JP2013067521A - Method for producing silica particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing silica particles which suppresses variation in properties of silica particles obtained through a step of bringing supercritical carbon dioxide into contact with silica particles.SOLUTION: The method for producing silica particles includes a first step of bringing supercritical carbon dioxide into contact with a silica particle dispersion or silica particles contained in a treatment vessel by introducing the supercritical carbon dioxide into the treatment vessel and discharging it, and a second step of detecting information on supercritical carbon dioxide discharged from the treatment vessel and terminating the first step based on the detected information.

Description

  The present invention relates to a method for producing silica particles.

Patent Document 1 discloses that a gel having a skeleton of (SiO ₂ ) _m (m is a positive integer) and having a silanol group is hydrophobized with a silylating agent that generates ammonia as a by-product during hydrophobizing treatment. In producing hydrophobic airgel by hydrophobizing using the agent and then supercritical drying, the treated liquid after the hydrophobized treatment is brought into contact with carbon dioxide, and ammonia in the treated liquid is precipitated as ammonium carbonate. And a process for producing a hydrophobic airgel that can be removed in the past ”.

  Patent Document 2 discloses a “processing step of forming toner particles in a liquid medium, filtering the toner particles to obtain a wet cake, and contacting the wet cake with at least one of a supercritical fluid and a subcritical fluid. Has been proposed.

  Patent Document 3 states that “a wet cake in which fluorenone-based bisazo pigment particles represented by the following general formula (I) are formed in a liquid solvent and the fluorenone-based bisazo pigment is collected by filtration or a crude dried product obtained by drying the wet cake. Contacting with a mixed fluid of an entrainer with at least one of a supercritical fluid and a subcritical fluid, or contacting with a fluid that can be used as the entrainer, and then contacting with at least one of a supercritical fluid and a subcritical fluid A method for producing a fluorenone-based bisazo pigment having a treatment step has been proposed.

In Patent Document 4, “a method of recovering a surfactant from a water-carbon dioxide system containing at least one surfactant, contacting the water-carbon dioxide system with a dehydrating agent to remove water, The present invention also relates to a method for recovering a surfactant, and the present invention relates to a circulation line for circulating a mixed system containing carbon dioxide, a surfactant and / or a cosolvent compatible with carbon dioxide, and an object to be removed. A method for selectively removing the removal target incorporated in the surfactant and / or cosolvent by providing a selective removal device for the removal target and circulating the mixed system has been proposed.
In addition, Patent Documents 5 to 6 propose methods for selectively removing a removal target by providing an apparatus for selectively removing the removal target in the circulation line.

  Patent Document 7 states that “a processed product of vegetables containing lycopene is finally dehydrated with 90% or more of ethyl alcohol, and then the dehydrated product is extracted with supercritical carbon dioxide, and the extract is converted into vegetable oil. A method for producing lycopene oil characterized by dissolving "has been proposed.

  Patent Document 8 proposes “a purified extract obtained by removing a low-polar fraction by a supercritical extraction method using a carbon polar solvent extract as a solvent and carbon dioxide gas” as a solvent.

JP 11-335115 A JP 2006-3513 A JP 2007-332350 A International Publication 2004/112952 Pamphlet JP 2003-249475 A JP 2009-297665 A Japanese Unexamined Patent Publication No. 7-147929 JP 2003-342157 A

  The subject of this invention is providing the manufacturing method of the silica particle which suppressed the characteristic fluctuation | variation of the silica particle obtained through the process made to contact a supercritical carbon dioxide.

The above problem is solved by the following means. That is,
The invention according to claim 1
A first step of introducing and discharging supercritical carbon dioxide into a treatment tank containing silica particle dispersion or silica particles, and bringing the supercritical carbon dioxide into contact with the silica particle dispersion or silica particles;
Detecting the information of supercritical carbon dioxide discharged from the treatment tank, and based on the detected information, a second step of stopping the first step;
The manufacturing method of the silica particle which has this.

The invention according to claim 2
The first step is a step of introducing hexamethyldisilazane (HMDS) into the treatment tank to perform a hydrophobic treatment of the silica particles;
The second step introduces and discharges supercritical carbon dioxide into the treatment tank, detects the ammonia concentration contained in the supercritical carbon dioxide discharged from the treatment tank, and based on the detected ammonia concentration, The method for producing silica particles according to claim 1, which is a step of stopping the first step.

According to the first aspect of the present invention, the supercritical carbon dioxide discharged from the treatment tank is detected, and the supercritical carbon dioxide is detected based on the detected information as compared with the case where the contact of the supercritical carbon dioxide is not stopped. It is possible to provide a method for producing silica particles that suppresses fluctuations in characteristics of the silica particles obtained through the contacting step.
According to the invention which concerns on Claim 2, when introducing the hexamethyldisilazane (HMDS) into a processing tank and performing the hydrophobic treatment of a silica particle, the ammonia concentration contained in the supercritical carbon dioxide discharged | emitted from the processing tank is set. It is possible to provide a method for producing silica particles that is detected and suppresses fluctuations in the properties of the resulting silica particles as compared to when the contact of supercritical carbon dioxide is not stopped based on the detected ammonia concentration.

It is a schematic block diagram which shows the manufacturing apparatus of the silica particle which concerns on this embodiment.

  Hereinafter, an embodiment which is an example of the present invention will be described in detail.

  FIG. 1 is a schematic configuration diagram showing an apparatus for producing silica particles according to the present embodiment.

As shown in FIG. 1, the silica particle manufacturing apparatus 101 according to the present embodiment stores, for example, a silica particle dispersion containing silica particles and a dispersion medium (hereinafter referred to as a solvent), and processes the silica particle dispersion. A supercritical carbon dioxide introduction / discharge mechanism 20 (introduction / discharge) that introduces / discharges supercritical carbon dioxide to / from the treatment tank 10 to bring the supercritical carbon dioxide into contact with the silica particles or the dispersion medium. An example of mechanism means) and hexamethyldisilazane introduction mechanism 60 (example of hexamethyldisilazane introduction means) for introducing hexamethyldisilazane (HMDS) into the treatment tank 10 in order to hydrophobize the surface of the silica particles: Hereinafter, the HMDS introduction mechanism 60) and a solvent amount detector 71 (an example of detection means) for detecting the amount of solvent contained in the supercritical carbon dioxide discharged from the processing tank 10 When provided with a ammonia concentration meter 72 for detecting an ammonia concentration in the supercritical carbon dioxide was discharged from the processing tank 10 (an example of detecting means), a. However, the solvent amount detector 71 is provided as necessary.
The silica particle manufacturing apparatus 101 according to the present embodiment includes a control unit 80 that controls the operation of the silica particle manufacturing apparatus 101.
In FIG. 1, SA indicates the silica particle dispersion or silica particles after removal of the solvent, and SB indicates the solvent.

The treatment tank 10 is, for example, a treatment tank that performs a treatment for removing the dispersion medium from the silica particle dispersion (so-called drying treatment) and a hydrophobic treatment for hydrophobizing the surface of the silica particles.
As the processing tank 10, for example, a high-pressure processing tank having a stirring blade such as an anchor and a heating source such as a heater is applied in order to perform the above processing. In the figure, 11 indicates a stirring blade.

  The supercritical carbon dioxide introduction / discharge mechanism 20 includes, for example, a supercritical carbon dioxide introduction unit 30, a supercritical carbon dioxide discharge unit 40, and a supercritical carbon dioxide regeneration unit 50.

The supercritical carbon dioxide introduction unit 30 includes a liquefied carbon dioxide storage tank 31 that stores liquefied carbon dioxide (liquid carbon dioxide), and a supercritical carbon dioxide that brings the liquefied carbon dioxide into a supercritical state, that is, generates supercritical carbon dioxide. A carbon generating unit 32.
In addition, the supercritical carbon dioxide introduction unit 30 is also provided with a liquefied carbon dioxide introduction pipe 35 that connects the liquefied carbon dioxide storage tank 31 and the supercritical carbon dioxide generation unit 32.
The supercritical carbon dioxide introduction part 30 is also provided with a supercritical carbon dioxide introduction pipe 36 that connects the supercritical carbon dioxide generation part 32 and the treatment tank 10. An opening / closing valve 37 (for example, a severe condition valve HN series manufactured by Swagelok Co., Ltd.) is provided in the course of the supercritical carbon dioxide introduction pipe 36.

The supercritical carbon dioxide generating unit 32 is, for example, a heating source 33 (for example, a heater) that heats the liquefied carbon dioxide provided in the course of the liquefied carbon dioxide introduction pipe 35 and a high pressure that applies pressure to the liquefied carbon dioxide. And a pump 34.
In the supercritical carbon dioxide generating unit 32, the temperature and pressure exceeding the critical point are applied to the liquefied carbon dioxide introduced from the liquefied carbon dioxide storage tank 31 through the liquefied carbon dioxide introduction pipe 35 by the heating source 33 and the high pressure pump 34. Apply and make liquefied carbon dioxide critical, generating supercritical carbon dioxide.

The supercritical carbon dioxide discharge unit 40 includes a separation tank 41 for separating the supercritical carbon dioxide and the solvent contained therein from the supercritical carbon dioxide discharged from the processing tank 10.
Further, the supercritical carbon dioxide discharge section 40 is provided with a supercritical carbon dioxide discharge pipe 42 that connects the separation tank 41 and the processing tank 10. An opening / closing valve 43 (for example, a severe condition valve HN series manufactured by Swagelok Co., Ltd.) is provided in the course of the supercritical carbon dioxide discharge pipe 42.

The separation tank 41 is provided with a cooling device (not shown). The cooling device reduces the pressure of supercritical carbon dioxide containing the solvent, lowers the temperature, cancels the supercritical state, and increases the solubility of carbon dioxide in the solvent. Reduce and separate gaseous carbon dioxide and solvent.
The separated solvent is stored and recovered at the bottom of the separation tank 41. On the other hand, gaseous carbon dioxide is sent to the supercritical carbon dioxide regeneration unit 50.

The supercritical carbon dioxide regeneration unit 50 includes a carbon dioxide liquefaction tank 51 that liquefies gaseous carbon dioxide.
The supercritical carbon dioxide regeneration section 50 is also provided with a vaporized carbon dioxide discharge pipe 52 that connects the carbon dioxide liquefaction tank 51 and the separation tank 41.
The supercritical carbon dioxide regeneration unit 50 is also provided with a liquefied carbon dioxide introduction pipe 53 that connects the carbon dioxide liquefaction tank 51 and the liquefied carbon dioxide storage tank 31.

  In the carbon dioxide liquefaction tank 51, the inside of the tank is set to a high pressure, and pressure is applied to gaseous carbon dioxide to cause liquefaction. The liquefied liquid carbon dioxide is introduced into the liquefied carbon dioxide storage tank 31 through the liquefied carbon dioxide introduction pipe 53 and reused.

  Although the supercritical carbon dioxide introduction / discharge mechanism 20 is provided with a supercritical carbon dioxide regeneration unit 50 and reuses carbon dioxide, the present invention is not limited to this. For example, the embodiment does not reuse carbon dioxide. In other words, the liquid carbon dioxide may be supplied to the liquefied carbon dioxide storage tank 31 from the outside, or the liquefied carbon dioxide storage tank 31 may be replaced.

The HMDS introduction mechanism 60 includes a HMDS storage tank 61 that stores hexamethyldisilazane (HMDS).
The HMDS introduction mechanism 60 is also provided with an HMDS introduction pipe 62 that connects the HMDS storage tank 61 and the processing tank 10. An introduction pump 63 and an opening / closing valve 64 (for example, a severe condition valve HN series manufactured by Swagelok Co., Ltd.) are provided in the middle of the route of the HMDS introduction pipe 62.

The solvent amount detector 71 is, for example, a concentration sensor that measures the ratio (solvent concentration) of the solvent contained in the supercritical carbon dioxide discharged from the processing tank 10, and the weight of the solvent separated and stored at the bottom of the separation tank 41. A meter for measuring, a level meter for measuring the liquid level of the solvent separated and stored in the bottom of the separation tank 41, and the like can be mentioned.
In the present embodiment, as the solvent amount detector 71, a mode is shown in which a meter for measuring the weight of the solvent separated and stored in the bottom of the separation tank 41 is provided in the separation tank 41.
Of course, as the solvent amount detector 71, two or more concentration sensors, level meters, and metering meters may be provided.

The ammonia concentration meter 72 is provided inside the supercritical carbon dioxide discharge pipe 42 in order to detect the ammonia concentration contained in the supercritical carbon dioxide discharged from the treatment tank 10.
When the ammonia concentration meter 72 is discharged from the treatment tank 10 together with supercritical carbon dioxide, for example, ammonia generated by the hydrophobization reaction on the surface of the silica particles with hexamethyldisilazane (HMDS), which is a hydrophobizing agent. A concentration meter that measures the concentration of ammonia contained in the supercritical carbon dioxide, for example, a laser gas analyzer (manufactured by Toko Keiki Co., Ltd .: GM700) or the like is applied.

The control unit 80 is connected to each part (for example, various pumps, various opening / closing valves, various heating sources, a solvent amount detector, an ammonia concentration meter 72, etc.) of the silica particle manufacturing apparatus 101 so that signals are transmitted and received. Yes.
Although not shown, the control unit 80 is configured as a computer, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a nonvolatile memory, and an input / output interface (I / O). In the I / O, each part of the silica particle production apparatus 101 (for example, various pumps, various open / close valves, various heating sources, a solvent amount detector, an ammonia concentration meter 72 is provided. Etc.) are connected.
The nonvolatile memory stores a control program for processing (for example, solvent removal processing, hydrophobization processing, etc.), various table data, and the like. The control program stored in the nonvolatile memory is read and executed by the CPU. The control program may be provided by a recording medium such as a CD-ROM or a DVD-ROM USB memory.

Next, the manufacturing method of the silica particle which concerns on this embodiment is demonstrated.
Here, the manufacturing method of the silica particle which concerns on this embodiment is performed as a process performed in the control part 80 of the silica particle manufacturing apparatus which concerns on this embodiment.

-Silica particle dispersion containing step-
First, the silica particle dispersion is accommodated in the treatment tank 10.

The silica particle dispersion to be accommodated is, for example, a silica particle dispersion containing silica particles and a solvent (for example, alcohol and water).
The silica particle dispersion may be prepared by, for example, a wet method (for example, a sol-gel method). In particular, the silica particle dispersion is subjected to a sol-gel method as a wet process, specifically, a tetraalkoxylane in the presence of an alkali solvent obtained by adding an alkali solvent to an alcohol and water solvent (hydrolysis reaction, condensation reaction). It is preferable that the particles are produced by generating silica particles.
The silica particles may be formed in a spherical shape or an irregular shape.

Here, the silica particle dispersion to be contained preferably has a mass ratio of water to alcohol of, for example, 0.01 or more and 0.5 or less, desirably 0.05 or more and 0.35 or less, and more desirably 0. .1 or more and 0.3 or less.
If the water mass ratio is less than 0.01, the water content of the dried silica particles after removal of the solvent will be low, and therefore the degree of hydrophobicity may not be so high even if a hydrophobic treatment is performed. If the mass ratio of water exceeds 0.5, excessive water will be present in the silica particle dispersion at the time of depressurization in the step of removing the solvent by supercritical carbon dioxide, which will be described later, and the pressure will be reduced to atmospheric pressure. When the water is evaporated, liquid crosslinking force of the silica particles is likely to be generated, and coarse powder tends to be easily generated.

Further, the silica particle dispersion to be stored preferably has a mass ratio of water to silica particles of, for example, 0.02 or more and 3 or less, preferably 0.05 or more and 1 or less, more preferably 0.1 or more and 0.00. 5 or less.
If the mass ratio of water is less than 0.02, the volatile matter (for example, moisture) of the dried silica particles after removing the solvent will be low, so that the hydrophobizing agent is not sufficiently hydrolyzed during the hydrophobizing treatment. As a result, the degree of hydrophobicity may not be so high. Moreover, when the mass ratio of water exceeds 3, when water is excessively present in the silica particle dispersion at the time of depressurization in the step of removing the solvent by supercritical carbon dioxide, which will be described later, the pressure is reduced to atmospheric pressure. In addition, due to the evaporation of water, liquid crosslinking force of silica particles is likely to be generated, and coarse powder tends to be easily generated.

Further, the silica particle dispersion to be accommodated has a mass ratio of silica particles to the silica particle dispersion of, for example, 0.05 to 0.5, preferably 0.1 to 0.45, more preferably 0. .2 or more and 0.4 or less.
When the mass ratio of the silica particles is less than 0.05, productivity may be deteriorated. On the other hand, when the mass ratio of the silica particles exceeds 0.5, the silica particles are gelated in the step of removing the solvent by supercritical carbon dioxide, which will be described later, and coarse powder tends to be easily generated.

-Solvent removal treatment process-
Next, supercritical carbon dioxide is introduced into and discharged from the treatment tank 10, and the supercritical carbon dioxide is brought into contact with the dispersion medium of the silica particle dispersion to perform a solvent removal treatment of the silica particle dispersion.

Specifically, for example, the stirring blade 11 is rotated to open the opening / closing valve 37 and the opening / closing valve 43 is closed to drive the high-pressure pump 34, and the liquefied carbon dioxide is treated through the supercritical carbon dioxide introduction pipe 36. Fill inside.
Next, while driving the high-pressure pump 34, the heating source (not shown) of the processing tank 10 is driven together with the heating source 33 of the supercritical carbon dioxide generating unit 32, and the temperature of the liquid carbon dioxide is increased and the pressure is increased. State.
Next, the opening / closing valve 43 is opened, and supercritical carbon dioxide is introduced into and discharged from the processing tank 10.
As a result, the supercritical carbon dioxide dissolves the solvent (alcohol and water) and is accompanied by the solvent to the outside of the silica particle dispersion (outside of the treatment tank 10), thereby removing the solvent.

  In addition, the start of the solvent removal processing of the silica particle dispersion is performed by, for example, turning on the power of the silica particle manufacturing apparatus 101 or receiving a signal for starting the solvent removal processing of the silica particle dispersion by user operation. Perform by Taka etc.

  Here, supercritical carbon dioxide is carbon dioxide in a state of temperature and pressure above the critical point, and has both gas diffusibility and liquid solubility.

The temperature condition of the solvent removal treatment, that is, the temperature of supercritical carbon dioxide is, for example, preferably 31 ° C. or higher and 350 ° C. or lower, preferably 60 ° C. or higher and 300 ° C. or lower, more preferably 80 ° C. or higher and 250 ° C. or lower.
When this temperature is less than the above range, the solvent is difficult to dissolve in supercritical carbon dioxide, and thus it may be difficult to remove the solvent. Moreover, coarse powder may be easily generated due to the liquid crosslinking force of a solvent or supercritical carbon dioxide. On the other hand, when this temperature exceeds the above range, coarse powder such as secondary aggregates may be easily generated due to condensation of silanol groups on the surface of the hydrophilic silica particles.

  Further, the temperature condition of the solvent removal treatment varies depending on the mass ratio of water to alcohol in the silica particle dispersion. Water tends to be less soluble in supercritical carbon dioxide than alcohol, but the solubility tends to increase by raising the temperature of supercritical carbon dioxide.

On the other hand, the pressure condition of the solvent removal treatment, that is, the pressure of supercritical carbon dioxide is, for example, 7.38 MPa or more and 40 MPa or less, desirably 10 MPa or more and 35 MPa or less, and more desirably 15 MPa or more and 25 MPa or less.
If this pressure is less than the above range, the solvent tends to be difficult to dissolve in supercritical carbon dioxide. On the other hand, if the pressure exceeds the above range, the equipment tends to be expensive.

-Solvent removal treatment stop process-
Next, the amount of solvent contained in the supercritical carbon dioxide discharged from the treatment tank 10 is detected, and the solvent removal process is stopped based on the detected amount of solvent.

Specifically, for example, first, the amount of solvent contained in the supercritical carbon dioxide discharged from the processing tank 10 by the solvent amount detector 71 (the cumulative amount of solvent: that is, the amount of solvent removed from the silica particle dispersion). ) Is detected.
Then, it is determined whether or not the amount of solvent (solvent removal amount) contained in the discharged supercritical carbon dioxide has reached a predetermined amount. When the amount reaches a predetermined amount, the solvent removal process is stopped.
The solvent removal process is stopped, for example, by closing the open / close valve 37 to stop the introduction of supercritical carbon dioxide into the processing tank 10 and driving the heating source 33 and the high-pressure pump 34 of the supercritical carbon dioxide generator 32. Then, the driving of the heating source (not shown) of the processing tank 10 is stopped, the inside of the processing tank 10 is reduced to a predetermined internal pressure, and then the on-off valve 43 is closed.
In this way, the solvent removal process is stopped.

Here, the solvent amount (solvent removal amount), which is a set value for stopping the solvent removal treatment, is obtained in advance by experimentation or the like for the moisture (residual moisture amount) of the silica particles after removal of the target solvent. Specifically, the solvent amount (solvent removal amount) was obtained by adding the silica particle solid content amount obtained from the silica particle concentration in the silica dispersion solution from the total amount of the silica particle dispersion solution and the solvent amount (volatilization) content after the solvent removal. Find by subtracting the amount.
Then, the solvent amount (solvent removal amount), which is a set value for stopping the solvent removal process obtained in advance, is stored in the ROM, RAM, or nonvolatile memory, and detected by the solvent amount detector 71 (meter). By comparing with the result, it is determined whether or not the solvent removal process is stopped.
In the present embodiment, the solvent amount (solvent removal amount) is detected by a meter that measures the weight of the solvent separated and stored at the bottom of the separation tank 41 as the solvent amount detector 71.

-Hydrophobization process-
Next, while introducing hexamethyldisilazane (HMDS) into the treatment tank 10 and introducing and discharging supercritical carbon dioxide, the silica particles of the silica particle dispersion are in contact with the supercritical carbon dioxide ( In other words, the silica particles are hydrophobized in supercritical carbon dioxide.

Specifically, for example, after the solvent removal process is stopped, the introduction pump 63 is driven, the opening / closing valve 64 is opened, and hexamethyldisilazane (HMDS) is treated from the HMDS storage tank 61 through the HMDS introduction pipe 62. 10 is introduced.
Next, the agitating blade 11 is rotated, the opening / closing valve 37 is opened, the opening / closing valve 43 is closed, the high-pressure pump 34 is driven, and the treatment tank 10 is filled with liquefied carbon dioxide through the supercritical carbon dioxide introduction pipe 36. .
Thereafter, the high-pressure pump 34 is driven to raise the temperature and pressure of the liquid carbon dioxide in the treatment tank 10 to be in a supercritical state, and then the opening and closing valve 37 is closed to set the temperature and pressure at which the supercritical state is established. Hold for hours.
Next, after holding for a predetermined time, the opening / closing valve 37 and the opening / closing valve 43 are opened, and the heating source 33 and the high-pressure pump 34 of the supercritical carbon dioxide generating unit 32 are driven to bring the supercritical carbon dioxide into the treatment tank 10. Introduce, discharge, and distribute carbon.
Thereby, in the supercritical carbon dioxide, hexamethyldisilazane (HMDS) is reacted to perform the hydrophobic treatment of the silica particles.

In the hydrophobization treatment step, the amount of silica particles relative to the volume of the treatment tank 10 (that is, the charged amount) is, for example, 50 g / L or more and 600 g / L or less, desirably 100 g / L or more and 500 g / L or less, more desirably. 150 g / L or more and 400 g / L or less.
When this amount is less than the above range, the concentration of the hydrophobic treatment agent with respect to supercritical carbon dioxide is lowered, the contact probability with the silica surface is lowered, and the hydrophobic reaction is difficult to proceed. On the other hand, if this amount is larger than the above range, the concentration of the hydrophobic treatment agent with respect to supercritical carbon dioxide becomes high, and the hydrophobic treatment agent cannot be completely dissolved in supercritical carbon dioxide, resulting in poor dispersion and easy generation of coarse aggregates. Become.

The density of supercritical carbon dioxide is, for example, 0.10 g / ml or more and 0.60 g / ml or less, preferably 0.10 g / ml or more and 0.50 g / ml or less, more preferably 0.2 g / ml or more and 0 or less. .30 g / ml or less).
When this density is lower than the above range, the solubility of the hydrophobic treating agent in supercritical carbon dioxide tends to decrease, and aggregates tend to be generated. On the other hand, when the density is higher than the above range, the diffusibility to the silica pores is lowered, and thus the hydrophobization treatment may be insufficient. In particular, sol-gel silica containing a large amount of silanol groups needs to be hydrophobized in the above density range.
The density of supercritical carbon dioxide is adjusted by temperature, pressure, and the like.

  The amount of hexamethyldisilazane (HMDS) introduced is not particularly limited, but in order to obtain a hydrophobizing effect, for example, it is preferably 1% by mass to 60% by mass with respect to the silica particles, desirably It is 5 mass% or more and 40 mass% or less, More desirably, it is 10 mass% or more and 30 mass% or less.

Here, the temperature condition of the hydrophobization treatment (temperature condition under reaction), that is, the temperature of supercritical carbon dioxide is, for example, 80 ° C. or more and 300 ° C. or less, preferably 100 ° C. or more and 300 ° C. or less, more preferably 150 ° C. It is at least 250 ° C.
When this temperature is less than the above range, the reactivity between the hydrophobizing agent and the surface of the hydrophilic silica particles decreases. On the other hand, when the temperature exceeds the above range, the condensation reaction between the silanol groups of the hydrophilic silica particles proceeds, and as a result, the reaction sites are reduced and the degree of hydrophobicity may not be improved. In particular, a sol-gel silica containing a large amount of silanol groups needs to be hydrophobized in the above temperature range.

  On the other hand, the pressure condition of the hydrophobization treatment (temperature condition under reaction), that is, the pressure of supercritical carbon dioxide may be a condition that satisfies the above-mentioned density. 25 MPa or less, more desirably 15 MPa or more and 20 MPa or less.

-Hydrophobic treatment stop process-
Next, the ammonia concentration contained in the supercritical carbon dioxide discharged from the treatment tank 10 is detected, and the hydrophobization process is stopped based on the detected ammonia concentration.
Specifically, first, the ammonia concentration meter 72 detects the ammonia concentration contained in the supercritical carbon dioxide discharged from the treatment tank 10.
Then, it is determined whether the ammonia concentration contained in the discharged supercritical carbon dioxide has reached a predetermined concentration or less. When the ammonia concentration has reached a predetermined concentration or less, the hydrophobization process is stopped.
That is, since the reaction of hexamethyldisilazane (HMDS) accompanying the hydrophobization treatment generates ammonia, when the produced ammonia is discharged from the treatment tank 10 together with the supercritical carbon dioxide, it is distributed (introduction / discharge). ) Measure the concentration of ammonia contained in the supercritical carbon dioxide, determine whether it has reached a predetermined concentration or less, and if it has reached a predetermined concentration or less, flow of supercritical carbon dioxide (that is, processing) The introduction / discharge of supercritical carbon dioxide into the tank 10 is stopped.

For example, the hydrophobization process is stopped by closing the open / close valve 37 and stopping the introduction of the supercritical carbon dioxide into the processing tank 10 and driving the heating source 33 and the high-pressure pump 34 of the supercritical carbon dioxide generator 32. Then, the driving of the heating source (not shown) of the processing tank 10 is stopped, the inside of the processing tank 10 is reduced to a predetermined internal pressure, and then the on-off valve 43 is closed.
In this way, the hydrophobization process is stopped.

Here, the ammonia concentration, which is a set value for stopping the hydrophobization treatment, is obtained in advance by experiments or the like from the ammonia concentration of the target silica particles after the hydrophobization treatment. Specifically, supercritical carbon dioxide is circulated (contacted) to hydrophobized silica particles with known ammonia concentration, and the ammonia concentration contained in supercritical carbon dioxide after distribution (contact) is measured. A calibration curve is created from the measured values.
Then, the ammonia concentration (the calibration curve), which is a set value for stopping the hydrophobization treatment obtained in advance, is stored in the ROM, RAM, or nonvolatile memory, and detected by the solvent amount detector 71 (meter). By comparing with the result, it is determined whether or not the solvent removal process is stopped.

-Other processes-
In the solvent removal process and the hydrophobization process, the supercritical carbon dioxide discharged from the processing tank 10 is sent to the separation tank 41 through the supercritical carbon dioxide discharge pipe 42, and the supercritical state is released in the separation tank 41. And separated from ammonia.
The separated solvent and ammonia are stored at the bottom of the separation tank 41 and then collected.
The supercritical carbon dioxide discharged and the ammonia contained therein may be separated by adjusting the temperature and pressure at the stage of moving to the separation tank 41.

  The supercritical state is released, and the separated gaseous carbon dioxide is sent to the carbon dioxide liquefaction tank 51 through the vaporized carbon dioxide discharge pipe 52, pressurized in the carbon dioxide liquefaction tank 51, liquefied, and then liquefied carbon dioxide. It is again introduced into the liquefied carbon dioxide storage tank 31 through the carbon introduction pipe 53 and reused.

  The manufacturing method of the silica particle which concerns on this embodiment is complete | finished through the above process (process). And the above process (process) is repeatedly performed as 1 cycle, and the manufacturing method of the silica particle which concerns on this embodiment is performed.

In the present embodiment described above, after the silica particle dispersion is accommodated in the treatment tank 10, supercritical carbon dioxide is introduced into and discharged from the treatment tank 10, and the supercritical carbon dioxide is brought into contact with the silica particles or the dispersion medium. The process (in this embodiment, a solvent removal process process, a hydrophobization process process) is made.
Then, information on the supercritical carbon dioxide discharged from the treatment tank 10 (in this embodiment, the amount of solvent and ammonia concentration contained in the supercritical carbon dioxide) is detected, and the supercritical carbon dioxide is contacted based on the detected information. The process to be stopped is stopped.

For this reason, in this embodiment, in the production of silica particles that is repeatedly performed, based on the information on the supercritical carbon dioxide discharged from the processing tank 10, a step of contacting the supercritical carbon dioxide (in this embodiment, a solvent removal treatment step) , The hydrophobization process step) is stopped, so that fluctuations in the stop conditions of this step are reduced.
Therefore, characteristic fluctuations of the obtained silica particles are also reduced.

In particular, in the present embodiment, supercritical carbon dioxide is introduced into and discharged from the treatment tank 10, the supercritical carbon dioxide is brought into contact with the dispersion medium of the silica particle dispersion, and the solvent removal treatment of the silica particle dispersion is performed.
And the amount of solvent contained in supercritical carbon dioxide discharged from processing tank 10 is detected, and solvent removal processing is stopped based on the detected amount of solvent.

  Here, the amount of solvent (for example, the amount of alcohol and water) of the silica particle dispersion to be produced varies not a little from one production rod to another. For this reason, when the conditions for the solvent removal treatment are fixed, the amount of solvent remaining in the silica particles after removal of the solvent also varies. If the amount of solvent remaining in the silica particles after removal of the solvent fluctuates, the hydrolyzing state of the hydrophobizing agent will change during the next process (for example, hydrophobizing). The reactivity with the surface changes, and as a result, characteristics such as the degree of hydrophobicity, hygroscopicity, chargeability and the like change.

In contrast, in the present embodiment, in the repeated production of silica particles, the solvent removal treatment process is stopped based on the amount of solvent (solvent removal amount) contained in the supercritical carbon dioxide discharged from the treatment tank 10. Therefore, the fluctuation of the stop condition of the solvent removal process is reduced. That is, the amount of solvent remaining on the silica particles after removal of the solvent also varies.
Therefore, the fluctuation | variation of the characteristic (for example, hygroscopicity, charging property, hydrophobicity) of the silica particle obtained is suppressed.

Here, when supercritical carbon dioxide is circulated and the solvent of the silica particle dispersion liquid is removed by supercritical carbon dioxide, the supercritical carbon dioxide has the property that “interfacial tension does not work”. It is considered that the solvent can be removed without aggregation of particles due to the liquid crosslinking force. Also, due to the property of supercritical carbon dioxide, such as “carbon dioxide in a state of temperature and pressure above the critical point and having both gas diffusibility and liquid solubility”, it is relatively low temperature (for example, 250 ° C. In the following), the supercritical carbon dioxide is efficiently contacted and the solvent is dissolved. By removing the supercritical carbon dioxide dissolved in this solvent, coarse powder such as secondary aggregates due to condensation of silanol groups can be obtained. It is considered that the solvent in the silica particle dispersion can be removed without being generated.
For this reason, it is thought that the silica particle with few generation | occurrence | production of coarse powder is obtained.

Further, in the present embodiment, hexamethyldisilazane (HMDS) is introduced into the treatment tank 10 and supercritical carbon dioxide is introduced / discharged to bring the supercritical carbon dioxide into contact with the silica particles of the silica particle dispersion. In such a state (that is, in supercritical carbon dioxide), the silica particles are hydrophobized.
And the ammonia concentration contained in the supercritical carbon dioxide discharged | emitted from the processing tank 10 is detected, and the hydrophobization process is stopped based on the detected ammonia concentration.

Ammonia generated as a by-product from the reaction of a hydrophobizing agent (hexamethyldisilazane) is used as a catalyst and dispersion stabilizer in forming silica particles. It becomes.
On the other hand, in order to avoid residual ammonia in the silica particles after the hydrophobization treatment, it is conceivable that the silica particles are heated for an excessively long time following the hydrophobization treatment. The amount of waste is increased in terms of both energy efficiency and production efficiency.

On the other hand, in the present embodiment, the hydrophobization treatment is stopped because the hydrophobization treatment process is stopped based on the ammonia concentration contained in the supercritical carbon dioxide discharged from the treatment tank 10 in the repeated production of silica particles. Fluctuations in process stop conditions are reduced.
In other words, the hydrophobization treatment process can be stopped without applying excessive heating, and fluctuations in the properties of the silica particles after the hydrophobization treatment (BET specific surface area, water remaining amount, residual ammonia amount) are suppressed. Also, the ammonia concentration can be reduced.
Therefore, the fluctuation | variation of the characteristic (for example, hygroscopicity, charging property, hydrophobicity) of the silica particle obtained is suppressed. Moreover, since the fluctuation | variation of the quantity is suppressed in the state which reduced the ammonia residual amount of the silica particle obtained, the odor resulting from the residual ammonia and a hygroscopic deterioration are also suppressed.

  Here, when hydrophobizing the surface of silica particles with a hydrophobizing agent (hexamethyldisilazane), if the processing is performed in supercritical carbon dioxide, the hydrophobic treating agent is dissolved in supercritical carbon dioxide. Conceivable. Since supercritical carbon dioxide has the characteristic of extremely low interfacial tension, the hydrophobic treatment agent dissolved in supercritical carbon dioxide diffuses deeply into the pores on the surface of silica particles together with supercritical carbon dioxide. It is thought that it will be easy to reach. Thus, it is considered that the hydrophobic treatment is performed not only on the surface of the silica particles but also deep in the hole.

In the present embodiment, both the solvent removal treatment step and the hydrophobization treatment step are steps for introducing and discharging supercritical carbon dioxide into the treatment tank 10 and bringing the supercritical carbon dioxide into contact with the silica particles or the dispersion medium. Although the form which performed was demonstrated, the form which performs only any process may be sufficient.
Moreover, although the form which implements a solvent removal treatment process and a hydrophobization treatment process continuously was demonstrated, it is not restricted to this, The form (namely, after performing a solvent removal treatment process, once a processing tank is performed) The silica particles may be taken out from the No. 10 and the silica particles and the hydrophobizing agent may be accommodated in the treatment tank 10 again to perform the hydrophobizing treatment step.

  The configuration of the silica particle production apparatus 101 according to the present embodiment is not limited to the above configuration, and supercritical carbon dioxide is introduced into and discharged from the treatment tank 10 to bring the supercritical carbon dioxide into contact with the silica particles or the dispersion medium. Any configuration may be used as long as the steps (in this embodiment, the solvent removal treatment step and the hydrophobization treatment step) are realized.

Specifically, the silica particle manufacturing apparatus 101 according to the present embodiment includes:
A treatment tank for containing a silica particle dispersion or silica particles, and treating the silica particle dispersion or silica particles;
Supercritical carbon dioxide introduction / discharge means for introducing / exhausting supercritical carbon dioxide into the treatment tank in order to bring the supercritical carbon dioxide into contact with the silica particle dispersion or the silica particles;
Detection means for detecting information of supercritical carbon dioxide discharged from the treatment tank;
Control means for controlling the introduction / discharge means based on the information detected by the detection means and stopping the introduction of supercritical carbon dioxide into the treatment tank,
Any apparatus for producing silica particles may be used.

In particular, the silica particle manufacturing apparatus 101 according to the present embodiment includes:
In order to perform a hydrophobization treatment on the surface of the silica particles, further comprising hexamethyldisilazane introduction means for introducing hexamethyldisilazane (HMDS) into the treatment tank,
The detection means is a detection means for detecting the ammonia concentration contained in the supercritical carbon dioxide discharged from the treatment tank after introducing hexamethyldisilazane (HMDS),
The control means may be a control means for controlling the introduction / discharge means based on the ammonia concentration detected by the detection means and stopping the introduction of supercritical carbon dioxide into the treatment tank.

Hereinafter, the present invention will be described more specifically with reference to examples. However, these examples do not limit the present invention.

Example 1
The silica particle dispersion prepared by the sol-gel method was concentrated with a DCF (dynamic crossflow filter) to obtain a silica particle dispersion having a silica particle solid content of 35% by mass.
300 parts by mass of this silica particle dispersion was collected. And the water | moisture content (residual water content) of the silica particle at the time of completion | finish of a solvent removal process (at the time of completion | finish of drying) is set to 5 mass%, and the solvent amount (solvent removal amount) removed is 189.75 (= 300 mass parts-(300 Mass part × 35 mass% × 1.05).

Next, the collected silica particle dispersion was put into a 0.65 L high-pressure treatment tank equipped with an anchor stirrer and a heater and sealed.
Next, while rotating the anchor type stirring blade at 110 rpm, liquefied carbon dioxide was filled, and the inside of the high-pressure treatment tank was heated up to a temperature of 80 ° C. and a pressure of 20 MPa, so that the carbon dioxide was brought into a supercritical state. . Then, with the stirring blade rotating at 110 rpm, supercritical carbon dioxide was introduced into and discharged from the high-pressure treatment tank by the supercritical carbon dioxide introduction / discharge mechanism. The distribution speed at this time was 20 L / min.
Supercritical carbon dioxide discharged from the high-pressure treatment tank was sent to a separation tank equipped with a cooling device, cooled in the separation tank, the solvent contained in supercritical carbon dioxide was separated, and the separated solvent was stored in the separation tank. .
Next, when the stored solvent amount (solvent removal amount) reaches the set value of 189.75 g by the meter provided in the separation tank, the introduction (circulation) of supercritical carbon dioxide is stopped, and the high-pressure treatment tank Was reduced to 10 MPa to complete the solvent removal treatment.

Next, after introducing hexamethyldisilazane (HMDS) into the high-pressure treatment tank by the HMDS introduction mechanism, the temperature is raised and raised in the high-pressure treatment tank to 160 ° C. and 20 MPa, and the temperature and pressure are maintained. Hydrophobization treatment was performed for 30 minutes, and after 30 minutes, the pressure in the high-pressure treatment tank was released, and the hydrophobic treatment was completed.
Then, the hydrophobized silica particles were taken out from the high-pressure treatment tank, and the hydrophobization degree and water content (residual water content) of the silica particles were evaluated.

  Also, 300 g of silica particle dispersions having different silica particle solids (silica particle solids described in Table 1) are prepared, and the amount of solvent removed from each silica particle dispersion (solvent removal described in Table 1) is set. The same solvent removal treatment and hydrophobization treatment were performed, and the hydrophobization degree and moisture (residual moisture content) of the silica particles were evaluated.

(Comparative Example 1)
300 g of a silica particle dispersion having a different silica particle solid content (silica particle solid content shown in Table 2) was prepared, and the solvent removal treatment and the hydrophobization treatment were performed in the same manner as described above. ) Was evaluated.
However, the stopping condition of the solvent removal treatment (drying treatment) is performed with the supercritical carbon dioxide circulation time fixed at 33 minutes, regardless of the amount of solvent removed from the silica particle dispersion (solvent removal amount described in Table 1). It was. The solvent removal amount in Table 2 indicates the solvent removal amount when the supercritical carbon dioxide circulation time is fixed at 33 minutes and the solvent removal treatment (drying treatment) is stopped.

From the above results, it can be seen that Example 1 has less variation in the degree of hydrophobicity and moisture (residual moisture content) of the silica particles obtained than in Comparative Example 1.
Since moisture (residual moisture amount) affects the chargeability of the Syria particles, it can be seen that the variation in the chargeability of the silica particles is less in Example 1 than in Comparative Example 1.

(Example 2)
Dry silica particles after removal of the solvent (water content of silica particles (residual water content) 5%) were prepared.
The dried silica particles were put into a 0.65 L high pressure treatment tank equipped with an anchor type stirrer and a heater and sealed.
Next, 30 g of hexamethyldisilazane (HMDS) is introduced into the high-pressure treatment tank by the HMDS introduction mechanism while rotating the anchor blade at 110 rpm, and then the liquefied carbon dioxide is filled therein. The temperature was increased and the pressure was increased to 20 MPa, and carbon dioxide was brought into a supercritical state. Then, after reaching a temperature of 150 ° C. and a pressure of 20 MPa, the temperature and pressure were maintained for 30 minutes to perform a hydrophobic treatment. After 30 minutes, supercritical carbon dioxide was introduced into and discharged from the high-pressure treatment tank by a supercritical carbon dioxide introduction / discharge mechanism. The distribution speed at this time was 22 L / min.
When the ammonia concentration contained in the supercritical carbon dioxide discharged from the high-pressure treatment tank is measured with a laser gas analyzer (manufactured by Toko Keiki Co., Ltd .: GM700), the ammonia concentration decreases and reaches 0.02% Then, the introduction (distribution) of supercritical carbon dioxide was stopped, the pressure of the high-pressure treatment tank was released, and the hydrophobization treatment was completed.
Then, the hydrophobized silica particles were taken out from the high-pressure treatment tank, and the ammonia concentration and moisture (residual moisture amount) of the silica particles were evaluated. The distribution time (introduction / discharge time) of supercritical carbon dioxide was also investigated.

  Further, 100 g of dry silica particles having different water contents (water content in Table 3: solvent water content) were prepared and subjected to the same hydrophobizing treatment as described above, and the ammonia concentration and water content (residual water content) of the silica particles were evaluated.

(Comparative Example 2)
100 g of dry silica particles having different water contents (water content in Table 4: residual water content) were prepared and subjected to the same hydrophobizing treatment as in Example 1 to evaluate the ammonia concentration and water (residual water content) of the silica particles.
However, the suspension time for the hydrophobization treatment is fixed at 11.6 minutes, regardless of the ammonia concentration of the supercritical carbon dioxide discharged from the high-pressure treatment tank. went.

From the above results, it can be seen that Example 2 has less variation in the ammonia concentration and moisture (residual moisture content) of the silica particles than in Comparative Example 2.
Moreover, in Example 2, it turns out that the fluctuation | variation is few in the state which reduced the ammonia concentration of the silica particle.
Since moisture (residual moisture amount) affects the chargeability of Syria particles and ammonia concentration affects hygroscopicity, the chargeability and moisture absorption of silica particles in Example 2 are higher than those in Comparative Example 2. It can be seen that there is little variation in sex.

  The hydrophobization degree of the silica particles is 50 ml of ion-exchanged water, 0.2 parts by mass of silica particles as a sample are put in a beaker, methanol is dropped from a burette while stirring with a magnetic stirrer, and the total amount of the sample sinks. The methanol mass fraction in the methanol water mixed solution was determined as the degree of hydrophobicity.

  Moreover, the water | moisture content (residual water content) of a silica particle is when it heats up from 30 degreeC to 250 degreeC by the temperature increase rate of 20 degrees C / min in nitrogen stream using TGA-DTA2000S (brand name) by Seiko. The mass reduction rate was determined as moisture (residual moisture content).

Further, the ammonia concentration of the silica particles after the hydrophobization treatment is determined as follows.
50 ml of hydrophobized silica particles as samples are weighed precisely in 0.1 g each in a polypropylene (PP) measuring flask, and 2 ml of tetrahydroxyfuran (THF) is added thereto to wet the silica particles. After adding ultrapure water to make up to 50 ml, shake well and apply to an ultrasonic disperser for 6 minutes. Next, the silica dispersion is filtered with a syringe filter previously washed with ultrapure water to obtain a measurement sample. And ammonia concentration is calculated | required on condition of the following using a measurement sample.
・ Measurement device: ICS2000 ion chromatograph manufactured by Dionex ・ Measurement sample introduction amount: 25 μl
・ Eluent: Methanesulfonic acid 20 mM
Separation column: IonPac CS12A 4 mmφ × 250 mm
・ Detector: Electric conductivity meter

DESCRIPTION OF SYMBOLS 10 Treatment tank 11 Stirring blade 20 Supercritical carbon dioxide introduction and discharge mechanism 30 Supercritical carbon dioxide introduction part 31 Liquefied carbon dioxide storage tank 32 Supercritical carbon dioxide generation part 33 Heat source 34 High pressure pump 35 Liquefied carbon dioxide introduction pipe 36 Supercritical Carbon dioxide introduction pipe 37 Open / close valve 40 Supercritical carbon dioxide discharge part 41 Separation tank 42 Supercritical carbon dioxide discharge pipe 43 Open / close valve 50 Supercritical carbon dioxide regeneration part 51 Carbon dioxide liquefaction tank 52 Vaporized carbon dioxide discharge pipe 53 Liquid carbon dioxide introduction Pipe 60 Hexamethyldisilazane introduction mechanism 61 HMDS storage tank 62 HMDS introduction pipe 63 Introduction pump 64 On-off valve 71 Solvent amount detector 72 Ammonia concentration meter 80 Control unit 101 Silica particle production apparatus

Claims (2)

A first step of introducing and discharging supercritical carbon dioxide into a treatment tank containing silica particle dispersion or silica particles, and bringing the supercritical carbon dioxide into contact with the silica particle dispersion or silica particles;
Detecting the information of supercritical carbon dioxide discharged from the treatment tank, and based on the detected information, a second step of stopping the first step;
A method for producing silica particles having The first step is a step of introducing hexamethyldisilazane (HMDS) into the treatment tank to perform a hydrophobic treatment of the silica particles;
The second step introduces and discharges supercritical carbon dioxide into the treatment tank, detects the ammonia concentration contained in the supercritical carbon dioxide discharged from the treatment tank, and based on the detected ammonia concentration, The method for producing silica particles according to claim 1, which is a step of stopping the first step.

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