Nano zinc stannate modified urushiol composite coating and preparation method thereof

Abstract

The invention relates to the technical field of composite coatings, in particular to a nano zinc stannate modified urushiol composite coating and a preparation method thereof. The paint comprises urushiol and zinc stannate powder. According to the invention, the urushiol is subjected to oxidative polymerization with a long alkyl side chain through a high-activity phenolic hydroxyl group of the urushiol, so that a three-dimensional cross-linked network skeleton is formed, and basic film-forming property and adhesive force are provided; zinc stannate nanoparticles and urushiol molecular chains form hydrogen bonds / chemical bonds through surface hydroxyl groups, and the zinc stannate nanoparticles are embedded into pores of a cross-linked network to construct a rigid reinforcement phase, so that the interface bonding strength is synergistically improved; zinc / tin ions released by zinc stannate are chelated with the urushiol degradation intermediate, a compact ceramic barrier layer is formed at a high temperature, free radicals are captured, oxygen diffusion is inhibited, and therefore hardness strengthening, adhesive force improving and heat stability enhancing are synergistically achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite coatings, in particular to a nano-zinc stannate modified urushiol composite coating and a preparation method thereof. BACKGROUND

[0002] Natural raw lacquer is also known as "national lacquer" or "big lacquer", which is a pure natural cream white coating secreted by lacquer tree, and is known as "the king of coatings". The main film-forming material is urushiol, which will continuously absorb oxygen and gradually turn into brown paint film under the catalysis of lacquer enzyme after contacting with air. The paint film is hard and glossy, has good durability, acid resistance and insulation, etc., and is the earliest natural resin used by human beings.

[0003] However, the paint film also has some disadvantages, such as poor alkali resistance, large brittleness, poor flexibility, poor metal adhesion, etc., which limits its application range. Therefore, it is necessary to modify the raw lacquer to improve its comprehensive performance.

[0004] At present, the methods for modifying urushiol mainly include urushiol modified resin, hydrophilic modification, reaction modification with element compounds and nano-particle modification, wherein: When the urushiol is modified by urushiol modified resin and hydrophilic modification, the introduction of other components will dilute the active groups of urushiol or increase the polarity, interfere with the generation of dense cross-linked network, and cause the hardness to decrease, and the internal stress or polarity mismatch brought by the hydrophilic group will weaken the adhesion to the low polarity substrate; When the urushiol is modified by reaction with element compounds, the inorganic-organic hybrid structure formed by reaction with Si, Ti and the like is easy to increase brittleness. If the rigid inorganic phase is not well combined with the organic phase interface, the toughness of the coating is insufficient, and the coating is easy to crack and peel off when impacted or the substrate is deformed, so that the adhesion is invalid; When the urushiol is modified by nano-particle, the uneven dispersion and poor interface combination are the core problems. The particle agglomeration becomes a stress concentration point, which reduces the strength uniformity; the poor interface compatibility seriously hinders the effective infiltration and bonding of urushiol and the substrate, which leads to the significant deterioration of adhesion, and even if the hardness is improved, the peeling is easy.

[0005] In summary, while pursuing functionalization, the existing modification methods often interfere with the film-forming mechanism, increase brittleness / internal stress or introduce interface defects, and it is difficult to consider or even damage the inherent hardness and adhesion of urushiol. SUMMARY

[0006] The purpose of the present application is to avoid the damage to the inherent hardness and adhesion of urushiol caused by the introduction of other components and the like when modifying urushiol.

[0007] The present application aims to provide a kind of nano zinc stannate modified urushiol composite coating and its preparation method, by preparing nano zinc stannate, and as modifier is added to urushiol to prepare composite coating, reach the effect of improving the hardness, adhesion and other properties of paint film.

[0008] To achieve the above object, one of the purposes of the present application is to provide a kind of nano zinc stannate modified urushiol composite coating, including the following mass ratio of raw materials: Urushiol 90-98%, the rest is zinc stannate powder.

[0009] As a further improvement of the technical solution, the mass of zinc stannate powder is 2-10% of the mass of urushiol.

[0010] The second purpose of the present application is also to provide a preparation method for preparing the above-mentioned nano zinc stannate modified urushiol composite coating, comprising the following steps: Step S1: add tin tetrachloride pentahydrate, zinc chloride and hydrochloric acid solution to a three-necked bottle, stir at room temperature until completely dissolved, to obtain a premixed solution; Step S2: add the premixed solution dropwise to ammonia water, adjust PH=11, and age for 2h to obtain a turbid liquid containing precipitate, and the precipitate in the turbid liquid is suction filtered to obtain a filter cake; Step S3: the filter cake obtained above is dried and ground into powder, and then calcined to obtain zinc stannate powder; Step S4: dissolve natural raw lacquer in ethanol solvent, filter after sufficient stirring, separate insoluble impurities, retain the ethanol solution containing urushiol, and then perform vacuum distillation on the ethanol solution to finally obtain urushiol; Add zinc stannate powder to urushiol, stir at room temperature to obtain uniform modified urushiol.

[0011] As a further improvement of the technical solution, in step S1, the hydrochloric acid solution is prepared by mixing hydrochloric acid and water in a volume ratio of 1:2.

[0012] As a further improvement of the technical solution, in step S2, deionized water is used for washing during suction filtration, and the washing is stopped after no chloride ions are detected in the suction filtrate.

[0013] As a further improvement of the technical solution, in step S3, the temperature during drying and grinding is 70-90°C.

[0014] As a further improvement of the technical solution, in step S3, the calcination treatment is calcination at 600°C for 1-3h.

[0015] As a further improvement of the technical solution, in step S4, the natural raw lacquer is first filtered through gauze and then dissolved in ethanol solution.

[0016] As a further improvement of the technical solution, in the step S4, the stirring at room temperature lasts for 2-4 hours.

[0017] In the present application, the comprehensive performance of the urushiol is improved by preparing nano-zinc stannate and adding it as a modifier into the urushiol to prepare a composite coating.

[0018] Compared with the prior art, the present application has the following beneficial effects: In the nano-zinc stannate modified urushiol composite coating and the preparation method thereof, the urushiol is oxidized and polymerized through the high-activity phenolic hydroxyl group and the long alkyl side chain to form a three-dimensional cross-linked network skeleton, thereby providing basic film-forming property and adhesion; the zinc stannate nanoparticles form hydrogen bonds / chemical bonds with the urushiol molecular chain through the surface hydroxyl groups, are embedded in the cross-linked network pores to construct a rigid reinforcing phase, and synergistically improve the interfacial bonding strength; and then the zinc / silver ions released from the zinc stannate are chelated with the urushiol degradation intermediates to form a dense ceramic barrier layer at high temperature, thereby capturing free radicals and inhibiting oxygen diffusion, so as to synergistically achieve hardness strengthening, adhesion improvement, and thermal stability enhancement. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The flowchart of the present application is shown in the figure. Figure 2 The surface SEM diagram of the urushiol film before and after modification by zinc stannate is shown in the figure. Figure 3 The TG diagram of the zinc stannate modified urushiol film is shown in the figure. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0021] One of the objects of the present application is to provide a nano-zinc stannate modified urushiol composite coating, which comprises the following raw materials in mass percentage: Urushiol 90-98%, and the balance is zinc stannate powder.

[0022] Further, the mass of the zinc stannate powder is 2-10% of the mass of the urushiol.

[0023] Please refer to Figure 1 The second object of the present application is to provide a preparation method for preparing the above-mentioned nano-zinc stannate modified urushiol composite coating, which comprises the following steps: Step S1: tin tetrachloride pentahydrate, zinc chloride, and hydrochloric acid solution are added to a three-necked bottle, and stirred at room temperature until completely dissolved to obtain a premixed solution.

[0024] Step S2: The premixed solution is added dropwise into ammonia water, the PH is adjusted to 11, and is aged for 2h to obtain a turbid liquid containing precipitates, the precipitates in the turbid liquid are subjected to suction filtration, deionized water is used for washing during the suction filtration, and the washing is stopped after no chloride ion is detected in the suction filtrate, to obtain a filter cake.

[0025] Step S3: The filter cake obtained above is dried and ground into powder, and then is subjected to calcination treatment to obtain zinc stannate powder, wherein the temperature during the drying and grinding is 70-90℃, and the calcination treatment is calcination at 600℃ for 1-3h.

[0026] Step S4: The natural raw lacquer is first filtered through gauze, and then is dissolved in an ethanol solution, filtered after being fully stirred, and insoluble impurities (such as gum, moisture, etc.) are separated out, and the ethanol solution containing urushiol is retained, and the ethanol solution is subjected to vacuum distillation to remove ethanol and residual moisture, and finally high-purity urushiol is obtained, and the mass fraction of the effective component (urushiol) is 94%.

[0027] The zinc stannate powder is added to the urushiol, and is stirred at room temperature for 2-4h to obtain a uniform modified urushiol.

[0028] In the present application, the urushiol is oxidized and polymerized through the high-activity phenolic hydroxyl group and the long alkyl side chain to form a three-dimensional cross-linked network skeleton, providing basic film-forming property and adhesion; the zinc stannate nanoparticles form hydrogen bonds / chemical bonds with the urushiol molecular chain through the surface hydroxyl groups, are embedded in the cross-linked network pores to construct a rigid reinforcing phase, and synergistically improve the interfacial bonding strength; and then the zinc / silver ions released by the zinc stannate chelate with the urushiol degradation intermediates, form a dense ceramic barrier layer at high temperature, capture free radicals and inhibit oxygen diffusion, thereby synergistically achieving hardness strengthening, adhesion improvement, and thermal stability enhancement.

[0029] In the present application, the natural raw lacquer is selected from Hubei Maoba lacquer, which is used as a coating base material, has the largest proportion, and provides film-forming property and basic performance. And the following materials are respectively from: Tetrachloride tin pentahydrate (SnCl4·5H2O): Shanghai Aladdin Biochemical Technology Co., Ltd.; Ammonia water (NH3·H2O): National Pharmaceutical Group Chemical Reagent Co., Ltd.; Zinc chloride (ZnCl2): Shandong Keyuan Biochemical Co., Ltd.; Hydrochloric acid (HCl): National Pharmaceutical Group Chemical Reagent Co., Ltd.

[0030] The hydrochloric acid solution is prepared by mixing hydrochloric acid and water in a volume ratio of 1:2.

[0031] A kind of nano zinc stannate modified urushiol composite coating and a preparation method thereof provided by the present application are further described by specific embodiments. Embodiment

[0032] Step S1: Add tin tetrachloride pentahydrate, zinc chloride, and hydrochloric acid solution into a three-necked flask, stir at room temperature until completely dissolved to obtain a premixed solution.

[0033] Step S2: Add the premixed solution into ammonia water, adjust PH = 11, and age for 2h to obtain a turbid liquid containing precipitates. The precipitates in the turbid liquid are subjected to suction filtration, and deionized water is used for washing during suction filtration until no chloride ions can be detected in the filtrate, and then the washing is stopped to obtain a filter cake.

[0034] Step S3: The filter cake obtained above is dried and ground into powder, and then calcined to obtain zinc stannate powder, wherein the temperature during drying and grinding is 80°C, and the calcination treatment is calcination at 600°C for 2h.

[0035] Step S4: The natural raw lacquer is first filtered through gauze, then dissolved in an ethanol solution, fully stirred, filtered to separate insoluble impurities, and the ethanol solution containing lacquering is retained. The ethanol solution is subjected to vacuum distillation to remove ethanol and residual water, and finally high-purity lacquering is obtained, with the effective ingredient mass ratio reaching 94%.

[0036] In the lacquering, 2%, 4%, 6%, 8%, and 10% of zinc stannate powder by mass of the lacquering is added, and the mixture is stirred at room temperature for 3h to obtain a uniform modified lacquering.

[0037] A QTS type rod film applicator is used to coat the film on the substrate according to the national standard GB1727-2021 Film Preparation Method to prevent blank and overflow, and an unmodified lacquering film (i.e. containing only lacquering, with 0 content of zinc stannate powder) is prepared for comparison.

[0038] Then the physical and mechanical properties of the lacquer film are tested as follows: The coated film is placed in a 120°C constant temperature drying oven for 30min, then taken out and cooled, and the surface dry time of the film is tested by finger touch. Then every 5min, the film is taken out from the drying oven and cooled, and the surface is considered to be dry when it feels slightly sticky but no indentation is left. The data are recorded in Table 1.

[0039] Table 1 Effect of zinc stannate content on film surface dry time Zinc stannate content / % 0 2 4 6 8 10 Tack-free time / min 130 215 190 220 180 175 As can be seen from Table 1, the surface dry time of the unmodified lacquer film is 130min, and the surface dry time of the modified lacquer film is prolonged after the addition of zinc stannate. This may be because the zinc stannate particles fill the holes of molecular motion, making it difficult for water to escape, thereby prolonging the surface dry time.

[0040] ​The coated paint film was dried at 140°C for 3h, and its general physical and mechanical properties were tested. The hardness of the paint film was tested according to GB / T6739-2006 using a QHQ-A type portable pencil scratch tester. The hardness of the paint film was determined by scratching the film with a pencil hardness gauge, and the grade was evaluated according to the scratch. The test results are shown in Table 2.

[0041] Table 2 Effect of zinc stannate content on the hardness of the paint film Zinc stannate content / % 0 2 4 6 8 10 Pencil hardness 2H 2H 3H 3H 4H 4H As can be seen from Table 2, the hardness of the unmodified paint film was 2H, and the hardness of the paint film increased as the amount of zinc stannate increased. When the zinc stannate content increased from 8% to 10%, the hardness of the zinc stannate no longer changed significantly. This indicates that zinc stannate can increase the pencil hardness of the paint film, which may be due to the fact that zinc stannate can be well dispersed in the paint film matrix, thereby enhancing the hardness of the paint film.

[0042] The adhesion of the paint film was tested using a cross-hatch knife according to GB / T9286-2023, and the gloss was tested using a JFL-B60° gloss meter according to GB1743-1993. The adhesion of the paint film before and after modification was tested using a cross-hatch knife, and the test results are shown in Table 3.

[0043] Table 3 Effect of zinc stannate content on the adhesion of the paint film Zinc stannate content / % 0 2 4 6 8 10 Adhesion 3B 4B 5B 4B 4B 4B As can be seen from Table 3, the adhesion of the unmodified paint film was 3B, while the adhesion of the paint film with zinc stannate was 4B and 5B, and the edges of the cut were completely smooth, with no peeling at the edges of the grid. This indicates that zinc stannate can improve the adhesion of the paint film, with the best results being obtained when the zinc stannate content is 4%. This may be due to the fact that zinc stannate has strong activity and a large specific surface energy, which can form strong chemical bonds or hydrogen bonds with the paint film, resulting in more complete curing of the paint film. On the other hand, zinc stannate penetrates into the pores of the paint film, thereby enhancing the adhesion of the paint film.

[0044] The chemical resistance was tested by immersing the paint film in 10% HCl solution, 10% NaOH solution and 10% NaCl solution according to GB1763-1993, and observing the changes in the coating after 14 days. The gloss of the paint film before and after modification was tested using a gloss meter, and the data are shown in Table 4.

[0045] Table 4 Effect of zinc stannate content on the gloss of the paint film Zinc stannate content / % 0 2 4 6 8 10 Gloss / GU 127.7 117.7 108.9 103.7 93.5 74.7 As can be seen in Table 4, compared with the unmodified paint film, the gloss gradually decreases with increasing zinc stannate content. This indicates that the addition of zinc stannate reduces the gloss of the paint film. This is because the addition of zinc stannate increases the roughness of the paint film surface. The higher the content of nanoparticles, the more obvious the roughness. According to the principle of diffuse reflection of light, light transmitted on a relatively rough surface is reflected to a greater extent in all directions, resulting in a decrease in the gloss of the paint film. After urushiol is completely cured, it forms a polymer with a network structure. The solvent resistance of the paint film reflects the degree of curing of the paint film to a certain extent. The chemical medium performance of the paint film is measured as follows: At room temperature, the dried paint film was added to 10% HCl solution, 10% NaOH solution, and 10% NaCl solution and soaked for 7 days. The coating surface was then thoroughly cleaned with pure water. The paint film was observed for gloss loss, discoloration, wrinkling, blistering, and shedding. The results are shown in Table 5.

[0046] Table 5 Effect of zinc stannate content on solvent resistance of paint films Zinc stannate content / % 0 2 4 6 8 10 10% HCI No change No change No change No change No change No change 10% NaOH Significant flaking Significant blistering Significant flaking Significant blistering Significant blistering Slight blistering 10% NaCI No change No change No change No change No change No change As can be seen from Table 5, there is no significant effect on the acid and salt resistance of the paint film before and after zinc stannate modification. As the zinc stannate content increases, the alkali resistance of the paint film improves, indicating that the paint film and zinc stannate work synergistically to enhance the stability in alkaline environments.

[0047] The paint film before and after zinc stannate modification was measured using an S3400 scanning electron microscope. The surface SEM images of the paint film before and after zinc stannate modification were taken as follows: Figure 1 shown.

[0048] Depend on Figure 1 As can be seen, the paint film without zinc stannate addition showed no obvious agglomeration. As the zinc stannate content increased, the agglomeration phenomenon intensified, with more pronounced particle accumulation and agglomerated morphology. This indicates that at high zinc stannate content, it is difficult to disperse zinc stannate in the paint film and it is easy to form large agglomerated structures, which may affect the paint film properties (such as density and mechanical properties). This indicates that zinc stannate modification allows for more complete film curing, which further demonstrates that zinc stannate modification can enhance the hardness of the paint film.

[0049] In addition, the experiment was conducted using a synchronous thermal analyzer STA449-F3. The paint film samples were heated at a constant heating rate of 10°C / min in the temperature range of 28-800°C.

[0050] like Figure 2As can be seen, in the low-temperature range (approximately 0-300°C), paint films with varying zinc stannate contents experience minimal mass loss, indicating good thermal stability within this temperature range. This loss is primarily due to the loss of adsorbed water and low-molecular-weight volatiles. In the medium- to high-temperature range (around 300-500°C), mass rapidly decreases, driven by decomposition and oxidation of the film's primary organic components (such as resins), resulting in significant mass loss as temperature increases. In the high-temperature range (above 500°C), mass stabilizes, with inorganic residues (including zinc stannate) remaining. Inorganic components like zinc stannate are thermally stable and therefore remain. Increasing zinc stannate content increases the mass remaining in the high-temperature range. This suggests that zinc stannate can increase the carbon residue rate and enhance thermal stability of the paint film. Due to its stable inorganic structure, zinc stannate can remain at high temperatures, slowing the decomposition of organic components.

[0051] According to GB / T2406.2-2009 standard, the flame retardancy of the paint film was determined by the limiting oxygen index. The results are shown in Table 6.

[0052] Table 6 Oxygen index test data Zinc stannate content / % 0 2 4 6 8 10 Limiting oxygen index (LOI) 21.1 23.5 24.2 24.8 25.3 26.8 As can be seen from Table 6, as the zinc stannate content increases from 0% to 10%, the oxygen index continues to rise, from 21.1 to 26.8, indicating that zinc stannate has a flame retardant effect, can effectively improve the oxygen index of the material, enhance the flame retardant properties of the material, and make the material more difficult to ignite and burn more slowly.

[0053] In summary, the present invention uses nano-zinc stannate and urushiol to blend to prepare modified urushiol. The experimental results show that the addition of nano-zinc stannate prolongs the surface drying time of the paint film, improves the hardness and adhesion performance of the paint film, reduces the glossiness, and at the same time improves the hardness, adhesion, chemical resistance, thermal stability and flame retardancy of the paint film.

[0054] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely preferred examples of the present invention and are not intended to limit the present invention. Various changes and improvements may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and improvements fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a nano zinc stannate modified urushiol composite coating, characterized in that: The following steps are involved: Step S1: Add tin tetrachloride pentahydrate, zinc chloride, and hydrochloric acid solution to a three-necked flask and stir at room temperature until completely dissolved to obtain a premixed solution; Step S2: adding the premixed solution dropwise to aqueous ammonia, adjusting the pH to 11, and aging for 2 hours to obtain a turbid solution containing a precipitate, and filtering the precipitate in the turbid solution to obtain a filter cake; Step S3: drying and grinding the filter cake obtained above into powder, and then calcining it to obtain zinc stannate powder; Step S4: dissolving the natural raw lacquer in an ethanol solvent, stirring thoroughly, and filtering to separate insoluble impurities, retaining the ethanol solution containing urushiol, and then performing reduced pressure distillation on the ethanol solution to finally obtain urushiol; Zinc stannate powder is added to urushiol and stirred at room temperature to obtain uniform modified urushiol.

2. The method for preparing the nano zinc stannate modified urushiol composite coating according to claim 1, wherein: In step S1, the hydrochloric acid solution is prepared by mixing hydrochloric acid and water in a volume ratio of 1:

2.

3. The method for preparing the nano zinc stannate modified urushiol composite coating according to claim 1, wherein: In the step S1, the natural lacquer is first filtered through gauze and then dissolved in an ethanol solution.

4. The method for preparing the nano zinc stannate modified urushiol composite coating according to claim 1, wherein: In step S2, deionized water is used for washing during filtration, and washing is stopped when chloride ions can no longer be detected in the filtrate.

5. The method for preparing the nano zinc stannate modified urushiol composite coating according to claim 1, wherein: In step S3, the temperature during drying and grinding is 70-90°C.

6. The method for preparing the nano zinc stannate modified urushiol composite coating according to claim 1, wherein: In the step S3, the calcination treatment is performed at 600° C. for 1-3 hours.

7. The method for preparing the nano zinc stannate modified urushiol composite coating according to claim 1, wherein: In step S4, the natural lacquer is first filtered through gauze and then dissolved in an ethanol solution.

8. The method for preparing the nano zinc stannate modified urushiol composite coating according to claim 1, wherein: In step S4, the mass of the zinc stannate powder is 2-10% of the mass of the urushiol.

9. The method for preparing the nano zinc stannate modified urushiol composite coating according to claim 1, wherein: In step S4, stirring at room temperature takes 2-4 hours.

10. The nano zinc stannate modified urushiol composite coating prepared by the preparation method according to any one of claims 1 to 9, characterized in that: Including the following ingredients: Urushiol and zinc stannate powder; wherein: The urushiol acts as a film-forming matrix phase, and its highly active phenolic hydroxyl groups and long alkyl side chains form a three-dimensional cross-linked network through oxidative polymerization, providing basic adhesion and film-forming properties; The zinc stannate powder acts as a nano-reinforcement phase, forming strong bonds with urushiol molecules through surface hydroxyl groups, filling the pores of the paint film and constructing a rigid skeleton, thereby synergistically improving the hardness and interfacial bonding strength. At the same time, the zinc / tin ions released by the zinc stannate at high temperatures chelate with the degradation products of urushiol to form a dense barrier layer, inhibiting thermal oxidative decomposition and capturing free radicals, thereby enhancing thermal stability and flame retardancy.

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