JPH09197704A - Electrophotographic toner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure satisfactory flowability, heat resistance and fixability by specifying the rate of coating with inorg. fine particles and the absolute value of the quantity of electric charges. SOLUTION: Toner particles are surface-treated with inorg. fine particles having >=20nm, preferably 20-300nm, especially preferably 20-250nm average particle diameter of primary particles on area basis so that the rate of coating with the inorg. fine particles is regulated to <=50%, preferably 15-50%, especially preferably 25-40%. The absolute value of the quantity of electric charges of the resultant surface-treated toner is regulated to >=15μC/g, preferably 15-30μC/g. The inorg. fine particles have such electrostatic charging ability as to increase the absolute value of the quantity of electric charges of the toner particles by >=2 times, preferably about 2-4 times that of the toner before surface treatment by the surface treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic toner used in an image forming apparatus utilizing an electrophotographic process such as an electrostatic copying machine, a laser printer and a facsimile, and more specifically, it has excellent low temperature fixing property. And an electrophotographic toner.

[0002]

2. Description of the Related Art A toner used as a developer in an image forming apparatus utilizing the above electrophotographic process is usually prepared by dispersing a colorant such as carbon black in a fixing resin and granulating it to a predetermined particle size. The obtained toner particles are surface-treated with inorganic fine particles such as silica for the purpose of further increasing the fluidity.

In recent years, in order to reduce the energy consumption of an image forming apparatus, it is required to lower the fixing temperature of toner. However, the above-mentioned inorganic fine particles have a problem that they hinder or have a bad influence on the fixing property of the toner, and particularly when the fixing temperature is low, the problem of lowering the fixing property is remarkable. Therefore, in order to improve the fixing property of the toner, an attempt has been made to perform surface treatment with resin fine particles instead of the inorganic fine particles. For example, JP-A-3-41465
For electrophotography, the surface of toner particles containing a specific wax is surface-treated with resin fine particles having an average particle diameter of 0.05 to 0.5 μm and a glass transition temperature Tg of 120 ° C. or less. Toners are disclosed.

[0004]

However, when the surface treatment is performed with resin fine particles, there is a problem that the fluidity of the toner is lowered and blocking occurs. Therefore, when actually used, it is necessary to use the resin fine particles and the inorganic fine particles together. Further, as described in the above publication, even when the particle size of the resin fine particles used for the surface treatment is regulated or the glass transition temperature Tg of the resin fine particles is regulated in order to further improve the fixing property at low temperature. When the compatibility between the fixing resin forming the toner particles and the resin fine particles is low, the fixing property of the toner may be deteriorated.

On the other hand, there is a method of using a fixing resin having a low glass transition temperature Tg in order to lower the fixing temperature of the toner, but in this case, the heat resistance of the toner is lowered and the strength of the toner is lowered. Therefore, image fog, toner scattering, toner blocking, and the like may occur.
Therefore, an object of the present invention is to provide an electrophotographic toner having sufficient fluidity and heat resistance, and having sufficient fixability even at a low temperature.

[0006]

As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention have found that toner particles are prepared by using inorganic fine particles having an average primary particle size of 20 nm or more. The surface-treated electrophotographic toner has sufficient fluidity and heat resistance when the inorganic fine particle coverage is 50% or less and the absolute value of the charge amount is 15 μC / g or more. In addition, the present invention has been completed by discovering a new fact that an electrophotographic toner having a sufficient fixing property can be obtained even at a low temperature.

In the present invention, "coverage of inorganic fine particles"
Represents the ratio (%) of the area covered by the inorganic fine particles to the surface area of the toner particles constituting the toner, and is calculated using the following formula.

[0008]

[Equation 1]

(Wherein f is the coverage of the inorganic fine particles, D is the average particle diameter (μm) of the toner particles, d is the area-based average particle diameter (μm) of the inorganic fine particles, and ρ _t is the true specific gravity of the toner particles. , Ρ
_i represents the true specific gravity of the inorganic fine particles. Also, C is the following formula:

[0010]

[Equation 2]

It is represented by When the toner particles are surface-treated within the above-mentioned coverage, the absolute value of the charge amount of the electrophotographic toner is 2 relative to the absolute value of the charge amount of the toner particles themselves before the surface treatment. It is preferably double or more. That is, as the inorganic fine particles used in the present invention, in addition to the average particle size (area standard) of the primary particles being in the above range, the surface treatment condition that the coverage is in the above range It is preferable to have a charging ability to increase the amount (absolute value) more than twice.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The electrophotographic toner of the present invention will be described in detail below. In the present invention, inorganic fine particles are used as a surface treatment agent for toner particles. Examples of the inorganic fine particles that can be used in the present invention include fine particles of silica, alumina, titanium and the like. Of these inorganic fine particles, silica fine particles are particularly preferably used from the viewpoint of toner fluidity and chargeability.

The inorganic fine particles used in the present invention have a primary particle having an average particle size (area standard) of 20 nm or more and a surface treatment of 50% or less so that the toner is charged. It is suitable that the absolute value of the amount has a charging ability to increase the absolute value of the charged amount of the toner particles themselves before the surface treatment by a factor of 2 or more, preferably 2 to 4 times. Since the absolute value of the charge amount of the toner particles is usually about 5 to 10 μC / g, it is necessary to increase the absolute value of the charge amount of the toner more than twice the absolute value of the charge amount of the toner particles themselves. If it is not possible, the charge amount of the toner may be insufficient.

The average particle size (based on area) of the primary particles of the inorganic fine particles is preferably 20 nm or more, preferably 20 to 300 nm, more preferably 20 to 250 nm. If the average particle diameter is less than the above range, the chargeability and heat resistance of the toner are deteriorated, which is not preferable. On the other hand, the upper limit of the average particle size is not particularly limited, but the average particle size is 500 nm.
When it exceeds, the inorganic fine particles become too large with respect to the toner particles, are easily detached from the toner particles, and fogging due to poor charging and toner scattering occur, which is not preferable.

It is preferable that the coverage of the inorganic fine particles is 50% or less, preferably 15 to 50%, more preferably 25 to 40%. When the coverage exceeds the above range, the fixing property is deteriorated, which is not preferable. On the other hand, the lower limit of the coverage is not particularly limited, but when the coverage is less than 15%, the charge amount of the toner may become insufficient, or the fluidity and heat resistance of the toner may deteriorate.

To set the coverage of the inorganic fine particles within the above range, the toner particles and the inorganic fine particles may be added to a Henschel mixer, a Nauter mixer, a V-type mixer or the like and mixed. The addition amount of the inorganic fine particles is usually set in the range of 0.1 to 5% by weight with respect to the toner particles. However, the addition amount varies depending on the specific gravity of the inorganic fine particles to be used, and is therefore limited to the above range. Not something.

The charge amount of the toner after the surface treatment is usually 15 μC / g or more in absolute value, preferably 15 to
It is in the range of 30 μC / g. The charge amount is selected to be either positive or negative depending on the desired charge polarity. If the absolute value of the charge amount of the toner is less than the above range, the toner may be scattered or fog, which is not preferable.

The fluidity of the toner can be evaluated, for example, by the amount of toner that falls within a fixed time. The fluidity of the toner in the present invention was evaluated by filling the toner in a container, measuring the amount of toner dropped from the opening at the bottom of the container within a certain period of time, and evaluating this as an index of fluidity. The container used for the measurement had a taper angle of 60 °, an opening having a length of 100 mm and a width of 0.1 mm was provided at the bottom of the container, and a diameter of 16 mm having an uneven surface on the upper part of the opening.
It has a brass roller of mm. To measure the amount of toner drop, set the roller rotation speed to 3 revolutions per minute and
The drop amount was calculated from the amount of toner that dropped per minute.

The amount of toner dropped is preferably 4 g / 5 minutes or more. When the falling amount is below the above range, the fluidity of the toner becomes insufficient. The heat resistance of the toner was evaluated using the temperature at which toner blocking occurs. That is,
Put 5g of toner in a glass cylinder with an inner diameter of 25mm,
After placing a weight of 100 g on it and allowing it to stand at any temperature for 30 minutes, it was confirmed whether the toner was blocking, and the upper limit of the temperature at which blocking did not occur was determined.
The upper limit of the temperature at which blocking does not occur is preferably 52 ° C or higher. When this temperature is below 52 ° C,
The heat resistance of the toner becomes insufficient.

The fixability of the toner is determined by applying a predetermined load to the image formed on the paper and rubbing it to obtain the amount of change in the image density before and after the rubbing, and then using the following formula: ) Can be evaluated.

[0021]

(Equation 3)

The fixing ratio in the present invention was measured by using an electrostatic copying machine to form a black solid image on plain paper. For the friction of the formed image, a weight (20 g / cm ² ) made of a mild steel cylinder (height: 26 mm, diameter: 50 mm) with a cotton cloth coated on the bottom was used, and the formed image was forcibly rubbed 10 times. I went. The fixing rate of the toner may be equal to or higher than the fixing rate of the toner particles themselves which are not surface-treated with the inorganic fine particles.

As the toner particles in the electrophotographic toner of the present invention, any known toner particles conventionally used in the dry developing method can be used. Examples of the fixing resin include styrene-acrylic polymers, styrene polymers, acrylic polymers, olefin polymers such as chlorinated polystyrene, polypropylene, ionomers, polyvinyl chloride, polyesters, polyamides, polyurethanes, and epoxies. Resin, diallyl phthalate resin,
Examples thereof include silicone resin, ketone resin, polyvinyl butyral resin, phenol resin, rosin-modified phenol resin, xylene resin, rosin-modified maleic resin, and rosin ester. Among these, it is preferable to use an acrylic polymer or a styrene-acrylic polymer from the viewpoints of controlling the molecular weight and facilitating the operations such as pulverization after producing the toner particles. Further, when used for a full-color toner, it is preferable to use polyester having excellent color mixing properties.

As the colorant to be dispersed in the fixing resin,
Various conventionally known dyes and pigments are used, and in the case of black toner, carbon black, acetylene black, aniline black and the like are used. In the case of full-color toner, magenta, cyan and yellow pigments are used. In addition to colorants, the above-mentioned fixing resins include known charge control agents and release agents (anti-offset agents).
Various additives such as can be blended.

The charge control agent is blended in order to control the triboelectric charging property of the toner, and there are two types, one for positive charge charging and the other for negative charge control according to the charging characteristics of the toner. Examples of the charge control agent for controlling the positive charge include organic compounds having a basic nitrogen atom, such as basic dyes, aminopyrine, pyrimidine compounds, polynuclear polyamino compounds and aminosilanes.

Examples of the charge control agent for controlling the negative charge include oil-soluble dyes such as nigrosine base, oil black and spirone black, metal-containing azo dyes, metal salts of naphthenic acid, metal salts of alkylsalicylic acid, fatty acid soaps, resin acids. Examples include soap. The amount of charge control agent added is 100
It is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 8 parts by weight, based on parts by weight.

Examples of the offset preventing agent include fatty hydrocarbons, aliphatic metal salts, higher fatty acids, fatty acid esters or partially saponified products thereof, silicone oil, and various waxes. Among them, the weight average molecular weight is 10
Aliphatic hydrocarbons of about 00 to 10,000 are preferable.
Specifically, one or a combination of two or more of low molecular weight polypropylene, low molecular weight polyethylene, paraffin wax, a low molecular weight olefin polymer composed of olefin units having 4 or more carbon atoms, silicone oil and the like is suitable.

The amount of the offset inhibitor added is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 8 parts by weight, based on 100 parts by weight of the fixing resin.
Toner particles are prepared by dispersing a colorant in the fixing resin, further blending the above-mentioned components as required, and homogenizing and premixing the components with a dry blender, a Henschel mixer, a ball mill, and further using a Banbury mixer and a roll. It is produced by uniformly melt-kneading using a kneading device such as a uniaxial or biaxial extrusion kneader, cooling the resulting kneaded product, pulverizing, and, if necessary, classifying.

The particle size of the toner particles is not particularly limited in the present invention, but is usually set so that the average particle size is 6 to 15 μm, preferably 7 to 12 μm. The absolute value of the charge amount of the toner particles is usually 15 μC / g or more, preferably 15 to 30 μC / g.
When the absolute value of the charge amount of the toner particles is less than the above range, the charge amount of the toner obtained by surface-treating the toner particles becomes insufficient, or the amount of inorganic fine particles required for the surface treatment becomes too large. However, there is a possibility that problems such as a decrease in toner fixability may occur.

When the toner of the present invention is used as a magnetic toner, magnetic powder may be blended. The magnetic substance is a substance that is strongly magnetized in that direction by a magnetic field, and is preferably chemically stable, and is preferably a fine powder having a particle size of 1 μm or less, particularly about 0.01 to 1 μm. Typical magnetic materials include, for example, iron oxides such as magnetite, hematite, and ferrite, as well as metals such as iron, cobalt, and nickel, or these metals and aluminum, copper, lead, magnesium, tin, zinc, antimony. , Beryllium, bismuth, cadmium, calcium,
Examples thereof include alloys with manganese, selenium, titanium, tungsten, vanadium, and mixtures thereof. The amount of the magnetic powder added is 20 to 100 parts by weight of the fixing resin.
The amount is preferably 300 parts by weight, more preferably 50 to 150 parts by weight.

In addition, various additives such as stabilizers may be added to the fixing resin in an appropriate ratio.

[0032]

【Example】

Reference Example (Production of Toner Particles) Polyester (MH-21 manufactured by Kao Corporation) was used as a fixing resin.
To 100 parts by weight of carbon black, 10 parts by weight of carbon black, 1.5 parts by weight of a charge control agent for controlling the negative charge (metal-containing azo dye, TRH manufactured by Hodogaya) and wax (polypropylene, viscol manufactured by Sanyo Kasei Co., Ltd.) 660P) (2.5 parts by weight), melt-kneaded, pulverized and classified to prepare toner particles having an average particle diameter of 10 μm. Examples 1 to 2 and Comparative Examples 1 to 8 (Production of Electrophotographic Toner) The surface treatment agent shown in Table 1 below was used in a ratio (% by weight) shown in Table 1 to 2 kg of the toner particles. The surface treatment was performed by mixing for 2 minutes with a Henschel mixer.

As the surface treatment agent, either silica fine particles or acrylic resin fine particles were used. The used surface treatment agent is as follows. (Silica fine particles) TS720: manufactured by Cabot Corporation, average particle size (area standard)
14 nm ・ HDK1303: Hoechst, average particle size (area standard) 23 nm ・ HDK3004: Hoechst, average particle size (area standard) 10 nm ・ SO-C1: Admatex, average particle size (area standard) 200 nm ( Acrylic resin fine particles) ・ MP1451: manufactured by Soken Chemical Industry Co., Ltd., average particle size (area standard)
150nm MP5000: manufactured by Soken Chemical Industry Co., Ltd., average particle size (area standard)
400nm Type of surface treatment agent, average particle size of surface treatment agent (area standard)
The amount (% by weight) of the surface treating agent used is as shown in Table 1 below. (Measurement of Coverage of Inorganic Fine Particles) The coverage of inorganic fine particles in the toners obtained in the above Examples and Comparative Examples was calculated according to the above-mentioned formula. (Evaluation of Toner Charging Property) With respect to the toners obtained in the above-mentioned Examples and Comparative Examples, the charging amount (μC / g) was determined by the blow-off measurement method, and the toner charging property was evaluated. (Evaluation of Toner Fluidity) With respect to the toners obtained in the above Examples and Comparative Examples, the amount of drop (g / 5 minutes) was determined according to the above-mentioned measuring method, and the fluidity of the toner was evaluated. (Evaluation of Heat Resistance of Toner) With respect to the toners obtained in the above Examples and Comparative Examples, the upper limit of the temperature (° C.) at which blocking does not occur was determined according to the method described above, and the heat resistance of the toner was evaluated. (Evaluation of Toner Fixability) A black solid image was formed using the toners obtained in the above Examples and Comparative Examples, and the toner fixing rate (%) was determined according to the method described above.

Images were formed by using an electrostatic copying machine (model number DC-4685) manufactured by Mita Kogyo Co., Ltd. The image density is measured by a reflection densitometer (TC-6 manufactured by Tokyo Denshoku Co., Ltd.).
D). Table 1 shows the evaluation results of the coverage rate of the inorganic fine particles, the charge amount of the toner, the dropping amount, the heat resistance, and the fixing rate.

[0035]

[Table 1]

As shown in Table 1, in the toners of Comparative Examples 1 to 7, at least one of the particle size of the inorganic fine particles, the coverage, the toner charge amount, the drop amount, the heat resistance, and the fixing ratio is in accordance with the present invention. Out of range. For example, in the toners of Comparative Examples 1 to 3 and 5, since the particle size of the silica fine particles is below the range of the present invention, when the coverage is small, the chargeability, heat resistance and fluidity are insufficient, and the coverage is low. When is large, the fixing rate becomes insufficient. Further, the toner of Comparative Example 4 is
The particle size of the silica fine particles satisfies the range of the present invention, but the charge amount is insufficient.

On the other hand, in the toners of Examples 1 and 2, the particle size of silica fine particles, the coverage, and the charge amount of the toner are
Since it satisfies the range of the present invention, it has excellent fluidity, heat resistance, and fixability.

[0038]

According to the present invention, it is possible to obtain a toner having sufficient fluidity and heat resistance, and having sufficient fixability even at a low temperature. In addition, the toner of the present invention has a practically sufficient amount of charge. Therefore, the electrophotographic toner of the present invention is suitable for use in an image forming apparatus utilizing an electrophotographic process such as an electrostatic copying machine, and also has an image forming apparatus in which a fixing temperature is lowered in order to reduce energy consumption. Can also be accommodated.

Claims (2)

[Claims] 1. An area-based average particle diameter of primary particles is 20 nm.
An electrophotographic toner having surface-treated toner particles with the above-mentioned inorganic fine particles, wherein the coverage of the inorganic fine particles is 50% or less and the absolute value of the charge amount is 15 μC / g or more. Toner for electrophotography. 2. The toner for electrophotography according to claim 1, wherein the absolute value of the charge amount of the electrophotographic toner is at least twice the absolute value of the charge amount of the toner particles themselves before the surface treatment.