JPH0314176B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a magnetic toner for developing electrostatic images used in electrophotography, electrostatic recording, magnetic recording, and the like. In the field of image forming technology, various photographic, recording, or printing methods have been known for forming an electrical latent image (electrostatic latent image) and then visualizing it using colored fine powder called toner. It is being For example, electrophotography is
Specification No. 2297691, Japanese Patent Publication No. 42-23910, and
Many methods are described in Japanese Patent Publication No. 43-24748, etc., but in general, an electrical latent image is formed by various means on a photoreceptor using a photoconductive substance, and then the latent image is After developing with toner and, if necessary, transferring a powder image made of toner to a transfer material such as paper, it is fixed by heat, pressure, solvent vapor, etc. to obtain a copy. Examples of methods for visualizing an electrical latent image, that is, an electrostatic latent image using toner include the magnetic brush method described in U.S. Pat. No. 2,874,063, and U.S. Pat.
The cascade development method described in No. 2221776 and the powder cloud method described in No. 2221776 are known. The developer used in these development methods is a one-component type consisting only of colored fine powder, generally called toner, which can be selectively attracted or repelled by electrostatic charge, and a carrier such as iron powder or glass beads. It is broadly divided into so-called two-component systems that use a substance (carrier) in combination. The former developer forms a latent image due to the electric charge induced from the conductor of the magnetic metal sleeve for supporting it, or the frictional electric charge with the sleeve, and the latter developer forms a latent image due to the triboelectric electric charge with the carrier. It is to be developed. Among these, the so-called induction development method (for example, described in Japanese Patent Publication No. 37-491) is well known as a development method using a one-component developer consisting only of toner. In short, this method involves attaching conductive and magnetic toner to a sleeve containing a magnet to form a magnetic brush using the toner, and then bringing the magnetic brush into contact with an electrostatic latent image carrier to transfer the latent image using the toner. It is to be developed. In this developing method, when the magnetic brush is opposed to the electrostatic latent image because the toner has conductivity, an electric charge of opposite polarity to that of the electrostatic latent image is induced in the toner. The latent image is developed based on the electrical attraction between the toner and the electrostatic latent image. In addition, insulating magnetic toner is attached to a sleeve containing a magnet to form a toner magnetic brush, the toner is charged by friction with the sleeve, and the magnetic brush is brought into contact with or close to the electrostatic latent image carrier. A method of developing a latent image with toner is also known. For example, JP-A-49-17739 using capsule magnetic toner;
A developing method using an insulating magnetic toner is described in detail in JP-A-50-45639. In these developing methods using one-component developers, since the developer does not contain a carrier, there is no need to adjust the mixing ratio of carrier and toner, and a stirring operation is required to mix the carrier and toner sufficiently uniformly. Since this is not particularly necessary, it has the advantage that the entire developing device can be constructed simply and compactly. Furthermore, there is no problem such as deterioration in developed image quality due to deterioration of the carrier over time. These magnetic toners are made by mixing and dispersing a considerable amount of magnetic particles in a binder resin, but magnetic materials generally have poor dispersibility in the binder resin, so it is difficult to manufacture them uniformly without variations. It is difficult to obtain, and it is not possible to mix a large amount of magnetic material. Therefore, the spikes of magnetic toner on the sleeve of the developing device are insufficient, making it impossible to achieve good development, and the resulting visible image is of low quality. Furthermore, since the degree of exposure of the magnetic material on the surface of each toner particle is not uniform, the triboelectric charging characteristics of the toner are not uniform and the charging state is not uniform, which also makes it impossible to obtain a good visible image. It is the cause. The present invention has been made based on the above-mentioned circumstances, and provides an electrostatic image development system in which a magnetic material is uniformly dispersed in toner particles, triboelectric charging properties are uniform, and the image forming property is good and safe. The purpose of the present invention is to provide a magnetic toner for use. The above purpose is to apply 60 to 90 parts by weight of styrenic monomer to 0.5 to 4.8 parts by weight of unsaturated polyester obtained by condensing polybasic acid containing 5 to 90 mol% of unsaturated dibasic acid and polyhydric alcohol. % and 40 to 10% by weight of acrylic esters and/or methacrylic esters 99.5 to 99.5%
Obtained by graft polymerizing 95.2 parts by weight, temperature
This is achieved by a magnetic toner for developing electrostatic images, which is characterized in that it uses a graft polymer having a melt viscosity of 10 ⁴ to 10 ⁷ poise at 140° C. as a binder and contains a magnetic material. The present invention will be specifically explained below. In the present invention, a binder made of the following specific graft polymer is used, and fine magnetic powder is dispersed therein, and if necessary, a colorant and other additives are also added to create a magnetic material for developing electrostatic images. Use toner. Here, the specific graft polymer refers to a polybasic acid containing an unsaturated dibasic acid having an unsaturated bond formed by a carbon-carbon double bond in a proportion within a specific range, and a corresponding amount of a polyhydric alcohol. Condensation is performed to obtain an unsaturated polyester, and a vinyl monomer consisting of 60 to 90% by weight of a styrene monomer and 40 to 10% by weight of an acrylic ester and/or a methacrylic ester, based on the unsaturated polyester. It is a graft polymer obtained by graft polymerizing at a ratio within a specific range. According to the present invention, since the binder is made of the above graft polymer, it is possible to obtain a toner in which the magnetic material is well dispersed. That is, since the graft polymer has a relatively high viscosity in a molten state, a large shearing force can be applied to the polymer in the kneading process in toner production, and the graft polymer has long grafted polymer chains. It is thought that this is because since the polymer chains are entangled, the effect of the applied shearing force is large, and the magnetic fine particles can effectively enter between each polymer chain. In other words, each polymer molecule entangled in the side chain has a large degree of freedom to behave individually due to shear force, and therefore the magnetic material can penetrate between these molecules. On the other hand, in a simple linear polymer, the viscosity is low and the shear force during kneading does not act effectively, and some of the polymer molecules behave as a group, resulting in poor dispersion of the magnetic material. Moreover, in the case of a crosslinked polymer, the molecules are huge, so even if fine particles of magnetic material enter between the molecules, it is thought that the entire structure will become non-uniform. In the present invention, since the magnetic material can be uniformly dispersed in this way, the magnetic material can be mixed and dispersed in a large proportion as a whole, and the degree of exposure of the fine particles of the magnetic material on the surface of the toner particles can be reduced. Because of the uniformity, the toner has uniform triboelectric charging characteristics, and during development, good spikes are formed and good development is achieved, and as a result, an extremely good visible image can be formed. Its characteristics will be exhibited stably. Further, in the present invention, since the graft polymer used as the binder is a graft polymer of a specific unsaturated polyester, the following effects can be obtained. In other words, even if the above unsaturated polyester graft polymer has a high molecular weight, its softening point is very low compared to other resins with the same molecular weight, and since the softening point of the binder resin is low, the toner is Even when fixing is carried out at low temperatures, it has high fluidity when melted and has great permeability to paper, so it has a great anchoring effect on paper and is difficult to peel off from paper after fixing. becomes. In addition, by increasing the molecular weight, the toner becomes tough, and after fixing, the toner forming the image may be partially ground due to friction, causing the image to become blurred or stick to fingers, etc. Furthermore, since the mold releasability during melting is high, it does not stick to the heating roller, and offset development is prevented. Furthermore, the graft polymer has relatively high elasticity due to its molecular chain state, and therefore, the toner does not crack and peel off when the paper is folded after fixing. In this way, by using a graft polymer of unsaturated polyester as a binder, it is possible to obtain sufficient fixing properties at low temperatures, and
Not only can sufficient offset prevention properties be obtained, but furthermore, since the presence of low molecular weight components in the binder is not required, brittleness is low, and therefore, it is undesirable in terms of contamination or scattering during pulverization in the toner manufacturing process. The generation of ultrafine toner particles is small, the toner yield is improved, the toner can be manufactured advantageously, and a good visible image without fogging is formed. In addition to the above, the following advantages can also be obtained. That is, in the production of graft polymers, since unsaturated polyesters are susceptible to radical reactions, graft polymerization of vinyl monomers can be advantageously carried out with high efficiency. In addition, since the unsaturated polyester to be grafted is obtained by the condensation of a polybasic acid containing an unsaturated dibasic acid and a polyhydric alcohol, by changing the type and proportion of the unsaturated dibasic acid, it is possible to Various polyesters with different density or position of groups can be obtained. Therefore, by selecting an appropriate unsaturated polyester and the type of polyhydric alcohol, it is possible to further select the reaction conditions and adjust the molecular weight of the graft polymer. By carrying out this process, a binder resin having desired properties can be easily obtained, and as a result, desirable properties can be imparted to the toner. The polybasic acid used to obtain the unsaturated polyester, which is the raw material for the graft polymer used as the binder in the present invention, contains 5 to 90 mol% of an unsaturated dibasic acid having an unsaturated double bond that serves as a grafting reaction site. In particular, it is preferably contained in an amount of 20 to 80 mol%. If the proportion of unsaturated dibasic acid is less than 5 mol%, the resulting unsaturated polyester will have few grafting reaction sites, making it difficult to obtain a polyester containing the required proportion of tetrahydro-insoluble matter. Since the resulting graft polymer has a low molecular weight, a toner using this as a binder resin has poor scratch resistance and offset prevention properties. When the above ratio exceeds 90 mol %, the resulting graft polymer has a large molecular weight and a high softening point, resulting in a toner with low fixing properties. Unsaturated polyester has a number average molecular weight Mn
1000 to 20000, particularly 5000 to 10000, a weight average molecular weight Mw of 3000 to 30000, particularly 5000 to 20000, and a dispersity Mw/Mn value of 5.0 or less. Naturally, if the number average molecular weight or weight average molecular weight is small, a graft polymer with a large molecular weight cannot be obtained.
The toner will have low scratch resistance and anti-offset properties, and if these molecular weights are large, the molecular weight of the resulting graft polymer will be too high and the toner will have a high fixing temperature. In addition, unsaturated polyester has a softening point of 80~
The temperature is preferably 140°C, particularly 100-130°C.
It is preferable that the glass transition point is 40 to 90°C, particularly 50 to 80°C. If an unsaturated polyester with a softening point of less than 80°C or a glass transition point of less than 40°C is used, the toner will tend to aggregate; an unsaturated polyester with a softening point of more than 140°C or a glass transition point of more than 90°C If this is used, the toner tends to become too hard and have poor fixability. The above-mentioned unsaturated polyester is suitably obtained by condensing a mixed system of an unsaturated dibasic acid and another polybasic acid, preferably a saturated polybasic acid, with a polyhydric alcohol. Specific examples of unsaturated dibasic acids that are preferably used include maleic acid, maleic anhydride, fumaric acid, citraconic acid, itaconic acid, and others, which may be used alone or in combination. Specific examples of suitably used saturated polybasic acids include, for example, tetrachlorophthalic anhydride, hettic acid, tetrapromophthalic anhydride, phthalic anhydride,
Isophthalic acid, terephthalic acid, endomethylenetetrahydrophthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, succinic acid, adipic acid, azelaic acid, sebacic acid, other saturated dibasic acids, trimellitic acid, trimellitic anhydride, pyromellitic acid acid, pyromellitic anhydride, and other saturated polybasic acids, which can be used alone or in combination. Specific examples of suitably used polyhydric alcohols include ethylene glycol, propylene glycol, 1,4-butanediol, 1,3-butanediol, diethylene glycol, dipropylene glycol, triethylene glycol, 1,
5-pentanediol, 1,6-pentanediol, neopentyl glycol, hydrogenated bisphenol A, polyoxyethylenated bisphenol A, polyoxypropylenated bisphenol A,
Examples include other glycols, glycerin, and other polyhydric alcohols, which may be used alone or in combination. In the production of unsaturated polyester, in addition to the above-mentioned necessary components, a molecular weight regulator such as benzoic acid, and a reaction catalyst or reaction accelerator made of a metal organic compound are added. Conventional methods can be used for production, and the reaction is carried out in an inert gas atmosphere at a temperature of, for example, about 200°C, and the water produced as the reaction progresses is removed by a condenser under normal pressure or reduced pressure. . The progress of the reaction is monitored by successively measuring the acid value of the reaction product, and the reaction is terminated when the oxidation value reaches a desired value. A specific vinyl monomer consisting of a combination of 60 to 90% by weight of a styrene monomer and 40 to 10% by weight of an acrylic ester and/or a methacrylic ester based on the unsaturated polyester thus obtained. A graft polymer used as a binder in the present invention can be obtained by carrying out a grafting reaction at a ratio within a specific range. Here, the ratio of unsaturated polyester to vinyl monomer is 0.5 to 4.8:99.5 to 95.2 by weight. Specific examples of styrene monomers that are components of specific vinyl monomers include styrene,
o-methylstyrene, m-methylstyrene, p-
Methylstyrene, α-methylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-n
-butylstyrene, p-tert-butylstyrene,
p-n-hexylstyrene, p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene, p-n-dodecylstyrene, p-methoxystyrene, p-phenylstyrene, p-chlorostyrene , 3,4-dichlorostyrene, and the like. Specific examples of acrylic esters and methacrylic esters include methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, n-octyl acrylate, and dodecyl acrylate. , lauryl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, acrylic acid 2
- Acrylic esters such as chloroethyl, phenyl acrylate, methyl a-chloroacrylate: methyl methacrylate, ethyl methacrylate, propyl methacrylate, n methacrylate
-butyl, isobutyl methacrylate, n-octyl methacrylate, dodecyl methacrylate,
Examples include lauryl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate, dimethylaminoethyl methacrylate, and diethylaminoethyl methacrylate. By using the above-mentioned specific vinyl monomers, a graft polymer is formed that provides a toner that is preferable in terms of softening point, impact resistance, anti-offset properties, and non-agglomeration properties. That is, when the styrene monomer content is less than 60% by weight, the resulting graft polymer tends to soften at low temperatures, resulting in a highly cohesive toner, and when the styrene monomer content exceeds 90% by weight, The resulting graft polymer becomes hard and has a high degree of softening, resulting in a toner with low fixing properties. The above-mentioned grafting reaction of a vinyl monomer to an unsaturated polyester can be carried out by a bulk polymerization method, a solution polymerization method, a suspension polymerization method, an emulsion polymerization method, etc., but among these, a suspension polymerization method is preferable. . When using the suspension polymerization method, usually
Water containing 0.1-5% by weight of dispersion stabilizer 60-90
Using parts by weight as a medium, 40 to 10 parts by weight of a monomer solution obtained by dissolving an unsaturated polyester, a polymerization catalyst, a molecular weight regulator, etc. in a vinyl monomer are added to the medium with stirring. The reaction is carried out in a state in which the monomer solution is suspended in the form of fine particles. The reaction temperature is 50 to 120°C, and after the reaction is completed, the dispersion stabilizer is removed from the solid by washing with water and separately. Examples of polymerization catalysts used in this grafting reaction include peroxide polymerization initiators such as benzoyl peroxide and lauroyl peroxide, azo polymerization initiators such as azobisisobutyronitrile, and other polymerization initiators. It is used in a range of 0.1 to 10% by weight based on the body weight. Further, as the molecular weight regulator, for example, dodecyl mercaptan, butyl mercaptan, etc. are used in an amount of 0 to 10% by weight based on the monomer. Furthermore, in order to make the polymer obtained by grafting have a three-dimensional crosslinked structure, a crosslinking agent can be added to the reaction system. Compounds having two or more double bonds, such as divinylbenzene, divinylnaphthalene, derivatives thereof, and other aromatic divinyl compounds; such as ethylene glycol diacrylate, ethylene glycol dimethacrylate, trimethylolpropane triacrylate, and other double bonds. carboxylic acid esters; others can be mentioned, and the amount used is as follows:
The amount is in the range of 0 to 10% by weight based on the monomer. In the present invention, the above graft polymer having a melt viscosity of 10 ⁴ to ^{10 7} poise at a temperature of 140° C. is used as the binder. The binder of the toner of the present invention preferably contains the above-mentioned graft polymer as a main component in an amount of 60% by weight or more, and may contain other resins in an amount less than 40% by weight of the entire binder. good.
Other resins include polyester, polyamide, polyurethane, polyurea, epoxy resin,
Examples include phenol-formalin resin and others, and these may be used alone or in a mixture of two or more. In the toner of the present invention, magnetic fine powder is contained in the above-mentioned binder resin, and this magnetic material is a substance that is strongly magnetized in that direction by a magnetic field, and is preferably black in color and highly dispersible in the resin. It is desirable that the material be chemically stable and easily obtainable in the form of fine particles with a particle size of 1 μm or less. In particular, magnetite (triiron tetroxide) is most preferred. Typical magnetic or magnetizable materials include metals such as cobalt, iron, nickel: aluminum, cobalt, steel, lead, magnesium, nickel, tin, zinc, antimony, beryllium, bismuth, cadmium, calcium,
Alloys and mixtures of metals such as manganese, selenium, titanium, tungsten, vanadium; aluminum oxide, iron oxide, copper oxide, nickel oxide,
Metal compounds containing metal oxides such as zinc oxide, titanium oxide, and magnesium oxide can be suitably used. The content of these magnetic substances is set to be 40 to 70% by weight of the toner. The toner of the present invention usually further contains colorants and other additives. Any suitable pigment or dye can be used as the colorant here. Coloring agents include carbon black, nigrosine dye (CI No. 50415B), and aniline blue (CI No.
50405), Calco Oil Blue (CINo.azoec Blue)
3), Chrome Yellow (CINo.14090), Ultramarine Blue (CINo.77103), Dupont Oil Red (CINo.26105), Quinoline Yellow (CINo.
47005), methylene blue chloride (CINo.
52015), Phthalocyanine Blue (CINo.74160),
Malachite Green Oxalate (CINo.
42000), lampblack (CI No. 77266), rose bengal (CI No. 45435), mixtures thereof, and others. These colorants account for about 3 to 20% by weight in the final toner product.
The proportion shall be such that it will be contained in a proportion of . The toner of the present invention further includes an offset prevention agent,
A prepolymer, a charge control agent, a fluidizing agent, a liquid resin, etc. can be added. Examples of the offset inhibitor include low molecular weight polyolefins, preferably those having a number average molecular weight of 500 to 10,000 and a softening point of 100 to 180°C. The toner of the present invention can be manufactured using a conventionally known method, for example, by kneading toner materials using a heated roll, heated extruder, etc., followed by cooling, pulverizing, and classifying. . The image forming member to which the toner of the present invention is applied may be any member as long as it can hold an electrostatic charge image on its surface. Photoconductive members such as negatively charged photoreceptors in which a molecular compound is coated on a conductive support, and image forming members such as dielectric recording materials in which an insulating resin is coated on a conductive support can be suitably used. can. In order to form an electrostatic charge image on this image forming member, for example, the surface of the image forming member is uniformly charged with a charger and then subjected to imagewise exposure, an electrostatic recording needle or an ion flow control electrode is used. A method of directly forming an electrostatic charge image on an image forming member by such means as described above, and others are used. Examples of the present invention will be described below, but the present invention is not limited thereto. [Production of unsaturated polyester (1)] In a four-necked flask with a capacity of 3 equipped with a thermometer, a stirrer, a gas introduction tube, and a flowing-down condenser,
Add 1720g (5 moles) of polyoxypropylene-2,2'-bis(4-hydroxyphenyl)propane, introduce nitrogen gas through the gas introduction tube to create an inert atmosphere, and then raise the temperature to 50℃. Contains 166 g (1 mol) of terephthalic acid and 392 g of maleic anhydride.
A mixture of (4 moles) was added into the container, and then the temperature of the system was set to 200°C and reaction was carried out for 6 hours. Water produced as the reaction progressed was trapped and removed by a condenser. After that, the gas introduction pipe and condenser were removed, a vacuum line equipped with a trap was connected, and while the generated water was removed by the trap under reduced pressure, the gas was further heated to 200℃ for 6 hours.
The reaction was carried out for a period of time, thereby producing unsaturated polyester A. [Manufacture of unsaturated polyester (2)] 664 g (4 mol) of terephthalic acid as a polybasic acid
An unsaturated polyester B was produced in the same manner as in the production of unsaturated polyester (1) except that 98 g (1 mole) of maleic anhydride was used. [Production of unsaturated polyester (3)] Polyoxypropylene-2,2'-bis(4-hydroxyphenyl)propane 1720 g (5 mol),
Terephthalic acid 498g (3.0mol), maleic acid 145g
Unsaturated polyester C was produced in the same manner as in Production of unsaturated polyester (1) except that a mixture of (1.25 mol) and 87 g (0.75 mol) of fumaric acid was used. [Manufacture of graft polymer (1)] Unsaturated polyester A 2 parts by weight Styrene 80 parts by weight Butyl acrylate 20 parts by weight Benzoyl peroxide 4 parts by weight A graft composition comprising the above substances was prepared.
Meanwhile, in a four-necked flask equipped with a stirrer, thermometer, and gas inlet tube, 2% by weight of calcium phosphate was added.
Add 600 ml of water containing 0.2% by weight of surfactant,
The inside of the container was made into a nitrogen gas atmosphere through a gas inlet pipe, and 200 g of the above graft composition was added and suspended at room temperature with stirring, and then the temperature was raised to 90°C and reacted for about 3 hours. Ta. After the reaction was completed, the system was cooled, and the solids were repeatedly separated and washed with water, and then dried to obtain Graft Polymer I. This graft polymer I had a softening point of 128°C and a melt viscosity of 9×10 ⁴ poise at a temperature of 140°C. [Production of graft polymer (2)] A graft polymer was obtained in the same manner as in Production of graft polymer (1) except that 5 parts by weight of polyester B was used instead of 2 parts by weight of unsaturated polyester A. Ta. The softening point of this graft polymer is 134℃,
The melt viscosity at a temperature of 140°C was 7×10 ⁵ poise. [Production of graft polymer (3)] In place of the graft composition in production of graft polymer (1), unsaturated polyester C 10 parts by weight Styrene 65 parts by weight Butyl methacrylate 35 parts by weight Benzoyl peroxide 4 parts by weight A graft polymer was obtained in the same manner except that the graft composition was used. The softening point of this graft polymer is 145℃,
The melt viscosity at a temperature of 140°C was 8×10 ⁶ poise. [Production of graft polymer (4)] A graft polymer was produced in the same manner as in Production of graft polymer (3) except that 0.2 parts by weight of unsaturated polyester C was used instead of 10 parts by weight of unsaturated polyester C. I got it. The softening point of this graft polymer is 122℃,
The melt viscosity at a temperature of 140°C was 5×10 ⁴ poise. Example 1 Graft polymer 40 parts by weight magnetite "RB-BL" (manufactured by Titan Kogyo Co., Ltd.)
60 parts by weight Nigrosine base "EX" (manufactured by Orient Chemical Co., Ltd.)
1 part by weight or more of the materials were mixed in a ball mill, melt-kneaded with two rolls, cooled, coarsely pulverized, further finely pulverized, and classified to produce a magnetic toner of the present invention having an average particle size of 12 microns. This is referred to as "toner 1". Example 2 A magnetic toner of the present invention was produced in the same manner as in Example 1 except that a graft polymer was used instead of the graft polymer. This will be referred to as "toner 2". Example 3 Styrene 80 parts by weight Butyl acrylate 20 parts by weight Benzoyl peroxide 4 parts by weight The above compositions were reacted to obtain styrene-butyl acrylate copolymer a. Graft polymer 30 parts by weight Above styrene-butyl acrylate copolymer a
10 parts by weight magnetite "RB-BL" (manufactured by Titan Kogyo Co., Ltd.)
60 parts by weight Nigrosine base "EX" (manufactured by Orient Chemical Co., Ltd.)
A magnetic toner of the present invention was produced in the same manner as in Example 1 using 1 part by weight or more of the substance. This will be referred to as "toner 3." Comparative Example 1 Styrene-butyl acrylate copolymer a
40 parts by weight magnetite "RB-BL" (manufactured by Titan Kogyo Co., Ltd.)
60 parts by weight Nigrosine base "EX" (manufactured by Orient Chemical Co., Ltd.)
A magnetic toner for comparison was produced in the same manner as in Example 1 except that 1 part by weight or more of the substance was used. This is referred to as "comparison toner 1." Comparative Example 2 Graft polymer 20 parts by weight Styrene-butyl acrylate copolymer a
20 parts by weight magnetite “RB-BL” (manufactured by Titanium Kogyo Co., Ltd.)
60 parts by weight Nigrosine base "EX" (manufactured by Orient Chemical Co., Ltd.)
A magnetic toner for comparison was produced in the same manner as in Example 1 except that 1 part by weight or more of the substance was used. This is referred to as "comparison toner 2." Comparative Example 3 A comparative magnetic toner was produced in the same manner as in Example 1 except that a graft polymer was used instead of the graft polymer. This is referred to as "comparison toner 3." Comparative Example 4 A comparative magnetic toner was produced in the same manner as in Example 1 except that a graft polymer was used instead of the graft polymer. This is referred to as "comparison toner 4". The dispersibility of the magnetic material was investigated for each of the above toners. That is, 1 g of toner was dissolved in 10 ml of tetrahydrofuran, and the solution was overtreated using Paper No. 1 (manufactured by Toyo Paper Co., Ltd.), and the extent to which the magnetic material passed through the paper was examined. Also, depending on each toner,
A copy test was conducted 10,000 times using an electrophotographic copying machine "U-Bix T" (manufactured by Konishiroku Photo Industry Co., Ltd.), and the resulting copied images were evaluated for image distortion and fog. The results are shown in the table below.

【table】

[Table] As described above, the magnetic toner of the present invention has good dispersibility of the magnetic material and uniform properties, and exhibits excellent image forming properties stably.

Claims (1)

[Claims] 1. 60 to 4.8 parts by weight of an unsaturated polyester obtained by condensing a polybasic acid containing 5 to 90 mol% of an unsaturated dibasic acid and a polyhydric alcohol, and 60 to 4.8 parts by weight of a styrenic monomer. It is obtained by graft polymerizing 99.5 to 95.2 parts by weight of a vinyl monomer consisting of 90% by weight and 40 to 10% by weight of acrylic esters and/or methacrylic esters, and has a melt viscosity of 10 ⁴ at a temperature of 140°C. 1. A magnetic toner for developing electrostatic images, characterized in that it uses a graft polymer of ~10 ⁷ poise as a binder and contains a magnetic material. 2 The binder contains 60% by weight of the graft polymer.
The magnetic toner for developing an electrostatic image according to claim 1, which contains the following.