JP2000098650A - Negative charging toner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a negative charge toner having excellent electrification rising property and electrification stability with time by using acidic carbon black having specified pH as a coloring agent and using hydrophobic titanium oxide and metal silicate as external additive fine particles. SOLUTION: Hydrophobic titanium oxide and metal silicate are externally added to negative charge toner particles containing a binder resin and acidic carbon black of pH >=1 and <7 as a coloring agent. The metal silicate is preferably at least one compd. selected from strontium silicate, magnesium silicate, zirconium silicate, cobalt silicate and manganese silicate. The amt. of hydrophobic titanium oxide added is preferably 0.05 to 3 wt.%, preferably 0.1 to 2.0 wt.% to toner particles. The weight ratio of hydrophobic titanium oxide to metal silicates added is 8:1 to 1:1.2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a toner for developing an electrostatic latent image, and more particularly to a negatively charged toner used in a digital image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus, an analog system such as a copying machine which forms an electrostatic latent image on a photosensitive member by irradiating a document with light from a light source and irradiating a reflected light thereof to a photosensitive member. Image forming apparatus is generally used. In addition, as a digital image forming apparatus for developing by supplying a developer containing toner to an electrostatic latent image obtained by digital writing, image information read by a printer or an image reader used for output of a computer terminal is used. Digital copiers, electrophotographic facsimile machines, and the like, which form images based on image data, have been put to practical use.

In a digital image forming apparatus,
An electrostatic latent image is formed in units of dots on a negatively chargeable organic photoreceptor by digital writing such as irradiating a light beam, and the latent image is reversely developed with a negatively charged toner. The image is formed by transferring and fixing the image on a recording medium such as. As described above, the toner used in the digital system is required to have excellent dot reproducibility. That is, when developing the electrostatic latent image formed on the photoreceptor, it is necessary to have faithful reproducibility in dot units, and a characteristic that this reproducibility does not decrease even after repeated use is required.

In order to satisfy such characteristics, it is required that the toner has excellent charge rising characteristics and excellent charge stability. That is, for example, in a two-component developer, the toner is mixed and stirred with the carrier in the developing device and triboelectrically charged, but quickly reaches a desired charge amount in a short stirring time, and thereafter, even if mixed and stirred, the toner is charged. It is necessary to have a charging stability over time such that the amount does not increase or the amount of charging slightly decreases. If the charging stability over time is poor, noise such as fogging is generated on the image due to repeated copying, and if the charging start-up property is poor, noise such as fogging is generated from the beginning and poses a problem.

[0005] In order to solve such a problem, attempts have been made to improve the above-described charging startability and charging stability over time from the viewpoint of fluidity. That is, by ensuring and maintaining good fluidity, good frictional charging is performed on the toner particles, thereby enabling rapid rise of charging of the toner and stable charging over time. .

As a means for improving the fluidity of a toner, it has been common practice to externally add inorganic fine particles such as silica, titanium oxide, and aluminum oxide to toner particles. At present, the above problem cannot be completely solved even by externally adding the particles.

In addition, the toner is required to have not only the charge rising property and the charge stability over time during repeated use, but also the charge stability against environmental fluctuations such as temperature and humidity, particularly temperature change due to temperature rise in the apparatus. Have been.

Further, in order to enhance the reproducibility, it is required to prevent shaving and filming of the photosensitive member.

Furthermore, it is important that the toner has excellent transferability in order to enhance the reproducibility. That is,
If transferability is insufficient, sufficient reproducibility cannot be obtained during transfer even if the electrostatic latent image is faithfully reproduced and developed.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a negatively chargeable toner which is excellent in charge rising property and charging stability with time.

Another object of the present invention is to provide a negatively chargeable toner having excellent charge stability against environmental fluctuations.

Another object of the present invention is to provide a negatively chargeable toner which has improved the problem of shaving the photoconductor and filming on the photoconductor.

Another object of the present invention is to provide a negatively chargeable toner having excellent transferability from an electrostatic latent image carrier such as a photoreceptor to a sheet.

[0014]

The present invention relates to a negatively chargeable toner comprising negatively chargeable toner particles containing at least a binder resin and a colorant and fine particles of an external additive, wherein the colorant has a pH of 1 to 7; The negatively chargeable toner is characterized in that the external additive fine particles are at least hydrophobic titanium oxide and a metal silicate.

The toner of the present invention is obtained by externally adding at least hydrophobic titanium oxide and a metal silicate to negatively charged toner particles containing at least a binder resin and acidic carbon black having a pH of 1 to less than 7. In this specification,
"External addition" refers to adding inorganic fine particles after obtaining toner particles once so that the inorganic fine particles exist on the surface of the toner particles.

In the toner of the present invention, the titanium oxide externally added to the negatively charged toner particles is preferably surface-treated with a hydrophobizing agent by a known method. Specifically, while mixing and stirring titanium oxide having a BET specific surface area of 70 to 250 m ² / g and an average primary particle size of 10 to 50 nm in an aqueous system, a hydrophobizing agent is added at a ratio of 5 to 45% by weight with respect to titanium oxide. Mix, dry and crush the mixture to obtain hydrophobic titanium oxide. Examples of the hydrophobizing agent include known silane coupling agents, silicone oils, organosilicon compounds, titanate compounds, and the like, which are conventionally used for hydrophobizing inorganic fine particles.

The titanium oxide to be subjected to the hydrophobizing treatment may be a commercially available one, or may be produced by a known method, for example, a sulfuric acid method. Preferably, the diameter is within the above range. This is because the subsequent hydrophobicization of titanium oxide is effectively performed. More specifically, when titanium oxide is produced by the sulfuric acid method, the BET specific surface area and the average primary particle size are controlled within the above ranges by changing the hydrolysis rate in the step of obtaining the hydrated titanium oxide, and the hydrated titanium oxide is produced. After being obtained, it is washed and calcined at 600 to 950 ° C. to obtain titanium oxide.

The hydrophobicity of the hydrophobic titanium oxide is preferably at least 50%, more preferably at least 65%. If the degree of hydrophobicity is less than 50%, the environmental resistance deteriorates. The degree of hydrophobicity refers to a value measured by a methanol titration method. Specifically, first, 0.2 g of the hydrophobized external additive was added to 5 parts.
Mix with 0 ml of distilled water in an Erlenmeyer flask. While stirring with a magnetic stirrer, titrate by dropping methanol with a burette. The end point is the point at which the entire amount of the external additive is suspended in the liquid.
Expressed as a volume percentage of methanol in a mixture of water.

In the present invention, the hydrophobic titanium oxide is BE
T specific surface area is 50 to 200 (m ² / g), preferably 6
0 to 190 (m ² / g), more preferably 70 to 180
(M ² / g). When the BET specific surface area is less than 50 (m ² / g), the average primary particle diameter is generally relatively large, so that it is difficult to obtain desired fluidity of the obtained toner, and the charge rising property and the time-dependent charge It is difficult to achieve both stability. Meanwhile, 2
If it exceeds 00 (m ² / g), the average primary particle diameter generally becomes too small, and it becomes difficult to control the adhesion to the toner.

As the hydrophobic titanium oxide as described above,
Commercially available STT30A (manufactured by Titanium Industry Co., Ltd.), T8
05 (manufactured by Nippon Aerosil Co., Ltd.) and the like.

The amount of the hydrophobic titanium oxide is 0.05 to 3% by weight, preferably 0.1 to 2.0% by weight based on the toner particles.
% By weight is preferred. If it is less than 0.05% by weight, environmental stability of charging cannot be obtained. On the other hand, if it exceeds 3% by weight, separation easily occurs, and it becomes easy to form BS on the photoreceptor, which causes noise on the image.

In the toner of the present invention, examples of the metal silicate externally added to the negatively chargeable toner particles together with the hydrophobic titanium oxide include strontium silicate, magnesium silicate, zirconium silicate, cobalt silicate and manganese silicate. These can be used alone or in combination of two or more. The metal silicate salt may or may not be subjected to a hydrophobizing treatment, but is preferably subjected to the hydrophobizing treatment with the above hydrophobizing agent from the viewpoint of environmental resistance.

In the present invention, the metal silicate has a BET specific surface area of 2 to 30 (m ² / g), preferably 3 to 20 (m ² / g).
/ G), more preferably 5 to 15 (m ² / g). When the BET specific surface area is less than 2 (m ² / g), the average primary particle size is generally too large, so that the adhesion to the toner is deteriorated, detachment is liable to occur, and accumulation and charging in the developing device are caused. Cause alienation. Furthermore, it is not supplied to the cleaning section, and the effect as an abrasive cannot be obtained. On the other hand, if it exceeds 30 (m ² / g), the average primary particle diameter generally becomes relatively small, so that it becomes difficult to obtain the effect of polishing the fine particles on the surface of the photoconductor, and filming occurs on the surface of the photoconductor. Easier to do.

The metal silicate has an average primary particle size of 150.
８００800 nm, preferably 180-720 nm, more preferably 200-700 nm. When the particle diameter is less than 150 nm, it is difficult to obtain an appropriate polishing effect on the surface of the photoreceptor, so that filming is easily generated on the surface of the photoreceptor. On the other hand, when the particle size is 800
Above nm, detachment occurs due to poor adhesion.

The metal silicate as described above can be produced by any known method. For example, when producing strontium silicate, after strontium carbonate and silicon oxide are wet-mixed for 8 to 15 hours by a ball mill, the mixture is filtered and dried, and then the mixture is 3 to 10 kg / cm.
It is molded at a pressure of ² and calcined at 900 to 1500 ° C. for 4 to 8 hours, and is crushed by a mechanical crusher while controlling the particle size to obtain strontium silicate fine particles.

In the present invention, by externally adding such a hydrophobic titanium oxide and a metal silicate to the negatively chargeable toner particles, not only the charge rising property and the charging stability over time are improved, but also the high temperature It is possible to prevent a decrease in the charge amount in a humid environment, and in particular, it is possible to maintain the charge amount in a normal temperature environment even in a 50 ° C. environment, and to improve the charge stability against environmental changes. Further, by externally adding the above-mentioned hydrophobic titanium oxide and metal silicate, the fluidity of the toner, the transferability from the photoreceptor to the paper, and the anti-fogging property during printing are improved, and the filming on the photoreceptor is improved. Photoconductor shaving can be prevented.

In the toner of the present invention, the weight ratio of the hydrophobic titanium oxide to the metal silicate is 8: 1 to 1: 1.
1: 1.2, preferably 7: 1 to 1: 0.9, more preferably 6: 1 to 1: 0.9, and the following formula (1); S = Sto × Vto + Ssm × Vsm (1) ( In the formula, Sto is the specific surface area of the hydrophobic titanium oxide (m ² /
g), Vto is the amount of the hydrophobic titanium oxide added to the toner particles (% by weight), and Ssm is the specific surface area of the metal silicate (m
² / g) and Vsm represent the amount (% by weight) of the metal silicate added to the toner particles. ) Is preferably added so that the total specific surface area S of the external additive represented by the formula (3) is 40 to 150, preferably 50 to 140, and more preferably 50 to 130.

If the addition amount of the hydrophobic titanium oxide exceeds eight times the addition amount of the metal silicate, the environmental fluctuation range of charging increases and filming easily occurs. Conversely, the addition amount of the hydrophobic titanium oxide is 0.83 (= 1/1) of the addition amount of the metal silicate.
If the ratio is less than 1.2) times, the rise of charging becomes worse or the amount of scraping of the photoreceptor increases.

If the external additive total specific surface area S is less than 40, the desired toner fluidity cannot be obtained, the replenishment to the developing device is poor, and the chargeability is unstable. Conversely, if it exceeds 150, handling becomes difficult due to excessive fluidity.

By adding the hydrophobic titanium oxide and the metal silicate in a specific weight ratio and a specific total specific surface area as described above, the fluidity of the toner, the charging stability against the environmental fluctuation of the toner, the photoreceptor, and the like are improved. The transferability from paper to paper and the fog prevention during printing can be further improved, and filming on the photoreceptor and shaving of the photoreceptor can be more sufficiently prevented.

In the present invention, in addition to the above-mentioned hydrophobic titanium oxide and metal silicate, for example, silicon carbide,
Boron carbide, titanium carbide, zirconium carbide, hafnium carbide, vanadium carbide, tantalum carbide, niobium carbide,
Various carbides such as tungsten carbide, chromium carbide, molybdenum carbide, calcium carbide, boron nitride, titanium nitride,
Various nitrides such as zirconium nitride, various borides such as zirconium boride, aluminum oxide, silica, iron oxide, chromium oxide, calcium oxide, magnesium oxide,
Various oxides such as zinc oxide and copper oxide, sulfides such as molybdenum disulfide, fluorides such as magnesium fluoride and carbon fluoride, various metal soaps such as aluminum stearate, zinc stearate, magnesium stearate, and titanic acid Strontium, metal titanate such as magnesium titanate, or, emulsion polymerization method, soap-free emulsion polymerization method,
Styrene, (meth) acrylic, olefin, fluorinated (meth) acrylic, nitrogen-containing (meth) acrylic, epoxy, silicon granulated by wet polymerization such as non-aqueous dispersion polymerization, gas phase method, etc. Various organic fine particles such as benzoguanamine, melamine and the like and copolymers thereof may be added to the toner particles alone or in combination.

In a preferred embodiment of the present invention, of the above, silica, strontium titanate, etc. are added alone or in combination with the above-mentioned hydrophobic titanium oxide and metal silicate.

The negatively charged toner particles constituting the toner of the present invention contain at least a binder resin and a colorant.

The binder resin is not particularly limited as long as it is a known thermoplastic resin conventionally used as a binder resin for a toner. Examples of the binder resin include a polyester resin, a styrene resin, an acrylic resin, and a styrene resin. An acrylic resin, an epoxy resin or a mixture thereof can be exemplified.

In the toner of the present invention, the binder resin has an acid value of 5 to 50 KOH mg / g, preferably 1 to 50 KOH mg / g.
A polyester resin of 0 to 40 KOH mg / g is preferably used. By using a polyester resin having such an acid value, the dispersibility of carbon black described later can be improved, and a toner having a sufficient negative charge amount can be obtained. Acid value is 5KOH
If the acid value is less than 50 mg / g, the stability of the toner charge amount against environmental fluctuations, particularly humidity fluctuations, will be impaired.

In the present invention, it is preferable to use a polyester resin obtained by polycondensing a polyhydric alcohol component and a polycarboxylic acid component as the polyester resin. In such a polyester resin, the acid value can be adjusted by the amount of the polyvalent carboxylic acid component used.

As the dihydric alcohol component of the polyhydric alcohol component, for example, polyoxypropylene (2,
2) -2,2-bis (4-hydroxyphenyl) propane, polyoxypropylene (3,3) -2,2-bis (4-hydroxyphenyl) propane, polyoxypropylene (6) -2,2-bis (4-hydroxyphenyl) propane, polyoxyethylene (2,0) -2,2
Bisphenol A alkylene oxide adducts such as -bis (4-hydroxyphenyl) propane, ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl Glycol, 1,4-butenediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polytetramethylene glycol, bisphenol A, hydrogenated bisphenol A And the like.

Examples of the trivalent or higher valent alcohol component include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol,
2,4-butanetriol, 1,2,5-pentanetriol, glycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, 1,3
5-trihydroxymethylbenzene and the like.

Examples of the divalent carboxylic acid component of the polycarboxylic acid component include, for example, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, and cyclohexanedicarboxylic acid. Succinic acid, adipic acid, sebacic acid, azelaic acid, malonic acid, n-dodecenyl succinic acid, isododecenyl succinic acid, n-dodecyl succinic acid, isododecyl succinic acid, n-octenyl succinic acid, isooctenyl succinic acid, Examples thereof include n-octylsuccinic acid, isooctylsuccinic acid, anhydrides and lower alkyl esters of these acids.

Examples of the trivalent or higher carboxylic acid component include 1,2,4-benzenetricarboxylic acid (trimellitic acid), 1,2,5-benzenetricarboxylic acid, and 2,2,4-benzenetricarboxylic acid.
5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanenetricarboxylic acid, 1,3
-Dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra (methylenecarboxyl) methane, 1,2,2
7,8-octanetetracarboxylic acid, pyromellitic acid,
Empol trimer acids, anhydrides of these acids, lower alkyl esters and the like.

In the present invention, a mixture of a raw material monomer of the polyester resin, a raw material monomer of the vinyl resin, and a monomer which reacts with the raw material monomers of both resins is used as the polyester resin in the same container. A resin obtained by performing a polycondensation reaction for obtaining a polyester resin and a radical polymerization reaction for obtaining a vinyl resin in parallel can also be suitably used. The monomers that react with the raw material monomers of both resins are, in other words, monomers that can be used for both the condensation polymerization reaction and the radical polymerization reaction. That is, it is a monomer having a carboxy group capable of undergoing a polycondensation reaction and a vinyl group capable of undergoing a radical polymerization reaction, and examples thereof include fumaric acid, maleic acid, acrylic acid, and methacrylic acid.

The raw material monomers for the polyester resin include the above-mentioned polyhydric alcohol component and polycarboxylic acid component.

Examples of the raw material monomers for the vinyl resin include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-ethylstyrene, 2,4-dimethylstyrene,
Styrene or styrene derivatives such as p-tert-butylstyrene and p-chlorostyrene; ethylenically unsaturated monoolefins such as ethylene, propylene, butylene and isobutylene; methyl methacrylate and n-methacrylic acid
Propyl, isopropyl methacrylate, n-methacrylate
-Butyl, isobutyl methacrylate, t-methacrylate
Butyl, n-pentyl methacrylate, isopentyl methacrylate, neopentyl methacrylate, methacrylic acid 3
-(Methyl) butyl, hexyl methacrylate, octyl methacrylate, nonyl methacrylate, decyl methacrylate, undecyl methacrylate, dodecyl methacrylate and the like; alkyl methacrylates; methyl acrylate, n-propyl acrylate, isopropyl acrylate , N-butyl acrylate, isobutyl acrylate, t-butyl acrylate, n-pentyl acrylate, isopentyl acrylate, neopentyl acrylate, 3- (methyl) butyl acrylate, hexyl acrylate, octyl acrylate, acrylic acid Nonyl, decyl acrylate,
Alkyl acrylates such as undecyl acrylate and dodecyl acrylate; acrylic acid, methacrylic acid,
Unsaturated carboxylic acids such as itaconic acid and maleic acid; acrylonitrile, maleic ester, itaconic ester, vinyl chloride, vinyl acetate, vinyl benzoate, vinyl methyl ethyl ketone, vinyl hexyl ketone, vinyl methyl ether, vinyl ethyl ether and vinyl isobutyl ether And the like.

Examples of the polymerization initiator for polymerizing the raw material monomer of the vinyl resin include 2,2′-azobis (2,4-dimethylvaleronitrile, 2,2′-azobisisobutyronitrile, 1'-azobis (cyclohexane-1-carbonitrile), 2,2'-azobis-
Examples include azo-based or diazo-based polymerization initiators such as 4-methoxy-2,4-dimethylvaleronitrile, and peroxide-based polymerization initiators such as benzoyl peroxide, methyl ethyl ketone peroxide, isopropyl peroxy carbonate, and lauroyl peroxide. Can be

In the present invention, it is preferable to use two kinds of polyester resins having different softening points as the polyester resin in order to improve the fixing property and the offset resistance. That is, the first polyester resin having a softening point of 95 to 120 ° C. is used to improve the fixing property, and the softening point is 13 to improve the offset resistance.
It is preferable to use a second polyester resin at 0 to 160 ° C. In this case, if the softening point of the first polyester resin is lower than 95 ° C., the offset resistance is lowered or the dot reproducibility is lowered. If the softening point is higher than 120 ° C., the effect of improving the fixability becomes insufficient. If the softening point of the second polyester resin is lower than 130 ° C, the effect of improving the offset resistance becomes insufficient, and if it is higher than 160 ° C, the fixability decreases. From such a viewpoint, the softening point of the first polyester resin is more preferably 100 to 115 ° C, and the softening point of the second polyester resin is more preferably 135 to 155.
° C. It is desirable that the first and second polyester resins have a glass transition point of 50 to 75 ° C, preferably 55 to 70 ° C. This is because if the glass transition point is low, the heat resistance of the toner becomes insufficient, and if the glass transition point is too high, the pulverizability at the time of production is lowered and the production efficiency is lowered.

The first polyester resin is a polyester resin obtained by polycondensation of the above-mentioned polyhydric alcohol component and polyhydric carboxylic acid component. In particular, the polyhydric alcohol component contains bisphenol A alkylene oxide adduct as a main component. A polyester resin obtained by using at least one polycarboxylic acid selected from the group consisting of terephthalic acid, fumaric acid, dodecenylsuccinic acid, and benzenetricarboxylic acid as a polycarboxylic acid component as a main component is preferable.

Further, as the second polyester resin,
Polycondensation reaction and vinyl resin to obtain polyester resin in the same container using a mixture of raw material monomer of polyester resin, raw material monomer of vinyl resin, and a bi-reactive monomer that reacts with raw material monomer of both resins The polyester resin obtained by performing the radical polymerization reaction in parallel with the above is preferable from the viewpoint of improving the dispersibility of the wax, the toughness, the fixability, and the offset resistance of the toner.
The content of the vinyl resin in the second polyester resin is 5
-40% by weight, preferably 10-35% by weight. If the content of the vinyl resin is less than 5% by weight, the fixing strength of the toner decreases, and if the content exceeds 40% by weight, the offset resistance, the toughness of the toner, the negative charge level and the like tend to be reduced. It is because it becomes. When the toner contains wax, if the content of the vinyl resin is less than 5% by weight, the dispersibility of the polyethylene wax decreases, and
If the amount is more than 10% by weight, the dispersibility of the polypropylene wax tends to decrease.

The weight ratio of the first polyester resin to the second polyester resin is 7: 3 to 2: 8, preferably 6: 3.
It is preferable to set it to 4: 3: 7. By using the first polyester-based resin and the second polyester-based resin in such a range, as a toner, the spread due to crushing at the time of fixing is small and the dot reproducibility is excellent, and the toner is excellent in low-temperature fixability and low in speed. Excellent fixability can be ensured even in a high-speed image forming apparatus. Also, excellent dot reproducibility can be maintained even when forming a double-sided image (when passing through the fixing device twice). If the proportion of the first polyester resin is smaller than the above range, the low-temperature fixability becomes insufficient and a wide fixability cannot be secured. When the proportion of the second polyester resin is less than the above range, the offset resistance is reduced, and the toner is crushed at the time of fixing, and the dot reproducibility tends to be reduced.

In this specification, the softening point of the resin is determined by using a flow tester (CFT-500: manufactured by Shimadzu Corporation).
Die pores (diameter 1mm, length 1mm), pressurized 20kg
The temperature corresponding to 1/2 of the height from the outflow start point to the outflow end point when a 1 cm ² sample was melted out under the conditions of / cm ² and a heating rate of 6 ° C./min was defined as the softening point. The glass transition point was measured using a differential scanning calorimeter (DSC-200: manufactured by Seiko Denshi Co., Ltd.) using alumina as a reference and measuring 10 m.
g of the sample at a rate of 10 ° C./min.
The temperature was measured between 0 ° C., and the shoulder value of the main endothermic peak was defined as the glass transition point. The acid value was determined by dissolving a 10 mg sample in 50 ml of toluene and titrating with a pre-specified N / 10 potassium hydroxide / alcohol solution using a mixed indicator of 0.1% bromthymol blue and phenol red. / 10 This is a value calculated from the consumption amount of potassium hydroxide / alcohol solution.

The colorant contained in the negatively charged toner particles constituting the toner of the present invention is acidic carbon black having a pH of 1 or more and less than 7, preferably 1 to 6, more preferably 2 to 5. By including carbon black having such a pH, it is possible to improve the charge rising characteristics including the charge amount distribution and the stability of the charge amount during repeated use. Acidic carbon black of such a pH,
It is considered that this acts well on the negative chargeability of the toner. When a neutral or alkaline carbon black having a pH of 7 or more is used, the above-described excellent charging startability and charging stability over time cannot be obtained.

The carbon black contained in the toner of the present invention has an average primary particle size of 40 from the viewpoint of safety.
nm or less, preferably 10 to 40 nm,
More preferably, it is desirable to use one having a thickness of 15 to 35 nm. Those having a diameter of more than 40 nm have a large amount of PAH, and may be carcinogenic.

As the above carbon black, commercially available Mogal L (manufactured by Cabot), MA-7
7 (manufactured by Mitsubishi Chemical Corporation) and the like.

The content of the acidic carbon black with respect to 100 parts by weight of the binder resin is 6 to 12 parts by weight, preferably 7 to 10 parts by weight. If the content is less than 6 parts by weight, the above-mentioned effects of improving the charge rising property and the charging stability over time will be insufficient. If the content is more than 12 parts by weight, the charge amount of the toner will decrease, and toner fog and spillage will occur. Problem arises.

The negatively charged toner particles constituting the toner of the present invention may contain toner components conventionally contained in the toner, such as a charge controlling agent, as long as the charge rising property and the charging stability over time are not impaired. Wax, magnetic powder and the like can be contained.

The charge control agent is not particularly limited as long as it can further stabilize the negative charge of the toner, and a known negative charge control agent can be used. Examples thereof include a salicylic acid derivative metal complex, a calixarene-based compound, an organic boron compound, a fluorinated quaternary ammonium salt-based compound, a monoazo metal complex, an aromatic hydroxycarboxylic acid-based metal complex, and an aromatic dicarboxylic acid-based metal complex. . Charge control agent is binder resin 10
0.1 to 10 parts by weight, preferably 0.1 to 10 parts by weight, based on 0 parts by weight.
It is preferable to use 1 to 6 parts by weight.

Examples of the wax include polyethylene wax, polypropylene wax, carnauba wax, rice wax, sasol wax, montan ester wax, Fischer-Tropsch wax and the like, and these may be used alone or in combination. By including a wax, properties such as offset resistance of the toner can be improved. In the case where the wax is contained in the toner as described above, the content is preferably 0.5 to 5 parts by weight with respect to 100 parts by weight of the binder resin in order to obtain the effect of the addition without causing a problem such as filming. Is preferred. When two or more types of waxes are used in combination, the total content of them should be within the above range.

From the viewpoint of improving the offset resistance, it is preferable to contain a polypropylene wax, and it is also preferable to use a smearing property (a roller is required for automatic paper feeding or double-sided copying when paper of an image already formed on one side is fed). From the viewpoint of improving the image quality such as bleeding or smearing of the image due to rubbing of the image. Particularly preferred from the above viewpoints are polypropylene waxes having a melt viscosity at 160 ° C. of 50 to 300 cps, a softening point of 130 to 160 ° C. and an acid value of 1 to 20 KOHmg / g. Melt viscosity at 1000C is 1000-800
A polyethylene wax having 0 cps and a softening point of 130 to 150 ° C. That is, the polypropylene wax having the above-mentioned melt viscosity, softening point and acid value is excellent in dispersibility in the above-mentioned binder resin, and can improve the offset resistance without causing a problem due to the free wax. Further, the polyethylene wax having the above-mentioned melt viscosity and softening point also has excellent dispersibility in the above-mentioned binder resin, and achieves an improvement in smear property by reducing the coefficient of friction of the fixed image surface without causing problems due to free wax. Can be. In addition, the melt viscosity of the wax is a value measured by a Brookfield viscometer.

As the magnetic powder, fine particles of a known magnetic substance such as ferrite, magnetite, and iron can be used, and may be contained from the viewpoint of preventing toner scattering. The content is 0.5 to 10 parts by weight, preferably 0.5 to 8 parts by weight, more preferably 1 to 5 parts by weight, based on 100 parts by weight of the binder resin. Content is 10
If the amount is more than the weight part, the magnetic restraining force of the developer carrying member (built-in magnet roller) with respect to the toner becomes strong, and the developing property decreases. On the other hand, if the amount is less than 0.5 part by weight, the effect of adding the magnetic powder is lost, and toner scattering occurs.

The toner particles constituting the toner of the present invention include:
Using the above-mentioned binder resin, colorant and other desired toner components, it is manufactured by a kneading and pulverizing method, a suspension polymerization method, an emulsion polymerization method, an emulsion dispersion granulation method, an encapsulation method and other known methods. be able to. Among these manufacturing methods, kneading and mixing are considered from the viewpoint of manufacturing cost and manufacturing stability.
Pulverization is preferred.

The kneading and pulverizing method includes a step of mixing a binder resin, a colorant, and other desired toner components with a mixer such as a Henschel mixer, a step of melting and kneading the mixture, and a step of cooling and kneading the kneaded material. The toner particles are manufactured by the following steps: a step of pulverizing the coarsely pulverized particles; and a step of classifying the obtained finely pulverized particles.

In the present invention, the volume average particle diameter of the toner particles is preferably adjusted to 3 to 9 μm, more preferably 6 to 9 μm, from the viewpoint of improving the reproducibility of high-definition images.

The negatively chargeable toner of the present invention is obtained by externally adding the above-mentioned hydrophobic titanium oxide, metal silicate and desired fine particles to the above toner particles and mixing them with a mixer such as a Henschel mixer. Obtainable.

The toner of the present invention can be used in either a two-component developer used with a carrier or a one-component developer without a carrier. As the carrier used in the two-component developer, conventionally known carriers can be used. For example, a carrier composed of magnetic particles such as iron powder, ferrite, and magnetite, and a coat in which the surface of the magnetic particles is coated with a coating material such as a resin. Any of a carrier and a dispersion type carrier obtained by dispersing a magnetic fine powder in a binder resin can be used. As such a carrier, those having a volume average particle size of 15 to 100 μm, preferably 20 to 80 μm are suitable.

In addition, among the above carriers, the negatively charged toner of the present invention is preferably used together with a carrier having a positively charged resin on the surface. For this reason, acrylic resins, styrene-acrylic resins, silicone resins, and the like can be effectively used as resins used in the production of carriers.

The negatively chargeable toner of the present invention is particularly useful for a digital image forming apparatus, but can also be used for an analog image forming apparatus. Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto.

[0066]

EXAMPLES (Production Example of Polyester Resin L) Thermometer,
A polyoxypropylene (2,2) -2,2-bis (4-hydroxyphenyl) was placed in a glass four-necked flask equipped with a stirrer, a falling condenser, and a nitrogen inlet tube.
Propane, polyoxyethylene (2,2) -2,2-bis (4-hydroxyphenyl) propane, isododecenyl succinic anhydride, terephthalic acid and fumaric acid were adjusted to a weight ratio of 82: 77: 16: 32: 30. And dibutyltin oxide as a polymerization initiator. This was reacted in a mantle heater under a nitrogen atmosphere at 220 ° C. with stirring. The obtained polyester resin L has a softening point of 110 ° C., a glass transition point of 60 ° C., and an acid value of 17.
It was 5 KOHmg / g.

(Production Example of Polyester Resin H) Styrene and 2-ethylhexyl acrylate were added in a weight ratio of 1
The mixture was adjusted to 7: 3.2 and placed in a dropping funnel together with a polymerization initiator, digyl peroxide. Meanwhile, a thermometer,
A polyoxypropylene (2,2) -2,2-bis (4-hydroxyphenyl) was placed in a glass four-necked flask equipped with a stirrer, a falling condenser, and a nitrogen inlet tube.
Propane, polyoxyethylene (2,2) -2,2-bis (4-hydroxyphenyl) propane, isododecenyl succinic anhydride, terephthalic acid, 1,2,4-benzenetricarboxylic anhydride and acrylic acid in a weight ratio of 42: 1
The mixture was adjusted to 1: 11: 11: 8: 1 and added together with dibutyltin oxide as a polymerization initiator. This was stirred in a mantle heater under a nitrogen atmosphere at 135 ° C., and styrene and the like were dropped from a dropping funnel. Obtained polyester resin H
Has a softening point of 150 ° C., a glass transition point of 62 ° C. and an acid value of 2
It was 4.5 KOHmg / g.

(Production example of metal silicate: strontium silicate) 1000 g of strontium carbonate and 400 g of silicon oxide
After wet-mixing with a ball mill for 10 hours, the mixture was filtered, dried, molded at a pressure of 5 kg / cm ² , and calcined at 1250 ° C. for 6 hours. This was pulverized with a mechanical pulverizer to obtain small-diameter strontium silicate fine particles (average primary particle diameter: 240 nm, BET specific surface area: 15 m ² / g).

The strontium silicate fine particles formed in the same manner as the method for producing the small strontium silicate fine particles were pulverized and adjusted to obtain fine strontium silicate fine particles (average primary particle diameter: 350 n
m, BET specific surface area 10 m ² / g) and large-diameter strontium silicate fine particles (average primary particle diameter: 700 nm, BET specific surface area 5 m ² / g).

(Production Example of Hydrophobic Titanium Oxide) In the step of obtaining hydrous titanium oxide by a sulfuric acid method, two kinds of hydrous titanium oxide having different particle diameters are obtained by changing the hydrolysis rate.
After washing this, it is baked at 300 ° C. and has an average primary particle size of 15%.
nm, titanium oxide A having a BET specific surface area of 180 m ² / g, an average primary particle size of 50 nm, and a BET specific surface area of 100 m ² / g
Of titanium oxide B was obtained. The titanium oxides A and B were separately mixed at a ratio of 2% by weight in an aqueous system, and n-butyltrimethoxysilane was added as a hydrophobizing agent at a ratio of 10% by weight to the titanium oxide while stirring. The mixture was dried and crushed to obtain a BET specific surface area of 112.
m ² / g, hydrophobic titanium oxide fine particles A having an average primary particle size of 15 nm, a BET specific surface area of 75 m ² / g, and an average primary particle size of 5
0 nm hydrophobic titanium oxide fine particles B were obtained.

(Example 1) A polyester resin L of 40
Parts by weight, 60 parts by weight of polyester resin H, polyethylene wax (800P; manufactured by Mitsui Petrochemical Industries, Ltd .; 16 parts by weight)
Melt viscosity at 0 ° C. 5400 cps; softening point 140
° C) 2 parts by weight, polypropylene wax (TS-20
0; manufactured by Sanyo Chemical Industries, Ltd .; melt viscosity at 160 ° C. 12
0 cps; softening point 145 ° C .; acid value 3.5 KOHmg /
g) 2 parts by weight, acidic carbon black (Mogal L; manufactured by Cabot; pH 2.5; average primary particle size 24 nm) 8
Parts by weight and 3 parts by weight of a negative charge control agent (S-34; manufactured by Orient Chemical Co., Ltd.) were sufficiently mixed with a Henschel mixer.
After melt-kneading with a twin-screw extruder, the mixture was cooled, coarsely pulverized with a hammer mill, finely pulverized with a jet pulverizer, and classified to obtain toner particles having a volume average particle diameter of 7.5 μm. Hydrophobic titanium oxide fine particles A0.6
% By weight and 0.3% by weight of medium-sized strontium silicate fine particles were added and mixed to obtain a toner.

Example 2 A toner was obtained in the same manner as in Example 1, except that 0.3% by weight of the medium-sized strontium silicate fine particles was changed to 0.2% by weight of the small-sized strontium silicate fine particles. . (Example 3) A toner was obtained in the same manner as in Example 1, except that the addition amount of the hydrophobic titanium oxide fine particles A was changed to 1.0% by weight. (Example 4) In Example 1, the addition amount of the hydrophobic titanium oxide fine particles A was changed to 1.2% by weight, and 0.3% by weight of the medium-sized strontium silicate fine particles was replaced with the large-sized strontium silicate fine particles 0.2%. Except that the weight%
A toner was obtained in the same manner as in Example 1.

(Example 5) A toner was obtained in the same manner as in Example 1, except that the hydrophobic titanium oxide fine particles A (0.6% by weight) were changed to the hydrophobic titanium oxide fine particles B (0.8% by weight). Was. (Example 6) In Example 1, the addition amount of the hydrophobic titanium oxide fine particles A was changed to 0.7% by weight, and the hydrophobic silica fine particles H2000 (manufactured by Hoechst; B
A toner was obtained in the same manner as in Example 1, except that 0.2% by weight (ET specific surface area 140 m ² / g) was added. (Example 7) In Example 6, the amount of the hydrophobic titanium oxide fine particles A was changed to 0.5% by weight, and the BET specific surface area was 10 m ² / g, and the average primary particle size was 350.
A toner was obtained in the same manner as in Example 6, except that 0.2% by weight of fine particles of strontium titanate was added.

(Comparative Example 1) A toner was obtained in the same manner as in Example 1 except that fine strontium silicate fine particles were not added. (Comparative Example 2) A toner was obtained in the same manner as in Example 1, except that the hydrophobic titanium oxide fine particles A were not added. (Comparative Example 3) A toner was obtained in the same manner as in Example 1, except that 8 parts by weight of REGAL330 (manufactured by Cabot; pH 9.0; average primary particle size: 25 nm) was used as carbon black.

The toners obtained above were evaluated as described below, and the results are shown in Table 1 together with various production conditions. (Toner fluidity) The loose specific gravity of each of the toners obtained above was measured using a powder tester (manufactured by Hosokawa Micron Corporation), and the loose apparent specific gravity was 0.42 cc /.
g or more and less than 0.47 cc / g, “○”, 0.38
"△", less than 0.38 cc / g or 0.47 c
Those having a practical problem at c / g or more were evaluated as "x".

(Environment resistance) 1.5 g of each of the obtained toners and 28.5 g of a carrier for a digital copying machine (Di30; manufactured by Minolta) (toner: carrier = 5: 95 by weight ratio)
Was placed in a 50 cc polybin, which was rotated at 120 rpm by a ball mill base and mixed for 30 minutes to prepare a developer. This developer is used in other evaluations described below. The obtained developer was placed in an H / H environment (3
0 ° C, 85% RH) or L / L environment (10 ° C, 15% RH)
% RH) for 3 hours, the charge amount (μc / g) of each developer was measured, and the absolute value of the charge amount difference was 10 μc
/ G of less than 10 μc / g
Those with less than g were evaluated as “Δ”, and those with 15 μc / g or more were evaluated as “x”.

(Transferability) Using a digital copying machine Di30 (manufactured by Minolta Co., Ltd.), each developer was subjected to an image output test of 3,000 sheets, and the image was visually checked. The sample was evaluated as “○”, the one with slight loss but no practical problem was rated as “△”, and the one with image loss and practical problem was rated as “x”.
Note that “image loss due to poor transfer” means “hollowout” which is generally referred to.

(Charge rising property) In a 50 cc polybin, 1.5 g of toner and 28.5 g of carrier were put.
This was rotated at 120 rpm by a ball mill stand, mixed, and then mixed for 5 minutes, 10 minutes, 30 minutes, 60 minutes, 120 minutes, and 7 minutes.
After 80 minutes, each charge amount was measured (under 25 ° C. and 45% RH environment). The ratio of the charge amount after 5 minutes to the maximum charge amount [(charge amount after 5 minutes / charge amount maximum value) × 100] is 90.
% Or more, very good start-up property is “○”, the ratio is 80% or more and less than 90%, and those practically usable are “△”, the ratio is less than 80%. Those having practical problems were evaluated as "x".

(Chargeability under high temperature environment) 1.5 g of toner and 28.5 g of carrier were put in 50 cc polybin,
After leaving for 2 hours in a 50 ° C. environment, 50 ° C., 45% RH
Under an environment, the mixture was rotated by a ball mill stand at 120 rpm, mixed, and the charge amount after 10 minutes (hereinafter referred to as charge amount at 50 ° C.) was measured. 25 ° C.).
Ratio of the charge amount at 50 ° C. to the charge amount at 50 ° C. [(50
80% of the charge amount at 25 ° C./the charge amount at 25 ° C.) × 100]
The results are as follows: "O" indicates that the charge is maintained even at a high temperature, and "Δ" indicates that the charge is 70% or more and less than 80% and is practically usable. It was evaluated as "x".

(Initial and post-print fog) Using a digital copying machine Di30 (manufactured by Minolta), an image forming test was performed on 100,000 sheets of each developer, and the initial printing was performed (after 100 sheets).
The image after printing was visually confirmed, and the image without fogging was evaluated as “○”, and the image with slight fogging but having no practical problem was rated “△”. Problems were evaluated as "x".

(Photoconductor Filming) Digital Copier D
10 for each developer using i30 (Minolta)
After conducting an image test on 10,000 sheets and observing the filming on the photoreceptor, "○" indicates that no filming occurred, and "△" indicates that there was some filming but no practical problem. Those having practical problems due to occurrence of filming were evaluated as "x".

(Sharpness of Photoconductor) Digital Copier Di3
0 (manufactured by Minolta Co., Ltd.) was tested for 100,000 sheets of each developer, and the change in the thickness of the photoreceptor before and after printing was determined as the abrasion amount, and the abrasion amount was less than 6.5 μm. Was evaluated as “○”, those with 6.5 μm or more and less than 8.0 μm as “Δ”, and those with 8.0 μm or more that had practical problems were evaluated as “×”. In addition, the shaving amount is before the photoconductor,
The average value of the shaving amount at three locations, the center and the back side, is used.

[0083]

[Table 1]

In the present specification, the pH of carbon black refers to a value measured by the following method. First, 5 g of the sample (CB) is placed in a beaker, and 50 ml of distilled water is added. Cover it with a watch glass and boil for 15 minutes. After boiling, the mixture is cooled to room temperature, and the supernatant is removed by centrifugation to remove the mud. Glass electrode pH in it
The electrode of the meter is inserted, and the pH is measured by the method of JIS Z8802. The measurement is performed three times by stirring the slurry so that the mud adheres well around the electrode. This operation is repeated until the measured value falls within the error range of 0.1 or less.

[0085]

The toner of the present invention is excellent in fluidity, excellent in charging start-up characteristics and in charging stability over time.
Further, the toner of the present invention has excellent charging stability against environmental changes. Further, the toner of the present invention is excellent in transferability from an electrostatic latent image carrier such as a photoconductor to paper. Further, the toner of the present invention can avoid the problem of shaving of the photoconductor and filming on the photoconductor.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yoshitaka Sekiguchi 2-3-13 Azuchicho, Chuo-ku, Osaka-shi, Osaka F-term in Osaka International Building Minolta Co., Ltd. 2H005 AA01 AA08 CA08 CA26 CB07 CB08 CB18 DA02 EA07 EA10

Claims (6)

[Claims] 1. A negatively-chargeable toner comprising negatively-chargeable toner particles containing at least a binder resin and a colorant and fine particles of an external additive, wherein the colorant is acidic carbon black having a pH of 1 or more and less than 7. Negatively chargeable toner, wherein the external additive fine particles are at least hydrophobic titanium oxide and a metal silicate. 2. The method according to claim 1, wherein the metal silicate is at least one selected from the group consisting of strontium silicate, magnesium silicate, zirconium silicate, cobalt silicate and manganese silicate.
2. The negatively chargeable toner according to claim 1, wherein the metal silicate is one of two metal silicates. 3. The binder resin has an acid value of 5 to 50 KOHm.
The negatively chargeable toner according to claim 1, which is a g / g polyester resin. 4. The hydrophobic titanium oxide having a BET specific surface area of 5
Negatively chargeable toner according to claim 1, characterized in that a 0~150 (m ² / g). 5. The metal silicate salt having a BET specific surface area of 2 to 30.
Negatively chargeable toner according to claim 1, wherein the a (m ² / g). 6. The negatively chargeable toner according to claim 1, wherein the content of carbon black is 6 to 12 parts by weight based on 100 parts by weight of the binder resin.