JPH03101743A - Magnetic toner - Google Patents

Abstract

PURPOSE:To obtain the magnetic toner which does not contaminate a background and has excellent environmental stability by incorporating a magnetic material of an octahedron having a specific average grain size and coefft. of change into the toner. CONSTITUTION:The spherical magnetic material 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 expressed in term of % is incorporated into the magnetic toner. Namely, 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 not contaminate the background in spite of the high image density, in spite of 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. 2,297,69
Specification No. 1, Japanese Patent Publication No. 42-23910 (U.S. Patent No. 3,666,363) and Japanese Patent Publication No. 43-24
A number of methods are known, such as those described in U.S. Pat. An electrical latent image is formed on the body, and then the latent image is developed with toner to become a visible image, and if necessary, after the toner image is transferred to a transfer material such as paper, it is transferred by heat, pressure, etc. It is fixed and a copy is obtained.

Various developing methods are also known for making electrostatic latent images into visible images 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. 2,221,776, the powder cloud method, the fur brush development method, and the liquid development method. ing. Among these developing methods, the magnetic brush method, the cascade method, and the liquid developing method, which use a developer mainly consisting of toner and carrier, have been widely put into practical use. All of these methods are excellent methods in which good images can be obtained relatively stably, 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 development methods using a one-component developer made only of toner have been proposed, but among them, many methods using a developer made of magnetic toner particles are superior.

U.S. Patent No. 3,909. No. 258 proposes a developing method using electrically conductive magnetic toner. In this system, conductive magnetic toner is supported on a cylindrical conductive sleeve that has magnetism inside, and is brought into contact with an electrostatic image to develop it. 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, thereby creating a connection between the image area of the electrostatic image and the image area of the electrostatic image. Toner particles adhere to the image area due to Coulomb force and are undeveloped. The developing method using this conductive magnetic toner is the conventional 2
This is an excellent method that avoids the problems associated with component development methods, but on the other hand, since the toner is conductive, it is difficult to electrostatically transfer the developed image from the recording medium to the final support material such as plain paper. The disadvantage is that it is difficult to 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, as copying machines are moving toward 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 a printer, there is a similar high performance requirement, but in terms of high durability, it is used as a computer output, so the output frequency is high, and the durability is comparable to that of a copier. There are things that are even more severe.

Furthermore, it is no longer sufficient for an image 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 thickness is 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 lower prices, they are now often used in harsh environments where they were not used before.

In particular, when a toner is used at home in a harsh environment for many days and occasionally copies several copies, extremely high performance is required of 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.

Magnetic Toner C Among the materials used, magnetic substances in particular account for about 20 to 70% by weight of the entire toner, and therefore greatly influence 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. High resolution and fine line reproducibility for images are no longer sufficient.

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

Furthermore, Japanese Patent Application Laid-Open No. 58-187951 also describes the particle size distribution of a magnetic material, with a volume-based 50% diameter of 1.
5 to 4.5 strokes, similarly the 20% diameter in terms of volume is 1.0
~4.0 pm, 75% diameter is 2.5 ~6.0 p
It has been proposed that one having a particle size distribution of m is good;
This is for color toners and is not suitable for regular black images. That is, the blackness is insufficient and undesirable.

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 it reduces the image density of solid black. In general, increasing the image density also tends to cause background stains, and particularly if the toner is left in a low temperature, low humidity environment for a long time, background stains may become noticeable. That is, 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 present invention is to provide 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.

Further, the purpose of the present invention is to stably maintain midtone and fine line reproducibility.
It provides magnetic toner that lasts for a long 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 pm, and the coefficient of change {(σ/X) The magnetic toner contains the following octahedral magnetic material.

The average particle diameter and change coefficient (%) of the magnetic material are as follows:
After magnifying a photograph of a magnetic material 10,000 times larger than that obtained using a transmission electron microscope to a 40,000 times larger 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 the magnetic material was considered primarily for toner transportability, and other materials were only considered from the standpoint of improving dispersibility with the binder resin. 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 becomes unevenly 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 pm, 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 O. 19gm, more preferably 0.15
~0.191 Lm.

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 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 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 35 g/cc or more, more preferably 0.40 g/cc or more, and even more preferably 0.40 g/cc or more. 50 g/cc or more, furthermore, 0.60 g/cc, furthermore, 0.60 g/cc. 70g
/cc or more. In particular, the particle diameter of the magnetic material is 0.2H
When the particle size is further reduced to 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, Eboxy resin, polyvinyl butyral, polyacrylic acid, phenol resin, aliphatic or alicyclic hydrocarbon resin, petroleum resin, chlorinated paraffin, 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 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 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.

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

Is there magnetite inside such a magnetic material? Describe. Magnetite is prepared by mixing a ferrous salt solution and an alkaline aqueous solution at a temperature of 70 to 100°C. It is obtained by producing a suspension containing ferrous hydroxide with a pH of 10 or higher, and then passing an oxygen-containing gas through the suspension. The shape of the magnetite particles exhibits an octahedral particle shape depending on the generation conditions.

An octahedral particle is one in which at least one vertex of the particle consists of four ridge lines in a scanning electron micrograph, and 50% of 250 randomly selected particles
The material described above is called an octahedral magnetic material. It is better if it is 60% or more, and even better if it is 70% or more.

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.

A water-soluble silicate such as sodium silicate or potassium silicate (0.1 to 2.0% by weight in terms of SiO2 based on the generated magnetite particles) is present in the suspension containing ferrous hydroxide. This is preferable because the distribution of the generated magnetite can be further improved.

Temperature 70-100"C. pHl containing ferrous hydroxide obtained by mixing an alkaline aqueous solution and a ferrous salt aqueous solution.
By passing an oxygen-containing gas through the suspension while heating it to a suspension with a concentration of O or higher, magnetite particles with fine particle size and sharp particle size distribution, that is, with a small coefficient of variation, can be obtained.

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 cm and an internal volume of 5042 cm was used as a reactor. Ferrous sulfate aqueous solution containing 1.75 mof/f 18 g of 4.4 N sodium hydroxide aqueous solution, 4β water and sodium silicate (No. 3) (S10
22L55 wt%) 18.9g (corresponds to 0.23 wt% in terms of SiO2 based on the produced magnetite.

) was used to prepare a suspension containing Fe(OH)- at a temperature of 88°C and 42°C at pi{13.

The above Fe(OH). A black precipitate was produced by bubbling 100 g/min of air through the suspension containing the following for 120 minutes at a temperature of 90'C. The generated particles are washed with water, filtered, and separated by conventional methods.
Dried and crushed. As a result of observation using an electron microscope, the obtained magnetite particles had an average particle size of 0. The particles had an octahedral shape with a 16H variation coefficient of 19%. This is called magnetite A. Among the above reaction conditions, Fe'' concentration, temperature, and pH when producing a suspension containing ferrous hydroxide.
Magnetite B, C,
...I got J. Table 1 summarizes the reaction conditions, the average particle diameter of the produced magnetite, and the coefficient of change.

(The following is a blank space) 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.

Seven powders were combined, and this was heat-kneaded for about 20 minutes in a roll mill set at 140°C, and after cooling, it was coarsely pulverized and then finely pulverized (jet mill). Furthermore, fine powder and coarse powder were cut using a zigzag classifier manufactured by Alpine, and the volume average diameter was determined to be 12.4μ by measurement using T^-II manufactured by Coulter Counter.
L 20.2μm or more is 1.5%, 683 in number distribution
A toner with a particle size of 16% or less was obtained. This was done by modifying Canon's copier m NP-8580 to print 80 sheets/minute at 85
Evaluation was made using a modified machine with a speed of 1 sheet per 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 1.43. Ta.

Furthermore, even in a continuous image printing test of 100,000 sheets under a low temperature and low humidity environment, there was no charge-up phenomenon, no background stains (hereinafter referred to as fog), and both image density and quality were good and stable.

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 12.2 μm, 1.9% is 20.2 μm or more, and 18.9% is 6.35 μm or less in the number distribution.
0% toner was obtained.

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

As a result, in the durability test under normal environment, the level was almost good for practical use, but after the durability test I-140,000 sheets, fine line reproducibility, gradation reproducibility, etc. began to deteriorate slightly.

In addition, in a test under a low temperature and low humidity environment, a charge-up phenomenon occurred slightly after about 50,000 sheets, and as a result, some fogging occurred. 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 11.6 μm, 0.5% for toner larger than 20.2 μm, and 14% for 6.35 μm or smaller in number distribution.
Met. This was put into a Canon laser beam printer LBP-8 1+ modified from 6 sheets/minute to 12 sheets/minute for evaluation. 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.

Further, the image density was high and stable at 1.38 to 1.42.

In particular, durability tests under low temperature and low humidity environments showed similar stability and no background fog.

Furthermore, the cartridge was left in a low temperature and low humidity environment for about 5 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 is 11.8 μm, 0.7%. It was 16%.

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

As a result, the resolution and halftones deteriorated slightly near the toner exhaustion, but in practical terms it remained stable enough to cause no problems. 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, Toner was made from Kannai Ritan. The particle sizes of the toners were 11.7 μm, 1.2%, and 15.0%, respectively. This was evaluated using a modified Canon digital copier NP-9030 that increased the number of sheets per minute from 30 sheets per minute to 40 sheets per minute. As a result, in durability tests under normal conditions, the image density was high from the initial stage to 10,000 copies, exceeding 1.37, and was very stable, especially in the middle tones. In addition, durability tests under low temperature and low humidity environments also showed good performance and stability.

In particular, the resolution of fine lines in the digital latent image was at a good level, and there was no fogging.

Toners were produced in the same manner as in Example 3 except that Magnetic Material J was used as the magnetic material in Example 3.The particle sizes of the toners were as follows.
It was 11.91m, 1.0%, 18%. This was evaluated in the same manner as in Example 3.

As a result, in a durability test under a normal environment, there were almost no practical problems after 50,000 copies, but as the durability increased, resolution, halftones, etc. began to deteriorate 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 fine lines became somewhat uneven as the image became more durable, and the image quality deteriorated.

Furthermore, the fixing properties were also poor.

4-6 Te4 The magnetic material of Example 2 was replaced with magnetic material F (Example 4) and G, respectively.
(Example 5), H (Example 6), I (Comparative Example 4)
A toner was produced and evaluated in the same manner as in Example 2, except that the following was changed. 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. The ground is clean and has excellent environmental stability.

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 in % (σ/@X@) × 100 is ( A magnetic toner containing 40% or less of octahedral magnetic material.