A colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg and its preparation method

Abstract

The present invention discloses a colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg and a preparation method thereof. The present invention prepares a mercapto-terminated oligomer by reacting a mercaptan and an isocyanate, then adds an olefinated epoxy compound to react and prepare a mercapto-terminated epoxy compound, then adds an epoxy resin and an acid anhydride compound to obtain an epoxy resin prepolymer, and then adds a thermal initiator, a light stabilizer, and an ultraviolet absorber to obtain a colorless, transparent, yellowing-resistant epoxy resin system. After coating, the system is composited with glass fiber to obtain a glass fiber reinforced epoxy resin prepreg. The prepreg of the present invention can be cured at medium temperature, the cured product has a light transmittance of ≥89%, and can be outdoor for a long time without yellowing. At the same time, it has good impact resistance and can be applied to the field of replacing glass such as the front plate and back plate of photovoltaic panels.

Description

Technical Field

[0001] The invention belongs to the technical field of composite materials, and in particular relates to a colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg and a preparation method thereof. Background Art

[0002] Photovoltaic panels are often located outdoors in bright sunlight, placing stringent requirements on the transparency and yellowing resistance of the front and back panels of photovoltaic modules. Traditional photovoltaic modules use tempered glass for the front and back panels, which is heavy and brittle, easily breaking in inclement weather, affecting power generation efficiency. In contrast, epoxy composite materials offer low density, excellent processing properties, corrosion resistance, and mechanical properties, making them less susceptible to deformation and damage, ensuring the stability of photovoltaic modules. They are suitable replacements for tempered glass in photovoltaic panels.

[0003] Traditional epoxy prepregs mostly use bisphenol A epoxy resin (refractive index 1.55-1.60) and amine curing system (such as dicyandiamide, tertiary amine accelerator). The benzene ring structure in its molecule easily absorbs ultraviolet light to generate oxidation reaction, and the material has poor yellowing resistance. In addition, the free amines remaining in the amine curing agent react with oxygen to generate quinone chromophores under a hot and humid environment, further exacerbating yellowing, resulting in poor yellowing resistance of epoxy prepreg. In order to improve the yellowing resistance of epoxy prepreg resin, the prior art attempts to use epoxy resin without benzene rings, because it has good UV resistance, but the resin refractive index does not match glass fiber (refractive index 1.54), and light undergoes Fresnel reflection loss at the interface, resulting in low transmittance; At the same time, the viscosity of the system is low at room temperature, and it is difficult to prepare prepreg; In addition, the cured product after the above-mentioned epoxy resin is cured using a thermal cationic system is brittle and has poor impact resistance of the composite material.

[0004] Therefore, there is still a need to develop an epoxy resin thermal cationic curing system that matches the refractive index of glass fiber. This system must not only meet the prepreg preparation process requirements, but also have the characteristics of excellent impact performance, colorless transparency and good yellowing resistance of the composite materials prepared by this system, so as to break through the performance bottleneck of lightweight materials for photovoltaic modules. Summary of the Invention

[0005] In order to solve at least some of the technical problems existing in the above-mentioned prior art, the present invention adopts two technical innovation routes:

[0006] First, a mercaptan-terminated oligomer is generated by reacting a thiol with an isocyanate, which is then reacted with an olefinated epoxy compound to produce a mercapto-terminated epoxy compound. This reaction, without the use of tertiary amine accelerators, introduces sulfur-containing groups into the epoxy resin structure via a specific reaction pathway, achieving a match between the resin's refractive index and that of the glass fiber. The resulting composite exhibits excellent transparency and yellowing resistance. Furthermore, the resulting polythiocarbamate exhibits excellent toughness, resulting in excellent impact resistance for the composite.

[0007] Secondly, using terminal mercapto groups as promoters, epoxy resin is pre-crosslinked with acid anhydride to prepare a resin system with suitable viscosity, which is suitable for the prepreg preparation process.

[0008] Based on the above technology, the present invention successfully prepared a colorless, transparent, and yellowing-resistant glass fiber reinforced epoxy resin prepreg for photovoltaic panels, the specific contents of which are as follows.

[0009] A first aspect of the present invention provides a method for preparing a colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg, comprising the following steps:

[0010] (1) reacting a thiol compound with an isocyanate at 40-100° C. for 2-6 hours, and then adding an olefinated epoxy compound and reacting for 3-5 hours to obtain a thiol-terminated epoxy compound, wherein the molar ratio of the thiol group, the isocyanate group, and the double bond in the olefinated epoxy compound is (2.05-2.10):1:0.8;

[0011] (2) adding an epoxy resin and an acid anhydride compound to the thiol-terminated epoxy compound obtained in step (1) in sequence, and reacting at 60-140° C. until the viscosity of the material reaches 50,000-100,000 cps at 70° C., wherein the molar ratio of the thiol group in the thiol-terminated epoxy compound, the anhydride group in the acid anhydride compound, and the epoxy group in the epoxy resin is (0.020-0.050):(0.2-0.4):1;

[0012] (3) controlling the temperature of the material obtained in step (2) to be 40-90° C., adding a thermal initiator, a light stabilizer, and an ultraviolet absorber, and mixing them uniformly to obtain a colorless, transparent, and yellowing-resistant epoxy resin system, wherein the thermal initiator accounts for 0.1-1.0% of the total amount of the colorless, transparent, and yellowing-resistant epoxy resin system, the light stabilizer accounts for 0.01-1.0% of the total amount of the colorless, transparent, and yellowing-resistant epoxy resin system, and the ultraviolet absorber accounts for 0.01-1.0% of the total amount of the colorless, transparent, and yellowing-resistant epoxy resin system;

[0013] (4) The colorless, transparent, yellowing-resistant epoxy resin system coating obtained in step (3) is compounded with glass fiber prepreg to obtain a colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg.

[0014] In certain embodiments, according to the method for preparing the colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg of the present invention, the refractive index of the thiol compound is greater than 1.5200.

[0015] In certain embodiments, according to the method for preparing the colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg of the present invention, the thiol compound includes one or more of pentaerythritol tetrakis (3-mercaptopropionate), thiodiglycol mercaptan, 2,3-dithio (2-mercapto)-1-propanethiol, and other thiols without aromatic rings; the isocyanate includes one or more of isophorone diisocyanate, dicyclohexylmethane diisocyanate, 1,6-hexamethylene diisocyanate, trimethylhexane diisocyanate, and other isocyanates without aromatic rings.

[0016] In certain embodiments, according to the method for preparing the colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg of the present invention, the general structural formula of the olefinated epoxy compound is CH2=CR-XE, wherein R includes hydrogen or an alkyl group, X includes hydrogen, an alkyl group, an alkenyl group, an ester group or an ether bond, and E includes an alicyclic epoxy group or an aliphatic epoxy group.

[0017] In certain embodiments, according to the method for preparing the colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg of the present invention, the epoxy resin includes one or more of 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexylcarboxylate, 4,5-epoxycyclohexane-1,2-dicarboxylic acid diglycidyl ester, dicyclopentadiene diepoxide, 1,4-cyclohexanedimethanol bis(3,4-epoxycyclohexanecarboxylic acid) ester, and hydrogenated bisphenol A epoxy resin.

[0018] In certain embodiments, according to the method for preparing the colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg of the present invention, the acid anhydride compound comprises one or more of maleic anhydride and its adducts, methylhexahydrophthalic anhydride, hydrogenated methylnadic anhydride, methyltetrahydrophthalic anhydride, and other acid anhydrides without aromatic rings;

[0019] In certain embodiments, according to the method for preparing the colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg of the present invention, the thermal initiator is selected from one or more of iodonium salt initiators and sulfonium salt initiators; the light stabilizer includes one or more of hindered amines and hindered phenol light stabilizers; and the ultraviolet absorber includes one or more of benzophenone and benzotriazole ultraviolet absorbers.

[0020] In certain embodiments, according to the method for preparing the colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg of the present invention, the glass fiber comprises at least one of E glass fiber and S glass fiber.

[0021] A second aspect of the present invention provides a colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg, which is obtained by the preparation method of the present invention.

[0022] The third aspect of the present invention provides the use of the colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg of the present invention in replacing glass in photovoltaic panel front panels, back panels, etc.

[0023] The composite material prepared by the present invention has the following advantages:

[0024] 1. High transparency. The present invention designs a reaction route to introduce sulfur atoms into the epoxy resin structure, so that the refractive index of the resin system reaches 1.5350-1.5450, which is consistent with the refractive index of glass fiber. The prepared composite material has high light transmittance.

[0025] 2. Excellent yellowing resistance. It adopts a cycloaliphatic epoxy thermal cationic curing system and abandons tertiary amine accelerators, effectively avoiding the yellowing problem caused by the participation of amine substances in the reaction. The prepared product has good yellowing resistance. Under the synergistic effect of specific UV absorbers and light stabilizers, the composite material is not prone to yellowing under long-term light exposure.

[0026] 3. Outstanding impact performance: The polythiocarbamate generated by the reaction of thiol and isocyanate has good toughness. The prepared composite material has good impact performance, which improves the durability and reliability of the material.

[0027] Fourth, to meet the requirements of the prepreg preparation process, the terminal thiol group is used as a promoter and the epoxy resin is pre-crosslinked with anhydride to prepare a resin system with suitable viscosity that meets the requirements of the prepreg preparation process. 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 rather 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 particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges in the present invention, it should be understood that the upper and lower limits of the ranges and each intermediate value therebetween are specifically disclosed. Each smaller range between any stated value or intermediate value within a stated range and any other stated value or intermediate value within the stated range is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0030] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning 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 any 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 colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg. In a preferred embodiment, the preparation method of the present invention comprises the following steps:

[0033] (1) reacting a thiol compound with an isocyanate at 40-100° C., 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100° C.; adding an olefinated epoxy compound and continuing the reaction to obtain a thiol-terminated epoxy compound, wherein the molar ratio of the thiol group, the isocyanate group, and the double bond in the olefinated epoxy compound is (2.05-2.10):1:0.8; for example, 2.05:1:0.8, 2.06:1:0.8, 2.07:1:0.8, 2.08:1:0.8, 2.09:1:0.8, or 2.10:1:0.8;

[0034] (2) reacting the anhydride compound, the epoxy resin and the mercapto-terminated epoxy compound at 60-140° C., for example, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140° C., to make the viscosity of the material at 70° C. reach 50,000-100,000 cps, preferably 55,000-100,000 cps, further preferably 60,000-100,000 cps, for example, 60,000, 65,000, 70,000, 75,000, 76,000, 77,000, 78,000, , 79000, 80000, 81000, 82000, 83000, 84000, 85000, 86000, 87000, 88000, 89000, 90000, 91000, 92000, 93000, 94000, 95000, 96000, 97000, 98000, 99000, 100000 cps to obtain an epoxy prepolymer, wherein the molar ratio of the thiol group in the thiol-terminated epoxy compound, the anhydride group in the anhydride compound, and the epoxy group in the epoxy resin is (0.020-0.050): (0.2-0 .4):1; preferably (0.02-0.04): (0.2-0.4):1; for example 0.02:0.2:1, 0.02:0.3:1, 0.02:0.4:1, 0.022:0.2:1, 0.022:0.3:1, 0.022:0.4:1, 0.024:0.2:1, 0.024:0.3:1, 0.024:0.4:1, 0.026:0.2:1, 0.026:0.3:1, 0.026:0.4:1, 0.028:0.2:1, 0.028:0.3:1, 0.028:0.4:1 , 0.03:0.2:1, 0.03:0.3:1, 0.03:0.4:1, 0.032:0.2:1, 0.032:0.3:1, 0.032:0.4:1, 0.034:0.2:1, 0.034:0.3:1, 0.034:0.4:1, 0.036:0.2:1, 0.036:0.3:1, 0.036:0.4:1, 0.038:0.2:1, 0.038:0.3:1, 0.038:0.4:1, 0.04:0.2:1, 0.04:0.3:1, 0.04:0.4:1;

[0035] (3) mixing the epoxy prepolymer with a light stabilizer and an ultraviolet absorber at 40-90° C., for example, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, or 90° C., adding a thermal initiator for reaction, and preferably stirring to obtain a colorless, transparent, and yellowing-resistant epoxy resin system, wherein the thermal initiator accounts for 0.1-1.0% of the total amount of the colorless, transparent, and yellowing-resistant epoxy resin system, preferably 0.1-0.9%, further preferably 0.1-0.8%, and more preferably 0.1-0.7%, for example 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, or 0.7%; the light stabilizer accounts for 0.1% of the total amount of the colorless, transparent, and yellowing-resistant epoxy resin system. The UV absorber accounts for 0.01-1.0% of the total amount of the colorless, transparent, yellowing-resistant epoxy resin system, preferably 0.01-0.9%, further preferably 0.01-0.8%, more preferably 0.01-0.7%, for example 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7%; the UV absorber accounts for 0.01-1.0% of the total amount of the colorless, transparent, yellowing-resistant epoxy resin system, preferably 0.01-0.9%, further preferably 0.01-0.8%, more preferably 0.01-0.7%, for example 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7%;

[0036] (4) The colorless, transparent, yellowing-resistant epoxy resin system coating obtained in step (3) is compounded with glass fiber prepreg to obtain a colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg.

[0037] In a preferred embodiment, after the isocyanate compound is added in step (1), stirring is continued for 1-10 hours, preferably 2-10 hours, and more preferably 2-6 hours, such as 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, and 6 hours. After the olefinated epoxy compound is added, the reaction time is 1-10 hours, preferably 2-10 hours, and more preferably 2-6 hours, and more preferably 3-5 hours, such as 3, 3.5, 4, 4.5, and 5 hours.

[0038] In a preferred embodiment, in step (2), the reaction is carried out for 1-10 h, preferably 1-9 h, further preferably 1-8 h, more preferably 1-6 h, for example 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6 h.

[0039] In a preferred embodiment, the thiol compound includes one or more of pentaerythritol tetrakis (3-mercaptopropionate), thiodiglycol mercaptan, 2,3-dithio (2-mercapto)-1-propanethiol, 1,5-pentanedithiol, trimethylolpropane tris (3-mercaptopropionate), and other thiols without aromatic rings. In a specific embodiment, the thiol compound is pentaerythritol tetrakis (3-mercaptopropionate). In another specific embodiment, the thiol compound is thiodiglycol mercaptan. In yet another specific embodiment, the thiol compound is 2,3-dithio (2-mercapto)-1-propanethiol.

[0040] In a preferred embodiment, the isocyanate includes one or more of isophorone diisocyanate, dicyclohexylmethane diisocyanate, 1,6-hexamethylene diisocyanate, trimethylhexane diisocyanate, and other isocyanates that do not contain aromatic rings. In a specific embodiment, the isocyanate is isophorone diisocyanate. In another specific embodiment, the isocyanate is dicyclohexylmethane diisocyanate. In yet another specific embodiment, the isocyanate is 1,6-hexamethylene diisocyanate.

[0041] In a preferred embodiment, the refractive index of the thiol compound is greater than 1.5200.

[0042] In a preferred embodiment, the alkenyl epoxy compound has the general structural formula CH2=CR-XE, wherein R comprises hydrogen or an alkyl group, X comprises hydrogen, an alkyl group, an alkenyl group, an ester group or an ether bond, and E comprises an alicyclic epoxy group or an aliphatic epoxy group.

[0043] In one specific embodiment, the olefinated epoxy compound is glycidyl methacrylate. In another specific embodiment, the olefinated epoxy compound is allyl glycidyl ether. In yet another specific embodiment, the olefinated epoxy compound is 3,4-epoxycyclohexyl methacrylate.

[0044] In a preferred embodiment, the acid anhydride compound includes one or more of maleic anhydride and its adducts, methylhexahydrophthalic anhydride, hydrogenated methylnadic anhydride, methyltetrahydrophthalic anhydride, and other acid anhydrides without aromatic rings. In a specific embodiment, the acid anhydride compound is methylhexahydrophthalic anhydride. In another specific embodiment, the acid anhydride compound is hydrogenated methylnadic anhydride. In yet another specific embodiment, the acid anhydride compound is methyltetrahydrophthalic anhydride.

[0045] In a preferred embodiment, the epoxy resin includes two or more of 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate, 4,5-epoxycyclohexane-1,2-dicarboxylic acid diglycidyl ester, dicyclopentadiene diepoxide, and 1,4-cyclohexanedimethanol bis(3,4-epoxycyclohexanecarboxylate), one of which is selected from dicyclopentadiene diepoxide. In a specific embodiment, the epoxy resin is a hydrogenated bisphenol A epoxy resin. In another specific embodiment, the epoxy resin is a combination of 4,5-epoxycyclohexane-1,2-dicarboxylic acid diglycidyl ester and a hydrogenated bisphenol A epoxy resin. In yet another specific embodiment, the epoxy resin is a combination of 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate and a hydrogenated bisphenol A epoxy resin.

[0046] In a preferred embodiment, the thermal initiator includes a thermal cationic initiator (for example, but not limited to diphenyliodonium hexafluorophosphate, triphenylsulfonium hexafluoroantimonate, etc.); the light stabilizer includes hindered amine and hindered phenol light stabilizers (for example, but not limited to hindered amine light stabilizers UV-123, UV-292, UV-622, UV-765, UV-770, UV-783, UV-791, UV-944); the ultraviolet absorber includes one or more of benzophenones and benzotriazoles, for example, but not limited to ultraviolet absorbers UV-81, UV-234, UV-327, UV-328, UV-571.

[0047] In a preferred embodiment, the glass fiber includes at least one of E glass fiber and S glass fiber.

[0048] Glass fiber reinforced epoxy resin prepreg

[0049] One aspect of the present invention provides a colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg, which is obtained by the preparation method of the present invention. The colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin of the present invention has a refractive index of 1.5350-1.5450 (consistent with the refractive index of glass fiber), has good bending strength and impact strength, and has excellent yellowing resistance, and can persist outdoors for a long time without yellowing. The performance of the glass fiber reinforced epoxy resin prepreg of the present invention can be tested using methods and devices known in the art, without particular limitation.

[0050] In the present invention, the colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg is prepared from the following raw materials: 5-30 parts by mass of a thiol compound, 1-20 parts by mass of an isocyanate, 5-20 parts by mass of an olefinated epoxy compound, 20-50 parts by mass of an acid anhydride compound, 50-150 parts by mass of an epoxy resin, 0.01-5 parts by mass of an initiator, 0.01-5 parts by mass of a light stabilizer, and 0.01-5 parts by mass of a UV absorber. Also preferably, the colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg is prepared from the following raw materials: 5-30 parts by mass (e.g., 5, 10, 15, 20, 25, 30 parts by mass) of a thiol compound, 1-20 parts by mass (e.g., 1, 5, 10, 15, 20 parts by mass) of an isocyanate, 5-20 parts by mass (e.g., 5, 10, 15, 20 parts by mass) of an olefinic epoxy compound, 20-80 parts by weight of anhydride compound (e.g., 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80 parts by weight), 50-150 parts by weight (e.g., 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 15 0 parts by mass) of epoxy resin, 0.01-5 parts by mass (e.g., 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 parts by mass) of initiator, 0.01-5 parts by mass (e.g., 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5 , 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 parts by mass) of a light stabilizer, and 0.01-5 parts by mass (e.g., 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 parts by mass) of a UV absorber. Unless otherwise specified, the viscosity values ​​mentioned herein are those measured at 70°C. The viscosity value can be measured using viscosity measurement methods and apparatus known in the art and is not particularly limited thereto.

[0051] Example 1

[0052] This embodiment shows a method for preparing a colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg.

[0053] (1) Preparation of a mercapto-terminated epoxy compound: 20.00 g of pentaerythritol tetrakis(3-mercaptopropionate) was placed in a three-necked flask, the temperature was raised to 100° C., 8.88 g of isophorone diisocyanate was added, and the mixture was stirred for 2 h. 9.08 g of glycidyl methacrylate was added and the mixture was reacted for 3 h to obtain a mercapto-terminated epoxy compound;

[0054] (2) Preparation of epoxy prepolymer: 31.58 g of methyl hexahydrophthalic anhydride and 100 g of hydrogenated bisphenol A epoxy resin were weighed and added to the thiol-terminated epoxy compound prepared in step (1) in sequence, and the mixture was heated to 60° C. and stirred for 5 h. The viscosity of the mixture at 70° C. reached 82175 cps, thereby obtaining an epoxy prepolymer.

[0055] (3) Preparation of colorless, transparent, yellowing-resistant prepreg epoxy resin: The material obtained in step (2) was cooled to 90° C., 0.01 g of light stabilizer and 1.00 g of ultraviolet absorber were added, and after stirring evenly, 0.10 g of thermal cationic initiator was added. The material was stirred evenly again and then discharged to obtain a colorless, transparent, yellowing-resistant epoxy resin;

[0056] (4) The colorless, transparent, yellowing-resistant epoxy resin is coated with a film coating machine, and finally compounded with glass fiber, and cured according to the curing process of 140°C*40min to obtain the colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg, wherein the glass fiber is 108g / m 2 of alkali-free glass fiber.

[0057] Example 2

[0058] This embodiment shows a method for preparing a colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg.

[0059] (1) Preparation of a thiol-terminated epoxy compound: 15.00 g of thiodiglycol mercaptan was placed in a three-necked flask, the temperature was raised to 40° C., 12.15 g of dicyclohexylmethane diisocyanate was added, and the mixture was stirred for 6 h. 8.46 g of allyl glycidyl ether was added and the mixture was reacted for 5 h to obtain a thiol-terminated epoxy compound;

[0060] (2) Preparation of epoxy prepolymer: Weigh 22.39 g of hydrogenated methyl nadic anhydride, 40 g of 4,5-epoxycyclohexane-1,2-dicarboxylic acid diglycidyl ester and 60 g of hydrogenated bisphenol A epoxy resin and add them to the thiol-terminated epoxy compound prepared in step (1) in sequence, raise the temperature to 140° C., and continue stirring for 1.5 hours until the viscosity of the material reaches 99117 cps at 70° C., thereby obtaining the epoxy prepolymer;

[0061] (3) Preparation of colorless, transparent, yellowing-resistant prepreg epoxy resin: The material obtained in step (2) was cooled to 40° C., 1.00 g of light stabilizer and 0.01 g of ultraviolet absorber were added, and after stirring evenly, 1.00 g of thermal cationic initiator was added. The material was stirred evenly again and then discharged to obtain a colorless, transparent, yellowing-resistant epoxy resin;

[0062] (4) The colorless, transparent, yellowing-resistant epoxy resin is coated with a film coating machine, and finally compounded with glass fiber, and cured according to the curing process of 120°C*60min, wherein the glass fiber is 108g / m 2 of alkali-free glass fiber.

[0063] Example 3

[0064] This embodiment shows a method for preparing a colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg.

[0065] (1) Preparation of a mercapto-terminated epoxy compound: 10.00 g of 2,3-dithio(2-mercapto)-1-propanethiol was placed in a three-necked flask, the temperature was raised to 70° C., 4.68 g of 1,6-hexamethylene diisocyanate was added, and the mixture was stirred for 3.5 h. 8.74 g of 3,4-epoxycyclohexyl methacrylate was added, and the mixture was reacted for 4 h to obtain a mercapto-terminated epoxy compound;

[0066] (2) Preparation of epoxy prepolymer: 31.47 g of methyltetrahydrophthalic anhydride, 60 g of 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexylcarboxylate and 40 g of hydrogenated bisphenol A epoxy resin were weighed and added to the thiol-terminated epoxy compound prepared in step (1) in sequence, and the temperature was raised to 100° C. and stirred for 3 h. The viscosity of the material at 70° C. reached 79314 cps, thereby obtaining an epoxy prepolymer;

[0067] (3) Preparation of colorless, transparent, yellowing-resistant epoxy resin for prepreg: The material obtained in step (2) was cooled to 70° C., 0.30 g of light stabilizer and 0.20 g of ultraviolet absorber were added, and after stirring evenly, 0.30 g of thermal cationic initiator was added. The material was stirred evenly again and then discharged to obtain a colorless, transparent, yellowing-resistant epoxy resin;

[0068] (4) The colorless, transparent, yellowing-resistant epoxy resin is coated with a film coating machine, and finally compounded with glass fiber and cured according to the curing process of 130°C*50min, wherein the glass fiber is 108g / m 2 of alkali-free glass fiber.

[0069] Comparative Example 1

[0070] This comparative example illustrates a method for preparing a modified epoxy resin prepreg.

[0071] Put 20.00g of pentaerythritol tetrakis (3-mercaptopropionic acid) into a three-necked flask, heat it to 60℃, add 30g of 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexylcarboxylate and 70g of hydrogenated bisphenol A epoxy resin, stir continuously for 3.5h, then raise the material temperature to 90℃, add 0.01g of light stabilizer and 1.00g of ultraviolet absorber, stir evenly, add 0.10g of thermal cationic initiator, stir evenly again and discharge the material to modify the epoxy resin. Since the obtained resin is a viscous liquid at room temperature, it is impossible to coat it to prepare prepreg. The obtained resin is compounded with glass fiber by hand lay-up process and cured at 140℃*40min according to the curing process. Among them, the glass fiber adopts 108g / m 2 of alkali-free glass fiber.

[0072] Comparative Example 2

[0073] This comparative example illustrates a method for preparing a modified epoxy resin prepreg.

[0074] Put 15.00g of thiodiglycol mercaptan into a three-necked flask, heat it to 40°C, add 12.15g of dicyclohexylmethane diisocyanate, and continue stirring for 6h; 22.39g of hydrogenated methyl nadic anhydride, 60g of 4,5-epoxycyclohexane-1,2-dicarboxylic acid diglycidyl ester and 40g of hydrogenated bisphenol A epoxy resin, heat it to 140°C, and continue stirring for 0.5h until the viscosity of the material at 70°C reaches 90918cps, thereby obtaining an epoxy prepolymer; reduce the temperature of the obtained material to 40°C, add 1.00g of light stabilizer and 0.01g of ultraviolet absorber, stir evenly, then add 1.00g of thermal cationic initiator, stir evenly again, and discharge the material to obtain a modified epoxy resin. The colorless, transparent, yellowing-resistant epoxy resin is coated with a film coating machine, and finally compounded with glass fiber, and cured according to the curing process of 120°C*60min, wherein the glass fiber is 108g / m 2 of alkali-free glass fiber.

[0075] Comparative Example 3

[0076] This comparative example illustrates a method for preparing a modified epoxy resin prepreg.

[0077] 10.00g of 2,3-dithio (2-mercapto) -1-propanethiol was placed in a three-necked flask, heated to 70 ° C, 50g of 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexyl carboxylate and 50g of hydrogenated bisphenol A epoxy resin were added, and 0.05g of triethylamine was added. After reacting for 6 hours, the viscosity of the material at 70 ° C reached 82771cps. 0.30g of light stabilizer and 0.20g of ultraviolet absorber were added, and 0.30g of thermal cationic initiator was added after stirring evenly. After stirring evenly again, the material was discharged to obtain a modified epoxy resin. Since the obtained resin is a viscous liquid at room temperature, it is impossible to coat the prepreg. The obtained resin is compounded with glass fiber by hand lay-up process and cured according to the curing process of 130 ° C * 50min. Among them, the glass fiber is 108g / m 2 The alkali-free glass fiber is added to obtain a modified epoxy resin prepreg.

[0078] Comparative Example 4

[0079] This comparative example illustrates a method for preparing a modified epoxy resin prepreg.

[0080] 40g of 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexylcarboxylate and 60g of hydrogenated bisphenol A epoxy resin were placed in a three-necked flask, heated to 90°C, 0.01g of light stabilizer and 1.00g of ultraviolet absorber were added, stirred evenly, and 0.10g of thermal cationic initiator was added. Stir evenly again and discharge the material to obtain the modified epoxy resin. Since the obtained resin is a viscous liquid at room temperature, it cannot be coated to prepare prepreg. The obtained resin was compounded with glass fiber using a hand lay-up process and cured at 140°C*40min according to the curing process. The glass fiber was 108g / m 2 The alkali-free glass fiber is added to obtain a modified epoxy resin prepreg.

[0081] test:

[0082] Resin shelf life test: The epoxy resin system is allowed to stand at 25°C and 50% RH. During this process, samples are taken to test the viscosity at a constant temperature of 70°C. When the viscosity reaches twice the initial viscosity, the material is considered expired.

[0083] Resin refractive index test: Use Abbe refractometer to test the resin refractive index.

[0084] Composite material transmittance test: tested according to ASTM D1003 standard.

[0085] Composite double 85 test: According to the test standard: GB / T 9535, the obtained prepreg composite material is placed in a hot and humid environment with a temperature of 85±2℃ and a relative humidity of 85±5% for 1000h, and the bending performance retention rate is tested. The performance retention rate is required to be ≥70%.

[0086] Composite material bending performance test: Tested in accordance with standard GB / T3356.

[0087] Composite material impact performance test: tested in a standard pendulum electronic impact tester according to ASTM D7136.

[0088] Composite UV aging test: Tested according to ISO4892-2, with an acceleration rate of 62.57. One year of outdoor UV exposure is equivalent to 70 hours of indoor UV exposure.

[0089] The performance data of the resins and composite materials of Examples 1, 2 and 3 and Comparative Examples 2, 3 and 4 are shown in Table 1 below, wherein Comparative Example 1 was not cured and remained uncured even after the curing time was extended.

[0090] Table 1 Properties of resin and composite materials

[0091]

[0092]

[0093] Comparison of Examples 1, 2, and 3 with Comparative Example 2 reveals that the resins in Examples 1, 2, and 3 all have a shelf life of ≥25 days, demonstrating a good shelf life. In contrast, the resin in Comparative Example 2 has a shelf life of only two days. This is because the presence of mercapto groups in the epoxy resin anhydride system forms a trimolecular complex, causing the resin's viscosity to increase rapidly at room temperature, making it difficult to store the resin for an extended period of time, which can affect subsequent use.

[0094] By comparing Examples 1, 2 and 3 with Comparative Example 3, it can be seen that the catalyst of tertiary amines is not added to the resin of the embodiment of the present invention, and its initial yellowing index (YI) is ≤1.40, which meets the requirement of the initial yellowing index (YI) of photovoltaic glass ≤1.50. Relatively speaking, the catalyst of tertiary amines is added to Comparative Example 3, and its initial yellowing index (YI) reaches 4.61, which far exceeds the requirement of the initial yellowing index of photovoltaic glass. After the subsequent simulated accelerated aging test, the increment (ΔYI) of the yellowing index of Examples 1, 2 and 3 is only 2.93, 2.97 and 3.00 in 30 days, which meets the technical requirement of the increment (ΔYI) of the yellowing index after the accelerated aging test of the photovoltaic panel ≤3, which is equivalent to it being able to persist in not yellowing for 10 years outdoors, and can ensure the light transmittance of the photovoltaic panel. The ΔYI (30 days) of Comparative Example 3 has reached 18.35, and the sample is seriously yellowed, and the transmittance is significantly reduced.

[0095] A detailed comparison of Examples 1, 2, and 3 with Comparative Example 4 shows that the light transmittance of the present invention embodiments is ≥89% when the refractive index of the resin system is between 1.5350 and 1.5450, meeting the requirements for high light transmittance of the front and back panels of photovoltaic panels. The mechanical properties test results of the composite materials show that the flexural strength of Examples 1, 2, and 3 are all ≥350 MPa and the impact strength is ≥43.0 kJ·m -2 , excellent mechanical properties. In comparison, the comparative example 4 does not meet the prepreg preparation process, and the composite material has a bending strength of only 210MPa and an impact strength of only 17.0kJ·m -2 , poor performance.

[0096] It can be seen that the prepreg composite material of the present invention has high transparency, excellent yellowing resistance, and good impact resistance. It can be used to replace the front panel and back panel glass of photovoltaic modules, etc., and has broad application prospects.

[0097] Finally, it should be noted that the above embodiments are intended only to illustrate the technical solutions of the present invention, and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may be modified or some of the technical features thereof may be replaced with equivalents. Such modifications or replacements do not deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing a colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg, characterized in that: It includes the following steps: (1) reacting a thiol compound with an isocyanate at 40-100° C. for 2-6 hours, and then adding an olefinated epoxy compound and reacting for 3-5 hours to obtain a thiol-terminated epoxy compound, wherein the molar ratio of the thiol group, the isocyanate group, and the double bond in the olefinated epoxy compound is (2.05-2.10):1:0.8; the refractive index of the thiol compound is greater than 1.5200; the isocyanate comprises one or more of isophorone diisocyanate, dicyclohexylmethane diisocyanate, 1,6-hexamethylene diisocyanate, trimethylhexane diisocyanate, and other isocyanates without an aromatic ring; the general structural formula of the olefinated epoxy compound is CH2=CR-XE, R comprises hydrogen or an alkyl group, X comprises hydrogen, an alkyl group, an alkenyl group, an ester group, or an ether bond, and E comprises an alicyclic epoxy group or an aliphatic epoxy group; (2) adding an epoxy resin and an acid anhydride compound to the thiol-terminated epoxy compound obtained in step (1) in sequence, and reacting at 60-140° C. to make the viscosity of the material reach 50,000-100,000 cps at 70° C., wherein the molar ratio of the thiol group in the thiol-terminated epoxy compound, the anhydride group in the acid anhydride compound, and the epoxy group in the epoxy resin is (0.020-0.050):(0.2-0.4):1; (3) controlling the temperature of the material obtained in step (2) to be 40-90° C., adding a thermal initiator, a light stabilizer, and an ultraviolet absorber, and mixing them uniformly to obtain a colorless, transparent, and yellowing-resistant epoxy resin system, wherein the thermal initiator accounts for 0.1-1.0% of the total amount of the colorless, transparent, and yellowing-resistant epoxy resin system, the light stabilizer accounts for 0.01-1.0% of the total amount of the colorless, transparent, and yellowing-resistant epoxy resin system, and the ultraviolet absorber accounts for 0.01-1.0% of the total amount of the colorless, transparent, and yellowing-resistant epoxy resin system; (4) The colorless, transparent, yellowing-resistant epoxy resin system coating obtained in step (3) is compounded with glass fiber prepreg to obtain a colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg.

2. The method for preparing the colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg according to claim 1, characterized in that: The thiol compound includes one or more of pentaerythritol tetrakis (3-mercaptopropionate), thiodiglycol mercaptan, 2,3-dithio (2-mercapto)-1-propanethiol and other thiols without aromatic rings.

3. The method for preparing the colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg according to claim 1, characterized in that: The epoxy resin includes one or more of 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexylcarboxylate, 4,5-epoxycyclohexane-1,2-dicarboxylic acid diglycidyl ester, dicyclopentadiene diepoxide, 1,4-cyclohexanedimethanol bis(3,4-epoxycyclohexanecarboxylate), and hydrogenated bisphenol A epoxy resin.

4. The method for preparing the colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg according to claim 1, characterized in that: The acid anhydride compound includes one or more of maleic anhydride and its adducts, methylhexahydrophthalic anhydride, hydrogenated methylnadic anhydride, methyltetrahydrophthalic anhydride and other acid anhydrides without aromatic rings.

5. The method for preparing the colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg according to claim 1, characterized in that: The thermal initiator includes one or more of an iodonium salt initiator and a sulfonium salt initiator, the light stabilizer includes one or more of a hindered amine and a hindered phenol light stabilizer, and the ultraviolet absorber includes one or more of a benzophenone and a benzotriazole ultraviolet absorber.

6. The method for preparing the colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg according to claim 1, characterized in that: The glass fiber includes one or more of E glass fiber and S glass fiber.

7. A colorless, transparent, yellowing-resistant glass fiber reinforced epoxy resin prepreg, characterized in that: The method is obtained according to any one of claims 1 to 6.

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