Polyamide resins, compositions, and their use in engineering plastics

Abstract

The present disclosure provides a polyamide resin, a composition, and its use in engineering plastics. The polyamide resin comprises a diamine structural unit and a dicarboxylic acid structural unit, and has a water extractable content of 0.7% by weight or less and a hypophosphite content of 10 ppm to 500 ppm in terms of P. The preparation method of the polyamide resin according to the present disclosure is simple, easy to control process parameters, does not require large-scale equipment, and is convenient for mass production. The polyamide resin composition has the advantages of a short molding cycle, a fast crystallization rate, good appearance quality, and good corrosion resistance, and can be used in acidic environments such as outer packaging and containers for acidic foods.

Description

Detailed Description of the Invention

[0001] 〔Technical Field〕 The present disclosure belongs to the field of polymer materials, and specifically relates to polyamide resins, their preparation methods, compositions, and fiber products.

[0002] 〔Background Art〕 Polyamide has been widely used and attracted attention as a material for clothing materials, industrial materials, fibers, or materials for general engineering plastics due to its excellent properties and ease of melt molding. Polyamide 5X is a linear long-chain polymer synthesized from bio-based pentanediamine and a series of dicarboxylic acids. Since amide bonds are likely to form hydrogen bonds, polyamide 5X fibers have high strength and excellent moisture absorption. During the polymerization of polyamide 5X, due to the occurrence of cyclization reactions, the polymer macromolecular chains are cleaved into two segments during the intramolecular amide group exchange reaction, or linear low-molecular substances directly undergo dehydration reactions to produce low-molecular polymers. Generally, water extracts are low-molecular polymers ranging from monomers to decamers, such as dimers and trimers, and include linear and cyclic structures. The presence of these water extracts may affect the performance and applications of the resin.

[0003] For example, in the case of ultra-thin articles (thickness 0.3 mm to 0.4 mm) such as relays and capacitors, since these articles are very thin, they require injection molding at high temperatures and high speeds. Under such conditions, the heating and shearing of the material itself are significantly higher than other injection molding conditions, and the generation of mold fouling is particularly prominent, which requires regular cleaning of the mold surface during continuous processing, resulting in a decrease in production efficiency. Furthermore, in severe cases, problems such as white spots may occur on the surface of the articles, which may seriously affect the appearance of the products.

[0004] 〔Summary of the Invention〕 To address the deficiencies of the prior art technologies and products, one objective of the present disclosure is to provide polyamide resins.

[0005] The polyamide resin contains diamine structural units and dicarboxylic acid structural units, has a water extract content of 0.7% by weight or less, and a hypophosphate content of 10 ppm to 500 ppm in terms of phosphorus.

[0006] According to some embodiments of the present disclosure, the water extract content is 0.6% by weight or less, preferably 0.5% by weight or less. The water extract is mainly an oligomer produced from monomer raw materials during the polymerization process, for example, from linear or cyclic monomers to decamers.

[0007] In some preferred embodiments of this disclosure, when the water extract content is within the range defined above, the resistance to yellowing of the polyamide resin and the resin composition containing it, as described later, is improved.

[0008] In some preferred embodiments of this disclosure, when the water extract content is within the range defined above, the mechanical properties of the polyamide resin and the resin composition containing it, as described later, are improved.

[0009] In some preferred embodiments of this disclosure, when the water extract content is within the range defined above, the polyamide resin and the resin composition containing it, as described later, have good appearance quality and do not exhibit any apparent precipitation.

[0010] In some preferred embodiments of this disclosure, when the water extract content is within the range defined above, the acid corrosion resistance of the polyamide resin and the resin composition containing it, as described later, is improved.

[0011] In some preferred embodiments of this disclosure, the polyamide resin has a water extract content of 0.05% by weight or more, preferably 0.1% by weight or more, more preferably 0.2% by weight or more, and even more preferably 0.25% by weight or more. If the water extract content falls below the range defined above, the performance of the polyamide resin and the resin composition containing it, as described later, will be reduced to some extent.

[0012] The water extract content of the polyamide resin is the percentage of the mass of components that can be extracted into water after the extraction treatment relative to the mass of the polyamide resin before the extraction treatment, when the polyamide resin is heated in deionized water for extraction (for example, when the polyamide resin is extracted in water at 97°C to 100°C for 24 hours).

[0013] Water extract content (%) = [(Mass of polyamide resin before water extraction (m1) - Mass of polyamide resin after water extraction (m2)) / Mass of polyamide resin before water extraction (m1)] × 100%.

[0014] The extraction conditions include, for example, extracting the polyamide resin for 24 hours using water at 97°C to 100°C, with a mass ratio of polyamide resin to water of 1:48 to 51, for example, 1:50.

[0015] Furthermore, the method for measuring the water extract content is as follows: The polyamide resin sample is dried in an air-drying oven at 130°C for 7 hours, then sealed in an aluminum plastic bag and cooled in a drying oven. Subsequently, approximately 2 g of the polyamide resin sample is weighed and its actual mass (m1) is recorded; the polyamide resin sample is placed in a 250 mL round-bottom flask, 100 mL of deionized water is added, and the resulting mixture is refluxed at 97°C to 100°C for 24 hours to extract the polyamide resin sample with water. After that, the polyamide resin sample is removed from the water, washed three times with deionized water, and then dried in an air-drying oven at 130°C for 7 hours; then the polyamide resin sample is transferred to a pre-weighed aluminum plastic bag, sealed in the aluminum plastic bag, and cooled in a dryer. The total weight of the aluminum plastic bag and the polyamide sample, as well as the weight of the aluminum plastic bag, are weighed, and the weight of the latter is subtracted from the former to obtain the weight of the polyamide sample after water extraction (m2). The water extract content is calculated from the difference in weight of the polyamide sample before and after water extraction. Water extract content (%)=[(m1-m2) / m1]×100%.

[0016] Furthermore, when measuring the water extract content of a polyamide resin molten material, the molten material is introduced into a sealed container, cooled, sampled, and measured according to the method described above.

[0017] According to some embodiments of this disclosure, the aqueous extract has a number-average molecular weight of 200 g / mol to 2,000 g / mol, as determined by the GPC method.

[0018] According to some embodiments of this disclosure, the aqueous extract comprises one or two of the following structures: [ka] Here, n1 and n2 are independently selected from integers 1 to 8, preferably n1 and n2 are independently selected from integers 1 to 6, more preferably n1 and n2 are independently selected from integers 1 to 5, even more preferably n1 is 2, 3 or 4, n2 is 2, 3, 4 or 5, m1 is 4, and m2 is 4.

[0019] In preferred embodiments of this disclosure, the hypophosphate is included in a content of 10 ppm to 300 ppm, preferably 10 ppm to 200 ppm, in terms of P.

[0020] In preferred embodiments of the present disclosure, the hypophosphate comprises alkali metal hypophosphates and alkaline earth metal hypophosphates, and preferably comprises one of sodium hypophosphate, potassium hypophosphate, calcium hypophosphate, and magnesium hypophosphate, or a combination of two or more of the above.

[0021] According to some embodiments of the present disclosure, the pentanediamine structural units in the polyamide resin can be obtained from chemically derived pentanediamine or biologically derived pentanediamine, preferably biologically derived 1,5-pentanediamine.

[0022] In a preferred embodiment of the present disclosure, 90 mol% or more of the dicarboxylic acid structural units are derived from adipic acid, and 90 mol% or more of the diamine structural units are derived from 1,5-pentanediamine.

[0023] In a preferred embodiment of the present disclosure, 95 mol% or more, preferably 97 mol% or more of the diamine structural units in the polyamide resin are derived from 1,5-pentanediamine.

[0024] Furthermore, the diamine structural units in the polyamide resin may further include one or more structural units derived from butanediamine, hexanediamine, decanediamine, and dodecanediamine.

[0025] In a preferred embodiment of the present disclosure, 95 mol% or more, preferably 97 mol% or more of the dicarboxylic acid structural units in the polyamide resin are derived from adipic acid.

[0026] According to some embodiments of the present disclosure, the dicarboxylic acid structural units in the polyamide resin may further include one or more structural units derived from succinic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, decanedioic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, tetradecanedioic acid, pentadecanedioic acid, hexadecanedioic acid, heptadecanedioic acid, octadecanedioic acid, terephthalic acid, isophthalic acid, and phthalic acid.

[0027] In a preferred embodiment of the present disclosure, the content of the polyamide (main polymer) composed of the diamine structural units and the dicarboxylic acid structural units in the polyamide resin is 90% by weight or more, preferably 95% by weight or more, more preferably 97% by weight or more, and still more preferably 99% by weight or more. The diamine structural units and the dicarboxylic acid structural units are defined as above.

[0028] According to some embodiments of the present disclosure, the polyamide resin contains an additive in addition to the hypophosphite.

[0029] The additive includes, but is not limited to, any one of a terminal blocking agent, a nucleating agent, an antioxidant, an antifoaming agent, and a fluidity improver, or a combination of two or more thereof. The terminal blocking agent includes lauric acid, stearic acid, benzoic acid, and acetic acid.

[0030] In some preferred embodiments of the present disclosure, the additive in the polyamide resin is present in a content of 10% by weight or less, preferably 5% by weight or less, more preferably 3% by weight or less, and still more preferably 1% by weight or less.

[0031] According to some embodiments of the present disclosure, the polyamide resin is a polyamide 56 resin. The polyamide 56 resin has a polyamide 56 content of 90% by weight or more, further 95% by weight or more, further 97% by weight or more, and further 99% by weight or more.

[0032] In a preferred embodiment of the present disclosure, the polyamide resin has a relative viscosity of 1.8 to 4.0, preferably 2.2 to 3.5, and more preferably 2.4 to 3.3.

[0033] In a preferred embodiment of the present disclosure, the polyamide resin has a yellowness of less than 7, preferably less than 5, and more preferably less than 4.2.

[0034] The second object of the present disclosure is to provide a method for preparing the polyamide resin.

[0035] According to some embodiments of the present disclosure, the method includes the following steps: S1. Prepare a nylon salt solution in an inert gas atmosphere; S2. Heat the nylon salt solution to increase the pressure of the nylon salt solution reaction system to 0.5 to 2.5 MPa, maintain the pressure by degassing for 0.5 to 4 hours, then reduce the pressure to reduce the pressure in the reaction system to 0 to 0.7 MPa (gauge pressure), and then evacuate the reaction system to a vacuum degree of -0.01 to -0.08 MPa to obtain a polyamide melt; and S3. The molten polyamide is discharged and formed into strand pellets to obtain polyamide chips.

[0036] Unless otherwise stated or unless otherwise clearly contradicted, the pressures referred to in this disclosure refer to gauge pressures. In this disclosure, the nylon salts and polyamide salts can be used interchangeably.

[0037] In step S1, 1,5-pentanediamine and a dicarboxylic acid are used in a molar ratio of (1-1.1):1 to prepare the nylon salt solution.

[0038] In step S2, the temperature of the reaction system is 232°C to 260°C at the end of pressure maintenance.

[0039] In step S2, the temperature of the reaction system is 240°C to 295°C at the end of the reduced pressure, and further 243°C to 288°C.

[0040] In step S2, the temperature of the reaction system after vacuuming is 250°C to 290°C, and further 252°C to 285°C.

[0041] In step S2, the vacuum level is maintained for a period of 11 to 75 minutes after vacuuming.

[0042] In step S3, the strand pelletization is carried out in water at a water temperature of 15°C to 50°C in order to obtain polyamide chips or polyamide pellets.

[0043] According to some embodiments of this disclosure, the method further includes the following steps: S4, after mixing the polyamide chips with water in the reactor to obtain a mixture, the air in the reactor is replaced with an inert gas; and S5. The mixture is heated and filtered in an inert gas atmosphere, and the polyamide tips are rinsed and / or dried to obtain the polyamide resin.

[0044] In step S4, the reactor can be formed in a closed environment. In step S4, the reactor may be, for example, a continuous extraction column or a batch reactor.

[0045] Preferably, in step S4, the air in the reactor can be replaced using a vacuum pump to create a vacuum in the reactor, and then the reactor can be refilled with nitrogen gas or an inert gas. The above operation for replacing the air in the reactor can be repeated two or more times.

[0046] In step S4, the water is deionized water, and further deionized water that has undergone a deoxygenation treatment, where the deoxygenation treatment may be one of thermal deoxygenation, ultrasonic deoxygenation, vacuum deoxygenation, chemical deoxygenation, decomposition deoxygenation, or any other deoxygenation method, or a combination of two or more thereof. In some preferred embodiments, after the deoxygenation treatment, the deionized water has a dissolved oxygen content of 0.5 mg / L or less, and further 0.1 mg / L or less.

[0047] In step S4, the water is used in an amount of 1 to 12 times, preferably 2 times or more, the mass of the polyamide chip, for example, 1 to 12 times, 1 to 10 times, 2 to 10 times, 2 to 6 times, 1.5 times, 2.3 times, 2.5 times, 3 times, 5 times, or 8 times.

[0048] In steps S1, S4, and S5, the inert gas includes one or two of the following: argon gas and helium gas, and more preferably high-purity argon gas and high-purity helium gas.

[0049] According to some embodiments of the present disclosure, the air replacement in step S4 is carried out as follows: the reactor is evacuated to a vacuum of -0.1 MPa to -0.001 MPa (gauge pressure), held for 5 to 20 minutes, then refilled with nitrogen gas or an inert gas, and more preferably the air replacement operation is repeated 5 to 15 times, more preferably 8 to 10 times.

[0050] According to some embodiments of the present disclosure, in step S5, the mixture is heated for 4 to 50 hours, preferably 8 to 45 hours.

[0051] According to some embodiments of the present disclosure, in step S5, the mixture is heated to a temperature of 80°C to 140°C, preferably 85°C to 120°C.

[0052] According to some embodiments of this disclosure, the rinsing in step S5 is carried out with hot water at a temperature of 50°C to 100°C.

[0053] According to some embodiments of the present disclosure, the drying in step S5 is carried out by one or more of the following: vacuum drying, freeze-drying, airflow drying, microwave drying, infrared drying, and high-frequency drying.

[0054] A third object of this disclosure is to provide a resin composition comprising the following components in parts by weight: 100 parts polyamide resin and 10 to 70 parts glass fiber.

[0055] In preferred embodiments of the present disclosure, the glass fibers have a length-to-diameter ratio of (2-800):1, and further (200-650):1.

[0056] In a preferred embodiment of the present disclosure, the glass fiber has a length of 3 mm to 12 mm, preferably 3 mm to 8 mm.

[0057] In some preferred embodiments of the present disclosure, the mechanical properties of the resin composition are improved if the glass fibers have parameters within the range defined above.

[0058] Furthermore, the composition may contain one of the following, or a combination of two or more of the following: antioxidants, nucleating agents, lubricants, flame retardants, coupling agents, heat stabilizers, light stabilizers, antistatic agents, ultraviolet absorbers, and colorants.

[0059] Furthermore, the antioxidant is present in an amount of 0.02 to 2 parts by weight, and preferably includes one of the following: a hindered phenol antioxidant, a hindered amine antioxidant, and a phosphite antioxidant, for example, one of the following: antioxidant 168, antioxidant 1098, antioxidant 1010, and antioxidant S9228, or a combination of two or more of the above.

[0060] In a preferred embodiment of this disclosure, in an acid resistance test, precipitates (floating fibers) are absent or present in small quantities on the surface of the resin composition.

[0061] In preferred embodiments of the present disclosure, there is no obvious mold contamination or only a small amount of mold contamination after injection molding of the resin composition.

[0062] In preferred embodiments of this disclosure, the polyamide resin is defined as described above.

[0063] A method for preparing a polyamide resin composition, comprising the following steps: The aforementioned components are added to a twin-screw extruder and mixed, then extruded from the twin-screw extruder, cooled, and pelletized to obtain a polyamide composition.

[0064] Furthermore, during the mixing process, the glass fibers are supplied from the side feed port of the twin-screw extruder.

[0065] Furthermore, the components are mixed and melted in the twin-screw extruder at a temperature of 210°C to 290°C.

[0066] In embodiments of the present disclosure, during mixing, the twin-screw extruder employs a 7-zone heating mode, where the temperature of zone 1 is 210°C to 250°C, and / or the temperature of zone 2 is 210°C to 250°C, and / or the temperature of zone 3 is 240°C to 260°C, the temperature of zone 4 is 260°C to 280°C, and / or the temperature of zone 5 is 270°C to 290°C, and / or the temperature of zone 6 is 270°C to 290°C, and / or the temperature of zone 7 is 255°C to 285°C; where the direction from zone 1 to zone 7 is the direction from the feed port to the die.

[0067] The die temperature of the twin-screw extruder is 260°C to 275°C.

[0068] The screw speed of the twin-screw extruder is 350 r / min to 500 r / min.

[0069] The twin-screw extruder has a D / L ratio (diameter to length ratio) of 1:(30~50), preferably 1:40.

[0070] A fourth object of this disclosure is to provide the use of the aforementioned polyamide resins or compositions in engineering plastics.

[0071] This disclosure has at least the following advantages over the prior art: 1. The method for preparing polyamide resin according to this disclosure is simple, process parameters are easy to control, large-scale equipment is not required, and mass production is convenient.

[0072] 2. The polyamide resin composition has the advantages of a short molding cycle, a fast crystallization rate, less mold contamination during injection molding, and good appearance quality. Therefore, the polyamide resin composition can be applied to devices in the electrical and electronic fields.

[0073] 3. The polyamide resin composition has the advantage of acid corrosion resistance and can be used in acidic environments, such as for outer packaging and containers of acidic foods.

[0074] [Detailed explanation] To further clarify the purpose, technical solutions, and benefits of this disclosure, the technical solutions in the embodiments of this disclosure are described below clearly and completely in conjunction with the embodiments of this disclosure. Clearly, the embodiments described are not all embodiments, but only a portion of the embodiments of this disclosure. All other embodiments that can be achieved by those skilled in the art without creative work based on the embodiments of this disclosure fall within the scope of this disclosure.

[0075] 1. Method for measuring relative viscosity ηr Concentrated sulfuric acid method using a Ubberohde viscometer: Accurately weigh 0.5 ± 0.0002 g of a dry polyamide resin sample, dissolve it in 50 mL of concentrated sulfuric acid (98%), and measure and record the flow time of the concentrated sulfuric acid (t0) and the flow time of the polyamide resin solution (t) in a constant temperature water bath at 25°C. Formula for calculating relative viscosity: Relative viscosity ηr = t / t0.

[0076] 2. Method for measuring the aqueous extract content of polyamide resin Each polyamide resin sample is dried in an air-drying oven at 130°C for 7 hours, then sealed in an aluminum plastic bag, cooled in a dryer, and approximately 2 g of the polyamide resin sample is accurately weighed to obtain the actual mass (m1). The weighed polyamide resin sample is placed in a 250 mL round-bottom flask, 100 mL of deionized water is added, and the resulting mixture is heated under reflux at 97°C to 100°C for 24 hours to extract the polyamide resin sample with water. Then the polyamide resin sample is removed, washed three times with deionized water, and then dried in an air-drying oven at 130°C for 7 hours. The polyamide resin sample is transferred to a pre-weighed aluminum plastic bag, sealed in the aluminum plastic bag, cooled in a dryer, and the total weight of the aluminum plastic bag and the polyamide resin sample, as well as the weight of the aluminum plastic bag, are weighed separately. The weight of the polyamide resin sample after water extraction is obtained by subtracting the latter from the former (m2). The amount of water extract is calculated from the difference in weight between the polyamide sample before and after water extraction. Water extract content (%) = [(m1-m2) / m1] × 100%.

[0077] When measuring the water extract content of a polyamide resin molten material, the molten material is introduced into a sealed container, cooled, sampled, and measured according to the method described above.

[0078] 3.Yellowness (YI) Yellowness is tested according to HG / T 3862.

[0079] 4. Crystallinity test Each polyamide resin sample is subjected to crystallinity analysis using differential scanning calorimetry (DSC): Each polyamide resin sample obtained from the examples and comparative examples is heated from room temperature to 280°C at a heating rate of 50°C / min, held at 280°C for 3 minutes, and then cooled to room temperature at a rate of 10°C / min to obtain the crystallization temperature and semi-crystallization time.

[0080] 5. Tensile strength Tensile strength is tested at a tensile speed of 50 mm / min in accordance with ISO 527-2.

[0081] 6. Bending strength The bending strength is tested at a speed of 2 mm / min according to ISO 178.

[0082] 7. Acid resistance test Each polyamide resin sample was immersed in a 10% by weight aqueous acetic acid solution at 40°C for 180 days, and the precipitates on the surface of each sample were observed and graded from 1 to 5. Here, grade 1 is the worst, as a large amount of precipitate is formed, and grade 5 is the best, as no apparent precipitate is formed.

[0083] Preparation Example 1 (1) Under nitrogen gas conditions, 1,5-pentanediamine, adipic acid, and water were uniformly mixed in a molar ratio of 1,5-pentanediamine to adipic acid of 1.08:1 to prepare a 60% by weight (where %) is the mass percentage of the nylon salt solution; a sample of the nylon salt solution was taken and diluted to a concentration of 10% by weight. The pH value at this time was 7.85.

[0084] (2) 1200 g of nylon salt solution and 500 ppm of sodium hypophosphite were added to the polymerization reactor and heated to increase the pressure in the reaction system to 2.3 MPa in 1.5 hours. The pressure was then maintained for 3 hours by degassing. At the end of the pressure holding process, the temperature of the reaction system was 245°C. The pressure in the reaction system was then reduced to 0.003 MPa (gauge pressure) in 1 hour, and the temperature of the reaction system after degassing was 273°C. The reaction system was evacuated for 32 minutes and maintained at a vacuum of -0.06 MPa. The temperature of the reaction system after evacuating was 272°C to obtain a molten polyamide 56.

[0085] (3) The molten material obtained in step (2) was discharged and strand pelletized under water cooling at a water temperature of 20°C to obtain polyamide 56 chips.

[0086] Example 1 (a) The polyamide 56 chips and deoxygenated deionized water prepared in Preparation Example 1 were added to the reactor in a mass ratio of 1:6. The air in the reactor was replaced with nitrogen gas as follows: The reactor was evacuated to a vacuum of -0.09 MPa (gauge pressure), maintained at this vacuum for 10 minutes, then refilled with nitrogen gas, and the nitrogen gas replacement was repeated 9 times.

[0087] (b) The mixture obtained was heated at 90°C for 32 hours under a nitrogen gas atmosphere, then filtered to separate the chips from the water, the obtained chips were rinsed with water at 95°C, and then vacuum dried at 105°C for 15 hours to obtain polyamide 56 resin.

[0088] Example 2 (1) Under a nitrogen gas atmosphere, 1,5-pentanediamine, adipic acid, and water were uniformly mixed in a molar ratio of 1:1 between 1,5-pentanediamine and adipic acid to prepare a 70% by weight (where %) is the mass percentage of the nylon salt solution; a sample of the nylon salt solution was taken and diluted to a concentration of 10% by weight. The pH value at this time was 7.96.

[0089] (2) 1200 g of nylon salt solution and 300 ppm of sodium hypophosphite were added to the polymerization reactor and heated to increase the pressure in the reaction system to 2.0 M in 1.5 hours. The pressure was then maintained at 2.40 MPa for 3 hours by degassing. At the end of the pressure holding process, the temperature of the reaction system was 243°C. The pressure in the reaction system was then reduced to 0.005 MPa (gauge pressure) over 1 hour, and the temperature of the reaction system after depressurization was 290°C. The reaction system was evacuated for 30 minutes and maintained at a vacuum of -0.08 MPa. The temperature of the reaction system after evacuation was 290°C to obtain a molten polyamide 56.

[0090] (3) The molten material obtained in step (2) was discharged and strand pelletized under water cooling at 20°C to obtain polyamide 56 chips.

[0091] (4) Polyamide 56 chips and deoxygenated deionized water were added to the reactor in a mass ratio of 1:6 between the chips and the deoxygenated deionized water. The air was replaced with nitrogen gas as follows: The reactor was evacuated to a vacuum of -0.07 MPa (gauge pressure), maintained at this vacuum for 10 minutes, then refilled with nitrogen gas, and the nitrogen gas replacement was repeated 10 times.

[0092] (5) Nitrogen gas was introduced into the reactor in step (4) for protection, the resulting mixture was heated at 96°C for 46 hours, then filtered to separate the chips from the water, the resulting chips were rinsed with water at 95°C, and then vacuum-dried at 105°C for 15 hours to obtain the polyamide 56 resin.

[0093] Example 3 (a) The polyamide 56 chips and deoxygenated deionized water prepared in Preparation Example 1 were added to the reactor in a mass ratio of 1:12 between the chips and the deoxygenated deionized water. The air in the reactor was replaced with nitrogen gas as follows: The reactor was evacuated to a vacuum of -0.09 MPa (gauge pressure), maintained at this vacuum for 10 minutes, then refilled with nitrogen gas, and the nitrogen gas replacement was repeated 10 times.

[0094] (b) Nitrogen gas was introduced into the reactor in step (a) for protection, the resulting mixture was heated at 95°C for 55 hours, then filtered to separate the chips from the water, the resulting chips were rinsed with hot water at 95°C, and then vacuum-dried at 105°C for 15 hours to obtain the polyamide 56 resin.

[0095] Example 4 (1) Under a nitrogen gas atmosphere, 1,5-pentanediamine, adipic acid, and water were uniformly mixed in a molar ratio of 1,5-pentanediamine to adipic acid of 1.05:1 to prepare a 60% by weight (where %) is the mass %) of the nylon salt solution; a sample of the nylon salt solution was taken and diluted to a concentration of 10% by weight. The pH value at this time was 7.98.

[0096] (2) 1200 g of nylon salt solution and 1200 ppm of sodium hypophosphite were added to the polymerization reactor and heated to increase the pressure in the reaction system to 2.0 MPa in 1.5 hours. The pressure was then maintained for 3 hours by degassing. At the end of the pressure holding process, the temperature of the reaction system was 243°C. The pressure in the reaction system was then reduced to 0.005 MPa (gauge pressure) in 1 hour, and the temperature of the reaction system after degassing was 290°C. The reaction system was evacuated for 30 minutes and maintained at a vacuum of -0.08 MPa. The temperature of the reaction system after evacuating was 290°C to obtain a molten polyamide 56.

[0097] (3) The molten material obtained in step (2) was discharged and strand pelletized under water cooling at 20°C to obtain polyamide 56 chips.

[0098] (4) The chips were vacuum-dried at 105°C for 15 hours to obtain polyamide 56 resin.

[0099] Example 5 (1) Under a nitrogen gas atmosphere, 1,5-pentanediamine, adipic acid, and water were uniformly mixed in a molar ratio of 1,5-pentanediamine to adipic acid of 1.05:1 to prepare a 60% by weight (where %) is the mass %) of the nylon salt solution; a sample of the nylon salt solution was taken and diluted to a concentration of 10% by weight. The pH value at this time was 7.98.

[0100] (2) 1200 g of nylon salt solution and 2400 ppm of sodium hypophosphite were added to the polymerization reactor and heated to increase the pressure in the reaction system to 2.0 MPa in 1.5 hours. The pressure was then maintained for 3 hours by degassing. At the end of the pressure holding process, the temperature of the reaction system was 243°C. The pressure in the reaction system was then reduced to 0.005 MPa (gauge pressure) in 1 hour, and the temperature of the reaction system after depressurization was 290°C. The reaction system was evacuated for 30 minutes and maintained at a vacuum of -0.08 MPa. The temperature of the reaction system after evacuation was 290°C to obtain a molten polyamide 56.

[0101] (3) The molten material obtained in step (2) was discharged and strand pelletized under water cooling at a water temperature of 20°C to obtain polyamide 56 chips.

[0102] (4) The chips were vacuum-dried at 105°C for 15 hours to obtain polyamide 56 resin.

[0103] Example 6 (1) Under a nitrogen gas atmosphere, 1,5-pentanediamine, adipic acid, and water were uniformly mixed in a molar ratio of 1,5-pentanediamine to adipic acid of 1.05:1 to prepare a 60% by weight (where %) is the mass %) of the nylon salt solution; a sample of the nylon salt solution was taken and diluted to a concentration of 10% by weight. The pH value at this time was 7.98.

[0104] (2) 1200 g of nylon salt solution and 85 ppm of sodium hypophosphite were added to the polymerization reactor and heated to increase the pressure in the reaction system to 2.0 MPa in 1.5 hours. The pressure was then maintained for 3 hours by degassing. At the end of the pressure holding process, the temperature of the reaction system was 243°C. The pressure in the reaction system was then reduced to 0.005 MPa (gauge pressure) in 1 hour, and the temperature of the reaction system after degassing was 290°C. The reaction system was evacuated for 30 minutes and maintained at a vacuum of -0.08 MPa. The temperature of the reaction system after evacuating was 290°C to obtain a molten polyamide 56.

[0105] (3) The molten material obtained in step (2) was discharged and strand pelletized under water cooling at a water temperature of 20°C to obtain polyamide 56 chips.

[0106] (4) The chips were vacuum-dried at 105°C for 15 hours to obtain polyamide 56 resin.

[0107] The polyamide resins obtained in Examples 1 to 6 were tested for relative viscosity, water extract content, hypophosphorous acid content (in P equivalent), crystallization temperature, semi-crystallization time, acid resistance, and yellowness. The test results are shown in Table 1.

[0108] [Table 1]

[0109] Polyamide compositions were prepared using the polyamide resins, glass fibers, and antioxidants from Examples 1 to 6 as raw materials. The formulations of these compositions are shown in Table 2.

[0110] The aforementioned composition was prepared as follows: Polyamide resin, glass fibers, and antioxidants were used as raw materials and kneaded in a twin-screw extruder. The strands extruded from the twin-screw extruder were then cooled in water as a cooling medium to a temperature below the melting point of the polyamide, and pelletized to obtain a polyamide resin composition. The twin-screw extruder employed a 7-zone heating mode, with temperatures in zones 1 through 7 being 250°C, 260°C, 260°C, 280°C, 270°C, 270°C, and 270°C consecutively. The die temperature was 260°C, the screw speed was 480 r / min, and the D / L ratio of the twin-screw extruder was 1:40.

[0111] The obtained polyamide resin composition was dried at 110°C for 5 hours, and then injection molded with a sample thickness of 3 mm under the following conditions: barrel temperature 280°C and mold surface temperature 110°C. Injection molding was performed 50 times consecutively, and mold contamination on the high-gloss surface of the mold was observed and evaluated on a 5-point scale. Here, the amount of mold contamination decreased sequentially from grade 1 to grade 5, with grade 1 being the worst due to a large amount of mold contamination and grade 5 being the best due to no obvious mold contamination. The test results of the injection molded samples are shown in Table 2.

[0112] [Table 2]

[0113] Finally, it should be noted that the embodiments described above are intended solely to illustrate, and not to limit, the technical solutions of the present disclosure. Although the present disclosure has been described in detail with reference to the embodiments described above, those skilled in the art should understand that modifications may be made to the technical solutions described in the embodiments above, or that some or all of their technical features may be replaced with equivalent substitutions, and that such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions in the embodiments of the present disclosure.

Claims

1. A polyamide resin comprising diamine structural units and dicarboxylic acid structural units, having a water extract content of 0.5% by weight or less, and a hypophosphate content of 10 ppm to 200 ppm in terms of P, wherein 90 mol% or more of the dicarboxylic acid structural units are derived from adipic acid, and 90 mol% or more of the diamine structural units are derived from 1,5-pentanediamine.

2. Hypophosphates include alkali metal hypophosphates and alkaline earth metal hypophosphates; and / or, The polyamide resin has a water extract content of 0.05% by weight or more; and / or, The polyamide resin has a relative viscosity of 1.8 to 4.0; and / or, The polyamide resin has a yellowness of less than 7. The polyamide resin according to claim 1.

3. Hypophosphates include one or more of the following: sodium hypophosphate, potassium hypophosphate, calcium hypophosphate, and magnesium hypophosphate; and / or, The polyamide resin has a water extract content of 0.1% by weight or more; and / or, The polyamide resin has a relative viscosity of 2.2 to 3.5; and / or, The polyamide resin has a yellowness of less than 5. The polyamide resin according to claim 2.

4. The polyamide resin has a water extract content of 0.2% by weight or more; and / or, The polyamide resin has a relative viscosity of 2.4 to 3.

3. The polyamide resin according to claim 2.

5. The polyamide resin has a water extract content of 0.25% by weight or more. The polyamide resin according to claim 2.

6. A composition containing the polyamide resin described in claim 1, wherein the composition contains the following components by weight: 100 parts polyamide resin and 10 to 70 parts glass fiber.

7. The glass fiber has a length-to-diameter ratio of (2-800):1; and / or, The glass fibers have a length of 3 mm to 12 mm; and / or, The composition according to claim 6, wherein the composition contains an additive in addition to hypophosphate, the additive being one of the following: antioxidants, nucleating agents, lubricants, flame retardants, coupling agents, heat stabilizers, light stabilizers, antistatic agents, ultraviolet absorbers, and colorants, or a combination of two or more of these.

8. The glass fiber has a length-to-diameter ratio of (200-650):1; and / or, The composition according to claim 7, wherein the glass fibers have a length of 3 mm to 8 mm.

9. A method for preparing polyamide resin, The method involves the following steps: S1. Prepare a nylon salt solution in an inert gas atmosphere; S2. The nylon salt solution is heated to raise the pressure of the nylon salt solution reaction system to 0.5 to 2.5 MPa, and the pressure is maintained by degassing for 0.5 to 4 hours. Then, the pressure is reduced to 0 to 0.7 MPa by depressurizing, and then the reaction system is evacuated to a vacuum of -0.01 to -0.08 MPa to obtain a polyamide molten product; S3. The molten polyamide is discharged and formed into strand pellets to obtain polyamide chips; S4, after mixing the polyamide chips with water in the reactor to obtain a mixture, the air in the reactor is replaced with an inert gas; and S5, heating and filtering the mixture in an inert gas atmosphere, rinsing and / or drying the polyamide tips to obtain the polyamide resin, A method for preparing a polyamide resin, wherein the polyamide resin has a water extract content of 0.5% by weight or less and a hypophosphate content of 10 ppm to 200 ppm in terms of P.

10. In step S1, 1,5-pentanediamine and a dicarboxylic acid are used in a molar ratio of (1 to 1.1):1 for the preparation of the nylon salt solution; and / or, In step S2, the reaction system has a temperature of 232°C to 260°C at the end of pressure maintenance; and / or, In step S2, the reaction system has a temperature of 240°C to 295°C at the end of reduced pressure; and / or, In step S2, the reaction system has a temperature of 250°C to 290°C after vacuuming; and / or, In step S2, the vacuum level is maintained for 11 to 75 minutes after vacuuming; and / or, In step S3, the strand pelletization is carried out in water at a water temperature of 15°C to 50°C. The method according to claim 9.

11. In step S4, the reactor is selected from a continuous extraction column and a batch reactor; and / or In step S4, the air in the reactor is replaced by evacuating the reactor using a vacuum pump, and then refilling the reactor with nitrogen gas or an inert gas; and / or, In step S4, the operation to replace the air in the reactor is repeated two or more times; and / or, In step S4, the water is deionized water; and / or, In step S4, the water is used in a mass of one or more times the mass of the polyamide chip; and / or, In steps S4 and S5, the inert gas contains one or two of argon gas and helium gas. The method according to claim 9.

12. In step S4, the water is deionized water that has undergone deoxygenation treatment; and / or, The method according to claim 11, wherein in step S4, the water used is in an amount equal to 1 to 12 times the mass of the polyamide chip.

13. In step S5, the mixture is heated for 4 to 50 hours; and / or, In step S5, the mixture is heated to 80°C to 140°C; and / or, In step S5, the rinsing is performed using hot water at a temperature of 50°C to 100°C; and / or, The method according to claim 9, wherein in step S5, the drying is carried out by one or more selected from vacuum drying, freeze-drying, airflow drying, microwave drying, infrared drying, and high-frequency drying.

14. In step S5, the mixture is heated for 8 to 45 hours; and / or, The method according to claim 13, wherein in step S5, the mixture is heated to 85°C to 120°C.

15. Use of the polyamide resin according to claim 1 or the composition according to claim 6 in engineering plastics.

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