JP3010917B2 - Method for developing one-component insulating magnetic toner - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing method for developing an electrostatic latent image by an electrophotographic method, an electrostatic recording method or the like using an insulating magnetic one-component toner.

[0002]

2. Description of the Related Art In recent years, electrophotographic toners have been widely used not only in copiers but also in printers and facsimile machines.
The dry type is mainly used for its ease of handling. Dry toner includes two-component toner (carrier component and toner).
Toner component) and a one-component toner (toner
And no carrier component is required) . Two-component
A developing method using a toner (hereinafter , referred to as a two-component developing method) is currently the most proven and widely used and has relatively good image quality, but has the following disadvantages.

(1) In developing, the toner in the two-component toner
Since only component is consumed at all times one the density of toner components
This requires a toner component replenishing means and an adjusting mechanism to keep the toner component constant, and the machine becomes large and complicated. To triboelectric charging (2) toner component and a carrier component, the stirring of the 2-component toner must be done sufficiently and quickly, requiring a large power, a developer also large. (3) The life of the two-component toner is short due to contamination of the surface of the carrier component by the toner component . (4) Due to the problem (3) above, it is necessary to replace the toner from time to time.
Toner or toner drops due to a decrease in the triboelectric charge of the toner.
The inside of the machine is dirty and there is a need for extensive cleaning inside the machine
Due to the above problems, maintenance by specialists is indispensable. (5) The triboelectric charging property of the two-component toner is easily affected by environmental humidity, and easily causes problems such as fogging and image density reduction.

Further, a two-component developing method is applied to a large machine or a high-speed machine.
The development mechanism becomes more complicated and larger
It is extremely difficult to replace toner during maintenance.
Increase the downtime that accompanies
As a hindrance, demands for these improvements are increasing. one
Recently, copying machines, printers,
Miniaturization and personalization of kushimi etc. are rapidly progressing
Small, simple and especially
It requires no maintenance, and can be used in any
One component that provides stable images even under high temperature and high humidity
Establish one-component development method, which is a development method using toner
It is becoming more and more important.

[0005] The one-component toner containing no carrier component includes a magnetic one-component toner containing a magnetic powder in a developing device , and a non-magnetic one-component toner containing no magnetic powder.
There is a component toner. There is advantage that the non-magnetic one-component toner is capable vivid color toner of the already Various development methods have been proposed, despite the one-component developing system, constantly stable toner charge amount it is difficult to maintain image quality, also has the disadvantage that the toner and the developing device life is short.

On the other hand, magnetic one-component toners are also relatively widely used because high quality images can be obtained by a conventional magnetic brush developing method. At first, a conductive magnetic toner as disclosed in U.S. Pat. Nos. 3,639,245 and 3,909,258 was used as the magnetic one-component toner. Unlike the insulating toner, the developing using the conductive toner is performed by using the charge induced by the electric field from the electrostatic induction action, and thus has the following advantages as compared with the insulating toner.

(1) Since the electrostatic charge due to the triboelectric charge is not used, the influence of the image deterioration due to the humidity can be eliminated. (2) When selecting resins, pigments, additives, and the like, which are components of the conductive toner , it is not necessary to consider the charging polarity, so the range of selection is wide. (3) Since a uniform charge can be given to the conductive toner , an image with less background smear and excellent resolution can be obtained. (4) One-component development without difficulty becomes possible. (5) Since the frictional charging mechanism is unnecessary, the structure of the developing device is simplified, and the size can be reduced. (6) Both normal development and reverse development can be performed with the same conductive toner .

[0008] Despite the many advantages described above,
The conductive toner is applied to plain paper by a plain paper transfer method using electrostatic force, that is, a conductive or dielectric roller to which a corona discharge or bias is applied, which is widely used in a process using an insulating toner. Due to the biggest drawback that good transfer is difficult, plain paper copiers (PP
C), facsimile is impossible, and at present, it is hardly used except for those using a large-size and low-efficiency adhesive transfer method.

The reason why the transferability of the conductive toner deteriorates in the plain paper transfer system using electrostatic force is presumed to be as follows. That is, in principle, the conductive toner performs development and transfer using electrostatic induction charges generated by an electric field. For this reason, it is considered that, particularly under high humidity, the electric resistance value decreases due to the transfer paper absorbing moisture, and as a result, the injected electric charge leaks through the paper, so that an effective electric field does not work on the conductive toner and transfer is not performed. . Therefore, in order to prevent this phenomenon, electrostatic recording paper which has been subjected to insulation treatment has been used conventionally, but the paper becomes thick and expensive.

Therefore, in order to enable PPC, an attempt has been made to improve the transferability by increasing the electric resistance of the conductive toner as disclosed in, for example, Japanese Patent Application Laid-Open No. 50-92137. However, as the electric resistance of the conductive toner increases, mainly the polarization of the conductive toner due to electrostatic induction or dielectric polarization becomes insufficient, and the developability deteriorates . Especially 1
If it exceeds 0 ¹² Ωcm, it is not practical at all . Therefore,
In order to enable the magnetic one-component development method by PPC, the following measures have been considered.

(1) Developing with a conductive toner having relatively high resistance as described in, for example, JP-A-53-39752 and JP-A-53-131044, and transferring by devising transfer paper. Improve the problem. (2) Use a toner exceeding 10 ¹² Ωcm (hereinafter referred to as an insulating toner) to improve its developability. Sufficient results have not yet been obtained for the above measure (1), but some useful measures have been found in (2). Insulating toners need to be further classified by their charging mechanism.

Many documents have already been reported on the charging mechanism of the insulating magnetic one-component toner. However, they are roughly classified into a method that does not use frictional charging and a method that uses frictional charging. As a developing method utilizing triboelectric charging, for example, "BMT disclosed in JP-B-59-44627" is disclosed.
A developing method called "developing method";
Japanese Patent Application Laid-Open No. Sho 57-114163 discloses a developing method called "magnetic jumping developing method" as disclosed in Japanese Patent Application Publication No.
"FEED development method" disclosed in Japanese Unexamined Patent Publication No. These developing methods actually provide a compact, simple and maintenance-free developing device which is an advantage of the above-described one-component developing method. However, since these use frictional charging for development, the charge amount of the toner becomes insufficient particularly under high humidity, and the charge amount tends to be high under low humidity, and a stable image is always obtained regardless of the use environment. Is still not enough for that purpose. Therefore, in order to achieve the purpose of always obtaining a stable image regardless of the use environment, in order to achieve the purpose, the charging mechanism is not affected by the use environment in principle, charge injection or electrostatic induction or dielectric polarization. It is absolutely necessary to put the insulative magnetic one-component developing method using electric charges to practical use. In addition, in the developing method that does not use such triboelectric charging, in addition to the above-described advantages, it is possible to develop both positive and negative electrostatic latent images using the same toner. Benefits arise. This is because triboelectric charging is only charged to a certain polarity due to the inherent property (mainly work function) of the substance, whereas charging by electrostatic induction or dielectric polarization can change its polarity due to an external electric field. . As a result, for example, normal development and reverse development can be performed using the same photoconductor and toner, so that a copier and a laser beam printer can be used in common, and further, there are merits such as simplification of consumable types.

It is also possible to use a charge applying method other than charge injection or electrostatic induction without using triboelectric charge, which has the above-mentioned advantages. For example, US Pat. No. 3,645,770.
And Japanese Patent Application Laid-Open No. 50-117432, however, are not yet sufficient mainly in terms of stability.

As an insulative magnetic one-component developing method utilizing charge injection, there is, for example, a developing method disclosed in US Pat. No. 4,121,931. For the development mechanism of this development method, see Field, "A MODEL TO DESCRIBE ELECTROGRAPHI
C DEVELOPMENT OF RESISTIVEONE-COMPONENT TONER SYST
EMS ", IEEE / IAS Conference Records p.973, which is an excellent one-component developing method that is less susceptible to the environment because it does not use triboelectric charging for toner charging. The law still has the following problems:

(1) The toner electrically contacts a toner carrier (mainly a magnetic sleeve) having a conductive portion (electrode) in an electric field created by an electrostatic latent image on a photoreceptor. Charge is injected from the substrate and is forcibly charged. At this time, adding a power supply to the electrodes is almost a necessary requirement for enhancing the effect, but as a result, the mechanism becomes complicated. In addition, the application of a voltage for injecting a charge having a polarity opposite to that of the photoreceptor has an effect of a reverse bias at the time of development, which causes fog. Also,
According to the methods described in this publication and the literature, when actually examined, the developability greatly changes depending on the type of the photoconductor, the type of the toner, the magnetic force of the magnetic sleeve, and the like. Because of this factor, a practical one-component magnetic toner developing method cannot be obtained from this method alone.

(2) The toner particles into which electric charges have been injected from the magnetic sleeve must move quickly to the upper layer of the toner layer to develop an electrostatic image. So fast and intense physical
Disturbance is required for the toner layer, which complicates the mechanism of the developing device. Further, when the principle of development is further considered , this method can be used to solve the poor developing property of the insulating toner as described above.
It is being addressed by the increase of the toner movement speed of conveying the toner to the electrostatic image at a high speed of more than 10 cm / sec,
Conversely, the high-speed contact between the electrostatic image and the toner promotes the cleaning effect of the photoconductor by the toner magnetic brush on the magnetic sleeve, and lowers the developing efficiency. Further, since a shearing force is applied to the toner due to strong stirring as described above, problems such as accelerated deterioration of the toner also occur. As a method for solving such a problem related to the rotation of the magnetic sleeve,
For example, a method in which only the sleeve is rotated and the speed difference between the sleeve and the photosensitive member is limited to a predetermined range as disclosed in Japanese Patent Application Laid-Open No. Sho 53-1229639.
A method of setting the speed, direction, and number of magnetic poles of a sleeve and internal magnetic poles to predetermined values as disclosed in Japanese Patent Application Laid-Open No. 6-106, etc. is disclosed. Although these measures are intended to improve various problems relating to the rotation of the magnetic sleeve, when actually examined, the developability also greatly changes depending on the type of the photoreceptor, the type of the toner, and the like. Since the selection is a very large factor, it is not possible to obtain a practically stable magnetic one-component toner developing method only by this method.

On the other hand, an insulative magnetic one-component developing system utilizing an electrostatic induction effect is disclosed in, for example, JP-A-54-1346.
There is a method disclosed in Japanese Patent Publication No. 40-240. In this development method, toner having a surface in which charge-movable regions such as carbon black are mainly scattered in an insulating main region is used, and an insulating toner carrier constituting a developing unit is used. Is used to make the toner developable by the latent image charge in the image area . The developing mechanism is described in more detail below. Using magnetic toner particles in which a conductor such as carbon is dispersed, and considering two toner particles whose exposed carbon parts are in contact with each other in an electric field of a developing field, each toner particle is electrostatically induced through its contact point. Positive and negative charges are induced in the carbon part. The toner particles in a charged state that can contribute to development develop the latent image when they come into contact with the latent image. The fact that the toner charge is not due to charge injection (from the sleeve) is evident from the fact that an insulative toner is used in the developing section as the toner carrier. However, this developing method has the following problems.

Considering the easiness of electrostatic induction, it is desirable that the above-mentioned charge-transferable region has a low electric resistance such as carbon black. However, when the resistance becomes low, polarization is likely to occur, but at the same time, the charge neutralization rate when the toner particles separate again increases, and this publication does not consider this point. High developability cannot be obtained. Further, actual experiments of this type of developing method show that the image density is remarkably reduced particularly under high humidity, and it is not practical.

Thus, there has been much discussion on which item, such as triboelectric charging, charge injection, or electrostatic induction, is dominant in the various developing systems that have already been proposed as described above. The general view is that all effects exist, even if they differ in magnitude, and that no single item is effective. It is clear that even if an insulative toner is used in the developing section as the toner carrier, good charge development is possible without any charge injection from the sleeve. The toner carrier is desirably conductive from the viewpoint of reducing the moving speed of the carrier (sleeve, internal magnet) and improving the image quality.

As a method utilizing electrostatic induction (polarization), there is another method disclosed in, for example, JP-A-58-186765. This is described in Japanese Patent Application Laid-Open No. 54-13 / 1979.
Since the discussion is based only on the resistance value of the toner particles and not on the microscopic consideration as in JP-A-4640, the developability is not sufficient, and the photoconductors that can be used are limited.

Further, in JP-A-57-58162, in the case of rotating the magnetic toner carrying member and / or the magnet roll, charge control such that the surface potential of the toner layer becomes the same polarity as the electrostatic image A high-resistance magnetic one-component toner is disclosed. Among them, the added charge control agent has an effect of facilitating the charge injection by the charge injection or the electrostatic induction from the conductive toner carrier or the like, in addition to the control of the frictional charge performance, which is the intended purpose. Although there is a description suggesting the existence of, there is no description of a specific method or the like.

In order to obtain a good image by the insulative magnetic one-component development, it is very important to select not only the mechanical and electrical aspects of the developing mechanism but also the type of toner used for it. Regarding the properties of the toner, see, for example, JP-A-54-365.
In Japanese Patent Application Laid-Open No. 54-139545, there is disclosed a method in which not only the electrical resistance value of the toner but also the relative dielectric constant is taken into consideration and the developability and the transfer property are compatible by setting the value within an appropriate range. A method is disclosed in which the electrical resistance of the toner is changed within a specific range by a voltage, and the developability and the transfer rate are improved by setting the dielectric constant to a specific value.
In many other patent publications, attempts have been made to improve the above-mentioned problem by specifying the physical properties of the toner. However, in practice, even if the physical properties of the toner are the same, there are many differences in the developing property and the transfer rate, Unless the physical properties of the individual materials are selected, a practical magnetic one-component toner developing method cannot be obtained.

Further, during a long-term printing test in an actual machine, the cause is not fixed, but as a phenomenon, a change in the toner charge amount causes a large change in image density, and consequently a problem of aggregation. This phenomenon is also described in the above-mentioned Japanese Patent Application Laid-Open No. 54-134640. In this case, in order to prevent accumulation of toner particles having opposite polarity charges, it is necessary to provide a reverse polarity charge removing means. It is necessary. This phenomenon can be explained by, for example,
This cannot be prevented unless a specific toner composition is used, except that a second electric means for forcibly adding or removing charge to the toner is provided as disclosed in JP-A-6-130767. Such accumulation of the opposite polarity charge is one of the great advantages of the above-mentioned development method that does not utilize triboelectric charging.
Both positive development and reverse development and positive charge / negative charge development hinder the development with the same toner, and only the electrostatic latent image of one polarity can be developed. Therefore, it is desired that any toner can be stably developed for a long period of time by specifying a toner formulation without providing a special charge removing unit.

[0024]

From the above discussion, the inventors of the present invention have found that a development system that does not use triboelectric charging is most advantageous for the development of an insulating magnetic one-component toner. Has come to the conclusion that the problem can be solved. In addition, the development method not using triboelectric charging can also be performed in principle with the same toner for both positive development and reverse development, and both positive development and negative development. Only latent images could be developed. Therefore, as a result of intensive studies, the present inventors have found that, when the toner composition used in a specific developing device satisfies a specific requirement, the toner is charged mainly by electrostatic induction and a good electrostatic latent image is obtained. The image was found to develop.

[0025]

SUMMARY OF THE INVENTION Namely, the present invention contains at least a thermoplastic resin, magnetic powder, charge stabilizers, and coloring agents, thermoplastic resins volume resistivity 1
× 10 ¹⁴ Ωcm or more , and the charge stabilizer has a volume resistivity
1 × 10 ⁴ to 1 × 10 ¹² Ωcm , and a mixture containing at least one kind of each having a positive charge property and a negative charge property, and the magnetic powder and the colorant have a volume resistivity of 1 ×
An electrostatic latent image formed on an electrostatic image carrier is held by magnetically holding a magnetic one-component toner of 10 ⁴ to 1 × 10 ¹² Ωcm on a toner carrier having a conductive surface at least in a developing field. A method for developing an insulative magnetic one-component toner, wherein the latent image is visualized by bringing the magnetic one-component toner into contact with the toner, and charging mainly by electrostatic induction or dielectric polarization by an electric field of the electrostatic latent image. About.

The present invention will be described more specifically. In the present invention
The volume resistivity of the toner and toner composition used is measured as follows. Into a commercially available tablet molding machine for infrared absorption spectrum measurement (circle with a molding inner cross section of 20 mm), about 0.8 g of the toner previously left for 24 hours in a thermo-hygrostat at 23 ° C. and 50% RH was placed, and a hydraulic press was used. 400kg /
Pressing in cm ² produces a cylindrical pellet about 2 mm thick and both ends 20 mm in diameter. A main electrode having a diameter of 10 mm is applied in close contact with the center of both circular end faces of the pellet by applying a silver paste, and one end is grounded. Next, a guard electrode, one end of which is grounded, is provided along the outer periphery of the pellet, a DC voltage is applied to the main electrode, the current flowing between the main electrodes is directly read with an ammeter, and the volume is calculated from the current value at a stable stage. Calculate the specific resistance value.

The one-component insulating magnetic toner used in the present invention needs to have a predetermined specific volume resistance value of the composition. As a method for producing the insulating magnetic one-component toner of the present invention , a binder component containing a thermoplastic resin as a main component, a magnetic powder, a colorant, a charge stabilizer, and other components that are added as necessary are used. Extrusion kneader, 2 roll mill,
After hot-melt kneading using a kneader such as a pressure kneader, it is common to cool, solidify, finely pulverize using a pulverizer such as a jet mill, and adjust to a desired particle size distribution with an airflow classifier or the like. . In recent years, various methods for directly producing toner particles by a suspension polymerization method, an emulsion polymerization method, and the like have been proposed, and toners produced by these methods can also be used. The toner needs to have a volume-based average particle size of 5 to 15 μm. If the upper limit is exceeded, the roughness of the image becomes remarkable, and if it is smaller than the lower limit, the replenishing property due to the deterioration of the fluidity of the toner becomes remarkable in a usual developing device and developing method, which is not preferable.

The thermoplastic resin may be any of those usually used for toners, such as polystyrene, copolymers containing styrene with acrylate or methacrylate, acrylonitrile or maleate, Examples include polyacrylate, polymethacrylate, polyester, polyamide, epoxy, phenol, hydrocarbon, and petroleum resins.

Known magnetic powders such as various ferrites, magnetites and hematites can be used, and various shapes such as cubic, octahedral, spherical, and acicular can be used. In this case, the particle diameter is desirably 1 μm or less from the problems of uneven distribution of the amount of magnetic powder between toner particles and generation of free magnetic powder. In terms of magnetic properties, the saturation magnetization is not particularly limited as long as it is about 50 emu / g or more, but the coercive force is desirably 200 Oe or less mainly due to the problem of the mobility of the toner particles on the toner carrier. More preferably, it is 120 Oe or less and 40 Oe or more. There is no problem if magnetic powder is used as it is,
When used after being subjected to surface treatment with a fatty acid, a silane coupling agent, or the like, if necessary, by improving the wettability to the resin when hot melt kneading the thermoplastic resin and coating the magnetic powder itself, Exposure of the magnetic powder to the toner surface can be prevented. As a result, environmental resistance, image quality, and the like may be improved due to the effect of preventing frictional electrification between toners. Regarding the amount of magnetic powder to be added, a necessary amount is added depending on the strength of the magnetic field on the toner carrier in order to impart a magnetic force for holding the toner particles on the toner carrier. From the relation between the force and the attraction to the electrostatic latent image, the amount is preferably 20 to 60% by weight based on the toner.

As the charge stabilizer, a specific charge control agent is used among various charge control agents which have been used in various developing methods using ordinary triboelectric charging. More specifically, an excellent effect has been recognized on a substance having a predetermined volume specific resistance, which is capable of frictionally charging a thermoplastic resin in a polarity opposite to that of an electrostatic latent image on an electrostatic image carrier. The polarity of the electrostatic latent image is opposite to that of the potential when uniformly charging the surface of the photoreceptor during regular development, and the unexposed portion becomes the ground potential due to the bias voltage during reversal development. It has the same polarity as the potential when the body surface is uniformly charged.

The charge stabilizer used in the present invention includes those known per se. However, basically, the charge stabilizer is not provided with triboelectricity as in the prior art, but is added in an insulating binder component. The charge stabilizer generates charge by electrostatic induction or dielectric polarization, and has the effect of retaining the generated charge and the effect of preventing the same polarity charge as the latent image charge from accumulating in the toner during actual development running. It has an effect completely different from the conventional one. That is, triboelectric chargeability itself, such as the conventional charge control agents are secondary related to developing property of definitive to the present invention, the charge stabilizer definitive to the present invention are primarily the resistance problem. The property that the thermoplastic resin can be frictionally charged to the opposite polarity to the electrostatic latent image on the electrostatic image carrier has a correlation with the retention of the resulting charge. Unreported so far. As has already been verified in many documents, the effects of friction, charge injection, and electrostatic induction are rarely independent of each other in the development of the insulating one-component development method, and the effects of each are small at the same time. Exist. However, at least, it can be said that this toner and this developing method facilitated application of electric charge and stabilization of environment and printing durability as compared with any conventional magnetic one-component developing method.

The effect of the charge stabilizer will be described in more detail. FIG. 1 shows a conceptual diagram of a toner charging mechanism in the developing method of the present invention. The toner 3 held by the magnet 2 on the toner carrier 1 forms a magnetic brush and is in contact with the electrostatic image carrier 4. Basically, whether the surface of the toner carrier is conductive or insulative, the electrostatic latent image on the electrostatic image carrier can be developed. However, the conductive property improves the developability. Next, toner particles 3a close to the electrostatic image carrier 4 ;
Attention is now focused on 3b. The following two mechanisms are considered for the toner particles to acquire a charge that can contribute to development. One is, as shown in FIG. 1 (a), an electric field generated between the electrostatic latent image 5 and the toner particles 3b existing close to the electrostatic latent image 5, and the electrostatic latent image is dispersed by the action of the charge stabilizer dispersed in the binder resin. Electrostatic induction or dielectric polarization occurs between the toner particles contacting or approaching the image, and the toner particles 3a close to the electrostatic latent image
Have a charge of the opposite polarity to the electrostatic latent image, and are developed by Coulomb force with the electrostatic latent image. Here, an important function of the charge stabilizer is a property of retaining a charge having a polarity contributing to development and not retaining a charge having the same polarity as a latent image generated by polarization. For this reason, the same polarity charges of the toner particles 3b diffuse into the air,
It is also presumed that the toner is lost due to contact with the toner carrier or other developing device surfaces. Therefore, as another mechanism, as shown in FIG. 1 (b), it is also conceivable that a charge having the same polarity as the latent image generated by the polarization of the single particle is scattered from the toner surface and consequently acquires a charge which contributes to development. Still further, such polarization does not occur only between the two particles in the uppermost layer in the toner layer, but also occurs as shown in FIG.
It is considered that the transfer of the electric charge is transmitted to the third and lower layers from the top as shown in FIG. Actual charge transfer in a system in which pigments and the like are dispersed in an insulating binder resin as described above is based on the PIP method (Persistent Internal Polarization), Pho
tographic Science & Engineer 6 # 2 p-65〜70, '62, Ka
It can also be inferred from the electron avalanche phenomenon in llmann & Rennert and a single-layer phthalocyanine photoreceptor (see JP-A-2-302759). It is considered that charge injection from the electrostatic image carrier to the toner particles did not occur. Because, in this case, the same polarity charge as the electrostatic latent image is injected into the toner.
It is because it is.

Of course, as already mentioned, the effect of the triboelectric charging of the charge stabilizer on the release of charges of the same polarity cannot be denied. However, even if the effects on the triboelectrification are almost the same, there is a case where the above-mentioned same-polarity charge releasing effects are greatly different and the development properties are different, so it is certain that the development mechanism of FIG. 1 is dominant. It is considered that the electrostatic induction or the dielectric polarization does not occur only in the charge stabilizer but also in the contact between the exposed magnetic powders or the contact between the magnetic powder and the charge stabilizer. In addition, since the toner used in the developing method of the present invention utilizes charges induced by electrostatic induction, the electrostatic latent image of either polarity is favorably developed regardless of whether the polarity is positive or negative. However, when using only a charge stabilizer having the same polarity as the triboelectric chargeability of the electrostatic latent image,
As the image is developed as described above, charges having the same polarity as the latent image accumulate in the toner layer, so that the image density decreases.
Therefore, in order to develop an electrostatic latent image of any polarity regardless of whether it is positive polarity or negative polarity, positive development or reverse development with the same toner over a long period of time, the triboelectricity of the charge stabilizer is positive and negative. It turns out that you have to use together. Here, the frictional chargeability of the charge stabilizer is charging polarity of the charge stabilizer when using the carrier particles of ferrite or iron is not subjected to coating treatment in the normal two-component toner.

As the charge stabilizer that can contribute to such a charging mechanism, melt-kneading and dispersing with other toner raw materials , pulverizing,
It has a particle size that does not release from the toner particles obtained by classification, has a volume resistivity of 10 ⁴ to 10 ¹² Ωcm , and makes the thermoplastic resin the opposite polarity to the electrostatic latent image on the electrostatic image carrier. Those having the property of being capable of being triboelectrically charged are effective, and those which are conventionally used as charge control agents for toner utilizing triboelectric charging can also be used. Examples of such substances include nigrosine-based oil-soluble dyes, crystal violet, triphenylamine, quaternary ammonium salts, azo-based metal complex salts, varatin dyes, and metal complex salt dyes such as orazole dyes. Also, as long as the volume resistivity and the charging polarity are appropriate, various pigments, for example, various non-ferrous metal oxides, zinc white, yellow iron oxide, Hansa yellow, disazo yellow, quinoline yellow, permanent yellow,
Bengala, Lithor red, Watchang red calcium salt, Watchang red manganese salt, pyrazolone red, lake red C, lake red D, brilliant carmine 3B, navy blue, phthalocyanine blue, titanium oxide and the like can be used. From these materials, two or more types are selected and mixed depending on the suitability of the charging polarity experimentally obtained. Charging polarity here charge stabilizer is measured the same way as normal two-component toner, for toner <br/> over the definitive to the present invention is not utilizing mainly triboelectric charging, only the frictional chargeability Cannot judge suitability for development. That is, the effect on triboelectric charging and the effect on electrostatic induction are not the same depending on the type of the charge stabilizer. The amount of each of the charge stabilizers cannot be unconditionally determined because the effect varies depending on each charge stabilizer, but the total amount is desirably 10% by weight or less and 1% by weight or more. If the amount exceeds 10% by weight, the fixing property may deteriorate. If the amount is less than 1% by weight, the effect of the charge stabilizer may not be sufficiently exerted.

The coloring agent is not necessarily required since the magnetic powder is black, brown or dark blue, but pigments and dyes which are usually used can be used. Metal oxide, zinc white, yellow iron oxide,
Hansa Yellow, Disazo Yellow, Quinoline Yellow, Permanent Yellow, Bengala, Lisor Red, Watchang Red Calcium Salt, Watchang Red Manganese Salt, Pyrazolone Red, Lake Red C,
Pigments such as Lake Red D, Brilliant Carmine 3B, navy blue, phthalocyanine blue and titanium oxide, or oil-soluble dyes can be used. With respect to the amount of the colorant added, a necessary amount for imparting the desired coloring property to the toner is added, but if the amount is excessive, the free colorant particles may act as a triboelectric charging aid, From the viewpoint of, for example, soiling the carrier, the electrostatic image carrier, and the like, the content is preferably 10% by weight or less based on the toner. In addition, carbon black has been conventionally most commonly used as a black colorant in terms of price, versatility, and the like, but is determined to be inappropriate in the present invention because of its low volume resistivity.

Other necessary components include lubricants such as various waxes. Further, in order to improve the fluidity of the toner , silica or the like is dry-mixed as needed. Of toner
For the volume resistivity, the measurement method as described above is used, but the volume resistivity may change depending on the applied voltage, and is particularly remarkable in a toner in which a low resistivity material such as carbon black is dispersed. As a conventional method of applying electric charge to toner using electrostatic induction, there is a method of using a phenomenon in which the volume resistivity decreases as the applied voltage increases. However, such a characteristic is rather used in the toner used in the present invention. It is not preferable that it is unsuitable, for example, 10 ¹² Ωcm or less under an electric field of 10,000 V / cm.
The toner definitive to the present invention substantially shows a constant resistance value is measured under a low electric field of about 500~2000V / cm.

As shown in FIG. 2, for example, the toner carrier has a plurality of magnetic poles 6 therein, and a mechanism for transporting the toner layer regulated by the doctor blade 8 when the conductive sleeve 7 rotates. Is the most common. The internal magnetic pole 6 may be fixed or rotated. In the case of fixing, applying an AC electric field between the electrostatic latent image and the sleeve has an effect of improving image and developability, which is effective. The conductive sleeve is preferably electrically grounded from the viewpoint of generating an electric field in the developing field between the electrostatic latent image and leaking charges of the same polarity as the latent image on the toner. . In addition, in the case of an organic or inorganic photoreceptor, if there is a residual potential in the background due to insufficient exposure, etc., it is necessary to apply a DC bias having the same polarity as the electrostatic latent image for the purpose of preventing background contamination. is there. However, application of a DC voltage to the sleeve may cause a decrease in image density due to charge injection into the toner. Therefore, it is desirable to suppress the absolute value to about 300 V or less. However, in the case of reversal development, since the bias acts in the direction of improving the image density, there is no problem even if 300 V or more is applied. The gap between the toner carrier and the doctor blade and the distance between the toner carrier and the electrostatic image carrier are:
It is necessary to adjust the toner layer so that it contacts or comes very close to the electrostatic image carrier. The gap between the toner carrier and the doctor blade is preferably about 0.2 mm or more and about 1 mm or less. When the thickness is less than about 0.2 mm, the effect of frictional charging between the toner and the sleeve increases, and the environmental stability and running stability of the image deteriorate. The gap between the toner carrier and the doctor blade, and the gap between the toner carrier and the electrostatic image carrier can be made larger than usual, because the dimensional accuracy in mechanical design can be roughened. It is extremely advantageous for copiers and the like, and further has the advantage that the performance between machines is stabilized because fine adjustment is not required. As a method of forming an electrostatic latent image on an electrostatic image carrier, a method of forming a corona in a state where light is not applied to an electrostatic image carrier such as an inorganic photosensitive body such as a Se-based or a-silicon based body and an organic photosensitive body. It is most common to form an electrostatic latent image by exposing image information after uniformly distributing the charge by charging using discharge or the like. In addition, a method of directly recording an electrostatic latent image on an electrostatic recording paper or the like using a needle-shaped electrode, an ion flow recording, or the like may be used. Thereafter, when a toner carrier holding the toner is brought into contact with the electrostatic latent image by, for example, a magnetic force, the toner selectively adheres to the electrostatic latent image by the mechanism described above and develops the toner.

The following phenomena clearly show that the developing method of the present invention is in principle different from the conventional method using charge injection and the method utilizing mutual friction. Toner particles charged from a conductive toner carrier
The mechanism in which the toner moves to the upper layer of the toner layer due to the physical disturbance of the toner layer and develops by contacting the electrostatic latent image does not depend on the fact that the developing is performed even if the toner carrier is an insulator. It turns out there is. In addition, it is desirable that carbon black or the like be attached to the surface as a charge injection site. However, in the present invention, it is better not to substantially contain a substance of less than 10 ⁴ Ωcm. Is completely different.

Also, the mechanism utilizing frictional charging between toner particles is clearly different from the following points. (1) Assuming that the magnetic powder is charged positively and the resin is negatively charged due to mutual friction between the binder resin portion on the toner surface and the exposed magnetic powder portion, the amount of the magnetic powder is reduced by 5%.
Even if it is changed from 50% to 55%, a large change in developability does not appear. (2) The toner used in the present invention does not actively expose the magnetic powder to the surface of the toner particles . Further, even if the surface of the toner particles is completely covered with another resin by, for example, a coacervation method, the developability of the toner does not decrease. (3) Developability is not affected by the environment because triboelectric charging is not used. Regarding the developability of the electrostatic latent image, 7 ° C. 20% RH
From 30 ° C. to 85% RH, a stable and constant image quality can be obtained. As of course already mentioned, the development of the present invention
In the method , electrostatic induction or dielectric polarization is dominant, but since particles and compounds of necessary components are mixed in an insulating resin as a toner, some effects of charge injection and mutual friction are excluded. Is impossible.

[0040]

According to the present invention, the thermoplastic resin has a volume resistivity.
1 × 10 ¹⁴ Ωcm or more , and the charge stabilizer is volume resistivity
1 × 10 ⁴ to 1 × 10 ¹² Ωcm , and the charge stabilizer is a mixture containing at least one kind each having a positive charge property and a negative charge property, and the magnetic powder and the colorant have a volume resistivity of 1 ×. 10 ⁴ to 1 × 10 ¹² Ωcm , and 10 ⁴
A magnetic one-component toner substantially free of a substance of less than Ωcm , charged mainly by electrostatic induction or dielectric polarization by an electric field of an electrostatic latent image using a toner carrier having a conductive surface at least in a developing field. Is characterized in that the latent image is visualized by

The present invention has the following features because it uses an insulating magnetic one-component toner. (1) Suitable for electrostatic transfer due to insulating toner, PPC
Is possible. (2) 1 for component developing method, a developing mechanism is simplified, the current
It is easy to reduce the size of the imager . Also, maintenance is easier or unnecessary than before. Further, since the developing method of the present invention does not utilize triboelectric charging or charge injection, it has the following features. (1) There is no dependence on the operating environment (especially humidity). This greatly improves printing quality and machine reliability. (2) Even in long-term printing, the charge amount of the toner was extremely stable without using any special electric means, and the reliability of the image was greatly improved. (3) The development speed can be increased, and the development mechanism of a large machine can be simplified and maintenance-free. (4) The dimensional accuracy of the developing device may be rougher than before. (5) Developability is good even at a sleeve speed (10 cm / sec or less) lower than before. Furthermore, since the charge stabilizer is a mixture containing at least one kind of each having a positive charge property and a negative charge property, good development can be performed for a long time in both positive charge / negative charge and positive development / reverse development. It is now possible.

[0042]

EXAMPLES Production Example, Insulating Magnetic Toner Toner raw materials having the following composition were preliminarily mixed. Parts represent parts by weight. Styrene-acrylic resin (trade name: Almatex PA-201, manufactured by Mitsui Toatsu Chemicals, Inc., volume resistivity = 5 × 10 ¹⁵ Ωcm) 63.0 parts Magnetite (trade name: MG-WMK, Mitsui Kinzoku Kogyo) 35.0 parts Charge stabilizer 2.0 parts 3 kg of the above-mentioned raw material was mixed with a 20-liter mixer (trade name: trade name: 5 × 10 ⁸ Ωcm).
Henschel mixer, manufactured by Mitsui Miike Seisakusho Co., Ltd.)
The mixture was mixed at 00 rpm for 5 minutes. This was melt-kneaded by a twin-screw extruder (trade name: PCM-30, manufactured by Ikegai Iron Works Co., Ltd.), pulverized by a jet mill, and classified by an airflow classifier to obtain a volume-based average particle size of about 11 μm. And 5μ or less and 2
A toner having a particle diameter substantially not including a range of 0 μ or more
Base particles. And mainly to improve the fluidity of the toner
Therefore, 100 parts by weight of the hydrophobic silica is added to the toner base particles.
And dry-mixed to obtain a toner. Prototype example, copy test machine

A printing test of the above toner was actually performed using an experimental machine obtained by modifying a commercially available copying machine. As a copying machine, a machine using a positively charged Se (surface potential +800 V) photoreceptor as a photoreceptor and a negatively charged OPC (surface potential −600 V) are used.
V) A copying machine using a photoreceptor was used. The former is referred to as experimental machine A, and the latter as experimental machine B. The same developing device was used for each experimental machine. The structure and setting conditions of the developing device are as follows. Basic mechanism of the developing device: ・ Internal magnetic pole: 8 poles, 1000 gauss, rotating at 1000 rpm in the opposite direction to the photoreceptor ・ Conductive sleeve: 24 mmφ in diameter, rotating in the same direction as the photoreceptor at a peripheral speed of 15 cm / sec (with the photoreceptor The relative speed is 10 cm / sec or less.-Doctor blade-conductive sleeve gap: 0.3 mm-Photoconductor-conductive sleeve gap: 0.3 mm-Sleeve is electrically grounded. As the charge stabilizer, substances shown in Table 1 are suitable for the present invention. The polarity in Table 1 refers to a commercially available ferrite carrier without a surface coating treatment (trade name: F-
100, manufactured by Powder Tech Co., Ltd. (100 parts) and the polarity of the blow-off charge amount when 2 parts of the charge stabilizer are mixed with 100 parts.

[0044]

[Table 1]

(Examples 1 to 3) As charge stabilizers, the following I (Example 1) and II (Example
Example 2), III (Example 3) was selected and used in two parts to produce
Each toner was manufactured according to the example. These toners
Put 50g into the developing unit and print 50 solid black images continuously
An experiment was conducted, and the initial printing (1st sheet) and the 50th sheet of 3 × 3
The reflection density of a solid black part of a cm square was measured (reflection densitometer,
Beth RD-918). This was tested with the same toner and
B. The results are shown in Table 2. As Example 1 charge stabilizers I, nigrosine dye (Nigrosine Base EX: Orient of
2.0 parts of Gaku Kogyo Co., Ltd.) and an azo-based metal-containing dye
4. Pyrone Black TRH: Hodogaya Chemical Industry Co., Ltd.)
Mixture with 0 parts.

Example 2 Nigrosine dye (Bontron N-07: Orient Chemical Co., Ltd.) was used as the charge stabilizer II.
2.0 parts of phthalocyanine dye (Riono Co., Ltd.)
Blue SL: 5.0 parts by Toyo Ink Mfg. Co., Ltd.
Mixture. Example 3 As a charge stabilizer III, spirit black (spirit black SB:
2.0 parts of Ento Chemical Industry Co., Ltd.) and azo metal-containing dye
(Bontron S-34: manufactured by Orient Chemical Industry Co., Ltd.)
Mixture with 3.0 parts.

[0047]

[Table 2]

Since the toner of the present invention utilizes charges induced by electrostatic induction, it has been found that electrostatic latent images of either polarity, either positive polarity or negative polarity, are developed equally well. Furthermore,
Environment at 7 ° C / 20% RH, 23 ° C / 50% during printing experiment
RH, 30 ° C./85% RH and Examples 1-3
A similar printing experiment was conducted, but no deterioration in image density or image quality was observed in any environment because triboelectric charge was not used for charging.

(Comparative Examples 1 to 9 ) Printing tests were carried out in the same manner as in Examples 1 to 3, except that 2 parts of each of the various charge stabilizers shown in Table 1 were used alone. The results are shown in Table 3. Initially, electrostatic latent images of either polarity are developed in the same way, but the accumulation of charges of opposite polarity progresses according to the number of printed sheets, and as a result, it turns out that only electrostatic latent images of one polarity are possible did.

[0050]

[Table 3]

(Comparative Examples 10 to 18 ) Furthermore, various charge stabilizers as shown in Table 4 were listed as Comparative Examples. Toners were manufactured by using two of these alone in the same manner as in Comparative Examples 1 to 9, and a printing test was performed. Note that only Sample Nos. 17 and 18 had a small volume resistivity of carbon black, so that the amount was 1 part (the styrene-acrylic resin was 64.0 parts) , and the results are shown in Table 5.

[0052]

[Table 4]

[0053]

[Table 5]

[0054] Since Comparative Examples 10 to 11 and 13 to 16 high volume resistivity, the effect of frictional charging becomes larger than the effect of electrostatic induction or dielectric polarization, in the initial bipolar electrostatic latent image It was unsuitable in terms of developability and reduction in image density after 50 sheets of solid black. However, in the development with respect to the polarity of the latent image having an appropriate property, it is stable as in Comparative Examples 1 to 9 . However, the above three environmental conditions (7 ° C., 20% R
H, 23 ° C. and 50% RH, and 30 ° C. and 85% RH), the image density changed due to the humidity dependence of triboelectric charging, and was unsuitable. Therefore, it is understood that these are different from the developing method according to the present invention. Comparative Examples 17 to
In No. 18 , the electrostatic latent image of both polarities was developed in the same manner because of its low volume resistivity, but the charge retention and dissipative properties were inferior. Comparative Example 1
For No. 2 , the triboelectric chargeability was poor and the image density was insufficient for both polarities.

(Reference Example 1) The amount of magnetic powder was changed as follows, and
A prototype toner was produced. The raw materials used are the same as in Example 1.

[0056]

[Table 6] The best amount of magnetic powder was 35 to 50%. Regarding the toner samples A and B, there is no problem with respect to the developability of the electrostatic latent image, and since the magnetic force of the toner carrier is constant, it is considered that the developability is simply inappropriate in this experimental machine.

[0057] For the case (Comparative Example 19) charge stabilizer is less than 10 ⁴ [Omega] cm, shown in Table 7
The toner by changing the carbon black amount in Suyo
It was manufactured and subjected to a printing test using an experimental machine B. The carbon black used in Comparative Example 18 was used.

[0058]

[Table 7] Even when the amount of carbon black added was very small, the image density decreased in accordance with the amount . In addition, the electrostatic transferability was deteriorated, which was not suitable.

(Example 4) In the charge stabilizer I used in the example 1, the amount of the charge stabilizer was changed, and a toner was prototyped according to the production example.
Then, a printing test was performed. The results are shown in Table 8. Both were good.

[0060]

[Table 8]

Reference Example 2 The toner F used in Example 1 and Comparative Example 19 and the toner containing 0.1% of carbon in the toner used in Example 1 were similarly evaluated. As shown in Table 9
Thus, the toner L is much better than the toner F,
It has been found that if the effect of the charge stabilizer is sufficient, it can be used even if it contains a low-resistance substance in a very small amount.

[0062]

[Table 9]

[0063]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing the concept of the developing method of the present invention. (A) Enlarged view in the circle of FIG. 1 (b) Enlarged view of the charged state of toner alone particles (c) Concept of charge state in toner magnetic brush Cross section showing

[0064]

FIG. 2 is a cross-sectional view illustrating the concept of a toner carrier according to the present invention . 1. toner carrier 2. magnetic pole 3. toner particles 4. electrostatic image carrier 5. electrostatic image 6 Magnetic pole 7 Conductive sleeve 8 Doctor blade

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI G03G 15/09 101 G03G 9/08 344

Claims (1)

(57) [Claims] Claims: 1. A thermoplastic resin comprising at least a thermoplastic resin, a magnetic powder, a charge stabilizer, and, if necessary, a colorant, wherein the thermoplastic resin has a volume resistivity of 1 × 10 ¹⁴ Ωcm or more. volume is resistivity ^{1 × 10 4 ~1 × 10 12} Ωcm, and those having a positively chargeable and negatively chargeable a mixture comprising at least one or more, respectively, the magnetic powder, the colorant volume resistivity 1 × An electrostatic latent image formed on an electrostatic image carrier is held by magnetically holding a magnetic one-component toner of 10 ⁴ to 1 × 10 ¹² Ωcm on a toner carrier having a conductive surface at least in a developing field. A magnetic one-component toner, and the latent image is visualized not by triboelectric charging but mainly by electrostatic induction or dielectric polarization due to the electric field of the electrostatic latent image. Component toner development method.