Preparation method of silicon dioxide applied to anticorrosive paint

Abstract

The invention provides a preparation method of silicon dioxide applied to anticorrosive paint, which comprises the following steps: synthesizing a fluoroalkyl-containing hydrophobic treatment agent and preparing silicon dioxide, the fluoroalkyl-containing hydrophobic treatment agent is generated by copolymerization of fluoroalkyl siloxane, an amino silane coupling agent and alkyl siloxane, the fluorine-containing alkyl hydrophobic treatment agent is added into a reactant or a product in the process of preparing silicon dioxide. Compared with the prior art, the preparation method of the silicon dioxide applied to the anti-corrosion coating has the advantage that the silicon dioxide additive capable of meeting the requirements of the coating with a strong anti-corrosion function is prepared.

Description

Technical Field

[0001] This invention relates to the field of functionalized nanoparticle preparation technology, and in particular to a method for preparing silica for use in anti-corrosion coatings. Background Technology

[0002] Anti-corrosion coatings are liquid or solid materials used to coat the surface of objects to form a protective film. Due to their excellent acid and alkali resistance, anti-corrosion coatings are widely used in various industries. Silica is an important additive in anti-corrosion coatings. Silica can form a three-dimensional network structure with the film-forming substances in the anti-corrosion coating, thereby increasing the viscosity of the coating and preventing the sedimentation of fillers and pigments. At the same time, it gives the coating anti-sagging properties, which is conducive to thick coating application.

[0003] To improve the corrosion resistance of anti-corrosion coatings, silica needs to be modified to be hydrophobic. Highly hydrophobic silica can effectively block the penetration of corrosive media such as water, oxygen and chloride ions, thereby reducing the occurrence of penetrating bubbles and corrosion (hydrophobic silica dispersed in the coating makes it difficult for water molecules to pass through, thereby reducing the overall water vapor permeability of the coating, and can significantly increase the contact angle between the coating and water, making it difficult for water droplets to spread and exhibiting the "lotus effect"). Currently, the main methods for modifying hydrophobic silica are as follows: (1) using silanizing agents to eliminate hydroxyl groups on the surface of silica, such as hexamethyldisilazane and dimethyldichlorosilane (refer to patents CN105377758, GB1005473, CA1117734); (2) introducing hydrophobic alkyl groups, such as methyl, ethyl, vinyl, octyl, hexadecyl, octadecyl, etc., onto the surface of silica (refer to patents CN104876230, CN104910656, CN100575255); (3) using silicone oil coating to treat silica (refer to patents CN110337469, CA1109640, CN1161997). However, the hydrophobicity of silica modified by the above methods is not good enough (its methanol value is all below 40), and its chemical corrosion resistance is weak, which cannot meet the high acid and alkali resistance requirements of anti-corrosion coatings. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing silica for use in anti-corrosion coatings, so as to prepare silica additives that can meet the requirements of coatings with strong anti-corrosion function.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing silica for use in anti-corrosion coatings, comprising:

[0007] Synthesis of fluorinated alkyl hydrophobic agents: Fluorinated alkyl siloxanes, aminosilane coupling agents and alkyl siloxanes are copolymerized to generate fluorinated alkyl hydrophobic agents;

[0008] The preparation of silicon dioxide includes the following steps:

[0009] (1) Stir the bottom water and heat it to the specified temperature F;

[0010] (2) Add water glass or sulfuric acid to adjust the pH value to 4.0-11.0, and keep the temperature and pH value constant;

[0011] (3) Add water glass and sulfuric acid simultaneously, and adjust the amount of water glass added to control the solid content of the suspension after the reaction to be maintained at 20-100 g / L;

[0012] (4) Acidification;

[0013] (5) Pressure filtration and water washing;

[0014] (6) Pulping;

[0015] (7) Dry and pulverize to the specified particle size;

[0016] Temperature F is 30–100℃;

[0017] The water glass concentration is 5-30%, and the modulus is 3.0-3.8;

[0018] The sulfuric acid concentration is 5-50%;

[0019] The fluorinated alkyl hydrophobic agent may be added to the mixture in any of steps (1) to (4), and / or the fluorinated alkyl hydrophobic agent may be mixed with silica in any of steps (6) to (7).

[0020] Compared with the prior art, the method for preparing silica for anti-corrosion coatings of the present invention has the following beneficial effects:

[0021] (1) The silica prepared by this method has fluoroalkyl groups with extremely low surface tension introduced on its surface, which gives it strong hydrophobicity. When silica is added to the coating, the hydrophobicity of the coating can be significantly improved, thereby effectively blocking the penetration of corrosive media such as water, oxygen and chloride ions. This plays a key role in preventing electrochemical corrosion in anti-corrosion coatings and has excellent acid and alkali resistance.

[0022] (2) The silica prepared by this method contains highly active amino groups on its surface, which can react with the active groups (epoxy, hydroxy, carboxyl, vinyl, etc.) on the film-forming material in the anti-corrosion coating to form a dense three-dimensional network structure, further reducing the overall water vapor permeability of the coating, thereby improving the anti-corrosion properties of the anti-corrosion coating.

[0023] (3) The silica prepared by this method is coated with a fluorinated alkyl copolymer. The silica surface is extremely hydrophobic, which effectively isolates the corrosive medium on the silica surface and prevents the interior from contacting the corrosive medium, thus giving it high acid and alkali resistance.

[0024] (4) Existing methods for hydrophobic modification of silica all require the addition of flammable and explosive organic solvents such as ethanol, methanol, xylene, and hexane, which have high requirements for production equipment and some substances in the reaction process are not environmentally friendly. This method does not require the addition of any organic solvents (such as ethanol, methanol, xylene, hexane, etc.) in the process of synthesizing fluorinated alkyl hydrophobic treatment agents and preparing silica. The equipment is simple and there are no VOC emissions, which is conducive to large-scale industrial production.

[0025] Preferably, the step of synthesizing the fluorinated alkyl hydrophobic agent includes: reacting fluorinated alkyl siloxane, amino silane coupling agent and alkyl siloxane at a specified temperature K for a predetermined time T under the action of an alkaline catalyst to copolymerize and generate the fluorinated alkyl hydrophobic agent; the mass ratio of fluorinated alkyl siloxane, amino silane coupling agent and alkyl siloxane is 1:1-40:1-40.

[0026] In this scheme, the introduction of low surface energy groups is one of the key factors in the synthesis of superhydrophobic materials. The known order of surface free energy of these groups is: -CF3 < -CF2H < -CFH2 < -CH3 < -CH2-. The fluorocarbon chains (such as -CF3) on fluoroalkylsiloxanes have extremely low surface energy (approximately 10–20 mN / m), far lower than the surface tension of water (72 mN / m), and even lower than hydrophobic groups such as methyl, ethyl, and octyl. The hydrophobic fluorocarbon chains on fluoroalkylsiloxanes are oriented, which significantly reduces the surface free energy of silica, making it difficult for water droplets to spread, thus significantly improving the hydrophobicity of silica. Furthermore, the added alkylsiloxanes, under the action of alkaline or acidic catalysts, generate active centers, from... The chain growth reaction is triggered, and the hydrophobic alkyl groups such as methyl, ethyl, and octyl on different types of alkylsiloxanes also play an important role in improving the hydrophobicity of silica. The added aminosilane coupling agent, due to the high reactivity and hydrophilicity of amino groups, facilitates the dispersion of the synthesized fluorinated alkyl hydrophobic treatment agent into water to react with silica. On the other hand, it can react with the active groups on the film-forming material of the anti-corrosion coating to generate a three-dimensional network structure, thereby improving the acid and alkali resistance of the anti-corrosion coating.

[0027] Preferably, the mass ratio of alkylsiloxane to fluoroalkylsiloxane is 1-40:1.

[0028] The higher the mass ratio of alkylsiloxane to fluoroalkylsiloxane, the fewer fluoroalkyl groups the polymer contains, resulting in relatively higher surface tension and reduced hydrophobicity. Consequently, the modified silica exhibits poorer acid and alkali resistance. Conversely, the lower the mass ratio of alkylsiloxane to fluoroalkylsiloxane, the more fluoroalkyl groups the polymer contains, which significantly reduces its surface tension and enhances hydrophobicity. This results in stronger acid and alkali resistance in the modified silica. However, an increase in the proportion of fluoroalkylsiloxane leads to a corresponding increase in cost.

[0029] Preferably, the mass ratio of alkylsiloxane to aminosilane coupling agent is 1:0.05-20.

[0030] A higher mass ratio of alkylsiloxane to aminosilane coupling agent results in a polymer with lower amino content, poorer hydrophilicity, and lower reactivity. This makes it difficult to disperse in water and react with silica, leading to poor grafting efficiency. Consequently, the modified silica exhibits decreased hydrophobicity and acid / alkali resistance. Conversely, a lower mass ratio of alkylsiloxane to aminosilane coupling agent results in a polymer with increased amino content, enhanced hydrophilicity, and increased reactivity. This facilitates dispersion in water and reaction with silica, increasing grafting efficiency. Therefore, the modified silica exhibits increased hydrophobicity and acid / alkali resistance. However, the proportion of aminosilane coupling agent should not be too high. Otherwise, the hydrophilicity of amino groups can actually decrease hydrophobicity if their content is too high. Furthermore, excessively high amino content can generate large amounts of small-molecule byproducts such as methanol and ethanol during polymerization, causing chain termination and preventing the formation of a copolymer.

[0031] Preferably, the alkylsiloxane is one or more of ethyltrimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diethyldiethoxysilane, octamethylcyclotetrasiloxane, octyltrimethoxysilane, isooctyltrimethoxysilane, isooctyltriethoxysilane, n-dodecyltrimethoxysilane, n-dodecyltriethoxysilane, n-dodecyltriethoxysilane, hexadecyltrimethoxysilane, hexadecyltriethoxysilane, octadecyltrimethoxysilane, octadecyltrimethoxysilane, octadecyltriethoxysilane, octadecylmethyldimethoxysilane, and octadecylmethyldiethoxysilane; the fluoroalkylsiloxane is 3,3,3-trifluoropropyltrimethoxysilane, 3,3,3-trifluoropropylmethyldimethoxysilane, trifluoropropyltriethoxysilane, and trifluoropropyltriethoxysilane. The aminosilane coupling agent is one or more of the following: γ-aminopropyltriethoxysilane, tridecafluorooctyltrimethoxysilane, tridecafluorooctyltriethoxysilane, heptadecafluorodecyltrimethoxysilane, and heptadecafluorodecyltriethoxysilane;

[0032] Preferably, the added alkylsiloxane includes reagent A and reagent B; reagent A is composed of one or more of octamethylcyclotetrasiloxane, dimethyldimethoxysilane, and dimethyldiethoxysilane; reagent B is composed of one or more of siloxanes containing octyl, isooctyl, dodecyl, hexadecyl, or octadecyl.

[0033] Reagent A generates active centers under the action of alkaline or acidic catalysts, thereby initiating chain growth reactions. Reagent B can further improve hydrophobicity and acid and alkali resistance.

[0034] Preferably, the alkaline catalyst is one or more of potassium hydroxide, tetramethylammonium hydroxide, and tetrabutylphosphine hydroxide; the amount of alkaline catalyst used is 0.001 to 1% of the total amount of alkylsiloxane, fluoroalkylsiloxane, and aminosilane coupling agent.

[0035] Preferably, the reaction temperature K for preparing the fluorinated alkyl hydrophobic treatment agent is 60–180 degrees Celsius, and the reaction time T is 0.5–20 h.

[0036] The temperature of the copolymerization reaction is related to the type of catalyst. The stronger the basicity of the catalyst, the lower the required reaction temperature. However, if the reaction temperature is too low, the reaction rate will be reduced and the reaction efficiency will be affected. If the reaction temperature is too high, the catalyst will decompose and the chain growth reaction will not occur. The optimal reaction temperature K for preparing fluorinated alkyl hydrophobic treatment agents is 60-180 degrees Celsius, preferably 80-150 degrees Celsius, and the optimal reaction time T is 0.5-20 hours, preferably 2-6 hours.

[0037] Preferably, the amount of the fluorinated alkyl hydrophobic agent used is 1 to 20% of the weight of the product silica. Detailed Implementation

[0038] Embodiments of the present invention:

[0039] A method for preparing silica for use in anti-corrosion coatings, comprising:

[0040] Synthetic fluorinated alkyl hydrophobic agents:

[0041] The steps for synthesizing fluorinated alkyl hydrophobic agents include: fluorinated alkyl siloxanes, amino silane coupling agents, and alkyl siloxanes reacting at a specified temperature K for a predetermined time T under the action of an alkaline catalyst to copolymerize and generate fluorinated alkyl hydrophobic agents; the mass ratio of fluorinated alkyl siloxanes, amino silane coupling agents, and alkyl siloxanes is 1:1-40:1-40.

[0042] In this scheme, the introduction of low surface energy groups is one of the key factors in the synthesis of superhydrophobic materials. The known order of surface free energy of these groups is: -CF3 < -CF2H < -CFH2 < -CH3 < -CH2-. The fluorocarbon chains (such as -CF3) on fluoroalkylsiloxanes have extremely low surface energy (approximately 10–20 mN / m), far lower than the surface tension of water (72 mN / m), and even lower than hydrophobic groups such as methyl, ethyl, and octyl. The hydrophobic fluorocarbon chains on fluoroalkylsiloxanes are oriented, which significantly reduces the surface free energy of silica, making it difficult for water droplets to spread, thus significantly improving the hydrophobicity of silica. Furthermore, the added alkylsiloxanes, under the action of alkaline or acidic catalysts, generate active centers, from... The chain growth reaction is triggered, and the hydrophobic alkyl groups such as methyl, ethyl, and octyl on different types of alkylsiloxanes also play an important role in improving the hydrophobicity of silica. The added aminosilane coupling agent, due to the high reactivity and hydrophilicity of amino groups, facilitates the dispersion of the synthesized fluorinated alkyl hydrophobic treatment agent into water to react with silica. On the other hand, it can react with the active groups on the film-forming material of the anti-corrosion coating to generate a three-dimensional network structure, thereby improving the acid and alkali resistance of the anti-corrosion coating.

[0043] The mass ratio of alkylsiloxane to fluoroalkylsiloxane is 1-40:1. Preferably, the mass ratio of alkylsiloxane to fluoroalkylsiloxane is 5-20:1.

[0044] The higher the mass ratio of alkylsiloxane to fluoroalkylsiloxane, the fewer fluoroalkyl groups the polymer contains, resulting in relatively higher surface tension and reduced hydrophobicity. Consequently, the modified silica exhibits poorer acid and alkali resistance. Conversely, the lower the mass ratio of alkylsiloxane to fluoroalkylsiloxane, the more fluoroalkyl groups the polymer contains, which significantly reduces its surface tension and enhances hydrophobicity. This results in stronger acid and alkali resistance in the modified silica. However, an increase in the proportion of fluoroalkylsiloxane leads to a corresponding increase in cost.

[0045] The mass ratio of alkylsiloxane to aminosilane coupling agent is 1:0.05-20. The preferred mass ratio is 1-15:1.

[0046] A higher mass ratio of alkylsiloxane to aminosilane coupling agent results in a polymer with lower amino content, poorer hydrophilicity, and lower reactivity. This makes it difficult to disperse in water and react with silica, leading to poor grafting efficiency. Consequently, the modified silica exhibits decreased hydrophobicity and acid / alkali resistance. Conversely, a lower mass ratio of alkylsiloxane to aminosilane coupling agent results in a polymer with increased amino content, enhanced hydrophilicity, and increased reactivity. This facilitates dispersion in water and reaction with silica, increasing grafting efficiency. Therefore, the modified silica exhibits increased hydrophobicity and acid / alkali resistance. However, the proportion of aminosilane coupling agent should not be too high. Otherwise, the hydrophilicity of amino groups can actually decrease hydrophobicity if their content is too high. Furthermore, excessively high amino content can generate large amounts of small-molecule byproducts such as methanol and ethanol during polymerization, causing chain termination and preventing the formation of a copolymer.

[0047] Alkylsiloxanes are one or more of ethyltrimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diethyldiethoxysilane, octamethylcyclotetrasiloxane, octyltrimethoxysilane, isooctyltrimethoxysilane, isooctyltriethoxysilane, n-dodecyltrimethoxysilane, n-dodecyltriethoxysilane, hexadecyltrimethoxysilane, hexadecyltriethoxysilane, octadecyltrimethoxysilane, octadecyltrimethoxysilane, octadecyltriethoxysilane, octadecylmethyldimethoxysilane, and octadecylmethyldiethoxysilane; fluoroalkylsiloxanes are 3,3,3-trifluoropropyltrimethoxysilane, 3,3,3-trifluoropropylmethyldimethoxysilane, and trifluoropropyltriethoxysilane. One or more of the following: alkyl, tridecylfluorooctyltrimethoxysilane, tridecylfluorooctyltriethoxysilane, heptadecafluorodecyltrimethoxysilane, and heptadecafluorodecyltriethoxysilane; the aminosilane coupling agent is one or more of the following: γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltriethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropylmethyldiethoxysilane, phenylaminomethyltriethoxysilane, phenylaminomethyltrimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, N-cyclohexyl-γ-propylmethyldimethoxysilane, and γ-piperazinylpropylmethyldimethoxysilane.

[0048] In this embodiment, the fluoroalkylsiloxane is preferably one or more of heptadecafluorodecyltrimethoxysilane and heptadecafluorodecyltriethoxysilane to minimize the surface tension of the coating and thus improve its corrosion resistance; the aminosilane coupling agent is preferably one or more of N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltriethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and N-β-(aminoethyl)-γ-aminopropylmethyldiethoxysilane. These aminosilane coupling agents contain two amino groups, have high reactivity and strong hydrophilicity, which is beneficial for the copolymer to disperse in water and react with silica, thereby improving the hydrophobicity and acid and alkali resistance of the modified silica.

[0049] The added alkylsiloxanes include reagent A and reagent B; reagent A consists of one or more of octamethylcyclotetrasiloxane, dimethyldimethoxysilane, and dimethyldiethoxysilane; reagent B consists of one or more of siloxanes containing octyl, isooctyl, dodecyl, hexadecyl, or octadecyl.

[0050] Specifically, reagent B may consist of one or more of the following: octyl-containing siloxanes, isooctylsiloxanes, n-dodecylsiloxanes, hexadecylsiloxanes, and octadecylsiloxanes.

[0051] Reagent A generates active centers under the action of alkaline or acidic catalysts, thereby initiating chain growth reactions. Reagent B can further improve hydrophobicity and acid and alkali resistance.

[0052] The alkaline catalyst is one or more of potassium hydroxide, tetramethylammonium hydroxide, and tetrabutylphosphine hydroxide; the amount of alkaline catalyst used is 0.001 to 1% of the total amount of alkylsiloxane, fluoroalkylsiloxane, and aminosilane coupling agent.

[0053] The stronger the alkalinity of the alkaline catalyst, the higher its catalytic activity and the stronger its catalytic ability. The less catalyst is required, which can effectively improve the preparation efficiency and reduce the difficulty of catalysis. In addition, the reaction time is related to the catalyst concentration and the reaction temperature. The higher the catalyst concentration and the reaction temperature, the shorter the time required for the reaction to reach equilibrium, and vice versa. The optimal amount of alkaline catalyst is 0.01 to 0.4% of the total amount of alkylsiloxane, fluoroalkylsiloxane and aminosilane coupling agent.

[0054] The reaction temperature K for preparing fluorinated alkyl hydrophobic agents is 60–180 degrees Celsius, and the reaction time T is 0.5–20 h.

[0055] The temperature of the copolymerization reaction is related to the type of catalyst. The stronger the basicity of the catalyst, the lower the required reaction temperature. However, if the reaction temperature is too low, the reaction rate will be reduced and the reaction efficiency will be affected. If the reaction temperature is too high, the catalyst will decompose and the chain growth reaction will not occur. The optimal reaction temperature K for preparing fluorinated alkyl hydrophobic treatment agents is 60-180 degrees Celsius, preferably 80-150 degrees Celsius, and the optimal reaction time T is 0.5-20 hours, preferably 2-6 hours.

[0056] The amount of fluorinated alkyl hydrophobic agent used is 1 to 20% of the weight of the product silica.

[0057] As the amount of fluorinated alkyl hydrophobic agent increases, the hydrophobic effect of the resulting silica gradually increases, and the acid and alkali resistance is enhanced, but the cost increases accordingly. If the amount is too small (less than 1% of the silica weight), the effect on improving hydrophobicity and acid and alkali resistance is not obvious. The optimal amount of fluorinated alkyl hydrophobic agent is 3 to 6% of the silica weight.

[0058] The reaction process involved in the synthesis of fluorinated alkyl hydrophobic agents:

[0059] The reaction principle of copolymers:

[0060] Alkylsiloxanes generate active centers under the catalysis of acids or bases, initiating chain growth reactions; fluoroalkylsiloxanes and aminosilane coupling agents are introduced into polymer chains through condensation reactions, thereby generating copolymers.

[0061] This fluorinated alkyl hydrophobic treatment agent is a polymer formed under the action of an alkali. The alkali used is a hydroxide of K, Na, or Li, or a quaternary ammonium hydroxide or a quaternary phosphorus hydroxide. When potassium hydroxide is used, the reaction temperature is relatively high, at 130–140 degrees Celsius; when tetramethylammonium hydroxide is used, the reaction temperature is lower, at 70–90 degrees Celsius.

[0062] The reaction mechanism is described below using octamethylcyclotetrasiloxane, N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, and 3,3,3-trifluoropropylmethyldimethoxysilane as monomers and tetramethylammonium hydroxide as catalyst.

[0063] The overall reaction equation is as follows:

[0064]

[0065] The above reaction involves the anionic ring-opening polymerization of octamethylcyclotetrasiloxane under the catalysis of tetramethylammonium hydroxide, generating a hydroxyl-terminated active chain, which is then polycondensed with N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane and 3,3,3-trifluoropropylmethyldimethoxysilane. After the reaction reaches equilibrium, a fluorinated alkyl hydrophobic treatment agent is obtained.

[0066] The chain initiation process is as follows:

[0067]

[0068] Octamethylcyclotetrasiloxane, catalyzed by tetramethylammonium hydroxide, yields alkylsiloxane anion active centers, thereby initiating a chain propagation reaction. However, the tetramethylammonium hydroxide catalyst alone cannot catalyze the monomers N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane and 3,3,3-trifluoropropylmethyldimethoxysilane, failing to yield the corresponding siloxane anion active centers. Therefore, without the presence of octamethylcyclotetrasiloxane, the chain propagation reaction cannot be initiated.

[0069] If moisture is present in the system at this point, the water will strongly attack the active siloxane anions, leading to the following reaction: This causes the active centers of the siloxane anions to become inactive, preventing the polymerization of octamethylcyclotetrasiloxane. The reaction is as follows:

[0070]

[0071] Simultaneously, methanol generated from the hydrolysis of monomers N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane and 3,3,3-trifluoropropylmethyldimethoxysilane also attacks the active siloxane anion, leading to the deactivation of the siloxane anion's active center. The reaction is as follows:

[0072]

[0073] Therefore, at the start of the reaction, the system should not contain too many small molecules such as water, methanol, and ethanol; otherwise, the polymerization reaction will be difficult to proceed.

[0074] The chain growth process is as follows:

[0075] The active siloxane anions initiated by the catalyst attack octamethylcyclotetrasiloxane, triggering a chain growth reaction.

[0076]

[0077] The hydroxyl-terminated active chain obtained by polymerization can undergo a condensation reaction with monomers N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane and 3,3,3-trifluoropropylmethyldimethoxysilane to obtain a methoxyl-terminated active chain. This methoxyl-terminated active chain undergoes hydrolysis in the presence of water, yielding another hydroxyl-terminated active chain. This chain then continues to react with N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane and 3,3,3-trifluoropropylmethyldimethoxysilane, and this cycle repeats until equilibrium is reached.

[0078] The hydroxyl-terminated active chain reacts with the monomer N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane as follows:

[0079]

[0080] The hydroxyl-terminated active chain can react with the monomer 3,3,3-trifluoropropylmethyldimethoxysilane as follows:

[0081]

[0082] The above example illustrates the reaction in the presence of octamethylcyclotetrasiloxane. In actual production, as long as an alkaline catalyst is used (the above reaction requires a strong base and is independent of the pH value of the environment), active silicon-oxygen anions can be generated, which can initiate a chain growth reaction.

[0083] Preparation of silicon dioxide:

[0084] Includes the following steps:

[0085] (1) Stir the bottom water and heat it to the specified temperature F;

[0086] (2) Add water glass or sulfuric acid to adjust the pH value to 4.0-11.0, and keep the temperature and pH value constant;

[0087] (3) Add water glass and sulfuric acid simultaneously, and adjust the amount of water glass added to control the solid content of silica in the suspension after the reaction to be maintained at 20-100 g / L;

[0088] (4) Acidification;

[0089] (5) Pressure filtration and water washing;

[0090] (6) Pulping;

[0091] (7) Dry and pulverize to the specified particle size;

[0092] Temperature F is 30–100℃;

[0093] The water glass concentration is 5-30%, and the modulus is 3.0-3.8;

[0094] The sulfuric acid concentration is 5-50%;

[0095] The fluorinated alkyl hydrophobic agent may be added to the mixture in any of steps (1) to (4), and / or the fluorinated alkyl hydrophobic agent may be mixed with silica in any of steps (6) to (7).

[0096] The preferred temperature F is 40–80℃, which provides mild reaction conditions and facilitates production.

[0097] The water glass concentration is preferably 15-25%, and the modulus is preferably 3.3-3.5.

[0098] The sulfuric acid concentration is 15-25%.

[0099] In step (2), the pH value is preferably 7.0 to 9.0. Within this range, the silica has a lighter bulk density and better extinction properties.

[0100] In step (3), the solid content is preferably 40-60 g / L; the higher the solid content, the higher the bulk ratio and the worse the extinction; if the solid content is too low, the production capacity per unit time will decrease.

[0101] In step (3), during the parallel flow process, the flow rate of water glass is fixed, and the flow rate of sulfuric acid is adjusted to keep the pH of the reaction suspension constant. At the same time, the amount of water glass added is controlled to adjust the solid content of silica in the suspension after the reaction.

[0102] In step (4), the pH value of acidification is 1.0 to 8.0, preferably 4.0 to 6.0.

[0103] If the acidification pH is too low, some of the fluorinated alkyl hydrophobic treatment agents will dissociate from the silica surface, resulting in poorer hydrophobicity; if the acidification pH is too high, the reaction byproduct sodium sulfate will not easily be washed out from the silica pores, and the water washing time will be longer.

[0104] In step (5), pure water is used to wash the silica to remove sulfate and sodium ions. The conductivity of the water is controlled below 80 μS / cm to prevent electrochemical corrosion caused by excessive ion concentration.

[0105] In step (6), the solid content of the pulp is 5-30%, preferably 8-18%.

[0106] If the solid content is too low, the drying temperature will increase, energy consumption will increase, and output will decrease; if the solid content is too high, the viscosity of the dispersion will increase, making feeding difficult and easily clogging the pipeline.

[0107] In step (7), the drying is carried out by either flash drying or spray drying; the particle size of the pulverized material is 2 to 12 μm, preferably 3 to 8 μm.

[0108] When the fluorinated alkyl hydrophobic agent is added in steps (1) to (4) and / or in any step (6), due to the hydrophilicity of the amino group, it rapidly disperses into the water under high-speed stirring and reacts with the silica, thus grafting onto the silica surface. Because the fluorinated alkyl hydrophobic agent exists in the reaction system as a dispersion, it can be uniformly mixed with the silica suspension. Furthermore, it can react not only with the hydroxyl groups on the silica surface but also with the internal hydroxyl groups, resulting in a good grafting effect. However, due to the presence of water, the concentration of the fluorinated alkyl hydrophobic agent decreases accordingly, reducing the probability of contact with the silica and hindering the grafting reaction. Therefore, the water content should not be too high. When the fluorinated alkyl hydrophobic agent is added in step (7), it is generally added by spraying or dripping. The mixing effect is relatively poor, and some silica particles fail to come into contact with the fluorinated alkyl hydrophobic agent, resulting in poor hydrophobicity. At the same time, the fluorinated alkyl hydrophobic agent can only come into contact with the silica surface and cannot react with the hydroxyl groups inside the particles. A large number of new unmodified surfaces will be generated during crushing. Therefore, the hydrophobicity and alkali resistance are relatively poor.

[0109] In one embodiment, in step (7), the fluorinated alkyl hydrophobic treatment agent is added to the silica by direct spraying or dripping.

[0110] The following describes the preparation and testing of silica according to the above scheme.

[0111] 1. Determination of the physicochemical properties of silicon dioxide:

[0112] 1.1. BET specific surface area, pore volume, and pore diameter

[0113] Instrument: Tristar IIPlus; Test method refers to GB / T 19587-2017.

[0114] 1.2. Oil absorption value

[0115] Weigh approximately 1 g of a sample that has been dried to constant weight at 105±2℃ for 2 hours, accurate to 0.01 g, and record it as m. Place it on a glass plate and add it dropwise using a dropping bottle containing dibutyl phthalate (DBP) of known mass m1. Begin with a relatively fast dropping rate. When the amount added is equivalent to 3 / 4 of the sample's absorbance value, gently mix it with a spatula to ensure the DBP is evenly wetted into the sample. Then, continue mixing and pressing to break up any granular sample, and continue adding DBP at a slower rate while continuously mixing and pressing. The endpoint is reached when the sample and DBP form a transparent, non-loose cake, and no oil residue appears on the glass plate. Weigh the DBP dropping bottle and record it as m2, accurate to 0.01 g. The operation should be completed within 10–15 minutes. The oil absorption value W can be obtained using the following formula. Refer to industry standard HG / T4526-2013 for details.

[0116]

[0117] 1.3. Packing density

[0118] The stacking ratio is based on DIN EN ISO 787.

[0119] 1.4. Average particle size (D50)

[0120] Instrument: Mastersizer 3000 (Malvern Panalytical). Take a certain amount of sample according to the requirements of the laser particle size analyzer, add approximately 400 mL of water (for samples with poor water solubility, add a small amount of anhydrous ethanol first), ultrasonically disperse the sample solution for 15–60 s, and determine the particle size according to the laser particle size analyzer procedure. Refer to industry standard HG / T4526-2013 for details.

[0121] 1.5. Methanol value

[0122] The hydrophobicity of silica can be evaluated by its methanol value; the higher the methanol value, the better the hydrophobicity. The test method is as follows: Add 0.2g of surface-modified silica to a beaker containing 50mL of pure water and stir with a magnetic stirrer. The powder will float on the surface. Add methanol to the beaker through a burette (with the burette tip inserted into the water). As methanol is added, the amount of silica powder floating on the surface gradually decreases. When all the hydrophobic silica is completely dissolved in the water, record the volume of methanol consumed, A (mL). The methanol value, V, can be obtained using the following formula:

[0123]

[0124] 2. Evaluation methods for the application effects of silicon dioxide:

[0125] (1) Preparation of anti-corrosion coating

[0126] First, prepare a mixed solution of xylene, n-butyl acetate, and n-butanol in a ratio of 50:35:15. Take 15 parts of the mixed solvent, add 22 parts of epoxy resin E12 (Baling Petrochemical) and 5 parts of epoxy resin E20 (Baling Petrochemical) for pre-dispersion, then add 8 parts of titanium dioxide, 1.8 parts of bentonite, 35 parts of silica powder, 4 parts of the mixed solvent, 1.7 parts of dispersant BYK110, and 7.5 parts of the silica sample prepared in this invention, and disperse evenly.

[0127] (2) Plate making process:

[0128] After removing the oil from the sandblasted steel plate, clean it with solvent, spray it, and cure it at 200℃ for 2-3 minutes. Take it out and let it stand for seven days before use. The dry film thickness should be controlled at 50um.

[0129] (3) Acid and alkali resistance test:

[0130] Acid and alkali resistance was determined according to GB 1763-79(89) "Determination of Chemical Reagent Resistance of Coatings".

[0131] 3. Preparation of reagents and control reagents:

[0132] Example 1

[0133] Synthesis of fluorinated alkyl hydrophobic agent: 3200g of dimethyldimethoxysilane, 200g of heptadecafluorodecyltrimethoxysilane, and 600g of N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane were added to 12.0g of KOH and reacted at 140℃ for 12 hours to obtain the fluorinated alkyl hydrophobic agent.

[0134] Silica synthesis: Stirring was started, and 130L of bottom water and 800g of fluorinated alkyl hydrophobic treatment agent were added. The temperature was raised to 80±3℃, and the pH was adjusted to 7.5–8.0 using water glass (18.25%) with a modulus of 3.4 and sulfuric acid (10%). While maintaining the temperature, 57.0Kg of water glass and approximately 44Kg of sulfuric acid were added simultaneously and in parallel flow. After the parallel flow was complete, the silica solid content in the suspension was 47g / L. The pH was then adjusted to 5.0 with sulfuric acid. After washing and filtration, the resulting filter cake was redispersed and slurried with pure water, controlling the solid content of the slurry to 10%. The slurry was spray-dried and pulverized to 4.0–4.5μm.

[0135] Example 2

[0136] The dimethyldimethoxysilane was replaced with octamethylcyclotetrasiloxane, the heptadecafluorodecyltrimethoxysilane was replaced with 3,3,3-trifluoropropyltrimethoxysilane, and the N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane was replaced with γ-aminopropyltrimethoxysilane, and the rest were the same as in Example 1.

[0137] Example 3

[0138] Replace 3200g of dimethyldimethoxysilane with 2600g of dimethyldimethoxysilane and 600g of octadecylmethyldimethoxysilane, replace potassium hydroxide with tetramethylammonium hydroxide, change the amount to 2.0g, change the reaction temperature to 100 degrees, and keep the same as in Example 1.

[0139] Example 4

[0140] The fluorinated alkyl hydrophobic agent was added during the pulverization process by spraying and atomizing, and the rest was the same as in Example 1.

[0141] Example 5

[0142] During the synthesis of silica, the pH was changed to 9.3-9.8, and the rest was the same as in Example 1.

[0143] Example 6

[0144] When synthesizing silica, the amount of water glass used in the co-current flow was changed to 74.0 kg, and the amount of sulfuric acid added was about 57 kg. At this time, the solid content of the suspension after co-current flow became 57 g / L, and the rest was the same as in Example 1.

[0145] Comparative Example 1

[0146] Without the addition of heptadecafluorodecyltrimethoxysilane, the rest is the same as in Example 1.

[0147] Comparative Example 2

[0148] Without N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, otherwise the same as in Example 1.

[0149] Comparative Example 3

[0150] During the synthesis of silica, no fluorinated alkyl hydrophobic treatment agent was added, and the rest was the same as in Example 1.

[0151] Comparative Example 4

[0152] Hexamethyldisilazane was selected as the hydrophobic modifier, and the other conditions were the same as in Example 4.

[0153] Table 1. Physicochemical properties of each sample

[0154]

[0155]

[0156] Table 2. Alkali resistance test results for each sample

[0157]

[0158] Experimental conclusion:

[0159] (1) Comparing Example 1 and Example 2, the monomers used to synthesize the fluorinated alkyl hydrophobic agent are different. The fluorinated alkyl siloxane is changed from the long-chain heptadecafluorodecyltrimethoxysilane to the short-chain 3,3,3-trifluoropropyltrimethoxysilane, and the aminosilane coupling agent is changed from N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane to γ-aminopropyltrimethoxysilane. The hydrophobicity of the resulting silica decreases slightly, and the methanol value decreases slightly. However, the synthesis process of silica is the same, and other indicators are similar. Therefore, when tested in epoxy-based anti-corrosion coatings, the acid and alkali resistance decreases slightly, but not significantly.

[0160] (2) Comparing Example 1 and Example 3, the introduction of long-chain octadecylmethyldimethoxysilane significantly increased the hydrophobicity of the resulting silica; while the silica synthesis process remained unchanged, and other indicators showed little difference. When applied to epoxy-based anti-corrosion coatings, the enhanced hydrophobicity significantly improved their acid and alkali resistance.

[0161] (3) Comparing Examples 1 and 4, the addition of the fluorinated alkyl hydrophobic treatment agent during pulverization resulted in uneven mixing. A small portion of the silica particles had relatively poor hydrophobicity due to not being in contact with the treatment agent, leading to a lower methanol value. However, the silica synthesis process remained unchanged, and other indicators showed little difference. When applied to epoxy-based anti-corrosion coatings, the acid and alkali resistance significantly decreased due to the reduced hydrophobicity.

[0162] (4) Comparing Examples 1 and 5, the synthesis process of the fluorinated alkyl hydrophobic treatment agent is the same, so the hydrophobicity is similar; however, when synthesizing silica, the co-current pH increases, the bulk ratio increases, and the oil absorption value decreases. When the anti-corrosion coatings applied to the epoxy system are tested for acid and alkali resistance, there is no significant difference in acid and alkali resistance because the hydrophobicity is similar.

[0163] (5) Comparing Examples 1 and 6, the increased amount of water glass during parallel flow resulted in increased silica production, while the amount of fluorinated alkyl hydrophobic agent remained unchanged, leading to a decrease in its proportion of silica. Consequently, hydrophobicity decreased, and the methanol value became lower. Simultaneously, the increased amount of water glass during parallel flow increased the bulk density of the resulting silica, resulting in a decrease in oil absorption value. When tested in epoxy-based anti-corrosion coatings, the decreased hydrophobicity resulted in poorer acid and alkali resistance.

[0164] (6) Comparing Example 1 and Comparative Example 1, when synthesizing the hydrophobic treatment agent, the hydrophobicity of Comparative Example 1 decreased significantly and the methanol value decreased because no fluoroalkylsiloxane was added; while the carbon dioxide synthesis process remained unchanged, and other indicators were not significantly different. When the anti-corrosion coating used in the epoxy system was tested, its acid and alkali resistance decreased significantly due to the decrease in hydrophobicity.

[0165] (7) Comparing Example 1 and Comparative Example 2, when synthesizing the hydrophobic treatment agent, Comparative Example 2, due to the absence of an aminosilane coupling agent, could not disperse in water and lacked active amino groups, thus failing to react with silica and resulting in hydrophobic silica with a methanol value of zero. In contrast, the silica synthesis process remained unchanged, with little difference in other indicators. When tested on anti-corrosion coatings used in epoxy systems, the coatings exhibited poor acid and alkali resistance, showing numerous small bubbles and peeling after 24 hours of immersion.

[0166] (8) Comparing Example 1 and Comparative Example 3, when synthesizing silica, Comparative Example 3 did not add a fluorinated alkyl hydrophobic treatment agent, and the resulting silica did not have hydrophobicity; while the synthesis process remained unchanged, and other indicators were not significantly different. When the anti-corrosion coating used in the epoxy system was tested, it had very poor acid and alkali resistance, and after soaking for 24 hours, a large number of small bubbles appeared, and there was also peeling.

[0167] (9) Comparing Example 4 and Comparative Example 4, Comparative Example 4 used the commonly used hexamethyldisilazane as a modifier, which significantly reduced hydrophobicity and lowered methanol value; while the silica synthesis process remained unchanged, and other indicators showed little difference. When the anti-corrosion coating used in the epoxy system was tested, its acid and alkali resistance deteriorated.

[0168] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A method for preparing silica for use in anti-corrosion coatings, characterized in that, include: Synthesis of fluorinated alkyl hydrophobic agents: Fluorinated alkyl siloxanes, aminosilane coupling agents and alkyl siloxanes are copolymerized to generate fluorinated alkyl hydrophobic agents; The preparation of silicon dioxide includes the following steps: (1) Stir the bottom water and heat it to the specified temperature F; (2) Add water glass or sulfuric acid to adjust the pH value to 4.0-11.0, and keep the temperature and pH value constant; (3) Add water glass and sulfuric acid simultaneously, and adjust the amount of water glass added to control the solid content of the suspension after the reaction to be maintained at 20-100 g / L; (4) Acidification; (5) Pressure filtration and water washing; (6) Pulping; (7) Dry and pulverize to the specified particle size; Temperature F is 30–100℃; The water glass concentration is 5-30%, and the modulus is 3.0-3.8; The sulfuric acid concentration is 5-50%; The fluorinated alkyl hydrophobic agent may be added to the mixture in any of steps (1) to (4), and / or the fluorinated alkyl hydrophobic agent may be mixed with silica in any of steps (6) to (7).

2. The method for preparing silica for use in anti-corrosion coatings according to claim 1, characterized in that, The steps for synthesizing fluorinated alkyl hydrophobic agents include: Fluoroalkylsiloxanes, aminosilane coupling agents, and alkylsiloxanes are copolymerized at a specified temperature K for a predetermined time T under the action of an alkaline catalyst to generate a fluorinated alkyl hydrophobic treatment agent. The mass ratio of fluoroalkylsiloxane, aminosilane coupling agent and alkylsiloxane is 1:1-40:1-40.

3. The method for preparing silica for use in anti-corrosion coatings according to claim 2, characterized in that, The mass ratio of alkylsiloxane to fluoroalkylsiloxane is 1-40:

1.

4. The method for preparing silica for use in anti-corrosion coatings according to claim 2, characterized in that, The mass ratio of alkylsiloxane to aminosilane coupling agent is 1:0.05-20.

5. The method for preparing silica for use in anti-corrosion coatings according to any one of claims 1 to 4, characterized in that, Alkylsiloxanes are one or more of the following: ethyltrimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diethyldiethoxysilane, octamethylcyclotetrasiloxane, octyltrimethoxysilane, isooctyltrimethoxysilane, isooctyltriethoxysilane, n-dodecyltrimethoxysilane, n-dodecyltriethoxysilane, n-dodecyltriethoxysilane, hexadecyltrimethoxysilane, hexadecyltriethoxysilane, octadecyltrimethoxysilane, octadecyltriethoxysilane, octadecyltriethoxysilane, octadecylmethyldimethoxysilane, and octadecylmethyldiethoxysilane. The fluoroalkylsiloxane is one or more of 3,3,3-trifluoropropyltrimethoxysilane, 3,3,3-trifluoropropylmethyldimethoxysilane, trifluoropropyltriethoxysilane, tridecafluorooctyltrimethoxysilane, tridecafluorooctyltriethoxysilane, heptadecafluorodecyltrimethoxysilane, and heptadecafluorodecyltriethoxysilane. The aminosilane coupling agent is one or more of the following: γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltriethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropylmethyldiethoxysilane, phenylaminomethyltriethoxysilane, phenylaminomethyltrimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, N-cyclohexyl-γ-propylmethyldimethoxysilane, and γ-piperazinylpropylmethyldimethoxysilane.

6. The method for preparing silica for use in anti-corrosion coatings according to any one of claims 1 to 4, characterized in that, The added alkylsiloxanes include reagent A and reagent B; Reagent A consists of one or more of octamethylcyclotetrasiloxane, dimethyldimethoxysilane, and dimethyldiethoxysilane; Reagent B consists of one or more siloxanes containing octyl, isooctyl, n-dodecyl, hexadecyl, or octadecyl.

7. The method for preparing silica for use in anti-corrosion coatings according to claim 2, characterized in that, The alkaline catalyst is one or more of potassium hydroxide, tetramethylammonium hydroxide, and tetrabutylphosphine hydroxide; The amount of alkaline catalyst used is 0.001 to 1% of the total amount of alkylsiloxane, fluoroalkylsiloxane and aminosilane coupling agent.

8. The method for preparing silica for use in anti-corrosion coatings according to claim 2, characterized in that, The reaction temperature K for preparing fluorinated alkyl hydrophobic agents is 60–180 degrees Celsius, and the reaction time T is 0.5–20 h.

9. The method for preparing silica for use in anti-corrosion coatings according to claim 1, characterized in that, The amount of fluorinated alkyl hydrophobic agent used is 1 to 20% of the weight of the product silica.

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