JPH0293544A - Magnetic toner and production thereof - Google Patents

Abstract

PURPOSE:To provide the magnetic toner which allows easy electrostatic charge, exhibits stable developability and exhibits excellent transferability by coating the surface of core particles with a conductive material and insulating material having specific electric conductivity and specifying the weight average particle sizes thereof. CONSTITUTION:The surface of the core particles constituted of a binder consisting of resin components, magnetic powder and additives is coated with the conductive material having <=1mum weight average particle size and >=10<-8>(OMEGA.cm)<-1> electric conductivity and is further coated with the insulating material having 0.1 to 1.0mum weight average particle size and <=10<-8>(OMEGA.cm)<-1> electric conductivity in such a manner that the conductive material is not exposed to at least the outermost layer. The magnetic toner having 5 to 50mum weight average grain size is thus obtd. The electrostatic transfer is enabled by properly selecting the material compsn. and production conditions and the electric conductivity characteristic to stabilize the conduction development is obtd. The stable development is executed in this way and further, the electrostatic transfer to plain paper is possible as the toner exhibits a stable insulating characteristic in a static state.

Description

DETAILED DESCRIPTION OF THE INVENTION (Prior Art) The present invention relates to a magnetic toner for an electrostatographic process, and in particular to toner particles that behave as conductive toner during development and can be transferred to plain paper, and a method for producing the same. be.

(Prior Art) (2) A two-component image is a typical developing method in the electrostatic photographic process.

In this method, the conductivity is Q-1! (Ω・cm)-
'By mixing the following insulating toner and carrier particles approximately 5 to 2.00 times the diameter of the toner, the toner is triboelectrified, and the latent image area is selectively charged according to the electric field strength of the developing device. It develops toner particles.

In this two-component development method, it is necessary to keep the concentration of carrier and toner constant, and to triboelectrically charge the toner particles, so that the charge amount distribution is sharp and stable. is complicated, and furthermore, stability of toner and carrier is required.

■, Also, the conductivity of the toner is 10-3 to 10-6 (Ω・
A one-component conductive toner development system has been proposed in which toner particles are charged by electrostatic induction in the development field using conductive particles of approximately C11)-'.

This development method has the advantage that, in principle, a clear image can be obtained compared to a two-component development method, such as a simpler developing device, uniform toner charging, and less edge effect.

Direct recording type facsimile machines and electrostatic plotters have been put into practical use using this conductive toner.

However, in the indirect transfer type electrophotographic process, since the toner is conductive, there is a problem in that charge leakage occurs when electrostatically transferring the toner to paper, resulting in significant image disturbance.

(2) A one-component insulating development system in which the conductivity of the toner is 10-6 (Ω·CI) or less has been put into practical use.

This method allows electrostatic transfer and solves the above problems, but during development, the toner is insulative, and in order to charge the toner particles by frictional charging with a toner support member, etc., friction is applied to the developing device side. A mechanism that makes charging uniform is required.

(2) Some of the following proposals have been made to improve the contradictory conductivity characteristics of toner.

(1) A developing method using a toner that exhibits conductivity in an agitated state (US Pat. No. 3,639.245).

That is, when the toner is in a static state, the electric field strength is 10 kv/c.
The present invention proposes a developing method in which insulating particles with a conductivity of 10 -6 (Ω·cm) or less and which behave electrically conductively by being stirred on a developing sleeve.

The toner used in this method has a structure in which a conductive substance is exposed on the surface, and stable electrostatic transfer cannot be expected.

(ii) Toner exhibiting conductivity in a magnetic field (JP-A-57-1
89145).

That is, the magnetic powder in the toner is magnetized to match the direction of the magnetic dipole with the direction of conductivity, thereby imparting conductivity to the toner particles when a magnetic brush is formed, that is, during development.

This method is impractical due to high toner production costs.

(in) Toner with electrolytic dependence of conductivity (JP-A-60
-125849).

That is, the toner is conductive in a high electric field and insulative in a low electric field by utilizing the difference between the electric field strength during development and the electric field strength during transfer. This toner basically has two layers coated on the surface of the core particle, and the electrical resistance of each layer is determined.

The conductivity of a toner having this specific composition and structure exhibits a high electric field dependence, but the conductivity changes largely with respect to the developing electric field strength which changes over a wide range, which is not preferable because the development becomes unstable.

In addition, toner that exhibits conductivity in a high electric field shows conductivity only after being transported to the development site, and by the time it reaches the development site, the toner exhibits insulating properties. After being loaded into the machine, the toner is stirred inside the machine and charged by friction between toner particles. Since there is no high electric field applied to the surface of the developing sleeve other than where it faces the electrostatic latent image carrier, the insulating toners come into contact with each other and frictional charging is unavoidable.At this time, the toner becomes fully charged. There are some that are negatively charged and others that are negatively charged.

This conductive development method is characterized by accurately developing the information in the latent image by selectively charging uncharged toner to one polarity using the latent image on the electrostatic latent image carrier by electrostatic induction. .

From this point of view, it is not preferable for the toner to be charged across both poles in advance, and a good image cannot be expected if the conductivity of the toner is simply dependent on the electric field.

(Problems to be Solved by the Invention) The problems to be solved by the present invention are to provide a developer that is easy to charge, exhibits stable developability, and exhibits excellent transferability in a developing system using a component magnetic brush. However, until now, there has not been anything that has been fully satisfactory.

(Means for solving the problem) General magnetic toner mainly consists of a binder consisting of a resin component, magnetic powder, an electrical resistance adjusting agent, a coloring agent, a charge adjusting agent,
Although it is composed of lubricants, etc., it is not completely ohmic over a wide field strength range, and shows a gradual increase in conductivity as the field strength increases.To make this field dependence noticeable, As conceptually shown in FIG.
It has been conventionally known that a structure in which layer 3 is covered and further covered with a second layer 4 made of an insulating material is effective.

As mentioned above, the present inventor has made extensive studies on the structure of toner that exhibits stable developability and excellent transferability, and as a result, as shown in FIG.
It is possible to have a structure that does not contain a conductive substance such as carbon Bragg, that is, the second layer 4 is made of an insulating substance, and at the same time has a structure in which the conductive substance coated on the first layer 3 is not exposed on the surface of the outermost layer. , was found to be extremely effective, leading to the present invention.

That is, the toner of the present invention has a core particle having a weight average particle diameter of 1 μm or less and an electrical conductivity of 10−·(Ω·Cm) on the surface of the core particle composed of a binder made of a resin component, magnetic powder, and additives.
-' or more conductive material is coated, the weight average particle size is 0.1 to 1.0 om, and the conductivity is 10-6 (Ω・el).
1) A magnetic toner having a weight average particle size of 5 to 50 μm, characterized by being coated with the following insulating material and having a structure in which no conductive material is exposed in at least the outermost layer.

This toner is basically a one-component magnetic toner, but by appropriately selecting the material composition and manufacturing conditions, it can satisfy the electrical conductivity characteristics described below, and can be made into a more preferable embodiment. becomes.

■ Measure the conductivity of the toner with the toner sandwiched between flat plates, and calculate the conductivity (ρ8) with an electric field strength of 5,000 V/cm.
．． S) is less than or equal to IQ-II(Ω-C11)-'.

■ With the magnetic brush formed and the magnetic brush rotating, conductivity is measured by contacting a conductor facing the magnetic brush, and the electric field strength is 1o, oOoV, /cm ~ 30+0
At 00 V/C11, the conductivity is 10-■ (Ω・CI)
−' or more.

■(ρD1..)/(ρ.,.) <10.

In addition, ρ8. ．． I, ρ. , respectively, are the conductivities according to specific measurement methods described below, and the subscript X is the electric field strength in kv/cm.

Schematically, the conductivity characteristics are shown in FIG.

The line a is the conductivity characteristic due to the flat plate (■), and the line b is the conductivity characteristic due to the rotating magnetic brush (■).

The electrical properties (1) are necessary conditions for electrostatic transfer to be possible, and (2) to (4) are conditions for stably realizing conductive development.

Next, one aspect of the present invention will be specifically described.

The core particles include a binder, magnetic powder, and if necessary,
Composed of various additives. The particle size of the core particles can be calculated theoretically depending on the particle size of the toner to be finally obtained, but particles having a weight average particle size of about 3 to 48 μm are used.

As a binder, monomers such as styrenes, (meth)acrylic acid esters 1-6 (here, the letters in parentheses may or may not be read), and nitriles can be used. The obtained (co)polymer resin, polyester resin, epoxy resin, urethane resin, phenol resin, etc. can be used.

As the magnetic powder, single metals such as iron, nickel, cobalt, and manganese, alloys, or oxides of these metals can be used, and those having a weight average particle size of about 0.1 to 1 μm are preferable.

In addition to the above, the core particles may optionally contain conventionally known additives such as electrical resistance regulators, colorants, charge regulators, and lubricants. Waxes may also be added as additives.

The magnetic powder should be blended in an amount of 30 to 70% by weight based on the total weight of the core particles. This ratio is called the magnetic powder ratio.
The magnetic powder ratio has a great influence on the development performance of the toner in terms of magnetic force since the toner is held by the magnet in the development field, and it also has a bearing on the electric field dependence of the toner's conductivity, which in turn affects the electrostatic force. This also affects development performance.

If the magnetic powder ratio is less than 30% by weight, toner scattering around the developing device is likely to occur, and toner scattering on the white background area of the image (so-called "fogging") will increase significantly, which is undesirable.
When the magnetic powder ratio exceeds 70% by weight, the developing density decreases,
Furthermore, the fixing performance deteriorates, which is also undesirable.

There are no particular restrictions on the method for producing the core particles, but some preferred examples include heating and melting the above-mentioned binder, magnetic powder, and, if necessary, various additives in a kneader or the like. Knead. After cooling this, the kneaded material is processed using a rotary pulverizer (
For example, coarsely pulverize to a diameter of about 1 mm or less using a free pulverizer manufactured by Nara Kikai Co., Ltd.).

Furthermore, this coarsely pulverized and kneaded product is processed by a jet mill etc. for 3 to 4 hours.
Finely pulverized to about 8 μm and classified using a wind classifier to obtain the desired particle size distribution.
A toner with a diameter of about 20 μm is preferable from the viewpoint of image resolution because it is easy to crush and classify.

Further, as the core particles, magnetic particles described in Japanese Patent Application No. 132778/1988 can also be used. That is, polymer particles obtained by conventionally known suspension polymerization, classified particles if necessary, or polymers obtained by the so-called two-stage swelling method disclosed in Japanese Patent Publication No. 57-24369. Particles can also be obtained by magnetizing polymer particles obtained by the dispersion polymerization method disclosed in US Pat. No. 4,524,199.

In order to make the electrical conductivity of the toner significantly dependent on the electric field, first, a conductive substance is fixed to the surface of the core particle.

The conductive substance must have a weight average particle diameter of 1 μm or less and a conductivity of 10 −@(Ω·1) −1 or more. Examples of these substances include conductive carbon black, nickel powder, copper powder, etc., but conductive carbon black is most preferred for ordinary black toners.

The particle size ratio of the core particle to the conductive substance is preferably set to 10/1 or more, more preferably 20/1 or more.

It is preferable to use 99 to 70 parts by weight and 1 to 30 parts by weight of the core particles and the conductive substance, respectively.The conductivity of the powder is measured with the conductive substance fixed, and the conductivity is 10. -'' to 10-'(Ω・ell)-' The mixing ratio of both and the fixing operation conditions are selected.

Next, the fixing method will be specifically explained.

First, a core particle and a conductive substance are weighed to have a desired conductive substance content, and they are mixed to electrostatically adhere the conductive substance to the surface of the core particle.

A dry mechanical mixing method can then preferably be used to substantially fix the conductive material. Specific examples of these include rotary granulators, powder mixers (tumble mixers, V-type mixers), impact type surface treatment equipment 11F (for example, Nara Kikai Hybridizer), and grinding type surface treatment equipment ( For example, a high-speed rotary powder mixer (for example, Henschel mixer manufactured by Mitsui Miike Kakoki), etc. can be mentioned.

In order to achieve more complete adhesion, it is preferable to apply large impact energy to the particle surface, and from this point of view, an impact type powder surface modification device (for example, a hybridizer manufactured by Nara Kikai Co., Ltd.) is a preferable example. can be mentioned.

To describe the preferred operating conditions in more detail, the electrostatic adhesion operation has a blade tip speed of 1 to 10 m/s and a processing time of 2 to 3 m/s.
Substantial fixation, which is carried out in about 0 minutes, is preferably carried out by putting the mixture into a hyperdizer or the like, at a blade tip speed of 100 m/s or more, and for a processing time of about 3 to 20 minutes.

There are no particular restrictions on the temperature conditions for fixation, but depending on the content of the conductive substance, good results may be obtained by heating the core particle to a temperature above the glass transition point. When using core particles with a glass transition point of 50 to 60° C. at 30%, fixing is promoted by processing at a macroscopic temperature of the fixing device that is 5 to 10° C. higher than the glass transition point.

Although the principle behind the adhesion of conductive substances to the particle surface is not fully understood, the conductive substance is electrostatically attached to the surface of the core particle by relatively gentle mixing, and then by relatively high mechanical Thermal energy is applied to the contact area between the core particle and the conductive material, causing an instantaneous temperature rise.
It is presumed that in some cases, the temperature rises to exceed the melting point and it becomes solid.

When the force applied to the particles and the processing time are increased, extremely small primary particles such as carbon black become embedded in the core particle resin and the conductivity decreases.

This is because the moment the conductive substance is fixed into the core particle, the temperature locally rises, and the nearby resin melts or deforms elastically, creating a hole corresponding to the size of the conductive substance. This is thought to be because the particles return to their original state to close the holes as they cool. Furthermore, the electrical conductivity changes depending on the glass transition point of the core particle and the processing temperature.

From the point of view of making it easier to fix the second layer (described later) (it is easier to fix the core particle surface with a resin component), the conductive substance is completely embedded in the core particle and the above conductivity is It is better to achieve this.

Therefore, at the same time as selecting the mixing ratio of core particles/conductive material, it is necessary to give large enough energy to the core particles and conductive material to make them stick, and the processing time, rotation speed, and temperature must be adjusted appropriately. You need to choose.

After fixing the conductive substance, the surface has a conductivity of 1.
0-6(Ω・C■)-1 or less, and the weight average particle size is 0
．． 1-1. 0 μm insulating material mentioned above,
Fix it using a method.

These insulating materials can be obtained from one or more monomers selected from styrenes, (meth)acrylic esters, nitriles, vinyl acetate, vinyl chloride, and alkylenes such as ethylene and propylene. be (joint)
Polymers, as well as polyester resins, phenolic resins, higher fatty acids, higher fatty acid metal salts, rosin derivatives,
Resins similar to those used as binders for core particles such as polyolefins, waxes, epoxy-modified phenolic resins, and polyurethane, as well as titanium oxide, barium titanate,
Examples include inorganic materials such as zinc oxide.

Assuming an actual development site, a magnetic brush is formed, and when the conductivity (ρ., 8) is measured by contacting a conductor facing the magnetic brush while the magnetic brush is rotating, the conductivity is Inorganic materials are preferred to reduce changes.

In order to make the conductivity have a remarkable electric field dependence, it is preferable that the surface insulating layer be thin, but if the surface of the insulating layer is unevenly fixed and the underlying conductive material is exposed widely on the surface, When measuring the conductivity of toner by applying a high voltage, leakage may occur in the toner, and there is a risk that an unstable phenomenon may occur even when an image is actually output.

For this purpose, the second layer should be formed in such a way that the ratio of the amount of insulating particles that should be completely covered with one layer, based on the projected area of the insulating particles to be fixed to the second layer, to the surface area of the particles to which the conductive substance is fixed is determined. Calculate, determine the mixing ratio of the insulating particles based on the mixing ratio, and fix the insulating particles.

As a condition for a thin and uniform insulating layer, the particle diameter of the insulating layer is 0.
．． It is preferable to fix it at a mixing ratio of 1 to 1.011 m and a mixing ratio of 0.2 to 2 times the theoretical mixing ratio for complete coating of one layer.

If the mixing ratio is smaller than the calculated mixing ratio for complete coverage of one layer (the above mixing ratio is 1 times or less), it is thought that the conductive material is partially exposed on the toner surface, and this is not consistent with the above explanation. contradictory.

However, when a mechanical force is applied to the toner by a surface fixing device, the conductive substance is buried in the resin of the core particles, and the resin of the core particles apparently acts as an insulating layer.

Furthermore, the insulating particles of the second layer may be plastically deformed. Therefore, even if the insulating material to be fixed to the second layer is less than the above-mentioned theoretical value, it may be completely covered.

In addition, if the material composition includes a conductive substance such as magnetic powder or carbon black as the substance to be fixed to the second layer, even if the fixing processing conditions are changed (for example, by increasing the fixing processing time or by increasing the processing temperature). ), it is difficult and undesirable to suppress the exposure of the conductive substance to the surface.

In summary, preferably,
The conductivity (ρ5..) is 10-13 (Ω・
CI)-' or less, ■, form a magnetic brush, and measure the conductivity by contacting a conductor facing the magnetic brush with the magnetic brush rotating, and the electric field strength is 10.000.
v/cm~30. ooo When V/CI, the conductivity (ρ., 1.), (ρ., 3.) is 10-'(Ω・C1
1) −' or more, and (ρ., 3・) ~ (ρ. 5
．． . ), the mixing ratio of the core particles/first layer conductive material, the mixing ratio of the core particles/second layer insulating material, and the rotation of the surface fixing device are required to produce a toner exhibiting conductivity characteristics with a change of 10 times or less. Operating conditions such as number, processing time, and temperature need to be selected.

(Explanation of measurement method) (1) Measurement of electrical conductivity (ρ1.X) using a flat plate.

Measurement is performed using a measuring device as shown in FIG. 3 and a commercially available electrometer.

The aluminum main electrode 5 and the aluminum guard electrode 6 are set to a positive potential, and the aluminum sub-electrode 7 on the opposite side is set to a negative potential, toner is sandwiched between the electrodes and a current flows between the main electrode 5 and the sub-electrode 7. The electrical resistance of the toner is determined and the electrical conductivity is calculated.

The reproducibility is determined by the way the toner is filled, so place a little more toner on the sub-electrode 7, place a smooth metal plate on the surface of the Teflon case 8 and move it, and then move the toner between the sub-electrode 7 and the Teflon case 8. The space on the formed rectangular parallelepiped is filled with toner in a free state (in an uncompressed state).

It is preferable to determine a predetermined sample amount based on the apparent specific gravity of the toner with respect to the volume of the space.

The electrode dimensions used in the measurement are as shown in Figure 3. If the main electrode is 32 mm square and the electrode spacing is 1 mm, 100 times the measured resistance value corresponds to the volume resistance expressed in Ω・1, and If it is 100 mm square and 1 mm, it will be 1,000 times larger, which is easy to understand.

In order to eliminate the influence of the ends, the electrode dimensions may be of any size as long as the distance between the main electrode 5 and the guard electrode 6 is 5 mm or more, and the width of the guard electrode 6 is 10 mm or more.

The entire measuring device is placed in a grounded shield box for measurements.

(2) Toner conductivity measurement (ρD, buy) while rotating the magnetic brush.

Figure 4 shows the measuring device.

An aluminum drum 11 with a diameter of 30 mm and a length of 250 mm and an aluminum sleeve 12 with a diameter of 16 mm are opposed to each other with an interval of 300 μm, and the drum 11 is rotated at 5 CI/s and the sleeve 12 is rotated at 71/s in opposite directions. .

A six-pole fixed magnet 13 is provided inside the sleeve 12, and the maximum magnetic flux density on the surface of the sleeve 12 is approximately 750 Gauss.

An aluminum spike regulating plate 14 of 200 μm is attached to the sleeve 12.
Arrange at intervals of m. The toner to be measured is placed on the sleeve 12 to form an l component magnetic brush. The height of the panicle is
600 to 900 μm in the part facing the aluminum drum 11
Considering the distance between the drum 11 and the sleeve 12, the toner is definitely in contact with the surface of the drum 11.

An electrometer 15 is placed between the sleeve 12 and the drum 11.
The electrical resistance of the toner is measured while the sleeve 12 and drum 11 are rotated at the above speed. The contact area of the drum part (2 mm x 250 mm) and the distance between the drum and the sleeve (0.3 mm) are used as the reference area and height when converting into conductivity.

Regarding the two conductivity measurement methods (1) and (2), we investigated whether the measured conductivity can be treated on the same scale based on the filling state of the toner to be measured and the difference in reference area and height. The electrical conductivity measured by two measurement methods was compared using several types of commercially available insulating toners with low conductivity. Its (ρ.

, , )/(ρ8.

(Operations and Effects of the Invention) The magnetic toner of the present invention has stable conductivity over a wide range of high electric field strength in a development method using an l-component magnetic brush. Stable development can be performed, and furthermore, since it exhibits stable insulation properties in a static state, it can be electrostatically transferred to plain paper.

Example 1 Resin and magnetic powder having the following composition were kneaded in a kneader of 130"
When the mixture was kneaded for 10 minutes at C and cooled, it was taken out and coarsely pulverized, a mixture of resin and magnetic powder with a size of about 1 mm was obtained. It was pulverized with a jet mill and classified with an air classifier to obtain core particles.

Polystyrene resin (Sanyo Chemical TB-1000)
・・・・・・48% by weight polyethylene wax (Sanyo Chemical Sunwax 131P) ・・・・・・
...2% by weight magnetic powder magnetite (Toda Kogyo type EP
T-1000) ・・・・・・・・・50% by weight
The particle size distribution of the core particles is DI6/D on a weight basis.
? It was approximately 8 μm/17 μm in m.

In addition, the electrical conductivity measured by the plate method in (1) is 10-6(
Ω・CI)-' or less.

Based on 100% by weight of this core particle, the conductive material of the first layer was Cabot's Conductive Power-Bonplak Monarch 70.
0 was electrostatically deposited at a mixing ratio of 5% by weight under operating conditions of a powder mixer blade tip peripheral speed of 4 m/s for 5 minutes.

Circumferential speed of 100m/
s, carbon black was adhered to the surface under operating conditions of 1 minute. The maximum temperature during the treatment was 52°C.

When the conductivity of the particles was measured by the flat plate method in (1) with the first layer fixed, the particles became conductive at 10-'(Ω·cm)-' or more.

In order to examine the degree of adhesion of carbon black,
A sample was placed on thick felt, a vacuum was applied from the other side using a vacuum cleaner, and the state of adhesion of carbon black was observed using an electron microscope.

Primary particles of the carbon blank were observed at magnifications of about 10,000 times to 100,000 times, but there was no difference in the dispersion state of carbon black on the surface before and after vacuum suction. By the way, the surface condition of the particles is not completely carbon black,
It is also observed that carbon black is buried in the core particle resin, and parts of the resin are exposed on the surface.

The second layer has a weight average particle size of 0.25 μm and a conductivity of 10-@
(Ω·C■)-1 zinc oxide was mixed at 20% by weight with respect to 100% by weight of particles to which carbon black was fixed, and electrostatically deposited.

The operating conditions are the same as in the case of the first layer, the blade tip speed is 4 m.
/s, and the processing time was 5 minutes.

These mixtures were similarly fixed using a hyperdizer. The operating conditions were a peripheral speed of 100 m/s for 6 minutes. The maximum temperature during treatment was 65°C.

The weight average particle size of the obtained toner was 12 μm.

When the conductivity was measured using the plate method in (1), it was found to be 2.000.
v/ell, 5+OOOV/CIJ, 10,0OO
v/cm, respectively (ρ3.鵞)<10−” (ρs,
5)=4XIQ-1% (ρ1.1゜)=1.2X
10-''(Ω·CI)-'.

In addition, when the conductivity was measured using the magnetic brush rotation method in (2), it was found to be 10.0OOV/C11, 30,000v/
(p l to) = 3X10-” (ρ
o, so) = 10-@(Ω·cm)-'.

10゜000v/cta ~30. 000 V/C
The conductivity changes approximately three times over 1B.

(1) The conductivity value of 5+000 V/ell as measured by the flatness measurement and (2) 30,0O as determined by the magnetic brush method measurement.
The ratio of OV/C11 to the conductivity value ((ρ., 3.)
/ (ρ3..S)) is (10-.)/(4X10-1
'), which is 10 times more toner.

From this, it can be said that the toner is conductive during development and insulating during transfer.

A graph of the relationship between electric field strength and conductivity, including Example 2.3 described later, is shown in Figure 5. In Figure 0, the twisted letter a indicates the flatness measurement in (1), and b indicates the magnetic brush in (2). Represents a legal measurement.

Similar to the first layer of carbon black, the degree of adhesion of zinc oxide was determined by observation before and after vacuum suction and elemental analysis using X-rays (X-ray microanalyzer). Black made sure he wasn't exposed.

Using this toner, we applied the same DC potential as the surface potential of the unexposed area of the photosensitive drum to the developing sleeve in an electrophotographic process experiment machine for image evaluation, and evaluated the appearance of the image in reversal development. A great image was obtained.

In addition, when we made the developing sleeve potential equal to the surface potential of the exposed part of the photoreceptor and further switched the applied polarity of the corona transfer device for electrostatic transfer to negative, we evaluated the appearance of images during forward development. Similarly, good images were obtained on plain paper.

From this result, it is thought that the toner of Example 1 was charged negatively and positively by the reverse and forward development methods, respectively, and that the toner was charged by electrostatic induction between the electrostatic latent image carrier and the toner in the development field. It will be done.

Example 2 A toner was prototyped using the same materials and operating conditions as in Example 1, except that barium titanate was used as the insulating material fixed to the second layer.

The first layer was fixed at a mixing ratio of carbon black of 2% by weight with respect to 100% by weight of the core particles.

The weight average particle size of barium titanate to be fixed to the second layer was 0.2 μ-, and the conductivity was 10-6 (Ω・1)-gourd. On the other hand, the mixing ratio of barium titanate is 10% by weight.
It is. The weight average particle size of the obtained toner was 12 μm. The measured conductivity values of this toner are shown in FIG.

(ρ., 1°) and (ρ1.3°) are almost constant.

Also, (ρ9,3°)/(ρ8.S) is approximately 10'.

As in Example 1, good images were obtained on plain paper in both reverse and forward development.

Example 3 A toner was prototyped using the same materials and manufacturing method as in Example 1, except that polymethyl methacrylate was used for the fixed particles of the second layer.

The weight average particle size of polymethyl methacrylate is 0.15
μm, 100% by weight of particles fixed with carbon black
In contrast, the mixing ratio of polymethyl methacrylate is 5
Weight%. The weight average particle size of the obtained toner was 12μ
It was m.

The measured conductivity values are shown in FIG.

(ρ., 3°) and (ρ., 1.) are five times larger. Also, (ρ.9..)/(ρ83.) is approximately 4.0
It is 00.

As in Example 1, good images were obtained on plain paper in both reverse and forward development.

Comparative Example 1 A toner was prototyped using the same materials and manufacturing method as in Example 2, except for the mixing ratio of the conductive substance fixed to the first layer.

The mixing ratio of the conductive substance fixed to the first layer is 1 core particle 1
00% by weight, carbon black is 5% by weight.

When measuring the electrical conductivity of this toner, a value almost the same as that of the example was obtained, but toner occasionally leaked and exhibited unstable electrical characteristics.When observed with an electron microscope, it was found that this toner was It was observed that there was insufficient coverage of the second layer of insulating material over the conductive material adhered as a layer.

When this toner was used to evaluate the appearance of images using an electrophotographic process experimental machine for image evaluation, the images were found to be defective, with black streaks occasionally appearing in the images.

Comparative Example 2 A toner was prototyped using the same materials and manufacturing method as in Example 1, except that the magnetic powder ratio of the core particles was 20% by weight and the wax was 3% by weight.

When this toner was used to form a magnetic brush using a developing device of an experimental machine for image evaluation, the toner was scattered by the rotation of the magnetic brush. In addition, the image had a lot of fog, which was not desirable.

Comparative Example 3 A toner was experimentally produced using the same materials and manufacturing method as in Example 1, except that the magnetic powder ratio of the core particles was 755% by weight and the wax content was 1% by weight.

When this toner was used to evaluate image appearance using an electrophotographic process experimental machine for image evaluation, the image density was extremely low and unfavorable.

Table 1 shows measurement data for Examples 1-3 and Comparative Examples 1-3.

The specifications of the electrophotographic process experimental machine used for image evaluation are described below.

An organic photosensitive drum was used as an electrostatic latent image carrier, and the evaluation was carried out by a reversal development method with a negative charge.

■Drum speed ・・・・・・・・・ l0CII/S ■Exposure (LED array)... 300 DPI■Surface potential of non-exposed area ・・・・-600v■Surface potential of exposed area ・・・・-120v ■Maximum magnetic flux density on the sleeve... 720 Gauss ■Development clearance...
450 μm ■ Ear standing height 600 ~
800μ Sleeve top toner speed... 38
cm/s ■Transfer... + Electrostatic transfer by corona [
Phase] Fixation...Heat roll In addition, in Table 1, the fog in the image evaluation is 1 mm on a white background? This is the number of toner particles per unit, and was measured using a microscope with a magnification of 100 times.

The resolution is 6 black lines and 6 white lines per 1 (so-called 6
The determination was made based on whether or not the line pair/mai) could be distinguished by magnification of 20 times.

Further, the transfer efficiency was calculated from the weight of the developing machine and the discharged toner box after printing about 2,000 sheets.

[Brief explanation of drawings]

FIG. 1 is a graph showing the conductivity characteristics of the magnetic toner of the present invention. FIG. 2 is a diagram schematically showing the layer structure of the magnetic toner of the present invention in percent. FIG. 3 is a diagram schematically showing a flat plate measuring device used to measure the conductivity of the magnetic toner of the present invention. FIG. 4 is a diagram conceptually showing a magnetic brush rotation type measuring device used to measure the conductivity of magnetic toner of the present invention. FIG. 5 is a graph showing the relationship between electric field strength and conductivity for an example of the magnetic toner of the present invention. l: Core particle 2: Magnetic powder 3: First layer made of conductive material 4: Second layer made of insulating material 5: Main electrode 6: Guard electrode 7: Sub-electrode 8: Teflon case 9: Teflon cover 10 : Electrometer 11 Ni-aluminum roll 12 : Aluminum sleeve 13 : 6-pole fixed magnet 14 : Ear standing regulation plate 15 : Nire chromatometer - sword 11 Figure 1 Electric field strength (V/crrL) Figure 2 Figure 3 Figure 5 Electric field strength (V/cJ

Claims (2)

[Claims] (1) The surface of the core particle, which is composed of a binder made of a resin component, magnetic powder, and additives, has a weight average particle diameter of 1 μm or less and an electrical conductivity of 10^-^6 (Ω cm)^-^. coated with one or more conductive substances, and further has a weight average particle size of 0.1 to
Electrical conductivity at 1.0μm is 10^-^6 (Ω・cm)^-^
A magnetic toner having a weight average particle size of 5 to 50 μm and having a structure in which at least one insulating material is coated and no conductive material is exposed in the outermost layer. (2) The method for producing a magnetic toner according to claim (1), wherein the surface of the core particle is sequentially coated with a conductive substance and an insulating substance in a dry process.