Preparation method of fiber reinforced polyamide 6 material

Abstract

The invention provides a preparation method of a fiber-reinforced polyamide 6 material, which comprises the following steps: mixing basic components such as caprolactam, water, a molecular weight regulator, a cyclic oligomer inhibitor and the like in proportion, preheating, adding into a VK tube, and carrying out polymerization reaction to obtain a polyamide 6 basic melt; and further conveying the basic melt into a devolatilization reactor to remove monomers and part of cyclic oligomers, thereby obtaining the polyamide 6 final polymer. And blending the polyamide 6 final polymer and a certain proportion of fiber reinforced material through a screw extruder to obtain the fiber reinforced polyamide 6 material. A metal ion compound is selected as a cyclic oligomer inhibitor, the oligomer content in the polyamide 6 polymerization process is reduced through the metal ion compound, and the high-quality polyamide 6 melt is obtained in combination with devolatilization. Meanwhile, the metal ion compound can improve the flowing property of the polyamide 6 and can improve the dispersing property of the fiber reinforced material in the polyamide 6, and finally the fiber reinforced polyamide 6 material with good performance is obtained.

Description

Technical Field

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

[0002] Due to its excellent properties such as light weight, good toughness, good chemical resistance and durability, and easy molding and processing, polyamide 6 is widely used in the fields of fibers, engineering plastics, and films. With the rapid development of the domestic electronics, electrical, communication, and household appliance industries, the demand for polyamide 6 is increasing, and the requirements for materials are also significantly improved. Therefore, the use of reinforcing materials to compound with polyamide 6 to obtain high-strength and wear-resistant polyamide 6 materials has become a research hotspot in recent years.

[0003] Currently, fiber-reinforced polyamide 6 composites are mainly prepared by melt blending polyamide 6 chips prepared by hydrolysis polymerization of caprolactam with fiber reinforcing materials through a screw extruder. The composites prepared by this method have less residual monomers and oligomers, and the product properties are stable. However, the production cycle of preparing polyamide 6 by hydrolysis ring-opening polymerization is up to dozens of hours, and a hot water extraction process of dozens of hours is required to remove about 10% of the residual monomers and oligomers in polyamide 6 before it can be melt blended with fiber reinforcing materials to prepare composites. When the fiber reinforcing material is mixed with polyamide 6, the fluidity of polyamide 6 is poor, which easily causes insufficient injection molding filling or uneven fiber distribution, seriously affecting the quality of the product. Generally, a plasticizer needs to be added additionally to improve the melt fluidity of polyamide 6 to improve the performance of the composite material. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of a fiber-reinforced polyamide 6 material, which reduces the residual monomers and cyclic oligomers during the polymerization process, and further removes the residual monomers and oligomers by combining with a devolatilization technology to prepare high-quality polyamide 6. The high-quality polyamide 6 can be directly melt blended with fiber reinforcing materials to prepare fiber-reinforced polyamide 6 materials.

[0005] The present invention selects a metal ion compound as a cyclic oligomer inhibitor. By coordinating metal ions with amide bonds, it inhibits the back-biting attack of the amino group at the end of the polyamide 6 molecular chain on the amide bond during polymerization, reducing the formation of cyclic oligomers. After the polyamide 6 melt undergoes further devolatilization reaction to remove unreacted monomers and some cyclic oligomers, it can be directly blended with fiber-reinforced materials to obtain fiber-reinforced polyamide 6 materials. This method saves steps such as pelletizing, hot water extraction, drying, and re-melting, saving a large amount of energy and time. Moreover, the coordination of metal ions with the carbonyl oxygen in polyamide 6 weakens the hydrogen bonds between molecular chains, thereby improving the melt flow properties, facilitating the uniform dispersion of fiber-reinforced materials in the melt, and solving problems such as poor fluidity during melt injection molding, resulting in a decline in product quality.

[0006] To achieve the above objectives, the present technical solution provides a method for preparing a fiber-reinforced polyamide 6 material, including the following steps: (1) Mix caprolactam, water, a molecular weight regulator, and a cyclic oligomer inhibitor in proportion, and after preheating, add them to a VK tube for polymerization reaction to prepare a polyamide 6 base melt; (2) Transport the polyamide 6 base melt through a pipeline to a devolatilization reactor to remove monomers and some cyclic oligomers to prepare a polyamide 6 final polymer; (3) Add the polyamide 6 final polymer and fiber-reinforced materials to a screw extruder in proportion for blending to obtain a fiber-reinforced polyamide 6 material.

[0007] The fiber-reinforced polyamide 6 material prepared by the method for preparing a fiber-reinforced polyamide 6 material provided in this solution can be directly used for injection molding.

[0008] In some embodiments, additives can be added to the basic components for modification or other components can be added for copolymerization according to specific application ranges. In other words, caprolactam, water, a molecular weight regulator, a metal ion compound, and additives are mixed in proportion according to functional requirements.

[0009] Correspondingly, the additives are selected from one or more of antioxidants, colorants, flame retardants, antibacterial agents, antistatic agents, and ultraviolet protection agents, and the addition amount of the additives is not more than 5 wt%.

[0010] 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, bis(salicylidene)diamine antioxidants, and thio propionate antioxidants.

[0011] The colorant is one or more of carbon black, phthalocyanine pigments, quinacridone pigments, triarylmethane pigments, benzimidazolone pigments, azo pigments, dioxazines, isoindolinones, anthraquinones, and perinones.

[0012] 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.

[0013] The antibacterial agent is one or more of silver nanoparticles, copper nanoparticles, zinc oxide, cuprous oxide, copper oxide, acyl aniline compounds, imidazole compounds, thiazole compounds, isothiazolone derivatives, quaternary ammonium salt compounds, biguanide compounds, chitin, and chitosan; the antistatic agent is one or more of carbon black, graphene, carbon nanotubes, metal powders, alkali metal alkyl sulfonates, alkali metal alkyl phosphates, alkali metal dithiocarbamates, alkyl quaternary ammonium salts, alkyl phosphates, alkyl phosphonium salts, and ethoxylated aliphatic alkylamine antistatic agents.

[0014] The ultraviolet inhibitor is one or more of carbon black, iron oxide red, zinc oxide, salicylate ultraviolet absorbers, benzophenone ultraviolet absorbers, benzotriazole ultraviolet absorbers, substituted acrylonitrile ultraviolet absorbers, triazine ultraviolet absorbers, and hindered amine ultraviolet absorbers.

[0015] 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 1.5 wt% or less; the molecular weight regulator is a combination of one or more of organic monocarboxylic acids, organic dicarboxylic acids, organic monoamines, and organic diamines.

[0016] In some embodiments, the organic monocarboxylic acid is H(CH2) n COOH (n = 1 to 10), benzoic acid, or naphthoic acid; the organic dicarboxylic acid is COOH(CH2) m COOH (m = 1 to 10), terephthalic acid, phthalic acid, isophthalic acid, or naphthalenedicarboxylic acid; the organic monoamine is H(CH2) x NH2 (x = 1 to 10), aniline, or naphthylamine; the organic diamine is, H2N(CH2) y NH2 (y = 1 to 10), p-phenylenediamine, o-phenylenediamine, m-phenylenediamine, or naphthalenediamine.

[0017] In some embodiments, the metal ion compound as the cyclic oligomer inhibitor can be one MY or a mixture of multiple MYs, and the addition amount of the metal ion compound is 0.01 wt% to 2.0 wt% of caprolactam.

[0018] 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 ion is 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 ion is Be 2+ , Mg 2+ , Ca 2+ ; the metal cation M can also be selected from one of Li + , Al 3+ .

[0019] 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 monocarboxylate ion H(CH2) n COO - (n = 0~12), benzoate ion, naphthoate ion, organic dicarboxylate ion COO - (CH2) m COO - (m = 0~12), terephthalate ion, phthalate ion, isophthalate ion or naphthalenedicarboxylate ion, saturated fatty acid ion C x H 2x+1 COO -(x = 13 - 20), unsaturated fatty acid root ions (oleate ion C 17 H 33 COO - , linoleate ion C 17 H 31 COO - , α-linolenate ion C 17 H 29 COO - , arachidonate ion C 19 H 31 COO - , palmitoleate ion C 15 H 29 COO - ), 6-aminohexanoate ion NH2C5H 10 COO - , an amino acid root ion (glycinate ion, alaninate ion, valinate ion, leucinate ion, isoleucinate ion, prolinate ion, phenylalaninate ion, methioninate ion, serine ion, threonine ion, asparagine ion, glutamine ion, aspartate ion, glutamate ion, cysteinate ion, tyrosine ion, selenocysteinate ion).

[0020] In the preparation method of the fiber-reinforced polyamide 6 material as described above, in step (3), the fiber-reinforced material is one or more of glass fiber, carbon fiber, aramid fiber, silicon carbide fiber, natural fiber, and basalt fiber, and the addition amount is 10 - 60 wt% of polyamide 6.

[0021] In some embodiments, if the system is well dispersed, the dispersant may not be added. If the system is poorly dispersed, the dispersant can be added simultaneously when adding the fiber-reinforced material. The dispersant can be one or more of a polymer type dispersant, a surfactant type dispersant, a coupling agent modified type dispersant, a composite functional type dispersant, and a traditional dispersant such as silicone and wax, and the addition amount is not more than 1 wt% of polyamide 6.

[0022] In the preparation method of a fiber-reinforced polyamide 6 material as described above, in step (1), the VK tube reactor 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 polyamide 6 base melt obtained is 1.5~3.0; when the VK tube reactor is a two-stage reactor, the reaction temperature of the pre-polymerization reactor is 200~270 °C, the reaction pressure is 0.1 MPa~1.0 MPa, the reaction temperature of the post-polymerization reactor is 240~280 °C, the reaction pressure is 0.01 MPa~0.2 MPa, and the viscosity of the polyamide 6 base melt obtained is 1.8~3.5.

[0023] In the preparation method of a fiber-reinforced polyamide 6 material as described above, in step (2), the devolatilization reactor is a vertical devolatilization reactor or two vertical devolatilization reactors connected in series. A condensation collector with a buffer tank is connected behind each devolatilization reactor to collect the removed steam, and a vacuum pump is connected behind the condensation collector to provide vacuum power.

[0024] Correspondingly, when the devolatilization reactor is a single vertical devolatilization reactor, the reaction temperature is 240~280 °C, and the reaction pressure is 20~200 Pa; when the devolatilization reaction system consists 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.

[0025] Correspondingly, the condensation collector can also be a caprolactam spray pump or a caprolactam injection pump with a buffer tank added in front of the pump; the vacuum pump can be 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 connected in series or in parallel combination.

[0026] In the preparation method of a fiber-reinforced polyamide 6 material as described above, the relative viscosity of the polyamide 6 base melt obtained in step (1) is 1.5~3.5, the monomer content is less than 9.5 wt%, the cyclic oligomer content is less than 2.5 wt%, and the hot water extractable content is less than 10.5 wt%; the relative viscosity of the polyamide 6 end polymer is 2.3~4.2, the monomer content is less than 0.1 wt%, the cyclic oligomer content is less than 1.5 wt%, and the hot water extractable content is less than 0.5 wt%.

[0027] In the preparation method of the fiber-reinforced polyamide 6 material described above, in step (3), the screw extruder is one or a series combination 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. The temperature of the screw extruder is set to 230-280 °C, and the rotation speed is set to 20-300 rpm.

[0028] In the preparation method of the fiber-reinforced polyamide 6 material described above, the tensile strength of the fiber-reinforced polyamide 6 material obtained in step (3) is ≥90 MPa.

[0029] As Figure 1 shown, in this solution, caprolactam, water, a molecular weight regulator, and a cyclic oligomer inhibitor are mixed in proportion, preheated, and then 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 end polymer; the polyamide 6 end polymer and the fiber-reinforced material are added to a screw extruder in proportion for blending.

[0030] Compared with the prior art, this technical solution has the following characteristics and beneficial effects: (1) The introduction of the cyclic oligomer inhibitor metal ion compound makes the content of cyclic oligomers in the polyamide 6 base melt lower than 2.5 wt%, which is 0.5-1.0 wt% lower than that of the slice without adding the cyclic oligomer inhibitor. After devolatilization, the content of hot water extractables in the polyamide 6 end polymer is lower than 0.5 wt%, and it has the quality of excellent-grade polyamide 6.

[0031] (2) The introduction of metal ions can coordinate with the carbonyl oxygen in polyamide 6, weaken the hydrogen bonds between molecular chains, thereby improving the flowability of the melt. The dispersion performance of the subsequent fiber-reinforced material is significantly improved to obtain a higher-quality fiber-reinforced polyamide 6 material. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a schematic structural diagram of the preparation method of the fiber-reinforced polyamide 6 material provided by this solution. DETAILED DESCRIPTION OF THE INVENTION

[0033] In order to further illustrate the present invention, the following examples are used to describe in detail a method and application for preparing high-quality polyamide 6 fibers with a short process provided by the present invention, but they should not be construed as limiting the protection scope of the present invention.

[0034] The present invention uses an ultra-high performance liquid chromatograph to measure the contents of monomers and cyclic oligomers in the polyamide 6 base melt and end polymer. The specific condition parameters are as follows: —— Chromatographic column: T3 column, 100 mm × 2.1 mm (inner diameter) × 1.7 μm, or equivalent; —— Column temperature: 30 °C; —— Flow rate: 0.3 mL / min; —— Detection wavelength: 200 nm; —— Injection volume: 2 μL; —— Elution program (as shown in the following table): Mobile phase A is water, and mobile phase B is acetonitrile.

[0035]

[0036] Comparative example (1) Fresh caprolactam, water, and terephthalic acid were mixed in a ratio of 100:2:0.375, preheated, and then added to a one-stage VK tube for a polymerization reaction for 8 h. The reaction temperature was 250 °C, and the reaction pressure was 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% (where the cyclic dimer content was 0.65 wt%), and a hot water extractable content of 8.92 wt% was prepared; (2) The base melt was transported through a pipeline to a first-stage vertical devolatilization reactor for the removal of monomers and some cyclic oligomers. The reaction temperature was 260 °C, and the reaction pressure was 120 Pa. Finally, a polyamide 6 end polymer with a relative viscosity of 2.8, a monomer content of 0.07 wt%, a cyclic oligomer content of 2.10 wt% (where the cyclic dimer content was 0.35 wt%), and a hot water extractable content of 0.75 wt% was obtained.

[0037] (3) The polyamide 6 end polymer can be subjected to hot water extraction, dried, remelted, and then injection molded. The injection molding temperature was 270 °C, the injection molding pressure was 10 MPa, and the tensile strength of the polyamide 6 material after injection molding was 55 MPa.

[0038] Example 1 A preparation method of a fiber-reinforced polyamide 6 material, the specific steps are as follows: (1) Fresh caprolactam, water, terephthalic acid, and lanthanum aminohexanoate were mixed in a ratio of 100:2:0.375:0.6, preheated, and then added to a one-stage VK tube for a polymerization reaction for 10 h. The reaction temperature was 250 °C, and the reaction pressure was 0.4 MPa. Finally, 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% (where the cyclic dimer content was 0.43 wt%), and a hot water extractable content of 8.90 wt% was prepared; (2)The base melt is transported through a pipeline to a first-stage vertical devolatilization reactor for the removal of monomers and some cyclic oligomers. The reaction temperature is 260 °C, and the reaction pressure is 70 Pa. Finally, a polyamide 6 end-polymer with a relative viscosity of 2.8, a monomer content of 0.07 wt%, a cyclic oligomer content of 1.45 wt% (where the cyclic dimer content is 0.08 wt%), and a hot water extractable content of 0.42 wt% is obtained.

[0039] (3)The polyamide 6 end-polymer and glass fiber are added to a screw extruder in a ratio of 1:0.3 for blending. The resulting glass fiber-reinforced polyamide 6 material can be directly used for injection molding. The injection temperature is 270 °C, the injection pressure is 10 MPa, and the tensile strength of the glass fiber-reinforced polyamide 6 material after injection is 145 MPa.

[0040] Example 2 A preparation method of a fiber-reinforced polyamide 6 material, the specific steps are as follows: (1)Fresh caprolactam, water, terephthalic acid, and cerium formate are mixed in a ratio of 100:2:0.375:1.0, and after preheating, they are added to a one-stage VK tube for polymerization reaction for 14 h. The reaction temperature is 230 °C, and the reaction pressure is 0.3 MPa. Finally, 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% (where the cyclic dimer content is 0.33 wt%), and a hot water extractable content of 8.65 wt% is prepared; (2)The base melt is transported through a pipeline to a first-stage vertical devolatilization reactor for the removal of monomers and some cyclic oligomers. The reaction temperature is 260 °C, and the reaction pressure is 150 Pa. Finally, a polyamide 6 end-polymer with a relative viscosity of 2.6, a monomer content of 0.09 wt%, a cyclic oligomer content of 1.35 wt% (where the cyclic dimer content is 0.07 wt%), and a hot water extractable content of 0.38 wt% is obtained.

[0041] (3)The polyamide 6 end-polymer and carbon fiber are added to a screw extruder in a ratio of 1:0.15 for blending. The resulting carbon fiber-reinforced polyamide 6 material can be directly used for injection molding. The injection temperature is 265 °C, the injection pressure is 8.5 MPa, and the tensile strength of the carbon fiber-reinforced polyamide 6 material after injection is 105 MPa.

[0042] Example 3 A preparation method of a fiber-reinforced polyamide 6 material, the specific steps are as follows: (1) Mix fresh caprolactam, water, terephthalic acid, and lanthanum acetate in a ratio of 100:2:0.375:0.8. After preheating, add them to a one-stage VK tube for polymerization reaction for 14 h. The reaction temperature is 250 °C, and the reaction pressure is 0.42 MPa. Finally, 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% (where the cyclic dimer content is 0.47 wt%), and a hot water extractable content of 8.85 wt% is prepared; (2) Transport the base melt through a pipeline to a two-stage series vertical devolatilization reactor for the removal of monomers and some cyclic oligomers. The reaction temperature of devolatilization reactor 1 is 250 °C, and the reaction pressure is 1500 Pa. The reaction temperature of devolatilization reactor 2 is 260 °C, and the reaction pressure is 110 Pa. Finally, a polyamide 6 end polymer with a relative viscosity of 3.4, a monomer content of 0.07 wt%, a cyclic oligomer content of 1.30 wt% (where the cyclic dimer content is 0.06 wt%), and a hot water extractable content of 0.32 wt% is obtained.

[0043] (3) Add the polyamide 6 end polymer and carbon fiber to a screw extruder in a ratio of 1:0.3 for blending. The obtained carbon fiber reinforced polyamide 6 material can be directly used for injection molding. The injection temperature is 275 °C, the injection pressure is 10 MPa, and the tensile strength of the carbon fiber reinforced polyamide 6 material after injection is 170 MPa.

[0044] Example 4 A preparation method of a fiber-reinforced polyamide 6 material, the specific steps are as follows: (1) Mix fresh caprolactam, water, terephthalic acid, and yttrium benzoate in a ratio of 100:2:0.375:1.5. After preheating, add them to a one-stage VK tube for polymerization reaction for 8 h. The reaction temperature is 240 °C, and the reaction pressure is 0.35 MPa. Finally, 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% (where the cyclic dimer content is 0.32 wt%), and a hot water extractable content of 8.56 wt% is prepared; (2) Transport the base melt through a pipeline to a two-stage series vertical devolatilization reactor for the removal of monomers and some cyclic oligomers. The reaction temperature of devolatilization reactor 1 is 250 °C, and the reaction pressure is 3000 Pa. The reaction temperature of devolatilization reactor 2 is 250 °C, and the reaction pressure is 80 Pa. Finally, a polyamide 6 end polymer with a relative viscosity of 2.5, a monomer content of 0.08 wt%, a cyclic oligomer content of 1.35 wt% (where the cyclic dimer content is 0.06 wt%), and a hot water extractable content of 0.38 wt% is obtained.

[0045] (3) Mix the polyamide 6 end-polymer and glass fiber in a ratio of 1:0.4 and add them to a screw extruder for blending. The obtained glass fiber-reinforced polyamide 6 material can be directly used for injection molding. The injection temperature is 265 °C, the injection pressure is 9 MPa, and the tensile strength of the glass fiber-reinforced polyamide 6 material after injection is 165 MPa.

[0046] Example 5 A preparation method of a fiber-reinforced polyamide 6 material, the specific steps are as follows: (1) Mix fresh caprolactam, water, terephthalic acid, and zinc formate in a ratio of 100:2:0.375:0.5, preheat and then add them to a one-stage VK tube for polymerization reaction for 10 h. The reaction temperature is 260 °C, and the reaction pressure is 0.48 MPa. Finally, 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% (where the cyclic dimer content is 0.46 wt%), and a hot water extractable content of 8.80 wt% is prepared; (2) Transport the base melt through a pipeline to a first-stage vertical devolatilization reactor to remove monomers and some cyclic oligomers. The reaction temperature is 270 °C, and the reaction pressure is 50 Pa. Finally, a polyamide 6 end-polymer with a relative viscosity of 3.2, a monomer content of 0.06 wt%, a cyclic oligomer content of 1.32 wt% (where the cyclic dimer content is 0.07 wt%), and a hot water extractable content of 0.35 wt% is prepared.

[0047] (3) Mix the polyamide 6 end-polymer and aramid fiber in a ratio of 1:0.1 and add them to a screw extruder for blending. The obtained aramid fiber-reinforced polyamide 6 material can be directly used for injection molding. The injection temperature is 265 °C, the injection pressure is 8.5 MPa, and the tensile strength of the aramid fiber-reinforced polyamide 6 material after injection is 110 MPa.

[0048] Example 6 A preparation method of a fiber-reinforced polyamide 6 material, the specific steps are as follows: (1) Mix fresh caprolactam, water, terephthalic acid, scandium terephthalate, and lithium nitrate in a ratio of 100:2:0.375:0.3:0.3, preheat and then add them to a one-stage VK tube for polymerization reaction for 10 h. The reaction temperature is 240 °C, and the reaction pressure is 0.4 MPa. Finally, 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% (where the cyclic dimer content is 0.38 wt%), and a hot water extractable content of 8.85 wt% is prepared; (2) The base melt is transported through a pipeline to a first-stage vertical devolatilization reactor for the removal of monomers and some cyclic oligomers. The reaction temperature is 265 °C and the reaction pressure is 60 Pa. Finally, a polyamide 6 end-polymer with a relative viscosity of 2.8, a monomer content of 0.05 wt%, a cyclic oligomer content of 1.20 wt% (where the cyclic dimer content is 0.04 wt%), and a hot water extractable content of 0.26 wt% is obtained.

[0049] (3) The polyamide 6 end-polymer and glass fiber are added to a screw extruder in a ratio of 1:0.2 for blending, and the resulting glass fiber-reinforced polyamide 6 material can be directly used for injection molding. The injection temperature is 265 °C, the injection pressure is 9 MPa, and the tensile strength of the glass fiber-reinforced polyamide 6 material after injection is 125 MPa.

[0050] Example 7 A preparation method of a fiber-reinforced polyamide 6 material, the specific steps are as follows: (1) Fresh caprolactam, water, terephthalic acid, cerium formate, and nickel adipate are mixed in a ratio of 100:2:0.375:0.5:0.5, preheated and then added to a one-stage VK tube for polymerization reaction for 10 h. The reaction temperature is 230 °C and the reaction pressure is 0.3 MPa. Finally, 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% (where the cyclic dimer content is 0.31 wt%), and a hot water extractable content of 8.57 wt% is prepared; (2) The base melt is transported through a pipeline to a first-stage vertical devolatilization reactor for the removal of monomers and some cyclic oligomers. The reaction temperature is 260 °C and the reaction pressure is 100 Pa. Finally, a polyamide 6 end-polymer with a relative viscosity of 2.5, a monomer content of 0.09 wt%, a cyclic oligomer content of 1.42 wt% (where the cyclic dimer content is 0.08 wt%), and a hot water extractable content of 0.45 wt% is obtained.

[0051] (3) The polyamide 6 end-polymer and glass fiber are added to a screw extruder in a ratio of 1:0.5 for blending, and the resulting glass fiber-reinforced polyamide 6 material can be directly used for injection molding. The injection temperature is 280 °C, the injection pressure is 10.5 MPa, and the tensile strength of the glass fiber-reinforced polyamide 6 material after injection is 190 MPa.

[0052] Example 8 A preparation method of a fiber-reinforced polyamide 6 material, the specific steps are as follows: (1) Mix fresh caprolactam, water, terephthalic acid, decanediamine, and magnesium isophthalate in a ratio of 100:2:0.2:0.2:0.6. After preheating, add it to a one-stage VK tube for a polymerization reaction for 10 h. The reaction temperature is 240 °C, and the reaction pressure is 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% (where the cyclic dimer content is 0.45 wt%), and a hot water extractable content of 8.84 wt% is prepared; (2) Transport the base melt through a pipeline to a first-stage vertical devolatilization reactor to remove monomers and some cyclic oligomers. The reaction temperature is 260 °C, and the reaction pressure is 80 Pa. Finally, a polyamide 6 end polymer with a relative viscosity of 3.0, a monomer content of 0.06 wt%, a cyclic oligomer content of 1.42 wt% (where the cyclic dimer content is 0.07 wt%), and a hot water extractable content of 0.45 wt% is obtained.

[0053] (3) Add the polyamide 6 end polymer and silicon carbide fibers to a screw extruder in a ratio of 1:0.25 for blending. The obtained silicon carbide fiber-reinforced polyamide 6 material can be directly used for injection molding. The injection temperature is 285 °C, the injection pressure is 11 MPa, and the tensile strength of the silicon carbide fiber-reinforced polyamide 6 material after injection is 185 MPa.

[0054] Example 9 A method for preparing a fiber-reinforced polyamide 6 material, the specific steps are as follows: (1) Mix fresh caprolactam, water, terephthalic acid, lanthanum acetate, and carbon black in a ratio of 100:2:0.375:0.8:1.0. After preheating, add it to a one-stage VK tube for a polymerization reaction for 12 h. The reaction temperature is 240 °C, and the reaction pressure is 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% (where the cyclic dimer content is 0.42 wt%), and a hot water extractable content of 8.90 wt% is prepared; (2) Transport the base melt through a pipeline to two series-connected vertical devolatilization reactors to remove monomers and some cyclic oligomers. The reaction temperature of devolatilization reactor 1 is 250 °C, and the reaction pressure is 800 Pa. The reaction temperature of devolatilization reactor 2 is 260 °C, and the reaction pressure is 80 Pa. Finally, a black polyamide 6 end polymer with a relative viscosity of 3.0, a monomer content of 0.05 wt%, a cyclic oligomer content of 1.18 wt% (where the cyclic dimer content is 0.04 wt%), and a hot water extractable content of 0.25 wt% is obtained.

[0055] (3) The black polyamide 6 end-polymer and carbon fiber are added to a screw extruder at a ratio of 1:0.2 for blending, and the obtained black carbon fiber-reinforced polyamide 6 material can be directly used for injection molding. The injection temperature is 270 °C, the injection pressure is 9.5 MPa, and the tensile strength of the black carbon fiber-reinforced polyamide 6 material after injection is 140 MPa.

[0056] Example 10 A preparation method of a fiber-reinforced polyamide 6 material, the specific steps are as follows: (1) Fresh caprolactam, water, terephthalic acid, lithium nitrate, and a phosphorus-based flame retardant are mixed at a ratio of 100:2:0.375:1.5:1.5, and after preheating, they are added to a one-stage VK tube for a polymerization reaction for 10 h. The reaction temperature is 240 °C, and the reaction pressure is 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% (where the cyclic dimer content is 0.32 wt%), and a hot water extractable content of 8.58 wt% is prepared; (2) The base melt is transported through a pipeline to a two-stage series vertical devolatilization reactor for the removal of monomers and some cyclic oligomers. The reaction temperature of devolatilization reactor 1 is 250 °C, the reaction pressure is 2500 Pa, the reaction temperature of devolatilization reactor 2 is 250 °C, and the reaction pressure is 70 Pa. Finally, a flame-retardant polyamide 6 end-polymer with a relative viscosity of 2.6, a monomer content of 0.07 wt%, a cyclic oligomer content of 1.38 wt% (where the cyclic dimer content is 0.06 wt%), and a hot water extractable content of 0.41 wt% is prepared.

[0057] (3) The flame-retardant polyamide 6 end-polymer and glass fiber are added to a screw extruder at a ratio of 1:0.35 for blending, and the obtained glass fiber-reinforced flame-retardant polyamide 6 material can be directly used for injection molding. The injection temperature is 260 °C, the injection pressure is 8.5 MPa, and the tensile strength of the glass fiber-reinforced flame-retardant polyamide 6 material after injection is 160 MPa.

[0058] Performance characterization of the polyamide 6 base melt and polyamide 6 end-polymer of the comparative example and Examples 1 to 10 gives the performance characterization table as shown in Table 1 below: Table 1 Performance characterization table of the polyamide 6 base melt and polyamide 6 end-polymer of the comparative example and Examples 1 to 10 .

[0059] The above embodiments merely represent several implementation manners of the present application. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all fall within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the appended claims.

Claims

1. A method for preparing a fiber-reinforced polyamide 6 material, characterized in that It includes the following steps: (1) Caprolactam, water, a molecular weight regulator, and a cyclic oligomer inhibitor are mixed in proportion, preheated, and then added to a VK tube for polymerization reaction to prepare a polyamide 6 base melt, where the metal ion compound serves as the cyclic oligomer inhibitor; (2) The polyamide 6 base melt is transported through a pipeline to a devolatilization reactor to remove monomers and some cyclic oligomers to prepare a polyamide 6 end polymer; (3) The polyamide 6 end polymer and a fiber reinforcing material are added to a screw extruder in proportion for blending to obtain a fiber-reinforced polyamide 6 material.

2. The preparation method of the fiber-reinforced polyamide 6 material according to claim 1, characterized in that In step (1), the metal ion compound serving as the cyclic oligomer inhibitor has a structure of MY, where M is a metal cation and Y is an inorganic anion or an organic anion. The metal cation M is selected from transition metal ions, lanthanide metal ions, group IIA metal ions, and Li + , Al 3+ ; 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, an organic monocarboxylate ion, benzoate ion, naphthoate ion, an organic dicarboxylate ion, terephthalate ion, phthalate ion, isophthalate ion or naphthalenedicarboxylate ion, a saturated fatty acid root ion, an unsaturated fatty acid root ion, 6-aminohexanoate ion, or an amino acid root ion.

3. The preparation method of 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.

4. The preparation method of 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. A condensation collector with a buffer tank is connected behind each devolatilization reactor to collect the removed steam, and a vacuum pump is connected behind the condensation collector to provide vacuum power.

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

6. The preparation method of the fiber-reinforced polyamide 6 material according to claim 1, characterized in that, The relative viscosity of the polyamide 6 base melt is 1.5 - 3.5, the monomer content is less than 9.5 wt%, the cyclic oligomer content is less than 2.5 wt%, and the hot water extractable content is less than 10.5 wt%; the relative viscosity of the polyamide 6 end polymer is 2.3 - 4.2, the monomer content is less than 0.1 wt%, the cyclic oligomer content is less than 1.5 wt%, and the hot water extractable content is less than 0.5 wt%.

7. The preparation method of the fiber-reinforced polyamide 6 material according to claim 1, characterized in that, The temperature of the screw extruder is set at 230 - 280 °C, and the rotation speed is set at 20 - 300 rpm.

8. The preparation method of 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. The added additive is selected from one or more of antioxidants, colorants, flame retardants, antibacterial agents, antistatic agents, and ultraviolet inhibitors, and the addition amount of the additive is less than 5 wt%.

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