JP2005054130A - Adsorptive silica filler and its manufacturing method and resin composition for sealing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adsorptive silica filler which exhibits a low viscosity when compounded with a resin and exhibits good moldability. <P>SOLUTION: The adsorptive silica filler satisfies the following requirements: (a) an average particle size of at least 2.5 μm and less than 6 μm; (b) a specific surface area of at least 100 m<SP>2</SP>/g and at most 300 m<SP>2</SP>/g; and (c) a viscosity of at most 36,000 mPa s as measured at a revolution number of a viscometer of 2.5 rpm at 50°C in the viscosity measurement of a mixture of the adsorptive silica filler with a bisphenol A liquid epoxy resin in a mass ratio of 60:40. The manufacturing method of the adsorptive silica filler is also provided. The resin composition for sealing is obtained by using the adsorptive silica filler. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an adsorptive silica filler and a method for producing the same. More specifically, the present invention relates to a silica filler and a sealing resin composition suitable for IC sealing resin and the like.

  In recent years, with the rapid development of the electronic industry, high-purity silica has been used for electronic materials and semiconductor manufacturing. In particular, in sealing materials, silica is an indispensable material as a filler for resin sealing. Resin sealing was thought to be inferior in sealing reliability compared to ceramic sealing, but the reliability could be improved to a level that could withstand practical use by increasing the silica filling rate. Resin sealing has spread rapidly with the improvement of reliability because the sealing cost is lower than that of ceramic sealing. However, ceramic sealing is used in some devices due to moisture permeability issues. For example, in a CCD (image element) device, it is fatal that dew condensation occurs in the lens because light is received inside, and it is problematic that moisture enters the package after sealing.

In resin sealing, it is conceivable to impart adsorptivity to the silica filler as one of the methods for preventing moisture permeation. In order to impart adsorbability to the filler, it is necessary to make the filler porous. However, since the porous silica filler has a very high resin compounding viscosity when blended with the resin, there is a problem in moldability. (For example, see Patent Document 1)
JP-A-9-208809

  An object of the present invention is to solve the above-mentioned problems of the prior art and provide an adsorptive silica filler having a low resin compounding viscosity and good moldability.

  As a result of intensive studies to solve the above problems, the present inventors have found an adsorptive filler having a low resin compounding viscosity when it has an equivalent adsorption amount as compared with silica according to the prior art. Furthermore, the adsorptive silica filler can control the adsorptivity and the resin blending viscosity by controlling the specific surface area, and has various specific surface areas by appropriately selecting the specific surface area according to the required adsorptivity. The present invention has been completed by finding that the adsorptive silica filler can be used effectively.

  That is, the first invention of the present invention is “adsorptive silica filler satisfying the following items.

(a) Average particle size of 2.5 μm or more and less than 6 μm
(b) Specific surface area of 100 m ² / g or more and 300 m ² / g or less
(c) Viscosity measurement when adsorbing silica filler and bisphenol A type liquid epoxy resin are mixed at a mass ratio of 60:40, viscosity at viscometer rotation speed of 2.5rpm is 36000mPa · s or less at 50 ℃ " And

  The second invention of the present invention is “adsorptive silica filler satisfying the following items.

(a) Average particle size of 2.5 μm or more and less than 6 μm
(b) Specific surface area of 50 m ² / g or more and less than 100 m ² / g
(c) In the viscosity measurement when adsorbing silica filler and bisphenol A liquid epoxy resin are mixed at a mass ratio of 60:40, the viscosity of the viscometer at 2.5 rpm is less than 12000 mPa · s at 50 ° C " The gist.

  The third invention of the present invention is “adsorptive silica filler satisfying the following items.

(a) Average particle size of 2.5 μm or more and less than 6 μm
(b) Specific surface area of 15 m ² / g or more and less than 50 m ² / g
(c) Viscosity measurement when adsorbing silica filler and bisphenol A-type liquid epoxy resin are mixed at a mass ratio of 60:40, the viscosity of the viscometer at 2.5 rpm is less than 6000 mPa · s at 50 ° C And

  In the present invention, by improving the sphericity and surface smoothness of the adsorptive silica filler, and controlling the specific surface area, when the filler is blended with the resin, while providing the adsorptivity, The moldability can be maintained. In particular, by adsorbing spherical silica gel obtained by the reaction of alkali silicate and aqueous mineral acid under predetermined conditions, it is possible to provide an adsorptive silica filler whose adsorptive capacity and flow characteristics at the time of resin blending are controlled. In particular, the adsorptive silica filler of the present invention can be suitably used for a sealing resin composition that prevents intrusion of moisture such as a CCD (image analysis element) device.

The adsorptive silica filler of the present invention has an average particle size of 2.5 μm or more and less than 6 μm and a large specific surface area of 15 m ² / g or more and 300 m ² / g or less. In a viscosity measurement when mixing bisphenol A type liquid epoxy resin with a mass ratio of 60:40, the viscosity of the viscometer at a rotational speed of 2.5 rpm is 6000 to 36000 mPa · s at 50 ° C., indicating a relatively low resin blending viscosity.

  The adsorbing silica filler of the present invention has various gas adsorbing properties, but is particularly useful for moisture adsorption. The resin composition blended and cured with the adsorptive silica filler of the present invention has a moisture adsorptivity and can be controlled to an arbitrary adsorption capacity.

  Although the adsorptive silica filler of the present invention has adsorptivity, the reason why the resin blending viscosity is suppressed to 36000 mPa · s or less is considered to be due to its high sphericity and extremely good surface smoothness. It is done. Moreover, since the average pore diameter is 0.05 to 1 nm and the pore volume is about 0.01 to 1.0 ml / g, the reason why the resin blending viscosity is kept low is that the porosity in the particles is small.

  In general, the resin blending viscosity varies depending on the specific surface area of the filler. Also for the adsorptive silica filler of the present invention, the smaller the specific surface area, the smaller the resin compounding viscosity. However, compared with the conventional adsorptive silica, the resin compounding viscosity with respect to a specific surface area is small, and the moldability after resin compounding can be secured.

  When used as a filler such as a sealing material, a filler having a smaller maximum particle size than the average particle size in the particle size distribution is preferred. The adsorptive silica filler of the present invention can have a good distribution of coarse grain breakage such that the maximum particle size is 4 times or less than the average particle size. Further, when used as a filler for a sealing material, it is desirable that the variation coefficient of the particle diameter indicating the breadth of the particle size distribution is 15% or more. This does not mean that the distribution is narrow, but it is a distribution that contains a small amount of particles smaller than the average particle size but has a small content on the coarse particle side larger than the average particle size. Desirable in terms.

  Regarding the adsorptive silica filler of the present invention, the particle size distribution is desirably within a predetermined range. A variation coefficient is mentioned as one of the indexes indicating the particle size distribution. The variation coefficient (Cv) of the particle diameter in the present invention is represented by the formula (I) as a ratio of the standard deviation σ and the average particle diameter d [μm].

Cv = 100 × σ / d (I)
A particle group having a maximum particle size of 4 times or less of the average particle size has a large coefficient of variation means that it contains a lot of fine powder. By containing a large amount of fine powder, the resin compounding viscosity increases. Therefore, the variation coefficient is desirably in the range of 15 to 100%. From the viewpoint of flow characteristics, the coefficient of variation is particularly preferably in the range of 25 to 60%.

In the present invention, the viscosity when silica and bisphenol A type liquid epoxy resin are mixed at a mass ratio of 60:40 corresponds to the specific surface area of the adsorptive silica filler. When the specific surface area is 100 m ² / g or more and 300 m ² / g or less, the resin compounding viscosity is 36000 mPa · s or less. When the specific surface area is 50 m ² / g or more and less than 100 m ² / g, the resin compounding viscosity is 12000 mPa · s or less. When the specific surface area is 15 m ² / g or more and less than 50 m ² / g, the resin compounding viscosity is 6000 mPa · s or less.

The lower the viscosity at the time of blending the resin, the better in terms of moldability. Therefore, the viscosity when mixing silica and bisphenol A type liquid epoxy resin at a mass ratio of 60:40 has a specific surface area of 100 m ² / g or more and 300 m ² / In the case of g or less, the resin compounding viscosity is desirably 15000 mPa · s or less. Further, when the specific surface area is 50 m ² / g or more and less than 100 m ² / g, the resin compounding viscosity is desirably 4000 mPa · s or less. Furthermore, when the specific surface area is 15 m ² / g or more and 50 m ² / g, the viscosity is desirably 3000 mPa · s or less.

  The bisphenol A type liquid epoxy resin used for viscosity measurement is a mixture of bisphenol A type liquid epoxy resin and butyl glycidyl ether (a mixture with a mass ratio of 89:11), with an epoxy equivalent of 181 to 191 and a viscosity of 25 ° C. 9 to 12 poise is used. Industrially, Epicoat 815 (trade name) manufactured by Yuka Shell Epoxy Co., Ltd. is applicable. The viscosity is a value at a measurement temperature of 50 ° C. and a rotation speed of 2.5 rpm. In the present invention, an E-type viscometer (RE80R type manufactured by Toki Sangyo) was used as the viscometer. When used for a sealing material, it is desirable to exhibit a low thixo ratio. The thixo ratio means η1 / η2 when the viscosity value at a rotational speed of 0.5 rpm of the viscometer is η1 and 2.5 rpm is η2. When used for a sealing material, η1 / η2 is desirably less than 1.0.

The adsorptive silica filler of the present invention can arbitrarily control the adsorption capacity by controlling the specific surface area. That is, the adsorptive silica filler can be controlled to an arbitrary moisture absorption rate by controlling the specific surface area. When the specific surface area is 100 m ² / g or more and 300 m ² / g or less, the moisture absorption rate is 3% by mass or more and less than 15% by mass. Further, when the specific surface area is 50 m ² / g or more and less than 100 m ² / g, the moisture absorption rate is 1.5% by mass or more and less than 5% by mass. Furthermore, when the specific surface area is 15 m ² / g or more and 50 m ² / g, the moisture absorption rate is 0.5% by mass or more and less than 4% by mass. The moisture absorption A [%] is expressed by the formula (II). M1 is the mass of the adsorptive silica filler in the absolutely dry state, and represents the mass of the adsorbable silica filler after moisture absorption by M2. Hygroscopicity is measured by placing 0.1 g of dry dry adsorbent silica filler in a tray (M1), and then separating the tray into a 50 ml capacity Teflon (registered trademark) container (up and down with a metal mesh, with pure water at the bottom. 15ml, put sample on top), put Teflon (registered trademark) container in SUS sealed container and let stand in 121 ° C constant temperature bath for 24 hours, take out tray from container, measure mass (M2), formula The moisture absorption rate of the adsorptive silica filler was calculated from (II).

A [%] = 100 x (M2-M1) / M1 (II)
High purity is generally required for materials used in semiconductors. In particular, alkali metals such as Na, K and Li, alkaline earth metals such as Ca and Mg, and ionic impurities such as Cl cause corrosion of aluminum wiring. It is desirable that substantially no impurities are contained. In addition, radioactive elements are severely restricted to suppress the occurrence of soft errors. If the radioactive element exceeds 2 ppb in silica for sealing materials, it may cause a soft error, which is not preferable. In this method, alkali metals and alkaline earth metals are substantially suppressed to 1 ppm or less, and the content of radioactive impurities is suppressed to 2 ppb or less. can do. The radioactive elements here are U and Th. That is, it is desirable that the total content of U and Th is 2 ppb or less. Furthermore, it is desirable that the total content of U and Th is 1 ppb or less. The content of these impurities can be directly measured by an appropriate analysis means. In the present invention, silica is heated and dissolved in an aqueous hydrogen fluoride solution, the silica content is vaporized as SiF ₄ , and the residue is ICP-MS. The impurity concentration was specified by analyzing the above. For ICP-MS, ModelPMS-2000 manufactured by Yokogawa Electric Corporation was used.

  The particle size distribution defined in the present invention desirably has a maximum particle size of 4 times or less of the average particle size. This is a particle size distribution measured by a laser diffraction scattering method (LS-130 manufactured by Coulter Inc.). is there. Moreover, an average particle diameter means a median diameter.

  Specific surface area SA is used as a measure of adsorptivity. In general, the specific surface area SA of a true sphere having a diameter of d (μm) and having no pores can be expressed by the formula (II) when the true specific gravity is D. Adsorption characteristics are strongly influenced by pore diameter and pore volume. The adsorptive silica filler in the present invention preferably has an average pore diameter of 0.05 to 1 nm and a pore volume of 0.01 to 1.0 ml / g. In particular, the pore volume is preferably 0.1 to 0.3 ml / g in order to suppress the resin compounding viscosity.

  The adsorptive silica filler in the present invention has a sphericity of 0.9 or more and a particle content of 90% or more. The sphericity is a ratio between the maximum diameter (d1) and the minimum diameter (d2) of the particle, and is expressed by the formula (III).

Sphericality = d2 / d1 (III)
For the particle content with a sphericity of 0.9 or more, in the electron micrograph of the adsorptive silica filler particles, randomly select 20 particles, measure the maximum diameter and the minimum diameter, and the sphericity is 0.9. The ratio of the above particles was calculated. That is, 18 or more of 20 randomly selected particles have a sphericity of 0.9 or more.

  The adsorptive silica filler of the present invention is excellent in surface smoothness and can be prepared by preparing true spherical silica gel particles and firing them under predetermined conditions. Spherical silica gel particles with excellent surface smoothness can be prepared by various liquid phase reactions. In particular, spherical silica gel obtained by the reaction of alkali silicate and mineral acid aqueous solution has high sphericity and surface smoothness. Is excellent. Examples of a method for preparing a spherical silica gel by reaction of an alkali silicate and a mineral acid aqueous solution and adjusting an adsorbent silica filler using the spherical silica gel include the following methods.

<Preparation of water-containing spherical silica gel particles and impurity extraction and removal step>
An emulsion containing an aqueous alkali silicate solution as a dispersed phase and a mineral acid aqueous solution are brought into contact with each other to react to produce hydrous spherical silica gel particles having an average particle size of 3 μm or more and less than 7 μm. After the neutralization reaction is completed, solid-liquid separation is performed. Without removing impurities by heating to 50 ° C. or higher to obtain water-containing spherical silica gel particles having a high purity and a porous average particle size of 3 μm or more and less than 7 μm.

<Drying, crushing, firing process of hydrous spherical silica gel particles>
A step of imparting the physical properties defined in the present invention by crushing and firing the hydrous spherical silica gel particles obtained in <Preparation of hydrous spherical silica gel particles and impurity extraction and removal step> or at the time of drying.

Hereinafter, the respective steps will be sequentially described.

<Preparation of water-containing spherical silica gel particles and impurity extraction and removal step>
(1) Emulsification step of preparing a water-in-oil (W / O) emulsion in which an aqueous alkali silicate solution is dispersed finely as a dispersed phase. An emulsion containing an aqueous alkali silicate solution as a dispersed phase is prepared. That is, a water-in-oil type (W / O type) emulsion is produced in which a liquid immiscible with an aqueous alkali silicate solution is used as a continuous phase, and an aqueous alkali silicate solution is dispersed in the form of fine particles.

  An aqueous alkali silicate solution, a liquid for forming a continuous phase, and an emulsifier are mixed and emulsified using an emulsifier or the like to prepare a W / O type emulsion containing the aqueous alkali silicate solution as a dispersed phase. By changing the rotation speed of the emulsifier during emulsification, the particle size can be controlled. Further, the particle diameter can be made finer by diluting the aqueous alkali silicate solution with water. Conversely, the particle size can be increased by increasing the viscosity by concentration.

The alkali silicate used includes sodium silicate, potassium silicate, lithium silicate and the like, and sodium silicate is generally used. The silica concentration (as SiO ₂ ) of the alkali silicate aqueous solution is preferably in the range of 1 to 40% by mass, and more preferably in the range of 5 to 35%. Commercially available JIS No. 3 alkali silicate is easy to handle.

  The alkali silicate aqueous solution used as a raw material is an alkali silicate aqueous solution (hereinafter also referred to as high-purity water glass) whose total content of other metals excluding alkali metals and Si is 0.1% by mass or less. Silica filler can be produced. An alkali silicate aqueous solution having a total content of metals other than alkali metals and Si of 0.1% by mass or less can be prepared by dissolving high-purity natural silica or synthetic silica with an alkaline aqueous solution. Synthetic silica is not particularly limited, but high-purity silica using alkali silicate as a raw material is desirable in terms of production cost. An aqueous alkali solution is advantageous in the subsequent extraction of impurities with an aqueous sodium hydroxide solution. When high purity silica or synthetic silica is dissolved in an alkaline aqueous solution, the dissolution time can be shortened by heating. It is also effective to pressurize with an autoclave or the like. In addition, when using as raw materials, such as an electronic material, it is desirable that the sum total of other metal content except an alkali metal and Si is 0.01% or less. Further, the content of radioactive elements is preferably as small as possible, and the total of U and Th is desirably 10 ppb.

  As the liquid for forming the continuous phase, a liquid that does not react with the aqueous alkali silicate solution and the mineral acid aqueous solution and is immiscible is used. The type is not particularly limited, but from the viewpoint of demulsification treatment, it is desirable to use an oil having a boiling point of 100 ° C. or higher and a specific gravity of 1.0 or lower. The mass ratio of the alkali silicate aqueous solution to the oil is 8: 2 to 2: 8. Preferably it is 8: 2 to 6: 4.

  The oil as the liquid for forming the continuous phase is, for example, n-octane, gasoline, kerosene, isoparaffinic hydrocarbon oil and other aliphatic hydrocarbons, cyclononane, cyclodecane and other alicyclic hydrocarbons, toluene, xylene Aromatic hydrocarbons such as ethylbenzene and tetralin can be used. Isoparaffinic saturated hydrocarbons are desirable from the viewpoint of emulsion stability.

  The emulsifier is not particularly limited as long as it has a function of stabilizing a W / O emulsion, and a highly lipophilic surfactant such as a polyvalent metal salt of fatty acid or a poorly water-soluble cellulose ether can be used. From the viewpoint of post-treatment, it is desirable to use a nonionic surfactant. Specific examples include sorbitan fatty acid esters such as sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan monooleate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan mono Polyoxyethylene such as stearate, polyoxyethylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monooleate, polyoxyethylene monolaurate, polyoxyethylene monopalmitate, polyoxyethylene monostearate, polyoxyethylene monooleate Examples include fatty acid esters, glycerin fatty acid esters such as stearic acid monoglyceride and oleic acid monoglyceride.

  An appropriate amount of the emulsifier is 0.05 to 5% by mass with respect to the aqueous alkali silicate solution to be emulsified. Moreover, when the process in each process is considered, 0.5-1 mass% is desirable.

(2) A coagulation step in which the water-in-oil (W / O) emulsion prepared in (1) is mixed with a mineral acid aqueous solution to produce hydrous spherical silica gel particles having an average particle size of 2.9 μm to less than 7 μm. An emulsion containing an aqueous alkali silicate solution as a dispersed phase and an aqueous mineral acid solution are mixed with stirring. Water-containing spherical silica gel particles having an average particle size of 2.9 μm or more and less than 7 μm are generated by the neutralization reaction between the mineral acid and the alkali silicate. The order of the mixing method is not limited. However, when adding a mineral acid aqueous solution to an emulsion containing an alkali silicate aqueous solution, there is a risk of causing an extreme decrease in mineral acid concentration during the reaction. It is desirable to add to an aqueous mineral acid solution. The molar ratio of mineral acid / alkaline content (Na ₂ O content in water glass) during the reaction is 2 or more to obtain the desired hydrous spherical silica gel particles, but the molar ratio is preferably 5 or less in consideration of productivity.

  As the mineral acid, sulfuric acid, nitric acid, hydrochloric acid and the like can be used, but sulfuric acid is most desirable because it has a strong dehydrating action and is inexpensive. The aqueous alkali silicate solution is preferably in contact with 15% by mass or more of mineral acid. More preferably, contact with 20% by mass or more of sulfuric acid is preferable. When an emulsion containing an aqueous alkali silicate solution is brought into contact with an aqueous mineral acid solution of less than 15% by mass, the water-containing spherical silica gel particles having a particle size distribution with a good coarse grain cut intended by the present invention cannot be obtained. The upper limit of the concentration of the mineral acid aqueous solution is preferably 50% by mass. Considering sphericity and monodispersity, the mineral acid concentration is preferably 15 to 35% by mass. In addition, after the reaction with the aqueous alkali silicate solution is completely completed, it is desirable that the free mineral acid concentration of the aqueous phase reaction liquid is 10% by mass or more. The free mineral acid concentration is a concentration of a mineral acid that does not substantially form a salt with a metal ion or the like.

  Although it depends on the stirring method, the neutralization reaction between the emulsion containing the alkali silicate aqueous solution and the mineral acid aqueous solution is almost completed in 5 to 120 minutes. The neutralization reaction is completed when the temperature of the reaction solution shows a downward trend.

  After completion of the neutralization reaction, the temperature is increased as it is without separating the reaction solution. By this temperature rise, the emulsion-like reaction liquid can be extracted and removed together with the demulsification treatment in which the emulsion phase is separated into an oil phase and a silica gel particle-dispersed sulfuric acid aqueous solution phase. The temperature should be 50 ° C or higher. The treatment is preferably performed in the range of 50 to 120 ° C, more preferably 80 to 100 ° C, and the treatment time may be appropriately selected from 1 minute to 5 hours. Usually, it can be processed in about 30 minutes to 1 hour. When the high-purity water glass is used as a raw material, high-purity water-containing spherical silica gel particles can be obtained without performing extraction by heating.

  In extraction of impurities, it is also effective to add a chelate before or after the reaction. The chelate is not particularly limited, but a chelate that exhibits efficacy under acidic conditions is desirable. Moreover, reprecipitation of impurities such as Th after cooling can be prevented by adding nitric acid before and after the reaction. The amount of nitric acid added is 0.1 to 5% with respect to the total amount of added acid, and an effect of suppressing reprecipitation is obtained. A range of 0.5 to 3% is preferable. When the high-purity water glass is used as a raw material, addition of a chelate is unnecessary.

  In the present invention, the particle size shrinks to about 85% as the pores are blocked in the firing steps (6) and (7). In order to prepare an adsorptive silica filler having an average particle size of 2.5 μm or more and less than 6 μm, it is necessary to produce hydrous spherical silica gel particles having a particle size of 2.9 μm or more and less than 7 μm in this step.

(3) Washing step for washing hydrous spherical silica gel particles in (2) The hydrous spherical silica gel particles obtained in (2) contain a large amount of sulfuric acid aqueous solution used for reaction and extraction in the particles after extraction. Since this sulfuric acid aqueous solution contains a large amount of metal impurities, it must be washed with pure water. The washing method is not particularly limited, but repulp rinse or cake rinse is effective. At the time of washing, when pure water is used at the initial stage of washing, the pH increases rapidly, so that the extracted metal impurities are adsorbed on the hydrous spherical silica gel particles. Therefore, it is desirable to perform cleaning using an extremely dilute acidic aqueous solution at the initial stage of cleaning. As the acidic aqueous solution, mineral acids such as sulfuric acid, nitric acid and hydrochloric acid are desirable in terms of pH. The acid concentration is preferably 0.001 to 5% by mass in order to wash the acid used with pure water after washing with an acidic aqueous solution. After washing, it is desirable to remove the water-containing spherical silica gel particles as much as possible with a centrifuge.

  Since impurity metals such as alkali metals and alkaline earth metals cause inter-particle sintering during firing in the next step, the concentration of each metal is preferably 1 ppm or less during cleaning. Particularly for alkali metals, the melting point of silica tends to be lowered, so 0.5 ppm or less is desirable.

<Drying, crushing, firing process of hydrous spherical silica gel particles>
(4) Drying step of drying the hydrous spherical silica gel particles washed in (3) Moisture is still retained in the hydrous spherical silica gel particles from which impurities have been extracted and removed in the previous step. This moisture is divided into adhering water and bound water. Usually, adhering water can be easily removed by heating at a temperature of about 100 ° C., but it is difficult to completely remove bound water even at a temperature of 400 ° C. or higher. A drying process is performed to remove the adhering water, and a baking process is performed to remove the bound water and to densify the spherical silica gel particles to an arbitrary level.

  In the drying and firing steps, when drying is performed in a stationary state during drying and firing is performed in that state, sintering occurs between some particles, which increases the particle size. Sintering between particles can be suppressed by crushing and firing at the time of drying or after drying, and even after firing, the particle size distribution is a coarse particle with a maximum particle size of 4 times the average particle size or less. Good particle size distribution can be maintained.

  Since the fluid dryer is crushed while drying, it is more effective. The drying treatment conditions for removing the adhering water are preferably 50 to 500 ° C., and practically 100 to 300 ° C. What is necessary is just to select processing time suitably in the range of 1 minute-40 hours according to drying temperature. Usually, it can be dried in 10 to 30 hours.

(5) Crushing step of crushing dry spherical silica gel particles at the time of drying or after drying of (4) By performing crushing after drying, even if the silica is not kept in a fluid state during drying and firing treatment, The particles can be fired without sintering. When firing to an adsorptive silica filler having an average particle size of 2.5 μm or more and less than 6 μm, crushing after drying is effective for preventing interparticle sintering.

  For crushing before firing, a screen having an opening of 10 times or less the maximum particle size is used. It is preferable to use a screen having an opening of 1 to 5 times. More preferably, a screen having an opening of 1 to 3 times may be used. The method of crushing using a screen is not particularly limited, but by using a vibrating sieve or an ultrasonic sieve or by feeding the raw material into a horizontal cylindrical screen and rotating the blade attached inside the screen at high speed And a continuous crushing method (for example, a turbo screener manufactured by Turbo Industry). The material of the sieve is preferably free from metal contamination. In order to satisfy this, a resin sieve is desirable. The type of resin is not particularly limited, but polyethylene, polypropylene, nylon, carbon, acrylic, polyester, polyimide, fluorine resin, and the like can be used. In order to suppress static electricity during crushing, a resin with suppressed chargeability is effective. It is also possible to work under high humidity. It is also possible to add some moisture.

  Moreover, crushing and classification can be performed simultaneously by using a screen having a sieve having a maximum particle size of the raw silica before crushing. From the particle size distribution of the raw silica, a sieve having an opening equal to or larger than the particle size corresponding to 10% on the sieve is industrially useful.

(6) Primary firing step of firing the dried spherical silica gel particles crushed in (5) at 300 to 700 ° C The firing method after pulverization is in two stages in each range of 300 to 700 ° C and 700 to 1150 ° C. Firing is necessary. In the primary firing step, oil, a surfactant, and the like are used during the reaction, and therefore the purpose is to remove these organic substances. The primary firing is optimally in the range of 300 to 700 ° C. Normally, the specific surface area and pore volume of silica can be controlled by controlling the calcination temperature. However, in order to reduce the specific surface area of porous silica, a temperature of 700 ° C. or higher is required. Firing with the organic matter remaining makes it difficult to control the temperature due to the latent heat of vaporization of the organic matter and heat generated by combustion, so it is important to remove the organic matter beforehand by primary firing.

(7) Secondary firing step of firing the spherical silica gel particles primarily fired in (6) at 700 to 1100 ° C (excluding 700 ° C)
Firing at 700 to 1150 ° C. aims to block the pores inside the particles to an arbitrary level. Therefore, the specific surface area can be controlled by baking at a temperature of 300 to 700 ° C. for about 10 minutes to 30 hours and then baking at 700 to 1150 ° C. for about 10 minutes to 30 hours. The firing time is not a problem as long as the silica itself is held at the set temperature for 2 hours or more. Although it is possible to control the specific surface area and pores by extremely slowing the temperature rising rate even in one-stage firing, it is desirable to fire in two stages in consideration of productivity.

  As the firing means, a cart-type firing furnace, a fluid firing furnace, a rotary kiln, a flame firing furnace, or the like can be used. In some cases, extremely weak agglomeration may be observed after firing, but an adsorbable silica filler free from inter-particle sintering and agglomeration can be obtained by crushing again using a screen.

  As an atmosphere for performing the baking treatment, oxygen, carbon dioxide gas, or the like may be used, and an inert gas such as nitrogen or argon may be used as necessary. Practically, it is better to use air. As an apparatus used when performing a baking process, the baking furnace which processes in the state which left the silica particle stationary can be used. It is also possible to use an apparatus for firing the dried spherical silica gel particles while maintaining the fluidized state, for example, a fluid firing furnace, a rotary kiln, or a flame firing furnace. As the heating source, electric heat or combustion gas can be used. The moisture content of the silica gel before firing is not particularly defined, but it is desirable to fire the dried spherical silica gel particles with a water content reduced as much as possible in order to prevent interparticle consolidation during firing.

The specific surface area of the dried spherical silica gel particles before firing is not particularly limited, but the spherical silica gel obtained by a liquid phase reaction or the like has a specific surface area of 400 m ² / g or more. The specific surface area of the spherical silica gel before firing is preferably 350 to 700 m ² / g. If the specific surface area is less than 350 m ² / g, the adsorptivity after firing is insufficient, and if it exceeds 700 m ² / g, sintering between particles is likely to occur during firing, so the flow characteristics at the time of resin blending are Getting worse.

  In the present invention, by crushing before firing, inter-particle sintering does not occur during firing. That is, after forming a spherical silica gel having a maximum particle size of 4 times or less with respect to the average particle size, the adsorbent silica filler having a maximum particle size of 4 times or less with respect to the average particle size is crushed before firing. Can be manufactured.

  Since the adsorptive silica filler of the present invention easily adsorbs moisture, it is desirable that cooling after drying be performed in an atmosphere of an inert gas such as dry air or nitrogen or argon, and immediately after cooling, packaging with excellent gas barrier properties. It is desirable to store it in a bag or container. An aluminum bag etc. can be used as a packaging bag excellent in gas barrier property.

  Although the adsorptive silica filler prepared in the present invention has hygroscopicity, it has a relatively low viscosity when mixed with a resin, so as a filler for a sealing material that requires hygroscopicity. It can be used suitably. In addition, since the coarse particle size distribution is good, it can be suitably used as an adsorptive filler even in a sealing material having a thin resin phase thickness. In particular, it can be suitably used as a filler for a sealing resin for an image element device.

Example 1
<Preparation of spherical silica gel particles and impurity extraction and removal step>
(1) An emulsification process for preparing a water-in-oil (W / O) emulsion in which an aqueous alkali silicate solution is dispersed finely as a dispersed phase. Adjust water content of JIS No. 3 water glass as water glass to 400 cp at 25 ° C. Adjusted, isoparaffinic hydrocarbon oil (manufactured by Nippon Petrochemical Co., Ltd., product name: Isosol 400) as the liquid for forming the continuous phase, and sorbitan monooleate (product name: Leodol SP-O10, manufactured by Kao Corporation) as the emulsifier Weighed 20 kg, 7.5 kg, and 0.18 kg of water glass, Isozol 400, and Rhedol SP-O10, respectively, mixed each raw material, coarsely stirred with a stirrer, and then emulsified at 2980 rpm with an emulsifier. 415 g of the emulsion was collected.

(2) A coagulation step in which the water-in-oil (W / O) emulsion prepared in (1) is mixed with a mineral acid aqueous solution to produce spherical silica gel particles having an average particle size of 2.9 μm or more and less than 7 μm.
575 g of 28% sulfuric acid aqueous solution was prepared, and the above emulsion was added thereto while stirring at room temperature. After the addition was complete, stirring was continued for an additional 40 minutes at room temperature. Next, 40 g of 62% industrial nitric acid was added under stirring, and the mixture was further stirred for 20 minutes, then heated to 100 ° C. with stirring and held for 30 minutes. By this treatment, the emulsion-like reaction liquid was separated into an oil phase (upper layer) and an aqueous phase (lower layer) in which spherical silica gel particles were dispersed.

(3) Washing step for washing the hydrous spherical silica gel particles in (2) The spherical silica gel particles in the aqueous phase were filtered and washed by a conventional method except for the oil phase. Washing was carried out by substituting and washing the reaction solution with 0.01% sulfuric acid aqueous solution and then using pure water until the pH of the washing solution became 4 or more. Using Nutsche, dehydration was performed to obtain hydrous spherical silica gel particles.

<Drying, crushing, firing process of hydrous spherical silica gel particles>
(4) Drying step for drying the hydrous spherical silica gel washed in (3) The obtained hydrous spherical silica gel particles were dried at a temperature of 120 ° C. for 20 hours to obtain 100 g of dry spherical silica gel particles.

(5) Crushing step of crushing dry spherical silica gel particles during or after drying in (4) Dry spherical silica gel particles were passed through a 33 μm sieve made of polyester and crushed.

(6) Primary firing step of firing the dried spherical silica gel particles crushed in (5) at 300 to 700 ° C
(7) Secondary firing process in which spherical silica gel particles primarily fired in (6) are fired at 700 to 1100 ° C (not including 700 ° C). The crushed dry silica gel particles are filled into a quartz beaker (1 liter). Baked. Firing was carried out at 200 ° C./hr, held at 700 ° C. for 15 hours, further heated to 850 ° C. and held at 850 ° C. for 8 hours to obtain an adsorptive silica filler.

Table 1 shows the silica physical properties of the adsorptive silica filler obtained by firing. The average particle size was 4.3 μm, the maximum particle size was 13 μm, and the true specific gravity was 2.19. The specific surface area measured by the BET method was 155 m ² / g. Further, from the electron micrograph, it was spherical with a content rate of particles having a sphericity of 0.9 or more and 90% or more, and the surface smoothness was also good.

  The moisture absorption A was calculated from the formula (II). M1 is the mass of the adsorptive silica filler in the absolutely dry state, and represents the mass of the adsorbable silica filler after moisture absorption by M2. 0.1 g of an absolutely dry adsorbent silica filler was placed in a tray (M1: precisely weighed), and a Teflon (registered trademark) container was placed in a SUS sealed container and left in a 121 ° C. constant temperature bath for 24 hours. After 24 hours, the tray was removed from the container and the mass was measured (M2).

A [%] = 100 x (M2-M1) / M1 (II)
The concentration of each element of alkali metals such as Na, K and Li, alkaline earth metals such as Ca and Mg, and transition metals such as Cr, Fe and Cu is 1 ppm or less, and the radioactive elements of U and Th The total was less than 0.1 ppb.

  Table 2 shows the characteristics of the adsorbable silica filler obtained when the resin was blended. The epoxy resin is a mixture of bisphenol A liquid epoxy resin and butyl glycidyl ether (a mixture with a mass ratio of 89:11, an epoxy equivalent of 181 to 191 and a viscosity at 25 ° C of 9 to 12 poise, Japan Epoxy) Resin Co., Ltd., trade name: Epicoat 815) was used. Was used. The blending ratio was: epoxy resin = 60: 40 mass ratio. The resin compounding viscosity was measured at 50 ° C. using RE-80R manufactured by Toki Sangyo Co., Ltd.

  The obtained sample was mixed with an epoxy resin mixed with a curing agent in advance and defoamed, and then a curing accelerator was added and cured. The compounding ratio was filler: epoxy resin: curing agent = 6: 2: 2 (mass%), and a curing accelerator was added at 0.1 mass% with respect to the epoxy resin. Epicoat 815 was used as the epoxy resin. The curing agent used was Ricacid MT-500 (manufactured by Shin Nippon Rika Co., Ltd.). Curazole 2E4MZCN (Shikoku Chemical Industry Co., Ltd.) was used as the curing accelerator. The resin composition mixed at a predetermined compounding ratio was poured into a disk-shaped mold having a diameter of 2 cm and was cured at 150 ° C. for 1 hour.

  Put the hardened material in a disk shape into a 50 ml Teflon (registered trademark) container (divided vertically with a metal mesh, 15 ml of pure water at the bottom, put the sample at the top), and place the Teflon (registered trademark) container in the The container was placed in a SUS sealed container and left in a constant temperature bath at 121 ° C. for 24 hours. After 24 hours, the cured product sample was taken out of the container, the mass was measured, and the moisture absorption rate was calculated.

Example 2
After maintaining the calcination temperature at 700 ° C. for 15 hours, the temperature was further raised to 950 ° C., and an adsorptive silica filler was obtained in the same manner as in Example 1 except that the temperature was maintained at 950 ° C. for 15 hours.

Example 3
After maintaining the calcination temperature at 700 ° C. for 15 hours, the temperature was further raised to 1050 ° C., and an adsorbable silica filler was obtained in the same manner as in Example 1 except that the calcination temperature was maintained at 1050 ° C. for 8 hours.

Comparative Example 1
After maintaining the firing temperature at 700 ° C. for 15 hours, the temperature was further raised to 1150 ° C., and a silica filler was obtained in the same manner as in Example 1 except that the firing temperature was maintained at 1150 ° C. for 8 hours.

Comparative Example 2
A silica filler was obtained in the same manner as in Example 1 except that the firing temperature was increased to 850 ° C. at a rate of 300 ° C./hr and held at 850 ° C. for 8 hours. When observed by SEM, fusion between particles was observed in several places. Although the specific surface area was small compared with Example 2, the viscosity at the time of resin compounding showed a high value.

Comparative Example 3
The firing temperature was maintained at 700 ° C. for 15 hours, and then cooled and recovered. Others are the same as Example 1. An attempt was made to measure the resin compounding viscosity under the same conditions as in Example 1. However, when the adsorbing silica filler was mixed with the epoxy resin at a predetermined ratio, the resin composition did not have fluidity. Viscosity could not be measured (<250000 mPa · s).

Reference example 1
The viscosity of the epoxy resin was measured at 50 ° C. Moreover, 0.1 mass% of epoxy resin: curing agent = 1: 1 (mass%) and a curing accelerator were added to the epoxy resin to prepare a cured resin product containing no filler. The moisture absorption rate of the obtained resin cured product was measured.

Claims (8)

Adsorbing silica filler that satisfies the following items:
(a) Average particle size of 2.5 μm or more and less than 6 μm
(b) Specific surface area of 100 m ² / g or more and 300 m ² / g or less
(c) When measuring the viscosity when adsorbing silica filler and bisphenol A liquid epoxy resin are mixed at a mass ratio of 60:40, the viscosity of the viscometer at 2.5 rpm is 36000 mPa · s or less at 50 ° C. Adsorbing silica filler that satisfies the following items:
(a) Average particle size of 2.5 μm or more and less than 6 μm
(b) Specific surface area of 50 m ² / g or more and less than 100 m ² / g
(c) When measuring the viscosity when adsorbing silica filler and bisphenol A type liquid epoxy resin are mixed at a mass ratio of 60:40, the viscosity of the viscometer at 2.5 rpm is less than 12000 mPa · s at 50 ° C. Adsorbing silica filler that satisfies the following items:
(a) Average particle size of 2.5 μm or more and less than 6 μm
(b) Specific surface area 15m ² / g or more and less than 50m ² / g Adsorbable silica filler and bisphenol A type liquid epoxy resin are mixed at a mass ratio of 60:40. Viscosity at 2.5rpm is 6000mPa ・ s or less   When adsorbing silica filler and bisphenol A type liquid epoxy resin are mixed at a mass ratio of 60:40, viscosity measurement at 50 ° C is η1 for the viscosity of the viscometer and η2 for 2.5rpm. The absorptive silica filler according to claim 1, wherein η1 / η2 <1.0 is satisfied.   The adsorptive silica filler according to any one of claims 1 to 4, wherein the total amount of radioactive elements is 2 ppb or less. A method for producing an adsorptive silica filler comprising the following steps (1) to (7):
(1) An emulsification step of preparing a water-in-oil (W / O) emulsion in which an aqueous alkali silicate solution is dispersed in a fine granular form as a dispersed phase
(2) A coagulation step in which the water-in-oil (W / O) emulsion prepared in (1) is mixed with a mineral acid aqueous solution to produce hydrous spherical silica gel particles having an average particle size of 2.9 μm to less than 7 μm.
(3) Cleaning process for cleaning the hydrous spherical silica gel particles in (2)
(4) Drying step of drying the hydrous spherical silica gel particles washed in (3)
(5) Crushing step of crushing dry spherical silica gel particles during or after drying of (4)
(6) Primary firing step of firing the dried spherical silica gel particles crushed in (5) at 300 to 700 ° C
(7) Secondary firing step of firing the spherical silica gel particles primarily fired in (6) at 700 to 1100 ° C (excluding 700 ° C)   A sealing resin composition comprising the at least one adsorptive silica filler according to claim 1.   The sealing resin composition according to claim 7, wherein the sealing resin composition is for an image element device.