JP4758655B2 - Surface-treated silica fine particles - Google Patents

Description

  The present invention relates to a novel surface-treated silica fine particle. Specifically, when it is used as an external additive for toner for electrophotography, the surface can effectively suppress the change in charge amount due to stress on the toner and can exhibit an excellent effect of improving transfer efficiency. Treated silica particulates are provided.

  The electrophotographic method typically forms a latent image on the surface of a photoreceptor by charging and exposure, develops the latent image with charged toner, transfers the toner on the surface of the photoreceptor to paper, an intermediate transfer body, etc. The toner transferred onto paper or the like is fixed by applying heat. An external additive such as silica adheres to the surface of the toner and exhibits effects such as imparting fluidity to the toner and improving charging efficiency.

  In recent years, reduction of environmental load has been regarded as important, and devices using electrophotography such as copiers and printers are required to reduce power consumption and toner consumption.

  In order to reduce the power consumption, it is important to reduce the heat applied when fixing the toner. For this reason, the softening point of the toner resin tends to decrease. As the softening point of the toner resin decreases, the durability of the toner tends to deteriorate. Specifically, the external additive is likely to be buried in the toner due to the stress applied to the toner generated in the apparatus, for example, the shearing force received from the carrier or the charging blade when the toner is charged.

  As described above, when the external additive is buried, there arises a problem that the charge amount of the toner changes. In order to solve this problem, it is known that when an external additive having a large primary particle diameter of about 50 to 200 nm is added to the toner, the burying of the external additive is suppressed (Patent Document 1). 2, 3). There is also a report of treating the external additive having a large particle size with silicone oil (see Patent Documents 4, 5, and 6).

  However, even in the external additive having a large particle diameter treated with the above-described silicone oil, it is difficult to sufficiently suppress the change in the charge amount, and improvement has been demanded.

JP-A-60-3260 JP-A 64-68765 JP 2002-154820 A JP-A-5-346682 Japanese Patent Laid-Open No. 7-271087 JP-A-8-292598

  Accordingly, an object of the present invention is to provide surface-treated silica fine particles having characteristics that can be suitably used as an external additive for a toner capable of effectively suppressing a change in toner charge amount due to stress on the toner. There is.

  The inventors of the present invention have made extensive studies to solve the above problems. As a result, when silica fine powder treated with silicone oil having an average primary particle size of 50 to 200 nm is used as an external additive, the difference in hydrophobicity of silica fine powder and uniformity of silicone oil adhesion state is That silica having an average primary particle size of 50 to 200 nm is significantly more coherent than silica of other particle sizes and is not subjected to uniform silicone oil treatment. Got.

  As a result of further investigation based on the above findings, the present inventors achieved a uniform silicone oil treatment on the surface of the silica fine particles by performing the silicone oil treatment under a condition in which the cohesiveness of the silica fine particles was controlled. The present invention succeeded in obtaining the surface-treated silica fine particles, and found that the object could be achieved by using the surface-treated silica fine particles, and succeeded in the present invention.

  That is, according to the present invention, in the surface-treated silica fine particles treated with silicone oil and having an average primary particle diameter of 50 to 200 nm, the hydrophobization degree of the surface-treated silica fine particles by the methanol titration method is 65% by volume. There are provided the surface-treated silica fine particles characterized in that the floatability in methanol water having a methanol concentration of 60 vol% is 90% or more.

  Furthermore, according to the present invention, there is provided an external additive for toner comprising the surface-treated silica fine particles.

  In the present invention, the hydrophobization degree of the surface-treated silica fine particles by the methanol titration method was determined by adding the surface-treated silica fine particles to water, adding methanol by titration with stirring, and suspending the whole amount of the surface-treated silica fine particles in water. In this case, the value of the concentration (vol%) of methanol in the methanol-water mixed solvent was obtained.

  Further, in the surface-treated silica fine particles, the buoyancy rate in methanol water having a methanol concentration of 60 vol% is determined by adding a certain amount of surface-treated silica fine particles to a container containing a certain amount of methanol water having a methanol concentration of 60 vol% and stirring The weight of the surface-treated silica fine particles is measured, and the ratio of the surface-treated silica fine particles floating to the weight of the surface-treated silica fine particles used in the measurement is determined.

  In any case, the detailed method is as described in the examples.

  Since the surface-treated silica fine particles of the present invention are uniformly treated with silicone oil so that the floating rate in methanol water having a methanol concentration of 60 vol% is 90% or more, the average primary particle diameter is 50 to 200 nm. In combination with this, when used as an external additive for toner, it is possible to effectively suppress a change in charge amount due to stress on the toner.

  Another effect of the surface-treated silica fine particles of the present invention is that the treatment with silicone oil is performed so that the degree of hydrophobicity is 65 vol% or more, and the average primary particle diameter is 50 to 200 nm. Therefore, when used as an external additive for toner, the transfer efficiency of toner from the photoreceptor can be remarkably improved, and the effect of reducing toner consumption is exhibited.

  In the present invention, silica fine particles before treatment with silicone oil (hereinafter referred to as raw silica fine particles) having an average primary particle diameter in the range of 50 to 200 nm are used. That is, when the average primary particle diameter is small outside this range, there is no effect in suppressing the change in charge amount due to stress on the toner and improving the transfer efficiency. If the average primary particle size is larger than this range, desorption from the toner particles occurs, causing image defects. For the purpose of improving transferability to toner, the average primary particle diameter is preferably 70 nm or more, and preferably 100 nm or less for the purpose of suppressing detachment from toner particles.

  The average primary particle diameter of the raw silica fine particles in the present invention is obtained by image analysis of an image taken with a scanning electron microscope.

  As the raw silica fine particles, silica having an average primary particle diameter of 50 to 200 nm can be used without any particular limitation. Typical examples include fumed silica and sol-gel silica.

  The fumed silica refers to silica particles produced by burning a silicon compound or metal silicon in a flame, for example, an oxyhydrogen flame. In particular, a silicon compound such as silicon tetrachloride is generally used. The fumed silica is sometimes referred to as “dry silica” or “vapor phase silica” to distinguish it from silica produced by a wet method such as precipitated silica.

  Sol-gel silica is produced by hydrolyzing a silicon alkoxide such as tetramethoxysilane or tetraethoxysilane in an acidic or alkaline water-containing organic solvent.

  Of the above fumed silica and sol-gel silica, fumed silica that does not contain aggregated particles formed during drying can be suitably used because no solvent is used. When the aggregated particles increase, it becomes difficult not only to obtain surface-treated silica fine particles uniformly treated so that the buoyancy in methanol water having a methanol concentration of 60 vol% is 90% or more, but also from the toner. Separation easily occurs and causes image defects.

The raw silica fine particles have a fractal shape parameter α _{1 in the} analysis target range of 50 nm to 150 nm and a fractal shape parameter α ₂ in the analysis target range of 150 nm to 353 nm in the small angle X-ray scattering measurement, which are expressed by the following formulas (1) and (2):
−0.0068S + 2.548 ≦ α ₁ ≦ −0.0068S + 3.748 (1)
−0.0011S + 1.158 ≦ α ₂ ≦ −0.0011S + 2.058 (2)
(In the above formula, S represents the BET specific surface area (m ² / g) of the active silica fine particles.)
It is preferable that the condition shown by is satisfied. That is, when the fractal shape parameter is within the above range, the adhesion force of the toner to the surface is improved and the intended function tends to be effectively performed.

  In general, it is known that a fractal shape parameter (α value) determined from a scattering pattern obtained when a small-angle X-ray scattering measurement is performed on a powder serves as an index representing the degree of complexity of the shape of independent particles. That is, the closer the α value is to 4, the closer the particle shape is to a true spherical particle (the α value of the true spherical particle is 4), and the smaller the value, the more complicated the particle shape.

  Since there is a relationship of the following formula among the scattering intensity (I), the scattering vector (k), and the fractal shape parameter (α) in the small-angle X-ray scattering, the small angle X plotted with the horizontal axis as k and the vertical axis as I. The α value can be determined from the line scattering curve.

I∝k ^-α
(However, k = 4πλ ⁻¹ sin θ)
The unit of k is nm ⁻¹ , π is the pi, λ is the wavelength of incident X-rays (unit is nm), θ is the X-ray scattering angle (θ is the detector scanning angle of 0.5). It is a doubled value).

  In order to obtain small-angle X-ray scattering, first, monochromatic X-rays are finely narrowed using slits and blocks, irradiated onto the sample, and the X-rays scattered by the sample are changed while changing the scanning angle of the detector. Detection and plotting the horizontal axis as k and the vertical axis as I.

If the logarithmic scale is plotted at this time, the slope of the tangent at k of the scattering curve becomes equal to -α, so that the α value can be obtained. Further, when the analysis target range is D, the Bragg equation between D, the X-ray scattering angle θ, and the incident X-ray wavelength λ:
2Dsin θ = λ
Therefore, the relationship of the following equation is established between k and D.

D = 2πk ⁻¹
Therefore, the horizontal axis of the logarithmic plot of k and I is
Logk = −1.377 to −0.902 (D = 50 to 150 nm)
and,
Logk = −1.750 to −1.377 (D = 150 to 353 nm)
And by approximating the curve of each divided range with a straight line and obtaining the slope of the approximate curve, the fractal shape parameters α ₁ and α ₂ for each analysis target range can be determined.

The α ₁ indicates the complexity of the shape in a relatively small aggregate particle size range among the particles having various shapes and particle sizes in which a plurality of primary particles are fused to each other, and the α ₂ Indicates the complexity of the shape in a relatively large aggregate particle size range. In general, α ₁ and α ₂ have a relationship of α ₁ > α ₂ . When α ₁ and α ₂ exceed the upper limit of the range of the formulas (1) and (2), the particle shape becomes nearly spherical, so that the fixing property to the toner particles is deteriorated, and the change in charge amount is caused. There is a tendency for the effect of suppressing the decrease. Moreover, when it is less than the lower limit of this range, it tends to be inferior in the effect of improving transferability.

The raw silica fine particles having the fractal shape parameters α ₁ and α _{2 in} the range of the formulas (1) and (2) can be obtained by a reaction in a flame such as a flame hydrolysis method or a flame pyrolysis method. In particular, it can be obtained by partial welding while adjusting the aggregation of particles in the flame.

Specifically, hydrogen and / or hydrocarbons (hereinafter these gases are collectively referred to as flammable gases) and oxygen are respectively supplied to the outer periphery of the supply port for supplying the raw material silicon compound in the form of gas to form an outer flame. The silicon compound is converted into silica fine particles and appropriately welded in a flame, and then the fused silica fine particles are cooled and repaired in a dispersed state (for example, after passing through the piping) By repairing with a bug filter, it is possible to obtain raw silica fine particles in which the fractal shape parameters α ₁ and α ₂ are in the range of the formulas (1) and (2).

  In the above production method, one of the conditions that particularly affects the value of the fractal shape parameter is the flow velocity at the outlet of the burner, and the flow velocity is preferably adjusted between 0.5 and 10 m / second.

Another condition that particularly affects the value of the fractal shape parameter is the concentration of the raw silicon compound, that is, the silica concentration in the flame, and this concentration is 0.05 to 5 mol in terms of SiO _2. / M ³ , particularly 0.1 to 3 mol / m ³ is preferred.

  Further, in the production method of the raw silica fine particles having the fractal shape parameters of the formulas (1) and (2), the adjustment of the average primary particle diameter and specific surface area is carried out by adjusting the concentration of the raw silicon compound, the burner outlet flow velocity, the peripheral flame. In addition to the above conditions, the length and the like and the value of the fractal shape parameter can be adjusted by adjusting the temperature of the peripheral flame.

  Generally, when the concentration of the raw material silicon compound is increased, the average primary particle size is increased, the specific surface area is decreased, and the value of the fractal shape parameter is increased. Further, when the outlet flow rate of the burner is increased, the average primary particle size is decreased, the specific surface area is increased, and the value of the fractal shape parameter is decreased. Further, when the length of the peripheral flame is increased, the average primary particle diameter is increased, the specific surface area is decreased, and the value of the fractal shape parameter is increased. Furthermore, when the temperature of the peripheral flame is increased, the average primary particle diameter increases, the specific surface area decreases, and the value of the fractal shape parameter increases.

  In the production method of the raw silica fine particles having the fractal shape parameters of the formulas (1) and (2), the silicon compound can be used without any particular limitation. For example, siloxanes such as hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, hexamethyldisiloxane and octamethyltrisiloxane, silazanes such as hexamethyldisilazane and hexaethyldisilazane, tetramethoxy Silane, tetraethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, alkoxytrines such as methyltriethoxysilane, monochlorosilane, dichlorosilane, trichlorosilane, tetrachlorosilane and other silicon halides, monosilane, disilane and other inorganic silane compounds Can be used as a raw material silicon compound.

  In particular, by using siloxanes and / or silazanes or alkoxylanes as the silicon compound, it is possible to obtain a higher-purity silicon oxide (silica fine particles) in which impurities such as chlorine are significantly reduced, In addition, handleability is improved.

  One feature of the surface-treated silica fine particles of the present invention is that the hydrophobization degree by methanol titration method is 65 vol% or more and the buoyancy in methanol water having a methanol concentration of 60 vol% is 90% or more.

  When the degree of hydrophobicity is less than 65 vol%, when used as an external toner additive for electrophotography, the effect on improving transfer efficiency is small, and the floating ratio with respect to methanol water having a methanol concentration of 60 vol% is less than 90%. However, since the adhesion state of the silicone oil becomes uneven, the effect of suppressing the change in the charge amount due to the stress on the toner is small. Furthermore, it is preferable that the hydrophobization degree is 70% by volume or more, and the floating ratio at 60% by volume is 95% or more.

  On the other hand, the surface-treated silica fine particles obtained by performing the silicone oil treatment on the original silica fine particles having an average primary particle diameter of 50 to 200 nm have a low degree of hydrophobicity or are in a non-uniform treatment state. There was a problem that processing was performed. The reason for this is presumed that by adding unnecessary operations such as unnecessary mixing to the raw silica fine particles, aggregation proceeded before the silicone oil treatment, and the uniform silicone oil treatment was not sufficiently achieved.

  The surface-treated silica fine particles of the present invention can achieve the object by satisfying the above-described configuration, but it is preferable to further adjust the surplus of silicone oil adhering to the raw silica fine particles to a specific range. . When the excessive amount of silicone oil is too large, the fluidity of the toner tends to be lowered when used as an external additive for toner. Further, if the excess amount of the silicone oil is too small, the effect of suppressing the change in the charge amount due to the stress on the toner tends to be difficult to obtain.

The surplus of the silicone oil can be determined by the difference (ΔC (%)) between the carbon amount C ₁ (%) and the carbon amount C ₂ (%) after chloroform extraction. ΔC (%) is preferably in the range of 0.5 to 3.0, and more preferably in the range of 1.5 to 2.1.

The amount of carbon C ₂ after chloroform extraction of the surface-treated silica fine particles of the present invention is preferably within the range of the following formula (3). Carbon content C ₂ of chloroform extraction is related to the amount of silicone oil is reacted with the silica surface. If the carbon content C ₂ is smaller than this range, tends to be difficult to increase the hydrophobicity of the surface-treated silica fine particles, it is difficult to obtain a greater beyond this range.

32.4S / (S + 1000) ≦ C ₂ ≦ 97.2S (3S + 1000) (3)
(In the above formula, S represents the BET specific surface area (m ² / g) of the active silica fine particles.)
In the present invention, the BET specific surface area of the raw silica fine particles refers to a one-point value measured by a nitrogen adsorption method. The specific surface area of the raw silica fine particles is adhered to the surface after holding the surface-treated silica fine particles at about 500 ° C. for 1 hour or more in a nitrogen atmosphere even after treatment with silicone oil. Silicone oil can be removed and measured. It can be confirmed by the carbon content measurement method shown in the examples described later that the operation of removing the silicone oil is performed reliably.

The BET specific surface area of the raw silica fine particles is related to the average primary particle diameter. When the average primary particle diameter is 50 to 200 nm, it is generally 10 to 50 m ² / g.

  In the present invention, the silicone oil treatment is not particularly limited as long as the treated silica is included in the scope of the present invention, but agglomeration occurs in the raw silica fine particles by the dry treatment method described later. It is preferable to carry out by spraying silicone oil on the raw silica fine particles that are not allowed to be mixed and in a good mixed state, and then heat-treating at an appropriate temperature.

  In the silicone oil treatment, a liquid silicone oil and the surface of silica fine particles are reacted by a predetermined heat treatment. As a treatment method, a method in which silicone oil is dissolved in a solvent such as toluene, silica is dispersed in the solution, the solvent is evaporated, the silicone oil is adhered to the silica surface, and a predetermined heat treatment is performed. (Wet treatment method) and a method in which silicone oil is sprayed on the silica fine particles while mixing in a mixer or a fluidized bed, the silicone oil is adhered to the surface of the silica fine particles, and a predetermined heat treatment is performed (dry method) Treatment method).

  Among the above wet processing methods and dry processing methods, the dry processing method is used because of the reason that silica particles processed more uniformly are obtained and because an organic solvent is not used, the cost, safety, and environment are superior. It is preferable to use it.

  In the dry processing method described above, it is preferable to avoid the operation of promoting the contact between the particles until the raw silica fine particles are produced and introduced into a mixer or a fluidized bed. As a specific example, it is preferable not to use an apparatus such as a screw feeder when the raw silica fine particles are taken out from the hopper.

  In the dry treatment method, spraying the silicone oil in a good mixed state is important for performing uniform silicone oil treatment. The raw material having an average primary particle size of 50 to 200 nm used in the present invention has a particularly strong adhesion, and when mixed with a too strong force, a phenomenon occurs in which silica fine particles increase or adhere to the wall surface, and the silicone oil treatment May be non-uniform. Further, when mixing is performed with a very weak force, the frequency of silicone oil exchange between the silica fine particles is reduced, and therefore, there is a tendency that the silicone oil treatment is uneven.

  In the dry processing method, a mixer is preferable as a method of mixing the silica fine powder. Compared with mixing in a fluidized bed, mixing with a mixer has a higher collision frequency between silica particles, and silicone oil is frequently exchanged between the silica particles, resulting in more uniformly treated surface-treated silica particles. It tends to be.

  When the dry treatment method is performed with a mixer, the peripheral speed of stirring is preferably in the range of 30 to 300 m / min. When the peripheral speed is smaller than this range, mixing is insufficient and the silicone oil treatment tends to be uneven. On the other hand, if it is larger than this range, the silica fine particles are extremely charged and adhere to the reactor wall surface, so that the mixing is insufficient and the silicone oil treatment tends to be uneven.

  In addition, the mixing of the silica fine particles with the mixer is preferably carried out under a condition that the mixing degree, which is an index of the mixing degree, exceeds 0.95 within 1 minute. Various methods for obtaining the degree of mixing have been proposed. In the present invention, the degree of mixing is obtained by the following method. In other words, put a marker substance at an appropriate point in the mixer, move the mixer for an arbitrary time, sample from multiple points in the mixer, analyze the content of the marker substance, The variation in quantity is quantified by a coefficient of variation, and is obtained by subtracting the value of the coefficient of variation from 1.

  As a specific example of the above-mentioned degree of mixing, silica fine particles are put in a mixer, 10 μm acrylic resin is put in any one place in the mixer, the mixer is moved for any time, and sampling is carried out from any six places in the mixer. Then, the carbon content of the mixture of silica fine particles and acrylic resin is measured, and the coefficient of variation at six points is obtained, and the value of the coefficient of variation is subtracted from 1. The addition amount of the acrylic resin is within a range in which the carbon amount can be measured, and is preferably as small as possible, and an addition amount of about 2% with respect to the silica fine particles is good. In addition, since the silica fine particles have different fluidity depending on their average primary particle diameter, the mixing coefficient is obtained for each raw silica fine particle used in the treatment, and the peripheral speed of the mixer, the stirring blades are set within a suitable range. It is preferable to select the shape.

  In the present invention, when the silicone oil treatment is performed by the dry treatment method, it is preferable to include a step of drying the moisture of the raw silica fine particles. Specifically, it can be performed by circulating an inert gas for 10 minutes or more in an environment of 200 to 300 ° C. before spraying the silicone oil. The raw silica fine particles having an average primary particle size of 50 to 200 nm used in the present invention have a particularly strong adhesion, but it is possible to weaken the adhesion by drying the water, and a good mixing state is obtained. It is easy to be done. It is preferable to adjust the water content of the raw silica fine particles to 0.1% or less by the drying step.

  In the present invention, when the silicone oil treatment is performed by the dry treatment method, the spray particle size when spraying the silicone oil is preferably 80 μm or less. By setting the spray particle size within this range, it is easy to perform uniform processing. As a spraying device for silicone oil, a one-fluid nozzle, a two-fluid nozzle, or the like can be used. It is preferable to use a two-fluid nozzle because it is possible to spray with a smaller particle size.

In the present invention, as the silicone oil to be used, commercially available products can be used without limitation. Dimethyl silicone oil, methyl phenyl silicone oil, methyl hydrogen silicone oil, amino modified silicone oil, epoxy modified silicone oil, carboxy modified silicone oil, carbinol modified silicone oil, polyether modified silicone oil, alkyl modified silicone oil, fluorine modified silicone An oil etc. are mentioned. The viscosity of the silicone oil is not particularly limited, but a silicone oil having a viscosity of 20 to 500 cSt can be preferably used. When the viscosity of the silicone oil is small beyond this range, the silicone oil becomes volatile, so that a predetermined amount tends to be difficult to adhere to the surface of the silica fine particles. It tends to be non-uniform. It is also possible to use a mixture of two or more of the above silicone oils. For the purpose of increasing the amount of carbon C ₂ after extraction described later, it is effective to use reactive silicone oil such as carboxylic acid-modified silicone oil and carbinol-modified silicone oil. Furthermore, by using silicone oil modified with polar functional groups such as carboxylic acid and amine, it is possible to change the charge amount and the stability of charging against frictional mixing. preferable.

  In the present invention, it is preferable that the silicone oil treatment is performed by a predetermined heat treatment after the silicone oil is adhered to the surface of the raw silica fine particles. The heat treatment can be carried out by holding in an environment of preferably 200 to 300 ° C., more preferably 220 ° C. to 280 ° C., preferably about 15 minutes to 120 minutes, more preferably about 30 minutes to 90 minutes.

  In the present invention, an external additive for electrophotographic toner comprising the above-mentioned surface-treated silica fine particles is also provided.

  As a toner to which the external additive for toner of the present invention can be applied, any of black toner and color toner can be used, and any electrophotographic system such as magnetic one component, non-magnetic one component, two component, etc. Can also be used. The binder resin for the toner can also be applied without particular limitation, such as commonly used styrene / acrylic copolymer resins, polyester resins, epoxy resins and the like. The toner production method can be applied not only to mainstream pulverization / kneading methods but also to toners obtained by polymerization methods such as suspension polymerization and emulsion polymerization.

  The toner external additive of the present invention can also be applied to toners that are arbitrarily blended with other toner constituent materials. Black colorants, color colorants such as cyan, magenta, and yellow, positive and negative charge control agents, and release agents such as wax can be used without any limitation in materials normally used in this field.

  The amount of the external additive of the present invention added to the toner is not particularly limited as long as the obtained toner has desired characteristics, but is usually 0.05 to 5% by mass, preferably 0.1 to 0.1%. The amount is preferably 4% by mass and can be added to the toner by a known method.

  Furthermore, the external additive of the present invention is not necessarily used alone in the production of a toner. If necessary, hydrophobic silica particles other than the external additive of the present invention may be combined, titania, alumina Other additives such as oxide fine particles other than silica such as Teflon (registered trademark), zinc stearate, polyvinylidene fluoride, and other fixing aids such as polyethylene and polypropylene can be used in combination. .

  EXAMPLES Hereinafter, examples and comparative examples will be shown to specifically describe the present invention, but the present invention is not limited only to these examples.

  The physical properties and applied characteristics of the surface-treated silica fine particles of the present invention were measured by the following methods.

(Measurement of hydrophobicity)
0.2 g of the surface-treated silica fine particles were added to 50 ml of water in a beaker having a capacity of 250 ml, and stirred with a magnetic stirrer. To this, methanol was added using a burette, and titration was performed with the end point when the entire amount of the surface-treated silica fine particles was wetted and suspended in the solvent in the beaker. At this time, the tube was introduced into the solution by a tube so that the sample did not directly touch the sample. And the value of the vol% of methanol in the methanol-water mixed solvent in the end point of titration was made into the hydrophobic degree.

(Measurement of floating rate)
Into a glass container having a capacity of 110 ml, 0.5 g of surface-treated silica fine particles were added, and 90 ml of methanol water having a methanol concentration of 60 vol% was added and shaken for 30 minutes with a shaker. The shaken glass container was placed on a horizontal desk and allowed to stand for 4 hours, and then methanol water was extracted using a dropper or the like while preventing the floating surface-treated silica fine particles from being sucked. Next, the surface-treated silica fine particles that had been suspended were dried in a dryer at 120 ° C., and the weight was measured. Then, the ratio of the surface-treated silica fine particles that had floated with respect to 0.5 g, which is the weight of the surface-treated silica fine particles used for the measurement, was determined and used as the floating rate.

(Measurement of average primary particle size of active silica fine particles)
An image taken with a scanning electron microscope was obtained by image analysis. Specifically, at a magnification of 100,000, 50 images were taken with a scanning electron microscope while changing the field of view, and using this, the average primary particle diameter of 2500 primary silica fine particles was image-analyzed, and the number average Asked.

(Chloroform extraction of surface-treated silica fine particles)
1.0 g of the surface-treated silica fine particles were suspended in 40 ml of chloroform and dispersed with an ultrasonic disperser for about 30 minutes, and then the surface-treated silica fine particles were separated with a centrifuge. After the separation, the operation of further adding chloroform, ultrasonically dispersing, and separating the surface-treated silica fine particles with a centrifuge was repeated three times. Thereafter, chloroform contained in the surface-treated silica fine particles was completely removed by a vacuum dryer.

(Measurement of carbon content)
The carbon amount C ₁ of the surface-treated silica fine particles and the carbon amount C ₂ after chloroform extraction were measured using a carbon amount analyzer (trade name: EMIA-110 type) manufactured by Horiba.

(Small angle X-ray scattering measurement)
The base silica fine particles of the sample are filled in through-holes (40 mm long, 5 mm wide, 1 mm high) provided in the substrate, and both sides of the filled sample are held by being swollen with a 6 μm-thick polypropylene film. What was done was used for the measurement. Measurement was performed under the following conditions using a biaxial micronucleus X-ray scattering device (trade name: M18XHF ²² ) manufactured by Mac Science Co., Ltd. equipped with Kratzky-U-slit.

Incident X-ray: Cu-K _α- ray Tube voltage: 40 kv
Tube current: 300mA
Slit width: 10 μm
Detector scanning angle: 0.025 degrees to 0.900 degrees.

(Charge amount under normal conditions and stress conditions)
Styrene-acrylic resin (glass transition point 61 ° C.) was pulverized with a jet mill to obtain resin powder having an average particle size of 8 μm. A 250 ml polyethylene container containing 34.3 g of this resin powder, 1.4 g of surface-treated silica fine particles, and 0.7 g of Leoroseal HM-20S (manufactured by Tokuyama Corporation, bulk specific surface area 200 m ² / g, hexamethyldisilazane treated product) In addition, 200 g of 5 mm glass beads were added as a mixing aid, and shaken with a shaker for a certain period of time to prepare a pseudo toner. The shaking time was 30 minutes as a normal condition and 240 minutes as a stress condition. 1 g of the prepared pseudo toner and 99 g of a ferrite carrier coated with a silicone resin were placed in a sample bottle and conditioned for 12 hours or more in an environment of 25 ° C. and 50% RH. After humidity conditioning, in a similar environment, a bench roller mill is used to triboelectrically mix pseudo toner and ferrite carrier for 60 minutes, and a blow-off method charge measuring device (trade name: TB-200 type) manufactured by Toshiba Chemical Co., Ltd. The amount of charge was measured at. The charge amount of the pseudo toner shaken under the normal condition and the charge amount of the pseudo toner shaken under the stress condition were compared, and the effect of improving the durability of the toner was evaluated.

(Evaluation of transfer efficiency)
A pseudo toner was prepared in the same manner as when measuring the charge amount. The shaking time was 30 minutes. When the 5 mm glass beads added as a mixing aid and the pseudo toner were sieved, the amount of pseudo toner remaining on the surface of the 5 mm glass beads was measured to evaluate the transfer efficiency. The smaller the amount of pseudo toner remaining, the better the transfer efficiency.

Example 1
By burning and oxidizing octamethylcyclotetrasiloxane in an oxyhydrogen flame in an outer flame formed by an oxygen-hydrogen flame, a specific surface area of 35 m ² / g, an average primary particle diameter of 80 nm, a fractal shape parameter α ₁ , Raw material silica fine particles having α ₂ of 2.766 and 1.293 were obtained. Care was taken not to perform any operation such as mixing on the raw silica fine particles to promote contact between the fine particles.

  The raw silica fine particles were put into a mixer, and stirring was started under conditions where the temperature in the mixer was 250 ° C., the peripheral speed was 94 m / s, and the mixing degree for 1 minute was 98%, and nitrogen was circulated. This was maintained for 30 minutes to dry the raw silica fine particles. By this operation, the water content of the raw silica fine particles became 0.1% or less.

  Subsequently, stirring of the mixer was continued under the same conditions, and 11 parts by weight of dimethyl silicone oil (viscosity 50 cSt) was sprayed with 100 parts by weight of the raw silica fine particles using a two-fluid nozzle to adhere to the raw silica fine particles. It was.

  Furthermore, stirring of the mixer was continued under the same conditions and held for 60 minutes to obtain surface-treated silica fine particles. Various physical properties of the obtained surface silica fine particles are shown in Tables 2 and 3.

Examples 2-4
The treatment was performed under the same conditions as in Example 1 except that the amount of silicone oil added and the type of silicone oil were changed to the conditions shown in Table 1. Various physical properties of the obtained surface silica fine particles are shown in Tables 2 and 3.

Example 5
By burning and oxidizing octamethylcyclotetrasiloxane in an oxyhydrogen flame in an outer flame formed by an oxygen-hydrogen flame, a specific surface area of 11 m ² / g, an average primary particle diameter of 190 nm, a fractal shape parameter α ₁ , alpha ₂ was respectively obtain a bulk silica fine 3.112,2.135. Care was taken not to perform any operation such as mixing on the raw silica fine particles to promote contact between the fine particles.

  The raw silica fine particles were put into a mixer, stirring was started under the conditions of a mixer internal temperature of 250 ° C., a peripheral speed of 61 m / s and a mixing degree of 95% for 1 minute, and nitrogen was circulated. This was maintained for 30 minutes to dry the raw silica fine particles. By this operation, the water content of the raw silica fine particles became 0.1% or less.

  Subsequently, stirring of the mixer is continued under the same conditions, and 7 parts by weight of dimethyl silicone oil (viscosity 50 cSt) is sprayed with respect to 100 parts by weight of the raw silica fine particles using a two-fluid nozzle to adhere to the raw silica fine particles. It was.

  Furthermore, stirring of the mixer was continued under the same conditions and held for 60 minutes to obtain surface-treated silica fine particles. Various physical properties of the obtained surface silica fine particles are shown in Tables 2 and 3.

Comparative Example 1
20 g of the raw silica fine particles of Example 1 were dispersed in 200 ml of toluene, and 2.2 g of dimethyl silicone oil (50 cSt) was added. After stirring for 60 minutes with a stirrer, toluene was distilled off with an evaporator. Thereafter, it was placed in an electric furnace at 250 ° C. and held for 1 hour. Various physical properties of the obtained surface silica fine particles are shown in Tables 2 and 3.

Comparative Example 2
The raw silica fine particles of Example 1 were put into a mixer, and stirring was started at room temperature at a peripheral speed of 980 m / s, and 11 parts by weight of dimethyl silicone oil (viscosity 50 cSt) with respect to 100 parts by weight of raw silica fine particles. ) Was sprayed using a two-fluid nozzle and adhered to the raw silica fine particles.

  Thereafter, the silica fine particles to which the silicone oil was adhered were taken out of the mixer, put into an electric furnace, and kept at 120 ° C. for 60 minutes. Various physical properties of the obtained surface-treated silica fine particles are shown in Tables 2 and 3.

Comparative Example 3
The treatment was performed in the same manner as in Comparative Example 2 except that the temperature of the electric furnace was 250 ° C. Various physical properties of the obtained surface-treated silica fine particles are shown in Tables 2 and 3.

Comparative Example 4
The raw silica fine particles of Example 1 were put in a reactor, and 20 parts of hexamethyldisilazane were introduced into the mixer under a nitrogen atmosphere under the condition that the temperature inside the reactor was 250 ° C. The pressure in the reactor was 100 kPa as a gauge pressure. This was maintained for 60 minutes, and the inside of the reactor was replaced with nitrogen. Various physical properties of the obtained surface-treated silica fine particles are shown in Tables 2 and 3.

  The surface-treated silica fine powder produced by the above examples has the physical properties described in the claims of the present invention, and when added to the toner, the effect of suppressing the change in charge amount, and the transfer efficiency Excellent in improving the effect.

  The surface-treated silica fine powder described in Comparative Examples 1 and 3 has a low floating rate in 60 vol% methanol water, and the adhesion state of silicone oil is not uniform, so that the effect of suppressing the change in charge amount is inferior. .

  Since the surface-treated silica fine powder described in Comparative Example 2 has a low degree of hydrophobicity, the effect of improving transfer efficiency is poor.

  Since the surface-treated silica fine powder described in Comparative Example 4 is not treated with silicone oil, the effect of suppressing the change in charge amount is inferior.

Claims (4)

  Surface-treated silica fine particles having an average primary particle size of 50 to 200 nm treated with silicone oil, the degree of hydrophobicity of the surface-treated silica fine particles by methanol titration method is 65% by volume or more, and the methanol concentration is 60 Surface-treated silica fine particles characterized by having a buoyancy ratio of 90% or more in a volume% methanol water. In the small-angle X-ray scattering measurement of the surface-treated silica fine particles with respect to the raw silica fine particles, the fractal shape parameter α _{1 in the} analysis target range 50 nm to 150 nm and the fractal shape parameter α _{2 in} the analysis target range 150 nm to 353 nm are expressed by the following formula (1) and (2):
−0.0068S + 2.548 ≦ α ₁ ≦ −0.0068S + 3.748 (1)
−0.0011S + 1.158 ≦ α ₂ ≦ −0.0011S + 2.058 (2)
(In the above formula, S represents the BET specific surface area (m ² / g) of the active silica fine particles.)
The surface-treated silica fine particles according to claim 1, which satisfy the condition represented by: In the surface-treated silica fine particles, the difference (ΔC (%)) between the carbon amount C ₁ (%) and the carbon amount C ₂ (%) after chloroform extraction is in the range of 0.5 to 3.0. The surface-treated silica fine particles according to claim 1 or 2. An electrophotographic toner external additive comprising the surface-treated silica fine particles according to any one of claims 1 to 3 .