Weather-resistant cardanol epoxy curing agent and preparation method thereof

Abstract

The invention provides a weather-resistant cardanol epoxy curing agent and a preparation method thereof. The curing agent is prepared from the following raw materials: modified cardanol, polyamine and formaldehyde, the modified cardanol is 1, 1, 1, 3, 5, 5, 5-heptamethyltrisiloxane modified cardanol, and the modified cardanol is 1, 1, 1, 3, 5, 5-heptamethyltrisiloxane modified cardanol. The curing agent prepared by the preparation method disclosed by the invention is applied to an epoxy coating, has relatively good adhesive force, impact resistance, salt spray corrosion resistance and cold and heat cycle resistance, is good in mechanical property, good in weather resistance and high in stability, and can meet the use requirements of long-term outdoor or harsh environments.

Description

Technical Field

[0001] This invention belongs to the field of epoxy coating technology, and particularly relates to a weather-resistant cashew phenol epoxy curing agent and its preparation method. Background Technology

[0002] Epoxy resin curing agents are the core components that determine the performance of epoxy materials. Cashew phenol, as a renewable natural resource extracted from cashew nut shell liquid, has become one of the ideal raw materials for epoxy curing agents because it combines the rigidity of benzene rings with the flexibility of long aliphatic chains, and is widely available and inexpensive.

[0003] However, epoxy curing agents prepared from conventional cashew phenol or its simple derivatives still have significant shortcomings when used in long-term outdoor or harsh environments: on the one hand, their limited hydrophobicity and heat resistance make it difficult for the coating to meet high-end protection requirements in terms of water resistance, corrosion resistance, and resistance to high and low temperature alternation; on the other hand, while pursuing high crosslinking density to obtain good chemical resistance, the flexibility and impact resistance of the coating are often sacrificed, resulting in high brittleness of the coating, which is prone to cracking and peeling under stress or temperature changes.

[0004] To improve performance, existing technologies have attempted to modify cashew phenol. For example, modification with phosphorus-containing compounds or nitrogen-containing structures with rigid rings can improve weather resistance to some extent, but the improvement in molecular flexibility and compatibility with the resin matrix of the modified chain segments is limited, and the stability in long-term use and harsh environments remains poor.

[0005] Therefore, how to provide a curing agent that simultaneously possesses good compatibility, excellent mechanical properties, and high weather resistance is a problem that this invention urgently needs to solve. Summary of the Invention

[0006] The purpose of this invention is to provide a weather-resistant cashew phenol epoxy curing agent and its preparation method, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides a weather-resistant cashew nut shell epoxy curing agent, characterized in that the raw materials for preparing the curing agent include the following components: modified cashew nut shell, polyamine, and formaldehyde; The modified cashew phenol is 1,1,1,3,5,5,5-heptamethyltrisiloxane-modified cashew phenol.

[0008] As a further improvement, the molar ratio of the modified cashew phenol, polyamine, and formaldehyde is 1:(1.7-2):(1.4-1.6).

[0009] As a further improvement, the synthesis of the modified cashew phenol includes the following steps: (1) In an inert gas atmosphere, acetic anhydride and cashew phenol were added to a flask equipped with a reflux condenser. The mixture was heated and stirred in an oil bath at 110-130℃ for 2-4 hours. After the reaction was completed, cashew phenol acetate was obtained. (2) In an inert gas atmosphere, cashew phenol acetate, 1,1,1,3,5,5,5-heptamethyltrisiloxane and platinum catalyst were added to a flask equipped with a reflux condenser. The reaction was carried out at 110-130℃ for 3-6 h. After the reaction was completed, the product was post-processed to obtain 1,1,1,3,5,5,5-heptamethyltrisiloxane cashew phenol acetate. (3) Under an inert gas atmosphere, add 1,1,1,3,5,5,5-heptamethyltrisiloxane cashew phenol acetate and dilute hydrochloric acid solution to a flask equipped with a reflux condenser. The hydrolysis reaction is carried out for 2-4 hours. After the reaction is completed, the product is post-processed to obtain 1,1,1,3,5,5,5-heptamethyltrisiloxane modified cashew phenol.

[0010] As a further improvement, the cashew phenol is monoene cashew phenol; the CAS number of the monoene cashew phenol is: 501-26-8.

[0011] As a further improvement, the molar ratio of cashew phenol acetate and 1,1,1,3,5,5,5-heptamethyltrisiloxane in step (2) is 1.2-1.5:1.

[0012] As a further improvement, the platinum catalyst in step (2) is platinum(0)-1,3-diethylene-1,1,3,3-tetramethyldisiloxane.

[0013] As a further improvement, the concentration of the dilute hydrochloric acid solution in step (3) is 0.5-1.5 mol / L.

[0014] As a further improvement, the polyamine is an alicyclic amine; the polyamine is at least one of isophorone diamine, cyclohexane diamine, and 4,4'-diaminodicyclohexylmethane.

[0015] Alicyclic amines possess certain chemical resistance (especially acid and solvent resistance), outstanding UV resistance and yellowing resistance. When reacted with modified cashew phenol and formaldehyde, they can improve the weather resistance and safety of the curing agent while maintaining a balance between high rigidity and toughness.

[0016] This invention also provides a method for preparing a weather-resistant cashew phenol-based epoxy curing agent, characterized by comprising the following steps: Modified cashew phenol was added to a flask, and polyamine was slowly added dropwise while stirring at 40-60℃. After the addition was completed, the temperature was raised to 60℃-70℃, and formaldehyde was added in batches. The mixture was stirred and mixed evenly, and the temperature was raised to 80-90℃ and kept at that temperature for 1-3 hours. Then the temperature was raised to 100-120℃ and the reaction was continued for 1-2 hours. After the reaction was completed, the cashew phenol epoxy curing agent was obtained through post-treatment.

[0017] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a weather-resistant cashew phenol-based epoxy curing agent and its preparation method. The curing agent, when applied to epoxy coatings, exhibits good adhesion, impact resistance, salt spray corrosion resistance, and resistance to thermal cycling, indicating good mechanical properties, good weather resistance, and strong stability. The long fatty chain and flexible siloxane segments in the modified cashew phenol prepared in this invention serve as flexible components, effectively absorbing and dispersing stress. The cross-linked network formed by the reaction with polyamines can provide a certain degree of rigidity. When applied to epoxy coatings, it can give the coating good adhesion and excellent impact resistance. 1,1,1,3,5,5,5-heptamethyltrisiloxane has extremely low surface energy and excellent hydrophobicity, which can effectively block the penetration of moisture, oxygen and corrosive media. The introduction of this siloxane segment can improve the corrosion resistance, high and low temperature resistance, weather resistance and durability of the curing agent, and can meet the requirements of long-term outdoor or harsh environment use. Detailed Implementation

[0018] 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.

[0019] In the following examples, except for 1,1,1,3,5,5,5-heptamethyltrisiloxane-modified cashew phenol and n-butyl-1,1,3,3-tetramethyldisiloxane-modified cashew phenol, all other compound monomers and related reagents used were commercially available. Cashew phenol was purchased from Shanghai Chunyou Biotechnology Co., Ltd., product number P3766; E51 epoxy resin was purchased from Sichuan Shunmei New Materials Co., Ltd., product number 6101.

[0020] The preparation of 1,1,1,3,5,5,5-heptamethyltrisiloxane-modified cashew phenol includes the following steps: (1) Under a nitrogen atmosphere, 0.24 mol of acetic anhydride and 0.2 mol of cashew phenol were added to a flask equipped with a reflux condenser. The mixture was heated and stirred in an oil bath at 130 °C for 3 h. After the reaction was completed, the low-boiling-point substances were removed by vacuum distillation at 140 °C. The mixture was then cooled to room temperature to obtain cashew phenol acetate. (2) Under a nitrogen atmosphere, 0.26 mol of cashew phenol acetate, 0.2 mol of 1,1,1,3,5,5,5-heptamethyltrisiloxane and 0.003 mmol of platinum(O)-1,3-diethylene-1,1,3,3-tetramethyldisiloxane were added to a flask equipped with a reflux condenser. The reaction was carried out at 130 °C for 5 h. After the reaction was completed, the unreacted raw materials were removed by vacuum distillation. Then, dichloromethane was added for washing, filtration, and rotary evaporation to obtain 1,1,1,3,5,5,5-heptamethyltrisiloxane cashew phenol acetate. (3) Under a nitrogen atmosphere, 0.1 mol of 1,1,1,3,5,5,5-heptamethyltrisiloxane cashew phenol acetate and 200 mL of 1 mol / L hydrochloric acid solution were added to a flask equipped with a reflux condenser. The hydrolysis reaction was carried out at 100 °C for 3 h. After the reaction was completed, the mixture was cooled to room temperature, extracted with dichloromethane and separated into layers, and then rotary evaporated to obtain 1,1,1,3,5,5,5-heptamethyltrisiloxane modified cashew phenol.

[0021] The preparation of n-butyl-1,1,3,3-tetramethyldisiloxane-modified cashew phenol includes the following steps: (1) Under a nitrogen atmosphere, 0.24 mol of acetic anhydride and 0.2 mol of cashew phenol were added to a flask equipped with a reflux condenser. The mixture was heated and stirred in an oil bath at 130 °C for 3 h. After the reaction was completed, the low-boiling-point substances were removed by vacuum distillation at 140 °C. The mixture was then cooled to room temperature to obtain cashew phenol acetate. (2) Under a nitrogen atmosphere, 0.26 mol of cashew phenol acetate, 0.2 mol of n-butyl-1,1,3,3-tetramethyldisiloxane and 0.003 mmol of platinum(O)-1,3-diethylene-1,1,3,3-tetramethyldisiloxane were added to a flask equipped with a reflux condenser. The reaction was carried out at 130 °C for 4 h. After the reaction was completed, the unreacted raw materials were removed by vacuum distillation. Then, dichloromethane was added for washing, filtration, and rotary evaporation to obtain n-butyl-1,1,3,3-tetramethyldisiloxane cashew phenol acetate. (3) Under a nitrogen atmosphere, 0.1 mol of n-butyl-1,1,3,3-tetramethyldisiloxane cashew phenol acetate and 200 mL of 1 mol / L hydrochloric acid solution were added to a flask equipped with a reflux condenser. The hydrolysis reaction was carried out at 100 °C for 3 h. After the reaction was completed, the mixture was cooled to room temperature, extracted with dichloromethane and separated into layers, and then rotary evaporated to obtain n-butyl-1,1,3,3-tetramethyldisiloxane modified cashew phenol.

[0022] Example 1 Preparation of a weather-resistant cashew phenol-based epoxy curing agent: 0.2 mol of 1,1,1,3,5,5,5-heptamethyltrisiloxane-modified cashew phenol was added to a flask. 0.36 mol of isophorone diamine was slowly added dropwise while stirring at 40°C. After the addition was complete, the temperature was raised to 65°C, and then 0.3 mol of formaldehyde was added in two portions at 20-minute intervals. The mixture was stirred until homogeneous, and the temperature was raised to 80°C and kept at that temperature for 3 hours. Then the temperature was raised to 110°C and the reaction was continued with stirring for 1 hour. After the reaction was completed, water was removed by vacuum distillation at 105°C, and then the mixture was cooled to room temperature to obtain a cashew phenol-based epoxy curing agent.

[0023] Example 2 Preparation of a weather-resistant cashew phenol-based epoxy curing agent: 0.2 mol of 1,1,1,3,5,5,5-heptamethyltrisiloxane-modified cashew phenol was added to a flask. 0.34 mol of cyclohexanediamine was slowly added dropwise under stirring at 50°C. After the addition was complete, the temperature was raised to 60°C, and then 0.32 mol of formaldehyde was added in two portions at 20-minute intervals. The mixture was stirred and homogenized, and the temperature was raised to 85°C and maintained for 3 hours. Then the temperature was raised to 110°C and the reaction was continued with stirring for 1.5 hours. After the reaction was completed, water was removed by vacuum distillation at 105°C, and then the mixture was cooled to room temperature to obtain a cashew phenol-based epoxy curing agent.

[0024] Example 3 Preparation of a weather-resistant cashew phenol-based epoxy curing agent: 0.2 mol of 1,1,1,3,5,5,5-heptamethyltrisiloxane-modified cashew phenol was added to a flask. 0.36 mol of diethylenetriamine was slowly added dropwise at 40°C with stirring. After the addition was complete, the temperature was raised to 65°C, and then 0.3 mol of formaldehyde was added in two portions at 20-minute intervals. The mixture was stirred and mixed thoroughly. The temperature was raised to 80°C and kept at that temperature for 3 hours. Then the temperature was raised to 110°C and the reaction was continued with stirring for 1 hour. After the reaction was completed, water was removed by vacuum distillation at 105°C, and then the mixture was cooled to room temperature to obtain a cashew phenol-based epoxy curing agent.

[0025] Example 4 It is basically the same as Example 1, except that 0.36 mol isophorone diamine is replaced with 0.3 mol isophorone diamine.

[0026] Comparative Example 1 The method is basically the same as in Example 1, except that 0.2 mol of 1,1,1,3,5,5,5-heptamethyltrisiloxane-modified cashew phenol is replaced with 0.2 mol of n-butyl-1,1,3,3-tetramethyldisiloxane-modified cashew phenol.

[0027] Comparative Example 2 The method is basically the same as in Example 1, except that 0.2 mol of 1,1,1,3,5,5,5-heptamethyltrisiloxane-modified cashew phenol is replaced with 0.2 mol of cashew phenol.

[0028] The cashew phenol-based epoxy curing agents obtained in Examples 1-4 and Comparative Examples 1-2 were mixed with commercially available E51 epoxy resin at a mass ratio of 30:100 to prepare an epoxy coating. The resulting epoxy coating was applied to the surface of a metal sheet and cured at 25°C to form a 30 μm thick coating. The coating properties were tested for adhesion, impact resistance, neutral salt spray resistance, and thermal cycling resistance. The specific test methods are as follows: Adhesion: The adhesion grade is determined according to GB / T 1720-2020, with grade 1 being the best and grade 7 being the worst. Impact resistance: tested according to GB / T 1732-1993; Resistance to neutral salt spray: The corrosion width was determined after 1000 hours according to GB / T 1771-2007; Resistance to thermal cycling: Place the sample in a high and low temperature cycling test chamber with a temperature of 80℃ and a relative humidity of 95%. After storing it at 80℃ and 95% relative humidity for 4 hours, first lower the temperature to -40℃ at a rate of 1℃ / min and keep it at that temperature for 4 hours. Then raise the temperature to 80℃ at a rate of 1℃ / min and keep it at that temperature for another 4 hours. This constitutes one cycle. The sample is considered qualified if the paint film does not change color, does not bubble, and does not crack.

[0029] The test results are shown in Table 1, and are as follows: Table 1 As can be seen from the test results of Example 1 and Comparative Examples 1-2 in Table 1, compared with the use of n-butyl-1,1,3,3-tetramethyldisiloxane-modified cashew phenol or conventional cashew phenol in the preparation of curing agents, the curing agent prepared by using 1,1,1,3,5,5,5-heptamethyltrisiloxane-modified cashew phenol exhibits better adhesion, impact resistance, salt spray corrosion resistance, and thermal cycling resistance when applied to epoxy coatings. This indicates that the introduction of 1,1,1,3,5,5,5-heptamethyltrisiloxane can improve the compatibility between cashew phenol and epoxy resin through its flexible siloxane segments, further enhancing the interfacial bonding force between the epoxy coating and the substrate, thereby achieving excellent mechanical properties, good weather resistance, and strong stability, meeting the requirements for long-term outdoor or harsh environments.

[0030] The test results of Examples 1-4 show that the curing agent prepared by the method provided by this invention exhibits good adhesion, impact resistance, salt spray corrosion resistance, and resistance to thermal cycling when applied to epoxy coatings. This indicates that by preparing 1,1,1,3,5,5,5-heptamethyltrisiloxane-modified cashew nut shell powder, the present invention introduces siloxane segments into the curing agent, fundamentally improving the material's resistance to high and low temperature cycling. Furthermore, the reaction with polyamines and formaldehyde forms a cross-linked network, enhancing mechanical properties and stability. Moreover, the test results of Examples 1 and 3-4 show that when the molar ratio of alicyclic amines, modified cashew nut shell powder, polyamines, and formaldehyde is within a suitable range, the resulting curing agent exhibits superior performance.

[0031] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A weather-resistant cashew nut shell epoxy curing agent, characterized in that, The raw materials for preparing the curing agent include the following components: modified cashew nut phenol, polyamine, and formaldehyde; the modified cashew nut phenol is 1,1,1,3,5,5,5-heptamethyltrisiloxane modified cashew nut phenol.

2. The weather-resistant cashew nut phenolic epoxy curing agent according to claim 1, characterized in that, The molar ratio of the modified cashew nut phenol, polyamine, and formaldehyde is 1:(1.7-2):(1.4-1.6).

3. The weather-resistant cashew nut shell epoxy curing agent according to claim 1, characterized in that, The synthesis of the modified cashew phenol includes the following steps: (1) In an inert gas atmosphere, acetic anhydride and cashew phenol were added to a flask equipped with a reflux condenser. The mixture was heated and stirred in an oil bath at 110-130℃ for 2-4 hours. After the reaction was completed, cashew phenol acetate was obtained. (2) In an inert gas atmosphere, cashew phenol acetate, 1,1,1,3,5,5,5-heptamethyltrisiloxane and platinum catalyst were added to a flask equipped with a reflux condenser. The reaction was carried out at 110-130℃ for 3-6 h. After the reaction was completed, the product was post-processed to obtain 1,1,1,3,5,5,5-heptamethyltrisiloxane cashew phenol acetate. (3) Under an inert gas atmosphere, add 1,1,1,3,5,5,5-heptamethyltrisiloxane cashew phenol acetate and dilute hydrochloric acid solution to a flask equipped with a reflux condenser. React for 2-4 hours. After the reaction is completed, perform post-treatment to obtain 1,1,1,3,5,5,5-heptamethyltrisiloxane modified cashew phenol.

4. The weather-resistant cashew phenol-based epoxy curing agent according to claim 1, characterized in that, The cashew phenol is a monoene cashew phenol.

5. The weather-resistant cashew nut shell epoxy curing agent according to claim 3, characterized in that, In step (2), the molar ratio of cashew phenol acetate to 1,1,1,3,5,5,5-heptamethyltrisiloxane is 1.2-1.5:

1.

6. The weather-resistant cashew nut shell epoxy curing agent according to claim 3, characterized in that, The platinum catalyst in step (2) is platinum(0)-1,3-diethylene-1,1,3,3-tetramethyldisiloxane.

7. The weather-resistant cashew nut shell epoxy curing agent according to claim 3, characterized in that, The concentration of the dilute hydrochloric acid solution in step (3) is 0.5-1.5 mol / L.

8. The weather-resistant cashew nut shell epoxy curing agent according to claim 1, characterized in that, The polyamine is an alicyclic amine; the polyamine is at least one of isophorone diamine, cyclohexane diamine, and 4,4'-diaminodicyclohexylmethane.

9. A weather-resistant cashew nut shell epoxy curing agent according to claim 8, characterized in that, The polyamine is at least one of isophorone diamine and cyclohexanediamine.

10. A method for preparing a weather-resistant cashew phenol-based epoxy curing agent according to any one of claims 1-9, characterized in that, Includes the following steps: Modified cashew phenol was added to a flask, and polyamine was slowly added dropwise while stirring at 40-60℃. After the addition was completed, the temperature was raised to 60℃-70℃, and formaldehyde was added in batches. The mixture was stirred and mixed evenly, and the temperature was raised to 80-90℃ and kept at that temperature for 1-3 hours. Then the temperature was raised to 100-120℃ and the reaction was continued for 1-2 hours. After the reaction was completed, the cashew phenol epoxy curing agent was obtained through post-treatment.

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