A preparation method of fiber-reinforced polyamide 6 material

Abstract

This solution provides a preparation method for a fiber-reinforced polyamide 6 material. The basic components such as caprolactam, water, a molecular weight regulator, and a cyclic oligomer inhibitor are mixed in proportion. After preheating, a VK tube is added to carry out polymerization reaction to obtain a polyamide 6 basic melt. The basic melt is further transported to a devolatilization reactor to remove monomers and some cyclic oligomers to obtain a polyamide 6 endpolymer. The polyamide 6 endpolymer and a certain proportion of fiber-reinforced material are blended through a screw extruder to obtain a fiber-reinforced polyamide 6 material. The present invention selects a metal ion compound as a cyclic oligomer inhibitor, utilizes the metal ion compound to reduce the oligomer content of the polyamide 6 polymerization process, and combines devolatilization to obtain a high-quality polyamide 6 melt. At the same time, the metal ion compound can improve the flow properties of polyamide 6 and can improve the dispersion properties of the fiber-reinforced material in polyamide 6, ultimately obtaining a fiber-reinforced polyamide 6 material with good performance.

Description

Technical Field

[0001] The present invention relates to the field of polyamide 6 reinforced materials, in particular to a method for preparing a fiber-reinforced polyamide 6 material, and more particularly to a method for improving melt fluidity by using a metal ion compound to obtain a high-quality fiber-reinforced polyamide 6 material. Background Art

[0002] Polyamide 6 (PA6) is widely used in fibers, engineering plastics, and films due to its excellent properties, including light weight, excellent toughness, chemical resistance, durability, and ease of molding and processing. With the rapid development of the domestic electronics, electrical, communications, and home appliance industries, the demand for PA6 is increasing, and the requirements for the material are also significantly higher. Therefore, the use of reinforcing materials combined with PA6 to produce high-strength and wear-resistant PA6 materials has become a research hotspot in recent years.

[0003] Currently, fiber-reinforced polyamide 6 composites are primarily prepared by melt-blending polyamide 6 chips, prepared by hydrolysis and polymerization of caprolactam, with fiber-reinforced materials through a screw extruder. The composites produced by this method have low residual monomers and oligomers and stable product properties. However, the production cycle for preparing polyamide 6 through hydrolysis and ring-opening polymerization can take dozens of hours, and a hot water extraction process is required to remove the approximately 10% of monomers and oligomers remaining in the polyamide 6 before blending with the fiber-reinforced materials to prepare the composite. When fiber-reinforced materials are mixed with polyamide 6, polyamide 6 has poor fluidity, which can easily lead to insufficient injection mold filling or uneven fiber distribution, seriously affecting the quality of the product. Therefore, it is generally necessary to add additional plasticizers to improve the fluidity of the polyamide 6 melt to enhance the performance of the composite. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing a fiber-reinforced polyamide 6 material, which reduces the residual monomers and cyclic oligomers during the polymerization process, and combines the devolatilization technology to further remove the residual monomers and oligomers to prepare high-quality polyamide 6. The high-quality polyamide 6 can be directly blended with a fiber-reinforced material to prepare a fiber-reinforced polyamide 6 material.

[0005] The present invention uses metal ion compounds as cyclic oligomer inhibitors. The metal ions coordinate with amide bonds to inhibit the amino groups at the ends of the polyamide 6 molecular chains from backbiting and attacking the amide bonds during polymerization, thereby reducing the formation of cyclic oligomers. After further devolatilization to remove unreacted monomers and some cyclic oligomers, the polyamide 6 melt can be directly blended with a fiber-reinforced material to produce a fiber-reinforced polyamide 6 material. This method eliminates the steps of pelletizing, hot water extraction, drying, and remelting, saving significant energy and time. Furthermore, the coordination of the metal ions with the carbonyl oxygen in polyamide 6 weakens hydrogen bonds between molecular chains, thereby improving the melt's flow properties and facilitating the uniform dispersion of the fiber-reinforced material in the melt. This addresses the problem of poor flow during melt injection molding, which can lead to reduced product quality.

[0006] To achieve the above objectives, the present technical solution provides a method for preparing a fiber-reinforced polyamide 6 material, comprising the following steps:

[0007] (1) Caprolactam, water, molecular weight regulator, and cyclic oligomer inhibitor are mixed in proportion, preheated, and added to a VK tube for polymerization reaction to prepare a polyamide 6 base melt;

[0008] (2) transporting the polyamide 6 base melt to a devolatilization reactor through a pipeline to remove monomers and some cyclic oligomers to prepare a polyamide 6 final polymer;

[0009] (3) The polyamide 6 final polymer and the fiber reinforcement material are added into a screw extruder in proportion and blended to obtain a fiber-reinforced polyamide 6 material.

[0010] The fiber-reinforced polyamide 6 material prepared by the preparation method of the fiber-reinforced polyamide 6 material provided in this solution can be directly used for injection molding.

[0011] In some embodiments, additives may be added to the base component for modification or other components may be added for copolymerization according to specific application scope. In other words, caprolactam, water, molecular weight regulator, metal ion compound, and additives are mixed in proportion according to functional requirements.

[0012] Correspondingly, the additive is selected from one or more of antioxidants, colorants, flame retardants, antibacterial agents, antistatic agents, and UV inhibitors, and the amount of the additive added is not more than 5wt%.

[0013] The antioxidant is one or more of phenolic antioxidants, hindered phenolic antioxidants, semi-hindered phenolic antioxidants, phosphite antioxidants, benzofuranone antioxidants, hydroxylamine antioxidants, tertiary amine nitrogen oxide antioxidants, bisphenol monoacrylate antioxidants, disalicylidene diamine antioxidants, and thiopropionate antioxidants.

[0014] The colorant is one or more of carbon black, phthalocyanine pigments, quinacridone pigments, triarylmethane pigments, benzimidazolone pigments, azo pigments, dioxazine, isoindolinone, anthraquinone, and perylene.

[0015] The flame retardant is one or more of phosphorus-based flame retardants, phosphorus-nitrogen-based flame retardants, nitrogen-based flame retardants, magnesium hydroxide, aluminum hydroxide, silicon-based flame retardants, zinc borate, and ammonium polyphosphate.

[0016] The antibacterial agent is one or more of nanosilver, nanocopper, zinc oxide, cuprous oxide, cupric oxide, anilide compounds, imidazole compounds, thiazole compounds, isothiazolone derivatives, quaternary ammonium salt compounds, bisguanidine compounds, chitin, and chitosan; the antistatic agent is one or more of carbon black, graphene, carbon nanotubes, metal powder, alkali metal alkyl sulfonate, alkali metal alkyl phosphate, alkali metal dithiocarbamate, alkyl quaternary ammonium salt, alkyl phosphate, alkyl phosphonium salt, and ethoxylated aliphatic alkylamine antistatic agents.

[0017] The UV inhibitor is one or more of carbon black, red iron oxide, zinc oxide, salicylate UV absorbers, benzophenone UV absorbers, benzotriazole UV absorbers, substituted acrylonitrile UV absorbers, triazine UV absorbers, and hindered amine UV absorbers.

[0018] In the preparation method of the fiber-reinforced polyamide 6 material as described above, the content of the molecular weight regulator in step (1) is less than 1.5 wt %; the molecular weight regulator is a combination of one or more of an organic monobasic acid, an organic dibasic acid, an organic monoamine, and an organic diamine.

[0019] In some embodiments, the organic monobasic acid is H(CH2) n COOH (n = 1 ~ 10), benzoic acid or naphthoic acid; the organic dibasic acid is COOH (CH2) m COOH (m = 1 ~ 10), terephthalic acid, phthalic acid, isophthalic acid or naphthalene dicarboxylic acid; the organic monoamine is H (CH2) x NH2 (x = 1 ~ 10), aniline or naphthylamine; the organic diamine is H2N (CH2) y NH2 (y = 1 ~ 10), p-phenylenediamine, o-phenylenediamine, m-phenylenediamine or naphthalenediamine.

[0020] In some embodiments, the metal ion compound used as the cyclic oligomer inhibitor can be one MY or a mixture of multiple MYs, and the added amount of the metal ion compound is 0.01 wt % to 2.0 wt % of caprolactam.

[0021] Specifically, the metal cation M is selected from one of transition metal ions, lanthanide metal ions, and Group IIA metal ions. When the metal cation M is selected from transition metal ions, the metal cation M is Sc 3+ 、Ni 2+ 、Zn 2+ 、Y 3+ 、Zr 4+ 、Ru 4+ , Rh 3 + When the metal cation M is selected from lanthanide metal ions, the lanthanide metal ions are La 3+ 、Ce 3+ 、Pr 3+ 、Nd 3+ 、Sm 3+ 、Eu 3 + 、Gd 3+ 、Tb 3+ 、Dy 3+ 、Ho 3+ 、Er 3+ 、Tm 3+ 、Lu 3+ 、Yb 3+ When the metal cation M is selected from Group IIA metal ions, the Group IIA metal ions are Be 2+ Mg 2+ , Ca 2+ ; The metal cation M can also be selected from Li + 、Al 3+ One of them.

[0022] The inorganic anion or organic anion Y is selected from F - 、Cl - 、NO3 - 、SO4 2- PO4 3- , citrate ion, salicylate ion, 3-hydroxybutyrate ion, L-aspartate ion, lactate ion, malate ion, 2-hydroxypropionate ion, organic monobasic acid ion H(CH2) n COO - (n=0~12), benzoate ion, naphthoate ion, organic dibasic acid ion COO - (CH2) m COO - (m=0~12), terephthalate ion, phthalate ion, isophthalate ion or naphthalene dicarboxylate ion, saturated fatty acid root ion C x H 2x+1 COO -(x=13~20), unsaturated fatty acid root ions (oleate root ions C 17 H 33 COO - , linoleate ion C 17 H 31 COO - , α-linolenic acid ion C 17 H 29 COO - , arachidonic acid ion C 19 H 31 COO - 、palmitoleate ion C 15 H 29 COO - ), aminocaproate ion NH2C5H 10 COO - , one of the amino acid root ions (glycine root ion, alanine root ion, valine root ion, leucine root ion, isoleucine root ion, proline root ion, phenylalanine root ion, methionine root ion, serine root ion, threonine root ion, asparagine root ion, glutamine root ion, aspartic acid root ion, glutamate root ion, cysteine ​​root ion, tyrosine root ion, selenocysteine ​​root ion).

[0023] In the preparation method of the fiber-reinforced polyamide 6 material as described above, the fiber-reinforced material in step (3) is one or more of glass fiber, carbon fiber, aramid fiber, silicon carbide fiber, natural fiber, and basalt fiber, and the added amount is 10-60 wt% of the polyamide 6.

[0024] In some embodiments, if the system is well dispersed, a dispersant may not be added. If the system is poorly dispersed, a dispersant may be added simultaneously with the fiber reinforcement. The dispersant may be one or more of a polymer dispersant, a surfactant dispersant, a coupling agent-modified dispersant, a composite functional dispersant, or a conventional silicone or wax dispersant, with the added amount not exceeding 1 wt% of the polyamide 6.

[0025] In the preparation method of the fiber-reinforced polyamide 6 material as described above, the VK tube reactor in step (1) is a one-stage reactor or a two-stage reactor; when the VK tube reactor is a one-stage reactor, the reaction temperature is 200-270 °C, the reaction pressure is 0.1 MPa-0.8 MPa, and the viscosity of the obtained polyamide 6 base melt is 1.5-3.0; when the VK tube reactor is a two-stage reactor, the reaction temperature of the front polymerization reactor is 200-270 °C, the reaction pressure is 0.1 MPa-1.0 MPa, and the reaction temperature of the rear polymerization reactor is 240-280 °C, the reaction pressure is 0.01 MPa-0.2 MPa, and the viscosity of the obtained polyamide 6 base melt is 1.8-3.5.

[0026] In the above-mentioned method for preparing a fiber-reinforced polyamide 6 material, the devolatilization reactor in step (2) is a vertical devolatilization reactor or two vertical devolatilization reactors connected in series, each devolatilization reactor is connected to a condensation collector with a buffer tank for collecting the removed steam, and a vacuum pump is connected to the condensation collector to provide vacuum power.

[0027] Correspondingly, when the devolatilization reactor is a vertical devolatilization reactor, the reaction temperature is 240~280 °C and the reaction pressure is 20~200 Pa; when the devolatilization reaction system is composed of two vertical devolatilization reactors connected in series, the reaction temperature of devolatilization reactor 1 is 240~280 °C and the reaction pressure is 200~4000 Pa; the reaction temperature of devolatilization reactor 2 is 240~280 °C and the reaction pressure is 20~400 Pa.

[0028] Correspondingly, the condensate collector can also be a caprolactam spray pump or a caprolactam jet pump with an additional buffer tank in front of the pump; the vacuum pump can be a series or parallel combination of one or more of a rotary vane vacuum pump, a liquid ring vacuum pump, a Roots vacuum pump, a reciprocating vacuum pump, a screw vacuum pump, and a steam jet pump.

[0029] In the above-mentioned method for preparing a fiber-reinforced polyamide 6 material, the relative viscosity of the polyamide 6 base melt obtained in step (1) is 1.5-3.5, the monomer content is less than 9.5wt%, the cyclic oligomer content is less than 2.5wt%, and the hot water extractable content is less than 10.5wt%; the relative viscosity of the polyamide 6 final polymer is 2.3-4.2, the monomer content is less than 0.1wt%, the cyclic oligomer content is less than 1.5wt%, and the hot water extractable content is less than 0.5wt%.

[0030] In the preparation method of the fiber-reinforced polyamide 6 material as described above, the screw extruder in step (3) is a series combination of one or more of a single-screw extruder, a co-rotating twin-screw extruder, a counter-rotating twin-screw extruder, an intermeshing twin-screw extruder, a non-intermeshing twin-screw extruder, a planetary screw extruder, a four-screw extruder, a reciprocating single-screw extruder, and a continuous mixer, and the temperature of the screw extruder is set to 230-280°C, and the speed is set to 20-300 rpm.

[0031] In the method for preparing a fiber-reinforced polyamide 6 material as described above, the tensile strength of the fiber-reinforced polyamide 6 material obtained in step (3) is ≥90 MPa.

[0032] like Figure 1 As shown, in this scheme, caprolactam, water, a molecular weight regulator, and a cyclic oligomer inhibitor are mixed in proportion, preheated, and added to a VK tube for polymerization reaction to prepare a polyamide 6 base melt; the polyamide 6 base melt is transported to a devolatilization reactor through a pipeline to remove monomers and some cyclic oligomers to prepare a polyamide 6 final polymer; the polyamide 6 final polymer and a fiber reinforcement material are added to a screw extruder in proportion for blending.

[0033] Compared with the existing technology, this technical solution has the following characteristics and beneficial effects:

[0034] (1) The introduction of a cyclic oligomer inhibitor metal ion compound reduces the cyclic oligomer content in the polyamide 6 base melt to less than 2.5 wt%, a 0.5-1.0 wt% reduction compared to chips without the addition of a cyclic oligomer inhibitor. The hot water extractable content in the polyamide 6 final polymer after devolatilization is less than 0.5 wt%, demonstrating the quality of a premium polyamide 6 product.

[0035] (2) The introduction of metal ions can coordinate with the carbonyl oxygen in polyamide 6, weakening the hydrogen bonds between molecular chains, thereby improving the flow properties of the melt. The dispersion properties of subsequent fiber-reinforced materials have been significantly improved, resulting in higher quality fiber-reinforced polyamide 6 materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a schematic diagram of the structure of the preparation method of the fiber-reinforced polyamide 6 material provided in this solution. DETAILED DESCRIPTION

[0037] To further illustrate the present invention, a method for preparing high-quality polyamide 6 fiber by a short process and its application provided by the present invention are described in detail below in conjunction with examples, but they should not be understood as limiting the scope of protection of the present invention.

[0038] The present invention uses ultra-high performance liquid chromatography to measure the content of monomers and cyclic oligomers in the polyamide 6 base melt and final polymer. The specific conditions and parameters are as follows:

[0039] --Chromatographic column: T3 column, 100 mm × 2.1 mm (inner diameter) × 1.7 μm, or equivalent;

[0040] ——Column temperature: 30℃;

[0041] Flow rate: 0.3 mL / min

[0042] ——Detection wavelength: 200 nm;

[0043] Injection volume: 2 μL

[0044] ——Elution procedure (as shown in the table below): Mobile phase A is water, and mobile phase B is acetonitrile.

[0045]

[0046] Comparative Example

[0047] (1) Fresh caprolactam, water, and terephthalic acid were mixed in a ratio of 100:2:0.375, preheated, and added to a one-stage VK tube for polymerization for 8 h at a reaction temperature of 250 °C and a reaction pressure of 0.4 MPa. Finally, a polyamide 6 base melt with a relative viscosity of 2.5, a monomer content of 7.90 wt%, a cyclic oligomer content of 2.86 wt% (including a cyclic dimer content of 0.65 wt%), and a hot water extractable content of 8.92 wt% was prepared;

[0048] (2) The base melt was transported to a primary vertical devolatilization reactor through a pipeline to remove monomers and some cyclic oligomers. The reaction temperature was 260 °C and the reaction pressure was 120 Pa. Finally, a polyamide 6 final polymer with a relative viscosity of 2.8, a monomer content of 0.07 wt%, a cyclic oligomer content of 2.10 wt% (including a cyclic dimer content of 0.35 wt%), and a hot water extractable content of 0.75 wt% was obtained.

[0049] (3) The polyamide 6 final polymer can be extracted with hot water, dried and then melted for injection molding. The injection molding temperature is 270 °C and the injection molding pressure is 10 MPa. The tensile strength of the polyamide 6 material after injection molding is 55 MPa.

[0050] Example 1

[0051] A method for preparing a fiber-reinforced polyamide 6 material, comprising the following steps:

[0052] (1) Fresh caprolactam, water, terephthalic acid, and lanthanum aminocaproate were mixed in a ratio of 100:2:0.375:0.6, preheated, and added to a one-stage VK tube for polymerization for 10 h at a reaction temperature of 250 °C and a reaction pressure of 0.4 MPa. A polyamide 6 base melt with a relative viscosity of 2.5, a monomer content of 7.92 wt%, a cyclic oligomer content of 2.35 wt% (of which the cyclic dimer content was 0.43 wt%), and a hot water extractable content of 8.90 wt% was finally prepared.

[0053] (2) The base melt was transported to a primary vertical devolatilization reactor through a pipeline to remove monomers and some cyclic oligomers. The reaction temperature was 260 °C and the reaction pressure was 70 Pa. Finally, a polyamide 6 final polymer with a relative viscosity of 2.8, a monomer content of 0.07 wt%, a cyclic oligomer content of 1.45 wt% (including a cyclic dimer content of 0.08 wt%), and a hot water extractable content of 0.42 wt% was obtained.

[0054] (3) The polyamide 6 final polymer and glass fiber were added to a screw extruder at a ratio of 1:0.3 and blended. The resulting glass fiber reinforced polyamide 6 material was directly used for injection molding. The injection molding temperature was 270 °C, the injection molding pressure was 10 MPa, and the tensile strength of the glass fiber reinforced polyamide 6 material after injection molding was 145 MPa.

[0055] Example 2

[0056] A method for preparing a fiber-reinforced polyamide 6 material, comprising the following steps:

[0057] (1) Fresh caprolactam, water, terephthalic acid, and cerium formate were mixed in a ratio of 100:2:0.375:1.0, preheated, and added to a one-stage VK tube for polymerization for 14 h at a reaction temperature of 230 °C and a reaction pressure of 0.3 MPa. A polyamide 6 base melt with a relative viscosity of 2.4, a monomer content of 8.05 wt%, a cyclic oligomer content of 2.08 wt% (of which the cyclic dimer content was 0.33 wt%), and a hot water extractable content of 8.65 wt% was finally prepared;

[0058] (2) The base melt was transported to a primary vertical devolatilization reactor through a pipeline to remove monomers and some cyclic oligomers. The reaction temperature was 260 °C and the reaction pressure was 150 Pa. Finally, a polyamide 6 final polymer with a relative viscosity of 2.6, a monomer content of 0.09 wt%, a cyclic oligomer content of 1.35 wt% (including a cyclic dimer content of 0.07 wt%), and a hot water extractable content of 0.38 wt% was obtained.

[0059] (3) The polyamide 6 final polymer and carbon fiber were added to a screw extruder at a ratio of 1:0.15 and blended. The resulting carbon fiber reinforced polyamide 6 material was directly used for injection molding. The injection molding temperature was 265 °C, the injection molding pressure was 8.5 MPa, and the tensile strength of the carbon fiber reinforced polyamide 6 material after injection molding was 105 MPa.

[0060] Example 3

[0061] A method for preparing a fiber-reinforced polyamide 6 material, comprising the following steps:

[0062] (1) Fresh caprolactam, water, terephthalic acid, and lanthanum acetate were mixed in a ratio of 100:2:0.375:0.8, preheated, and added to a one-stage VK tube for polymerization for 14 h at a reaction temperature of 250 °C and a reaction pressure of 0.42 MPa. A polyamide 6 base melt with a relative viscosity of 2.8, a monomer content of 7.85 wt%, a cyclic oligomer content of 2.42 wt% (of which the cyclic dimer content was 0.47 wt%), and a hot water extractable content of 8.85 wt% was finally prepared;

[0063] (2) The base melt was transported to a two-stage series vertical devolatilization reactor through a pipeline to remove monomers and part of the cyclic oligomers. The reaction temperature of the devolatilization reactor 1 was 250 °C and the reaction pressure was 1500 Pa. The reaction temperature of the devolatilization reactor 2 was 260 °C and the reaction pressure was 110 Pa. Finally, a polyamide 6 final polymer with a relative viscosity of 3.4, a monomer content of 0.07 wt%, a cyclic oligomer content of 1.30 wt% (including a cyclic dimer content of 0.06 wt%), and a hot water extractable content of 0.32 wt% was obtained.

[0064] (3) The polyamide 6 final polymer and carbon fiber were added to a screw extruder at a ratio of 1:0.3 and blended. The resulting carbon fiber reinforced polyamide 6 material was directly used for injection molding. The injection molding temperature was 275 °C, the injection molding pressure was 10 MPa, and the tensile strength of the carbon fiber reinforced polyamide 6 material after injection molding was 170 MPa.

[0065] Example 4

[0066] A method for preparing a fiber-reinforced polyamide 6 material, comprising the following steps:

[0067] (1) Fresh caprolactam, water, terephthalic acid, and yttrium benzoate were mixed in a ratio of 100:2:0.375:1.5, preheated, and added to a one-stage VK tube for polymerization for 8 h at a reaction temperature of 240 °C and a reaction pressure of 0.35 MPa. A polyamide 6 base melt with a relative viscosity of 2.2, a monomer content of 8.10 wt%, a cyclic oligomer content of 1.95 wt% (of which the cyclic dimer content was 0.32 wt%), and a hot water extractable content of 8.56 wt% was finally prepared;

[0068] (2) The base melt is transported to a two-stage series vertical devolatilization reactor through a pipeline to remove monomers and part of the cyclic oligomers. The reaction temperature of the devolatilization reactor 1 is 250 °C and the reaction pressure is 3000 Pa. The reaction temperature of the devolatilization reactor 2 is 250 °C and the reaction pressure is 80 Pa. Finally, a polyamide 6 final polymer with a relative viscosity of 2.5, a monomer content of 0.08 wt%, a cyclic oligomer content of 1.35 wt% (including a cyclic dimer content of 0.06 wt%), and a hot water extractable content of 0.38 wt% is obtained.

[0069] (3) The polyamide 6 final polymer and glass fiber were added to a screw extruder at a ratio of 1:0.4 and blended. The resulting glass fiber reinforced polyamide 6 material was directly used for injection molding. The injection molding temperature was 265 °C, the injection molding pressure was 9 MPa, and the tensile strength of the glass fiber reinforced polyamide 6 material after injection molding was 165 MPa.

[0070] Example 5

[0071] A method for preparing a fiber-reinforced polyamide 6 material, comprising the following steps:

[0072] (1) Fresh caprolactam, water, terephthalic acid, and zinc formate were mixed in a ratio of 100:2:0.375:0.5, preheated, and added to a one-stage VK tube for polymerization for 10 h at a reaction temperature of 260 °C and a reaction pressure of 0.48 MPa. A polyamide 6 base melt with a relative viscosity of 2.8, a monomer content of 7.79 wt%, a cyclic oligomer content of 2.40 wt% (of which the cyclic dimer content was 0.46 wt%), and a hot water extractable content of 8.80 wt% was finally prepared;

[0073] (2) The base melt was transported to a primary vertical devolatilization reactor through a pipeline to remove monomers and some cyclic oligomers. The reaction temperature was 270 °C and the reaction pressure was 50 Pa. Finally, a polyamide 6 final polymer with a relative viscosity of 3.2, a monomer content of 0.06 wt%, a cyclic oligomer content of 1.32 wt% (including a cyclic dimer content of 0.07 wt%), and a hot water extractable content of 0.35 wt% was obtained.

[0074] (3) The polyamide 6 final polymer and aramid fiber were added to a screw extruder at a ratio of 1:0.1 and blended. The resulting aramid fiber reinforced polyamide 6 material was directly used for injection molding. The injection molding temperature was 265°C, the injection molding pressure was 8.5 MPa, and the tensile strength of the aramid fiber reinforced polyamide 6 material after injection molding was 110 MPa.

[0075] Example 6

[0076] A method for preparing a fiber-reinforced polyamide 6 material, comprising the following steps:

[0077] (1) Fresh caprolactam, water, terephthalic acid, scandium terephthalate, and lithium nitrate were mixed in a ratio of 100:2:0.375:0.3:0.3, preheated, and added to a one-stage VK tube for polymerization for 10 h at a reaction temperature of 240 °C and a reaction pressure of 0.4 MPa. A polyamide 6 base melt with a relative viscosity of 2.3, a monomer content of 8.05 wt%, a cyclic oligomer content of 2.20 wt% (of which the cyclic dimer content was 0.38 wt%), and a hot water extractable content of 8.85 wt% was finally prepared;

[0078] (2) The base melt was transported to a primary vertical devolatilization reactor through a pipeline to remove monomers and some cyclic oligomers. The reaction temperature was 265 °C and the reaction pressure was 60 Pa. Finally, a polyamide 6 final polymer with a relative viscosity of 2.8, a monomer content of 0.05 wt%, a cyclic oligomer content of 1.20 wt% (including a cyclic dimer content of 0.04 wt%), and a hot water extractable content of 0.26 wt% was obtained.

[0079] (3) The polyamide 6 final polymer and glass fiber were added to a screw extruder at a ratio of 1:0.2 and blended. The resulting glass fiber reinforced polyamide 6 material was directly used for injection molding. The injection molding temperature was 265 °C, the injection molding pressure was 9 MPa, and the tensile strength of the glass fiber reinforced polyamide 6 material after injection molding was 125 MPa.

[0080] Example 7

[0081] A method for preparing a fiber-reinforced polyamide 6 material, comprising the following steps:

[0082] (1) Fresh caprolactam, water, terephthalic acid, cerium formate, and nickel adipate were mixed in a ratio of 100:2:0.375:0.5:0.5, preheated, and added to a one-stage VK tube for polymerization for 10 h at a reaction temperature of 230 °C and a reaction pressure of 0.3 MPa. A polyamide 6 base melt with a relative viscosity of 2.2, a monomer content of 8.07 wt%, a cyclic oligomer content of 2.03 wt% (of which the cyclic dimer content was 0.31 wt%), and a hot water extractable content of 8.57 wt% was finally prepared.

[0083] (2) The base melt was transported to a primary vertical devolatilization reactor through a pipeline to remove monomers and some cyclic oligomers. The reaction temperature was 260 °C and the reaction pressure was 100 Pa. Finally, a polyamide 6 final polymer with a relative viscosity of 2.5, a monomer content of 0.09 wt%, a cyclic oligomer content of 1.42 wt% (including a cyclic dimer content of 0.08 wt%), and a hot water extractable content of 0.45 wt% was obtained.

[0084] (3) The polyamide 6 final polymer and glass fiber were added to a screw extruder at a ratio of 1:0.5 and blended. The resulting glass fiber reinforced polyamide 6 material was directly used for injection molding. The injection molding temperature was 280 °C, the injection molding pressure was 10.5 MPa, and the tensile strength of the glass fiber reinforced polyamide 6 material after injection molding was 190 MPa.

[0085] Example 8

[0086] A method for preparing a fiber-reinforced polyamide 6 material, comprising the following steps:

[0087] (1) Fresh caprolactam, water, terephthalic acid, decanediamine, and magnesium isophthalate were mixed in a ratio of 100:2:0.2:0.2:0.6, preheated, and added to a one-stage VK tube for polymerization for 10 h at a reaction temperature of 240 °C and a reaction pressure of 0.35 MPa. Finally, a polyamide 6 base melt with a relative viscosity of 2.7, a monomer content of 7.88 wt%, a cyclic oligomer content of 2.43 wt% (of which the cyclic dimer content was 0.45 wt%), and a hot water extractable content of 8.84 wt% was prepared;

[0088] (2) The base melt was transported to a primary vertical devolatilization reactor through a pipeline to remove monomers and some cyclic oligomers. The reaction temperature was 260 °C and the reaction pressure was 80 Pa. Finally, a polyamide 6 final polymer with a relative viscosity of 3.0, a monomer content of 0.06 wt%, a cyclic oligomer content of 1.42 wt% (including a cyclic dimer content of 0.07 wt%), and a hot water extractable content of 0.45 wt% was obtained.

[0089] (3) The polyamide 6 final polymer and silicon carbide fiber were added to a screw extruder at a ratio of 1:0.25 and blended. The resulting silicon carbide fiber-reinforced polyamide 6 material was directly used for injection molding. The injection molding temperature was 285 °C, the injection molding pressure was 11 MPa, and the tensile strength of the silicon carbide fiber-reinforced polyamide 6 material after injection molding was 185 MPa.

[0090] Example 9

[0091] A method for preparing a fiber-reinforced polyamide 6 material, comprising the following steps:

[0092] (1) Fresh caprolactam, water, terephthalic acid, lanthanum acetate, and carbon black were mixed in a ratio of 100:2:0.375:0.8:1.0, preheated, and added to a one-stage VK tube for polymerization for 12 h at a reaction temperature of 240 °C and a reaction pressure of 0.36 MPa. Finally, a black polyamide 6 base melt with a relative viscosity of 2.5, a monomer content of 7.97 wt%, a cyclic oligomer content of 2.30 wt% (including a cyclic dimer content of 0.42 wt%), and a hot water extractable content of 8.90 wt% was prepared;

[0093] (2) The base melt is transported to a two-stage series vertical devolatilization reactor through a pipeline to remove monomers and part of the cyclic oligomers. The reaction temperature of the devolatilization reactor 1 is 250 °C and the reaction pressure is 800 Pa. The reaction temperature of the devolatilization reactor 2 is 260 °C and the reaction pressure is 80 Pa. Finally, a black polyamide 6 final polymer with a relative viscosity of 3.0, a monomer content of 0.05 wt%, a cyclic oligomer content of 1.18 wt% (including a cyclic dimer content of 0.04 wt%), and a hot water extractable content of 0.25 wt% is obtained.

[0094] (3) The black polyamide 6 final polymer and carbon fiber were added to a screw extruder at a ratio of 1:0.2 and blended. The resulting black carbon fiber reinforced polyamide 6 material was directly used for injection molding. The injection molding temperature was 270 °C, the injection molding pressure was 9.5 MPa, and the tensile strength of the black carbon fiber reinforced polyamide 6 material after injection molding was 140 MPa.

[0095] Example 10

[0096] A method for preparing a fiber-reinforced polyamide 6 material, comprising the following steps:

[0097] (1) Fresh caprolactam, water, terephthalic acid, lithium nitrate, and phosphorus flame retardant were mixed in a ratio of 100:2:0.375:1.5:1.5, preheated, and added to a one-stage VK tube for polymerization for 10 h at a reaction temperature of 240 °C and a reaction pressure of 0.35 MPa. Finally, a flame-retardant polyamide 6 base melt with a relative viscosity of 2.3, a monomer content of 8.02 wt%, a cyclic oligomer content of 1.98 wt% (of which the cyclic dimer content was 0.32 wt%), and a hot water extractable content of 8.58 wt% was prepared;

[0098] (2) The base melt is transported to a two-stage series vertical devolatilization reactor through a pipeline to remove monomers and part of the cyclic oligomers. The reaction temperature of the devolatilization reactor 1 is 250 °C and the reaction pressure is 2500 Pa. The reaction temperature of the devolatilization reactor 2 is 250 °C and the reaction pressure is 70 Pa. Finally, a flame-retardant polyamide 6 final polymer with a relative viscosity of 2.6, a monomer content of 0.07 wt%, a cyclic oligomer content of 1.38 wt% (including a cyclic dimer content of 0.06 wt%), and a hot water extractable content of 0.41 wt% is obtained.

[0099] (3) The flame-retardant polyamide 6 final polymer and glass fiber were added to a screw extruder at a ratio of 1:0.35 and blended. The resulting glass fiber reinforced flame-retardant polyamide 6 material was directly used for injection molding. The injection molding temperature was 260 °C, the injection molding pressure was 8.5 MPa, and the tensile strength of the glass fiber reinforced flame-retardant polyamide 6 material after injection molding was 160 MPa.

[0100] The performance of the polyamide 6 base melt and polyamide 6 final polymer of the comparative example and Examples 1 to 10 was characterized to obtain a performance characterization table as shown in Table 1 below:

[0101] Table 1 Performance characterization table of polyamide 6 base melt and polyamide 6 final polymer of comparative example 1 to example 10

[0102] .

[0103] The above embodiments merely illustrate several embodiments of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be determined by the appended claims.

Claims

1. A method for preparing a fiber-reinforced polyamide 6 material, characterized in that The following steps are involved: (1) caprolactam, water, a molecular weight regulator, and a cyclic oligomer inhibitor are mixed in proportion, preheated, and added to a VK tube for polymerization reaction to prepare a polyamide 6 base melt, wherein the cyclic oligomer inhibitor is selected from one or a combination of lanthanum aminocaproate, cerium formate, lanthanum acetate, yttrium benzoate, zinc formate, scandium terephthalate, nickel adipate, magnesium isophthalate, and lanthanum acetate, and the amount of the metal ion compound of the cyclic oligomer inhibitor added is 0.01wt%~2.0wt% of the caprolactam; (2) transporting the polyamide 6 base melt to a devolatilization reactor through a pipeline to remove monomers and some cyclic oligomers to prepare a polyamide 6 final polymer, wherein the relative viscosity of the polyamide 6 base melt is 1.5-3.5, the monomer content is less than 9.5wt%, the cyclic oligomer content is less than 2.5wt%, and the hot water extractable content is less than 10.5wt%, and the relative viscosity of the polyamide 6 final polymer is 2.3-4.2, the monomer content is less than 0.1wt%, the cyclic oligomer content is less than 1.5wt%, and the hot water extractable content is less than 0.5wt%; (3) The polyamide 6 final polymer and the fiber reinforcement material are added into a screw extruder in proportion and blended to obtain a fiber-reinforced polyamide 6 material.

2. The method for preparing the fiber-reinforced polyamide 6 material according to claim 1, characterized in that In step (1), the VK tube reactor is a one-stage reactor or a two-stage reactor.

3. The method for preparing the fiber-reinforced polyamide 6 material according to claim 1, characterized in that In step (2), the devolatilization reactor is a vertical devolatilization reactor or two vertical devolatilization reactors connected in series, each devolatilization reactor is connected to a condensation collector with a buffer tank for collecting the removed steam, and a vacuum pump is connected to the condensation collector to provide vacuum power.

4. The method for preparing the fiber-reinforced polyamide 6 material according to claim 1, characterized in that In step (3), the fiber reinforcement material is one or more of glass fiber, carbon fiber, aramid fiber, silicon carbide fiber, natural fiber, and basalt fiber, and the added amount is 10-60 wt% of polyamide 6.

5. The method for preparing the fiber-reinforced polyamide 6 material according to claim 1, characterized in that: The temperature of the screw extruder was set to 230–280 °C, and the speed was set to 20–300 rpm.

6. The method for preparing the fiber-reinforced polyamide 6 material according to claim 1, characterized in that: Caprolactam, water, a molecular weight regulator, a cyclic oligomer inhibitor and an additive are mixed in proportion, wherein the additive is selected from one or more of an antioxidant, a colorant, a flame retardant, an antibacterial agent, an antistatic agent and an anti-ultraviolet agent, and the amount of the additive is less than 5wt%.

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