PA6 material suitable for two-color injection molding oil valve components with excellent adhesion

Abstract

The present invention provides a PA6 material suitable for a two-color injection-molded oil valve assembly with excellent adhesion. It includes a PA6 resin using an aromatic dicarboxylic acid as a capping agent and conventional additives. An oil valve assembly with excellent adhesion can be obtained through two-color injection molding with a polyolefin material, and then a firm sealed assembly with the plastic fuel tank housing material can be achieved through welding molding, greatly reducing the fuel penetration amount. It is particularly suitable for components such as one-way valves, gravity valves, and fuel filling limit valves at the fuel filling port of plastic fuel tanks.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and particularly relates to a PA6 material suitable for a two-color injection molding oil valve assembly with excellent adhesion and a preparation method thereof. Background Art

[0002] The fuel tank is an important component in an automobile for storing fuel. Using lightweight plastics instead of metal materials to manufacture fuel tanks is of great significance for vehicle lightweighting. Compared with metal fuel tanks, it has excellent properties such as light weight, large freedom in shape design, high space utilization rate, good corrosion resistance, easy processing and molding, low thermal conductivity, and good low-temperature impact resistance.

[0003] Since the chemical structure of polyethylene is similar to that of fuel, both being aliphatic hydrocarbons and having compatibility, when used as a fuel tank, fuel will penetrate and diffuse through the inner wall to the outside and vaporize and be lost, that is, its barrier performance to the effective components of fuel is relatively low. Therefore, the earlier polyethylene fuel tanks have been replaced by nylon fuel tanks. After years of development and continuous improvement of emission regulations, currently, multilayer blow molding coextrusion technology is commonly used for gasoline plastic fuel tanks in China. The outer layer and the inner layer materials are high-density polyethylene (HDPE), and the barrier layer material is ethylene vinyl alcohol copolymer (EVOH). The fuel penetration value of this type of plastic fuel tank can be lower than 10 mg / 24 h. However, in order to meet the functional requirements such as fuel filling, ventilation, rollover safety, and fuel pump installation, the fuel tank will inevitably include an oil filling check valve, a gravity valve, a fuel filling limit valve, and a fuel pump installation structural member, etc. These oil valve components generally adopt methods such as open sealing and penetration welding. Considering the adhesiveness with the fuel tank shell material (HDPE), the welding component material generally also uses HDPE material, but its fuel barrier performance is very low, and fuel vapor molecules escape through the open welding components of the fuel tank, and the fuel penetration value rises to 300 - 500 mg / 24 h. Therefore, the number of openings on the fuel tank surface and the fuel barrier ability of the welding components are the main factors affecting its evaporation emission level.

[0004] Referring to the design experience of the California LEV II standard in the United States, the evaporation emission index of the fuel tank is generally set to be lower than 100 mg / 24 h, generally between 60 - 80 mg / 24 h. Therefore, it is necessary to use a PA6 material with a low fuel permeation coefficient (10 mg / 24 h) to replace an HDPE material with a high fuel permeation coefficient (500 mg / 24 h) as the welding component material. Further, in order to meet the welding strength requirements with the fuel tank outer shell material (HDPE), it is appropriate to select a PE material as the adhesive transition layer. Therefore, the PA6 / PE two-color injection molding oil valve assembly becomes a better welding component material solution.

[0005] Two-color injection molding mainly uses two material pipes of a two-color molding machine and two sets of molds to obtain products through two molding processes in sequence. Simply put, factories without a two-material pipe injection molding machine will choose to first mold a bonding layer of PE material with a simple structure, then place it as an insert into the mold, and then inject with PA6 material to form an integral fuel valve assembly product.

[0006] To ensure that the welded part can meet the functional requirements such as fuel filling, ventilation, rollover safety, and fuel pump installation, it is required that the welded fuel valve assembly can withstand an external thrust of more than 500N without loosening, that is, the material adhesion force. PA6 / PE is an incompatible system. If PA6 is modified with maleic anhydride-based and carboxylic acid-based compatibilizers, the fuel permeability coefficient of PA6 will be significantly increased, which obviously violates the original intention. Currently, improving the adhesion of PA6 / PE two-color injection molded parts generally relies on the injection molding factory to optimize the process and the host factory to optimize the design: such as increasing the mold temperature and injection processing temperature, preheating the insert before secondary injection molding, and designing serrated grooves on the product to increase the contact surface, etc. There is no public report on the solutions at the material end. Summary of the Invention

[0007] To solve the above problems, the present invention provides a PA6 material with excellent adhesion suitable for two-color injection molding of fuel valve assemblies, identifies and summarizes the corresponding relationship between the special property indexes of raw materials at the synthesis end and the special uses at the terminal, and by regulating the end-capping agent, without changing the melting point and mechanical properties of the material itself, a PA6 resin with excellent adhesion can be obtained, providing a solution at the material end for customers (injection molding factories).

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] A PA6 material with excellent adhesion suitable for two-color injection molding of fuel valve assemblies, comprising the following components in parts by weight:

[0010] PA6 resin with aromatic dicarboxylic acid as the end-capping agent 50 - 100 parts

[0011] Reinforcing material 0 - 50 parts

[0012] Conventional additives 0.5 - 2 parts

[0013] The aromatic dicarboxylic acid is one or more of terephthalic acid, phthalic acid, or isophthalic acid; the melting point of the PA6 resin with aromatic dicarboxylic acid as the end-capping agent is 220°C, and the viscosity is 2.0 - 3.0.

[0014] The reinforcing material can be selected from glass fiber, carbon fiber, glass microspheres, magnesium sulfate whiskers, talc powder, wollastonite, calcium carbonate, etc.;

[0015] The conventional additives include antioxidants, light stabilizers, heat stabilizers, lubricants, colorants, etc.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1) The present invention can meet the special field applications through simple customization. Only the capping agent needs to be adjusted, without changing other polymerization processes and without reducing the melting point. PA6 resin with excellent adhesion can be obtained, which is suitable for two-color injection molding of oil valve components. The adhesion of the two-color injection molding joint surface is strong, and the welding force between the oil valve component and the fuel tank is strong.

[0018] 2) Through the research and understanding of the relationship among materials, processes, and parts, the present invention identifies and summarizes the corresponding relationship between the special characteristic indexes of the synthetic terminal raw materials and the special terminal applications, providing a reference for the upstream and downstream of the industry to develop customized solutions. Description of the Drawings

[0019] Figure 1 Schematic diagram of PA6 / PE two-color injection molding tensile spline of the present invention;

[0020] Figure 2 Schematic diagram of PA6 / PE two-color injection molding oil valve component and fuel tank housing of the present invention. Detailed Embodiments

[0021] To make the technical solution of the present invention clearer and more definite, the present invention is further described below. Any solution obtained by equivalent replacement of the technical features of the technical solution of the present invention and through conventional reasoning falls within the protection scope of the present invention. All materials used in the present invention are obtained through regular commercial channels.

[0022] Example 1

[0023] 1) Preparation of PA6 resin: Caprolactam, 6-aminocaproic acid, and 0.5% terephthalic acid are polymerized, extracted, and dried to obtain PA6. Its relative viscosity is detected to be 2.42, and the melting point is 220°C.

[0024] 2) Preparation of PA6 composite material: 98.5 parts of the PA6 prepared in step 1), 0.5 part of N54 / 1033, 0.5 part of OP wax, and 0.3 part of H318 are mixed and then granulated by a twin-screw extruder at a temperature of 250°C and a rotation speed of 480 rpm.

[0025] 3) PA6 / PE two-color injection molding tensile spline: First, a semi-root tensile spline made of PE material is molded, then it is placed into the mold as an insert, and then injection molding is carried out with the PA6 composite material to form an integral tensile spline (as shown in the attached Figure 1 ).

[0026] 4) PA6 / PE Two-color Injection Molding Oil Valve Product: Put the PA6 composite material into the first material pipe of the two-color molding machine and inject the main body of the product end cover; after flipping the mold, put PE into the second material pipe of the two-color molding machine and inject the remaining circular part of the product.

[0027] Example 2

[0028] 69 parts of the PA6 resin prepared in Example 1 were mixed with 0.5 part of N54 / 1044, 0.3 part of calcium stearate, 0.2 part of antioxidant 1098, and 0.2 part of antioxidant 168, and then fed into the main feeder of the twin-screw extruder. 30 parts of glass fiber were fed into the side feeder for pelletizing. Other steps were the same as those in Example 1.

[0029] Example 3

[0030] The difference from Example 2 was the difference in the amount of glass fiber, and the PA6 content decreased accordingly.

[0031] Example 4

[0032] The difference from Example 2 was that the reinforcing material was changed from glass fiber fed into the main feeder to wollastonite fed into the main feeder.

[0033] Example 5

[0034] PA6 was obtained by polymerizing, extracting, and drying caprolactam, 6-aminocaproic acid, and 1% terephthalic acid. Its relative viscosity was detected to be 2.81 and its melting point was 220°C. Other steps were the same as those in Example 2.

[0035] Example 6

[0036] PA6 was obtained by polymerizing, extracting, and drying caprolactam, 6-aminocaproic acid, and 0.5% isophthalic acid. Its relative viscosity was detected to be 2.29 and its melting point was 220°C. Other steps were the same as those in Example 2.

[0037] Example 7

[0038] Step 3) PA6 / PE Two-color Injection Molding Tensile Specimen: First, use the PA6 composite material to mold half of the tensile specimen, then put it into the mold as an insert, and then use the PE material for injection molding to form the overall tensile specimen. Other steps were the same as those in Example 2.

[0039] Example 8

[0040] Step 4) PA6 / PE Two-color Injection Molding Oil Valve Product: Put PE into the second material pipe of the two-color molding machine and inject the circular part of the product; after flipping the mold, put the PA6 composite material into the first material pipe of the two-color molding machine and inject the main body of the product end cover. Other steps were the same as those in Example 2.

[0041] Comparative Example 1

[0042] Caprolactam, 6 - aminocaproic acid, and 1% adipic acid were polymerized, extracted, and dried to obtain PA6. Its relative viscosity was measured to be 2.41, and its melting point was 220°C. Other steps were the same as in Example 2.

[0043] Comparative Example 2

[0044] The difference from Comparative Example 1 was that 5 parts of toughening agent N413A were added, and the content of PA6 was correspondingly reduced.

[0045] Comparative Example 3

[0046] The difference from Comparative Example 1 was that 0.5 part of calcium chloride was added, and the content of PA6 was correspondingly reduced.

[0047] Comparative Example 4

[0048] Caprolactam, 6 - aminocaproic acid, and 0.5% sebacic acid were polymerized, extracted, and dried to obtain PA6. Its relative viscosity was measured to be 2.78, and its melting point was 220°C. Other steps were the same as in Comparative Example 1.

[0049] Product performance test methods:

[0050] (1) Crystallization temperature: DSC 822 type, heating rate 10°C / min;

[0051] (2) Tensile strength: According to ISO 527 method, specimen size 170*10*4 mm, test speed 5 mm / min;

[0052] (3) Tensile load of PA6 / PE two - color injection - molded specimen: Universal material testing machine, (such as Figure 1 ) specimen size 170*10*4 mm, test speed 50 mm / min;

[0053] (4) Thrust experiment of oil valve product: The A6 / PE two - color injection - molded oil valve product was rotationally welded to a multi - layer blow - molded co - extruded fuel tank (such as Figure 2 ), and a lateral thrust loading experiment was carried out according to the enterprise standard;

[0054] (5) Total fuel penetration value: According to the enterprise standard.

[0055] Table 1 Performance test results of examples and comparative examples

[0056]

[0057] As can be seen from the examples, using the PA6 material of the present invention does not affect the melting point and mechanical properties of the material itself. After two-color injection molding with PE material, the adhesion is excellent, and the tensile load of the PA6 / PE two-color injection molded spline is significantly improved. When it is used to produce oil valve products, after welding with the fuel tank, the thrust test is qualified, meeting the functional requirements such as fuel filling, ventilation, tipping safety, and fuel pump installation. The total fuel penetration value is <80mg / 24h, which is better than the design of the California LEVⅡ standard.

[0058] As can be seen from the comparative examples, due to differences in material thermal conductivity, specific heat capacity, etc., the heat dissipation rate is uneven, the heat dissipation transition difference between PE and PA6 is large, the material shrinkage and crystallization are uneven, defects are easily generated, and the interfacial adhesion is poor. Moreover, although some additives have an improving effect, they will bring other risks, such as chemical stress concentration, changes in melting point and mechanical properties, etc.

[0059] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto.

Claims

1. A PA6 material suitable for two-color injection molding oil valve components with excellent adhesion, characterized in that, It is prepared from the following components by weight parts: PA6 resin with aromatic dicarboxylic acid as the end-capping agent: 50 - 100 parts; Reinforcing material: 0 - 50 parts; Conventional additives: 0.5 - 2 parts; The aromatic dicarboxylic acid is one or both of terephthalic acid and isophthalic acid; the melting point of the PA6 resin with the aromatic dicarboxylic acid as the end-capping agent is 220°C, and the viscosity is 2.0 - 3.0; the conventional additives are antioxidant, light stabilizer, heat stabilizer, lubricant, and colorant.

2. The PA6 material for the oil valve assembly suitable for two-color injection molding with excellent adhesion force according to claim 1, characterized in that: The reinforcing material is selected from glass fiber, carbon fiber, glass microbead, magnesium sulfate whisker, talc powder, wollastonite, and calcium carbonate.

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