JP2015067691A - Filler for silicone and silicone composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filler for silicone which provides silicone excellent in strength, transparency, and thickening properties and small in temperature dependence of permeability, and a silicone composition.SOLUTION: A silicone filler consists of an aerogel which has a specific surface area of 400-1,000 m/g, by the BET method, a peak pore volume of 3-8 ml/g and a peak pore radii of 10-50 nm, respectively, by the BJH method, and a volume-based accumulation 50% radius (D50) value of 1-20 μm, measured by the laser diffraction type particle size distribution.

Description

  The present invention relates to an airgel capable of obtaining silicone having excellent strength and transparency when filled into silicone, and a silicone composition containing the airgel.

  Silicone is a material exhibiting excellent heat resistance, cold resistance, weather resistance, and electrical insulation, and is usefully used as a packing material for home appliances and OA equipment, and a sealing material for LEDs. Silica is generally added to the silicone for the purpose of improving viscosity and strength.

  As the above-mentioned silica, fumed silica is usually used because of its excellent effect of developing strength. However, when the filling amount of fumed silica is increased, there is a problem that transparency inherent in silicone is impaired. As a means for avoiding this problem, there is a method of matching the refractive index of silicone rubber with the refractive index of silica. However, according to the above means, a silicone rubber having good transparency can be obtained at room temperature. However, since the temperature dependence of the refractive index of silica and silicone rubber is different, it becomes opaque in a high temperature region. There was a problem. Therefore, in the case where the temperature changes due to heat generation as in the case of an LED sealing material, there remains a problem in the transparency of silicone such that the transmittance decreases as the temperature increases.

JP-A-10-120906

  Accordingly, an object of the present invention is to provide a silicone-filled airgel capable of improving the strength and viscosity of a resin without impairing the transparency of the silicone. It is another object of the present invention to provide a silicone-filled airgel and a silicone composition that can maintain transparency even with respect to temperature changes and have a low temperature dependency of transmittance.

  The inventors of the present invention have made extensive studies in order to solve the above problems. As a result, by using a specific airgel having a high specific surface area and a large pore volume as a filler for silicone, silicone having excellent strength without impairing the transparency specific to silicone Was found to be obtained. The present inventors have further studied, and by setting the volume-based cumulative 50% diameter (D50 diameter) of the airgel to a specific range, a silicone having excellent strength and transparency and low temperature dependence of transmittance is obtained. The inventors have found that the present invention can be obtained and have completed the present invention.

That is, the present invention has a specific surface area according to the BET method of 400 to 1000 m ² / g, and pore volume and pore radius peaks according to the BJH method are 3 to 8 ml / g and 10 to 50 nm, respectively. A silicone-filled airgel characterized by a volume-based cumulative 50% diameter (D50 diameter) measured by a particle size distribution of 1 to 20 μm.

  The airgel of the present invention is excellent in improving the resin strength when filled in silicone, without losing the transparency specific to silicone, and can maintain excellent transparency regardless of temperature change. It can be suitably used as a filler for various products made of silicone, for example, protective films for electrical equipment, intermediate layers of safety glass, contact lenses and the like. By filling the airgel of the present invention, a silicone excellent in strength and transparency can be obtained, and its industrial utility value is very large.

  Hereinafter, the present invention will be described in more detail.

The airgel of the present invention refers to a solid material having a high porosity and a gas as a dispersion medium, and particularly a solid material having a porosity of 60% or more. In addition, the said porosity is the value which represented the quantity of the gas contained in the apparent volume by the volume percentage.
The substance constituting the airgel is not particularly limited, but is preferably a metal oxide, and the metal oxide is not particularly limited as long as it is a metal element that constitutes an oxide that is stable at room temperature and pressure and in the atmosphere. Instead, a single metal oxide and a composite oxide containing two or more metal elements can be used.

  When it is a single metal oxide, specifically, silica (silicon dioxide), alumina, titania, zirconia, magnesia (MgO), iron oxide, copper oxide, zinc oxide, tin oxide, tungsten oxide, vanadium oxide and the like can be mentioned. Among them, silica is preferable because the resin composition can be reduced in weight, that is, the bulk density can be further reduced, and it is inexpensive and easily available.

  In the case of a complex oxide, specific examples include silica-alumina, silica-titania, silica-titania-zirconia, and when a complex oxide is used, a single oxide is relatively sensitive to moisture. An alkali metal or alkaline earth metal (period 4th period (Ca) or later) can be included as a constituent metal element, but a composite oxide mainly composed of silica is preferable. In the composite oxide containing silica as a main component, the molar ratio of silicon (Si) in the element group other than oxygen contained in the composite oxide is 50% or more and less than 100% of silica in a molar ratio, preferably 65% or more, more preferably 75% or more, and further preferably 80% or more.

In the composite oxide containing silica as a main component, preferable metal elements other than silicon include Group II metals of the periodic table such as magnesium, calcium, strontium and barium; aluminum, yttrium, indium and boron Group III metals of the periodic table such as lanthanum (note that boron is treated as a metal element); and Group IV metals of the periodic table such as titanium, zirconium, germanium, tin, etc. Among these, Al, Ti, and Zr can be particularly preferably employed. The composite oxide containing silica as a main component may contain two or more metal elements in addition to silicon.
In the present invention, the silica-based airgel refers to the above-mentioned silica or an airgel composed of a composite oxide containing silica as a main component.

Airgel of the present invention has a specific surface area by BET method is 400 to 1000 m ² / g, preferably 500~800m ² / g, and more preferably from 500~650m ² / g. The specific surface area depends on the particle size of the primary particles constituting the airgel. The larger the particle size, the smaller the primary particle size. For example, when the specific surface area is 600 m ² / g, the primary particle size Is about 5 nm.

When the silicone is filled as the specific surface area increases, the strength, viscosity increase, and transparency are improved, but if it exceeds the above range, it becomes difficult to maintain the pore structure of the airgel, The pores are easily crushed. When the specific surface area is smaller than the above range, the resin strength, viscosity increase, and transparency when the aerogel is filled in silicone are lowered.
The above “specific surface area by BET method” is the measurement of the sample to be measured for 2 hours or more at a temperature of 150 ° C. under a vacuum of 1 kPa or less, and then measuring the adsorption isotherm only on the nitrogen adsorption side at the liquid nitrogen temperature. The value obtained by analyzing the adsorption isotherm by the BET method, and the pressure range used for the analysis at that time is a range of a relative pressure of 0.1 to 0.25.

  The airgel of the present invention has a pore volume by the BJH method of 3 to 8 ml / g, preferably 4 to 7 ml / g, and more preferably 4 to 6 ml / g. The pore structure peculiar to an airgel is a network, and when the resin is filled, the resin penetrates into the gaps between the pores, so that the effect of improving the strength of the resin can be obtained. And when the airgel of the same weight is filled in silicone, the larger the pore volume per unit weight, the larger the volume ratio occupied by the pore structure in the silicone, that is, excellent dispersibility, and resin strength. improves. The smaller the pore volume exceeds the above range, the smaller the volume ratio occupied by the pore structure in the silicone, that is, the inferior dispersibility, so that the effect of developing the resin strength cannot be sufficiently obtained. In that case, it is possible to maintain the resin strength by increasing the filling amount and maintaining the volume ratio occupied by the pore structure, but this is not preferable because the transparency is lowered by increasing the filling amount.

  In addition, it is difficult to obtain an airgel having a pore volume exceeding the above range, and even when obtained, the strength of the framework forming the pore structure is reduced, so that the pores are reduced due to the load applied during resin kneading. There is a risk of crushing.

  The above-mentioned “pore volume by BJH method” means that the sample to be measured is dried at a temperature of 150 ° C. for 2 hours or more under a vacuum of 1 kPa or less, and then an adsorption isotherm of only the nitrogen adsorbent at the liquid nitrogen temperature. Pores obtained and analyzed by the BJH method (Barrett, E.P .; Joyner, LG; Halenda, P.P., J. Am. Chem. Soc. 73, 373 (1951)). It is a pore volume derived from pores having a radius of 1 nm to 100 nm.

  The pore radius peak according to the BJH method of the airgel of the present invention is in the range of 10 to 50 nm, more preferably 20 to 40 nm. The peak of the pore radius by the BJH method is obtained by analyzing the adsorption isotherm by the BJH method in the same manner as the pore volume, and the differential of the cumulative pore volume by the logarithm of the pore radius is plotted on the vertical axis. The pore distribution curve (volume distribution curve) plotted with the pore radius taken along the horizontal axis is the pore radius having the maximum peak.

  The airgel of the present invention in which the pore volume by the BJH method and the peak of the pore radius are in the above range has a strong framework for forming the pore structure, and the pore structure is resistant to the load applied during kneading and molding. It is possible to keep it sufficiently.

  The silicone filled with the airgel of the present invention having the above-mentioned physical properties is excellent in transparency, specifically, has a high transmittance and a high haze value, and surprisingly the temperature dependence of the transmittance. Is small. The details of the mechanism in which the silicone filled with the airgel of the present invention has a high transmittance is not clear, but the substance that refracts and scatters the visible light incident on the silicone because the silicone penetrates the gaps in the pores of the airgel. The primary particles constituting the pore structure of the airgel. The primary particle size of the airgel is about several nanometers, and is excellent in transparency because it is as small as a few tenths to several hundredths compared with the wavelength of general visible light (about 380 nm to 750 nm). I guess that was obtained. The primary particle diameter of fumed silica is small and is about 10 nm. In fumed silica produced by flame hydrolysis, it is difficult to produce one having a primary particle size of several nanometers.

  Furthermore, the volume-based cumulative 50% diameter (hereinafter also referred to as D50) measured by the laser diffraction particle size distribution of the airgel of the present invention is in the range of 1 to 20 μm. When D50 is in the above range, the silicone to which the airgel is added has high strength and good transparency.

  And the present inventors discovered that the haze value which shows the ratio of the diffused light among the transmitted light became large, so that said D50 was large in an airgel. That is, it is possible to change the haze value by changing D50 within the above range by grinding or the like. When D50 is larger than the above range, the dispersibility is lowered when the silicone is filled, and the resin strength is lowered. When it is smaller than the above range, handling such as powder scattering during kneading becomes difficult.

  Since the airgel of the present invention is excellent in strength and transparency when filled into silicone, it is suitable as a filler for various products made of silicone, for example, protective films for electrical equipment, intermediate layers of safety glass, contact lenses, etc. Can be used. Also, since it has high transmittance and high haze value, and the temperature dependency of transmittance is small, it can be used very effectively when light is to be transmitted and diffused, and the temperature changes. Can withstand the environment. For example, it can be suitably used for lighting applications such as LEDs, light diffusion plates for lighting, and the like.

  In the airgel of the present invention, a ratio (D10 / D90) of a volume-based cumulative 10% diameter (hereinafter also referred to as D10) and a volume-based cumulative 90% diameter (hereinafter also referred to as D90) measured by a laser diffraction particle size distribution. Is preferably 0.3 or more. As the above (D10 / D90) is larger, the particle size distribution is sharper and does not contain many coarse particles, so the dispersibility in the resin is improved. Moreover, since the said haze value has a correlation with the particle diameter of an airgel, when a particle size distribution is sharp, it can use suitably, when it wants to approximate a desired haze value.

  The airgel of the present invention is preferably surface-treated with a hydrophobizing agent. When the surface-treated airgel is filled in silicone, the dispersibility of the airgel in the resin is improved, the familiarity with the resin on the surface of the filler is improved, and the resin easily penetrates to the details of the gaps in the pore structure. Thus, a material having higher strength and transparency can be obtained.

As the hydrophobizing agent, known ones can be used without particular limitation, and are represented by the general formula R _n SiX _4-n (R is a hydrocarbon group, X is an alkoxy group, halogen, n is an integer of 1 to 3). And silazanes represented by the general formula R ₃ SiNHSiR ₃ . Of these, trimethylchlorosilane, dimethyldichlorosilane (hereinafter, DMDCS), monomethyltrichlorosilane (hereinafter, MTS), hexamethyldisilazane, and the like can be suitably used.

  The manufacturing method of the airgel of this invention which has the above-mentioned physical property is not specifically limited, It can carry out by a well-known method. According to the study by the present inventors, it can be produced by the following method.

  That is, the aerogel for filling silicone of the present invention is produced by an atmospheric drying method in which a metal oxide sol is prepared, and the sol is gelled, aged, washed, solvent substituted, hydrophobized, and dried in order. be able to.

Hereinafter, the case where the metal oxide is silica (SiO ₂ ) will be described in detail as an example.

Among the above steps, the silica (metal oxide) sol preparation step may be performed by appropriately selecting a known method. As raw materials for producing the silica sol, metal alkoxide, alkali metal silicate, and the like can be used. Specific examples of the metal alkoxide that can be used as a raw material for the silicone-filled airgel of the present invention include tetramethoxysilane and tetraethoxysilane. Examples of the alkali metal silicate include potassium silicate and sodium silicate. The chemical formula is represented by the following formula 1.
m (M ₂ O) · n (SiO ₂ ) (Formula 1)
(In the formula, m and n represent a positive integer, and M represents an alkali metal atom.)
Among the raw materials for producing the silica sol, an alkali metal silicate can be preferably used from the viewpoint of inexpensiveness, and sodium silicate which is easily available is preferable.

When an alkali metal silicate is used as a silica sol preparation material for an airgel used in the silicone filler of the present invention, a method of neutralizing with a mineral acid such as hydrochloric acid or sulfuric acid, or the counter ion is H ^+. A silica sol can be produced by a method using a cation exchange resin (hereinafter referred to as “acid-type cation exchange resin”).

  Examples of the method for preparing the silica sol by neutralizing with the acid described above include a method of adding an alkali metal silicate solution with stirring to an acid solution, and a method of collision mixing in a pipe. . The amount of acid used is preferably 1.05 to 1.2 as the molar ratio of the alkali metal silicate salt to the alkali content. When the amount of acid is within this range, the pH of the produced silica sol is about 1 to 3.

  Moreover, the method for producing silica sol using the above acid type cation exchange resin can be performed by a known method, and the alkali metal silicate having an appropriate concentration in the packed bed filled with the acid type cation exchange resin. The acid type cation exchange resin is separated by adding the acid type cation exchange resin to the alkali metal silicate solution, mixing, removing the alkali metal, and then separating by filtration. This can be done. At that time, the amount of the acid-type cation exchange resin to be used must be equal to or greater than the amount capable of exchanging alkali metals contained in the solution.

  A commercially available acid-type cation exchange resin can be used. For example, styrene-based, acryl-based, methacryl-based, etc., and those having a sulfonic acid group or a carbonyl group substituted as the ion-exchange group can be used. Among these, a so-called strong acid type cation exchange resin having a sulfonic acid group can be suitably used.

  In addition, after using said acid type cation exchange resin for replacement | exchange of an alkali metal, a reproduction | regeneration process can be performed by letting sulfuric acid and hydrochloric acid pass. The amount of acid used for regeneration is usually 2 to 10 times the exchange capacity of the ion exchange resin.

  The concentration of the silica sol produced by the above method is preferably about 50 to 150 g / L as the concentration of silica. By making it 50 g / L or more, the gelation time can be shortened moderately and efficiently produced, and since the silica content in the silica sol is large, the formation of the airgel skeleton structure is likely to be sufficient, and shrinkage occurs during drying. Since it does not easily occur, the pore volume tends to increase. Furthermore, there is a low possibility that the pores will be crushed by the external pressure when filled in a closed container or the like, and when stirring and mixing, a strong agglomerated structure is obtained, and the performance as a good silicone filler can be exhibited. It becomes like this.

  Moreover, by setting it as 150 g / L or less, since the density of an airgel becomes small and the number of silica particles contained per unit mass increases, it becomes possible to obtain silicone with high intensity | strength even if it adds a little.

  In order to produce the airgel of the present invention, following the preparation of the sol, ammonia water (for example, about 5%), caustic soda, alkali metal salt, etc. are added to the silica sol to adjust the pH to 3-6. Gelate. The gel is pulverized through a sieve having an appropriate opening while crushing the gel so that the gel has an appropriate particle size (for example, about 150 μm to 4 mm) to obtain an aqueous gel slurry having an appropriate particle size. If the pH is lower than 3, it takes time to gel and the efficiency is poor, and if the pH exceeds 6, it immediately gels and it becomes difficult to form a uniform gel. Furthermore, the primary particles are coalesced or grown, the primary particle diameter is increased, the specific surface area tends to be reduced, the fine aggregate structure is difficult to form, the pore volume is reduced, and the desired airgel tends not to be formed. .

  The time required for the gelation depends on the temperature and the concentration of the silica sol, but when the pH is 5.0, 50 ° C. and the silica concentration in the silica sol is 80 g / L, gelation occurs after several minutes.

  When producing the airgel of the present invention, following the above gelation, when the silica concentration is as low as 50 to 80 g / L or when the gelation pH is as low as 3 to 4, the silica skeleton structure strength of the gelled product In order to strengthen the strength, aging is preferably performed. The specific surface area of the airgel varies depending on the pH, temperature, and time during the aging. The higher the pH, the higher the temperature, and the longer the time, the lower the specific surface area, but the airgel's skeletal structure becomes stronger, so it has the effect of suppressing drying shrinkage and increasing the pore volume. When used as an agent, since the pores can be kept intact, it is preferable to adjust the physical property balance and determine the conditions.

  The range of the aging temperature is preferably 30 to 80 ° C. If the ripening temperature is high outside this range, the amount of heat required to raise the temperature is large, and if the ripening temperature is low outside this range, the time required to obtain the aging effect is large. become longer. Moreover, as a range of said aging time, when pH to gelatinize is 3-4, about 5 to 24 hours are preferable. Moreover, when the pH to gelatinize is 4-6, about 0 to 24 hours immediately after gelatinization are preferable. When the aging time exceeds 24 hours, the primary particles of silica are coalesced or grown during aging, the primary particle size increases, the specific surface area decreases, the fine aggregate structure is difficult to form, and the pore volume decreases. Tend.

  The washing operation is an operation for removing the salt contained in the gel by washing the aqueous gel slurry with water. Therefore, this cleaning operation is not necessary when a sol is produced using an acid type cation exchange resin. In order to produce an airgel used for a silicone filler, this washing is preferably performed until the conductivity of the washing solution is 100 μS / cm or less. The washing operation can be performed by a known method. For example, a method of repeatedly adding a certain amount of water to the gel and draining the washing water after standing for a certain time, a method of allowing a certain amount of water to pass through the gel placed in the column, and the like can be mentioned. When washing with a column, it can be performed under a pressure of about 0.2 to 1.0 MPa for the purpose of increasing efficiency.

  In order to produce the airgel of the present invention, solvent replacement is performed. This solvent replacement replaces the water used for preparing the gel with a solvent having a small surface tension so that the drying shrinkage does not occur when the gel obtained by the above method is dried. Since it is difficult to directly replace water with a solvent having a low surface tension, this solvent replacement is usually performed in two stages. The selection criteria for the solvent used in the first stage include good miscibility with water and the solvent used for the second stage solvent substitution.

  For the first-stage solvent replacement, a so-called hydrophilic organic solvent that can be mixed with water such as methanol, ethanol, isopropyl alcohol, and acetone at an arbitrary ratio can be used, and preferably methanol or ethanol is used. be able to. The selection criteria for the solvent used in the second stage include that it does not react with the treatment agent used in the subsequent hydrophobization treatment and that the surface tension is small so as not to cause drying shrinkage. As the solvent used in the second stage, hexane, dichloromethane, methyl ethyl ketone, heptane, or the like can be used, and hexane can be preferably used. Of course, if necessary, further solvent substitution may be performed between the first-stage solvent substitution and the second-stage solvent substitution.

  The first-stage solvent replacement can be performed by a known method. For example, a method of repeatedly adding a certain amount of solvent to the gel and leaving it for a certain time and then removing the solvent, a method of allowing a certain amount of solvent to pass through the gel placed in the column, etc. In order to save the solvent used for substitution, a method using a column is preferred. Moreover, when replacing by a column, it can carry out under the pressurization of about 0.2-1 Mpa for the purpose of raising efficiency.

  The amount of the solvent used for the solvent replacement is preferably an amount that can sufficiently replace the moisture in the gel. The water content in the gel after substitution is preferably 10% or less with respect to the silica content. When the method is employed with the above-mentioned column, the solvent can be used in an amount 5 to 10 times the gel volume.

  The second-stage solvent replacement can be performed in the same manner as the first-stage solvent replacement, and can be performed in an amount that can sufficiently replace the solvent used in the first stage. When the column method is employed, 5 to 10 times as much solvent as the gel volume can be used.

  The solvent used for the above substitution is preferably collected and reused after purification of the distillation column in order to save the cost of the solvent.

The airgel for silicone filler of the present invention can be subjected to a hydrophobic treatment after the above solvent replacement. As the treating agent used for the hydrophobizing treatment, those having a structure represented by the general formula R _n SiX _4-n (R is a hydrocarbon group, X is an alkoxy group, halogen, n is an integer of 1 to 3), Silazanes represented by the general formula R ₃ SiNHSiR ₃ are preferably used. Preferred are trimethylchlorosilane, dimethyldichlorosilane (hereinafter referred to as DMDCS), monomethyltrichlorosilane (hereinafter referred to as MTS), and hexamethyldisilazane.

  The amount of the treatment agent used in the above hydrophobic treatment depends on the kind of the treatment agent. For example, when DMDCS is used as the treatment agent, the amount is 50 to 150 parts by mass with respect to 100 parts by mass of silica. is there. When the amount of the DMDCS treatment agent is less than 50 parts by mass, drying shrinkage occurs during solvent drying in the subsequent step, and the target pore volume cannot be obtained, or the aerogel has the target pore volume. However, the repulsion between the particles (spring back effect) is reduced and the pores are crushed when an external force is applied. More preferably, it is 80-130 mass parts.

  The conditions for the above-described hydrophobizing treatment can be performed by adding a certain amount of solvent to the liquid containing the gel after the solvent substitution treatment, adding a hydrophobizing agent, and reacting for a certain time. When DMDCS is used as the hydrophobizing agent and the treatment temperature is 50 ° C., the treatment can be performed by holding for about 12 hours or more.

  In order to obtain the airgel of the present invention, after the solvent replacement or hydrophobization treatment, it is filtered off, the unreacted treatment agent is washed with a solvent, and then dried. The drying temperature is preferably not less than the boiling point of the solvent and not more than the decomposition temperature of the surface treatment agent, and the pressure is preferably normal or reduced.

  The airgel in the present invention can be obtained by pulverizing the lump-shaped dry airgel obtained as described above by a known method.

  However, since airgel having a sharp particle size distribution is difficult to obtain by wet pulverization, dry pulverization is preferably performed. The mechanism of these causes is not clear, but in wet grinding, the grinding energy applied to each particle is too large, or it is difficult to uniformly apply energy to the particles, so the proportion of small particles significantly below the average particle size increases, conversely It is considered that an airgel having a sharp particle size distribution is difficult to obtain due to an increase in the proportion of coarse particles having a large particle size that remain without being pulverized, or both phenomena. Therefore, dry pulverization is preferably performed to obtain the airgel of the present invention.

  In addition, a method of applying a strong force for a relatively short time, such as a jet mill, can obtain a sharp particle size distribution rather than a method of applying a strong force for a relatively long time, such as a ball mill. Is preferable in that it is difficult to break down, and thus it is difficult to reduce the specific surface area and pore volume.

Furthermore, when pulverizing with a jet mill to obtain an airgel having the desired particle size distribution, the powder concentration in an inert gas such as compressed air or N ₂ is 10 g / m ³ or more and 220 g / m ³ or less, preferably 15 g / m ³ or more and 190 g / m ³ or less, more preferably 15 g / m ³ or more and 30 g / m ³ or less. By setting the powder concentration, the powder concentration in the pulverizing chamber of the jet mill is increased and the pulverizing ability is improved. However, the pulverizing force applied to the individual particles is dispersed even if the powder concentration is excessively increased. Body concentration is preferred.

  Furthermore, when it is difficult to obtain the supply amount, an airgel having a desired particle size distribution can be obtained by pulverizing the material once pulverized several times.

  As described above, the strength of the network structure of the airgel tends to be difficult to pulverize because the higher the pH during gel aging, the longer the aging time, and the higher the aging temperature, the stronger. Therefore, in order to obtain the airgel of the present invention, there is a tendency that the necessity of increasing the pulverization pressure / air volume or subjecting it to multiple pulverizations is high.

  By such pulverization, pulverization is preferably performed until D50 becomes 1 to 20 μm.

  Of course, the above-described production method is an example, and the airgel of the present invention is not limited to the one obtained by the production method described above, and other known pulverization, pulverization, classification, etc. are appropriately selected and carried out. It may be manufactured.

  In the silicone composition of the present invention, the amount of the airgel of the present invention having the above-mentioned physical properties is 10 to 150 parts by weight, preferably 30 to 100 parts by weight, based on 100 parts by weight of silicone. When the amount of the airgel is smaller than the above range, it is difficult to obtain the strength of the silicone, and when it exceeds the above range, it is difficult to disperse in the silicone.

  The silicone is an oligomer or polymer having a siloxane bond (—Si—O—) composed of silicon and oxygen as a main skeleton, and is composed of organopolysiloxane. The kind is not specifically limited, A modified silicone is also included. For example, a branched or straight chain can be mentioned, and the side chain or terminal of the organopolysiloxane is a hydrogen atom, a methyl group, an ethyl group, a propyl group, a butyl group, a hexyl group, an octyl group or other alkyl group, Cyclopentyl group, cycloalkyl group such as cyclohexyl group, alkenyl group such as vinyl group, allyl group, propenyl group, aralkyl group such as benzyl group, 2-phenylethyl group, amino group, hydroxyl group, carboxyl group, polyether group and An epoxy group, or a group in which part or all of the hydrogen atoms of these groups are substituted with a halogen atom or a cyano group can be mentioned.

  The shape of the silicone can be suitably used without particular limitation, such as oil, emulsion, resin, varnish, rubber and powder. In particular, silicone resins and silicone rubbers obtained by filling the resin and rubber with the above-mentioned fillers have excellent strength without impairing the transparency inherent in silicones. It can be suitably used for lighting devices such as protective films for devices, safety glass intermediate layers, contact lenses, LEDs, and light diffusion plates for lighting, and the effects of the present invention can be exhibited.

  When the compounding amount of the airgel with respect to the silicone is smaller than the above range, it is difficult to obtain the strength of the silicone.

  In the silicone composition of the present invention, a known dispersant can be blended in order to improve the dispersibility of the airgel. The type and blending amount of the dispersing agent are not particularly limited. For example, if a dispersing agent such as a low molecular weight αω hydroxypolysiloxane or hexamethyldisiloxane is blended in an amount of about 3 to 30 parts by weight with respect to 100 parts by weight of silicone. Good.

The method of filling the airgel of the present invention into silicone is not particularly limited, and can be performed by a known method such as a two-roll, kneader, or Banbury mixer.
Furthermore, a vulcanizing agent such as an organic peroxide or a platinum or palladium curing catalyst is added to the silicone composition filled with the airgel of the present invention, and after molding into a desired shape, it is cured by thermosetting or addition polymerization. be able to.
In addition, as long as it fills the said airgel as a filler of the silicone of this invention, it can also use together with other well-known fillers, such as a metal oxide.

  Hereinafter, examples will be shown to specifically describe the present invention. However, the present invention is not limited only to these examples.

<Method for evaluating properties of airgel>
(Measurement of particle size distribution by laser diffraction)
0.1 g of the spherical metal oxide was added to 40 ml of isopropyl alcohol and dispersed for 6 minutes at an output of 100 w using UT-105S manufactured by Sharp Manufacturing Co., Ltd. The particle size distribution of the dispersion was measured using Microtrac MT3000 manufactured by JGC apparatus Co., Ltd. The refractive index of the solvent was 1.38, and the refractive index of the particles was 1.46. From the obtained particle size distribution, D10, D50 and D90 with respect to the volume distribution were evaluated.
(Measurement of other airgel properties)
The BET specific surface area, BJH pore volume, and pore radius peak were measured by BELSORP-mini manufactured by Nippon Bell Co., Ltd. according to the above-mentioned definitions.

<Method for evaluating physical properties of silicone>
(1) Silicone rubber compound preparation (kneader kneading method)
Momentive Performance Materials (MPM) silicone raw rubber GS-610 50 parts by weight, GS-620 50 parts by weight Aerogel or fumed silica 40 parts by weight, dispersant (MPM XC96- 723 (viscosity: 30 mPa · s) 8 parts by weight are kneaded with a pressure kneader (DS 0.5-3MHB-E manufactured by Moriyama) for 30 minutes at 50 ° C. without pressure, and then under pressure up to 185 ° C. Kneading while raising the temperature. Thereafter, kneading was carried out at 185 ° C. for 30 minutes without releasing the pressure, and a silicone rubber compound was prepared.
The obtained silicone rubber compound was allowed to stand for 24 hours, and then 0.5 parts by weight of a vulcanizing agent (TC-8 manufactured by MPM) was added uniformly to 100 parts by weight of the silicone rubber compound using a 4 inch two roll Until kneaded. Vulcanization was performed by primary vulcanization (180 ° C., 15 minutes) and secondary vulcanization (200 ° C., 4 hours) to obtain silicone rubber sheets having thicknesses of 2 mm and 12 mm. Using this sheet, the reinforcing property, transparency, and specific gravity of the rubber were evaluated.
Evaluation of reinforcing properties Tensile strength and elongation: Measured according to JIS K6251.
Tear strength: Measured according to JIS K6252.
Evaluation of transparency A silicone rubber sheet having a thickness of 12 mm was evaluated.

Haze, total light transmittance: Measured according to JIS K7136 (ISO14782) and JIS K7361-1 (ISO13468-1).
Evaluation of specific gravity It measured by Archimedes method using SD-200L made from Alpha Mirage.
Evaluation of Silicone Viscosity To 100 parts by weight of silicone oil (SH200 1000cs manufactured by Toray Dow Corning), 5.5 parts by weight of airgel and fumed silica to be measured are added, and a homomixer (manufactured by Primix, TK After mixing for 2 minutes under the condition of 10000 rpm using a HOMOMIKER MARK 2), the viscosity was measured under the condition of 60 rpm with a BH viscometer (rotor NO6). The viscosity was also measured at 6 rpm, and the thixotropy index (TI) was determined by dividing the viscosity at 60 rpm by the viscosity at 6 rpm. Detailed measurement conditions were performed according to JIS K5400.

<Example 1>
An airgel was produced under the following conditions.

No. 3 sodium silicate (JIS K1408) was diluted until the SiO ₂ concentration became 16.5 g / 100 mL, and this sodium silicate and sulfuric acid (9.5 g / 100 mL) were mixed and reacted at room temperature to obtain silica sol (SiO ₂ concentration 8%, pH 2) 1000 ml. To the silica sol, No. 3 sodium silicate diluted to a SiO ₂ concentration of 8% was added to obtain a pH of 6.0, and the mixture was aged in a water bath at 40 ° C. for 24 hours. Thereafter, the crushed gel was passed through a 2 mm net into a liquid column, and water was passed to a conductivity of 100 μS or less to wash the gel. Then, in a liquid flow column, the water concentration was replaced with ethanol to 0.2 wt% or less, and further, the ethanol concentration was replaced with toluene to 0.1 wt% or less.

  The obtained gel using toluene as a dispersion medium was placed in a 2000 ml glass container, 60 g of DMDCS was added, and the mixture was stirred at 60 ° C. for 6 hours. After the reaction, the gel was separated by suction filtration and dried at 120 ° C. under normal pressure and nitrogen atmosphere for 12 hours to obtain a crude airgel.

  The hydrophobicity of the crude airgel thus obtained was confirmed by placing 1 g of the airgel in a beaker of 100 mL of water, stirring for several tens of seconds, and then allowing it to stand to completely separate into an airgel phase and an aqueous phase.

The crude airgel was pulverized with a jet mill (manufactured by Seishin Enterprise Co., Ltd., STJ-100) to obtain the desired airgel. At this time, the feed pressure and the mill pressure were both 0.1 MPa and compressed air of 0.2 m ³ / min, the feed rate of the bulk was 35 g / min, and 187 g / m ³ per unit air volume. The obtained airgel had a specific surface area of 590 m ² / g, a pore volume of 4.1 ml / g, a pore radius peak of 25 nm, a D50 of 7.6 μm, and a D10 / D90 of 0.13. Table 1 shows physical property values of the silicone filled with the airgel.
<Example 2>
The airgel obtained in Example 1 was pulverized again with a jet mill to obtain an airgel having a smaller D50. The conditions for this re-grinding were as follows: feed pressure and mill pressure were both 0.5 MPa, 0.9 m ³ / min of compressed air, the feed rate of the bulk was 24 g / min, and the unit air volume was 26 g / m ³ . went. The obtained airgel had a specific surface area of 590 m ² / g, a pore volume of 4.1 ml / g, a pore radius peak of 25 nm, a D50 of 2.7 μm, and a D10 / D90 of 0.34. Table 1 shows physical property values of the silicone filled with the airgel.
<Comparative Example 1>
The physical properties of silicone filled with QS-30 (manufactured by Tokuyama Co., Ltd., hydrophilic Leoroseal, specific surface area 300 m ² / g) as fumed silica were evaluated. The results are shown in Table 1.
<Comparative Example 2>
The physical properties of silicone filled with hydrophobic HM-30S (manufactured by Tokuyama Co., Ltd., Leolo Seal, specific surface area before surface treatment of 300 m ² / g) as fumed silica without adding a dispersant were evaluated. The results are shown in Table 1.

Claims (5)

Specific surface area according to BET method is 400 to 1000 m ² / g, and pore volume and pore radius peaks according to BJH method are 3 to 8 ml / g and 10 to 50 nm, respectively, measured by laser diffraction particle size distribution. A filler for silicone, comprising an airgel having a volume-based cumulative 50% diameter (D50) value of 1 to 20 μm.   The filler for silicone according to claim 1, wherein the airgel is a silica-based aerogel.   The airgel has a ratio (D10 / D90) of a volume-based cumulative 10% diameter (D10) and a volume-based cumulative 90% diameter (D90) measured by a laser diffraction particle size distribution of 0.3 or more. The filler for silicone according to claim 1 or 2.   The said airgel is hydrophobized with the hydrophobizing agent, The filler for silicones as described in any one of Claims 1-3 characterized by the above-mentioned.   A silicone composition comprising 10 to 150 parts by weight of the airgel according to claim 1 to 100 parts by weight of silicone.