JP2566804B2 - Method of manufacturing magnetic toner - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a toner used in an electrophotographic method, an electrostatic printing method, a magnetic recording method, and the like, and particularly to a method for producing a magnetic toner.

BACKGROUND ART Toner that visualizes an electrical or magnetic latent image or the like is used in various processes for forming and recording a figure.

An electrophotographic method, which is one of such image forming processes, is disclosed in U.S. Pat. No. 2,297,691 and Japanese Patent Publication No.
Many methods are known as described in Japanese Patent Publication No. 3910, Japanese Patent Publication No. 43-24748, etc., but in general, a photoconductive material is used and various methods are applied to the photoreceptor. Form an electrical latent image on the surface, then develop the latent image with toner, transfer the toner image to a transfer material such as paper, if necessary, and then fix it by heating, pressure or solvent vapor to make a copy. You get what you get. When the step of transferring the toner image is included, a step for removing the residual toner is usually provided.

As a developing method for visualizing an electric latent image using toner, for example, a magnetic brush method described in U.S. Pat.No. 2,874,063, a cascade developing method described in 2,618,552 and 2,221,776 are described. The powder cloud method described in the specification and the method using a conductive magnetic toner described in US Pat. No. 3,909,258 are known.

As a toner applied to these developing methods, a fine powder in which a colorant such as a dye or a pigment is dispersed in a natural or synthetic resin is conventionally used. For example, 1 in which a coloring colorant is dispersed in a binder resin such as polystyrene is used.
Particles finely pulverized to about 30 μm are used as toner. Further, as the magnetic toner, a toner containing magnetic particles such as magnetite is used. In the case of a system using a so-called two-component developer, the toner is usually used by being mixed with carrier particles such as glass beads and iron powder.

Recently, a one-component developing method using an insulating magnetic toner has been developed. This one-component developing method is
Compared to the method that uses a component type developer, the copying machine can be made compact, the cost of the developer can be reduced, the life can be extended, and the developer can be handled easily. are doing.

Development of magnetic powder has been vigorously carried out in order to appropriately provide the characteristics of the magnetic toner used in the one-component developing method having such characteristics. For example, Japanese Patent Laid-Open No. 56-91241.
In Japanese Patent Publication No. 56-91242 and Japanese Patent Publication No. 56-91242, magnetic powders that define magnetic properties, bulk density, shape, etc. are proposed.

On the other hand, as a method for producing a toner, Japanese Patent Publication No.
A method of dissolving a binder and a colorant in a solution and forming a toner by spraying, as described in Japanese Patent Application Laid-Open Publication No. Sho.
57-154253 and 59-28165, a method of dispersing a monomer and a colorant and polymerizing the monomer to obtain a desired toner, or a binder and a colorant or a magnetic agent. A known method is known in which a powder and a powder are melt-kneaded and the resulting mixture is pulverized to a desired particle size to obtain a toner.

In the toner manufacturing method as described above, as the binder resin, those obtained by various polymerization methods can be usually used. For example, the binder resin obtained by bulk polymerization or solution polymerization has undergone a pulverization step. Later, it is melt-kneaded with the magnetic powder. On the other hand, in the case of a bead-shaped resin obtained by suspension polymerization, it is possible to easily obtain a resin having a uniform particle size suitable for the above-mentioned heat melting and kneading by controlling the polymerization conditions, and therefore it is possible to use it as it is for melt kneading. is there.

On the other hand, in JP-A-60-46566, W cone,
It is proposed that the binder resin powder and the magnetic powder are premixed using a mixer such as a V blender or a Henschel mixer, and then hot melt kneading is performed using a pressure kneader, a Banbury mixer, a heat roll, an extruder or the like. ing.

Thus, pre-mixing the magnetic powder and the binder before the hot melt kneading enhances the dispersibility of the magnetic powder in the binder resin, and the toner in which the magnetic powder is uniformly dispersed in the binder resin. In order to obtain, it is generally considered to be a preferable method, but depending on the type of binder resin or magnetic powder to be mixed,
On the contrary, it may not be preferable.

In particular, according to the study by the present inventors, a bead-shaped resin powder obtained by the suspension polymerization method as described above,
When used in combination with a magnetic powder having excellent properties as shown in JP-A-91242, a toner having suitable properties cannot be obtained by melt-kneading these, and moreover, melting as described above It has been found that when the preliminary dispersion is carried out before the kneading, the mechanical troubles in the preliminary mixing step and the serious problems such as the deterioration of the quality of the toner occur and the mass production of the toner becomes difficult.

OBJECT OF THE INVENTION An object of the present invention is to provide a method for producing a magnetic toner having excellent electrophotographic characteristics.

Another object of the present invention is to provide a manufacturing method suitable for mass production of magnetic toner.

SUMMARY OF THE INVENTION As a result of intensive studies, the present inventors have found that when spherical resin particles are used, a problem caused by mixing before hot melt kneading occurs rather depending on the powder characteristics of the magnetic powder to be mixed with the spherical resin particles. Furthermore, in order to solve this problem, it has been found that it is essential to crush the spherical particles to achieve a specific degree of fineness in relation to the packing density of magnetic powder.

The method for producing a magnetic toner of the present invention is based on the above findings, and more specifically, in producing a toner containing at least a resin and a magnetic material, a resin obtained by pulverizing spherical resin particles before hot melt kneading. Powder and magnetic powder are dispersed and mixed, and the bulk density A of the magnetic powder and the fineness B of the resin powder have a relationship of 5 <B / A <60. The reason why the above-described effects are obtained in the present invention is not always clear, but according to the findings of the present inventors, it is presumed as follows.

That is, the spherical resin particles, from the uniformity of their shape,
Originally, it is thought that it is suitable for uniform dispersion and mixing with magnetic powder, but powder which is an aggregate of such resin particles,
Since the packing density (or bulk density) is relatively high (that is, the air content of the powder is small), when it is mixed with the magnetic powder, the most densely packed agglomerate (coagulant) composed of the resin particles. It is highly probable that the air content of the aggregate was small) was not easily destroyed.

Therefore, in the conventional toner manufacturing method, not only the resin powder and the magnetic powder were not mixed well, but also the shearing force at the time of mixing caused the magnetic powder to adhere to the inner wall of the mixer and / or the rotary blade. That is, a non-selective desorption of the magnetic powder during continuous operation caused a serious problem in toner production such as fluctuation of magnetic powder content in the toner and deterioration of developer quality. Presumed.

On the other hand, in the toner manufacturing method of the present invention,
Resin powder obtained by crushing spherical particles that has a specific degree of fineness corresponding to the bulk density of magnetic powder and has a large surface area and air content as powder is used. Therefore, the most densely packed agglomerate as described above is not substantially formed, and the resin powder agglomerate and the magnetic powder agglomerate are destroyed, and further the resin powder and the magnetic powder are efficiently mixed. It is estimated that the magnetic powder does not adhere to the inner wall of the mixer as described above.

In particular, in the pre-dispersion step, when a fixed container type mixer that utilizes the shearing force of the rotary blades is used, in the conventional method, the magnetic powder having a large bulk density contains a small amount of air, so the rotary blades are stirred. Even though it could not soar into the container, it is presumed that the magnetic powder was pressed against the inner wall of the container due to the centrifugal force and the shearing force between the inner wall of the container and the rotating blades, and it was easily adhered (see the attached drawing. A schematic side sectional view of the fixed tank in such a case is shown).

On the other hand, in the present invention, since the resin particles having a high degree of fineness (that is, the air content and the surface area of the powder are large) and the magnetic powder are mixed, the magnetic powder appropriately rises in the fixed tank. Therefore, it is presumed that the sticking phenomenon of the magnetic powder is suppressed.

Hereinafter, the present invention will be described in more detail. In the following description, “%” and “part” representing the quantitative ratio are based on weight unless otherwise specified.

DETAILED DESCRIPTION OF THE INVENTION In the magnetic toner manufacturing method of the present invention, a resin powder obtained by pulverizing spherical resin particles is used as the binder resin to be mixed with the magnetic powder.

In the present invention, as the above-mentioned spherical resin particles, resin particles obtained by a suspension polymerization method or resin particles having a similar spherical morphology are preferably used.

In the suspension polymerization method, resin particles having a particle diameter of about 0.1 mm to several mm can be easily obtained by selecting a dispersant used for suspending the monomer and stirring conditions, or adjusting the amount of the monomer to the aqueous layer. . However, if the particle diameter is set to 0.1 mm or less, a large amount of the dispersant is usually required, and the moisture resistance of the toner tends to deteriorate.

Here, the above-mentioned fineness degree refers to a measured value obtained as follows.

A powder tester PTD type (manufactured by Hosokawa Iron Works) is used as the measuring instrument. Follow the procedure below to attach and fix the following accessories on the vibrating table of this powder tester.

(1) By blow chute (2) Space ring (3) Fleur (200 mesh) (4) Fleur (100 mesh) (5) Fleur (60 mesh) Adjust the rheostat of the powder tester to 4V,
After gently placing 5.00 g of the resin powder as a sample on the sieve (60 mesh), the vibrating table is vibrated for 2 minutes. After this, the weights of the following residues on the screen are measured respectively.

x: Weight of resin on 60 mesh (g) y: 100 〃 (g) z: 200 〃 (g) w: Weight of resin on 200 mesh pass (g) Based on the measured value obtained as above The degree of fineness is defined as follows.

As the actual measured values (x, y, z, w), the average value of 10 measurements was used.

Toner resins synthesized by suspension polymerization usually have a particle size of 0.
It is 1 mm or more, and is about 1 at most in the above fineness. In suspension polymerization, it is possible to further reduce the particle size, but as described above, it is usually necessary to use a large amount of a dispersant, and there is a problem in developability, especially in high temperature and high humidity. Is likely to occur.

In the present invention, the resin particles (beads) having a spherical shape as described above are crushed by a mechanical crusher, an air crusher, or the like to change the shape.

The above-mentioned fineness (B) of the pulverized resin powder in the present invention is preferably about 3 to 70, more preferably about 9 to 70. As this resin powder, two or more kinds of resins may be blended and used, but in this case, the fineness degree (B) of the resin powder after blending is used.

On the other hand, the magnetic powder mixed with the resin powder has magnetic properties,
Desirable ones are selected from the viewpoint of electrical characteristics, shape, powder characteristics, etc., but from the viewpoint of electrophotographic characteristics, for example, the bulk density A as described in the above-mentioned JP-A-56-91242 is used. Is preferably 0.45 g / ml or more, more preferably 0.45 to 1.20 g / ml magnetic powder.

Here, the bulk density A is a value measured according to JIS standard K5101.

In the preliminary dispersion step in the toner manufacturing method of the present invention, that is, in the dispersion / mixing step before hot melt kneading, the above-mentioned bulk density A of the magnetic powder and the fineness B of the resin powder are 5
It is necessary to use magnetic powder and resin powder having a relationship of <B / A <60, and it is preferable that 10 ≦ B / A ≦ 60, and further 15 ≦ B / A ≦ 60.

When the relationship between the bulk density A and the fine particles B is B / A ≦ 5,
During the pre-mixing or pre-mixing, the adhered substance of the magnetic powder in the mixer is purified. On the other hand, in the case of B / A ≧ 60, in the next kneading step, the phenomenon that the agglomeration of magnetic powder and resin powder by shearing force (shear) and mutual mixing do not occur well (so-called “bite”) Worsening)
It causes a delay in the production process.

As the mixer used for mixing the resin powder and the magnetic powder described above, any of a rotary container type mixing device and a fixed container type mixing device can be used, but particularly when a fixed container type mixing device is used, The effect is remarkable.

The rotary container type mixing device referred to here is one in which the container itself is moved to perform mixing, and the fixed container type mixing device is to fix the container itself and to move the stirring blade inside the container. Mixing is performed.

As the mixer, a Henschel mixer (manufactured by Mitsui Miike Kogyo) is particularly preferably used.

 Hereinafter, the present invention will be described in more detail with reference to examples.

Production Example 1 Resin fine particles comprising a styrene-n-butyl acrylate copolymer obtained by suspension polymerization (monomer molar ratio 8
0:20, weight average molecular weight 100,000, fineness B = 0.11) was mechanically crushed using a speed mill manufactured by Okada Seiko, and fineness B was 1.21, 1.78, 3.84, 9.09, and 15.9. Binder resin powder of was obtained.

Furthermore, pneumatic crusher (manufactured by Nippon Pneumatic Mfg. Co., Ltd.,
I mill) was used to obtain two kinds of binder resin powders having a fineness of 19.6 and 25.6.

Experimental Example 1 Eight types (1 type of spherical particles, 7 types of crushed particles) of resin powder having a fineness degree obtained in the above Production Example 1 and a bulk density of 0.3
A magnetic matrix consisting of seven kinds of Fe ₃ O ₄ (so-called magnetite) of 1, 0.39, 0.50, 0.65, 0.72, 0.83, and 0.95 g / cm ³ is used to form a matrix of these combinations,
Henschel Mixer FM-10B (Mitsui Miike Industry Co., Ltd.)
A mixing test was conducted using a ZO-SO blade with a rotation speed of 2450 rpm, and the results shown in Table 1 below were obtained. The mixing time was 30 seconds, and the composition ratio of the resin powder and the magnetic powder was 10
It was 0 to 60 (parts by weight).

Table 2 shows the ratio (B / A) of the fine particles B of the resin powder used at this time and the bulk density A of the magnetic powder.

Experimental Example 2 Henschel Mixer FM75C (Mitsui Miike Industry Co., Ltd.)
Was used and a mixing test was conducted using a matrix of a combination of resin powder and magnetic powder shown in Table 3 below, and the results shown in Table 3 were obtained.

At this time, 6 kg of magnetic powder was placed in a fixed tank for 10 kg of resin powder, and mixed for 30 seconds at a rotating blade rotation speed of 1000 rpm.

EFFECTS OF THE INVENTION According to the present invention as described above, spherical resin particles obtained by suspension polymerization or the like have a specific degree of fineness corresponding to the bulk density (filling density) of the magnetic powder to be mixed therewith. After that, by pre-mixing with the magnetic powder before heat kneading, the phenomenon of sticking of the magnetic powder to the mixer can be eliminated, and good quality toner can be obtained by smooth plant operation.

[Brief description of drawings]

The drawing is a schematic side cross-sectional view showing one embodiment of magnetic powder fixation in the mixer fixing tank in the preliminary dispersion step of the conventional toner manufacturing method.

Front Page Continuation (72) Inventor Keita Nozawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-56-101150 (JP, A) JP-A-60-46566 ( JP, A) JP 56-91242 (JP, A)

Claims (2)

(57) [Claims] 1. When producing a toner containing at least a resin and a magnetic material, the method includes a step of dispersing and mixing resin powder obtained by pulverizing spherical resin particles and magnetic material powder before hot melt kneading, Moreover, the bulk density A of the magnetic powder and the fineness B of the resin powder have a relationship of 5 <B / A <60. 2. The method for producing a magnetic toner according to claim 1, wherein the resin powder and the magnetic powder are dispersed and mixed by using a fixed container type mixing device.