JP6112888B2 - Dry silica fine particles - Google Patents

Description

  The present invention relates to a novel dry silica fine particle. Specifically, the BET specific surface area is small, and it is more dispersible than the existing dry silica fine particles of the same size, and the particle size distribution at the time of dispersion is narrow, so that excellent gap permeability can be expressed in the added resin composition. In particular, the present invention provides novel high-purity dry silica fine particles that can be suitably used as a filler added to a resin composition used for a semiconductor encapsulant or the like.

  In recent years, miniaturization, thinning, and high-density mounting of semiconductor devices are rapidly progressing. For example, in flip chip mounting, a narrowing gap is progressing from several μm to several tens of μm. Accordingly, semiconductor sealing agents and semiconductor mounting adhesives that are epoxy resin compositions are required to have excellent gap penetration.

Conventionally, as a resin composition filler for flip chip mounting, a BET specific surface area of 5 to 30 m ² / g, converted into a primary particle diameter, high-purity silica fine particles having a particle diameter of about 100 to 600 nm have been used. The existing silica fine particles having the BET specific surface area have poor dispersibility and a wide particle size distribution at the time of dispersion, so that the penetration into the narrow gaps is not sufficient, and the molding becomes defective. That is, there is a problem that silica fine particles having a BET specific surface area of 5 to 30 m ² / g cannot cope with the narrow gap of flip chip mounting.

For this reason, although it is a silica fine particle having a BET specific surface area of 5 to 30 m ² / g, it has a high purity and is better dispersed in the desired particle size than the existing silica fine particles of the same size and the particle size distribution at the time of dispersion. As a result, there has been a demand for silica fine particles that have narrow characteristics, and as a result, the resin composition when the silica fine particles are filled in an epoxy resin acquires excellent crevice permeability.

Conventionally, the following five methods are known as a method for producing 5 to 30 m ² / g of silica fine particles.
(1) Sol-gel method (Patent Document 1)
(2) Flame hydrolysis method of chlorosilane (Patent Document 2)
(3) Combustion method of silicon powder (Patent Document 3)
(4) Alkoxysilane combustion method (Patent Document 4)
(5) Combustion method of siloxane (Patent Literature 5, Patent Literature 6).

  In the case of the sol-gel method (1), there is a problem in dispersibility because particles are strongly aggregated or fused / welded in the drying and firing steps for removing moisture contained in silica.

  In the case of the flame hydrolysis method of chlorosilane (2) above, a chlorine compound is by-produced and adsorbed on the generated silica, so a deoxidation step for removing this is necessary. In the deoxidation step, the silica is exposed to a high temperature. As a result, the particles are strongly aggregated and partially fused and welded, causing a problem in dispersibility. In addition, removal of the chlorine compound is insufficient even after the deoxidation step, and about tens of ppm of chlorine remains on the silica, which is not suitable for semiconductor device applications.

  In the case of the combustion method of silicon powder (3), evaporation of silicon powder, mixing of silicon vapor and oxygen generated by evaporation, reaction of silicon vapor and oxygen, and growth of silica fine particles generated by the reaction are simultaneously performed in the same flame. Since it proceeds, the flame is non-uniform, and reflecting this, it is not possible to obtain a product having excellent dispersibility and a narrow particle size distribution at the time of dispersion.

  In the case of the combustion method of alkoxysilane of (4), since the ratio of hydrocarbon to silicon in the raw material molecule is large, the temperature range where the primary particles are fused is wide, and the fusion / welding of the particles proceeds. Only dispersible ones can be obtained.

  In the case of siloxane combustion method (5), in the case of droplet spray combustion or diffusion combustion in which siloxane is not preliminarily mixed with a combustion supporting gas such as oxygen, the flame becomes non-uniform, similar to the silicon powder combustion method of (3). As a result, silica fine particles having excellent dispersibility and a narrow particle size distribution at the time of dispersion cannot be obtained.

  As a method for obtaining fine silica particles with excellent dispersibility, a premixed combustion method in which siloxane is mixed with a combustion-supporting gas such as oxygen in advance has been proposed, but the narrow gap clearance permeability required for flip chip mounting is proposed. Insufficient dispersibility and narrow particle size distribution at the time of dispersion are insufficient to meet the requirements.

Japanese Patent Laid-Open No. 4-21515 JP 2002-003213 A JP 60-255602 A JP-A-2-188421 JP 2002-060214 A JP 2008-19157 A

An object of the present invention, the BET specific surface area BET specific surface area 5 to 30 m ² / g, in particular, ^{5 m} 2 / g or more, a range of less than ^{30 m} 2 / g, than the silica fine particles of the existing of the same size, dispersibility In addition, since the particle size distribution at the time of dispersion is narrow, the dry resin fine particles having excellent crevice permeability in the added resin composition and having high purity and useful as a filler for resin for semiconductors are obtained. It is to provide.

  In order to solve the above-mentioned problems, the present inventors have conducted extensive studies on dry silica fine particles that are produced by combustion of a siloxane compound and grow and aggregate in and near the flame. As a result, dry silica fine particles are produced. By adjusting not only the flame conditions but also the cooling conditions of the combustion flame, 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 siloxane, which satisfies all of the following conditions.

(A) The BET specific surface area is 5 m ² / g or more and less than 30 m ² / g.

(B) median diameter _{D CS} satisfies the following formula (1).

D _CS ≦ 2 × D _B (1)
(However, D _CS is a median diameter based on weight particle size distribution obtained by the centrifugal sedimentation method, D _B is the surface area in terms of diameter BET ratio.)
(C) The geometric standard deviation σg of the weight-based particle size distribution obtained by the centrifugal sedimentation method is 1.30 or less.
(D) In the weight-based particle size distribution obtained by the centrifugal sedimentation method, the content of particles having a particle diameter that is at least 3 times the BET specific surface area converted diameter is 0.18% by mass or less.

  (E) The contents of chlorine, sodium and potassium are each 1 ppm or less.

In the dry silica fine particles of the present invention, the BET specific surface area is 10 to 25 m ² / g, the median diameter is 150 to 350 nm, and the moisture content measured by the loss on drying method at 130 ° C. is 0.5. It is a more preferable aspect that it is less than mass%.

  In the present invention, as described in the examples, the particle size distribution by the centrifugal sedimentation method described above is a weight obtained by measuring the dispersed particles obtained by dispersing the dry silica fine particles in water with a particle size distribution measuring device of the centrifugal sedimentation method. Reference particle size distribution.

The dry silica fine particle of the present invention has a BET specific surface area of 5 m ² / g or more and less than 30 m ² / g, and has an excellent dispersion performance that is substantially dispersed to primary particles and a narrow particle size distribution at the time of dispersion. Therefore, the resin composition filled therewith exhibits excellent permeability. Therefore, the dry silica fine particles of the present invention are extremely useful as a filler for underfill in flip chip mounting that requires permeability to a narrow gap of several μm to several tens of μm.

The dry silica fine particles of the present invention are silica fine particles produced by combustion of siloxane, grown in the flame and in the vicinity of the flame, and agglomerated, silica fine particles obtained by the dry method,
(A) The BET specific surface area is 5 m ² / g or more and less than 30 m ² / g,
(B) Excellent dispersibility,
(C) The particle size distribution of the dispersed particles is narrow,
(D) In the particle size distribution of the dispersed particles, do not draw a long tail on the large particle size side (E) high purity,
It has the characteristic.

When the BET specific surface area is 30 m ² / g or more, as a result of an increase in the interface between the resin and the silica fine particles in the resin composition, the viscosity of the resin composition when flowing at a low speed increases, and sufficient narrow gap permeability is obtained. I can't. On the other hand, when the BET specific surface area is less than 5 m ² / g, the viscosity of the resin composition is low, but the silica fine particles with respect to the gaps are too large. However, sufficient narrow gap permeability cannot be obtained.

In addition, it is a more preferable aspect that a BET specific surface area is 10-25 m < ² > / g at the point which can provide sufficient intensity | strength to the hardening composition which is a resin composition after hardening.

The characteristic (B) excellent in the dispersibility is specified by D _CS ≦ 2 × D _B. Here, D _CS is the median diameter of the weight-based particle size distribution of wherein the drying type silica fine particles by centrifugal sedimentation, D _B is a diameter converted from the BET specific surface area. BET specific surface area in terms of diameter _{D B} was calculated using the following equation (2).

D _B = 6000 / (ρ _Si × S _B ) (2)
ρ _Si : Silica true density (g / cm ³ )
S _B : BET specific surface area (m ² / g)
The true silica density was 2.2 g / cm ³ .

  The characteristic (C) where the particle size distribution of the dispersed particles is narrow is specified by σg being 1.30 or less. σg is a geometric standard deviation calculated from the logarithmic normal distribution fitting (least square method) of the weight-based particle size distribution obtained by the centrifugal sedimentation method in the range of the cumulative frequency of 10 mass% to 90 mass%.

The characteristic (D) that the long particle is not drawn on the particle size side where the particle size distribution of the dispersed particles is large is that the particle size is 3 times or more of the BET specific surface area converted diameter in the weight-based particle size distribution obtained by the centrifugal sedimentation method. The content is specified to be 0.18% by mass or less, particularly 0.15% by mass or less, and further 0.12% by mass or less.
The high purity property (E) is specified by the content of chlorine, sodium and potassium being 1 ppm or less.

Such dry silica fine particles having a BET specific surface area in the range of 5 m ² / g or more and less than 30 m ² / g and satisfying all the characteristics shown in the characteristics (B) to (E) are conventionally used. There are no manufactured examples, which are provided for the first time by the present invention.

That is, it means that the dry silica fine particles of the present invention represented by the characteristic (B) have an extremely high dispersion performance in which even the primary particles are dispersed in the medium. As described later, the particle size distribution of the centrifugal sedimentation method represents the particle size distribution of dispersed particles dispersed in the medium, and the BET specific surface area equivalent diameter represents the particle size distribution of primary particles. For this reason, D _CS ≦ 2 × D _B means that there are no or almost no particles formed by chemical bonds between silica particles and particles that are physically aggregated so as not to be dispersed. Is shown.

  Furthermore, having the characteristic (C) in accordance with the characteristic (B) means that there are almost no tens of nanometer particles or aggregates that cause thickening in the dispersed state.

  In addition, having the above characteristic (D) in accordance with the above characteristic (B) means that large particles that become penetration obstacles at the time of narrow gap penetration, or extremely large coarse particles that cause voids, and primary It means that there are almost no large aggregates formed by particle chemical bonds or strong physical bonds.

  Therefore, satisfying all three conditions (B), (C), and (D) guarantees excellent narrow gap permeability and reliability of the resin composition to which the silica fine particles of the present invention are added. To do.

  Satisfying the above characteristic (E) means that in semiconductor devices using the resin composition to which the dry silica fine particles are added, there are no problems caused by corrosion caused by chloride ions or leakage currents caused by sodium or potassium ions. Means.

On the other hand, dry silica fine particles manufactured by conventional methods are agglomerated physically strongly so that they cannot be dispersed due to chemical bonds between silica particles due to differences in the manufacturing method described later. As a result of the generation of fine particles, large particles and coarse particles cannot be avoided, the resulting dry silica fine particles are out of the range indicated by the characteristics (B) to (D). The effect of the present invention cannot be exhibited. In addition, when a dry classification operation is performed on conventional dry silica fine particles, silica fine particles having a specific surface area of 5 m ² / g or more have higher cohesiveness in the powder than other silica fine particles, and are primary particles in an air stream. Classification is not possible because it is not dispersed. Furthermore, when conventional dry silica fine particles are dispersed in a liquid and subjected to a classification operation, strong agglomerated particles are formed by the drying step after classification, and the dispersibility is significantly deteriorated. Therefore, the dry silica fine particles obtained by carrying out the classification operation on the conventional dry silica fine particles are out of the range indicated by the characteristics (B) to (D), and the effects of the present invention cannot be exhibited.

  The dry silica fine particles of the present invention are suitably used as a filler for a resin composition requiring narrow cap permeability, particularly as an underfill filler in flip chip mounting because of having the above properties.

Dry silica particles of the present invention, as long as it has the properties, although other properties are not particularly limited, it is more preferable median diameter D _CS is 150 to 350 nm.

  Furthermore, if the moisture content measured by the loss on drying method at 130 ° C. is 0.5% by mass or less, it is possible to suppress the formation of strong aggregate particles due to moisture adsorption over time of the silica fine particles, and the above-mentioned even after long-term storage. This is a more preferable form.

(Method for producing dry silica fine particles)
The dry silica fine particles of the present invention are obtained by a flame combustion reaction of siloxane. The combustion flame needs to have a wide particle growth region so that the generated dry silica fine particles are excellent in dispersibility and can achieve a characteristic that the particle size distribution of the dispersed particles is narrow. That is, the dry silica fine particles of the present invention can be obtained by setting the temperature of the combustion flame to 4500 K or more and suppressing the cooling of the combustion flame.

  The dry silica fine particles of the present invention are preferably produced using a multi-tube burner. The multi-tube burner is composed of a center tube and a plurality of annular tubes extending concentrically from the center tube. For example, a quadruple burner composed of a central tube and three annular tubes can be mentioned.

  Hereafter, the manufacturing method of the dry-type silica fine particle of this invention is explained in full detail with the quadruple-tube burner which is a typical example.

  Vaporized siloxane and oxygen are mixed and introduced into the central tube of the quadruple burner. It is essential that the oxygen to be mixed is mixed in an amount equal to or greater than the equivalent amount required for siloxane combustion. At this time, an inert gas such as nitrogen may be mixed.

  A flammable gas such as hydrogen or hydrocarbon is introduced into the first annular tube outside the central tube to form a combustion auxiliary flame. At this time, an inert gas such as nitrogen and / or a combustion-supporting gas such as oxygen may be mixed.

  A combustion-supporting gas such as oxygen is introduced into the second annular tube outside the first annular tube to form a combustion auxiliary flame. At this time, an inert gas such as nitrogen may be mixed.

  A gas mixture of oxygen and nitrogen is introduced into the outermost third annular tube for flame cooling and flame combustion stabilization.

  As the siloxane that is a silica raw material, a cyclic siloxane that satisfies the following formula (3), a chain siloxane that satisfies the following formula (4), or a mixture thereof can be used.

(SiOR ¹ R ² ) _m (3)
R ¹ ₃ SiO (SiOR ² R ³ ) _n SiR ¹ ₃ (4)
m ≧ 3 and n ≧ 0, and m and n are integers. R ^{1 to} R ³ are either a hydrocarbon group or a hydrogen atom, and may be the same as or different from each other.

  Examples of the siloxane include hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, and hexamethyldisiloxane. These siloxanes are preferably used with a low content of impurities such as chlorine, sodium, and potassium so that high-purity silica can be obtained.

In the method for producing dry silica fine particles of the present invention, the flame temperature is preferably 4500K to 6000K. When the flame temperature is less than 4500 K, as a result of the flame temperature being too low, the melting time of the silica fine particles is short even if the BET specific surface area of the generated silica fine particles is 30 m ² / g or more or less than 30 m ² / g. Therefore, the fused large particles / coarse particles formed by the chemical bond between the silica particles and the large particles / coarse particles that are physically aggregated so strongly that they cannot be dispersed do not disappear and remain. On the other hand, when the temperature exceeds 6000 K, a part of the generated silica fine particles decomposes into silicon monoxide vapor and oxygen in the combustion flame and precipitates again as other silica fine particles. The particle size distribution at the time of dispersion increases.

  Further, it is essential that the combustion flame is a complete premixed flame, specifically, that the amount of oxygen introduced into the central tube is equal to or greater than the equivalent amount required for combustion of siloxane. If not a complete premixed flame, non-uniform combustion in which particle growth that proceeds with premixed oxygen and particle growth that proceeds with reaction of unburned raw material with oxygen introduced from the second annular tube proceeds simultaneously Because of the reaction, the particle size distribution is broadened.

  The flame temperature is adjusted by the gas composition of the central tube and the gas temperature of the central tube. The flame temperature is calculated from the gas composition and gas temperature of the central tube. That is, first, the adiabatic flame temperature is calculated on the assumption that the temperature of the central tube is 298K. Thereafter, the temperature difference between the actual gas temperature of the central tube and 298K, for example, 473K-298K = 175K when the gas temperature is 473K, is added to the adiabatic flame temperature. This is the flame temperature. In addition, regarding the specific heat of the substance required for the calculation of the adiabatic flame temperature, the expression is “JANAF Thermochemical Table SECOND Edition”, Horikoshi Laboratories (1975) in the ranges of less than 2000K and more than 2000K with 2000K as the boundary. ) Using a sixth-order polynomial of the temperature obtained by fitting the value of the value by the method of least squares.

  In order to obtain the dry silica fine particles of the present invention, it is important to minimize the cooling of the combustion flame as long as the combustion stability is not hindered.

In order to obtain the dry silica fine particles of the present invention, it is particularly important to suppress the cooling of the combustion flame. That is, the following two elements are satisfied by suppressing the cooling of the combustion flame.
The first factor is that since the temperature is high, the viscosity of the melted silica melt is sufficiently low, and the shape change of the silica fine particles is facilitated.
The second factor is that a region where shape change is easy can be taken.
If these two elements are satisfied, the generation of fused large particles / coarse particles formed by chemical bonding between silica particles and physically strongly aggregated large particles / coarse particles that cannot be dispersed are suppressed. Or disappearance promotion by shape change occurs. As a result, the dry silica fine particles can exhibit excellent dispersibility, a narrow dispersed particle size distribution, and a characteristic that does not draw a long tail on the side of particles having a particularly large dispersed particle size distribution.

  The combustion flame is cooled by adjusting the amount of gas introduced into the third annular tube in accordance with the amount of silica produced by the combustion reaction of siloxane. More specifically, the amount of gas introduced into the third annular tube per 1 kg of the produced silica is adjusted so as to satisfy the following formula (5).

0.7 <N _G3 / M _Si <2.5 (5)
N _G3 : Third annular pipe introduction gas amount (Nm ³ / H)
M _Si : Weight of silica produced (kg / H).

When N _G3 / M _Si is 0.7 (Nm ³ / kg) or less, the buoyancy of the high-temperature combustion gas disturbs the gas flow, and the generated silica fine particles return to the flame again, resulting in large particles or extremely large particles. Coarse particles and large aggregates formed by chemical bonds or strong physical bonds of primary particles are generated.

On the other hand, if the above N _G3 / _MSi is 2.5 (Nm ³ / kg) or more, the combustion flame is rapidly cooled, resulting in the problem that fine particles of several tens of nanometers are generated, and the molten silica melt There is a problem that the region having a high viscosity increases and the shape change becomes difficult, and aggregates formed by chemical bonds or strong physical bonds of primary particles are generated. In addition, there is a problem that the specific surface area of the dry silica fine particles tends to be 30 m ² / g or more.

  In the dry silica fine particle production method of the present invention, since the combustion flame is completely premixed, it is necessary to adjust the flame temperature within a range in which there is no risk of backfire of the flame and blowout. 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 tube introduction gas and the second annular tube introduction gas are intended to fix the flame at the tip of the burner for stable combustion, stable operation, and stable operation. For this purpose, the outlet flow velocity of the first annular tube introduction gas is preferably 10 to 200 Nm / s, and more preferably 50 to 150 Nm / s. The outlet flow rate of the second annular tube introduction gas is preferably 5 to 50 Nm / s, and more preferably 10 to 30 Nm / s. Furthermore, the second annular tube introduction gas 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.

  The dry silica fine particles of the present invention can be obtained by generating, growing and agglomerating in and near the flame, but the recovery can be performed by filtering with a metal filter, ceramic filter, back filter, etc., or by centrifugal separation with a cyclone, etc. It is done by separating and collecting.

  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) BET specific surface area Using a BET specific surface area measuring device SA-1000 (trade name) manufactured by Shibata Rikagaku Corporation, the BET specific surface area was measured by the nitrogen adsorption BET one-point method.

(2) Centrifugal sedimentation particle size distribution (Measurement sample preparation)
An aqueous 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, internal volume 30 ml, outer diameter about 28 mm), and an ultrasonic cell crusher (BRANSON Sonifier II Model 250D (trade name), Set the sample tube bottle with the sample so that the bottom surface of the probe tip of the probe (1.4 inch) is 15 mm below the water surface, disperse the silica fine particles in distilled water under the conditions of an output of 20 W and a dispersion time of 3 minutes. A silica suspension with a silica concentration of 1.5% by weight was prepared.

(Measurement)
The particle size distribution was measured using a CPS disk centrifugal sedimentation type particle size distribution analyzer DC-24000 (trade name). The measurement conditions were a rotation speed of 18000 rpm, a true silica density of 2.2 g / cm ^3, and calibration was performed with 0.476 μm PVC particles for each measurement.

(3) Purity analysis (Measurement sample preparation)
5 g of silica was added to 50 g of ultrapure water and heated at 120 ° C. for 24 hours using a Teflon (registered trademark) decomposition vessel. Ultrapure water and silica were weighed to the nearest 0.1 mg. Thereafter, the silica solid content was separated using a centrifugal separator to obtain a sample for ion chromatography measurement. In addition, the said operation was performed only with ultrapure water and the blank sample was obtained.

(Measurement)
The concentration of chlorine, sodium, and potassium in the measurement sample was measured using an ion chromatography system ICS-2100 (trade name) manufactured by Nippon Dionex. The chlorine, sodium, and potassium contents of silica were calculated using the following formula (6).

C _Silica = (C _Sample −C _Blank ) × M _PW / M _Silica (6)
C _Silica : ion concentration in silica (ppm)
C _Sample : ion concentration (ppm) in the measurement sample
C _Blank : Ion concentration (ppm) in the blank sample
M _PW : Ultrapure water weight (g)
M _Silica : Silica weight (g)
In addition, all C _Blank of each ion was 0 ppm.

(4) Water content Measured by the loss on drying method at 130 ° C.

(5) Crevice permeability evaluation (Measurement sample preparation)
42.84 g of Nippon Steel Chemical's epoxy resin ZX-1059 (trade name) is added to 28.56 g of silica, and 8 at a rotational speed of 1000 rpm using a planetary mixer AR-500 (trade name) manufactured by Shinky Corporation. Pre-kneading was carried out by stirring for 2 minutes and then defoaming for 2 minutes at 2000 rpm. Then, the epoxy resin composition was obtained by kneading | mixing using the 3 roll mill BR-150HCV (brand name) by an Imex company. The gap between the rolls was 20 μm. The resin composition was kept for 1 week at 20 ° C. after kneading.

(Measurement)
A gap having a width of 10 mm, a length of 20 mm, and a height of 30 μm was formed using two slide glasses having a width of 26 mm and a length of 76 mm and a double-sided tape having a thickness of 30 μm and a length of 30 mm.

  Next, after the glass slide bonded with the tape was kept at 100 ° C., the epoxy resin composition was dropped so that there was no bias at the gap entrance, and the time when the penetration distance reached 20 mm was recorded. Moreover, the presence or absence of the void was visually confirmed after measuring time measurement. The glass temperature was adjusted to be within ± 2 ° C.

Examples 1-4, Comparative Examples 1-3
As described below, octamethylcyclotetrasiloxane was burned in a quadruple burner to produce dry silica fine particles.

  Heat-vaporized octamethylcyclotetrasiloxane was mixed with oxygen and nitrogen and introduced into the central tube at 473K. Further, hydrogen and nitrogen were introduced into the first annular tube, oxygen was introduced into the second annular tube, and air was introduced into the third annular tube. Table 1 shows details of the production conditions and the physical properties of the produced silica fine particles.

The definitions of the oxygen ratio R _O , oxygen concentration, R _SFL , and R _cmbts in Table 1 are as follows.

The oxygen ratio R _O is defined by the following formula (7).

R _O = N _O0 / N _DO (7)
N _O0 : Oxygen amount in the central tube introduction gas N _DO : Oxygen amount necessary for complete combustion of siloxane stoichiometrically The oxygen concentration in the central tube introduction gas is defined by the following formula (8) .

Oxygen concentration = 100 × N _O0 / N _G0 (8)
N _G0 : Total amount of center pipe introduction gas.

R _SFL is defined by the following formula (9).

_{R SFL = N H / 32N D} (9)
N _H : amount of hydrogen introduced into the first annular tube N _D : amount of siloxane introduced into the central tube.

R _cmbts is defined by the following formula (10).

_{R cmbts = N O2 / 16N D} (10)
N _O2 : Amount of oxygen introduced into the second annular tube.

  In addition, regarding the calculation of the adiabatic flame temperature necessary for the calculation of the flame temperature, the standard generation enthalpy of octamethylcyclotetrasiloxane, which is a raw material, uses the value of “J. Lipowitz, J. Fire & Flammability 7,482 (1976)”. For the standard production enthalpy and specific heat of materials other than those described above, the values of “JANAF Thermochemical Table SECOND Edition”, Horikoshi Laboratories (1975) were used.

Comparative Examples 4-5
The measurement similar to Example 1 was performed about commercially available dry-type silica fine particles. The results are shown in Table 1.

  From Table 1, it is clear that Examples 1 to 4 of this patent are more excellent in gap penetration than Comparative Examples 1 to 5.

Claims (4)

Dry silica particulates, characterized by satisfying the following under conditions.
(A) The BET specific surface area is 5 m ² / g or more and less than 30 m ² / g.
(B) median diameter _{D CS} satisfies the following formula (1).
D _CS ≦ 2 × D _B (1)
(However, D _CS is a median diameter based on weight particle size distribution obtained by the centrifugal sedimentation method, D _B is the surface area in terms of diameter BET ratio.)
(C) The geometric standard deviation σg of the weight-based particle size distribution obtained by the centrifugal sedimentation method is 1.30 or less.
(D) In the weight-based particle size distribution obtained by the centrifugal sedimentation method, the content of particles having a particle diameter that is at least 3 times the BET specific surface area converted diameter is 0.18% by mass or less.
(E) The contents of chlorine, sodium and potassium are each 1 ppm or less. The dry silica fine particle according to claim 1, wherein the BET specific surface area is 10 to 25 m ² / g. Dry silica fine particles according to any one of claims 1-2 median diameter _{D CS} is 150 to 350 nm.   The dry silica fine particles according to any one of claims 1 to 3, wherein the moisture content measured by a loss on drying method at 130 ° C is 0.5 mass% or less.