Preparation method of modified silica sol in acidic system

Abstract

The invention discloses a preparation method of stable modified silica sol in an acidic system, which comprises the following steps: under the action of a zwitterionic polymer, directly grafting a silane coupling agent treated by amino acid on the surfaces of silica particles, so that the grafting rate of the coupling agent on the surfaces of the small-particle-size silica particles in the acidic system is effectively improved; meanwhile, the silane coupling agent treated by the amino acid can also reduce agglomeration among silicon dioxide particles, so that the acid stability of the silicon dioxide particles is improved. The thermal expansion microspheres prepared by the method are low in deslagging rate and good in stability.

Description

Technical Field

[0001] The invention belongs to the field of microsphere preparation, and particularly relates to a method for preparing modified silica sol. Background Art

[0002] Heat-expandable thermoplastic microspheres are a type of foaming material that can soften its shell under heating and expand into a sphere by relying on the foaming agent inside the microspheres. This material has important application prospects in industries such as automotive interior and exterior decoration, building materials, and household appliances. The typical preparation process of heat-expandable thermoplastic microspheres is internal polymerization of oil droplets in an emulsion system. In order for the reaction to proceed normally, the stability of the oil droplets is generally improved by using a Pickering emulsion of silica. Therefore, the prerequisite for the stable preparation of microspheres is to improve the stability of the silica dispersion.

[0003] The stability of silica dispersion depends on many factors, including particle size, solid content, pH value, surface hydrophilicity, etc. In an acidic system, stabilizing small-sized silica particles has always been a problem, because the smaller the particle size, the more silanol groups on the particle surface, the greater the surface energy, the easier it is for the particles to agglomerate, and the isoelectric point of silica particles is close to 0 in acidic conditions, so the particles are more unstable under acidic conditions. At present, the most effective way to prepare acidic silica sols with small particle size, high solid content, and long-term stability is surface modification.

[0004] People have never stopped exploring modified silica sols. Patent CN112094509A proposes to use a small molecule organic acid to form a dense hydration layer on the surface of silica particles in combination with a silane coupling agent, so that the surface of silica is coated with a large number of organic groups, reducing the further agglomeration of a large number of silanols, dimers and polymers produced by the hydrolysis of ethyl orthosilicate. However, from the results, the viscosity of the silica sol increased after being placed for 12 months. Obviously, its process is not suitable for application scenarios with higher requirements. Patent CN115703931 proposes that under acidic conditions, colloidal silica is modified with a hydrolyzed silane coupling agent, which can effectively inhibit the generation of floccules, precipitates or gelation of the silane coupling agent during and after addition. However, the particle size of the silica particles modified by this method will become larger, and the particles will reagglomerate after standing, and it is not suitable for high solid content systems. Some studies have also used silane coupling agents and some sterically hindered additives or zwitterionic compounds to be grafted onto silica particles. The silica particles prepared by this method are stable and the degree of modification is easy to control. For example, patent CN113713625 proposes to modify silica particles with silane coupling agents and zwitterionic compounds, and then polymerize zwitterionic compounds after drying the powder particles. This method requires multiple drying processes, so the uniformity and stability of the particles are difficult to ensure, and the process is cumbersome and the cycle is long, which is not suitable for industrialization.

[0005] Therefore, the preparation of modified silica sol still needs continuous exploration to improve the stability and uniformity of silica particles, simplify the process flow, and meet its high requirements in specific fields. Summary of the invention

[0006] In view of the above problems, the present invention innovatively proposes a method for preparing stable acidic silica sol, which realizes the stable storage of silica sol under acidic conditions. The present invention prepares a modified silica sol whose particle size does not change after being placed at room temperature for one year; in addition, the amount of thermal expansion microspheres prepared by using the silica sol of the present invention is small, and the microspheres are stable.

[0007] Another object of the present invention is to provide such modified silica sol.

[0008] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solution:

[0009] A method for preparing modified silica sol in an acidic system comprises the following steps:

[0010] 1) Pre-hydrolysis of silane coupling agent: adding a certain amount of amino acid, inorganic acid or organic acid to water to obtain an aqueous solution of amino acid;

[0011] The silane coupling agent is uniformly dissolved in ethanol, added to the aqueous solution of amino acid, and placed in a low-temperature water bath to obtain liquid A;

[0012] 2) Preparation of acidic silica sol: Add inorganic acid or organic acid to water, stir evenly and then drop silica sol into the water to obtain liquid B;

[0013] 3) Modification of acidic silica sol: Take liquid A and zwitterionic compound, stir them evenly, and then drop them into liquid B together. After placing them in a water bath at a certain temperature for a certain period of time, modified silica sol is obtained.

[0014] In a specific embodiment, in steps 1 and 2), the added water is preferably high-purity water, and the mass of the water in step 1) is 70-90 parts, preferably 75-80 parts;

[0015] In a specific embodiment, in step 1), the amino acid is one or more of glycine, alanine, valine, leucine, isoleucine, methionine (methionine), proline, tryptophan, serine, tyrosine, cysteine, phenylalanine, asparagine, glutamyl, threonine, L-aspartic acid, glutamic acid, lysine, arginine and histidine, preferably glutamic acid or L-aspartic acid;

[0016] In a specific embodiment, in steps 1 and 2), the inorganic acid or organic acid is selected from one or more of nitric acid, hydrochloric acid, phosphoric acid, sulfuric acid, acetic acid, citric acid or perchloric acid; the pH of the aqueous solution of amino acids in step 1) is controlled at 3-4, and the pH of the aqueous solution after adding silica sol in step 2) is controlled at 2-3.

[0017] In a specific embodiment, in step 1), the silane coupling agent may be one or more of γ-aminopropyltriethoxysilane (KH550), γ-glycidyloxypropyltrimethoxysilane (KH560), γ-methacryloxypropyltrimethoxysilane (KH570), and mercaptopropyltrimethoxysilane (KH580);

[0018] The amount of silane coupling agent added is 5-10 parts, and in order to quickly dissolve the silane coupling agent, the amount of ethanol added is 10-20 parts; in step 1), the molar ratio of the amino acid to the silane coupling agent is 1:1 to 3:1.

[0019] In a specific embodiment, in step 1), the temperature of the low-temperature water bath is 5-20°C; the water bath duration is 0.5-3h, preferably 0.5-1h.

[0020] In a specific embodiment, in step 2), the mass of water is 10-20 parts. The amount of silica sol added is at least 75 parts, preferably 75-80 parts, and its source is not limited to the silica sol prepared by sol-gel method or ion exchange method or hydrolysis of silicon powder, and its solid content is not less than 40wt%, for example 40-60%.

[0021] In a specific embodiment, the dropping speed of the silica sol in step 2) does not exceed 10 ml / min, preferably 3-5 ml / min; and the stirring time after the dropping of the silica sol is completed does not exceed 30 min.

[0022] In a specific embodiment, in step 3), the amount of liquid A added is 0.3-3 parts, preferably 0.9-2.4 parts.

[0023] In a specific embodiment, in step 3), the zwitterionic compound can be one or more of polymethacrylate carboxy betaine (PCBMA), polymethacrylate sulfobetaine (PSBMA), and polyphosphobetaine (PPC); the molar ratio of the added amount to the silane coupling agent in the added A liquid is 3:1 to 6:1.

[0024] In a specific embodiment, in step 3), the dropping speed of solution A and the zwitterionic compound does not exceed 5 ml / min, preferably 0.5-3 ml / min.

[0025] In a specific embodiment, in step 3), the water bath temperature is 30-70°C, preferably 40-60°C, and the water bath time is 2-12h, preferably 3-9h.

[0026] Another object of the present invention is to provide such modified silica sol.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1) The present invention uses amino acids to modify the silane coupling agent after hydrolysis, so that the molecular structure of the silane coupling agent has strong hydrophilicity and hydrophobicity, thereby hindering the agglomeration of silicon dioxide particles.

[0029] 2) The present invention uses zwitterionic compounds to directly graft silica under acidic conditions. The method is simple and easy to operate, and provides a reliable preparation method for the preparation of acidic silica sol. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 These are the modified silica sol particles prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0031] In order to better understand the technical solution of the present invention, the following examples will further illustrate the method provided by the present invention, but the present invention is not limited to the listed examples, and should also include any other known changes within the scope of the claims of the present invention.

[0032] The main raw materials used in the following examples and comparative examples are shown in Table 1:

[0033] Table 1 Main raw materials

[0034]

[0035]

[0036] Detection method:

[0037] The secondary particle size of the modified silica sol particles was tested by dynamic light scattering (DLS) and Malvern laser particle size detector.

[0038] The morphology of the modified silica sol particles was observed using TEM.

[0039] Example 1

[0040] Add 7g of glutamic acid and 10vol% hydrochloric acid to 75g of water and stir evenly, the pH is 3.25;

[0041] 10g KH550 was dissolved in 15.8g ethanol and then poured into the aqueous solution of glutamic acid. The mixture was placed in a low-temperature thermostatic bath at 5°C and stirred at a rate of 400r / min for 30min to obtain liquid A.

[0042] 80 g of silica sol (40 wt%) was pumped into 15 g of water to which nitric acid was added at a rate of 3 ml / min using a peristaltic pump, the pH value was 2.1, and stirred for 10 min to obtain liquid B.

[0043] Take 1.2 g of solution A, add 8 g of water and 0.8 g of PSBMA, add to solution B at a rate of 0.5 ml / min, place in a water bath at 60° C. and stir for 3 h to obtain modified acidic silica sol.

[0044] Example 2

[0045] 80g water was added with 9g L-aspartic acid and 10vol% nitric acid and stirred evenly, the pH was 3.89;

[0046] 8 g KH560 was dissolved in 19.7 g ethanol and then poured into an aqueous solution of L-aspartic acid. The mixture was placed in a low-temperature thermostatic bath at 10°C and stirred at a rate of 300 r / min for 45 min to obtain liquid A.

[0047] 75 g of silica sol (40 wt%) was pumped into 12 g of water to which hydrochloric acid was added at a rate of 4 ml / min using a peristaltic pump, the pH value was 2.3, and stirred for 20 min to obtain liquid B.

[0048] Take 1.6 g of solution A, add 10 g of water and 0.56 g of PCBMA, add to solution B at a rate of 1 ml / min, place in a 40° C. water bath and stir for 9 h to obtain modified acidic silica sol.

[0049] Example 3

[0050] Add 9.8g leucine and 10vol% sulfuric acid to 78g water and stir evenly, the pH is 3.67;

[0051] 7 g KH570 was dissolved in 17 g ethanol and then poured into the aqueous solution of glutamic acid. The mixture was placed in a low-temperature thermostatic bath at 15°C and stirred at a rate of 400 r / min for 60 min to obtain liquid A.

[0052] 77 g of silica sol (40 wt%) was pumped into 14 g of water to which sulfuric acid was added at a rate of 5 ml / min using a peristaltic pump, the pH value was 2.71, and stirred for 30 min to obtain liquid B.

[0053] Take 2.4 g of liquid A, add 17.7 g of water and 0.72 g of PPC, add to liquid B at a rate of 3 ml / min, place in a 40° C. water bath and stir for 10 h to obtain modified acidic silica sol.

[0054] Example 4

[0055] Add 9g of serine and 10vol% phosphoric acid to 77g of water and stir evenly, the pH is 3.68;

[0056] 8.1 g of KH580 was dissolved in 16.8 g of ethanol and then poured into the aqueous solution of serine. The mixture was placed in a low-temperature thermostatic bath at 10°C and stirred at a rate of 500 r / min for 120 min to obtain liquid A.

[0057] 79 g of silica sol (40 wt%) was pumped into 10 g of water added with 10 vol % phosphoric acid at a rate of 3 ml / min using a peristaltic pump, the pH value was 2.47, and stirred for 25 min to obtain liquid B.

[0058] Take 1.8 g of solution A, add 11 g of water and 0.42 g of PCBMA, add to solution B at a rate of 2 ml / min, place in a water bath at 60° C. and stir for 5 h to obtain modified silica sol.

[0059] Example 5

[0060] Add 14.5g lysine and 10vol% acetic acid to 80g water and stir evenly, the pH is 3.17;

[0061] 9.6 g KH580 was dissolved in 16.1 g ethanol and then poured into the aqueous solution of lysine. The mixture was placed in a low-temperature thermostatic bath at 13° C. and stirred at a rate of 400 r / min for 150 min to obtain liquid A.

[0062] 80 g of silica sol (40 wt%) was pumped into 14.6 g of water to which 10 vol % acetic acid was added at a rate of 3 ml / min using a peristaltic pump, the pH being 2.99, and stirred for 20 min to obtain liquid B.

[0063] Take 1.9 g of solution A, add 7 g of water and 0.81 g of PCBMA, add into solution B at a rate of 1 ml / min, place in a water bath at 45°C and stir for 5 h to obtain modified silica sol.

[0064] Comparative Example 1

[0065] 10 vol% nitric acid was added to 80 g of water and the pH was controlled to 3.89;

[0066] 8 g KH560 was dissolved in 19.7 g ethanol, then poured into aqueous nitric acid solution, placed in a low-temperature thermostatic bath at 10°C and stirred at a rate of 300 r / min for 45 min to obtain liquid A.

[0067] 75 g of silica sol (40 wt%) was pumped into 12 g of water added with 10 vol % hydrochloric acid at a rate of 4 ml / min using a peristaltic pump, pH was 2.3, and stirred for 20 min to obtain liquid B.

[0068] Take 1.5 g of solution A, add 10 g of water and 0.56 g of PCBMA, add to solution B at a rate of 1 ml / min, place in a 40° C. water bath and stir for 9 h to obtain modified silica sol.

[0069] Comparative Example 2

[0070] 80g water was added with 9g L-aspartic acid and 10vol% nitric acid and stirred evenly, the pH was 3.89;

[0071] 8 g KH560 was dissolved in 19.7 g ethanol and then poured into an aqueous solution of L-aspartic acid. The mixture was placed in a low-temperature thermostatic bath at 10°C and stirred at a rate of 300 r / min for 45 min to obtain liquid A.

[0072] 75 g of silica sol (40 wt%) was pumped into 12 g of water added with 10 vol % hydrochloric acid at a rate of 4 ml / min using a peristaltic pump, pH was 2.3, and stirred for 20 min to obtain liquid B.

[0073] Take 1.6 g of solution A and add 10.9 g of water, then add the mixture into solution B at a rate of 1 ml / min. Place the mixture in a water bath at 40° C. and stir for 9 h to obtain a modified acidic silica sol.

[0074] Comparative Example 3

[0075] 80g water was added with 10vol% nitric acid and stirred evenly, the pH was 3.89;

[0076] 8 g KH560 was dissolved in 19.7 g ethanol and then poured into a nitric acid aqueous solution. The mixture was placed in a low-temperature thermostatic bath at 10°C and stirred at a rate of 300 r / min for 45 min to obtain liquid A.

[0077] 75 g of silica sol (40 wt%) was pumped into 12 g of water added with 10 vol % hydrochloric acid at a rate of 4 ml / min using a peristaltic pump, pH was 2.3, and stirred for 20 min to obtain liquid B.

[0078] Take 1.6 g of solution A and add 10.9 g of water, then add the mixture into solution B at a rate of 1 ml / min. Place the mixture in a water bath at 40° C. and stir for 9 h to obtain a modified acidic silica sol.

[0079] In order to evaluate the stability of the modified silica sol, the silica sol was placed in a 60°C oven for aging observation (according to industry experience, the aging effect of a 60°C oven is equivalent to 15 times the aging time at room temperature). The dynamic light scattering method was used to regularly observe the change in particle size to characterize the stability of the acidic silica sol. The results are shown in Table 2.

[0080] Table 2 Changes in silica sol particle size

[0081]

[0082] Evaluation of the application of modified silica sol in the preparation of thermoplastic expandable microspheres:

[0083] The embodiment of patent CN115197519B was used to evaluate the stability of the modified silica particles by evaluating the amount of residue obtained when the microsphere slurry passed through a 100-mesh filter.

[0084] The specific process is as follows:

[0085] S1: Weigh 110 g of water, 6.5 g of potassium chloride, and 5 g of colloidal silicon dioxide, and mix them to form a mixture A.

[0086] S2: Weigh 10 g of acrylonitrile, 2 g of methacrylonitrile, 8 g of methyl acrylate, 5 g of methyl methacrylate, 0.25 g of diallyl phthalate, 1.5 g of blowing agent isobutane, and 0.375 g of polymerization initiator dilauroyl peroxide, and mix them to prepare a mixture B.

[0087] S3: Mixture A and mixture B were added into sealed containers respectively, and stirred at 1200 rpm for 25 min to form an emulsion.

[0088] S4: The formed emulsion was polymerized at 62°C and 500 rpm for 20 hours. The expandable microspheres were obtained by drying in an oven at 60°C. The obtained microspheres were passed through a 100-mesh sieve and the quality of the residue remaining on the sieve was tested. The results are shown in the following table:

[0089] Example Filter residue amount / % Example 1 0.09 Example 2 0.12 Example 3 0.09 Example 4 0.10 Example 5 0.08 Comparative Example 1 24.8 Comparative Example 2 25.6 Comparative Example 3 27.9

[0090] In the examples, a stable acidic silica sol can be prepared by adding different types of amino acids and zwitterionic polymers, with a solid content of approximately 30 wt%, and a particle size that is almost unchanged after aging in an oven at 60°C for 1 month (equivalent to 15 months at room temperature according to industry experience), and the amount of filter residue of the prepared thermoplastic microspheres is very low, indicating that the microspheres can stably encapsulate the oil droplet phase. By comparing Example 2 with Comparative Examples 1-3, it can be found that amino acids and zwitterionic polymers are the key to the stability of the acidic silica sol.

[0091] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as limiting the present invention. Those skilled in the art will appreciate that, under the guidance of this specification, some modifications or adjustments may be made to the present invention. These modifications or adjustments should also be limited by the claims of the present invention.

Claims

1. A method for preparing modified silica sol in an acidic system, comprising the following steps: 1) Pre-hydrolysis of silane coupling agent: adding a certain amount of amino acid, inorganic acid and / or organic acid to water to obtain an aqueous solution of amino acid; Dissolve the silane coupling agent in ethanol, mix with the aqueous solution of amino acid, and place in a low-temperature water bath to obtain solution A; 2) Preparation of acidic silica sol: Add inorganic acid and / or organic acid to water, stir evenly and then slowly add silica sol into the water. Get liquid B; 3) Modification of acidic silica sol: Take liquid A and zwitterionic compound, stir them evenly, and then slowly add them into liquid B, and obtain modified silica sol after water bath.

2. The method according to claim 1, characterized in that: The amino acid described in step 1) is one or more of glycine, alanine, valine, leucine, isoleucine, methionine (methionine), proline, tryptophan, serine, tyrosine, cysteine, phenylalanine, asparagine, glutamyl, threonine, L-aspartic acid, glutamic acid, lysine, arginine and histidine, preferably glutamic acid and / or L-aspartic acid.

3. The method according to claim 1 or 2, characterized in that: The silane coupling agent in step 1) is one or more of γ-aminopropyltriethoxysilane (KH550), γ-glycidyloxypropyltrimethoxysilane (KH560), γ-methacryloxypropyltrimethoxysilane (KH570), and mercaptopropyltrimethoxysilane (KH580); Preferably, in step 1), the molar ratio of the amino acid to the silane coupling agent is 1:1 to 3:

1.

4. The method according to any one of claims 1 to 3, characterized in that: In step 1), the inorganic acid or organic acid is selected from one or more of nitric acid, hydrochloric acid, phosphoric acid, sulfuric acid, acetic acid, citric acid or perchloric acid; Preferably, the pH of the aqueous solution of amino acids in step 1) is 3-4.

5. The method according to any one of claims 1 to 4, characterized in that: In step 1), the temperature of the low-temperature water bath is 5-20° C.; the water bath time is 0.5-3 h, preferably 0.5-1 h.

6. The method according to claim 1, characterized in that In step 2), the inorganic acid or organic acid is one or more of nitric acid, hydrochloric acid, phosphoric acid, sulfuric acid, acetic acid, citric acid or perchloric acid, and the amount added is such that the pH is between 2 and 3 after the addition of the silica sol.

7. The method according to claim 1, characterized in that In step 2), the addition rate of silica sol does not exceed 10 ml / min, preferably 3-5 ml / min; the stirring time after adding silica sol does not exceed 30 min; Preferably, the solid content of the silica sol is not less than 40 wt %.

8. The method according to claim 1, characterized in that In step 3), the zwitterionic compound is one or more of polymethacrylate carboxy betaine (PCBMA), polymethacrylate sulfobetaine (PSBMA), and polyphosphobetaine (PPC); preferably, the molar ratio of the zwitterionic compound to the silane coupling agent in the added A liquid is 3:1 to 6:

1.

9. The method according to claim 1 or 8, characterized in that: In step 3), the addition rate of solution A and zwitterionic compound does not exceed 5 ml / min, preferably 0.5-3 ml / min; Preferably, in step 3), the water bath temperature is 30-70° C., preferably 40-60° C., and the water bath time is 2-12 h, preferably 3-9 h.

10. The method according to any one of claims 1 to 9, characterized in that: The amount of components used in each step is: in step 1), the mass of water is 70-90 parts, preferably 75-80 parts; In step 1), the amount of silane coupling agent added is 5-10 parts, and the amount of ethanol added is 10-20 parts; In step 2), the mass of water is 10-20 parts, and the mass of silica sol is 75-80 parts; In step 3), the amount of liquid A added is 0.3-3 parts, preferably 0.9-2.4 parts.

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