JPH0695229B2 - Insulating magnetic toner - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an insulating magnetic toner for dry development of electrostatic latent images such as electrophotography and ionography.

(Prior Art) Conventionally, as a dry development method, a method of using a two-component developer in which toner particles are mixed with carrier particles, that is, glass beads or magnetic powder, and a method of imparting magnetism to the toner particles themselves is used. There is a method of using a component type toner, and more recently, a method of using a non-magnetic single component type toner excellent in environment resistance has been proposed. The toner is classified into a conductive toner and an insulating toner according to the electric resistance of the toner, but an insulating toner capable of copying plain paper is generally used.

Conventional methods for producing these toners include thermoplastic resin, magnetic powder, coloring agents such as pigments and dyes, wax,
Additives such as plasticizers and charge control agents are heated and melted, and the secondary agglomerated magnetic powder pigments are kneaded by applying a strong shearing force to form a uniform composition, which is cooled and then crushed. 、 Most of the methods of classification.

However, in terms of quality, the magnetic toner obtained by this pulverizing method has different toner particles in different sizes and shapes, and generally has an irregular shape. In addition, there is a drawback in that the fluidity of the toner is poor and replenishment is difficult, which causes troubles. Further, in the case of a magnetic toner, the exposure of the magnetic powder to the toner surface or the separation of the magnetic powder, which is generated during the pulverization, becomes a serious problem. In fact, in magnetic toner, it has been found by visual observation with an electron microscope that the magnetic powder normally contained on the toner surface is partially exposed. It is considered that this is because the fracture surface that occurs when the toner is crushed is likely to occur along the boundary surface between the portions of different materials. The exposed or separated magnetic powder generated in this way scratches the photosensitive drum, deteriorates the triboelectrification characteristics of the toner surface, and causes soiling.
It may cause scattering in the machine or deterioration of environment resistance. Further, for the same reason as above, other components contained in the toner are also easily separated from the toner particles, which causes scumming, scattering in the machine, and deterioration of environment resistance.

(Problems to be Solved by the Invention) The present invention solves the above problems, prevents the magnetic powder from being directly exposed on the toner surface or prevents the magnetic powder from being separated from the toner, and has a particle shape To provide a toner that is more rounded (having rounded corners), has a relatively uniform particle size, has excellent fluidity and triboelectrification characteristics, and is economically advantageous compared to toner. It is intended.

[Structure of Invention]

(Means for Solving the Problems) The present invention is directed to thermoplastic resin particles (A) having an average particle size of 5 to 15 μm, containing magnetic powder, wax and pigment, and thermoplastic resin fine particles (B) having an average particle size of 2 μm or less (B). ) And fine particles of the charge control agent are mixed by applying a mechanical strain force under the condition that the average particle diameter is in the range of 5 to 20 μ, and the resin fine particles (B) and the fine particles of the charge control agent are substantially An insulating magnetic toner formed by coating the surface of resin particles (A).

In this specification, the particle size is measured by using a Coulter Counter TAII type (manufactured by Coulter Electronics Co., Ltd.) on a volume basis.

Examples of the thermoplastic resin used in the present invention include polystyrene type, styrene-acrylic acid ester, methacrylic acid ester, copolymer system containing styrene with acrylonitrile or maleic acid ester, polyacrylic acid ester type, polymethacrylic acid ester. Examples of known binder resins such as resins, polyesters, polyamides, polyvinyl acetates, epoxy resins, hydrocarbon resins, petroleum resins, and chlorinated paraffins can be used alone or in combination. Can be used.

In the present invention, in order to prepare the thermoplastic resin particles (A) having an average particle size of 5 to 15 µ, various methods can be applied without any particular limitation. In addition to the magnetic powders described below, the thermoplastic resin particles (A) are used for lubricants such as wax, colorants such as pigments and dyes, fluidity-imparting agents such as colloidal silica, charge control agents, and low molecular weight polyolefins. It can be used together depending on the case.

The magnetic powder used in the present invention is not particularly limited, but
It is preferable to use fine magnetic powder having an average particle size of μ or less, preferably 1 μ or less, and various ferrites, magnetites, hematites, and other alloys or compounds of iron, zinc, cobalt, nickel, manganese, and the like are known per se. The magnetic powder may be classified according to the purpose, or may be a surface treatment known per se, such as a hydrophobic treatment or a silane coupling agent treatment. Good.

The means for preparing the thermoplastic resin fine particles (B) having an average particle size of 2 μ or less is not particularly limited, and examples thereof include pulverization / classification,
Besides the methods such as suspension polymerization, dissolution / precipitation and spraying, spherical fine particles produced by emulsion polymerization may be used.
When the average particle size of the resin fine particles (B) is 2 μm or more, coating of the resin particles (A) surface by heat melting is insufficient and is not suitable.

In the present invention, as a method of mixing the thermoplastic resin particles (A) and the thermoplastic resin particles (B) by applying mechanical strain force under the condition that the average particle diameter is in the range of 5 to 20 μ, The conditions are such that the plastic resin particles (A) are not fused and formed into a large lump, or conversely, the strain force is too large to be finely crushed, and the surface of the resin particles (A) is thermoplastic. The conditions are such that the resin fine particles (B) are thermally melted by the frictional heat generated while adhering. As a concrete method that satisfies both of these conditions, a mortar is used in the laboratory, but it is not practically sufficient. Industrially, it can be used by changing the operating conditions such as a grinder, a ball mill, a side mill, or other disperser, which has the same effect as a mortar, the processing amount, and the dispersion medium, so that the above purpose is achieved. It is possible.

However, a mortar requires several hours to several tens of days, and a ball mill and a sand mill also require a long time. Therefore, industrially, a powder mixer is a fluidized bed, and a mixer or an impact machine that moves at high speed with airflow is used. It is a mixer having blades, a hammer, etc. attached to it, and an example of such a mixer is SI mill (manufactured by Toyo Ink Mfg. Co., Ltd.,
For the outline, refer to Japanese Examined Patent Publication No. 57-43051), atomizer, free crusher (Nara Machinery Co., Ltd.), Kawasaki Heavy Industries, Ltd.
A crushing machine (KTM-1) and the like can be exemplified, and these devices can be used as they are or after being appropriately improved according to the purpose of the present invention. If possible, use a circulating system, and a closed system is desirable.

The effect of coating the surface of the resin particles (A) with the effect that the thermoplastic resin particles (B) adhere to the surfaces of the thermoplastic resin particles (A) and are melted by heat by such mixing treatment is generated. It is considered that (A) and the resin fine particles (B) collide with each other or with a dispersion medium such as walls, blades, beads, etc., and the temperature becomes instantaneously and partially considerably high. The airflow temperature rises to near the glass transition temperature (Tg) of the resin, and it may be necessary to cool the system. The above phenomenon can be understood by observing electron micrographs before and after pre-mixing only. That is, before the mixing treatment, the thermoplastic resin particles (A) having a relatively large particle size distribution,
The thermoplastic resin fine particles (B) are partially aggregated,
After the treatment, the surface of the thermoplastic resin particles (A) is smooth, almost no particles of the thermoplastic resin particles (B) are seen, and it is covered with a thin layer of the resin particles (B). The particles have been hard to break even after running tests.

It is also observed that the thermoplastic resin particles (A) after the treatment have a small number of small particles and have a uniform particle size, and the corners of the particles are rounded. That is, it is considered that the resin particles (A) having a small particle size are sized into particles having a constant size by the mixing process.

Various factors can be considered for obtaining the above effect, but according to the study by the present inventors, the velocity of the air flow is the highest, and it is preferable to set it to several tens m / sec to several hundreds m / sec.

In the present invention, the particle size of the toner is such that the average particle size is in the range of several μ to 20 μ, and it is preferable that the toner of 5 μ or less and 25 μ or more is not substantially contained. If the amount of toner having a particle diameter of 5 μm or less increases, the fluidity deteriorates and scumming occurs. Also, if the amount of toner of 25 μm or more increases, the image becomes discolored, reducing the commercial value.

The charge control agents used in the present invention are known per se, and include, for example, Fett Schwarz-HBN, Nigrosine base, Brilliant Schwarz, Zavon Schwarz X,
There are dyes such as Ceres Schwarz RG and dyes containing gold, and other CI solvent black 1,2,3,5,7, CI acid black 123,22,23,28,42,43, oil black (CI2615
0), dyes such as spirone black, naphthenic acid metal salts, and fatty acid metal soaps.

Since the charge control agent is intended to control the surface charge of the toner, it should be attached or coated on the toner by the same operation after being mixed with the resin fine particles (B) or after being mixed with the resin fine particles (B). Is preferred.

The present invention will be described below with reference to specific examples. The middle part of an example shows a weight part.

Example 1 Styrene-acrylic resin (Japan Carbide Industry Co., Ltd.)
Manufactured by Toda Kogyo Co., Ltd., 80 parts of trade name NC-6157)
EPT500) 15 parts, carbon black (Cabot, Mog
2 parts of ul-L) and 3 parts of low molecular weight polypropylene (manufactured by Sanyo Kasei Co., Ltd., trade name VISCOL 550P) are premixed with a Henschel mixer, melted and kneaded with a twin-screw extruder, and allowed to cool. A resin particle (A1) having an upper limit particle size of 25 μ or less and an average particle size of about 10 μ was prepared by roughly crushing this kneaded product with a type I jet mill grinder.

100 parts of the resin particles (A1), 3 parts of polymethylmethacrylate fine particles (B1) having an average particle size of 0.4 μm, and 0.3 parts of a charge control agent (Hodogaya Chemical Co., Ltd., Spiron Black TRH) are supermixed. The resin particles (B1) and the charge control agent were electrostatically attached to the surface of the resin particles (A1) by premixing for 1 minute at a rotation speed of 2500 rpm. Then, this was introduced into a free mill M-3, and the internal rotation speed was set to 5000 rpm. At this time, the air velocity in the free mill was about 90 m / sec, the average residence time of the introduced mixture in the system was about 3 seconds, and the mixture discharged to the collector was passed through the free mill a total of 7 times. The desired toner was obtained.

The average particle size of the toner particles is 12μ,
There were virtually no particles above 25μ and no classification was required. Further, 0.3 part of colloidal silica (trade name: R-972, manufactured by Nippon Aerosil Co., Ltd.) was mixed with 100 parts of the toner to prepare a toner sample.

15 parts of this toner and ferrite carrier (Nippon Iron Powder Co., Ltd.)
(Trade name: F-141-400, manufactured by Matsushita Electric Industrial Co., Ltd., trade name: FP-2520) manufactured by Matsushita Electric Industrial Co., Ltd. ), And copied on plain paper in continuous operation using the test chart.

In this copying, since the release of the magnetic powder and the exposure to the toner surface were suppressed, the scratches on the photosensitive drum were eliminated, and the toner fixability, charge stability, blocking resistance, and
And the anti-offset property are very good, and in the running image test in which the toner of the present invention is put into the toner supply hopper in the copying machine, the image equivalent to the initial image is maintained for 60,000 sheets, and the toner supply property is good. Was also good.

Comparative Example 1 The same raw material as in Example 1 was used to carry out production by a conventional method. That is, 1 part of the charge control agent (increasing the amount because it is not a surface coating), 80 parts of styrene-acrylic resin,
15 parts of magnetic powder, 2 parts of carbon black, and 3 parts of low molecular weight polypropylene are mixed and premixed with a Henschel mixer, then they are melted and kneaded with a twin-screw extruder and allowed to cool, and this kneaded material is roughly crushed. The type I jet mill grinder has an upper limit particle size of 25μ or less and an average particle size of approximately 12μ, 5
A toner obtained by cutting toner having a size of μ or less was obtained. Further, colloidal silica was mixed in the same manner as in Example 1 to obtain a toner sample.

When this toner was used and tested in the same manner as in Example 1, as compared with the toner of the present invention, scumming was observed, and according to a running test, the occurrence of scratches on the photosensitive drum was recognized on about 5,000 sheets. A bridging phenomenon was observed in the refill hopper.

Example 2 Styrene-acrylic resin (Japan Carbide Industry Co., Ltd.)
Manufactured by Nikalite NC-6100) 53 parts, carbon black (made by Cabot Co., product name Mogul-L) 2 parts, low molecular weight polypropylene (manufactured by Sanyo Kasei Co., product name VISCOL 550P) 3 parts, and magnetite ( Magnetic particles) 40 parts by trade name EPT-500 manufactured by Toda Kogyo Co., Ltd. and resin particles (A2) having an average particle diameter of about 10 μm were prepared in the same manner as in Example 1.

98 parts of the resin particles (A2), 1.5 parts of spherical polymethylmethacrylate fine particles having an average particle size of 0.4 μm, and a charge control agent (Hodogaya Chemical Co., Ltd., trade name Spiron Black TRH)
0.3 part was premixed with a super mixer at a rotation speed of 2800 rpm for 1 minute, and this was introduced into an atomizer which was a closed system, and the rotation speed of the internal rotary blades was 4500 rpm. The air velocity at this time was 80 m / sec, and the introduced mixture stayed for 30 seconds and was discharged to the Sancron collector to obtain toner.

The average particle size of this toner was 12.5μ, and particles below 5μ and above 25μ were not measured.

Furthermore, colloidal silica (Japan Aerosil Co., Ltd.)
(Trade name: R-812) manufactured by Mitsui Chemical Co., Ltd. was mixed and used as a toner sample.

200 g of this magnetic toner was set in a developing machine in a commercial copying machine (Canon NP-500, trade name of Canon Inc.), and a test chart was copied on plain paper to obtain a clear image.

Toner fixability, charge stability and blocking resistance,
The anti-offset property was extremely good, and when a running test was performed while adding toner, an image equivalent to the initial image was obtained over 50,000 sheets, and no toner bridging phenomenon was observed.

Comparative Example 2 Using the same raw material as in Example 2, a one-component magnetic toner was obtained by a conventional method. That is, 1 part of the charge control agent, 53 parts of styrene-acrylic resin, 2 parts of carbon black, 3 parts of low molecular weight polypropylene and 40 parts of magnetic powder are premixed with a Henschel mixer, and melted and kneaded with a biaxial extruder.
It was left to cool, coarsely pulverized by a cutting mill, then finely pulverized by an I-type jet mill pulverizer, and then fine particles of 5 μ or less and particles of 25 μ or more were removed by an Alpine classifier to obtain a toner having an average particle diameter of 13 μ. Further, colloidal silica was mixed in the same manner as in Example 2 to obtain a toner sample.

Using this toner, the same test as in Example 2 was carried out, and as a result, the occurrence of background smear was observed more frequently than the toner of the present invention. Further, the toner particles retain an excessive electric charge due to the magnetic powder exposed on the toner surface, resulting in wavy unevenness on the magnetic sleeve and uneven solid image. Furthermore, the image density decreased after printing on about 10,000 sheets, and a bridging phenomenon was observed in the hopper.

Example 3 Instead of the styrene-acrylic resin in Example 1,
The toner obtained in the same manner except that the polyester resin (KTR-2500, manufactured by Kao Corporation) was used showed the same good suitability.

(Effects of the Invention) The electrophotographic toner according to the present invention is a smooth, non-angular particle in which only the charge control agent is present on the surface of the resin, has a surface that is not easily broken, and has a relatively small particle size. Because they are aligned, they have excellent fluidity and charge stability, and show good characteristics even during long-term running tests.

Claims (1)

[Claims] 1. A thermoplastic resin particle (A) having an average particle size of 5 to 15 μm, which contains magnetic powder, wax and pigment, and an average particle size of 2 μm.
The following thermoplastic resin fine particles (B) and fine particles of the charge control agent are mixed by applying a mechanical strain force under the condition that the average particle diameter is in the range of 5 to 20 μm, and the resin fine particles (B) and the charge control agent are mixed. Insulating magnetic toner obtained by coating the surface of resin particles (A) with the fine particles.