A front-line polymeric carbon fiber reinforced epoxy composite material and a method for manufacturing the same

Abstract

The application discloses a front-line polymerization carbon fiber reinforced epoxy resin matrix composite material and a preparation method thereof. A photoacid initiator and a thermal free radical initiator are put into an epoxy resin, mixed at 40-60 DEG C and vacuum degassed to obtain a low-viscosity front-line polymerization resin system. When curing, a light or heat stimulus is applied to one end or a local area of a component to initiate a free radical-induced cationic front-line polymerization, and the curing front is self-sustained and outwardly propagated by using reaction heat, so that the whole rapid curing of the composite material is completed. The method does not need to continuously heat the whole component, the curing speed is high, and the molding energy consumption can be reduced; the axial heat conduction characteristics of the carbon fiber can promote the transfer of the reaction heat to the uncured area, and the vacuum bag pressure can reduce the porosity and improve the molding density. The technology is suitable for low-cost manufacturing, on-orbit manufacturing, rapid repair and other scenes of the composite material.

Description

Technical Field

[0001] This invention belongs to the field of low-energy-consumption rapid curing technology of thermosetting resin-based composite materials, specifically involving the synergistic design between front-line polymer resin and continuous carbon fiber reinforcement, hand lay-up impregnation / resin film impregnation / RTM / VARTM liquid molding process, vacuum bag compression structure, light-transmitting encapsulation material, and front-line propagation speed control. Background Technology

[0002] Carbon fiber reinforced epoxy resin matrix composites possess advantages such as lightweight, high specific strength, high specific modulus, and strong designability, making them widely used in aerospace, transportation, and high-end equipment. Traditional thermosetting resin matrix composites typically rely on equipment such as ovens, autoclaves, or hot presses for overall heating, requiring prolonged holding at high temperatures and external pressures to achieve a stable cured structure. This type of process suffers from high energy consumption, long manufacturing cycles, significant equipment size limitations, and heavy thermal management burdens, particularly pronounced in large components, on-site repairs, and energy-constrained environments.

[0003] Frontline polymerization is a chain-like curing method that initiates a polymerization reaction through localized light or heat stimulation, and then uses the heat released from the reaction to drive the continued curing of adjacent areas. This method typically does not require continuous heating of the entire component, and features low energy consumption, rapid curing, and directional propagation of spatial regions. Existing technologies have disclosed frontline polymerization methods for cationic polymerizable monomers, enabling frontline polymerization through photoacid generators and heat stimulation; other technologies have disclosed the use of light sources to initiate frontline polymerization at the resin mixture front to prepare lightweight epoxy resin substitutes for wood, or the use of thermally initiated frontline polymerization for trenchless pipeline repair materials. These technologies demonstrate that frontline polymerization resin systems and the concept of localized initiation curing have a certain research and technological foundation.

[0004] However, when applying frontier polymerization to continuous fiber-reinforced composites, the technical challenges extend beyond simply whether the resin can undergo frontier polymerization. It also requires consideration of the synergistic matching between resin exothermicity, fiber thermal conductivity, fiber content, fiber orientation, encapsulation light transmittance, external compaction conditions, and frontier propagation velocity. Carbon fibers possess high axial thermal conductivity, which can promote the transfer of reaction heat to uncured areas; however, as the carbon fiber volume fraction increases, the amount of reactive resin per unit volume decreases, weakening the overall exothermic capacity of the system. Improper matching can lead to problems such as slow frontier propagation, frontier quenching, localized overheating, or uneven curing along the thickness direction. Low thermal conductivity fibers such as glass fibers may also inhibit frontier propagation due to insufficient heat transfer.

[0005] Existing patents related to epoxy resin compositions, prepregs, and carbon fiber composites mostly focus on resin viscosity, tackifying temperature, prepreg preparation, or conventional thermosetting conditions. Related photosensitive resin patents include reinforcing materials such as carbon fibers, but their focus is usually on the preparation of photocurable resins, and they do not establish quantitative process conditions or process optimization methods around the heat transfer-exothermic matching, pore control, and thickness direction curing consistency in front-end polymerization of continuous carbon fiber composites. Summary of the Invention

[0006] The purpose of this invention is to provide a front-line polymerized carbon fiber reinforced epoxy resin matrix composite material and its preparation method, so as to solve the problems of unstable and asynchronous front-line propagation, easy quenching of curing reaction, uneven curing, difficulty in controlling fiber content, and high porosity of composite material when using existing front-line polymerized resins to prepare carbon fiber composite materials.

[0007] To achieve the above objectives, the present invention adopts the following technical solution.

[0008] A method for preparing a front-line polymerized carbon fiber epoxy composite material includes the following steps:

[0009] (1) Resin system preparation: Mix bisphenol A type epoxy resin with optional alicyclic epoxy resin, add photoacid initiator and thermal free radical initiator, stir at 40-60℃ for 60-180 min to make the initiator uniformly dissolved or dispersed, and then vacuum degas for 10-30 min.

[0010] (2) Carbon fiber reinforcement layup, impregnation and encapsulation: Select continuous carbon fiber unidirectional cloth or fabric, lay it on the surface of the isolation membrane or mold in the predetermined layup direction, and select hand layup impregnation, resin film impregnation or liquid molding process such as RTM and VARTM to introduce front-line polymer resin according to the component structure and molding requirements.

[0011] When using hand lay-up or resin film impregnation, the front-line polymerized resin is directly coated onto the surface of the carbon fiber reinforcement, or a resin film is made and alternately laid with the carbon fiber reinforcement. A specific process is used to promote the full impregnation of the resin into the fiber bundles and interlayer regions. Pre-compaction is performed every 2 to 6 layers, followed by the sequential placement of a transparent cover plate or light-transmitting pressure plate, breathable material, and vacuum bag film. The light-transmitting vacuum bag is then sealed using putty strips or sealing strips.

[0012] When using liquid molding processes such as RTM, VARTM, or vacuum-assisted impregnation, the dry carbon fiber reinforcement is first laid in the mold to form a preform. Then, the release cloth, flow medium, glue inlet, glue outlet, breathable material, and vacuum bag film are arranged in sequence, and sealed with putty strips or sealing strips. After the vacuum reaches the set vacuum level, the front-line polymer resin is injected into the preform by pressure or vacuum negative pressure to complete the impregnation.

[0013] (3) Selection criteria for transparent vacuum bags: The vacuum bag film, transparent cover plate, or transparent pressure plate used shall have a transmittance of not less than 60%, preferably not less than 80%, within the local initiation wavelength range to ensure that ultraviolet light can pass through the vacuum bag film and / or transparent cover plate to reach the local initiation area of ​​the resin. After encapsulation, the vacuum is drawn to -0.06 to -0.10 MPa, and pressure is maintained continuously during resin impregnation, local initiation, and front-line propagation to reduce porosity, improve the compaction degree of the layup, and ensure stable front-line propagation.

[0014] (4) Local initiation and frontal propagation control: Apply ultraviolet light and / or thermal stimulation to the end or upper surface of the resin-containing carbon fiber layup to achieve a self-sustaining frontal propagation state in the local initiation area; then, based on the results of infrared thermal imaging or thermocouple monitoring, adjust the initiator dosage, initial resin temperature, irradiation time, carbon fiber volume fraction, fiber orientation, and vacuum compaction conditions to control the polymerization frontal propagation at a rate of 1.0–8.0 min. -1 The propagation speed is controlled at 180-280℃.

[0015] (5) Curing quality control: The porosity of the composite material is not higher than 3%, the difference in the start time of temperature rise between different layers in the thickness direction is not greater than 30 s, and the content of insoluble components in the resin is not less than 90%.

[0016] Specifically, this invention claims a method for preparing a front-line polymerized carbon fiber reinforced epoxy resin matrix composite material, comprising the following steps:

[0017] (1) Prepare an epoxy resin mixture capable of undergoing free radical-induced cationic frontier polymerization, wherein the epoxy resin mixture comprises an epoxy resin matrix, a photoacid initiator and a thermal free radical initiator;

[0018] (2) The epoxy resin mixture is used to impregnate the carbon fiber reinforcement to form a resin-containing carbon fiber layup;

[0019] (3) The resin-containing carbon fiber layup is placed in a vacuum bag compression structure including a substrate, a separator, a transparent cover plate and a vacuum bag film, and a vacuum is drawn and negative pressure is maintained for compaction;

[0020] (4) Apply ultraviolet light and / or heat stimulation to the local initiation area of ​​the resin-containing carbon fiber layup through the light-transmitting area of ​​the vacuum bag film and / or transparent cover plate to initiate the polymerization front;

[0021] (5) Adjust the amount of photo-acid initiator, the amount of thermal free radical initiator, the volume fraction of carbon fiber, the fiber orientation and the vacuum compaction conditions so that the polymerization front line can continuously propagate in the carbon fiber reinforcement at a preset front line propagation speed and complete the curing.

[0022] The preset front-line propagation velocity is 1.0–8.0 cm·min. -1 The porosity of the composite material after curing is no higher than 3%.

[0023] The carbon fiber reinforcement has a volume fraction of 20-60% in the composite material, preferably 25-55%.

[0024] When the carbon fiber volume fraction is 20-30%, the amount of photo-acid initiator is 0.6-1.5 wt% of the epoxy resin matrix, and the amount of thermal free radical initiator is 0.5-1.5 wt% of the epoxy resin matrix. When the carbon fiber volume fraction is greater than 30% but not higher than 60%, the amount of photo-acid initiator is 1.0-2.5 wt% of the epoxy resin matrix, and the amount of thermal free radical initiator is 1.0-2.0 wt% of the epoxy resin matrix, in order to avoid the impact of increased thermal conductivity of carbon fiber and decreased heat release of resin on the propagation of polymerization front.

[0025] The photoinitiator is a diaryliodomonium salt and / or a triarylthiomonium salt, and the thermal free radical initiator is one or more of benzinophene, peroxide thermal initiators, or azo thermal initiators.

[0026] The epoxy resin matrix includes bisphenol A type epoxy resin, and may further include alicyclic epoxy resin and other types of epoxy resin; the alicyclic epoxy resin accounts for 0-60% of the total mass of the epoxy resin matrix; other types of epoxy resin account for 0-30% of the total mass of the epoxy resin matrix.

[0027] The alicyclic epoxy resin includes 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylate and / or 4,5-epoxyhexane-1,2-dicarboxylic acid diglycidyl ester; by adjusting the type and content of the alicyclic epoxy resin, the peak temperature before polymerization is made to be 180-280℃.

[0028] The vacuum bag film has a transmittance of not less than 60% in the wavelength range of 320-420 nm, preferably not less than 80%, and does not melt and crack or shrink significantly at the peak temperature of front-line polymerization;

[0029] The transparent cover plate is made of quartz glass, borosilicate glass, heat-resistant transparent resin board, fiberglass, or a pressure plate with a light-transmitting area. The transparent cover plate is used to simultaneously provide a pressing surface and a local light-initiating channel.

[0030] The vacuum level in step (3) is -0.06 to -0.10 MPa, preferably -0.08 to -0.10 MPa; the vacuum or pressure is maintained continuously during the propagation of the polymerization front.

[0031] The carbon fiber reinforcement is a unidirectional carbon fiber fabric, a multidirectional carbon fiber fabric, a carbon fiber warp-knitted fabric, or a combination thereof; the angle between the carbon fiber axis and the direction of polymerization front propagation is 0 to 45°, preferably 0 to 15°.

[0032] The location, peak temperature, interlayer temperature rise onset time, and in-plane curing uniformity of the polymerization front are monitored by infrared thermal imager or thermocouple array. Based on the monitoring results, the ultraviolet light power, irradiation time, initial resin temperature, or vacuum pressure are adjusted to ensure that the temperature rise onset time difference between different layers in the thickness direction is no more than 30 s.

[0033] The local initiation region is located at one end or the upper surface of the resin-containing carbon fiber layup. The ultraviolet light irradiation time is 5 to 120 seconds, and the irradiation stops after a self-sustaining polymerization front is formed.

[0034] When the propagation velocity at the polymerization front is less than 1.0 cm·min -1 At this time, increasing the amount of photoinitiator, increasing the initial resin temperature, increasing the alicyclic epoxy resin content, or decreasing the fiber volume fraction can help; when the front-line propagation velocity before polymerization is higher than 8.0 cm·min -1 If the peak temperature is higher than 280℃, reduce the amount of photoinitiator, reduce the initial temperature of the resin, reduce the content of exothermic alicyclic epoxy resin, or improve the heat dissipation capacity.

[0035] The resin-containing carbon fiber layup is pre-compacted every 2 to 6 layers. The resin impregnation method is hand layup impregnation, resin film impregnation, vacuum-assisted impregnation, or liquid molding processes such as RTM / VARTM.

[0036] This invention also claims a front-line polymerized carbon fiber epoxy composite material, prepared by the above method, wherein the composite material comprises a front-line polymerized and cured epoxy resin matrix and a continuous carbon fiber reinforcement, the composite material porosity is not higher than 3%, and the content of insoluble resin components is not less than 90%.

[0037] The difference in curing start time between different layers in the thickness direction of the composite material is no more than 30 s.

[0038] The present invention further claims the use of the composite material for low-energy-consumption rapid curing structural components, in-orbit manufacturing components, field repair components, or large composite material locally cured components.

[0039] This invention further claims a front-line polymerized carbon fiber composite material preparation system, comprising an ultraviolet light source, a vacuum bag film, a silicone rubber pad or end elastic block, a carbon fiber layup, a transparent cover plate, a separator film, and a substrate or mold base plate, wherein the substrate or mold base plate is used to support the carbon fiber layup and provide a molding reference surface, the separator film is disposed between the carbon fiber layup and the substrate or mold base plate, the vacuum bag film is used to form a sealed encapsulation space for the carbon fiber layup, the transparent cover plate and the separator film, the transparent cover plate is disposed above the carbon fiber layup, and is used to provide a pressing surface for bonding the upper surface of the composite material, so that the carbon fiber layup maintains stable thickness and interlayer bonding under the negative pressure of the vacuum bag film.

[0040] Furthermore, Figure 1 The vacuum bag compression local initiation structure shown is not merely a schematic diagram of an experimental device, but a concrete manifestation of the key protection points of the composite material of this invention: it integrates light-transmitting vacuum encapsulation, elastic end thermal management, continuous carbon fiber thermal conduction channels, and compaction and demolding structure into one unit, enabling frontline polymerization in the composite material layup to have the engineering conditions of being able to start, propagate, compact, and demold.

[0041] The ultraviolet light source 1 is used to provide local initiation energy to the end or upper surface of the carbon fiber layup 4, so that the local resin first generates free radicals to induce the cationic front polymerization reaction; the ultraviolet light source 1 only needs to work before the polymerization front is formed, and can stop continuous irradiation after the self-sustaining propagation front is formed.

[0042] The vacuum bag film 2 is used to form a sealed encapsulation space for the carbon fiber layup 4, the transparent cover plate 5 and the separator 6, and to convert the external atmospheric pressure into continuous pressure after vacuuming; preferably, the vacuum bag film 2 has an ultraviolet transmittance of not less than 60%, more preferably not less than 80% in the wavelength range of 320 to 420 nm, so as to ensure that local photoinitiation is completed under vacuum compaction.

[0043] Silicone rubber pads / end elastic blocks 3 are disposed at one or both ends of the carbon fiber layup 4 to limit the resin flow boundary, compensate for layup thickness differences and form elastic holding ends; at the same time, the low thermal conductivity of silicone rubber material helps to reduce the rapid dissipation of heat at the ends, improve the heat accumulation capacity of the local initiation area and the front-line initiation stability.

[0044] The carbon fiber layup 4 is a continuous carbon fiber reinforcement containing front-line polymerized epoxy resin, which is the main molding object of this invention. Its fiber axis is consistent with the predetermined propagation direction of the polymerization front or forms an angle of 0 to 45°, so that the thermal conductivity of the carbon fiber axis can be used to promote the transfer of reaction heat to the uncured area, while controlling the fiber volume fraction to avoid insufficient heat release of the resin.

[0045] The transparent cover plate 5 is placed above the carbon fiber layup 4 to provide a pressing surface for bonding the upper surface of the composite material, so that the carbon fiber layup 4 maintains stable thickness and interlayer bonding under the negative pressure of the vacuum bag film 2; at the same time, the transparent cover plate 5 can serve as a light-transmitting area for ultraviolet light to enter the local initiation area, thereby achieving "compaction-initiation" synchronization.

[0046] The release membrane 6 is disposed between the carbon fiber layup 4 and the substrate / mold base plate 7 and / or adjacent to the transparent cover plate 5 to prevent the resin from sticking to the mold or cover plate and to ensure that the composite material can be completely demolded after curing; the release membrane 6 can also work with the vacuum bag film 2 and the transparent cover plate 5 to maintain the layup boundary morphology.

[0047] The base / mold base plate 7 is used to support the carbon fiber layup 4 and provide a molding reference surface. Its material can be silicone rubber, metal, ceramic or composite mold material. Preferably, the thermal conductivity of the base / mold base plate 7 is matched with the frontal propagation speed and peak temperature to avoid excessive heat dissipation leading to frontal quenching or excessive insulation leading to local overheating.

[0048] based on Figure 1 The structural innovations of this invention, as shown, include: First, the vacuum bag film 2 and the transparent cover plate 5 together form an encapsulation structure that combines negative pressure compaction and light transmission initiation functions, enabling the carbon fiber composite material to directly initiate frontline polymerization under vacuum compaction; Second, the silicone rubber pad / end elastic block 3 combines end flow restriction, elastic compensation, and thermal management functions, which helps improve end initiation stability; Third, the fiber thermal conduction direction of the carbon fiber layup 4 is designed in coordination with the frontline polymerization propagation direction, so that the carbon fiber is not only a reinforcing material but also participates in the regulation of frontline heat transfer; Fourth, the isolation film 6 and the substrate / mold base plate 7 together define the layup boundary and demolding interface, so that low porosity and good thickness consistency can still be maintained during rapid frontline curing.

[0049] In summary, this invention aims to use the frontier polymerized epoxy resin formulation as a basic condition, and to integrate factors such as initiator dosage, carbon fiber type, volume fraction, fiber thermal conductivity, encapsulation material, compaction method, frontier propagation velocity, and peak temperature into a synergistic control system. This system achieves stable frontier propagation, low porosity, and uniform curing from the perspective of composite material molding and curing quality. Compared with existing technologies, the beneficial effects of this invention are:

[0050] (1) The focus of protection of this invention is not on the resin formulation alone, but on the synergistic control of the frontier polymerized resin and the molding conditions of the carbon fiber composite material. By establishing a correspondence between factors such as carbon fiber volume fraction, initiator dosage, resin exothermic capacity and frontier velocity, frontier quenching caused by insufficient resin exothermic capacity under high fiber content can be avoided, as well as local overheating and uneven curing caused by high initiator dosage or high exothermic resin.

[0051] (2) By selecting a vacuum bag film and / or a light-transmitting cover plate with ultraviolet transmittance, local photoinitiation is completed under vacuum conditions, which takes into account both front-line polymerization initiation and composite material compaction molding, and solves the problem that it is difficult to carry out local photoinitiation under ordinary opaque packaging conditions.

[0052] (3) By continuously compressing under negative pressure during the polymerization process, air bubbles can be expelled, resin impregnation and interlayer bonding can be promoted, porosity can be reduced, and curing density can be improved under rapid curing conditions.

[0053] (4) By monitoring and controlling the synchronization of frontal velocity, peak temperature and thickness direction temperature rise, carbon fiber composite materials can achieve rapid, low porosity and relatively uniform curing without the need for long-term overall heating. Attached Figure Description

[0054] Figure 1 This is a schematic cross-sectional view of the front-line polymerized carbon fiber composite material preparation system in an embodiment of the present invention.

[0055] Figure 1 In the diagram, 1 is the ultraviolet light source, 2 is the vacuum bag film, 3 is the silicone rubber pad / end elastic block, 4 is the carbon fiber layup, 5 is the transparent cover plate, 6 is the isolation film, and 7 is the substrate / mold base plate.

[0056] Figure 2 This is a schematic diagram of the polymerization front propagation direction under the isometric state of carbon fiber layup according to the present invention. Detailed Implementation

[0057] The technical solution of the present invention will be further described below with reference to embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Those skilled in the art can make equivalent substitutions for the resin system, initiation method, fiber type, encapsulation material, and monitoring method without departing from the concept of the present invention.

[0058] The setup of the embodiment is as follows Figure 1 1-Ultraviolet light source (used to apply ultraviolet light stimulation to the ends of carbon fiber layups or local initiation areas, so that the front-line polymerization resin generates initial active centers and forms a self-sustaining propagating polymerization front);

[0059] 2- Vacuum bag film (used to form a sealed vacuum space together with the substrate / mold base plate, and to continuously apply negative pressure to compact the carbon fiber layup after vacuuming; it has ultraviolet transmittance at least in the local initiation area to ensure that photoinitiation can still be performed in the encapsulated state).

[0060] 3-Silicone rubber pad / end elastic stop (used to limit the end position of resin and carbon fiber layup, prevent resin from overflowing during vacuuming and frontal propagation, and provide elastic compensation and a certain thermal insulation effect, which is conducive to the stable formation of polymerization front in the end initiation area).

[0061] 4- Carbon fiber layup (formed by impregnation of continuous carbon fiber reinforcement with front-line polymerized epoxy resin, which is a preform of composite material to be cured; its fiber direction is preferably consistent with the direction of front-line polymerization or forms a small angle, so as to utilize the axial heat conduction of carbon fiber to promote the heat transfer of reaction).

[0062] 5- Transparent cover plate (used to provide a bonding and pressing surface for the upper surface of the carbon fiber layup, and to work with the vacuum bag film to achieve thickness control and uniform compaction; it can be made of materials with ultraviolet transmittance such as glass, fiberglass, and plexiglass, so that ultraviolet light can pass through the cover plate to irradiate the localized initiation area).

[0063] 6-Resettling membrane (placed between the carbon fiber layup and the substrate / mold base plate to prevent the cured composite material from sticking to the mold, facilitate demolding, keep the bottom surface of the layup flat and reduce resin leakage).

[0064] 7-Base / Mold base plate (used to support components such as the release liner, carbon fiber layup, silicone rubber pad and transparent cover, and as a supporting base for vacuum bag compression sealing to ensure dimensional stability and bottom surface flatness during the composite material molding process).

[0065] 8. An infrared thermal imager or a thermocouple array attached to the carbon fiber layup is used to monitor the location of the polymerization front, peak temperature, interlayer temperature rise onset time, and analyze the in-plane curing uniformity.

[0066] Example 1: Frontline Polymerization Base Forming Method for Carbon Fiber Composite Materials

[0067] 98 parts by weight of E51 epoxy resin, 1 part by weight of diaryliodonium salt photoinitiator, and 1 part by weight of benzylpinazone thermal free radical initiator were weighed and stirred at 50°C for 120 min, followed by vacuum degassing for 15 min to obtain front-line polymerized epoxy resin. Unidirectional carbon fiber fabric was selected as the reinforcement, and 8 layers were laid with the fiber axis aligned with the predetermined front-line propagation direction. Each layer of carbon fiber fabric was uniformly coated with the front-line polymerized epoxy resin, and pre-compaction was performed after every 4 layers.

[0068] The impregnated carbon fiber layup is placed on a release membrane, a transparent cover plate is placed on its upper surface, and then a vacuum bag membrane is applied. The vacuum bag membrane has an ultraviolet transmittance of not less than 80% at 365 nm, and the vacuum degree is maintained at -0.08 to -0.10 MPa. One end of the layup is irradiated with an ultraviolet light source for 10 to 60 seconds to form a stable polymerization front, after which continuous irradiation is stopped. The polymerization front propagates along the carbon fiber axis and completes the curing process.

[0069] Example 2: Matching different carbon fiber volume fractions with frontline propagation velocity

[0070] Using the same E51 resin and initiator system as in Example 1, the carbon fiber volume fraction was adjusted by changing the number of carbon fiber fabric layers. Experimental and simulation results show that when the carbon fiber volume fraction is low, the axial thermal conductivity of the carbon fiber is beneficial to increasing the frontier propagation velocity; when the carbon fiber volume fraction is too high, the decrease in resin content leads to a decrease in the system's exothermic capacity, and the frontier propagation velocity no longer increases.

[0071]

[0072] Therefore, the carbon fiber content should be matched with the exothermic capacity of the resin system. In this invention, the carbon fiber volume fraction is preferably controlled between 25% and 55%, and the amount of photoinitiator is adjusted accordingly or the exothermic capacity of the resin is increased based on the fiber volume fraction to ensure continuous propagation of the polymerization front.

[0073] Example 3: Synergistic control of initiation dose and fiber content

[0074] When the carbon fiber volume fraction is 20-30%, 0.6-1.5 wt% of photoacid initiator (PAG) and 0.5-1.5 wt% of thermal free radical initiator (RTI) can be selected. When the carbon fiber volume fraction is greater than 30% but not higher than 60%, due to the decrease in resin volume fraction, it is preferable to adjust the photoacid initiator to 1.0-2.5 wt% and the thermal free radical initiator to 1.0-2.0 wt%, and 10-60 wt% of alicyclic epoxy resin can be introduced to improve the system's exothermic capacity or reaction propagation rate.

[0075]

[0076] The aforementioned range is used to define the process control range of this invention. In actual preparation, the position and peak temperature of the polymerization front can be monitored using an infrared camera and thermocouples. When the rate is lower than the target range, the amount of PAG or the exothermic capacity of the resin can be increased; when the peak temperature is too high or the rate is too fast, the amount of PAG can be reduced or the heat dissipation capacity can be increased.

[0077] Example 4: Effect of UV-transmitted vacuum bag pressure on porosity and curing uniformity

[0078] An epoxy resin system with E51:E221 = 1:1 and PAG:RTI = 1wt%:1wt% was used to compare three molding methods: no external pressure, simple clamping, and UV-transmitted vacuum bagging. The results showed that vacuum bagging can significantly increase fiber content and reduce porosity.

[0079]

[0080] Therefore, transparent or semi-transparent vacuum bags should not only be used for vacuum compaction but also meet the requirements for localized UV initiation. Compared with ordinary opaque vacuum bags, UV-transmitting vacuum bags enable the composite material to complete front-line initiation under encapsulation and compaction conditions, thereby reducing air bubble residue and interlayer voids during rapid curing.

[0081] Example 5: Control of curing uniformity in the thickness direction

[0082] Multiple thermocouples are arranged within the 8-layer carbon fiber layup, or infrared thermal imaging is used to monitor the frontal propagation process. By controlling the vacuum level, the holding state of the transparent cover plate, and the frontal propagation speed, the onset time of temperature rise between different layers is made substantially synchronized. Preferably, the difference in the onset time of temperature rise between different layers in the thickness direction is no more than 30 s, more preferably no more than 10 s; the peak temperature difference between layers is controlled within an acceptable range to reduce local uncured areas and local overheating.

[0083]

[0084] Comparative Example 1: Using only the front-line polymer resin formulation without controlling the composite material processing conditions

[0085] If only epoxy resin, photo-acid initiator, and thermal free radical initiator are used in the formulation, without controlling the carbon fiber volume fraction, vacuum bag film transmittance, and front-line propagation speed, then when the fiber content is too high, the resin's heat release will be insufficient, and the polymerization front will easily slow down or quench. When the initiator dosage is too high, the local temperature will be too high, which may cause cracking, thermal stress concentration, or uneven curing. Therefore, using front-line polymerization resin cannot guarantee the smooth curing and quality compliance of carbon fiber composite materials.

[0086] Comparative Example 2 uses ordinary opaque vacuum bag film.

[0087] If a conventional vacuum bag film without localized initiation light transmittance is used, the resin inside the layup cannot be stably initiated directly by ultraviolet light after encapsulation. If initiation is performed before encapsulation, it is difficult to maintain compaction during the frontline polymerization process, easily leading to porosity. Therefore, the ultraviolet transmittance and heat resistance of the vacuum bag film are important process conditions for the frontline polymerization molding of the composite material of this invention.

Claims

1. A method for preparing a front-line polymerized carbon fiber reinforced epoxy resin matrix composite material, characterized in that, Includes the following steps: (1) Prepare an epoxy resin mixture capable of undergoing free radical-induced cationic frontier polymerization, wherein the epoxy resin mixture comprises an epoxy resin matrix, a photoacid initiator and a thermal free radical initiator; (2) The epoxy resin mixture is used to impregnate the carbon fiber reinforcement to form a resin-containing carbon fiber layup; (3) The resin-containing carbon fiber layup is placed in a vacuum bag compression structure including a substrate, a separator, a transparent cover plate and a vacuum bag film, and a vacuum is drawn and negative pressure is maintained for compaction; (4) Apply ultraviolet light and / or heat stimulation to the local initiation area of ​​the resin-containing carbon fiber layup through the light-transmitting area of ​​the vacuum bag film and / or transparent cover plate to initiate the polymerization front; (5) Adjust the amount of photo-acid initiator, the amount of thermal free radical initiator, the volume fraction of carbon fiber, the fiber orientation and the vacuum compaction conditions so that the polymerization front line can continuously propagate in the carbon fiber reinforcement at a preset front line propagation speed and complete the curing. The preset front-line propagation velocity is 1.0–8.0 cm·min. -1 The porosity of the composite material after curing is no higher than 3%.

2. The preparation method according to claim 1, characterized in that: The carbon fiber reinforcement has a volume fraction of 20-60% in the composite material, preferably 25-55%; When the carbon fiber volume fraction is 20-30%, the amount of photo-acid initiator is 0.6-1.5 wt% of the epoxy resin matrix, and the amount of thermal free radical initiator is 0.5-1.5 wt% of the epoxy resin matrix. When the carbon fiber volume fraction is greater than 30% but not higher than 60%, the amount of photo-acid initiator is 1.0-2.5 wt% of the epoxy resin matrix, and the amount of thermal free radical initiator is 1.0-2.0 wt% of the epoxy resin matrix, in order to avoid the influence of increased thermal conductivity of carbon fiber and decreased heat release of resin on the propagation of polymerization front.

3. The preparation method according to claim 1, characterized in that: The photoacid initiator is a diaryliodomonium salt and / or a triarylthiomonium salt, and the thermal free radical initiator is one or more of benzinolide, peroxide thermal initiators, or azo thermal initiators; The epoxy resin matrix includes bisphenol A type epoxy resin, and may further include at least one of alicyclic epoxy resin, bisphenol F type epoxy resin, and phenolic epoxy resin; the alicyclic epoxy resin accounts for 0-60% of the total mass of the epoxy resin matrix; other types of epoxy resin account for 0-30% of the total mass of the epoxy resin matrix.

4. The preparation method according to claim 3, characterized in that: The alicyclic epoxy resin includes 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexylcarboxylate and / or 4,5-epoxyhexane-1,2-dicarboxylic acid diglycidyl ester; by adjusting the type and content of the alicyclic epoxy resin, the peak temperature before polymerization is made to be 180-280℃.

5. The preparation method according to claim 1, characterized in that: The vacuum bag film has a transmittance of not less than 60% in the wavelength range of 320-420 nm, preferably not less than 80%, and does not melt and crack or shrink significantly at the peak temperature of front-line polymerization; the transparent cover plate is made of quartz glass, borosilicate glass, heat-resistant transparent resin plate, fiberglass, or a pressure plate with a light-transmitting area, and the transparent cover plate is used to simultaneously provide a pressure surface and a local light-initiating channel.

6. The preparation method according to claim 1, characterized in that: The vacuum degree in step (3) is -0.06 to -0.10 MPa, preferably -0.08 to -0.10 MPa, and is maintained continuously during the polymerization front-line propagation; The carbon fiber reinforcement is a unidirectional carbon fiber fabric, a multidirectional carbon fiber fabric, a carbon fiber warp-knitted fabric, or a combination thereof; the angle between the carbon fiber axis and the direction of polymerization front propagation is 0 to 45°, preferably 0 to 15°; The position of the polymerization front line, peak temperature, interlayer temperature rise onset time and in-plane curing uniformity are monitored by infrared thermal imager or thermocouple array. The ultraviolet light power, irradiation time, resin initial temperature or vacuum pressure are adjusted according to the monitoring results to ensure that the temperature rise onset time difference between different layers in the thickness direction is no more than 30 s. The local initiation region is located at one end or the upper surface of the end of the resin-containing carbon fiber layup. The ultraviolet light irradiation time is 5 to 120 seconds. The irradiation stops after the formation of a self-sustaining polymerization front. When the propagation velocity at the polymerization front is less than 1.0 cm·min -1 At this time, increasing the amount of photoinitiator, increasing the initial resin temperature, increasing the alicyclic epoxy resin content, or decreasing the fiber volume fraction can help; when the front-line propagation velocity before polymerization is higher than 8.0 cm·min -1 Or when the peak temperature is higher than 280℃, reduce the amount of photoinitiator, reduce the initial temperature of the resin, reduce the content of exothermic alicyclic epoxy resin, or improve the heat dissipation capacity. The resin-containing carbon fiber layup is pre-compacted every 2 to 6 layers. The resin impregnation method is hand layup impregnation, resin film impregnation, vacuum-assisted impregnation, or liquid molding processes such as RTM / VARTM.

7. A front-line polymerized carbon fiber epoxy composite material, characterized in that: The composite material is prepared by the method described in any one of claims 1 to 6, and the composite material comprises a front-line polymerized and cured epoxy resin matrix and a continuous carbon fiber reinforcement, wherein the porosity of the composite material is not higher than 3% and the content of insoluble resin components is not less than 90%.

8. The front-line polymerized carbon fiber epoxy composite material according to claim 7, characterized in that: The difference in curing start time between different layers in the thickness direction of the composite material is no more than 30 s.

9. The use of the frontline polymerized carbon fiber epoxy composite material according to claim 7 or 8, characterized in that: The composite material is used for low-energy-consumption, rapid-curing structural components, in-orbit manufacturing components, field-repaired components, or large composite material locally cured components.

10. A front-line polymerized carbon fiber composite material preparation system, comprising an ultraviolet light source (1), a vacuum bag film (2), a silicone rubber pad or end elastic block (3), a carbon fiber layup (4), a transparent cover plate (5), a separator film (6), and a substrate or mold base plate (7), wherein the substrate or mold base plate (7) is used to support the carbon fiber layup (4) and provide a molding reference surface, the separator film (6) is disposed between the carbon fiber layup (4) and the substrate or mold base plate (7), the vacuum bag film (2) is used to form a sealed encapsulation space for the carbon fiber layup (4), the transparent cover plate (5) and the separator film (6), the transparent cover plate (5) is disposed above the carbon fiber layup (4) and is used to provide a pressing surface for bonding the upper surface of the composite material, so that the carbon fiber layup (4) maintains stable thickness and interlayer bonding under the negative pressure of the vacuum bag film (2).

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