Polyamide resin composition as well as preparation method and application thereof

Abstract

The invention belongs to the field of polyamide resin, and particularly relates to a polyamide resin composition as well as a preparation method and application thereof. The polyamide resin composition disclosed by the invention is composed of polyamide resins with different viscosities and necessary additives, so that the melt flowability and the product crystallization forming speed in the technological process are improved while the raw materials and injection molding products of the raw materials maintain the performance advantages of the high-viscosity polyamide resins; and internal shrinkage cavities or surface recesses are not easy to generate under the conventional injection molding process.

Description

Technical Field

[0001] This invention belongs to the field of polyamide resins, and specifically relates to a polyamide resin composition, its preparation method and application. Background Technology

[0002] Injection molding is a convenient, fast, and efficient production method, and one of the main processing methods for thermoplastic plastics such as polyamides. With the development of science and technology, the demand for thick-walled injection-molded products in industries such as automotive trim and household appliances is constantly increasing. However, current technology makes it difficult to avoid changes in the appearance and internal structure of parts with a certain thickness or locally significant thickness due to the cooling and crystallization shrinkage of the molten material. This process is affected by various factors such as material properties, part wall thickness, and injection molding process. When the molten material enters the mold cavity, the temperature difference between the surface and core layers of the injection-molded part is large. The surface material cools and crystallizes first, while the remaining material crystallizes and shrinks along the surface direction. If the surface strength and rigidity of the product are insufficient, collapse will occur in the thicker areas, resulting in obvious indentations and causing the product shape to deviate from the expected shape. If the surface layer of the thick-walled part has already solidified, its strength and rigidity are sufficient to resist the shrinkage stress in the core, then shrinkage cavities will form inside the thick-walled part, subsequently affecting the product's strength and structure. This phenomenon is common in the injection molding of polyamide products (such as polyamide 66).

[0003] However, polyamide 66 resin possesses unique advantages in strength and toughness, making it irreplaceable in many applications. High-viscosity polyamide 66, in particular, has a longer molecular chain, resulting in higher crystallization potential and better chain entanglement, leading to superior toughness, impact resistance, fatigue resistance, low-temperature resistance, performance stability, and long-term reliability. However, the longer molecular chain also brings problems such as poor melt flowability and reduced molecular chain segment mobility. The latter results in a slower crystallization rate, increasing the time difference between the internal and external cooling and hardening of the injection-molded part, thus exacerbating internal shrinkage cavities. Summary of the Invention

[0004] This invention addresses the aforementioned problems in the prior art by proposing a polyamide resin composition, its preparation method, and its applications. The polyamide resin composition of this invention comprises polyamide resins of varying viscosities and necessary additives, enabling the raw materials and injection-molded products to retain the advantages of high-viscosity polyamide resins while improving melt flow and product crystallization speed during the process. Furthermore, it reduces the likelihood of internal shrinkage cavities or surface depressions under conventional injection molding processes.

[0005] Specifically, the present invention provides a polyamide resin composition comprising a first component, a second component, and an additive; The first component is selected from one or both of polyamide resin I and polyamide resin II; The second component is selected from one or both of polyamide resin III and polyamide resin IV; The relative viscosity value of polyamide resin I is denoted as a1, the relative viscosity value of polyamide resin II is denoted as a2, the relative viscosity value of polyamide resin III is denoted as b1, and the relative viscosity value of polyamide resin IV is denoted as b2. a1, a2, b1, and b2 satisfy the following: a1 is 1.8~2.8; a2 is 2.7~3.5; b1 is 3.4~4.6; b2 is 4.5~6.8; a1 <a2<b1<b2。

[0006] In one or more embodiments, polyamide resin I, polyamide resin II, polyamide resin III and polyamide resin IV are each independently selected from one or more of polyamide 66 resin, polyamide 56 resin, polyamide 66 / 6T copolymer resin, polyamide MXD6 resin, polyamide 610 resin and polyamide 612 resin.

[0007] In one or more embodiments, polyamide resin I, polyamide resin II, polyamide resin III and polyamide resin IV are all polyamide 66 resins.

[0008] In one or more embodiments, the first component has a mass fraction of 2% to 40% in the polyamide resin composition, the second component has a mass fraction of 55% to 97.9% in the polyamide resin composition, and the additive has a mass fraction of 0.01% to 5% in the polyamide resin composition.

[0009] In one or more embodiments, the mass fraction of polyamide resin I in the polyamide resin composition is denoted as x1, the mass fraction of polyamide resin II in the polyamide resin composition is denoted as x2, the average viscosity of the first component is denoted as A, A=(a1x1+a2x2) / (x1+x2); the mass fraction of polyamide resin III in the polyamide resin composition is denoted as y1, the mass fraction of polyamide resin IV in the polyamide resin composition is denoted as y2, and the average viscosity of the second component is denoted as B, B=(b1y1+b2y2) / (y1+y2); The values ​​of A and B satisfy the following relationship: 0.5 ≤ BA ≤ 4.

[0010] In one or more implementations, the values ​​of A and B also satisfy the following relationship: (BA) / A≥0.15.

[0011] In one or more embodiments, the first component is polyamide resin I and polyamide resin II, and the second component is polyamide resin III and polyamide resin IV.

[0012] In one or more embodiments, the first component is polyamide resin I and polyamide resin II, and the second component is polyamide resin III.

[0013] In one or more embodiments, the first component is polyamide resin I and polyamide resin II, and the second component is polyamide resin IV.

[0014] In one or more embodiments, the first component is polyamide resin I, and the second component is polyamide resin III and polyamide resin IV.

[0015] In one or more embodiments, the first component is polyamide resin II, and the second component is polyamide resin III and polyamide resin IV.

[0016] In one or more embodiments, the first component is polyamide resin I and the second component is polyamide resin III.

[0017] In one or more embodiments, the first component is polyamide resin I and the second component is polyamide resin IV.

[0018] In one or more embodiments, the first component is polyamide resin II and the second component is polyamide resin IV.

[0019] In one or more embodiments, the first component is polyamide resin II and the second component is polyamide resin III.

[0020] In one or more embodiments, the additive comprises one or more of the following: heat stabilizer, UV absorber, lubricant, nucleating agent, plasticizer, and colorant.

[0021] In one or more embodiments, the additive comprises one or more of a heat stabilizer, a lubricant, and a nucleating agent.

[0022] In one or more embodiments, the additive comprises a heat stabilizer, a lubricant, and a nucleating agent.

[0023] In one or more embodiments, the heat stabilizer is selected from one or more of hindered phenolic antioxidants, amine antioxidants, phosphorus antioxidants, thioether antioxidants and metal passivators.

[0024] In one or more embodiments, the heat stabilizer is one or more selected from N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,3-phenylenediamide, sodium hypophosphite monohydrate, and sodium phosphite.

[0025] In one or more embodiments, the lubricant is one or more selected from lignite acid, sodium lignite, calcium lignite, lignite ester, ethylene bis-stearamide, erucamide, tungsten disulfide, molybdenum disulfide, graphite, and barium sulfate.

[0026] In one or more embodiments, the nucleating agent is one or more selected from talc, silica, phthalate whiskers, magnesium oxide, aluminum oxide, zinc oxide, organophosphorus sodium, silicates, acetates, and powdered polymers with a melting point above 300°C.

[0027] In one or more embodiments, the powdered polymer with a melting point above 300°C is one or more selected from polyamide 6T, polyamide 9T, polyamide 10T, polyamide 12T and their copolymers.

[0028] Another aspect of the present invention provides a method for preparing a polyamide resin composition according to any embodiment of the present invention, the method comprising: mixing a first material and a second material by dry mixing to obtain a polyamide resin composition; the first material comprising one or more of polyamide resin I, polyamide resin II and additives, and the second material comprising one or more of polyamide resin III, polyamide resin IV and additives.

[0029] In one or more embodiments, polyamide resin I is prepared by salt solution polymerization, or by salt solution polymerization followed by solid-state polycondensation; polyamide resin II is prepared by salt solution polymerization, or by salt solution polymerization followed by solid-state polycondensation; polyamide resin III is prepared by salt solution polymerization, or by salt solution polymerization followed by solid-state polycondensation; and polyamide resin IV is prepared by solid-state polycondensation, or by salt solution polymerization followed by solid-state polycondensation.

[0030] In one or more embodiments, the auxiliary is added during salt solution polymerization or solid-phase polycondensation.

[0031] In one or more embodiments, the auxiliary agent is added during salt solution polymerization.

[0032] In one or more embodiments, polyamide resin I is prepared by salt solution polymerization; polyamide resin II is prepared by salt solution polymerization or obtained by solid-phase polycondensation of polyamide resin I; polyamide resin III is prepared by salt solution polymerization or obtained by solid-phase polycondensation of polyamide resin I or polyamide resin II; and polyamide resin IV is obtained by solid-phase polycondensation of polyamide resin I, polyamide resin II, or polyamide resin III.

[0033] In one or more embodiments, polyamide resin III is obtained by solid-phase polycondensation of polyamide resin I or polyamide resin II.

[0034] In one or more embodiments, the additive is added to the polyamide resin composition during the preparation of polyamide resin I, polyamide resin II, or polyamide resin III by salt solution polymerization.

[0035] In one or more embodiments, the additive is not added to the polyamide resin composition during solid-state polycondensation or dry mixing.

[0036] Another aspect of the present invention provides a component comprising the polyamide resin composition described in any embodiment of the present invention or the polyamide resin composition prepared by the method described in any embodiment of the present invention.

[0037] In one or more embodiments, the component is a railway fastener part, gear, bearing, or engine cover.

[0038] Another aspect of the invention provides the use of the polyamide resin composition described in any embodiment of the invention or the polyamide resin composition prepared by the method described in any embodiment of the invention in the manufacture of components for railway fasteners.

[0039] The polyamide composition of the present invention can not only improve fluidity and act as a plasticizer by adding a low-viscosity component to the high-viscosity component, but also accelerate the crystallization rate and avoid shrinkage pores in the injection molded products.

[0040] The additives added in this invention preferably include three types: first, nucleating agents, which promote polymer crystallization during the injection molding of the final polyamide resin composition; second, lubricants, which improve melt flowability during the injection molding of the final polyamide resin composition; and third, heat stabilizers, which are conventional additives used in the polymerization process to promote the polymerization reaction and give the resin product better color. In this invention, the additives undergo the entire polymerization process (e.g., high temperature, high pressure, negative pressure), so not just any nucleating agent or lubricant can be used. The boiling points of the additives suitable for this invention must meet the corresponding requirements. The polyamide resin composition prepared by the method of this invention exhibits more uniform additive dispersion and better crystallization promotion.

[0041] This invention adds an auxiliary agent during the polymerization of low-viscosity polyamide and then thickens it, so that the product has both the characteristics of rapid crystallization promoted by the auxiliary agent and high viscosity. At the same time, this invention combines polyamide products with different viscosities in a gradient, so that the product can have the performance advantages of high-viscosity polyamide (such as fatigue resistance, impact resistance, low temperature resistance, long-term stability, etc.) and the processing advantages of low-viscosity polyamide (mainly in improving product flowability and increasing crystallization speed). Detailed Implementation

[0042] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used herein are explained and defined in general terms below. Unless otherwise specified, all technical and scientific terms used herein have the common meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0043] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0044] In this document, the terms “contains,” “includes,” “containing,” and similar terms encompass the meanings of “basically composed of” and “composed of.” For example, when this document discloses “A contains B and C,” “A is basically composed of B and C” and “A is composed of B and C” should be considered as having been disclosed in this document.

[0045] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0046] Unless otherwise specified, percentages refer to mass percentages and proportions refer to mass ratios in this article.

[0047] In this article, the sum of the percentages of all components in the composition is 100%.

[0048] In this document, when describing embodiments or examples, it should be understood that it is not intended to limit the invention to those embodiments or examples. Rather, all alternatives, modifications, and equivalents of the methods and materials described herein are covered within the scope of this invention.

[0049] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0050] Polyamide resin composition

[0051] The polyamide resin composition of the present invention comprises a first component, a second component, and an additive; the first component is selected from one or both of polyamide resin I (relative viscosity value denoted as a1) and polyamide resin II (relative viscosity value denoted as a2); the second component is selected from one or both of polyamide resin III (relative viscosity value denoted as b1) and polyamide resin IV (relative viscosity value denoted as b2); a1 <a2<b1<b2。

[0052] In the polyamide resin composition of the present invention, polyamide resin I generally refers to a polyamide resin with a relative viscosity value (a1) of 1.8 to 2.8 (e.g., 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, and any range between two values); polyamide resin II generally refers to a polyamide resin with a relative viscosity value (a2) of 2.7 to 3.5 (e.g., 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, and any range between two values); and polyamide resin III generally refers to a polyamide resin with a relative viscosity value (b1) of 3.4 to 4. Polyamide resin with a relative viscosity (b2) of 6 (e.g., 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, and any range between two values) is generally referred to as polyamide resin.

[0053] In the polyamide resin composition of the present invention, polyamide resin I, polyamide resin II, polyamide resin III, and polyamide resin IV are each independently selected from one or more of polyamide 66 resin, polyamide 56 resin, polyamide 66 / 6T copolymer resin, polyamide MXD6 resin, polyamide 610 resin, and polyamide 612 resin. In some embodiments, polyamide resin I, polyamide resin II, polyamide III, and polyamide resin IV are all polyamide 66 resin.

[0054] In the polyamide resin composition of the present invention, the first component has a mass fraction of 2% to 40% in the polyamide resin composition, for example, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, and any range between any two values. The mass fraction of the second component in the polyamide resin composition is 55% to 97.9%, for example, 55%, 56%, 57%, 58%, 59%, 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 97.1%, 97.2%, 97.3%, 97.4%, 97.5%, 97.6%, 97.7%, 97.8%, 97.9%, and any range between two values; controlling the mass fraction of the second component within the above range is beneficial to retaining the performance advantages of the high-viscosity component. The mass fraction of the additive in the polyamide resin composition is 0.01% to 5%, for example, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3%, 4%, 5%, and any range between any two values. It should be understood that the sum of the mass fractions of the first component, the second component, and the additive should be 100%.

[0055] In the polyamide resin composition of the present invention, the mass fraction of polyamide resin I in the polyamide resin composition is denoted as x1, and the mass fraction of polyamide resin II in the polyamide resin composition is denoted as x2. The average viscosity of the first component is denoted as A, then A = (a1x1 + a2x2) / (x1 + x2); the mass fraction of polyamide resin III in the polyamide resin composition is denoted as y1, and the mass fraction of polyamide resin IV in the polyamide resin composition is denoted as y2. The average viscosity of the second component is denoted as B, then B = (b1y1 + b2y2) / (y1 + y2).

[0056] In this invention, the viscosity difference between the low-viscosity component and the high-viscosity component should not be too large, i.e., (BA) should not be too large, otherwise it will affect the mechanical properties of the high-viscosity component. Simultaneously, the viscosity difference between the low-viscosity component and the high-viscosity component should not be too small, otherwise their flowability and crystallinity properties will be similar, which is not conducive to obtaining the polyamide resin composition of this invention that is less prone to shrinkage cavities during the injection molding of thick-walled parts. In some embodiments, the values ​​of A and B satisfy relationship 1: 0.5 ≤ BA ≤ 4. In some embodiments, the values ​​of A and B satisfy relationship 2: (BA) / A ≥ 0.15. Controlling the values ​​of A and B within the above relationships is beneficial to obtaining the polyamide resin composition of this invention that is less prone to shrinkage cavities during the injection molding of thick-walled parts.

[0057] In this invention, by introducing polyamide resin I and / or polyamide resin II with shorter molecular chains into polyamide III and / or polyamide IV, the polyamide resin composition of this invention can shorten the injection molding cycle of the product by increasing the melt flow rate, shortening the plasticizing injection time, and accelerating the crystallization speed during injection molding.

[0058] In the polyamide resin composition of the present invention, when the first component is polyamide resin I, the second component may be polyamide resin III, polyamide resin IV, or a combination of polyamide resin III and polyamide resin IV.

[0059] In the polyamide resin composition of the present invention, when the first component is polyamide resin II, the second component may be polyamide resin III, polyamide resin IV, or a combination of polyamide resin III and polyamide resin IV.

[0060] In the polyamide resin composition of the present invention, when the first component is a combination of polyamide resin I and polyamide resin II, the second component may be polyamide resin III, polyamide resin IV, or a combination of polyamide resin III and polyamide resin IV.

[0061] In some preferred embodiments, the first component is polyamide resin I and the second component is polyamide resin III.

[0062] In some preferred embodiments, the first component is polyamide resin II and the second component is polyamide resin IV.

[0063] In the polyamide resin composition of the present invention, the additives include one or more of heat stabilizers, lubricants, and nucleating agents. Furthermore, various additives commonly found in the art can also be added to the additives suitable for the present invention.

[0064] In some embodiments, the polyamide resin composition of the present invention comprises polyamide resin I, polyamide resin II, polyamide resin III, polyamide resin IV, and additives.

[0065] In some embodiments, the polyamide resin composition of the present invention comprises polyamide resin I, polyamide resin II, polyamide resin III and additives.

[0066] In some embodiments, the polyamide resin composition of the present invention comprises polyamide resin I, polyamide resin II, polyamide resin IV, and additives.

[0067] In some embodiments, the polyamide resin composition of the present invention comprises polyamide resin I, polyamide resin III, polyamide resin IV, and additives.

[0068] In some embodiments, the polyamide resin composition of the present invention comprises polyamide resin II, polyamide resin III, polyamide resin IV, and additives.

[0069] In some embodiments, the polyamide resin composition of the present invention comprises polyamide resin I, polyamide resin III, and additives.

[0070] In some embodiments, the polyamide resin composition of the present invention comprises polyamide resin I, polyamide resin IV, and additives.

[0071] In some embodiments, the polyamide resin composition of the present invention comprises polyamide resin II, polyamide resin III, and additives.

[0072] In some embodiments, the polyamide resin composition of the present invention comprises polyamide resin II, polyamide resin IV, and additives.

[0073] In some preferred embodiments, the polyamide resin composition of the present invention consists of polyamide resin I, polyamide resin III and additives, or polyamide resin II, polyamide resin IV and additives.

[0074] In some preferred embodiments, the additives include heat stabilizers, lubricants, and nucleating agents.

[0075] The heat stabilizer suitable for use in this invention is one or more selected from hindered phenolic antioxidants, amine antioxidants, phosphorus antioxidants, thioether antioxidants, and metal passivators, such as Nylostab. TM S-EED TM (SEED), sodium hypophosphite monohydrate, sodium phosphite, stabilizer TFB117, etc.

[0076] The lubricant suitable for this invention can be an organic lubricant and / or an inorganic lubricant. The organic lubricant suitable for this invention must meet the following requirements: boiling point ≥ 360℃, such as one or more of lignite acid, sodium lignite, calcium lignite, lignite esters, ethylene bis-stearamide (EBS), and erucamide. The inorganic lubricant suitable for this invention can be selected from one or more of tungsten disulfide, molybdenum disulfide, graphite, and barium sulfate.

[0077] The nucleating agents suitable for use in this invention include, but are not limited to, one or more of the following: talc, silica, phthalate whiskers, magnesium oxide, aluminum oxide, zinc oxide, organophosphorus sodium, silicates, acetates, and powdered polymers with a melting point above 300°C, wherein the powdered polymers include, but are not limited to, one or more of polyamide 6T, polyamide 9T, polyamide 10T, polyamide 12T, and their copolymers.

[0078] This invention introduces functional additives such as nucleating agents and lubricants, which promote crystallization in both low-viscosity and high-viscosity components, accelerating the crystallization rate of the product. Because these additives are added early in the molecular chain formation process, they can exist very uniformly in the resin; furthermore, due to their relatively small molecular structure, they can also interweave between molecular chains, providing lubrication. Therefore, the polyamide resin composition of this invention can shorten the injection molding cycle by increasing the melt flow rate and reducing the plasticizing injection time during product injection molding.

[0079] Preparation method of polyamide resin composition

[0080] A polyamide resin composition is obtained by dry mixing the first material and the second material; wherein the first material includes one or more of polyamide resin I, polyamide resin II and additives, and the second material includes one or more of polyamide resin III, polyamide resin IV and additives.

[0081] Polyamide resin I can be prepared by salt solution polymerization; polyamide resin II can be prepared by salt solution polymerization or by solid-phase polycondensation of polyamide resin I.

[0082] Polyamide resin III can be prepared by salt solution polymerization or by solid-phase polycondensation of polyamide resin I or polyamide resin II, preferably by solid-phase polycondensation of polyamide resin I or polyamide resin II; polyamide resin IV is obtained by solid-phase polycondensation of polyamide resin I, polyamide resin II or polyamide resin III.

[0083] In this article, the raw materials applicable to polyamide resin I, polyamide resin II and polyamide resin III include diamine monomers and dicarboxylic acid monomers, wherein the diamine monomers may include one or more of hexamethylenediamine, 1,5-pentanediamine and m-phenylenediamine; and the dicarboxylic acid monomers may include one or more of adipic acid, terephthalic acid, sebacic acid and dodecanoic acid.

[0084] The salt solution polymerization method of the present invention includes: mixing diamine monomer, dicarboxylic acid monomer, and water in a protective atmosphere, and carrying out a salt formation reaction at 50°C to 80°C for 20 to 30 minutes, adjusting the pH to 7.00 to 7.80 to obtain a polyamide salt solution with a mass concentration of 40% to 60%; mixing the polyamide salt solution and an auxiliary agent at 50°C to 80°C, raising the temperature, and concentrating the mass concentration of the polyamide salt solution to 60% to 70% when the pressure of the reaction system reaches 0.15 MPa to 0.20 MPa; and continuing to raise the temperature until the pressure of the reaction system reaches 0.15 MPa to 0.20 MPa. At a pressure of 0.8 MPa to 1.3 MPa, the mass of the polyamide salt solution is concentrated to 70% to 90%. The temperature is then increased until the pressure of the reaction system reaches 1.6 MPa to 2.0 MPa, and the mass concentration of the polyamide salt solution is concentrated to 92% to 97%. The temperature is then increased and the pressure is decreased to drain the water, and the pressure of the reaction system is reduced to atmospheric pressure. The polymerization reaction is carried out at 260°C to 290°C and a pressure of -0.01 MPa to -0.1 MPa for 5 to 30 minutes to obtain polyamide resin I, polyamide resin II, or polyamide resin III of the present invention.

[0085] In some embodiments, the salt solution polymerization method of the present invention specifically includes the following steps: In a protective atmosphere, hexamethylenediamine, adipic acid, and water are mixed and subjected to a salt-forming reaction at 50°C to 80°C for 20 to 30 minutes, adjusting the pH to 7.00 to 7.80 to obtain a polyamide 66 salt solution with a mass concentration of 40% to 60%; at 50°C to 80°C, the polyamide 66 salt solution and additives are mixed, and the temperature is increased until the pressure of the reaction system reaches 0.15 MPa to 0.20 MPa, concentrating the mass concentration of the polyamide 66 salt solution to 60% to 70%; and the temperature is further increased. The reaction system pressure is raised to 0.8 MPa to 1.3 MPa, and the mass concentration of the polyamide 66 salt solution is concentrated to 70% to 90%. The temperature is then raised further until the reaction system pressure reaches 1.6 MPa to 2.0 MPa, and the mass concentration of the polyamide 66 salt solution is concentrated to 92% to 97%. The temperature is then raised and the pressure is lowered to drain the water, and the pressure of the reaction system is reduced to atmospheric pressure. The polymerization reaction is carried out at 260℃ to 290℃ and a pressure of -0.01 MPa to -0.1 MPa for 5 min to 30 min to obtain polyamide resin I, polyamide resin II, or polyamide resin III.

[0086] It should be understood that the temperature and pressure in salt solution polymerization can be adjusted appropriately according to actual needs, but should not deviate too much from the range discussed in this article.

[0087] The solid-phase polycondensation of the present invention can be performed using either a positive pressure method or a negative pressure method.

[0088] The solid-state polycondensation positive pressure method of the present invention includes: The polyamide resin I, polyamide resin II, or polyamide resin III of this invention is introduced into a solid-phase polycondensation reactor. Nitrogen gas is used to replace the gas in the solid-phase polycondensation reactor, raising the temperature of the reactor to 150°C~260°C and maintaining it for 0.5~30 hours. Then, the temperature is lowered to 20~70°C before discharge. Throughout the entire process from heating to cooling, the pressure inside the reactor is maintained higher than the external atmospheric pressure (i.e., gauge pressure > 0 kPa) using one of the following methods: A, B, C, or D. Method A: Continuously introduce nitrogen gas and continuously exhaust it until the gauge pressure is 10~100kPa; Method B: Continuously introduce nitrogen gas and intermittently vent it. Vent the gas when the gauge pressure reaches 15~100kPa, and stop venting when the gauge pressure reaches 0~15kPa (excluding 0kPa). Vent the gas again when the gauge pressure rises back to 15~100kPa. Repeat this operation. Method C: Intermittently introduce nitrogen gas and continuously vent it. When the gauge pressure is 0~15kPa (excluding 0kPa), introduce nitrogen gas to 15~100kPa. When the gauge pressure slowly drops to 0~15kPa (excluding 0kPa), repeat the nitrogen gas introduction operation. Method D: Intermittently introduce nitrogen gas and intermittently exhaust gas. Introduce nitrogen gas until the gauge pressure is 15~100kPa. After a period of time, exhaust gas until the gauge pressure is 0~15kPa (excluding 0kPa). Then immediately introduce nitrogen gas until the gauge pressure is 15~100kPa. Repeat the operation.

[0089] The solid-phase polycondensation negative pressure method of the present invention includes: The polyamide resin I, polyamide resin II, or polyamide resin III of this invention is introduced into a solid-phase polycondensation reactor. The gas in the solid-phase polycondensation reactor is replaced with nitrogen. The temperature of the solid-phase polycondensation reactor is raised to 150°C~260°C and maintained for 0.5~30 hours. Then, the temperature is lowered to 20~70°C and the material is discharged. Throughout the entire process from heating to cooling, the vacuum degree in the reactor is maintained at <200 Pa.

[0090] In this invention, by adding additives during the polymerization of monomers into polymers, the additives can be more evenly dispersed while maintaining the original viscosity of the resin and preserving the excellent properties of high-viscosity resins, thereby fully exerting their modifying effect. In order to maintain the viscosity of the high-viscosity resin and obtain a polyamide resin composition with superior toughness and durability, it is preferable to add the additives during the polymerization of monomers into polymers, rather than by screw melt blending and granulation after solid-phase polycondensation. To ensure that the additives are not lost during polymerization, the additives suitable for this invention should have a high boiling point (≥320℃, preferably ≥350℃).

[0091] parts

[0092] The articles of the present invention are parts prepared using the polyamide resin composition described in any embodiment of the present invention, and the parts can be railway fastener components, gears, bearings, engine covers, etc.

[0093] Specifically, the railway fastener components described herein include, but are not limited to, all types and specifications of gauge blocks, joint gauge blocks, gauge block seats, block seats, insulating blocks, gauge blocks, insulating gauge blocks, joint insulating gauge blocks, pads, rail pads, rail height adjustment pads, elastic pads, filling pads, washers, flat washers, and embedded sleeves. In some implementation schemes, the railway fastener components described herein include, but are not limited to, seven specifications of insulating gauge blocks G4 and G4J (numbers 7, 8, 9, 10, 11, 12, and 13), seven types of gauge blocks G5 (numbers 2, 3, 4, 5, 6, 7, and 8), WJ7 insulating blocks, WJ8 insulating gauge blocks, WJ8 gauge blocks, embedded sleeves D1, and embedded sleeves D2. In some implementation schemes, the railway fasteners described herein include, but are not limited to, type WJ-1 fasteners, type WJ-2 fasteners, type WJ-7 fasteners, type WJ-8 fasteners, type WJ-12 fasteners, type WJ-14 fasteners, type WJ-15 fasteners, type W300 fasteners, type I elastic clip fasteners, type II elastic clip fasteners, type III elastic clip fasteners, type IV elastic clip fasteners, type V elastic clip fasteners, type VI elastic clip fasteners, type VII elastic clip fasteners, type FC fasteners, type SFC fasteners, type TR-Y fasteners, type TF-M fasteners, type ZX-2 fasteners, as well as conventional fasteners and height-adjusting fasteners of the aforementioned railway fasteners.

[0094] The present invention will be described below by way of specific embodiments. It should be understood that these embodiments are merely illustrative and are not intended to limit the scope of the invention. The methods, reagents, and materials used in the embodiments and comparative examples are conventional methods, reagents, and materials in the art, unless otherwise stated. The starting material compounds in the embodiments and comparative examples are all commercially available.

[0095] In this invention, viscosity refers to the relative viscosity of the polymer solution measured by the sulfuric acid method. The viscosity testing method is as follows: The high-viscosity polyamide resin of this invention was dissolved in 96wt% sulfuric acid as a solvent and prepared into a sample solution with a polymer concentration of 0.01±0.00001g / mL at 25°C for testing. Specific operating details are in accordance with standard GB / T 12006.1-2009 (ISO 307:2007).

[0096] In this invention, the melt flow index was tested in accordance with the national standard GB / T 3682, and the test conditions were 275℃ and 2.16kg.

[0097] Aggregation Example 1

[0098] Under a nitrogen protective atmosphere, 31025 g of hexamethylenediamine and 39051 g of adipic acid were dissolved in 70036 g of pure water and stirred at 60 °C for 30 min to form a salt. An appropriate amount of adipic acid was added to adjust the pH of the salt solution to 7.30. Then, 90 g of end-capping agent acetic acid, 42 g of SEED, 60.5 g of nucleating agent P22, and 300 g of sodium lignite were added and stirred until homogeneous. The salt solution was transferred to a polymerization reactor, heated to 130 °C, and the pressure inside the reactor was controlled at 0.16 to 0.18 MPa. The solution was then diluted to concentrate the polyamide 66 salt solution to 65% by mass. After this, the temperature was increased to 230 to 250 °C, and the pressure inside the reactor was controlled at 1.70 to 1.90 MPa. Drainage continued for 40 to 50 min. The pressure was then gradually reduced to atmospheric pressure. A polyamide 66 resin with a relative viscosity of 1.8 was obtained.

[0099] Example 2 of Aggregation

[0100] The polyamide 66 resin of this polymerization example was synthesized using a method similar to that of polymerization example 1, but the difference was that after gradually reducing the pressure to atmospheric pressure in the reactor, the pressure was reduced to a vacuum of -0.08 to -0.02 MPa, and the reaction was carried out for 20 minutes to obtain a polyamide 66 resin with a relative viscosity of 3.2.

[0101] Example 3 of Aggregation

[0102] The polyamide 66 resin of this polymerization example was synthesized using a method similar to that of polymerization example 1, but with the following differences: 1) 42g of SEED, 60.5g of nucleating agent P22 and 300g of sodium lignite were replaced with 42g of sodium hypophosphite monohydrate and 121g of nucleating agent 6T / 66 copolymer powder (melting point 310℃); 2) after gradually reducing the pressure in the reactor to atmospheric pressure, the pressure was reduced to a vacuum of -0.08 to -0.02MPa, and the reaction was carried out for 10min to obtain polyamide 66 resin with a relative viscosity of 2.7.

[0103] Example 4 of Aggregation

[0104] The polyamide 66 resin of this polymerization example was synthesized using a method similar to that of polymerization example 1, but with the following differences: 1) 42g of SEED, 60.5g of nucleating agent P22, and 300g of sodium lignite were replaced with 42g of sodium phosphite, 181.5g of nucleating agent silica, and 121g of barium sulfate; 2) after gradually reducing the pressure to atmospheric pressure, the pressure was reduced to a vacuum of -0.08 to -0.02 MPa, and the reaction was carried out for 5 minutes to obtain polyamide 66 resin with a relative viscosity of 2.4.

[0105] Example 5 of Aggregation

[0106] The polyamide 66 resin of this polymerization example was synthesized using a method similar to that of polymerization example 1, but with the following differences: 1) 42g of SEED, 60.5g of nucleating agent P22 and 300g of sodium lignite were replaced with 42g of stabilizer TFB117 and 36.3g of nucleating agent talc; 2) after gradually reducing the pressure to atmospheric pressure in the reactor, the pressure was reduced to a vacuum of -0.08 to -0.02 MPa, and the reaction was carried out for 15 minutes to obtain polyamide 66 resin with a relative viscosity of 3.1.

[0107] Condensation example 1

[0108] The polyamide 66 resin (viscosity 3.2) obtained from polymerization example 2 was introduced into a solid-phase polycondensation reactor. The gas in the reactor was replaced with nitrogen, and the temperature of the reactor was raised to 190°C and maintained for 3 hours. Then, the temperature was lowered to 60°C before discharge. Throughout the heating and cooling process, nitrogen was continuously introduced, and venting was intermittent. Venting was performed when the gauge pressure reached 50 kPa, and stopped when the gauge pressure reached 10 kPa. Venting was repeated once the gauge pressure returned to 50 kPa. This process was repeated until a polyamide 66 resin with a viscosity of 4.0 was obtained.

[0109] Condensation example 2

[0110] The polyamide 66 resin (viscosity 3.2) obtained from polymerization example 2 was introduced into a solid-phase polycondensation reactor. The gas in the reactor was replaced with nitrogen, and the temperature of the reactor was raised to 230°C and maintained for 5 hours. Then, the temperature was lowered to 60°C before discharge. Throughout the entire heating and cooling process, nitrogen was continuously introduced and vented, maintaining the gauge pressure at 20 kPa. Finally, polyamide 66 resin with a viscosity of 6.2 was obtained.

[0111] Condensation example 3

[0112] The polyamide 66 resin (viscosity 2.7) obtained in polymerization example 3 was introduced into a solid-phase polycondensation reactor. The gas in the reactor was replaced with nitrogen, and the temperature of the reactor was raised to 220°C and maintained for 4 hours. Then, the temperature was lowered to 60°C before discharge. Throughout the heating and cooling process, nitrogen was intermittently introduced and vented. Nitrogen was introduced until the gauge pressure reached 60 kPa, and after a period of time, the gas was vented until the gauge pressure reached 5 kPa. Then, nitrogen was immediately introduced until the gauge pressure reached 60 kPa, and this process was repeated. Finally, polyamide 66 resin with a viscosity of 5.2 was obtained.

[0113] Condensation example 4

[0114] The polyamide 66 resin (viscosity 2.4) obtained in polymerization example 4 was introduced into a solid-phase polycondensation reactor. The gas in the reactor was replaced with nitrogen, and the temperature of the reactor was raised to 210°C and maintained for 6 hours. Then, the temperature was lowered to 60°C before discharge. Throughout the heating and cooling process, nitrogen was intermittently introduced while venting was continuous. When the gauge pressure reached 10 kPa, nitrogen was introduced to raise the pressure to 40 kPa. Once the gauge pressure slowly decreased to 10 kPa, the nitrogen introduction process was repeated. Finally, a polyamide 66 resin with a viscosity of 4.5 was obtained.

[0115] Condensation example 5

[0116] The polyamide 66 resin (viscosity 3.1) obtained in polymerization example 5 was introduced into a solid-phase polycondensation reactor. The gas in the solid-phase polycondensation reactor was replaced with nitrogen, and the temperature of the solid-phase polycondensation reactor was raised to 210°C and maintained for 1 hour, then cooled to 60°C and discharged. Throughout the entire process from heating to cooling, the vacuum degree in the reactor was maintained at <200 Pa. Finally, polyamide 66 resin with a viscosity of 3.6 was obtained.

[0117] Condensation example 6

[0118] The polyamide 66 resin (viscosity 2.7) obtained in polymerization example 3 was introduced into a solid-phase polycondensation reactor. The gas in the reactor was replaced with nitrogen, and the temperature of the reactor was raised to 220°C and maintained for 7 hours. Then, the temperature was lowered to 60°C before discharge. Throughout the heating and cooling process, nitrogen was intermittently introduced and vented. Nitrogen was introduced until the gauge pressure reached 60 kPa, and after a period of time, the gas was vented until the gauge pressure reached 5 kPa. Then, nitrogen was immediately introduced until the gauge pressure reached 60 kPa, and this process was repeated. Finally, polyamide 66 resin with a viscosity of 6.7 was obtained.

[0119] Condensation example 7

[0120] The polyamide 66 resin (viscosity 3.1) obtained in polymerization example 5 was introduced into a solid-phase polycondensation reactor. The gas in the solid-phase polycondensation reactor was replaced with nitrogen, and the temperature of the solid-phase polycondensation reactor was raised to 210°C and maintained for 0.8 h, then cooled to 60°C and discharged. Throughout the entire process from heating to cooling, the vacuum degree in the reactor was maintained at <200 Pa. Finally, polyamide 66 resin with a viscosity of 3.4 was obtained.

[0121] Example 1

[0122] Polyamide 66 resin (viscosity 1.8) from polymerization example 1, polyamide 66 resin (viscosity 3.2) from polymerization example 2, polyamide resin (viscosity 4.0) from condensation example 1, and polyamide resin (viscosity 6.2) from condensation example 2 were dry-mixed in proportions of 2 parts by mass, 10 parts by mass, 30 parts by mass, and 58 parts by mass, respectively, to obtain polyamide resin composition 1.

[0123] Example 2

[0124] Polyamide 66 resin (viscosity 2.7) from polymerization example 3 and polyamide resin (viscosity 5.2) from condensation example 3 were dry-mixed at a mass ratio of 2:8 to obtain polyamide resin composition 2.

[0125] Example 3

[0126] Polyamide 66 resin (viscosity 2.4) from polymerization example 4 and polyamide resin (viscosity 4.5) from condensation example 4 were dry-mixed at a mass ratio of 5:95 to obtain polyamide resin composition 3.

[0127] Example 4

[0128] Polyamide 66 resin (viscosity 3.1) from polymerization example 5 and polyamide resin (viscosity 3.6) from condensation example 5 were dry-mixed at a mass ratio of 3:7 to obtain polyamide resin composition 4.

[0129] Example 5

[0130] Polyamide 66 resin (viscosity 2.7) from polymerization example 3 and polyamide resin (viscosity 6.7) from condensation example 6 were dry-mixed at a mass ratio of 2:8 to obtain polyamide resin composition 5.

[0131] Comparative Example 1

[0132] Polyamide 66 resin IIc was prepared using the polymerization method of Example 3, but the difference was that the nucleating agent 6T / 66 copolymer powder was not added, and the relative viscosity of the polyamide 66 resin IIc obtained by polymerization was 2.7.

[0133] Polyamide 66 resin IVc was prepared using the method of solidification example 3, except that the raw material was changed from the polyamide 66 resin (viscosity 2.7) obtained in polymerization example 3 to the polyamide 66 resin IIc in this comparative example, and a polyamide 66 resin IVc with a viscosity of 5.2 was obtained.

[0134] Polyamide 66 resin IIc and polyamide 66 resin IVc were dry-mixed at a mass ratio of 2:8 to obtain polyamide resin composition 6.

[0135] Comparative Example 2

[0136] Polyamide 66 resin (viscosity 3.4) from solidification example 7 and polyamide resin (viscosity 3.6) from solidification example 5 were dry-mixed at a mass ratio of 3:7 to obtain polyamide resin composition 7.

[0137] Comparative Example 3

[0138] Polyamide 66 resin (viscosity 1.8) from polymerization example 1 and polyamide resin (viscosity 6.2) from condensation example 2 were dry-mixed in a ratio of 12 parts by mass and 88 parts by mass to obtain polyamide resin composition 8.

[0139] The values ​​of A and B in each embodiment and comparative example are shown in Table 1.

[0140] Table 1

[0141] Application Example 1

[0142] The polyamide resin composition 1 obtained in Example 1 was dried in a hot air dryer at 100°C for 4 hours, and its melt index was measured to be 47.3 g / 10 min. The dried resin composition was added to an injection molding machine at a melt temperature of 300°C and a mold temperature of 60°C. After injection molding and a 60-minute water boiling conditioning process, WJ8-I9 type insulating track gauge block was obtained. The injection cycle per mold required to achieve normal demolding and obtain a normal-looking part is 72 seconds.

[0143] Six WJ8-I9 type insulated gauge block samples were randomly selected and longitudinally cut along the thickest part of the component; none of them had shrinkage cavities inside. Six WJ8-I9 type insulated gauge block samples were also randomly selected, and impact toughness tests were conducted according to standard TB / T 3570. All six randomly selected samples showed no damage after impact, and the test was qualified. The WJ8-I9 type insulated gauge block from Example 1 was assembled onto a WJ-8 type railway fastener, and fatigue tests were conducted according to the requirements of TB / T 3396.4. After 3×10⁻⁶ cycles... 6 After several load cycles, the product showed no damage. This indicates that the parts made from the polyamide composition of Example 1 have good toughness and fatigue resistance.

[0144] Application Example 2

[0145] The polyamide resin composition 2 obtained in Example 2 was dried in a hot air dryer at 100°C for 4 hours, and its melt index was measured to be 18.2 g / 10 min. Under the same conditions, the melt index of the polyamide resin with a viscosity of 5.2 used in Example 2 was 5.3 g / 10 min. This indicates that the addition of a relatively low viscosity component is beneficial to the flowability of high viscosity polyamide resin.

[0146] The dried resin composition 2 is added to the injection molding machine. The melt temperature is 300℃ and the mold temperature is 60℃. After injection molding and a 60-minute boiling and humidification process, the baffle seat product is obtained. The injection cycle per mold required to achieve normal demolding and obtain normal parts with the same appearance is 81s.

[0147] Six baffle seats were randomly selected and longitudinally cut along the thickest part of the part; none of them had shrinkage cavities inside. Six baffle seats were then randomly selected again, and impact toughness tests were conducted according to standard TB / T 1495. All six randomly selected samples showed no damage after impact, and the test was passed. The baffle seats of Example 2 were assembled onto the elastic bar type I railway fastener, and fatigue tests were conducted according to the requirements of TB / T 3519. After 3×10⁻⁶ cycles… 6 After several load cycles, the product showed no damage. This indicates that the parts made from the polyamide composition of Example 2 have good toughness and fatigue resistance.

[0148] Application Comparative Example 1

[0149] The polyamide resin with a viscosity of 6.2 from the shrinkage example 2 was used, and its melt index was measured to be 20.5 g / 10min. The WJ8-I9 type insulating gauge block of this comparative example was prepared using a method similar to that of application example 1. The injection cycle per mold required to achieve normal demolding and obtain a normal part with the same appearance was 101s.

[0150] Six WJ8-I9 type insulated gauge block samples were randomly selected and longitudinally cut along the thickest part of the component. Two of the samples had internal shrinkage cavities. Due to the internal shrinkage cavities, the mechanical properties and performance stability of the components could not be guaranteed, therefore impact toughness and fatigue performance tests were not performed.

[0151] This example, compared with Application Example 1, illustrates the necessity of a relatively low-viscosity component in a polyamide resin composition.

[0152] Application Comparative Example 2

[0153] The polyamide resin composition 6 from Comparative Example 1 was taken, and its melt index was measured to be 18.3 g / 10 min. The baffle seat product of this comparative example was prepared using a method similar to that of Application Example 2. The injection cycle per mold required to achieve normal demolding and obtain a normal part with the same appearance was 119 s.

[0154] Six baffle seat samples were randomly selected and longitudinally cut along the thickest part of the part. Three of them had shrinkage cavities inside. Due to the internal shrinkage cavities, the mechanical properties and service performance stability of the part could not be guaranteed, therefore impact toughness and fatigue performance tests were not performed.

[0155] This example, compared with Application Example 2, illustrates the necessity of adding additives to polyamide resin compositions.

[0156] Application Comparative Example 3

[0157] The polyamide resins or polyamide resin compositions obtained from polymerization example 5, solidification example 5, solidification example 7, example 4, and comparative example 2 were dried and their melt flow index was measured. The results are shown in Table 2. The melt flow index of the polyamide resin composition of example 4 was increased by 9.4 g / 10 min relative to its high-viscosity component, while the melt flow index of the polyamide resin composition of comparative example 2 was only increased by 1.4 g / 10 min relative to its high-viscosity component. This indicates that when the viscosities of the two polyamide resins in the composition are too close, the effect on improving the flowability of the high-viscosity component is poor.

[0158] Table 2: Melt index and variation of polyamide resins (compositions) with different components (unit: g / 10min)

[0159] Application Comparative Example 4

[0160] The polyamide resin composition 8 from Comparative Example 3 was taken, and its melt index was measured to be 31.4 g / 10min. The WJ8-I9 type insulating gauge block of this comparative example was prepared using a method similar to that of Application Example 1. The injection cycle per mold required to achieve normal demolding and obtain a part with the same appearance was 85s. If the holding pressure time was reduced, some areas of the part showed deformation during demolding, indicating that the low-viscosity and high-viscosity components were not sufficiently mixed due to their large difference, resulting in some areas being dominated by the high-viscosity resin and exhibiting uneven crystallization and curing speeds.

[0161] Six WJ8-I9 type insulated track gauge block samples were randomly selected and longitudinally cut along the thickest part of the component. One of the blocks had a shrinkage cavity inside; the other six blocks were retested and no shrinkage cavities were found. The occasional shrinkage cavity phenomenon is also caused by the high and low viscosity components not being fully interleaved and mixed.

[0162] Six additional baffle seats were randomly selected and subjected to impact toughness testing according to standard TB / T 1495. Three of the six randomly selected samples broke after impact. The low viscosity component had excessively low viscosity, which affected the overall mechanical properties of the resin composition.

[0163] This example, compared with Application Example 1, illustrates that the viscosity difference between the relatively low-viscosity component and the high-viscosity component in a polyamide resin composition should not be too large.

Claims

1. A polyamide resin composition, characterized in that, The polyamide resin composition comprises a first component, a second component, and additives; The first component is selected from one or both of polyamide resin I and polyamide resin II; The second component is selected from one or both of polyamide resin III and polyamide resin IV; The relative viscosity value of polyamide resin I is denoted as a1, the relative viscosity value of polyamide resin II is denoted as a2, the relative viscosity value of polyamide resin III is denoted as b1, and the relative viscosity value of polyamide resin IV is denoted as b2. a1, a2, b1, and b2 satisfy the following: a1 is 1.8~2.8; a2 is 2.7~3.5; b1 is 3.4~4.6; b2 is 4.5~6.8; a1 <a2<b1<b2。 2. The polyamide resin composition according to claim 1, characterized in that, Polyamide resin I, polyamide resin II, polyamide resin III and polyamide resin IV are each independently selected from one or more of polyamide 66 resin, polyamide 56 resin, polyamide 66 / 6T copolymer resin, polyamide MXD6 resin, polyamide 610 resin and polyamide 612 resin; preferably, polyamide resin I, polyamide resin II, polyamide resin III and polyamide resin IV are all polyamide 66 resin.

3. The polyamide resin composition according to claim 1, characterized in that, The first component has a mass fraction of 2% to 40% in the polyamide resin composition, the second component has a mass fraction of 55% to 97.9% in the polyamide resin composition, and the additive has a mass fraction of 0.01% to 5% in the polyamide resin composition.

4. The polyamide resin composition according to claim 1, characterized in that, The mass fraction of polyamide resin I in the polyamide resin composition is denoted as x1, the mass fraction of polyamide resin II in the polyamide resin composition is denoted as x2, and the average viscosity of the first component is denoted as A, where A = (a1x1 + a2x2) / (x1 + x2); the mass fraction of polyamide resin III in the polyamide resin composition is denoted as y1, the mass fraction of polyamide resin IV in the polyamide resin composition is denoted as y2, and the average viscosity of the second component is denoted as B, where B = (b1y1 + b2y2) / (y1 + y2). The values ​​of A and B satisfy the following relationship: 0.5≤BA≤4; preferably, the values ​​of A and B also satisfy the following relationship: (BA) / A≥0.

15.

5. The polyamide resin composition according to claim 1, characterized in that, The first component is polyamide resin I and polyamide resin II, and the second component is polyamide resin III and polyamide resin IV; or, The first component is polyamide resin I and polyamide resin II, and the second component is polyamide resin III; or, The first component is polyamide resin I and polyamide resin II, and the second component is polyamide resin IV; or, The first component is polyamide resin I, and the second component is polyamide resin III and polyamide resin IV; or, The first component is polyamide resin II, and the second component is polyamide resin III and polyamide resin IV; or, The first component is polyamide resin I, and the second component is polyamide resin III; or, The first component is polyamide resin I, and the second component is polyamide resin IV; or, The first component is polyamide resin II, and the second component is polyamide resin IV; or, The first component is polyamide resin II, and the second component is polyamide resin III; Preferably, the first component is polyamide resin I and polyamide resin II, and the second component is polyamide resin III and polyamide resin IV; or, the first component is polyamide resin I and the second component is polyamide resin III; or, the first component is polyamide resin II and the second component is polyamide resin IV; or, the first component is polyamide resin II and the second component is polyamide resin III. More preferably, the first component is polyamide resin I and the second component is polyamide resin III; or, the first component is polyamide resin II and the second component is polyamide resin IV.

6. The polyamide resin composition according to claim 1, characterized in that, The additives include one or more of the following: heat stabilizers, UV absorbers, lubricants, nucleating agents, toughening agents, plasticizers, and colorants. Preferably, the additive comprises one or more of a heat stabilizer, a lubricant, and a nucleating agent; more preferably, the additive comprises a heat stabilizer, a lubricant, and a nucleating agent. Preferably, The heat stabilizer is selected from one or more of hindered phenolic antioxidants, amine antioxidants, phosphorus antioxidants, thioether antioxidants and metal passivators; more preferably, it is selected from one or more of N,N'-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,3-phenylenediamide, sodium hypophosphite monohydrate and sodium phosphite. The lubricant is selected from one or more of lignite acid, sodium lignite, calcium lignite, lignite ester, ethylene bis-stearamide, erucamide, tungsten disulfide, molybdenum disulfide, graphite and barium sulfate; The nucleating agent is selected from one or more of talc, silica, phthalate whiskers, magnesium oxide, aluminum oxide, zinc oxide, sodium hypophosphite, silicates, acetates, and powdered polymers with a melting point higher than 300°C; more preferably, the powdered polymer with a melting point higher than 300°C is selected from one or more of polyamide 6T, polyamide 9T, polyamide 10T, polyamide 12T, and their copolymers.

7. A method for preparing the polyamide resin composition according to any one of claims 1-6, characterized in that, The method includes: mixing a first material and a second material by dry mixing to obtain a polyamide resin composition; the first material includes one or more of polyamide resin I, polyamide resin II and additives, and the second material includes one or more of polyamide resin III, polyamide resin IV and additives.

8. The method as described in claim 7, characterized in that, Polyamide resin I is prepared by salt solution polymerization, or by salt solution polymerization followed by solid-state polycondensation. Polyamide resin II is prepared by salt solution polymerization, or by salt solution polymerization followed by solid-state polycondensation. Polyamide resin III is prepared by salt solution polymerization, or by salt solution polymerization followed by solid-state polycondensation. Polyamide resin IV is prepared by solid-state polycondensation, or by polymerization in salt solution followed by solid-state polycondensation. Preferably, the additive is added during salt solution polymerization or solid-phase polycondensation, and more preferably during salt solution polymerization.

9. A component, characterized in that, The component comprises the polyamide resin composition of any one of claims 1-6 or the polyamide resin composition prepared by the method of claim 7 or 8; preferably, the component is a railway fastener part, gear, bearing or engine cover.

10. Use of the polyamide resin composition according to any one of claims 1-6 or the polyamide resin composition prepared by the method of claim 7 or 8 in the manufacture of components for railway fasteners.

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