Silicone resin nano-coating solution, preparation method and application thereof

Abstract

The present application relates to the technical field of metal surface treatment, and particularly relates to a kind of silicone resin nano plating solution and its preparation method and application, the silicone resin nano plating solution, with 100% mass percentage, comprising the following raw materials: hyperbranched organosilicon resin 5-15%, silane coupling agent 5-10%, antirust agent 5-8%, non-ionic surfactant 3-5%, penetrant 5-8%, the balance is water.The silicone resin nano plating solution prepared by the present application has excellent adhesion, wear resistance and corrosion resistance and can be used to protect metal workpieces.The silicone resin nano plating solution prepared by the present application applied in the field of traditional metal surface treatment not only can simplify process flow and improve production efficiency, but also reduces the use of harmful chemicals to the environment, reduces wastewater discharge, is more in line with environmental protection requirements, and can reduce energy consumption and cost, while improving product quality, has good economic benefits.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal surface treatment, in particular to a silicone nano-coating solution and a preparation method and application thereof. BACKGROUND

[0002] In the field of traditional metal surface treatment, the process is complicated and the environmental burden is heavy, which is a recognized problem in the industry. The phosphating solution used in the traditional method contains P, Ni, Mn and other ions, which need to fully meet the national water quality discharge standard to enter the urban pipe network system. The traditional phosphating process needs to go through processes such as degreasing, washing, surface adjustment, and phosphating, and water cleaning is required after each process. This process not only consumes a large amount of water resources, but also causes great pressure on the environment due to the use of chemical substances containing P, Ni, Mn and other heavy metals. The treatment and discharge of these heavy metal treatment agents have become a difficult problem that needs to be solved urgently. In addition, the chemicals used in the current process, such as strong acid, strong base, hydrofluoric acid, and fluorozirconic acid, are highly dangerous, not only posing a serious threat to the health of operators, but also greatly increasing the safety risk in the production process. Moreover, most of the current processes need to go through processes such as degreasing, washing, silane treatment, and washing, which also have the problem of large water resource consumption. These problems also need to be solved urgently.

[0003] Patent CN117900104A discloses a preparation method of a metal nano-composite coating, comprising the following steps: 1) ultrasonic cleaning: the surface of the mold is cleaned with an ultrasonic machine before coating to ensure that the surface of the mold is free of dirt and grease; 2) drying; 3) nano-coating; 3-1) preparing a nano-coating stock solution, when the mold is an organic metal material, the nano-coating stock solution is 100% modified polysiloxane resin; when the mold is an inorganic metal material, the nano-coating stock solution is 100% perfluoropolyether; 3-2) the nano-coating stock solution is loaded into a spraying vessel and shaken evenly; 3-3) a spray gun is configured, and spraying is performed at a spraying distance of 150-200 mm, with the spray gun being kept perpendicular to the mold base; 3-4) after spraying one side of the mold, the mold is rotated to sequentially spray the upper and lower sides of the mold; 4) baking: a baking temperature of 80-220°C is used for baking for 1-2h; 5) performance testing: the performance of the mold is tested after cooling. The metal nano-composite coating prepared by the present application has self-lubricating anti-sticking property, air permeability, stability, and durability, but the low reactivity of the modified polysiloxane resin will result in poor adhesion of the coating.

[0004] Patent CN114989650A discloses a self-drying type metal surface nano coating agent and a preparation method thereof. The nano coating agent is prepared from the following raw materials in the following weight ratio: tetraethyl orthosilicate 32-42%, maleic anhydride 1-3%, polyurethane resin 13-23%, silane coupling agent 28-38%, and isocyanate propyl triethoxysilane 5-15%. The self-drying type metal surface nano coating agent prepared by the invention can eliminate the high-temperature baking process in the coating construction, and directly spray on the metal surface, which can quickly dry and solidify into a film at room temperature, and the substrate surface has a nano self-cleaning function. However, the polyurethane resin has poor corrosion resistance.

[0005] Therefore, there is an urgent need in the market for a silicon resin nano coating solution with excellent adhesion and corrosion resistance. SUMMARY

[0006] In view of the problems in the prior art, the purpose of the present application is to obtain a silicon resin nano coating solution with excellent adhesion, wear resistance and corrosion resistance.

[0007] To achieve the above purpose, the technical solution adopted by the present application is as follows:

[0008] The present application provides a silicon resin nano coating solution in the first aspect, which comprises the following raw materials in 100% by mass: hyperbranched organosilicon resin 5-15%, silane coupling agent 5-10%, anti-rust agent 5-8%, non-ionic surfactant 3-5%, penetrating agent 5-8%, and the balance being water.

[0009] The silicon resin nano coating solution prepared by blending the hyperbranched organosilicon resin, silane coupling agent, anti-rust agent, non-ionic surfactant, penetrating agent and water has excellent adhesion and corrosion resistance. The hyperbranched organosilicon resin has a multi-branched isomer structure and has very strong penetration ability, which can penetrate thin layer of oil stains. Its special macromolecular silicon resin structure can polymerize into a dense nanoscale crystal structure on the surface of the substrate, thereby increasing the specific surface area and having super strong adhesion.

[0010] In some embodiments, the preparation method of the hyperbranched organosilicon resin comprises the following steps:

[0011] A1, 3-isocyanate propyl triethoxysilane, 9-fluorenyl alcohol and organotin catalyst are added to tetrahydrofuran, and reacted at 70-80℃ for 2-3h, dried to obtain a modifier;

[0012] A2, the alkyl-containing siloxane monomer, the vinyl-containing siloxane monomer and the catalyst are added into deionized water, stirred at 20-30℃ for 3-6h, then reacted at 70-90℃ for 2-6h, cooled to 40-60℃, the pH is adjusted to 4-6, the modifier obtained in step A1 is added and reacted for 1-2h to obtain a reaction solution; the blocking agent is added into an aqueous ethanol solution, stirred at 60-80℃ for 30-40min, then added into the reaction solution and continued to react for 2-4h, rotary evaporation under reduced pressure to obtain the hyperbranched silicone resin.

[0013] The modified agent obtained by reacting 3-isocyanate propyl triethoxysilane with 9-fluorenylmethanol, and the hyperbranched silicone resin segment obtained by reacting the modified agent with the alkyl-containing siloxane monomer and the vinyl-containing siloxane monomer, contain a rigid fluorene structure, which can improve the heat resistance and wear resistance of the silicone resin nano-coating solution, and the urethane groups in the hyperbranched silicone resin can form hydrogen bonds or coordination bonds with active groups or metal oxides on the surface of the metal substrate, further improving the adhesion of the silicone resin nano-coating solution.

[0014] In some embodiments, the mass ratio of the 3-isocyanate propyl triethoxysilane and the 9-fluorenylmethanol is 1: (0.7-1).

[0015] By limiting the ratio of 3-isocyanate propyl triethoxysilane and 9-fluorenylmethanol, the silicone resin nano-coating solution has better adhesion and corrosion resistance, which may be because the isocyanate groups in the system are not easy to remain, reducing the occurrence of side reactions in the system and affecting the hyperbranched structure of the hyperbranched silicone resin.

[0016] In some embodiments, the mass ratio of the alkyl-containing siloxane monomer and the vinyl-containing siloxane monomer is 1: (0.8-1).

[0017] In some embodiments, the mass ratio of the alkyl-containing siloxane monomer and the modifier in step A2 is 1: (0.25-0.35).

[0018] By limiting the ratio of the alkyl-containing siloxane monomer and the vinyl-containing siloxane monomer, and the ratio of the alkyl-containing siloxane monomer and the modifier, the silicone resin nano-coating solution has excellent wear resistance and higher adhesion, which may be because the rigid structure in the system is uniformly distributed under this ratio, avoiding the problem of adhesion reduction of the silicone resin nano-coating caused by stress concentration.

[0019] In some embodiments, the monomer of the alkyl-containing siloxane is one or more of dimethyldimethoxysilane, dimethyldiethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-hexyltriethoxysilane, isobutyltriethoxysilane, cyclohexyltrimethoxysilane.

[0020] In some embodiments, the monomer of the vinyl-containing siloxane is one or more of methylvinyl dimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, dimethyldiethoxysilane, diphenyldiethoxysilane, vinyltris(2-methoxyethoxy)silane, vinyltriisopropoxysilane.

[0021] In some embodiments, the mass ratio of the alkyl-containing siloxane monomer and the end-capping agent is 1: (0.2-0.4).

[0022] Preferably, the end-capping agent is hexamethyldisiloxane.

[0023] In some embodiments, the rust-preventing agent is one or more of an amine rust-preventing agent, a phosphate rust-preventing agent, a carboxylic acid rust-preventing agent, a heterocyclic compound rust-preventing agent.

[0024] In some embodiments, the non-ionic surfactant is one or more of a fatty alcohol polyoxyethylene ether, an alkylphenol polyoxyethylene ether, a fatty acid glyceride, a Span, a Tween.

[0025] In some embodiments, the penetrating agent is one or more of ethanol, isopropyl alcohol, acetone, butanone, ethylene glycol butyl ether, diethylene glycol butyl ether.

[0026] Preferably, the penetrating agent is diethylene glycol butyl ether.

[0027] The second aspect of the present application provides a preparation method of a silicon resin nano-coating solution, comprising the following steps: adding hyperbranched organosilicon resin, silane coupling agent, and non-ionic surfactant into water, stirring at 40-50℃ for 10-20min, and then adding a rust-preventing agent and a penetrating agent and stirring for 20-30min to obtain the silicon resin nano-coating solution.

[0028] The third aspect of the present application provides an application of a silicon resin nano-coating solution, comprising the following steps:

[0029] (1) gas phase oil removal: spraying the metal workpiece with an organic alkali solution with a pH of 8-10 for 3-10min;

[0030] (2) coating the silicon resin nano-coating solution: immersing / spraying at 20-40℃ for 2-5min;

[0031] (3) drying: drying at 130-180℃ for 10-25min.

[0032] (4) Spraying: the workpiece temperature is 180-200 DEG C after spraying epoxy-polyester mixed powder curing 10-15 min.

[0033] Compared with the prior art, the present application has the following beneficial effects:

[0034] (1) The silicon resin nano coating solution prepared by blending the hyperbranched organosilicon resin, silane coupling agent, antirust agent, non-ionic surfactant, penetrant and water has excellent adhesion and corrosion resistance. The hyperbranched organosilicon resin has a multi-branched isomer structure and has very strong penetration ability, which can penetrate thin layer of oil stains. The special macromolecular silicon resin structure can polymerize into a dense nanoscale crystal structure on the surface of the substrate, thereby enhancing the specific surface area and having super strong adhesion.

[0035] (2) The modified agent obtained by reacting 3-isocyanate propyl triethoxysilane with 9-fluorene methanol, and the hyperbranched organosilicon resin segment obtained by reacting the modified agent with a siloxane monomer containing silicon-containing vinyl and a siloxane monomer containing alkyl, contain a fluorene rigid structure, which can improve the heat resistance and wear resistance of the silicon resin nano coating solution. The urethane groups in the hyperbranched organosilicon resin can form hydrogen bonds or coordination bonds with active groups or metal oxides on the surface of the metal substrate, thereby further improving the adhesion of the silicon resin nano coating solution.

[0036] (3) The silicon resin nano coating solution prepared by the present application can not only reduce the processing steps, simplify the traditional metal surface treatment process, improve the production efficiency, but also reduce the use of harmful chemicals to the environment, reduce wastewater discharge, and is more in line with environmental protection requirements. In addition, the energy consumption and cost are reduced, the product quality is improved, and good economic benefits are obtained. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 The film forming electron microscope photo of the silicon resin nano coating solution prepared in Example 1. DETAILED DESCRIPTION

[0038] The present application will be described below in conjunction with specific embodiments. It should be noted that the following examples are only used to illustrate the present application, and are not used to limit the present application. Other combinations and various modifications within the concept of the present application can be made without departing from the spirit or scope of the present application.

[0039] In the following examples, the compounds and related reagents used, except for the hyperbranched silicone resin, are commercially available. Among them, the effective ingredient content of the epoxy-polyester mixed powder is 90%, and the density is 1.2 g / cm, which is purchased from Shandong Saider New Material Co., Ltd.; the type of non-ionic surfactant is HM293D, which is purchased from Shanghai Gushen Chemical Technology Co., Ltd.

[0040] Preparation Example 1

[0041] The preparation method of the hyperbranched silicone resin-1 comprises the following steps:

[0042] A1, 10 g of 3-isocyanate propyl triethoxysilane, 8.5 g of 9-fluorenylmethanol and 0.1 g of dibutyltin dilaurate are added into 50 g of tetrahydrofuran, and reacted at 75°C for 2.5 h, and then dried to obtain a modifier;

[0043] A2, 10 g of methyl trimethoxysilane, 9 g of vinyl tri(2-methoxyethoxy)silane and 0.15 g of 37 wt% hydrochloric acid aqueous solution are added into 50 ml of deionized water, stirred at 25°C for 4.5 h, and then reacted at 80°C for 4 h, cooled to 50°C, adjusted to pH 5, and then 3 g of the modifier obtained in step A1 was added and reacted for 1.5 h to obtain a reaction solution; 3 g of hexamethyldisiloxane was added into 10 g of 92 wt% ethanol aqueous solution, stirred at 70°C for 35 min, and then added into the reaction solution to continue to react for 3 h, and then rotary evaporated at 0.09 MPa and 55°C to obtain the hyperbranched silicone resin-1.

[0044] Preparation Example 2

[0045] The preparation method of the hyperbranched silicone resin-2 is the same as that of Preparation Example 1, except that the addition amount of 9-fluorenylmethanol is 6 g.

[0046] Preparation Example 3

[0047] The preparation method of the hyperbranched silicone resin-3 is the same as that of Preparation Example 1, except that the addition amount of vinyl tri(2-methoxyethoxy)silane is 12 g.

[0048] Preparation Example 4

[0049] The preparation method of the hyperbranched silicone resin-4 is the same as that of Preparation Example 1, except that the addition amount of the modifier in step A2 is 4.5 g.

[0050] Preparation Example 5

[0051] The preparation method of the hyperbranched silicone resin-5 comprises the following steps: 10 g of dimethyldiethoxysilane, 9 g of vinyltris(2-methoxyethoxy)silane and 0.15 g of 37 wt% hydrochloric acid aqueous solution are added into 50 ml of deionized water, stirred at 25 DEG C for 4.5 h, then reacted at 80 DEG C for 4 h to obtain a reaction solution; 3 g of hexamethyldisiloxane is added into 10 g of 92 wt% ethanol aqueous solution, stirred at 70 DEG C for 35 min, then added into the reaction solution to continue to react for 3 h, and rotary evaporated at 0.09 MPa and 55 DEG C to obtain the hyperbranched silicone resin-5.

[0052] Example 1

[0053] A silicon resin nano coating solution, containing the following raw materials in 100% by mass: hyperbranched silicone resin-1 10%, KH-550 silane coupling agent 7%, benzotriazole 7%, AEO-9 fatty alcohol polyoxyethylene ether 4%, diethylene glycol butyl ether 6%, deionized water 66%.

[0054] The preparation method of the silicon resin nano coating solution of the example comprises the following steps: hyperbranched silicone resin-1, KH-550 silane coupling agent, AEO-9 fatty alcohol polyoxyethylene ether are added into deionized water, stirred at 45 DEG C for 15 min, then benzotriazole and diethylene glycol butyl ether are added and stirred for 25 min to obtain the silicon resin nano coating solution.

[0055] Figure 1 The silicon resin nano coating solution prepared in Example 1 is used to prepare a film, and a film electron microscope photo of the film is shown.

[0056] Example 2

[0057] A silicon resin nano coating solution, containing the following raw materials in 100% by mass: hyperbranched silicone resin-1 5%, KH-550 silane coupling agent 5%, benzotriazole 5%, AEO-9 fatty alcohol polyoxyethylene ether 3%, diethylene glycol butyl ether 5%, deionized water 77%.

[0058] The preparation method of the silicon resin nano coating solution of the example comprises the following steps: hyperbranched silicone resin-1, KH-550 silane coupling agent, AEO-9 fatty alcohol polyoxyethylene ether are added into deionized water, stirred at 40 DEG C for 10 min, then benzotriazole and diethylene glycol butyl ether are added and stirred for 30 min to obtain the silicon resin nano coating solution.

[0059] Example 3

[0060] A silicon resin nano coating solution, containing the following raw materials in 100% by mass: hyperbranched silicone resin-1 15%, KH-550 silane coupling agent 10%, benzotriazole 8%, AEO-9 fatty alcohol polyoxyethylene ether 5%, diethylene glycol butyl ether 8%, deionized water 54%.

[0061] The preparation method of the silicone resin nano coating solution of the embodiment comprises the following steps: adding hyperbranched silicone resin-1, KH-550 silane coupling agent, and AEO-9 fatty alcohol polyoxyethylene ether into deionized water, stirring at 50°C for 20 min, then adding benzotriazole and diethylene glycol butyl ether and stirring for 20 min, and the preparation is completed.

[0062] Embodiment 4

[0063] A silicone resin nano coating solution and a preparation method thereof, the specific embodiment is the same as that of embodiment 1, and the difference lies in that the hyperbranched silicone resin-1 is replaced by an equal amount of hyperbranched silicone resin-2.

[0064] Embodiment 5

[0065] A silicone resin nano coating solution and a preparation method thereof, the specific embodiment is the same as that of embodiment 1, and the difference lies in that the hyperbranched silicone resin-1 is replaced by an equal amount of hyperbranched silicone resin-3.

[0066] Embodiment 6

[0067] A silicone resin nano coating solution and a preparation method thereof, the specific embodiment is the same as that of embodiment 1, and the difference lies in that the hyperbranched silicone resin-1 is replaced by an equal amount of hyperbranched silicone resin-4.

[0068] Embodiment 7

[0069] A silicone resin nano coating solution and a preparation method thereof, the specific embodiment is the same as that of embodiment 1, and the difference lies in that the hyperbranched silicone resin-1 is replaced by an equal amount of hyperbranched silicone resin-5.

[0070] Performance test

[0071] The silicone resin nano coating solution obtained in each of the above embodiments is subjected to performance test.

[0072] 1. Preparation of test sample

[0073] The method for preparing the test sample comprises the following steps:

[0074] (1) Oil removal in gas phase: spraying the tinplate with a pH 9 triethanolamine aqueous solution for 6 min;

[0075] (2) Coating of the silicone resin nano coating solution: 3 min of immersion at 30°C;

[0076] (3) Drying: 15 min of drying at 150°C;

[0077] (4) Powder spraying: after the metal workpiece temperature reaches 190°C, spraying of the epoxy-polyester mixed powder for curing for 12 min.

[0078] Figure 1 SEM photos of the film formed by the silicon resin nano-coating solution obtained in Example 1.

[0079] 2. Adhesion

[0080] The sample was subjected to grid test according to the standard of GB / T 9286-2021 to determine the adhesion of the silicon resin nano-coating solution.

[0081] 3. Wear resistance

[0082] The sample was subjected to wear resistance test according to the standard of GB / T 1768-2006.

[0083] 4. Neutral salt spray resistance

[0084] Twenty-one samples to be tested corresponding to Examples 1-7 were prepared, with 3 samples in each group.

[0085] After the samples to be tested were placed in a 25℃, 30% humidity environment for 5 days, the test began. The test method was based on the national standard GB / T1771-2007 "Determination of the resistance of color paint and varnish to neutral salt spray". The test data was taken as the average value, and the test results are shown in Table 1.

[0086] The aluminum alloy plate samples to be tested corresponding to Examples 1-7 were placed in a salt spray chamber, with the steel sample coating at an angle of 20° to the vertical. The temperature of the salt spray chamber was set to 35℃, and the salt spray pressure was 1kg / cm 2 . The air source was 5kg / cm 2 . Periodic continuous spraying was carried out with an atomized 5wt% sodium chloride aqueous solution. During the spraying period, the changes in the coating sample substrate were observed. The samples were observed regularly, and the time when corrosion began to appear was recorded. In the neutral salt spray resistance test, the longer the time when corrosion appears, the better the corrosion resistance of the coating.

[0087] Table 1

[0088]

[0089] From the data in Table 1, it can be seen that the silicone resin nano-coating solution of Examples 1-3 has excellent adhesion, wear resistance and salt spray resistance. From the comparison between Example 4 and Example 1, it can be seen that changing the ratio of 3-isocyanate propyl triethoxysilane and 9-fluorene methanol will make the isocyanate group easily remain, causing side reactions to occur, which will reduce the wear resistance and salt spray resistance of the silicone resin nano-coating solution. From the comparison between Example 5, 6 and Example 1, it can be seen that changing the ratio of alkyl-containing siloxane monomer and vinyl-containing siloxane monomer or modifier will make the rigid group unevenly distributed, which will reduce the adhesion, wear resistance and salt spray resistance of the silicone resin nano-coating solution. From the comparison between Example 7 and Example 1, it can be seen that the silicone resin nano-coating solution prepared using conventional hyperbranched silicone resin has poor adhesion, wear resistance and salt spray resistance.

[0090] The above embodiments are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the spirit and essence of the present application should be covered within the protection scope of the present application.

Claims

1. A silicone resin nano-coating solution, characterized in that, Based on a 100% weight percentage, it contains the following raw materials: 5-15% hyperbranched silicone resin, 5-10% silane coupling agent, 5-8% rust inhibitor, 3-5% nonionic surfactant, 5-8% penetrant, and the balance is water. The preparation method of the hyperbranched organosilicon resin includes the following steps: A1. Add 3-isocyanate-propyltriethoxysilane, 9-fluorenylmethanol and organotin catalyst to tetrahydrofuran, react at 70-80℃ for 2-3 h, and dry to obtain the modifier; A2. Add alkyl-containing siloxane monomers, vinyl-containing siloxane monomers and catalysts to deionized water, stir at 20-30℃ for 3-6 hours, then react at 70-90℃ for 2-6 hours, cool to 40-60℃, adjust pH to 4-6, add the modifier obtained in step A1 and react for 1-2 hours to obtain a reaction solution; add the end-capping agent to an ethanol aqueous solution, stir at 60-80℃ for 30-40 minutes, then add to the reaction solution and continue reacting for 2-4 hours, then evaporate under reduced pressure to obtain hyperbranched organosilicon resin.

2. The silicone resin nano-coating solution according to claim 1, characterized in that, The mass ratio of 3-isocyanate-propyltriethoxysilane to 9-fluorenylmethanol is 1:(0.7-1).

3. The silicone resin nano-coating solution according to claim 1, characterized in that, The mass ratio of the alkyl-containing siloxane monomer to the vinyl-containing siloxane monomer is 1:(0.8-1).

4. The silicone resin nano-coating solution according to claim 1, characterized in that, The mass ratio of the alkyl-containing siloxane monomer to the modifier in step A2 is 1:(0.25-0.35).

5. The silicone resin nano-coating solution according to claim 1, characterized in that, The mass ratio of the alkyl-containing siloxane monomer to the capping agent is 1:(0.2-0.4).

6. The silicone resin nano-coating solution according to claim 1, characterized in that, The rust inhibitor is one or more of the following: amine rust inhibitors, phosphate rust inhibitors, carboxylic acid rust inhibitors, and heterocyclic compound rust inhibitors.

7. The silicone resin nano-coating solution according to claim 1, characterized in that, The penetrant is one or more of ethanol, isopropanol, acetone, butanone, ethylene glycol butyl ether, and diethylene glycol butyl ether.

8. A method for preparing a silicone resin nano-coating solution according to any one of claims 1-7, characterized in that, The process includes the following steps: adding hyperbranched silicone resin, silane coupling agent, and nonionic surfactant to water, stirring at 40-50℃ for 10-20 minutes, then adding rust inhibitor and penetrant and stirring for 20-30 minutes to obtain the final product.

9. The application of a silicone resin nano-coating solution according to any one of claims 1-7 or a silicone resin nano-coating solution obtained by the preparation method according to claim 8, characterized in that, Includes the following steps: (1) Vapor phase degreasing: Spray the metal workpiece with an organic alkaline solution with a pH of 8-10 for 3-10 minutes; (2) Coating with silicone resin nano-coating solution: Immerse / spray at 20-40℃ for 2-5 minutes; (3) Drying: Dry at 130-180℃ for 10-25 minutes; (4) Powder spraying: After the workpiece temperature is 180-200℃, spray epoxy-polyester mixed powder and cure for 10-15 minutes.

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