JPH0527108B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a toner used for developing an electrical latent image or a magnetic latent image in electrophotography or electrostatic printing, and particularly to a toner for electrophotography with significantly improved image quality. Regarding magnetic toner.

Traditionally, electrophotography has been subject to U.S. patents.
As described in Japanese Patent Publication No. 2297691, Japanese Patent Publication No. 42-23910 (U.S. Patent No. 3666363), Japanese Patent Publication No. 43-24748 (U.S. Patent No. 4071361), etc., on the photoconductive layer. By uniformly charging the document and exposing it to a light image corresponding to the document, the charge in the exposed portion is eliminated and a latent image is formed. Development is carried out by depositing a fine powder electrostatic substance, so-called toner, on the obtained electrostatic latent image. The toner is attracted to the electrostatic latent image depending on the amount of charge on the photoconductive layer, forming a toner image with shading. This toner image is transferred to a support surface such as paper or cloth as necessary, and permanently fixed on the support surface by heating, pressure, or the like. Alternatively, if it is desired to omit the toner image transfer step, the toner image can be fixed to the photoconductor layer. In addition to the fixing method described above, it is also possible to use other means such as solvent treatment and overcoating treatment.

Many developing methods are known for this electrophotography, and up until now, there has been a developing method that uses carrier particles as a two-component toner, as disclosed in the US patent.
The cascade development method described in US Pat. No. 2,618,552 and the magnetic brush method described in US Pat. No. 2,874,063 have been widely used.

However, in recent years, a developing method using a one-component magnetic toner that does not use carrier particles has come into use. The developing method using this one-component magnetic toner does not require a toner temperature detection and control mechanism, compared to that using the two-component toner described above. The developing device can be made simple and compact. It has many advantages such as less edge effect and good reproduction of solid black areas.

Generally, two-component toner is charged by frictional contact between carrier particles and toner as they are stirred in a developing device. The toner and carrier have opposite polarities, and the polarity of the toner is selected to develop the electrostatic latent image on the photoconductive layer.

The charging of the toner in two-component toner has a considerably high charge amount because there are many contact opportunities such as frictional mixing with carrier particles, frictional contact with the developing sleeve, and friction with the side wall of the developing device. be able to.

On the other hand, since the dominant factor in frictional charging in one-component magnetic toner is the contact between the toner, the developing sleeve, and the magnetic toner, the charging is considerably lower than that in two-component toner. Therefore, adverse effects tend to occur in terms of electrophotographic characteristics.

The magnetic toner on the developing sleeve is held based on the magnetic force between the toner and a magnet placed inside the sleeve. At this time, the magnetic toner near the surface of the developing sleeve can still have a high charge amount because it can directly rub against the sleeve, but as the contact with the sleeve decreases, it also separates from the developing sleeve and the toner The upper magnetic toner layer, which is charged only by mutual friction, can only obtain a weaker charge amount. When such magnetic toner that retains only a weak amount of charge is used as a developing toner, image quality deterioration such as image disturbance is likely to occur. This is because magnetic toner, which has only a weak charge, is only attached to the photoconductive layer and the transfer support with weak adhesion during the development and transfer process due to electrostatic attraction. In other words, magnetic toner is developed by electrostatic interaction between the charge held by the magnetic toner and a photoconductive layer charged with the opposite polarity. The smaller the electric charge of the magnetic toner, the weaker the attractive force will be generated and the weaker the magnetic toner will be attached to the photoconductive layer. The same applies to the transfer process; in the case of corona transfer, the smaller the charge on the toner is for a given corona transfer voltage, the more
Weakly adheres to the transfer support. In this case, when the magnetic toner on the surface of the support with a weak adhesive force enters the fixing roller, it is affected by the impact and the rupture of air in the space formed by the fixing roller, the magnetic toner, and the support. As a result, the toner scatters and the edges of the image, especially the edges of the text area, are left trailing (hereinafter referred to as trailing), which occurs. Such image disturbances are more likely to occur with single-component magnetic toners, which can hold only a weak charge, than with two-component toners, and selenium photoconductors, which cannot achieve a very high corona transfer voltage, are more likely to be affected by cadmium sulfide photoconductors than with two-component toners. Image disturbance is more likely to occur with single-component magnetic toner. Furthermore, from an environmental standpoint, high temperature and high humidity conditions are poor conditions, as it is difficult to charge the battery, and even if it is charged, the charge tends to leak.

An object of the present invention is to provide a magnetic toner for electrophotography in which the inherently weak charging properties of the magnetic toner are significantly improved compared to two-component toners.

Another objective is to significantly improve transfer efficiency and
The present invention provides a magnetic toner for electrophotography with high image density.

Another object is to provide a magnetic toner with improved image quality (tailing).

Another object is to provide a long-life magnetic toner with improved continuous durability.

It has been found that the object of the present invention can be achieved by adding inorganic fine powder made of a fired product of ZnO and Al ₂ O ₃ to a magnetic toner.

That is, the present invention uses magnetic toner and ZnO90.0.
99.8% by weight and an inorganic fine powder formed from a fired product obtained by firing a mixture whose main components are 0.01 to 10.0% by weight of Al ₂ O ₃ . Regarding.

The inorganic fine powder applied to the present invention is weakly positively charged when the charge amount is measured by a two-component mesh method. Of course, the magnetic toner is highly negatively charged in the above charge amount measurement. When such a weakly positively charged inorganic fine powder is added and mixed with magnetic toner and placed on a developing sleeve, the frictional electrification of the magnetic toner is caused not only by the conventional developing sleeve and toner but also by the above inorganic fine powder. Friction seems to act as an important factor. That is, the fine powder maintains a function as a friction carrier for the magnetic toner, and there is an opportunity for frictional contact between the magnetic toner and the inorganic fine powder to maintain a sufficient amount of charge on the developing sleeve. Secured. Therefore, magnetic toner can have a high amount of negative charge, and development and transfer are performed in this state, so it is thought that the above-mentioned image disturbance (tailing) does not occur.

At this time, what should be taken into consideration in particular is that any combination of a weakly positively charged substance on the one hand and a negatively charged magnetic toner on the other hand does not mean that image quality will not be disturbed. do not have. This is because whether or not the toner can have a high amount of negative charge in combination with a magnetic toner depends on the frictional charge with the added substance.
This is because the charge amount measurement using the two-component mesh method is only a rough guide.

In fact, in the process of completing the present invention, the present inventors discovered a substance that has a weak positive charge using the two-component mesh method, but does not have any effect on image quality disturbance.

However, the inorganic fine powder provided in the present invention is
ZnO90.0~99.8wt%, _{Al2O30.01 ~} 10.0wt%
The main component is A more preferable ingredient is
ZnO is 95 to _99.8 % by weight, and _Al2O3 is 0.01 to 5.00% by weight. More preferable components include ZnO97~
99.8% by weight, _{Al2O3 0.01-2.00} % by weight.

The above inorganic fine powder is 0.2
It is desirable to add and contain up to 5.0% by weight, preferably 0.5 to 4.0% by weight, more preferably 1.0 to 4.5% by weight.

The particle size is 20μ or less, preferably 0.2~
It is 1.5μ, more preferably 0.3 to 1.2μ.

All known binder resins can be used in the present invention, including monopolymers of styrene and its substituted products such as polystyrene, poly p-chlorostyrene, and polyvinyltoluene; styrene-p-chlorostyrene; Donor polymer, styrene-propylene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer,
Styrene-alpha chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer combination, styrene-isoprene copolymer, styrene-acrylonitrile-indene copolymer,
Styrenic copolymers such as styrene-maleic acid copolymers and styrene-maleic acid ester copolymers; polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate,
polyethylene, polypropylene, polyester,
Polyurethane, epoxy resin, polyvinyl butyral, polyamide, polyacrylic acid resin, rosin, modified rosin, terpene resin, phenolic resin, aliphatic or alicyclic hydrocarbon resin, aromatic petroleum resin, chlorinated paraffin, paraffin, wax, etc. can be used alone or in combination.

When this binder resin contains a magnetic substance and is made into particles, the particle size is 5 to 5, which is the general toner particle size.
20μ is preferred.

In addition, the magnetic substances contained in the binder resin include ferromagnetic elements, alloys containing these, and compounds such as magnetite, hematite, and ferrite, as well as alloys and compounds of iron, cobalt, nickel, and manganese, and other ferromagnetic alloys. etc. can be used as appropriate.

The particle size is 100~800mμ, preferably 300~
500 mμ, 30-70% by weight relative to polymer particles
The content is preferably 40 to 65% by weight, more preferably 50 to 60% by weight.

In addition, the present invention will not be hindered in any way even if a charge control agent, a flow modifier, a colorant, a lubricant, etc. are added and contained in the present magnetic toner as necessary.

In producing the magnetic toner of the present invention, the constituent materials are well kneaded using a heat kneader such as a heat roll, kneader, or extruder, and then mechanically pulverized.
Method of obtaining by classification.

Furthermore, as a method for adding the inorganic fine powder to the magnetic toner, a known mixer can be used, for example,
Rotating container type mixers such as a V-type mixer, turbula mixer, etc., and fixed container type mixers such as ribbon type, screw type, rotary blade type, and others can be used as appropriate.

Alternatively, a material such as magnetic powder is dispersed in a binder resin solution and then spray-dried. Alternatively, a predetermined material is mixed with the monomers that constitute the binder resin, and then this emulsified suspension is polymerized. Each method can be applied, such as a polymerization method to produce a magnetic toner.

In the measurement of the amount of charge in the present invention, the test substance is
Mix in a ratio of 1:10 with iron powder carrier having a particle size of 200/300 mesh. The mixture is 0.5~
Precisely weigh 1.5g and suction it with a pressure of 25cmH ₂ O on a metal 100 mesh screen connected to an electrometer, then separate and calculate the amount of charge per unit weight from the amount of toner sucked and its charge amount. .

The present invention will be explained in more detail with reference to Examples below.

Production of inorganic fine powder of the present invention For 100 mol of zinc oxide, aluminum oxide,
Dry mix 0.001-3.0 mol until homogeneous.
This mixture is heated to 900 to 1100℃ in the presence of carbon.
Bake for 0.5 to 2.0 hours.

Next, this fired product is cooled to room temperature in a non-oxidizing atmosphere to obtain the desired inorganic fine powder.

The quantitative ratio of ZnO and Al ₂ O ₃ in the inorganic fine powder obtained at this time was measured using a fluorescent X-ray device (manufactured by Rigaku Denki) and a diffraction X-ray device (manufactured by Rigaku Denki).

Example 1 Styrene-acrylic resin 100 parts Fe ₃ O ₄ 70 parts Charge control agent 2 parts The above toner materials were kneaded and pulverized, and then classified to obtain negatively charged one-component magnetic toner particles with a particle size of 5 to 30 μm. Manufactured. The toner particles are mixed with 2.0% by weight of an inorganic fine powder made of a fired product mainly composed of 99.0% by weight of ZnO and 0.35% by weight of Al ₂ O ₃ produced as described above, and also containing moisture and trace metals. A magnetic toner of the present invention was obtained. This inorganic fine powder was found to be positive when measured by the two-component mesh method.
It showed 0.85μc/g.

Images were produced using the magnetic toner of the present invention in the following manner in a high temperature, high humidity environment (35° C., 90% RH) using the apparatus shown in the figure. A positive electrostatic latent image is formed on the well-known CDS photoreceptor, and the sleeve is fixed with a rotating magnet with a sleeve surface magnetic flux density of 700 Gauss and a distance between the ear cutting blade and the sleeve surface of 0.2 mm as shown in the figure (the peripheral speed of the sleeve is similar to that of the drum). A developing device (same as that of , but with the rotation direction reversed) was set at a distance of 0.25 mm between the photosensitive drum surface and the sleeve surface, and a 1.2 k
Develop with the magnetic toner by applying an alternating current of Hz 1.2 kv and a direct current bias of +150 V, and then transfer the powder image while irradiating the transfer paper with a direct current corona of +5.9 kV from the back side to obtain a copy image. Ta. The remaining developer on the photosensitive drum is removed using a magnetic brush cleaner, and the fixing is done using a commercially available plain paper copier (product name: NP).
-200J, manufactured by Canon). The initial image obtained was clear and good with no trailing, and after 10,000 copies were made continuously, the image after 10,000 copies had a desirable image density and was comparable to the initial image. It had good image quality.

Example 2 Using the same magnetic toner as in Example 1, 3.5% by weight of an inorganic fine powder consisting of a fired product whose main components are 98.2% by weight of ZnO and 1.5% by weight of Al ₂ O ₃
The toner of the present invention was obtained by addition and mixing.

When this toner was imaged using a selenium photoreceptor under high temperature and high humidity in the same manner as in Example 1, the image was clear and free of image disturbance.

Example 3 100 parts of polyester resin, 80 parts of γ-Fe ₂ O ₃ , and 4 parts of charge control agent were kneaded, pulverized, and classified to obtain a one-component magnetic toner having a particle size of 3 to 25 μm. To this, ZnO99.8% by weight,
The toner of the present invention was obtained by containing 0.8% by weight of an inorganic fine powder made of a fired product containing 0.04% by weight of Al ₂ O ₃ as a main component.

When this toner was printed using a commercially available NP-400RE copying machine (manufactured by Canon), the image was good and had no disturbance or trailing.

Comparative Example 1 Magnetic toner similar to Example 1 and 2% by weight of zinc oxide fine powder containing 99.999% by weight ZnO as its component.
When the toner obtained by mixing was printed in the same manner as in Example 1 under high temperature and high humidity (35°C, 90% RH), an image with severe trailing in the line area was obtained, which seems to be impractical for practical use. It became.

Comparative Example 2 A magnetic toner was prepared by mixing magnetic toner particles prepared in the same manner as in Example 1, 1.98% by weight of zinc oxide fine powder containing 99.999% by weight of ZnO, and 0.02% by weight of Al ₂ O ₃ fine powder. However, when image formation was carried out under high temperature and high humidity conditions in the same manner as in Example 1, trailing occurred in the line portions, and no improvement effect was achieved by mixing the Al ₂ O ₃ fine powder. .

[Brief explanation of the drawing]

The figure is a sectional view of an embodiment of a developing process to which the toner of the present invention can be applied. 1...Photosensitive drum, 2...Nonmagnetic cylinder, 3...
Magnetroll, 4...Hopper, 5...Doctor blade, 6...Magnetic color toner.

Claims (1)

[Scope of Claims] 1. An inorganic fine powder formed of a fired product obtained by firing a mixture of magnetic toner particles and a mixture whose main components are 90.0 to 99.8% by weight of ZnO _{and 0.01} to 10.0% by weight of Al ₂ O 3 A magnetic toner for electrophotography, comprising: 2. Add inorganic fine powder to magnetic toner particles at a ratio of 0.2 to
The magnetic toner for electrophotography according to claim 1, which contains the additive in an amount of 5.0% by weight. 3 The magnetic toner particles have a particle size of 30 to 90 with respect to the binder resin.
Claim 1 containing % by weight of magnetic material
Magnetic toner for electrophotography as described in .