CN111017935A - Preparation method of silica sol and application of silica sol in ceramic coating - Google Patents
Preparation method of silica sol and application of silica sol in ceramic coating Download PDFInfo
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- CN111017935A CN111017935A CN201911309469.2A CN201911309469A CN111017935A CN 111017935 A CN111017935 A CN 111017935A CN 201911309469 A CN201911309469 A CN 201911309469A CN 111017935 A CN111017935 A CN 111017935A
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B33/00—Silicon; Compounds thereof
- C01B33/113—Silicon oxides; Hydrates thereof
- C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
- C01B33/14—Colloidal silica, e.g. dispersions, gels, sols
- C01B33/146—After-treatment of sols
- C01B33/148—Concentration; Drying; Dehydration; Stabilisation; Purification
- C01B33/1485—Stabilisation, e.g. prevention of gelling; Purification
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- C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
- C04B28/24—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing alkyl, ammonium or metal silicates; containing silica sols
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- C—CHEMISTRY; METALLURGY
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- C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
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- C04B2111/00525—Coating or impregnation materials for metallic surfaces
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Abstract
The invention relates to the technical field of inorganic nano materials, in particular to a preparation method of silica sol and application of the silica sol in ceramic paint. The preparation method of the silica sol comprises the following steps: 1) preparing acidic silica sol by cation exchange of the alkaline silica sol, wherein the pH value of the acidic silica sol is 2.0-6.0; adding a coupling agent into the acidic silica sol obtained in the step 1) to obtain coupling agent modified silica sol; 2) adjusting the pH value of the coupling agent modified silica sol obtained in the step 2) to 3.5-5.5. According to the invention, partial hydroxyl on the surface of the acidic silica sol colloid particle reacts with the coupling agent by adding the coupling agent, so that the steric hindrance between the particles is increased, and the metastable silica sol solution becomes more stable. The pH value of the prepared coupling agent modified acidic silica sol is adjusted to be 3.5-5.5, and the acidic silica sol is suitable for hydrolysis reaction of a silane coupling agent. The silica sol with the stable pH value of 3.5-5.5 is used for preparing the ceramic coating, and an acid catalyst is not required to be additionally added.
Description
Technical Field
The invention relates to the technical field of inorganic nano materials, in particular to a preparation method of silica sol and application of the silica sol in ceramic paint.
Background
The ceramic coating originated in the 70 th 20 th century, and was prepared by adopting Sol-Gel (Sol-Gel) technology. With the rapid development of the coating industry, people's attention to the green environmental protection problem of the coating is increasing day by day, and the traditional organic coating of the organic polymer system has many worried problems in the environmental protection aspect and is gradually not in accordance with the green concept of environment friendliness, energy conservation and emission reduction in the present generation. The ceramic coating takes a nano inorganic compound as a main component, and is prepared by carrying out hydrolysis reaction on inorganic sol and a silane coupling agent and then combining the inorganic sol and an inorganic pigment and filler. Compared with organic coatings, the coating takes inorganic substances as main film-forming substances, and organic high-molecular polymers are not used any more. The production and construction links of the coating reduce the use and emission of organic matters. The inorganic coating prepared by the ceramic coating is superior to an organic coating system in the aspects of hardness, heat resistance, fire resistance, stain resistance, corrosion resistance, weather resistance and the like, and is a high-performance special functional coating.
The ceramic coating is mainly applied to the field of architectural metal decorative coatings at present, such as architectural curtain walls, sectional materials, wall plates, wrapping columns and other architectural interior and exterior decorative materials, and is used on cookers and stoves with high temperature resistance requirements. Although ceramic coatings have been a focus of research in the area of highly new coatings and are increasingly recognized by researchers in the coatings field, there has been much research into improving the properties of ceramic coatings and expanding the areas of application of ceramic coatings. And there are few studies on the optimization of the reaction process of the coating.
The reaction mechanism of the ceramic coating is Sol-Gel chemical reaction (Sol-Gel), siloxane monomer is hydrolyzed and self-condensed in the water phase of silica Sol, and meanwhile, the condensation polymerization product and nano SiO2 particles are subjected to condensation polymerization again, and each component in the system is slowly polymerized to generate a large amount of structural Gel of a space network, and then the structural Gel is mixed with functional pigment and filler slurry to form the ceramic coating. In the above reaction mechanism, the process of hydrolyzing and curing the siloxane monomer in the silica sol is important. The general siloxane monomers have weak capability of hydrolysis and condensation in neutral aqueous solution, so that a catalyst needs to be added to improve the hydrolysis and condensation reaction capability. The most common hydrolytic condensation catalysts for siloxanes are acids and bases. Due to the extremely severe process of alkaline catalysis, the resulting hydrolysate cannot be stored efficiently and is prone to gel blocking due to the formation of highly crosslinked polycondensates. The acidic catalysis process generates silanol with a long-chain structure, and the obtained prepolymer has a relatively long storage time. A common hydrolytic condensation catalyst for ceramic coatings is therefore an acid.
According to studies, the pH of the silica sol has a significant influence on the preparation of the ceramic coating and the pot life thereof. When the environmental temperature is 25 +/-5 ℃ and the pH is 4.0-5.0, the ceramic coating can be used for a long time after reaction, namely the ceramic coating after hydrolysis has a long construction period which can reach more than 24 hours. And when the pH is less than 4.0 or more than 5.0, the ceramic coating can be used for less than one day after reaction. The acid for adjusting the pH is used as a catalyst, when the pH is less than 4.0, the use amount of the catalyst is too much, so that the reaction rate is accelerated, the usable time of the coating is shortened, and the coating is crosslinked too fast and is easy to crack; when the pH is more than 5.0 and even close to neutral, the silica sol cannot exist stably in the range, thereby causing the use time to be shortened and even direct gelation to be caused; therefore, the optimal control range of the pH value of the silica sol applied to the ceramic coating is 4.0-5.0, or other researchers believe that 3.5-5.5 is more beneficial to the reaction of the ceramic coating.
In the development of ceramic coatings, there are two ways to achieve an acidic catalytic environment. Firstly, the silica sol is regulated by an acid catalyst, and secondly, the acid silica sol is directly used. Most paint manufacturers currently use the first method and most purchase imported silica sol for the relevant tests. For different suppliers or different kinds of silica sol, it is necessary to selectively use acid catalysts and optimize the addition amount and kinds thereof, such as formic acid, acetic acid, hydrochloric acid, nitric acid, and the like. Improper selection of the acid catalyst type or improper addition of the acid catalyst causes problems such as slow reaction or vigorous reaction. In addition, the acid catalyst is usually provided as a separate component and added in appropriate proportions to carry out the hydrolysis reaction. Such methods often cause inconvenience in the storage and production links. Acid is a volatile, irritant and corrosive compound, which requires special management for storage and transport, and as a risk factor, may leak or cause physical damage to workers. In addition, in the process of adding acid to silica sol to adjust a proper pH, the speed of adding acid and the accuracy of the amount of addition need to be controlled, otherwise, the batch-to-batch variability of the product is easily caused.
A second approach, the selection of acidic silica sols for experimentation, has also been taken by some paint manufacturers. In the case of the acid-base property of silica sol, there can be classified into acid and alkali silica sols according to their pH values. The pH value of the system has great influence on the stability of the system, and the alkaline silica sol is more stable than the acidic silica sol. When the pH is 8.5 to 10.5, the surface charge density of the particles is high, the zeta potential is high, and the repulsive force between the particles is dominant, so that the stable state can be maintained for a long period of time. When the pH is 5 to 7, the charge density on the particle surface decreases, the zeta potential decreases, the particles are likely to collide to form a gel, the pH decreases to about 2 to 4, and the zeta potential of the silica sol particles changes from the original negative to positive, and is metastable, and thus has good stability. Generally, the acidic silica sol product is prepared under the acidic condition of pH 2, most of the acidic silica sol products are adjusted within the range of 2-3, and the sol can be kept in a metastable state. Even in this case, the silica sol in a metastable state is likely to gel, and it is difficult to prepare an acidic silica sol having a high concentration.
According to the above, in the region of 2< pH <4, acidic silica sols have a broader metastable zone; the stability of the silica sol rapidly decreases in the region of a pH value close to 5-6. The optimal control range of the pH value of the ceramic coating under the hydrolysis condition is 4-5, and the optimal control range is just at the edge of the acid silica sol metastable state. The pH range of the acidic silica sols which are commercially available in practice is therefore unsuitable for the development of ceramic coatings.
Disclosure of Invention
In view of the above-mentioned drawbacks of the prior art, the present invention aims to provide a method for preparing a silica sol for a catalyst-free ceramic coating, in particular to provide a method for preparing a silica sol which is stable in a pH range of 3.5 to 5.5, and to provide an application method for preparing a catalyst-free ceramic coating using the silica sol.
In order to achieve the above and other related objects, according to one aspect of the present invention, there is provided a method for preparing a silica sol, the method comprising the steps of:
1) preparing acidic silica sol by cation exchange of alkaline silica sol, wherein the pH of the acidic silica sol is 2.0-6.0; adding a coupling agent into the acidic silica sol obtained in the step 1) to obtain coupling agent modified silica sol;
2) adjusting the pH value of the coupling agent modified silica sol in the step 2) to 3.5-5.5.
In some embodiments of the present invention, in the step 1), the silica content of the alkaline silica sol is 10 to 50%, and the particle size of the alkaline silica sol is 10 to 200 nm.
In some embodiments of the present invention, the coupling agent in step 2) is selected from one or more of silane coupling agent, titanate coupling agent, aluminate coupling agent, phosphate coupling agent, borate coupling agent, zirconate coupling agent, tin coupling agent, aluminum-titanium composite coupling agent, aluminum-zirconium composite coupling agent, rare earth composite coupling agent, and chromium complex.
In some embodiments of the present invention, in the step 2), the coupling agent is added in an amount of 0.5 to 5 wt% based on the acidic silica sol obtained in the step 1).
In some embodiments of the invention, the pH adjustment in step 3) is performed with an acid selected from the group consisting of formic acid, acetic acid, sulfuric acid, citric acid, nitric acid, and combinations of one or more thereof;
in some embodiments of the present invention, the pH in step 3) is adjusted by using a base, wherein the base is one of sodium hydroxide, ammonia water, triethylamine, dimethylethanolamine and triethanolamine;
in some embodiments of the invention, the coupling agent modified silica sol after the pH is adjusted to 3.5-5.5 in the step 3) is filtered by using a filter cloth.
The invention also provides a silica sol prepared by the preparation method of the silica sol.
In another aspect, the invention provides the use of the silica sol according to the invention in ceramic coatings.
The invention also provides a ceramic coating, which comprises the following raw materials in percentage by weight:
20-50 wt% of silica sol;
30-40 wt% of a silane coupling agent;
10-50 wt% of color paste;
wherein the silica sol is prepared by the preparation method of the silica sol.
In some embodiments of the invention, the silane coupling agent is selected from the group consisting of methyltrimethoxysilane, dimethyldimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, tetramethoxysilane, tetraethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, diphenyldimethoxysilane, 3- (2, 3-glycidoxy) propyltrimethoxysilane, 3- (2, 3-glycidoxy) propylmethyldiethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane in combinations of one or more thereof;
in some embodiments of the present invention, the mill base comprises a combination of a plurality of water, aqueous adjuvant, inorganic filler, inorganic pigment.
In another aspect, the present invention provides a method for preparing the ceramic coating of the present invention, the method comprising: adding a silane coupling agent into the silica sol, and stirring to obtain a silica sol/silane hydrolysis mixed solution; and adding the color paste into the silica sol/silane hydrolysis mixed solution, and stirring to obtain the ceramic coating.
The invention has the beneficial effects that:
1) in the preparation method of the silica sol, partial hydroxyl on the surface of the acidic silica sol colloid particles reacts with the coupling agent by adding the coupling agent, so that the steric hindrance between the particles is increased, and the metastable silica sol solution becomes more stable;
2) the pH value of the coupling agent modified acidic silica sol prepared by the invention is adjusted to be 3.5-5.5, and the coupling agent modified acidic silica sol is suitable for hydrolysis reaction of a silane coupling agent. In this pH range, the hydrolysis rate of the silane coupling agent and the storable time after hydrolysis are adjusted in a balanced manner.
3) The silica sol with the stable pH value of 3.5-5.5 is used for preparing the ceramic coating, an acid catalyst is not required to be additionally added, complicated processes of selecting the type of acid in a coating preparation link, adjusting and controlling the addition amount of the acid and the like are avoided, batch difference caused by improper addition of the acid can be avoided, and risk factors caused by inconvenient storage of the acid are reduced. The silica sol is used for preparing the catalyst-free ceramic coating, is a product which is more acceptable in the coating manufacturing industry, and has good application prospect.
4) The ceramic coating prepared by the invention is coated on an aluminum plate subjected to passivation treatment, the hardness of the coating can reach 6-8H, the Baige adhesion is 0 grade, the temperature resistance is higher than 600 ℃, and the coating is only slightly discolored after being boiled in water for 2 hours.
Detailed Description
The preparation of the silica sol of the present invention and its use in ceramic coating materials are described in detail below.
The first aspect of the present invention provides a method for preparing a silica sol, comprising the steps of:
1) preparing acidic silica sol by cation exchange of alkaline silica sol, wherein the pH of the acidic silica sol is 2.0-6.0;
2) adding a coupling agent into the acidic silica sol obtained in the step 1) to obtain coupling agent modified silica sol;
3) adjusting the pH value of the coupling agent modified silica sol in the step 2) to 3.5-5.5.
In the preparation method of the silica sol, step 1) is to react alkaline silica sol with cation exchange resin to prepare acidic silica sol, wherein the pH of the acidic silica sol is 2.0-6.0, and in some embodiments, the pH of the acidic silica sol is 3.0-5.0, 2.0-3.0, 3.0-4.0, 4.0-5.0, or 5.0-6.0. In general, the silica content of the alkaline silica sol and the particle size of the alkaline silica sol are not particularly limited, and the silica content of the alkaline silica sol or silica sols having different particle sizes may be used and mixed as necessary. In some embodiments, the alkaline silica sol in step 1) has a silica content of 10 to 50% and a particle size of 10 to 200 nm. In some preferred embodiments, the silica content of the alkaline silica sol in step 1) is 30 to 50%, 10 to 30%, 20 to 40%, 10 to 20%, 20 to 30%, 30 to 40%, or 40 to 50%. The particle size of the alkaline silica sol in the step 1) is 10-100 nm, 100-200 nm, 10-50 nm, 50-100 nm, 50-150 nm, 100-150 nm, or 150-200 nm.
In the preparation method of the silica sol provided by the invention, the step 2) is to add a coupling agent into the acidic silica sol in the step 1) to obtain a coupling agent modified silica sol. Specifically, the coupling agent is selected from one or more of silane coupling agent, titanate coupling agent, aluminate coupling agent, phosphate coupling agent, borate coupling agent, zirconate coupling agent, tin coupling agent, aluminum-titanium composite coupling agent, aluminum-zirconium composite coupling agent, rare earth composite coupling agent and chromium complex. Preferably, the coupling agent is selected from one or more of silane coupling agent, titanate coupling agent, borate coupling agent, zirconate coupling agent. Wherein the silane coupling agent is selected from one or more of methyltrimethoxysilane, methyltriethoxysilane, aminopropyltrimethoxysilane, aminopropyltriethoxysilane, 3- (2, 3-glycidoxy) propyltrimethoxysilane and 3- (2, 3-glycidoxy) propyltriethoxysilane. The titanate coupling agent is selected from one or more of bis (dioctyloxypyrophosphate) ethylene titanate and isopropyl tri (dioctylphosphonoxy) titanate. The borate coupling agent is selected from one or more of LD-100P, PRA-100. The zirconate coupling agent is selected from one or more of tetra-n-propyl zirconate coupling agent and bis (diethyl citrate) dipropoxy zirconate coupling agent.
Further, in the step 2), if the coupling agent is a liquid (or is soluble in water to prepare an aqueous solution), the coupling agent needs to be added to the acidic silica sol in the step 1) in a dropwise manner, and if the coupling agent is a non-water-soluble solid coupling agent, the non-water-soluble solid coupling agent needs to be crushed and then added to the acidic silica sol in the step 1) in multiple times.
Further, in the step 2), the addition amount of the coupling agent is 0.5-5 wt% of the acidic silica sol obtained in the step 1). In some embodiments, the coupling agent is added in an amount of 1 to 4 wt%, 2 to 3 wt%, 0.5 to 1 wt%, 1 to 2 wt%, 2 to 3 wt%, or 3 to 4 wt% of the acidic silica sol of step 1). Coupling agents within the above range may be better able to modify the acidic silica sol.
Further, in the step 2), the stirring is continued during the process of adding the coupling agent into the acidic silica sol in the step 1), and the stirring time is not particularly limited, and in some embodiments, the stirring time is 2 to 48 hours. More specifically, the stirring time can be 2-48 h, 5-40 h, 10-45 h, 15-40 h, 20-35 h, or 25-30 h.
In the preparation method of the silica sol, the pH value of the coupling agent modified silica sol in the step 2) is adjusted to 3.5-5.5 in the step 3). Specifically, in the step 3), the pH value of the coupling agent modified silica sol in the step 2) is adjusted to 4-5, 3.5-4, 4.5-5.5, 3.5-4, 4-4.5, 4.5-5, or 5-5.5. The pH can be adjusted with acids or bases. In some embodiments, the acid is selected from a combination of one or more of formic acid, acetic acid, sulfuric acid, citric acid, nitric acid, preferably the acid is selected from formic acid and/or acetic acid. The alkali is one of sodium hydroxide, ammonia water, triethylamine, dimethylethanolamine and triethanolamine. The base is preferably selected from one or more of sodium hydroxide, ammonia water and triethylamine. In general, the coupling agent modified silica sol after the pH is adjusted to 3.5 to 5.5 needs to be filtered by a filter cloth to obtain a silica sol which is stably stored, and the mesh number of the filter cloth is not particularly limited, for example, the filter cloth is 400 mesh.
In a second aspect, the present invention provides a silica sol prepared by the method for preparing a silica sol according to the first aspect of the present invention.
In a third aspect, the present invention provides the use of the silica sol according to the second aspect of the present invention in the field of ceramic coatings.
The fourth aspect of the invention provides a ceramic coating, which comprises the following raw materials in percentage by weight:
20-50 wt% of silica sol;
30-40 wt% of a silane coupling agent;
10-50 wt% of color paste.
Wherein the silica sol is prepared by the method for preparing the silica sol according to the first aspect of the present invention.
In the ceramic coating provided by the invention, the silane coupling agent is selected from one or more of methyltrimethoxysilane, dimethyldimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, tetramethoxysilane, tetraethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, diphenyldimethoxysilane, 3- (2, 3-glycidoxy) propyltrimethoxysilane, 3- (2, 3-glycidoxy) propylmethyldiethoxysilane, vinyltrimethoxysilane and vinyltriethoxysilane. Preferably, the silane coupling agent is selected from one or more of methyltrimethoxysilane, dimethyldimethoxysilane, methyltriethoxysilane, phenyltrimethoxysilane, 3- (2, 3-glycidoxy) propyltrimethoxysilane.
In the ceramic coating provided by the invention, the color paste comprises a combination of a plurality of water, aqueous auxiliary agents, inorganic fillers and inorganic pigments. In a specific embodiment, the color paste is composed of water, an aqueous auxiliary agent, an inorganic filler and an inorganic pigment. Specifically, the water is preferably deionized water. The water-based auxiliary agent is selected from water-based paint common auxiliary agents and comprises a dispersing agent, a flatting agent, a wetting agent, a defoaming agent, a thickening agent, an anti-settling agent, an antibacterial agent, a hydrophobic agent, a non-stick auxiliary agent and the like. The inorganic filler comprises one or more of barium sulfate, alumina, calcium carbonate, crystal whisker silicon, talcum powder, mica powder and silicon dioxide powder; the inorganic pigment is one or a combination of more of titanium dioxide, iron yellow, iron red, cobalt blue, cobalt green, molybdenum chrome red, copper chrome black and carbon black. The color paste component is prepared by mixing the materials and grinding the mixture until the particle size is less than 25 mu m.
A fifth aspect of the present invention provides a method for preparing the ceramic dope according to the fourth aspect of the present invention, the method comprising: adding a silane coupling agent into the silica sol, and stirring to obtain a silica sol/silane hydrolysis mixed solution; and adding the color paste into the silica sol/silane hydrolysis mixed solution, and stirring to obtain the ceramic coating.
According to the preparation method of the ceramic coating, the silane coupling agent is added into the silica sol, the mixture is stirred to prepare the silica sol/silane hydrolysis mixture, and the mixture is stirred for 2-6 hours, or stirred for 3-5 hours, 2-4 hours or 4-6 hours, and needs to be stirred slowly.
The invention has the beneficial effects that:
1) in the preparation method of the silica sol, partial hydroxyl on the surface of the acidic silica sol colloid particles reacts with the coupling agent by adding the coupling agent, so that the steric hindrance between the particles is increased, and the metastable silica sol solution becomes more stable;
2) the pH value of the coupling agent modified acidic silica sol prepared by the invention is adjusted to be 3.5-5.5, and the coupling agent modified acidic silica sol is suitable for hydrolysis reaction of a silane coupling agent. In this pH range, the hydrolysis rate of the silane coupling agent and the storable time after hydrolysis are adjusted in a balanced manner.
3) The silica sol with the stable pH value of 3.5-5.5 is used for preparing the ceramic coating, an acid catalyst is not required to be additionally added, complicated processes of selecting the type of acid in a coating preparation link, adjusting and controlling the addition amount of the acid and the like are avoided, batch difference caused by improper addition of the acid can be avoided, and risk factors caused by inconvenient storage of the acid are reduced. The silica sol is used for preparing the catalyst-free ceramic coating, is a product which is more acceptable in the coating manufacturing industry, and has good application prospect.
4) The ceramic coating prepared by the invention is coated on an aluminum plate subjected to passivation treatment, the hardness of the coating can reach 6-8H, the Baige adhesion is 0 grade, the temperature resistance is higher than 600 ℃, and the coating is only slightly discolored after being boiled in water for 2 hours.
The following description of the embodiments of the present invention is provided for illustrative purposes, and other advantages and effects of the present invention will become apparent to those skilled in the art from the present disclosure.
It is to be understood that the processing equipment or apparatus not specifically identified in the following examples is conventional in the art.
Furthermore, it is to be understood that one or more method steps mentioned in the present invention does not exclude that other method steps may also be present before or after the combined steps or that other method steps may also be inserted between these explicitly mentioned steps, unless otherwise indicated; it is also to be understood that a combined connection between one or more devices/apparatus as referred to in the present application does not exclude that further devices/apparatus may be present before or after the combined device/apparatus or that further devices/apparatus may be interposed between two devices/apparatus explicitly referred to, unless otherwise indicated. Moreover, unless otherwise indicated, the numbering of the various method steps is merely a convenient tool for identifying the various method steps, and is not intended to limit the order in which the method steps are arranged or the scope of the invention in which the invention may be practiced, and changes or modifications in the relative relationship may be made without substantially changing the technical content.
Example 1
(1) 10kg of an alkaline silica sol (silica content 30 wt%, pH 9.7, particle size 20nm) was added to a reaction vessel and stirred;
(2) adding dried cationic resin into a reaction vessel, carrying out ion exchange with the alkaline silica sol obtained in the step (1) to reduce the pH value to about 5.5, and filtering to remove the cationic resin to obtain acidic silica sol;
(3) diluting 100g of silane coupling agent selected from 3- (2, 3-glycidoxy) propyltrimethoxysilane to a coupling agent-modified solution with a concentration of 20 wt% by using water;
(4) slowly and dropwise adding the coupling agent modified solution obtained in the step (3) into the acidic silica sol obtained in the step (2) at room temperature under the condition of continuous stirring, and after stirring for 48 hours, adjusting the pH of the silica sol to 5.0 by using acetic acid to obtain the silane coupling agent modified silica sol.
Example 2
(1) 10kg of an alkaline silica sol (silica content 40 wt%, pH 10.3, particle size 50nm) was added to a reaction vessel and stirred;
(2) adding dried cationic resin into a reaction vessel, carrying out ion exchange with the alkaline silica sol obtained in the step (1) to reduce the pH value to about 2.5, and filtering to remove the cationic resin to obtain acidic silica sol;
(3) diluting 80g of a titanate coupling agent with water to form 20 wt% of a coupling agent modification solution, wherein the titanate coupling agent is selected from bis (dioctyloxy pyrophosphate) ethylene titanate;
(4) slowly and dropwise adding the coupling agent modified solution obtained in the step (3) into the acidic silica sol obtained in the step (2) under the condition of continuous stirring at room temperature, and continuously stirring for 24 hours, and then adjusting the pH of the silica sol to about 5.5 by using ammonia water to obtain the titanate coupling agent modified silica sol.
Example 3
(1) 10kg of an alkaline silica sol (silica content 45 wt%, pH 9.8, particle size 150nm) was added to a reaction vessel and stirred;
(2) adding dried cationic resin into a reaction vessel, carrying out ion exchange with the alkaline silica sol obtained in the step (1) to reduce the pH value to about 3.0, and filtering to remove the cationic resin to obtain acidic silica sol;
(3) adding 30g of zirconate coupling agent into water, and dissolving into 10% of coupling agent modified solution; the zirconate is selected from tetra-n-propyl zirconate;
(4) slowly and dropwise adding the coupling agent modified solution obtained in the step (3) into the acidic silica sol obtained in the step (2) at room temperature under the condition of continuous stirring, and after continuously stirring for 10 hours, adjusting the pH of the silica sol to about 4.5 by using sodium hydroxide to obtain the zirconate coupling agent modified silica sol.
Example 4
(1) 10kg of an alkaline silica sol (silica content 20 wt%, pH 10.2, particle size 15nm) was added to a reaction vessel and stirred;
(2) adding dried cationic resin into a reaction vessel, carrying out ion exchange with the alkaline silica sol obtained in the step (1) to reduce the pH value to about 3.5, and filtering to remove the cationic resin to obtain acidic silica sol;
(3) adding 200g of borate coupling agent into water, and dissolving into 10% of coupling agent modified solution, wherein the borate coupling agent is selected from LD-100P;
(4) slowly dripping the coupling agent modified solution obtained in the step (3) into the acidic silica sol obtained in the step (2) under the conditions of room temperature and continuous stirring, continuously stirring for 10 hours, and adjusting the pH of the silica sol to about 4.0 by using sodium hydroxide to obtain the borate coupling agent modified acidic silica sol
Example 5
(1) Mixing three kinds of alkaline silica sol with different particle sizes, and adding 5kg of alkaline silica sol 1 (the content of silica is 40 wt%, the pH value is 10.3, and the particle size is 50nm), 3kg of alkaline silica sol 2 (the content of silica is 40 wt%, the pH value is 9.5, and the particle size is 10nm) and 2kg of alkaline silica sol 3 (the content of silica is 40 wt%, the pH value is 9.7, and the particle size is 80nm) into a reaction vessel for stirring;
(2) adding dried cationic resin into a reaction vessel, carrying out ion exchange with the alkaline silica sol obtained in the step (1) to reduce the pH value to about 4.5, and filtering to remove the cationic resin to obtain acidic silica sol;
(3) diluting 100g of silane coupling agent selected from 3- (2, 3-glycidoxy) propyltrimethoxysilane to a coupling agent-modified solution with a concentration of 20 wt% by using water;
(4) slowly and dropwise adding the coupling agent modified solution obtained in the step (3) into the acidic silica sol obtained in the step (2) at room temperature under the condition of continuous stirring, and after stirring for 48 hours, adjusting the pH of the silica sol to about 3.5 by using sulfuric acid to obtain the silane coupling agent modified silica sol.
The silica sols obtained in examples 1 to 5 were all stored for 1 year or longer as a result of the stability storage experiment.
Examples 6 to 10
The silica sols prepared in examples 1 to 5 were used to prepare ceramic coatings.
Firstly, preparing color paste components, weighing various raw materials according to the proportion in the table 1, uniformly mixing, adding 120 wt% of zirconium beads, and grinding for about 2 hours at the speed of 1500r-3000r/min until the fineness of the slurry is lower than 25 mu m.
TABLE 1 color paste raw material composition and proportion
| Raw materials | Proportion of addition |
| Deionized water | 45g |
| Aqueous dispersant | 0.2g |
| Aqueous leveling agent | 0.1g |
| Water-based anti-settling agent | 0.5g |
| Non-stick aid | 0.2g |
| Alumina oxide | 8g |
| Whisker silicon | 7g |
| Mica powder | 13g |
| Talcum powder | 6g |
| Titanium white powder | 20g |
| Total up to | 100g |
Preparing the ceramic coating according to the preparation steps of the ceramic coating: (1) gradually adding a silane coupling agent into the silica sol according to a proportion, and stirring at a low speed for 2-6 h to prepare a silica sol/silane hydrolysis mixed solution; (2) and (3) adding the color paste component into the hydrolysis mixed liquid prepared in the step (1), and uniformly stirring to prepare the water-based ceramic coating. The ceramic coating prepared in the embodiments 6 to 10 has the use aging of the silica sol/silane hydrolysate of more than 24 hours
TABLE 2 Components and amounts thereof in examples 6-10
Example 11
The ceramic coating prepared in examples 6 to 10 was applied to a passivated aluminum plate. And the coating hardness, the hundred-grid adhesion, the temperature resistance and the water boiling were tested. The test results are detailed in table 3.
The hardness test method for the coating is referred to the hardness test requirements as described in GBT-23433.
The test method for hundred lattice adhesion is referred to the adhesion test requirements described in GBT-23433.
The temperature resistance test method comprises the following steps: and (3) placing the coating in a muffle furnace at 600 ℃ for 30min, taking out the coating, cooling to normal temperature, and visually observing the appearance of the coating, wherein only slight color change is required.
Boiling test method: the coating was placed in boiling water for 2h and after removal the appearance of the coating was visually observed requiring only a slight colour change.
Table 3 coating hardness, adhesion, temperature resistance and boiling test results in examples 6-10
While the invention has been described with respect to a preferred embodiment, it will be understood by those skilled in the art that the foregoing and other changes, omissions and deviations in the form and detail thereof may be made without departing from the scope of this invention. Those skilled in the art can make various changes, modifications and equivalent arrangements, which are equivalent to the embodiments of the present invention, without departing from the spirit and scope of the present invention, and which may be made by utilizing the techniques disclosed above; meanwhile, any changes, modifications and variations of the above-described embodiments, which are equivalent to those of the technical spirit of the present invention, are within the scope of the technical solution of the present invention.
Claims (10)
1. A method for the preparation of a silica sol, said method comprising the steps of:
1) preparing acidic silica sol by cation exchange of alkaline silica sol, wherein the pH of the acidic silica sol is 2.0-6.0;
2) adding a coupling agent into the acidic silica sol obtained in the step 1) to obtain coupling agent modified silica sol;
3) adjusting the pH value of the coupling agent modified silica sol in the step 2) to 3.5-5.5.
2. The method for preparing the silica sol according to claim 1, wherein in the step 1), the silica content of the alkaline silica sol is 10 to 50%, and the particle diameter of the alkaline silica sol is 10 to 200 nm.
3. The method for preparing silica sol according to claim 1, wherein the coupling agent in step 2) is selected from one or more of silane coupling agent, titanate coupling agent, aluminate coupling agent, phosphate coupling agent, borate coupling agent, zirconate coupling agent, tin coupling agent, aluminum-titanium composite coupling agent, aluminum-zirconium composite coupling agent, rare earth composite coupling agent, and chromium complex.
4. The method for preparing silica sol according to claim 1, wherein in the step 2), the amount of the coupling agent added is 0.5 to 5 wt% of the acidic silica sol obtained in the step 1).
5. The method of claim 1, further comprising one or more of the following technical features: A1) adjusting the pH in the step 3) by using acid, wherein the acid is selected from one or more of formic acid, acetic acid, sulfuric acid, citric acid and nitric acid;
A2) adjusting the pH value in the step 3) by adopting alkali, wherein the alkali is one of sodium hydroxide, ammonia water, triethylamine, dimethylethanolamine and triethanolamine;
A3) and 3) filtering the coupling agent modified silica sol with the pH adjusted to 3.5-5.5 by using filter cloth.
6. A silica sol produced by the method for producing a silica sol according to claim 1 to 5.
7. Use of a silica sol according to claim 6 in ceramic coatings.
8. The ceramic coating comprises the following raw materials in percentage by weight:
20-50 wt% of silica sol;
30-40 wt% of a silane coupling agent;
10-50 wt% of color paste;
wherein the silica sol is prepared by the method for preparing the silica sol as claimed in claims 1 to 5.
9. The ceramic coating of claim 8, further comprising one or more of the following technical features:
B1) the silane coupling agent is selected from one or more of methyltrimethoxysilane, dimethyldimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, tetramethoxysilane, tetraethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, diphenyldimethoxysilane, 3- (2, 3-glycidoxy) propyltrimethoxysilane, 3- (2, 3-glycidoxy) propylmethyldiethoxysilane, vinyltrimethoxysilane and vinyltriethoxysilane;
B2) the color paste comprises a combination of a plurality of water, aqueous auxiliary agents, inorganic fillers and inorganic pigments.
10. A method of preparing a ceramic coating as claimed in any one of claims 8 to 9, the method comprising: adding a silane coupling agent into the silica sol of claim 6, and stirring to obtain a silica sol/silane hydrolysis mixed solution; and adding the color paste into the silica sol/silane hydrolysis mixed solution, and stirring to obtain the ceramic coating.
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