Radiation resistant self-healing epoxy resin coating and method of making same

Abstract

The present application relates to the technical field of epoxy resin coating, and particularly relates to a radiation-resistant self-repairing epoxy resin coating and a preparation method thereof.The raw materials of the radiation-resistant self-repairing epoxy resin coating include component A, component B and component C, and the mass ratio of component A, component B and component C is 50-70:40-50:10-20.The raw materials of component A include, in parts by mass, 50-60 parts of bisphenol F type epoxy resin, 8-12 parts of calix[5]arene, 1-2 parts of zinc acetylacetonate and 15-20 parts of solvent.The raw materials of component B include, in parts by mass, 30-40 parts of octamethylcyclotetrasiloxane, 5-10 parts of gamma-aminopropyltriethoxysilane, 1-3 parts of vanillin, 0.5-1 part of a catalyst and 0.1-0.3 part of p-toluenesulfonic acid.Component C is an amine curing agent.

Description

Technical Field

[0001] The present invention relates to the technical field of epoxy resin coatings, and in particular to a radiation-resistant self-repairing epoxy resin coating and a preparation method thereof. Background Art

[0002] With the rapid development of the global shipping industry, the protective performance of marine coatings faces increasingly severe challenges. In the unique marine environment, coating materials must not only withstand the continuous erosion of high-intensity ultraviolet radiation and ionizing radiation, but also cope with multiple damaging factors such as mechanical collisions and seawater corrosion during navigation.

[0003] Conventional marine coatings are mostly based on epoxy resins, which are susceptible to molecular chain breakage under long-term radiation exposure, leading to coating powdering and shedding. Furthermore, existing radiation-blocking fillers lack interfacial bonding strength with the resin matrix, susceptible to microcracks when subjected to external forces. Currently, microencapsulated repair agents are used, but these microcapsules cannot regenerate after rupture, and the repair agents are susceptible to seawater penetration, leading to premature failure.

[0004] Currently, marine coatings must simultaneously achieve enhanced radiation resistance, scratch resistance, and self-healing properties during service. While surface hardness can be increased by adding hard fillers, this often sacrifices the coating's flexibility, leading to stress cracks when the hull deforms. Developing epoxy resin coatings that combine radiation resistance, impact resistance, and self-healing properties offers promising research prospects. Summary of the Invention

[0005] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a radiation-resistant self-repairing epoxy resin coating and a preparation method thereof.

[0006] A radiation-resistant self-healing epoxy resin coating, the raw materials of which include component A, component B, and component C, wherein the mass ratio of component A, component B, and component C is 50-70:40-50:10-20; the raw materials of component A include, by mass, 50-60 parts of bisphenol F epoxy resin, 8-12 parts of cup[5]arene, 1-2 parts of zinc acetylacetonate, and 15-20 parts of solvent; the raw materials of component B include, by mass, 30-40 parts of octamethylcyclotetrasiloxane, 5-10 parts of γ-aminopropyltriethoxysilane, 1-3 parts of vanillin, 0.5-1 part of catalyst, and 0.1-0.3 parts of p-toluenesulfonic acid; and component C is an amine curing agent.

[0007] Preferably, the epoxy value of the bisphenol F epoxy resin is 0.56-0.57 eq / 100 g.

[0008] Preferably, the solvent is at least one of propylene glycol methyl ether, dipropylene glycol methyl ether, and dipropylene glycol butyl ether.

[0009] Preferably, the catalyst is tetramethylammonium hydroxide or potassium hydroxide.

[0010] Preferably, the amine curing agent is at least one of diethylenetriamine, triethylenetetramine, polyetheramine, 593 curing agent, T-31 curing agent, 591 curing agent, and D-8 curing agent.

[0011] Preferably, component A is prepared by the following specific steps: bisphenol F epoxy resin and calix[5]arene are mixed, added to a solvent, refluxed at 120-135° C. for 4-8 hours, and then added with zinc acetylacetonate for ultrasonic treatment for 1-2 hours.

[0012] More preferably, the ultrasonic power is 400-500 W, and the ultrasonic frequency is 30-40 kHz.

[0013] Preferably, component B is prepared by the following specific steps: octamethylcyclotetrasiloxane, γ-aminopropyltriethoxysilane, vanillin, and a catalyst are uniformly mixed at room temperature, reacted at 80-100° C. for 1-2 hours under nitrogen protection, cooled to 50-60° C., p-toluenesulfonic acid is added, reacted for 1-2 hours, heated to 140-146° C., continued to react for 3-6 hours, and the pH value of the system is adjusted to 6.5-7.

[0014] The preparation method of the radiation-resistant self-repairing epoxy resin coating comprises the following steps: mixing components A, B and C, heat treating at 70-80° C. for 10-30 minutes, and heating to 120-130° C. for 10-30 minutes.

[0015] Beneficial effects:

[0016] The present invention uses calix[5]arene to modify bisphenol F epoxy resin to provide a high-density rigid aromatic ring structure, while octamethylcyclotetrasiloxane in component B undergoes ring-opening polymerization to form a three-dimensional Si-O-Si network; during the heat treatment process, the low-temperature stage promotes the epoxy-amine curing system to form a primary crosslinking, and the high-temperature stage activates the siloxane condensation to form an interpenetrating network, avoiding phase separation, ensuring the uniformity and weather resistance of the coating, and being suitable for extreme environments such as ships.

[0017] When the coating formed by the present invention is irradiated, microcracks are generated in the epoxy phase, while the flexible siloxane network absorbs stress through deformation. At the same time, the cavity structure of the cup[5]arene limits crack propagation, significantly reduces the crack propagation rate, and has excellent impact resistance.

[0018] This invention utilizes the aldehyde group of vanillin and the amino group generated by hydrolysis of γ-aminopropyltriethoxysilane to form a dynamic imine bond. This, combined with the Zn-N coordination bond formed by zinc acetylacetonate and an amine curing agent, effectively inhibits the hydrolysis of the imine bond in high-humidity environments. Experiments have shown that this invention maintains high repair efficiency in high-humidity environments, increasing the number of repair cycles to five.

[0019] The present invention achieves excellent impact resistance while maintaining radiation resistance through the synergy of multiple components, and its self-repair efficiency and cycle times are better than similar products, making it suitable for applications in extreme environments such as ship coatings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 1-2 is a comparison chart of the impact resistance of the coating films prepared using the epoxy resin coatings obtained in Example 5 and Comparative Examples 1-2.

[0021] Figure 2 The impact resistance and impact resistance retention rate of the coating films prepared using the epoxy resin coatings obtained in Example 5 and Comparative Examples 1-2 after irradiation treatment.

[0022] Figure 3 This is a comparison chart of the self-repair rates of the coating films prepared using the epoxy resin coatings obtained in Example 5 and Comparative Examples 1-2 after the first scratch-self-repair cycle and the fifth scratch-self-repair cycle. DETAILED DESCRIPTION

[0023] The present invention will be further explained below with reference to specific embodiments.

[0024] Preferably, the epoxy value of the bisphenol F epoxy resin is 0.56-0.57 eq / 100 g.

[0025] Example 1

[0026] A radiation-resistant self-repairing epoxy resin coating, comprising raw materials including component A, component B, and polyetheramine, wherein the mass ratio of component A, component B, and polyetheramine is 50:40:10. Component A comprises 500g of bisphenol F epoxy resin, 80g of calix[5]arene, 10g of zinc acetylacetonate, and 150g of propylene glycol methyl ether; and component B comprises 300g of octamethylcyclotetrasiloxane, 50g of γ-aminopropyltriethoxysilane, 10g of vanillin, 5g of potassium hydroxide, and 1g of p-toluenesulfonic acid.

[0027] Component A is prepared by the following specific steps: bisphenol F epoxy resin and calix[5]arene are mixed, added into propylene glycol methyl ether, refluxed at 120°C for 4 hours, and then added with zinc acetylacetonate and ultrasonically treated for 1 hour at an ultrasonic power of 400 W and an ultrasonic frequency of 30 kHz.

[0028] Component B is prepared by the following specific steps: octamethylcyclotetrasiloxane, γ-aminopropyltriethoxysilane, vanillin, and potassium hydroxide are uniformly mixed at room temperature, reacted at 80°C for 1 hour under nitrogen protection, with a stirring speed of 200 r / min, cooled to 50°C, p-toluenesulfonic acid is added, reacted for 1 hour, heated to 140°C, continued to react for 3 hours, and the pH value of the system is adjusted to 6.5-7.

[0029] The preparation method of the above-mentioned radiation-resistant self-healing epoxy resin coating includes the following steps: mixing component A, component B, and polyetheramine, stirring at a speed of 500 r / min for 10 minutes, heat treating at a temperature of 70°C for 10 minutes, and heating to 120°C for heat treating for 10 minutes.

[0030] Example 2

[0031] A radiation-resistant self-repairing epoxy resin coating, comprising raw materials including component A, component B, and polyetheramine, wherein the mass ratio of component A, component B, and polyetheramine is 70:50:20. Component A comprises 600 g of bisphenol F epoxy resin, 120 g of calix[5]arene, 20 g of zinc acetylacetonate, and 200 g of propylene glycol methyl ether; and component B comprises 400 g of octamethylcyclotetrasiloxane, 100 g of γ-aminopropyltriethoxysilane, 30 g of vanillin, 10 g of potassium hydroxide, and 3 g of p-toluenesulfonic acid.

[0032] Component A is prepared by the following specific steps: bisphenol F epoxy resin and calix[5]arene are mixed, added into propylene glycol methyl ether, refluxed at 135°C for 8 h, added with zinc acetylacetonate and ultrasonically treated for 2 h, with an ultrasonic power of 500 W and an ultrasonic frequency of 40 kHz.

[0033] Component B is prepared by the following specific steps: octamethylcyclotetrasiloxane, γ-aminopropyltriethoxysilane, vanillin, and potassium hydroxide are uniformly mixed at room temperature, reacted at 100°C for 2 hours under nitrogen protection, with a stirring speed of 300 r / min, cooled to 50-60°C, p-toluenesulfonic acid is added, reacted for 2 hours, heated to 146°C, continued to react for 6 hours, and the pH value of the system is adjusted to 6.5-7.

[0034] The preparation method of the above-mentioned radiation-resistant self-healing epoxy resin coating includes the following steps: mixing component A, component B, and polyetheramine, stirring at a speed of 1500r / min for 30 minutes, heat treating at a temperature of 80°C for 30 minutes, and heating to 130°C for heat treating for 30 minutes.

[0035] Example 3

[0036] A radiation-resistant self-repairing epoxy resin coating, comprising raw materials including component A, component B, and polyetheramine, wherein the mass ratio of component A, component B, and polyetheramine is 55:48:13. Component A comprises 580 g of bisphenol F epoxy resin, 90 g of calix[5]arene, 17 g of zinc acetylacetonate, and 170 g of propylene glycol methyl ether; and component B comprises 370 g of octamethylcyclotetrasiloxane, 70 g of γ-aminopropyltriethoxysilane, 25 g of vanillin, 7 g of potassium hydroxide, and 2.5 g of p-toluenesulfonic acid.

[0037] Component A is prepared by the following specific steps: bisphenol F epoxy resin and calix[5]arene are mixed, added into propylene glycol methyl ether, refluxed at 125°C for 7h, added with zinc acetylacetonate and ultrasonically treated for 80min, with an ultrasonic power of 480W and an ultrasonic frequency of 33kHz.

[0038] Component B was prepared by the following specific steps: octamethylcyclotetrasiloxane, γ-aminopropyltriethoxysilane, vanillin, and potassium hydroxide were mixed uniformly at room temperature, reacted at 95°C for 80 minutes under nitrogen protection, stirred at 280 r / min, cooled to 52°C, added with p-toluenesulfonic acid, reacted for 100 minutes, heated to 142°C, continued to react for 5 hours, and adjusted the pH value of the system to 6.5-7.

[0039] The preparation method of the above-mentioned radiation-resistant self-healing epoxy resin coating includes the following steps: mixing component A, component B, and polyetheramine, stirring at a speed of 800 r / min for 25 minutes, heat treating at a temperature of 73°C for 25 minutes, and heating to 122°C for heat treating for 25 minutes.

[0040] Example 4

[0041] A radiation-resistant self-repairing epoxy resin coating, comprising raw materials including component A, component B, and polyetheramine, wherein the mass ratio of component A, component B, and polyetheramine is 65:42:17. Component A comprises 520 g of bisphenol F epoxy resin, 110 g of calix[5]arene, 13 g of zinc acetylacetonate, and 190 g of propylene glycol methyl ether; and component B comprises 330 g of octamethylcyclotetrasiloxane, 90 g of γ-aminopropyltriethoxysilane, 15 g of vanillin, 9 g of potassium hydroxide, and 1.5 g of p-toluenesulfonic acid.

[0042] Component A is prepared by the following specific steps: bisphenol F epoxy resin and calix[5]arene are mixed, added into propylene glycol methyl ether, refluxed at 130°C for 5 hours, added with zinc acetylacetonate and ultrasonically treated for 100 minutes, with an ultrasonic power of 420W and an ultrasonic frequency of 39kHz.

[0043] Component B was prepared by the following specific steps: octamethylcyclotetrasiloxane, γ-aminopropyltriethoxysilane, vanillin, and potassium hydroxide were uniformly mixed at room temperature, reacted at 85°C for 100 minutes under nitrogen protection, with a stirring speed of 220 r / min, cooled to 58°C, p-toluenesulfonic acid was added, reacted for 80 minutes, heated to 144°C, continued to react for 4 hours, and adjusted the pH value of the system to 6.5-7.

[0044] The preparation method of the above-mentioned radiation-resistant self-healing epoxy resin coating includes the following steps: mixing component A, component B, and polyetheramine, stirring at a speed of 1200 r / min for 15 minutes, heat treating at a temperature of 77°C for 15 minutes, and heating to 128°C for heat treating for 15 minutes.

[0045] Example 5

[0046] A radiation-resistant self-repairing epoxy resin coating, comprising raw materials including component A, component B, and polyetheramine, wherein the mass ratio of component A, component B, and polyetheramine is 60:45:15. Component A comprises 550 g of bisphenol F epoxy resin, 100 g of calix[5]arene, 15 g of zinc acetylacetonate, and 180 g of propylene glycol methyl ether; and component B comprises 350 g of octamethylcyclotetrasiloxane, 80 g of γ-aminopropyltriethoxysilane, 20 g of vanillin, 8 g of potassium hydroxide, and 2 g of p-toluenesulfonic acid.

[0047] Component A is prepared by the following specific steps: bisphenol F epoxy resin and calix[5]arene are mixed, added into propylene glycol methyl ether, refluxed at 128°C for 6 hours, added with zinc acetylacetonate and ultrasonically treated for 90 minutes, with an ultrasonic power of 450W and an ultrasonic frequency of 36kHz.

[0048] Component B was prepared by the following specific steps: octamethylcyclotetrasiloxane, γ-aminopropyltriethoxysilane, vanillin, and potassium hydroxide were uniformly mixed at room temperature, reacted at 90°C for 90 minutes under nitrogen protection, with a stirring speed of 250 r / min, cooled to 55°C, p-toluenesulfonic acid was added, reacted for 90 minutes, heated to 143°C, continued to react for 4.5 hours, and adjusted the pH value of the system to 6.5-7.

[0049] The preparation method of the above-mentioned radiation-resistant self-healing epoxy resin coating includes the following steps: mixing component A, component B, and polyetheramine, stirring at a speed of 1000 r / min for 20 minutes, heat treating at a temperature of 75°C for 20 minutes, and heating to 125°C for heat treating for 20 minutes.

[0050] Comparative Example 1

[0051] A radiation-resistant self-repairing epoxy resin coating, comprising raw materials including component A, component B, and polyetheramine, wherein the mass ratio of component A, component B, and polyetheramine is 60:45:15. Component A comprises 550 g of bisphenol F epoxy resin, 100 g of calix[5]arene, 15 g of zinc acetylacetonate, and 180 g of propylene glycol methyl ether; and component B comprises 350 g of octamethylcyclotetrasiloxane, 80 g of γ-aminopropyltriethoxysilane, 20 g of vanillin, 8 g of potassium hydroxide, and 2 g of p-toluenesulfonic acid.

[0052] Component A is prepared by the following specific steps: bisphenol F epoxy resin and calix[5]arene are mixed, added into propylene glycol methyl ether, refluxed at 128°C for 6 hours, added with zinc acetylacetonate and ultrasonically treated for 90 minutes, with an ultrasonic power of 450W and an ultrasonic frequency of 36kHz.

[0053] Component B was prepared by the following specific steps: octamethylcyclotetrasiloxane, γ-aminopropyltriethoxysilane, vanillin, and potassium hydroxide were uniformly mixed at room temperature, reacted at 90°C for 90 minutes under nitrogen protection, with a stirring speed of 250 r / min, cooled to 55°C, p-toluenesulfonic acid was added, reacted for 90 minutes, heated to 143°C, continued to react for 4.5 hours, and adjusted the pH value of the system to 6.5-7.

[0054] The preparation method of the radiation-resistant self-repairing epoxy resin coating comprises the following steps: mixing component A, component B, and polyetheramine, stirring at a speed of 1000 r / min for 20 minutes, and heat treating at a temperature of 125° C. for 20 minutes.

[0055] Comparative Example 2

[0056] A radiation-resistant self-repairing epoxy resin coating, comprising raw materials including component A, component B, and polyetheramine, wherein the mass ratio of component A, component B, and polyetheramine is 60:45:15. Component A comprises 550g of bisphenol F epoxy resin, 115g of calix[5]arene, and 180g of propylene glycol methyl ether; and component B comprises 450g of octamethylcyclotetrasiloxane, 8g of potassium hydroxide, and 2g of p-toluenesulfonic acid.

[0057] Component A is prepared by the following specific steps: bisphenol F epoxy resin and calix[5]arene are mixed, added into propylene glycol methyl ether, and refluxed at a temperature of 128° C. for 6 hours.

[0058] Component B was prepared by the following specific steps: octamethylcyclotetrasiloxane and potassium hydroxide were mixed uniformly at room temperature, reacted at 90°C for 90 minutes under nitrogen protection, stirred at a speed of 250 r / min, cooled to 55°C, p-toluenesulfonic acid was added, reacted for 90 minutes, heated to 143°C, continued to react for 4.5 hours, and adjusted the pH value of the system to 6.5-7.

[0059] The preparation method of the above-mentioned radiation-resistant self-healing epoxy resin coating includes the following steps: mixing component A, component B, and polyetheramine, stirring at a speed of 1000 r / min for 20 minutes, heat treating at a temperature of 75°C for 20 minutes, and heating to 125°C for heat treating for 20 minutes.

[0060] Q195 steel plates were used as substrates. After cleaning and polishing, the epoxy resin coatings obtained in Example 5 and Comparative Examples 1-2 were sprayed on the steel plates. The plates were left at room temperature for 24 hours, and the appearance of the coatings was observed. The coatings were then tested for water resistance, acid resistance (10% sulfuric acid solution), and alkali resistance (30% sodium hydroxide solution) according to GB / T 1733-1993, "Determination of Water Resistance of Paint Films." Their salt spray resistance was tested according to GB / T 10125-2012, "Artificial Atmosphere Corrosion Test Salt Spray Test." Their wet heat resistance was also tested according to GB / T 1740-2007, "Determination of Wet Heat Resistance of Paint Films." The results are shown in Table 1.

[0061] Table 1 Epoxy resin coating film results obtained in Example 5 and Comparative Examples 1-2

[0062]

[0063] It can be seen from Table 1 that the coating film prepared using the epoxy resin coating obtained in Example 5 has the best performance in various humid environments, while the coating film prepared using the epoxy resin coating obtained in Comparative Example 2 has insufficient performance in various humid environments.

[0064] The impact resistance of each group of coatings mentioned above was measured with reference to GB / T 1732-2020 "Determination of impact resistance of paint films", and the height of the cracks was used to characterize the impact resistance. Figure 1 As shown, the coating film prepared using the epoxy resin coating obtained in Example 5 has the best impact resistance, which is slightly higher than that of Comparative Example 2 and significantly higher than that of Comparative Example 1.

[0065] use 60 The coatings in the above groups were irradiated with Co-γ rays at a dose rate of 2 kGy / h and a cumulative dose of 50 kGy. The impact resistance of the irradiated coatings was tested.

[0066] like Figure 2 As shown, the coating film prepared by using the epoxy resin coating obtained in Example 5 still has the best impact resistance after irradiation treatment, and the impact resistance retention rate is also the highest, which is better than that of Comparative Examples 1-2 (P < 0.05).

[0067] Referring to ASTM D7027-05, "Test Method for Scratch Recovery of Plastics," each of the aforementioned coatings was scratched using a multi-finger scratch tester with a stainless steel tip of 1mm in diameter. The test load was 15N, the scratch speed was 100mm / s, and the scratch length was 100mm. The surface scratch width was observed using a laser confocal microscope. The samples were then left in an environment of 25°C and 80% RH for 24 hours. The scratch width was then observed again, and the self-repair rate was calculated. Four more scratch-repair cycles were then performed at the same location. The self-repair rate was calculated after the fourth scratch-repair cycle.

[0068] Self-repair rate = width of surface scratch after standing at room temperature ÷ width of original surface scratch × 100%

[0069] like Figure 3 As shown, after the first scratch-self-repair cycle, the self-repair rates of the coatings prepared using the epoxy resin coatings obtained in Example 5 and Comparative Example 1 were both higher than 90%, indicating that both had good self-repair properties; and after 5 scratch-self-repair cycles, only the self-repair rate of the coating prepared using the epoxy resin coating obtained in Example 5 was higher than 90%, indicating that as the number of scratch-self-repair cycles increased, the coating prepared using the epoxy resin coating obtained in Comparative Example 1 gradually lost its self-repair properties.

[0070] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A radiation-resistant self-repairing epoxy resin coating, characterized in that: The raw materials include component A, component B, and component C, wherein the mass ratio of component A, component B, and component C is 50-70:40-50:10-20; The raw materials of component A include, by mass, 50-60 parts of bisphenol F epoxy resin, 8-12 parts of calix[5]arene, 1-2 parts of zinc acetylacetonate, and 15-20 parts of solvent; Component A is prepared by the following specific steps: bisphenol F epoxy resin and calix[5]arene are mixed, added into a solvent, refluxed at 120-135° C. for 4-8 hours, and then added with zinc acetylacetonate for ultrasonic treatment for 1-2 hours; The raw materials of component B include, by mass, 30-40 parts of octamethylcyclotetrasiloxane, 5-10 parts of γ-aminopropyltriethoxysilane, 1-3 parts of vanillin, 0.5-1 parts of catalyst, and 0.1-0.3 parts of p-toluenesulfonic acid; The catalyst is tetramethylammonium hydroxide or potassium hydroxide; Component B is prepared by the following specific steps: octamethylcyclotetrasiloxane, γ-aminopropyltriethoxysilane, vanillin, and a catalyst are uniformly mixed at room temperature, reacted at 80-100°C under nitrogen protection for 1-2 hours, cooled to 50-60°C, p-toluenesulfonic acid is added, reacted for 1-2 hours, heated to 140-146°C, continued to react for 3-6 hours, and the pH value of the system is adjusted to 6.5-7; Component C is an amine curing agent; The preparation of the radiation-resistant self-repairing epoxy resin coating comprises: mixing components A, B, and C, heat-treating at 70-80° C. for 10-30 minutes, and heating to 120-130° C. for 10-30 minutes.

2. The radiation-resistant self-repairing epoxy resin coating according to claim 1, characterized in that: The epoxy value of bisphenol F epoxy resin is 0.56-0.57eq / 100g.

3. The radiation-resistant self-repairing epoxy resin coating according to claim 1, characterized in that: The solvent is at least one of propylene glycol methyl ether, dipropylene glycol methyl ether and dipropylene glycol butyl ether.

4. The radiation-resistant self-repairing epoxy resin coating according to claim 1, characterized in that: The amine curing agent is at least one of diethylenetriamine, triethylenetetramine, polyetheramine, 593 curing agent, T-31 curing agent, 591 curing agent, and D-8 curing agent.

5. The radiation-resistant self-repairing epoxy resin coating according to claim 1, characterized in that: During the ultrasonic treatment, the ultrasonic power is 400-500W and the ultrasonic frequency is 30-40kHz.

6. A method for preparing the radiation-resistant self-repairing epoxy resin coating according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: mixing components A, B and C, performing heat treatment at 70-80° C. for 10-30 minutes, and heating the mixture to 120-130° C. for 10-30 minutes.

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