Low temperature curing resin system suitable for heavy weight infusion and method of manufacture and use

Abstract

The application discloses a low-temperature curing resin system suitable for heavy weight impregnation, a preparation method and application, relates to the field of composite materials, and raw materials of the low-temperature curing resin system include 50-70 parts of a first epoxy resin, 15-30 parts of an epoxy modified block polymer containing CTBN, 3-7 parts of a thickening agent, 1-3 parts of a defoaming agent and 6-21 parts of a curing agent in terms of weight percentage. The low-temperature curing resin system provided in the application is in a liquid state with low viscosity under room temperature conditions, can well impregnate heavy weight reinforcing materials under low-temperature conditions, can occur chelation reaction in the later standing process, can increase molecular chains, can increase apparent viscosity of the resin, can reach the resin viscosity for prepreg, can increase toughness of the resin system, and has good operability. The prepreg can be cured under a medium-low temperature environment (75-105 DEG C).

Description

Technical Field

[0001] This invention relates to the field of composite materials, and more specifically, to low-temperature curing resin systems suitable for high-grammage impregnation, their preparation methods, and applications. Background Technology

[0002] As the core component of wind turbines, wind turbine blades are the power source for wind energy conversion. Their excellent design, reliable quality, and superior performance are decisive factors in ensuring the normal and stable operation of the turbine and are a key link in promoting the large-scale development of wind turbines. Currently, most onshore wind turbine blades in China use all-glass fiber reinforced composite materials as the main solution, while offshore wind power has become a much larger blue ocean market. To better utilize offshore wind power, high-wattage wind turbine designs have undergone repeated innovations. The generation of high power ratings requires larger and longer blades for support, which has also spurred innovation in the downstream materials industry. Innovatively, carbon fiber is used as the internal main beam of offshore wind turbine blades to improve the overall stiffness and fatigue resistance of the blades, thereby enabling the manufacture of longer blades for low wind speeds.

[0003] Prepreg is an abbreviation for "pre-impregnation," referring to a uniform pre-cured material formed by impregnating fiber bundles or fiber cloth with resin. Pre-cured materials can be directly used in the manufacture of composite structures such as wind turbine blades. Prepregs can be classified according to their physical state into unidirectional, bidirectional, and tridirectional prepregs; according to the resin matrix, into thermosetting resin prepregs and thermoplastic resin prepregs; according to the reinforcing material, into carbon fiber prepregs, glass fiber prepregs, and aramid prepregs; and according to the curing temperature, into medium-temperature curing (120℃) prepregs, high-temperature curing (180℃) prepregs, and prepregs with curing temperatures exceeding 200℃.

[0004] However, most carbon fiber prepregs are low-weight products. For carbon plates with a thickness of about 5mm, they cannot realize their advantages and instead have disadvantages, such as more layers, higher cost, higher curing temperature (120-180℃), and most equipment cannot meet the uniformity of the curing temperature range.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a low-temperature curing resin system suitable for large weight impregnation, its preparation method, and its application.

[0007] This invention is implemented as follows:

[0008] In a first aspect, the present invention provides a low-temperature curing resin system suitable for heavy-weight impregnation, wherein the raw materials, by weight, include 50-70 parts of a first epoxy resin, 15-30 parts of an epoxy-modified block polymer containing CTBN, 3-7 parts of a thickener, 1-3 parts of a defoamer, and 6-21 parts of a curing agent.

[0009] In an optional embodiment, the preparation method of the epoxy modified block polymer containing CTBN includes: mixing a second epoxy resin and CTBN in a functionality ratio of 1-3 (epoxy group): 1 (carboxyl group), introducing a protective gas after mixing, heating to 80-120°C, reacting for 2-3 hours, and then cooling to room temperature to obtain the product.

[0010] Preferably, the protective gas is nitrogen.

[0011] In an optional embodiment, the thickener is active magnesium oxide.

[0012] In an optional embodiment, the curing agent comprises a curing component and an accelerator in a mass ratio of 6-16:1-5;

[0013] Preferably, the curing component includes one or more combinations of diaminodiphenylmethane, dicyandiamide and its derivatives, modified polyamines, 1,3-bis(aminomethyl)cyclohexane and 3-aminomethyl-3,5,5-trimethylcyclohexylamine.

[0014] Preferably, the accelerator comprises one or more combinations of modified imidazole accelerators and modified organic urea accelerators;

[0015] Preferably, the modified imidazole accelerator includes one or more combinations of 1-(2-aminoethyl)-2-ethylimidazole and 1-(2-aminoethyl)-2-methylimidazole.

[0016] In an optional embodiment, the first epoxy resin and the second epoxy resin each independently comprise one or more of the following: bisphenol F epoxy resin, phenolic epoxy resin with a viscosity of 1100-1700 cps, phenolic epoxy resin with a viscosity of 3500-6000 cps, bisphenol A type epoxy resin, and polyurethane modified epoxy resin.

[0017] In an optional embodiment, the defoamer includes one or more of BYK-320, BYK-A530, and BYK-1974.

[0018] Secondly, the present invention provides a method for preparing a low-temperature curing resin system suitable for heavy-weight impregnation, which includes uniformly mixing the raw materials as described in any of the foregoing embodiments.

[0019] In an optional embodiment, both the thickener and the curing agent are pre-mixed evenly with a portion of the first epoxy resin;

[0020] The thickener and a portion of the first epoxy resin are pre-dispersed at a ratio of 1:2-10 at a speed of 1000-2000 rpm for 8-12 minutes. After discharge, the pre-dispersed thickener is obtained by grinding 2-4 times.

[0021] The curing agent and a portion of the first epoxy resin are pre-dispersed at a ratio of 1:1-10 at a speed of 2000-3000 rpm for 3-5 minutes. After discharge, the pre-dispersed curing agent is obtained by grinding 1-2 times.

[0022] In an optional embodiment, mixing the raw materials uniformly includes: first dispersing the remaining first epoxy resin at 50-70°C until uniform, cooling it to 25-35°C, and then adding the pre-dispersed curing agent, the epoxy modified block polymer containing CTBN, the pre-dispersed thickener, and the defoamer, and mixing them uniformly.

[0023] Thirdly, the present invention provides a low-temperature curing prepreg for high-weight impregnation, comprising a reinforcing material and a low-temperature curing resin system suitable for high-weight impregnation as described in any of the foregoing embodiments or a low-temperature curing resin system suitable for high-weight impregnation prepared by a method for preparing a low-temperature curing resin system suitable for high-weight impregnation as described in any of the foregoing embodiments, wherein the reinforcing material and the low-temperature curing resin system are impregnated at 40-50°C.

[0024] Preferably, the reinforcing material comprises unidirectional fabric or patterned fabric with a unidirectional face weight of 400-800 gsm; the pattern of the patterned fabric includes plain weave, twill weave and satin weave fabrics.

[0025] Fourthly, the present invention provides a low-temperature curing laminate, which is obtained by molding and curing the high-grammage impregnated low-temperature curing prepreg described in the foregoing embodiments. The molding and curing includes first curing at 75-85°C for 2-3 hours, and then curing at 95-105°C for 2-3 hours.

[0026] The present invention has the following beneficial effects:

[0027] The low-temperature curing resin system suitable for heavy-weight impregnation provided in this application comprises an epoxy-modified block polymer containing CTBN. This block polymer is obtained by chemical copolymerization of bisphenol A type epoxy resin and carboxyl-terminated butadiene nitrile, which can increase the molecular weight of the resin. Furthermore, the epoxy-modified block polymer containing CTBN can chelate with the thickener component in this application at room temperature. The resulting low-temperature curing resin system suitable for heavy-weight impregnation has low viscosity at room temperature and remains in a liquid state initially. At low temperatures (40-50°C), it can effectively impregnate heavy-weight (400-800 gsm) reinforcing materials (unidirectional and fabric). This allows for good permeability of the reinforcing material during prepreg preparation. In the subsequent settling process, the molecular chains of each component in the resin system are further "increased" macroscopically through intermolecular forces, increasing the apparent viscosity of the resin to the viscosity required for prepreg. The resin system also exhibits increased toughness and good workability. This method helps reduce internal stress in composite laminates during the curing process and the requirements for equipment and other auxiliary materials, thereby reducing defects such as cracks and energy consumption, and lowering the manufacturing cost of composite materials. This approach makes prepreg molding a low-cost, simple, and effective method. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0029] This invention provides a low-temperature curing resin system suitable for heavy-weight impregnation, the raw materials of which include, by weight, 50-70 parts of a first epoxy resin, 15-30 parts of an epoxy-modified block polymer containing CTBN, 3-7 parts of a thickener capable of chelating with the epoxy-modified block polymer containing CTBN, 1-3 parts of a defoamer, and 6-21 parts of a curing agent.

[0030] The preparation method of the epoxy modified block polymer containing CTBN includes: mixing the second epoxy resin and CTBN in a functionality ratio of 2 (epoxy group): 1 (carboxyl group), passing a protective gas through the mixture, heating to 80-120℃, reacting for 2-3 hours, and then cooling to room temperature to obtain the product.

[0031] Carboxyl-terminated nitrile butadiene rubber (CTBN) exhibits strong polarity due to the presence of nitrile groups in its molecules, resulting in good compatibility with the second epoxy resin. Furthermore, the terminal carboxyl groups can bond with the epoxy resin to form CTBN-containing epoxy-modified block polymers, increasing the molecular chain size and further enhancing the compatibility between the two, while also improving the toughness of the resin system.

[0032] The protective gas in this application includes, but is not limited to, nitrogen. The reaction temperature of the second epoxy resin and the carboxyl-terminated butadiene nitrile rubber (CTBN) can be, for example, any one or any two of 80, 85, 90, 95, 100, 105, 110, 115, and 120°C. The reaction time can be, for example, any one or any two of 2, 2.2, 2.4, 2.5, 2.6, 2.8, and 3 hours.

[0033] The thickener is active magnesium oxide. The active magnesium oxide in this application can chelate with the epoxy-modified block polymer containing CTBN at room temperature, further "increasing" the molecular chains of each component in the resin system macroscopically through intermolecular forces, which manifests as an increase in the viscosity of the resin system. The curing agent includes a curing component and an accelerator in a mass ratio of 6-16:1-5; preferably, the curing component includes one or more combinations of diaminodiphenylmethane, dicyandiamide and its derivatives, modified polyamines, 1,3-bis(aminomethyl)cyclohexane, and 3-aminomethyl-3,5,5-trimethylcyclohexylamine. Preferably, the accelerator includes one or more combinations of modified imidazole accelerators and modified organic urea accelerators; preferably, the modified imidazole accelerator includes one or more combinations of 1-(2-aminoethyl)-2-ethylimidazolium and 1-(2-aminoethyl)-2-methylimidazolium.

[0034] The curing agent in this application is selected by combining a curing component and an accelerator. The curing component is a modified curing component for medium and low temperatures, while the addition of the accelerator can promote the ring-opening of the curing component and crosslink it with the chelate (obtained by chelation reaction of active magnesium oxide and epoxy modified block polymer containing CTBN), thereby enabling the resin system to gel rapidly under low temperature conditions.

[0035] The first epoxy resin and the second epoxy resin are, independently, including but not limited to, one or more of the following: bisphenol F epoxy resin, low-viscosity phenolic epoxy resin (1100-1700 cps at 50°C), medium-viscosity phenolic epoxy resin (3500-6000 cps at 50°C), bisphenol A type epoxy resin, and polyurethane modified epoxy resin.

[0036] Defoamers include, but are not limited to, one or more of BYK-320, BYK-A530, and BYK-1974.

[0037] Furthermore, the present invention also provides a method for preparing a low-temperature curing resin system suitable for high-grammage impregnation, which includes uniformly mixing the above-mentioned raw materials, specifically including the following steps:

[0038] S1. Preparation of epoxy-modified block polymers containing CTBN

[0039] The second epoxy resin and carboxyl-terminated butadiene-acrylonitrile rubber (CTBN) are mixed in a functionality ratio of 2 (epoxy group): 1 (carboxyl group). After mixing, a protective gas is introduced, the temperature is raised to 80-120℃, and the reaction is carried out for 2-3 hours. Then, the mixture is cooled to room temperature to obtain the final product.

[0040] S2. Prepare a pre-dispersed thickener.

[0041] The thickener is pre-mixed evenly with a portion of the first epoxy resin; specifically, the thickener and a portion of the first epoxy resin are pre-dispersed at a ratio of 1:2-10 at a speed of 1000-2000 rpm for 8-12 minutes, and after discharge, the pre-dispersed thickener is obtained by grinding 2-4 times.

[0042] In this application, by pre-mixing the thickener with a portion of the first epoxy resin, uniform dispersion of the thickener can be achieved, facilitating a more uniform chelation reaction with the CTBN-containing epoxy-modified block polymer. Compared to directly adding dry powdered active magnesium oxide, pre-dispersion in this application results in a more stable thickening effect and more stable mechanical properties of the prepared composite material.

[0043] S3. Prepare the pre-dispersed curing agent.

[0044] The curing agent is pre-mixed evenly with a portion of the first epoxy resin; specifically, the curing agent and a portion of the first epoxy resin are pre-dispersed at a ratio of 1:1-10 at a speed of 2000-3000 rpm for 3-5 minutes, and after discharge, the pre-dispersed curing agent is obtained by grinding 1-2 times.

[0045] In this application, the curing agent can be uniformly mixed with a portion of the first epoxy resin in advance, which facilitates more uniform curing in the subsequent process.

[0046] S4. Mix the raw materials evenly.

[0047] First, disperse the remaining first epoxy resin at 50-70℃ until it is uniform. After cooling to 25-35℃, add the pre-dispersed curing agent, epoxy modified block polymer containing CTBN, pre-dispersed thickener and defoamer, and mix them evenly.

[0048] In this embodiment, the first epoxy resin has a lower viscosity at 50-70°C, making it easier to mix. Subsequently, the temperature is lowered to 25-35°C, which can effectively reduce the premature reaction of the subsequently added pre-dispersed curing agent, CTBN-containing epoxy modified block polymer, pre-dispersed thickener, and defoamer. Therefore, the low-temperature curing resin system suitable for large-gram impregnation provided in this application can be in a liquid state at room temperature, which is more conducive to the resin system impregnating the reinforcing material. At the same time, during subsequent impregnation, heating (75-105°C) can complete the curing.

[0049] Correspondingly, this invention provides a high-grammage impregnation low-temperature curing prepreg, comprising a reinforcing material and the aforementioned low-temperature curing resin system suitable for high-grammage impregnation, wherein the reinforcing material and the low-temperature curing resin system are impregnated at 40–50°C. In this application, the reinforcing material comprises a unidirectional fabric or patterned fabric with a unidirectional face weight of 400–800 gsm; the pattern of the patterned fabric includes plain weave, twill weave, and satin weave fabrics. The prepared high-grammage impregnation low-temperature curing prepreg exhibits good lay-up processability and excellent board performance.

[0050] Furthermore, this invention also provides a low-temperature curing laminate, obtained by molding and curing the aforementioned high-grammage impregnated low-temperature curing prepreg. The molding and curing process includes first curing at 75-85°C for 2-3 hours, followed by curing at 95-105°C for 2-3 hours. The high-grammage impregnated low-temperature curing prepreg provided by this invention can be cured at medium-low temperatures of 75-105°C, with a room temperature tack life ≥18 days.

[0051] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0052] Resin System Example 1

[0053] This embodiment provides a low-temperature curing resin system suitable for heavy-weight impregnation, the raw materials of which include 54 parts by weight of first epoxy resin, 25 parts of epoxy modified block polymer containing CTBN, 5 parts of thickener, 2 parts of defoamer and 14 parts of curing agent.

[0054] The first epoxy resin comprises bisphenol A type epoxy resin E44 and polyurethane modified epoxy resin in a mass ratio of 2:1; the second epoxy resin is bisphenol A epoxy resin; the thickener is active magnesium oxide; the defoamer is BYK-320; and the curing agent comprises modified imidazole accelerator 1-(2-aminoethyl)-2-ethylimidazolium and dicyandiamide derivative EH3842 in a mass ratio of 1:6.

[0055] Methods for preparing low-temperature curing resin systems include:

[0056] S1. Preparation of epoxy-modified block polymer containing CTBN: The second epoxy resin and CTBN are mixed in a functionality ratio of 2 (epoxy group): 1 (carboxyl group). After mixing, nitrogen gas is introduced and the mixture is heated to 100°C under nitrogen protection. After reacting for 2 hours, it is cooled to room temperature to obtain the final product.

[0057] S2. Preparation of pre-dispersed thickener: The thickener and part of the first epoxy resin are pre-dispersed at a ratio of 1:4 at a speed of 1500 rpm for 8 minutes. After discharge, the pre-dispersed thickener is obtained by grinding 3 times.

[0058] S3. Preparation of pre-dispersed curing agent: The curing agent and part of the first epoxy resin are pre-dispersed at a ratio of 1:3 at a speed of 2500 rpm for 3 minutes. After discharge, the pre-dispersed curing agent is obtained by grinding once.

[0059] S4. Mix the raw materials evenly: First, disperse the remaining first epoxy resin at 60°C until it is uniform. After cooling to 30°C, add the pre-dispersed curing agent, epoxy modified block polymer containing CTBN, pre-dispersed thickener and defoamer, mix evenly, and obtain low-temperature curing resin system 1.

[0060] Resin System Examples 2-3

[0061] Examples 2-3 are basically the same as Example 1, except that the raw materials used in the low-temperature curing resin system suitable for large weight impregnation are different.

[0062] In Example 2 of the resin system, the raw materials for the low-temperature curing resin system suitable for high-grammage impregnation include, by weight, 52 parts of a first epoxy resin, 20 parts of an epoxy-modified block polymer containing CTBN, 7 parts of a thickener, 3 parts of a defoamer, and 18 parts of a curing agent. The first epoxy resin comprises bisphenol A type epoxy resin E44 and polyurethane-modified epoxy resin in a mass ratio of 6:5. The second epoxy resin is bisphenol A epoxy resin. The thickener is active magnesium oxide, the defoamer is BYK-A530, and the curing agent comprises modified organic urea accelerator 1-(2-aminoethyl)-2-methylimidazole and modified polyamine EH5031S in a mass ratio of 1:8.

[0063] In Example 3 of the resin system, the raw materials, by weight, suitable for low-temperature curing resin systems with high-grammage impregnation, include 66 parts of a first epoxy resin, 15 parts of an epoxy-modified block polymer containing CTBN, 3 parts of a thickener, 2 parts of a defoamer, and 14 parts of a curing agent. The first epoxy resin comprises bisphenol A type epoxy resin E44 and polyurethane-modified epoxy resin in a mass ratio of 5:2. The second epoxy resin is bisphenol A epoxy resin. The thickener is magnesium oxide. The defoamer comprises BYK-320 and BYK-1974 in a mass ratio of 1:1. The curing agent comprises modified imidazole accelerator 1-(2-aminoethyl)-2-ethylimidazolium and dicyandiamide derivative EH3842 in a mass ratio of 1:6.

[0064] Resin System Examples 4-5

[0065] The resin systems in Examples 4-5 are basically the same as those in Example 1, except that the preparation methods are different.

[0066] The preparation method of the low-temperature curing resin system in Example 4 includes:

[0067] S1. Preparation of epoxy-modified block polymer containing CTBN: The second epoxy resin and CTBN are mixed in a functionality ratio of 3 (epoxy group): 1 (carboxyl group). After mixing, nitrogen gas is introduced and the mixture is heated to 120°C under nitrogen protection. After reacting for 1 hour, it is cooled to room temperature to obtain the final product.

[0068] S2. Preparation of pre-dispersed thickener: The thickener and part of the first epoxy resin are pre-dispersed at a ratio of 1:8 at a speed of 1000 rpm for 12 minutes. After discharge, the pre-dispersed thickener is obtained by grinding 3 times.

[0069] S3. Preparation of pre-dispersed curing agent: The curing agent and part of the first epoxy resin are pre-dispersed at a ratio of 1:10 at a speed of 3000 rpm for 3 minutes. After discharge, the pre-dispersed curing agent is obtained by grinding once.

[0070] S4. Mix the raw materials evenly: First, disperse the remaining first epoxy resin at 50°C until it is uniform. After cooling to 25°C, add the pre-dispersed curing agent, epoxy modified block polymer containing CTBN, pre-dispersed thickener and defoamer, mix evenly, and obtain the low-temperature curing resin system 4.

[0071] The preparation method of the low-temperature curing resin system in Example 5 includes:

[0072] S1. Preparation of epoxy-modified block polymer containing CTBN: The second epoxy resin and CTBN are mixed in a functionality ratio of 2 (epoxy group): 1 (carboxyl group). After mixing, nitrogen gas is introduced and the mixture is heated to 100°C under nitrogen protection. After reacting for 2 hours, it is cooled to room temperature to obtain the final product.

[0073] S2. Mix the raw materials evenly: First, disperse the first epoxy resin at 60°C until it is uniform. After cooling to 30°C, add the curing agent, epoxy modified block polymer containing CTBN, thickener and defoamer, mix evenly, and obtain the low-temperature curing resin system 5.

[0074] Prepreg Examples 1-5

[0075] This embodiment provides a high-grammage impregnated low-temperature curing prepreg, which is a high-grammage unidirectional prepreg with an areal density of 600 gsm composed of two parts: carbon fiber of specification HF10J-24K (Jiangsu Hengshen Co., Ltd.) and the low-temperature curing resin system provided in Examples 1-5.

[0076] The preparation method of the prepreg includes: using Jiangsu Hengshen HF10J-24K carbon fiber as the reinforcing material, and combining the low-temperature curing resin system provided in Examples 1-5 with the reinforcing material by a one-step impregnation method at low temperature (40-50℃) to form a unidirectional prepreg. The areal density of the prepared unidirectional prepreg is 600 gsm, and they are respectively used as prepregs 1-5.

[0077] Prepreg Example 6

[0078] This embodiment provides a high-grammage impregnated low-temperature curing prepreg, which is composed of two parts: a carbon fiber fabric of specification HFW650T-A2-2 / 2-1000 (Jiangsu Hengshen Co., Ltd.) and a low-temperature curing resin system provided in Example 1. The high-grammage fabric prepreg 6 has an areal density of 650 gsm.

[0079] Comparative Example 1 of Resin System

[0080] This comparative example provides a conventional prepreg resin system. The conventional unidirectional prepreg resin system consists of two parts: 91 parts resin components and 9 parts curing agent components. The resin components include 40 parts phenolic epoxy resin, 6 parts phenoxy resin, and 45 parts bisphenol A resin composition. The curing agent components include 2 parts organic urea accelerator and 7 parts dicyandiamide composition.

[0081] Resin preparation: In a star-shaped stirrer, add the resin components and stir evenly at 95°C. Cool down to 65°C, add the curing agent composition, and stir evenly until the desired resin state is achieved.

[0082] Comparative Example 2 of Resin System

[0083] This comparative example is basically the same as the example, except that the epoxy modified block polymer containing CTBN in Example 1 is replaced with carboxyl-terminated butadiene nitrile rubber CTBN in this comparative example.

[0084] Comparative Example 3 of Resin Systems

[0085] This comparative example is basically the same as the example example, except that the active magnesium oxide in Example 1 is replaced with the thickener magnesium hydroxide in this comparative example.

[0086] Prepreg Comparative Example 1

[0087] This comparative example provides a non-high grammage low-temperature curing unidirectional prepreg, which consists of two parts: carbon fiber fabric of specification HFW133PA-3KHF10A-1 / 1-1000 (Jiangsu Hengshen Co., Ltd.) and a resin system of conventional prepreg resin system provided in Comparative Example 1.

[0088] Prepreg preparation: Jiangsu Hengshen HFW133PA-3KHF10A-1 / 1-1000 (Jiangsu Hengshen Co., Ltd.) carbon fiber unidirectional fabric was used as the reinforcing material. The conventional prepreg resin system provided in Comparative Example 1 was combined with the reinforcing material by melt impregnation to form a low-grammage unidirectional prepreg.

[0089] Prepreg Comparison Example 2-3

[0090] This comparative example provides a non-high grammage low-temperature curing unidirectional prepreg, which consists of two parts: carbon fiber fabric of specification HFW133PA-3KHF10A-1 / 1-1000 (Jiangsu Hengshen Co., Ltd.) and the prepreg resin system provided in Comparative Examples 2-3.

[0091] Prepreg Comparative Example 4

[0092] This comparative example provides a non-high grammage low-temperature curing fabric prepreg, which consists of two parts: carbon fiber fabric of specification HFW200T-A2-2 / 2-1000 (Jiangsu Hengshen Co., Ltd.) and a resin system of conventional prepreg resin system provided in Comparative Example 1.

[0093] Prepreg preparation: Jiangsu Hengshen HFW200T-A2-2 / 2-1000 (Jiangsu Hengshen Co., Ltd.) carbon fiber fabric was used as the reinforcing material. The conventional prepreg resin system provided in Comparative Example 1 was combined with the reinforcing material by melt impregnation to form a non-high weight low temperature curing unidirectional prepreg.

[0094] Prepreg Comparative Example 5

[0095] This comparative example provides a high-grammage conventionally cured fabric prepreg, which consists of two parts: carbon fiber fabric of specification HFW650T-A2-2 / 2-1000 (Jiangsu Hengshen Co., Ltd.) and a conventionally cured resin system provided in Comparative Example 1.

[0096] Prepreg preparation: Jiangsu Hengshen HFW650T-A2-2 / 2-1000 (Jiangsu Hengshen Co., Ltd.) carbon fiber fabric was used as the reinforcing material. The conventional prepreg resin system provided in Comparative Example 1 was combined with the reinforcing material by melt impregnation to form a high-grammage conventional cured fabric prepreg.

[0097] Experimental Example 1

[0098] The physicochemical properties of the resin systems provided in Examples 1-5 and Comparative Examples 1-3 are compared in Table 1:

[0099] Table 1. Physicochemical properties of resin system a and resin system b in the examples and comparative examples.

[0100]

[0101]

[0102] Table 2. Tack life of prepregs prepared from resin systems at the same impregnation level

[0103]

[0104] As can be seen from the data in Tables 1 and 2, the viscosity of any resin system in the embodiments of this invention at 60°C is much lower than that of the traditional prepreg resin (Comparative Example 1). During the subsequent prepreg manufacturing process, such as impregnation at 40–50°C as mentioned above, the resin can quickly and unimpededly penetrate into the fabric carrier. Furthermore, this application found that the resin can achieve a rapid increase in viscosity within a short period at room temperature. This is mainly due to the hydrogen-bonding chelation effect between the active magnesium oxide and the CTBN-modified epoxy resin in the resin system of this application. This effect is even more pronounced during the subsequent prepreg manufacturing process. As can be clearly seen from Table 2, in the preparation of traditional high-grammage prepregs, if the impregnation degree is increased to 85% or above, it is mostly done by continuously increasing the impregnation temperature. This leads to a loss or even disappearance of the tack life of the prepreg in subsequent operations. In Comparative Example 1 of Table 2, the prepreg with an 85% impregnation degree only has a tack life of 2 days remaining, becoming a prepreg without latency, which greatly affects the subsequent application and application of the prepreg. In contrast, the prepreg resin system of the present invention can effectively avoid the problem of reduced tack life. The methods used in Comparative Examples 2 and 3 are not within the scope of the present invention, and they also have different degrees of disadvantages compared to the examples, such as excessively long non-destructive separation time of the PE film on the prepreg, which will have an adverse impact on the efficiency of industrial applications.

[0105] Experimental Example 2

[0106] Laminates were prepared by molding and curing the prepregs provided in Examples 1-6 at 80℃ / 2h + 100℃ / 2h. Laminates were also prepared by molding and curing the prepregs provided in Comparative Examples 1-5 at 120℃ / 2h + 150℃ / 2h. The mechanical and physicochemical properties of the laminates are shown in Table 3 below.

[0107] Table 3. Mechanical and physicochemical properties of prepreg laminates after curing in the examples and comparative examples.

[0108]

[0109]

[0110] The results from Prepreg Example 1 and Prepreg Comparative Example 1 show that the chemical copolymerization of bisphenol A epoxy resin and carboxyl-terminated butadiene nitrile (NBR) increases the molecular chain size through a ring-opening crosslinking reaction. The copolymer chelates with the active magnesium oxide thickener at room temperature, further increasing the molecular chain size of each component in the resin system macroscopically through intermolecular forces, which manifests as an increase in the resin system's viscosity. Furthermore, the low-temperature curing resin has low viscosity at room temperature and remains in a liquid state, exhibiting good permeability to reinforcing materials during prepreg preparation. This helps reduce internal stress in the composite laminate during curing and lowers the requirements for equipment and other auxiliary materials, resulting in better mechanical properties compared to the comparative example. The effective combination of curing agents ensures both the degree of curing of the prepreg and energy consumption, while simultaneously reducing the manufacturing cost of the composite material.

[0111] The results from Prepreg Examples 1-5 and Prepreg Comparative Example 2 show that the carboxyl-terminated nitrile rubber (CTBN) is directly mixed into the epoxy resin through physical blending. Although the carboxyl-terminated nitrile rubber is distributed as dispersed phase particles in the matrix resin, and the purpose of toughening the matrix epoxy resin is achieved by dispersing stress to suppress crack generation, it is mainly through physical action without a chemical reaction process. As a result, the mechanical properties of the cured board are not as good as those in Example 1. At the same time, the reason why the prepreg prepared in Comparative Example 2 requires too long a time for non-destructive separation of the PE film and the prepreg has been explained in the resin comparison. This will also affect the efficiency of subsequent applications.

[0112] The results from prepreg Examples 1-5 and Prepreg Comparative Example 3 show that after adding magnesium hydroxide instead of active magnesium oxide as a thickener to the resin matrix, it exhibits the same problem as Comparative Example 2 - "the time required for non-destructive separation of PE film and prepreg is too long", and the time required is even longer, up to 15 days, which greatly reduces the efficiency of downstream applications and makes continuous production impossible.

[0113] Example 6 and Comparative Example 4 of prepreg show that the heavy-weight fabric prepreg achieves better mechanical properties of composite materials than conventional prepregs, while improving the efficiency of the laying process and reducing production costs.

[0114] The results of Example 6 and Comparative Example 5 show that the performance of the heavy-weight fabric prepreg remains excellent during the energy-saving low-temperature curing process. At the same time, the low-temperature curing stage provides a longer process window for the resin, which allows the resin to better penetrate the reinforcing material, thereby ensuring the uniformity of the resin inside the prepreg during the curing process. This results in excellent mechanical properties on a macroscopic scale.

[0115] In summary, the low-temperature curing resin system suitable for heavy-weight impregnation provided in this application comprises an epoxy-modified block polymer containing CTBN. This block polymer is obtained by chemical copolymerization of bisphenol A type epoxy resin and carboxyl-terminated butadiene nitrile, which can increase the molecular weight of the resin. Furthermore, the epoxy-modified block polymer containing CTBN can chelate with the thickener component in this application at room temperature. The resulting low-temperature curing resin system suitable for heavy-weight impregnation has low viscosity at room temperature and remains in a liquid state initially. At low temperatures (40-50°C), it effectively impregnates heavy-weight (400-800 gsm) reinforcing materials (unidirectional and fabric) thoroughly. This allows for good permeability of the reinforcing material during prepreg preparation. In the later impregnation process, the molecular chains of each component in the resin system are further "increased" macroscopically through intermolecular forces, increasing the apparent viscosity of the resin to the viscosity required for prepregs, thus providing good operability. This method helps reduce internal stress in composite laminates during the curing process and the requirements for equipment and other auxiliary materials, thereby reducing defects such as cracks and energy consumption, and lowering the manufacturing cost of composite materials. This approach makes prepreg molding a low-cost, simple, and effective method.

[0116] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A low-temperature curing resin system suitable for high-grammage impregnation, characterized in that, Its raw materials, by weight, include 50-70 parts of first epoxy resin, 15-30 parts of epoxy modified block polymer containing CTBN, 3-7 parts of thickener, 1-3 parts of defoamer and 6-21 parts of curing agent; The preparation method of the epoxy modified block polymer containing CTBN includes: mixing the second epoxy resin and CTBN in a functional ratio of epoxy group:carboxyl group of 1-3:1, passing a protective gas through the mixture, heating to 80-120℃, reacting for 2-3 hours, and then cooling to room temperature to obtain the product. The thickener is active magnesium oxide.

2. The low-temperature curing resin system suitable for large-grammage impregnation according to claim 1, characterized in that, The protective gas is nitrogen.

3. The low-temperature curing resin system suitable for large-grammage impregnation according to claim 1, characterized in that, The curing agent comprises a curing component and an accelerator component in a mass ratio of 6-16:1-5.

4. The low-temperature curing resin system suitable for large-grammage impregnation according to claim 3, characterized in that, The curing components include one or more combinations of diaminodiphenylmethane, dicyandiamide and its derivatives, modified polyamines, 1,3-bis(aminomethyl)cyclohexane and 3-aminomethyl-3,5,5-trimethylcyclohexylamine.

5. The low-temperature curing resin system suitable for large-grammage impregnation according to claim 3, characterized in that, The promoting component includes one or more combinations of modified imidazole accelerators and modified organic urea accelerators.

6. The low-temperature curing resin system suitable for large-grammage impregnation according to claim 5, characterized in that, The modified imidazole accelerators include one or more combinations of 1-(2-aminoethyl)-2-ethylimidazole and 1-(2-aminoethyl)-2-methylimidazole.

7. The low-temperature curing resin system suitable for large-grammage impregnation according to claim 1, characterized in that, The first epoxy resin and the second epoxy resin each independently comprise one or more of the following: bisphenol F epoxy resin, phenolic epoxy resin with a viscosity of 1100~1700cps, phenolic epoxy resin with a viscosity of 3500~6000cps, bisphenol A type epoxy resin, and polyurethane modified epoxy resin.

8. The low-temperature curing resin system suitable for large-grammage impregnation according to claim 1, characterized in that, The defoamer includes one or more of BYK-320, BYK-A530, and BYK-1974.

9. A method for preparing a low-temperature curing resin system suitable for high-grammage impregnation, characterized in that, It includes uniformly mixing the raw materials in the low-temperature curing resin system suitable for heavy weight impregnation as described in any one of claims 1-8.

10. The method for preparing a low-temperature curing resin system suitable for large-grammage impregnation according to claim 9, characterized in that, Both the thickener and the curing agent are pre-mixed evenly with a portion of the first epoxy resin; The thickener and a portion of the first epoxy resin are pre-dispersed at a ratio of 1:(2-10) at a speed of 1000-2000 rpm for 8-12 minutes. After discharge, the pre-dispersed thickener is obtained by grinding 2-4 times. The curing agent and a portion of the first epoxy resin are pre-dispersed at a ratio of 1:(1-10) at a speed of 2000-3000 rpm for 3-5 minutes. After discharge, the pre-dispersed curing agent is obtained by grinding 1-2 times.

11. The method for preparing a low-temperature curing resin system suitable for large-grammage impregnation according to claim 10, characterized in that, Mixing the raw materials uniformly includes: first dispersing the remaining first epoxy resin at 50-70°C until it reaches a uniform state, then cooling it to 25-35°C, and then adding the pre-dispersed curing agent, the epoxy modified block polymer containing CTBN, the pre-dispersed thickener, and the defoamer, and mixing them uniformly.

12. A high-grammage impregnated low-temperature curing prepreg, characterized in that, It includes a reinforcing material and a low-temperature curing resin system suitable for heavy-weight impregnation prepared by the preparation method of the low-temperature curing resin system suitable for heavy-weight impregnation as described in any one of claims 1-8 or as described in any one of claims 9-11, wherein the reinforcing material and the low-temperature curing resin system are impregnated at 40-50°C.

13. The high-grammage impregnated low-temperature curing prepreg according to claim 12, characterized in that, The reinforcing material includes unidirectional fabric or patterned fabric with a unidirectional surface weight of 400-800 gsm; the pattern of the patterned fabric includes plain weave, twill weave and satin weave fabric.

14. A low-temperature curing laminate, characterized in that, The high-grammage impregnated low-temperature curing prepreg as described in any one of claims 12-13 is obtained by compression molding, wherein the compression molding includes first curing at 75-85°C for 2-3 hours, and then curing at 95-105°C for 2-3 hours.

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