Preparation method of water- and salt spray-resistant magnesium ion-exchanged silica for waterborne coatings

Abstract

The invention discloses a preparation method of water and salt spray resistant magnesium ion-exchanged silica for waterborne coatings, which comprises the following steps: adding water into a reaction kettle, adjusting the pH to be acidic, keeping the condition after stirring evenly, and then adding the prepared water glass solution and sulfuric acid solution into the reaction kettle in a pressurized convection manner for aging. After the aging is completed, adjusting the pH to be weakly acidic, then adding a magnesium source, and carrying out ion exchange for 1-8 hours; The invention prepares a water and salt spray resistant magnesium ion-exchanged silica anti-rust pigment for waterborne coatings by adding a magnesium source and carrying out water resistance modification during the preparation process of the product. It can reduce the surface layer of the coating, improve the water resistance, make up for the defects on the surface and inside of the coating, and enhance the salt spray resistance and anti-rust performance of the coating.

Description

Technical Field

[0001] The present invention relates to the field of chemical engineering technology, and particularly to a preparation method of water and salt spray resistant magnesium ion exchange type silica for waterborne coatings. Background Art

[0002] At present, automotive parts mainly include automotive chassis, axles, drive shafts, etc. The coating is mainly a single-component black waterborne epoxy primer (paint), and the film-forming substances used are mainly waterborne epoxy esters or two-component waterborne epoxy resins. However, in recent years, automobile factories have increasingly higher requirements for the salt spray resistance of parts coatings. In addition, there is a large gap between the standards adopted for the salt spray test of waterborne epoxy coatings and the requirements for the dry film thickness in the salt spray test. The film thickness required in the automotive parts market is relatively low, and the film thickness has a great influence on the salt spray resistance of the coating film. Therefore, the requirements for the active ingredients in the coating are getting higher and higher. In recent years, many studies have been carried out on two-component waterborne epoxy primers, but there are few studies on the influence of the anti-rust pigments, especially environmentally friendly anti-rust pigments, in the active ingredients on the salt spray resistance of the coating film. In addition, with the development of technology and the enhancement of people's environmental awareness, waterborne polyurethane using water as a dispersion medium instead of organic solvents has gradually come into people's view. Waterborne polyurethane (paint) is non-flammable, pollution-free, and low-cost, but because hydrophilic groups are introduced during the preparation process, its water resistance is poor.

[0003] First, in order to effectively improve the water resistance of waterborne polyurethane (such as paint), modifying polyurethane by adding inorganic water-resistant particles is a simple and effective method. Nano-silica particles have a large specific surface area and can combine with polymer chains to form a three-dimensional network structure, improving various properties such as the denseness, flatness, water resistance, and moisture permeability of the coating film. They are often used as inorganic particles in the application of improving coating performance. However, the surface of nano-silica particles has abundant silanol groups and strong hydrophilicity, making it difficult to disperse and wet in the organic phase. Therefore, the surface of nano-silica must be modified. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of water and salt spray resistant magnesium ion exchange type silica for waterborne coatings to solve the problems raised in the above background art.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] Preparation method of water - resistant and salt - fog - resistant magnesium ion - exchanged silica for water - based coatings, comprising the following steps: Add water to a reaction kettle, adjust the pH to be acidic, and after stirring evenly, maintain this condition and then add the prepared water - glass solution and sulfuric acid solution into the reaction kettle in a pressurized convection manner for aging. After the aging is completed, adjust the pH to be weakly acidic, then add a magnesium source, and conduct ion exchange for 1 - 8 hours. After the ion exchange is completed, wash the reaction product successively with an ammonium salt aqueous solution and pure water. After washing, conduct uniform dispersion in a disperser, then perform spray drying on the completed slurry, and obtain the preliminary magnesium ion - exchanged silica powder through air - flow pulverization. Then add an amphiphilic cyclic - film - type silane coupling agent to methanol in a reaction flask to prepare a solution of about 0.5% - 2%, and add it to the silica. Use a magnetic stirrer to fully and evenly mix the solution. Place the reaction flask in a warm water bath, adjust the temperature to 40°C - 50°C, and continue stirring and reacting for 6 - 8 hours so that the cyclic - film - type silane coupling agent molecules are fully adsorbed on the silica surface and form modified silica. After the reaction is completed, transfer the reactant to a drying oven for drying treatment, and maintain a low - pressure state in the drying oven to promote the drying and stabilization treatment of the silica. Finally, the dried silica is the water - resistant and salt - fog - resistant magnesium ion - exchanged silica.

[0007] As a further technical solution of the present invention: The silica concentration in the water - glass solution is 10wt% - 20wt%.

[0008] As a further technical solution of the present invention: The sulfuric acid concentration in the sulfuric acid solution is 30wt% - 50wt%.

[0009] As a further technical solution of the present invention: The magnesium source includes Mg(NO3)2, MgCl2, MgSO4 or a 50%Mg(NO3)2 + 50%MgSO4 mixed solution.

[0010] As a further technical solution of the present invention: The cyclic - film - type silane coupling agent is dimethylcyclohexasiloxane.

[0011] As a further technical solution of the present invention: The temperature in the drying oven is controlled at 80°C - 100°C.

[0012] Compared with the prior art, the beneficial effects of the present invention are:

[0013] (1) By adopting a special synthesis process, this application adds a magnesium ion exchanger during the reaction for ion exchange. At the cathode, oxygen absorption occurs to produce hydroxide ions, and at the anode, electrons are obtained to form magnesium ions. Hydroxide ions and silicon dioxide form silicate ions, and finally a magnesium silicate passivation layer is formed to create a passivation protective film, thereby blocking the electrode reactions between the anode and the cathode. The magnesium ion type silicon dioxide rust inhibitor pigment, as a component of the rust inhibitor, is environmentally friendly and non-toxic, and is a magnesium ion exchange type silica gel rust inhibitor pigment without heavy metals. Compared with the process of calcium ion exchange type rust inhibitor pigments, the process is simpler, the exchange efficiency is higher, and at the same time, the rust inhibition ability is stronger. Compared with heavy metal rust inhibitor pigments such as zinc phosphate and chromium, the magnesium ion rust inhibitor pigment is more environmentally friendly. The magnesium ion rust inhibitor pigment can enhance the salt spray resistance and rust prevention performance of the coating during the application test.

[0014] (2) After preparing the magnesium ion exchange type silicon dioxide powder in the early stage, this application mixes and reacts it with an amphiphilic cyclic film type silane coupling agent that has both hydrophilic and hydrophobic properties to prepare a water and salt spray resistant magnesium ion exchange type silicon dioxide for waterborne coatings. The amphiphilic cyclic film type silane coupling agent is a special silane coupling agent. One group of such coupling agents is hydrophilic, such as hydroxyl groups, ethoxy groups, etc., and the other is hydrophobic, such as methyl groups, styryl groups, etc. In applications, the amphiphilic silane coupling agent can combine its hydrophilic end with the surface of the substrate (such as inorganic particles, organic polymers, etc.) and undergo a chemical reaction, while the hydrophobic end can provide good water resistance, moisture resistance, scratch resistance, and wear resistance to the outside. Due to its dual hydrophilic and hydrophobic properties, this amphiphilic silane coupling agent can play a unique role in different application fields.

[0015] (3) The cyclic film type silane coupling agent contains a six-membered ring in the molecule, and this six-membered ring can be connected to other six-membered rings to form a polymer substance similar to a "bead chain" structure. Compared with traditional linear silane coupling agents, it has better stability and is not easily decomposed. Specific embodiments

[0016] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0017] A preparation method of water and salt spray resistant magnesium ion exchange type silicon dioxide for waterborne coatings, the content of which includes the following steps:

[0018] Add water to the reaction kettle, adjust the pH to be acidic, and keep the condition after stirring evenly. Then add the prepared water glass solution (the concentration of silicon dioxide in the water glass solution is 10 wt% - 20 wt%) and sulfuric acid solution (the concentration of sulfuric acid is 30 wt% - 50 wt%) into the reaction kettle by means of pressurized convection for aging. After the aging is completed, adjust the pH to be weakly acidic, then add different magnesium sources (Mg(NO3)2, MgCl2, MgSO4, 50%Mg(NO3)2 + 50%MgSO4 mixed solution), and carry out ion exchange for 1 - 8 hours. After the ion exchange is completed, wash the reaction product successively with ammonium salt aqueous solution and pure water, carry out uniform dispersion in a disperser, and then spray-dry the completed slurry. The pre-stage magnesium ion-exchanged silica powder is obtained after airflow pulverization.

[0019] Then add an amphiphilic cyclic film type silane coupling agent (such as dimethylcyclohexasiloxane) to the methanol containing the reaction flask to prepare a solution of about 0.5% - 2%, and add it to the silica. Use a magnetic stirrer to mix the solution fully and evenly. Place the reaction flask in a warm water bath and adjust the temperature to 40°C - 50°C. Continue to stir and react for 6 - 8 hours to make the cyclic film type silane coupling agent molecules fully adsorbed on the silica surface and form modified silica. After the reaction is completed, transfer the reactant to a drying oven (the temperature is controlled at 80°C - 100°C) for drying treatment, and keep the low-pressure state in the drying oven to promote the drying and stabilization treatment of the silica. Finally, the dried silica is the water- and salt-spray-resistant magnesium ion-exchanged silica.

[0020] (1) Specific surface area test: Automatic specific surface area and porosity analyzer Micromeritics: TriStar II 3020;

[0021] (2) Average particle size: Laser particle size analyzer, Malvern 3000;

[0022] (3) Pore volume test: Weigh 1.00 g of the base material sample dried to constant weight at 150 ± 5°C and place it in a dry 50 mL Erlenmeyer flask with a ground glass stopper. First, weigh the dropping bottle containing distilled water accurately to 0.01 g. Open the ground glass stopper of the Erlenmeyer flask, add distilled water drop by drop, cover the ground glass stopper, and shake the Erlenmeyer flask to make the sample loose. Open the ground glass stopper, alternate adding distilled water and shaking the Erlenmeyer flask until the powder shows adhesion and adheres to the bottle wall, continue to shake for half a minute until the adhesion phenomenon does not disappear, which is the end point. Cover the ground glass stopper and weigh accurately to 0.01 g. Take the arithmetic mean of the parallel determination results as the determination result.

[0023] (4) Determination of oil absorption value: The amount of dibutyl phthalate absorbed by 1 g of silica; Refer to the industry standard HG / T3072 - 2008;

[0024] (5)Determination of D50: Malvern 3000 laser particle size analyzer;

[0025] (6)Determination of magnesium element content: Refer to US EPA Method 3052:1996 for determination and analyze using ICP-OES.

[0026] Physicochemical test results of (preparing exchangeable silica with different magnesium sources):

[0027] Table 1 Physicochemical test results:

[0028]

[0029] It can be seen from the physicochemical test results that the pore volume, oil absorption value, particle size, specific surface area and magnesium element content of the products obtained by adding different magnesium sources will be different. When the added mass is the same, the larger the molecular weight of the magnesium source, the lower the content of magnesium ions, the lower the degree of exchange, the slightly smaller particle size, and the larger the oil absorption value and pore size.

[0030] Plate-making process:

[0031] Prepare the main agent of the waterborne coating according to the formula in Table 2 and prepare the curing agent of the waterborne coating according to the formula in Table 3.

[0032] Mix the main agent and curing agent of the waterborne coating and deionized water evenly at a ratio of 4:1:0.8~1. For salt spray resistance test, use sandblasted steel plate, degrease it first, then clean it with solvent, spray a dry film with a thickness of 40-50μm, flash dry for 15min, bake at 60℃ for 30min, and then cure at a constant temperature for 7 days for testing.

[0033] Table 2 Formula of the main agent of the waterborne coating:

[0034]

[0035] Test results:

[0036] Neutral salt spray resistance is determined according to GB / T 1771-1991 "Determination of Resistance to Neutral Salt Spray of Paints and Varnishes".

[0037] Water resistance is determined according to GB / T 1733-1993 "Method for Determining Water Resistance of Paint Films".

[0038] Table 4 Salt spray test results:

[0039]

[0040]

[0041] As shown by the salt spray test results in Table 4, magnesium ion-exchanged silica continuously adsorbs external H through ion exchange + , and the slowly released Mg 2+ is successively deposited on the metal interface, forming a passivation layer with silicate ions, covering the metal interface, and forming a long-term protection. However, it is not that the higher the magnesium element content, the better. When the magnesium element reaches a certain level and the ion exchange reaches saturation, Mg 2+ no longer works. Under the condition of adding the same mass of magnesium source, the Mg 2+ content is the highest in the system with MgCl2 as the magnesium source, followed by MgSO4, Mg(NO3)2 + MgSO4, and Mg(NO3)2. It can be seen from the test results that the system with MgSO4 as the magnesium source has the best salt spray resistance performance.

[0042] Table 5 Water resistance test results:

[0043] As shown by the water resistance test results in Table 5, by using the cyclic film type silane coupling agent as the water resistance modification substance, compared with the commonly used silane coupling agents for hydrophobic modification of common silica, the amphiphilic cyclic film type silane coupling agent is a silane coupling agent with a cyclic structure. The molecule contains a six-membered ring, and this six-membered ring can be connected to other six-membered rings to form a polymer substance similar to a "bead chain" structure. Compared with the traditional linear silane coupling agent, the cyclic film type silane coupling agent has stronger hydrophilic and hydrophobic properties. One group is hydrophilic, such as hydroxyl, ethoxy, etc., and the other is hydrophobic, such as methyl, styryl, etc. In application, the amphiphilic silane coupling agent can make its hydrophilic end combine with the surface of the substrate (such as inorganic particles, organic polymers, etc.) and undergo a chemical reaction, while the hydrophobic end can provide good water resistance, moisture resistance, scratch resistance, and wear resistance to the outside world. Obviously, the water resistance of foreign and domestic competing products is much worse from the water resistance test results.

[0044] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to embrace all changes falling within the meaning and scope of the equivalent elements of the claims in the present invention.

[0045] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. Preparation method of water and salt spray resistant magnesium ion-exchanged silica for waterborne coatings, characterized in that, The following steps are included: Add water into a reaction kettle, adjust the pH to be acidic. After stirring evenly and maintaining this condition, add the prepared sodium silicate solution and sulfuric acid solution into the reaction kettle in a pressurized convection manner, and conduct aging. After the aging is completed, adjust the pH to be weakly acidic, then add a magnesium source, and conduct ion exchange for 1 - 8 hours. After the ion exchange is completed, wash the reaction product successively with an ammonium salt aqueous solution and pure water. After washing, conduct uniform dispersion in a disperser, then conduct spray drying on the completed slurry, and obtain the preliminary magnesium ion-exchanged silica powder through airflow pulverization. Then add an amphiphilic ring film type silane coupling agent into a reaction flask containing methanol to prepare a 0.5% - 2% solution, and add it to the silica. Use a magnetic stirrer to fully and evenly mix the solution. Place the reaction flask in a warm water bath, adjust the temperature to 40°C - 50°C, and continue stirring and reacting for 6 - 8 hours to enable the ring film type silane coupling agent molecules to be fully adsorbed on the silica surface and form modified silica. After the reaction is completed, transfer the reactants to a drying oven for drying treatment, and maintain a low-pressure state in the drying oven to promote the drying and stabilization treatment of the silica. Finally, the dried silica is the water- and salt-fog-resistant magnesium ion-exchanged silica, and the magnesium source is MgSO4.

2. The preparation method of the water and salt spray resistant magnesium ion exchange type silica for waterborne coatings according to claim 1, characterized in that, The concentration of silica in the sodium silicate solution is 10wt% - 20 wt%.

3. The preparation method of the water and salt spray resistant magnesium ion-exchanged silica for waterborne coatings according to claim 1, characterized in that, The concentration of sulfuric acid in the sulfuric acid solution is 30wt% - 50wt%.

4. The preparation method of the water and salt spray resistant magnesium ion exchange type silica for waterborne coatings according to claim 1, characterized in that, The temperature in the drying oven is controlled at 80°C - 100°C.

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