Modified epoxy resin suitable for oven molding and preparation method and application thereof

Abstract

The invention discloses modified epoxy resin suitable for oven forming and a preparation method and application thereof, and belongs to the technical field of resin-based composite materials. The modified epoxy resin comprises the following raw materials in parts by mass: 45-60 parts of bisphenol A epoxy resin; 10 to 15 parts of glycidyl amine tetrafunctional epoxy resin; 15 to 20 parts of glycidyl ester type trifunctional epoxy resin; 10 to 16 parts of a toughening agent; 40 to 45 parts of 4, 4 '-diaminodiphenyl sulfone; the toughening agent is thermoplastic phenolphthalein polyaryletherketone resin or thermoplastic phenolphthalein polyethersulfone resin, and the obtained modified epoxy resin has similar viscosity-temperature characteristics, highest exothermic temperature and relatively long gelation time as MTM45-1 oven molding resin applied in airbus certification, and is suitable for being used in preparation of oven molding prepregs. And the obtained oven molded prepreg has good stability, and the difference of products in each batch is small.

Description

Technical Field

[0001] The present invention relates to the technical field of resin-based composite materials, and in particular to a modified epoxy resin suitable for oven molding, a preparation method and an application thereof. Background Art

[0002] Oven-molded epoxy prepreg eliminates the need for autoclave molding, bypassing the limitations of autoclave size and enabling the production of large parts. This eliminates the expense of autoclave equipment and reduces the manufacturing cost of composite structures. For parts of the same size, oven molding can reduce manufacturing costs by 50% to 70% compared to autoclave molding.

[0003] However, since there is only a vacuum pressure during the oven molding and curing process, it is difficult to expel gas at atmospheric pressure, resulting in a high porosity in composite parts. This greatly limits the application of oven-molded epoxy prepregs in large-scale parts. Therefore, the viscosity characteristics and gel time of the resin are crucial. The resin viscosity cannot be too low to prevent a large amount of loss during the curing process; the viscosity cannot be too high, otherwise the resin will not be fully impregnated due to poor fluidity. The resin matrix needs to maintain an unobstructed exhaust channel before gelation and have a sufficiently wide process window for exhaust.

[0004] The MTM45-1 oven-curable epoxy resin developed by ACG in the United States has passed Airbus material specification certification. Fuselage panels prepared using MTM-45 prepreg curing ovens have been successfully used in the manufacture of an 18-meter-long all-composite fuselage for an ACCA cargo aircraft. MTM45-1 prepreg is also used in the primary structure of the "White Knight 2" and in the composite fuselages and wings of military transport and trainer aircraft. However, there are currently few reports of large-scale oven-cured parts in China. Therefore, it is necessary to benchmark the properties of MTM45-1 epoxy resin and develop a novel method to produce oven-curable epoxy resin to meet material requirements.

[0005] At present, traditional oven-molded epoxy prepregs use dry fibers that have not been impregnated with resin as air paths. For example, the invention patent application with publication number "CN110561648A" and invention name "A method for preparing a non-autoclave molded medium-temperature curing prepreg" requires that the thickness of the fibers impregnated with the resin film be controlled to account for 20-30% of the total fiber thickness. Another example is the patent application with publication number "CN104647636A" and titled "A method for preparing a gradient prepreg with an intra-layer air path". In this scheme, the resin film is required to form an air path of 10-20% of the dry fiber thickness in the middle part of the dry fiber. Another example is the patent application with publication number "CN107987473A" and titled "An epoxy resin for vacuum bag molded prepreg and its preparation method". In this scheme, the penetration rate of the film is required to be 40-80%. As can be seen, in the prior art, the production of oven-molded prepregs achieves partial impregnation by controlling the degree of impregnation of dry fibers. This requires controlling the gap between the rollers, the impregnation temperature, and the impregnation speed. This necessitates the exploration and adjustment of multiple process parameters for partial impregnation during the production of oven-molded prepregs, significantly impacting production efficiency. Furthermore, the ratio of the fiber thickness impregnated with the resin film to the total fiber thickness is difficult to precisely control, leading to variations in the degree of impregnation between batches of prepreg, which in turn affects the performance stability of oven-molded prepregs. Summary of the Invention

[0006] The present invention aims to provide a modified epoxy resin suitable for oven molding and a preparation method thereof. The obtained modified epoxy resin has similar viscosity-temperature characteristics, maximum exotherm temperature, and similarly long gel time as the MTM45-1 oven molding resin certified for use by Airbus, and is suitable for use in the preparation of oven molding prepregs.

[0007] The present invention is achieved through the following technical solutions: A modified epoxy resin suitable for oven molding, comprising the following raw materials in parts by mass: 45-60 parts of bisphenol A epoxy resin; 10-15 parts of glycidylamine tetrafunctional epoxy resin; 15-20 parts of glycidyl ester trifunctional epoxy resin; 10-16 parts of toughening agent; 40-45 parts of 4,4'-diaminodiphenyl sulfone; The toughening agent is a thermoplastic phenolphthalein type polyaryletherketone resin or a thermoplastic phenolphthalein type polyethersulfone resin.

[0008] The method for preparing the modified epoxy resin suitable for oven molding as described above comprises the following steps: a. Add bisphenol A epoxy resin, glycidylamine tetrafunctional epoxy resin, and glycidyl ester trifunctional epoxy resin into a reaction kettle according to the ratio of claim 1, and stir at a speed of 100-600 rpm for 8-15 minutes to fully mix the materials; b. Add toughening agent and stir for 10-20 minutes; c. Heat to 110-130°C and keep warm, stirring for 80-100 minutes until the mixture is completely uniform to obtain a prepolymer; d. Cool down to 75-85°C, add 4,4'-diaminodiphenyl sulfone, and stir for 18-25 minutes; e. Cooling to room temperature, mixing evenly and then discharging the material to obtain a modified epoxy resin composition suitable for oven molding.

[0009] Preferably, in step a, the stirring rate is 100-600 rpm, and the stirring is performed for 10 minutes to mix the materials; In step c, the temperature is raised to 120° C. and then kept warm, and stirred for 90 minutes at a stirring rate of 400 to 800 rpm to obtain a prepolymer; In step d, the temperature is lowered to 80° C., and then 4,4′-diaminodiphenyl sulfone is added, and the mixture is stirred at a stirring rate of 400-800 rpm for 20 min.

[0010] The use of any of the aforementioned modified epoxy resins in the preparation of oven-molded prepregs can solve the problems in the prior art of varying degrees of impregnation between different batches of prepregs and poor performance stability of oven-molded prepregs.

[0011] Furthermore, the oven-formed prepreg includes a PE embossed film, a carbon fiber layer and a release paper, the carbon fiber layer is impregnated with a modified epoxy resin, the release paper serves as a carrier, the carbon fiber layer is laminated on top of the release paper, the PE embossed film is laminated on top of the carbon fiber layer and is used to isolate air and impurities, one side of the PE embossed film is a smooth surface, and the other side is a rough surface with a concave-convex structure, and then the carbon fiber layer impregnated with the modified epoxy resin is laminated to the rough surface of the PE embossed film, and after lamination, a PE embossed film-carbon fiber composite material with a concave-convex structure is formed, and the gaps between the concave-convex structures serve as air guide channels for the prepreg.

[0012] Furthermore, the oven-molded prepreg is prepared by a two-step hot melt molding process of hot melt coating and hot melt dipping.

[0013] Furthermore, in the hot melt gluing section, the resin melt is poured into the glue groove between the gluing roller and the metering roller, and the temperature of the melt plate is controlled to 85~95°C, the temperature at the cooling plate is controlled to 11~21°C, the gap between the gluing / metering roller is set to 0.05~0.25mm, and the production rate is 2.0±0.5m / min.

[0014] Furthermore, in the hot melt dipping section, a double-sided dipping method is adopted to compound the carbon fiber after yarn spreading with the modified epoxy resin film, and then the rough surface of the PE embossed film is combined with the carbon fiber impregnated with the film. Under the action of the pressing roller, the carbon fiber impregnated with the film forms a concave-convex structure. In the pressing section, the temperature of heating zone 1 is controlled at 60~70°C, the temperature of heating zone 2 is controlled at 80~90°C, and the temperature of heating zone 3 is controlled at 75~85°C, and the pressing gap is set to 0.35±0.2mm.

[0015] Compared with the prior art, the present invention has the following advantages and beneficial effects: First, the present invention utilizes a glycidylamine-based tetrafunctional epoxy resin and a glycidylester-based trifunctional epoxy resin to adjust the heat resistance and rheological properties of the original bisphenol A-based epoxy resin. By adjusting the ratio of the main resin, modifier, thermoplastic toughening agent, and diaminodiphenyl sulfone, as well as the preparation process, a modified epoxy resin suitable for oven molding is prepared. This modified epoxy resin exhibits moderate fluidity for fiber impregnation and offers a sufficiently wide process window for venting, maintaining unobstructed venting channels prior to gelation, making it suitable for oven molding.

[0016] Second, the modified epoxy resin prepared using the raw materials and raw material ratios described in this invention exhibits similar viscosity-temperature characteristics, maximum exotherm temperature, and long gel time to the MTM45-1 oven-molding resin certified for Airbus. Furthermore, the heat release during curing is relatively uniform and stable, and the viscosity is low in the temperature range of 110-180°C, making it easier to expel air voids in the resin during vacuum bagging. This allows the prepreg to maintain an appropriate viscosity for a period of time, facilitating the expulsion of entrained gases and volatiles.

[0017] 3. In the present invention, the proportions of the resin components are selected based on the viscosity and curing process of the resins, and are verified through extensive experiments. Glycidylamine-based tetrafunctional epoxy resins and glycidyl ester-based trifunctional epoxy resins are highly reactive, and their usage is preferably within the range of 10-15 parts and 15-20 parts, respectively. Excessive amounts will cause the resins to react too quickly and release heat in a concentrated manner; too low an amount will result in low viscosity at room temperature after mixing, which is not conducive to the prepreg layup construction. The amount of toughening agent is preferably controlled within the range of 10-16 parts. Excessive amounts of toughening agent will result in excessive resin viscosity and poor fluidity; too low an amount will result in insignificant toughening effects. The amount of 4,4'-diaminodiphenyl sulfone is preferably controlled within the range of 40-45 parts. Excessive amounts of the curing agent 4,4'-diaminodiphenyl sulfone will shorten the resin gel time, which is not conducive to the storage time of the prepreg; too low an amount will affect the degree of curing of the resin.

[0018] 4. In the present invention, a PE embossed film is used to prepare an oven-molded prepreg, and the rough surface of the PE embossed film with a concave-convex structure is combined with the carbon fiber impregnated with the adhesive film. Under the action of a pressing roller, the carbon fiber impregnated with the adhesive film forms a concave-convex structure, which is used as an air guide channel for the prepreg. This innovative method for preparing an oven-molded prepreg is provided, and the method is convenient, easy to control and implement.

[0019] 5. In the present invention, a method for preparing prepregs using a modified epoxy resin suitable for oven molding is used to form a concave-convex structure in the carbon fiber impregnated with the adhesive film, which can be used as an air guide channel for the prepreg. By simply replacing the PE film with a PE embossed film, the process parameters for preparing prepregs by the hot melt method for forming prepregs in a traditional autoclave can be changed slightly, making it easy to operate and implement. At the same time, since semi-impregnation is no longer required, the difficulty of regulating and controlling multiple process parameters such as the gap between the pressure rollers, the temperature of the heating and cooling zones, and the production rate is reduced, which helps to improve the production efficiency of oven-molded prepregs and effectively avoids the problem of inconsistent semi-impregnation levels of different batches of prepregs, thereby helping to ensure the stability of the prepreg performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 1 is a viscosity-temperature curve of the modified epoxy resin obtained in Example 1.

[0021] Figure 2 This is the DSC curve of the modified epoxy resin obtained in Example 1.

[0022] Figure 3 2 is a viscosity-temperature curve of the modified epoxy resin obtained in Example 2.

[0023] Figure 4 This is the DSC curve of the modified epoxy resin obtained in Example 2.

[0024] Figure 5This is a schematic diagram of the oven-molded prepreg structure, where 1a is the PE embossed film layer, 1b is the film-impregnated carbon fiber layer, and 1c is the release paper layer.

[0025] Figure 6 This is a photo of the oven molding prepreg preparation process.

[0026] Figure 7 It is an oven-forming prepreg with embossed printing. DETAILED DESCRIPTION

[0027] The present invention will be further described in detail below with reference to the examples, but the embodiments of the present invention are not limited thereto.

[0028] Example 1 In this embodiment, the raw materials (in parts by mass) were taken according to Table 1 below, and a modified epoxy resin suitable for oven molding was prepared according to the following preparation method.

[0029] Table 1 The preparation method of the modified epoxy resin comprises the following steps: a. Take the raw materials according to the reagents and reagent ratios in Table 1, add bisphenol A epoxy resin E-54, glycidylamine tetrafunctional epoxy resin TT410, and glycidyl ester trifunctional epoxy resin TT310 to the reactor, turn on the agitator, control the speed at 500 rpm, control the temperature at 60±5°C, and stir for 10 minutes to fully mix the materials. In this step, after testing, the stirring speed of the agitator is preferably controlled at 100-600 rpm.

[0030] b. Add phenolphthalein polyethersulfone and stir for 15 minutes. In this step, the speed of the stirrer is set at 100-600 rpm and the stirring time is set at 10-20 minutes.

[0031] c. While maintaining the agitator speed, start the disperser at 700 rpm. Raise the temperature to 120°C and maintain. Start timing when the displayed temperature reaches 110°C. Stir for 90 minutes until the mixture is completely homogenized to obtain the prepolymer. During this step, the disperser speed should preferably be controlled between 400 and 800 rpm.

[0032] d. While maintaining the stirring and dispersion, cool the mixture to 80°C (generally 75-85°C is appropriate). Add 4,4'-diaminodiphenyl sulfone (DDS) and stir for 20 minutes until completely dispersed. In this step, stirring for 18-25 minutes has been shown to completely disperse the materials in the reactor.

[0033] e. Cool to room temperature, mix thoroughly, and discharge to obtain a modified epoxy resin composition suitable for oven molding. Then, turn off the disperser and control the agitator to a low speed until loading is complete. The resin volume should not exceed two-thirds and not be less than one-third of the reactor volume. The resin is viscous at room temperature, can be bent without breaking, and has a certain strength and toughness.

[0034] Example 2 The only difference between this embodiment and embodiment 1 is the ratio of the raw materials. Specifically, the raw materials (by mass) were taken according to Table 2 below and the modified epoxy resin suitable for oven molding was prepared according to the preparation method of embodiment 1.

[0035] Table 2 Example 3 The only difference between this embodiment and embodiment 1 is the ratio of the raw materials. Specifically, the raw materials (by mass) were taken according to Table 3 below and the modified epoxy resin suitable for oven molding was prepared according to the preparation method of embodiment 1.

[0036] Table 3 Example 4 The only difference between this embodiment and embodiment 1 is the ratio of the raw materials. Specifically, the raw materials (by mass) were taken according to Table 4 below and the modified epoxy resin suitable for oven molding was prepared according to the preparation method of embodiment 1.

[0037] Table 4 Example 5 The only difference between this embodiment and embodiment 1 is the ratio of the raw materials. Specifically, the raw materials (by mass) were taken according to Table 5 below and the modified epoxy resin suitable for oven molding was prepared according to the preparation method of embodiment 1.

[0038] Table 5 Example 6 The only difference between this embodiment and embodiment 1 is the ratio of the raw materials. Specifically, the raw materials (by mass) were taken according to Table 6 below and the modified epoxy resin suitable for oven molding was prepared according to the preparation method of embodiment 1.

[0039] Table 6 Performance testing of modified epoxy resin.

[0040] Performance tests were conducted on the modified epoxy resins obtained in the aforementioned embodiments and comparative examples. The modified epoxy resins obtained in the aforementioned embodiments all achieved similar viscosity-temperature characteristics, maximum exotherm temperatures, and similarly long gel times as the MTM45-1 oven molding resin certified for use by Airbus. Furthermore, the heat release during curing was relatively uniform and stable, and the viscosity was relatively low in the temperature range of 110-180°C.

[0041] The performance test results of the modified epoxy resins obtained in Examples 1 and 2 and MTM45-1 resin (OOA resin from ACG Company) are shown in Table 7.

[0042] The test methods involved are as follows: The maximum curing exotherm temperature was determined using differential scanning calorimetry (DSC). The temperature was measured at a heating rate of 10°C / min over a temperature range of 40°C to 250°C. The maximum exotherm temperature was determined by measuring the temperature at which the main exotherm peak of the reaction reached its maximum heat flow rate on the DSC curve during a constant heating rate.

[0043] For the gel time test, take (1.5±0.5) g of resin sample and use a resin gel time tester or hot stage to test it. The test end point is when the resin no longer draws strings. The test temperature is (150±2)℃.

[0044] Table 7: From Table 7, Figure 1 、 3 It can be seen that according to NCMVP's "Material Characterization for Processing: ACG MTM45-1" and with reference to the performance of MTM45-1 resin (OOA resin), the modified epoxy resin suitable for oven molding obtained by using the raw material ratio and preparation method of the present invention has similar viscosity-temperature characteristics, maximum exotherm temperature, and similarly long gel time as the MTM45-1 resin.

[0045] In addition, the prior art (CN113512273A) - "An Epoxy Resin Composition for OOA Molded Hot Melt Prepreg" document mentions that if the minimum viscosity of the OOA epoxy resin is too low, the resin will flow too quickly, which may cause the resin to block the air guide channel before the entrained gas is effectively discharged. If the minimum viscosity is too high, the resin will not be able to flow well under a limited atmospheric pressure, and will not be able to fully wet the fibers, and the porosity of the composite material will increase. Therefore, "the minimum viscosity of the viscosity-temperature rheological curve is between 1000 and 3000 mPa·s." The minimum viscosities of Examples 1 and 2 of the present invention, 1480 mPa·s and 1450 mPa·s, are both between 1000 and 3000 mPa·s, meeting the viscosity requirements of OOA resins.

[0046] The publication number is "CN107987473A", and it is mentioned in "An Epoxy Resin for Vacuum Bag Molding Prepreg and Its Preparation Method": OOA resin "has a long gel time of 50 to 100 minutes at 110°C to 150°C. The composite material molding process has an insulation step between 110°C and 150°C, and the insulation time is greater than 60 minutes. This facilitates the resin to penetrate the reinforcing fiber." In Examples 1 and 2 of the present invention, the gel time at 150°C is 72 minutes and 66 minutes respectively, both greater than 60 minutes, which also meets the OOA resin gel time requirement.

[0047] Figure 1 、 3 They are respectively the viscosity-temperature curves of the modified resins in Examples 1 and 2, Figure 2 、 4 They are the DSC curves of the modified resins in Examples 1 and 2 respectively.

[0048] Depend on Figure 2 、 4 The differential scanning calorimetry (DSC) curves of the modified epoxy resins in Examples 1 and 2 show a wide half-width (FWHM) and a single peak, indicating stable and uniform heat release during curing. Furthermore, the modified epoxy resins obtained in both examples exhibit low viscosities between 110°C and 180°C, making it easier to expel pores in the resin during vacuum bagging. When used to prepare prepregs, these modified epoxy resins can maintain the prepreg in an appropriate viscosity range for a period of time, facilitating the expulsion of entrained gases and volatiles.

[0049] Application of modified epoxy resin in the preparation of prepreg for oven molding.

[0050] The modified epoxy resin obtained in Examples 1 and 2 was used to prepare oven-molded prepreg. Figure 5 、 6 The oven-molded prepreg includes a PE embossed film, a carbon fiber layer and a release paper. The carbon fiber layer is impregnated with a modified epoxy resin. The release paper is a carrier. The carbon fiber layer is attached to the release paper. The PE embossed film is attached to the top of the carbon fiber layer and is used to isolate air and impurities.

[0051] One side of the PE embossed film is smooth; the other side is a rough surface with a concave-convex structure. A carbon fiber layer impregnated with modified epoxy resin is then laminated to the rough surface of the PE embossed film. After being pressed by a pressing roller, a PE embossed film-carbon fiber composite material with a concave-convex structure is formed. The gaps between the concave-convex structures serve as air guide channels for the prepreg. Figure 7 , Figure 7 It is an oven-forming prepreg with embossed printing.

[0052] A molding method for oven-molded prepregs.

[0053] The relevant process parameters for preparing adhesive films and hot-melt prepregs were determined based on the rheological properties, gel time and DSC of the modified epoxy resin.

[0054] The fiber surface density of the oven-molded prepreg is set within the range of 100±2g / m 2 The resin content is set at 33±2%. The prepreg is prepared using a two-step hot melt method (hot melt coating + hot melt dipping).

[0055] Hot melt gluing: The temperature of the gluing roller is a key parameter in the gluing process. This temperature is closely related to the viscosity of the resin matrix. Higher temperatures result in lower viscosity and better fluidity, making it easier to penetrate the fiber. However, too low a viscosity can cause resin loss, affecting the resin content. Lower temperatures result in higher viscosity and poorer fluidity, making it difficult to penetrate the fiber.

[0056] The modified epoxy resin obtained in Example 1 was used. The viscosity of the resin at 80°C was 138~203Pa.s. When the temperature of the glue roller was set to 80°C, the resin fluidity was suitable, the resin could be stably transferred, and the glue coating was stable. The resin melt was poured into the glue groove between the glue roller and the metering roller. The process parameters were adjusted. The melt plate temperature was set to 90°C, the cooling plate temperature was set to 16°C, the glue coating / metering roller gap was set to 0.15mm, and the production rate was 2.0±0.5m / min. The resin matrix was evenly coated on the release paper. The glue coating accuracy was controlled by a thickness gauge. After passing the test, the film was reeled up for use. The gram weight of the obtained resin film met the requirements.

[0057] During the dipping process, the gap between the rollers should be small. Otherwise, the resin will not penetrate the fibers easily, resulting in dry yarn in the prepreg and uneven resin distribution, which will cause resin-poor and resin-rich areas. Sometimes, gaps will appear in the prepreg, which is particularly prominent in thin prepregs. The gap between the rollers should also be small. If it is too small, the carbon fibers will be crushed, resulting in broken fibers, a large amount of fuzz or pilling, and seriously affecting the appearance and mechanical properties of the prepreg.

[0058] The carbon fibers after unwinding are compounded with a resin film by double-sided dipping. The concave-convex side of the PE embossed film is then combined with the film-impregnated carbon fibers, and the film-impregnated carbon fibers are formed into a concave-convex structure by the action of a pressing roller.

[0059] After adjusting the process parameters—heating zone 1 at 65°C, heating zone 2 at 85°C, heating zone 3 at 80°C, the cooling plate at 16°C, and the press gap at 0.35±0.2mm—the resulting unidirectional prepreg had a smooth surface with no bubbles and even edges.

[0060] Table 8: Forming process of oven-formed prepreg.

[0061] The modified epoxy resin suitable for oven molding is obtained by the preparation method of the present invention, and the process parameters are adjusted according to the process requirements of Table 8 above to make an oven-molded prepreg. A concave-convex structure is formed by embossing as an air guide channel of the prepreg, without the need for semi-impregnation, which solves the problem of difficult control of the impregnation degree of dry fibers that are not impregnated with resin as air guide channels in the prior art.

[0062] At the same time, a large number of experiments have shown that oven-molded prepregs that meet the requirements can also be made by using modified epoxy resins such as those in Examples 3 to 6.

[0063] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A modified epoxy resin suitable for oven molding, characterized in that: The following raw materials are included in parts by mass: 45-60 parts of bisphenol A epoxy resin; 10-15 parts of glycidylamine tetrafunctional epoxy resin; 15-20 parts of glycidyl ester trifunctional epoxy resin; 10-16 parts of toughening agent; 40-45 parts of 4,4'-diaminodiphenyl sulfone; The toughening agent is a thermoplastic phenolphthalein type polyaryletherketone resin or a thermoplastic phenolphthalein type polyethersulfone resin.

2. The method for preparing a modified epoxy resin suitable for oven molding according to claim 1, wherein: The steps include: a. Add bisphenol A epoxy resin, glycidylamine tetrafunctional epoxy resin, and glycidyl ester trifunctional epoxy resin into a reaction kettle according to the ratio of claim 1, and stir at a speed of 100-600 rpm for 8-15 minutes to fully mix the materials; b. Add toughening agent and stir for 10-20 minutes; c. Heat to 110-130°C and keep warm, stirring for 80-100 minutes until the mixture is completely uniform to obtain a prepolymer; d. Cool down to 75-85°C, add 4,4'-diaminodiphenyl sulfone, and stir for 18-25 minutes; e. Cooling to room temperature, mixing evenly and then discharging the material to obtain a modified epoxy resin composition suitable for oven molding.

3. The method for preparing a modified epoxy resin suitable for oven molding according to claim 2, wherein: In step a, the stirring rate is 100-600 rpm, and the stirring is performed for 10 minutes to mix the materials.

4. The method for preparing a modified epoxy resin suitable for oven molding according to claim 2, wherein: In step c, the temperature is raised to 120° C. and then kept warm, and stirred at a stirring rate of 400-800 rpm for 90 minutes to obtain a prepolymer.

5. The method for preparing a modified epoxy resin suitable for oven molding according to claim 2, wherein: In step d, the temperature is lowered to 80° C., and then 4,4′-diaminodiphenyl sulfone is added, and the mixture is stirred at a stirring rate of 400-800 rpm for 20 min.

6. Use of the modified epoxy resin according to any one of claims 1 to 5 in the preparation of oven-molded prepregs.

7. The use according to claim 6, characterized in that: The prepreg formed in the oven includes a PE embossed film, a carbon fiber layer and a release paper. The carbon fiber layer is impregnated with a modified epoxy resin. The release paper is a carrier. The carbon fiber layer is attached to the release paper. The PE embossed film is attached to the carbon fiber layer and is used to isolate air and impurities. One side of the PE embossed film is smooth, and the other side is a rough surface with a concave-convex structure. The carbon fiber layer impregnated with modified epoxy resin is then laminated to the rough surface of the PE embossed film to form a PE embossed film-carbon fiber composite material with a concave-convex structure. The gaps between the concave-convex structures serve as air guide channels for the prepreg.

8. The use according to claim 6, characterized in that: The oven-molded prepreg is prepared by adopting a two-step hot melt molding process of hot melt coating and hot melt dipping.

9. The use according to claim 8, characterized in that: In the hot melt coating section, the resin melt is poured into the glue groove between the coating roller and the metering roller, and the temperature of the melt plate is controlled at 85-95°C, the temperature at the cooling plate is controlled at 11-21°C, the gap between the coating roller and the metering roller is set at 0.05-0.25mm, and the production rate is 2.0±0.5m / min.

10. The use according to claim 8, characterized in that: In the hot melt dipping section, a double-sided dipping method is adopted to compound the carbon fiber after the yarn is spread with the modified epoxy resin film, and then the rough surface of the PE embossed film is combined with the carbon fiber impregnated with the film. Under the action of the pressing roller, the carbon fiber impregnated with the film is formed into a concave-convex structure. In the pressing section, the temperature of heating zone 1 is controlled at 60~70℃, the temperature of heating zone 2 is controlled at 80~90℃, and the temperature of heating zone 3 is controlled at 75~85℃, and the pressing gap is set to 0.35±0.2mm.

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