High-strength sand casting water-based paint and method for preparing the same

Abstract

The application discloses a high-strength sand casting water-based paint and a preparation method thereof, and relates to the technical field of paint. The preparation method comprises the following steps: firstly, preparing a sepiolite reinforcing body by performing heat treatment, acid treatment and surface modification on natural sepiolite in sequence by using gamma-aminopropyl triethoxysilane and isopropyl trioleate; then, modifying silicon nitride nanoparticles by hydroxylation, organic silicon resin coating and lanthanum nitrate modification to obtain modified silicon nitride nanoparticles; treating bentonite by using an ammonium chloride solution, grinding the bentonite with polyethylene glycol, and then compounding the bentonite with xanthan gum to obtain a composite suspending agent; finally, mixing refractory aggregate, the sepiolite reinforcing body, the composite suspending agent, sodium lignosulfonate and deionized water to obtain a premix, adding the modified silicon nitride nanoparticles, performing ultrasonic dispersion and high-speed stirring, adding sodium carboxymethyl cellulose, and performing high-speed stirring and vacuum degassing, so that the sand casting water-based paint is obtained. The sand casting water-based paint prepared by the method has excellent mechanical strength.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of coating technology, in particular to a high-strength sand casting water-based coating and a preparation method thereof. BACKGROUND

[0002] Sand casting is one of the most widely used casting processes in the field of mechanical manufacturing, and it occupies an important position in many industries such as automobiles, engineering machinery, aerospace, etc. due to its low cost, short production cycle, and suitability for complex shape casting. Sand casting water-based coating, as a key auxiliary material for this process, is mainly coated on the surface of the sand mold cavity. Its core role is to isolate the high-temperature metal liquid from the sand mold matrix, prevent casting defects such as sand sticking and sand inclusion, and improve the surface roughness and dimensional accuracy of the casting, which is irreplaceable in ensuring the quality of the casting.

[0003] With the increasing demand for casting performance and quality in modern industry, especially the increasing application of large and complex castings and high-strength alloy castings, the use environment of sand casting water-based coating is becoming more and more demanding. However, the sand casting water-based coatings on the market generally have the technical pain point of insufficient strength, which is specifically manifested as follows: after the coating is dried, the normal temperature compressive strength, bonding strength and high temperature strength of the coating are difficult to meet the actual production requirements. In the casting pouring process, the impact and scouring action of high-temperature metal liquid and the thermal expansion stress of the sand mold can easily cause the coating to crack, fall off, and powder, which not only cannot effectively play the role of isolation and protection, but also may cause casting defects such as sand sticking and surface inclusion due to coating damage, seriously affecting the yield and performance of the casting. At the same time, the insufficient strength also limits the application of the coating in the production of large and thick-walled castings and high-precision castings, and restricts the further development of the sand casting process in the high-end manufacturing field. Therefore, it has become a technical problem to be solved in the current industry to develop a high-strength sand casting water-based coating. SUMMARY

[0004] The purpose of the present application is to provide a high-strength sand casting water-based coating and a preparation method thereof to solve the technical problem of insufficient mechanical strength of the sand casting water-based coating in the background art.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0006] A preparation method of a high-strength sand casting water-based coating, comprising the following steps:

[0007] S1, crushing and sieving natural sepiolite, then heat treating to obtain activated sepiolite, adding the activated sepiolite into a hydrochloric acid solution and stirring to react, then filtering, washing and drying after the reaction to obtain acid pretreated sepiolite;

[0008] S2, the acid pretreated sepiolite is added into anhydrous ethanol and ultrasonically dispersed, then γ-aminopropyl triethoxysilane is added and the pH value is adjusted, and a reflux reaction is carried out, after the reaction is completed, the product is filtered and dried to obtain silane modified sepiolite;

[0009] S3, the silane modified sepiolite is added into anhydrous ethanol to form a suspension, then isopropyl trioleate is added, and the product is stirred and reacted, after the reaction is completed, the product is centrifuged, washed, vacuum dried and ground to pass through a sieve to obtain sepiolite reinforcing bodies;

[0010] S4, the silicon nitride nanoparticles are subjected to an activation reaction, after the reaction is completed, the product is filtered, washed and dried to obtain hydroxylated silicon nitride nanoparticles;

[0011] S5, the hydroxylated silicon nitride nanoparticles are added into anhydrous ethanol and ultrasonically dispersed, then methylphenyl silicone resin is added, and the product is reacted under nitrogen protection, after the reaction is completed, the product is filtered, washed and vacuum dried to obtain silicone resin coated silicon nitride nanoparticles;

[0012] S6, the silicone resin coated silicon nitride nanoparticles are added into deionized water and ultrasonically dispersed, then lanthanum nitrate is added and the pH value is adjusted, and the product is stirred and reacted, after the reaction is completed, the product is centrifuged, dried and ground to pass through a sieve to obtain modified silicon nitride nanoparticles;

[0013] S7, bentonite is added into an ammonium chloride solution and stirred and reacted, after the reaction is completed, the product is filtered, washed and dried, then is mixed with polyethylene glycol and ground to obtain modified bentonite, and the modified bentonite is uniformly mixed with xanthan gum to obtain a composite suspending agent;

[0014] S8, refractory aggregate, sepiolite reinforcing bodies, a composite suspending agent, sodium lignosulfonate and deionized water are weighed out and mixed and stirred to obtain a premix, modified silicon nitride nanoparticles are added to the premix, deionized water is added, and ultrasonic dispersion and high-speed stirring are sequentially carried out to obtain an intermediate material, sodium carboxymethyl cellulose is added to the intermediate material and high-speed stirring is carried out, then vacuum defoaming treatment is carried out to obtain the high-strength sand casting water-based coating.

[0015] In the technical scheme of the present application, the mechanical strength of the sand casting water-based coating is improved from two aspects. On the one hand, after the progressive treatment of sepiolite through high-temperature activation, acid pretreatment, silane modification and titanate compound modification, not only the deep removal of surface impurities and the optimization of lattice structure are realized, but also the surface properties highly adapted to the coating system are obtained through the grafting of the modifier. High-temperature activation makes sepiolite form more open pores, acid pretreatment further purifies the lattice and increases the surface hydroxyl group, providing sufficient sites for efficient grafting of subsequent modifiers; silane modification improves the lipophilicity of sepiolite, making it better integrated into the organic-inorganic composite system, and the titanate coupling agent further strengthens the interfacial bonding force between sepiolite and refractory aggregate, binder and other components, avoiding the peeling risk caused by poor interfacial compatibility between components. Its inherent and more regular fibrous structure after modification is uniformly dispersed in the coating, and the fibers interweave to form a high-density three-dimensional network structure, covering the entire coating, like a macro-mechanical skeleton running through the entire coating. This network structure can effectively bear the impact load, thermal stress and mechanical stress of the molten metal after cooling during casting, quickly dispersing the locally concentrated load to the entire coating system, greatly reducing the local stress peak value and avoiding coating cracking or falling off due to stress concentration. At the same time, the high aspect ratio of sepiolite fibers forms an interwoven anchoring effect, tightly engaging with the surrounding components. Even in a high-temperature environment, its lattice structure remains stable, the three-dimensional network does not collapse or decompose, and it continues to provide rigid support for the coating, ensuring that the compressive strength and erosion resistance of the coating do not significantly decay at high temperatures, and building a stable and reliable mechanical support foundation for the coating from a macroscopic perspective.

[0016] On the other hand, the silicon nitride nanoparticles are treated by hydroxylation, silicone resin coating and lanthanum doping, which solves the problems of easy agglomeration, poor compatibility with the system and insufficient high-temperature stability of the nanoparticles, and becomes the micro-filling reinforcing phase for strengthening the mechanical properties of the coating. The hydroxylation treatment improves the surface activity and hydrophilicity of the particles, which makes them initially dispersed uniformly in the water-based system; the dense protective layer formed by the silicone resin coating not only effectively blocks the agglomeration force between the nanoparticles, but also ensures the integrity of the particles by virtue of the excellent high-temperature resistance of the resin, so that the particles do not oxidize and decompose in the high-temperature casting environment; the doping of rare earth element lanthanum strengthens the interfacial bonding force between the nanoparticles and the composite suspending agent and the surface functional groups of sepiolite in the coating system through coordination, so that the particles and the surrounding components form a stable interfacial bonding layer, avoiding the relative slipping between the particles and the matrix under stress. The nano-size effect of the nanoparticles can precisely fill the micro-pores in the three-dimensional network of sepiolite, and fill the nanoscale micropores generated by water evaporation and component shrinkage during the curing process of the coating, so that the internal structure of the coating tends to be dense and the porosity is significantly reduced. The dense coating structure reduces the weak points of mechanical properties, effectively blocks the initiation and propagation of cracks, and at the same time, utilizes the strong interfacial bonding force with the matrix to transfer the local stress to the surrounding sepiolite skeleton and refractory aggregate, avoiding the convergence and extension of cracks at the pores. In the high-temperature environment, the high-temperature resistance of the silicon nitride nanoparticles makes them maintain a stable filling form, and the silicone resin coating layer and the sepiolite skeleton work together to resist the thermal stress caused by the difference in thermal expansion coefficient, further inhibiting the risk of cracking of the coating at high temperature. Finally, the silicon nitride nanoparticles and the sepiolite skeleton form a synergistic system of macro-skeleton and micro-filling, which not only bears and disperses the macro-load through the sepiolite network, but also fills the micro-defects and strengthens the local mechanical properties through the nanoparticles, achieving a significant improvement in the mechanical strength of the coating.

[0017] Preferably, in the step S1, the heat treatment temperature is 800-850℃, and the heat treatment time is 2-3h.

[0018] Preferably, in the step S2, the mass ratio of the acid pretreated sepiolite to γ-aminopropyl triethoxysilane is 100:(5-10).

[0019] Preferably, in the step S3, the mass ratio of the silane modified sepiolite to isopropyl trioleate is 100:(3-6).

[0020] Preferably, in the step S5, the mass ratio of the hydroxylated silicon nitride nanoparticles to methyl phenyl silicone resin is 50:(10-15).

[0021] Preferably, in the step S6, the mass ratio of the silicone resin coated silicon nitride nanoparticles to lanthanum nitrate is 50:(0.5-1.2).

[0022] Preferably, in step S7, the mass ratio of the modified bentonite to the xanthan gum is 4:(1.0-1.5).

[0023] Preferably, in step S8, the sepiolite reinforcing agent is subjected to a modification treatment, including the following steps:

[0024] S81, the nanometer silicon dioxide is added into anhydrous ethanol, ultrasonic dispersion is performed to form a uniform suspension, gamma-glycidyl ether oxypropyl trimethoxysilane is added, the pH of the system is adjusted to be acidic, heating and stirring are performed for reaction, after the reaction is completed, centrifugal separation is performed, the precipitate is washed with anhydrous ethanol, vacuum drying is performed, and thus modified nanometer silicon dioxide with surface grafted epoxy groups is obtained;

[0025] S82, the sepiolite reinforcing agent is added into an ethanol and water mixed solvent, ultrasonic dispersion is performed, the modified nanometer silicon dioxide is added, the pH of the system is adjusted to be neutral, heating and stirring are performed for reaction, after the reaction is completed, centrifugal separation is performed, drying is performed, and grinding and sieving are performed, and thus the modified sepiolite reinforcing agent is obtained.

[0026] In the technical scheme of the present application, through in-depth research by the research team, it is found that after the sepiolite is subjected to silane-titanate composite modification, the surface amino groups are protonated to form -NH 3+ in a water-based system, and present weak positive electric characteristics; and after the silicon nitride nanoparticles are subjected to organic silicon resin coating and lanthanum doping, the surface residual hydroxyl groups present weak negative electric characteristics, and the two are attracted to each other due to electrostatic attraction, so that the silicon nitride nanoparticles cannot be uniformly dispersed in the interstices of the sepiolite three-dimensional network, but are instead directionally adsorbed on the surface of the sepiolite fibers to form micron-level agglomerates, so that the silicon nitride nanoparticles cannot fill the network interstices of the sepiolite, a large number of pore defects are formed in the coating, and microcracks are easily induced at high temperatures, which seriously affects the mechanical properties of the coating and further affects the synergistic effect of the two. In order to further solve this technical problem, the modified nanometer silicon dioxide with surface grafted epoxy groups is reacted with the sepiolite reinforcing agent, a covalent bond is formed through the nucleophilic ring-opening reaction of the epoxy groups and the amino groups, the nanometer silicon dioxide is directionally anchored on the surface of the sepiolite, so that the positive charge on the surface of the sepiolite can be effectively neutralized, and the silicon nitride nanoparticles are forced to be uniformly dispersed in the interstices of the sepiolite three-dimensional network through the steric hindrance effect, which significantly improves the coating density and high-temperature mechanical properties, and fully realizes the synergistic effect of skeleton support and filling enhancement.

[0027] Preferably, in step S82, the mass ratio of the sepiolite reinforcing agent to the modified nanometer silicon dioxide is 100:(5-10).

[0028] A high-strength sand casting water-based coating is prepared by the above method.

[0029] Compared with the prior art, the present application has the following beneficial effects:

[0030] 1. The three-dimensional network skeleton formed by modifying sepiolite bears macro stress, while the micro defects are filled with silicon nitride nanoparticles, and the two work together to make the coating have excellent impact resistance, crack resistance and overall mechanical strength.

[0031] 2. By multi-step surface modification of sepiolite and silicon nitride, the dispersibility of sepiolite and silicon nitride in water-based paint is effectively improved, and the interfacial bonding force with other components of the paint is strengthened, avoiding performance degradation due to poor compatibility and agglomeration.

[0032] 3. The modified sepiolite skeleton and silicon nitride filling phase both have excellent high temperature resistance and can maintain structural stability at high casting temperatures; the filling of nanoparticles and the solution of electrostatic adsorption problems together make the internal structure of the coating more dense and the porosity lower, effectively inhibiting the generation and expansion of cracks at high temperatures, further improving the mechanical strength. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 SEM image of the coating surface of the sand casting water-based paint prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0035] Example 1

[0036] A preparation method of a high-strength sand casting water-based paint, comprising the following steps:

[0037] Step 1: 100g of natural sepiolite is crushed through a 200 mesh sieve and placed in a muffle furnace to be heated at a rate of 5℃ / min to 830℃, and then naturally cooled for 2.5 hours to obtain activated sepiolite; 100g of activated sepiolite is added to 1000mL of 10% hydrochloric acid solution, stirred at 350rpm in a 60℃ constant temperature water bath for 2.5 hours, then filtered and washed with deionized water until the filtrate pH=7, and then dried in a 110℃ oven for 10 hours to obtain acid pretreated sepiolite.

[0038] Step 2: 100g of acid pretreated sepiolite is added to 800mL of anhydrous ethanol, and dispersed by ultrasonic at 350W for 40 minutes, then 9g of γ-aminopropyl triethoxysilane is added, the pH is adjusted to 5.0 with dilute acetic acid, and then transferred to a 75℃ reflux device for stirring and reflux reaction for 4 hours, then filtered and dried to obtain silane modified sepiolite.

[0039] Step 3: Take 100 g of silane-modified sepiolite and add 800 mL of anhydrous ethanol to form a suspension, then add 5 g of isopropyl trioleate, and stir at 400 rpm in a 80°C constant temperature water bath for 3 hours. After centrifugal separation, wash with anhydrous ethanol for 3 times, and dry at 105°C for 8 hours. Grind through a 300 mesh sieve to obtain sepiolite reinforcing agent.

[0040] Step 4: Take 50 g of silicon nitride nanoparticles with a particle size of 50-100 nm, add 750 mL of mixed solution (30% hydrogen peroxide: 10% dilute nitric acid = 3:1, volume ratio), and stir at 45°C in a constant temperature water bath for 3 hours. After suction filtration, wash with deionized water until the filtrate is neutral, and dry in a 100°C oven for 6 hours to obtain hydroxylated silicon nitride nanoparticles.

[0041] Step 5: Take 50 g of hydroxylated silicon nitride nanoparticles and add 300 mL of anhydrous ethanol, and ultrasonic dispersion for 30 minutes at 400 W. Then add 14 g of methyl phenyl silicone resin, and then add 0.5 g of dibutyltin dilaurate as catalyst. Blow in nitrogen at 0.5 L / min for protection, and heat to 90°C for stirring reaction for 6 hours. After cooling, suction filtration, wash with anhydrous ethanol for 2 times, and dry at 80°C for 10 hours to obtain silicone resin coated silicon nitride nanoparticles.

[0042] Step 6: Take 50 g of silicone resin coated silicon nitride nanoparticles and add 400 mL of deionized water, then add 0.5 g of sodium dodecyl benzene sulfonate, and ultrasonic dispersion for 30 minutes at 400 W. Then add 1.0 g of lanthanum nitrate, and adjust the pH to 6.2 with dilute hydrochloric acid. Stir at 350 rpm in a 70°C constant temperature water bath for 2 hours. Centrifuge at 8000 rpm for 10 minutes, discard the supernatant, and dry in a 110°C oven for 7 hours. Grind through a 400 mesh sieve to obtain modified silicon nitride nanoparticles.

[0043] Step 7: Take 100 g of bentonite and add 800 mL of 6% ammonium chloride solution, and stir at 55°C in a constant temperature water bath for 2 hours. After suction filtration, wash with deionized water until the filtrate is free of chloride ions. Dry and mix with 8 g of polyethylene glycol to obtain modified bentonite. Take 40 g of modified bentonite and mix with 14 g of xanthan gum to obtain a composite suspension agent.

[0044] Step 8: 10 g of nano-silica was added to 200 mL of anhydrous ethanol and ultrasonically dispersed to form a uniform suspension. Then, 0.5 g of γ-glycidoxypropyltrimethoxysilane was added, and the pH was adjusted to 4.5. The mixture was heated and stirred at 60°C for 3 hours. After centrifugal separation, the precipitate was washed with anhydrous ethanol and vacuum dried to obtain modified nano-silica with surface grafted epoxy groups. 100 g of sepiolite reinforcement was added to ethanol-water (volume ratio 1:1) and ultrasonically dispersed. Then, 9 g of modified nano-silica was added, 0.3 g of triethylamine was added, and the pH was adjusted to 9.0. The mixture was heated and stirred at 70°C for 4 hours. After centrifugal separation and drying, the mixture was ground through a 300 mesh sieve to obtain modified sepiolite reinforcement.

[0045] 75 parts of refractory aggregate (corundum powder: silicon carbide: cordierite = 7:3:2), 12 parts of modified sepiolite reinforcement, 9 parts of composite suspending agent, 1.0 part of sodium lignosulfonate, and 50 parts of deionized water were weighed by weight parts. The material temperature was controlled at 40°C, and the mixture was stirred at 400 r / min for 60 minutes to obtain a premix. 7 parts of modified silicon nitride nanoparticles were added to the premix, and 35 parts of deionized water was added. After ultrasonic dispersion at 400 W for 50 minutes, the mixture was stirred at 600 r / min for 40 minutes to obtain an intermediate material. 5 parts of sodium carboxymethyl cellulose was added to the intermediate material, and the stirring speed was adjusted to 800 r / min for 30 minutes. Then, the mixture was degassed at a vacuum degree of 0.08 MPa for 40 minutes to obtain a high-strength sand casting water-based coating.

[0046] Example 2

[0047] A method for preparing a high-strength sand casting water-based coating, comprising the following steps:

[0048] Step 1: 100 g of natural sepiolite was ground through a 200 mesh sieve and placed in a muffle furnace. The temperature was increased to 830°C at a rate of 5°C / min, and the mixture was kept at this temperature for 2.5 hours before being naturally cooled. The resulting activated sepiolite was obtained. 100 g of activated sepiolite was added to 1000 mL of 10% hydrochloric acid solution, and the mixture was stirred at 350 rpm in a 60°C constant temperature water bath for 2.5 hours. After filtration, the mixture was washed with deionized water until the pH of the filtrate was 7. The mixture was dried in an oven at 110°C for 10 hours to obtain acid pretreated sepiolite.

[0049] Step 2: 100 g of acid pretreated sepiolite was added to 800 mL of anhydrous ethanol and ultrasonically dispersed at 350 W for 40 minutes. Then, 6 g of γ-aminopropyltriethoxysilane was added, and the pH was adjusted to 5.0 with dilute acetic acid. The mixture was transferred to a 75°C reflux device and stirred and refluxed for 4 hours. After filtration and drying, the mixture was obtained as silane modified sepiolite.

[0050] Step 3: Take 100 g of silane-modified sepiolite and add 800 mL of anhydrous ethanol to form a suspension, then add 4 g of isopropyl trioleate, and stir at 400 rpm in a 80°C constant temperature water bath for 3 hours. After centrifugal separation, wash with anhydrous ethanol for 3 times, and dry at 105°C for 8 hours. Grind through a 300 mesh sieve to obtain sepiolite reinforcing agent.

[0051] Step 4: Take 50 g of silicon nitride nanoparticles with a particle size of 50-100 nm, add 750 mL of mixed solution (30% hydrogen peroxide: 10% dilute nitric acid = 3:1, volume ratio), and stir at 45°C in a constant temperature water bath for 3 hours. After suction filtration, wash with deionized water until the filtrate is neutral, and dry in a 100°C oven for 6 hours to obtain hydroxylated silicon nitride nanoparticles.

[0052] Step 5: Take 50 g of hydroxylated silicon nitride nanoparticles and add 300 mL of anhydrous ethanol, and ultrasonically disperse for 30 minutes at 400 W. Then add 12 g of methyl phenyl silicone resin, and then add 0.5 g of dibutyltin dilaurate as a catalyst. Blow in nitrogen at 0.5 L / min for protection, and heat to 90°C for stirring reaction for 6 hours. After cooling, suction filtration, and washing with anhydrous ethanol for 2 times, dry at 80°C for 10 hours to obtain silicone resin coated silicon nitride nanoparticles.

[0053] Step 6: Take 50 g of silicone resin coated silicon nitride nanoparticles and add 400 mL of deionized water, then add 0.5 g of sodium dodecyl benzene sulfonate, and ultrasonically disperse for 30 minutes at 400 W. Then add 0.6 g of lanthanum nitrate, and adjust the pH to 6.2 with dilute hydrochloric acid. Stir at 350 rpm in a 70°C constant temperature water bath for 2 hours. Centrifuge at 8000 rpm for 10 minutes, discard the supernatant, and dry in an oven at 110°C for 7 hours. Grind through a 400 mesh sieve to obtain modified silicon nitride nanoparticles.

[0054] Step 7: Take 100 g of bentonite and add 800 mL of 6% ammonium chloride solution, and stir at 55°C in a constant temperature water bath for 2 hours. After suction filtration, wash with deionized water until the filtrate is free of chloride ions. Dry and mix with 8 g of polyethylene glycol to obtain modified bentonite. Take 40 g of modified bentonite and 12 g of xanthan gum, mix evenly to obtain a composite suspension agent.

[0055] Step 8: 10 g of nano-silica was added to 200 mL of anhydrous ethanol and ultrasonically dispersed to form a uniform suspension. Then, 0.5 g of γ-glycidoxypropyltrimethoxysilane was added, and the pH was adjusted to 4.5. The mixture was heated and stirred at 60°C for 3 hours. After centrifugal separation, the precipitate was washed with anhydrous ethanol and vacuum dried to obtain modified nano-silica with surface grafted epoxy groups. 100 g of sepiolite reinforcement was added to ethanol-water (volume ratio 1:1) and ultrasonically dispersed. Then, 6 g of modified nano-silica was added, followed by the addition of 0.3 g of triethylamine. The pH was adjusted to 9.0, and the mixture was heated and stirred at 70°C for 4 hours. After centrifugal separation and drying, the mixture was ground through a 300 mesh sieve to obtain modified sepiolite reinforcement.

[0056] 75 parts of refractory aggregate (corundum powder: silicon carbide: cordierite = 7:3:2), 12 parts of modified sepiolite reinforcement, 9 parts of composite suspending agent, 1.0 part of sodium lignosulfonate, and 50 parts of deionized water were weighed by weight parts. The material temperature was controlled at 40°C, and stirring was performed at 400 r / min for 60 minutes to obtain a premix. 7 parts of modified silicon nitride nanoparticles were added to the premix, and 35 parts of deionized water were added. After ultrasonic dispersion at 400 W for 50 minutes, high-speed stirring was performed at 600 r / min for 40 minutes to obtain an intermediate material. 5 parts of sodium carboxymethyl cellulose were added to the intermediate material, and stirring was continued at 800 r / min for 30 minutes. Then, degassing was performed at a vacuum degree of 0.08 MPa for 40 minutes to obtain a high-strength sand casting water-based coating.

[0057] Example 3

[0058] A method for preparing a high-strength sand casting water-based coating, comprising the following steps:

[0059] Step 1: 100 g of natural sepiolite was ground through a 200 mesh sieve and placed in a muffle furnace. The temperature was increased to 830°C at a rate of 5°C / min, and the temperature was maintained for 2.5 hours. Then, the mixture was naturally cooled to obtain activated sepiolite. 100 g of activated sepiolite was added to 1000 mL of 10% hydrochloric acid solution, and the mixture was stirred at 350 rpm in a 60°C constant temperature water bath for 2.5 hours. After filtration, the filter was washed with deionized water until the pH of the filtrate was 7. The mixture was dried in an oven at 110°C for 10 hours to obtain acid pretreated sepiolite.

[0060] Step 2: 100 g of acid pretreated sepiolite was added to 800 mL of anhydrous ethanol and ultrasonically dispersed at 350 W for 40 minutes. Then, 8 g of γ-aminopropyltriethoxysilane was added, and the pH was adjusted to 5.0 with dilute acetic acid. The mixture was transferred to a 75°C reflux device and stirred and refluxed for 4 hours. After filtration and drying, silane modified sepiolite was obtained.

[0061] Step 3: Take 100 g of silane-modified sepiolite and add 800 mL of anhydrous ethanol to form a suspension, then add 4.5 g of isopropyl trioleate, and stir at 400 rpm in a 80°C constant temperature water bath for 3 hours. After centrifugal separation, wash with anhydrous ethanol for 3 times, and dry at 105°C for 8 hours. Grind through a 300 mesh sieve to obtain sepiolite reinforcing agent.

[0062] Step 4: Take 50 g of silicon nitride nanoparticles with a particle size of 50-100 nm, add 750 mL of mixed solution (30% hydrogen peroxide: 10% dilute nitric acid = 3:1, volume ratio), and stir at 45°C in a constant temperature water bath for 3 hours. After suction filtration, wash with deionized water until the filtrate is neutral, and dry in a 100°C oven for 6 hours to obtain hydroxylated silicon nitride nanoparticles.

[0063] Step 5: Take 50 g of hydroxylated silicon nitride nanoparticles and add 300 mL of anhydrous ethanol, and ultrasonic dispersion for 30 minutes at 400 W. Then add 13 g of methyl phenyl silicone resin, and then add 0.5 g of dibutyltin dilaurate as catalyst. Blow in nitrogen at 0.5 L / min for protection, and heat to 90°C for stirring reaction for 6 hours. After cooling, suction filtration, and washing with anhydrous ethanol for 2 times, dry at 80°C for 10 hours to obtain silicone resin coated silicon nitride nanoparticles.

[0064] Step 6: Take 50 g of silicone resin coated silicon nitride nanoparticles and add 400 mL of deionized water, then add 0.5 g of sodium dodecyl benzene sulfonate, and ultrasonic dispersion for 30 minutes at 400 W. Then add 0.8 g of lanthanum nitrate, and adjust the pH to 6.2 with dilute hydrochloric acid. Stir at 350 rpm in a 70°C constant temperature water bath for 2 hours. Centrifuge at 8000 rpm for 10 minutes, discard the supernatant, and dry in a 110°C oven for 7 hours. Grind through a 400 mesh sieve to obtain modified silicon nitride nanoparticles.

[0065] Step 7: Take 100 g of bentonite and add 800 mL of 6% ammonium chloride solution, and stir at 55°C in a constant temperature water bath for 2 hours. After suction filtration, wash with deionized water until the filtrate is free of chloride ions. Dry and mix with 8 g of polyethylene glycol to obtain modified bentonite. Take 40 g of modified bentonite and mix with 13 g of xanthan gum to obtain a composite suspension agent.

[0066] Step 8: 10 g of nano-silica was added to 200 mL of anhydrous ethanol and ultrasonically dispersed to form a uniform suspension. Then, 0.5 g of γ-glycidoxypropyltrimethoxysilane was added, and the pH was adjusted to 4.5. The mixture was heated and stirred at 60°C for 3 hours. After centrifugal separation, the precipitate was washed with anhydrous ethanol and vacuum dried to obtain modified nano-silica with surface grafted epoxy groups. 100 g of sepiolite reinforcement was added to ethanol-water (volume ratio 1:1) and ultrasonically dispersed. Then, 8 g of modified nano-silica was added, 0.3 g of triethylamine was added, and the pH was adjusted to 9.0. The mixture was heated and stirred at 70°C for 4 hours. After centrifugal separation and drying, the mixture was ground through a 300 mesh sieve to obtain modified sepiolite reinforcement.

[0067] 75 parts of refractory aggregate (corundum powder: silicon carbide: cordierite = 7:3:2), 12 parts of modified sepiolite reinforcement, 9 parts of composite suspending agent, 1.0 part of sodium lignosulfonate, and 50 parts of deionized water were weighed by weight parts. The material temperature was controlled at 40°C, and stirring was performed at 400 r / min for 60 minutes to obtain a premix. 7 parts of modified silicon nitride nanoparticles were added to the premix, and 35 parts of deionized water was added. After ultrasonic dispersion at 400 W for 50 minutes, high-speed stirring was performed at 600 r / min for 40 minutes to obtain an intermediate material. 5 parts of sodium carboxymethyl cellulose was added to the intermediate material, and stirring was continued at 800 r / min for 30 minutes. Then, degassing was performed at a vacuum degree of 0.08 MPa for 40 minutes to obtain a high-strength sand casting water-based coating.

[0068] Example 4

[0069] A method for preparing a high-strength sand casting water-based coating, comprising the following steps:

[0070] Step 1: 100 g of natural sepiolite was ground through a 200 mesh sieve and placed in a muffle furnace. The temperature was increased to 850°C at a rate of 5°C / min, and the temperature was maintained for 3 hours before natural cooling. The activated sepiolite was obtained. 100 g of activated sepiolite was added to 1000 mL of 10% hydrochloric acid solution, and the mixture was stirred at 350 rpm in a 60°C constant temperature water bath for 2.5 hours. After filtration, the filter was washed with deionized water until the pH of the filtrate was 7. The acid pretreated sepiolite was dried in an oven at 110°C for 10 hours.

[0071] Step 2: 100 g of acid pretreated sepiolite was added to 800 mL of anhydrous ethanol and ultrasonically dispersed at 350 W for 40 minutes. Then, 10 g of γ-aminopropyltriethoxysilane was added, and the pH was adjusted to 5.0 with dilute acetic acid. The mixture was transferred to a 75°C reflux device and stirred and refluxed for 4 hours. After filtration and drying, the silane modified sepiolite was obtained.

[0072] Step 3: Take 100 g of silane-modified sepiolite and add 800 mL of anhydrous ethanol to form a suspension, then add 6 g of isopropyl trioleate, and stir at 400 rpm in a 80°C constant temperature water bath for 3 hours. After centrifugal separation, wash with anhydrous ethanol for 3 times, and dry at 105°C for 8 hours. Grind through a 300 mesh sieve to obtain sepiolite reinforcing agent.

[0073] Step 4: Take 50 g of silicon nitride nanoparticles with a particle size of 50-100 nm, add 750 mL of mixed solution (30% hydrogen peroxide: 10% dilute nitric acid = 3:1, volume ratio), and stir at 45°C in a constant temperature water bath for 3 hours. After suction filtration, wash with deionized water until the filtrate is neutral, and dry in a 100°C oven for 6 hours to obtain hydroxylated silicon nitride nanoparticles.

[0074] Step 5: Take 50 g of hydroxylated silicon nitride nanoparticles and add 300 mL of anhydrous ethanol, and ultrasonically disperse for 30 minutes at 400 W. Then add 15 g of methylphenyl silicone resin, and then add 0.5 g of dibutyltin dilaurate as a catalyst. Blow in nitrogen at 0.5 L / min for protection, and heat to 90°C for stirring reaction for 6 hours. After cooling, suction filtration, and washing with anhydrous ethanol for 2 times, dry at 80°C for 10 hours to obtain silicone resin coated silicon nitride nanoparticles.

[0075] Step 6: Take 50 g of silicone resin coated silicon nitride nanoparticles and add 400 mL of deionized water, then add 0.5 g of sodium dodecylbenzenesulfonate, and ultrasonically disperse for 30 minutes at 400 W. Then add 1.2 g of lanthanum nitrate, and adjust the pH to 6.2 with dilute hydrochloric acid. Stir at 350 rpm in a 70°C constant temperature water bath for 2 hours. Centrifuge at 8000 rpm for 10 minutes, discard the supernatant, and dry in an oven at 110°C for 7 hours. Grind through a 400 mesh sieve to obtain modified silicon nitride nanoparticles.

[0076] Step 7: Take 100 g of bentonite and add 800 mL of 6% ammonium chloride solution, and stir at 55°C in a constant temperature water bath for 2 hours. After suction filtration, wash with deionized water until there is no chloride ion in the filtrate. Dry and mix with 8 g of polyethylene glycol to obtain modified bentonite. Take 40 g of modified bentonite and 15 g of xanthan gum, mix evenly to obtain a composite suspension agent.

[0077] Step 8: 10 g of nano-silica was added to 200 mL of anhydrous ethanol and ultrasonically dispersed to form a uniform suspension. Then, 0.5 g of γ-glycidoxypropyltrimethoxysilane was added, and the pH was adjusted to 4.5. The mixture was heated and stirred at 60°C for 3 hours. After centrifugal separation, the precipitate was washed with anhydrous ethanol and vacuum dried to obtain modified nano-silica with surface grafted epoxy groups. 100 g of sepiolite reinforcement was added to ethanol-water (volume ratio 1:1) and ultrasonically dispersed. Then, 10 g of modified nano-silica was added, followed by the addition of 0.3 g of triethylamine. The pH was adjusted to 9.0, and the mixture was heated and stirred at 70°C for 4 hours. After centrifugal separation and drying, the mixture was ground through a 300 mesh sieve to obtain modified sepiolite reinforcement.

[0078] 75 parts of refractory aggregate (corundum powder: silicon carbide: cordierite = 7:3:2), 12 parts of modified sepiolite reinforcement, 9 parts of composite suspending agent, 1.0 part of sodium lignosulfonate, and 50 parts of deionized water were weighed out in parts by weight. The material temperature was controlled at 40°C, and the mixture was stirred at 400 r / min for 60 minutes to obtain a premix. 7 parts of modified silicon nitride nanoparticles were added to the premix, and 35 parts of deionized water were added. After ultrasonic dispersion at 400 W for 50 minutes, the mixture was stirred at 600 r / min for 40 minutes to obtain an intermediate material. 5 parts of sodium carboxymethyl cellulose were added to the intermediate material, and the stirring speed was adjusted to 800 r / min for 30 minutes. Then, the mixture was degassed at a vacuum degree of 0.08 MPa for 40 minutes to obtain a high-strength sand mold casting water-based coating.

[0079] Example 5

[0080] A method for preparing a high-strength sand mold casting water-based coating, comprising the following steps:

[0081] Step 1: 100 g of natural sepiolite was ground through a 200 mesh sieve and placed in a muffle furnace. The temperature was increased to 800°C at a rate of 5°C / min, and the mixture was kept at this temperature for 2 hours before being naturally cooled. Then, 100 g of the activated sepiolite was added to 1000 mL of a 10% hydrochloric acid solution. The mixture was stirred at 350 rpm in a 60°C constant temperature water bath for 2.5 hours. After filtration, the mixture was washed with deionized water until the pH of the filtrate was 7. Finally, the mixture was dried in an oven at 110°C for 10 hours to obtain acid pretreated sepiolite.

[0082] Step 2: 100 g of the acid pretreated sepiolite was added to 800 mL of anhydrous ethanol and ultrasonically dispersed at 350 W for 40 minutes. Then, 5 g of γ-aminopropyltriethoxysilane was added, and the pH was adjusted to 5.0 with dilute acetic acid. The mixture was transferred to a 75°C reflux device and stirred and refluxed for 4 hours. After filtration and drying, the mixture was obtained as silane modified sepiolite.

[0083] Step 3: Take 100 g of silane-modified sepiolite and add 800 mL of anhydrous ethanol to form a suspension, then add 3 g of isopropyl trioleate, and stir at 400 rpm in a 80°C constant temperature water bath for 3 hours. After centrifugal separation, wash with anhydrous ethanol for 3 times, and dry at 105°C for 8 hours. Grind through a 300 mesh sieve to obtain sepiolite reinforcing agent.

[0084] Step 4: Take 50 g of silicon nitride nanoparticles with a particle size of 50-100 nm, add 750 mL of mixed solution (30% hydrogen peroxide: 10% dilute nitric acid = 3:1, volume ratio), and stir at 45°C in a constant temperature water bath for 3 hours. After suction filtration, wash with deionized water until the filtrate is neutral, and dry in a 100°C oven for 6 hours to obtain hydroxylated silicon nitride nanoparticles.

[0085] Step 5: Take 50 g of hydroxylated silicon nitride nanoparticles and add 300 mL of anhydrous ethanol, and ultrasonically disperse for 30 minutes at 400 W. Then add 10 g of methylphenyl silicone resin, and then add 0.5 g of dibutyltin dilaurate as a catalyst. Blow in nitrogen at 0.5 L / min for protection, and heat to 90°C for stirring reaction for 6 hours. After cooling, suction filtration, and washing with anhydrous ethanol for 2 times, dry at 80°C for 10 hours to obtain silicone resin coated silicon nitride nanoparticles.

[0086] Step 6: Take 50 g of silicone resin coated silicon nitride nanoparticles and add 400 mL of deionized water, then add 0.5 g of sodium dodecylbenzenesulfonate, and ultrasonically disperse for 30 minutes at 400 W. Then add 0.5 g of lanthanum nitrate, and adjust the pH to 6.2 with dilute hydrochloric acid. Stir at 350 rpm in a 70°C constant temperature water bath for 2 hours. Centrifuge at 8000 rpm for 10 minutes, discard the supernatant, and dry in an oven at 110°C for 7 hours. Grind through a 400 mesh sieve to obtain modified silicon nitride nanoparticles.

[0087] Step 7: Take 100 g of bentonite and add 800 mL of 6% ammonium chloride solution, and stir at 55°C in a constant temperature water bath for 2 hours. After suction filtration, wash with deionized water until there is no chloride ion in the filtrate. Dry and mix with 8 g of polyethylene glycol to obtain modified bentonite. Take 40 g of modified bentonite and 10 g of xanthan gum, mix evenly to obtain a composite suspension agent.

[0088] Step 8: 10 g of nano-silica was added to 200 mL of anhydrous ethanol and ultrasonically dispersed to form a uniform suspension. Then, 0.5 g of γ-glycidoxypropyltrimethoxysilane was added, and the pH was adjusted to 4.5. The mixture was heated and stirred at 60°C for 3 hours. After centrifugal separation, the precipitate was washed with anhydrous ethanol and vacuum dried to obtain modified nano-silica with surface grafted epoxy groups. 100 g of sepiolite reinforcement was added to ethanol-water (volume ratio 1:1) and ultrasonically dispersed. Then, 5 g of modified nano-silica was added, followed by the addition of 0.3 g of triethylamine. The pH was adjusted to 9.0, and the mixture was heated and stirred at 70°C for 4 hours. After centrifugal separation and drying, the mixture was ground through a 300 mesh sieve to obtain modified sepiolite reinforcement.

[0089] 75 parts of refractory aggregate (corundum powder: silicon carbide: cordierite = 7:3:2), 12 parts of modified sepiolite reinforcement, 9 parts of composite suspending agent, 1.0 part of sodium lignosulfonate, and 50 parts of deionized water were weighed out in parts by weight. The material temperature was controlled at 40°C, and the mixture was stirred at 400 r / min for 60 minutes to obtain a premix. 7 parts of modified silicon nitride nanoparticles were added to the premix, and 35 parts of deionized water was added. After ultrasonic dispersion at 400 W for 50 minutes, the mixture was stirred at 600 r / min for 40 minutes to obtain an intermediate material. 5 parts of sodium carboxymethyl cellulose was added to the intermediate material, and the stirring speed was adjusted to 800 r / min for 30 minutes. Then, the mixture was degassed under a vacuum of 0.08 MPa for 40 minutes to obtain a high-strength sand casting water-based coating.

[0090] Comparative Example 1: Comparative Example 1 differed from Example 1 in that steps 1-3 were omitted in the coating preparation process, and no modified sepiolite reinforcement was added in step 8.

[0091] Comparative Example 2: Comparative Example 2 differed from Example 1 in that steps 4-6 were omitted in the coating preparation process, and no modified silicon nitride nanoparticles were added in step 8.

[0092] Comparative Example 3: Comparative Example 2 differed from Example 1 in that the modified sepiolite reinforcement was replaced by sepiolite reinforcement in step 8 of the coating preparation process.

[0093] Performance Test:

[0094] 1. Ambient temperature compressive strength test: The coating of each example and comparative example was poured into a 40 mm × 40 mm × 40 mm standard mold for coating, and after leveling, it was naturally dried at 25°C and 60% relative humidity for 72 hours until complete curing and demolding. The coating was tested for axial uniform speed compression using a coating-specific microcomputer-controlled electronic universal testing machine at a loading rate of 2.0 mm / min. The maximum pressure at the time of failure of the test block was recorded. Five parallel samples were tested for each sample, and the average value was taken as the ambient temperature compressive strength value. The test results are shown in Table 1.

[0095] 2. High temperature compressive strength test: after drying and curing, 40mm x 40mm x 40mm paint test block was put into a special high temperature test box for paint, and the temperature was raised to 1000℃ at a rate of 5℃ / min, and the temperature was kept for 30min to ensure uniform temperature of the test block; immediately transfer the high temperature test block to the matching high temperature pressure testing machine, and perform the compression test at a rate of 1.5mm / min under the condition of 1000℃ constant temperature, and record the breaking load, each sample test 3 parallel samples, and take the average value. The test results are shown in Table 1.

[0096] 3. Bonding strength test: the paint was uniformly coated on the surface of the sand core (φ50mm x 20mm) by brushing, and the coating thickness was controlled to be 1.0mm, and dried at 25℃, relative humidity 60% for 48h; using paint interface bonding strength tester, the maximum stress when the coating and sand core interface peeled off was tested at a rate of 1mm / min, each sample test 5 parallel samples, and take the average value. The test results are shown in Table 1.

[0097] 4. Impact strength test: the paint was coated on the surface of 2mm thick cold rolled steel plate (steel plate size 120mm x 50mm) by spraying, and the dry film thickness was controlled to be 1.0mm, and cured at 25℃ for 48h; using paint film impact tester with 50cm impact height and 1kg weight, the coating was subjected to impact test, and the maximum impact energy when the coating did not crack and fall off was recorded, and converted to impact strength, each sample test 5 parallel samples, and take the average value. The test results are shown in Table 1.

[0098] Table 1:

[0099]

[0100] Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement to part of the technical features, any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a high-strength water-based coating for sand casting, characterized in that, Includes the following steps: S1. After crushing and sieving natural sepiolite, heat treatment is performed to obtain activated sepiolite. The activated sepiolite is added to hydrochloric acid solution and stirred to react. After the reaction is completed, it is filtered, washed and dried to obtain acid-pretreated sepiolite. S2. Add acid-pretreated sepiolite to anhydrous ethanol and disperse it by ultrasonication. Then add γ-aminopropyltriethoxysilane and adjust the pH value. Perform reflux reaction. After the reaction is completed, filter and dry to obtain silane-modified sepiolite. S3. Add silane-modified sepiolite to anhydrous ethanol to form a suspension, then add isopropyltrioleoyl oxytitanate, stir to react, centrifuge, wash, vacuum dry, grind and sieve to obtain sepiolite reinforcement. S4. The silicon nitride nanoparticles are activated by a reaction. After the reaction is completed, the nanoparticles are filtered, washed and dried to obtain hydroxylated silicon nitride nanoparticles. S5. Hydroxylated silicon nitride nanoparticles were added to anhydrous ethanol and ultrasonically dispersed. Then, methylphenyl organosilicon resin was added and the reaction was carried out under nitrogen protection. After the reaction was completed, the nanoparticles were filtered, washed, and vacuum dried to obtain organosilicon resin-coated silicon nitride nanoparticles. S6. Add organosilicon resin-coated silicon nitride nanoparticles to deionized water and disperse by ultrasonication. Then add lanthanum nitrate and adjust the pH value. Stir the reaction and after the reaction is completed, centrifuge, dry, grind and sieve to obtain modified silicon nitride nanoparticles. S7. Add bentonite to ammonium chloride solution and stir to react. After the reaction is complete, filter, wash and dry. Then mix and grind with polyethylene glycol to obtain modified bentonite. Mix the modified bentonite with xanthan gum evenly to obtain a composite suspension. S8. Weigh refractory aggregate, sepiolite reinforcement, composite suspending agent, sodium lignosulfonate and deionized water, mix and stir to obtain a premix, add modified silicon nitride nanoparticles to the premix, add deionized water, and then perform ultrasonic dispersion and high-speed stirring in sequence to obtain an intermediate material. Add sodium carboxymethyl cellulose to the intermediate material, stir at high speed, and then perform vacuum degassing treatment to obtain the high-strength sand casting water-based coating. The sepiolite reinforcement undergoes modification treatment, including the following steps: S81. Add nano-silica to anhydrous ethanol, disperse it by ultrasonication to form a uniform suspension, add γ-glycidoxypropyltrimethoxysilane, adjust the pH of the system to acidic, heat and stir the reaction, centrifuge after the reaction is completed, wash the precipitate with anhydrous ethanol, and vacuum dry to obtain modified nano-silica with surface grafted epoxy groups. S82. Add the sepiolite reinforcement to a mixed solvent of ethanol and water, disperse it by ultrasonication, add modified nano-silica, the mass ratio of sepiolite reinforcement to modified nano-silica is 100:(5~10), adjust the pH of the system to neutral, heat and stir the reaction, centrifuge after the reaction is completed, dry, grind and sieve to obtain the modified sepiolite reinforcement.

2. The method for preparing a high-strength sand casting water-based coating according to claim 1, characterized in that, In step S1, the heat treatment temperature is 800-850℃ and the heat treatment time is 2-3 hours.

3. The method for preparing a high-strength sand casting water-based coating according to claim 1, characterized in that, In step S2, the mass ratio of acid-pretreated sepiolite to γ-aminopropyltriethoxysilane is 100:(5-10).

4. The method for preparing a high-strength sand casting water-based coating according to claim 1, characterized in that, In step S3, the mass ratio of silane-modified sepiolite to isopropyltrioleoyl oxytitanate is 100:(3-6).

5. The method for preparing a high-strength sand casting water-based coating according to claim 1, characterized in that, In step S5, the mass ratio of hydroxylated silicon nitride nanoparticles to methylphenyl organosilicon resin is 50:(10-15).

6. The method for preparing a high-strength sand casting water-based coating according to claim 1, characterized in that, In step S6, the mass ratio of silicone resin-coated silicon nitride nanoparticles to lanthanum nitrate is 50:(0.5-1.2).

7. The method for preparing a high-strength sand casting water-based coating according to claim 1, characterized in that, In step S7, the mass ratio of modified bentonite to xanthan gum is 4:(1.0-1.5).

8. A high-strength water-based coating for sand casting, characterized in that, It is prepared by the method described in any one of claims 1 to 7 above.

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