Method for preparing silica sol by using booster catalyst, and silica sol prepared using same

Abstract

The present invention relates to a method for preparing silica nanoparticles in a short time by using a sol-gel method and, to: a method in which a booster catalyst is used during a sol-gel reaction so as to increase a reaction rate, thereby reducing the time it takes for a reaction with a conversion rate of 100% or more to reach completion and, simultaneously, suppressing an increase in particle size; and a method for preparing a high-concentration silica sol by using same. More specifically, in a process of forming silica nanoparticles from a tetravalent alkoxy silane by means of a sol-gel reaction, after the reaction conversion rate reaches 40-80%, a booster catalyst or a booster catalyst and water are added and the reaction is completed, and thus the time it takes to reach a conversion rate of 100% can be reduced and, simultaneously, an increase in particle size can be suppressed. In addition, when the amount of a tetravalent alkoxy silane is increased in order to prepare a high-concentration silica sol, the tetravalent alkoxy silane is divided and added twice, and after the reaction conversion rate of a primary tetravalent alkoxy silane precursor reaches 80% or more, a booster catalyst and water are added together with a secondary alkoxy silane and the reaction is completed, and thus a high-concentration silica sol can be prepared while an increase in particle size is suppressed.

Description

Method for preparing silica sol using a booster catalyst and silica sol prepared therefrom

[0001] The invention relates to a method for producing silica nanoparticles in a short time by a sol-gel method, and more specifically, to a method for increasing the reaction rate by using a booster catalyst during the sol-gel reaction to shorten the time to complete the reaction to a conversion rate of over 100% and simultaneously suppressing the increase in particle size, and a method for producing a high-concentration silica sol using the same.

[0002] Silica nanoparticles are utilized in the manufacture of various polymer nanocomposites due to their high strength, high permeability, and excellent insulation properties, and related research has been steadily ongoing. In particular, research on silica nanoparticles has been actively conducted because they can be easily prepared via a solution process using the sol-gel method.

[0003] Various prior art technologies for controlling the size of such sol-gel silica nanoparticles are known, including Korean Published Patent No. 10-2009-0053155 (Organic solvent-type silica sol and method for manufacturing the same) and Korean Published Patent No. 10-2014-0067501 (Method for manufacturing high-purity silica sol from tetravalent alkoxysilane using high-temperature reaction conditions and organic solvent-dispersed high-purity silica sol manufactured by this method).

[0004] According to the prior art described above, sol-gel silica nanoparticles are synthesized in the form of a silica sol in which silica nanoparticles are dispersed in a solvent through the hydrolysis and condensation reactions of a tetravalent alkoxysilane precursor. At this time, the particle size varies depending on the control of the basic catalyst and water content, and generally, the particle size increases as the catalyst and water content increase. Many studies have been conducted on the formation and growth of sol-gel silica particles, which are mainly explained based on the monomer-addition model or the aggregation model (Advances in Colloid and Interface Science (2023) 314, 102888). The monomer addition model explains that growth occurs as silanol monomers, which are reactants, are adsorbed onto the surface after the formation of particle nuclei at the beginning of the reaction, while the aggregation model explains that particle formation occurs through the aggregation of seeds formed at the beginning of the reaction, and particle growth occurs continuously during the reaction period through aggregation between seeds and particles. Although there are many cases that are difficult to explain simply with two models, it is generally understood that uniform particle formation under high-content catalysts is adequately explained by the monomer-addition model, and heterogeneous particle size formation under low-content catalysts is adequately explained by the aggregation model (Langmuir (2017) 33, 5879).

[0005] Nanoparticles of smaller size are generally advantageous for realizing properties differentiated from conventional microparticles. However, when manufacturing silica nanoparticles via the sol-gel reaction, reducing particle size requires lowering the catalyst and water content, which slows down the reaction rate and limits the ability to secure efficient productivity. Furthermore, the reaction rate is proportional to the reactant concentration; as the reaction progresses, the concentration of unreacted reactants decreases, causing the reaction rate to slow down. In particular, once the reaction conversion rate exceeds 90%, the reactant concentration becomes very dilute, resulting in a long time required to reach reaction completion (100% conversion rate). These small amounts of unreacted alkoxysilanes can act as impurities; for instance, materials added for surface treatment of the formed silica nanoparticles may react with these unreacted residues rather than the nanoparticle surface, making surface treatment control difficult. Therefore, there is a need to develop technology capable of manufacturing small-sized silica nanoparticles to reach reaction completion within a short period of time.

[0006] Furthermore, silica sol, a dispersion of silica nanoparticles produced by the sol-gel method, is typically prepared with a solid content of approximately 7 wt% or less due to issues such as particle aggregation and non-uniformity of particle size during the reaction (Journal of Colloid and Interface Science (2010) 341, 23). Silica nanoparticles are widely used to manufacture organic-inorganic nanocomposites with organic materials such as polymers; however, since most polymers lack affinity for water and alcohol, which are solvents used in silica sol synthesis, silica sol is generally evaporated to obtain silica solid particles for use, or the solvent is replaced with one that is compatible with the polymer. Consequently, the low solid content of silica sol is disadvantageous in terms of cost and process, as it requires the removal of a large amount of water / alcohol solvent. Therefore, there is a need to develop technology to increase the solid content of silica sol to form high-concentration silica sol.

[0007] Accordingly, the inventors have completed the present invention by developing a method to suppress particle size increase while shortening the reaction time by using a booster catalyst in the process of manufacturing silica nanoparticles by a sol-gel reaction, and a method to produce a high concentration of silica sol using this method.

[0008]

[0009] Therefore, the present invention has as a technical problem to provide a method for producing a silica sol having a uniform particle size distribution by using a booster catalyst to ensure rapid reaction completion during the synthesis of silica nanoparticles by a sol-gel reaction and simultaneously suppressing the increase in particle size, and to provide the silica sol produced therefrom.

[0010] In addition, the present invention has another technical problem to solve by providing a method for rapidly producing a high-concentration silica sol having a uniform particle size distribution by suppressing particle size growth through the additional addition of an alkoxysilane precursor and water when a booster catalyst is added, and by providing the silica sol produced therefrom.

[0011]

[0012] In order to solve the above technical problem, the present invention,

[0013] A first step of preparing a silane precursor solution by mixing a tetravalent alkoxysilane with an organic solvent;

[0014] A second step of forming silica particles through a sol-gel reaction in the mixture by adding a basic catalyst and water to the above silane precursor solution and mixing them;

[0015] A third step of producing silica nanoparticles by adding a booster catalyst and completing the reaction after the conversion rate of the sol-gel reaction in the second step reaches 40 to 80%; comprising

[0016] In the second step above, the silica particles are formed as the particle seeds aggregate by a sol-gel reaction, and

[0017] Characterized by adding a booster catalyst in the third step to additionally form silica particles and accelerate the sol-gel reaction, while relatively suppressing the growth of the silica particles formed in the second step due to aggregation, thereby producing a silica sol containing silica nanoparticles with uniformly controlled particle size.

[0018] A method for manufacturing silica sol using a booster catalyst is provided.

[0019] In the present invention, the silica nanoparticles are characterized by having a particle diameter of up to 30 nm.

[0020] In the present invention, the booster catalyst is characterized by being one or more selected from the group consisting of ammonium hydroxide, ammonium hydroxide, ammonium chloride, methyl amine, ethyl amine, propyl amine, isopropyl amine, butyl amine, cyclohexyl amine, dimethyl amine, diethyl amine, trimethyl amine, and triethyl amine.

[0021] In the present invention, the concentration of the booster catalyst is characterized as being 0.01 to 0.1 M.

[0022]

[0023] In addition, the present invention comprises a first step of preparing a silane precursor solution by mixing a primary tetravalent alkoxysilane with an organic solvent;

[0024] A second step of forming silica particles through a sol-gel reaction in the mixture by adding a basic catalyst and water to the above silane precursor solution and mixing them;

[0025] A third step of preparing silica nanoparticles by further mixing a secondary tetravalent alkoxysilane and water with a booster catalyst and completing the reaction after the conversion rate of the sol-gel reaction in the second step reaches 80%;

[0026] In the second step above, the silica particles are formed as the particle seeds aggregate by a sol-gel reaction, and

[0027] Characterized by the fact that, while additionally forming silica particles and accelerating the sol-gel reaction by adding a booster catalyst in the third step, the growth of the silica particles formed in the second step due to aggregation is relatively suppressed, thereby producing a high-concentration silica sol containing silica nanoparticles with uniformly controlled particle size.

[0028] A method for manufacturing silica sol using a booster catalyst is provided.

[0029] In the present invention, the silica sol is.

[0030] It is characterized by being a high-concentration silica sol with a solid content of 10 to 15 wt%.

[0031] In the present invention,

[0032] The above booster catalyst is characterized by being one or more selected from the group consisting of ammonium hydroxide, ammonium hydroxide, ammonium chloride, methyl amine, ethyl amine, propyl amine, isopropyl amine, butyl amine, cyclohexyl amine, dimethyl amine, diethyl amine, trimethyl amine, and triethyl amine.

[0033] In the present invention, the concentration of the booster catalyst is characterized as being 0.01 to 0.1 M.

[0034]

[0035] According to the present invention, by suitably using a booster catalyst in the sol-gel reaction, the reaction is completed more quickly, enabling high-speed manufacturing, and at the same time, by suppressing the increase in particle size, a silica sol having a uniform particle size distribution can be produced.

[0036] According to one result of the present invention, for silica particles of 20 nm or less, the reaction completion time to reach a conversion rate of 100% can be shortened by about twofold from 48 hours to 24 hours by applying a booster catalyst, and the particle size is also maintained.

[0037] In addition, by splitting the input of an alkoxysilane precursor and applying a booster catalyst, it is possible to obtain a high concentration of silica sol in a uniform particle form in a short period of time. Through this, a silica sol with a solid content of 10 to 15 wt% can be produced within 48 hours in a reaction-completed state with a conversion rate of 100% without an increase in particle size.

[0038]

[0039] FIG. 1 is a schematic diagram of the high-speed production of silica nanoparticles (a) and the production process of high-concentration silica sol (b) according to the present invention.

[0040] FIG. 2 is a graph showing the results of measuring the reaction conversion rate over time according to Comparative Example 1 (a) and Comparative Example 2 (b) of the present invention.

[0041] Figure 3 is a figure showing the timing of adding the booster catalyst and water from Comparative Example 1 and the range of conversion rate values ​​at that time.

[0042] Figure 4 is an SEM image showing the morphology of silica nanoparticles obtained according to the time of adding the booster catalyst after the start of the reaction during the preparation of silica nanoparticles using the booster catalyst in Example 1. ((a) No addition of booster catalyst, (b) 2 hours after the start of the reaction, (c) 4 hours after the start of the reaction, (d) 6 hours after the start of the reaction)

[0043] Figure 5 is an SEM image showing the morphology of silica nanoparticles obtained according to the time of addition of the booster catalyst / water after the start of the reaction during the preparation of silica nanoparticles using the booster catalyst / water in Example 2. ((a) No addition of booster catalyst, (b) 2 hours after the start of the reaction, (c) 4 hours after the start of the reaction, (d) 6 hours after the start of the reaction)

[0044] FIG. 6 is an SEM image observing the morphology of silica nanoparticles obtained according to the Comparative Example and Example for obtaining a high-concentration silica sol ((a) Comparative Example 3, (b) Comparative Example 4, (c) Example 3, (d) Example 4).

[0045]

[0046] The present invention will be described in detail below.

[0047] First, the present invention is capable of various modifications and may have various embodiments, and specific embodiments are illustrated in the drawings and described in detail. However, this is not intended to limit the present invention to specific embodiments, and it should be understood that it includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0048] The terms used in this invention are used merely to describe specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this invention, terms such as "comprising" or "having" are intended to specify the presence of the features, numbers, steps, reactions, components, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, reactions, components, or combinations thereof.

[0049] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this application.

[0050]

[0051] The present invention relates to a method for rapidly producing silica sol using a booster catalyst, comprising: a first step of preparing a silane precursor solution by mixing a tetravalent alkoxysilane and an organic solvent; a second step of forming silica particles through a sol-gel reaction in the mixture by adding a basic catalyst and water to the silane precursor solution and mixing; and a third step of producing silica nanoparticles by adding a booster catalyst and completing the reaction after the conversion rate of the sol-gel reaction in the second step reaches 40 to 80%.

[0052] The process of manufacturing high-speed silica nanoparticles according to one embodiment of the present invention will be explained in detail with reference to Fig. 1(a), which shows a schematic diagram of the process.

[0053] Step 1 (S1) of preparing a silane precursor solution by mixing a tetravalent alkoxysilane and an organic solvent

[0054] Here, the tetravalent alkoxysilane is a silane having four OR (alkoxy groups) and may be one or more selected from the group consisting of tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetraisopropoxysilane, tetrabutoxysilane, tetraphenoxysilane, and tetraacethoxysilane, and preferably may be tetraethoxysilane (TEOS) or tetramethoxysilane (TMOS).

[0055] The above organic solvent may be an alcohol-based solvent and / or a non-alcohol-based solvent, and preferably, an alcohol-based solvent such as methyl alcohol, ethyl alcohol, or isopropyl alcohol is used.

[0056] The above alcohol-based solvent may be one or more selected from the group consisting of methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol, tert-butyl alcohol, pentyl alcohol, and benzyl alcohol.

[0057] The above-mentioned non-alcoholic solvent may be one or more selected from the group consisting of acetone, N-methylformamide, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, glycerol, propylene glycol, butylene glycol, tetrahydrofuran, tetrahydropyran, etc.

[0058] In addition, various organic solvents can be used in the form of organic solvents and mixed solvents that are capable of dissolving the alkoxysilane while simultaneously having an affinity for water. When particle growth occurs due to the aggregation of initial seed particles during a sol-gel reaction, the aggregation between particles depends on the polarity of the surrounding dispersion solvent; therefore, the reaction rate and particle size can be controlled by appropriately adjusting the polarity of the organic solvent. Since heterogeneous reactions and resulting non-uniformity in particle size occur when the organic solvent separates from the reactant, the organic solvent can be used in the form of organic solvents and mixed solvents that are capable of dissolving the alkoxysilane precursor while simultaneously having an affinity for water.

[0059] A second step (S2) of forming silica particles through a sol-gel reaction in the mixture by adding a basic catalyst and water to the above silane precursor solution and mixing them.

[0060] The above basic catalyst is characterized by being one or more selected from the group consisting of ammonium hydroxide, ammonium hydroxide, ammonium chloride, methyl amine, ethyl amine, propyl amine, isopropyl amine, butyl amine, cyclohexyl amine, dimethyl amine, diethyl amine, trimethyl amine, and triethyl amine. Preferably, it may be ammonium hydroxide.

[0061] The above catalyst is related to the reaction rate and silica particle size, and as the catalyst content increases, the silica particle size increases. The appropriate catalyst content varies depending on conditions such as reaction temperature, reactant concentration, and catalyst type; however, generally, if the above catalyst is used at a concentration of 0.1M or higher, there is a risk that the silica particle size will become excessively large, exceeding several hundred nm, and if the catalyst content is less than 0.01M, the reaction rate becomes too slow, leading to an excessively long reaction time and a risk that the reaction will not be completed. Therefore, it is preferable to use the above catalyst at a concentration of 0.01M to 0.1M.

[0062] It is preferable to use distilled water for the above water. The silica nanoparticles are formed through the hydrolysis and condensation reactions of the precursor, tetravalent alkoxysilane. Since 1 mole of tetravalent alkoxysilane reacts with 4 moles of water to undergo hydrolysis and 2 moles of water are generated during the condensation reaction, the reaction stoichiometric ratio requires 2 moles of water per 1 mole of tetravalent alkoxysilane precursor. However, in actual reactions, the reaction rate in the later stages proceeds excessively with a water content of 2 moles, making it difficult to complete the reaction. Therefore, it is preferable to use 3 M or more of water relative to 1 M of tetravalent alkoxysilane.

[0063] The silica particles are formed as the particle seeds aggregate through the above sol-gel reaction, and this sol-gel reaction can proceed at a temperature between 30°C and 70°C. If the reaction temperature is below 30°C, the sol-gel reaction is slow, and it may take an excessively long time to reach a conversion rate of 100%. If the reaction temperature is higher than 70°C, the reaction mode changes and becomes difficult to control because solvent and catalyst volatilization may occur during the reaction. Furthermore, since a separate device must be used to trap these volatile substances, it becomes disadvantageous in terms of process control and cost when applying the product.

[0064] A third step (S3) of producing silica nanoparticles by adding a booster catalyst and completing the reaction after the conversion rate of the sol-gel reaction in the second step reaches 40 to 80%.

[0065] The above booster catalyst is characterized by being one or more selected from the group consisting of ammonium hydroxide, ammonium hydroxide, ammonium chloride, methyl amine, ethyl amine, propyl amine, isopropyl amine, butyl amine, cyclohexyl amine, dimethyl amine, diethyl amine, trimethyl amine, and triethyl amine. Preferably, it may be ammonium hydroxide.

[0066] It is preferable to use the above booster catalyst at a concentration of 0.01M to 0.1M in the total solution. If the concentration is lower than 0.01M, it is difficult to properly obtain the reaction acceleration effect, and if it is higher than 0.1M, the unreacted alkoxy precursor at the time of adding the booster catalyst reacts too rapidly, so the growth of newly formed particles and existing particles becomes non-uniform, and the particle size may become non-uniform.

[0067] The above reaction conversion rate (Xc) is calculated by subtracting the measured value of silica solids (TSC, total solid content) in the reaction solution at each reaction time from the theoretical solid content (TSC * It represents the percentage divided by ), where the above theoretical solid content (TSC * ) refers to the solid content in the reaction solution when all the added tetravalent alkoxysilane (Si(OR)4) is converted into silica (SiO2) through hydrolysis and condensation reactions.

[0068] In other words, for example, when tetraethoxysilane (TEOS, molecular weight 208.33 g / mol) is converted into silica (SiO2, molecular weight 60.08 g / mol) upon reaction completion, the accompanying weight change is 60.08 / 208.33 (28.8 wt%). That is, when the reaction is completely finished, the yield becomes 28.8 wt%. This applies when there are no solvents or additives other than TEOS; however, since organic solvents and catalysts are actually introduced, the theoretical solid content (TSC*) decreases accordingly depending on the organic solvents and catalysts used. For example, when 100 parts by weight of TEOS are dissolved in a total of 300 parts by weight of organic solvents and additives and the reaction is completed, the theoretical solid content becomes 28.8 / 400, or 7.2 wt%. The reaction conversion rate at this time is defined as 100%, and the conversion rate during the reaction, for example, a conversion rate of 50% means that half of the input TEOS has undergone a sol-gel reaction, and the solid content of the sampled specimen is 3.6 wt%.

[0069] In the sol-gel reaction, the reaction begins immediately after the addition of the basic catalyst and water. The effect of the present invention can be suitably obtained by adding the booster catalyst and water after the reaction has occurred to a certain extent and particles have been stably formed.

[0070] According to the embodiments and comparative examples of the present invention, the reaction of the alkoxysilane precursor during the sol-gel reaction accelerates as the catalyst and water content increase, and the particle size also increases. If a booster catalyst and water are added at a point where the reaction conversion rate is less than 40%, the particle size may become larger or non-uniform due to the increased catalyst and water content. However, by adding the booster catalyst and water after the reaction conversion rate reaches 40% or more, the reaction rate can be boosted without disturbing the initial reaction pattern as much as possible. Consequently, it becomes possible to suppress the increase in particle size while shortening the time required to reach the 100% reaction completion rate, which is the objective of the present invention. Furthermore, even if the booster catalyst is added after the conversion rate reaches 80% or more, the function described above is present, but the role of reducing the reaction rate becomes relatively insignificant.

[0071] Therefore, by simultaneously adding a booster catalyst and water after the reaction conversion rate reaches 40 to 80%, and by adding the booster catalyst and water after the reaction conversion rate reaches a certain level and particle formation is achieved to some extent, the reaction rate can be accelerated (boosted) without disturbing the initial reaction mode as much as possible, thereby shortening the time to reach the completion of the reaction, which is the objective of the present invention, while suppressing the increase in particle size and maintaining particle uniformity.

[0072] That is, by adding a booster catalyst in the third step, additional silica particles are formed and the sol-gel reaction is accelerated, while the growth caused by aggregation of the silica particles formed in the second step is relatively suppressed, thereby making it possible to produce a silica sol containing silica nanoparticles with uniformly controlled particle sizes.

[0073] According to a preferred embodiment of the present invention, when a booster catalyst and water are introduced simultaneously after the reaction conversion rate reaches 40 to 80%, the conversion rate can reach 100% within 24 hours, and it can be confirmed that the final particle diameter is up to 30 nm. More preferably, the introduction can be performed after the reaction conversion rate reaches 50 to 70%.

[0074]

[0075] In addition, the present invention relates to a method for producing a high-concentration silica sol having a uniform particle distribution using a booster catalyst, comprising: a first step of preparing a silane precursor solution by mixing a primary tetravalent alkoxysilane and an organic solvent; a second step of forming silica particles through a sol-gel reaction in the mixture by adding a basic catalyst and water to the silane precursor solution and mixing; and a third step of producing silica nanoparticles by further mixing a secondary tetravalent alkoxysilane and water together with a booster catalyst and completing the reaction after the conversion rate of the sol-gel reaction in the second step reaches 80%.

[0076] Generally, as the concentration of alkoxysilane increases, the reaction rate accelerates, and non-uniform aggregation and growth occur between particles, leading to a decrease in the uniformity of particle size and shape. Therefore, by adding a high concentration of alkoxysilane in divided portions to maintain a low reactant concentration at the beginning of the reaction, the initial reaction rate and non-uniform aggregation between particles can be suppressed, thereby allowing the particle size to be kept small and uniform. Additionally, by adding a secondary alkoxysilane after the reaction conversion rate of the primary alkoxysilane has been sufficiently reached, the complexity and non-uniformity of the reaction pattern can be minimized; furthermore, by adding a booster catalyst and water at this point, a high concentration of silica sol can be obtained more quickly.

[0077] The above primary and secondary alkoxysilanes, catalyst, and water are introduced in a one-shot manner at each respective point of introduction. By introducing the secondary alkoxysilane, catalyst, and water all at once, new particle formation is induced during the secondary reaction, so that new particle formation occurs mainly rather than the continuous growth of particles formed during the primary reaction, thereby allowing a high concentration of silica sol with a uniform particle size to be obtained without an increase in particle size.

[0078] The process of manufacturing a high-concentration silica sol according to one embodiment of the present invention will be explained in detail with reference to Fig. 1(b), which shows a schematic diagram of the process.

[0079] Step 1 (S1') of preparing a silane precursor solution by mixing a primary tetravalent alkoxysilane and an organic solvent

[0080] The above tetravalent alkoxysilane and organic solvent may be the same as the group of tetravalent alkoxysilanes and organic solvents mentioned in step S1.

[0081] A second step (S2') of forming silica particles through a sol-gel reaction in the mixture by adding a basic catalyst and water to the above silane precursor solution and mixing them.

[0082] The above basic catalyst and water can be the same materials mentioned in step S2, and the silica particles are formed as the particle seeds aggregate through the sol-gel reaction.

[0083] Step 3 (S3'), in which, after the conversion rate of the sol-gel reaction in Step 2 reaches 80%, a secondary tetravalent alkoxysilane and water are further mixed with a booster catalyst and the reaction is completed to produce silica nanoparticles.

[0084] It is preferable to use the above booster catalyst at a concentration of 0.01M to 0.1M in the total solution. If the concentration is lower than 0.01M, it is difficult to properly obtain the reaction acceleration effect, and if it is higher than 0.1M, the unreacted alkoxy precursor at the time of adding the booster catalyst reacts too rapidly, so the growth of newly formed particles and existing particles becomes non-uniform, and the particle size may become non-uniform.

[0085] The above secondary alkoxysilane, booster catalyst, and water can be added after the conversion rate of the above primary alkoxysilane reaction reaches 80% or more. If the secondary alkoxysilane is added when the conversion rate of the primary reaction is less than 80%, that is, when 20% or more of the unreacted alkoxysilane precursor remains, the particle size may increase because the initial precursor concentration of the secondary reaction increases.

[0086] The content of the above secondary alkoxysilane is used at less than half of the total alkoxysilane. If the ratio of the secondary alkoxysilane content exceeds half of the total, the concentration of the reactant during the secondary reaction becomes higher than at the beginning of the primary reaction, and consequently, the particle size may increase due to the secondary reaction. Therefore, in order to obtain a silica sol with a high solid content through precursor splitting while suppressing the increase in particle size, it is desirable to set the ratio of the secondary precursor content to less than half.

[0087] In addition, the above primary and secondary alkoxysilanes, catalyst, and water are characterized by being introduced simultaneously at each respective point of introduction (one-shot method). In particular, when the secondary alkoxysilane precursor is introduced slowly and continuously, there is a high probability that particle formation based on the monomer-addition model will occur. That is, because the concentration of the secondary reactant is maintained at a low level in real time, the particles grow by adsorbing onto the surface of the particles formed in the primary reaction and reacting, and in this case, the particle size continuously increases. On the other hand, when the secondary alkoxysilane, catalyst, and water are introduced simultaneously, the secondary catalyst not only acts as a booster for the primary reaction but also promotes the formation of new seeds from the high concentration of the secondary precursor introduced at once, thus increasing the probability of new particle formation. In this case, new particle formation occurs mainly rather than the continuous growth of the particles formed in the primary reaction, allowing a high-concentration silica sol to be obtained without an overall increase in particle size. In order for the secondary reaction to proceed independently and be stably controlled as described above, it is preferable to introduce the secondary alkoxysilane at a point when the primary precursor reaction has progressed to a certain extent, that is, in the present invention, when the reaction conversion rate reaches 80% or more.

[0088] According to a preferred embodiment of the present invention, by adding an increased amount of tetravalent alkoxysilane in two stages, a high concentration silica sol with a solid content of 10 to 15 wt% can be produced within 48 hours in a reaction-completed state with a conversion rate of 100% without an increase in particle size.

[0089] That is, as described above, by adding a secondary alkoxysilane, a booster catalyst, and water, the secondary reaction can be uniformly led, and through this, a high concentration of silica sol can be obtained in a reaction-completed state with a conversion rate of 100% in a short time without increasing particle size.

[0090]

[0091] The present invention will be described in more detail below with reference to an embodiment thereof. However, the following embodiment is merely an example to aid in understanding the present invention, and the scope of the present invention is not limited thereby.

[0092]

[0093] <Comparative Example 1> Preparation of silica sol by the sol-gel method-1

[0094] In Comparative Example 1, silica nanoparticles were prepared by a general sol-gel method without using a booster catalyst for comparison.

[0095] Experiments were conducted using 4M water based on 1M tetraethoxysilane (TEOS) and ammonia water concentrations of 0.075, 0.1, 0.15, and 0.2M. Ethanol was used as the organic solvent, and the theoretical solid content was 7.2 wt% (62.5 parts by weight of TEOS and 250.8 parts by weight of the total solution). Specifically, TEOS was dissolved in ethanol in a reagent bottle and maintained at 60°C for 30 minutes, after which ammonia water and water were added and reacted until the theoretical solid content was reached to prepare a silica sol.

[0096] Samples were collected at regular intervals during the reaction to measure the solid content. Small amounts of collected samples were dried at 200°C for 1 hour, and the solid content was determined from the weight before and after drying. The particle size of the prepared silica sol was analyzed using the dynamic light scattering (DLS) method. The results are shown in Table 1 below.

[0097] Comparative Example 1 Solid Content (wt%) (Conversion Rate (%)) Final Particle Diameter (nm) Catalyst Content (M) 3h 6h 9h 24h 48h 0.07 5 3.25 (45.3) 4.72 (65.7) 6.02 (83.8) 6.90 (96.1) 7.62 (106.1) 12.4 0.1 4.06 (56.5) 5.43 (75.6) 6.61 (92.1) 7.10 (98.9) 7.65 (106.5) 22.3 0.1 5 4.75 (66.2) 6.08 (84.7) 7.08 (98.6) 7.30 (101.7) 7.62 (106.1) 38.6 0.2 5.24 (73.0) 6.69 (93.2)7.47(104.0)7.50(104.5)7.53(104.9)62.7

[0098]

[0099] In Table 1 above, it can be seen that the solid content at reaction times of 24 to 48 hours exceeds the theoretical solid content (7.2 wt%). In other words, the conversion rate is measured to exceed 100%. This is because, although hydrolysis can occur on the silica surface, there are no silanes that can be bonded via condensation reaction on the outer surface, and accordingly, the silica surface is not in the form of SiO2, but an additional -SiOH(silanol) layer exists. As a result of repeated experiments in the present invention, the final conversion rate after the completion of the reaction was found to be about 5 to 10% higher than the theoretical 100%.

[0100] The above results are shown in a graph in Fig. 2(a). As can be seen in Fig. 2(a), the reaction conversion rate increases rapidly up to 80–90%, but it takes a very long time for the reaction to be completed and the conversion rate to exceed 100%. It can be observed that as the catalyst content increases, the reaction completion time is shortened, but the particle size increases.

[0101]

[0102] <Comparative Example 2> Preparation of silica sol by sol-gel method-2

[0103] In Comparative Example 2, silica nanoparticles were prepared with an increased water content to compare with Comparative Example 1, which did not use a booster catalyst.

[0104] Specifically, experiments were conducted using 10 M water based on 1 M tetraethoxysilane (TEOS) and ammonia water concentrations of 0.075, 0.1, 0.15, and 0.2 M, with a theoretical solid content of 7.0 wt%. The subsequent experimental procedure was carried out in the same manner as Comparative Example 1, and the results are shown in the table below.

[0105] Comparative Example 2 Solid Content (wt%) (Conversion Rate (%)) Final Particle Diameter (nm) Catalyst Content (M) 0.5h 3h 6h 9h 24h 0.07 50.49 (7.0) 5.89 (84.3) 6.49 (92.8) 7.15 (102.3) 7.66 (109.6) 103 0.10.54 (7.7) 6.08 (87.0) 7.13 (102.0) 7.23 (103.4) 7.66 (109.6) 135 0.15 1.30 (18.6) 6.82 (97.6) 7.25 (103.7) 7.39 (105.7) 7.80 (111.6) 213 0.21.65 (23.6)7.14(102.1)7.58(108.4)7.63(109.1)7.74(110.7)245

[0106] The results of Table 2 above are also shown as a graph in Figure 2(b). As can be seen in Table 2 and Figure 2(b), increasing the water content significantly accelerates the reaction rate, just as increasing the amount of basic catalyst does. This is attributed to the accelerated hydrolysis reaction of the alkoxysilane precursor by water. However, as shown in Table 2, in this case, the particle size becomes very large, ranging from 100 to 200 nm, making it unsuitable for synthesizing small-diameter silica nanoparticles.

[0107]

[0108] <Example 1> Preparation of silica nanoparticles using a booster catalyst-1

[0109] The process of synthesizing silica sol using 0.075 M ammonia water in Comparative Example 1 (water content 4 M) was the same as that of Comparative Example 1 above, but after the reaction was initiated by adding the catalyst and water, 0.075 M ammonia water catalyst was added as a booster catalyst at 2, 4, and 6 hours, respectively, to complete the reaction and produce silica sol. The experimental results are shown in Table 3 below.

[0110] Initial catalyst content (M) Booster catalyst input time, Booster catalyst content (M) Solids (wt%) (Conversion rate (%)) Final particle diameter (nm) 8h 24h 0.075 Not input, 0 (Comparative Example 1) 5.46 (76.0) 6.90 (96.1) 12.4 0.075 2h after reaction, 0.075 6.44 (89.7) 7.53 (104.9) 12.4 0.075 4h after reaction, 0.075 6.39 (89.0) 7.57 (105.4) 13.8 0.075 6h after reaction, 0.075 5.75 (80.1) 7.57 (105.8) 11.5

[0111] As shown in Table 3 above, when a booster catalyst is added, it can be seen that the conversion rate measured at 8 and 24 hours after the reaction increases, and in particular, when added earliest after the reaction (2 hours), the increase in conversion rate is the greatest.

[0112] In Comparative Example 1, in which no booster catalyst was added, the conversion rate did not reach 100% even after 24 hours of reaction time, but reached a solid content of 7.62 wt% and a conversion rate of over 100% (106.1%) at 48 hours. However, in Example 1, in which a booster catalyst was added, the conversion rate reached over 100% after 24 hours, and the particle size was maintained at a level of 10 to 20 nm. On the other hand, in Comparative Example 1, in which the total ammonia water content (initial content 0.075 M + booster content 0.075 M) was the same (ammonia water 0.15 M), the reaction rate was faster, but the particle size increased to 38.6 nm. Thus, it is confirmed that the booster catalyst has the effect of reducing the time to complete the reaction while suppressing the increase in particle size.

[0113]

[0114] <Example 2> Preparation of Silica Nanoparticles Using Booster Catalyst and Water Together-2

[0115] The process of synthesizing silica sol was identical to that of Example 1 above, using 1 M TEOS, 0.075 M ammonia water, and 4 M water. However, after the reaction was initiated by adding the catalyst and water, 6 M water was simultaneously added along with 0.075 M ammonia water catalyst as a booster catalyst at 2, 4, and 6 hours to complete the reaction and produce silica sol. The experimental results are shown in Table 4 below.

[0116] Initial catalyst / water content (M) Booster catalyst / water addition time, Booster catalyst / water content (M) Solid content (wt%) (Conversion rate (%)) Final particle diameter (nm) 8h 24h 0.075 / 10 No addition, 0 / 0 (Comparative Example 2) 6.83 (97.7) 7.66 (109.6) 103 0.075 / 4 After reaction 2h, 0.075 / 67.27 (104.0) 7.69 (110.0) 39 0.075 / 4 After reaction 4h, 0.075 / 67.09 (101.4) 7.66 (109.6) 22 0.075 / 4 After reaction 6h, 0.075 / 66.85 (98.0) 7.79 (111.4) 19

[0117] As shown in Table 4 above, when the booster catalyst and water are added together, the reaction rate becomes faster, and it can be confirmed that the reaction conversion rate is higher compared to the value at 8 hours in Table 3. As described in Comparative Example 2 above, increasing the water content also accelerates the reaction rate and increases the particle size. On the other hand, as in Example 2, when the booster catalyst and water are added together after a certain amount of time has passed since the reaction, the increase in particle size is reduced. To stably obtain silica particles of the 20 nm level in a reaction-completed state, it is determined that the appropriate time for adding the booster catalyst and water is around 4 hours after the start of the reaction. Figure 3 shows the change in conversion rate over time for Comparative Example 1 (0.075 M ammonia solution, 4 M water), which serves as the basis for Example 2. For the times when the booster catalyst and water are added—at 2, 4, and 6 hours after the start of the reaction—the conversion rates are approximately 30%, 50%, and 70%, respectively. In other words, from these results, when the booster catalyst / water is added at a conversion rate of 30%, the phenomenon of particle size increase still exists (39 nm), but when added at a conversion rate of 50 or 70%, the reaction speed is fast and the particle size (~20 nm) can be maintained small.

[0118] In Example 1, the timing of adding the booster catalyst did not have a significant effect, but considering Examples 1 and 2 together, it is determined that the timing of adding the booster catalyst or booster catalyst / water is appropriate when the conversion rate after the start of the reaction is in the range of about 40 to 80%.

[0119] Figures 4 and 5 show scanning electron microscope (SEM) images of the silica nanoparticles prepared in Examples 1 and 2. Compared to Figures 4(a) and 5(a) in which the booster catalyst and booster catalyst / water were not added, it can be confirmed that uniform particles were formed in all images of Figures 4(b) to (d) and Figures 5(b) to (d). Therefore, it can be confirmed that particle uniformity is maintained even when the reaction completion rate is accelerated when the booster catalyst and water are added in the present invention.

[0120]

[0121] <Comparative Example 3> Preparation of high-concentration silica sol by the sol-gel method

[0122] In Comparative Example 3, a high-concentration silica sol was prepared by increasing the concentration of the tetravalent alkoxysilane precursor using the conventional sol-gel method of Comparative Example 1 for comparison.

[0123] Specifically, the experiment was conducted using 6 M water based on 1.5 M tetraethoxysilane (TEOS) and 0.075 M ammonia water. Ethanol was used as the organic solvent, and the theoretical solid content was 10.5 wt% (93.8 parts by weight of TEOS and 258 parts by weight of the total solution). The subsequent experimental procedure was carried out in the same manner as in Comparative Example 1.

[0124] <Comparative Example 4> Preparation of high-concentration silica sol by the sol-gel method

[0125] In Comparative Example 4, a high-concentration silica sol was prepared and compared by further increasing the concentration of the alkoxysilane precursor compared to Comparative Example 3.

[0126] Specifically, the experiment was conducted using 8 M water based on 2 M tetraethoxysilane (TEOS) and 0.075 M ammonia water. Ethanol was used as the organic solvent, and the theoretical solid content was 13.6 wt% (125 parts by weight of TEOS and 265 parts by weight of the total solution). The subsequent experimental procedure was carried out in the same manner as in Comparative Example 1.

[0127] <Example 3> Preparation of High-Concentration Silica Sol by Precursor Splitting

[0128] In Example 3, a high-concentration silica sol was prepared by using a tetravalent alkoxysilane divided into two portions compared to Comparative Example 4 (TEOS 2M).

[0129] Specifically, a first reaction was carried out for 12 hours under ethanol using an amount corresponding to 1M TEOS, 4M water, and 0.075M ammonia water from the total mixture of 2M tetraethoxysilane (TEOS), 8M water, and 0.075M ammonia water. Subsequently, the remaining 1M TEOS and 4M water were added all at once to carry out a second reaction. At this time, the theoretical solid content for the first reaction was 10.0 wt% (62.5 parts by weight of TEOS and 180.1 parts by weight of the total first solution), similar to Comparative Example 3, and the theoretical solid content for the second reaction was 13.6 wt% (125 parts by weight of TEOS and 265 parts by weight of the total solution). The remaining experimental procedures were carried out in the same manner as Comparative Example 3.

[0130] <Example 4> Preparation of High-Concentration Silica Sol by Precursor Splitting and Booster Catalyst

[0131] In Example 4, a high-concentration silica sol was prepared by using a tetravalent alkoxysilane divided into two portions and a booster catalyst, in contrast to Example 3.

[0132] Specifically, a first reaction was carried out for 12 hours under ethanol using an amount corresponding to 1M TEOS, 4M water, and 0.075M ammonia water from the total mixture of 2M tetraethoxysilane (TEOS), 8M water, and 0.075M ammonia water. Subsequently, a second reaction was carried out by adding an additional 0.075M ammonia water all at once along with the remaining 1M TEOS and 4M water. At this time, the theoretical solid content for the first and second reactions was 10.0 wt% and 13.6 wt%, respectively. The remaining experimental procedures were carried out in the same manner as in Example 3.

[0133] Table 5 below shows the results for Comparative Example 3 and Examples 3 and 4 above.

[0134] 1st Reaction Composition Ratio (M) (TEOS / Catalyst / Water) 2nd Reaction Composition Ratio (M) (TEOS / Booster Catalyst / Water) Solids (wt%) (Conversion Rate (%)) Final Particle Diameter (nm) 12h 24h Comparative Example 3 1.5 / 0.075 / 6 No Input 9.8 (93.6) 9.98 (95.3) 76.6 Comparative Example 42 / 0.075 / 8 No Input 12.78 (94.1) 12.76 (94.0) 199 Example 31 / 0.075 / 41 / 0 / 49.84 (98.9) 11.60 (85.4) 76.1 Example 41 / 0.075 / 41 / 0.075 / 49.71 (97.4) 14.07 (103.5)80.4

[0135] As shown in Comparative Examples 3 and 4, it can be seen that increasing the concentration of the alkoxysilane precursor leads to an increase in particle size. As seen in the SEM images of Fig. 6(a) (Comparative Example 3) and (b) (Comparative Example 4), along with an increase in average particle size, the particle shape also exhibits a heterogeneous morphology in which large and small particles are mixed. Furthermore, regarding the conversion rate, it can be seen that it does not reach 100% even after 24 hours following the reaction. This appears to be due to conditions where the reaction is difficult to complete because the catalyst content is insufficient relative to the increased amount of alkoxysilane precursor.

[0136] Example 3 is a case where 2M of total TEOS and 8M of water were added in equal halves in the first and second stages, and it can be seen that the particle size was significantly reduced compared to Comparative Example 4, which used 2M of TEOS. This can be explained by the effect of maintaining a low concentration at the beginning of the reaction. However, the conversion rate did not reach 100% even after 24 hours, which appears to be an environment where there is insufficient catalyst for the silane precursor added in the second stage, as in Comparative Examples 3 and 4, to complete the reaction.

[0137] Example 4 is a case in which TEOS and water were divided into two portions as in Example 3, but a booster catalyst was added during the second TEOS addition. Similar to Example 3, it can be seen that the particle size was significantly reduced compared to Comparative Example 4. Furthermore, in this case, it was confirmed that the conversion rate reached over 100% after 24 hours following the addition of the second precursor. This indicates that the reaction of the TEOS, which was increased by the booster catalyst, can be completed.

[0138] Looking at the SEM images of Fig. 6(c) (Example 3) and (d) (Example 4), it can be seen that when the increased amount of TEOS is added all at once, the particles are formed much more uniformly than in (a) and (b).

[0139] It is noteworthy that the theoretical solid content concentration after the addition of the primary precursor in Examples 3 and 4 is 10.5 wt%, which is similar to the environment of 10.0 wt% in Comparative Example 1, and that the respective average particle sizes are also similar at the level of ~80 nm. In other words, while it is generally expected that the particle size will continuously grow by reacting on the surface of existing particles when reactants are continuously added, it is inferred that in the present invention, the secondary TEOS added does not grow the particles formed during the first reaction but rather forms them independently. This is because, referring to Figure 2 which shows the change in conversion rate over time in Comparative Example 1 (ammonia water 0.075 M, water 4 M), the reaction proceeded significantly to over 98-99% during the 12 hours following the addition of the primary precursor, and because the secondary reactant precursor was added all at once, new seeds were formed at a high concentration during the secondary reaction, and these seeds grew separately into particles. Due to these features of the present invention, it is believed that a high concentration of silica sol is obtained uniformly while suppressing an increase in particle size.

[0140]

[0141] Therefore, due to these characteristics, the technology capable of high-speed manufacturing and high concentration while suppressing the increase in size of the silica nanoparticles is expected to be utilized as an organic-inorganic nanocomposite material in various industrial fields.

[0142]

[0143] The foregoing description is merely an illustrative explanation of the technical concept of the present invention, and those skilled in the art to which the present invention pertains will be able to make various modifications and variations within the scope of the essential characteristics of the present invention. Accordingly, the embodiments disclosed in the present invention are intended to explain, not limit, the technical concept of the present invention, and the scope of the technical concept of the present invention is not limited by such embodiments. The scope of protection of the present invention shall be interpreted by the claims, and all technical concepts within an equivalent scope shall be interpreted as being included within the scope of rights of the present invention.

Claims

A first step of preparing a silane precursor solution by mixing a 1,4-valent alkoxysilane with an organic solvent; A second step of forming silica particles through a sol-gel reaction in the mixture by adding a basic catalyst and water to the above silane precursor solution and mixing them; A third step of producing silica nanoparticles by adding a booster catalyst and completing the reaction after the conversion rate of the sol-gel reaction in the second step reaches 40 to 80%; comprising In the second step above, the silica particles are formed as the particle seeds aggregate by a sol-gel reaction, and Characterized by adding a booster catalyst in the third step to additionally form silica particles and accelerate the sol-gel reaction, while relatively suppressing the growth of the silica particles formed in the second step due to aggregation, thereby producing a silica sol containing silica nanoparticles with uniformly controlled particle size. Method for preparing silica sol using a booster catalyst.

2. In Paragraph 1, A method for preparing a silica sol using a booster catalyst, characterized in that the silica nanoparticles have a particle diameter of up to 30 nm.

3. In Paragraph 1, A method for preparing a silica sol using a booster catalyst, characterized in that the booster catalyst is one or more selected from the group consisting of ammonium hydroxide, ammonium hydroxide, ammonium chloride, methyl amine, ethyl amine, propyl amine, isopropyl amine, butyl amine, cyclohexyl amine, dimethyl amine, diethyl amine, trimethyl amine, and triethyl amine.

4. In Paragraph 1, The concentration of the above booster catalyst is, A method for producing silica nanoparticles using a booster catalyst, characterized by being 0.01 to 0.1M. 5.1st step of preparing a silane precursor solution by mixing a primary tetravalent alkoxysilane and an organic solvent; A second step of forming silica particles through a sol-gel reaction in the mixture by adding a basic catalyst and water to the above silane precursor solution and mixing them; A third step of preparing silica nanoparticles by further mixing a secondary tetravalent alkoxysilane and water with a booster catalyst and completing the reaction after the conversion rate of the sol-gel reaction in the second step reaches 80%; In the second step above, the silica particles are formed as the particle seeds aggregate by a sol-gel reaction, and Characterized by adding a booster catalyst in the third step to additionally form silica particles and accelerate the sol-gel reaction, while relatively suppressing the growth of the silica particles formed in the second step due to aggregation, thereby producing a silica sol containing a high concentration of silica nanoparticles with uniformly controlled particle size. Method for preparing silica sol using a booster catalyst.

6. In Paragraph 5, The above silica sol. A method for producing a silica sol using a booster catalyst, characterized by being a high-concentration silica sol having a solid content of 10 to 15 wt%.

7. In Paragraph 5, A method for preparing a silica sol using a booster catalyst, characterized in that the booster catalyst is one or more selected from the group consisting of ammonium hydroxide, ammonium hydroxide, ammonium chloride, methyl amine, ethyl amine, propyl amine, isopropyl amine, butyl amine, cyclohexyl amine, dimethyl amine, diethyl amine, trimethyl amine, and triethyl amine.

8. In Paragraph 5, The concentration of the above booster catalyst is, A method for preparing a silica sol using a booster catalyst, characterized by being 0.01 to 0.1M.

9. A silica sol characterized by being manufactured according to any one of claims 1 to 8.

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