JPS6012556A - Toner for developing electrostatic charge image - Google Patents

Abstract

PURPOSE:To obtain an excellent transfer characteristic by limiting the content of ultrafine magnetic powder. CONSTITUTION:Ultrafine magnetic powder is powder consisting of magnetic particles having <=0.1mum number average grain size and is incorporated into a toner at <=20wt% thereof. The ultrafine magnetic powder has a large coloring power and the amt. to be incorporated of <=20wt% is enough in an empirical point of view and the amt. of >=5wt% is more preferable in terms of magnetic force and coloration. Any material which exhibits magnetism or is magnetizable is usable for the ultrafine magnetic powder, for example, ultrafine powders of metals including iron, manganese, nickel, cobalt, chromium, etc., alloys including iron-cobalt, iron-nickel, etc. and various ferrites are usable.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a toner for developing electrostatic images in electrophotography, electrostatic recording, electrostatic printing, etc., and particularly relates to a magnetic toner. No. 2.297.69
Although many methods are known, as described in Japanese Patent Publication No. 1, Japanese Patent Publication No. 42-23910, and Japanese Patent Publication No. 43-24748, etc., they generally utilize photoconductive substances and perform various methods. forming an electrical latent image on the polyphotoreceptor by means;
The latent image is then developed using toner, and if necessary, the toner image is transferred to a transfer material such as paper, and then fixed by heat, pressure, solvent vapor, or the like to obtain a copy.

Various developing methods are also known in which an electrostatic latent image is visualized using toner. For example, the magnetic brush method described in U.S. Pat. No. 2,874,063;
A large number of development methods are known, such as the cascade development method described in No. 2,221,776, the fur brush development method, and the liquid development method. Among these developing methods, a magnetic brush method, a cascade method, a liquid developing method, and the like, 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 have been proposed that use a one-component developer that provides good toner quality, but among these, many methods that use a developer that consists of magnetic toner particles are superior.

U.S. Pat. No. 3,909,258 specification 1'' proposes a method of developing using magnetic toner that is electrically conductive. A conductive magnetic developer is supported on the electrostatic image and developed by bringing it into contact with the electrostatic image.At this time, a conductive path is formed between the recording medium surface and the sleeve surface by toner particles in the developing section, and this An electric charge is applied to the toner particles (from the sleeve via the conductive path), and the toner particles adhere to the image area due to the Coulomb force between them and the image area of the electrostatic image and are developed.

This developing method using conductive magnetic toner is an excellent method that avoids the problems associated with conventional two-component developing methods, but on the other hand, because the toner is conductive, the developed image can be transferred from the recording medium to the final product such as plain paper. It has the disadvantage that it is difficult to electrostatically transfer it to a force supporting member.

As a developing method using a high-resistance magnetic toner that can be electrostatically transferred, JP-A-52-94140 discloses a developing method that utilizes dielectric polarization of toner particles.

However, such a method has disadvantages such as a slow development speed and an inability to obtain a developed image with sufficient density, making it difficult in practice.

Other developing methods using high-resistance magnetic toner include
A method is known in which toner particles are frictionally charged by friction between toner particles, friction between toner particles and a sleeve, etc., and the toner particles are brought into contact with an electrostatic image holding member and developed. However, these methods have drawbacks such as the small number of times the toner particles come into contact with the friction member, which tends to result in insufficient triboelectric charging, and the Coulomb force between the charged toner particles and the sleeve increases, making them apt to aggregate on the sleeve. However, in Japanese Patent Application Laid-open No. 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.

According to this method, by applying an extremely thin layer of magnetic toner on the sleeve, the chances of contact between the sleeve and the toner are increased, and sufficient frictional electrification is possible.The toner is supported by magnetic force, and the magnet and toner By moving the toner particles relative to each other, the agglomeration of the toner particles is eliminated and sufficient friction is created with the sleeve.The toner is supported by magnetic force and is developed by facing the electrostatic image, thereby eliminating ground force blur. By preventing this, excellent images can be obtained. However, in the insulating toner used in this developing method, a considerable amount of fine powder magnetic material is mixed and dispersed in the toner, and a part of the magnetic material is exposed on the surface of the toner particles, so The degree of dispersion of the body into the resin is
This greatly affects the fluidity or triboelectric charging properties of the magnetic toner, and may affect fluctuations and deterioration of the toner's development characteristics, durability, etc. Furthermore, the degree of dispersion of the magnetic material is associated with, for example, compositional non-uniformity of toner particles after pulverization in the toner manufacturing process, and greatly influences toner performance. Furthermore, when the fluidity of the toner is reduced, such as when the environment in which it is used is highly humid, toner agglomeration occurs, and the toner aggregation cannot be sufficiently broken down by magnetic force, resulting in frictional electrification of the toner. Insufficient (5) There is a risk of deterioration of image quality and image density.

As described above, the above-mentioned improved development method has unstable factors related to the characteristics of the magnetic material and may be easily influenced by environmental conditions.

On the other hand, conventional magnetic powders for magnetic toner include ferromagnetic elements and alloys and compounds containing them, such as magnetite,
Compounds containing iron, cobalt, nickel, manganese, zinc, etc., such as magnetite and ferrite, are known. The magnetic properties required for such magnetic powder include, for example, (1) a maximum magnetizing force σ of about 40 amu711 or more;
m,'(2) Holding force HC of about 150 to 5000e
1 (3) 102~107 Ω - Empty specific electrical resistivity, (4
) It is known for its practically sufficient blackness, (5) good moisture resistance, and (6) good mixability with resins. Usually, magnetite, which is called iron black and is widely used as a pigment, is often used as a magnetic toner, and there are many examples described in various patent documents. Magnetite generally satisfies the above requirements, but for magnetic toners it is difficult to mix with resin, toner cohesiveness, triboelectricity, durability, high humidity stability,
In terms of fixability (6), a thorough examination of its properties is required.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a magnetic toner that has good charging properties regardless of humidity, exhibits stable charging properties during use, and is capable of producing clear, fog-free images.

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

A further object of the present invention is to provide a magnetic toner that has excellent fluidity and does not cause aggregation.

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

That is, the present invention can be achieved by containing the magnetic ultrafine powder in an amount of 20 wt % or less of the toner.

The magnetic ultrafine powder mentioned here has a number average particle size of O31μ.
It is a powder consisting of magnetic particles with a size of less than m.

The number average particle size described here is measured for particles that are considered to be 100 or more primary particles in a circundum as seen in a transmission electron microscope photograph taken at a magnification of 50,000 to 10,000 times.

In conventional magnetic toner containing magnetic powder, if the magnetic force of the magnetic powder is not large (e.g. coercive force less than 5000e), the coloring power is not large. had to be contained in an amount of approximately 30 wt% or more. As a result, a large proportion of the magnetic material is exposed, which lowers the resistance.The charging characteristics of the magnetic material surface also affect the toner charging properties, and it is necessary to control the transfer characteristics, chargeability, and humidity characteristics. Control: It was difficult to control the chargeability during durability.

In order to facilitate and improve these controls, the inventors of the present invention investigated various types of magnetic materials, and as a result, the inventors of the present invention have found that they can be applied to toner using materials with significantly greater magnetic force than conventional materials. We have found that this can be achieved by including much lower amounts.

When it comes to magnetic powders that have a strong magnetic force, it is known that they contain compounds such as strontium and cobalt, but these have a large particle size and have weak coloring power, so if only a small amount of these is contained, the magnetic force is sufficient. Even so, the coloring strength becomes significantly worse. In this respect, magnetic ultrafine powder has a large coloring power, and experimentally it is sufficient to use 20wt% or less.From the relationship between magnetic force and coloring, 5wt% or more is preferable.・The number average particle size of magnetic ultrafine powder is 0.5wt% or less. If it is larger than 1 μm, the coloring power is weak, and therefore, if a large amount is included in the toner, the magnetic force cannot be adjusted.

The magnetic ultrafine powder used in the present invention may be any material that exhibits magnetism or can be magnetized, such as iron, manganese, nickel, cobalt, chromium-1-metal (D metal, iron/cobalt, iron/nickel, etc.). It is an ultrafine powder of alloys of , various types of ferrite, etc. Therefore, ultrafine powders of conventionally known materials can be used.

Various methods for producing magnetic ultrafine powder are known, including evaporation in gas, freeze-drying, plasma evaporation, hydrogen arc heating, oil surface evaporation, gas reduction, and amalgam methods. Among these, the evaporation method in gas, which is currently the new mainstream, will be explained. Metals at low pressure (0.1 to several 10
0 Torr) inert gas, e.g.
This is a method of obtaining i-type ultrafine particles by heating and evaporating in Ar (9), but ultrafine particles with various particle sizes can be obtained depending on the manufacturing conditions, and chemical methods have relatively clean surfaces. It is characterized by the fact that it can be obtained. As an industrial manufacturing device, a method is used in which a target metal or the like is heated and melted under low pressure by high-frequency heating, evaporated, and ultrafine particles attached to a wall surface are recovered. The particle size of ultrafine particles depends on atmospheric pressure, inert gas species, metal melt concentration, equipment shape,
affected by size.

Other methods of heating are being considered, such as lasers, electron beams, arc discharges, and plasma jets.

The characteristics of the magnetic ultrafine powder obtained by these methods include extremely large surface area, large magnetic force, large degree of blackness (coloring power), and high electrical resistance. Furthermore, the magnetic ultrafine powder may be used after surface treatment, such as titanium treatment, silane treatment, or grafting.

Accordingly, in the present invention, the toner contains 20 wt % or less of magnetic ultrafine powder. Also, it is necessary to contain approximately (■0) 5Wt or more.

Moon as a binder resin? Homopolymers of styrene and its substituted products, such as listyrene, poly-p-chlorostyrene, polyvinyltoluene, styrene-p-chlorostyrene copolymer, and styrene-vinyltoluene copolymer, and copolymers thereof; styrene-methyl acrylate copolymers Polymer, styrene/acrylic ethyl copolymer, styrene-acrylic acid n
- Copolymers of styrene and acrylic esters such as butyl copolymers; styrene-methyl methacrylate copolymers,
Copolymers of styrene and methacrylic esters such as styrene-ethyl methacrylate copolymer and styrene-n-butyl methacrylate copolymer; multi-element copolymers of styrene and acrylic esters and methacrylic esters; other styrene- Acrylonitrile copolymer, styrene vinyl methyl ether copolymer, styrene butadiene copolymer, styrene vinyl methyl ketone copolymer, styrene acrylonitrile), indene copolymer, styrene-maleate ester copolymer, etc. Styrenic copolymers of styrene and other vinyl thread monomers; polymethyl methacrylate, polybutyl methacrylate, polyvinyl acetate polyester, polyamide, epoxy resin, polyvinyl butyral, polyacrylic acid phenolic resin, aliphatic or alicyclic hydrocarbon Resin, petroleum resin, chlorinated/4' rough-in, etc. can be used alone or in combination.

In addition, low molecular weight polyethylene, low molecular weight polypropylene,
Ethylene vinyl acetate copolymer, ethylene acrylate copolymer, higher fatty acid, polyamide resin, polyester resin, etc. can be used alone or in combination.

Furthermore, a charge control agent, a colorant, and a fluidity modifier may be added to the magnetic toner of the present invention as necessary, and the charge control agent and fluidity modifier are mixed with the toner (external addition). It may also be used as As the charge control agent, metal-containing dyes, nigrosine, etc. can be used.As the coloring agent, conventionally known dyes and pigments can be used.As the fluidity modifier, colloidal silica, fatty acid, etc. can be used. metal salts, etc.

Further, for the purpose of increasing the amount, fillers such as calcium carbonate and finely divided silica can be incorporated into the magnetic toner in an amount of 0.5 to 20 wt%. Furthermore, in order to prevent mutual aggregation of toner particles and improve their fluidity, a fluidity improver such as fine Teflon powder may be added, and this is for the purpose of improving mold releasability during hot roll fixing. A waxy substance such as low molecular weight polyethylene, low molecular weight polypropylene, microcrystalline wax, carnauba wax, and Sasol wax can also be added in an amount of about 15 to 5 wt% O.

In manufacturing this magnetic toner, we use a hot roll, a kneader,
After thoroughly kneading the constituent materials with a heat kneader such as an extruder, mechanical crushing and classification are performed, or after dispersing materials such as magnetic powder in a binder resin solution,
A method of producing a magnetic toner by spray drying, or a polymerization method in which a magnetic toner is obtained by mixing a specified material with a monomer to constitute a binder resin and then polymerizing the emulsified suspension. Each method can be applied.

The present invention will be specifically explained below using examples.

r13) Note that all parts in the following formulations are parts by weight.

Example 1 Magnetic ultrafine powder Fe-N1 particle size approximately 300XHc 1300
0e (20 parts by weight of F15150 emu/9, the particle size is taken from a 50,000x photograph taken with a transmission electron microscope, - Measured on particles considered to be particulates, randomly measured about 100 particles, average particle size It was about 300!

Styrene-butyl acrylate copolymer (monomer ratio 75
/25, weight average molecular weight Mw = 200,000) 100 parts by weight, 4 parts by weight of low molecular weight polypropylene (Viscol 300P; manufactured by Sanyo Chemical Co., Ltd.), and 4 parts by weight of a negative charge control agent (Gentron S-31 manufactured by Orient Chemical Industry Co., Ltd.) were milled using a roll mill. Melt and knead, cool and extract, coarsely grind with a turmill, 2uL
The following shall apply. Next, after finely pulverizing with an air pulverizing jet mill, classification is performed with a zigzag classifier to obtain particles with a particle size of 3 to 20.
Obtain μ magnetic toner.

To the obtained toner, hydrophobic silica R-972 (Nippon Aerosil!) was added as a fluidity imparting agent (14) and subjected to development. That is, Canon NP using a CDS/resin layer as a photoreceptor. A copying test was conducted under normal copying conditions by placing the above magnetic toner in the developing device of a -400REi copying machine. However, the distance between the developing sleeve and the photoreceptor was 25
0 μ development bias DC component 1004 superimposed AC bias 10
The conditions were 00 Hz x 1300 V, -.

As a result, we conducted continuous durability tests in an environment of high temperature and high humidity (35°C, 85%), but when printing 100,000 images continuously, changes in image density were detected by the reflection densitometer, and the original was 1.1 5 mm
The black circle of φ was 1.05 to 1.15, and it was clear and had no fog. In conventional toners using magnetic powder, a similar change in image density is 1.0 to 1.2. This indicates that the toner of the present invention exhibits stable chargeability. In addition, when calculating the transfer rate for 100,000 sheets durability, it is approximately 90 wt%,
It was shown that most of the toner was transferred, and this can be said to be much better than that of ordinary magnetic toner, which is around 80 wt%.

However, this toner had good fluidity, and the fixing temperature was about 10° C. lower than that of a conventional toner containing magnetic powder.

As described above, the toner of the present invention is superior to conventional toners in terms of resource saving and energy saving.

Examples 2-3, Comparative Examples 1-2 As shown in Table 1, magnetic toner was prepared in the same manner as in Example 1, except that the type of magnetic ultrafine powder was changed (same manufacturing method, different characteristics). conducted a test. The second result is
Shown in the table.

Table 1 Table 2 *Evaluation 1. Especially good, 2. Good, 3 Minoru Kawakami good, 4.
Bad, 5. Particularly bad (evaluation is based on intuition, but standard 5)
The particle size of the toner (compared to the graded sample)
This is a value measured using a counter type n type with an aperture of 100μ calibrated using styrene standard beads.

Example 4 Fe-Ni ultrafine powder particle size approximately 300 x 20 parts, low molecular weight polyethylene (Mitsui Petrochemical High Wax 200 P) 1
00 parts, a negative charge control agent (Puntron S-31 manufactured by Orient Chemical Industry Co., Ltd.) was melt-kneaded in a 4ftl roll mill,
After cooling, it is coarsely pulverized with a cutter mill to obtain particles of 211 TIL or less. Next, it is finely pulverized with an air pulverizing jet (17) mill, and then classified with a zigzag classifier to obtain particles with a particle size of 3~
A 20μ magnetic toner was obtained.

Hydrophobic silica was added as a fluidity imparting agent to the obtained toner, and the toner was subjected to development. Commercially available Canon NP-
The above magnetic toner was placed in a 120 copying machine, and a test was conducted in the same manner as in Example 1. In this case, as a comparative example, B
L-200 (manufactured by Titanium Industries) magnetic powder (particle size 0.3μ
It was prepared in the same manner as in Example 4 using 60 parts of m). The results are shown in Table 3.

Table 3 (18)

Claims (1)

[Scope of Claims] 1. A toner for developing electrostatic images, characterized in that it contains 20 vtrt% or less of magnetic ultrafine powder. 2. The toner for developing electrostatic images according to claim 1, wherein the magnetic ultrafine particles have a number average particle diameter of 0.1 μm or less.