JPH0576628B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field to Which the Invention Pertains] The present invention relates to a two-component developer comprising a carrier and a toner for developing electrostatic latent images formed in electrophotography. [Description of Prior Art] Conventionally, as an electrophotographic method, U.S. Patent No. 2297691
Specification of No. 42-23910 and Special Publication No. 1973
Various methods are described in, for example, Japanese Patent No. 24748. All of these methods create an electrostatic charge image, that is, an electrostatic latent image, by applying a uniform charge onto a photoreceptor using a photoconductive substance and irradiating a light image corresponding to the original onto the photoreceptor. The latent image is then developed using colored fine powder called toner to become a visible image, and if necessary, after being transferred to a transfer material such as paper,
Copies are obtained by permanent fixing using heat, pressure, solvent vapor, etc. This electrostatic latent image development process is a process in which charged toner particles are attracted by electrostatic attraction and adhered to the surface of the photoreceptor, thereby visualizing the electrostatic latent image. A method for developing such an electrostatic latent image using a toner is to use a so-called two-component developer consisting of toner and a toner carrier called a carrier, and by stirring and rubbing the toner and carrier, they are mutually separated. There is a method of charging toner with different polarities and using this charged toner to visualize the electrostatic latent image described above having a polarity opposite to that of the toner. Conventionally, the toner used is one in which a colorant such as carbon black is dispersed in a binder such as polystyrene, which is finely pulverized to about 1 to 30 μm.On the other hand, the carrier is usually iron powder or Glass beads etc. are used. Conventionally, in a developing method using such a two-component developer, when a large number of copies are made, toner fogging occurs after 10,000 to 30,000 copies are made, and image density often decreases. The reason for this is that when making multiple copies, the toner that adheres firmly to the carrier surface due to the Coulomb force between the carrier and toner in the initial state is not carried over to the latent image, and tens of thousands of copies are made. In some cases, toner components with relatively low molecular weights are fused to the carrier surface due to heat such as mechanical pressure or mechanical heat or impact, and the carrier to which the toner is fused is free from frictional electrification with the toner. This results in fog in the image and low image density. Therefore, in two-component developers, it is important to maintain a balance between the releasability between the carrier and the toner and the transportability of the toner by the carrier. [Object of the Invention] An object of the present invention is to provide a two-component developer for electrophotography which has improved these problems. That is, an object of the present invention is to provide an electrophotographic developer that can stably charge a toner, have sufficient toner transportability, and have good developability based thereon. A further object of the present invention is to provide an electrophotographic developer that does not suffer from deterioration such as toner adhesion even after long-term use. A further object of the present invention is to provide an electrophotographic developer that has stable developability even under special environments such as high temperature and high humidity, low temperature and low humidity. [Structure of the Invention] The above objects are achieved by adjusting the carrier in the two-component developer into a specific shape and by subjecting the carrier to a specific surface treatment. That is, in the present invention, when the carrier is assumed to be a rectangular parallelepiped circumscribing the carrier, one side of each rectangular parallelepiped is a>b>c or a>b=
When a, b, and c are defined so that c or a=b>c, the average of b/a is 0.4 to 1.0, and c/
It has a shape such that the average of a is 0.05 to 0.5,
and a compound A whose surface of the carrier is located in the opposite direction to the toner with respect to the surface of the toner carrier in the triboelectric charging series, and a compound B which is located between the compound A and the toner on the triboelectric charging series. It is characterized by being processed by. As mentioned above, in a two-component developer, it is important to maintain a balance between the releasability between the carrier and the toner and the transportability of the toner by the carrier. We have discovered that this can be achieved by adjusting the surface treatment as described above. The present invention will be specifically explained below. Examples of carriers used in the present invention include magnetic particles such as surface oxidized or unoxidized metals such as iron, nickel, cobalt, manganese, chromium, rare earths, and alloys or oxides thereof, and non-magnetic particles such as glass beads. Particles can be used and there are no particular restrictions on the method of manufacturing them. In the present invention, the shape of the carrier is defined as follows. First, a photograph of the carrier is taken using an SEM (scanning electron microscope) at an appropriate magnification. At this time, for the same particle, take several screens in which the electron beam hits the sample stage on which the carrier is perpendicular, and several screens in which it hits as horizontally as possible, and circumscribe one particle from these. Draw a rectangular parallelepiped. Furthermore, one side of each of this rectangular parallelepiped is a>b>c or a
>b=c or a=b>c so that a,
Set b and c, and measure a, b, and c. The above operation is performed randomly for at least 20 particles, and the average of b/a and c/a is determined. In the present invention, a carrier having a shape with an average of b/a of 0.4 to 1.0 and an average of c/a of 0.05 to 0.5 is used, preferably an average of b/a of 0.5 to 1.0, Average c/a is 0.1~
It falls within the range of 0.4. Next, the surface treatment of the carrier used in the present invention is carried out as follows. That is, the treatment method using Compound A and Compound B used in the present invention includes a method in which these compounds are mixed with a carrier in a powder state, and then melted or softened with heat to be attached to the surface of the carrier particles, or a method in which Compound A or B is applied to the surface of the carrier particles. Any method known in the art for carrier particles can be applied, such as a method of dissolving or dispersing it in a solvent and applying it to the carrier particles so that it adheres to the surface of the carrier particles. The processing amount of compounds A and B used in the present invention is 0.1 to 30% in total based on the carrier of the present invention.
% by weight, preferably 0.5 to 20% by weight, and the ratio of compound A to compound B is 10:90 to 99:
1, preferably 20:80 to 90:10, particularly preferably
30:70 to 80:20. Next, a method for measuring the amount of triboelectric charge of the toner and carrier surface treatment material in the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory diagram of an apparatus for measuring the amount of triboelectric charge. First, a material for surface treatment of the carrier is adjusted using a Coulter Counter (manufactured by Coulter Inc.) so that it can be considered to have approximately the same particle size as the toner. Next, a metal measuring container 2 with a conductive screen 1 of 400 mesh (the size can be changed as appropriate so that carrier particles do not pass through) on the bottom is used to measure the amount of triboelectric charge. and amorphous iron powder with a particle size between 200 and 300 mesh (the surface is untreated and has virtually no triboelectrification on its own like the toner carrier) in a weight ratio of about 1:9. Add 4g and cover with metal lid 3. Weigh the entire weight of the measurement container 2 at this time,
Let W ₁ (g). Next, in the suction device 4 (at least the part in contact with the measurement container 2 is an insulator), suction is drawn from the suction port 5, the air volume control valve 6 is adjusted, and the vacuum gauge 7
The pressure of is 70mmHg. This condition is sufficient (about 1
2 minutes) to suction off the toner or carrier surface treatment material. The potential of the electrometer 8 at this time is assumed to be V (volt). Further, the capacitance of the capacitor 9 used here is assumed to be C (μF). Next, weigh the entire measurement container after suction, _and
(g). At this time, the amount of triboelectric charge T (μC/g)
is calculated as follows. T (μC/g) = C×V/W ₁ −W ₂ However, the measurement conditions are 23°C and 60% RH. Compound A and compound B used in the present invention
varies depending on the toner material and the material of the carrier which is the toner carrier, but for example, when a metal such as aluminum or stainless steel is used as the carrier and the toner is positively charged, compound A may be polytetrafluorocarbon. Ethylene, monochlorotrifluoroethylene polymer, polyvinylidene fluoride, silicone resin, polyester resin, metal complex of ditertiary butylsalicylic acid, etc., and compound B includes styrene resin, acrylic resin, polyamide, silicone resin, polyvinyl butyral, etc. and if the toner is negatively charged, the compound A may be nigrosine,
Aminoacrylate resins, acrylic resins, basic dyes and lakes thereof, etc. are used, and as compound B, it is appropriate to use styrene resins, silicone resins, polyester resins, etc., but the invention is not necessarily limited to these. . In the present invention, compound A has the role of imparting sufficient charge to the toner and strongly drawing the toner around the carrier, and compound B has the role of improving the releasability of the toner and carrier during development. It is thought that it is in charge. Next, the toner used in the present invention will be explained. Examples of the binder resin of the toner used in the present invention include monopolymers of styrene and its substituted products such as polystyrene, poly p-chlorostyrene, and polyvinyltoluene; styrene-p-chlorostyrene copolymers, and styrene-propylene copolymers. 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-acrylic-aminoacrylic copolymer, styrene-aminoacrylic copolymer, styrene-α-chlor Methyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinylethyl ether copolymer,
Styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-acrylonitrile-indene copolymer, styrene-maleic acid copolymer, styrene-maleic acid ester copolymer, etc. Styrenic copolymers; polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyester, polyurethane, polyamide, epoxy resin, polyvinyl butyral, 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. Any suitable pigment or dye can be used as a colorant in the toner. For example, carbon black, iron black, phthalocyanine blue, ultramarine blue,
There are known dyes and pigments such as quinacridone and benzidine yellow. In addition, as a charge control agent, amino compounds, quaternary ammonium compounds, organic dyes, especially basic dyes and their salts, benzyldimethyl-hexadecyl ammonium chloride, decyl-trimethylammonium chloride, nigrosine base, nigrosine hydrochloride, safranin γ and Crystal violet, metal-containing dyes, salicylic acid metal-containing compounds, etc. may be added. Furthermore, magnetic powder may be added. The toner structure described above may be used in a developer produced by a commonly used mixing-pulverization method, or may be used as a wall material or a core material, or both, of a microcapsule developer. [Example] Hereinafter, the present invention will be explained in more detail according to Examples 1 to 3 and Comparative Examples 1 to 6, but the present invention is not limited thereto. In each of the Examples and Comparative Examples, iron powder with a particle size of 200 to 300 mesh was used as a carrier, and development was carried out using a so-called two-component magnetic brush method. The amount of triboelectric charge of the toner and carrier surface treatment substance used in each example and comparative example was measured,
A triboelectrification series shown in Table 1 was prepared in advance. Also,
Table 2 shows the shapes of the carriers used in each Example and Comparative Example. The combination of the toner and carrier surface treatment substances used and the associated image characteristics are as follows:
Table 3 is a summary of each example and comparative example. For the surface treatment of the carrier, the necessary amount of each treatment substance is dispersed in 1 kg of xylene, 1 kg of the carrier is immersed in it, and after removing the xylene,
℃ to complete the surface treatment. Example 1 Styrene-butyl acrylate (80:20) copolymer 100 parts by weight Nigrosine 2 parts by weight Carbon black 5 parts by weight A mixture of the above materials was melt-kneaded, pulverized, and classified to obtain a toner with an average particle size of 8 μm. . 10 parts by weight of this toner and 100 parts by weight of a carrier having the composition shown in Table 3 were mixed to form a developer, and the mixture was charged into a Canon NP-5000 copying machine to form a magnetic brush. Furthermore, by improving the development to form a negative electrostatic charge image with -500V in the dark area and 0V in the bright area, a good image with high image density was obtained, and 100,000 copies were made while sequentially replenishing toner. Even after doing this, there was no change in the image. In addition, similarly good results were obtained under special environments of high temperature, high humidity, and low temperature and low humidity. Comparative Example 1 The same procedure as in Example 1 was carried out except that untreated amorphous iron powder was used as the carrier. When 5,000 copies were made, the toner became difficult to separate from the carrier and the image density was significantly reduced. Comparative Example 2 The same procedure as in Example 1 was carried out except that the surface treatment substance of the carrier was changed to one that did not satisfy the conditions of the present invention. However, the carrier had a weak toner conveying force and was unable to transfer to the toner. Since the amount of triboelectric charge applied was not sufficient, only images with low image density and a lot of fog could be obtained. Comparative Example 3 All examples were the same as in Example 1, except that the surface treatment material of the carrier was only one that did not satisfy the conditions of the present invention.
When the same procedure as above was carried out, only the same results as in Comparative Example 2 were obtained. Comparative Example 4 All examples were the same as in Example 1 except that the carrier surface treatment material was only one that did not satisfy the conditions of the present invention.
When the same procedure as above was carried out, only the same results as in Comparative Example 1 were obtained. Example 2 Polyester resin 100 parts by weight Rhodamine lake pigment 5 parts by weight A mixture of the above materials was melt-kneaded, pulverized, and classified to obtain a toner having an average particle size of 9 μm. When 5 parts by weight of this toner and 100 parts by weight of the processing carrier shown in Table 3 were mixed to form a developer, the mixture was put into a Canon NP-5000 copying machine and 50,000 copies were made. The camera continued to produce high-quality images. Moreover, the environmental characteristics were also good. Comparative Example 5 The same procedure as in Example 2 was carried out except that the shape of the carrier was changed so that it did not satisfy the conditions of the present invention. However, since the carrier carried only a small amount of toner, only images with low image density were obtained. I couldn't help it. Comparative Example 6 The same procedure as in Example 2 was carried out except that the shape of the carrier was changed so that it did not satisfy the conditions of the present invention. However, the carrier shape was so distorted that uniform development could not be achieved. Example 3 The same procedure as in Example 2 was carried out except that the surface treatment substance of the carrier was changed to, and the same good results as in Example 2 were obtained.

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[Summary of effects of the invention]

In the present invention, as described above, the shape of the carrier is defined and the surface is treated to have a specific amount of triboelectric charge, thereby ensuring stable charge application to the toner and toner transportability. The above-mentioned stable charge imparting properties do not change even after long-term use or under special environments, so it has good developability, and there is no deterioration such as toner adhesion even after long-term use. - Stable developability even under special environments such as low temperature and low humidity.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram of a frictional charge amount measuring device according to the present invention. 1... Conductive screen, 2... Measurement container, 3
...Metal lid, 4...Suction device, 5...Suction port, 6...Air volume control valve, 7...Vacuum gauge, 8...Electrometer, 9...Condenser.

Claims (1)

[Claims] 1. In an electrophotographic developer containing a carrier and a toner, when the carrier is assumed to be a rectangular parallelepiped circumscribing the carrier, one side of each rectangular parallelepiped is a>b>c, a>b=c, or a. When a, b, and c are defined so that = b > c, the carrier has a shape in which the average of b/a is 0.4 to 1.0 and the average of c/a is 0.05 to 0.5, and the surface of the carrier is treated with a compound A located in a direction opposite to the toner with respect to the surface of the toner carrier in the triboelectrification series, and a compound B located between the compound A and the toner in the triboelectrification series. A two-component developer for electrophotography.