Dynamic disulfide bond-containing polyamide flexibilizer, preparation method and self-repairing powder coating composition

Abstract

The invention provides a polyamide flexibilizer containing dynamic disulfide bonds, a preparation method and a self-repairing powder coating composition. According to the polyamide toughening agent containing the dynamic disulfide bonds, the toughening agent is of an organic-inorganic composite structure; the organic structure comprises a polyamide main body, and the polyamide main body is formed by condensation polymerization of at least one binary aliphatic diacid, at least one binary aliphatic diamine and cystamine; the polyamide toughening agent containing the dynamic disulfide bond can form a stably dispersed tough phase in a powder coating system and effectively absorb and disperse external stress, so that the coating does not crack under a 180-degree bending condition, and the impact resistance and the flexibility of the coating are remarkably improved; after scratches or microcracks are generated on the surface of the coating, molecular rearrangement and reconstruction of disulfide bonds can occur under the mild heat treatment condition of about 60 DEG C, so that a damaged area is spontaneously healed, the scratches obviously disappear within 30 minutes, and the repairing efficiency can reach 85% or above.

Description

Technical Field

[0001] This invention relates to the field of self-healing coating technology, and in particular to a polyamide toughening agent containing dynamic disulfide bonds, its preparation method, and a self-healing powder coating composition. Background Technology

[0002] Powder coatings are widely used in home appliances, building materials, automotive parts, and industrial protection due to their advantages such as being solvent-free or virtually solvent-free, having high utilization rates, high application efficiency, and being environmentally friendly. As the application scenarios for powder coatings continue to expand, higher demands are being placed on the comprehensive performance of the coatings under complex service conditions, especially in terms of impact resistance, flexibility, and resistance to mechanical damage. However, existing powder coating systems typically use thermosetting resins with high crosslinking density (such as epoxy resins, polyester resins, or mixtures thereof). While these systems achieve high hardness and chemical resistance, they generally suffer from insufficient toughness, susceptibility to microcracks, and irreversible damage after scratches.

[0003] To improve the impact resistance and flexural properties of powder coatings, existing technologies typically incorporate rubber-based toughening agents, thermoplastic resin toughening agents, or inorganic fillers. While rubber-based toughening agents can improve the impact strength of the coating to some extent, they tend to reduce the coating's hardness, heat resistance, and solvent resistance, and can cause phase separation and migration during high-temperature curing or long-term service. Thermoplastic resin toughening agents, while improving elongation, often negatively impact the leveling properties, gloss, and application stability of the powder coating. Inorganic fillers primarily serve a reinforcing function, but their ability to inhibit crack propagation is limited, making it difficult to fundamentally solve the problem of coating failure after mechanical damage.

[0004] On the other hand, for the repair of scratches or microcracks on coating surfaces, existing self-healing technologies are mostly concentrated in solvent-based or water-based coatings, such as releasing repair agents through microcapsules or introducing reversible physical processes to achieve local repair. However, the above-mentioned technical solutions are difficult to apply directly to powder coating systems. This is because powder coatings require high-temperature melting and curing processes, which can easily damage the microcapsule structure and make it difficult for the repair components to remain stable. At the same time, existing self-healing systems based on physical processes have limited repair efficiency and the repair process is not repeatable, making it difficult to meet the durability requirements of industrial applications.

[0005] Furthermore, powder coatings inevitably generate scrap and recycled powder during production and application. Due to the irreversible molecular structure of existing highly crosslinked thermosetting powder coating systems, recycled powder is typically only used as a low-value filler, leading to material waste and increased costs. Therefore, achieving reprocessability and efficient resource utilization of powder coating systems without significantly reducing the mechanical and heat resistance properties of the coating is a pressing technical problem to be solved in this field.

[0006] In summary, existing powder coating toughening technologies generally suffer from drawbacks such as difficulty in simultaneously achieving toughening and mechanical properties, lack of self-repair capability after coating damage, low and non-repeatable repair efficiency, and difficulty in reusing scrap materials. Therefore, developing a powder coating toughening agent that combines excellent toughening effect, self-repair capability, and reprocessable characteristics, and achieving its stable application in powder coating systems, is of significant practical importance for improving the service reliability and resource utilization efficiency of powder coatings. Summary of the Invention

[0007] Purpose of the invention: The purpose of this invention is to provide a polyamide toughening agent containing dynamic disulfide bonds, its preparation method, and a self-healing powder coating composition. By introducing dynamic covalent disulfide bonds into the polyamide molecular structure, the toughening agent can not only significantly improve the flexibility and impact resistance of the coating in the powder coating system, but also achieve self-repair under mild external thermal stimulation after the coating is scratched or damaged by microcracks, thereby effectively extending the service life of the powder coating.

[0008] The technical solution of the present invention: In a first aspect, the present invention provides a polyamide toughening agent containing dynamic disulfide bonds, wherein the toughening agent is an organic-inorganic composite structure; the organic structure includes a polyamide host, wherein the polyamide host is formed by the polycondensation reaction of at least one dialiphatic diacid, at least one dialiphatic diamine and cystamine.

[0009] In some embodiments, the dialiphatic diacid is selected from one or more of adipic acid, azelaic acid, sebacic acid, cyclohexanedicarboxylic acid, 2-methyl adipic acid, diethylene glycol, dithiodiacetic acid, or dodecanoic acid.

[0010] Furthermore, the dialiphatic diacid is a mixed dialiphatic diacid of adipic acid, sebacic acid, and cyclohexanedicarboxylic acid; even further, the dialiphatic diacid is a mixed dialiphatic diacid of adipic acid, sebacic acid, and cyclohexanedicarboxylic acid in a molar ratio of 6-8:2-4:1.

[0011] In some embodiments, the dialiphatic diamine is selected from one or more combinations of 1,6-hexanediamine, 1,8-octanediamine, and 1,10-decanediamine.

[0012] In some embodiments, the molar ratio of the added dialiphatic diamine to cystamine is 80-95:5-20.

[0013] In some embodiments, the inorganic structure is SiO2.

[0014] In a second aspect, the present invention provides a method for preparing the polyamide toughening agent containing dynamic disulfide bonds, specifically comprising the following steps: (1) Disperse dry SiO2 in a solvent, add KH-550, heat under reflux to react, then centrifuge, wash and dry to obtain modified SiO2; (2) Modified SiO2 is dispersed in a solvent, a di-aliphatic diacid is added, and the mixture is heated and stirred until homogeneous; (3) Add the mixture of dialiphatic diamine and cystamine, and heat to carry out polycondensation reaction; (4) Dehydrate and cool under vacuum, then add a large amount of deionized water to precipitate, and after washing, filtering, drying and heat treatment, obtain a polyamide toughening agent containing dynamic disulfide bonds.

[0015] In some embodiments, the amount of KH-550 added is 5-10 wt% of dry SiO2.

[0016] In some embodiments, the heating temperature for reflux in step (1) is 70-90°C and the reflux time is 4-6 hours.

[0017] In some embodiments, the heating temperature for heating and stirring in step (2) is 70-90°C; the reaction temperature for polycondensation in step (3) is 140-160°C, and the reaction time is 4-6 hours.

[0018] In a third aspect, the present invention provides a self-healing powder coating composition, wherein the raw materials of the self-healing powder coating composition include the above-mentioned polyamide toughening agent containing dynamic disulfide bonds.

[0019] Beneficial effects: The polyamide toughening agent containing dynamic disulfide bonds provided by this invention can form a stable and dispersed tough phase in the powder coating system, effectively absorb and disperse external stress, so that the coating does not crack under 180° bending conditions, and significantly improves the impact resistance and flexibility of the coating.

[0020] Because dynamic disulfide bonds capable of reversible exchange reactions are introduced into the polyamide molecular chain, when scratches or microcracks occur on the coating surface, the disulfide bonds can undergo molecular rearrangement and reconstruction under mild heat treatment conditions of about 60°C, enabling the damaged area to spontaneously heal. The scratches disappear significantly within 30 minutes, and the repair efficiency can reach more than 85%.

[0021] The dynamic disulfide bond polyamide toughening agent can participate in the rearrangement of molecular structure during the melt extrusion and reprocessing of powder coatings, which is beneficial for the recycling of powder and scrap materials, thereby reducing material waste in the production and construction of powder coatings and showing good industrial application prospects. Detailed Implementation

[0022] The present invention will be described below with reference to specific embodiments. It should be noted that the following embodiments are examples of the present invention and are used only to illustrate the invention, not to limit it. Other combinations and various modifications within the scope of the present invention can be made without departing from its spirit or scope.

[0023] Unless otherwise specified, all raw materials used below can be readily obtained from commercial companies.

[0024] Unless otherwise specified, the post-processing steps such as "stirring", "filtration", "washing", "drying", and "water bath" used below are routine operations for those skilled in the art, and can be selected according to actual operation.

[0025] Example 1 (1) Disperse 10g of dry SiO2 in 50ml of anhydrous toluene, add 0.5g of KH-550, heat and reflux at 80℃ for 6h, then centrifuge, wash and dry to obtain modified SiO2; (2) Disperse 10g of modified SiO2 in 30ml of NMP, add 0.01 mol of adibasic aliphatic diacid, which is a mixture of adipic acid, sebacic acid and cyclohexanedicarboxylic acid in a molar ratio of 6:3:1, and heat and stir at 80℃ until homogeneous. (3) Add 0.008 mol of a mixture of 1,6-hexanediamine and 0.002 mol of cystamine, and heat to 140℃ for 4 hours to carry out polycondensation reaction; (4) Slowly vacuum -0.08 MPa, dehydrate for 1 hour, cool, then add 4 times the volume of deionized water to precipitate, wash, filter, dry, and then heat-treat in a nitrogen atmosphere at 80°C for 2 hours to obtain a polyamide toughening agent containing dynamic disulfide bonds.

[0026] Example 2 The preparation steps of Example 2 are basically the same as those of Example 1, except that the dialiphatic diacid is a mixed diacid of adipic acid, sebacic acid and cyclohexanedicarboxylic acid in a molar ratio of 8:4:1; and the dialiphatic diamine is 1,8-octanediamine instead of 1,6-hexanediamine.

[0027] Comparative Example 1 The preparation steps of Comparative Example 1 are basically the same as those of Example 1, except that the dialiphatic diacid is a mixed diacid composed of adipic acid, sebacic acid, and cyclohexanedicarboxylic acid in a molar ratio of 8:5:0.

[0028] Comparative Example 2 The preparation steps of Comparative Example 2 are basically the same as those of Example 1, except that the dialiphatic diacid is a mixed diacid composed of adipic acid, sebacic acid, and cyclohexanedicarboxylic acid in a molar ratio of 12:0:1.

[0029] Comparative Example 3 The preparation steps of Comparative Example 3 are basically the same as those of Example 1, except that the dialiphatic diacid is adipic acid.

[0030] Comparative Example 4 The preparation steps of Comparative Example 4 are basically the same as those of Example 1, except that the amount of 1,6-hexanediamine added is 0.01 mol and the amount of cystamine added is 0 mol.

[0031] Comparative Example 5 (1) Disperse 10g SiO2 in 30ml NMP, add 0.01 mol of adibasic aliphatic diacid, which is a mixture of adipic acid, sebacic acid and cyclohexanedicarboxylic acid in a molar ratio of 6:3:1, and heat at 80℃ and stir until homogeneous. (2) Add 0.008 mol of a mixture of 1,6-hexanediamine and 0.002 mol of cystamine, and heat to 140℃ for 4 hours to carry out polycondensation reaction; (3) Slowly vacuum -0.08 MPa, dehydrate for 1 hour, cool, then add 4 times the volume of deionized water to precipitate, wash, filter, dry, and then heat-treat in a nitrogen atmosphere at 80°C for 2 hours to obtain polyamide toughening agent.

[0032] By weight, 8 parts of the polyamide toughening agent prepared in the above examples and comparative examples were successively mixed with 270 parts of polyester resin, 21 parts of TGIC curing agent, 4 parts of leveling agent (PV88), 0.6 parts of ultraviolet absorber (nano zinc oxide), 2 parts of pigment and filler (rutile titanium dioxide) and 1.2 parts of antioxidant (168) in a high-speed mixer at 1000 rpm for 2 min to obtain a uniform dry mixture. The mixture was then melt-extruded in a twin-screw extruder, pressed into tablets, pulverized, and passed through a 160-mesh sieve to obtain the finished powder coating.

[0033] The polyester resin is a commercially available product of our company, model number P3902.

[0034] Performance testing The powder coating was electrostatically sprayed onto the substrate, achieving a film thickness of approximately 80 μm. The coating was then baked at 200 °C for 15 min, and its performance was finally tested. The test items and methods are as follows: 1. Gloss: The gloss of the coating was tested according to GB / T9754-2007 using a BYK miniature gloss meter.

[0035] 2. Pencil hardness: Tested according to GB / T6739-2022; 3. Impact performance: Tested according to GB / T 1732-2020; 4. T-bend performance: Tested according to GB / T13448-2019; 5. Self-repair rate test: After the coating has cured, a cross is made on the surface of the coating with a knife to damage it, and the changes in the coating before and after repair are observed using a 3D ultra-depth optical microscope.

[0036] The test results for each test item are shown in Table 1.

[0037] Table 1: Performance Test Results of Various Powder Coatings As shown in Table 1, the powder coatings prepared in Examples 1 and 2 are significantly superior to the comparative examples in terms of gloss, impact resistance, and flexibility. Example 1, in particular, achieved 0T without cracking in the T-bend test, indicating that the coating maintains excellent flexibility even under 180° bending conditions. Furthermore, after being artificially scratched and treated at 60°C for 30 minutes, Example 1 achieved a scratch repair rate of 88%, significantly higher than the comparative samples without the introduction of dynamic disulfide bonds or without SiO2 interface modification. This suggests that the dynamic disulfide bonds and the inorganic core-organic shell structure play a synergistic role in enhancing self-healing performance.

[0038] This invention can also be implemented in various other ways. Without departing from the spirit and essence of this invention, those skilled in the art can make various corresponding changes and modifications according to this invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims.

Claims

1. A polyamide toughening agent containing dynamic disulfide bonds, characterized in that, The toughening agent is an organic-inorganic composite structure; the organic structure includes a polyamide matrix, which is formed by the polycondensation reaction of at least one dialiphatic diacid, at least one dialiphatic diamine, and cystamine.

2. The polyamide toughening agent containing dynamic disulfide bonds according to claim 1, characterized in that, The dialiphatic diacid is selected from one or more of the following: azelaic acid, sebacic acid, cyclohexanedicarboxylic acid, 2-methyl adipic acid, diethylene glycol, dithiodiacetic acid, or dodecanoic acid.

3. The polyamide toughening agent containing dynamic disulfide bonds according to claim 1, characterized in that, The dialiphatic diacid is a mixture of adipic acid, sebacic acid, and cyclohexanedicarboxylic acid.

4. The polyamide toughening agent containing dynamic disulfide bonds according to claim 1, characterized in that, The aforementioned dialiphatic diacid is a mixture of adipic acid, sebacic acid, and cyclohexanedicarboxylic acid in a molar ratio of 6-8:2-4:

1.

5. The polyamide toughening agent containing dynamic disulfide bonds according to claim 1, characterized in that, The binary aliphatic diamine is selected from one or more combinations of 1,6-hexanediamine, 1,8-octanediamine, and 1,10-decanediamine.

6. The polyamide toughening agent containing dynamic disulfide bonds according to claim 1, characterized in that, The molar ratio of the added dialiphatic diamine to cystamine is 80-95:5-20.

7. The method for preparing the polyamide toughening agent containing dynamic disulfide bonds according to any one of claims 1-6, characterized in that, Includes the following steps: (1) Disperse dry SiO2 in a solvent, add KH-550, heat under reflux to react, then centrifuge, wash and dry to obtain modified SiO2; (2) Modified SiO2 is dispersed in a solvent, a di-aliphatic diacid is added, and the mixture is heated and stirred until homogeneous; (3) Add the mixture of dialiphatic diamine and cystamine, and heat to carry out polycondensation reaction; (4) Dehydrate and cool under vacuum, then add a large amount of deionized water to precipitate, and after washing, filtering, drying and heat treatment, obtain a polyamide toughening agent containing dynamic disulfide bonds.

8. The method for preparing the polyamide toughening agent containing dynamic disulfide bonds according to claim 6, characterized in that, The amount of KH-550 added is 5-10 wt% of dry SiO2.

9. The method for preparing the polyamide toughening agent containing dynamic disulfide bonds according to claim 6, characterized in that, The heating temperature for reflux in step (1) is 70-90℃ and the reflux time is 4-6h; the heating temperature for stirring in step (2) is 70-90℃; the reaction temperature for polycondensation in step (3) is 140-160℃ and the reaction time is 4-6h.

10. A self-healing powder coating composition comprising a polyamide toughening agent containing dynamic disulfide bonds as described in any one of claims 1-6.

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