JPH03101744A - Magnetic toner incorporating spherical magnetic material - Google Patents

Abstract

PURPOSE:To obtain the magnetic toner which does not contaminate a background and has excellent environmental atability by incorporating a spherical magnetic material having a specific average grain size and coefft. of change into the toner. CONSTITUTION:The magnetic material of an octahedron which has 0.1 to 0.2mum average grain size and has<=40% value (coefft. of change) which is obtd. after the standard deviation of the number average thereof is divided by the average grain size and which is expressed in term of % is incorporated into the magnetic toner. Namely, since the more particles of the magnetic material exist near the surface of the toner by using the magnetic material having the small grain size and the uniform grain size distribution. The toner surface is consequently more uniformized even when microscopically viewed. Thus, the magnetic toner which does to contaminate the background in spite of the high image density, high resolution and high gradation reproducibility and can form the good images stably for a long period even in low-temp. and low-humidity environment.

Description

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

[Prior Art] Conventionally, as an electrophotographic method, U.S. Patent No. 2,297,6
Specification No. 91, Japanese Patent Publication No. 42-23910 (U.S. Patent No. 3,666,363), and Japanese Patent Publication No. 43
A number of methods are known, such as those described in U.S. Pat. An electrical latent image is formed on the photoreceptor, and then the latent image is developed with toner to become a visible image. If necessary, after the toner image is transferred to a transfer material such as paper, heating, pressure, etc. The image is fixed and a copy is obtained.

Various developing methods are also 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;
．． A large number of development methods are known, such as the cascade development method described in No. 552, the Bauder Cloud method, the fur brush development method, and the liquid development method described in No. 2,221,776. There is. Among these development methods, the magnetic brush method, cascade method, liquid development method, etc., which use a developer mainly consisting of toner and carrier, are in particular widely put into practical use. All of these methods are excellent methods that can relatively stably produce good images, but on the other hand, they have common drawbacks associated with two-component developers, such as deterioration of the carrier and fluctuations in the mixing ratio of toner and carrier. In order to avoid such drawbacks, various fffi development methods have been proposed that use a one-component developer made only of toner, but among these, many are superior to methods that use a developer made of magnetic toner particles.

US Pat. No. 3,909,258 proposes a developing method using an electrically conductive magnetic toner. In this method, conductive magnetic toner is supported on a cylindrical conductive sleeve having magnetism inside, and is brought into contact with an electrostatic image to be developed. At this time, in the developing section, a conductive path is formed by the toner particles between the surface of the recording medium and the surface of the sleeve, and charges are guided from the sleeve to the toner particles through this conductive path, and between the image area of the electrostatic image and the image area of the electrostatic image. Coulomb force causes toner particles to adhere to the image area and develop.
This developing method using conductive magnetic toner is an excellent method that avoids the problems associated with conventional two-component developing methods, but on the other hand, since the toner is conductive, the developed image
It has the disadvantage that it is difficult to electrostatically transfer it from a recording medium to a final support member such as plain paper.

As a developing method using a high-resistance magnetic toner that can be electrostatically transferred, there is a developing method that utilizes dielectric polarization of toner particles. However, such a method inherently has drawbacks such as slow development speed and insufficient density of the developed image, and is difficult in practice.

Other developing methods using high-resistance magnetic toner include
A known method is to triboelectrically charge toner particles by friction between toner particles or friction between toner particles and a sleeve or the like, and then develop the toner particles by bringing them into contact with an electrostatic image holding member. However, these methods have drawbacks such as the number of times the toner particles come into contact with the friction member is small and frictional charging tends to be insufficient, and the Coulomb force between the charged toner particles and the sleeve increases and they tend to aggregate on the sleeve. This makes it difficult to implement in practice.

However, in JP-A-55-18656, etc.,
A new development method has been proposed which eliminates the above-mentioned drawbacks. This involves applying a very thin layer of magnetic toner onto the sleeve, triboelectrically charging it, and then developing it in close proximity to the electrostatic image. This method increases the chances of contact between the sleeve and the toner by applying an extremely thin layer of magnetic toner onto the sleeve, enabling sufficient frictional charging, supporting the toner with magnetic force, and moving the magnet and toner relative to each other. By moving the toner particles to prevent mutual agglomeration and creating sufficient friction with the sleeve, the toner is supported by magnetic force and developed by facing the electrostatic image without coming into contact with it, thereby preventing ground blurring. Excellent images can be obtained depending on what you do. A developing device used in such a developing method is characterized by a simple structure and a very small size.

For this reason, for example, in high-speed machines, there is more space around the photoreceptor, so several developing devices of other colors are placed.
Advantages include the ability to change colors with a single touch, use laser light at the same time as analog light, and make it easier to write on pages and text at the same time as copying.

Especially for small machines, the overall size can be made lighter and smaller.
This technology has become necessary for the personalization of copying machines.

In addition, a small LBP (laser beam printer)
As exemplified by , in printers, in order to achieve the contradictory performance of being quiet and high speed, which dot printers and thermal transfer printers do not have, it is possible to take up a very small developing unit space, and to be simple and lightweight. has become very effective. However, because this developing method is characterized by a simple, lightweight, and small developing device, the toner used in this method has better overall image quality, durability, and stability than conventional toners, unless it has higher performance. This includes the problem of not being able to have sex. In other words, the performance of such toner is often directly reflected in the performance of the system.

By the way, in particular, copying machines themselves have changed from the conventional analog type to ones that use digital latent images, and as a result, latent images can be written more minutely than ever before. A toner that can sufficiently follow such a fine latent image must have a high-resolution developing ability.

Furthermore, since copying machines are moving in the direction of higher speeds, toners must meet high standards such as high resolution, high speed development, and high durability.

When using this type of development method in printers, the same high level of performance is required, but in terms of high durability,
Because it is used as computer output,
The output frequency is high, and the durability performance is even more severe than that of copying machines.

In addition, it has become insufficient for images to simply be black.

In the case of copying machines, it is especially necessary to faithfully reproduce photographs (that is, reproduce halftones), and in the digital latent image method, halftones are expressed by differences in line density, so line If the thicknesses are not the same, it will not be possible to express the midtones in the same way, which will cause problems.

Reproduction of such gradation is also highly required, especially for digital latent image printers, and conventional toners are not sufficient to consistently output the same halftones at the beginning and end of life. It's safe to say that I haven't gotten it.

Furthermore, with regard to environmental stability, as copiers have become more personalized and LBPs have become more popular in households due to their lower prices, they are now often used in harsh environments where they could not be used in the past. In particular, when a toner is used at home in a harsh environment for many days and several copies are made from time to time, extremely high performance is required of the toner in terms of image stability and environmental dependence.

In order to meet these strict demands, research and development of toner is being carried out diligently.

Among the materials used in magnetic toner, magnetic substances in particular account for about 20 to 70% by weight of the entire toner, and therefore greatly affect the performance of the toner. Proposals have been made regarding the particle size and particle size distribution of the magnetic material.

JP-A-58-169153 discloses that the 50% number average diameter is 0.3 to 1.0 μm, and the 50% weight average diameter is 0.4 to 1.0 μm.
A magnetic toner containing magnetic powder having a particle size distribution of 1.3 μm and a particle size distribution in which the maximum value in the number particle size distribution is 0.4 to 1.3 μm has excellent image quality fidelity, stability, and background fog. It has been proposed because it eliminates phenomena, has high resolution, high concentration, and has good environmental characteristics.

It is true that conventional analog machines have sufficient performance for practical purposes, but today's high-speed machines that can process more than 50 sheets per minute require high-speed development, high durability, high gradation, and digital latency. Further improvements are required for high image resolution, fine line reproducibility, etc.

In particular, it is no longer sufficient to produce halftones stably over a long period of time.

In addition, Japanese Patent Application Laid-Open No. 187951/1983 also describes the particle size distribution of magnetic material, and the 50% diameter on a volume basis is 1
．． 5 to 4.5 gm, similarly, the 20% diameter on a volume basis is 1
．． It has been proposed that a particle size distribution of 0 to 4.0μsm175% diameter is 2.5 to 6.01m, but this is for color toner and is not suitable for normal black images. . That is, the blackness is insufficient and undesirable.

Further, Japanese Patent Publication No. 62-51208 proposes to improve dispersibility and provide a toner with excellent image density by using a spherical magnetic material.

It is true that spherical magnetic bodies have such advantages, but the problem is that they tend to have high electrical resistance. Therefore, as mentioned above, there are severe conditions, especially under conditions where toner tends to charge up in high-speed machines, small machines, etc. Generally, when the toner is charged up, the toner becomes difficult to separate from the toner carrier such as the developing sleeve, which may lower the image density, and may also cause a fogging phenomenon in which the background is smeared.

For example, if you try to simply achieve high resolution and fine line reproducibility with conventional toner, you can reduce the amount of toner applied,
One idea is to make the line thinner to prevent excess toner from scattering around the line. However, this method is not preferable because the solid black image density decreases. In general, increasing the image density tends to cause background stains, and background stains may become noticeable, especially if the toner is left in a low-temperature, low-humidity environment for a long time. In other words, it is not easy to improve image density, high resolution, and background stains to a high degree. [Problems to be Solved by the Invention] An object of the present invention is to provide a magnetic toner that solves these problems.

That is, an object of the present invention is to provide a magnetic toner having high resolution developing ability. Another object of the invention is to
The present invention provides a magnetic toner that provides stable images even during high-speed development.

A further object of the present invention is to provide a magnetic toner with excellent durability.

A further object of the present invention is to provide a magnetic toner with 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 with excellent environmental stability.

Another object of the present invention is to provide a magnetic toner that always provides stable images over a long period of time even when used infrequently.

In addition, the purpose of the present invention is to achieve high image density, high resolution, and high gradation reproducibility, without background stains, and to be able to stably produce good images over a long period of time, especially in low-temperature, low-humidity environments. The present invention provides magnetic toner.

[Means and effects for solving the problems] The present invention is characterized in that the average particle diameter X is 0.1 to 0.2 μrn
, and its variation coefficient {(a/X)x1oO} is 40
% or less of spherical magnetic material.

The average particle diameter and change coefficient (%) of the magnetic material are as follows:
After magnifying a photograph of a magnetic material obtained by a transmission electron microscope and magnifying it 10,000 times to 4 times and making it a 40,000 times photograph, 250 magnetic materials were randomly selected, their diameters were actually measured, and their diameters were measured. The number distribution is determined from the diameter and number of pieces. Note that the diameter is the horizontal direction Ferre diameter.

The variation coefficient is obtained by finding the standard deviation σ of the distribution, dividing it by the average value, multiplying it by 100, and expressing it in %.

Conventionally, the particle size of magnetic materials, particularly their particle size distribution, has not received much attention. The biggest reason for this is that magnetic materials were considered primarily for toner transportability, and other materials were considered only from the standpoint of improving the dispersibility of binder resins. However, in response to today's strict requirements for copying machines and printers, such as increased speed, miniaturization, and digitization, the present invention was achieved as a result of intensive study and improvement of the accuracy of how magnetic materials are perceived.

Without being bound by any theory, it is known that the particle size and particle size distribution of the magnetic material are related to the stabilization of toner charging during development, the selectivity of the toner during development, and fixing properties. I found it.

In particular, it is possible to control the amount of charge so that it does not increase more than necessary even in a situation where the developing sleeve, which is a member for imparting charge to the toner, is strongly charged by friction. This is because by using a magnetic material with a smaller particle size and a uniform particle size distribution than has been conventionally put into practical use, more magnetic particles are present near the surface of the toner than in conventional toners. This is because the toner surface becomes uniform even when viewed microscopically. In other words, when the toner is frictionally charged with the developing sleeve, if the part of the conventional toner that comes into contact with the sleeve is a place where there is no magnetic material on the toner surface, the charge on the toner surface will be increased accordingly.
The toner will be non-uniformly charged. If we attempt to obtain the same effect by increasing the content of magnetic material, the magnetic force of each toner will also increase, making it difficult for the toner to separate from the developing sleeve, resulting in a decrease in image density and poor fixing. Undesirable.

In particular, as the particle size is reduced, various problems will occur if the particle size distribution is not uniform. If there are too many fine particles, the fine particles have strong cohesive properties and cannot be sufficiently dispersed in the toner using ordinary toner manufacturing equipment, which is also unfavorable for fixing properties. Furthermore, if rough particles are present, a toner containing rough magnetic material will be selected during development, making it difficult to maintain a stable high-quality image over 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 obvious reddish, which is not practical, and furthermore, the cohesive force is large and it is difficult to unravel, resulting in poor dispersibility and durability. Problems such as image quality and image stability arise.

In addition, if it is larger than 0.2 pm, the magnetic material will not be uniformly contained in the toner, and unevenness will increase, especially in toner with a fine particle size, and image quality, especially in a low-temperature, low-humidity environment, will be affected, especially in midtones and fine line reproducibility. It is difficult to maintain the image stably over a long period of time, and it is particularly difficult to obtain a stable image over a long period of time with high-speed development. Preferably 0.14 to 0.19 pm, more preferably 0.15
~0.19H.

Furthermore, if the variation coefficient is greater than 40%, fixing performance may deteriorate, image quality may fluctuate during long-term durability, and fine line reproducibility may also become a problem. Furthermore, image density may decrease due to durability under low temperature and low humidity environments. We believe that this is a problem related to the dispersion of the magnetic material.

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

Moreover, the bulk density of the magnetic material is 0. It is preferably 60 g/cc or more, more preferably 0. 70g/cc or more, and furthermore, 0. It is 80 g/cc or more, and further, it is 0.90 g/cc or more. In particular, when the particle size of the magnetic material is 0.21 or less, further 0.18 pm or less, the magnetic material tends to contain air between particles, so a higher bulk density is preferable for dispersion.

As the binder resin for the toner, homopolymers of styrene and substituted products thereof, such as polystyrene, poly-p-chlorostyrene, polyvinyltoluene, styrene-p-chlorostyrene copolymer, and styrene-vinyltoluene copolymer, and copolymers thereof. Copolymers of styrene and acrylic acid esters 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 styrene-ethyl methacrylate copolymer, styrene-n-butyl methacrylate copolymer; multi-component copolymers of styrene and acrylic esters and methacrylic esters;
Others: styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-butadiene copolymer, styrene-vinyl methyl ketone copolymer,
Styrenic copolymers of styrene and other vinyl monomers such as styrene-acrylonitrile-indene copolymers and styrene-maleic acid ester copolymers; polymethyl methacrylate, polybutyl methacrylate, polyvinyl acetate, polyesters, polyamides, Epoxy resins, polyvinyl butyral, polyacrylic acid, phenol resins, aliphatic or alicyclic hydrocarbon resins, petroleum resins, chlorinated paraffins, etc. can be used alone or in combination.

In particular, as binder resins for toners used in pressure fixing systems, low molecular weight polyethylene, low molecular weight polypropylene, ethylene-vinyl acetate copolymers, ethylene-acrylic acid ester copolymers, higher fatty acids, polyamide resins, polyester resins, etc. are used. Can be used alone or in combination.

More desirable results can be obtained if 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. The magnetic material according to the present invention is preferably used in an amount of 20 to 120 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.

The magnetic material consists of ferromagnetic metal particles such as iron, cobalt, and nickel, ferromagnetic iron oxide particles such as magnetite, maghemite, and ferrite, or two or more types selected from iron, cobalt, nickel, and manganese. Examples include ferromagnetic alloy particles.

Among these magnetic materials, magnetite will be described.

Magnetite consisting of particles exhibiting a spherical shape is produced by mixing an aqueous ferrous salt solution and an alkaline aqueous solution of less than 1.0 equivalent to Fe in the ferrous salt aqueous solution at a temperature of 70 to 10
a first stage of producing magnetite particles by producing a suspension containing ferrous hydroxide at 0°C, and then bubbling oxygen-containing gas while heating at a temperature in the range of 70 to 100°C; After the completion of the reaction, 1.0 equivalent or more of an alkaline aqueous solution is added to the residual Fe'', and a two-stage reaction is carried out, including a second stage of heating and oxidation under the same conditions as the first stage reaction. The magnetite made of spherical particles thus obtained has a fine particle size and a sharp particle size distribution, that is, it has a small coefficient of variation.

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

It is produced when water-soluble silicates such as sodium silicate and potassium silicate (0.1 to 5.0 atomic % based on SL equivalent to Fe) are present in a suspension containing ferrous hydroxide. This is preferable because the spherical diameter, particle size distribution, and temperature stability of the magnetite particles can be further improved.

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

(Synthesis Example) A bubble oxidation type reaction tower with a diameter of 35 crO and an internal volume of 50° C. was used as a reactor. 20N of ferrous sulfate aqueous solution containing 1.6 moi'/i' of Fe', 20N of 3.07N sodium hydroxide aqueous solution (corresponding to 0.96 equivalent to Fe'), and sodium silicate (No. 3). ) (SiO
z28. 55wt%)20. 2 g (0.3 atomic % based on Fe) was used to produce a suspension containing Fe (OH) t at a temperature of 82 °C.

100 per minute after heating the suspension containing Fe(OH)* to 85°C! ! ．． of air was passed through the tube for 240 minutes to form magnetite particles. Then l. 34NNa
An OH aqueous solution 2β was added (corresponding to 1.05 equivalents to the residual Fe), and air was aerated at a rate of 100 n/min at a temperature of 85°C for an additional 30 minutes.The generated particles were washed with water and filtered by a conventional method. Separately, it was dried and pulverized.The obtained magnetite particles were observed with an electron microscope and were found to be spherical particles with an average particle size of 0.18 gm and a variation coefficient of 18%.This is referred to as magnetite A. Among the above reaction conditions, when producing a suspension containing ferrous hydroxide,
Magnetite B, C, .

Table 1 shows the relationship between the reaction conditions and the average particle diameter and variation coefficient of the produced magnetite.

Additives may be mixed with the toner as necessary. Examples of such additives include lubricants such as Teflon and zinc stearate, and metal oxides such as tin oxide as conductivity imparting agents.

[Example code] Hereinafter, all parts are by weight.

The mixture was mixed into powder, heat-kneaded for about 15 minutes in a roll mill set at 15°C (1°C), and after cooling, it was coarsely pulverized and finely pulverized (jet mill). Coarse powder was cut and measured with Coulter Counter's TA-I1, with a volume average diameter of 12.2μ.
m, 2% is 20.2μm or more, 6.35 in number distribution
A toner with 17% of micrometers or less was obtained.

This was done by modifying a Canon copier NP-8580.
Evaluation was performed using a modified machine that changed the speed from 0 sheets/minute to 85 sheets/minute.

As a result, even in a durability test of 200,000 sheets under normal conditions, the image density, fine line reproducibility, and gradation reproducibility were stable and very good, and the image density was particularly high at 1.40 to 1.45. Ta.

Furthermore, in continuous image output tests under low temperature and low humidity environments,
There is no charge-up phenomenon, and there is no background dirt (
There was no occurrence of fog (hereinafter referred to as fog), and both image density and quality were good and stable.

Comparative Example 1 Except for using magnetic material B instead of the magnetic material in Example 1,
A toner was produced in the same manner as in Example 1.

The volume average diameter of the toner is 12.4μrn, 20.2μm
2.4% or more, and 16 6.35μm or less in the number distribution
．． I got 2% toner. This was evaluated in the same manner as in Example I.

As a result, in the durability test under normal environment, it was at a good level for practical use, but after about 10,000 sheets of durability test, the fine line reproducibility, gradation reproducibility, etc. began to deteriorate slightly. In addition, in tests conducted under low temperature and low humidity environments, a slight charge-up phenomenon occurred, resulting in slight fogging.

Moreover, the gradation reproducibility also decreased as the durability progressed.

Furthermore, the fixing properties were slightly worse.

was made into a toner in the same manner as in Example 1. The volume average diameter of the toner is 1 l. 8μm, 0.8% for 20.2μm or more, 15% for 6.35μm or less in number distribution
Met.

This is a Canon laser beam printer LBP-8.
II was put into a printer modified from 6 pages/minute to 12 pages/minute and evaluated. As a result, the digital latent image was faithfully reproduced from the initial stage until the toner ran out, and the resolution and halftones were extremely stable.

Furthermore, the image density was high and stable at 1.4 to 1.45.

Particularly in durability tests under low temperature and low humidity environments, it was equally stable and there was no background capri.

Furthermore, the cartridge was left in a low temperature and low humidity environment for about 3 months.
When I printed an image, there were no problems at all, and the image quality was good and the image density was stable.

Comparative Example 2 Example 2 except that magnetic material D was used as the magnetic material of Example 2.
A toner was prepared in the same manner. The volume average diameter of the toner was 11.6 μm, 0.5%816%. This was evaluated in the same manner as in Example 2.

As a result, the resolution and halftones slightly deteriorated near the toner exhaustion, but they were stable enough to pose no problem in practical use.

However, in a durability test under a low temperature and low humidity environment, the image density slightly decreased with durability. This is because the thin lines have gradually become thinner compared to the initial stage. Also, the fog in the background has gotten a little worse.

Furthermore, the fixing properties were also poor.

In the same manner as in Example 1, Enao Wataru was made into a toner. The particle sizes of the toners were 11.5 μm, 1.0%, and 14.5%, respectively.

This was evaluated using a modified Canon digital copying machine NP-9030, which changed the number of sheets per minute from 30 sheets per minute to 40 sheets per minute.

As a result, in a durability test under normal conditions, from the initial stage to 10,000 copies, the image density was high, at 1.4 or higher, and was very stable, especially in the middle tones. In addition, durability tests under low temperature and low humidity environments showed similarly good and stable results. The resolution of fine lines in the digital latent image was particularly good, and there was no fog.

A toner was prepared in the same manner as in Example 3 except that Magnetic Material J was used as the magnetic material in Example 3. The particle size of the toner is
11.7μm, 1.2%. It was 16%. This was evaluated in the same manner as in Example 3.

As a result, in durability tests under normal environments, there were almost no practical problems, but as the durability went on, resolution, halftones, etc. deteriorated somewhat.

Furthermore, in continuous durability tests under low temperature and low humidity environments, not only durability but also slight fogging occurred and image density decreased slightly. In particular, the thin wires have become a little thinner as they become more durable.

Furthermore, the fixing properties were also poor.

Application plate 21 The magnetic material of Example 2 was replaced with magnetic material G (Example 4) and H, respectively.
(Example 5), Example 2 except that it was changed to I (Example 6)
A toner was prepared and evaluated in the same manner as above. The results are summarized in Table-2.

(The following is a blank space) [Effects of the Invention] By specifying both the particle size and particle size distribution of the magnetic material, the present invention achieves high image density, high resolution, and high gradation reproducibility. It has excellent environmental stability and does not affect the ground.

Claims (1)

[Claims] (1) The average particle size is 0.1 to 0.2 μm, and the standard deviation σ of the number distribution is divided by the average particle size @X@, and expressed as a percentage (σ/@X@) × 100 is 40 % or less of spherical magnetic material.