Preparation method and application of medium-temperature curing high-temperature resistant low-dielectric epoxy resin

Abstract

The present invention discloses a preparation method and application of a medium-temperature cured high-temperature resistant low-dielectric epoxy resin. The preparation method uses a cycloaliphatic diluent and a cyanate resin to prepare a cyanate oligomer, further reacts a multifunctional epoxy resin with a cyanate oligomer, and then performs a copolymerization reaction in the presence of an active agent to prepare a soluble cyanate-modified multifunctional epoxy resin, which is then compounded with a latent curing agent and an accelerator to prepare a high-temperature resistant low-dielectric epoxy resin, the resin can be cured at a medium temperature of 110-130°C, and the cured resin has good heat resistance and dielectric properties. The high-temperature resistant low-dielectric epoxy resin of the present invention can be applied to the field of composite material structural parts such as high-temperature resistant radar covers and antenna covers.

Description

Technical Field

[0001] The invention belongs to the field of composite materials, and particularly relates to a preparation method and application of a medium-temperature curing high-temperature resistant low-dielectric epoxy resin. Background Art

[0002] Wave-transmitting composite materials have good permeability to electromagnetic waves without changing the properties of electromagnetic waves. According to their use, wave-transmitting composite materials must have the following properties: (1) Dielectric properties, the dielectric constant is less than 3.5 in a wide frequency range, and the dielectric loss tangent is less than 0.02. (2) Thermal properties, a higher glass transition temperature (Tg) and a smaller thermal expansion coefficient in a larger operating temperature range. (3) Mechanical properties, as a load-bearing structural material, it has high strength and a certain rigidity at room temperature and high temperature (150°C), and the performance retention rate at 150°C is greater than 80%, to ensure that it will not deform or twist when subjected to stress at high temperature. On the other hand, most of the existing high-temperature resistant low-dielectric materials require medium- and high-temperature curing, and there are large residual stresses after curing, which affects the mechanical strength of large parts and the dimensional accuracy of the test pieces.

[0003] Although cyanate resin has good dielectric properties, heat resistance and mechanical properties, its curing temperature is high (≥180°C) and the curing time is long. Adding a catalyst can reduce the curing temperature of cyanate, but at the same time, there will be problems such as poor dielectric properties and shortened storage period at room temperature. In comparison, epoxy resin has good processing technology and mechanical properties, but the heat resistance of epoxy resin cured product is much lower than that of cyanate. A common improvement method is to introduce rigid groups such as benzene rings, naphthalene rings, biphenyls, heterocycles and condensed rings into the resin molecular skeleton. Chinese invention patent CN 105820513 A significantly improves the heat resistance of the product by using a matrix epoxy resin containing heat-resistant rigid groups such as aromatic rings and heterocycles on the molecular chain, but it still needs to be cured at 180-200°C to obtain good heat resistance, and the epoxy resin prepared by this method has high dielectric properties. Therefore, it is necessary to develop an epoxy resin system that can be cured at medium temperature (110-130°C) and have good heat resistance and dielectric properties. Summary of the invention

[0004] One of the technical problems to be solved by the present invention is that the epoxy resin prepared by the prior art has poor dielectric properties, insufficient temperature resistance and usually requires high temperature to obtain, which makes it difficult to meet the molding process and performance requirements of high-temperature resistant low-dielectric prepregs in radar covers and radomes. To this end, the present invention provides a medium-temperature curing high-temperature resistant low-dielectric epoxy resin. By reasonably controlling the self-polymerization reaction of cyanate ester, a soluble cyanate-modified multifunctional epoxy resin is obtained. The triazine ring generated by the cyanate ester significantly improves the heat resistance and dielectric properties of the resin, and a promoter is added to achieve medium-temperature curing of the resin.

[0005] The second technical problem to be solved by the present invention is to provide a method for preparing a medium-temperature curing high-temperature resistant low-dielectric epoxy resin, which comprises the following steps:

[0006] (1) Preparation of cyanate oligomer: reacting alicyclic diluent and cyanate resin at 100-140° C. until the viscosity of the material reaches 10,000-20,000 cps, and then stopping the reaction to obtain cyanate oligomer;

[0007] (2) Preparation of soluble cyanate modified multifunctional epoxy resin: a multifunctional epoxy resin is mixed with the above-mentioned cyanate oligomer, and the reaction is continued at 100-140° C. until the viscosity of the material increases to 30,000-60,000 cps; the temperature is lowered to 80-130° C., an activator is added, and the reaction is continued until the viscosity of the material reaches 40,000-100,000 cps, and the reaction is stopped to obtain a soluble cyanate modified multifunctional epoxy resin;

[0008] (3) Preparation of medium temperature curing high temperature resistant low dielectric epoxy resin: The soluble cyanate modified multifunctional epoxy resin is adjusted to a temperature of 60-80°C, and a latent curing agent and an accelerator are added to obtain a medium temperature curing high temperature resistant low dielectric epoxy resin.

[0009] In certain embodiments, according to the method for preparing the medium-temperature curing high-temperature resistant low-dielectric epoxy resin of the present invention, the mass ratio of the alicyclic diluent to the cyanate ester resin is (15-30):100.

[0010] In certain embodiments, according to the method for preparing the medium-temperature curing high-temperature resistant low-dielectric epoxy resin of the present invention, the mass ratio of the multifunctional epoxy resin to the soluble cyanate-modified multifunctional epoxy resin is (35-65.5):100.

[0011] In certain embodiments, according to the method for preparing the medium-temperature curing high-temperature resistant low-dielectric epoxy resin of the present invention, the mass ratio of the cyanate ester to the soluble cyanate ester modified multifunctional epoxy resin is (30-50):100.

[0012] In certain embodiments, according to the method for preparing the medium-temperature curing high-temperature resistant low-dielectric epoxy resin of the present invention, the mass ratio of the activator to the soluble cyanate-modified multifunctional epoxy resin is (0.3-5):100.

[0013] In certain embodiments, according to the method for preparing a medium-temperature curing high-temperature resistant low-dielectric epoxy resin of the present invention, the mass ratio of the soluble cyanate-modified multifunctional epoxy resin, the curing agent and the accelerator is 100:(8-13):(0.1-0.8).

[0014] In certain embodiments, according to the method for preparing a medium-temperature curing high-temperature resistant low-dielectric epoxy resin of the present invention, the cyanate ester resin includes at least one of bisphenol A cyanate ester, bisphenol E cyanate ester, bisphenol M cyanate ester and dicyclopentadiene bisphenol cyanate ester.

[0015] In certain embodiments, according to the method for preparing a medium-temperature-cured, high-temperature-resistant, low-dielectric epoxy resin of the present invention, the alicyclic diluent includes at least one of 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylate, bis(7-oxabicyclo[4.1.0]3-heptylmethyl)adipate, 3,4-epoxycyclohexanecarboxylic acid methyl ester, 1,4-cyclohexanedimethanol bis(3,4-epoxycyclohexanecarboxylic acid) ester and dicyclopentadiene epoxide.

[0016] In certain embodiments, according to the method for preparing a medium-temperature curing high-temperature resistant low-dielectric epoxy resin of the present invention, the multifunctional epoxy resin includes at least one of 4,4'-diaminodiphenylmethane tetraglycidylamine epoxy resin, N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenyl ether and tetraglycidyl-3,4'-diaminodiphenyl ether.

[0017] In certain embodiments, according to the method for preparing the medium-temperature curing high-temperature resistant low-dielectric epoxy resin of the present invention, the curing agent is dicyandiamide.

[0018] In certain embodiments, according to the method for preparing the medium temperature curing high temperature resistant low dielectric epoxy resin of the present invention, the accelerator is a urea or imidazole accelerator, such as 2-methylimidazole and 2-phenylimidazole.

[0019] In certain embodiments, according to the method for preparing a medium-temperature curing high-temperature resistant low-dielectric epoxy resin of the present invention, the activator is at least one of 4,4-diaminodiphenyl ether, 4,4-diaminodiphenyl sulfone and 3,3-diaminodiphenyl sulfone.

[0020] The present invention also provides a high temperature resistant low dielectric prepreg, which comprises the high temperature low dielectric epoxy resin material capable of being cured at a medium temperature of 110-130° C. described in the present invention.

[0021] The present invention also provides application of the high temperature resistant low dielectric prepreg of the present invention in radar covers and radomes.

[0022] The present invention has the following advantages:

[0023] First, by utilizing the characteristics of high activation energy and slow reaction speed of the reaction between alicyclic diluents and cyanate ester resins, low-viscosity alicyclic diluents are used as solvents for the self-polymerization of cyanate ester resins to increase the conversion rate of cyanate ester monomers to form triazine rings. On the other hand, after adding multifunctional epoxy resins, cyanate ester oligomers can further self-polymerize to form triazine ring structures, thereby significantly improving the heat resistance and dielectric properties of the resin system.

[0024] Second, the addition of the active agent can react with the cyanate oligomer and the multifunctional epoxy resin at the same time, which not only improves the cyanate conversion rate and reduces the residual -OCN group in the cyanate ester, but also ensures the solubility of the cyanate polymer in the multifunctional epoxy resin, thereby giving full play to the advantages of the heat resistance and dielectric properties of the cyanate. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is the Tg(DMA) of the resin in Example 1 of the present invention after being cured at 130°C for 4 hours.

[0026] Figure 2 It is the Tg(DMA) of the resin in Example 2 of the present invention after being cured at 120°C for 6h.

[0027] Figure 3 It is the Tg(DMA) of the resin in Example 3 of the present invention after being cured at 110°C for 8h. DETAILED DESCRIPTION

[0028] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0029] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that the upper and lower limits of the scope and each intermediate value therebetween are specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0030] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which the invention belongs. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0031] Preparation method

[0032] One aspect of the present invention provides a method for preparing a high temperature resistant low dielectric epoxy resin. In a preferred embodiment, the preparation method of the present invention comprises the following steps:

[0033] (1) Preparation of cyanate oligomer: An alicyclic diluent and a cyanate resin are reacted at 100-140° C. (preferably 100-138° C., more preferably 100-136° C., further preferably 100-134° C., more preferably 100-132° C., more preferably 100-130° C., for example, 100° C., 102° C., 104° C., 106° C., 108° C., 110° C., 112° C., 114° C., 116° C., 118° C., 120° C., 122° C., 124° C., 126° C., 128° C., 130° C.) for 3-6 h (preferably 3.1-5.9 h, further preferably 3.2-5.8 h, further preferably 3.3- 5.7h, more preferably 3.4-5.6h, more preferably 3.5-5.5h, for example 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5h), until the viscosity of the material reaches 10000-20000cps (for example 11000, 12000, 13000, 14000, 15000, 16000, 17000, 18000, 19000, 20000cps) and then stop the reaction to obtain a cyanate oligomer;

[0034] (2) Preparation of soluble cyanate-modified multifunctional epoxy resin: a multifunctional epoxy resin is mixed with the cyanate oligomer, and the reaction is continued at 100-140° C. for 1-2 h (e.g., 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2 h) until the viscosity of the material increases to 30000-60000 cps (preferably 30000-59000 cps, further preferably 30000-58000 cps, further preferably 30000-57000 cps, more preferably 30000-56000 cps, more preferably 30000-55000 cps, for example cps); adjusting the temperature to 80-130°C (preferably 85-120°C, also preferably 90-120°C, further preferably 95-120°C, more preferably 100-120°C, for example 100°C, 102°C, 104°C, 106°C, 108°C, 110°C, 112°C, 114°C, 116 ℃, 118 ℃, 120 ℃, 122 ℃, 124 ℃, 126 ℃, 128 ℃, 130 ℃), add the activating agent, and continue the reaction for 0.5-2h (preferably 0.6-1.9h, also preferably 0.7-1.8h, further preferably 0.8-1.7h, for example 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7h), so that the material viscosity is 40000-100000cps (preferably 41000-99000cps; also preferably 42000-98000cps, further preferably 43000-97000cps, more preferably 44000-96000cps, more preferably 45000-95000cps, such as 45000, 46000, 47000, 50000, 52000, 55000, 57000, 59000, 61000, 63000, 65000, 67000, 69000, 71000, 73000, 75000, 77000, 79000, 81000, 83000, 85000, 87000, 89000, 91000, 93000, 95000cps) and then stopping the reaction to obtain a soluble cyanate modified multifunctional epoxy resin;

[0035] (3) Preparation of medium temperature curing high temperature resistant low dielectric epoxy resin: The soluble cyanate modified multifunctional epoxy resin is adjusted to a temperature of 60-80°C (preferably a lower temperature within this range, for example, preferably 80, 79, 78, 77, 76, 75, 74, 73, 72, 71, 70, 69, 68, 67, 66, 65, 64, 63, 62, 61, 60°C), and a latent curing agent and an accelerator are added to obtain a medium temperature curing high temperature resistant low dielectric epoxy resin.

[0036] In a preferred embodiment, the present invention further comprises a step of curing the prepared medium temperature curing high temperature resistant low dielectric epoxy resin, wherein the curing temperature is 110-130°C, preferably 110-129°C, more preferably 110-128°C, for example 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128°C.

[0037] In a preferred embodiment, the mass ratio of the alicyclic diluent to the cyanate ester resin is (15-30): 100. Preferably (15-28): 100, more preferably (15-26): 100, further preferably (15-24): 100, more preferably (15-22): 100, more preferably (15-20): 100, for example, 15: 100, 17: 100, 19: 100, 21: 100, 23: 100, 25: 100.

[0038] In a preferred embodiment, the mass ratio of the multifunctional epoxy resin to the soluble cyanate-modified multifunctional epoxy resin is (35-65.5):100, preferably (37-65.5):100, also preferably (39-65.5):100, further preferably (41-65.5):100, more preferably (43-65.5):100, more preferably (45-65.5):100, for example 47:100, 49:100, 51:100, 53:100, 55:100, 130:57, 132:59, 61:100, 63:100, 65:100.

[0039] In a preferred embodiment, the mass ratio of cyanate ester to soluble cyanate modified multifunctional epoxy resin is (30-50):100, preferably (32-50):100, further preferably (34-50):100, further preferably (36-50):100, more preferably (38-50):100, more preferably (40-50):100, for example 42:100, 44:100, 46:100, 48:100, 50:100.

[0040] In a preferred embodiment, the mass ratio of the active agent to the soluble cyanate-modified multifunctional epoxy resin is (0.3-5):100, preferably (0.5-5):100, and further preferably (1-5):100, for example 2:100, 3:100, 4:100, 5:100.

[0041] In a preferred embodiment, the mass ratio of the cyanate modified multifunctional epoxy resin, the curing agent and the accelerator is 100: (8-13): (0.1-0.8), preferably 100: (8-13): (0.1-0.7); also preferably 100: (8-12): (0.1-0.7), further preferably 100: (8-12): (0.1-0.6), more preferably 100: (9-12): (0.1-0.6), for example 100: 9: 0.1, 100: 9: 0.2, 100: 9: 0.3, 100: 9: 0.4, 100: 9: 0.5 0.1, 100:10:0.2, 100:10:0.3, 100:10:0.4, 100:10:0.5, 100:10:0.6, 100:11:0.1, 100:11:0.2, 100:11:0.3, 100:11:0.4, 100:11:0.5, 100:11:0.6, 100:12:0.1, 100:12:0.2, 100:12:0.3, 100:12:0.4, 100:12:0.5, 100:12:0.6.

[0042] In a preferred embodiment, the cyanate resin includes at least one of bisphenol A cyanate, bisphenol E cyanate, bisphenol M cyanate and dicyclopentadiene bisphenol cyanate. In a specific embodiment, the cyanate resin is bisphenol A cyanate. In another specific embodiment, the cyanate resin is bisphenol A cyanate, dicyclopentadiene bisphenol cyanate. In another specific embodiment, the cyanate resin is bisphenol A cyanate.

[0043] In a preferred embodiment, the alicyclic diluent includes at least one of 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylate, bis(7-oxabicyclo[4.1.0]3-heptylmethyl)adipate, methyl 3,4-epoxycyclohexanecarboxylate, 1,4-cyclohexanedimethanol bis(3,4-epoxycyclohexanecarboxylate) and dicyclopentadiene epoxide. In a specific embodiment, the alicyclic diluent is 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylate. In another specific embodiment, the alicyclic diluent is bis(7-oxabicyclo[4.1.0]3-heptylmethyl)adipate. In yet another specific embodiment, the alicyclic diluent is 1,4-cyclohexanedimethanol bis(3,4-epoxycyclohexanecarboxylate).

[0044] In a preferred embodiment, the multifunctional epoxy resin includes at least one of 4,4′-diaminodiphenylmethane tetraglycidylamine epoxy resin, N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenyl ether and tetraglycidyl-3,4′-diaminodiphenyl ether. In a specific embodiment, the multifunctional epoxy resin is 4,4′-diaminodiphenylmethane tetraglycidylamine epoxy resin. In another specific embodiment, the multifunctional epoxy resin is N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenyl ether. In yet another specific embodiment, the multifunctional epoxy resin is tetraglycidyl-3,4′-diaminodiphenyl ether epoxy resin.

[0045] In the present invention, the medium-temperature curing high-temperature resistant low-dielectric epoxy resin material is prepared from the following raw materials: 4.5-15 mass parts of alicyclic diluent, 30-50 mass parts of cyanate resin, 35-65.5 mass parts of multifunctional epoxy resin, 0.3-5 mass parts of activator, 8-13 mass parts of latent curing agent and 0.1-0.8 mass parts of accelerator. Also preferably, the medium-temperature curing high-temperature resistant low-dielectric epoxy resin material is prepared from the following raw materials: 4.5-15 mass parts (for example, 5, 7, 9, 11, 13, 15 mass parts) of alicyclic diluent, 30-50 mass parts (for example, 30, 35, 40, 45, 50 mass parts) of cyanate resin, 35-65.5 mass parts (for example, 35, 40, 45, 50, 55, 60, 65 mass parts) of activator. The present invention relates to a multifunctional epoxy resin (for example, 0.5, 1, 2, 3, 4, 5 parts by mass), an activator (for example, 0.3-5 parts by mass), a latent curing agent (for example, 20, 25, 30, 35, 40, 45, 50 parts by mass), and an accelerator (for example, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 parts by mass). Unless otherwise specified, the viscosity values ​​mentioned herein are the viscosity values ​​measured at 70° C. The viscosity value can be measured by a viscosity measurement method and apparatus known in the art, and is not particularly limited thereto.

[0046] Example 1

[0047] This embodiment shows the preparation method of high temperature resistant low dielectric epoxy resin.

[0048] 1. Preparation of Cyanate Ester Oligomers

[0049] 30 parts by weight of bisphenol A cyanate were added into a three-necked flask, and 4.5 parts of 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylate were added. The temperature was raised to 140°C and stirred for 3 hours. At this time, the material was a brown viscous semisolid at room temperature and had a viscosity of 19215 mPa·s at 70°C, thus obtaining a cyanate oligomer.

[0050] 2. Preparation of soluble cyanate-modified multifunctional epoxy resin

[0051] 65.5 parts of 4,4'-diaminodiphenylmethane tetraglycidylamine epoxy resin are added to the cyanate oligomer obtained in the step (1), and the reaction is continued for 1 hour. At this time, the viscosity of the material at 70°C is 39281 cps; the temperature is adjusted to 80°C, and 0.3 parts of 4,4-diaminodiphenyl ether are continued to be added to the reactor, and stirring is continued for 2 hours until the viscosity of the material at 70°C is 46163 cps, thereby obtaining a soluble cyanate modified epoxy resin.

[0052] 3. Preparation of medium temperature curing high temperature resistant low dielectric epoxy resin

[0053] The temperature of the soluble cyanate modified epoxy resin obtained in step (3) is lowered to 60° C., 8 parts of dicyandiamide and 0.8 parts of an organic urea accelerator are added, and the mixture is stirred evenly to obtain a medium-temperature curing epoxy resin for high-temperature resistant low-dielectric prepreg.

[0054] 4. Resin performance testing

[0055] The obtained resin was cured at 130°C*4h according to the curing process and then tested for mechanical properties, heat resistance and dielectric properties.

[0056] Example 2

[0057] This embodiment shows the preparation method of high temperature resistant low dielectric epoxy resin.

[0058] 1. Preparation of Cyanate Ester Oligomers

[0059] Weigh 30 parts by weight of bisphenol A cyanate and 20 parts of dicyclopentadiene bisphenol cyanate into a three-necked flask, add 15 parts of bis(7-oxabicyclo[4.1.0]3-heptylmethyl)adipate, raise the temperature to 100°C, and continue stirring for 3 hours. At this time, the material is a brown viscous semisolid at room temperature and has a viscosity of 15324 mPa·s at 70°C, thus obtaining a cyanate oligomer.

[0060] 2. Preparation of soluble cyanate-modified multifunctional epoxy resin

[0061] 35 parts of N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenyl ether were added to the cyanate ester oligomer obtained in the step (1), and the reaction was continued for 1 hour. At this time, the viscosity of the material at 70° C. was 33127 cps; the temperature was adjusted to 130° C., and 5 parts of 4,4-diaminodiphenyl sulfone were continued to be added to the reactor. The stirring was continued for 0.5 hour until the viscosity of the material at 70° C. was 69557 cps, thereby obtaining a soluble cyanate ester modified epoxy resin.

[0062] 3. Preparation of medium temperature curing high temperature resistant low dielectric epoxy resin

[0063] The temperature of the soluble cyanate modified epoxy resin obtained in step (3) is lowered to 70° C., 13 parts of dicyandiamide and 0.1 parts of an organic urea accelerator are added, and the mixture is stirred evenly to obtain a medium-temperature curing epoxy resin for high-temperature resistant low-dielectric prepreg.

[0064] 4. Resin performance testing

[0065] The obtained resin was cured at 120°C for 6 hours and then tested for mechanical properties, heat resistance and dielectric properties.

[0066] Example 3

[0067] This embodiment shows the preparation method of high temperature resistant low dielectric epoxy resin.

[0068] 1. Preparation of Cyanate Ester Oligomers

[0069] Weigh 20 parts by weight of bisphenol A cyanate and 20 parts by weight of dicyclopentadiene bisphenol cyanate into a three-necked flask, add 9.5 parts of 1,4-cyclohexanedimethanol bis(3,4-epoxycyclohexanecarboxylate), raise the temperature to 130°C, and continue stirring for 2 hours. At this time, the material is a brown viscous semisolid at room temperature and has a viscosity of 17119 mPa·s at 70°C, thus obtaining a cyanate oligomer.

[0070] 2. Preparation of soluble cyanate-modified multifunctional epoxy resin

[0071] Add 50.5 parts of tetraglycidyl-3,4′-diaminodiphenyl ether epoxy resin to the cyanate ester oligomer obtained in the step (1), and continue the reaction for 1.5 hours. At this time, the viscosity of the material at 70°C is 35341 cps; adjust the material temperature to 120°C, continue to add 2.5 parts of 3,3-diaminodiphenyl sulfone to the reactor, and continue stirring for 1 hour until the viscosity of the material at 70°C is 81672 cps, thereby obtaining a soluble cyanate ester modified epoxy resin.

[0072] 3. Preparation of medium temperature curing high temperature resistant low dielectric epoxy resin

[0073] The temperature of the soluble cyanate modified epoxy resin obtained in step (3) is lowered to 65° C., 10.5 parts of dicyandiamide and 0.5 parts of an organic urea accelerator are added, and the mixture is stirred evenly to obtain a medium-temperature curing epoxy resin for high-temperature resistant and low-dielectric prepreg.

[0074] 4. Resin performance testing

[0075] The obtained resin was cured at 110°C*8h according to the curing process and then tested for mechanical properties, heat resistance and dielectric properties.

[0076] Comparative Example 1

[0077] This comparative example illustrates a method for preparing a modified epoxy resin.

[0078] 1. Preparation of modified epoxy resin

[0079] Weigh 30 parts by weight of bisphenol A cyanate and add it into a three-necked flask, add 4.5 parts of 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylate, raise the temperature to 140°C, add 65.5 parts of 4,4′-diaminodiphenylmethane tetraglycidylamine epoxy resin and 0.3 parts of 4,4′-diaminodiphenyl ether in sequence, lower the temperature to 60°C, add 8 parts of dicyandiamide and 0.8 parts of organic urea accelerator, stir evenly and discharge.

[0080] 2. Resin performance testing

[0081] The obtained resin was cured at 130°C*4h according to the curing process and then tested for mechanical properties, heat resistance and dielectric properties.

[0082] Comparative Example 2

[0083] This comparative example illustrates a method for preparing a modified epoxy resin.

[0084] 1. Preparation of modified epoxy resin

[0085] Weigh 30 parts by weight of bisphenol A cyanate and 20 parts of dicyclopentadiene bisphenol cyanate into a three-necked flask, add 15 parts of bis(7-oxabicyclo[4.1.0]3-heptylmethyl)adipate, raise the temperature to 100°C, add 35 parts of N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenyl ether, add 5 parts of 4,4-diaminodiphenyl sulfone, lower the temperature to 70°C, add 13 parts of dicyandiamide, add 0.1 parts of an organic urea accelerator, stir evenly and discharge to obtain a modified epoxy resin.

[0086] 2. Resin performance testing

[0087] The obtained resin was cured at 120°C for 6 hours and then tested for mechanical properties, heat resistance and dielectric properties.

[0088] Comparative Example 3

[0089] This comparative example illustrates a method for preparing a modified epoxy resin.

[0090] 1. Preparation of modified epoxy resin

[0091] Weigh 20 parts by weight of bisphenol A cyanate and 20 parts of dicyclopentadiene bisphenol cyanate and add them into a three-necked flask, heat to 130°C, add 9.5 parts of 1,4-cyclohexanedimethanol bis(3,4-epoxycyclohexanecarboxylate) and 50.5 parts of tetraglycidyl-3,4′-diaminodiphenyl ether, lower the temperature to 65°C, add 10.5 parts of dicyandiamide, 0.5 parts of organic urea accelerator and 2.5 parts of 3,3-diaminodiphenyl sulfone, stir evenly and discharge.

[0092] 2. Resin performance testing

[0093] The obtained resin was cured at 110°C*8h according to the curing process and then tested for mechanical properties, heat resistance and dielectric properties.

[0094] The resin performance data of Examples 1, 2 and 3 and Comparative Examples 1, 2 and 3 are shown in the following table:

[0095] Table 1 Properties of cured resin

[0096]

[0097] By comparing the examples with the comparative examples, it can be seen that the comparative examples are not completely cured within the temperature range of 110-130°C, and the curing degrees are only 81.2%, 80.3% and 79.1%. The resin cured in this way has poor performance, low heat resistance, and dielectric loss as high as 0.052, 0.050 and 0.043. In comparison, according to the preparation method shown in the present invention, the resin can be cured at a temperature below 130°C with a curing degree of ≥95%, heat resistance of ≥235°C, and the curing performance retention rate of the resin at 150°C after curing is ≥80%, and it can be used for a long time in an environment of 150°C, with a dielectric constant of ≤3.15 and a dielectric loss of ≤0.02.

[0098] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some of the technical features therein by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a medium temperature curing high temperature resistant low dielectric epoxy resin, characterized in that: The following steps are involved: (1) Preparing a cyanate oligomer: reacting an alicyclic diluent and a cyanate resin at 100-140° C. until the viscosity of the material reaches 10,000-20,000 cps, and then stopping the reaction to obtain a cyanate oligomer, wherein the mass ratio of the alicyclic diluent to the cyanate resin is (15-30):100, and the alicyclic diluent comprises at least one of 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylate, bis(7-oxabicyclo[4.1.0]3-heptylmethyl)adipate, 3,4-epoxycyclohexanecarboxylic acid methyl ester, 1,4-cyclohexanedimethanol bis(3,4-epoxycyclohexanecarboxylic acid) ester, and dicyclopentadiene epoxide; (2) Preparing a soluble cyanate-modified multifunctional epoxy resin: mixing a multifunctional epoxy resin with the above-mentioned cyanate oligomer, continuing to react at 100-140° C. until the viscosity of the material increases to 30,000-60,000 cps, lowering the temperature to 80-130° C., adding an activator, continuing the reaction until the viscosity of the material reaches 40,000-100,000 cps, and then stopping the reaction to obtain a soluble cyanate-modified multifunctional epoxy resin, wherein the mass ratio of the multifunctional epoxy resin to the soluble cyanate-modified multifunctional epoxy resin is (35-65.5):100, the mass ratio of the cyanate oligomer to the soluble cyanate-modified multifunctional epoxy resin is (30-50):100, and the mass ratio of the activator to the soluble cyanate-modified multifunctional epoxy resin is (0.3-5):100; (3) Preparation of medium-temperature curing high-temperature resistant low-dielectric epoxy resin: adjusting the temperature of the soluble cyanate-modified multifunctional epoxy resin to 60-80°C, adding a latent curing agent and an accelerator to obtain a medium-temperature curing high-temperature resistant low-dielectric epoxy resin, wherein the mass ratio of the soluble cyanate-modified multifunctional epoxy resin, the curing agent and the accelerator is 100:(8-13):(0.1-0.8).

2. The method for preparing the medium temperature curing high temperature resistant low dielectric epoxy resin according to claim 1, characterized in that: The cyanate ester resin includes at least one of bisphenol A cyanate ester, bisphenol E cyanate ester, bisphenol M cyanate ester and dicyclopentadiene bisphenol cyanate ester.

3. The method for preparing the medium temperature curing high temperature resistant low dielectric epoxy resin according to claim 1, characterized in that: The multifunctional epoxy resin includes at least one of 4,4'-diaminodiphenylmethane tetraglycidylamine epoxy resin, N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenyl ether and tetraglycidyl-3,4'-diaminodiphenyl ether.

4. The method for preparing the medium temperature curing high temperature resistant low dielectric epoxy resin according to claim 1, characterized in that: The curing agent is dicyandiamide; the accelerator is a urea or imidazole accelerator; and the activator is at least one of 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone and 3,3'-diaminodiphenyl sulfone.

5. A high temperature resistant low dielectric prepreg, characterized in that: The invention comprises a high temperature resistant low dielectric epoxy resin which can be cured at a medium temperature of 110-130° C. and is obtained by the preparation method according to any one of claims 1 to 4.

6. Use of the high temperature resistant low dielectric prepreg according to claim 5 in radar covers and radomes.

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