JPH0782247B2 - Magnetic toner - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a toner used in electrophotography, electrostatic recording and the like, and particularly to an insulating magnetic toner.

[Prior Art] Conventionally, a number of methods are known as electrophotography, but generally, a photoconductive substance is used to form an electric latent image on a photoconductor by various means, and then the electrophotographic image is formed. The latent image is developed with toner to form a visible image, and if necessary, the toner image is transferred to a transfer material such as paper and then fixed by heating, pressure or the like to obtain a copy.

On the other hand, in recent years, there has been a demand for a printer that is quiet and operates at high speed, as represented by an LBP (laser beam printer), and in order to satisfy these performances, there is a tendency for the developing device space to be small, simple and lightweight. . Therefore, there is a problem in that the toner used in such a developing device as a whole cannot have excellent image quality, durability, and stability unless it has higher performance than ever before. That is, the performance of the toner is often directly reflected in the performance of the system.

In addition, there are severe demands such as resolution improvement due to digitalization of copiers, durability, halftone reproducibility for copying of photographs, gradation reproducibility, etc., but conventional toners must sufficiently meet this demand. I can't.

Therefore, as proposed in JP-A-1-112253, it has been considered to reduce the particle size of the toner in order to satisfy these performances. This is usually 10-14μ
The particle diameter of the toner having a volume average diameter of m is 10 μm or less. Certainly, fine line reproducibility, halftone reproducibility, gradation reproducibility, etc. are considerably improved. However, if the conventional toner is simply made small, the amount of charge per gram is excessively increased, so that the image density and the image quality are deteriorated. In particular, it becomes remarkable in a small machine using a small diameter sleeve, a high speed machine, and further in a low temperature and low humidity environment. Therefore, various adjustments of the charge amount have been studied. However, if the charge amount is simply lowered, the image density and the image quality are deteriorated particularly in a high temperature and high humidity environment or when left for a long time.

Also, toner with a small particle size tends to scatter,
Further, the phenomenon of fogging that causes the background of the image to become dirty easily occurs.

When an octahedral magnetic material that is generally used in the past is used for a toner having a particle size of 10 μm or less, the cohesiveness is large because the remanent magnetization is large even though the cohesiveness is increased by the amount that the toner becomes smaller than the conventional one. It may become stronger, so that the image density may be difficult to appear, and the image quality tends to be poor. To improve this, it has been considered to add a fluidity-imparting agent such as colloidal silica, but the selection of its type and amount is delicate, and it may adversely affect the environmental characteristics and durability stability. is there. In addition, Japanese Examined Japanese Patent Sho 62-5120
No. 8, JP-A-59-64852, it is proposed to use a spherical magnetic material. Since such a magnetic material has a small residual magnetization, it has a small cohesive property, and therefore tends to have good imageability. However, such a magnetic material has a large amount of charge, and therefore control is often difficult.
If the developing device is complicated for this control, various harmful effects are likely to occur.

Therefore, in JP-A-56-91242 and JP-B-59-27901, there is proposed a toner using a cubic magnetic substance having a preferable range of 0.3 μm or more. It is said that such a magnetic material has good developing efficiency, transfer efficiency, scattering, and background stains. However, when this magnetic material is used for a toner having a volume average diameter of less than 10 μm, the charge amount becomes large. This is a tendency, and it tends to be difficult to control when considering environmental stability.

As described above, it is highly reliable that solves various problems.
Magnetic toners of μm or less have not been proposed.

[Problems to be Solved by the Invention] An object of the present invention is to solve the above-mentioned problems, to have excellent environmental stability and durability stability, and to be free from image quality, especially sharpness, scattering around images, and background stains. It is to provide an excellent magnetic toner.

[Means and Actions for Solving the Problem] The feature of the present invention is that the standard deviation σ of the number distribution is divided by the average particle size and the change coefficient (σ /
X) × 100 is 40% or less, average particle size 0.1 μm or more and 0.3 μm
Containing less than hexahedral magnetic body, the volume average diameter D is 10μ
m or less, the variation coefficient to the standard deviation σ _T (σ _T /
D) x100 is in magnetic toner with 25-35%.

The average particle diameter and the coefficient of change (%) of the magnetic material as used herein mean that a photograph of the magnetic material of 10,000 times obtained by a transmission electron microscope is magnified 4 times and made 40,000 times. , Randomly 25
Select 0 magnetic materials, measure their diameters, find the average particle diameter (horizontal ferret diameter) from the diameter and number, and the coefficient of change is
The standard deviation σ of the number distribution is obtained, divided by the average value, multiplied by 100, and expressed in%.

The average particle size is 0.1 μm or more and less than 0.3 μm, and preferably 0.1 μm or more and less than 0.2 μm.

If the average particle size is smaller than 0.1 μm, heat resistance becomes a problem, and the color is slightly reddish. Furthermore, dispersion is also difficult. If it is 0.3 μm or more, it becomes difficult to control charge and environmental stability becomes poor.

The coefficient of change of the magnetic material is preferably 40% or less, preferably 35% or less, more preferably 30% or less, further preferably 25% or less, further preferably 20% or less.
If this variation coefficient is larger than 40%, heat resistance, dispersibility, and charge controllability will become problems.

As for the shape of the magnetic body, 250 pieces are randomly selected from the above 40,000 times electron micrograph, and when 50% or more of what looks like a square is defined as a hexahedral magnetic body. If it is less than 50%, the cohesiveness of the toner increases and the image quality tends to deteriorate.

Furthermore, as magnetic properties, 1K, σs is 50-70emu /
g and σr are preferably 5 to 10 emu / g.

The bulk density of the magnetic material is preferably 0.35 g / cc or more,
More preferably 0.40 g / cc or more, further 0.50 g / cc
Or more, further, 0.60 g / cc or more, further, 0.
70g / cc or more. In particular, the particle size of the magnetic material is 0.2 μm
When the particle size is 0.18 μm or less, the magnetic material is likely to contain air between particles. Therefore, a higher bulk density is preferable for dispersion.

The particle size and particle size distribution of the toner are measured with a Coulter Counter TA-2 particle size distribution meter manufactured by Coulter Counter Co. using a 100 μm aperture. The volume average diameter of the toner is preferably 9 μm or less, more preferably 8 μm or less.

Although not bound by theory, as a result of diligent examination of magnetic materials, what is generally called a cubic magnetic material is a mixture of hexahedra and octahedra, which are polyhedra close to each other. Looking at the shape of one particle, most are octahedrons. It can be seen from the fact that Hc and σr among the magnetic properties are large. Therefore, the manufacturing conditions were adjusted, and most of the hexahedral magnetic materials were manufactured and examined. As a result, it was found that they are excellent in various points, especially when applied to a toner having a volume average particle diameter of 10 μm or less. . It is considered that this is because the magnetic property σr is small and there is an appropriate convex portion.

Examples of the binder resin of the toner include homopolymers of styrene and its substitution products such as polystyrene, poly-p-chlorostyrene, polyvinyltoluene, styrene-p-chlorostyrene copolymer, styrene-vinyltoluene copolymer, and their copolymers. Copolymers; copolymers of styrene and acrylic ester such as styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-n-butyl acrylate copolymer; styrene-methyl methacrylate copolymer Copolymers of styrene and methacrylic acid esters such as polymer, styrene-ethyl methacrylate copolymer and styrene-n-butyl methacrylate copolymer; multi-component copolymers of styrene and acrylic acid ester and methacrylic acid ester;
Other styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-butadiene copolymer, styrene-vinyl methyl ketone copolymer,
Styrene-based copolymers of styrene and other vinyl-based monomers such as styrene-acrylonitrile-indene copolymer and styrene-maleic acid ester copolymer; polymethylmethacrylate polybutylmethacrylate, polyvinyl acetate, polyester, polyamide, epoxy Resin, polyvinyl butyral, polyacrylic acid, phenol resin,
Aliphatic or alicyclic hydrocarbon resins, petroleum resins, chlorinated paraffins, etc. can be used alone or in combination.

In particular, as the binder resin for the toner to be used in the pressure fixing method, low molecular weight polyethylene, low molecular weight polypropylene,
Ethylene-vinyl acetate copolymer, ethylene-acrylic acid ester copolymer, higher fatty acid, polyamide resin, polyester resin and the like can be used alone or in combination.

If the polymer, copolymer or polymer blend used contains 40% by weight or more of a vinyl aromatic or acrylic monomer represented by styrene, more desirable results are obtained. The magnetic substance according to the present invention may be used in an amount of 20 to 150 parts by weight, preferably 30 to 120 parts by weight, based on 100 parts by weight of the binder resin.

Any suitable pigment or dye can be used as a colorant in the toner. For example, there are known dyes and pigments such as carbon black, phthalocyanine blue, ultramarine blue, quinacridone, and benzidine yellow.

Examples of the magnetic substance include co-magnetic elements such as iron, cobalt and nickel, alloys and compounds of iron, cobalt, nickel and manganese such as magnetite, maghemite and ferrite, and other ferromagnetic alloys.

Magnetite will be described from among such magnetic materials.

Magnetite is prepared by mixing a ferrous salt solution and an alkaline aqueous solution to form a suspension containing ferrous hydroxide having a temperature of 70 to 100 ° C and a pH of 8 or more, and then oxygen-containing gas is passed through the suspension. It is obtained by doing. The shape of the magnetite particles is a hexahedral particle shape depending on the generation conditions.

As the alkaline aqueous solution, hydroxides of alkali metals such as sodium hydroxide and potassium hydroxide and hydroxides of alkaline earth metals such as magnesium hydroxide and calcium hydroxide can be used.

Magnetite produced when water-soluble silicates such as sodium silicate and potassium silicate (0.1 to 2.0 wt% in terms of SiO ₂ with respect to the produced magnetite particles) are present in a suspension containing ferrous hydroxide. Is preferable because the distribution can be further improved.

When oxygen-containing gas is aerated while heating a suspension containing ferrous hydroxide obtained by mixing an alkaline aqueous solution and a ferrous salt aqueous solution at a temperature of 70 to 100 ° C and a pH of 8 or more, the particle size is fine and the particle size distribution is Is also sharp, that is, magnetite particles having a small coefficient of change are obtained.

The synthesis of magnetite used in the present invention will be described in detail in the following synthesis example.

(Synthesis Example) A bubble oxidation type reaction tower having a diameter of 35 cm and an internal volume of 50 was used as a reactor. Ferrous sulfate aqueous solution containing Fe ²⁺ 1.75mol / 20,4
Sodium hydroxide aqueous solution 15 of N, water 54 and sodium silicate (No. 3) (to produce magnetite, corresponding to 0.23 wt% in terms of SiO _2.) (SiO ₂ 28.55 wt%) 18.9 g using a temperature 88 A suspension containing 42 Fe (OH) ₂ at ℃, pH 8.5 was prepared.

10 minutes per minute at a temperature of 90 ° C. in a suspension containing Fe (OH) ₂
Zero air was bubbled through for 120 minutes producing a black precipitate. The produced particles were washed with water, filtered, dried and pulverized by a conventional method. As a result of observing with an electron microscope, the obtained magnetite particle powder was a hexahedral particle having an average particle size of 0.17 μm and a variation coefficient of 18.5%. This is designated as magnetite A. Among the above reaction conditions, Fe ²⁺ concentration when producing a suspension containing ferrous hydroxide, temperature, pH, the addition amount of sodium silicate and the temperature of the oxidizing conditions, except that the amount of air was changed, Magnetites B, C, ..., F were obtained under the same conditions as above. Summarizing the reaction conditions and the average particle size of the generated magnetite and the coefficient of variation together,
It becomes like Table 1.

[Examples] Hereinafter, all parts are parts by weight.

Example 1 Powder mixed with a roll mill set to 140 ° C for about 1
After kneading with heat for 5 minutes and cooling, coarse pulverization and fine pulverization (jet mill) were performed. Furthermore, fine powder and coarse powder were cut with a zigzag classifier manufactured by Alpine, and the volume average diameter was 7.9 μm, and the coefficient of change was 2
8% toner was obtained.

This is the Canon laser beam printer LBP-8II
The printing speed was increased from 8 sheets / minute to 10 sheets / minute and evaluated in a printer modified.

As a result, the environmental stability was good, but the image density was high even in an environment of high temperature and high humidity, the durability stability was excellent, the sharpness was excellent, and the image around the image was free from scatter and background stains. Obtained.

Comparative Example 1 Example 1 except that the magnetic body of Example 1 was changed to the magnetic body E
Toner was created in the same manner as in. Toner volume average diameter is 8.0
It was μm and the coefficient of change was 29%.

This was evaluated in the same manner as in Example 1.

As a result, particularly in continuous image output under low temperature and low humidity environment, the charge amount increased, the image density decreased, the background was stained, and the image became thick.

Example 2 In the same manner as in Example 1 to obtain a toner having a volume average diameter of 7.5 μm,
A toner having a coefficient of change of 25% was obtained.

This is from Canon Family Copier FC 6 sheets / minute
It was evaluated by a machine modified to 10 sheets / minute.

As a result, environmental stability is good, and even in continuous image output, it is excellent in image density and sharpness, and scatters around the image.
The background was clean.

Comparative Example 2 Example 2 except that the magnetic body of Example 2 was changed to the magnetic body F.
Toner was created in the same manner as in.

The obtained toner has a volume average diameter of 7.8 μm and a coefficient of variation of 24.
%Met.

This toner was evaluated in the same manner as in Example 2.

As a result, especially under high temperature and high humidity, near the end of the durability test, the image density was lowered, and the image quality was also particularly poor in sharpness.

Examples 3 and 4 In Example 1, the magnetic substance was changed to the magnetic substance C and the magnetic substance D, and toner was prepared and evaluated by a high-speed copying machine.

[Advantages of the Invention] As described above, when the toner of the present invention is used, a high-quality copied image can be obtained for a long period of time in any environment, and it can be sufficiently used for general household use and severe environment use. .

Claims (1)

[Claims] 1. A volume containing a hexahedral magnetic body having a number average particle diameter of 0.1 μm or more and less than 0.3 μm, and a coefficient of change obtained by dividing the standard deviation σ of the number distribution by the average particle diameter is 40% or less. A magnetic toner having an average diameter D of 10 μm or less and a coefficient of variation {(σ _T / D) × 100} of 25 to 35% when the standard deviation is σ _T.