JP2014028738A - Dry silica particulates - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide dry silica particulates exhibiting, despite comprising spherical primary particles whose specific surface areas are confined to a range of 20-60 m/g, a resin thickening aptitude superior to those of extant identically sized dry silica particulates, excellent in terms of dispersibility, and yielding dispersed particles having a sharp particle size distribution.SOLUTION: The provided dry silica particulates are dry silica particulates not only obtained as a result of combustion of a silicon compound but also comprising spherical primary particles as a result of adjustments, at the time of combustion, of not only flame conditions but also cooling conditions and endowed simultaneously with a BET specific surface area of 20-60 m/g, a median diameter/BET specific surface area-equivalent diameter of 2.5 or below, a geometric standard deviation of 1.33 or below, and, as an adequate aggregation structural parameter, a viscosity index of 15 g/mor above at an epoxy resin composition temperature of 25°C and at a shear rate of 10 s.

Description

  The present invention relates to a novel dry silica that can be suitably used as a filler, a thickener, a reinforcing agent for a resin composition, or an external additive for an electrophotographic toner.

Dry silica fine particles (hereinafter also referred to as “spherical silica fine particles”) having a specific surface area of 20 to 60 m ² / g in which the primary particles are spherical are used as a filler added to a semiconductor sealing agent or a semiconductor mounting adhesive. In addition, demand as an external additive for toner particles for electrophotography is expected.

That is, in recent years, with the downsizing and thinning of semiconductor devices, the particle size of the filler added to the semiconductor sealing agent and the semiconductor mounting adhesive, which are epoxy resin compositions, tends to decrease. Spherical silica fine particles having a surface area of 20 to 60 m ² / g and a primary particle diameter of about 50 to 150 nm are preferably used (see Patent Document 1).

  The spherical silica fine particles have a primary particle diameter larger than that of fumed silica produced by a flame hydrolysis method of chlorosilane, and the shape of the aggregated particles formed by the primary particles due to the spherical shape. Is simple and weak, and when it is used as a resin filler, the viscosity of the resin composition is low. For this reason, when the silica fine particles are filled in the resin, the thickening effect is small, and it is necessary to unnecessarily increase the filling rate into the resin.

On the other hand, dry silica fine particles having a specific surface area of 20 to 60 m ² / g in which primary particles are spherical can be embedded in toner resin particles even when used for a long period of time when used as an external additive for toner particles for electrophotography. Therefore, it is known that excellent fluidity can be imparted to the toner particles over a long period of use (see Patent Document 1).

The external additive for toner particles for electrophotography is required to have a property of being well dispersed to a desired particle size and having a sharp particle size distribution at the time of dispersion, but having an existing specific surface area of 20 to 60 m ² / g. As described above, although the dry silica fine particles have excellent dispersibility, in order to be applied as an external additive for electrophotographic toner particles, the particle size of the dispersed particles obtained by the dispersion treatment in the external addition / mixing step A narrower distribution was required.

JP 2008-19157 A

Therefore, the object of the present invention is to have a thicker resin than the existing dry silica fine particles of the same size and dispersibility while the primary particles are spherical and the specific surface area is in the range of ²⁰ to 60 m ² / g. Another object of the present invention is to provide the resin filler and the dry silica fine particles for toner, which are excellent in dispersion and have a sharp particle size distribution.

  In order to solve the above-mentioned problems, the present inventor has intensively studied dry silica fine particles produced by combustion of a silicon compound and growing and aggregating in and near the flame. By adjusting the above, the present inventors have succeeded in obtaining dry silica fine particles that have achieved the above object, and have completed the present invention.

  That is, the present invention is a dry silica fine particle obtained by combustion of a silicon compound, which satisfies all of the following conditions.

(1) It is composed of spherical primary particles, and has a BET specific surface area of 20 to 60 m ² / g.

  (2) Regarding the weight-based particle size distribution of the dispersed particles obtained by dispersing the dry silica fine particles in water at an output of 1.5% by mass with an output of 20 W and a dispersion time of 3 minutes, the ratio of the median diameter to the BET specific surface area equivalent diameter A certain median diameter / BET specific surface area equivalent diameter is 2.5 or less, and a geometric standard deviation is 1.33 or less.

(3) A one-to-one mixture of a bisphenol A type epoxy resin and a bisphenol F type epoxy resin, and a filling rate of the dry silica fine particles into a liquid epoxy resin having a viscosity of 2 Pa · s at a temperature of 25 ° C. and a shear rate of 10 s ⁻¹ The viscosity index of the epoxy resin composition obtained by adding at 40% by mass at a temperature of 25 ° C. and a shear rate of 10 s ⁻¹ is 15 g ² / m ⁴ or more.
(Here, the thickening index is expressed by the following formula.

Thickening index (P) = (η · η ₀ ⁻¹ · S ⁻² ) × 100
(Where η is the viscosity [Pa · s] of the resin composition, η ₀ is the viscosity of the resin [Pa · s], and S is the BET specific surface area [m ² / g] of the silica particles))
In the dry silica fine particles of the present invention,
(1) The water content measured by the loss on drying method at 130 ° C. is 0.5% by mass or less,
(2) the silicon compound is siloxane, in particular cyclic siloxane,
Is preferred.

  The present invention also provides hydrophobized silica in which the dry silica fine particles are surface-treated with a treating agent selected from at least one selected from the group consisting of silylating agents, silicone oils, siloxanes, and fatty acids.

The dry silica fine particles of the present invention are composed of spherical primary particles and have a moderate aggregation structure despite having a BET specific surface area of 20 to 60 m ² / g. It has a viscous action, can impart both viscosity and strength to the resin composition, and is useful as a resin filler, additive, and reinforcing agent.

  Further, since the dry silica fine particles of the present invention have an appropriate aggregation structure, they are well dispersed on the toner resin particles in the external addition / mixing step in the production of electrophotographic toner, and the dispersed particles after the dispersion Since the particle size distribution of the toner particles is sharp, there are few silica fine particles embedded or desorbed in the toner resin particles, providing excellent fluidity over a long period of time, and exhibiting the effect of suppressing variations in toner charge amount. It is also extremely useful as an external additive for toner for electrophotography.

  Therefore, the dry silica fine particles of the present invention can also be used in applications where the above-mentioned contradictory characteristics are required, and it is not necessary to prepare dry silica fine particles by a separate production method according to each application. The manufacturing cost can be further reduced.

Particle size distribution chart of dry silica fine particles obtained in Example 2 Particle size distribution chart of dry silica fine particles obtained in Example 4 Particle size distribution chart of dry silica fine particles obtained in Comparative Example 1 Particle size distribution chart of dry silica fine particles obtained in Comparative Example 2 Particle size distribution chart of dry silica fine particles obtained in Example 2 Particle size distribution chart of dry silica fine particles obtained in Example 4 Particle size distribution chart of dry silica fine particles obtained in Comparative Example 1 Particle size distribution chart of dry silica fine particles obtained in Comparative Example 2

The dry silica fine particles of the present invention are silica fine particles produced by burning a silicon compound and growing and agglomerating in a flame and in the vicinity of the flame, so-called “dry method”. (1) The primary particles are spherical. While the BET specific surface area is in the range of 20-60 m ² / g,
(2) Excellent dispersibility, sharp particle size distribution of dispersed particles,
(3) It has a characteristic that there is a thickening with respect to the resin viscosity than the existing dry silica fine particles of the same size.

The characteristics that the above-mentioned dispersibility is excellent and the particle size distribution of the dispersed particles is sharp are:
(2) Regarding the weight-based particle size distribution of the dispersed particles obtained by dispersing the dry silica fine particles in water at an output of 20% at a concentration of 1.5% by mass and a dispersion time of 3 minutes, the ratio of the median diameter to the BET specific surface area equivalent diameter It is specified by a certain median diameter / BET specific surface area equivalent diameter of 2.5 or less and a geometric standard deviation of 1.33 or less,
The viscosity increase relative to the resin viscosity is
(3) A one-to-one mixture of a bisphenol A type epoxy resin and a bisphenol F type epoxy resin, and a filling rate of the dry silica fine particles into a liquid epoxy resin having a viscosity of 2 Pa · s at a temperature of 25 ° C. and a shear rate of 10 s ⁻¹ An epoxy resin composition obtained by adding at 40% by mass has a viscosity index of 15 g ² / m ⁴ or more at a temperature of 25 ° C. and a shear rate of 10 s ⁻¹ .

(Here, the thickening index is expressed by the following formula.
Thickening index (P) = (η · η ₀ ⁻¹ · S ⁻² ) × 100
(Where η is the viscosity [Pa · s] of the resin composition, η ₀ is the viscosity [Pa · s] of the resin, and S is the BET specific surface area [m ² / g] of the silica particles))
Thus, the dry silica fine particles having a spherical primary particle and a BET specific surface area in the range of ²⁰ to 60 m ² / g, the uniform dispersibility shown in the above (2) and (3) and the thickening to the resin. As described above, the dry silica fine particles exhibiting the action and having the unique agglomeration characteristics are not provided in the prior art and are provided for the first time by the present invention.

  Since the dry silica fine particles of the present invention have the above properties, they can be suitably used in any application as a filler for a resin and as an external additive for an electrophotographic toner.

  That is, when the specific surface area is within the above range, an appropriate thickening effect on the resin as a resin filler is exhibited, and sufficient strength can be imparted to the resin composition. In addition, when applied as an external toner additive for electrophotography, the toner particles are not embedded in the toner resin particles, and the silica fine particles do not fall off from the surface of the toner resin, and have stable adhesion.

  In addition, the median diameter / BET specific surface area equivalent diameter shown in (2) is 2.5 or less, which means that the silica fine particles composed of primary particles can be dispersed to the same level as the primary particle diameter. By means of such properties, it means that when used as an electrophotographic toner external additive, the silica fine particles are dispersed on the surface of the toner resin particles up to a size that exerts a deterring effect on the toner resin, Good fluidity can be imparted. In addition, a geometric standard deviation of 1.33 or less means that the particle size distribution of the dispersed particles is extremely narrow. When used as an external toner additive for electrophotography, the silica fine particles embedded from the surface of the toner resin are detached. Both of the silica fine particles to be reduced can be reduced, and good fluidity can be imparted to the toner resin.

In the present invention, the thickening index is 15 g ² / m ⁴ or more means that the primary particles have moderately strong agglomeration in relation to the dispersibility represented by the median diameter / the BET specific surface area equivalent diameter of the dispersed particles. This means that it has a structure, and when added to the resin due to such properties, it can impart an appropriate thickening action to the resulting resin composition, and provide sufficient strength to the cured resin composition. Can be given. When a thickening action is desired to be achieved by adding a small amount of the dry silica fine particles of the present invention, the thickening index is preferably 20 g ² / m ⁴ or more, more preferably 25 g ² / m ⁴ or more. . However, if the thickening index is too high, the dispersibility tends to decrease, and the thickening index is preferably 50 g ² / m ⁴ or less.

In the present invention, “spherical” means that the sphericity defined below is 1.7 or less.
Sphericality [−] = BET specific surface area [m ² / g] / equivalent surface area [m ² / g]
(Here, the equivalent surface area of the circle is a circle equivalent diameter in which each particle is measured by arbitrarily selecting 2000 or more particles in a 100,000-fold image arbitrarily taken with a scanning electron microscope, and measuring the equivalent circle diameter. Is defined as a specific surface area calculated as a sphere with a diameter of
The weight-based particle size distribution of the dispersed particles obtained by dispersing the dry silica fine particles in water at a concentration of 1.5% by mass with an output of 20 W and a dispersion time of 3 minutes is measured with a centrifugal sedimentation type particle size distribution analyzer. As an example of a measuring machine, CPS Instruments Inc. Examples thereof include a disk centrifugal particle size distribution measuring apparatus DC24000. The BET specific surface area equivalent diameter (D) is a particle diameter calculated by the following equation.

D [nm] = 6000 / silica true density [g / cm ³ ] / BET specific surface area [m ² / g]
Furthermore, in the present invention, as a one-to-one mixture of bisphenol A type epoxy resin and bisphenol F type epoxy resin used for measuring the thickening index, an epoxy resin (trade name: ZX-1059) manufactured by Tohto Kasei is cited. It is done. In addition, a planetary mixer is used for kneading the epoxy resin and the dry silica particles, and specifically, a planetary mixer (trade name: AR-500) manufactured by Sinky Corporation may be used. Furthermore, as a device for measuring the viscosity, there is a rheometer rheostress (trade name: RS600) manufactured by Haake.

As described above, the thickening index is obtained from the viscosity of the epoxy resin measured at 25 ° C. and the shear rate of 10 s ⁻¹ , the viscosity value of the epoxy resin composition after kneading, and the BET specific surface area of the dry silica fine particles. It is done.

  The thickening index is based on the following Cozeny-Kalman equation that expresses the pressure loss when the fluid passes through the powder packed bed.

ΔP = kμ ₀ Luρ ² (1-ρ) ⁻³ S ²
Where ΔP is the pressure loss, k is a constant, μ ₀ is the viscosity of the fluid, L is the thickness of the powder packed bed, u is the velocity of the fluid passing through the powder packed bed, ρ is the powder packing rate, S Is the specific surface area of the powder. In the Cozeny-Kalman equation, when fine particles having a specific surface area S are spatially uniformly filled at a filling rate ρ to form a layer having a thickness L, the fluid flow path of the layer is regarded as a collection of uniform capillaries, and the fluid is This is a theoretical formula obtained as a laminar flow.

  When the flow rate is constant, the thickness is constant, and the filling rate is constant, the pressure loss is proportional to the square of the viscosity of the fluid and the specific surface area of the fine particles as follows.

ΔP∝μ ₀ S ²
The greater the pressure loss, the less fluid will flow. Pressure loss means the energy loss per unit cross section of the flow. When this is applied to the resin composition, the shear stress corresponds to the pressure loss. Furthermore, if the shear rate is constant, the shear stress corresponds to the viscosity of the resin composition. If the viscosity of the fluid is read as the viscosity of the resin and μ is the viscosity of the resin composition,
μ∝μ ₀ S ²
That is,
μ / μ ₀ ∝S ²
The specific viscosity μ / μ ₀ is proportional to the square of the specific surface area of the fine particles.

Μμ ₀ ⁻¹ S ⁻² corresponding to the proportionality coefficient in the above formula gives a true thickening effect by removing the influence of the size of the primary particles given by the specific surface area. The thickening index is obtained by multiplying μμ ₀ ⁻¹ S ⁻² by 100 using the BET specific surface area as S.

  The thickening index is a manifestation of the structure of aggregated particles formed of primary particles. That is, if the aggregated particles formed by the primary particles of the silica fine particles in the resin composition are large, the resin molecules are taken into the aggregated particles and the number of resin molecules that can move freely is reduced, and the thickening index is increased. On the other hand, if the aggregated particles are small, the resin molecules taken into the aggregated particles are small and the number of resin molecules that can freely move is increased.

  Furthermore, the structure of large aggregated particles is sparse and the structure of small aggregated particles is dense.

  As an example, a simple system in which fine particles having the same primary particle diameter form aggregated particles having the same diameter will be described. That is, in this case, the primary particles are also monodispersed, and the aggregated particles are also monodispersed. The following relationship exists between the aggregated particle diameter D and the number of primary particles N contained in one aggregated particle.

N Ｄ D ^dm
Here, dm is a mass / fractal dimension and takes a value of less than 3. The value is approximately 1.8. The mass density of the aggregated particles is proportional to the number of primary particles contained in the aggregated particles and inversely proportional to the volume of the aggregated particles. Therefore, the mass density of the aggregated particles is
ND- ³ = ^Ddm-3
Is proportional to Since dm-3 is a negative value, D ^dm-3 becomes smaller as the aggregated particles become larger. That is, when the aggregated particles are large, a sparse structure is obtained.

  The size of the agglomerated particles, that is, the sparse structure, is the bulk of the dry silica fine particles that are generated by the combustion reaction and are obtained by growing and aggregating in the flame and in the vicinity of the flame. Appears in density.

  The bulk density of silica fine particles having a large aggregate particle diameter, that is, having a loose aggregate structure, is small when compared with silica fine particles having the same specific surface area. That is, it is bulky.

  Although the bulk density value of the silica fine particles can be changed by compressing the dry silica fine particles, as a result of growth and aggregation in the flame and in the vicinity of the flame, the formed aggregate structure hardly changes. This is a characteristic that can be seen from the thickening index.

  Other characteristics of the dry silica fine particles of the present invention are not particularly limited as long as they have the above-mentioned characteristics. For example, the moisture content measured by the loss on drying method at 130 ° C. is 0.5 mass. % Or less, it is possible to suppress the formation of strong agglomerated particles over time due to the adsorbed moisture of the silica fine particles. As a result, the above advantages can be maintained even after long-term storage.

  The dry silica fine particles of the present invention may be treated on the surface of the silica fine particles with a treatment agent selected from at least one selected from the group consisting of silylating agents, silicone oils, siloxanes and fatty acids depending on the application.

  Specific silylating agents include tetramethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, o-methylphenyltrimethoxysilane, p-methylphenyltrimethoxysilane, n-butyltri Methoxysilane, i-butyltrimethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, tetraethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, diphenyl Diethoxysilane, i-butyltriethoxysilane, decyltriethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-glycine Sidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ Alkoxysilanes such as-(2-aminoethyl) aminopropyltrimethoxysilane and γ- (2-aminoethyl) aminopropylmethyldimethoxysilane, hexamethyldisilazane, hexaethyldisilazane, hexapropyldisilazane, hexabutyldi Examples thereof include silazanes such as silazane, hexapentyldisilazane, hexahexyldisilazane, hexaphenyldisilazane, divinyltetramethyldisilazane, and dimethyltetravinyldisilazane.

Silicone oils include dimethyl silicone oil, methyl hydrogen silicone oil, methylphenyl silicone oil, alkyl modified silicone oil, carboxylic acid modified silicone oil, fatty acid modified silicone oil, polyether modified silicone oil, alkoxy modified silicone oil, carbinol modified. Examples include silicone oil, amino-modified silicone oil, and terminal reactive silicone oil.
Examples of siloxanes include hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, hexamethyldisiloxane, and octamethyltrisiloxane.
As fatty acids, long-chain fatty acids such as undecyl acid, lauric acid, tridecylic acid, dodecylic acid, myristic acid, valmitic acid, pentadecylic acid, stearic acid, heptadecylic acid, arachidic acid, montanic acid, oleic acid, linoleic acid, arachidonic acid, etc. Is mentioned.

(Method for producing silica fine particles)
The dry silica fine particles of the present invention can be obtained by producing silica fine particles by a combustion reaction of a silicon compound and then causing primary particles to grow and lightly aggregate in and near the flame. More specifically, in the above-mentioned combustion reaction, a flame having a maximum temperature exceeding the melting point of silica (2000K) and having a gentle temperature gradient is formed, and the cooling rate of the generated silica fine particles is adjusted. It is obtained by doing.

  The dry silica fine particles of the present invention are preferably produced using a burner having a concentric multi-pipe structure. Hereinafter, the case where a concentric quadruple burner is used will be described in detail as a typical example.

  This concentric quadruple burner has a central tube, a first annular tube is disposed on the outer periphery of the central tube, a second annular tube is disposed on the outer periphery of the first annular tube, and a third annular tube is disposed on the outer periphery of the second annular tube. A burner with a tube.

  A silicon compound vaporized as a silica source and oxygen are mixed and introduced into the central tube in advance. At this time, an inert gas such as nitrogen may also be mixed. Further, when silica fine particles are generated by a hydrolysis reaction of a silicon compound, a fuel that generates water vapor when reacted with oxygen, such as hydrogen and hydrocarbons, is mixed and mixed.

  In addition, a fuel for forming an auxiliary flame, such as hydrogen or hydrocarbon, is introduced into the first annular pipe. At this time, an inert gas such as nitrogen may be mixed and introduced. Furthermore, oxygen may be mixed together.

  Further, oxygen for forming an auxiliary flame is introduced into the second annular pipe. At this time, an inert gas such as nitrogen may be mixed and mixed.

Furthermore, a mixed gas of an inert gas such as oxygen and nitrogen is introduced into the third annular tube. Since air can be easily introduced, it is preferable to introduce air.
The characteristics of dry silica fine particles obtained by forming, growing and agglomerating in the flame and in the vicinity of the flame very strongly reflect the temperature history experienced by the silica fine particles.

  In the method for producing dry silica fine particles of the present invention, it is essential that the maximum flame temperature exceeds the melting point of silica. When the maximum flame temperature is lower than the melting point of silica, the dispersion performance deteriorates, and it becomes impossible to obtain the dry silica fine particles of the present invention. In order to obtain the silica of the present invention, the maximum flame temperature is preferably 2400K or higher.

  In order to obtain the dry silica fine particles of the present invention, it is particularly important to adjust to a flame having a gentle temperature gradient, as will be described below.

  Due to the gentle temperature gradient, the silica fine particles can stay in the temperature region above the silica melting point for a long time, that is, because they can stay in the growth region for a long time, the silica fine particles can be dispersed to the level of the primary particle size, Dispersion particle size distribution can also give a sharp characteristic.

  Furthermore, since the time to the temperature at which the aggregation of the silica fine particles is completed can be extended by a gentle temperature gradient, that is, the silica fine particles can stay in the aggregation region for a long time, the aggregate particle diameter of the silica fine particles is increased. The structure of the agglomerated particles becomes sparse, and the silica fine particles acquire the characteristic of having a high viscosity index for the resin.

  The specific adjustment of the flame temperature distribution is carried out by adjusting the introduction composition of the central tube, the size of the central tube, the outlet flow velocity of the third annular tube, and the size of the third annular tube. For example, the maximum flame temperature can be adjusted with the composition introduced in the central tube. The maximum temperature of the flame is preferably monitored at a temperature obtained by adding the temperature of the introduced gas to the adiabatic flame temperature in a standard state that can be calculated from the introduced composition, and then subtracting the standard temperature (298K). In the application of this supervision method, it is essential to select a composition in which the reaction is completed only by chemical components introduced into the central tube, that is, a composition in which no unreacted silicon compound and fuel remain. For example, when only a silicon compound and oxygen are introduced into the central tube, it is essential that the amount of oxygen introduced is equal to or greater than the amount of oxygen necessary for the introduced silicon compound to completely burn.

  In the calculation of the adiabatic flame temperature, the thermodynamic property value may be referred to “JANAF Thermochemical Tables SECOND EDITION”, Horikoshi Laboratories (1975), or the like. Furthermore, the specific heat required for the calculation of the adiabatic flame temperature is more accurate from the viewpoint of supervision because it is more accurate to incorporate the temperature dependency of the specific heat than to use a specific temperature value. For example, it is preferable that the specific heat is approximated by a polynomial of temperature, for example, a sixth order polynomial, and the adiabatic flame temperature is calculated based on the approximation.

  Also, the flame temperature gradient can be adjusted by the size of the central tube. When the size of the central tube is increased, heat dissipation is suppressed and the flame temperature gradient becomes gentle. This is based on the following principle.

The heat capacity of the flame representing the difficulty of cooling the flame is substantially proportional to (π / 4) × (gas flow velocity of the center tube) × (center tube diameter) ² which is the amount of gas introduced into the center tube. On the other hand, the amount of heat released per unit time from the flame is substantially proportional to (π) × (gas flow velocity of the center tube) × (diameter of the center tube) corresponding to the contact area between the flame and the surroundings, that is, the heat dissipation area. Therefore, the heat dissipation area / heat capacity is inversely proportional to the diameter of the central tube. That is, the flame is hardly cooled in inverse proportion to the diameter of the central tube, and as a result, a flame having a gentle temperature gradient can be obtained.

  Further, when the outlet flow velocity of the third annular pipe is slowed, the heat transfer coefficient is reduced by the law of boundary film heat transfer, and the flame does not exchange heat with the surroundings. As a result, the flame is not cooled and has a gentle temperature gradient. Is obtained.

Further, when the size of the third annular pipe is reduced, the heat transfer coefficient is also reduced by the law of boundary film heat transfer, so that the flame is not cooled and a flame having a gentle temperature gradient is obtained.
In summary, the maximum flame temperature depends on the composition of the center tube, the heat transfer area between the flame and the surroundings at the center tube size, and the heat transfer coefficient between the flame and the surroundings at the outlet flow velocity and size of the third annular tube. This determines the flame temperature distribution. By using this, the dry silica fine particles of the present invention can be obtained by adjusting the temperature distribution of the flame.

  A more specific adjustment method may be appropriately determined by the above-described adjustment method according to the silicon compound to be used. However, in order to form a flame having a gentle temperature gradient, the cooling factor defined below is set to 400 Nm / m. / S or less is a preferred form for obtaining the dry silica fine particles of the present invention.

Cooling factor [Nm / m / s]
= (Dout / Din) ^0.5 * V / Dc * (Tmax-T0) / Tm
Here, Dout is the outer diameter [m] of the third annular tube, Din is the inner diameter [m] of the third annular tube, V is the outlet flow velocity [Nm / s] of the third annular tube, and Dc is the central tube. , Tmax represents the maximum flame temperature [K], T0 represents the gas temperature [K] of the third annular tube, and Tm represents 2000 K, which is the melting point of silica.
In the above equation, (Dout / Din) ^0.5 × V represents a heat transfer coefficient factor depending on the outlet flow velocity and size of the third annular tube, 1 / Dc represents a factor related to the heat radiation area, and (Tmax−T0) / Tm represents a temperature difference that becomes a driving force of heat transfer normalized at 2000 K, which is the melting point of silica.

  It should be noted that the adjustment of the flame temperature distribution must be carried out within a range where there is no risk of backfire and blow-off of the flame. For this reason, the gas flow rate of the central tube is preferably in the range of 10 to 200 Nm / s, and more preferably in the range of 20 to 180 Nm / s. Note that Nm / s, which is a unit of flow rate, is a flow rate when converted to a temperature of 273 K and atmospheric pressure.

  The first annular pipe and the second annular pipe are intended to fix a flame at the burner tip and perform stable combustion, stable operation, and stable operation. For this purpose, the outlet flow velocity of the first annular tube is preferably 10 Nm / s or more. The outlet flow rate of the second annular tube is preferably 5 Nm / s or more, and more preferably 10 Nm / s or more. Furthermore, the gas introduced into the second annular tube is preferably oxygen alone. The first annular pipe and the second annular pipe may be integrated into a single annular pipe as long as the flame is fixed at the burner tip and stable combustion, stable operation, and stable operation can be achieved.

Further, the third annular pipe mainly plays a role of adjusting the heat transfer coefficient between the flame and the surroundings, but also serves to stabilize the flame properties and stably burn. For this purpose, the outlet flow rate is preferably 0.5 Nm / s or more, more preferably 2 Nm / s or more.
As the silicon compound, those which are gaseous or liquid at normal temperature are used without any particular limitation. For example, cyclic siloxanes such as octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane, chain siloxanes such as hexamethyldisiloxane, alkoxysilanes such as tetramethoxysilane and tetraethoxysilane, trichlorosilane and tetrachlorosilane Chlorosilanes can be used as silicon compounds.
Use of siloxanes and alkoxysilanes that do not contain chlorine as the silicon compound is preferable because high purity dry silica fine particles with significantly reduced chlorine as an impurity can be obtained.

  When the adiabatic flame temperature of the above-mentioned silicon compound and oxygen combustion equivalent flame is calculated assuming that the silicon compound and oxygen are introduced at 298K, siloxanes are 5500 to 6000K, alkoxysilanes are 4500K to 5100K, and chlorosilanes. Then, it becomes 3000-4000K. Here, the chlorosilane was an equivalent flame of chlorosilane-hydrogen-oxygen.

  While it is only necessary to dilute the equivalent flame with an inert gas to achieve a lower adiabatic flame temperature than the oxy-combustion equivalent flame, it is impossible to obtain a flame higher than the oxy-combustion equivalent flame.

Agglomerates with high viscosity index, while dry silica fine particles have a BET specific surface area of 20-60 m ² / g, are dispersed to the primary particle size level, and have a sharp dispersion particle size distribution. In order to adjust the flame temperature distribution so as to have a structure, a silicon compound capable of achieving a high adiabatic flame temperature is preferable as the silicon compound to be used, and for this reason, siloxanes are preferably used as the silicon compound.

  Among siloxanes, cyclic siloxanes have fewer carbon atoms per silicon atom than chain siloxanes, so that they do not easily cause poor combustion such as generation of carbon and make the flame uniform. Siloxane is the most preferred form.

  The dry silica fine particles of the present invention can be obtained by generating, growing, and agglomerating in and near the flame. It is done by separating and collecting. The dry silica fine particles of the present invention have a feature that they have a large aggregate particle diameter regardless of whether they are filter separation or centrifugal separation.

  Examples and comparative examples are shown to specifically describe the present invention, but the present invention is not limited to these examples.

  In addition, various physical property measurements in the following examples and comparative examples are based on the following methods.

(1) Specific surface area The specific surface area was measured by a nitrogen adsorption BET one-point method using a specific surface area measuring device SA-1000 manufactured by Shibata Rikagaku.

(2) Particle size distribution (Preparation of measurement sample)
A silica suspension having a silica concentration of 1.5% by mass as a measurement sample was prepared as follows.
0.3 g of silica and 20 ml of distilled water are placed in a glass sample tube bottle (manufactured by ASONE, inner volume 30 ml, outer diameter about 28 mm), and an ultrasonic cell crusher (BRANSON Sonifier II Model 250D, probe: 1. A sample tube bottle with a sample is placed so that the bottom surface of the 4 inch probe tip is 15 mm below the water surface, and silica fine particles are dispersed in distilled water under the conditions of an output of 20 W and a dispersion time of 3 minutes. A 5% by weight aqueous suspension was prepared.

(Particle size distribution measurement)
CPS Instruments Inc. The weight-based particle size distribution was measured using a disk centrifugal particle size distribution measuring apparatus (DC24000). The measurement conditions were a rotation speed of 18000 rpm, a temperature of 32 ° C., and a true silica density of 2.2 g / cm ³ .

The median diameter was calculated from the obtained weight-based particle size distribution. From the median diameter and the BET specific surface area, the median diameter / BET specific surface area equivalent diameter was determined. In addition, a BET specific surface area equivalent diameter is calculated | required by a following formula.
BET specific surface area equivalent diameter [nm]
= 6000 / true silica density [g / cm ³ ] / BET specific surface area [m ² / g]
Even in the above formula, the true silica density was set to 2.2 g / cm ³ .

  In addition, log normal distribution fitting was performed within a cumulative frequency range of 10% by mass to 90% by mass, and a geometric standard deviation was calculated from the fitting.

(3) Thickening index (Preparation of epoxy resin composition)
42.84 g of Toto Kasei epoxy resin ZX-1059 was weighed and 28.56 g of silica was added thereto. Then, using a planetary mixer AR-500 manufactured by Sinky Corporation, the mixture was stirred for 8 minutes at a rotation speed of 1000 rpm and then degassed for 2 minutes at a rotation speed of 2000 rpm to obtain an epoxy resin composition. Then, the resin composition was left still for 1 hour or more in a 25 degreeC thermostat.

(Viscosity of epoxy resin composition)
The resin composition was taken out from the thermostatic bath at 25 ° C., and the viscosity was measured at a shear rate of 10 s ⁻¹ using a rheometer Rheo Stress RS600 manufactured by Haake. The measurement temperature is 25 ° C., the sensor used is C35 / 1 (cone plate type diameter 35 mm, angle 1 degree, titanium material), and the viscosity value after maintaining the shear rate of 10 s ⁻¹ for 3 minutes. It was set as the viscosity of the epoxy resin composition.

(Viscosity of epoxy resin)
The viscosity of the epoxy resin ZX-1059 manufactured by Tohto Kasei Co., Ltd. was measured at a shear rate of 10 s ⁻¹ using a rheometer Rheo Stress RS600 manufactured by Haake. The measurement temperature is 25 ° C., the sensor used is C35 / 1 (cone plate type diameter 35 mm, angle 1 degree, material titanium), and the viscosity value after maintaining the state of shear rate 10 s ⁻¹ for 3 minutes is epoxy. The viscosity of the resin was used.

(Thickening index)
The thickening index [g ² / m ⁴ ] was determined by the following formula.
Thickening index [g ² / m ⁴ ] = (η · η ₀ ⁻¹ · S ⁻² ) × 100
Here, η is the viscosity [Pa · s] of the resin composition, η ₀ is the viscosity [Pa · s] of the resin, and S is the BET specific surface area [m ² / g].

(4) Absorbance (Preparation of measurement sample)
It was exactly the same as the measurement sample in the particle size distribution.

(Absorption measurement)
Using a spectrophotometer V-530 manufactured by JASCO Corporation, the absorbance of an aqueous suspension having a silica concentration of 1.5 mass% with respect to light having a wavelength of 700 nm was measured. The measurement sample cell used was a synthetic quartz cell (5-sided transparent, 10 × 10 × 45H) manufactured by Tokyo Glass Instruments.

(5) Bulk density Bulk density was measured using a powder tester PT-R type manufactured by Hosokawa Micron. The sample was put on a sieve having an aperture of 1.4 mm, and the sieve was vibrated to drop the sample into a measuring cup having a capacity of 100 ml. Thereafter, the bulk density was calculated from the sample weight in the cup and the cup volume.

(6) Sphericality (Sample preparation for scanning electron microscope)
0.02 g of silica was added to 10 ml of acetone, and then ultrasonically dispersed for 10 minutes to obtain an acetone slurry of silica. After dropping several drops of this slurry onto a hydrophilized silicon wafer, the slurry was dried under reduced pressure to obtain a sample for a scanning electron microscope.

(Scanning electron microscope photography)
A 100,000 times image of the sample was taken with a field emission scanning electron microscope S-5500 manufactured by Hitachi High-Technologies.

(Measurement of equivalent circle diameter, equivalent surface area of equivalent circle)
Using a 100,000-fold image of the sample and Asahi Engineering's image analysis software IP-1000PC, 2000 or more silica fine particles were arbitrarily selected, and the equivalent circle diameter was measured. The measured silica fine particles were regarded as true spherical silica fine particles having a diameter equivalent to a circle, and the data of all the measured silica fine particles were used to obtain the equivalent surface area of the circle. The true density of the silica fine particles was 2.2 g / cm ³ .

(Sphericity)
Sphericality = BET specific surface area [m ² / g] / equivalent specific surface area [m ² / g]
According to the above, the sphericity was obtained.

Examples 1-5, Comparative Examples 1-4
Octamethylcyclotetrasiloxane was burned with a concentric quadruple burner to produce dry silica fine particles. Hereinafter, octamethylcyclotetrasiloxane is referred to as a raw material.

  The raw material heated and vaporized, oxygen and nitrogen were mixed and then introduced into the burner central tube. Further, hydrogen and nitrogen were mixed and introduced into a first annular tube disposed on the outer periphery of the central tube, and oxygen was introduced into a second annular tube disposed on the outer periphery of the first annular tube. Further, air was introduced into a third annular tube disposed on the outer periphery of the second annular tube. The obtained dry silica fine particles were collected with a metal filter, and the BET specific surface area, particle size distribution, thickening index, absorbance, bulk density, and sphericity were measured.

  Table 1 shows the production conditions and silica characteristics of Examples 1 to 5, and Table 2 shows the production conditions and silica characteristics of Comparative Examples 1 to 4, respectively.

  The sphericity of the dry silica fine particles of Examples 1 to 5 and Comparative Examples 1 to 4 was 1.7 or less, and all were spherical. Moreover, it confirmed that the moisture content measured by the drying loss method at 130 degreeC was 0.5 mass% or less.

The oxygen ratio in Tables 1 and 2 is (number of moles of oxygen introduced into the central tube) / (16 × number of moles of raw material introduced into the central tube), and the oxygen concentration is (of oxygen introduced into the central tube). The number of moles) / (number of moles of oxygen introduced into the central tube + number of moles of nitrogen introduced into the central tube) is expressed as a percentage. R _SFL is (number of moles of hydrogen introduced into the first annular tube) / (32 × number of moles of raw material introduced into the center tube), and R _cmbts is (number of moles of oxygen introduced into the second annular tube). / (16 × number of moles of raw material introduced into the central tube). 6 of the temperature obtained by the least square method based on “JANAF Thermochemical Tables SECOND EDITION”, Horikoshi Laboratories (1975) in each temperature range, with 2000K as the boundary of the specific heat expression for calculating the maximum flame temperature. A second order polynomial was used. The standard generation molar enthalpy value of the raw material octamethylcyclotetrasiloxane adopts the value of “J. Lipowitz, J. Fire & Flammability 7, 482 (1976)”, and the standard generation molar enthalpy value of other substances. Used is the value of Thermochemical Tables SECOND EDITION ", Horikoshi Laboratories (1975).

  In Examples 1 to 3, the same burner was used. In Examples 4 to 5 and Comparative Examples 1 and 2, the central tube, the first annular tube, and the second annular tube were the same as in Example 1, and the third annular tube was a burner that was larger than that in Example 1. Furthermore, in Comparative Examples 3 to 4, the central tube diameter is 1/2 of Example 1, the clearance (space) of the first annular tube and the cross-sectional area of the second annular tube are the same as those of Example 1, and the third annular tube The outer diameter used was 1.1 times that of Example 1.

  Further, the viscosity of the epoxy resin measured for obtaining the thickening index was 2.22 Pa · s.

  Regarding the particle size distribution of the silica fine particles obtained at the time of measuring the sphericity, the particle size distribution diagram of Example 2 in FIG. 1, Example 4 in FIG. 2, Comparative Example 1 in FIG. 3, and Comparative Example 2 in FIG. Indicates. These are primary particle size distributions of silica fine particles.

  Further, with respect to the weight-based particle size distribution of the dispersed particles measured by the disk centrifugal particle size distribution measuring apparatus, FIG. 5 shows Example 2, FIG. 6 shows Example 4, FIG. 7 shows Comparative Example 1, and FIG. The particle size distribution figure of Example 2 is shown.

Claims (5)

Dry silica fine particles obtained by combustion of a silicon compound and satisfying all of the following conditions.
(1) It is composed of spherical primary particles, and has a BET specific surface area of 20 to 60 m ² / g.
(2) The median which is the ratio of the median diameter to the BET specific surface area equivalent diameter for the weight-based particle size distribution of the particles after the dry silica fine particles are dispersed in water at an output of 20 W at a concentration of 1.5% by mass and dispersion time of 3 minutes. The diameter / BET specific surface area equivalent diameter is 2.5 or less and the geometric standard deviation is 1.33 or less.
(3) A one-to-one mixture of a bisphenol A type epoxy resin and a bisphenol F type epoxy resin, and filling the dry silica fine particles with a liquid epoxy resin having a viscosity of 2 Pa · s at a temperature of 25 ° C. and a shear rate of 10 s ⁻¹ The thickening index of the epoxy resin composition obtained by adding at a rate of 40% by mass at a temperature of 25 ° C. and a shear rate of 10 s ⁻¹ is 15 g ² / m ⁴ or more.
(Here, the thickening index is expressed by the following formula.
Thickening index (P) = (η · η ₀ ⁻¹ · S ⁻² ) × 100
(Where η is the viscosity [Pa · s] of the resin composition, η ₀ is the viscosity [Pa · s] of the resin, and S is the BET specific surface area [m ² / g] of the silica particles))   The dry silica fine particles according to claim 1, wherein the moisture content measured by a loss on drying method at 130 ° C is 0.5% by mass or less.   3. The dry silica fine particles according to claim 1, wherein the silicon compound is siloxane.   4. The dry silica fine particles according to claim 3, wherein the siloxane is a cyclic siloxane.   Hydrophobized dry silica, wherein the dry silica fine particles according to any one of claims 1 to 4 are surface-treated with a treatment agent selected from at least one selected from the group consisting of silylating agents, silicone oils, siloxanes, and fatty acids. Fine particles.

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