A high-crosslinked high-temperature resistant phenolic epoxy resin and its preparation method

Abstract

A highly cross-linked, high-temperature-resistant novolac epoxy resin and a preparation method thereof are disclosed. The preparation method comprises first uniformly mixing a novolac epoxy prepolymer with an amino monomer, fully reacting the mixture at 0-100°C to obtain a novolac epoxy resin prepolymer with ring-opened epoxy groups. The novolac epoxy resin prepolymer with ring-opened epoxy groups is then uniformly mixed with an acyl chloride monomer, and cross-linked at 0-80°C to obtain the highly cross-linked, high-temperature-resistant novolac epoxy resin. This method not only simplifies the preparation steps and allows for rapid cross-linking at relatively low temperatures, significantly reducing the construction difficulty of thermal insulation coatings, but also produces a high degree of cross-linking and excellent high-temperature resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and specifically relates to a highly cross-linked, high-temperature resistant phenolic epoxy resin and a preparation method thereof. The present invention is suitable for increasing the cross-linking degree of the phenolic epoxy resin while reducing the cross-linking curing temperature of the phenolic epoxy resin, thereby greatly reducing the difficulty of constructing a thermal insulation coating. Background Art

[0002] In the petrochemical, marine, and heating sectors, energy lost to heat dissipation in pipes accounts for approximately one-third of total energy consumption each year. Excessive heat dissipation in pipes can also deteriorate the working environment, posing numerous safety risks to production and operations. Thermal insulation technology is an important way to reduce energy dissipation and improve the working environment.

[0003] Thermal insulation coatings are a new type of functional coating that leverages heat transfer mechanisms to specifically reduce heat transfer within the substrate. Compared to traditional insulation materials, they offer a simpler application process and can fully cover special-shaped components such as elbows, tees, and valves. They also offer excellent insulation performance, making damage to equipment and pipelines easily detectable, significantly reducing system maintenance effort and costs. The coating's barrier effect also effectively prevents the accumulation of corrosion factors on pipeline surfaces, slowing the corrosion rate of equipment and insulation systems and extending their service life.

[0004] Long-lasting high-temperature resistant resin is one of the core components of thermal insulation coatings. The heat resistance of the resin determines the service life and thermal insulation capacity of the coating. Phenolic epoxy resin, also known as F-type epoxy resin, is a thermosetting polymer resin with excellent comprehensive performance and a wide range of uses. It can provide many cross-linking points when cured, and it is very easy to form a three-dimensional structure with a high degree of cross-linking. It has the properties of both phenolic resin and epoxy resin, and has excellent heat resistance, corrosion resistance and good strength. In particular, it plays an important role as a matrix adhesive resin in the preparation and application of composite materials. Compared with typical high-temperature resistant resins such as silicone, organic fluorine and polyimide, phenolic epoxy resin has become the main matrix resin for general thermal insulation coatings and an important future development direction because of its advantages such as easy availability of raw materials, low cost, high degree of cross-linking and high adhesion to the substrate.

[0005] Improving the comprehensive heat resistance of epoxy novolac resins is a key research focus. To improve the heat resistance of epoxy novolac resins, on the one hand, it is necessary to increase the Tg by introducing large rigid groups into the molecular skeleton, such as naphthol, fluorene, biphenyl, and bisphenol, which have relatively large rigid structures. However, the improvement in thermal properties is generally inversely correlated with the solubility, melt viscosity, and other processability properties of epoxy novolac resins. In other words, if large rigid groups are introduced into the molecular structure, the solubility in common solvents such as acetone and ethylene glycol monomethyl ether may be reduced, and the melt viscosity may be significantly increased, which is not conducive to processing and coating film formation. Therefore, in future research, major research institutions at home and abroad are seeking to achieve a balanced cross-linking of epoxy novolac resins. On the other hand, the high-temperature resistance of the resin is related to the degree of cross-linking. It is necessary to increase the cross-linking degree of epoxy novolac resins as much as possible. In addition, the cross-linking and curing of epoxy novolac resins requires a relatively high reaction temperature, usually above 50°C, and some reactions even require 150°C. Only at a high reaction temperature can the cross-linking and curing rate reach a high level. However, higher cross-linking and curing temperatures not only increase the production cost and safety risks of thermal insulation materials, but are also extremely unfavorable for the construction and maintenance of thermal insulation coatings. Summary of the Invention

[0006] The purpose of the present invention is to overcome the above problems existing in the prior art and provide a high-crosslinked high-temperature resistant novolac epoxy resin and a preparation method thereof, which can improve the crosslinking degree of the novolac epoxy resin and reduce the crosslinking curing temperature of the novolac epoxy resin.

[0007] To achieve the above objectives, the present invention provides the following technical solutions:

[0008] A highly cross-linked, high-temperature resistant novolac epoxy resin, comprising a novolac epoxy prepolymer segment, an amino monomer segment, and an acyl chloride monomer segment, wherein the highly cross-linked, high-temperature resistant novolac epoxy resin has the following structure:

[0009]

[0010] In the above formula, R1 and R2 are aliphatic or aromatic alkane structures, R3 is an amino structure or an ether structure having a functionality equal to or greater than 2, and m and n are the numbers of repeating chain structural units.

[0011] Calculated by mass percentage of the total high-crosslinked high-temperature resistant novolac epoxy resin, the contents of the novolac epoxy prepolymer segment, the amino monomer segment and the acyl chloride monomer segment are 20-80wt%, 5-50wt% and 5-60wt% respectively.

[0012] Calculated by mass percentage of the total high-crosslinked high-temperature resistant novolac epoxy resin, the contents of the novolac epoxy prepolymer segment, the amino monomer segment and the acyl chloride monomer segment are 30-70wt%, 10-40wt% and 10-50wt% respectively.

[0013] A method for preparing a highly cross-linked, high-temperature resistant phenolic epoxy resin, the method comprising the following steps in sequence:

[0014] S1. Evenly mixing the phenolic epoxy prepolymer and the amino monomer, and fully reacting them at 0-100° C. to obtain a phenolic epoxy resin prepolymer after the epoxy group is ring-opened;

[0015] S2. Evenly mix the phenolic epoxy resin prepolymer after the epoxy group is ring-opened with the acyl chloride monomer, and cross-link them at 0-80° C. to obtain a highly cross-linked high-temperature resistant phenolic epoxy resin.

[0016] In step S1, the novolac epoxy prepolymer and the amino monomer are dissolved in a first solvent for a ring-opening reaction, wherein the first solvent comprises any one or a combination of two or more of tetrahydrofuran, dichloromethane, acetone, butanone, toluene, xylene, and ethyl acetate.

[0017] In step S2, the phenolic epoxy resin prepolymer after the epoxy group ring opening and the acyl chloride monomer are dissolved in a second solvent for cross-linking, and the second solvent includes any one or a combination of two or more of acetone, tetrahydrofuran, dichloromethane, chloroform, diethyl ether, toluene, xylene, n-butyl ether, butanone, methyl ethyl ketone, and ethyl acetate.

[0018] In step S1, the ring-opening reaction lasts for 1 h to 3 d;

[0019] In step S2, the cross-linking reaction time is 5 minutes to 48 hours.

[0020] The novolac epoxy resin prepolymer includes any one of phenol-type novolac epoxy resin, bisphenol A-type novolac epoxy resin, and o-cresol-type epoxy resin, or a combination of two or more thereof.

[0021] The amino monomer includes any one or a combination of two or more of ethylenediamine, propylenediamine, diethylenetriamine, triethylenetetramine, piperazine, aminoethylpiperazine, phenylenediamine, cyclohexanediamine, triethylamine, diaminodiphenylmethane, diaminodiphenyl ether, diaminodiphenyl sulfone, phenylenediamine, benzyldimethylamine, isophoronediamine, 1,4-diaminopiperazine, diaminofluorene, diaminonaphthalene, 1,3,5-triaminobenzene, and 1,3,6-triaminohexane.

[0022] The acyl chloride monomer includes any one or a combination of two or more of phthaloyl chloride, succinoyl chloride, 1,7-heptanedioyl chloride, 4,4'-diphenyl ether dichloride, fumaric dichloride, 1,4-cyclohexanedichloride, 2,5-furandicarboxylic acid chloride, pyridinedicarboxylic acid chloride, 1,3-adamantanedioyl chloride, 3,4-thiophenedioyl chloride, naphthalene dicarboxylic acid chloride, and ferrocene dicarboxylic acid chloride.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention discloses a method for preparing a high-crosslinked high-temperature resistant phenolic epoxy resin. First, a phenolic epoxy prepolymer and an amino monomer are uniformly mixed, and after sufficient reaction at 0-100°C, an epoxy group-ring-opened phenolic epoxy resin prepolymer is obtained. Then, the epoxy group-ring-opened phenolic epoxy prepolymer and an acyl chloride monomer are uniformly mixed, and after crosslinking at 0-80°C, a high-crosslinked high-temperature resistant phenolic epoxy resin is obtained. Since the hydroxyl groups generated by the phenolic epoxy resin prepolymer after ring opening have low activity, they are difficult to be end-capped and cross-linked again, thereby becoming deterioration sites and molecular chain segment breakage points under high-temperature environments, thereby reducing the high-temperature resistance of the resin. On the one hand, the present invention utilizes a difunctional or multifunctional amino monomer as The "ring-opening agent" of the phenolic epoxy prepolymer makes the phenolic epoxy prepolymer after ring opening have more active functional groups and higher reactivity, makes full use of the hydroxyl group generated after the ring opening of the epoxy group and the amino group on the grafted end as a crosslinking point, significantly improves the crosslinking degree of the phenolic epoxy resin, thereby improving the high temperature resistance of the phenolic epoxy resin, on the other hand, compared with the crosslinking agent curing agent in the traditional high temperature resistant phenolic epoxy resin preparation technology, the acyl chloride has extremely high reactivity, not only can have high reactivity with the amino group, but also can efficiently react with the hydroxyl group generated after the ring opening of the epoxy group to generate an ester group, can be cross-linked and cured at a lower temperature, and then greatly reduce the construction difficulty of the thermal insulation coating. Therefore, the present invention can not only significantly improve the crosslinking degree of the phenolic epoxy resin, improve the high temperature resistance of the phenolic epoxy resin, but also can be cross-linked and cured at a lower temperature, greatly reducing the construction difficulty of the thermal insulation coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a reaction principle diagram of the present invention. DETAILED DESCRIPTION

[0026] The present invention will be further described below with reference to the accompanying drawings and specific implementation methods.

[0027] A highly cross-linked, high-temperature resistant novolac epoxy resin, comprising a novolac epoxy prepolymer segment, an amino monomer segment, and an acyl chloride monomer segment, wherein the highly cross-linked, high-temperature resistant novolac epoxy resin has the following structure:

[0028]

[0029] In the above formula, R1 and R2 are aliphatic or aromatic alkane structures, R3 is an amino structure or an ether structure having a functionality equal to or greater than 2, and m and n are the numbers of repeating chain structural units.

[0030] Calculated by mass percentage of the total high-crosslinked high-temperature resistant novolac epoxy resin, the contents of the novolac epoxy prepolymer segment, the amino monomer segment and the acyl chloride monomer segment are 20-80wt%, 5-50wt% and 5-60wt% respectively.

[0031] Calculated by mass percentage of the total high-crosslinked high-temperature resistant novolac epoxy resin, the contents of the novolac epoxy prepolymer segment, the amino monomer segment and the acyl chloride monomer segment are 30-70wt%, 10-40wt% and 10-50wt% respectively.

[0032] See also Figure 1 A method for preparing a highly cross-linked, high-temperature resistant phenolic epoxy resin, the method comprising the following steps:

[0033] S1. Evenly mixing the phenolic epoxy prepolymer and the amino monomer, and fully reacting them at 0-100° C. to obtain a phenolic epoxy resin prepolymer after the epoxy group is ring-opened;

[0034] S2. Evenly mix the phenolic epoxy resin prepolymer after the epoxy group is ring-opened with the acyl chloride monomer, and cross-link them at 0-80° C. to obtain a highly cross-linked high-temperature resistant phenolic epoxy resin.

[0035] In step S1, the novolac epoxy prepolymer and the amino monomer are dissolved in a first solvent for a ring-opening reaction, wherein the first solvent comprises any one or a combination of two or more of tetrahydrofuran, dichloromethane, acetone, butanone, toluene, xylene, and ethyl acetate.

[0036] In step S2, the phenolic epoxy resin prepolymer after the epoxy group ring opening and the acyl chloride monomer are dissolved in a second solvent for cross-linking, and the second solvent includes any one or a combination of two or more of acetone, tetrahydrofuran, dichloromethane, chloroform, diethyl ether, toluene, xylene, n-butyl ether, butanone, methyl ethyl ketone, and ethyl acetate.

[0037] In step S1, the ring-opening reaction lasts for 1 h to 3 d;

[0038] In step S2, the cross-linking reaction time is 5 minutes to 48 hours.

[0039] The novolac epoxy resin prepolymer includes any one of phenol-type novolac epoxy resin, bisphenol A-type novolac epoxy resin, and o-cresol-type epoxy resin, or a combination of two or more thereof.

[0040] The amino monomer includes any one or a combination of two or more of ethylenediamine, propylenediamine, diethylenetriamine, triethylenetetramine, piperazine, aminoethylpiperazine, phenylenediamine, cyclohexanediamine, triethylamine, diaminodiphenylmethane, diaminodiphenyl ether, diaminodiphenyl sulfone, phenylenediamine, benzyldimethylamine, isophoronediamine, 1,4-diaminopiperazine, diaminofluorene, diaminonaphthalene, 1,3,5-triaminobenzene, and 1,3,6-triaminohexane.

[0041] The acyl chloride monomer includes any one or a combination of two or more of phthaloyl chloride, succinoyl chloride, 1,7-heptanedioyl chloride, 4,4'-diphenyl ether dichloride, fumaric dichloride, 1,4-cyclohexanedichloride, 2,5-furandicarboxylic acid chloride, pyridinedicarboxylic acid chloride, 1,3-adamantanedioyl chloride, 3,4-thiophenedioyl chloride, naphthalene dicarboxylic acid chloride, and ferrocene dicarboxylic acid chloride.

[0042] The principle of the present invention is described as follows:

[0043] In view of the shortcomings of existing phenolic epoxy resin technology in terms of high cross-linking temperature, low cross-linking density and poor high temperature resistance of the product, the present invention provides a method for preparing a highly cross-linked and high temperature resistant phenolic epoxy resin by adopting a highly reactive acyl chloride as a cross-linking curing agent, thereby increasing the number of chemical cross-linking sites and reducing the cross-linking temperature, and utilizing the hydroxyl group generated after the epoxy ring opening as the second cross-linking point, thereby significantly improving the cross-linking density of the phenolic epoxy resin. After cross-linking and drying, a highly cross-linked and high temperature resistant phenolic epoxy resin is obtained, or a highly cross-linked and high temperature resistant phenolic epoxy resin coating is obtained after being coated on the surface of a substrate, cross-linked, cured and dried. This preparation method is not only simple in process and can be quickly cross-linked at a relatively low temperature, but also has readily available raw materials and is easy to use. The prepared phenolic epoxy resin has a high degree of cross-linking, and the mechanical strength and toughness of the resin and the applied coating can be adjusted over a wide range by adjusting the R1 and R2 segment structures. It has excellent high temperature resistance and has good application prospects.

[0044] During the preparation of the epoxy novolac prepolymer after epoxy ring-opening, it is necessary to ensure that the molar number of amino functional groups in the reaction system is greater than the molar number of epoxy groups in the prepolymer, with a preferred molar ratio of amino to epoxy groups being 1.5-4:1. This amino excess ratio has the key advantages of fully promoting the complete ring-opening of epoxy groups, increasing the crosslinking density of the epoxy novolac resin in the later stages, and preventing residual epoxy groups from affecting the resin's heat resistance. Furthermore, it effectively reduces the degree of crosslinking and curing of the epoxy novolac system at this stage, as well as the viscosity of the reaction system, providing favorable reaction conditions for the subsequent crosslinking and curing of the acyl chloride monomer.

[0045] The reaction conditions of the amino monomer ring-opening phenolic epoxy prepolymer are selected as a reaction temperature of 0-100°C and a reaction time of 1h-3d. The purpose is to increase the ring-opening speed and degree of the epoxy group by appropriately increasing the reaction temperature and reaction time, thereby improving the later crosslinking density and heat resistance.

[0046] The key role of adding the first and second solvents to the reaction system for preparing the epoxy novolac resin is to reduce the viscosity of the reaction system, accelerate the rapid and uniform mixing of the reaction raw materials, and avoid implosion caused by excessively rapid reaction rates. Furthermore, for the preparation of thermal insulation coatings, the addition of an appropriate amount of solvent facilitates the formation of a porous structure during the coating curing and drying process, thereby improving the thermal insulation properties of the coating. It is worth noting that for some reaction systems with lower viscosities, the addition of the first and second solvents is not necessary.

[0047] Example 1:

[0048] A method for preparing a highly cross-linked, high-temperature resistant phenolic epoxy resin is specifically carried out according to the following steps:

[0049] S1. First, add diaminodiphenylmethane and toluene solvent to a reaction flask equipped with a stirrer, a thermometer, a dropping funnel and a reflux condenser, slowly heat it to 80°C, then add the phenolic epoxy resin toluene solution (F51) dropwise while stirring, and control the molar ratio of the raw material amino group to the epoxy group to be 2:1. The addition time is controlled to be 1.5h. After the addition is completed, the reaction is continued at this temperature for 4h, and then cooled to room temperature to obtain a phenolic epoxy prepolymer solution after diaminodiphenylmethane ring opening. The ring opening reaction process is as follows:

[0050]

[0051] S2. Dissolving phthaloyl chloride in a toluene solution to obtain a toluene solution of phthaloyl chloride, and then adding the toluene solution to a novolac epoxy prepolymer solution obtained by ring-opening diaminodiphenylmethane, controlling the molar ratio of phthaloyl chloride to diaminodiphenylmethane in the raw materials to be 1:1, stirring thoroughly and continuing the reaction for 24 hours, and removing excess solvent to obtain a novolac epoxy resin cross-linked with acyl chloride. The chemical cross-linking process is as follows:

[0052]

[0053] Conventional phenolic epoxy resin preparation technology uses direct curing by directly adding ammonia or other curing agents, resulting in a large number of unreacted reactive functional groups (hydroxyl, amino, etc.) remaining in the resin, which in turn affects its thermal performance. This embodiment performs a ring-opening-crosslinking process on the phenolic epoxy prepolymer in steps and uses an acyl chloride monomer as a curing agent, thereby increasing the crosslinking reaction activity and reducing the number of unreacted reactive functional groups (hydroxyl, amino, etc.). This theoretically and practically improves the crosslinking chemical crosslink density and heat resistance.

[0054] For the preparation of the phenolic epoxy resin coating, a toluene solution of phthaloyl chloride and a phenolic epoxy prepolymer solution obtained by ring-opening diaminodiphenylmethane were mixed and stirred, and then coated on the substrate surface. After cross-linking and curing at room temperature for 24 hours and solvent evaporation, the phenolic epoxy resin coating was obtained.

[0055] For the preparation of phenolic epoxy resin-based thermal insulation coating, the phenolic epoxy prepolymer solution after ring-opening of diaminodiphenylmethane is fully mixed with fillers and additives such as hollow glass microspheres, and then a toluene solution of phthaloyl chloride is added and fully stirred, and then coated on the surface of the substrate. After 24 hours of cross-linking and solvent evaporation at room temperature, the phenolic epoxy resin-based thermal insulation coating is obtained.

[0056] Example 2:

[0057] A method for preparing a highly cross-linked, high-temperature resistant phenolic epoxy resin is specifically carried out according to the following steps:

[0058] S1. First, piperazine and tetrahydrofuran solvent are fully mixed, and then added to a reaction flask with a stirrer, a thermometer, a dropping funnel and a reflux condenser. The temperature is slowly raised to 70°C, and a phenolic epoxy resin toluene solution (F51) is added dropwise while stirring. The molar ratio of the raw material piperazine and the epoxy group is controlled to be 1:1. The addition time is controlled to be about 2 hours. After the addition is completed, the reaction is continued at this temperature for 8 hours, and then cooled to room temperature to obtain a phenolic epoxy prepolymer solution after piperazine ring opening. The ring-opening reaction process is as follows:

[0059]

[0060] S2. Dissolve 1,4-cyclohexanediyl chloride in anhydrous tetrahydrofuran solution to obtain a mixed solution, then add the mixed solution to the phenolic epoxy prepolymer solution after piperazine ring opening, control the molar ratio of 1,4-cyclohexanediyl chloride to piperazine in the raw materials to be 1:1, fully stir and continue the reaction for 24 hours, remove excess solvent to obtain acyl chloride cross-linked phenolic epoxy resin, the chemical cross-linking process is as follows:

[0061]

[0062] In this embodiment, piperazine has a cyclohexane-like structure and has a certain degree of molecular flexibility. By introducing flexible groups into the novolac epoxy resin system, the mechanical properties of the resin can be controlled. In addition, piperazine has an imine structure and no residual active hydrogen after reaction with epoxy or acyl chloride, which can further improve the water resistance of the novolac epoxy resin and reduce its water absorption rate.

[0063] The preparation method of the phenolic epoxy resin coating and the phenolic epoxy resin-based thermal insulation coating is the same as that in Example 1.

[0064] Example 3:

[0065] Same as Example 2, except that:

[0066] In step S1, aminoethylpiperazine and tetrahydrofuran solvent are first fully mixed, and then added to a reaction flask equipped with a stirrer, a thermometer, a dropping funnel and a reflux condenser. The temperature is slowly raised to 40° C., and a phenolic epoxy resin toluene solution (F51) is added to the mixture of aminoethylpiperazine and tetrahydrofuran solvent at one time while stirring to carry out a ring-opening reaction to obtain a phenolic epoxy prepolymer solution after aminoethylpiperazine ring-opening. The ring-opening reaction process is as follows:

[0067]

[0068] In step S2, the chemical cross-linking process is as follows:

[0069]

[0070] In this embodiment, the two imino groups in piperazine have similar chemical environments and identical reactivity. After one of the amino groups in piperazine participates in the ring-opening of the epoxy group, the reactivity of the remaining imino group in piperazine is essentially the same as that of the imino group in piperazine. Therefore, crosslinking is likely to occur during the ring-opening reaction of the epoxy group. Excessive crosslinking can easily lead to increased viscosity of the system, even to the formation of an insoluble solid, which is undesirable. However, the amino group in aminoethylpiperazine has higher reactivity than the amino group, and the epoxy group preferentially reacts with the primary amine, effectively avoiding the possibility of crosslinking. Furthermore, thanks to the higher reactivity of the aliphatic primary amine, the reaction can also be carried out at a lower temperature. In summary, this embodiment improves the preparation method and simplifies the reaction process by replacing the difunctional amino ring-opening monomer with a significantly different reactivity.

[0071] The preparation method of the phenolic epoxy resin coating and the phenolic epoxy resin-based thermal insulation coating is the same as that in Example 1.

[0072] Example 4:

[0073] Same as Example 2, except that:

[0074] In step S2, naphthalene dichloride is dissolved in anhydrous tetrahydrofuran solution to obtain a mixed solution, which is then added to the phenolic epoxy prepolymer solution after piperazine ring opening to perform chemical crosslinking. The chemical crosslinking process is as follows:

[0075]

[0076] In this embodiment, 1,4-cyclohexanediyl chloride is mainly composed of cyclohexane and has a certain molecular flexibility, while the diacyl naphthalene chloride has two connected phenyl groups, the molecular rigidity is very large, and the molecular structure is more stable, so it has a higher pyrolysis temperature and heat resistance. This embodiment can effectively improve the heat resistance of the phenolic epoxy resin by introducing a strong rigid chain segment into the acyl chloride monomer.

[0077] The preparation method of the phenolic epoxy resin coating and the phenolic epoxy resin-based thermal insulation coating is the same as that in Example 1.

[0078] Example 5:

[0079] A method for preparing a highly cross-linked, high-temperature resistant phenolic epoxy resin is specifically carried out according to the following steps:

[0080] Step S1: slowly adding the novolac epoxy resin (F51) to tris(2-aminoethyl)amine in three batches at room temperature and continuously stirring for 2 hours. The molar ratio of amino groups to epoxy groups in the raw materials is controlled to be 3:1. After the novolac epoxy resin is completely added, the reaction is continued at room temperature for 24 hours to obtain a novolac epoxy prepolymer solution after the tris(2-aminoethyl)amine ring-opening reaction. The ring-opening reaction process is as follows:

[0081]

[0082] Step S2: adding succinyl chloride to the novolac epoxy prepolymer solution after ring-opening with tris(2-aminoethyl)amine at room temperature, controlling the molar ratio of succinyl chloride to tris(2-aminoethyl)amine in the raw material to be 3:2, rapidly and thoroughly stirring and continuing the reaction for 24 hours, controlling the reaction temperature at 30° C., and obtaining a novolac epoxy resin cross-linked with acyl chloride after chemical cross-linking. The chemical cross-linking process is as follows:

[0083]

[0084] In this embodiment, the ring-opening monomer tris(2-aminoethyl)amine and the cross-linking monomer succinyl chloride are both liquid at room temperature, which is conducive to the uniform mixing of the reaction raw materials. By using monomers that are liquid at room temperature, this embodiment can avoid using any solvents in the preparation process of the phenolic epoxy resin, thereby simplifying the preparation process.

[0085] The preparation method of the phenolic epoxy resin coating and the phenolic epoxy resin-based thermal insulation coating is the same as that in Example 1.

[0086] Performance Testing

[0087] 1. Preparation of Comparative Examples 1-3

[0088] Comparative Example 1:

[0089] Diaminodiphenylmethane and toluene solvent are fully mixed to form a toluene solution of diaminodiphenylmethane, which is then added to a toluene solution of a phenolic epoxy resin (F51) and stirred thoroughly. The molar ratio of the amino group and the epoxy group of the raw materials is controlled to be 1:1. The temperature is slowly raised to 80°C and the reaction is continued at this temperature for 6 hours. After removing the excess solvent, a diaminodiphenylmethane-crosslinked phenolic epoxy resin is obtained. The chemical reaction in this process is as follows:

[0090]

[0091] For the preparation of the phenolic epoxy resin coating, a toluene solution of diaminodiphenylmethane and a phenolic epoxy prepolymer solution were fully stirred and the solution was made viscous before being coated on the substrate surface. The temperature was maintained at 80°C. After 24 hours of cross-linking and curing and solvent evaporation, the phenolic epoxy resin coating was obtained.

[0092] For the preparation of phenolic epoxy resin-based thermal insulation coating, the phenolic epoxy prepolymer solution is fully mixed with fillers such as hollow glass microspheres, additives and solvents, and then a toluene solution of diaminodiphenylmethane is added and fully stirred. The mixture is then coated on the surface of the substrate and the temperature is maintained at 80°C. After 24 hours of cross-linking and solvent evaporation, the phenolic epoxy resin-based thermal insulation coating is obtained.

[0093] Comparative Example 2:

[0094] The piperazine and tetrahydrofuran solvents were fully mixed, and then the mixture of piperazine and tetrahydrofuran was added to the toluene solution of the novolac epoxy resin (F51) and stirred thoroughly. The molar ratio of the amino group and epoxy group of the raw materials was controlled to be 1:1. The temperature was slowly raised to 80°C and the reaction was continued at this temperature for 6 hours. After removing the excess solvent, the piperazine-crosslinked novolac epoxy resin was obtained. The chemical reaction in this process is as follows:

[0095]

[0096] The preparation method of the phenolic epoxy resin coating and the phenolic epoxy resin-based thermal insulation coating is the same as that of Comparative Example 1.

[0097] Comparative Example 3:

[0098] Select heat-resistant phenolic epoxy resin F51 from Jiangsu Sanmu Group Co., Ltd.;

[0099] For the preparation of the phenolic epoxy resin coating, the heat-resistant phenolic epoxy resin F5 was mixed with the corresponding cross-linking agent and then coated on the substrate surface. After cross-linking and curing at room temperature for 24 hours and solvent evaporation, the phenolic epoxy resin coating was obtained.

[0100] For the preparation of phenolic epoxy resin-based thermal insulation coating, the heat-resistant phenolic epoxy resin F5 is fully mixed with fillers such as hollow glass microspheres, additives and solvents, and then the corresponding cross-linking agent is added and fully stirred. It is then coated on the surface of the substrate. After 24 hours of cross-linking and curing at room temperature and solvent evaporation, the phenolic epoxy resin-based thermal insulation coating is obtained.

[0101] 2. Performance comparison

[0102] The performance of the phenolic epoxy resin-based thermal insulation coatings prepared in Examples 1-5 and Comparative Examples 1-3 was tested, and the performance comparison results are shown in Table 1:

[0103] Table 1 Performance comparison results

[0104]

[0105] As can be seen from Table 1, the adhesion, temperature resistance, and salt spray resistance of the coatings prepared in Examples 1-5 are significantly higher than those in Comparative Examples 1-3, indicating that the preparation method of the present invention can indeed improve the crosslinking density of the phenolic epoxy resin, especially in terms of high temperature resistance. Moreover, the phenolic epoxy resins prepared in Examples 1-5 do not require additional heating in terms of film formation construction, just like the ordinary phenolic epoxy resins available on the market, thereby maintaining the convenience of construction. This is because the direct crosslinking and curing of the phenolic epoxy prepolymer with diaminodiphenylmethane in Comparative Example 1 and the piperazine in Comparative Example 2 requires a higher temperature to obtain a higher crosslinking density. Moreover, the amino group on diaminodiphenylmethane or the imine group on piperazine reacts with the epoxy group to produce a hydroxyl group. In this system, the hydroxyl group produced after the epoxy ring opening cannot serve as a crosslinking point for subsequent reactions and is easily oxidized and cracked at high temperatures, affecting the high temperature resistance of the resin. In addition, the hydroxyl group remaining after the epoxy ring opening reaction is a strong hydrophilic functional group, which causes the resin to have a certain hydrophilicity and a high water absorption rate, affecting its certain applications in the marine field.

Claims

1. A method for preparing a highly cross-linked, high-temperature resistant phenolic epoxy resin, characterized in that: The preparation method is used to prepare a highly cross-linked, high-temperature resistant novolac epoxy resin. The highly cross-linked, high-temperature resistant novolac epoxy resin is composed of a novolac epoxy prepolymer segment, an amino monomer segment, and an acyl chloride monomer segment. The highly cross-linked, high-temperature resistant novolac epoxy resin has the following structure: ； In the above formula, R1 and R2 are aliphatic or aromatic alkane structures, and m and n are the number of repeating chain structural units; The preparation method of the highly cross-linked high-temperature resistant phenolic epoxy resin comprises the following steps in sequence: S1. Evenly mixing the phenolic epoxy prepolymer and the amino monomer, and fully reacting them at 0-100° C. to obtain a phenolic epoxy resin prepolymer after the epoxy group is ring-opened; S2, uniformly mixing the phenolic epoxy resin prepolymer after the epoxy group ring opening and the acyl chloride monomer, and cross-linking at 0-80° C. to obtain a highly cross-linked high-temperature resistant phenolic epoxy resin; The acyl chloride monomer includes any one or a combination of two or more of phthaloyl chloride, succinoyl chloride, 1,7-heptanedioyl chloride, 4,4'-diphenyl ether dichloride, fumaric dichloride, 1,4-cyclohexanedichloride, 2,5-furandicarboxylic acid chloride, pyridinedicarboxylic acid chloride, 1,3-adamantanedioyl chloride, 3,4-thiophenedioyl chloride, naphthalene dicarboxylic acid chloride, and ferrocene dicarboxylic acid chloride.

2. The method for preparing a highly cross-linked high-temperature resistant phenolic epoxy resin according to claim 1, wherein: Calculated by weight percentage of the total high-crosslinked high-temperature resistant novolac epoxy resin, the contents of the novolac epoxy prepolymer segment, the amino monomer segment, and the acyl chloride monomer segment are 20-80wt%, 5-50wt%, and 5-60wt%, respectively.

3. The method for preparing a highly cross-linked high-temperature resistant phenolic epoxy resin according to claim 1, wherein: Calculated by weight percentage of the total high-crosslinked high-temperature resistant novolac epoxy resin, the contents of the novolac epoxy prepolymer segment, the amino monomer segment, and the acyl chloride monomer segment are 30-70wt%, 10-40wt%, and 10-50wt%, respectively.

4. The method for preparing a highly cross-linked high-temperature resistant phenolic epoxy resin according to claim 1, wherein: In step S1, the novolac epoxy prepolymer and the amino monomer are dissolved in a first solvent for a ring-opening reaction, wherein the first solvent comprises any one or a combination of two or more of tetrahydrofuran, dichloromethane, acetone, butanone, toluene, xylene, and ethyl acetate.

5. The method for preparing a highly cross-linked high-temperature resistant phenolic epoxy resin according to claim 4, wherein: In step S2, the phenolic epoxy resin prepolymer after the epoxy group ring opening and the acyl chloride monomer are dissolved in a second solvent for cross-linking, and the second solvent includes any one or a combination of two or more of acetone, tetrahydrofuran, dichloromethane, chloroform, diethyl ether, toluene, xylene, n-butyl ether, butanone, methyl ethyl ketone, and ethyl acetate.

6. The method for preparing a highly cross-linked high-temperature resistant phenolic epoxy resin according to claim 4, wherein: In step S1, the ring-opening reaction lasts for 1 h to 3 d; In step S2, the cross-linking reaction time is 5 minutes to 48 hours.

7. The method for preparing a highly cross-linked high-temperature resistant phenolic epoxy resin according to claim 4, wherein: The novolac epoxy resin prepolymer includes any one of phenol-type novolac epoxy resin, bisphenol A-type novolac epoxy resin, and o-cresol-type epoxy resin, or a combination of two or more thereof.

8. The method for preparing a highly cross-linked high-temperature resistant phenolic epoxy resin according to claim 4, wherein: The amino monomer includes any one or a combination of two or more of ethylenediamine, propylenediamine, diethylenetriamine, triethylenetetramine, piperazine, aminoethylpiperazine, phenylenediamine, cyclohexanediamine, triethylamine, diaminodiphenylmethane, diaminodiphenyl ether, diaminodiphenyl sulfone, phenylenediamine, benzyldimethylamine, isophoronediamine, diaminofluorene, diaminonaphthalene, 1,3,5-triaminobenzene, and 1,3,6-triaminohexane.

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