JPH04288557A - Electrophotographic toner - Google Patents

Abstract

PURPOSE:To obtain a stable copied image freed of fog, dust, and toner scattering by mixing a hydrophobic silica having a pH of 3.5-4.5 in toner particles containing a specified compound having a pH of 3-5 and dispersing the silica. CONSTITUTION:The hydrophobic fine silica powder having a pH of 3.5-4.5 are mixed and dispersed into the toner particles containing as an electric charge controller the azo type metal complex salt dye having a pH of 3-5 and represented by formula I in which each of R<1>-R<4> is independently H, halogen, or a group of formula II, but each is not H at the same time; Y is Cr, Fe, Co, Zn, or Ti; Z<+> is a cation of ammonium, H, Ka, or Na; and R<1> and R<4> are not H at the same time and each of R<5> and R<6> is independently alkyl or aryl, thus permitting charging characteristics to be stabilized and a stable image to be obtained, toner scattering to be also effectively prevented.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic toner, and more particularly to an electrophotographic toner used in image forming apparatuses such as electrostatic copying machines and laser beam printers.

0002

[Prior Art and Problems to be Solved by the Invention] In the above-mentioned image forming apparatus, an electrophotographic developer is brought into contact with an electrostatic latent image formed by exposure on the surface of a photoreceptor by a developing device, and the electrostatic latent image is Image formation is performed by electrostatically depositing toner in a photographic developer to visualize the electrostatic latent image as a toner image, then transferring this toner image from the surface of the photoreceptor onto paper and fixing it. .

[0003] Electrophotographic toners include a binder resin,
Toner particles containing a colorant such as carbon black, a charge control agent, a release agent, and, if necessary, a fluidity imparting agent, are generally used. As the charge control agent, an azo metal complex dye (such as an azo chromium dye) is generally used. Furthermore, in order to improve the fluidity of toner particles, it is widely practiced to mix and disperse fine silica powder, especially hydrophobic fine silica powder, as an external additive.

[0004] However, conventional electrophotographic toners have problems in that the charging characteristics are not stable, resulting in fogging, reduction in image density, dust, toner scattering, etc., making it impossible to obtain stable images. . SUMMARY OF THE INVENTION An object of the present invention is to provide an electrophotographic toner that can produce stable copied images free of fog, reduction in image density, dust, toner scattering, and the like.

[0005]

[Means and Effects for Solving the Problems] As a result of extensive research in order to solve the above problems, the present inventors have found that the pH value of an azo metal complex dye used as a charge control agent and the pH value of fine silica powder are Focusing on this, we obtained new knowledge that there is a difference in toner chargeability depending on both pH values, resulting in problems such as image defects (i.e., insufficient image density, fogging, etc.) and toner scattering.

[0006] Therefore, as a result of further research, the present inventor has developed the general formula (1):

[0007]

[Chemical formula 3]

[In the formula, R1, R2, R3 and R
4 are the same or different hydrogen atoms, halogen atoms or groups:

[0009]

[C4]

(wherein R5 and R6 are the same or different and represent an alkyl group or an aryl group), Y represents Cr, Fe, Co, Zn or Ti, and Z
+ represents a cation selected from the group consisting of ammonium ions, hydrogen ions, potassium ions, and sodium ions. However, R1, R2, R3 and R
4 cannot all be hydrogen atoms at the same time. ] The electrophotographic toner obtained by mixing and dispersing hydrophobic silica having a pH value of 3.5 to 4.5 into toner particles containing a compound represented by the following formula and having a pH value of 3 to 5 is the above-described toner. They have discovered that the problem can be solved and have completed the present invention.

[0011] The above pH value is based on JIS K 6221.
It is measured by the method described in . That is, 10g of sample
is added to 100 ml of distilled water, boiled for 15 minutes, cooled to room temperature, and then the pH value is measured. The electrophotographic toner of the present invention has a pH value of 3 to 5, and has the above general formula (
1) Since hydrophobic silica fine powder with a pH value of 3.5 to 4.5 is mixed and dispersed in toner particles containing the compound represented by as a charge control agent, charging characteristics are stabilized,
A stable image can be obtained. That is, if both the pH values of the compound represented by the above general formula (1) and the hydrophobic silica fine powder are lower than the above range, the amount of negative charge increases and it becomes difficult to separate from the carrier, resulting in a decrease in image density. This has the disadvantage of doing so. Furthermore, if both pH values are higher than the above range, the amount of negative charge will be small and adhesion with carrier will not be sufficient, resulting in drawbacks such as toner scattering and fogging.

The pH value of the compound represented by the general formula (1) is greatly influenced by the polar group bonded to this compound.
If so, the pH value tends to decrease. Therefore, the pH
Each group must be selected so that the value falls within the above range. Table 1 illustrates the relationship between each combination of substituents and pH value. However, the pH value is not a definitive value because it varies depending on the presence of impurities such as minute amounts of by-products and unreacted substances mixed in during the manufacturing process of compound (1).

[0013]

[Table 1]

[0014] The above-mentioned halogen atom includes a fluorine atom,
Examples include chlorine atom, bromine atom or iodine atom. Examples of the alkyl group include alkyl groups having 1 to 6 carbon atoms such as methyl, ethyl, propyl, isopropyl, butyl, t-butyl, pentyl, and hexyl groups.

Examples of the above-mentioned aryl group include phenyl group, tolyl group, xylyl group, biphenyl group, naphthyl group, anthryl group, and phenanthryl group. Such compound (1) is used as a charge control agent, a binder resin,
0.0% per 100 parts by weight of toner particles consisting of colorant etc.
It is used in a proportion of 5 to 8 parts by weight, preferably 1 to 3 parts by weight. When the amount of compound (1) used is less than the above range, the charging property becomes unstable, and when it is more than the above range, carrier adhesion occurs, which also causes toner scattering, fogging, etc.

The toner particles of the present invention contain a colorant, the above-mentioned compound (1) as a charge control agent, and a release agent (
It is manufactured by blending additives such as an anti-offset agent) and, if necessary, a fluidity imparting agent, and granulating the mixture to a predetermined particle size. That is, a mixture obtained by homogeneously preliminary kneading the above-mentioned components using a dry blender, Henschel mixer, ball mill, etc., is uniformly mixed using a kneading device such as a Banbury mixer, roll, single-screw or twin-screw extrusion kneader, etc. After melt-kneading, the obtained kneaded product is cooled and pulverized, and if necessary, it is manufactured by classifying, or by a suspension polymerization method or the like.

Examples of the binder resin include polystyrene, chloropolystyrene, poly-α-methylstyrene, styrene-chlorostyrene copolymer, styrene-propylene copolymer, styrene-butadiene copolymer, and styrene-vinyl chloride copolymer. styrene-vinyl acetate copolymer, styrene-maleic acid copolymer, styrene-acrylic acid ester copolymer (styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate) copolymers, styrene-octyl acrylate copolymers, styrene-phenyl acrylate copolymers, etc.), styrene-methacrylate copolymers (styrene-methyl methacrylate copolymers, styrene-ethyl methacrylate copolymers) , styrene-butyl methacrylate copolymer, styrene-phenyl methacrylate copolymer, etc.)
, styrenic resins (homopolymers or copolymers containing styrene or styrene substituted products) such as styrene-α-methyl chloroacrylate copolymer, styrene-acrylonitrile-acrylic acid ester copolymer, polyvinyl chloride,
Low molecular weight polyethylene, low molecular weight polypropylene, ethylene-ethyl acrylate copolymer, polyvinyl butyral, ethylene-vinyl acetate copolymer, rosin-modified maleic acid resin, phenol resin, epoxy resin, polyester resin, ionomer resin, polyurethane resin, silicone Examples include resins, ketone resins, xylene resins, polyamide resins, etc., and these may be used alone or in combination of two or more. Among these, styrene resins, particularly styrene-(meth)acrylic acid ester copolymers are preferred, and styrene-methyl methacrylate-butyl acrylate copolymers are preferably used. Especially styrene 75-8
5% by weight, 0.5-5% by weight of methyl methacrylate,
and butyl acrylate in an amount of 10 to 20% by weight.

[0018] As the coloring agent, carbon black such as furnace black, channel black, thermal, gas black, oil black, acetylene black, black coloring agent such as lamp black, aniline black, or red, yellow and black coloring agent are used. A brown coloring agent produced by mixing can be used, and among them, a black coloring agent is particularly preferably used. The colorant is used in an amount of 1 to 20 parts by weight, preferably 3 to 15 parts by weight, based on 100 parts by weight of the binder resin.

Examples of the mold release agent (offset inhibitor) include aliphatic hydrocarbons, aliphatic metal salts, higher fatty acids, fatty acid esters or partially saponified products thereof, silicone oil, various waxes, and the like. Among these, aliphatic hydrocarbons having a weight average molecular weight of about 1,000 to 10,000 are preferred. Specifically, one or a combination of two or more of low molecular weight polypropylene, low molecular weight polyethylene, paraffin wax, and low molecular weight olefin polymers consisting of olefin units having 4 or more carbon atoms are suitable. The mold release agent is used in an amount of 0.1 to 100 parts by weight of the binder resin.
It is used in a proportion of 10 parts by weight, preferably 1 to 5 parts by weight.

The particle size of the toner particles is 3 to 3 as in the conventional case.
It may be about 5 μm, especially about 5 to 25 μm, but it is preferable that the particle size distribution satisfies the following formula. N < -172.7C + 1.45 [In the above formula, N is 16 μm measured with a Coulter counter
It represents the number % of toner particles with a larger particle size, and C represents the surface dye concentration (g/g) of the toner particles. ] If the particle size distribution is within the above range, from the relationship with the surface dye concentration,
Furthermore, variations in toner charging characteristics can be eliminated.

[0021] In order to make the particle size distribution of the toner particles satisfy the above formula, there is a method of classifying the toner particles after pulverization and excluding particles with a particle size larger than 16 μm;
Examples include a method of reducing the content of particles with a diameter larger than 16 μm by pulverizing the toner particles so that the maximum distribution particle diameter shifts to the smaller diameter side. In the present invention, the hydrophobic silica fine powder to be mixed and dispersed with the toner particles has, for example, a (poly)alkyl group on the surface of the silica fine powder, a (poly)
Examples include those treated with alkylsilyl groups, (poly)alkylsilanes, silicone oils, etc. In particular, fine silica powder whose surface has been hydrophobized with a compound having a polymethylsilyl group is mentioned, and this powder has higher hydrophobicity than conventional fine silica powder treated with a compound having a low molecular weight alkyl group. It is something.

[0022] As a commercially available product of such fine silica powder, there is a trade name "Cabosil TS720" manufactured by Cabot Corporation. This product is a hydrophobic fumed silica fine powder, and is a high purity fumed silica fine powder (99.8% S
It is produced by treating iO2 ) with an organic silicone compound, and polymethylsilyl groups are present on the surface, increasing the hydrophobicity of the surface of the fine silica powder.

The particle size of the hydrophobized fine silica powder is preferably about 0.01 to 0.04 μm. The pH value of hydrophobic silica fine powder changes due to various factors, and although the factors are not necessarily clear, it is known that the surface functional groups are affected by reaction by-products.

The amount of the hydrophobic silica fine powder added is 0.01 to 5% by weight, preferably 0.01 to 5% by weight, based on the total amount of toner.
05 to 1% by weight. If the amount of hydrophobic silica fine powder added is greater than the above range, the amount of charge will be excessive, and if the amount added is less than the above range, no effect of improving the fluidity of the toner can be expected.

[0025]

EXAMPLES The electrophotographic toner of the present invention will be explained in more detail below with reference to Examples and Comparative Examples. Example 1 (components)
(Amount) Styrene-acrylic polymer
85% by weight carbon black
10% by weight Anti-offset agent (low molecular weight polypropylene) 3% by weight
Chromium-containing azo dye (pH 4.9)
Components of 2% by weight or more were melt-kneaded using a twin-screw kneader, and toner particles having an average particle size of 10 μm were obtained using a jet mill. The chromium-containing azo dye used as the charge control agent is a compound represented by formula (1), and each group is as shown in Table 2.

To the toner particles, 0.5% by weight of hydrophobized silica fine powder (particle size 0.02 μm, pH 3.7, trade name “Cabosil TS-720” manufactured by Cabot) was added to the total amount of the toner. Examples 2 to 4 and Comparative Examples 1 to 8 A metal-containing azo dye having a group shown in Table 2 and having a pH value shown in Table 4 as a charge control agent. A toner was obtained in the same manner as in Example 1, except that the hydrophobizing silica fine powder having the pH value shown in Table 4 was used.

[0027]

[Table 2]

<Evaluation Test> A ferrite carrier having an average particle size of 80 μm was added to each of the toners obtained in each example and comparative example, and the two-component developer with a toner concentration of 4% was prepared by uniformly stirring and mixing. did. And an electrophotographic copying machine manufactured by Sanda Kogyo Co., Ltd. (product name "DC-3255")
), changing the environmental conditions for each predetermined number of sheets, making a total of 8 sheets.
Ten thousand copies were made, and the image density, fog density, charge amount, and environmental resistance under various environmental conditions were examined. That is, Table 3
The environmental conditions were changed for each predetermined number of copies in the order shown below, and the above test was conducted after copying under each condition. However, the measured value at N/N (normal temperature and normal humidity) is after 80,000 copies were made.

[0029]

[Table 3]

[0030] Each test method is as follows. (1) Image density (ID) measurement Measured using a reflection densitometer (model number TC-6D, manufactured by Tokyo Denshoku Co., Ltd.). (2) Fog Density (F.D.) Measurement Using the same reflection densitometer as described above, the density of the margin portion of the copied image was measured and determined as the fog density. (3) Electrification amount Measured using a blow-off electrification meter manufactured by Toshiba Chemical Co., Ltd. (4) Environmental resistance Toner scattering was visually judged by the condition inside the copying machine and the surface of the copies, and evaluated according to the following criteria.

(Onboard)
(Copy) ◎:
Almost no toner scattering No toner scattering ○: Slight toner scattering
〃 ●: There is some toner scattering 〃
△: Toner scattering
Toner scattering ×: A large amount of toner scattering. Toner droplets. The test results are also shown in Table 4.

[0032]

[Table 4]

Table 4 shows that by adjusting the pH value of the hydrophobic silica fine powder and the charge control agent within a certain range, the chargeability can be stabilized and image density and toner scattering can be significantly reduced. .

[0034]

As described above, according to the electrophotographic toner of the present invention, the toner of the general formula (1) has a pH value of 3 to 5.
) Since hydrophobic silica fine powder with a pH value of 3.5 to 4.5 is mixed and dispersed in the toner particles containing the compound represented by the above as a charge control agent, the charging characteristics are stable and stable. This has the advantage that an image can be obtained and toner scattering can be effectively prevented.

Claims (1)

[Claims] [Claim 1] General formula (1): [Formula 1] [In the formula, R1, R2, R3 and R4 are the same or different and are a hydrogen atom, a halogen atom or a group: [Formula 2]
] (wherein R5 and R6 are the same or different and represent an alkyl group or an aryl group), and Y is Cr
, Fe, Co, Zn or Ti, and Z+ represents a cation selected from the group consisting of ammonium ions, hydrogen ions, potassium ions and sodium ions. However, R1, R2, R3 and R4 must not all be hydrogen atoms at the same time. Toner particles containing a compound represented by ] and having a pH value of 3 to 5,
An electrophotographic toner characterized in that hydrophobic silica having a pH value of 3.5 to 4.5 is mixed and dispersed.