Sandwich-configuration carbon fiber reinforced nylon foam and preparation method thereof

Abstract

The invention discloses sandwich-configuration carbon fiber reinforced nylon foam which comprises a carbon fiber reinforced nylon foam middle layer and continuous carbon fiber reinforced films compounded on the two sides, and the carbon fiber reinforced nylon foam comprises the following components in parts by weight: 68-95 parts of nylon; 5 to 40 parts of short carbon fiber; and the average length of the short carbon fibers is 0.1 to 20 mm. The carbon fiber reinforced nylon foam with the sandwich structure has the advantages that the compact skin layer is provided, the bonding property between the skin layer and the foam interface is high (without cracks), the bonding property between the continuous carbon fiber reinforced film and the skin layer is high, the pore diameter of the foam is small, the density of the foam is high, the foam is uniformly distributed, and the toughness is good.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of foamed polymer materials, in particular to a sandwich-structured carbon fiber reinforced nylon foam and a preparation method thereof. BACKGROUND

[0002] Polyamide (commonly known as nylon) is a kind of engineering plastic with repeating amide groups in the main chain. Due to its excellent mechanical strength, heat resistance, wear resistance and chemical corrosion resistance, it is widely used in the automotive, electronic and mechanical industries. The application of foaming process to nylon materials can produce lightweight, high-strength parts with heat and sound insulation functions, which has significant potential for cost reduction and high-performance application scenarios. In addition, to achieve lightweight and high performance, the existing technology often uses a sandwich structure preparation method to combine high-strength panels or films on both sides of the foam core.

[0003] However, the conventional nylon raw materials produced in the industry (such as nylon 6, nylon 66, etc.) have relatively low molecular weight, resulting in insufficient melt strength. This characteristic makes it challenging to produce a sandwich structure foam: First, the inherent material properties of nylon make it difficult to obtain a high-quality cell structure. The fast crystallization rate of nylon results in rapid crystallization of the melt during the cooling process, making the foaming process window extremely narrow and extremely sensitive to fluctuations in process parameters such as mold temperature, holding time, and cooling time. At the same time, due to its low melt strength, the cell wall is prone to rupture and coalescence during the foaming process, resulting in large cell size and open pores, poor interfacial bonding between the skin layer and the foam core layer, and easy skin-core interface peeling, which can cause defects in the product.

[0004] Second, unmodified nylon has a high crystallinity, and the cell size is large, so the cell wall is prone to become the starting point of crack initiation under load, and then brittle fracture occurs under dynamic load or impact, which severely limits its application in lightweight structural parts such as automobile impact-resistant parts that require high toughness and impact resistance.

[0005] Third, the weight reduction ratio of traditional low-pressure foaming injection molding process is limited, and the cell structure is easily oriented along the flow direction during injection, affecting its mechanical properties, making it difficult to meet the requirements of high-end scenarios. In addition, whether it is physical foaming or chemical foaming, the existing method is difficult to achieve high expansion and high-quality cell structure foaming in nylon materials. Physical foaming is limited by melt strength, and chemical foaming is limited by the dispersion and decomposition temperature of the foaming agent, both of which can easily result in large and uneven cell size in the product.

[0006] Fourth, in the high-pressure foaming injection molding process, the melt is injected into the mold by high pressure, and due to the low temperature of the mold surface, part of the melt will solidify on the mold surface (or the surface of the continuous carbon fiber film), so that a skin layer is formed between the mold and the foam. In the prior art, there is a gap between the skin layer and the foam, which reduces the interfacial bonding strength of the skin layer and the foam, and significantly reduces the impact resistance of the product.

[0007] Fifth, the current method for constructing such a sandwich structure mainly includes hot pressing and adhesive bonding. The hot pressing process requires laminating the preformed foam core and the panel under high temperature and high pressure, which easily causes the foam core to collapse and merge due to heat and pressure, resulting in loss of foam performance. At the same time, the hot pressing process has low production efficiency and is difficult to realize the molding of complex components. Adhesive bonding faces the problem of insufficient interfacial bonding strength between the panel and the core layer, which easily causes delamination after long-term use. Whether it is hot pressing or bonding, it is a secondary processing, which is complicated and difficult to accurately control the microstructure of the foam core and the interface between the core and the panel. It can be seen that the existing preparation method of sandwich structure foam has inherent defects such as complex process, low efficiency, easy damage to cell structure, low interfacial bonding strength, etc. It is limited in large-scale production and cannot realize the integrated rapid preparation of lightweight and high-strength. SUMMARY

[0008] The purpose of the present application is to overcome the above technical defects, and to provide a sandwich structured carbon fiber reinforced nylon foam with a dense skin layer, strong bonding between the skin layer and the foam interface (no gap), strong bonding between the continuous carbon fiber reinforced film and the skin layer, small cell diameter, high cell density, uniform cell distribution and good toughness, and a preparation method thereof.

[0009] The present application is realized by the following technical solutions: The present application discloses a sandwich structured carbon fiber reinforced nylon foam, which comprises a middle layer of carbon fiber reinforced nylon foam and two sides of continuous carbon fiber reinforced film. The carbon fiber reinforced nylon foam comprises the following components by weight: Nylon 68-95 parts; Chopped carbon fiber 5-40 parts; The average length of the chopped carbon fiber is 0.1-20mm; The thickness of the continuous carbon fiber reinforced film is ≤450 microns.

[0010] The foaming ratio of the carbon fiber reinforced nylon foam of the present application is 1.2-4.0 times, the average pore size of the pores is 10-400 microns, and the pore density is 1×10 5 -1×10 10 cm 3 .

[0011] In the sandwich structured carbon fiber reinforced nylon foam of the present application, the nylon content of the carbon fiber reinforced nylon foam is any one of 68 parts, 69 parts, 70 parts, 71 parts, 72 parts, 73 parts, 74 parts, 75 parts, 76 parts, 77 parts, 78 parts, 79 parts, 80 parts, 81 parts, 82 parts, 83 parts, 84 parts, 85 parts, 86 parts, 87 parts, 88 parts, 89 parts, 90 parts, 91 parts, 92 parts, 93 parts, 94 parts, 95 parts or a range value between any two of them, the chopped carbon fiber content is any one of 5 parts, 10 parts, 15 parts, 20 parts, 25 parts, 30 parts or a range value between any two of them, the average length of the chopped carbon fiber can be any one of 0.1 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, 19 mm, 20 mm or a range value between any two of them, the average diameter of the chopped carbon fiber is any one of 1 micron, 2 microns, 3 microns, 4 microns, 5 microns, 6 microns, 7 microns, 8 microns, 9 microns, 10 microns or a range value between any two of them, the thickness of the continuous carbon fiber reinforced film is any one of 150 microns, 180 microns, 200 microns, 220 microns, 250 microns, 270 microns, 300 microns, 320 microns, 350 microns, 380 microns, 400 microns or a range value between any two of them.

[0012] Preferably, the thickness of the continuous carbon fiber reinforced film is 100-300 microns, more preferably 100-200 microns.

[0013] Preferably, the average length of the chopped carbon fiber is 1-10 mm.

[0014] More preferably, the average length of the chopped carbon fiber is 1-3 mm.

[0015] The average diameter of the chopped carbon fiber is 1-10 microns.

[0016] The nylon is selected from at least one of aliphatic nylon and semi-aromatic nylon; the aliphatic nylon is selected from at least one of PA6, PA66, PA46, PA56, PA610, PA612, PA1010, PA1212, PA11, PA12, PA1313, PA1414, and the aromatic nylon is selected from at least one of PA6I, PA4T, PA9T, PA10T, PAMXD6; the nylon is all linear unmodified material.

[0017] Preferably, 0-10 parts by weight of an epoxy chain extender, more preferably 0.5-2 parts by weight, can be added; specifically, the epoxy chain extender can be at least one of styrene-glycidyl methacrylate, bisphenol A diglycidyl ether, isocyanuric acid triglycidyl ester, terephthalic acid bisglycidyl ester.

[0018] The nylon content of the epoxy chain extender is any one of 0 parts, 0.1 parts, 0.5 parts, 1 part, 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts, 5.5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts or a range value between any two of them. The modified material can be added according to actual needs: 0-5 parts by weight of PTFE, 0-0.5 parts by weight of antioxidant, 0-20 parts by weight of flame retardant, the flame retardant being at least one of phosphorus-based flame retardant, nitrogen-based flame retardant, bromine-based flame retardant, 0-30 parts by weight of dielectric filler, the dielectric filler being at least one of titanium dioxide, aluminum oxide, silicon nitride, aluminum nitride, silicon carbide.

[0019] The preparation method of the sandwich-structured carbon fiber reinforced nylon foam of the present application comprises the following steps: Step A: uniformly mix nylon, epoxy chain extender and chopped carbon fiber, and extrude and granulate through a double-screw extruder to obtain nylon particles; Step B: melt the nylon particles mixed with supercritical foaming gas into a mold with continuous carbon fiber reinforced film fixed on the inner front and rear surfaces through an injection molding machine and injection molding valve, and perform pressure holding at a pressure holding pressure of 10-200 MPa and a mold temperature of 40-260℃; Step C: after the mold is opened, a preset distance is retreated to initiate foaming, and after cooling and setting, the mold is opened to obtain the sandwich-structured carbon fiber reinforced nylon foam.

[0020] In step B, the pressure holding time in the pressure holding process is 2-10 seconds.

[0021] In step C, the opening distance is 1-12 mm.

[0022] The melt is injected into the mold by high pressure, and due to the low temperature of the mold surface, a part of the melt will solidify on the surface of the continuous carbon fiber reinforced film, so that the sandwich-structured carbon fiber reinforced nylon foam of the present application has a skin layer with a thickness of 300-1500 microns between the continuous carbon fiber reinforced film and the foam. The skin layer and the foam of the present application have good adhesion and no gap.

[0023] The present application has the following beneficial effects: Firstly, the present application improves the foaming behavior by forming heterogeneous nucleation points with chopped carbon fibers of specific parameters (average length, average diameter), controls the merging and rupture of the cells in the growth stage, strengthens the interface bonding between the skin layer and the foamed core layer, and improves the foaming performance.

[0024] Secondly, the chopped carbon fibers of specific parameters can improve the thermal conductivity, and the appropriate continuous carbon fiber layer can achieve good heat transfer, which not only improves the foaming performance, but also significantly improves the separation of the skin layer and the foam.

[0025] Thirdly, the addition of a specific content of epoxy chain extender can improve the melt strength, further improve the foaming performance, and also improve the gap between the foam and the skin layer.

[0026] In summary, a sandwich structure foam with uniform cells and no interface defects is finally obtained. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The carbon fiber reinforced nylon foam section electron microscope photo of the present application has no gap between the skin layer and the foam interface, small cell diameter, and uniform distribution.

[0028] Figure 2 The nylon foam section electron microscope photo of Comparative Example 4 has obvious gap between the skin layer and the foam interface, large cell diameter, and uneven distribution. DETAILED DESCRIPTION

[0029] The present application will be described in detail below with specific examples. The following examples will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be pointed out that, for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made. These all belong to the protection scope of the present application.

[0030] The raw materials used in the present application are sourced from the market: Continuous carbon fiber reinforced film A: thickness 150 μm, purchased from Qingdao Zhongji Chuaiying Composite Materials Technology Co., Ltd.; Continuous carbon fiber reinforced film B: thickness 250 μm, purchased from Qingdao Zhongji Chuaiying Composite Materials Technology Co., Ltd.; Continuous carbon fiber reinforced film C: thickness 400 μm, purchased from Qingdao Zhongji Chuaiying Composite Materials Technology Co., Ltd.; Continuous carbon fiber reinforced film D: thickness 500 μm, purchased from Qingdao Zhongji Chuaiying Composite Materials Technology Co., Ltd.; Chopped carbon fiber A: length 1-3 mm, average diameter about 7 μm, purchased from Toray Industries, Inc.; Chopped carbon fiber B: length 3-7 mm, average diameter about 7 μm, purchased from Toray Industries, Inc.; Chopped carbon fiber C: length 7-10 mm, average diameter about 7 μm, purchased from Toray Industries, Inc.; Chopped carbon fiber D: length 10-15 mm, average diameter about 7 μm, purchased from Toray Industries, Inc.; Chopped carbon fiber E: length 20-30 mm, average diameter about 7 μm, purchased from Toray Industries, Inc.; Epoxy chain extender: styrene-glycidyl methacrylate, purchased from BASF ADR-4468; PA6: grade, manufacturer BASF B3S Zytel BN0FBK; PA66: grade, manufacturer BASF A3W Zytel AN0FBK; Preparation method of sandwich structured carbon fiber reinforced nylon foam: Step A: mix nylon (PA6 or PA66), epoxy chain extender (optional, styrene-glycidyl methacrylate), chopped carbon fiber uniformly, and extrude and granulate through a twin-screw extruder to obtain nylon particles; Step B: melt the nylon particles mixed with supercritical foaming gas (nitrogen) (melt temperature PA66 285℃, PA6 245℃) through an injection molding machine and injection molding valve, and inject into a mold with continuous carbon fiber reinforced film fixed on the inner front / back surface to perform pressure holding, pressure holding pressure 10-200 MPa (see table for details), mold temperature 60-160℃ (see table for details), pressure holding for 6 seconds; Step C: after the mold is opened, retreat a distance of 1-12 mm (see table for details) to initiate foaming, and after cooling and setting, open the mold to obtain sandwich structured carbon fiber reinforced nylon foam.

[0031] Test methods: (1) Foaming ratio: tested by water displacement method.

[0032] (2) Average pore size / pore density of the cells: take scanning electron microscope photos, and use ImageJ software to count and calculate no less than 100 cells.

[0033] (3) Whether there is a gap between the skin layer and the foam interface: take scanning electron microscope photos, and observe the interface between the skin layer and the foam layer.

[0034] (4) Test method of crosslinking degree of carbon fiber reinforced nylon foam: use solvent to dissolve the modified nylon, and measure the gel content.

[0035] Table 1: Example 1-7 sandwich structured carbon fiber reinforced nylon foam ratio and test results Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 PA 6, parts 68 95 PA 66, parts 80 80 80 80 80 Chopped carbon fiber selection A A A A A B C Chopped carbon fiber content, parts 30 16 5 16 16 16 16 Continuous carbon fiber reinforced film selection A A A A A A A Pressure holding pressure, MPa 80 70 60 70 70 70 70 Mold temperature, °C 120 120 120 120 120 120 120 Mold opening distance, mm 4 4 4 1 12 4 4 Foaming ratio 2 2 2 1.2 4 2 2 Cell average pore size, microns 72 83 246 38 164 96 121 Cellular density, x 10 6 cells / cm 3 ]]> 22.6 14.6 2.5 68.3 6.3 12.2 9.3 Whether there is a gap between the skin layer and the foam interface No No No No No No No From Examples 2 / 6 / 7 / 8, it can be seen that the average pore size of the chopped carbon fiber is smaller and the pore density is higher when the length of the chopped carbon fiber is preferred.

[0036] Table 2: Formulation and test results of sandwich-configuration carbon fiber reinforced nylon foam of Example 8 Example 8 Example 9 Example 10 Example 11 Example 12 Example 13 Example 14 PA 66, parts 80 80 80 80 80 80 80 Chopped carbon fiber selection D A A A A A A Chopped carbon fiber content, parts 16 16 16 16 16 16 16 Continuous carbon fiber reinforced film selection A B C A A A A Epoxy chain extender 0 0 0 0.2 0.5 2 10 Pressure holding pressure, MPa 70 70 70 70 75 80 200 Mold temperature, °C 120 120 120 120 120 120 120 Mold opening distance, mm 4 4 4 4 4 4 4 Foaming ratio 2 2 2 2 2 2 2 Cell average pore size, microns 156 94 134 60 33 16 57 Cellular density, x 10 6 cells / cm 3 ]]> 7.2 13.1 4.9 32.1 84.3 315.6 35.8 Whether there is a gap between the skin layer and the foam interface No No No No No No No From Example 2 / 9 / 10, it can be seen that the continuous carbon fiber reinforced film with preferred thickness has smaller average cell size and higher cell density.

[0037] From Example 2 / 11-14, it can be seen that adding epoxy chain extender with specific content can effectively improve the melt strength and thus improve the foaming performance, but when the content of epoxy chain extender is too high, the melt strength is too high, and the foaming needs a larger holding pressure, which will be difficult to control the foaming.

[0038] Table 3: Formulation and test results of sandwich-configuration carbon fiber reinforced nylon foam of Comparative Example Comparative Example 1 Comparative Example 2 Comparative Example 3 PA 66, parts 80 80 80 Chopped carbon fiber selection E A A Chopped carbon fiber content, parts 16 16 16 Continuous carbon fiber reinforced film selection A D D Pressure holding pressure, MPa 70 70 70 Mold temperature, °C 120 120 100 Mold opening distance, mm 12 12 12 Foaming ratio 4 4 4 Cell average pore size, microns 580 437 488 Cellular density, x 10 6 Individuals / cm 3 ]]> 0.24 0.79 0.43 Whether there is a gap between the skin layer and the foam interface Yes Yes Yes From Comparative Example 1, it can be seen that when the average length of the chopped carbon fiber is too long, the foaming performance decreases significantly, which is because when the length of the chopped carbon fiber is too long, the direction of the carbon fiber is easy to distribute along the melt direction, which will seriously affect the foaming performance, and will cause obvious gaps between the skin layer and the foam interface.

[0039] From Comparative Example 2 / 3, it can be seen that when the continuous carbon fiber reinforced film is too thick, the thermal conductivity is poor, the melt volume heat of the foaming is too long, which will reduce the melt strength, and will deteriorate the foaming performance, and will cause obvious gaps between the skin layer and the foam interface.

Claims

1. A sandwich-configuration carbon fiber reinforced nylon foam comprising a middle layer of carbon fiber reinforced nylon foam and two sides of a composite continuous carbon fiber reinforced film, characterized in that, The carbon fiber reinforced nylon foam comprises the following components by weight: nylon 68-95 parts; short carbon fiber 5-40 parts; the average length of the short carbon fiber is 0.1-20 mm; the thickness of the continuous carbon fiber reinforced film is ≤450 microns.

2. The sandwich-configuration carbon fiber reinforced nylon foam according to claim 1, characterized in that, The foaming ratio of the carbon fiber reinforced nylon foam is 1.2-4.0 times, the average pore size of the foam cell is 10-400 microns, and the foam cell density is 1×10 5 -1×10 10 3 .​ 3. The sandwich-configuration carbon fiber reinforced nylon foam according to claim 1, wherein, the average length of the short carbon fiber is 1-10 mm, more preferably, the average length of the short carbon fiber is 1-3 mm and the average diameter is 1-10 microns.

4. The sandwich-configuration carbon fiber reinforced nylon foam of claim 1, wherein, the thickness of the continuous carbon fiber reinforced film is 100-300 microns, more preferably 100-200 microns.

5. The sandwich-configuration carbon fiber reinforced nylon foam according to claim 1, wherein, the nylon is selected from at least one of aliphatic nylon and aromatic nylon; the aliphatic nylon is selected from at least one of PA6, PA66, PA46, PA56, PA610, PA612, PA1010, PA1212, PA11, PA12, PA1313, PA1414, and the aromatic nylon is selected from at least one of PA6I, PA4T, PA9T, PA10T, and PAMXD6; the nylon is linear and unmodified.

6. The sandwich-configuration carbon fiber reinforced nylon foam of claim 1, wherein, 0-10 parts of epoxy chain extender by weight, more preferably 0.5-3 parts; the epoxy chain extender is selected from at least one of styrene-glycidyl methacrylate, bisphenol A diglycidyl ether, isocyanuric acid triglycidyl ester, and terephthalic acid bisglycidyl ester.

7. The sandwich-configuration carbon fiber reinforced nylon foam of claim 1, wherein, 0-5 parts of PTFE by weight, 0-0.5 parts of antioxidant by weight, 0-20 parts of flame retardant by weight, the flame retardant is selected from at least one of phosphorus-based flame retardant, nitrogen-based flame retardant, and bromine-based flame retardant; 0-30 parts of dielectric filler by weight, the dielectric filler is selected from at least one of titanium dioxide, aluminum oxide, silicon nitride, aluminum nitride, and silicon carbide.

8. The method of making sandwich structured carbon fiber reinforced nylon foam according to any one of claims 1-7, characterized in that, The following steps are included: Step A: uniformly mix the nylon, epoxy chain extender, and short carbon fiber, extrude and granulate through a double screw extruder to obtain nylon particles; Step B: melt the nylon particles mixed with supercritical foaming gas into a mold with continuous carbon fiber reinforced film fixed on the inner front and back surfaces through an injection molding machine and injection valve, and perform pressure holding, the pressure holding pressure is 10-200 MPa, and the mold temperature is 40-260℃; Step C: after the mold is opened, a preset distance is retreated to initiate foaming, and the mold is opened after cooling and setting to obtain a sandwich structure carbon fiber reinforced nylon foam.

9. The method of making sandwich structured carbon fiber reinforced nylon foam according to claim 8, wherein, The pressure holding time in the pressure holding process is 2-10 seconds.

10. The method of making sandwich structured carbon fiber reinforced nylon foam according to claim 8, wherein, In step C, the opening distance is 1-12 mm.

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