JPH0472226B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing magnetic particles for electrophotography.

Conventionally, in electrophotography, various developers have been used to develop an electrostatic image formed on a photoreceptor made of a photoconductive material.

By using a liquid developer, it is possible to obtain a fine-grained copy image with excellent resolution of an electrostatic charge image.
However, the use of organic solvents is not sanitary and is inconvenient to handle, so they are not used much at present.

Although dry developers are inferior to liquid developers in terms of resolution, they compensate for the above-mentioned drawbacks of liquid developers and have advantages such as high-speed copying, so they are now the mainstream developer used in copying machines. ing. Furthermore, in recent years, there has been active development of one-component magnetic toners which have the advantage of improving the maintainability of copying machines, such as having a virtually unlimited developer life and simplifying the mechanism of the developing machine.

As in the case of conventional two-component toner, one-component magnetic toner is produced by melt-kneading a resin composition containing at least a binder resin and magnetic powder, and then crushing the resin composition by colliding the particles with each other in a jet air stream. . However, the magnetic toner produced in this manner has a wider particle size distribution than a two-component toner, and must be classified before being used in a copying machine, and the yield after classification is also low, increasing manufacturing costs.

Regarding the magnetic toner obtained by so-called jet pulverization as described above, especially when the resin composition provides sufficient pressure fixing properties, the surface of the magnetic toner has severe unevenness, which deteriorates the fluidity of the toner, making it undesirable for use. .

A spray drying method is known as a method of making the surface of the toner spherical or nearly spherical in order to improve the fluidity of the toner. However, since the spray drying method uses a solvent, there is a risk of explosion, and since a device for recovering the solvent is required, the manufacturing equipment is large and expensive. Another method for making the surface shape of toner spherical is to treat pulverized toner in a hot air oven to melt the toner surface and make it spherical. In this method, to produce toner, it is further processed in a hot air oven after being crushed.
The number of manufacturing steps increases, and coarse particles are generated due to granulation by hot air treatment. Therefore, the toner must be reclassified to remove these coarse particles.

In addition, when a resin composition containing magnetic fine particles is melt-kneaded and pulverized after cooling to an average particle size of about 10 to 50 microns, the jet pulverization method has an average particle size of 2 to 3 microns.
Unground coarse particles with an average particle size of 150 microns or more are present together with fine particles of less than a micron, and only a small amount of particles of a predetermined size can be obtained. It is very difficult to prevent the occurrence of this disadvantageous phenomenon simply by controlling the grinding conditions.

Thus, the emergence of a safe and efficient manufacturing method for atomizing resin compositions containing magnetic fine particles has been awaited.

Therefore, an object of the present invention is to provide a method for producing magnetic particles for electrophotography, which eliminates the above-mentioned drawbacks and can produce a developer composition with high yield and efficiency using a special pulverization method. Our goal is to provide the following.

Another object of the present invention is to provide a method for producing magnetic particles for electrophotography, which can control the shape and surface structure of the developer and produce a developer composition with good powder fluidity.

Still another object of the present invention is to provide a method for producing electrophotographic magnetic particles with good developability and transferability by controlling the shape and surface structure of a developer.

Still another object of the present invention is to provide a method for producing electrophotographic magnetic particles that are stable against repeated use and environmental changes by adjusting the shape and surface structure of a developer using a special pulverization method. be.

The present inventors investigated a method of pulverizing a resin composition consisting of a melt-kneaded material consisting of at least a binder resin and 40 parts by weight or more of magnetic powder, and as a result, the present inventors developed a pulverizer equipped with rotating blades using a specific pulverizer. It has been found that electrophotographic magnetic particles having excellent powder characteristics can be efficiently produced by using the present invention under the following conditions.

That is, in a method for producing magnetic particles for electrophotography, which includes the step of pulverizing a kneaded material consisting of at least a binder resin and a magnetic powder, the binder resin and the kneaded material are
A step of melting and kneading at least 40 parts by weight of magnetic powder out of 100 parts by weight, and dividing the kneaded material into a small grinding chamber by an inlet and a plurality of partition plates, and rotating supported by the small grinding chamber. A process of crushing the kneaded material by colliding it with the crushing blades and the wall surface of the crushing chamber using a crushing device equipped with a crushing chamber equipped with crushing blades and a discharge port for taking out the crushed material. In the range of 50 microns,
The particle size distribution expressed by the ratio (d ₉₀ /d ₁₀ ) of the average particle diameter d ₉₀ corresponding to a cumulative weight fraction of 0.9 to the average particle diameter d ₁₀ corresponding to a cumulative weight fraction of 0.1 of the magnetic particles obtained is 4.2. The above-mentioned object of the present invention is achieved for the first time by a method for producing magnetic particles for electrophotography, which is characterized as follows.

The crushing apparatus used in the method for producing electrophotographic magnetic particles of the present invention will be explained below with reference to FIG.

The interior of the casing 6, which is provided with an inlet and an outlet for a melt-kneaded product made of at least a binder resin and 40 parts by weight or more of magnetic powder, is divided into an inlet volute chamber 9, a crushing chamber 8, and an outlet volute chamber 10. The grinding chamber 8 is divided into small grinding chambers by a partition disk 5. In each of the small crushing chambers, a rotating blade 4 is provided around the circumference of a rotor 2 that rotates in contact with a partition plate, and between the tip of this blade and a liner 7 having a large number of grooves on the inner wall surface of the casing, the crushed material is It forms a flow path.
On the inlet side of the pulverized material of the rotating shaft, there is a device for uniformly dispersing the material to be pulverized (a molten kneaded material consisting of at least a binder resin and 40 parts by weight or more of magnetic powder) that is put in contact with the rotor into the pulverizing chamber. A striviewer 3 is provided.

In this device, the rotor rotates at high speed, which generates intense vortices and pressure vibrations inside the machine. The raw material is sucked in through the input port together with air, given a swirling motion around the rotating shaft 1 in the inlet swirl chamber 9, accelerated by the distributor 3, and evenly distributed to the grinding chamber 8. Subsequently, the raw material is pulverized by the blade rotating impeller 4 and the liner (inner wall surface) 7 due to the violent swirling of air, and the raw material is discharged from the outlet volute chamber 10 together with air without being subjected to a shot bath.

In the conventional pulverization method using jet airflow (jet pulverization method), most of the pulverization is performed by collisions between particles. On the other hand, in a pulverization method using rotating blades or rotating needles (mechanical pulverization method), most of the pulverization is caused by collisions between particles and the rotating blades and the wall surface of the pulverizer. It is thought that this difference in the pulverization form is reflected in the particle size distribution and powder properties of the obtained fine particles, or even in the electrical properties.

The particle size and particle size distribution of the developer composition produced by the mechanical pulverization method of the present invention can be determined by changing the rotation speed of the rotary blade, the supply amount of the resin composition, and the distance between the rotary blade and the outer wall of the pulverizer. Therefore, it can be controlled. That is, the present inventors have achieved a particle size distribution of various electrophotographic magnetic particles in the range of approximately 2.6 to 4.2 by employing a mechanical pulverization method using a pulverizer as defined in the claims of the present specification. It was also confirmed that the average particle size could be controlled within the range of 10 to 50 microns. Here, the particle size distribution is determined by measuring the particle size using a Microtrack particle size analyzer (manufactured by Leeds & Northrup Co., Ltd.), and calculating the average particle size d ₉₀ , which corresponds to a cumulative weight fraction of fine powder of 0.9 to all particles, and the cumulative weight fraction of fine powder. It is expressed as the ratio d ₉₀ /d ₁₀ with respect to the average particle diameter d ₁₀ corresponding to a weight fraction of 0.1. In the jet pulverization method, it is very difficult to control the particle size distribution within the above range. When the content of magnetic fine particles in the resin composition is 40% by weight or more based on 100 parts by weight of a kneaded material consisting of at least a binder resin and magnetic powder, the particle size distribution tends to become broader. , the mechanical crushing method of the present invention is very effective.

When pulverized electrophotographic magnetic particles are used in a copying machine or the like, further classification may be required after pulverization. If the mechanical pulverization method of the present invention is used, the particle size distribution will be narrower than when the jet pulverization method is used, so the yield of the developer composition after classification will be higher than when the jet pulverization method is used. It is obvious that it is advantageous to compare cases where the particles have the same average particle size and the same particle size distribution.

The difference in particle size distribution between the mechanical pulverization method and the jet pulverization method for the same resin composition is due to the difference in the way the particles are pulverized between the two pulverization methods. It means that there is. The state of particle pulverization by each pulverization method is shown in FIGS. 2 and 3.

FIG. 2 schematically shows the manner in which particles are pulverized in the jet pulverization method. The particles 11 are pulverized along the pulverization line shown by the dashed line. The particles are crushed mainly from the outside along the crushing lines.
Therefore, crushing at B′B′ or C′C′ occurs preferentially over crushing at A′A′.

FIG. 3 schematically shows the particle pulverization mode in the mechanical pulverization method. The particles 11 are pulverized along the pulverization line shown by the dashed line as in the case of FIG. At the initial stage of crushing, comparatively large particles are crushed, as shown by the thick chain lines AA and then BB. Next, the particles, which have become slightly smaller in size, are sequentially crushed along the thin dot-dash line. In other words, in the case of jet pulverization, the particles are sequentially pulverized into small pieces starting from the periphery, whereas in the case of mechanical pulverization, the initial pulverization is pulverized into larger particles than in the case of jet pulverization, and these pulverized particles is further crushed and divided several times to obtain a suitable particle size.

Therefore, it is conceivable that the use of mechanical pulverization provides new advantages in addition to narrowing the particle size distribution. That is, according to the above-described crushing mechanism, in the case of a mechanical crushing method, the compositional deviation among the crushed particles is reduced. Therefore, deviations in powder properties, electrical properties, and magnetic properties between particles among the pulverized particles are reduced. Therefore,
It is possible to prevent the deterioration of copied images due to selective development of toner, which has often been seen with conventional single-component magnetic toners, and it is now possible to provide a single-component developer that provides stable images over a long period of time. Ta.

An additional advantage of utilizing the mechanical grinding system of the present invention is that the powder flow properties of the developer composition are better than those obtained with the jet grinding system. The inventors discovered the cause through electron microscopic observation. The shape of the toner produced by the mechanical pulverization method of the present invention is irregular, similar to the toner produced by the jet pulverization method, but the surface shape is more uneven than that of the toner produced by the jet pulverization method. It is smooth with little turbulence. That is, the toner produced by the mechanical pulverization method of the present invention has an irregular shape and a smooth surface. Since the surface condition of the toner is smooth even though the shape of the toner is irregular, the pulverized fluidity of the toner can be improved even if the pulverized toner is not subjected to, for example, spheroidization treatment to improve its fluidity. As an indicator of powder fluidity, the following formula C = 100 (ρ _TAP - ρ _APP ) / ρ _TAP (%) (where ρ _TAP is the tap density of the powder, and ρ _APP is the apparent density of the powder. ), the developer pulverized by the pulverizer used in the method of the present invention has a powder compressibility C of 3 to 7 compared to that of the conventional method.
%, and the powder fluidity becomes good.

If the mechanical pulverization method of the present invention is used, the fluidity is improved in this way, so that it becomes unnecessary to spheroidize the toner after pulverization.

Furthermore, the mechanical pulverization method of the present invention can be used for both heat fixing developer compositions and pressure fixing developer compositions. The binder resin used in the method for producing magnetic particles for electrophotography according to the present invention is not particularly limited. As a binder resin component,
It is particularly effective for pulverizing resinous materials containing binder resins that are poorly compatible with each other. Examples of combinations that are incompatible with each other include combinations of polyethylene wax, polypropylene wax, or other wax-like materials with styrene resins, acrylic resins, copolymer materials thereof, epoxy resins, or polyester resins. However, these are just a few examples, and in general, if the solubility parameters of two resins are δ ₁ and δ ₂ , respectively, then the absolute value Δδ of the difference between δ ₁ and δ ₂ satisfies Δδ>0.5. It is a combination of The solubility parameter values can be found in "Chemistry Handbook Applied Edition 2nd Edition (1973)" or "Polymer Handbook 2nd Ed. John wiley &
Please refer to ``Sons''.

Furthermore, according to the method for producing magnetic particles for electrophotography of the present invention, the resin composition contains at least magnetic fine particles.
When containing 40 parts by weight, preferably 50 parts by weight or more,
Particularly superior performance is demonstrated compared to the jet grinding method. Any material exhibiting magnetism can be used as the magnetic fine particles contained in the resin composition. Examples include metals such as iron, nickel, and cobalt, metal oxides, and alloys. When the developer composition is used as a magnetic toner, triiron tetroxide, iron sesquioxide, cobalt-added iron oxide, ferrite, nickel powder, etc. are used. Note that the particle size and shape of the magnetic fine powder are determined depending on the particle size of the developer composition and its characteristics, and are not particularly limited here.

Even with the pulverizing apparatus used in the method of the present invention, some resin compositions may not be pulverized in one pulverization process to an average particle size that can be used as a magnetic toner. In this case, it is possible to operate the grinding device used in the method of the invention as many times as necessary until the desired average particle size is achieved. The reason for this is that in the mechanical pulverization method, it is possible to set the limit pulverized particle size to, for example, 2 to 3 microns, so even if the pulverizer is used more than once, the number of 2 to 3 micron particles will be smaller than the number of 2 to 3 micron particles in the first pulverization. There is almost no increase in the number of particles, because in the second and subsequent pulverization, unpulverized coarse particles are sequentially pulverized.

In the crushing apparatus used in the method of the present invention, air at room temperature can be circulated within the apparatus, but the crusher generates heat due to friction between the air, the material to be crushed, or the material to be crushed, and the rotating blades or walls, so cooling is not possible. Preferably, the air is circulated. The temperature of the circulating air varies depending on the resinous composition to be pulverized, and an appropriate temperature can be selected within a wide range.

In a system that generates a lot of heat, it is possible to pre-cool the resin composition, for example, with liquid nitrogen, as necessary, and circulate nitrogen gas immediately after vaporization from the liquid nitrogen instead of air to crush it.

According to the pulverizing device used in the method of the present invention, it is possible to control the particle size distribution so that classification after pulverization is unnecessary, but if necessary, it is possible to classify the developer composition after pulverizing by the pulverizing device. May be manufactured. After pulverization by the pulverizer, or after pulverization and classification,
External additives may be mixed with the toner particles if necessary. External additives are used to further improve the fluidity, development, transferability, and storage stability of the developer composition, to prevent filming on the photoconductor surface, and to improve the cleaning properties of the toner. This is not intended to compensate for the drawbacks of the method of the present invention.

As described above, the developer particles obtained by the mechanical pulverization method of the present invention have a relatively smooth irregular surface structure with irregularities. Therefore, compared to conventional jet-pulverized particles or spherical particles obtained by spray drying, direct polymerization, etc., when external additives are mixed, the external additives are exposed to the Coulomb force and Van der Waals force on the developer particle surface. It also has the advantage of being easily held effectively and stably by force.

As external additives, long-chain fatty acids and derivatives thereof, resin fine powders such as fluororesins, and inorganic fine powders such as aluminum oxide, titanium oxide, silica, and carbon black can be used.

Note that the developer composition produced by the crushing device used in the present invention does not necessarily have to be composed of only one type of developer, and may be a composition of more than one type of developer. In addition, in the case where the developer composition is composed of two or more kinds of developer compositions, it is not necessary that all of these developer compositions are produced by the method according to the present invention, and at least one of the two or more kinds is produced according to the method according to the present invention. It is also effective as a developer composition produced by the method.

Typical usage patterns include cases where it is used as a magnetic toner in a one-component development method, and further used as a toner and/or carrier in a two-component development method. Furthermore, in the case of magnetic toner, it can be used not only for developing electrical latent images but also for developing magnetic latent images. When used as a carrier in a two-component development method, a magnetic powder-dispersed carrier with a particle size of several tens of microns is used. In particular, a developer containing 40 parts by weight or more of magnetic powder and a particle size distribution of 4.2 or less can have a narrow charge amount distribution and have good stability.

Some examples of the present invention are shown below, but of course the present invention is not limited only to these examples.

Note that parts in the examples are parts by weight.

Example 1 Polystyrene resin (Picolastick D-125, manufactured by Hercules) 35 parts Polyethylene wax (trade name E-300, manufactured by Sanyo Chemical Co., Ltd.) 5 parts Ethylene-vinyl acetate copolymer (Evaflex 420, manufactured by Mitsui Polychemicals Co., Ltd.) 10 Part triiron tetroxide (RB-BL manufactured by Titan Kogyo Co., Ltd.) 50 parts Carbon black (BP- manufactured by Kayabot Co., Ltd.)
1300) Two parts were melted and kneaded, and after cooling, a crusher of the type shown in Figure 1 was used to feed the mixture at a feed rate of 30 kg/h and a rotor rotation speed.
Grinding was performed at 6000 rpm and a distance between the blade and the outer wall of 3 mm. The average particle size of the obtained toner was 12.1μ, and the particle size distribution was 3.6. When this toner was observed under a microscope, it was found to have an irregular shape and a smooth surface with almost no irregularities. The powder compressibility of this toner was 49%. Furthermore, when the toner was classified using a wind classifier so that the content of particles below 5μ was 5wt% or less and the average particle size was 15μ, the classification yield was 65%.
It was hot. A one-component developer was installed in a Fuji Xerox Co., Ltd. 2300 copying machine, and the toner was developed. After being transferred to paper, the image was fixed using a fixing roll with a linear pressure of 20 kg/cm, and a good image was obtained. A further 5,000 copies were made, and the image quality was stable and good, and no contamination inside the machine was observed.

Comparative Example 1 The same kneaded composition as in Example 1 was pulverized using a jet pulverizer. The average particle size of the obtained toner was 11.9μ, and the particle size distribution was 5.6. Compared to Example 1, the particle size distribution is very wide although the average particle diameter is almost the same. When this toner was observed under a microscope, the shape of the toner was irregular, and many irregularities were observed on the surface. The compression ratio of this toner was 55%. The fluidity was worse than that of the toner obtained in Example 1. When the toner was classified using an air classifier so that the content of particles below 5μ in the toner was 5wt% or less and the average particle size was 15μ, the classification yield was 31%.

When copying image quality was evaluated using the same operations as in Example 1, it was found that although the material composition and particle size distribution were the same as the toner in Example 1, the reproduction of a solid black image was better than in Example 1. Furthermore, there was a phenomenon in which the image density decreased due to continuous copying. This is considered to be due to differences in toner shape, surface structure, distribution of material composition, etc. based on differences in pulverization methods.

Example 2 Styrene-butyl methacrylate copolymer (styrene component 70%) 16 parts Low molecular weight polyamide resin (manufactured by Henkel Japan)
Versamide 930) 16 parts styrene-butadiene copolymer (Ciel Chemical Co., Ltd.)
TR-1102) 8 parts Triiron tetroxide (BL-500, manufactured by Titan Kogyo Co., Ltd.) 60 parts were melted and kneaded, and after cooling, they were milled using a crusher of the type shown in Figure 1 at a feed rate of 60 kg/h and a rotor rotation speed.
The material was crushed at 5000 rpm and the distance between the blade and the outer wall was 3 mm. The average particle size of the obtained toner was 12.5μ, and the particle size distribution was 3.8. The shape and surface morphology of this toner were almost the same as in Example 1. The compression ratio of this toner was 44%.

When the particles were classified using a wind classifier under the same particle size conditions as in Example 1, the classification yield was 72%. 0.25 parts of carbon black (Monarch 1300, manufactured by Kayabot Co., Ltd.) was added to this toner and mixed to 100 parts of the above toner, and the copied images were evaluated in the same manner as in Example 1. Very good image quality was obtained. Ta.

Comparative Example 2 The same kneaded composition as in Example 2 was pulverized using a jet pulverizer. The particle size of the obtained toner is
The particle size distribution was 6.2 at 12.1μ. Compared to Example 2, the particle size distribution is very wide although the average particle size is almost the same. The shape and surface morphology of this toner were almost the same as those of Comparative Example 1. The compression ratio of this toner was 49%, and its fluidity was worse than that of the toner of Example 2. When the particles were classified using a wind classifier under the same particle size conditions as in Example 2, the classification yield was 32%.

As in Example 2, carbon black was further added and mixed, and when the copied images were compared, the same defects as in Comparative Example 1 were observed.

Example 3 Styrene-butyl methacrylate resin (styrene component 60%, weight average molecular weight 120,000) 47 parts low molecular weight polypropylene (melting point approximately 130°C) 3 parts zinc ferrite 50 parts were melt-kneaded, and after cooling, the same as Example 1 was prepared. A toner having an average particle size of 15.2μ, a particle size distribution of 3.4, and a powder compressibility of 29% was obtained. When this toner was adjusted to an average particle size of 14μ and a particle size distribution of 2.8 using a wind classifier,
The classification yield was 81%. To this toner, 0.3% by weight of carbon black was added and mixed, and the toner was developed and transferred using the same copying machine as in Example 1, and the temperature was further increased to 170°C.
When I fixed it with a hot roll fixing machine, I was able to consistently obtain good image quality during continuous copying of 5,000 sheets.

Comparative Example 3 When the same kneaded and pulverized product as in Example 3 was pulverized using the same jet pulverizer as in Comparative Example 1, the pulverized particle size of the toner was 14.7μ, the particle size distribution was 4.7, and the powder compressibility was 35.
It was %.

When this toner was adjusted to an average particle size of 14μ and a particle size distribution of 2.8 by wind classification, the classification yield was 43%.

When 0.3% by weight of carbon black was added to this toner and the image quality was evaluated in the same manner as in Example 3, the initial image quality was almost the same, but after about 300 copies, the image density A decrease was seen in

[Brief explanation of drawings]

Figure 1 is a schematic diagram of an example of a crushing device used in the method of the present invention, Figure 2 is a schematic diagram showing how particles are crushed in a jet crushing method, and Figure 3 is a schematic diagram showing how particles are crushed in a mechanical crushing method. FIG. Symbols in the figure: 1...rotating shaft, 2...rotor, 3
...Destrivator, 4...Blade, 5
...Partition disk, 6...Casing, 7...Liner, 8...Crushing chamber, 9...Inlet volute chamber, 10...
Outlet vortex chamber, 11...particles.

Claims (1)

[Claims] 1. In a method for producing magnetic particles for electrophotography, which includes the step of pulverizing a kneaded material consisting of at least a binder resin and magnetic powder, at least 40 parts by weight of the binder resin and the magnetic powder in 100 parts by weight of the kneaded material are melted. The process of kneading, an inlet for the kneaded material, a pulverizing chamber divided into small pulverizing chambers by a plurality of partition plates, and provided with pulverizing blades that are rotatably supported by the small pulverizing chambers, and an exhaust for taking out the pulverized material. The process includes a step of pulverizing the kneaded material by colliding with the pulverizing blades and the wall surface of the pulverizing chamber using a pulverizing device equipped with an outlet. The average particle size d ₉₀ corresponds to a ratio of 0.9 and the average particle size d ₁₀ corresponds to a cumulative weight fraction of 0.1.
1. A method for producing magnetic particles for electrophotography, characterized in that the particle size distribution expressed by the ratio (d ₉₀ /d ₁₀ ) is 4.2 or less.