Method for preparing carbon fiber prepreg through one-step method

Abstract

The invention relates to a method for preparing a carbon fiber prepreg by a one-step method, which comprises the following steps of: placing an epoxy resin composition which is prepared at present in gluing equipment, coating release paper with the liquid epoxy resin composition by utilizing the gluing equipment, and then contacting the release paper coated with the epoxy resin composition with continuous carbon fibers or fabrics, so as to obtain the carbon fiber prepreg. The preparation method comprises the following steps: winding the raw materials on a paper tube, sleeving the whole paper tube wound with the material into a plastic bag after winding, carrying out vacuum packaging treatment, and finally, standing at room temperature for more than 48 hours to obtain the carbon fiber prepreg. No solvent is used in the process, the method is more environmentally friendly and safer, and the porosity of a composite product is lower; compared with a hot melting method, the method has the advantages that multiple heating processes are omitted, the liquid epoxy resin composition forms a film through slow reaction of the dominant curing agent at room temperature, proper viscosity is achieved, the purpose of low-cost preparation of the prepreg is achieved, and the method has the advantages that raw materials are easy to obtain, the technological method is simple, and generalizability is high.

Description

Technical Field

[0001] This invention relates to the field of carbon fiber prepreg preparation technology, and in particular to a one-step method for preparing carbon fiber prepreg. Background Technology

[0002] Prepregs are composite materials made by impregnating continuous fibers or fabrics with a resin matrix under strictly controlled conditions, forming a combination of resin matrix and reinforcement. Prepregs can be classified into two types according to resin type: thermosetting prepregs and thermoplastic prepregs. Thermosetting prepregs, with their good processability and excellent mechanical properties, account for a large proportion of prepregs and are the preferred raw material for lightweight structural components in aerospace, military, industrial, and sports and leisure fields.

[0003] There are two main methods for preparing traditional thermosetting prepregs: One method is solution impregnation, in which the components of the resin matrix are dissolved in a low-boiling-point solvent in a specified ratio to form a solution of a certain concentration. Then, the fiber bundle or fabric is passed through the resin matrix solution at a specified speed to impregnate it with a certain amount of resin matrix. This method requires a solvent removal process and heating to bring the resin matrix to stage B (semi-curing stage) to obtain suitable viscosity. The disadvantages of this method are that the solvent needs to be removed in a drying oven or recycled, which is not safe and environmentally friendly. Furthermore, the solvent is difficult to remove completely, which can easily form voids during molding and affect the performance of the composite material. Another method is the hot-melt method, which involves heating and melting a semi-solid resin matrix at room temperature onto release paper to form a film. Then, through a "sandwich" structure of film / carbon fiber / film, the resin is impregnated into the carbon fiber bundles by secondary heating and pressure. Finally, the prepreg is cooled and wound up to obtain the desired prepreg. The disadvantages of this method are that it is difficult to impregnate thick prepregs, especially fabrics, and it is difficult to impregnate high-viscosity resins. The amount of release paper and film used is large, and the energy consumption is high due to multiple heating processes. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a one-step method for preparing carbon fiber prepreg that is safe and environmentally friendly, uses readily available raw materials, has a simple process, low cost, and is easy to promote, in order to overcome the shortcomings of the existing technology.

[0005] The technical problem to be solved by the present invention is achieved through the following technical solution. The present invention is a one-step method for preparing carbon fiber prepreg. The method is as follows: First, a freshly prepared epoxy resin composition is placed in a coating device, and then the liquid epoxy resin composition is coated onto release paper using the coating device. Subsequently, the release paper coated with the epoxy resin composition is brought into contact with continuous carbon fibers or fabric, and they are wound together onto a paper tube. After winding, the paper tube containing the material is placed into a plastic bag and vacuum-packed. Finally, it is left to stand at room temperature for more than 48 hours to obtain the carbon fiber prepreg.

[0006] The technical problem to be solved by the present invention can also be further achieved by the following technical solution: In the method for preparing carbon fiber prepreg by one step described above, the epoxy resin composition is prepared by the following components in the following weight ratio: liquid epoxy resin 50-70, toughening agent 5-20, latent curing agent 3-10, explicit curing agent 5-10, accelerator 0.5-5, and additive 0.1-5.

[0007] The technical problem to be solved by the present invention can also be further achieved by the following technical solution: In the one-step method for preparing carbon fiber prepreg described above, the liquid epoxy resin is selected from one or more of liquid bisphenol A type epoxy resin, bisphenol F type epoxy resin, aliphatic epoxy resin, alicyclic epoxy resin, phenolic epoxy resin, and multifunctional epoxy resin, and is diluted with an epoxy diluent.

[0008] The technical problem to be solved by the present invention can also be further achieved by the following technical solution: In the one-step method for preparing carbon fiber prepreg described above, the toughening agent is selected from any one of polyurethane modified epoxy, rubber modified epoxy, and core-shell toughened epoxy, and is in a liquid or semi-solid state at room temperature.

[0009] The technical problem to be solved by the present invention can also be further achieved by the following technical solution: In the one-step method for preparing carbon fiber prepreg described above, the latent curing agent is a solid powder of 5 to 20 micrometers and is selected from dicyandiamide or 4,4-diaminodiphenyl sulfone.

[0010] The technical problem to be solved by the present invention can also be further achieved by the following technical solution: In the one-step method for preparing carbon fiber prepreg described above, the active curing agent is any one of aliphatic amine, cycloaliphatic amine, aromatic amine, polyamide, polyether amine, etc., and the active hydrogen equivalent of the active curing agent is between 5% and 30% of the epoxy equivalent of the epoxy resin composition.

[0011] The technical problem to be solved by the present invention can also be further achieved by the following technical solution: In the one-step method for preparing carbon fiber prepreg described above, the accelerator is a solid powder accelerator with a particle size of 5 to 20 micrometers, and the accelerator is selected from any one of urea compounds, polyurea compounds, imidazole or imidazole derivatives.

[0012] The technical problem to be solved by the present invention can also be further achieved by the following technical solution: In the one-step method for preparing carbon fiber prepreg described above, the additive is one or more of the following: wetting agent, defoamer, dispersant, etc., and is in a liquid state at room temperature.

[0013] The technical problem to be solved by the present invention can also be further achieved through the following technical solution. The specific steps of the one-step method for preparing carbon fiber prepreg described above are as follows: (1) Preparation of epoxy resin composition: Accurately weigh the liquid epoxy resin, toughening agent, latent curing agent, visible curing agent, accelerator, and additives according to the specified proportions. Stir the liquid epoxy resin, toughening agent, latent curing agent, accelerator, and additives, and then grind them more than 3 times with a three-roll mill to ensure that the materials are fully mixed, thus obtaining the basic mixture. (2) Online coating and impregnation of carbon cloth: The base mixture and the visible curing agent are mixed online in a static mixer to obtain a liquid epoxy resin composition. Then, it is extruded into the glue tank of the coating equipment. The liquid epoxy resin composition is coated onto the release paper using the coating equipment. The epoxy resin composition coated onto the release paper is then brought into contact with carbon fiber or fabric and wound up. (3) Vacuum coating and room temperature curing: The rolled-up carbon fiber prepreg is placed into an air bag and vacuum-sealed. After standing at room temperature for more than 48 hours, a carbon fiber prepreg with a certain degree of self-adhesion is obtained.

[0014] The technical problem to be solved by the present invention can also be further achieved by the following technical solution: For the one-step method for preparing carbon fiber prepreg described above, the room temperature viscosity of the epoxy resin composition before the addition of the apparent curing agent is between 100 and 5000 cps, the room temperature viscosity after the addition of the apparent curing agent is between 100 and 2000 cps, and it can maintain a liquid state for at least 2 hours at room temperature of 25±5℃. After standing at room temperature for more than 48 hours, the viscosity of the epoxy resin composition at 70℃ is between 5000 and 100000 cps.

[0015] Compared with the prior art, the present invention provides a one-step method for preparing carbon fiber prepreg using a solvent-free liquid epoxy resin composition. The method employs a composite curing system of a latent curing agent and an active curing agent, where the liquid epoxy resin impregnates fiber bundles or fabrics at room temperature. After winding, the entire assembly is bagged and vacuum-sealed, and cured at room temperature for more than 48 hours to obtain a carbon fiber prepreg with suitable viscosity. The initial viscosity of the liquid epoxy resin composition is between 100 and 2000 cps, allowing the epoxy resin matrix to effectively wet the carbon fiber bundles even without heating. Furthermore, the bagging and vacuuming process further enhances the wettability of the liquid epoxy resin matrix on the carbon fiber bundles, while avoiding the high energy consumption problem of hot-melt prepreg preparation. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] This invention provides a one-step method for preparing carbon fiber prepreg using a solvent-free liquid epoxy resin composition. A significant feature of this liquid epoxy resin is the introduction of a composite curing system consisting of a latent curing agent and a visible curing agent. This allows the viscosity of the liquid epoxy resin composition to be controlled between 100 and 2000 cps at initial formulation, and it can maintain a liquid state for a relatively long time at room temperature. After standing at room temperature for more than 48 hours, the visible curing agent slowly cures, causing the resin matrix to transform from a liquid state to a semi-solid state at room temperature. This semi-solid resin matrix has a viscosity between 5000 and 100000 cps at 70°C, thereby ensuring good workability of the carbon fiber prepreg.

[0018] In this method, the epoxy resin composition consists of liquid epoxy resin, toughening agent, latent curing agent, explicit curing agent, accelerator, and additives, with the proportions of each component being 50-70: 5-20: 3-10: 5-10: 0.5-5: 0.1-5. In preparation, the freshly prepared epoxy resin composition is first placed in a coating device, and the liquid epoxy resin composition is coated onto release paper. Then, the epoxy resin composition is brought into contact with continuous carbon fibers or fabric and wound onto a paper tube. After winding, the paper tube and the mixture are placed into a plastic bag and vacuum-packed. After standing at room temperature for at least 48 hours, the carbon fiber prepreg is obtained. Specifically: 1. Preparation of epoxy resin composition: Accurately weigh the liquid epoxy resin, toughening agent, latent curing agent, accelerator, additives and other components according to the proportion, stir and then grind them more than 3 times with a three-roll mill to ensure that the materials are fully mixed and form a uniform epoxy resin composition. 2. Online adhesive application and carbon cloth impregnation: The epoxy resin composition and the curing agent are mixed online in a static mixer to ensure that they are fully and evenly mixed before being extruded into the glue tank of the coating machine. Then, it is coated onto the release paper. The release paper coated with the resin composition is then brought into contact with continuous carbon fibers or fabrics to allow the resin composition to fully impregnate the carbon fibers or fabrics. Finally, the impregnated carbon fibers or fabrics are wound onto a paper tube for winding. 3. Vacuum wrapping and room temperature curing: The rolled-up carbon fiber prepreg is placed into an air bag and vacuum-sealed. The sealed carbon fiber prepreg is then left to stand at room temperature for more than 48 hours to allow the curing agent to continue to react slowly, thereby gradually curing the resin matrix and finally obtaining a finished carbon fiber prepreg with certain self-adhesive properties.

[0019] The liquid epoxy resin is one or a combination of two or more of the following: liquid bisphenol A type epoxy resin, bisphenol F type epoxy resin, aliphatic epoxy resin, alicyclic epoxy resin, phenolic epoxy resin, and multifunctional epoxy resin. In order to adjust the viscosity and properties of the resin, it is also necessary to use an epoxy diluent to dilute it.

[0020] The toughening agent is any one of polyurethane modified epoxy, rubber modified epoxy, and core-shell toughened epoxy. When selecting, toughening agents that are liquid at room temperature are preferred. If liquid toughening agents are not available, semi-solid toughening agents can also be selected.

[0021] The latent curing agent is dicyandiamide or 4,4-diaminodiphenyl sulfone. To ensure that the curing agent can be uniformly dispersed in the resin composition, the curing agent is preferably a solid powder of 5 to 20 micrometers.

[0022] The active curing agent is any one of aliphatic amines, cycloaliphatic amines, aromatic amines, polyamides, polyether amines, etc. In order to control the rate and extent of the curing reaction, weakly active active curing agents such as polyamides and polyether amines are preferred, and the active hydrogen equivalent is between 5% and 30% of the epoxy equivalent of the epoxy resin composition.

[0023] The accelerator is any one of urea compounds, polyurea compounds, imidazole or imidazole derivatives, and a solid powder accelerator with a particle size of 5 to 20 micrometers is preferred for easy mixing with the resin composition.

[0024] The additive is one or more of the following: wetting agent, defoamer, dispersant, etc. In order to improve the compatibility between the additive and the resin composition, additives that are liquid at room temperature are preferred.

[0025] The initial viscosity of the epoxy resin composition at room temperature is between 100 and 5000 cps. After adding a visible curing agent, its initial viscosity is between 100 and 2000 cps. It can maintain a liquid state for at least 2 hours at room temperature of 25±5℃. After standing at room temperature for more than 48 hours, the viscosity of the resin composition at 70℃ is between 5000 and 100000 cps, so as to meet the preparation requirements of carbon fiber prepreg.

[0026] The one-step method for preparing carbon fiber prepreg provided by this invention has many significant advantages: 1. No solvent is used in the preparation process, which greatly reduces the emission of volatile organic compounds, making it more environmentally friendly and safer. At the same time, since no solvent is used, the porosity of the prepared composite material products is lower, which improves the quality and performance of the products. 2. Compared with the traditional hot melt method, the present invention eliminates the process of multiple heating, reduces energy consumption and production costs. By allowing the obvious curing agent to react slowly at room temperature, the liquid epoxy resin composition gradually forms a film and achieves suitable viscosity, thus achieving the purpose of low-cost preparation of prepreg. 3. The raw materials used in this invention are readily available, and the preparation process is simple and easy to understand. It has strong scalability and can provide effective technical support for the large-scale production of carbon fiber prepreg.

Claims

1. A method for preparing carbon fiber prepreg in one step, characterized in that: First, place the freshly prepared epoxy resin composition in a coating equipment, and then use the coating equipment to coat the liquid epoxy resin composition onto the release paper. Then, bring the release paper coated with the epoxy resin composition into contact with continuous carbon fiber or fabric, and wind them together onto a paper tube. After winding, put the paper tube containing the material into a plastic bag and vacuum pack it. Finally, let it stand at room temperature for more than 48 hours to obtain carbon fiber prepreg.

2. The method for preparing carbon fiber prepreg in one step according to claim 1, characterized in that: In this method, the epoxy resin composition is prepared using the following components in the indicated weight ratios: 50-70 parts liquid epoxy resin, 5-20 parts toughening agent, 3-10 parts latent curing agent, 5-10 parts overt curing agent, 0.5-5 parts accelerator, and 0.1-5 parts additives.

3. The method for preparing carbon fiber prepreg in one step according to claim 2, characterized in that: The liquid epoxy resin is selected from one or more of liquid bisphenol A type epoxy resin, bisphenol F type epoxy resin, aliphatic epoxy resin, alicyclic epoxy resin, phenolic epoxy resin, and multifunctional epoxy resin, and is diluted with an epoxy diluent.

4. The method for preparing carbon fiber prepreg in one step according to claim 2, characterized in that: The toughening agent is selected from any one of polyurethane modified epoxy, rubber modified epoxy, and core-shell toughened epoxy, and is in a liquid or semi-solid state at room temperature.

5. The method for preparing carbon fiber prepreg in one step according to claim 2, characterized in that: The latent curing agent is a solid powder of 5-20 micrometers and is selected from dicyandiamide or 4,4-diaminodiphenyl sulfone.

6. The method for preparing carbon fiber prepreg in one step according to claim 2, characterized in that: The active curing agent is any one of aliphatic amines, cycloaliphatic amines, aromatic amines, polyamides, polyether amines, etc., and the active hydrogen equivalent of the active curing agent is between 5% and 30% of the epoxy equivalent of the epoxy resin composition.

7. The method for preparing carbon fiber prepreg in one step according to claim 2, characterized in that: The accelerator is a solid powder accelerator with a particle size of 5 to 20 micrometers, and the accelerator is selected from any one of urea compounds, polyurea compounds, imidazole or imidazole derivatives.

8. The method for preparing carbon fiber prepreg in one step according to claim 2, characterized in that: The additive is one or more of the following: wetting agent, defoamer, dispersant, etc., and is in a liquid state at room temperature.

9. The method for preparing carbon fiber prepreg in one step according to claim 1, characterized in that: The specific steps of this method are as follows: (1) Preparation of epoxy resin composition: Accurately weigh the liquid epoxy resin, toughening agent, latent curing agent, visible curing agent, accelerator, and additives according to the specified proportions. Stir the liquid epoxy resin, toughening agent, latent curing agent, accelerator, and additives, and then grind them more than 3 times with a three-roll mill to ensure that the materials are fully mixed, thus obtaining the basic mixture. (2) Online coating and impregnation of carbon cloth: The base mixture and the visible curing agent are mixed online in a static mixer to obtain a liquid epoxy resin composition. Then, it is extruded into the glue tank of the coating equipment. The liquid epoxy resin composition is coated onto the release paper using the coating equipment. The epoxy resin composition coated onto the release paper is then brought into contact with carbon fiber or fabric and wound up. (3) Vacuum coating and room temperature curing: The rolled-up carbon fiber prepreg is placed into an air bag and vacuum-sealed. After standing at room temperature for more than 48 hours, a carbon fiber prepreg with a certain degree of self-adhesion is obtained.

10. The method for preparing carbon fiber prepreg in one step according to claim 9, characterized in that: The epoxy resin composition has a room temperature viscosity between 100 and 5000 cps before the addition of the visible curing agent, and a room temperature viscosity between 100 and 2000 cps after the addition of the visible curing agent. It can maintain a liquid state for at least 2 hours at room temperature of 25±5℃. After standing at room temperature for more than 48 hours, the viscosity of the epoxy resin composition at 70℃ is between 5000 and 100000 cps.