A water-based polyvinyl alcohol desalination peelable coating and its preparation method

Abstract

This invention belongs to the field of chemical decontamination technology, specifically relating to a water-based polyvinyl alcohol (PVA) desalination and peelable coating and its preparation method. The water-based PVA desalination and peelable coating comprises: modified PVA, deionized water, antifreeze, leveling agent, wetting agent, defoamer, dispersant, and peeling agent. The mass percentages of each component are as follows: modified PVA 50-70%, deionized water 25-40%, antifreeze 5-15%, leveling agent 0.3-3%, wetting agent 0.1-2%, defoamer 0.1-2%, dispersant 0.1-1%, and peeling agent 1-5%. The modified PVA is PVA with 15-crown-5 ether groups branched onto its side links.

Description

Technical Field

[0001] This invention belongs to the field of chemical decontamination technology, specifically relating to a water-based polyvinyl alcohol desalination peelable coating and its preparation method. Background Technology

[0002] Equipment operating in marine atmospheric environments faces severe corrosion problems, primarily caused by the deposition of salt on equipment surfaces in salt spray, leading to electrochemical corrosion. While direct rinsing with fresh water can solve the salt deposition problem, other non-destructive and simple salt cleaning methods are needed due to various reasons, such as the inability to directly rinse some precision equipment with clean water, the potential for salt deposition in equipment crevices and crevice corrosion caused by rinsing with clean water on equipment with a porous structure, and the lack of fresh water resources in some equipment operating areas with harsh conditions. Summary of the Invention

[0003] Purpose of the invention: To provide a water-based polyvinyl alcohol desalination peelable coating and its preparation method, so as to achieve non-destructive and simple salt cleaning.

[0004] Technical solution:

[0005] A water-based polyvinyl alcohol desalination and peelable coating comprises: modified polyvinyl alcohol, deionized water, antifreeze, leveling agent, wetting agent, defoamer, dispersant and peeling agent, wherein the mass percentage of each component is: modified polyvinyl alcohol 50-70%, deionized water 25-40%, antifreeze 5-15%, leveling agent 0.3-3%, wetting agent 0.1-2%, defoamer 0.1-2%, dispersant 0.1-1%, peeling agent 1-5%, and the modified polyvinyl alcohol is polyvinyl alcohol with 15-crown 5-ether groups branched on its side.

[0006] A method for preparing an aqueous polyvinyl alcohol desalination peelable coating includes:

[0007] Modified polyvinyl alcohol was obtained by chemically modifying polyvinyl alcohol with 2-formaldehyde-15-crown ether-5, 2-(epoxyethylenemethyl)-15-crown ether-5, 2-hydroxymethyl-15-crown ether-5 or 2-aminomethyl-15-crown ether-5.

[0008] Add 50-70% of modified polyvinyl alcohol to 25-40% of deionized water, stir at about 95°C for 24 hours until completely dissolved, and then lower the system temperature to 75°C to obtain solution A.

[0009] Add 0.3-3% leveling agent, 0.1-2% wetting agent, 0.1-2% defoamer, 0.1-1% dispersant and 1-5% stripping agent to solution A, and stir thoroughly to obtain solution B;

[0010] After solution B cools to room temperature, add 5-15% antifreeze and stir thoroughly to obtain water-based polyvinyl alcohol desalination peelable coating.

[0011] Furthermore, modified polyvinyl alcohol is obtained by chemically modifying polyvinyl alcohol using 2-formaldehyde-15-crown ether-5, specifically including:

[0012] Take 100 parts by weight of polyvinyl alcohol and add it to deionized water. Stir thoroughly and heat to 90-95℃ and keep warm for 1 hour to fully dissolve the polyvinyl alcohol.

[0013] After cooling to room temperature, dilute sulfuric acid is added dropwise to adjust the pH value to 2-3 to obtain the first solution;

[0014] Slowly add 5-20 parts of 2-formaldehyde-15-crown ether-5 dropwise to the first solution and stir until homogeneous. After the addition of 2-formaldehyde-15-crown ether-5 is complete, gradually raise the reaction temperature to 75°C and keep it at that temperature for 2 hours.

[0015] Add calcium hydroxide solution dropwise to adjust the pH of the system to 7;

[0016] The product is placed in an oven to remove moisture, resulting in modified polyvinyl alcohol with crown ether groups in the side chains.

[0017] Furthermore, modified polyvinyl alcohol is obtained by chemically modifying polyvinyl alcohol using 2-(epoxyalkylmethyl)-15-crown ether-5, specifically including:

[0018] Take 100 parts by weight of polyvinyl alcohol and add it to deionized water. Stir thoroughly and heat to 90-95℃ and keep warm for 1 hour to fully dissolve the polyvinyl alcohol.

[0019] After cooling to 60°C, a tertiary amine catalyst was added dropwise to obtain a second solution.

[0020] Dissolve 5-20 parts of 2-(epoxyalkylmethyl)-15-crown ether-5 in ethanol, slowly add it dropwise to the second solution and stir until homogeneous;

[0021] After maintaining the reflux temperature for 2 hours, the product was removed and dried in a 100°C oven. After drying, modified polyvinyl alcohol with crown ether groups in the side chain was obtained.

[0022] Furthermore, modified polyvinyl alcohol is obtained by chemically modifying polyvinyl alcohol using 2-hydroxymethyl-15-crown ether-5, specifically including:

[0023] Take 100 parts by weight of polyvinyl alcohol and add it to deionized water. Stir thoroughly and heat to 90-95℃ and keep warm for 1 hour to fully dissolve the polyvinyl alcohol.

[0024] After the temperature drops to 80℃, potassium hydroxide solution is added dropwise to adjust the pH of the system to 11.

[0025] Epichlorohydrin was added dropwise, and the epoxy grafting rate was controlled at 10%-20%. After reacting for 6 hours, the product was removed and dried in an oven at 80°C.

[0026] The dried product was placed in a Buchner funnel and washed with ice water or deionized water and filtered to remove residual potassium hydroxide and potassium chloride, thus obtaining epichlorohydrin modified polyvinyl alcohol.

[0027] Take 100 parts of epichlorohydrin-modified polyvinyl alcohol, add it to deionized water, stir thoroughly, heat to 90-95℃ and keep warm for 1 hour, then lower to 60℃ and add tertiary amine catalyst dropwise to obtain the third solution;

[0028] Based on the epoxy grafting rate, the amount of 2-hydroxymethyl-15-crown ether-5 was calculated and added to the third solution. After stirring evenly, the reaction temperature was gradually increased to the reflux temperature. After maintaining the reflux temperature for 2 hours, the product was taken out and placed in a 100℃ oven to dry. After drying, modified polyvinyl alcohol with crown ether groups in the side chain was obtained.

[0029] Furthermore, modified polyvinyl alcohol is obtained by chemically modifying polyvinyl alcohol using 2-hydroxymethyl-15-crown ether-5, specifically including:

[0030] Weigh out 2-hydroxymethyl-15-crown ether-5 and diisocyanate in a molar ratio of 1:1;

[0031] Diisocyanate was dissolved in N,N-dimethylformamide (DMF) and placed in a three-necked flask with magnetic stirring. The temperature was heated to 80°C and 2-hydroxymethyl-15-crown ether-5 was slowly added dropwise. After the addition of 2-hydroxymethyl-15-crown ether-5 was completed, the reaction was continued for 5 hours to obtain a DMF solution of 15-crown ether-5-NHCOO-NCO.

[0032] Take 100 parts of polyvinyl alcohol and dissolve it in N,N-dimethylformamide (DMF). Stir thoroughly, heat to 80-90℃ until fully dissolved, and then add an organotin catalyst to obtain a polyvinyl alcohol solution.

[0033] Based on the content of 15-crown ether-5-NHCOO-NCO in the solvent, 5-20 parts of the DMF solution of 15-crown ether-5-NHCOO-NCO were added to a polyvinyl alcohol solution for reaction. After 24 hours of reaction, a DMF solution of polyvinyl alcohol resin with crown ether groups in the side chain was obtained. Acetone was added to the DMF solution of polyvinyl alcohol resin with crown ether groups in the side chain to obtain a precipitate. The precipitate was placed in a Soxhlet extractor and the DMF was removed by acetone extraction to obtain modified polyvinyl alcohol with crown ether groups in the side chain.

[0034] Furthermore, modified polyvinyl alcohol is obtained by chemically modifying polyvinyl alcohol using 2-aminomethyl-15-crown ether-5, specifically including:

[0035] Take 100 parts by weight of polyvinyl alcohol and add it to deionized water. Stir thoroughly and heat to 90-95℃ and keep warm for 1 hour to fully dissolve the polyvinyl alcohol.

[0036] After the temperature drops to 80℃, potassium hydroxide solution is added dropwise to adjust the pH of the system to 11.

[0037] Epichlorohydrin was added dropwise, and the epoxy grafting rate was controlled at 10%-20%. After reacting for 6 hours, the product was removed and dried in an oven at 80°C.

[0038] The dried product was placed in a Buchner funnel and washed with ice water or deionized water and filtered to remove residual potassium hydroxide and potassium chloride, thus obtaining epichlorohydrin modified polyvinyl alcohol.

[0039] Take 100 parts of epichlorohydrin-modified polyvinyl alcohol, add it to deionized water, stir thoroughly, heat to 90-95℃ and keep warm for 1 hour, then cool to room temperature to obtain the fourth solution;

[0040] The amount of 2-aminomethyl-15-crown ether-5 was calculated based on the epoxy grafting rate and added to the fourth solution. The mixture was stirred evenly and reacted at room temperature for 5 hours. Then, the temperature was raised to 80°C and reacted for 2 hours. The product was then removed and dried in a 100°C oven. After drying, modified polyvinyl alcohol with crown ether groups in the side chain was obtained.

[0041] Furthermore, modified polyvinyl alcohol is obtained by chemically modifying polyvinyl alcohol using 2-aminomethyl-15-crown ether-5, specifically including:

[0042] Weigh out 2-aminomethyl-15-crown ether-5 and diisocyanate in a molar ratio of 1:1;

[0043] Diisocyanate was dissolved in N,N-dimethylformamide (DMF) and placed in a three-necked flask with magnetic stirring. 2-aminomethyl-15-crown ether-5 was slowly added dropwise at room temperature. After the addition of 2-hydroxymethyl-15-crown ether-5 was completed, the reaction was continued for 1 hour to obtain a DMF solution of 15-crown ether-5-NHCONH-NCO.

[0044] Take 100 parts of polyvinyl alcohol and dissolve it in N,N-dimethylformamide (DMF). Stir thoroughly, heat to 80-90℃ until fully dissolved, and then add an organotin catalyst to obtain a polyvinyl alcohol solution.

[0045] Based on the content of 15-crown ether-5-NHCONH-NCO in the solvent, take 5-20 parts of the DMF solution of 15-crown ether-5-NHCONH-NCO, add it to the polyvinyl alcohol solution for reaction, and after reacting for 24 hours, take out the DMF solution of polyvinyl alcohol resin with crown ether group in the side chain, add acetone to the DMF solution of polyvinyl alcohol resin with crown ether group in the side chain to obtain a precipitate, put the precipitate into a Soxhlet extractor and use acetone to extract and remove DMF to obtain modified polyvinyl alcohol with crown ether group in the side chain.

[0046] Beneficial effects:

[0047] This invention first uses chemical modification to graft 15-crown-5 ether onto the side chains of polyvinyl alcohol as the base resin for a water-based desalination and peelable coating. Then, by adjusting the types and proportions of stabilizers, antifreeze agents, leveling agents, wetting agents, defoamers, dispersants, and stripping agents, and thoroughly mixing them, a water-based polyvinyl alcohol desalination and peelable coating is obtained. This type of desalination and peelable coating can effectively complex sodium and magnesium ions. Its water-based formula will not damage the equipment surface, will not pollute the environment, and will not affect the health of construction personnel, making it ideal for cleaning salt from the surfaces of precision instruments and equipment in marine environments. Practical applications show that all implementation cases can effectively remove trace amounts of corrosive salt ions from equipment surfaces (removal rates are all above 97%, with a maximum of 99.2%), and the coating can easily achieve 100% peeling after salt adsorption. Detailed Implementation

[0048] To overcome the shortcomings of existing technologies, the present invention provides an aqueous polyvinyl alcohol desalination and peelable coating, comprising: modified polyvinyl alcohol, deionized water, antifreeze, leveling agent, wetting agent, defoamer, dispersant, and peeling agent, wherein the mass percentage of each component is: modified polyvinyl alcohol 50-70%, deionized water 25-40%, antifreeze 5-15%, leveling agent 0.3-3%, wetting agent 0.1-2%, defoamer 0.1-2%, dispersant 0.1-1%, and peeling agent 1-5%, wherein the modified polyvinyl alcohol is polyvinyl alcohol with 15-crown 5-ether groups branched on its side.

[0049] Example 1

[0050] Modified polyvinyl alcohol I 60%, deionized water 28%, antifreeze 6%, leveling agent 0.3%, wetting agent 0.5%, defoamer 0.5%, dispersant 0.7%, and release agent 4%.

[0051] Results: 98.1% decontamination rate, 100% peeling rate, tensile strength 42.9 MPa, and elongation at break 377%.

[0052] Example 2

[0053] Modified polyvinyl alcohol II 55%, deionized water 28%, antifreeze 10%, leveling agent 0.5%, wetting agent 0.5%, defoamer 0.5%, dispersant 1%, and release agent 4.5%.

[0054] Results: 98.8% decontamination rate, 100% peeling rate, tensile strength 35.6 MPa, and elongation at break 412%.

[0055] Example 3

[0056] Modified polyvinyl alcohol III 58%, deionized water 25%, antifreeze 10%, leveling agent 0.6%, wetting agent 0.4%, defoamer 0.5%, dispersant 0.5%, and release agent 5%.

[0057] Results: 99.2% decontamination rate, 100% peeling rate, tensile strength 33.1 MPa, elongation at break 441%.

[0058] Example 4

[0059] Modified polyvinyl alcohol IV 55%, deionized water 25%, antifreeze 14%, leveling agent 0.4%, wetting agent 0.4%, defoamer 0.3%, dispersant 0.9%, and release agent 4%.

[0060] Results: 97.6% decontamination rate, 100% peeling rate, tensile strength 38.5 MPa, elongation at break 455%.

[0061] Example 5

[0062] Modified polyvinyl alcohol V 60%, deionized water 25%, antifreeze 7%, leveling agent 1%, wetting agent 1%, defoamer 0.5%, dispersant 0.5%, and release agent 5%.

[0063] Results: 97.2% decontamination rate, 100% peeling rate, tensile strength 31.5 MPa, elongation at break 341%.

[0064] Example 6

[0065] Modified polyvinyl alcohol VI 58%, deionized water 26%, antifreeze 12%, leveling agent 0.3%, wetting agent 0.2%, defoamer 0.2%, dispersant 0.3%, and release agent 3%.

[0066] Results: 99.2% decontamination rate, 100% peeling rate, tensile strength 34.5 MPa, elongation at break 394%.

[0067] The above embodiments are merely one of the preferred embodiments of the present invention and should not be used to limit the scope of protection of the present invention. Any modifications or refinements made to the main design concept and spirit of the present invention that are not of substantial significance, but solve the same technical problem as the present invention, should be included within the scope of protection of the present invention.

[0068] After the peelable coating is applied to the surface to be cleaned, deionized water, as a solvent, can fully dissolve the deposited salt. The dissolved sodium and magnesium ions are fixed in the coating system by complexing with the crown ether groups and hydroxyl groups in the matrix resin. After the coating dries, the salt can be easily removed from the surface to be cleaned by peeling off the coating.

[0069] The preparation method of waterborne polyvinyl alcohol desalination peelable coating is as follows: First, 15-crown-5 ether groups are grafted onto the polyvinyl alcohol backbone through chemical modification to prepare a functional matrix resin that complexes sodium and magnesium ions. Then, the modified polyvinyl alcohol is used as the matrix resin, and the types and proportions of additives such as stabilizers, antifreeze agents, leveling agents, wetting agents, defoamers, dispersants, and stripping agents are adjusted and thoroughly mixed to obtain a waterborne polyvinyl alcohol desalination peelable coating suitable for salt cleaning of the surface of precision instruments and equipment in marine environments.

[0070] First, small molecules containing crown ether groups, such as 2-formaldehyde-15-crown ether-5, 2-(epoxyethylene methyl)-15-crown ether-5, 2-hydroxymethyl-15-crown ether-5, and 2-aminomethyl-15-crown ether-5, are used to chemically modify polyvinyl alcohol to obtain a base material for preparing water-based polyvinyl alcohol desalination and peelable coatings. The specific methods for modifying polyvinyl alcohol with each small molecule are as follows.

[0071] The specific method and process for modifying polyvinyl alcohol with 2-formaldehyde-15-crown ether-5 is as follows: Take 100 parts (by mass) of polyvinyl alcohol and an appropriate amount of deionized water (enough to dissolve polyvinyl alcohol), stir thoroughly, heat to 90-95℃ and keep warm for 1 hour to fully dissolve it. After cooling to room temperature, add a small amount of dilute sulfuric acid to adjust the pH of the system to 2-3 (e.g., 2.5). Slowly add 5-20 parts (by mass) of 2-formaldehyde-15-crown ether-5 to the reaction system and stir evenly. After the addition of 2-formaldehyde-15-crown ether-5 is complete, gradually raise the reaction temperature to 75℃ and keep warm for 2 hours. After the reaction is complete, add calcium hydroxide solution to adjust the pH of the system to 7. Finally, put it in an oven to remove moisture to obtain modified polyvinyl alcohol resin I with crown ether groups in the side chain. Its reaction mechanism and structure are shown in formula (I).

[0072]

[0073] The specific method and process for modifying polyvinyl alcohol with 2-(epoxyalkylmethyl)-15-crown ether-5 is as follows: Take 100 parts (by mass) of polyvinyl alcohol and an appropriate amount of deionized water (enough to dissolve polyvinyl alcohol), stir thoroughly, heat to 90-95℃ and keep warm for 1 hour until fully dissolved, then cool to 60℃ and add a small amount of tertiary amine catalyst. Dissolve 5-20 parts (by mass) of 2-(epoxyalkylmethyl)-15-crown ether-5 in at least a small amount of ethanol, slowly add it to the reaction system and stir evenly. During the addition process, the reaction temperature is gradually raised to the reflux temperature. After maintaining the reflux temperature for 2 hours, the product is taken out and placed in a 100℃ oven to dry. After drying, modified polyvinyl alcohol resin II with crown ether groups in the side chain is obtained. Its reaction mechanism and structure are shown in formula (II).

[0074]

[0075] There are two methods for modifying polyvinyl alcohol with 2-hydroxymethyl-15-crown ether-5, and the specific processes are as follows:

[0076] 1) Take 100 parts of polyvinyl alcohol and an appropriate amount of deionized water, stir thoroughly, heat to 90-95℃ and keep warm for 1 hour to fully dissolve it. After the temperature drops to 80℃, add a small amount of potassium hydroxide solution to adjust the pH of the system to 11. Then add epichlorohydrin dropwise, controlling the epoxy grafting rate at 10-20%. After reacting for about 6 hours, take out the product and put it into an 80℃ oven to dry. Put the dried product into a Buchner funnel, wash it with ice water (deionized water) and filter it to wash out the residual potassium hydroxide and potassium chloride, and obtain epichlorohydrin modified polyvinyl alcohol.

[0077] Take 100 parts of epichlorohydrin-modified polyvinyl alcohol and an appropriate amount of deionized water, stir thoroughly, heat to 90-95℃ and keep at that temperature for 1 hour until fully dissolved, then cool to 60℃ and add a small amount of tertiary amine catalyst. Calculate the amount of 2-hydroxymethyl-15-crown ether-5 based on the grafting rate of the epichlorohydrin-modified polyvinyl alcohol and add it to the reaction system. After stirring evenly, gradually raise the reaction temperature to the reflux temperature. After maintaining the reflux temperature for 2 hours, remove the product and dry it in a 100℃ oven. After drying, modified polyvinyl alcohol resin III with crown ether groups in the side chain is obtained. Its reaction mechanism and structure are shown in formula (III).

[0078]

[0079] 2) Weigh 2-hydroxymethyl-15-crown ether-5 and diisocyanate in a molar ratio of 1:1 and set aside. Dissolve the diisocyanate in N,N-dimethylformamide (DMF) and place it in a three-necked flask with magnetic stirring. Heat the mixture to 80°C and slowly add the weighed 2-hydroxymethyl-15-crown ether-5 dropwise. After the addition of 2-hydroxymethyl-15-crown ether-5 is complete, continue the reaction for 5 hours to obtain a DMF solution of 15-crown ether-5-NHCOO-NCO.

[0080] Take 100 parts of polyvinyl alcohol and a small amount of DMF, stir thoroughly, heat to 80-90℃ to fully dissolve, and then add an organotin catalyst to obtain a polyvinyl alcohol solution. Take 5-20 parts of a DMF solution of 15-crown ether-5-NHCOO-NCO (based on the content of 15-crown ether-5-NHCOO-NCO in the solvent) and add it to the polyvinyl alcohol solution for reaction. After reacting for 24 hours, take out the DMF solution of polyvinyl alcohol resin IV with crown ether groups in the side chain, add acetone to the solution to obtain resin IV precipitate, put the precipitate into a Soxhlet extractor and use acetone to extract and remove DMF to obtain modified polyvinyl alcohol resin IV with crown ether groups in the side chain. Its reaction mechanism and structure are shown in formula (Ⅳ).

[0081]

[0082] There are two methods for modifying polyvinyl alcohol with 2-aminomethyl-15-crown ether-5, and the specific processes are as follows:

[0083] 1) Take 100 parts of polyvinyl alcohol and an appropriate amount of deionized water, stir thoroughly, heat to 90-95℃ and keep warm for 1 hour to fully dissolve it. After the temperature drops to 80℃, add a small amount of potassium hydroxide solution to adjust the pH of the system to 11. Then add epichlorohydrin dropwise, controlling the epoxy grafting rate at 10-20%. After reacting for about 6 hours, take out the product and put it into an 80℃ oven to dry. Put the dried product into a Buchner funnel, wash it with ice water (deionized water) and filter it to wash out the residual potassium hydroxide and potassium chloride, and obtain epichlorohydrin modified polyvinyl alcohol.

[0084] Take 100 parts of epichlorohydrin-modified polyvinyl alcohol and an appropriate amount of deionized water, stir thoroughly, heat to 90-95℃ and keep warm for 1 hour until fully dissolved, cool to room temperature, calculate the amount of 2-aminomethyl-15-crown ether-5 according to the grafting rate of epichlorohydrin-modified polyvinyl alcohol, add it to the reaction system and stir evenly, react at room temperature for 5 hours, then raise the temperature to 80℃ and react for 2 hours, take out the product and put it in a 100℃ oven to dry, after drying, obtain modified polyvinyl alcohol resin V with crown ether groups in the side chain, and its reaction mechanism and structure are shown in formula (V).

[0085]

[0086] 2) Weigh 2-aminomethyl-15-crown ether-5 and diisocyanate in a molar ratio of 1:1 and set aside. Dissolve the diisocyanate in N,N-dimethylformamide (DMF) and place it in a three-necked flask with magnetic stirring. Slowly add the weighed 2-aminomethyl-15-crown ether-5 dropwise at room temperature. After the addition of 2-hydroxymethyl-15-crown ether-5 is complete, continue the reaction for 1 hour to obtain a DMF solution of 15-crown ether-5-NHCONH-NCO.

[0087] Take 100 parts of polyvinyl alcohol and a small amount of DMF, stir thoroughly, heat to 80-90℃ to dissolve completely, and then add an organotin catalyst to obtain a polyvinyl alcohol solution;

[0088] Take 5-20 parts of a DMF solution of 15-crown ether-5-NHCONH-NCO (based on the content of 15-crown ether-5-NHCONH-NCO in the solvent) and add it to a polyvinyl alcohol solution for reaction. After reacting for 24 hours, take out the DMF solution of polyvinyl alcohol resin VI with crown ether groups in the side chain, add acetone to the solution to obtain resin VI precipitate, put the precipitate into a Soxhlet extractor and use acetone to extract and remove DMF to obtain modified polyvinyl alcohol resin VI with crown ether groups in the side chain. Its reaction mechanism and structure are shown in formula (VI).

[0089]

[0090] The tertiary amine catalyst used in the modification of polyvinyl alcohol resin is at least one of triethylamine and triethanolamine, and the organotin catalyst is at least one of dibutyltin dilaurate and stannous octoate.

[0091] The diisocyanate used in modifying polyvinyl alcohol resin is at least one of hexamethylene diisocyanate, tetramethylene diisocyanate, isophorone diisocyanate, phenyl dimethylene diisocyanate, and diphenylmethane diisocyanate.

[0092] After chemically modifying polyvinyl alcohol (PVA) to obtain a base material containing crown ether groups in the side chains, the base material, deionized water, antifreeze, leveling agent, wetting agent, defoamer, dispersant, and stripping agent are mixed to obtain an aqueous PVA desalination and peelable coating. The mass percentages of each component are as follows: modified PVA 50-70%, deionized water 25-40%, antifreeze 5-15%, leveling agent 0.3-3%, wetting agent 0.1-2%, defoamer 0.1-2%, dispersant 0.1-1%, and stripping agent 1-5%.

[0093] The antifreeze is mainly ethanol. If the system becomes unstable due to excessively low temperature, one or more of isopropanol, ethylene glycol, propylene glycol, diethylene glycol, ethylene glycol butyl ether, and propylene glycol butyl ether may be added.

[0094] The leveling agent is at least one of polydimethylsiloxane, polyether-modified silicone, and silicone acrylate;

[0095] The wetting agent is at least one of acrylic acid copolymer, alkylphenol polyoxyethylene ether, and polyether-modified organosilicon;

[0096] The defoamer is at least one of mineral oil, organosilicon and silicon oxide polyether;

[0097] The dispersant is at least one of ammonium polyacrylate and polyethylene glycol;

[0098] The stripping agent is at least one of water-based silicone oil, zinc stearate, higher fatty acid esters, and paraffin.

[0099] After obtaining the chemically modified polyvinyl alcohol base material, the preparation of the water-based polyvinyl alcohol desalination peelable coating still requires the following steps:

[0100] a. Dissolve the modified polyvinyl alcohol in deionized water, stir at about 95°C for 24 hours, and after complete dissolution, lower the system temperature to 75°C to obtain solution A.

[0101] b. Add leveling agent, wetting agent, defoamer, dispersant and stripping agent to solution A, and stir thoroughly to obtain solution B;

[0102] c. After solution B cools to room temperature, add antifreeze and stir thoroughly to obtain water-based polyvinyl alcohol desalination peelable coating.

[0103] In practical application, after spraying or brushing the water-based polyvinyl alcohol desalination peelable coating onto the surface to be cleaned, the deionized water in the coating first fully dissolves the deposited salts. The dissolved sodium and magnesium ions then complex with the crown ether groups and hydroxyl groups in the base resin and become fixed in the coating system. After the coating dries, the salts can be easily removed from the surface by peeling off the coating. The diagram below illustrates the complexation of sodium and magnesium ions in the base resin.

[0104]

Claims

1. A method for preparing an aqueous polyvinyl alcohol desalination peelable coating, characterized in that, The coating comprises, by weight: 50-70% modified polyvinyl alcohol, 25-40% deionized water, 5-15% antifreeze, 0.3-3% leveling agent, 0.1-2% wetting agent, 0.1-2% defoamer, 0.1-1% dispersant, and 1-5% stripping agent. The modified polyvinyl alcohol is polyvinyl alcohol with 15-crown-5 ether groups branched onto its side links. The method includes: Modified polyvinyl alcohol was obtained by chemically modifying polyvinyl alcohol with 2-formaldehyde-15-crown ether-5, 2-(epoxyethylenemethyl)-15-crown ether-5, 2-hydroxymethyl-15-crown ether-5, or 2-aminomethyl-15-crown ether-5. Specifically, the process includes: adding 100 parts by mass of polyvinyl alcohol to deionized water, stirring thoroughly, heating to 90-95℃ and maintaining the temperature for 1 hour to fully dissolve the polyvinyl alcohol; cooling to room temperature and then adding dilute sulfuric acid to adjust the pH to 2-3 to obtain the first solution; slowly adding 5-20 parts of 2-formaldehyde-15-crown ether-5 to the first solution while stirring evenly; after the addition of 2-formaldehyde-15-crown ether-5 is complete, gradually raising the reaction temperature to 75℃ and maintaining the temperature for 2 hours; adding calcium hydroxide solution to adjust the pH of the system to 7; and placing the solution in an oven to remove moisture to obtain modified polyvinyl alcohol with crown ether groups in the side chains. Add 50-70% of modified polyvinyl alcohol to 25-40% of deionized water, stir at about 95°C for 24 hours until completely dissolved, and then lower the system temperature to 75°C to obtain solution A. Add 0.3-3% leveling agent, 0.1-2% wetting agent, 0.1-2% defoamer, 0.1-1% dispersant and 1-5% stripping agent to solution A, and stir thoroughly to obtain solution B; After solution B cools to room temperature, add 5-15% antifreeze and stir thoroughly to obtain water-based polyvinyl alcohol desalination peelable coating; The preparation of modified polyvinyl alcohol using 2-(epoxyalkylmethyl)-15-crown ether-5 includes: Take 100 parts by weight of polyvinyl alcohol and add it to deionized water. Stir thoroughly and heat to 90-95℃ and keep warm for 1 hour to fully dissolve the polyvinyl alcohol. After cooling to 60°C, a tertiary amine catalyst was added dropwise to obtain a second solution. Dissolve 5-20 parts of 2-(epoxyalkylmethyl)-15-crown ether-5 in ethanol, slowly add it dropwise to the second solution and stir until homogeneous; After maintaining the reflux temperature for 2 hours, the product was removed and placed in a 100°C oven to dry. After drying, modified polyvinyl alcohol with crown ether groups in the side chain was obtained. The preparation of modified polyvinyl alcohol using 2-hydroxymethyl-15-crown ether-5 specifically includes: Weigh out 2-hydroxymethyl-15-crown ether-5 and diisocyanate in a molar ratio of 1:1; Diisocyanate was dissolved in N,N-dimethylformamide (DMF) and placed in a three-necked flask with magnetic stirring. The temperature was heated to 80°C and 2-hydroxymethyl-15-crown ether-5 was slowly added dropwise. After the addition of 2-hydroxymethyl-15-crown ether-5 was completed, the reaction was continued for 5 hours to obtain a DMF solution of 15-crown ether-5-NHCOO-NCO. Take 100 parts of polyvinyl alcohol and dissolve it in N,N-dimethylformamide (DMF). Stir thoroughly, heat to 80-90℃ until fully dissolved, and then add an organotin catalyst to obtain a polyvinyl alcohol solution. Based on the content of 15-crown ether-5-NHCOO-NCO in the solvent, take 5-20 parts of the DMF solution of 15-crown ether-5-NHCOO-NCO, add it to the polyvinyl alcohol solution for reaction, and after reacting for 24 hours, obtain a DMF solution of polyvinyl alcohol resin with crown ether group in the side chain. Add acetone to the DMF solution of polyvinyl alcohol resin with crown ether group in the side chain to obtain a precipitate. Put the precipitate into a Soxhlet extractor and use acetone to extract and remove DMF to obtain modified polyvinyl alcohol with crown ether group in the side chain. The preparation of modified polyvinyl alcohol using 2-aminomethyl-15-crown ether-5 specifically includes: Weigh out 2-aminomethyl-15-crown ether-5 and diisocyanate in a molar ratio of 1:1; Diisocyanate was dissolved in N,N-dimethylformamide (DMF) and placed in a three-necked flask with magnetic stirring. 2-aminomethyl-15-crown ether-5 was slowly added dropwise at room temperature. After the addition of 2-aminomethyl-15-crown ether-5 was completed, the reaction was continued for 1 hour to obtain a DMF solution of 15-crown ether-5-NHCONH-NCO. Take 100 parts of polyvinyl alcohol and dissolve it in N,N-dimethylformamide (DMF). Stir thoroughly, heat to 80-90℃ until fully dissolved, and then add an organotin catalyst to obtain a polyvinyl alcohol solution. Based on the content of 15-crown ether-5-NHCONH-NCO in the solvent, take 5-20 parts of the DMF solution of 15-crown ether-5-NHCONH-NCO, add it to the polyvinyl alcohol solution for reaction, and after reacting for 24 hours, take out the DMF solution of polyvinyl alcohol resin with crown ether group in the side chain, add acetone to the DMF solution of polyvinyl alcohol resin with crown ether group in the side chain to obtain a precipitate, put the precipitate into a Soxhlet extractor and use acetone to extract and remove DMF to obtain modified polyvinyl alcohol with crown ether group in the side chain.

2. The method according to claim 1, characterized in that, Modified polyvinyl alcohol can also be prepared using 2-hydroxymethyl-15-crown ether-5 by the following methods: Take 100 parts by weight of polyvinyl alcohol and add it to deionized water. Stir thoroughly and heat to 90-95℃ and keep warm for 1 hour to fully dissolve the polyvinyl alcohol. After the temperature drops to 80℃, potassium hydroxide solution is added dropwise to adjust the pH of the system to 11. Epichlorohydrin was added dropwise, and the epoxy grafting rate was controlled at 10%-20%. After reacting for 6 hours, the product was removed and dried in an oven at 80°C. The dried product was placed in a Buchner funnel and washed with ice water or deionized water and filtered to remove residual potassium hydroxide and potassium chloride, thus obtaining epichlorohydrin modified polyvinyl alcohol. Take 100 parts of epichlorohydrin-modified polyvinyl alcohol, add it to deionized water, stir thoroughly, heat to 90-95℃ and keep warm for 1 hour, then lower to 60℃ and add tertiary amine catalyst dropwise to obtain the third solution; Based on the epoxy grafting rate, the amount of 2-hydroxymethyl-15-crown ether-5 was calculated and added to the third solution. After stirring evenly, the reaction temperature was gradually increased to the reflux temperature. After maintaining the reflux temperature for 2 hours, the product was taken out and placed in a 100℃ oven to dry. After drying, modified polyvinyl alcohol with crown ether groups in the side chain was obtained.

3. The method according to claim 2, characterized in that, Modified polyvinyl alcohol can also be prepared using 2-aminomethyl-15-crown ether-5 via the following method: Take 100 parts by weight of polyvinyl alcohol and add it to deionized water. Stir thoroughly and heat to 90-95℃ and keep warm for 1 hour to fully dissolve the polyvinyl alcohol. After the temperature drops to 80℃, potassium hydroxide solution is added dropwise to adjust the pH of the system to 11. Epichlorohydrin was added dropwise, and the epoxy grafting rate was controlled at 10%-20%. After reacting for 6 hours, the product was removed and dried in an oven at 80°C. The dried product was placed in a Buchner funnel and washed with ice water or deionized water and filtered to remove residual potassium hydroxide and potassium chloride, thus obtaining epichlorohydrin modified polyvinyl alcohol. Take 100 parts of epichlorohydrin-modified polyvinyl alcohol, add it to deionized water, stir thoroughly, heat to 90-95℃ and keep warm for 1 hour, then cool to room temperature to obtain the fourth solution; The amount of 2-aminomethyl-15-crown ether-5 was calculated based on the epoxy grafting rate and added to the fourth solution. The mixture was stirred evenly and reacted at room temperature for 5 hours. Then, the temperature was raised to 80°C and reacted for 2 hours. The product was then removed and dried in a 100°C oven. After drying, modified polyvinyl alcohol with crown ether groups in the side chain was obtained.

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