A protective coating and its method of preparation and use in the aerospace industry chemical milling

Abstract

The application discloses a protective coating and a preparation method and application thereof in chemical milling in the aviation industry. The protective coating comprises an A component and a B component; the A component comprises, in percentage by mass, 30-40% of a polymer of formaldehyde, ammonia and chloroethane, 1-2% of N-[(5-methyl-1H-benzotriazole-1-yl)methyl] diethanolamine, and 58-69% of a composite solvent; the composite solvent comprises D20 solvent oil and propylene glycol methyl ether acetate, and the mass ratio of the D20 solvent oil to the propylene glycol methyl ether acetate is 4:(1-1.5); the B component is 1,3,5-triglycidyl-S-triazine triketone; and the volume ratio of the A component to the B component is 10:(1-3). The coating obtained after construction of the protective coating has high elasticity, heat resistance, acid and alkali resistance, and the performance of resisting chemical milling liquid, has a good protective effect on metal, and can be manually peeled off and is not prone to breakage, and meets the standard HB 5453-2004 aluminum alloy chemical milling protective coating specification of the National Defense Science, Technology and Industry Committee.

Description

Technical Field

[0001] This invention relates to the field of coating technology, and in particular to a protective coating, its preparation method, and its application in chemical milling in the aerospace industry. Background Technology

[0002] In the aerospace manufacturing industry, sheet metal materials such as titanium alloys, aluminum alloys, magnesium alloys, and steel are chemically milled into designed patterns, requiring protective coatings to protect the parts that do not require chemical milling. During application, the protective coating is applied to the sheet metal material, dries to form a protective film, and is then peeled off after completion. Therefore, the protective coating must be resistant to acids and alkalis, possess good toughness and elongation at break, and be easy to peel off manually after completion. Currently, the market mainly uses imported protective coatings, such as AC-850 and AC-828, but these coatings use solvents such as tetrachloroethylene and toluene, which have significant impacts on the environment and worker health.

[0003] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a protective coating and its preparation method and its application in chemical milling in the aerospace industry, aiming to solve the problem of the high toxicity of solvents used in existing chemical milling protective coatings.

[0005] The technical solution of the present invention is as follows:

[0006] In a first aspect, the present invention provides a protective coating comprising component A and component B;

[0007] Component A, by mass percentage, comprises:

[0008] Formaldehyde polymers with ammonia and chloroethane comprise 30-40%;

[0009] N-[(5-methyl-1H-benzotriazol-1-yl)methyl]diethanolamine 1-2%;

[0010] Composite solvent 58-69%;

[0011] The composite solvent comprises D20 solvent oil and propylene glycol methyl ether acetate, wherein the mass ratio of D20 solvent oil to propylene glycol methyl ether acetate is 4:(1-1.5).

[0012] Component B is 1,3,5-triglycidyl-S-triazinetrione;

[0013] The volume ratio of component A to component B is 10:(1-3).

[0014] A second aspect of the present invention provides a method for preparing a protective coating as described in the first aspect, comprising:

[0015] Add the composite solvent, the polymer of formaldehyde, ammonia, and chloroethane, and N-[(5-methyl-1H-benzotriazol-1-yl)methyl]diethanolamine to the reaction vessel according to the mass percentage, and stir until uniformly mixed to obtain component A;

[0016] Component B is prepared by dispensing 1,3,5-triglycidyl-S-triazine trione by volume.

[0017] In a preferred embodiment, the stirring speed is 60-120 rpm and the stirring time is 20-30 minutes.

[0018] A third aspect of the present invention provides an application of a protective coating in chemical milling in the aerospace industry, wherein the protective coating prepared by the method described in the first aspect or the preparation method described in the second aspect is applied to the surface protection of metal materials in chemical milling in the aerospace industry.

[0019] The preferred technical solution, the method of using the protective coating in chemical milling in the aerospace industry, includes the following steps:

[0020] The components A and B are mixed evenly according to the volume ratio to obtain the mixed protective coating.

[0021] After the mixed protective coating has been left to stand for 10 to 20 minutes, it is transferred to the metal material and dried to form a protective coating.

[0022] In a preferred embodiment, the transfer process is selected from spraying, coating, or brushing.

[0023] In a preferred embodiment, the metal material is selected from one of titanium alloy, aluminum alloy, magnesium alloy, and steel.

[0024] In a preferred embodiment, the drying temperature is 10–40°C, and the drying time is 6–24 hours.

[0025] Beneficial Effects: The protective coating of this invention uses D20 solvent oil and propylene glycol methyl ether acetate as a composite solvent. Formaldehyde, ammonia, and chloroethane are polymerized with 1,3,5-triglycidyl-S-triazine trione through a ring-opening polymerization reaction to form a high-molecular-weight amino resin. N-[(5-methyl-1H-benzotriazol-1-yl)methyl]diethanolamine is added as a corrosion inhibitor. The resulting coating exhibits high elasticity, resistance to heat, acids, alkalis, and chemical milling liquids, provides good protection for metals, and can be manually peeled off without easily breaking, conforming to the National Defense Science and Industry Technology Committee standard HB5453-2004, Specification for Protective Coatings for Chemical Milling of Aluminum Alloys. Compared with existing technologies, the composite solvent in the protective coating of this invention does not contain halogenated hydrocarbons or toluene, resulting in less impact on the environment and worker health, and it can be applied to large-scale production. Detailed Implementation

[0026] This invention provides a protective coating and its preparation method, as well as its application in chemical milling in the aerospace industry. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below.

[0027] This invention provides a protective coating, which includes component A and component B;

[0028] Component A, by mass percentage, comprises:

[0029] Formaldehyde polymers with ammonia and chloroethane comprise 30-40%;

[0030] N-[(5-methyl-1H-benzotriazol-1-yl)methyl]diethanolamine 1-2%;

[0031] Composite solvent 58-69%;

[0032] The composite solvent comprises D20 solvent oil and propylene glycol methyl ether acetate, wherein the mass ratio of D20 solvent oil to propylene glycol methyl ether acetate is 4:(1-1.5).

[0033] Component B is 1,3,5-triglycidyl-S-triazinetrione;

[0034] The volume ratio of component A to component B is 10:(1-3).

[0035] Specifically, the formaldehyde-ammonia-chloroethane polymer (CAS No.: 63512-71-0) in component A is a low-polymer composed of formaldehyde, ammonia, and chloroethane in a molar ratio of 1:1:1, and is rich in amino groups. The formaldehyde-ammonia-chloroethane polymer used in the following specific examples 1-2 and comparative examples 1-4 is from Chemtura Corporation (USA). Base, but not limited to. The structural formula of component B, 1,3,5-triglycidyl-S-triazinetrione (CAS No.: 2451-62-9), is as follows: The structure contains three epoxy groups, and the amino groups of the polymer of formaldehyde with ammonia and chloroethane undergo ring-opening polymerization at room temperature to achieve molecular weight growth and polymerize into a high molecular weight amino resin. After the solvent evaporates, a dry coating with high elasticity and toughness that can be manually peeled off is formed to protect the metal.

[0036] The structural formula of N-[(5-methyl-1H-benzotriazol-1-yl)methyl]diethanolamine (CAS No.: 80584-88-9) of component A is: It is an effective metal corrosion inhibitor. Its mechanism is to adsorb or coordinate with metal ions on the metal surface to form a protective film that blocks corrosive liquids. Its effect is better than that of the commonly used metal slow-release agent benzotriazole.

[0037] The composite solvent of component A includes D20 solvent oil and propylene glycol methyl ether acetate (CAS No.: 108-65-6). D20 solvent oil, also known as D20, is a dearomaticated hydrogenated alkane solvent with a closed-cup flash point of 20–30°C. The D20 solvent oil used in the following specific examples 1–2 and comparative examples 1–4 is a product of China Petroleum & Chemical Corporation Maoming Branch, but is not limited to this. When the composite solvent of component A is entirely D20 solvent oil, the viscosity of the mixture of components A and B is the highest, the solution is turbid, prone to stratification, and the coating is not easy to level or defoam. When the composite solvent of component A is entirely propylene glycol methyl ether acetate, the viscosity of the mixture of components A and B is the lowest, which is not conducive to forming a coating of appropriate thickness on vertical workpieces and will increase the number of coatings. When the mass ratio of D20 solvent oil to propylene glycol methyl ether acetate in the composite solvent of component A is 4:(1~1.5), the mixture of components A and B has a suitable viscosity, is stable in storage, can be used directly without dilution, has good leveling performance and rapid defoaming performance, and can form a coating of appropriate thickness on vertical workpieces.

[0038] Components A and B are mixed at a volume ratio of 10:(1-3). After curing, the coating has an etching ratio of <1.1 (an indicator of the protective metal of chemical milling protective coatings; the higher this number, the larger the size of the corrosive liquid penetrating the boundary to the protected area during chemical milling; the HB 5453-2004 standard requires 0.9-1.1), and an elongation at break of >750%. Therefore, the protective coating of this invention forms a coating that is easy to peel off manually and not easily broken. Specifically, when the proportion of 1,3,5-triglycidyl-S-triazine trione increases, the etching ratio is lower, but the peeling difficulty increases, while the adhesion is stronger; when the proportion of 1,3,5-triglycidyl-S-triazine trione decreases, the etching ratio increases, which is detrimental to protection, and the adhesion also decreases.

[0039] This invention also provides a method for preparing the protective coating as described above, comprising:

[0040] Add the composite solvent, the polymer of formaldehyde, ammonia, and chloroethane, and N-[(5-methyl-1H-benzotriazol-1-yl)methyl]diethanolamine to the reaction vessel according to the mass percentage, and stir until uniformly mixed to obtain component A;

[0041] Component B is prepared by dispensing 1,3,5-triglycidyl-S-triazine trione by volume.

[0042] In some embodiments, the stirring speed is 60 to 120 revolutions per minute, and the stirring time is 20 to 30 minutes.

[0043] This invention also provides an application of a protective coating in chemical milling in the aerospace industry, wherein the protective coating described above or the protective coating prepared by the preparation method described above is applied to the surface protection of metal materials in chemical milling in the aerospace industry.

[0044] In some embodiments, the method of using the protective coating in chemical milling in the aerospace industry includes the steps of:

[0045] The components A and B are mixed evenly according to the volume ratio to obtain the mixed protective coating.

[0046] After the mixed protective coating has been left to stand for 10 to 20 minutes, it is transferred to the metal material and dried to form a protective coating.

[0047] In some embodiments, the transfer process is selected from spraying, coating, and brushing.

[0048] In some embodiments, the metallic material is selected from titanium alloys, aluminum alloys, magnesium alloys, and steel.

[0049] In some embodiments, the drying temperature is 10–40°C, and the drying time is 6–24 hours.

[0050] In one specific implementation, during construction, components A and B are mixed at a volume ratio of 10:(1-3), allowed to stand for 10-20 minutes before use, and can be applied to sheet metal materials using spraying, coating, or brushing techniques. Surface drying takes approximately 30-60 minutes at room temperature, and complete drying occurs after 6-8 hours, forming a highly elastic, corrosion-resistant metal protective coating. After the sheet metal material is cut into the specified shape in the chemical milling area, the coating on the parts to be corroded is manually peeled off, and the material is then placed in the liquid tank of the chemical milling area for chemical milling. The sheet metal material parts without peeled coating are protected from corrosion by the chemical milling fluid.

[0051] The present invention will be further described below through specific embodiments.

[0052] Example 1

[0053] This embodiment provides a protective coating, specifically including:

[0054] Component A:

[0055] Formaldehyde polymerized with ammonia and chloroethane (30%);

[0056] N-[(5-methyl-1H-benzotriazol-1-yl)methyl]diethanolamine 1%;

[0057] Composite solvent 69%;

[0058] The composite solvent is D20 solvent oil and propylene glycol methyl ether acetate in a mass ratio of 4:1.

[0059] Component B:

[0060] 1,3,5-Triglycidyl-S-triazinetrione;

[0061] The volume ratio of component A to component B is 10:1.

[0062] The preparation method of component A is as follows: add the composite solvent, the polymer of formaldehyde, ammonia and chloroethane (commercially available), and N-[(5-methyl-1H-benzotriazol-1-yl)methyl]diethanolamine (commercially available) to the mixing tank according to the mass percentage, start stirring at a speed of 120 minutes / revolution, stop stirring after 25 minutes, let stand for 30 minutes and then fill.

[0063] The preparation method of component B is as follows: 1,3,5-triglycidyl-S-triazinetrione (commercially available) is directly packaged.

[0064] During application, mix components A and B thoroughly and let stand for 15 minutes before use.

[0065] Example 2

[0066] This embodiment provides a protective coating, specifically including:

[0067] Component A:

[0068] Formaldehyde polymerized with ammonia and chloroethane, 40%;

[0069] N-[(5-methyl-1H-benzotriazol-1-yl)methyl]diethanolamine 2%;

[0070] Composite solvent 58%;

[0071] The composite solvent is D20 solvent oil and propylene glycol methyl ether acetate in a mass ratio of 4:1.5.

[0072] Component B:

[0073] 1,3,5-Triglycidyl-S-triazinetrione;

[0074] The volume ratio of component A to component B is 10:3.

[0075] The preparation method of component A is as follows: add the composite solvent, the polymer of formaldehyde, ammonia and chloroethane (commercially available), and N-[(5-methyl-1H-benzotriazol-1-yl)methyl]diethanolamine (commercially available) to the mixing tank according to the mass percentage, start stirring at a speed of 60 minutes / revolution, stop stirring after 25 minutes, let stand for 30 minutes and then fill.

[0076] The preparation method of component B is as follows: 1,3,5-triglycidyl-S-triazinetrione (commercially available) is directly packaged.

[0077] During application, mix components A and B thoroughly and let stand for 15 minutes before use.

[0078] Comparative Example 1

[0079] This comparative example provides a comparative protective coating, which differs from Example 1 only in that 1% of N-[(5-methyl-1H-benzotriazol-1-yl)methyl]diethanolamine in component A is replaced with 1% benzotriazole (commercially available), while the remaining components and preparation methods are the same.

[0080] Comparative Example 2

[0081] This comparative example provides a comparative protective coating, which differs from Example 1 only in that the volume ratio of component A to component B is changed from 10:1 to 10:0.5, while the other components and preparation methods are the same.

[0082] Comparative Example 3

[0083] This comparative example provides a protective coating that differs from Example 1 only in that the volume ratio of component A to component B is changed from 10:1 to 10:3, while the other components and preparation methods are the same.

[0084] Comparative Example 4

[0085] This comparative example provides a protective coating that differs from Example 1 only in that the volume ratio of component A to component B is changed from 10:1 to 10:4, while the other components and preparation methods are the same.

[0086] Performance testing

[0087] (1) The effect of the type of sustained-release agent on the sustained-release effect

[0088] The protective coating of Example 1 and the comparative protective coating of Comparative Example 1 were applied to 2A12 T4 aluminum alloy plates, respectively. After drying for 24 hours, they were immersed in acidic or alkaline solutions at 90°C-95°C, according to HB 5453-2004. The corrosion-free time of the aluminum alloy was recorded. The test results are shown in the table below.

[0089]

[0090] As shown in the table above, compared with the comparative protective coating of Comparative Example 1 using benzotriazole as a corrosion inhibitor, the protective coating of Example 1 using N-[(5-methyl-1H-benzotriazole-1-yl)methyl]diethanolamine as a corrosion inhibitor exhibits a longer acid and alkali resistance retention time and improved corrosion inhibition effect, meeting the specifications of the National Defense Science and Technology Commission standard HB5453-2004 for protective coatings for chemical milling of aluminum alloys (acid resistance for 30 minutes, alkali resistance for 8 hours). In contrast, the comparative protective coating of Comparative Example 1 does not meet the technical requirements of HB 5453-2004.

[0091] (2) Effect of the change in the volume ratio of component A and component B on the etching ratio

[0092] The protective coating of Example 1 and the comparative protective coatings of Comparative Examples 2-4 were applied to 2A12 T4 aluminum alloy plates, respectively. After drying for 24 hours, they were immersed in acidic or alkaline solutions at 90°C-95°C, according to HB 5453-2004. The etching ratio and peel strength were recorded. The test results are shown in the table below.

[0093] Comparative Example 2 Example 1 Comparative Example 3 Comparative Example 4 Volume ratio of component A to component B 10:0.5 10:1 10:3 10:4 Erosion ratio 1.6 1.0 0.9 0.7 Peel strength N / m 210 332 557 707

[0094] As shown in the table above, a higher content of component B results in a smaller etch ratio, increased adhesion, and increased difficulty in peeling.

[0095] (3) Physicochemical index tests of Examples 1 and 2

[0096] According to the standard HB 5453-2004 of the National Defense Science and Technology Commission, the physicochemical properties of Example 1 and Example 2 were tested, and the test results are shown in the table below.

[0097]

[0098]

[0099] As shown in the table above, the protective coatings of Examples 1 and 2 meet the technical requirements of aerospace milling coatings.

[0100] In summary, this invention provides a protective coating, its preparation method, and its application in chemical milling in the aerospace industry. The protective coating comprises component A and component B; component A, by mass percentage, comprises: 30-40% a polymer of formaldehyde, ammonia, and chloroethane; 1-2% N-[(5-methyl-1H-benzotriazol-1-yl)methyl]diethanolamine; and 58-69% a composite solvent; the composite solvent comprises D20 solvent oil and propylene glycol methyl ether acetate, wherein the mass ratio of D20 solvent oil to propylene glycol methyl ether acetate is 4:(1-1.5); component B is 1,3,5-triglycidyl-S-triazinetrione; and the volume ratio of component A to component B is 10:(1-3). The protective coating of this invention, after application, produces a coating with high elasticity and resistance to heat, acids, alkalis, and chemical milling liquids. It provides good protection for metals, and the coating can be manually peeled off without easily breaking, conforming to the National Defense Science and Technology Commission standard HB 5453-2004, "Specifications for Protective Coatings for Chemical Milling of Aluminum Alloys." Furthermore, this protective coating is free of halogenated hydrocarbons and toluene, minimizing its impact on the environment and worker health, and can be applied to large-scale production.

[0101] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A protective coating, characterized in that, The protective coating comprises component A and component B; Component A, by mass percentage, comprises: Formaldehyde polymers with ammonia and chloroethane comprise 30-40%; N-[(5-methyl-1H-benzotriazol-1-yl)methyl]diethanolamine 1-2%; Composite solvent 58-69%; The composite solvent comprises D20 solvent oil and propylene glycol methyl ether acetate, wherein the mass ratio of D20 solvent oil to propylene glycol methyl ether acetate is 4:(1-1.5). Component B is 1,3,5-triglycidyl-S-triazinetrione; The volume ratio of component A to component B is 10:(1-3).

2. A method for producing a protective coating as claimed in claim 1, characterized in that include: Add the composite solvent, the polymer of formaldehyde, ammonia, and chloroethane, and N-[(5-methyl-1H-benzotriazol-1-yl)methyl]diethanolamine to the reaction vessel according to the mass percentage, and stir until uniformly mixed to obtain component A; Component B is prepared by dispensing 1,3,5-triglycidyl-S-triazine trione by volume.

3. The preparation method according to claim 2, characterized in that, The stirring speed is 60-120 rpm, and the stirring time is 20-30 minutes.

4. Use of a protective coating in chemical milling in the aerospace industry, characterized in that, The protective coating as described in claim 1 or the protective coating prepared by the preparation method as described in any one of claims 2 to 3 is applied to the surface protection of metal materials in chemical milling in the aerospace industry.

5. Use according to claim 4, characterized in that, The method of using the protective coating in chemical milling in the aerospace industry includes the following steps: mixing component A and component B uniformly according to the volume ratio to obtain the mixed protective coating; allowing the mixed protective coating to stand for 10 to 20 minutes and then transferring it to a metal material for drying to form a protective coating.

6. Use according to claim 5, characterized in that, The transfer process is selected from either spraying or brushing.

7. Use according to claim 5, characterized in that, The metallic material is selected from one of titanium alloy, aluminum alloy, magnesium alloy, and steel.

8. The application according to claim 5, characterized in that, The drying temperature is 10–40°C, and the drying time is 6–24 hours.

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