High-transparency high-temperature-yellowing-resistant epoxy resin prepreg and preparation method thereof

Abstract

The invention provides a high-transparency high-temperature-yellowing-resistant epoxy resin prepreg as well as a preparation method and application thereof, and belongs to the technical field of epoxy resin materials. The liquid epoxy resin composition comprises the following components in parts by weight: 70-90 parts of liquid epoxy resin, 1-10 parts of a toughening agent, 5-20 parts of liquid dicyandiamide, 1-3 parts of a liquid curing accelerator and 0-2 parts of an antioxidant. The liquid amine solvent is adopted to dissolve powder dicyandiamide to prepare liquid dicyandiamide, so that compared with the prior art, the epoxy resin prepreg system prepared by the preparation method does not contain dicyandiamide particles in a solid form, the agglomeration problem does not exist, and the preparation method is simple and easy to operate. The problem of resin yellowing caused by local implosion due to agglomeration of solid dicyandiamide and the problem of white dots on the surface of a workpiece due to incomplete reaction of agglomerated dicyandiamide are solved.

Description

Technical Field

[0001] The present invention relates to a highly transparent, high-temperature resistant and yellowing-resistant epoxy resin prepreg, a preparation method thereof and an application thereof, belonging to the technical field of epoxy resin materials. Background Art

[0002] With the rise of new energy vehicles, driven by national policies, new energy vehicles have developed rapidly and gradually occupied the mainstream position in the domestic automotive industry. Electrification has become the development direction of the global automotive industry.

[0003] Composite products prepared from transparent prepregs are widely used in the interior parts of new energy vehicles because the texture of carbon fiber fabrics can be clearly seen, and they are lightweight, beautiful and have high strength.

[0004] Epoxy resin prepregs are composite systems composed of epoxy resins, curing systems and reinforcing fibers. Currently, powdered dicyandiamide is generally used as a curing agent in epoxy resin compositions for hot-melt prepregs. Since there is a large polarity difference between dicyandiamide and epoxy resin, the two cannot be mutually dissolved. The current mainstream method is to use a grinding method to disperse powdered dicyandiamide in epoxy resin in a solid form to form a curing agent pre-product, and then add it into epoxy resin to prepare epoxy resin prepregs.

[0005] However, since dicyandiamide exists in a solid form, during the subsequent hot-melt impregnation of reinforcing fibers to prepare prepreg cloth and the process of preparing composite materials by high-temperature molding, powdered dicyandiamide will agglomerate due to reasons such as epoxy resin loss, its own high polarity, and high surface energy of powder particles. The agglomerated dicyandiamide will adhere to the fiber fabric. On the one hand, explosive polymerization and yellowing will occur in the area where dicyandiamide agglomerates due to excessive local curing agent, ultimately resulting in obvious yellowing on the surface of the composite product. On the other hand, if the agglomerated dicyandiamide fails to react completely, white spots will appear on the surface of the composite product, which will also directly affect the appearance of the product.

[0006] In addition, existing epoxy resin prepregs need to have ultra-high viscosity to prevent excessive resin loss during high-temperature molding. Therefore, solid epoxy is inevitably added in the formulation design to increase the overall viscosity of the resin. However, solid epoxy will leave some impurities such as bisphenol A during the production process, and it is more likely to turn yellow at high temperatures than liquid epoxy. Therefore, it will further cause yellowing problems in epoxy resin prepregs.

[0007] In the comparative document CN102633987A, a method for preparing a latent epoxy resin curing agent using liquid dicyandiamide as a raw material is disclosed. In this technical solution, a solvent and an epoxy diluent are used. Among them, the addition of the solvent will volatilize when heated during the subsequent production of single-component hot-melt prepreg resin and the two-step impregnation process, causing pollution to the production environment and potential hazards to the health of workers. In addition, it will also cause defects such as pores on the surface of the prepreg cloth during impregnation and subsequent component manufacturing processes, affecting the mechanical properties of the final product and resulting in an excessive content of resin VOC (volatile organic solvents), which does not meet the requirements of relevant environmental protection regulations.

[0008] In addition, the prior art uses a large amount of epoxy resin diluent to modify dicyandiamide, and the epoxy resin diluent will significantly reduce the glass transition temperature of the prepreg resin after curing, thereby reducing the heat resistance of the final product.

[0009] Therefore, ensuring the transparency of the composite material, especially having no yellowing, no white spots, and high transparency under high-temperature compression molding process is a technical problem difficult to solve in the current industry.

[0010] Therefore, there is an urgent need in the art for a high-transparency, high-temperature yellowing-resistant epoxy prepreg, its preparation method, and applications. Summary of the Invention

[0011] The object of the present invention is to solve the problems of yellowing and surface white spots that occur in the preparation of composite parts using hot-melt prepregs for high-temperature compression molding in the prior art.

[0012] To achieve the above object, the technical solution adopted by the present invention is to provide a high-transparency, high-temperature yellowing-resistant epoxy prepreg and its preparation method.

[0013] In the first aspect of the present invention, a high-transparency, high-temperature yellowing-resistant epoxy prepreg is provided, which comprises the following components:

[0014]

[0015] Among them, each part is calculated by mass.

[0016] Preferably, the liquid epoxy resin is selected from one or more of bisphenol A liquid epoxy resin, bisphenol F liquid epoxy resin, phenolic liquid epoxy resin, and alicyclic liquid epoxy resin.

[0017] Preferably, the toughening agent includes one or more of thermoplastic resin, polyether-modified epoxy resin, and isocyanate-modified epoxy resin; among them, the thermoplastic resin includes one or more of phenoxy resin, polyphenylene ether, polycarbonate, and polysulfone.

[0018] Preferably, the liquid dicyandiamide is prepared by the following method: adding powdery dicyandiamide into a liquid amine solvent with stirring until the powdery dicyandiamide is completely dissolved in the liquid amine solvent, thus obtaining the liquid dicyandiamide.

[0019] Preferably, the weight fraction ratio of the powdery dicyandiamide to the liquid amine solvent is (1 - 3):1; the liquid amine solvent includes one or more of isophorone diamine, 4,4'-diaminodicyclohexylmethane, polyetheramine, or bis(4-amino-3-methylcyclohexyl)methane.

[0020] Preferably, the particle size of the powdery dicyandiamide is 4 - 8 μm, and the stirring temperature is 25 - 40°C.

[0021] Preferably, the liquid curing accelerator is prepared by the following method: adding powdery curing accelerator into a liquid amine solvent with stirring until the powdery curing accelerator is completely dissolved in the liquid amine solvent, thus obtaining the liquid curing accelerator.

[0022] Preferably, the weight fraction ratio of the powdery curing accelerator to the liquid amine solvent is (1 - 3):1; the liquid amine solvent includes one or more of isophorone diamine, 4,4'-diaminodicyclohexylmethane, polyetheramine, or bis(4-amino-3-methylcyclohexyl)methane.

[0023] Preferably, the stirring temperature is 25 - 40°C.

[0024] Preferably, the antioxidant includes one or more of hindered phenol antioxidants and phosphite antioxidants.

[0025] In the second aspect of the present invention, a method for preparing the above-mentioned high-transparency, high-temperature resistant and yellowing-resistant epoxy resin prepreg is provided, including the following steps:

[0026] Step 1: Heat the liquid epoxy resin to 80 - 120°C, after stirring evenly, add the toughening agent and antioxidant thereto, keep the temperature constant for 1 - 3 h and keep the stirring speed at 100 - 150 rpm, so that the toughening agent and antioxidant are fully melted and mixed evenly;

[0027] Step 2: Lower the heating temperature to 50 - 70°C, add the liquid dicyandiamide, keep the temperature constant for 3 - 6 h, and keep the stirring speed at 60 - 80 rpm. During the whole stirring process, cool water is introduced into the reaction kettle to ensure that the material temperature is lower than 100°C during the stirring process;

[0028] Step 3: Lower the heating temperature to 50 - 70°C, add the liquid curing accelerator, maintain a stirring speed of 60 - 80 rpm under vacuum conditions, and carry out a pre-reaction for 20 - 30 min to obtain the highly transparent, high-temperature resistant, yellowing-resistant epoxy resin prepreg.

[0029] Step 4: After obtaining the highly transparent, high-temperature resistant, yellowing-resistant epoxy resin prepreg, carry out vacuum packaging and store it in a cold storage, where the storage temperature in the cold storage is not higher than -10°C.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The present invention uses a liquid amine solvent to dissolve powdered dicyandiamide to prepare liquid dicyandiamide. Therefore, compared with the prior art, the epoxy resin prepreg system prepared by the present invention does not contain dicyandiamide particles in solid form, so there is no agglomeration problem, solving the resin yellowing problem caused by local explosive polymerization due to the agglomeration of solid dicyandiamide, and the white dot problem on the surface of the workpiece caused by the incomplete reaction of the agglomerated dicyandiamide.

[0032] (2) The liquid dicyandiamide prepared by the present invention can carry out a pre-reaction with liquid epoxy resin to obtain a high-viscosity epoxy resin prepreg. Compared with the prior art, it is not necessary to add solid epoxy resin in the formulation design, so it solves the problems of unstable molecular weight distribution of solid epoxy resin, many residual impurities, resulting in unstable viscosity of epoxy resin prepreg and yellowing of composite materials.

[0033] (3) The present invention uses a liquid amine curing agent to dissolve dicyandiamide. During the subsequent preparation process of the single-component hot-melt prepreg resin, the liquid amine curing agent will react completely with the epoxy resin. No organic solvents are added throughout the process, which is safe, environmentally friendly, low in VOC, and there will be no problems such as pore defects caused by the volatilization of organic solvents.

[0034] (4) The liquid dicyandiamide latent curing agent of the present invention does not contain any epoxy resin diluent, so it will not reduce the glass transition temperature after curing of the prepreg resin, nor will it reduce the heat resistance of the final product. Specific Embodiments

[0035] To make the present invention more obvious and understandable, the following is a detailed description with preferred embodiments:

[0036] The components and their corresponding mass percentages of each component in the raw materials used in Examples 1 - 3 and Comparative Examples 1 - 2 are shown in Table 1.

[0037] Table 1

[0038]

[0039]

[0040] Example 1

[0041] A highly transparent, high-temperature resistant and yellowing-resistant epoxy resin prepreg, the components and their corresponding mass percentages in the preparation raw materials are shown in Table 1, and it is obtained by the following steps:

[0042] Step 1): Heat the liquid epoxy resin to 120 °C, after stirring evenly, add the toughening agent and antioxidant into it, keep the temperature constant for 3 h and keep the stirring speed at 150 rpm, so that the toughening agent and antioxidant are fully dissolved and mixed evenly;

[0043] Step 2): Lower the heating temperature to 70 °C, add the liquid dicyandiamide, keep the temperature constant for 3 h and keep the stirring speed at 60 rpm. During the whole stirring process, cooling water is introduced into the reaction kettle to ensure that the material temperature is lower than 100 °C during stirring;

[0044] Step 3): Lower the heating temperature to 50 °C, add the liquid curing accelerator, keep the stirring speed at 60 rpm under vacuum conditions, and carry out a pre-reaction for 30 min to obtain the highly transparent, high-temperature resistant and yellowing-resistant epoxy resin prepreg.

[0045] Step 4) After obtaining the highly transparent, high-temperature resistant and yellowing-resistant epoxy resin prepreg, carry out vacuum packaging and store it in a cold storage, where the storage temperature of the cold storage is not higher than -10 °C.

[0046] Step 5) Prepare a carbon fiber prepreg with a fiber content of 55% from the epoxy resin prepreg obtained in step (4) by a two-step hot melting method;

[0047] Step 6) Put the carbon fiber prepreg prepared in step (5) into a molding die, turn on the vacuum pump to extract the air in the die and the carbon fiber prepreg laminate structure. The vacuuming time is 2 min and the vacuum degree is 30 mbar. After reaching complete vacuum, at a temperature of 155 °C, carry out mold pressing and curing for 30 min, and the mold pressing pressure > 5 MPa. Cool and shape at room temperature to form a highly transparent carbon fiber interior trim part.

[0048] Example 2

[0049] A highly transparent, high-temperature resistant and yellowing-resistant epoxy resin prepreg, the components and their corresponding mass percentages in the preparation raw materials are shown in Table 1. The difference from Example 1 is that the content of the toughening agent is reduced and the amount of liquid dicyandiamide is increased. In step 6, the mold pressing and curing temperature is 130 °C and the curing time is 60 min.

[0050] Example 3

[0051] A high-transparency, high-temperature resistant and yellowing-resistant epoxy resin prepreg, the components and their corresponding mass percentages in the preparation raw materials are shown in Table 1. The difference from Example 1 is that the content of the toughening agent is increased and the amount of liquid dicyandiamide is reduced. In Step 6, the molding and curing temperature is 170 °C and the curing time is 10 min.

[0052] Comparative Example 1

[0053] An epoxy resin prepreg was prepared by the prior art. Liquid epoxy resin and solid epoxy resin were melted together, and then powdered dicyandiamide and solid accelerator were added for dispersion. After cooling, the epoxy resin prepreg was prepared.

[0054] Comparative Example 2

[0055] A commercially available transparent epoxy resin prepreg was used to prepare carbon fiber prepreg cloth and transparent carbon fiber interior parts by the same process as in Example 1.

[0056] Performance detection experiment

[0057] Experimental samples: Examples 1-3 were sequentially numbered as test samples 1-3; Comparative Examples 1-2 were sequentially numbered as control samples 1-2.

[0058] Judgment method: The experimental samples were respectively cut into appropriate sizes, and their visible light transmittance, tensile properties, compressive properties were measured. After high-temperature and high-humidity treatment (85 °C, 85% RH, 1000 h), their visible light transmittance and yellow index were tested. The experimental results are shown in Table 2.

[0059] Table 2

[0060]

[0061]

[0062] Combined with Example 1, Comparative Examples 1-2 and the results in Table 2, it can be seen that compared with traditional epoxy resins, the composite materials prepared from the high-transparency, high-temperature resistant and yellowing-resistant epoxy resin prepreg provided by the present invention have higher light transmittance and lower yellow index, and can still maintain good yellowing resistance after high-temperature and high-humidity treatment.

[0063] Combined with Examples 1-3, Comparative Examples 1-2 and the results in Table 2, it can be seen that compared with traditional epoxy resins, the composite materials prepared from the high-transparency, high-temperature resistant and yellowing-resistant epoxy resin prepreg provided by the present invention have better mechanical properties.

[0064] The above are only the preferred embodiments of the present invention, and do not impose any formal or substantial limitations on the present invention. It should be noted that for those of ordinary skill in the art of this technology, without departing from the present invention, several improvements and supplements can still be made, and these improvements and supplements should also be regarded as within the protection scope of the present invention. Any equivalent changes in the form of slight modifications, decorations, and evolutions that can be made by those who are familiar with this specialty without departing from the spirit and scope of the present invention by using the technical content disclosed above are all equivalent embodiments of the present invention; at the same time, any equivalent changes in the form of modifications, decorations, and evolutions made to the above embodiments based on the substantial technology of the present invention still fall within the scope of the technical solutions of the present invention.

Claims

1. A highly transparent high temperature yellowing resistant epoxy resin prepreg, characterized in that: Includes the following components: Wherein, each number is calculated by mass.

2. The highly transparent, high temperature resistant, yellowing epoxy resin prepreg according to claim 1, characterized in that: The liquid epoxy resin is selected from one or more of bisphenol A liquid epoxy resin, bisphenol F liquid epoxy resin, phenolic liquid epoxy resin and alicyclic liquid epoxy resin.

3. The highly transparent high temperature yellowing resistant epoxy resin prepreg according to claim 1, characterized in that: The toughening agent includes one or more of thermoplastic resin, polyether modified epoxy resin and isocyanate modified epoxy resin; wherein the thermoplastic resin includes one or more of phenoxy resin, polyphenylene ether, polycarbonate and polyphenylene sulfone.

4. The highly transparent high temperature yellowing resistant epoxy resin prepreg according to claim 1, characterized in that: The liquid dicyandiamide is prepared by the following method: adding powdered dicyandiamide into a liquid amine solvent while stirring until the powdered dicyandiamide is fully dissolved in the liquid amine solvent, thereby obtaining the liquid dicyandiamide.

5. The highly transparent high temperature yellowing resistant epoxy resin prepreg according to claim 4, characterized in that: The weight fraction ratio of the powdered dicyandiamide to the liquid amine solvent is (1-3):1; the liquid amine solvent includes one or more of isophorone diamine, 4,4'-diaminodicyclohexylmethane, polyetheramine or bis(4-amino-3-methylcyclohexyl)methane.

6. The highly transparent high temperature yellowing resistant epoxy resin prepreg according to claim 4, characterized in that: The particle size of the powdered dicyandiamide is 4-8 μm, and the stirring temperature is 25-40° C.

7. The highly transparent high temperature yellowing resistant epoxy resin prepreg according to claim 1, characterized in that: The liquid curing accelerator is prepared by the following method: adding the powdered curing accelerator into a liquid amine solvent while stirring until the powdered curing accelerator is fully dissolved in the liquid amine solvent, thereby obtaining the liquid curing accelerator.

8. The highly transparent high temperature yellowing resistant epoxy resin prepreg according to claim 7, characterized in that: The weight fraction ratio of the powdered curing accelerator to the liquid amine solvent is (1-3):1; the liquid amine solvent includes one or more of isophorone diamine, 4,4'-diaminodicyclohexylmethane, polyetheramine or bis(4-amino-3-methylcyclohexyl)methane.

9. The highly transparent high temperature yellowing resistant epoxy resin prepreg according to claim 1, characterized in that: The antioxidant includes one or more of hindered phenol antioxidants and phosphite antioxidants.

10. A method for preparing the above-mentioned highly transparent high temperature yellowing resistant epoxy resin prepreg, characterized in that: The following steps are involved: Step 1, heating the liquid epoxy resin to 80-120° C., stirring evenly, adding the toughening agent and antioxidant thereto, maintaining a constant temperature for 1-3 hours, and maintaining a stirring speed of 100-150 rpm to fully melt the toughening agent and antioxidant and mix evenly; Step 2: lowering the heating temperature to 50-70° C., adding the liquid dicyandiamide, maintaining a constant temperature for 3-6 hours, and maintaining a stirring speed of 60-80 rpm, and introducing cooling water into the reactor during the entire stirring process to ensure that the material temperature is lower than 100° C. during the stirring process; Step 3: lower the heating temperature to 50-70° C., add the liquid curing accelerator, maintain a stirring speed of 60-80 rpm under vacuum conditions, and conduct a pre-reaction for 20-30 minutes to obtain the highly transparent, high temperature resistant, yellowing epoxy resin prepreg. Step 4: After obtaining the high-transparency, high-temperature-resistant, yellowing epoxy resin prepreg, vacuum-pack it and store it in a cold storage, wherein the storage temperature of the cold storage is not higher than -10°C.

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