Self-repairing plastic paint and preparation method thereof

Abstract

This invention relates to the field of plastic coatings, aiming to solve the problem that existing coatings, after the appearance of microcracks, are difficult to repair and prone to further expansion of cracks. It provides a method for preparing a self-healing plastic coating, comprising the following steps: S100, mixing and reacting isophorone diisocyanate, polycarbonate diol, and bismuth neodecanoate to obtain a first prepolymer; S200, adding dimethylolpropionic acid and bis(2-hydroxyethyl) disulfide dissolved in a solvent to the first prepolymer, reacting to obtain a second prepolymer; S300, adding triethylamine to the second prepolymer, reacting, then adding deionized water, and finally adding an aqueous solution of ethylenediamine dropwise to obtain a self-healing plastic coating. This invention introduces dynamic disulfide bonds through bis(2-hydroxyethyl) disulfide and constructs a structure in which hard segment micro-regions with sufficient mechanical strength are dispersed in a freely moving soft segment matrix. This allows the disulfide bonds to contact and exchange after the material is damaged, achieving self-repair.

Description

Technical Field

[0001] This invention relates to the field of plastic paints, and more specifically, to a self-healing plastic paint and its preparation method. Background Technology

[0002] Water-based plastic paint is a coating material used on substrates such as plastics. It is commonly used for surface decoration and protection of plastics. However, the surface structure of plastic products is often complex and not a simple plane, making them prone to stress concentration. Consequently, structural defects or performance weaknesses inevitably exist after coating formation and during use. Preventing the further propagation of microcracks on or inside the coating surface is one of the urgent technical problems to be solved. Summary of the Invention

[0003] The purpose of this invention is to provide a self-healing plastic paint and its preparation method, which solves the problem that existing coatings are difficult to repair and prone to further expansion after microcracks appear.

[0004] The embodiments of the present invention are achieved through the following technical solutions:

[0005] A method for preparing a self-healing plastic paint includes the following steps:

[0006] S100, after mixing and reacting isophorone diisocyanate, polycarbonate diol and bismuth neodecanoate, the first prepolymer is obtained;

[0007] S200. Dimethylolpropionic acid and bis(2-hydroxyethyl) disulfide, which are soluble in solvent, are added to the first prepolymer, and the reaction yields the second prepolymer.

[0008] S300: Triethylamine is added to the second prepolymer, and after the reaction, deionized water is added. Then, ethylenediamine aqueous solution is added dropwise and reacted. The solvent is removed by vacuum evaporation to obtain a self-healing plastic paint.

[0009] Water-based plastic paint is a coating material used on substrates such as plastics. It is commonly used for surface decoration and protection of plastics. However, the surface structure of plastic products is often complex and not a simple plane. Therefore, after the coating is formed, some structural defects or performance weaknesses are inevitable. The applicant hopes to improve water-based plastic paint to minimize or avoid the aforementioned problems as much as possible.

[0010] In step S200 of this invention, after introducing disulfide bonds, a second prepolymer containing carboxyl groups and disulfide bonds is obtained. The dynamic exchange reaction of the disulfide bonds can be used to achieve self-healing of the coating. The plastic paint of this invention contains a large number of flexible segments, such as PCDL, and disulfide bonds that can serve as dynamic crosslinking points. Under external force, energy is more easily dissipated, increasing the flexibility of the coating.

[0011] Reduced pressure evaporation can be performed using thin-film evaporation technology at a temperature of 50°C and a vacuum of 4 mbar. Specific temperature parameters can be adjusted according to the vacuum level. The solvent removal process is existing technology, and specific parameters are not limited in this invention; the goal is simply to effectively remove the solvent.

[0012] Preferably, by weight, the composition comprises: 22-26 parts isophorone diisocyanate, 80-120 parts polycarbonate diol, 0.05-0.1 parts bismuth neodecanoate, 4-8 parts dimethylolpropionic acid, 2-5 parts bis(2-hydroxyethyl) disulfide, 20-30 parts solvent, 2.5-5.5 parts triethylamine, and 600-1000 parts deionized water; the amount of ethylenediamine in the aqueous solution is 8-10 parts; and the concentration of the aqueous solution is 10 vt%-15 vt.

[0013] When the amount of bis(2-hydroxyethyl) disulfide is too low, the number of dynamic disulfide bonds in the network is insufficient, resulting in poor self-repair effect. When the amount of bis(2-hydroxyethyl) disulfide is too high, the mobility of polymer chain segments is reduced, inhibiting the exchange reaction of disulfide bonds and reducing repair efficiency.

[0014] Polycarbonate diol constitutes the soft segments of the material, whose long and flexible chains provide free volume for molecular movement. Sufficient soft segment content is a physical prerequisite for the segments to move at the repair temperature, allowing for contact at the fracture surfaces and exchange of dynamic bonds. The strong cohesive energy of the polycarbonate segments themselves also helps maintain the basic mechanical properties.

[0015] Controlling the amount of ethylenediamine can regulate the crosslinking density, reducing or avoiding the limitation of dynamic bond contact and exchange due to high crosslinking density, thereby limiting self-healing ability.

[0016] Dimethylolpropionic acid (DMPA) and triethylamine are related to the stability of the emulsion. Excessive DMPA can generate strong interionic forces, providing physical cross-linking points and restricting chain segment movement. This not only affects the coating's flexibility but also its self-healing properties. Triethylamine ensures the emulsion's neutralization degree is above 98%, avoiding insufficient neutralization which affects hydrophilicity. However, it should not be excessive either, as excess triethylamine can increase the coating's plasticity.

[0017] Preferably, the reaction temperature in step S100 is 75-85℃ and the reaction time is 1.5-2h.

[0018] Preferably, the reaction temperature in step S200 is 60-70℃ and the reaction time is 1.5-3h.

[0019] Preferably, the reaction temperature in step S300 is 30-40℃ and the reaction time is 10-20 min.

[0020] Preferably, step S200 specifically includes: mixing dimethylolpropionic acid, bis(2-hydroxyethyl) disulfide and N-methylpyrrolidone to obtain a mixed solution; adding the mixed solution dropwise to the first prepolymer for 15-20 min, and then keeping it at a warm temperature for 1.5-2 h to obtain the second prepolymer.

[0021] The dropwise addition method can avoid the formation of gels or uneven cross-linking caused by excessively rapid local reactions.

[0022] Preferably, 4,4'-dihydroxyazobenzene is dissolved in a solvent to obtain a stock solution; dimethylolpropionic acid, bis(2-hydroxyethyl) disulfide and N-methylpyrrolidone are mixed to obtain a mixed solution;

[0023] The S200 process specifically includes: adding 80-85% vt% of a mixed solution to the first prepolymer at a time of 12-16 min, reacting for 1-1.5 h, cooling to 40-45 °C, and simultaneously adding the remaining mixed solution and stock solution at a time of 3-4 min, reacting for 30-45 min to obtain the second prepolymer.

[0024] In its normal state, the 4,4'-dihydroxyazobenzene coating exhibits a rod-shaped trans structure. Upon UV triggering, it transforms into a V-shaped cis structure. In the cis structure, the interchain space of the polymer is expanded, and the interchain forces are weakened. This leads to localized property changes in the irradiated area, including a decrease in modulus and an increase in chain mobility, which in turn promotes disulfide bond exchange reactions. When UV irradiation ceases, the cis structure, being unstable, reverts to the trans structure, and the coating properties are restored.

[0025] The coating structure synthesized in this invention contains abundant carbon groups and amino groups, which have hydrogen bond anchoring effects with the phenolic hydroxyl groups in 4,4'-dihydroxyazobenzene, thereby reducing the migration of 4,4'-dihydroxyazobenzene.

[0026] N-methylpyrrolidone can be used as a solvent.

[0027] 4,4'-Dihydroxyazobenzene can exist in the system through either chemical crosslinking or physical doping. However, chemical crosslinking can hinder the structural changes of 4,4'-dihydroxyazobenzene to some extent. Therefore, the applicant devised a physical doping addition process. The difficulty of the physical doping process lies at least in how to reduce the migration of 4,4'-dihydroxyazobenzene. If 4,4'-dihydroxyazobenzene is added after all reactions are completed, the system viscosity is too high, making it difficult to disperse, and the dispersion process may even affect the stability of the emulsion. If 4,4'-dihydroxyazobenzene is added during the polymerization process, it may undergo extensive crosslinking, affecting its functionality. Therefore, this invention limits the addition process of 4,4'-dihydroxyazobenzene by first constructing a polymer backbone to a certain extent and introducing disulfide bonds, thereby reducing the concentration of residual -NCO in the system. Then, by utilizing a cooling process, the reaction of phenolic hydroxyl groups is inhibited, minimizing or avoiding the participation of 4,4'-dihydroxyazobenzene in the reaction as much as possible. At low temperatures, although the main reaction rate decreases to some extent, it ensures the main reaction can proceed, and at this temperature, 4,4'-dihydroxyazobenzene hardly participates in the reaction. The reaction temperature of S300 is also low enough that 4,4'-dihydroxyazobenzene is essentially in a physical doping state. Because 4,4'-dihydroxyazobenzene is added during the polymerization process, its dispersion uniformity and stability are significantly improved.

[0028] Preferably, 4,4'-dihydroxyazobenzene accounts for 1wt%-3wt% of the second prepolymer.

[0029] Preferably, a stock solution is obtained by dissolving 4,4'-dihydroxyazobenzene and polyethoxylated fatty alcohol in a solvent; the polyethoxylated fatty alcohol accounts for 8wt%-12wt% of 4,4'-dihydroxyazobenzene.

[0030] The addition of polyethoxylated fatty alcohols can act as a bridge for compatibility between 4,4'-dihydroxyazobenzene and the polymer matrix, further reducing the migration of 4,4'-dihydroxyazobenzene.

[0031] A self-healing plastic paint prepared by the aforementioned method.

[0032] The present invention has at least the following beneficial effects:

[0033] This invention introduces dynamic disulfide bonds through bis(2-hydroxyethyl) disulfide, and constructs a structure with sufficient mechanical strength by dispersing hard segment microregions in a freely moving soft segment matrix through high soft segment content, appropriate NCO:OH ratio, and precise ethylenediamine chain extension. By controlling the content of hydrophilic groups and the process, excessive binding forces are avoided, allowing the chain segments to move after damage and enabling sufficient opportunities for the disulfide bonds on the fracture surface to contact each other and undergo exchange reactions, thereby achieving self-repair. To fully utilize the self-repair function, this invention additionally adds 4,4'-dihydroxyazobenzene and limits the addition method, improving the self-repair effect while minimizing the migration tendency of 4,4'-dihydroxyazobenzene. Detailed Implementation

[0034] To make the objectives, methods, and advantages of the embodiments of the present invention clearer, the methods in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0035] Example 1: A method for preparing a self-healing plastic paint, comprising the following steps:

[0036] S100: 22 parts of isophorone diisocyanate, 80 parts of polycarbonate diol and 0.05 parts of bismuth neodecanoate were mixed and reacted at 75°C for 1.5 h to obtain the first prepolymer.

[0037] S200: Mix 4 parts of dimethylolpropionic acid, 2 parts of bis(2-hydroxyethyl) disulfide and 20 parts of N-methylpyrrolidone to obtain a mixed solution; add the mixed solution dropwise to the first prepolymer at 60°C for 15 min, and then keep it at the temperature for 1.5 h to obtain the second prepolymer.

[0038] S300, at 30℃, 2.5 parts of triethylamine were added to the second prepolymer. After 10 min of reaction, 600 parts of deionized water were added at 1000 rpm. After dispersion, ethylenediamine aqueous solution was added dropwise and reacted. The solvent was removed by vacuum evaporation to obtain a self-healing plastic paint. The amount of ethylenediamine in the ethylenediamine aqueous solution was 8 parts. The concentration of the ethylenediamine aqueous solution was 10 VT.

[0039] Example 2: A method for preparing a self-healing plastic paint, comprising the following steps:

[0040] S100: 26 parts of isophorone diisocyanate, 120 parts of polycarbonate diol and 0.1 parts of bismuth neodecanoate were mixed and reacted at 85°C for 2 hours to obtain the first prepolymer.

[0041] S200: Mix 8 parts of dimethylolpropionic acid, 5 parts of bis(2-hydroxyethyl) disulfide and 30 parts of N-methylpyrrolidone to obtain a mixed solution; add the mixed solution dropwise to the first prepolymer at 70°C for 20 min, and then keep it at the temperature for 2 h to obtain the second prepolymer.

[0042] S300, at 40℃, 5.5 parts of triethylamine were added to the second prepolymer. After 20 min of reaction, 1000 parts of deionized water were added at 1000 rpm. After dispersion, ethylenediamine aqueous solution was added dropwise and reacted. The solvent was removed by vacuum evaporation to obtain a self-healing plastic paint. The amount of ethylenediamine in the ethylenediamine aqueous solution was 10 parts. The concentration of the ethylenediamine aqueous solution was 15 VT.

[0043] Example 3: A method for preparing a self-healing plastic paint, comprising the following steps:

[0044] S100: 24 parts of isophorone diisocyanate, 100 parts of polycarbonate diol and 0.08 parts of bismuth neodecanoate were mixed and reacted at 80°C for 1.8 h to obtain the first prepolymer;

[0045] S200: Mix 6 parts of dimethylolpropionic acid, 3.5 parts of bis(2-hydroxyethyl) disulfide and 25 parts of N-methylpyrrolidone to obtain a mixed solution; add the mixed solution dropwise to the first prepolymer at 65°C for 18 min, and then keep it at the temperature for 1.6 h to obtain the second prepolymer.

[0046] S300, at 35℃, add 4 parts of triethylamine to the second prepolymer. After 15 min of reaction, add 800 parts of deionized water at 1000 rpm. After dispersion, add ethylenediamine aqueous solution dropwise and react. Then, evaporate under reduced pressure to remove the solvent to obtain a self-healing plastic paint. The amount of ethylenediamine in the ethylenediamine aqueous solution is 9 parts. The concentration of the ethylenediamine aqueous solution is 12vt.

[0047] Example 4: A method for preparing a self-healing plastic paint, comprising the following steps:

[0048] S100: 24 parts of isophorone diisocyanate, 100 parts of polycarbonate diol and 0.08 parts of bismuth neodecanoate were mixed and reacted at 80°C for 1.8 h to obtain the first prepolymer;

[0049] S200: Dissolve 4,4'-dihydroxyazobenzene in N-methylpyrrolidone to obtain a 10wt% stock solution; mix 6 parts of dimethylolpropionic acid, 3.5 parts of bis(2-hydroxyethyl) disulfide and 25 parts of N-methylpyrrolidone to obtain a mixed solution;

[0050] At 65°C, 80 wt% of the mixed solution was added dropwise to the first prepolymer over a period of 12 min. After reacting for 1 h, the temperature was lowered to 40°C, and the remaining mixed solution and stock solution were added dropwise simultaneously over a period of 3 min. After reacting for 30 min, the second prepolymer was obtained.

[0051] S300, at 35℃, add 4 parts of triethylamine to the second prepolymer. After 15 min of reaction, add 800 parts of deionized water at 1000 rpm. After dispersion, add ethylenediamine aqueous solution dropwise and react. Then, evaporate under reduced pressure to remove the solvent to obtain a self-healing plastic paint. The amount of ethylenediamine in the ethylenediamine aqueous solution is 9 parts. The concentration of the ethylenediamine aqueous solution is 12vt.

[0052] Example 5: A method for preparing a self-healing plastic paint, comprising the following steps:

[0053] S100: 24 parts of isophorone diisocyanate, 100 parts of polycarbonate diol and 0.08 parts of bismuth neodecanoate were mixed and reacted at 80°C for 1.8 h to obtain the first prepolymer;

[0054] S200: Dissolve 4,4'-dihydroxyazobenzene in N-methylpyrrolidone to obtain a 10wt% stock solution; mix 6 parts of dimethylolpropionic acid, 3.5 parts of bis(2-hydroxyethyl) disulfide and 25 parts of N-methylpyrrolidone to obtain a mixed solution;

[0055] At 65°C, 85% of a mixed solution was added dropwise to the first prepolymer over a period of 16 min. After reacting for 1.5 h, the temperature was lowered to 45°C, and the remaining mixed solution and stock solution were added dropwise simultaneously over a period of 4 min. After reacting for 45 min, the second prepolymer was obtained.

[0056] S300, at 35℃, add 4 parts of triethylamine to the second prepolymer. After 15 min of reaction, add 800 parts of deionized water at 1000 rpm. After dispersion, add ethylenediamine aqueous solution dropwise and react. Then, evaporate under reduced pressure to remove the solvent to obtain a self-healing plastic paint. The amount of ethylenediamine in the ethylenediamine aqueous solution is 9 parts. The concentration of the ethylenediamine aqueous solution is 12vt.

[0057] Example 6: A method for preparing a self-healing plastic paint, comprising the following steps:

[0058] S100: 24 parts of isophorone diisocyanate, 100 parts of polycarbonate diol and 0.08 parts of bismuth neodecanoate were mixed and reacted at 80°C for 1.8 h to obtain the first prepolymer;

[0059] S200: Dissolve 4,4'-dihydroxyazobenzene in N-methylpyrrolidone to obtain a 10wt% stock solution; mix 6 parts of dimethylolpropionic acid, 3.5 parts of bis(2-hydroxyethyl) disulfide and 25 parts of N-methylpyrrolidone to obtain a mixed solution;

[0060] At 65°C, 83% vt% of a mixed solution was added dropwise to the first prepolymer over a period of 14 min. After reacting for 1.2 h, the temperature was lowered to 42°C, and the remaining mixed solution and stock solution were added dropwise simultaneously over a period of 3.5 min. After reacting for 40 min, the second prepolymer was obtained.

[0061] S300, at 35℃, add 4 parts of triethylamine to the second prepolymer. After 15 min of reaction, add 800 parts of deionized water at 1000 rpm. After dispersion, add ethylenediamine aqueous solution dropwise and react. Then, evaporate under reduced pressure to remove the solvent to obtain a self-healing plastic paint. The amount of ethylenediamine in the ethylenediamine aqueous solution is 9 parts. The concentration of the ethylenediamine aqueous solution is 12vt.

[0062] Example 7: The difference from Example 6 is that polyethoxylated fatty alcohol is added to the stock solution, and the polyethoxylated fatty alcohol accounts for 8 wt% of 4,4'-dihydroxyazobenzene.

[0063] Example 8: The difference from Example 6 is that polyethoxylated fatty alcohol is added to the stock solution, and the polyethoxylated fatty alcohol accounts for 12 wt% of 4,4'-dihydroxyazobenzene.

[0064] Example 9: The difference from Example 6 is that polyethoxylated fatty alcohol is added to the stock solution, and the polyethoxylated fatty alcohol accounts for 10 wt% of 4,4'-dihydroxyazobenzene.

[0065] Comparative Example 1: The difference from Example 9 is that: at 65°C, all the mixed solution was added dropwise to the first prepolymer over a time of 17.5 min. After reacting for 1.2 h, the temperature was lowered to 42°C, and the stock solution was added dropwise simultaneously over a time of 3.5 min. After reacting for 40 min, the second prepolymer was obtained.

[0066] Comparative Example 2: The difference from Example 9 is that the mixed solution and the stock solution were simultaneously added to the first prepolymer at 65°C for 17.5 min, and the reaction was carried out for 112 min to obtain the second prepolymer.

[0067] Comparative Example 3: The difference from Example 9 is that: at 65°C, 83 wt% of the mixed solution was added dropwise to the first prepolymer over a time of 14 min. After reacting for 1.2 h, the temperature was not lowered, and the remaining mixed solution and stock solution were added dropwise simultaneously over a time of 3.5 min. After reacting for 40 min, the second prepolymer was obtained.

[0068] Experiment 1: The plastic paint prepared according to the processes provided in Examples 1-9 and Comparative Examples 1-3 was uniformly coated onto a PTFE board, leveled for 30 minutes, and then dried (wet film thickness 250 μm). Five cuts were made on the paint film surface, with a depth of 50% of the film thickness and cut lengths of 0.5 cm, 1 cm, 1.5 cm, 2 cm, and 2.5 cm, respectively. At 35°C, the paint film at 365 nm and 20 mW / cm²... 2 After irradiation under ultraviolet light for 3 minutes, the total length of the repaired incision was measured, and the repair rate was calculated as follows: repair rate = 100% * total length of the repaired incision / 7.5. The experimental results are shown in Table 1.

[0069] Table 1

[0070] Repair rate 61.42 64.29 65.08 86.82 88.30 88.94 Example 7 Example 8 Example 9 Comparative Example 1 Comparative Example 2 Comparative Example 3 Repair rate 90.15 91.33 92.71 82.49 67.72 71.57

[0071] As can be seen from the test results of Examples 1-9, the plastic paint provided by the present invention has a certain self-healing ability.

[0072] A comparison of the results of Examples 3 and 4-6 shows that adding 4,4'-dihydroxyazobenzene can significantly improve the self-healing efficiency of plastic paint.

[0073] A comparison of the results of Example 5 with those of Examples 7-9 shows that adding polyethoxylated fatty alcohol can improve the self-healing efficiency of plastic paint to a certain extent.

[0074] A comparison of the results of Comparative Example 1 and Example 9 shows that adding a stock solution after the mixed solution has reacted will affect the self-healing efficiency of the plastic paint to some extent.

[0075] A comparison of the results of Comparative Example 2 and Example 9 shows that when the stock solution is added synchronously with the mixed solution throughout the process and the reaction temperature is high, the self-healing ability of the plastic paint decreases significantly.

[0076] The comparison between the results of Comparative Example 3 and Example 9 shows that even if the stock solution is added after the mixed solution has reacted to a certain extent, the self-healing ability of the plastic paint will still be affected if a cooling operation is not performed.

[0077] Experiment 2: The plastic paint prepared according to the preparation process provided in Examples 1-9 was used to test the elongation at break (%) of the coating made from the plastic paint. The test results are shown in Table 2.

[0078] Table 2

[0079] Elongation at break 324 326 326 318 321 Example 6 Example 7 Example 8 Example 9 Elongation at break 325 330 328 331

[0080] As can be seen from the data in Table 2, the coating obtained by the plastic paint provided by the present invention has good flexibility, and is therefore more suitable for plastic products with complex surface structures.

[0081] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a self-repairing plastic paint, characterized by, By weight, the following steps are included: S100: 22-26 parts of isophorone diisocyanate, 80-120 parts of polycarbonate diol and 0.05-0.1 parts of bismuth neodecanoate are mixed and reacted to obtain the first prepolymer; S200: Dissolve 4,4'-dihydroxyazobenzene in 20-30 parts of solvent to obtain a stock solution; mix 4-8 parts of dimethylolpropionic acid, 2-5 parts of bis(2-hydroxyethyl) disulfide and N-methylpyrrolidone to obtain a mixed solution; Add 80-85% vt% of a mixed solution dropwise to the first prepolymer over a time of 12-16 min. After reacting for 1-1.5 h, cool the mixture to 40-45 °C and simultaneously add the remaining mixed solution and stock solution dropwise over a time of 3-4 min. After reacting for 30-45 min, the second prepolymer is obtained. S300: Add 2.5-5.5 parts of triethylamine to the second prepolymer, react, then add 600-1000 parts of deionized water, then add ethylenediamine aqueous solution dropwise, react, and then evaporate under reduced pressure to remove the solvent to obtain a self-healing plastic paint. The amount of ethylenediamine used in the aqueous solution is 8-10 parts; the concentration of the aqueous solution is 10vt%-15vt.

2. The preparation method according to claim 1, characterized in that, The reaction temperature in step S100 is 75-85℃, and the reaction time is 1.5-2h.

3. The preparation method according to claim 1, characterized in that, The reaction temperature in step S200 is 60-70℃, and the reaction time is 1.5-3h.

4. The preparation method according to claim 1, characterized in that, The reaction temperature in step S300 is 30-40℃, and the reaction time is 10-20 min.

5. The preparation method according to claim 1, characterized in that, 4,4'-Dihydroxyazobenzene accounts for 1wt%-3wt% of the first prepolymer.

6. The preparation method according to claim 1, characterized in that, After dissolving 4,4'-dihydroxyazobenzene and polyethoxylated fatty alcohol in a solvent, a stock solution was obtained; the polyethoxylated fatty alcohol accounted for 8wt%-12wt% of 4,4'-dihydroxyazobenzene.

7. A self-healing plastic paint prepared by the method according to any one of claims 1-6.