JP2009286645A - Silica gel and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing silica gel by which silica gel having excellent monodispersity is produced easily and inexpensively with a good yield. <P>SOLUTION: The method for producing the silica gel includes a process for supplying silica sol to a first flow passage, a process for supplying a liquid to a second flow passage, a process for bringing the silica sol into contact with the liquid in a laminar flow state at a junction where the first flow passage and the second flow passage join together, and a process for making the silica sol brought into contact with the liquid into gel. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to silica gel and a method for producing the same. More specifically, the present invention relates to a silica gel excellent in monodispersibility and a method for producing the same.

A sol-gel method is known as a method for producing silica particles or silica airgel. Since silica particles having a monodispersed particle size distribution (monodispersed silica particles) are useful in various applications, various attempts have been made. For example, it has been proposed to perform seed polymerization using silica particles obtained by the Staver method as a core (see Patent Document 1). However, this method has a problem in production efficiency because silica particles as cores are formed in advance to increase the particle diameter. In particular, when producing monodispersed silica particles having a large particle size (for example, several tens of μm to several hundreds of μm), there is a problem that not only the production efficiency but also the monodispersibility is inferior.
Japanese Patent Laid-Open No. 10-203820

  The present invention has been made to solve the above-described conventional problems, and a main object of the present invention is to produce silica gel excellent in monodispersibility with a high yield and at a low cost. Moreover, even if it is a case where it has a large particle diameter using this silica gel, it is in manufacturing a silica particle and silica aerogel excellent in monodispersibility with a sufficient yield, and simply and cheaply.

  In the method for producing silica gel of the present invention, the step of supplying silica sol to the first channel, the step of supplying liquid to the second channel, the first channel and the second channel A step of bringing the silica sol and the liquid into contact in a laminar flow state at a joining point where they join, and a step of gelling the silica sol brought into contact with the liquid.

  In a preferred embodiment, the second channel is formed so as to surround the outlet of the first channel.

  In a preferred embodiment, the shape of the outlet of the first flow path is substantially circular.

  In preferable embodiment, the internal diameter of the exit of the said 1st flow path is 10-300 micrometers.

  In a preferred embodiment, the contact angle between the first flow path and the silica sol is 45 to 100 °.

  In preferable embodiment, the Reynolds number of the said laminar flow is 0.1-1000.

  In a preferred embodiment, the ratio between the flow rate of the silica sol and the flow rate of the liquid is 1: 0.3 to 1: 4.

  In a preferred embodiment, the silica sol is prepared by adjusting the pH of water glass.

  In a preferred embodiment, the silica sol has a solid content concentration of 0.5 to 20 wt%.

  In a preferred embodiment, the liquid has a viscosity of 0.28 to 500 mPa · s.

  In a preferred embodiment, the gelation is performed by adjusting the pH of the silica sol.

  In another aspect of the invention, silica gel is provided. The silica gel of this invention is obtained by the said manufacturing method.

  In a preferred embodiment, the CV value is 20% or less.

  In yet another aspect of the invention, silica particles are provided. The silica particles of the present invention are obtained by drying and / or firing the above silica gel.

  In yet another aspect of the invention, a silica aerogel is provided. The silica airgel of the present invention is obtained by reacting the above silica gel with a silylating agent.

  According to the present invention, a silica gel excellent in monodispersibility can be produced with good yield and at a low cost. In addition, by using this silica gel, silica particles and silica airgel having excellent monodispersity (for example, CV value of 20% or less) can be obtained in a high yield, easily and inexpensively even when having a large particle size. Can be manufactured.

  Hereinafter, although preferable embodiment of this invention is described, this invention is not limited to these embodiment.

  The method for producing silica gel of the present invention comprises a step of supplying silica sol to the first flow path (step 1); a step of supplying liquid to the second flow path (step 2); a first flow path and a first flow path; A step of bringing the silica sol and the liquid into contact with each other in a laminar flow state at a junction where the two flow paths meet (step 3); and a step of gelling the silica sol in contact with the liquid (step 4). Step 1, step 2 and step 3 can be performed using any suitable apparatus. Preferably, a microreactor is used.

  FIG. 1A is a schematic view of a microreactor 10 used in a manufacturing method according to a preferred embodiment of the present invention as viewed from above, and FIG. It is sectional drawing seen from the direction. FIG. 2 is a perspective view of the microreactor 10. The microreactor 10 is formed by joining the first flow path 1 to which silica sol is supplied, the second flow path 2 to which liquid is supplied, and the first flow path 1 and the second flow path 2. And a merged flow path 3. In the present embodiment, the outlet of the first flow path 1 is surrounded by the second flow path 2, and the first flow path 1 and the second flow path 2 merge three-dimensionally. Further, the first flow path 1 and the second flow path 2 are partitioned by a partition wall 4 on the upstream side (right side in the illustrated example) of the confluence point (that is, the upstream end portion of the confluence flow path 3) 3a. ing. Further, the microreactor 10 includes a supply port 1 a to the first flow path 1 and supply ports 2 a and 2 a ′ to the second flow path 2.

  The shape of the outlet of the first channel can be designed in any suitable shape. Preferably, it is substantially circular as shown. By setting it as such a structure, the silica gel particle close | similar to a true sphere can be obtained.

  The inner diameter of the outlet of the first channel can be set to any appropriate value depending on, for example, the desired silica gel (silica particle, silica aerogel) particle diameter. Preferably it is 10-300 micrometers, More preferably, it is 30-200 micrometers, Most preferably, it is 50-150 micrometers. By providing such an inner diameter, the silica sol and the liquid can be more appropriately merged in a laminar flow state. In addition, the silica sol liquid column joined with the liquid can be uniformly divided, and silica gel particles with more excellent monodispersibility can be obtained. Furthermore, silica gel particles closer to true spheres can be obtained. The splitting of the silica sol (internal flow) can occur very uniformly due to the uniform shearing force from all directions from the liquid (external flow) and the difference in surface tension between the silica sol and the liquid.

  In this specification, the “inner diameter” of the flow path means the internal diameter when the cross-sectional shape viewed from the flow path direction is substantially circular, and the cross-sectional shape viewed from the flow path direction is other than circular. In this case, the length corresponding to the inner diameter is meant. For example, when the cross-sectional shape is substantially square, it means the length of the diagonal inside.

  FIG. 3 (a) is a schematic view of a microreactor 10 ′ used in the manufacturing method according to another preferred embodiment of the present invention as viewed from above, and FIG. It is sectional drawing seen from the flow path direction. As shown in these drawings, the microreactor 10 ′ may be provided with a flow path adjustment tool 20 that is inserted into the first flow path 1 and that can adjust at least the inner diameter of the outlet of the first flow path. The flow path adjuster 20 is formed with a through path 21 that can function as a first flow path. By providing such a flow path adjuster, the inner diameter of the first flow path can be easily adjusted. The cross-sectional shape of the through passage can be appropriately designed according to the shape of the outlet of the desired first flow path described above. The flow channel adjuster can be formed of any suitable material. Preferably, the flow path adjuster can be formed of epoxy resin, stainless steel, alumina ceramics, nickel, glass, or the like. This is because it can be easily and accurately produced.

  The first flow path and / or the peripheral wall of the through path may be subjected to any appropriate surface treatment. A water repellent treatment is preferred. This is because the contact angle with a silica sol described later can be easily adjusted, and desired silica gel particles can be obtained. Furthermore, durability can be improved. As the water repellent used in the water repellent treatment, a water repellent containing any appropriate resin can be employed. Specific examples of the resin include polyimide resins and fluorine resins.

  The shape of the outlet of the second flow path can be designed in any appropriate shape. Preferably, it is substantially circular as shown. Furthermore, it is preferable that the cross section of the second flow path including the outlet of the first flow path is substantially concentric. This is because the laminar flow state can be obtained efficiently.

  The inner diameter of the cross section of the second flow path including the outlet of the first flow path is preferably 0.3 to 3.0 mm, more preferably 0.6 to 2.2 mm, and particularly preferably 0.8 to 1.6 mm. By providing such an inner diameter, the silica sol and the liquid can be more appropriately combined in a laminar flow state, and desired silica gel particles can be obtained.

  The inner diameter of the merging channel is preferably 0.3 to 3.0 mm, more preferably 0.4 to 2.2 mm, and particularly preferably 0.6 to 1.6 mm. By providing such an inner diameter, the silica sol and the liquid can be more appropriately combined in a laminar flow state, and desired silica gel particles can be obtained.

  The cross-sectional shape along the flow path direction of the first flow path 1, the second flow path 2, and the merge flow path 3 can be designed in any appropriate shape. For example, as shown in FIGS. 1 to 3, the cross section along the flow path direction of the first flow path 1 is substantially linear, and the cross section along the flow path direction of the second flow path 2 is tapered. The cross section along the flow path direction of the merging flow path 3 is substantially linear. In another embodiment, the cross section along the flow path direction of the merge flow path 3 may be substantially tapered. In yet another embodiment, the cross section of the first flow path 1 along the flow path direction is substantially tapered and may be smaller than the taper of the second flow path. Also, for example, as shown in FIG. 1, the flow path from the supply port 1a to the first flow path 1 and the flow path from the supply port 2a (2a ′) to the second flow path 2 are in the flow path direction. It is also one of the preferable forms from the viewpoint of avoiding mixing of bubbles and the like that does not have a protruding part or a corner part that becomes an obstacle along the surface.

  The overall length of the first flow path 1 is typically 10 to 40 mm. The total length of the second flow path 2 is typically 10 to 40 mm. The total length of the merge channel 3 is typically 10 to 40 mm. The total length of the channel of the microreactor 10 (from the first channel inlet to the merged channel outlet) is typically 20 to 70 mm.

In the microreactor, the shape, number and position of the supply port can be appropriately designed according to the purpose. For example, as shown in FIGS. 1 to 3, the supply ports 1a, 2a, 2a ′ may all be located on the side surface, or the supply ports 1a, 2a, 2a ′ may be all located above. May be. As shown in FIGS. 1 to 3, the microreactor of the present invention preferably includes a plurality of liquid supply ports to the second flow path 2 (2 a and 2 a ′ in FIGS. 1 to 3). More preferably, it is 2-5, and still more preferably 2-3. With such a structure, it is possible to prevent the generation of bubbles in the second flow path 2 and to realize a sufficient laminar flow.

  The microreactor may include a flow rate control means for changing the flow rate of the silica sol in the first flow path 1 and the flow rate of the liquid in the second flow path 2. Preferably, the flow rate control means is provided closer to the supply port side than the outlet side (upstream side). Examples of the flow rate control means include a syringe pump and a gear pump, and a syringe pump is preferable. By providing the flow rate control means, the flow rate of the first silica sol and / or the liquid can be varied. As a result, the particle size of the silica sol obtained can be controlled. In addition, it is preferable that the connection between the flow path control unit and the first flow path and / or the second flow path be configured so as to avoid mixing of bubbles and the like.

  The microreactor may be manufactured by any method, but it is preferable to manufacture the microreactor by an optical modeling method in that it can be easily and accurately manufactured. The stereolithography method converts a 3D image designed with 3D CAD data into 2D slice data, and based on this data, the photocurable resin is cured layer by layer with a laser and laminated in 3D. It is a method of modeling. More specifically, a three-dimensional image designed with three-dimensional CAD data is sliced into thin layers of several layers and converted into two-dimensional slice data. Based on this two-dimensional slice data, the laser is inside the tank. The cross-sectional shape is drawn by scanning the surface of the photocurable resin. The portion irradiated with the laser is cured, and a cross-section for one layer is formed on the elevator. After that, the elevator descends one layer at a time, and several thin cross-sectional bodies are continuously laminated and three-dimensionally layered. Finally, by lifting the elevator, a three-dimensional layered model is taken out and subjected to post-processing to be completed. As an optical modeling apparatus that can be used for the optical modeling method, for example, an optical modeling apparatus (for example, SCS-1000HD) manufactured by Deemec Co., Ltd. may be used. Examples of the photocurable resin that can be used in the optical modeling method include a photocurable resin (for example, oxetane-based SCR950, etc.) manufactured by Deemec Co., Ltd. Examples of the laser include a He—Cd laser (peak wavelength = 325 nm). For example, the laser spot size is preferably φ10 to 100 μm, and more preferably φ30 to 70 μm. The thickness of one resin layer obtained by curing is preferably, for example, 10 to 50 μm, and more preferably 20 to 40 μm.

  The method for producing silica gel according to a preferred embodiment of the present invention includes a step of supplying silica sol to the first flow path (step 1); the second formed so as to surround the outlet of the first flow path. A step of supplying a liquid to the channel (step 2); a step of bringing the silica sol and the liquid into contact in a laminar flow state at a junction where the first channel and the second channel meet (step) 3); including a step (step 4) of gelling the silica sol brought into contact with the liquid.

  The silica sol may be an aqueous sol or an organic solvent sol. Preferably, it is an aqueous sol. An aqueous sol is excellent in stability, easy to produce, and can be obtained at low cost. Further, as described above, the microreactor is typically formed of a lipophilic material. Therefore, by using an aqueous sol, the silica sol can be excellently cut (droplet generation) when brought into contact with a liquid. As a result, silica gel particles with better monodispersibility can be obtained.

  The silica sol can be prepared by any suitable method. For example, it is prepared by adjusting the pH of an alkali metal silicate such as an aqueous sodium silicate solution (water glass). Preferably, it is prepared by neutralizing with an acid such as hydrochloric acid. In this case, the pH of the silica sol supplied to the first flow channel is preferably 1 to 6, more preferably 2 to 5, and particularly preferably 3 to 5. By adjusting to such pH, a stable silica sol can be obtained and gelation can be performed appropriately. It is possible to adjust the pH of the silica sol to be supplied to the first flow path to alkaline, but by adjusting the pH to acidic, the silica gel is more monodispersed, hard to break during drying, and closer to a true sphere. Particles can be obtained.

  As another method for preparing the silica sol, for example, a method in which a tetraalkyl orthosilicate and / or an oligomer thereof is hydrolyzed using an acid or an alkali as a catalyst and then the pH is appropriately adjusted may be mentioned. Specific examples of the tetraalkyl orthosilicate include tetramethyl orthosilicate, tetraethyl orthosilicate, and the like. Specific examples of the catalyst include inorganic acids such as hydrochloric acid, nitric acid and sulfuric acid; organic acids such as acetic acid; inorganic bases such as ammonia, sodium hydroxide, potassium hydroxide, sodium carbonate and sodium hydrogen carbonate; triethylamine, triethanolamine, Examples include organic bases such as ethanolamine and trimethylamine hydroxide. As another method for preparing the silica sol, for example, a method in which tetrachlorosilane is introduced into water for hydrolysis and then the pH is appropriately adjusted can be mentioned.

  The solid content concentration of the silica sol can be set to any appropriate value according to, for example, the desired silica particle or silica airgel particle diameter, porosity, and the like. Preferably it is 0.5-20 wt%, More preferably, it is 1-10 wt%, Most preferably, it is 2-6 wt%. It is because it can be made to gel appropriately. When the concentration is lower than 0.5 wt%, gelation is unlikely to occur, the gel structure is not uniform, and cracks may occur during drying, and it may be difficult to form a true sphere. On the other hand, when the concentration is higher than 20 wt%, it may be difficult to adjust the pH at the time of sol preparation or to control the gelation. By using the silica sol having such a solid concentration, the silica sol can be smoothly supplied to the first flow path.

  The viscosity of the silica sol is preferably 0.28 to 500 mPa · s, more preferably 1 to 100 mPa · s. By using a silica sol having such a viscosity, liquid can be sent stably.

  The contact angle between the silica sol and the first channel is preferably 45 to 100 °, more preferably 50 to 100 °, and particularly preferably 60 to 90 °. The liquid column of the silica sol that merged with the liquid can be more evenly divided, and silica gel particles with better monodispersity can be obtained. Furthermore, silica gel particles closer to true spheres can be obtained.

  The liquid may be lipophilic or hydrophilic, and can be appropriately selected depending on the properties of the silica sol. When the silica sol is an aqueous sol, the liquid is preferably lipophilic (immiscible with water). In this case, the liquid includes vegetable oil such as soybean oil, corn oil, olive oil and coconut oil, liquid oil such as kerosene; toluene, xylene, chlorobenzene, hexane, cyclohexane, ethyl acetate, butyl acetate, methyl isobutyl ketone, An organic solvent such as chloroform may be included. Among these, vegetable oil is preferably used. This is because it is inexpensive and excellent in safety.

  The liquid can contain optional ingredients. Examples of the optional component include a surfactant. By using a surfactant, it is easier to obtain monodispersed silica sol particles, and the stability of the silica sol particles in the liquid can be improved. Moreover, when performing the gelation process mentioned later by a batch type after collect | recovering the liquid mixture of a silica sol and a liquid, it can suppress that a silica sol gelatinizes under a laminar flow. Specific examples of the surfactant include nonionic surfactants and ionic surfactants. Preferably, a nonionic surfactant is used. Examples of the nonionic surfactant include sorbitol derivatives such as sorbitan alkylate; glycerin derivatives such as glycerin alkylate; and polyethylene glycol derivatives such as polyethylene glycol alkylate. These may be used alone or in combination of two or more. Among these, sorbitan monooleate, sorbitan monostearate, glycerol monostearate or a mixture thereof is preferably used. A surfactant having any appropriate HLB can be used depending on the type of the liquid oil and the organic solvent. Specifically, when the liquid contains vegetable oil such as soybean oil, the HLB of the surfactant is preferably 3.0 to 9.0.

  The viscosity of the liquid can be set to any appropriate value depending on, for example, the desired particle diameter of silica gel. It is preferably 0.28 to 500 mPa · s, more preferably 1 to 500 mPa · s, still more preferably 1 to 200 mPa · s, and particularly preferably 2 to 100 mPa · s. This is because a more stable laminar flow state can be formed.

  The contact angle between the liquid and the second flow path is preferably 0 to 40 °, more preferably 0 to 30 °, and particularly preferably 0 to 20 °.

  The silica sol and / or liquid is preferably subjected to defoaming treatment in advance. It is because generation | occurrence | production of a bubble etc. can be suppressed and the silica gel particle excellent in monodispersibility can be obtained. Specific examples of the defoaming process include a decompression process.

  By using the above-described microreactor, the silica sol and the liquid can form a laminar flow at the confluence point and the confluence channel of the microreactor. By bringing silica sol and liquid into contact in a laminar flow state, silica sol particles having a shape along the liquid / liquid interface can be stably generated in the direction of flow path, and extremely stable in a two-phase system (liquid / liquid). Reaction (for example, gelation) becomes possible. Further, by combining the first flow path and the second flow path in a three-dimensional manner, the silica sol and the liquid can be brought into more uniform contact in a laminar flow state, and the liquid column of the silica sol that has merged with the liquid is more uniform. Silica gel particles with better monodispersity can be obtained. Furthermore, silica gel particles closer to true spheres can be obtained.

  The Reynolds number of the laminar flow is preferably 0.1 to 1000, more preferably 0.1 to 500, still more preferably 0.1 to 200, and particularly preferably 0.1 to 100. With such a very small Reynolds number, it is possible to control the liquid width after merging by adjusting the flow rate ratio and flow rate ratio between the silica sol and the liquid. As a result, silica gel particles having a desired size can be generated very accurately. Further, by controlling the Reynolds number within the above range, even if the flow rate of the silica sol and / or liquid in the microreactor is increased, the laminar flow state is hardly disturbed and the productivity can be improved.

  The silica sol is preferably supplied continuously (ie substantially rectified) to the first flow path. The liquid is preferably continuously supplied to the second flow path. Arbitrary appropriate methods can be employ | adopted for the supply method to the said flow path of a silica sol and a liquid.

  The ratio between the flow rate of the silica sol and the flow rate of the liquid can be set to any appropriate value depending on, for example, the desired particle diameter of the silica gel. The ratio is preferably 1: 0.3 to 1: 4, more preferably 1: 0.5 to 1: 2, and particularly preferably 1: 0.7 to 1: 1.5. The liquid column of the silica sol that merged with the liquid can be more evenly divided, and silica gel particles with better monodispersity can be obtained. Furthermore, silica gel particles closer to true spheres can be obtained. The flow rate of the silica sol is preferably 0.5 to 50 mm / second, more preferably 1 to 30 mm / second, and particularly preferably 2 to 15 mm / second. The flow rate of the liquid is preferably 0.3 to 150 mm / second, more preferably 1 to 100 mm / second, and particularly preferably 2 to 50 mm / second. This is because the silica sol droplets formed by merging with the liquid can be prevented from being combined and separated. As a result, silica gel particles with better monodispersibility can be obtained. Furthermore, silica gel particles closer to true spheres can be obtained. In the present specification, “flow velocity” refers to linear velocity.

  Preferably, the silica sol flow rate is less than the liquid flow rate. This is because silica sol particles can be stably generated. Furthermore, by increasing the flow rate of the liquid, it is possible to prevent friction and blockage of the channel wall due to the generated silica sol particles in the merged channel. Specifically, the ratio of the silica sol flow rate to the liquid flow rate is preferably 1: 2 to 1: 5000, more preferably 1:10 to 1: 2500, and particularly preferably 1:50 to 1: 2000. . The flow rate of the silica sol is preferably 0.2 to 40 μl / min, more preferably 0.5 to 20 μl / min, and particularly preferably 1 to 10 μl / min. The flow rate of the liquid is preferably 50 to 10,000 μl / min, more preferably 100 to 5000 μl / min, and particularly preferably 200 to 2500 μl / min.

  Any appropriate method can be adopted as a method for gelling the silica sol (silica sol particles) in contact with the liquid. For example, a method of heating the silica sol, a method of adjusting the pH of the silica sol, a method of adding a curing agent (for example, a tin compound) to the silica sol, and the like can be mentioned. When employing the heating method, the heating is preferably performed in the microreactor (under laminar flow). This is because it can be gelled in a more stable sphere state. The heating temperature is preferably 40 to 95 ° C, more preferably 60 to 80 ° C. If the heating temperature is less than 40 ° C, the progress of gelation may be slow. On the other hand, if it exceeds 95 ° C., the gel produced by water vaporization / boiling may be destroyed. Specifically, the pH is adjusted by increasing the pH when the silica sol is acidic, and decreasing the pH when the silica sol is alkaline. When the silica sol is acidic, preferably the liquid contains a basic compound. The basic compound is preferably a compound that is soluble in both the liquid and water. As the basic compound, organic amines are preferably used. The basic compound can be diffused into the silica sol particles from the liquid / liquid interface to raise the pH, thereby promoting the curing reaction of the silica sol. As the organic amines, any of primary, secondary and tertiary amines can be used.

  The particle diameter of the silica gel particles can be controlled to any appropriate value depending on the particle diameter, porosity, etc. of the desired silica particles or silica airgel. The particle diameter can be controlled, for example, by appropriately adjusting the flow rate ratio of the silica sol and the liquid, the inner diameter of the outlet of the first flow path, the viscosity and surface tension of the liquid, the solid content concentration of the silica sol, and the like.

  The silica particles of the present invention can be obtained by subjecting the silica gel to any appropriate treatment. For example, the method of drying and / or baking the said silica gel is mentioned.

  The silica airgel of the present invention can be obtained by subjecting the silica gel to any appropriate treatment. For example, the silica gel (wet gel) and silylating agent are reacted and dried. Specifically, the silanol group (hydroxyl group) present on the pore surface of the silica gel reacts with the silylating agent (pore surface modification) to eliminate the reactivity of the silanol group, thereby drying the original gel skeleton. Returning to the form (springback), a silica aerogel can be obtained.

  As a specific example of the pore surface modification method, the silica gel (wet gel containing water) is introduced into an organic solvent miscible with water to convert the water in the pores into an organic solvent, and The method of making it react is mentioned. Here, it is preferable to sufficiently convert to an organic solvent and reduce the amount of water as much as possible. This is because if water remains, the silylating agent may be deactivated, and surface modification may not be performed sufficiently. Moreover, it is preferable to replace the organic solvent with an aprotic solvent that does not react with the silylating agent before the reaction with the silylating agent.

  As the organic solvent, an organic solvent miscible with water is preferably used. Specific examples include lower alcohols such as methanol, ethanol and isopropanol, acetone and tetrahydrofuran. Examples of the silylating agent include trimethylchlorosilane, hexamethyldisilazane, hexamethyldisiloxane, trimethylalkoxysilane, methyltrialkoxysilane, and the like. The silylating agent is preferably preliminarily dissolved and reacted in an aprotic solvent at a concentration of 0.1 to 10 wt%. The reaction temperature with the silylating agent is preferably about room temperature to 60 ° C. The reaction time is preferably 10 minutes to 2 days. Examples of the aprotic solvent include hexane, cyclohexane, toluene, kerosene, and the like.

  The drying performed after the reaction with the silylating agent is preferably performed after removing the unreacted silylating agent by solvent exchange or the like. Drying conditions are, for example, room temperature to 300 ° C. under atmospheric pressure or reduced pressure.

  The silica airgel obtained by the above-described method can have a pore surface hydrophobized and can be hydrophobic. As a result, it has water resistance, is hardly affected by moisture absorption, and can have stable characteristics in a low temperature region. In addition, by heat-treating this silica airgel (for example, 300 ° C. or more), the organic substance as the modifier can be thermally decomposed and vaporized, and a silica airgel having a hydrophilic pore surface can be obtained. This hydrophilic silica airgel is suitable for use in a high temperature region.

EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to these Examples. In addition, the particle diameter and CV value of the particle | grains obtained in each Example were measured by the method shown below. The viscosity and contact angle were measured by the methods shown below.
1. Particle diameter and CV value The obtained particles were observed with a microscope (manufactured by Keyence) and measured.
2. Viscosity Viscosity was measured with a vibration viscometer (VISCOMATE VM-1G).
3. Contact angle Measured with a contact angle meter (DM-500, manufactured by Kyowa Kagaku).

(Preparation of silica sol)
14.32 g of 10 wt% sodium silicate aqueous solution was added to 5.0 g of 6 mol / l hydrochloric acid, 9.32 g of water was further added, and the mixture was sufficiently stirred with a stirrer to prepare 5 wt% silica sol A. On the other hand, 18 g of water was added to 2.0 g of 10 w% sodium silicate aqueous solution and diluted to prepare a 1 wt% sodium silicate aqueous solution. The silica sol A had a pH of 2, and a silica sol having a pH of 3.8 was prepared by adding 0.16 g of a 1 wt% aqueous sodium silicate solution to 3.02 g of the silica sol A. The obtained silica sol had a viscosity of 5.1 mPa · s and a contact angle of 75 ° with the first flow path.

(Preparation of soybean oil solution)
30 g of sorbitan monooleate (Span 80) was added to 270 g of soybean oil and stirred well with a stirrer to prepare a soybean oil solution. The obtained soybean oil solution had a viscosity of 60 mPa · s and a contact angle of 15 ° with the second channel.

(Production of microreactor)
The microreactor shown in FIG. 3 is sliced into a number of thin cross-sections using a stereolithography apparatus (DEMEC Co., Ltd., trade name: SCS-1000HD), which is designed with 3D CAD data. Converted to two-dimensional slice data. A photo-curing resin (trade name: SCR950, manufactured by DEMEC Co., Ltd.) and an elevator are placed in the tank, and a laser (He-Cd laser, peak wavelength = 325 nm) is applied to the light in the tank based on the two-dimensional slice data. The surface of the curable resin was scanned to draw a cross-sectional shape. The laser spot size was φ50 μm. The portion irradiated with the laser was cured, and a cross section for one layer (thickness for one resin layer = 30 μm) was formed on the elevator. After that, the elevator descended one layer at a time, and several thin cross-sections were continuously laminated and three-dimensionally layered. Finally, by lifting the elevator, a three-dimensional layered model was taken out and subjected to post-processing to complete the microreactor shown in FIG.
As a flow path adjuster for the first flow path, a glass tube having a water repellent treated peripheral wall with a water repellent (trade name: Kapton, manufactured by Toray) containing a polyimide resin was inserted into the first flow path. .
The inner diameter of the outlet of the first channel of the obtained microreactor was 100 μm, and the inner diameter of the cross section of the second channel including the outlet of the first channel was 2 mm. The total length of the first flow path was 15 mm, and the total length of the second flow path was 15 mm.

(Preparation of silica gel)
Using the microreactor produced above, the silica sol obtained above was flowed into the first flow path, and the soybean oil solution obtained above was flowed into the second flow path. Both silica sol and soybean oil solution were continuously flowed using a syringe pump. The flow rate of silica sol is 2.0 μl / min (flow rate 4.2 mm / sec), the flow rate of soybean oil solution is 1000 μl / min (flow rate 4.4 mm / sec), and the flow rate ratio is 1: 500 (flow rate ratio is 1: 1.05). The silica sol and the soybean oil solution were brought into contact with each other at the junction of the microreactor, and a silica sol emulsion was prepared by the shearing force of the soybean oil solution.
The emulsion that passed through the microreactor was added to the soybean oil solution at 55 ° C. and heated to 55 ° C. to obtain silica gel. The silica gel was thoroughly washed with acetone. The obtained silica gel had a particle size of 131 μm and a CV value of 6.7%.

(Preparation of silica gel)
The silica gel was prepared in the same manner as in Example 1 except that the flow rate of the soybean oil solution was 1200 μl / min (flow rate 5.3 mm / sec) and the flow rate ratio was 1: 600 (flow rate ratio was 1: 1.24). Obtained. The obtained silica gel had a particle size of 103 μm and a CV value of 8.7%.

(Preparation of silica particles)
The silica gel obtained in Example 1 was dried at room temperature for 2 days and then calcined at 150 ° C. for 2 hours to obtain silica particles. The obtained silica particles had a particle size of 96 μm and a CV value of 7.3%.

(Preparation of silica airgel)
The silica gel obtained in Example 1 was put into ethanol, and the water in the gel pores was exchanged with ethanol. This operation was repeated twice. Next, it was put into hexane, and ethanol in the gel pores was exchanged with hexane. This operation was repeated twice. To this was added a hexane solution of trimethylchlorosilane and allowed to react at room temperature for 15 hours. Thereafter, it was washed with hexane, dried at room temperature, and finally dried at 150 ° C. for 2 hours to obtain a silica airgel. The particle diameter of the silica airgel obtained was 129 μm, which was almost the same as the particle diameter of the original silica gel, and the CV value was 7.2%.

  Each of the particles obtained in Examples 1 to 4 exhibited an excellent CV value despite having a relatively large particle size.

  The silica particles of the present invention are suitably used as a functional filler for, for example, a spacer of a liquid crystal display device or a sealing material for a semiconductor element. Moreover, the silica airgel of this invention is used suitably as a heat insulating material, a soundproof material, and a functional filler, for example.

(A) is the schematic which looked at the microreactor used for the manufacturing method by preferable embodiment of this invention from upper direction, (b) is sectional drawing seen from the flow path direction of the microreactor. It is a perspective view of the microreactor in FIG. (A) is the schematic seen from the microreactor used for the manufacturing method by another preferable embodiment of this invention, (b) is sectional drawing seen from the flow-path direction of the microreactor. 2 is an observation photograph of silica gel particles obtained in Example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Microreactor 20 Flow path adjustment tool 1 1st flow path 2 2nd flow path 3 Merge flow path 4 Partition 1a Supply port to 1st flow path 2a Supply port to 2nd flow path 2a '2nd Supply port to the flow path of 3a

Claims (15)

Supplying a silica sol to the first flow path;
Supplying a liquid to the second flow path;
Contacting the silica sol and the liquid in a laminar flow state at a junction where the first flow path and the second flow path merge;
And a step of gelling the silica sol in contact with the liquid.   The method for producing silica gel according to claim 1, wherein the second flow path is formed so as to surround an outlet of the first flow path.   The method for producing silica gel according to claim 1 or 2, wherein the shape of the outlet of the first flow path is substantially circular.   The method for producing silica gel according to any one of claims 1 to 3, wherein an inner diameter of the outlet of the first flow path is 10 to 300 µm.   The method for producing silica gel according to any one of claims 1 to 4, wherein a contact angle between the first flow path and the silica sol is 45 to 100 °.   The method for producing silica gel according to any one of claims 1 to 5, wherein the laminar flow has a Reynolds number of 0.1 to 1000.   The method for producing silica gel according to any one of claims 1 to 6, wherein a ratio of a flow rate of the silica sol and a flow rate of the liquid is 1: 0.3 to 1: 4.   The method for producing silica gel according to any one of claims 1 to 7, wherein the silica sol is prepared by adjusting the pH of water glass.   The manufacturing method of the silica gel in any one of Claim 1 to 8 whose solid content concentration of the said silica sol is 0.5-20 wt%.   The method for producing silica gel according to any one of claims 1 to 9, wherein the liquid has a viscosity of 0.28 to 500 mPa · s.   The method for producing silica gel according to any one of claims 1 to 10, wherein the gelation is performed by adjusting a pH of the silica sol.   A silica gel obtained by the production method according to claim 1.   The silica gel according to claim 12, wherein the CV value is 20% or less.   The silica particle obtained by drying and / or baking the silica gel of Claim 12 or 13.   A silica airgel obtained by reacting the silica gel according to claim 12 or 13 with a silylating agent.