JPH0782246B2 - Magnetic toner - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a toner used in electrophotography, electrostatic recording, etc., and particularly relates to an insulating magnetic toner.

[Background technology]

As a conventional electrophotographic method, U.S. Pat.No. 2,297,691, Japanese Patent Publication No. 42-23910 (US Pat. No. 3,666,363) and Japanese Patent Publication No. 43-24748 (US Pat. No. 4,071,3).
No. 61), etc., a number of methods are known. Generally, a photoconductive substance is used to form an electric latent image on a photoconductor by various means, and then, The latent image is developed with toner to form a visible image, and if necessary,
After the toner image is transferred onto a transfer material such as paper, it is fixed by heating, pressure or the like to obtain a subject.

Various developing methods are known in which an electrostatic latent image is visualized using toner. For example, the magnetic brush method described in U.S. Pat. No. 2,874,063, the cascade developing method described in U.S. Pat. No. 2,618,552, and the same No. 2,221,776.
A large number of developing methods such as the powder cloud method, the fur brush developing method, and the liquid developing method described in the specification are known. Among these developing methods, a magnetic brush method, a cascade method, a liquid developing method and the like, which use a developer mainly composed of toner and a carrier, have been widely put into practical use. All of these methods are excellent methods in which a good image can be obtained relatively stably, but on the other hand, they have the common drawbacks associated with a two-component developer, such as deterioration of the carrier and variation in the mixing ratio of the toner and the carrier.

In order to avoid such drawbacks, various developing methods using a one-component developer composed of only toner have been proposed. Among them, many are excellent in the method of using a developer composed of magnetic toner particles. .

U.S. Pat. No. 3,909,258 proposes a developing method using a magnetic toner having electrical conductivity. In this method, a conductive magnetic toner is supported on a cylindrical conductive sleeve having magnetism inside, and the conductive magnetic toner is brought into contact with an electrostatic image for development. At this time, in the developing section, a conductive path is formed by the toner particles between the surface of the recording material and the surface of the sleeve, and the electric charge is introduced from the sleeve to the toner particles through the conductive path, so that the conductive path between the electrostatic image and the image section is formed. The Coulomb force causes the toner particles to adhere to the image area and be developed. This developing method using a conductive magnetic toner is an excellent method that avoids the problems associated with the conventional two-component developing method, but on the other hand, since the toner is conductive, the developed image can be transferred from a recording medium to plain paper or the like. It has the drawback that it is difficult to electrostatically transfer it to the final support member.

As a developing method using a high-resistance magnetic toner that can be electrostatically transferred, there is a developing method using dielectric polarization of toner particles. However, such a method has drawbacks such that the developing speed is essentially slow and the density of a developed image cannot be sufficiently obtained, and it is practically difficult.

As another developing method using high-resistance magnetic toner,
A method is known in which toner particles are triboelectrically charged by friction between the toner particles, friction between the toner particles and a sleeve or the like, and the toner particles are brought into contact with an electrostatic image holding member to develop. However, these methods have drawbacks such that the number of contact between the toner particles and the friction member is small and triboelectrification tends to be insufficient, and the charged Coulombic force between the toner particles and the sleeve is apt to be agglomerated on the sleeve. It had, and was practically difficult.

However, in Japanese Patent Laid-Open No. 55-18656, a new developing method which eliminates the above-mentioned drawbacks has been proposed. This involves applying a very thin coat of magnetic toner on a sleeve, tribocharging it and then developing it in close proximity to the electrostatic image. This method increases the chances of contact between the sleeve and toner by applying a very thin coating of magnetic toner on the sleeve, and enables sufficient triboelectrification. To prevent the toner particles from agglomerating each other and sufficiently rub against the sleeve, and to prevent the background fog by supporting the toner by magnetic force and developing it by facing it without contacting the electrostatic image. By doing so, an excellent image can be obtained.

The developing device used in such a developing method is characterized in that it can be made very small with a simple structure.

Therefore, for example, in a high-speed machine, since there is a margin around the photoconductor, several developing devices of other colors are arranged,
There is an advantage that it is easy to change colors with one touch, and to use laser light at the same time as analog light to write pages and characters at the same time as copying.

Especially in a small-sized machine, since the whole can be made light and small, it has become a necessary technique for personalizing a copying machine.

Also, as represented by a small LBP (laser beam printer), the noise that a dot printer or a thermal transfer printer does not have is quiet in the printer, and the developing device space can be made very small in order to achieve the contradictory performance of high speed. Moreover, the fact that it is simple and lightweight is very effective.

However, this developing method is simple, light, and has a small developing device. Therefore, unless the toner used in this method has higher performance than conventional toner, it has excellent image quality, durability, and stability. It includes the problem of not being able to obtain sex. In other words, the performance of such toner is often directly reflected in the performance of the system.

By the way, in particular, the copying machine itself can be replaced with a conventional analog type and a digital latent image can be used, so that the latent image can be written finer than ever. Toner that sufficiently follows such a fine latent image must have a high-resolution developing ability. Further, since the copying machine is advancing toward higher speed, the toner has to be highly satisfied with high resolution, high speed development and high durability.

Even when such a developing system is used in a printer, the same high level of performance is required, but in terms of high durability, it is used as an output of a computer, so the output frequency is high and the durability is higher than that of a copying machine. There are some things that are severe.

Also, the fact that images are just black is becoming insufficient. In the case of a copying machine, it is particularly required to faithfully reproduce a photograph (that is, reproduction of halftone), and in the digital latent image method, halftone is expressed by the difference in line density.
If the line thickness is not the same, halftones cannot always be expressed in the same way, which is a problem.

Reproduction of such gradation is also highly required especially for digital latent image printers, and it is not possible with conventional toner to consistently output the same halftone at the beginning and end of durability. It's okay not to.

Furthermore, as for environmental stability, as personalization of copiers and price reduction of LBP have spread to households, it is often used in harsh environments that were not used in the past.

In particular, if the toner is used in a place where the environment is bad for many days and sometimes makes a number of copies, the toner requires very high performance in terms of image stability and environmental dependence.

In order to satisfy these performances, it has been considered to reduce the particle size of the toner. Usually, the particle diameter of the toner having a volume average diameter of 10 to 14 μm is set to 9 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 is lowered and the image quality is deteriorated. In particular, it becomes remarkable in a small machine using a small-diameter sleeve, a high-speed machine, and a constant temperature and low humidity environment. Therefore, various adjustments of the charge amount have been studied. However, if the charge amount is simply reduced, the image density and the image quality will be deteriorated in an environment of normal temperature and normal humidity, particularly in a high temperature and high humidity environment or after being left for a long time.

Also, toner with a small particle size tends to scatter,
The background of the image is liable to be stained and fogging is likely to occur.

In order to meet these severe demands, research and development of toner have been earnestly conducted.

Among the materials used for magnetic toner, since the magnetic substance is contained in the toner in an amount of 20 to 70% by weight, the performance of the toner is greatly affected. Proposals have been made regarding the particle size and particle size distribution of the magnetic material.

JP-A-58-169153 discloses a 50% number average diameter of 0.3 to 1.0.
Magnetic toner containing a magnetic powder having a particle size distribution of μm, a 50% weight average particle size of 0.4 to 1.3 μm, and a particle size giving a maximum value in the number particle size distribution of 0.4 to 1.3 μm. Furthermore, it has been proposed that the background fogging phenomenon is removed, the resolution is high, the density is high, and the environmental characteristics are good.

Certainly, the conventional analog type machine has sufficient performance in practical use, but it is capable of high-speed development, high durability, high gradation, and digital latent image with a high-speed machine of 50 sheets / min or more like today. It is no longer sufficient for high resolution and fine line reproducibility for images.

In particular, it cannot be said to be sufficient for producing a stable halftone in the long term. In particular, it is completely inadequate for toner having a small particle size.

Further, in Japanese Patent Laid-Open No. 58-187951, the particle size distribution of the magnetic substance is 1.5% to 4.5 .mu.m in terms of 50% by volume, and 20% in terms of volume is 1.0 to 4.0 .mu.m and 75% is 2.5%. ~
It is proposed that one having a particle size distribution of 6.0 μm is good, but this is for a color toner and is not suitable for a black image. That is, the blackness is insufficient, which is not preferable.

Besides, for example, when simply trying to achieve high resolution and high fine line reproducibility with conventional toner, the amount of toner sticking is reduced, the line is thinned, and excess toner is prevented from scattering around the line. It is possible. However, this method is not preferable because the image density of solid black is lowered. In general, when the image density is increased, the background stain tends to be generated. Particularly, when the toner is left for a long time in a low temperature and low humidity environment, the background stain may become remarkable. That is, it is not easy to improve the image density, high resolution, and background stain to a high degree.

[Object of the Invention]

An object of the present invention is to provide a magnetic toner that solves such problems.

An object of the present invention is to provide a magnetic toner having a high resolution phenomenon capability.

Another object of the present invention is to provide a magnetic toner that gives a stable image even at high speed development.

Furthermore, an object of the present invention is to provide a magnetic toner having excellent durability.

Furthermore, an object of the present invention is to provide a magnetic toner having excellent gradation reproducibility.

Another object of the present invention is to provide a magnetic toner that stably provides halftone and fine line reproducibility over a long period of time.

Another object of the present invention is to provide a magnetic toner excellent in environmental stability.

Further, an object of the present invention is to provide a magnetic toner which always gives a stable image for a long period of time even when the frequency of use is small.

Further, an object of the present invention is to provide a high image density, particularly high resolution, and high gradation reproducibility, but with no background dirt and little scattering, and particularly a stable and good image even in a low temperature and low humidity environment. The present invention provides a magnetic toner capable of producing a long term.

[Outline of Invention]

Specifically, in the present invention, in a magnetic toner containing at least a magnetic material, the average particle diameter of the magnetic material is 0.1 to 0.2 μm, and the standard deviation σ of the number distribution is divided by the average particle diameter to obtain a percentage. Represented. (Σ /) × 100 is 40% or less, it has an octahedral shape, and the volume average diameter D of the magnetic toner is 9
(μ _T / D) × 1 when μm or less and its standard deviation is σ _T
00 is 25 to 35%, and relates to a magnetic toner.

[Specific Description of the Invention]

In the present invention, the average particle diameter and the coefficient of change (%) of the magnetic material are the same as those obtained by a transmission electron microscope after magnifying the photograph of the magnetic material of 10,000 times by 4 times and making it 40,000 times. By randomly selecting 250 magnetic materials, measuring their diameters, and obtaining the number distribution from the diameters and the number, the calculation is performed.

The coefficient of variation is obtained by calculating the standard deviation σ of the distribution, dividing it by the average value, and multiplying by 100 to express it as a percentage.

Further, the volume average particle diameter of the toner is obtained from the distribution when using a Coulter counter particle size distribution measuring device (TA-II type) and using a 100 μm averter.

Heretofore, much attention has not been paid to the particle size of the magnetic material, especially the particle size distribution. The main reason for this is that the magnetic substance is considered mainly for the toner transporting property, and the others have been studied only from the viewpoint of improving the dispersibility with the binder resin. However, as a result of intensive investigations aimed at improving the accuracy of the magnetic substance, due to the demands of today's copiers and printers such as speeding up, downsizing, and digitization, as well as the particle size reduction of toner, which is related to high image quality. The present invention has been achieved.

Although not bound by any theory, the particle size and the particle size distribution of the magnetic material used for the toner having a reduced particle size are such that the toner charge stability in the development and the toner selectivity in the development, other scattering properties, I found out that it is related to the fixability.

In particular, it is possible to control the charging amount so that the charging amount does not increase more than necessary even under the condition of being strongly frictionally charged with the developing sleeve that is a charging member for the toner. This is because by using a magnetic material having a smaller particle size that has been practically used in the past and having a uniform particle size distribution, more magnetic particles than the conventional toner will be present near the surface of the toner. This is because the surface becomes uniform even when viewed microscopically. That is, when the toner is triboelectrically charged with the developing sleeve and the conventional toner has a portion in contact with the sleeve where there is no magnetic material on the toner surface, the toner surface is charged so much that the toner is unevenly charged. Becomes When the content of the magnetic substance is increased to obtain the same effect, the magnetic force of one toner also increases, so that it becomes difficult for the toner to separate from the developing sleeve, resulting in a decrease in image density and a deterioration in fixing property. Absent.

In particular, the particle size distribution also causes various problems if the particle size is not uniform because of the reduced particle size. If there are many fine particles, the fine particles have a strong cohesive property, so that they cannot be sufficiently dispersed in the toner in an ordinary toner manufacturing apparatus, and the fixing property is not preferable.
In addition, if a rough toner enters, a toner containing a rough magnetic material is selected in the development, and it is difficult to stably maintain a high image for a long period of time.

Here, if the particle size of the magnetic material is less than 0.1 μm, the color of the magnetic material becomes distinctly reddish, which is not preferable for practical use. Furthermore, since the cohesive force is large and it is difficult to loosen, the dispersibility deteriorates And image stability will become problems.

On the other hand, if it is larger than 0.2 μm, the magnetic substance does not uniformly enter into the toner, and especially the fine particles having non-uniform toner increase.
Especially in a low temperature and low humidity environment, it is difficult to maintain stable image quality, especially halftones and fine line reproducibility for a long time, and scattering and fog are likely to occur. In particular, it is difficult to obtain a stable image for a long time by high-speed development. . Preferably 0.14 to 0.19 μm,
More preferably, it is 0.15 to 0.19 μm.

If the coefficient of change is more than 40%, the fixability may be deteriorated, and image variation may occur during long-term durability, and reproducibility of fine lines may become a problem. Further, the image density may decrease due to durability in a low temperature and low humidity environment. This is considered to be a problem related to the dispersion of the magnetic substance.

The coefficient of change is preferably 35% or less, more preferably 30% or less, further preferably 25% or less, further preferably 20% or less.

The bulk density of the magnetic material is preferably 0.35 g / cc or more,
It is more preferably 0.40 g / cc, further 0.50 g / cc, further 0.60 g / cc, and further 0.70 g / cc. In particular, the particle size of the magnetic material is 0.2 μm or less, and more than 0.18
When the particle diameter is less than μm, the magnetic material is likely to contain air between particles, and therefore a higher bulk density is preferable for dispersion.

Examples of the binder resin for the toner include homopolymers of styrene and its substitution products such as polystyrene, poly-p-chlorostyrene, polyvinyltoluene, styrene-p-chlorostyrene copolymer, and styrene-vinyltoluene copolymer, and copolymers thereof. Polymers; 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 polymers, styrene-ethyl methacrylate copolymers, styrene-n-butyl methacrylate copolymers; multi-component copolymers of styrene and acrylic acid esters and methacrylic acid esters Other styrene-acrylonitrile copolymer, styrene-vinylmethyl Ether copolymer, styrene - butadiene copolymer, styrene - vinyl methyl ketone copolymer, styrene - acrylonitrile - indene copolymer,
Styrene-based copolymers of styrene and other vinyl-based monomers such as styrene-maleic acid ester copolymers; polymethyl methacrylate, polybutyl methacrylate, polyvinyl acetate, polyesters, polyamides, epoxy resins, polyvinyl butyral, polyacrylic acid , Phenol resin, aliphatic or alicyclic hydrocarbon resin, petroleum resin, chlorinated paraffin, etc. may be used alone or in combination.

In particular, as a binder resin for toner that is subjected to a pressure fixing method, low molecular weight polyethylene, low molecular weight polypropylene, ethylene-vinyl acetate copolymer, ethylene-acrylic ester copolymer, higher fatty acid, polyamide resin, polyester resin, etc. Can be used alone or in combination.

When the polymer, copolymer or polymer blend used contains a vinyl aromatic or acrylic monomer represented by styrene in an amount of 40 wt% or more, more desirable results are obtained.

For the toner, any suitable pigment or dye may be used in addition to the magnetic material. For example, there are known dyes and pigments such as carbon black, phthalocyanine blue, county blue, quinacridone, and benzidine yellow.

Examples of the magnetic substance include ferromagnetic 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.

Among these magnetic materials, magnetite will be described.

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 10 or more, and then adding an oxygen-containing gas to the suspension. Obtained by aeration. The shape of the magnetite particles has an octahedral particle size by selecting 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 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 10 or more, the particle size is fine and the particle size distribution is small. Also, magnetite particles that are sharp, that is, have a small coefficient of change are obtained.

Next, the synthesis of magnetite used in the present invention will be described in detail with experimental examples.

Experimental Example-1 As a reactor, a bubble oxidation type reaction tower having a diameter of 35 cm and an internal volume of 50 was used. Ferrous sulfate aqueous solution containing Fe ²⁺ 1.75mol / 20,4
N aqueous sodium hydroxide solution 18, (to produce magnetite, corresponding to 0.23 wt% in terms of SiO _2.) Water 54 and sodium silicate (No. _{3) (SiO 2 28.55wt%)} 18.9g using a temperature 88 A suspension containing 42 Fe (OH) ₂ at ℃, pH 13 was prepared.

10 minutes per minute at a temperature of 90 ° C. in a suspension containing Fe (OH) ₂
A 0 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 observation with an electron microscope, the obtained magnetite particle powder was an octahedral particle having an average particle diameter of 0.16 μm and a coefficient of change of 19%. This is called 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, Magnetiteons B, C ..., L were obtained under the same conditions as in Experimental Example-1. Table 1 shows the reaction conditions, the average particle size of the generated magnetite, and the coefficient of change together.

In the present invention, the magnetic substance is 2 per 100 parts by weight of the binder resin.
It is recommended to use 0 to 150 parts by weight, preferably 30 to 120 parts by weight.

You may mix an additive with a toner as needed. Examples of such additives include lubricants such as Teflon and zinc stearate, metal oxides such as tin oxide as a conductivity-imparting agent, and fluidity improvers such as hydrophobic colloidal silica.

Example 1 The above materials were mixed in powder form, heat-kneaded with a roll mill set at 140 ° C. for about 20 minutes, cooled, and then coarsely pulverized and finely pulverized (jet mill). Further, fine powder and coarse powder were set by a zigzag classifier manufactured by Alpine Co., and measured by TA-II manufactured by Coulter Counter Co., and the volume average diameter D was 8.1 μ.
A magnetic toner having m, (σ _T / D) × 100 of 29% was obtained.

To 100 parts by weight of the obtained magnetic toner, 0.5 parts by weight of hydrophobic colloidal silica was externally added, and this was added to a Canon copier NP-858.
It evaluated using 0.

As a result, the image density, fine line reproducibility and gradation reproducibility are stable and very good even in the durability test of 150,000 sheets under normal environment. Especially, the resolution of fine lines is stable at 5.5 to 6 lines / mm or more. There was no fog or scattering.

Furthermore, in the continuous image output test under low temperature and low humidity environment, there was no charge-up phenomenon, no fog occurred, and the image density and image quality were stable.

Comparative Example 1 Except that the magnetic material B was used instead of the magnetic material of Example 1,
A magnetic toner was prepared in the same manner as in Example 1. The volume average diameter D of the magnetic toner is 8.0 μm, and (σ _T / D) × 100 is 3
It was 0%.

The magnetic toner obtained was evaluated in the same manner as in Example 1.

As a result, in the durability test under the normal environment, although it is at a practically good level, the fine line reproducibility and gradation reproducibility have slightly deteriorated since the durability test of about 100,000 sheets.

Further, in the test under a low temperature and low quality environment, the charge-up phenomenon slightly occurred from about 30,000 sheets, and therefore, a little fog occurred. Further, the gradation reproducibility also decreased as the durability increased. In addition, the fixability was slightly worse.

Example 2 A magnetic toner was produced in the same manner as in Example 1 using the above materials. Toner volume average diameter is 7.6 μm, (σ _T / D) ×
100 was 33%.

0.5 parts by weight of hydrophobic silica was externally added to 100 parts by weight of the obtained magnetic toner, and this was added to a laser beam printer manufactured by Canon.
It put in LBP-8II and evaluated.

As a result, the digital latent image was faithfully reproduced from the initial stage to the toner exhaustion, and the resolution and halftone were very well stable.

Moreover, the image density was high at 1.38 to 1.4 and stable. Furthermore, there was no fog or scattering. Even in the durability test under low temperature and low humidity environment, it was similarly stable and there was no background fog. Further, the cartridge was left under a low temperature and low humidity for about 4 months to form an image, but there was no problem and the image quality and the image density were stable.

Comparative Example 2 A magnetic toner was prepared in the same manner as in Example 2 except that the magnetic substance D was used instead of the magnetic substance C in Example 2. The volume average diameter of magnetic toner is 7.7 μm, (σ _T / D) × 100 is 31%
Met.

The magnetic toner thus obtained was evaluated in the same manner as in Example 2.

As a result, the resolution and halftone are slightly lowered near the toner exhaustion. In a durability test under a low temperature and low humidity environment, the image density slightly decreased with durability. This is because the thin line is gradually becoming thinner than in the initial stage. Also, the fog on the backgrassland has become a little worse. In addition, the fixability also deteriorated.

Example 3 A magnetic toner was obtained in the same manner as in Example 1 using the above materials. The particle size of magnetic toner is 9.0 μm, (σ _T / D) × 100 is 2
It was 6%.

0.5 part by weight of hydrophobic colloidal silica was externally added to 100 parts by weight of the obtained magnetic toner, and this was evaluated using a digital copying machine NP-9030 manufactured by Canon.

As a result, in an endurance test under a normal environment, the image density was high from the initial stage to 50,000 sheets, and was 1.35 or more, and especially stable such as halftone, fog, and scattering. Especially fog and scattering were excellent. In addition, it was similarly good and stable in a durability test under a low temperature and low humidity environment. Especially, the resolution of fine lines in the digital latent image was good and there was no fog.

Comparative Example 3 A magnetic toner was prepared in the same manner as in Example 3 except that the magnetic substance K was used instead of the magnetic substance E of Example 3. The particle size of the magnetic toner was 8.9 μm, and (σ _T / D) × 100 was 27%.

This was evaluated in the same manner as in Example 3. As a result, in a durability test under a normal environment, after 40,000 sheets, there was almost no problem in practical use. Further, in a continuous durability test under a low temperature and low humidity environment, fog occurred a little with durability, and the image density slightly decreased. Especially, the fine wire is slightly durable and durable.
The image deteriorated. In addition, the fixability also deteriorated.

Examples 4 to 6 and Comparative Examples 4 to 5 Instead of the magnetic body C of Example 2, magnetic bodies G to K are used.
A magnetic toner was prepared in the same manner as in Example 2 except that
evaluated. The results are shown in Table 2.

Claims (1)

[Claims] 1. A magnetic toner containing at least a magnetic material, wherein the average particle diameter of the magnetic material is 0.1 to 0.2 μm, and the standard deviation σ of the number distribution is divided by the average particle diameter and expressed as% (σ /) × 100 is 40% or less, the magnetic material has an octahedral shape, the volume average diameter D of the magnetic toner is 9 μm or less, and the standard deviation thereof is σ _T , (σ _T / D) × 100 ,twenty five
Magnetic toner characterized by being ~ 35%.