Preparation method of silicon dioxide aqueous dispersion liquid

Abstract

The invention relates to a preparation method of a silicon dioxide aqueous dispersion liquid, which comprises 15-35% of silicon dioxide; 1%-4% of a silane coupling agent; the pH value of the dispersion liquid is 3 to 9; 90% of the total amount of deionized water is added into a dispersing and homogenizing all-in-one machine; uniformly mixing and stirring a coupling agent and ethanol, adding the mixture into an all-in-one machine, adding 1 / 4 of the total acid amount, starting a dispersion machine, and stirring for 40 minutes to 1.5 hours; adding silicon dioxide for 3-5 times, adding 15-30 minutes, adding 1 / 4 of the total acid amount after the silicon dioxide is added for the second time, adding the rest 1 / 2 of the acid after the silicon dioxide is added, and adjusting the pH value to a target value. Continuously stirring by the dispersion machine for 30 minutes to 1 hour; closing the dispersion machine, starting the high-speed homogenizer, and homogenizing for 1-2 hours at the speed of 2500-3000rpm; and closing the high-speed homogenizer, starting the dispersion machine for the second time, stirring and cooling for 1-2 hours to room temperature, and discharging and sub-packaging. The silicon dioxide aqueous dispersion liquid provided by the invention has the advantages of nanoscale particle size, high specific surface area, high solid content, low viscosity, no toxicity, environmental protection, good dispersion stability, long-term storage and suitability for large-scale industrialization, and can be applied to the fields of medical carriers, coating additives, high-air-permeability medical packaging materials, functional coating materials, biodegradable material modification and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of chemical materials, and particularly relates to a preparation method of a silica aqueous dispersion. BACKGROUND

[0002] Inorganic pigments are widely used in the fields of coatings, inks, plastics, ceramics and the like due to their excellent heat resistance, chemical stability and the like. Traditional inorganic pigments usually exist in the form of powder and need to be dispersed in actual application. However, the inorganic pigments have high surface energy and are easy to agglomerate, and are difficult to be stably dispersed in an aqueous system, which affects their application performance.

[0003] At present, common inorganic pigment dispersion methods include mechanical grinding and surface modification. The mechanical grinding has high energy consumption and low efficiency, and is easy to damage the structure of pigment particles; the surface modification has problems of complex process and high cost. Therefore, it is of great significance to develop an efficient, environmentally friendly and low-cost preparation method of an inorganic pigment aqueous dispersion.

[0004] Silica is a kind of inorganic material which is non-toxic, odorless and chemically stable, and is widely used in traditional fields such as coatings, latex, rubber, papermaking, textiles and the like, and gradually expands to emerging fields such as high-air-permeability medical packaging and biodegradable material modification. Silica is chemically stable, non-toxic and odorless. Micron-sized silica has poor dispersion stability, a complex dispersion system, difficulty in preparing a high-solid-content and low-viscosity dispersion, and limited storage time, which limits its application. Nanoscale amorphous silica has unique advantages such as surface effect, volume effect and quantum size effect, but the agglomeration is more serious, which leads to the re-aggregation of originally uniformly dispersed particles during storage, forming larger particles or precipitates, resulting in the decrease of dispersion stability, the deterioration of fluidity and the obvious stratification and precipitation. Especially in the field of medical packaging, although silica can significantly improve the air permeability, antibacterial property and antistatic property of materials, dispersion is still the key bottleneck restricting performance improvement. At present, it is urgent to optimize the dispersant formula, surface modification process and storage conditions, develop a high-stability, high-solid-content and low-viscosity silica dispersion system, and directly apply the modified silica to meet the strict requirements of industrial application on long-term storage stability and functional reliability. SUMMARY

[0005] In order to overcome the deficiencies of the prior art, the purpose of the present application is to provide a preparation method of a silica aqueous dispersion, which uses deionized water as the water requirement, and the dispersion has good dispersion stability, so as to solve the technical problems of easy agglomeration, poor dispersion and stability in the prior art.

[0006] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: A kind of aqueous dispersion of silicon dioxide, characterized in that, comprising the following composition by mass percentage: Nano-silica: 15%~35%; Silane coupling agent: 1%~4%; Ethanol: 5%~15%; The rest is deionized water, liquid pH value 3~9.

[0007] A preparation method of an aqueous dispersion of silicon dioxide, characterized in that, comprising the following steps: Step 1, add 90% of the total amount of deionized water in a dispersion homogenizer (referred to as an all-in-one machine); Step 2, mix and stir the coupling agent and ethanol uniformly, add them to the all-in-one machine, add 1 / 4 of the total acid, start the dispersion machine and stir for 40 min~1.5 h; Step 3, add the silicon dioxide in 3-5 times, and add it completely in 15~30 min; after adding the silicon dioxide for the second time, add 1 / 4 of the total acid, add the remaining 1 / 2 of the acid after adding the silicon dioxide completely, and adjust the pH to the target value. Continue stirring with the dispersion machine for 30 min~1 h; Step 4, turn off the dispersion machine, start the high-speed homogenizer, and homogenize at 2500~3000 rpm for 1~2 h; Step 5, turn off the high-speed homogenizer, start the dispersion machine again to stir and cool for 1~2 h to room temperature, and then discharge and package.

[0008] The remaining 10% of the deionized water in step 1 is used as a rinsing container after the coupling agent and ethanol in step 2 are fully stirred, and it is rinsed 2 to 3 times.

[0009] The silane coupling agent in step 2 is one of γ-aminopropyl triethoxysilane (KH550), γ-glycidyl ether propyl trimethyl silane (KH560), γ-methacryloyl propyl trimethoxysilane (KH570), and aqueous solution of epoxy silane polymer (FD-7262).

[0010] The total amount of acid in step 2 is calculated according to the pH of the dispersion being 3~9.

[0011] The rotation speed of the dispersion machine in step 2 is 1000 rpm.

[0012] In step 3, the silicon dioxide is added slowly, and the rotation speed of the dispersion machine is 1500 rpm; after adding it completely, continue to disperse for 30 min~1 h; in step 4, high-speed homogenization is required in the shearing homogenization process, the rotation speed is 2500~3000 rpm, and the homogenization time is 1~2 h; in step 5, the dispersion liquid cooling process, turn off the homogenizer, start the dispersion machine again at a rotation speed of 1000 rpm, stir for 1~2 h to reduce the temperature to room temperature.

[0013] The silica dispersion liquid has a silica dispersion liquid solid content of 15%-35%, a silica dispersion liquid pH of 3-9, or a silica average particle size of 15-25 microns.

[0014] The type of acid for adjusting the pH value of the silica dispersion liquid is one or more of acetic acid, citric acid, nitric acid, and hydrochloric acid.

[0015] The present application has the following advantages: 1) The silica aqueous dispersion provided by the present application has good dispersion stability, a storage stability of more than 6 months, and good rheological properties and porosity, and can adjust the color, hiding property, gloss, and air permeability of a coating.

[0016] 2) The inorganic pigment aqueous dispersion provided by the present application has a simple preparation method, is easy to operate, has a uniform particle size distribution, a solid content of 15%-35%, and good dispersion, is not prone to precipitation, is easy to store and transport, and has low preparation cost, and is suitable for industrial production.

[0017] 3) The silica aqueous dispersion provided by the present application can be widely applied in the fields of water-based paint, water-based ink, and water-based color paste, and has good application prospects.

[0018] 4) The silane coupling agent used in the present application is a kind of organosilicon compound, can be applied to enhance the heat sealing performance and peel strength of a coating and a substrate, and has wide application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 to improve the stability of the dispersion liquid; Figure 2 to improve the air permeability of the composite adhesive paper and medical adhesive cover paper; Figure 3 to improve the peel performance of the high-air-permeability medical adhesive cover paper; DETAILED DESCRIPTION

[0020] The present application is further described below in conjunction with examples, but is not limited to the following examples.

[0021] As shown in FIGS. Figure 1 , 2 , 3, in the specific embodiments of the present application, the dispersion process and the high-speed homogenization process both require sealed instruments to prevent liquid evaporation and dust diffusion.

[0022] The silica aqueous dispersion of the present application has high solid content, low viscosity, good dispersion stability, and can be stored for a long time, is suitable for large-scale industrialization, and is suitable for use as a matting agent in the paint industry, as a reinforcing agent in the latex industry, and the like. Example 1

[0023] 1) Add 70 kg of deionized water in the integrated machine.

[0024] 2) Use silane coupling agent γ-aminopropyl triethoxysilane (KH550) to modify silica, KH550 is added in an amount of 2.5 kg, mixed with 8 kg of ethanol and stirred uniformly for 10 min, 4-5 kg of deionized water is reserved for washing the container, then transferred to the integrated machine, add 1 / 4 acid, start the dispersion machine to stir for 40 min.

[0025] 3) Add 5 kg of silica each time, interval 3 to 5 min, after adding 1 / 4 acid after adding silica the second time, add the remaining 1 / 2 acid after adding silica the third time, adjust the pH to 4-5, continue stirring with the dispersion machine.

[0026] 4) Continue to disperse and stir for 30 min.

[0027] 5) Turn off the dispersion machine, start the high-speed homogenizer for 1 h.

[0028] 6) Turn off the high-speed homogenizer, start the dispersion machine again to stir for 1 h to cool down to room temperature.

[0029] The silica dispersion liquid obtained in this example has a solid content of 15.46%, after standing for 24 h, the solid content of the upper and lower dispersion liquids is measured to be 15.45% and 15.51% respectively, the stability coefficient is 0.02%; after secondary homogenization, the solid content of the upper and lower dispersion liquids is measured to be 15.54% and 15.63% respectively, the stability coefficient is 0.13%, the dispersion liquid is uniform and stable after secondary homogenization, and can be continuously used.

[0030] The composite primer is prepared by mixing the dispersion liquid obtained in this example with the primer in a certain proportion and homogenizing, and the composite primer paper has a permeability of 360 ml / min, a longitudinal / transverse tensile strength of 93.8 N / 44.7 N, and a longitudinal / transverse tear strength of 927.055 mN / 768.842 mN. The final medical cover paper has a permeability of 221 ml / min, a longitudinal / transverse tensile strength of 88.02 N / 44.75 N, a longitudinal / transverse tear strength of 1060.42 mN / 814.606 mN, a whiteness of 78.74, a roughness of 7.94 μm, and a peel strength of 5.13 N. Example 2

[0031] 1) Add 65 kg of deionized water in the integrated machine.

[0032] 2) Silica was modified by silane coupling agent γ-aminopropyl triethoxysilane (KH550), KH550 was added in an amount of 2 kg, mixed with 8 kg of ethanol and stirred uniformly for 10 min, 4-5 kg of deionized water was reserved for washing the container, then transferred to the all-in-one machine, 1 / 4 of the acid was added, and the dispersion machine was started to stir for 40 min.

[0033] 3) 6-7 kg of silica was added each time, with an interval of 3 to 5 min, 1 / 4 of the acid was added after the second addition of silica, and the remaining 1 / 2 of the acid was added after the third addition of silica, the pH was adjusted to 3-4, and the dispersion machine continued to stir.

[0034] 4) Continue to disperse and stir for 30 min.

[0035] 5) Turn off the dispersion machine, and start the high-speed homogenizer for 1 h.

[0036] 6) Turn off the high-speed homogenizer, and start the dispersion machine again to stir for 1 h, until the temperature reaches room temperature.

[0037] The solid content of the silica dispersion obtained in this example was 20.49%, and after standing for 24 h, a precipitate was formed, the solid content of the upper and lower dispersions was measured to be 20.56% and 20.58% respectively, and the stability coefficient was 0.08%, after secondary homogenization, the solid content of the upper and lower dispersions was measured to be 20.61% and 20.62% respectively, and the stability coefficient was 0.13%, after secondary homogenization, the dispersion was uniform and stable, and could be used continuously.

[0038] The dispersion obtained in this example was mixed with the primer in a certain proportion to prepare a composite primer by homogenization, and after coating, the composite primer paper had a permeability of 380 ml / min, a longitudinal / transverse tensile strength of 98.22 N / 58.8 N, and a longitudinal / transverse tear strength of 659.007 mN / 602.782 mN. The final medical cover paper had a permeability of 229 ml / min, a longitudinal / transverse tensile strength of 97.84 N / 55.2 N, a longitudinal / transverse tear strength of 740.075 mN / 713.924 mN, a whiteness of 78.29, a roughness of 6.92 μm, and a peel strength of 4.96 N.

[0039] Example 3

[0040] 1) Add 60 kg of deionized water to the all-in-one machine.

[0041] 2) Silica was modified by silane coupling agent γ-aminopropyl triethoxysilane (KH550), KH550 was added in an amount of 1.5 kg, mixed with 6 kg of ethanol and stirred for 10 min, 7-8 kg of deionized water was reserved for washing the container, then transferred to the all-in-one machine, 1 / 4 of the acid was added, and the dispersion machine was started to stir for 40 min.

[0042] 3) Add 6 kg of silica each time, with an interval of 3 to 5 min. After adding the silica the second time, add 1 / 4 of the acid. After adding the silica the fourth time, add the remaining 1 / 2 of the acid, adjust the pH to 3-4, and continue stirring with the disperser.

[0043] 4) Continue stirring with the disperser for 30 min.

[0044] 5) Turn off the disperser and start the high-speed homogenizer for 1 h.

[0045] 6) Turn off the high-speed homogenizer, start the disperser again, and cool for 1 h, until the temperature reaches room temperature.

[0046] The solid content of the silica dispersion obtained in this example was 24.37%. After standing for 24 h, the solid contents of the upper and lower dispersions were 23.87% and 24.65%, respectively, and the stability coefficient was 3.16%. After secondary homogenization, the solid contents of the upper and lower dispersions were 24.38% and 24.45%, respectively, and the stability coefficient was 0.29%. The dispersion after secondary homogenization was uniform and stable, and could be used continuously.

[0047] The composite base adhesive was prepared by mixing the dispersion obtained in this example with the base adhesive in a certain proportion and homogenizing. After coating, the composite base adhesive paper had a permeability of 366 ml / min, a longitudinal / transverse tensile strength of 98.58 N / 60.8 N, and a longitudinal / transverse tear strength of 687.773 mN / 673.369 mN. The final medical cover paper had a permeability of 275 ml / min, a longitudinal / transverse tensile strength of 100.9 N / 55.6 N, a longitudinal / transverse tear strength of 702.156 mN / 648.547 mN, a whiteness of 78.77, a roughness of 6.84 μm, and a peel strength of 4.89 N. Example 4

[0048] 1) Add 48 kg of deionized water to the all-in-one machine.

[0049] 2) Use KH560-modified silica, add 3.1 kg, mix with 14 kg of ethanol and stir for 10 min, reserve 4-5 kg of deionized water for washing the container, then transfer to the disperser, add 1 / 4 of the acid, and start stirring with the disperser for 40 min.

[0050] 3) Add 8 kg of silica each time, with an interval of 3 to 5 min. After adding the silica the second time, add 1 / 4 of the acid. After adding the silica the fourth time, add the remaining 1 / 2 of the acid, and adjust the pH to 2-3.

[0051] 4) Continue stirring with the disperser for 30 min.

[0052] 5) Turn off the disperser and start the high-speed homogenizer for 1 h.

[0053] 6) Turn off the high-speed homogenizer, restart the disperser and stir and cool for 1 hour until the temperature reaches room temperature.

[0054] The silica dispersion obtained in this embodiment has a solid content of 30.04%. After standing for 24 hours, the solid contents of the upper and lower layers of the dispersion were measured to be 29.98% and 30.15%, respectively, with a stability coefficient of 0.06%. After a second homogenization, the solid contents of the upper and lower layers of the dispersion were measured to be 30.05% and 30.09%, respectively, with a stability coefficient of 0.07%. The dispersion was homogeneous and stable after the second homogenization and can be used.

[0055] In this embodiment, the dispersion obtained was mixed and homogenized with the primer in a certain proportion to prepare a composite primer. After coating, the composite primer paper had an air permeability of 333 ml / min, longitudinal / transverse tensile strength of 101.17 N / 62.1 N, and longitudinal / transverse tear strength of 693.003 mN / 627.626 mN. The final medical cover paper had an air permeability of 225 ml / min, longitudinal / transverse tensile strength of 94.8 / 55.8 N, longitudinal / transverse tear strength of 763.615 mN / 661.622 mN, whiteness of 78.40, roughness of 6.42 mm, and peel strength of 5.21 N. Example 5

[0056] 1) Add 60kg of deionized water to the all-in-one machine and turn on the disperser to stir.

[0057] 2) Use FD-7252 to modify silica. Add 3kg of FD-7252 and 12kg of ethanol and mix evenly for 10min. Reserve 7-8kg of deionized water to rinse the container and transfer it to the integrated machine. Add 1 / 4 of the acid and start the disperser to stir for 40min.

[0058] 3) Add 6 kg of silica each time, with an interval of 3 to 5 minutes. After the second addition of silica, add 1 / 4 of the acid. After the fourth addition of silica, add the remaining 1 / 2 of the acid and adjust the pH to 7.5-8.5.

[0059] 4) Continue to disperse and stir for 30 minutes.

[0060] 5) Turn off the disperser and start the high-speed homogenizer to homogenize for 1 hour.

[0061] 6) Turn off the high-speed homogenizer, restart the disperser and stir and cool for 1 hour until the temperature reaches room temperature.

[0062] The solid content of the obtained silica dispersion liquid in this embodiment is 23.30%, and a precipitate is formed after standing for 24 h. The solid contents of the upper and lower dispersions are 23.14% and 23.27% respectively, and the stability coefficient is 0.56%. After secondary homogenization, the solid contents of the upper and lower dispersions are 23.26% and 23.35% respectively, and the stability coefficient is 0.39%. The dispersion liquid is uniform and stable after secondary homogenization, and can be continuously used.

[0063] In this embodiment, the obtained dispersion liquid is mixed with the base adhesive at a certain ratio to prepare a composite base adhesive by homogenization. After coating, the air permeability of the composite base adhesive paper is 347 ml / min, and the longitudinal / transverse tensile strength is 100.0 N / 55.5 N. The longitudinal / transverse tear strength is 757.074 mN / 712.615 mN. The final medical cover paper has an air permeability of 231 ml / min, a longitudinal / transverse tensile strength of 94.8 / 55.8 N, a longitudinal / transverse tear strength of 802.763 mN / 822.661 mN, a whiteness of 77.88, a roughness of 6.53 μm, and a peel strength of 5.17 N. Example 6

[0064] 1) Add 60 kg of deionized water to the disperser.

[0065] 2) Use KH550 modified silica. Mix 3 kg of KH550 with 12 kg of ethanol and stir for 10 min. Rinse the container with the remaining 7-8 kg of deionized water and transfer it to the all-in-one machine. Add 1 / 4 acid and start the disperser for 40 min.

[0066] 3) Add 6 kg of silica each time, with an interval of 3 to 5 min. After adding the second batch of silica, add 1 / 4 acid. After adding the fourth batch of silica, add the remaining acid. Adjust the pH of the dispersion liquid to 8-9.

[0067] 4) Continue to disperse and stir for 30 min.

[0068] 5) Turn off the disperser and start the high-speed homogenizer for 1 h.

[0069] 6) Turn off the high-speed homogenizer and start the disperser again for 1 h to cool down to room temperature.

[0070] The solid content of the obtained silica dispersion liquid in this embodiment is 25.6%, and a precipitate is formed after standing for 24 h. The solid contents of the upper and lower dispersions are 25.36% and 25.65% respectively, and the stability coefficient is 1.13%. After secondary homogenization, the solid contents of the upper and lower dispersions are 25.50% and 25.71% respectively, and the stability coefficient is 0.82%. The dispersion liquid is uniform and stable after secondary homogenization, and can be continuously used.

[0071] The dispersion obtained in the example is mixed with the primer in a certain ratio to prepare a composite primer, and the composite primer paper has a permeability of 351 ml / min, a longitudinal / transverse tensile strength of 97.4 N / 53.5 N, and a longitudinal / transverse tear strength of 739.057 mN / 722.612 mN. The final medical cover paper has a permeability of 242 ml / min, a longitudinal / transverse tensile strength of 89.4 / 44.7 N, a longitudinal / transverse tear strength of 863.134 mN / 813.491 mN, a whiteness of 78.17, a roughness of 5.81 μm, and a peeling force of 5.24 N.

Claims

1. A silica aqueous dispersion, characterized in that, It comprises the following components by weight percentage: Nano-silica: 15%–35%; Silane coupling agent: 1%–4%; Ethanol: 5%–15%; The rest is deionized water, with a liquid pH of 3-9.

2. A method for preparing an aqueous dispersion of silica, characterized in that, Includes the following steps: Step 1: Add 90% of the total amount of deionized water to the dispersion homogenizer; Step 2: Mix the coupling agent and ethanol evenly, add them to the integrated machine, add 1 / 4 of the total acid, and start the disperser to stir for 40 min to 1.5 h; Step 3: Add silica in 3-5 portions, completing the addition over 15-30 minutes. After the second addition of silica, add 1 / 4 of the total acid volume. After the silica is finished, add the remaining 1 / 2 of the acid and adjust the pH to the target value. Continue stirring in the disperser for 30 minutes to 1 hour. Step 4: Turn off the disperser and start the high-speed homogenizer. Homogenize at 2500~3000 rpm for 1~2 hours. Step 5: Turn off the high-speed homogenizer, restart the disperser to stir and cool for 1-2 hours to room temperature, and then discharge and package the material.

3. The method for preparing an aqueous silica dispersion according to claim 2, characterized in that, In step 1, 10% of the remaining deionized water is used to rinse the container after the coupling agent and ethanol have been thoroughly mixed in step 2, and the container is rinsed 2 to 3 times.

4. The method for preparing an aqueous silica dispersion according to claim 2, characterized in that, In step 2, the silane coupling agent is one of γ-aminopropyltriethoxysilane (KH550), γ-glycidyl etheroxypropyltrimethylsilane (KH560), γ-methacryloyloxypropyltrimethoxysilane (KH570), and an aqueous solution of epoxy silane polymer (FD-7262).

5. The method for preparing an aqueous silica dispersion according to claim 2, characterized in that, In step 2, the total amount of acid is calculated based on the pH of the dispersion being 3-9.

6. The method for preparing an aqueous silica dispersion according to claim 2, characterized in that, In step 2, the disperser rotates at 1000 rpm.

7. The method for preparing an aqueous silica dispersion according to claim 2, characterized in that, In step 3, silica is added slowly at a speed of 1500 rpm, and dispersion continues for 30 min to 1 h after addition. In step 4, the shearing homogenization process requires high-speed homogenization at a speed of 2500 to 3000 rpm for 1 to 2 h. In step 5, during the cooling process of the dispersion, the homogenizer is turned off and restarted at a speed of 1000 rpm for 1 to 2 h to cool down to room temperature.

8. The method for preparing an aqueous silica dispersion according to claim 2, characterized in that, The silica dispersion has a solid content of 15% to 35%, a pH of 3 to 9, or an average particle size of 15 to 25 μm.

9. The method for preparing an aqueous silica dispersion according to claim 2, characterized in that, The type of acid used to adjust the pH of the silica dispersion is one or more of acetic acid, citric acid, nitric acid, and hydrochloric acid.

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