White-dot-free carbon fiber composite material part and preparation method thereof

Abstract

The invention discloses a white-dot-free carbon fiber composite material workpiece and a preparation method. The workpiece comprises a carbon fiber felt layer which is arranged between an appearance layer and a main body reinforcing layer at the joint line position of the workpiece and the R angle position of the workpiece. The preparation method of the product comprises the following steps: material sheet paving: paving the appearance layer and the main body enhancement layer on the cavity surface of a mold in sequence according to the paving layer design, and paving the carbon fiber felt layer between the appearance layer and the main body enhancement layer corresponding to the mold closing seam position in the cavity and the R angle position of the product; bagging and sealing; and in the curing process, lag coupling temperature control is adopted from the heating stage to the heat preservation stage and from the heat preservation stage to the cooling stage. According to the method, the appearance white point defect, especially the white point defect at the joint line position and the R angle position of an existing carbon fiber composite material part, is overcome, and the appearance quality of the carbon fiber composite material part is improved.

Description

Technical Field

[0001] The invention relates to the technical field of carbon fiber composite materials, and in particular to a carbon fiber composite material component without white spots and a preparation method thereof. Background Art

[0002] In the production of most carbon fiber reinforced epoxy resin matrix composite materials in the prior art, latent curing agents, such as dicyandiamide, are added to the epoxy resin prepregs used. Due to its low price and low active hydrogen equivalent, a small amount added to the epoxy resin can achieve the effect of curing the resin, so it has become a commonly used curing agent in epoxy resin matrices for prepregs. However, after the prepregs using dicyandiamide curing agent are thermosetted, white spot defects are very likely to appear on the surface of the products, especially on the surface of carbon fiber composite products, where white spot defects are more likely to be prominent. For details, please refer to the attached Figure 1 (White spots appear on the entire large surface of the part). Even carbon fiber composite parts that originally had no white spots will have white spots or white spots after being washed with water, acetone, etc., affecting the appearance and acceptance rate of carbon fiber composite parts. Therefore, the white spot defect of carbon fiber composite parts has become one of the important problems in their application in automotive exterior parts.

[0003] Regarding the white spot defect, those skilled in the art believe that it is because the dicyandiamide curing agent is a latent curing agent of the heating curing agent class, which is solid at room temperature, insoluble in epoxy resin, and dispersed in the epoxy resin in the form of microparticles. Since the molecular polarity of the substance is relatively large, it is relatively easy to agglomerate. When the prepreg is formed, the agglomerated dicyandiamide will be partially unreacted, resulting in a large number of white spots on the final product. Therefore, the industry focuses on material modification to solve the white spot defect. For example, CN111004408A discloses a white spot-free fast-curing epoxy prepreg, which is prepared by mixing conventional epoxy resin, multifunctional resin, low-profile resin and curing agent to obtain a resin film raw material of a homogeneous epoxy resin system. The latent curing agent completes curing within 2-15 minutes at a temperature of 120-150°C, ensuring that the entire epoxy system can reach a mutually soluble state before or during curing, thereby eliminating the curing agent and other by-product residues, meeting the requirements of fast curing and realizing the production of white spot-free products. However, material modification is more suitable for laboratory environments. In actual production, the improvement of the resin system still cannot eliminate the white spot defects of carbon fiber composite parts. Due to the influence of factors such as layering and curing process, white spot defects will still occur. Especially in the autoclave process, white spots are very likely to appear at the parting line and the R corner of the part. See the attached Figure 2 (In the red circle area). Summary of the invention

[0004] The purpose of the present invention is to provide a carbon fiber composite material part without white spots and a preparation method, which solves the apparent white spot defects of existing carbon fiber composite material parts, especially the white spot defects located at the mold line position and R angle position of the part, and improves the apparent quality of the carbon fiber composite material parts.

[0005] In view of this, the first aspect of the present invention provides a carbon fiber composite material part without white spots, including an appearance layer and a main reinforcement layer, and a carbon fiber felt layer is also arranged between the appearance layer and the main reinforcement layer at the mold line position of the part and the R corner position of the part.

[0006] Optionally, the carbon fiber felt layer has a thickness of 0.05-0.3 mm and a gram weight of 40±10 g / ㎡.

[0007] Optionally, the appearance layer includes a layer of carbon fiber prepreg with a grammage of 200-300 g / ㎡, and the main reinforcement layer includes at least one layer of carbon fiber prepreg with a grammage of 600-800 g / ㎡.

[0008] Optionally, the prepreg may be a unidirectional prepreg layer or a fabric prepreg, and the fabric prepreg includes a plain fabric prepreg, a satin fabric prepreg, a twill fabric prepreg or a multi-axial prepreg.

[0009] Optionally, the resin system used in the carbon fiber prepreg has a viscosity of 20000±5000cps at 70±1°C, and the viscosity decreases with increasing temperature, and at 120°C, the viscosity of the resin matrix is ​​800±200cps.

[0010] The second aspect of the present invention provides a method for preparing a carbon fiber composite material part without white spots, which is used to prepare the carbon fiber composite material part without white spots according to any one of the first aspects, comprising the steps of: The carbon fiber prepreg sheets of the appearance layer and the main reinforcement layer are laid on the cavity surface of the mold in sequence according to the layer design. The carbon fiber felt is laid between the appearance layer and the main reinforcement layer at the mold seam position and the R corner position of the workpiece in the mold cavity.

[0011] The thickness of the carbon fiber felt is 0.08-0.5 mm.

[0012] At the mold joint, the resin flows in a direction perpendicular to the plane of the part, and the resin flows in the joint to form a hedge, resulting in excessive resin loss and accumulation of curing agent at the joint. At the R corner of the part, due to the complex shape and large depth, the curing agent in the resin is not easy to flow around during the pressurization process, and the curing is completed. Optionally, the mold is a mold of uniform wall thickness. When heated and cured in the autoclave, the mold thickness is not uniform, which will lead to different heating rates in different parts, and thus cause temperature differences in different parts of the product. The curing agent in the low-temperature part cannot be effectively dissolved, and eventually accumulates into white spots. The mold uniform wall thickness design can make the heating rate of the entire mold in the autoclave consistent, and the overall heating of the product is uniform.

[0013] Optionally, several temperature monitoring points or temperature monitoring holes are set on the surface or inside of the mold to connect thermocouples to directly monitor the mold temperature; the spacing between adjacent thermocouples is controlled at 500±50mm. Compared with monitoring the air temperature in the autoclave in the current autoclave process, monitoring the mold temperature is more accurate for temperature monitoring during the molding process, ensuring that the mold temperature is uniform and stable during the molding process, thereby ensuring that the curing agent in the resin system in the carbon fiber composite product is effectively dissolved and reacted, and avoiding the appearance of white spots on the surface of the product.

[0014] Optionally, a removable double-layer sealing structure is also provided on the periphery of the mold cavity. The double-layer sealing structure includes a first sealing structure close to the workpiece and a second sealing structure arranged outside the first sealing structure, and the distance between the first sealing structure and the second sealing structure is 15±10mm. The first sealing structure includes a first sealing groove and a first sealing strip, the depth of the first sealing groove is 3-5mm, the bottom chamfer is R1.5±0.1, and the cross-section of the first sealing strip is a round strip with a diameter of 4-6mm. The second sealing structure includes a second sealing groove and a second sealing strip, the depth of the second sealing groove is 9-10mm, the bottom chamfer is R1.5±0.1mm, and the cross-section of the second sealing strip is square with a side length of 9-11mm. When the surface where the sealing structure is set is a single curved surface or a flat smooth surface, the depth of the sealing groove is preferably 9-10mm, and when the surface where the sealing structure is set is a multi-curved surface or anisotropic complex surface, the depth of the sealing groove is preferably 9.5-10.5mm.

[0015] The method for preparing a carbon fiber composite material product without white spots further includes curing, which specifically includes: In the heating stage, the pressure is increased at a rate of 15 ± 5 Kpa / min to the required molding pressure of the carbon fiber prepreg used; at the same time, the temperature is increased at a rate of 2-8°C / min to the curing temperature of the carbon fiber prepreg; Insulation section: According to the characteristics of the carbon fiber prepreg used, the heat preservation and pressure maintenance are carried out for a certain period of time; Cooling section: After the prepreg is cured and formed, it is cooled at a rate of 2-8℃ / min.

[0016] From the heating section to the insulation section, and from the insulation section to the cooling section, the temperature control method adopted is hysteresis temperature control.

[0017] The hysteresis couple temperature control described in the present invention can ensure that the mold as a whole is evenly and effectively heated to the specified temperature set by the program before starting the next program, avoiding the phenomenon that the resin in a single area of ​​the mold still has high fluidity when entering the next stage without being heated to the specified temperature, which ultimately leads to the whitening of the workpiece.

[0018] The beneficial effects of the present invention are at least as follows: (1) By designing the layer structure of the carbon fiber composite material part, a carbon fiber felt layer is arranged at the parting line and the R corner position to solve the problem of curing agent aggregation caused by resin hedging and loss at the parting line during the vacuuming and pressurizing curing steps, so as to achieve the overall fullness of the resin on the surface of the carbon fiber composite material part, and no whitening phenomenon at the parting line and the R corner position of the part; (2) By optimizing the molding mold and designing it with equal wall thickness to achieve uniform mold temperature rise, and the double-layer sealing structure design can reduce the counter suction force during the vacuum adsorption process at the mold seam position, making it easier to clean the resin flash and trim the appearance materials during demolding; (3) By optimizing the autoclave process, including directly monitoring the mold temperature and using a hysteresis coupler to control the temperature, it is ensured that the mold is heated evenly and effectively to the set temperature during the curing step before entering the next stage, thereby effectively controlling the uniform curing of the entire part. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Attached Figure 1 A schematic diagram of white spot defects in carbon fiber composite material parts in the prior art; Attached Figure 2 A schematic diagram of white spot defects at the parting line / R angle position of a carbon fiber composite material part in the prior art; Attached Figure 3 This is a schematic diagram of the structure of a carbon fiber composite material without white spots of the present invention; Attached Figure 4 It is a schematic diagram of laying out the sheet of the carbon fiber composite material product without white spots of the present invention; Attached Figure 5 It is a three-dimensional schematic diagram of the mold structure of the present invention; Attached Figure 6 It is a top view schematic diagram of the mold structure of the present invention; Attached Figure 7 It is a schematic diagram of the AA section; Attached Figure 8 It is a schematic diagram of the BB section; Attached Fig. 9 This is an enlarged view of Part I; Attached Fig.10 This is a photo of the carbon fiber composite material obtained in Example 2; Attached Fig.11 This is a photo of the carbon fiber composite material product obtained in Example 3; Attached Fig.12 This is a photo of the carbon fiber composite material product obtained in Example 4; Wherein: 1-carbon fiber composite material part; 11-appearance layer; 12-main reinforcement layer; 13-carbon fiber felt layer; 2-mold; 21-mold body; 22-slider 1; 22-slider 2; 23-slider 3; 24-first sealing structure; 25-second sealing structure; 26-mold seam. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention. Example 1

[0022] The present embodiment provides a carbon fiber composite material part 1 without white spots, including an appearance layer 11 and a main reinforcement layer 12, and a carbon fiber stand layer 13 is further arranged between the appearance layer 11 and the main reinforcement layer 12 at the mold line position and the R corner position of the part, see the attached Figure 3 ; The carbon fiber felt layer has a thickness of 0.25 ± 0.25 mm and a weight of 40 ± 10 g / ㎡; The appearance layer includes a layer of carbon fiber prepreg with a gram weight of 200-300 g / ㎡; the main reinforcement layer includes at least one layer of carbon fiber prepreg with a gram weight of 600-800 g / ㎡; the carbon fiber prepreg can be a unidirectional prepreg or a fabric prepreg, and the fabric prepreg includes a plain fabric prepreg, a twill fabric prepreg, a satin fabric prepreg, and a multi-axial prepreg; The resin system used in the carbon fiber prepreg comprises, by weight of raw materials: Component A: 60-80 parts of a common epoxy resin mixed with at least one solid epoxy resin and at least one liquid epoxy resin; Component B: 20-30 parts of liquid epoxy resin; 4-8 parts of dicyandiamide; 0.5-3 parts of curing accelerator; 0.5-1 parts of thixotropic agent; 0.3-1 parts of thixotropic enhancer; The viscosity of the resin system at 70±1° C. is 20000±5000 cps, and the viscosity decreases as the temperature increases. At 120° C., the viscosity of the resin matrix is ​​800±200 cps. Example 2

[0023] This embodiment provides a method for preparing a carbon fiber composite material component without white spots.

[0024] A method for preparing a carbon fiber composite material part without white spots, comprising: Step 1: Lay the sheets. Lay the appearance layer carbon fiber prepreg sheets and the main reinforcement layer carbon fiber prepreg sheets on the mold cavity surface in sequence according to the layup design. Figure 4 As shown, a layer of carbon fiber felt layer 13 is laid between the appearance layer and the main reinforcement layer at the corresponding position of the cavity mold joint and the R angle position of the workpiece; the carbon fiber felt layer can be a whole piece, or a plurality of pieces can be overlapped according to the difficulty of laying the position; Step 2: Seal the bag and vacuum it; Step 3: Forming and curing, specifically including: In the heating stage, the pressure is increased at a rate of 15 ± 5 Kpa / min to the required molding pressure of the carbon fiber prepreg used; at the same time, the temperature is increased at a rate of 2-8°C / min to the curing temperature of the carbon fiber prepreg; Insulation section: According to the characteristics of the carbon fiber prepreg used, the heat preservation and pressure maintenance are carried out for a certain period of time; Cooling section: After the prepreg is cured and formed, it is cooled at a rate of 2-8℃ / min.

[0025] From the heating section to the insulation section, and from the insulation section to the cooling section, the temperature control method adopted is hysteresis temperature control.

[0026] Part testing method: First observe the white spots on the carbon fiber composite material part obtained in this embodiment, then spray water and ethanol on the surface of the part several times, especially at the mold seam and the R corner of the part, to observe whether white spots appear on the surface of the part.

[0027] Test results: As attached Fig.10 As shown, there are no white spot defects at the parting line and R corner of the workpiece. After wiping with alcohol, there are basically no obvious white spot defects. Example 3

[0028] This embodiment provides a method for preparing a carbon fiber composite material component without white spots.

[0029] The difference from Example 2 is that the mold is further optimized.

[0030] As attached Figure 5-9 As shown, the mold 2 in step 1 is a mold of equal wall thickness. Specifically, the mold includes a mold body 21, a slider 1 22, a slider 2 23, and a slider 3 24. A temperature detection hole (not shown in the figure) is also provided on the mold, and a thermocouple is provided in the temperature monitoring hole to directly monitor the temperature of the mold in the autoclave. The spacing between adjacent thermocouples is controlled to be 500±50mm.

[0031] As attached Figure 5-8 As shown, outside the mold paving line, a removable double-layer sealing structure is also provided on the mating surface of the mold body 1 and the slider 3 24. The double-layer sealing structure includes a first sealing structure 25 close to the workpiece and a second sealing structure 26 arranged outside the first sealing structure 25, and the distance between the first sealing structure 25 and the second sealing structure 26 is 15±10mm. The first sealing structure 25 includes a first sealing groove and a first sealing strip, the depth of the first sealing groove is 3-5mm, the bottom chamfer is R1.5±0.1, the first sealing strip is made of silicone material, the cross section is a round bar, and the diameter is 4-6mm. The second sealing structure 26 includes a second sealing groove and a second sealing strip, the depth of the second sealing groove is 9-10mm, the bottom chamfer is R1.5±0.1mm, and the cross section of the second sealing strip is square with a side length of 9-11mm. When the surface on which the sealing structure is set is a single curved surface or a flat smooth surface, the depth of the sealing groove is preferably 9-10 mm. When the surface on which the sealing structure is set is a multi-curved surface or an anisotropic complex surface, the depth of the sealing groove is preferably 9.5-10.5 mm.

[0032] Part testing method: The carbon fiber composite material part obtained in this embodiment is first visually inspected for white spots, and then water and ethanol are sprayed on the surface of the part several times, especially at the mold seam and the R corner of the part, to observe whether white spots appear on the surface of the part.

[0033] Test results: as attached Fig.11 As shown, there is no white spot defect on the whole part (the white substance is the untreated resin flash). After spraying alcohol, there is no white spot defect at the parting line and R angle. Example 4

[0034] This embodiment provides a method for preparing a carbon fiber composite material component without white spots.

[0035] The difference between this embodiment and embodiment 3 is that the curing and molding process is further optimized.

[0036] In the curing step, the temperature is controlled by a hysteresis couple from the heating stage to the insulation stage. That is, the multiple thermocouples connected to the mold will monitor different mold temperatures, some with high temperatures (called leading couples) and some with low temperatures (called lagging couples). Only when the temperature monitored by the hysteresis couple reaches the specified temperature set by the autoclave can the autoclave start the insulation program and put the mold into an insulation and pressure state.

[0037] Part testing method: The carbon fiber composite material part obtained in this embodiment is first visually inspected for white spots, and then water and ethanol are sprayed on the surface of the part several times, especially at the mold seam and the R corner of the part, to observe whether white spots appear on the surface of the part.

[0038] Test results: as attached Fig.12 As shown in the figure, there are no white spot defects at the mold seam and R corner of the part (the white substance is the untreated resin flash), and there are no white spot defects after wiping with alcohol, and the part reaches Grade A surface.

Claims

1. A carbon fiber composite material part without white spots, comprising an appearance layer and a main reinforcement layer, characterized in that: A carbon fiber felt layer is also arranged between the appearance layer and the main reinforcement layer at the mold seam position and the R corner position of the product.

2. The carbon fiber composite material part without white spots according to claim 1, characterized in that: The carbon fiber felt layer has a thickness of 0.05-0.3 mm and a surface density of 40±10 g / ㎡.

3. The carbon fiber composite material part without white spots according to claim 1, characterized in that: The appearance layer includes a layer of carbon fiber prepreg with a gram weight of 200-300 g / ㎡; the main reinforcement layer includes at least one layer of carbon fiber prepreg with a gram weight of 600-800 g / ㎡.

4. A method for preparing a carbon fiber composite material part without white spots, based on the carbon fiber composite material part according to any one of claims 1 to 3, characterized in that: include: The material sheets are laid, and the appearance layer and the main reinforcement layer are laid on the cavity surface of the mold in sequence according to the layer laying design. Corresponding to the mold seam position in the mold cavity and the R corner position of the workpiece, the carbon fiber felt layer is laid between the appearance layer and the main reinforcement layer.

5. The method for preparing a carbon fiber composite material product without white spots according to claim 4, characterized in that: The mold has a constant wall thickness.

6. The method for preparing a carbon fiber composite material product without white spots according to claim 4, characterized in that: A plurality of temperature monitoring points are arranged on the surface or inside of the mold, which are used to connect thermocouples to monitor the mold temperature, and the distance between adjacent thermocouples is controlled at 500±50mm.

7. The method for preparing a carbon fiber composite material product without white spots according to claim 4, characterized in that: The mold includes a mold body and a slider and / or an insert; a detachable sealing structure is also arranged on the matching surfaces of the mold body and the slider and / or the insert outside the mold paving line.

8. The method for preparing a carbon fiber composite material product without white spots according to claim 7, characterized in that: The sealing structure comprises: A first sealing structure, arranged near the end of the workpiece, comprises a first sealing groove and a first sealing strip, wherein the cross section of the first sealing strip is circular; The second sealing structure is arranged on the outer side of the first sealing structure, and comprises a second sealing adhesive groove and a second sealing adhesive strip, wherein the cross section of the second sealing adhesive strip is square.

9. The method for preparing a carbon fiber composite material product without white spots according to claim 8, characterized in that: The distance between the first sealing structure and the second sealing structure is 15±10 mm.

10. The method for preparing a carbon fiber composite material product without white spots according to claim 4, characterized in that: It also includes curing, which specifically includes: In the heating stage, the pressure is increased at a rate of 15 ± 5 Kpa / min to the required molding pressure of the carbon fiber prepreg used; at the same time, the temperature is increased at a rate of 2-8°C / min to the curing temperature of the carbon fiber prepreg; Insulation section: According to the characteristics of the carbon fiber prepreg used, the heat preservation and pressure maintenance are carried out for a certain period of time; Cooling section: After the prepreg is cured and formed, it is cooled at 2-8℃ / min; From the heating section to the insulation section, and from the insulation section to the cooling section, the temperature control method adopted is hysteresis temperature control.

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