JP2016138011A - Superfine silica powder and application thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a toner external additive excellent in preservable property, electrification characteristic and flowability and to provided a hydrophobized superfine silica powder suitable for the toner external additive.SOLUTION: In one embodiment, there is provided the superfine silica powder having an average particle diameter of 80 nm or more and less than 300 nm, an average sphericity of 0.50 or more and less than 0.80, an average aspect ratio of 1.0 or more and less than 1.50, and a moisture content of 0.05 wt% or more and less than 0.30 wt.%. The specific area is preferably 10.0 m/g or more and less than 150 m/g. In another embodiment, there is provided the superfine silica fine powder which is identical to the above superfine silica powder in the one embodiment except that the surface of superfine silica powder is treated with hexamethyldisilazane. There is also provided a toner external additive for static charge image development containing the superfine silica powder.SELECTED DRAWING: None

Description

The present invention relates to ultrafine silica powder and uses thereof.

Conventionally, in electrostatic toner image developing toners used in digital copying machines, laser printers, etc., surface-treated silica fine powder has been used as an external additive to improve fluidity and stabilize charging characteristics. ing. This silica fine powder is required to have high hydrophobicity in order to reduce the change in charge amount due to humidity, and to be highly dispersed with little aggregation so that the toner surface can be uniformly coated. As for the specific surface area of the silica fine powder, an ultrafine powder of about 200 to 500 m ² / g is used. As the image formation is repeated, the ultrafine powder of silica is embedded in the surface of the toner particles. It has been confirmed that fluidity, triboelectric charge, transferability, and the like are deteriorated to cause image defects.

In order to reduce the burying of the silica ultrafine powder, there are methods (Patent Document 1, Patent Document 2, and Patent Document 3) in which inorganic fine powder having a specific surface area of less than 80 m ² / g and a relatively large particle diameter is used in combination. An inorganic fine powder having a relatively large particle size exhibits a spacer effect that reduces stress caused by direct contact between toners. In this way, a method of suppressing the burying of the ultrafine silica powder and extending the life of the toner is taken.

In recent years, due to acceleration of low-temperature fixing of toners, when toners are stored for a long period of time, there is a serious problem that toner storage property, charging property, and fluidity are deteriorated due to blocking between toners. In general, an inorganic fine powder having a relatively large particle size is added to improve these problems. As inorganic fine powder having a relatively large particle diameter, colloidal silica synthesized by a sol-gel method and fumed silica produced by combustion hydrolysis of silicon tetrachloride are generally used. However, in the case of colloidal silica, the charge amount is low and the toner contacts with the toner only at one point. Therefore, there is a problem that the amount of detachment from the toner surface is large and the effect of improving the storage stability is low. Further, fumed silica has a structure structure, and since there are many contact points, the detachment from the toner surface is improved, but the resistance when the toners come into contact with each other is increased, so that the fluidity is deteriorated. . For this reason, ultrafine silica fine powders having moderately controlled sphericity and aspect ratio are required to improve storage stability, chargeability and fluidity.

JP-A-5-346682 JP 2000-81723 A JP 2004-67475 A

An object of the present invention is to provide a toner external additive excellent in storage stability, chargeability and fluidity, and to provide a hydrophobized ultrafine silica powder suitable for the toner external additive.

The present inventor has intensively studied to achieve the above object, and has found an ultrafine silica powder that achieves this. The present invention is based on such knowledge and has the following gist.
(1) The average particle size is 80 nm or more and less than 300 nm, the average sphericity is 0.50 or more and less than 0.80, the average aspect ratio is 1.0 or more and less than 1.50, and the water content is 0.05 wt% or more and 0.0. An ultrafine silica powder characterized by being less than 30 wt%.
(2) The ultrafine silica powder as described in (1) above, having a specific surface area of 10.0 m ² / g or more and less than 150 m ² / g.
(3) Ultra fine silica fine powder, wherein the ultra fine silica powder according to (1) or (2) is surface-treated with hexamethyldisilazane.
(4) A toner external additive for developing an electrostatic charge image, comprising the ultrafine silica powder according to any one of (1) to (3).

According to the present invention, a toner external additive suitable for preparing a toner excellent in storage stability, chargeability and fluidity is provided. Also provided is an ultrafine silica powder suitable for the toner external additive.

Hereinafter, the present invention will be described in detail.
The ultrafine silica powder of the present invention needs to have an average particle size of 80 nm or more and less than 300 nm as measured with a laser diffraction / scattering particle size distribution analyzer. When the average particle size is less than 80 nm, the amount of hydrophobic spherical silica fine powder having a size that does not contribute to prevention of blocking between the toners increases, and the storage stability cannot be improved when used as an external toner additive. On the other hand, when the average particle diameter is 300 nm or more, the charge amount of the hydrophobized spherical silica fine powder itself becomes small, and the chargeability when used as an external toner additive becomes insufficient. Therefore, a preferable average particle diameter is 90 nm or more and 250 nm or less, more preferably more than 100 nm and 200 nm or less.

The laser diffraction / scattering particle size distribution of the spherical silica fine powder of the present invention can be measured using “LS-230” manufactured by Beckman Coulter. In the measurement, water was used as a solvent, and dispersion treatment was performed with an output of 200 W using “Ultrasonic Generator UD-200 (with ultra-trace chip TP-040)” manufactured by Tommy Seiko Co., Ltd. for 2 minutes as a pretreatment. To do. In addition, the concentration of PIDS (Polarization Intensity Differential Scattering) is adjusted to 45 to 55% by mass. The analysis of the particle size distribution was performed by dividing the range of 0.04 to 2000 μm into 116 divisions with a particle diameter channel of log (μm) = 0.04. The refractive index of water was 1.33, and the refractive index of spherical silica fine powder was 1.50. In the measured particle size distribution, particles having a cumulative volume of 50% are average particle sizes.

The average sphericity of the ultrafine silica powder of the present invention needs to be 0.50 or more and less than 0.80. When the average sphericity is less than 0.50, a part of the external additive is easily embedded in the toner, the spacer effect is lowered, and the fluidity of the toner is deteriorated as a result. On the other hand, when the average sphericity is 0.80 or more, the contact point between the toner surface and the toner external additive is decreased, and the detachment of the external additive from the toner surface becomes remarkable, and the storage stability is deteriorated. Therefore, a preferable average sphericity is 0.55 or more and less than 0.75, more preferably 0.60 or more and less than 0.70.

The average sphericity of the ultrafine silica powder of the present invention is measured by the following method. After fixing ultrafine silica powder to the sample stage with carbon paste, osmium coating was performed, and an image taken with a scanning electron microscope “JSM-6301F type” manufactured by JEOL Ltd. with a magnification of 100,000 times and a resolution of 2048 × 1356 pixels Incorporated. Using this image analysis apparatus “MacView Ver. 4” manufactured by Mountec Co., Ltd., particles were recognized using a simple capture tool, and the sphericity was measured from the projected area (A) and the perimeter (PM) of the particles. . If the area of a perfect circle corresponding to the perimeter (PM) is (B), the sphericity of the particle is A / B, so a perfect circle having the same perimeter as the perimeter (PM) of the sample is assumed. Then, since PM = 2πr and B = πr2, B = π × (PM / 2π) ² , and the sphericity of each particle becomes sphericity = A / B = A × 4π / (PM) ^2. . When the photographed particles have a shape in which a plurality of primary particles are aggregated to form secondary particles, the secondary particles are regarded as a single particle, and the projected area (A) is the area of the entire secondary particle and the perimeter length. (PM) is the length measured along the interface of the secondary particles. The sphericity of 200 particles having an arbitrary projected area equivalent circle diameter of 50 nm or more thus obtained was determined, and the average value was defined as the average sphericity.

The average aspect ratio of the ultrafine silica fine powder of the present invention is required to be 1.0 or more and less than 1.50. When the average aspect ratio is 1.50 or more, the resistance at the time of contact between the toners increases due to the external additive having a high aspect ratio, and the fluidity of the toner deteriorates. Therefore, the preferable average aspect ratio is less than 1.40, more preferably less than 1.30.

  The aspect ratio of the ultrafine silica powder of the present invention is measured by the following method. After fixing ultrafine silica powder to the sample stage with carbon paste, osmium coating was performed, and an image taken with a scanning electron microscope “JSM-6301F type” manufactured by JEOL Ltd. with a magnification of 100,000 times and a resolution of 2048 × 1356 pixels Incorporated. Using this image, the image analysis apparatus “MacView Ver. 4” manufactured by Mountec Co., Ltd. was used to recognize the particles using a simple capture tool, and the ratio of the major axis (A) to the minor axis (B) of the particles (A / B) The aspect ratio was measured. The major axis (A) is defined as the maximum value of the distance between two points on the particle surface. The minor axis (B) is defined as the maximum value of the length of the line segment orthogonal to the major axis. When there are a plurality of local maximum values, the average value is defined as the minor axis (B). Further, when the photographed particles have a shape in which a plurality of primary particles are aggregated to form secondary particles, the secondary particles are regarded as single particles and measured. The aspect ratio of 200 particles having an arbitrary projected area equivalent circle diameter of 50 nm or more thus obtained was determined, and the average value was defined as the average aspect ratio.

Although details of the method for producing silica of the present invention will be described later, an oxidation reaction method of metal silicon is preferable. Examples of production methods include a method of spheroidizing metal silicon by throwing it into a high temperature field formed by a chemical flame or an electric furnace (for example, Japanese Patent No. 1568168), and metal silicon particle slurry in a flame And a method of spheroidizing by spraying on the surface (for example, Japanese Patent Application Laid-Open No. 2000-247626). In this case, the conventional manufacturing method is synthesis using a burner installed only at the top of the synthesis furnace, whereas in the present invention, in addition to the burner at the top of the synthesis furnace, the manufacturing method uses an afterburner in the middle of the synthesis furnace. Therefore, it is possible to control the shape of ultrafine silica powder having an unprecedented sphericity and aspect ratio.

  The water content of the ultrafine silica powder of the present invention needs to be 0.05 wt% or more and less than 0.30 wt%. The charge amount of the toner is caused by the moisture content of the external additive, and the printing characteristics vary depending on the charge amount. When the amount of water is less than 0.05 wt%, the amount of charge of the ultrafine silica powder itself becomes high, so that the amount of charge becomes excessive when used as an external toner additive, which causes stains on the printing surface. Further, when the water content is 0.30 wt% or more, since the charge amount of silica itself is low, the charge amount becomes insufficient when used as an external toner additive, and white spots occur frequently during printing. Therefore, the preferable water content is 0.10 wt% or more and less than 0.25 wt%, more preferably 0.15 wt% or more and less than 0.20 wt%.

The water content of the ultrafine silica powder of the present invention is measured by the Karl Fischer coulometric titration method. It can be measured by a Karl Fischer trace moisture measuring device, for example, “CA-100” (manufactured by Mitsubishi Chemical Corporation). Specifically, the sample surface adsorbed water can be measured by putting the sample in a moisture vaporizer and supplying the dehydrated argon gas as a carrier gas while heating up to 200 ° C. with an electric heater.

The specific surface area of the ultrafine silica fine powder in the present invention is preferably 10.0 m ² / g or more and less than 150 m ² / g. When the specific surface area is less than m ² / g, the amount of charge of the ultrafine silica powder itself becomes small, and the chargeability when used as an external toner additive may be insufficient. On the other hand, when the specific surface area exceeds 100 m ² / g, the size of the hydrophobized spherical silica fine powder that does not contribute to prevention of blocking between the toners increases, and when used as a toner external additive, the storage stability can be improved. There is a fear that it cannot be done. A more preferable specific surface area is 20 m ² / g or more and less than 90 m ² / g, most preferably 25 m ² / g or more and less than 80 m ² / g.

The specific surface area of the hydrophobized spherical silica fine powder of the present invention is a value based on the BET method, and is measured by the BET single point method using a specific surface area measuring machine “MacsorbHM model-1208” manufactured by Mountec. Prior to the measurement, pretreatment was performed by heating at 300 ° C. for 18 minutes in a nitrogen gas atmosphere. The adsorbed gas was a mixed gas of 30% nitrogen and 70% helium, and the flow rate was adjusted so that the indicated value of the main body flow meter was 25 ml / min.

The spherical silica fine powder of the present invention, for example, in a state where the ultrafine silica powder is suspended (fluidized) with a circulating gas in a fluidized bed, first, after spraying and mixing water to activate silanol groups, It is obtained by spraying and mixing hexamethyldisilazane to perform a hydrophobic treatment. Alternatively, there is a method in which a surface treatment agent is gasified and brought into contact with ultrafine silica fine powder. Airflow mixing in a fluidized bed has less force on the powder, so there is less agglomeration and hydrophobization treatment in a highly dispersed state is possible. Furthermore, fluidization with a circulating gas creates an apparent hermetic state, and processing efficiency Is increased. Formation of the fluidized bed by the circulating gas can be realized by sucking the gas in the system by the blower, returning the exhaust line to the inlet side again, and using it as the fluidizing gas.

The hydrophobized spherical silica fine powder of the present invention may be treated with hexamethyldisilazane alone or with two or more kinds of surface treatment agents. For example, when the aminosilane coupling agent is used in combination with an aminosilane coupling agent for imparting positive chargeability, the hydrophobization treatment method of the present invention may be carried out after the spherical silica fine powder is first treated with aminosilane.

The blending amount of the spherical silica fine powder subjected to the hydrophobization treatment into the toner is usually preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass with respect to 100 parts by mass of the toner. If the blending amount is too small, the amount of adhesion to the toner is small and a sufficient storage stability improving effect cannot be obtained. If the blending amount is too large, the chargeability of the toner may be adversely affected.

The silica powder of the toner external additive containing the spherical silica fine powder of the present invention is not limited to the spherical silica fine powder of the present invention used alone, for example, 200 to 500 m having a high fluidity-imparting effect. It can also be used in combination with ² / g ultrafine silica.

As the toner for developing an electrostatic charge image to which the toner external additive containing the spherical silica fine powder of the present invention is added, a known toner composed mainly of a binder resin and a colorant can be used. Moreover, the charge control agent may be added as needed.

The toner for developing an electrostatic charge image to which the toner external additive containing the spherical silica fine powder of the present invention is added can be used as a one-component developer, or mixed with a carrier and used as a two-component developer. You can also. When used as a two-component developer, the toner external additive may not be added to the toner particles in advance, but may be added when the toner and the carrier are mixed to coat the surface of the toner. As the carrier, iron powder or the like, or a known one whose surface is resin-coated is used.

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples.
Examples 1-13 Comparative Examples 1-13
The ultra fine silica powder is equipped with one double tube LPG-oxygen mixed burner that can form inner flame and outer flame at the top of the synthesis furnace, and two double tube LPG-oxygen mixed in the middle A type afterburner was installed, and the synthesis was performed using an apparatus in which a collection system line was directly connected to the lower part. A two-fluid nozzle for slurry spraying is further installed at the center of the top burner, and a slurry (metal silicon concentration: 10 to 70 mass) consisting of metal silicon powder (average particle size 9.8 μm) and water from the center. %) Was injected at a feed rate of 20.0 kg / Hr. Water vapor was supplied from around the burner and the two-fluid nozzle. The formation of the flame was performed by providing several tens of pores at the outlet of the double tube burner and injecting a mixed gas of LPG and oxygen therefrom. The total supply amount of LPG was 5 to 15 N ³ / hr. As described above, the slurry injected from the two-fluid nozzle at the top of the synthesis furnace is passed through a flame to synthesize spherical silica ultrafine powder. Furthermore, the synthesized spherical silica ultrafine powder was placed in a place in the middle of the synthesis furnace with the particles agglomerated, specifically, at a distance of 30 to 70 from the top of the furnace when the length of the synthesis furnace was 100. The mixture was melted again with a double-pipe LPG-oxygen mixed afterburner to obtain ultrafine silica powder, which was finally pneumatically transported from the collection line at the bottom of the synthesis furnace by a blower and collected by a bag filter. The afterburner was installed in parallel with the furnace body so that the furnace body lower direction was 0 degree, and the angle was 30 to 60 degrees, and the total amount of LPG supplied from the afterburner was 0 to 10 m ³ / hr. The particle diameter and specific surface area of the ultrafine silica powder were adjusted by adjusting the slurry concentration and the slurry feed amount. The sphericity and aspect ratio of the ultrafine silica powder were measured by using an afterburner in the middle of the synthesis furnace. Furthermore, the water content of the ultrafine silica powder was adjusted by adjusting the water content at the top of the synthesis furnace. The collected ultrafine silica fine powder was appropriately blended to obtain ultrafine silica powders A to M having various particle diameters, sphericity, aspect ratio and specific surface area. Further, as a comparative example, the ultrafine powder silica powder N was appropriately blended by adjusting the slurry concentration, the slurry feed amount, the LPG amount of the afterburner in the middle of the synthesis furnace, and the water vapor amount at the top of the synthesis furnace. ~ V was obtained. In addition, as a comparative example, ultrafine silica powders W to X were obtained by appropriately blending ultrafine silica powder obtained by a conventional synthesis method without using an afterburner.

100 g each of ultrafine silica fine powders A to X were charged in a fluidized bed (“Vibrating fluidized bed device VUA-15 type” manufactured by Chuo Kako Co., Ltd.) and fluidized with N ₂ gas to spray 2 g of water. After fluidly mixing for 4 minutes, 4 g of hexamethyldisilazane (“SZ-31” manufactured by Shin-Etsu Chemical Co., Ltd.) was sprayed and fluidly mixed for 30 minutes. After the fluid mixing, the temperature was raised to 130 ° C., and ammonia generated while removing nitrogen gas was removed to obtain hydrophobic ultrafine silica powders A to X. The hydrophobicity of the obtained hydrophobic ultrafine silica powder was 65% or more.

Moreover, not performed commercially available surface hydrophobic treatment, a specific surface area of 50 m 2 / ^g hydrophobic surface treatment respectively the same manner as described above the fluidized bed fumed silica Y and a specific surface area of m ^{2 /} g of colloidal silica Z of To obtain hydrophobic ultrafine silica powders Y and Z. The hydrophobicity of the obtained hydrophobic ultrafine silica powder was 65% or more and less than 80%.

  In order to evaluate the characteristics of the ultrafine powdered silica powder that has been subjected to a water-repelling treatment with hexamethyldisilazane as a toner external additive, storage stability, fluidity and chargeability were measured according to the following methods. The results are shown in Table 1.

(1) Storage stability 15 g of each of the above-obtained hydrophobic ultrafine silica powders A to Z and a polyester resin having a glass transition point of 62 ° C. are pulverized and adjusted so that the average particle diameter becomes 7.5 μm by a jet mill. 485 g of the resin powder thus obtained was put into a Henschel mixer (“FM-10B type” manufactured by Mitsui Miike Chemical Co., Ltd.) and mixed at 1000 rpm for 1 minute. 10 g of this mixture was weighed into a silicone cup and allowed to stand at a temperature of 62 ° C. for 3 hours, and then gently transferred onto a sieve having an opening of 74 μm, and a powder tester (“PT-E type” manufactured by Hosokawa Micron Corporation) was vibrated. I set it on the table. After setting the amplitude of the sieve to 1.0 mm and vibrating for 30 seconds, the mass of the mixture remaining on the sieve was measured. The smaller this value, the better the storage stability of the toner.

(2) Chargeability 970 g of the hydrophobic ultrafine silica powders A to Z obtained as described above and 970 g of a crosslinked styrene resin powder having an average particle diameter of 5 μm (trade name “SX-500H” manufactured by Soken Chemical Co., Ltd.) This was put into a mixer ("FM-10B type" manufactured by Mitsui Miike Chemical Co., Ltd.) and mixed at 1000 rpm for 1 minute to prepare a pseudo toner. The pseudo toner was allowed to stand for 24 hours under conditions of a temperature of 25 ° C. and a relative humidity of 55%, and then the blow-off charge amount was measured by the following method. Put 0.20 g of simulated toner and 3.80 g of a negatively charged polar toner standard carrier (distributed by the Imaging Society of Japan “N-01”) as a carrier in a 100 ml polyethylene container, close the container lid, and turn the container up and down. It was held in a hand and shaken 200 times at a speed of 2 times / second with a stroke of about 30 cm. Three minutes after shaking, the blow-off charge amount was measured with a suction separation type charge amount measuring device (“Sepasoft STC-1” manufactured by Sankyo Piotech Co., Ltd.) using 0.30 g of the mixture of the simulated toner and carrier. The suction time was 3 minutes, the suction pressure was 4.0 kPa, and a screen of 32 μm mesh was used for the screen used for separating the simulated toner and the carrier. The larger the negative value of the blow-off charge amount, the better the chargeability of the toner.

(3) Fluidity 15 g of each of the hydrophobic ultrafine silica powders AZ mixed with a Henschel mixer and 20 g of a polyester resin having a glass transition point of 62 ° C. are mixed with a powder tester (“Hosokawa Micron” The mixture was put on a 710 μm sieve placed on a shaking table of “PT-E type”), vibrated for 180 seconds, and the mixture dropped through the funnel was deposited on a table for measuring an angle of repose installed below. The flowability of the sediment formed in a conical shape was evaluated using the angle of the side surface with respect to the horizontal plane as the repose angle. The smaller the angle of repose, the better the fluidity.

As is clear from the comparison between the examples and the comparative examples, according to the present invention, an external toner additive excellent in storage stability, chargeability and fluidity is provided. Also provided is an ultrafine silica powder suitable for addition to the toner external additive.

The spherical silica fine powder of the present invention is used as an external additive for an electrophotographic toner used in a copying machine, a laser printer or the like.

Claims (4)

Average particle size is 80 nm or more and less than 300 nm, average sphericity is 0.50 or more and less than 0.80, average aspect ratio is 1.0 or more and less than 1.50, and water content is 0.05 wt% or more and less than 0.30 wt%. An ultrafine silica powder characterized by ^2. The ultrafine silica powder according to claim 1, wherein the specific surface area is 10.0 m < ² > / g or more and less than 150 m < ² > / g. An ultrafine silica fine powder, wherein the ultrafine silica powder according to claim 1 or 2 is surface-treated with hexamethyldisilazane. A toner external additive for developing an electrostatic charge image, comprising the ultrafine silica powder according to any one of claims 1 to 3.