with a Coulter counter, and the number of particles existing in a particle size range in which 90% by number or more of the magnetic toner itself exists is determined. Let this number be B.

From the measurement results A and B of both, the number% of particles containing the release agent as the main component is calculated according to the following formula.

Number of particles containing release agent as main component% = B /
(A + B) x 100

[0029]

The present invention will be described in detail below with reference to examples, but the embodiments of the present invention are not limited thereto. In the examples and comparative examples, “part” means “part by weight”.

(Preparation Example of Particles Containing Release Agent as Main Component) Preparation Example 1: Low molecular weight polypropylene = 100 parts and styrene-
Acrylic resin = 20 parts was mixed, and the mixture was kneaded and pulverized to obtain particles having a volume average particle diameter of 11.3 µm and a release agent as a main component. This is designated as "particle 1".

Preparation Example 2: "Particle 2" was obtained in the same manner as in Preparation Example 1 except that particles having a volume average particle diameter of 7.1 μm as a main component and a release agent were prepared by pulverization and classification.

Preparation Example 3: In Preparation Example 1, styrene-
Particles containing a release agent as the main component and having a volume average particle size of 9.3 μm were obtained in the same manner except that the acrylic resin was used in an amount of 10 parts. This is designated as "particle 3".

Preparation Example 4: In Preparation Example 1, styrene-
Particles having a volume average particle size of 11.2 μm and a release agent as a main component were similarly obtained except that 20 parts of a polyester resin was used instead of the acrylic resin. This is designated as "particle 4".

Preparation Example 5: "Particle 5" was obtained in the same manner as in Preparation Example 4, except that the particles having a volume average particle diameter of 6.3 μm as a main component and a release agent were prepared by pulverization and classification.

Comparative Particle Preparation Example 1: Volume average particle diameter = 11.3 μm in the same manner as in Preparation Example 1 except that low molecular weight polypropylene = 100 parts and styrene-acrylic resin = 30 parts.
To obtain comparative particles. This is designated as "Comparative Particle 1".

Comparative Particle Preparation Example 2 In Comparative Particle Preparation Example 1, 100 parts of polyester resin was used instead of styrene-acrylic resin, and comparative particles having a volume average particle size of 6.5 μm were obtained. This is designated as "Comparative Particle 2".

Comparative Particle Preparation Example 3 In Comparative Particle Preparation Example 1, the styrene-acrylic resin was not used, and the pulverization conditions were changed to obtain comparative particles having a volume average particle size of 6.9 μm. This is designated as “Comparative Particle 3”.

(Magnetic toner preparation example) Magnetic toner preparation example 1: 100 parts of styrene-acrylic resin, 50 parts of magnetic powder (magnetite), 5 parts of release agent (low molecular weight polypropylene), and charge control agent (metal complex of salicylic acid derivative) ) 1 part was mixed and the mixture was kneaded, crushed and classified according to the usual conditions to obtain magnetic colored particles having a volume average particle size of 11.3μ. Hydrophobic silica (number average primary particle size = 12n)
m) 0.4% by weight and "Particle 1" of the present invention were added and mixed to obtain a developer of the present invention.

Here, the particle size distribution of the magnetic toner is
The area where 90% or more of the number exists is 6.35 to 20.2 μm
Was the realm of. "Particle 1" was added, and the amount of "particle 1" existing in this range was added and mixed so as to be 5 × 10 ⁻³ number% to obtain a magnetic toner of the present invention. This is designated as "magnetic toner 1". Note that Dp / Dt = 1.0.

Magnetic toner preparation example 2: Magnetic toner preparation example 1
In this case, magnetic colored particles having a volume average particle size of 7.2 μm were obtained by pulverization classification. However, in the particle size distribution, the region in which 90% by number or more existed was the region of 3.17 to 12.7 μm. Add “particle 2” so that the amount of “particle 2” existing in this range is 3 × 10 ⁻² number%, and further add 0.9% by weight of hydrophobic silica (number average primary particle size = 15 nm) and mix. Then, a magnetic toner of the present invention was obtained. This is designated as "magnetic toner 2". Note that Dp / Dt = 0.99.

Magnetic toner preparation example 3: Magnetic toner preparation example 1
At this point, magnetic colored particles having a volume average particle diameter of 9.1 μm were obtained by pulverization classification. However, in the particle size distribution, the region in which 90% by number or more existed was in the region of 4.00 to 16.0 μm. Add “particles 3” so that the amount of “particles 3” existing in this range is 4 × 10 ⁻² number%, and 0.7% by weight of hydrophobic silica (number average primary particle size = 8 nm) is added and mixed. Then, a magnetic toner of the present invention was obtained. This is designated as "magnetic toner 3". Note that Dp / Dt = 1.02.

Magnetic toner preparation example 4: Polyester resin 10
Mix 0 parts, 50 parts magnetic powder (magnetite), 5 parts release agent (low molecular weight polypropylene) and 1 part charge control agent (metal complex of salicylic acid derivative) and mix according to normal conditions.
The particles were pulverized and classified to obtain magnetic colored particles having a volume average particle size of 10.8μ. 0.4% by weight of hydrophobic silica (number average primary particle size = 16 nm) and "Particle 4" of the present invention were added to and mixed with the magnetic colored particles to obtain a developer of the present invention.

Here, the particle size distribution of the magnetic toner is
The region where 90% or more of the number existed was the region of 6.35 to 20.2 μm. "Particle 4" was added, and the amount of "particle 4" existing in this range was added and mixed so as to be 3 × 10 ^-2 number%.
This is designated as "magnetic toner 4". Dp / Dt =
It is 1.08.

Magnetic toner preparation example 5: Magnetic toner preparation example 4
At this point, magnetic colored particles having a volume average particle size of 6.7 μm were obtained by pulverization classification. However, in the particle size distribution, the region in which 90% by number or more existed was the region of 3.17 to 12.7 μm. Add “particle 5” so that the amount of “particle 5” existing in this range is 1 × 10 ⁻² number%, and add 1.0% by weight of hydrophobic silica (number average primary particle size = 12 nm). Then, a magnetic toner of the present invention was obtained. This is designated as "magnetic toner 5". Note that Dp / Dt = 0.0.94.

Comparative Magnetic Toner Preparation Example 1 A comparative magnetic toner was obtained in the same manner as in Magnetic Toner Preparation Example 1 except that “Comparative Particle 1” was used instead of “Particle 1”. This is designated as “comparative magnetic toner 1”.

Comparative Magnetic Toner Preparation Example 2 A comparative magnetic toner was obtained in the same manner as in Magnetic Toner Preparation Example 5, except that “Comparative Particle 2” was used instead of “Particle 5”. This is designated as “comparative magnetic toner 2”.

Comparative Magnetic Toner Preparation Example 3 A comparative magnetic toner was obtained in the same manner as in Magnetic Toner Preparation Example 2 except that “Comparative Particle 3” was used instead of “Particle 2”. This is designated as “comparative magnetic toner 3”.

Comparative Magnetic Toner Preparation Example 4 A comparative magnetic toner was prepared in the same manner as in the preparation example 1 of the magnetic toner except that 1 × 10 ^-1 % by number of "particle 1" was added. This is designated as “comparative magnetic toner 4”.

Comparative Magnetic Toner Preparation Example 5 A comparative magnetic toner was prepared in the same manner as in the magnetic toner preparation example 1, except that 1 × 10 ⁻⁴ number% of “particle 1” was added. This is designated as “comparative magnetic toner 5”.

Comparative Magnetic Toner Preparation Example 6 A comparative magnetic toner was prepared in the same manner as in Magnetic Toner Preparation Example 1 except that “particle 2” was used instead of “particle 1”. this,
This is “Comparative Magnetic Toner 6”. In this case, Dp /
Dt = 0.63.

Comparative Magnetic Toner Preparation Example 7 A comparative magnetic toner was obtained in the same manner as in Magnetic toner preparation example 2 except that “particle 1” was used instead of “particle 2”. this,
This is “Comparative Magnetic Toner 7”. In this case, Dp /
Dt = 1.58.

Comparative Magnetic Toner Preparation Example 8 A comparative magnetic toner was obtained in the same manner as in the magnetic toner preparation example 1, except that "particle 1" was not added. This is "Comparative Magnetic Toner 8".
And

(Evaluation Method and Results) For the evaluation, the laser printer LP-3015 (manufactured by Konica Corp.) was modified so that the printing speed in A4 longitudinal feeding was 20 sheets / min, and a 6-pole fixed magnet was incorporated. It had a developing sleeve made of magnetic stainless steel with a diameter of 25 mm, the developing area gap: Dsd = 0.2 mm, and the toner layer on the developing device surface in the developing area was 0.15 mm, which was modified to a non-contact type. The photosensitive member is a laminated type organic photosensitive member, the developing portion potential is -500V, the developing bias is -50 to -550V from peak to peak, the AC bias of frequency 2kHz and -25.
A DC bias of 0V was applied.

The evaluation method is under high temperature and high humidity environment (33 ° C / 80%
RH) was used to determine the change in image density and the change in image quality. That is, using the above-mentioned developing device, images of 5% pixels were continuously printed on 100,000 sheets under the high temperature and high humidity condition, the image densities at the initial and after the printing were measured, and the presence or absence of fog and image defect was evaluated. did.

The image density was determined by printing a solid black image, measuring the absolute reflection densities at the 12 points, and averaging them to determine the average density. Further, as the image defect, the maximum density and the minimum density of the solid black image were obtained, and the unevenness of the image was evaluated by the difference. Fogging was printed on a blank sheet of paper, and the relative density at 12 points was measured. Relative density means the paper density of 0.00
The value was measured as 0. The results are shown in "Table 1" below.
Shown in.

[0056]

[Table 1]

As shown in the above results, it is understood that the developer of the present invention exhibits excellent durability even in a high temperature and high humidity environment.

[0058]

According to the present invention, it is possible to provide a one-component magnetic developer having good charging characteristics and excellent durability. Further, the one-component magnetic developer of the present invention can be suitably used in a so-called thin layer forming system in which a thin developer layer is conveyed to a developing area.

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Claims (2)

[Claims] 1. A one-component magnetic developer containing at least a resin, magnetic powder and a release agent, wherein the developer is 1 × 10 ^{−3 to} 5 × 10 5 with respect to a magnetic toner. ^-2 % by number of particles containing a releasing agent as a main component, and further, the volume average particle diameter (D
p) is relative to the volume average particle diameter (Dt) of the magnetic toner
A one-component magnetic developer characterized in that 0.8 <Dp / Dt <1.2. 2. A developer comprising a magnetic toner containing at least a resin, magnetic powder and a release agent is conveyed to a developing area in a layer thickness of 20 to 500 μm to develop an electrostatic latent image on a photoreceptor. In the developing method, the developer is composed of the magnetic toner and 1 × 10 ^{−3 to} 5 × 10 ⁻² number% of particles having a release agent as a main component with respect to the magnetic toner. The volume average particle diameter (Dp) of the particles containing the release agent as a main component is 0.8 <Dp / Dt <with respect to the volume average particle diameter (Dt) of the magnetic toner.
A developing method comprising using a developer of 1.2.