A polyamide resin, a composition thereof and applications thereof in engineering plastics

Abstract

The present invention provides a polyamide resin, a composition and an application in engineering plastics. The structural units of the polyamide include diamine structural units and dibasic acid structural units. The content of water-extractable substances in the polyamide resin is 0.7 wt% or less, and the polyamide resin contains hypophosphite, and the content calculated as P is 10-500 ppm. The preparation method of the polyamide resin of the present invention is simple, the process parameters are easy to control, and no large-scale instruments are required for assistance, which is convenient for quantitative production. The polyamide resin composition has the advantages of short molding cycle, fast crystallization rate, good appearance quality, etc. At the same time, it has the advantage of acid corrosion resistance and can be applied to acidic environments, such as the outer packaging and containers of acidic foods.

Description

Technical Field

[0001] The present invention belongs to the field of polymer materials, and particularly relates to a polyamide resin, a preparation method thereof, a composition, and a fiber product. Background Art

[0002] Due to its excellent properties and ease of melt molding, polyamide has been widely used as clothing, industrial materials, fibers, or general engineering plastics, and thus has received wide attention. Polyamide 5X is a linear long-chain macromolecule synthesized from bio-based pentamethylenediamine and a series of dibasic acids. Amide bonds are prone to form hydrogen bonds. Therefore, polyamide 5X fibers have high strength and good moisture absorption. During the polymerization of polyamide 5X, due to the occurrence of cyclization reactions, when the intramolecular amide group exchange reaction occurs, the polymer macromolecular chain will break into two segments, or the linear low-molecular substances directly undergo dehydration reactions, resulting in low-molecular polymers. Generally, water-extractable substances are low-molecular polymers from monomer to decamer, such as dimers, trimers, including linear and cyclic forms. The presence of these water-extractable substances may affect the performance and application of the resin.

[0003] For example, for ultra-thin parts (0.3 - 0.4 mm) such as relays and capacitors, due to the very thin parts, injection molding needs to be carried out at high temperature and high speed. The heat and shear on the material itself are significantly higher than other injection molding conditions, and the appearance of mold fouling is particularly obvious. This will result in the need to regularly clean the mold surface during continuous processing, causing low production efficiency. In severe cases, white spots may appear on the surface of the parts, seriously affecting the product appearance. Summary of the Invention

[0004] To solve the deficiencies of the prior art and products, one object of the present invention is to provide a polyamide resin.

[0005] The structural units of the polyamide include diamine structural units and dibasic acid structural units. The content of water-extractable substances in the polyamide resin is 0.7 wt% or less, and the polyamide resin contains hypophosphite, with the content in terms of P being 10 - 500 ppm.

[0006] According to some embodiments of the present invention, the content of the water-extractable substances is 0.6 wt% or less, further 0.5 wt% or less. The water-extractable substances are mainly oligomers generated from monomer raw materials during the polymerization stage.

[0007] In some preferred embodiments of the present invention, when the content of the water-extractable substances is within the above-defined range, the anti-yellowing performance of the obtained polyamide resin and the subsequent resin composition is improved.

[0008] In some preferred embodiments of the present invention, when the content of the water-extractable substances is within the above-defined range, the mechanical properties of the obtained polyamide resin and the subsequent resin composition are improved.

[0009] In some preferred embodiments of the present invention, when the content of the water-extractable matter is within the above-defined range, the obtained polyamide resin and the resin composition described hereinafter have good appearance quality and no obvious precipitation.

[0010] In some preferred embodiments of the present invention, when the content of the water-extractable matter is within the above-defined range, the acid corrosion resistance of the obtained polyamide resin and the resin composition described hereinafter is improved.

[0011] In some preferred embodiments of the present invention, the content of the water-extractable matter in the polyamide resin is 0.05 wt% or more, further 0.1% or more, further 0.2 wt% or more, and further 0.25% or more. When the content of the water-extractable matter is lower than the above-defined range, the performance of the polyamide resin and the composition described hereinafter is somewhat reduced.

[0012] The content of the water-extractable matter in the polyamide resin is the mass percentage of the components that can be extracted into water after extraction treatment by heating in deionized water (for example, extracting the polyamide resin with water at 97°C to 100°C for 24 h) to the polyamide resin before the extraction treatment.

[0013] The content of the water-extractable matter (%) = (the mass m1 of the polyamide resin before water extraction - the mass m2 of the polyamide resin after water extraction) / the mass m1 of the polyamide resin before water extraction * 100%.

[0014] The extraction conditions are, for example, extracting the polyamide resin with water at 97°C to 100°C for 24 h, and the mass ratio of the polyamide resin to water is 1:48 to 51, for example, 1:50.

[0015] Further, the test method for the content of the water-extractable matter is as follows: Dry the polyamide sample in a forced-air oven at 130°C for 7 hours, then put it into an aluminum-plastic bag, seal it, and put it into a desiccator to cool. Then accurately weigh about 2 g of the polyamide sample and record the actual mass (m1) of the polyamide sample. Place the polyamide sample in a 250 mL round-bottom flask, add 100 mL of deionized water, heat and reflux at 97°C to 100°C for 24 hours. Take the polyamide sample after water extraction, wash it three times with deionized water, then dry the polyamide sample in a forced-air oven at 130°C for 7 hours, then transfer it to a pre-weighed aluminum-plastic bag, seal it, and put it into a desiccator to cool. Weigh the total weight of the aluminum-plastic bag and the polyamide sample and the weight of the aluminum-plastic bag, and subtract the two to obtain the weight (m2) of the polyamide sample after water extraction. Calculate the content of the water-extractable matter by comparing the weight difference of the polyamide sample before and after water extraction. The content of the water-extractable matter (%) = (m1 - m2) / m1 * 100%.

[0016] Further, when detecting the content of water-extractable substances in the polyamide resin melt, the melt is introduced into a closed container, cooled, and sampled for detection according to the above method.

[0017] According to some embodiments of the present invention, the number-average molecular weight of the water-extractable substances is 200 to 2000.

[0018] According to some embodiments of the present invention, the water-extractable substances include one or two of the following structures:

[0019]

[0020] Among them, n1 and n2 are respectively selected from integers of 1 to 8. Preferably, n1 and n2 are respectively selected from integers of 1 to 6. More preferably, n1 and n2 are respectively selected from integers of 1 to 5. Further preferably, n1 is 2, 3 or 4; n2 is 2, 3, 4 or 5; m1 is 4 and m2 is 4.

[0021] As a preferred embodiment of the present invention, the content of the hypophosphite, calculated as P, is 10 to 300 ppm, further 10 to 200 ppm.

[0022] As a preferred embodiment of the present invention, the hypophosphite includes hypophosphites of alkali metals and hypophosphites of alkaline earth metals, and further includes any one or a combination of two or more of sodium hypophosphite, potassium hypophosphite, calcium hypophosphite, and magnesium hypophosphite.

[0023] According to some embodiments of the present invention, the pentamethylenediamine in the polyamide resin can be pentamethylenediamine from chemical sources or biological sources, and further 1,5-pentamethylenediamine from biological sources.

[0024] As a preferred embodiment of the present invention, more than 90 mol% of the dibasic acid structural units come from adipic acid, and more than 90 mol% of the diamine structural units come from 1,5-pentamethylenediamine.

[0025] As a preferred embodiment of the present invention, more than 95 mol%, preferably more than 97 mol% of the diamine structural units in the polyamide resin come from 1,5-pentamethylenediamine.

[0026] Further, the diamine structural units in the polyamide resin may further include structural units from one or more of butanediamine, hexanediamine, decanediamine, and dodecanediamine.

[0027] As a preferred embodiment of the present invention, more than 95 mol%, preferably more than 97 mol% of the dibasic acid structural units in the polyamide resin come from adipic acid.

[0028] According to some embodiments of the present invention, the dicarboxylic acid structural units in the polyamide resin may further include structural units derived from one or more of succinic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, tetradecanedioic acid, pentadecanedioic acid, hexadecanedioic acid, heptadecanedioic acid, octadecanedioic acid, terephthalic acid, isophthalic acid, and phthalic acid.

[0029] As a preferred embodiment of the present invention, the content of the polyamide (main polymer) composed of diamine structural units and dicarboxylic acid structural units in the polyamide resin is 90 wt% or more, further 95 wt% or more, further 97 wt% or more, and further 99 wt% or more. The diamine structural units and dicarboxylic acid structural units meet the above limitations.

[0030] According to some embodiments of the present invention, the polyamide resin contains additives other than hypophosphite.

[0031] The additives include, but are not limited to, any one or a combination of several of a capping agent, a nucleating agent, an antioxidant, an antifoaming agent, and a flow modifier. The capping agent includes lauric acid, stearic acid, benzoic acid, and acetic acid.

[0032] In some preferred embodiments of the present invention, the content of the additives in the polyamide resin is less than or equal to 10 wt%, preferably less than or equal to 5 wt%, more preferably less than or equal to 3 wt%, and more preferably less than or equal to 1 wt%.

[0033] According to some embodiments of the present invention, the polyamide resin is a polyamide 56 resin. The content of polyamide 56 in the polyamide 56 resin is 90 wt% or more, further 95 wt% or more, further 97 wt% or more, and further 99 wt% or more.

[0034] As a preferred embodiment of the present invention, the relative viscosity of the polyamide resin is 1.8 - 4.0, preferably 2.2 - 3.5, and further preferably 2.4 - 3.3.

[0035] As a preferred embodiment of the present invention, the yellowness index of the polyamide resin is less than 7, and further less than 5.

[0036] The second object of the present invention is to provide a method for preparing a polyamide resin.

[0037] According to some embodiments of the present invention, the method includes the following steps:

[0038] S1: Prepare a nylon salt solution under an inert gas atmosphere;

[0039] S2: Heat the nylon salt solution to increase the pressure of the nylon salt solution reaction system to 0.5 - 2.5 MPa, exhaust and maintain the pressure for 0.5 - 4 h, then reduce the pressure to make the pressure in the reaction system drop to 0 - 0.7 MPa (gauge pressure), and then evacuate to make the vacuum degree in the reaction system -0.01 - -0.08 MPa to obtain a polyamide melt;

[0040] S3: Discharge the obtained melt, strand pelletize to obtain polyamide chips.

[0041] Among them, the molar ratio of 1,5 - pentanediamine to dibasic acid used to prepare the nylon salt solution in step S1 is (1 - 1.1):1.

[0042] After the pressure - maintaining process in step S2, the temperature of the reaction system is 232 - 260 °C.

[0043] After the pressure - reducing process in step S2, the temperature of the reaction system is 240 - 295 °C, further 243 - 288 °C.

[0044] After evacuation in step S2, the temperature of the reaction system is 250 - 290 °C, further 252 - 285 °C.

[0045] After evacuation in step S2, the time for maintaining the vacuum degree is 11 - 75 min.

[0046] The pelletizing in step S3 is carried out in water, and the water temperature is 15 - 50 °C. Through the strand pelletizing in step S3, polyamide chips or polyamide pellets are obtained.

[0047] According to some embodiments of the present invention, the method further includes the following steps:

[0048] S4: Mix the polyamide chips with water and place them in a reactor, and displace the air in the reactor with an inert gas;

[0049] S5: Under an inert gas atmosphere, heat, filter, rinse, and dry to obtain the polyamide resin.

[0050] The reactor in step S4 is a reactor that can form a closed environment. The reactor in step S4 can be, for example, a continuous extraction tower or a batch reactor.

[0051] Preferably, in step S4, the method for displacing the air in the reactor includes evacuating with a vacuum pump and then filling with nitrogen or an inert gas. The above operation of displacing the air in the reactor can be repeated more than twice.

[0052] The water described in step S4 is deionized water, and further deionized water after deoxygenation treatment. Among them, the deoxygenation treatment can be one or a combination of several of thermal deoxygenation, ultrasonic deoxygenation, vacuum deoxygenation, chemical deoxygenation, analytical deoxygenation or any other deoxygenation method; in some preferred embodiments, the content of dissolved oxygen in the deionized water after deoxygenation treatment is less than or equal to 0.5 mg / L, and further less than or equal to 0.1 mg / L.

[0053] The mass of the water described in step S4 is more than 1 time the mass of the polyamide chips, and further more than 2 times, such as 1 - 12 times, 1 - 10 times, 2 - 10 times, 2 - 6 times, 1.5 times, 2.3 times, 2.5 times, 3 times, 5 times, 8 times.

[0054] The inert gas described in steps S1, S4 and step S5 includes one or two of argon, helium, etc., and high - purity argon and high - purity helium are further preferred.

[0055] According to some embodiments of the present invention, during the operation of replacing air in step S4, the vacuum is pumped to a vacuum degree of - 0.1 Mpa to - 0.001 Mpa (relative pressure), maintained for 5 - 20 min, and then nitrogen or inert gas is filled. Further preferably, the operation of replacing air is repeated 5 - 15 times, and further 8 - 10 times.

[0056] According to some embodiments of the present invention, the heating time in step S5 is 4 - 50 h, and further 8 - 45 h.

[0057] According to some embodiments of the present invention, the heating temperature in step S5 is 80 - 140 °C, and further 85 - 120 °C.

[0058] According to some embodiments of the present invention, the rinsing in step S5 is carried out with hot water at a temperature of 50 °C - 100 °C.

[0059] According to some embodiments of the present invention, the drying in step S5 is selected from one or several of vacuum drying, freeze - drying, fluidized - bed drying, microwave drying, infrared drying and high - frequency drying.

[0060] The third object of the present invention is to provide a resin composition, and the composition includes the following components in parts by weight: 100 parts of polyamide resin, 10 - 70 parts of glass fiber.

[0061] As a preferred embodiment of the present invention, the aspect ratio of the glass fiber is (2 - 800):1, and further (200 - 650):1.

[0062] As a preferred embodiment of the present invention, the length of the glass fiber is 3 - 12 mm, and further 3 - 8 mm.

[0063] In some preferred embodiments of the present invention, when the parameters of the glass fiber are within the above-defined range, the mechanical properties of the obtained resin composition are improved.

[0064] Furthermore, the composition may contain any one or more of antioxidants, nucleating agents, lubricants, flame retardants, coupling agents, heat stabilizers, light stabilizers, antistatic agents, ultraviolet absorbers, and colorants.

[0065] Furthermore, the content of the antioxidant is 0.02 to 2 parts. The antioxidant preferably includes hindered phenol antioxidants, hindered amine antioxidants, and phosphite antioxidants. For example, it includes any one or more of antioxidant 168, antioxidant 1098, antioxidant 1010, and antioxidant S9228.

[0066] As a preferred embodiment of the present invention, the polyamide resin has the above-mentioned definition.

[0067] The preparation method of the polyamide resin composition, the method comprising the following steps:

[0068] Add the components into a twin-screw extruder for mixing, and then extrude through the twin-screw extruder, cool, and pelletize to obtain the polyamide composition.

[0069] Furthermore, during mixing, the glass fiber is fed into the side feeding port of the twin-screw extruder.

[0070] Furthermore, the temperature for melt mixing the premix by the twin-screw extruder is 210 to 290 °C.

[0071] As an embodiment of the present invention, during the mixing process, the twin-screw extruder is in a seven-zone heating mode. The temperature of the first zone is 210 to 250 °C, and / or the temperature of the second zone is 210 to 250 °C, and / or the temperature of the third zone is 240 to 260 °C, the temperature of the fourth zone is 260 to 280 °C, and / or the temperature of the fifth zone is 270 to 290 °C, and / or the temperature of the sixth zone is 270 to 290 °C, and / or the temperature of the seventh zone is 255 to 285 °C; wherein, the direction from the first zone to the seventh zone is the direction from the feeding port to the die port.

[0072] The die temperature of the twin-screw extruder is 260 to 275 °C.

[0073] The screw speed of the twin-screw extruder is 350 to 500 r / min.

[0074] The length-diameter ratio of the twin-screw extruder is 1:(30 to 50), preferably 1:40.

[0075] A fourth object of the present invention is to provide an application of the above-mentioned polyamide resin or composition in engineering plastics.

[0076] Compared with the prior art, the implementation of the present invention has at least the following advantages:

[0077] 1. The preparation method of the polyamide resin of the present invention is simple, the process parameters are easy to control, and no large-scale instruments are required for assistance, which is convenient for quantitative production.

[0078] 2. The polyamide resin composition has the advantages of short molding cycle, fast crystallization speed, less injection mold fouling, and good appearance quality. It can be used in the production of parts in the field of electronic appliances.

[0079] 2. The polyamide resin composition has the advantage of acid corrosion resistance and can be applied to acidic environments, such as the outer packaging and containers of acidic foods. Specific Embodiments

[0080] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0081] 1. Detection method for relative viscosity ηr

[0082] Ubbelohde viscometer concentrated sulfuric acid method: Accurately weigh 0.5 ± 0.0002 g of the dried polyamide sample, add 50 mL of concentrated sulfuric acid (98%) to dissolve it, and measure and record the flowing time t0 of concentrated sulfuric acid and the flowing time t of the polyamide solution in a constant temperature water bath at 25°C. The calculation formula for relative viscosity number: relative viscosity ηr = t / t0.

[0083] 2. The test method for the water extractable content in polyamide resin is as follows: Dry the polyamide sample in a forced-air oven at 130 °C for 7 hours, then put it into an aluminum-plastic bag, seal it, and place it in a desiccator to cool. Then accurately weigh about 2 g of the polyamide sample, and record the actual mass (m1) of the polyamide sample. Place the polyamide sample in a 250 mL round-bottom flask, add 100 mL of deionized water, heat under reflux at 97 °C - 100 °C for 24 hours. Take out the polyamide sample after water extraction, wash it three times with deionized water, then dry the polyamide sample in a forced-air oven at 130 °C for 7 hours, and then transfer it to a pre-weighed aluminum-plastic bag. Seal it and place it in a desiccator to cool. Weigh the total weight of the aluminum-plastic bag and the polyamide sample and the weight of the aluminum-plastic bag, and subtract the two to obtain the weight (m2) of the polyamide sample after water extraction. Calculate the water extractable content by comparing the weight difference of the polyamide sample before and after water extraction. The water extractable content (%) = (m1 - m2) / m1 * 100%.

[0084] When detecting the water extractable content in the polyamide resin melt, introduce the melt into a sealed container, cool it, and then take a sample for detection according to the above method.

[0085] 3. Yellowness Index (YI)

[0086] Test according to HG / T 3862.

[0087] 4. Crystallinity test

[0088] Use a differential scanning calorimeter (DSC) to analyze the crystallinity of the polyamide sample: Heat the samples of the polyamides obtained in each example and comparative example from room temperature to 280 °C at a heating rate of 50 °C / min, maintain for 3 min, and then cool the sample to room temperature at a rate of 10 °C / min. Measure the crystallization temperature and the half-crystallization time.

[0089] 5. Tensile strength

[0090] Determine according to the method of ISO 527-2, and the tensile speed during the test is 50 mm / min.

[0091] 6. Flexural strength

[0092] Determine according to the method of ISO 178, and the test condition is 2 mm / min.

[0093] 7. Acid resistance test: Immerse the polyamide sample in an acetic acid solution with a mass fraction of 10 wt% at 40 °C for 180 days, observe the precipitation on the surface of the sample and rate it from 1 to 5 levels, where level 1 is the worst with a large amount of precipitation, and level 5 is the best with no obvious precipitation observed.

[0094] Preparation Example 1

[0095] (1) Under nitrogen gas condition, 1,5-pentanediamine, adipic acid and water are mixed evenly, wherein the molar ratio of 1,5-pentanediamine to adipic acid is 1.08:1, and a 60 wt.% nylon salt solution is prepared, and the percentage is the mass percentage of the nylon salt solution; the pH value of the nylon salt solution when the concentration is 10 wt.% is 7.85.

[0096] (2) 1200 g of the nylon salt solution and 500 ppm of sodium hypophosphite are added to a polymerization reactor and heated. The pressure in the reaction system rises to 2.3 Mpa, which takes 1 hour and 30 minutes. Then, the gas is exhausted and the pressure is maintained. The temperature of the reaction system at the end of the pressure maintenance is 245 °C, and the pressure maintenance takes 3 hours. Then, the pressure is reduced to make the pressure in the reaction system drop to 0.003 MPa (gauge pressure). The temperature of the reaction system after the pressure reduction is 273 °C, and the pressure reduction takes 1 hour. The vacuum is maintained at -0.06 Mpa for 32 minutes, and the temperature of the reaction system after the vacuum is 272 °C, obtaining a polyamide 56 melt.

[0097] (3) The melt obtained in step (2) is discharged, water-cooled and strand-cut into polyamide 56 chips; the granulation is carried out in water, and the water temperature is 20 °C.

[0098] Example 1

[0099] (a) Add the polyamide 56 chips prepared in Preparation Example 1 to a reaction kettle, and add deionized water after anaerobic treatment. The mass ratio of the chips to the deionized water after anaerobic treatment is 1:6; the air is displaced with nitrogen gas. The specific operation method is as follows: use a vacuum pump to evacuate, the vacuum degree is -0.09 Mpa (relative pressure), and after maintaining for 10 minutes, nitrogen gas is filled, and the replacement is repeated 9 times.

[0100] (b) Under a nitrogen atmosphere, heat at 90 °C for 32 h, then filter to separate the chips from the water, and then rinse the chips with water at 95 °C and dry them in vacuum at 105 °C for 15 h to obtain polyamide 56 resin.

[0101] Example 2

[0102] (1) Under nitrogen gas condition, 1,5-pentanediamine, adipic acid and water are mixed evenly, wherein the molar ratio of 1,5-pentanediamine to adipic acid is 1:1, and a 70 wt.% nylon salt solution is prepared, and the percentage is the mass percentage of the nylon salt solution; the pH value of the nylon salt solution when the concentration is 10 wt.% is 7.96.

[0103] (2) Add 1200 g of nylon salt solution and 300 ppm of sodium hypophosphite into the polymerization reactor and heat. The pressure in the reaction system rises to 2.0 Mpa, which takes 1 hour and 30 minutes. Then exhaust the gas, maintain the pressure at 2.40 Mpa. When the pressure maintaining ends, the temperature of the reaction system is 243 °C, and the pressure maintaining time is 3 hours. Then reduce the pressure to make the pressure in the reaction system drop to 0.005 MPa (gauge pressure). When the pressure reduction ends, the temperature of the reaction system is 290 °C, and the pressure reduction time is 1 hour. Vacuumize and maintain at -0.08 Mpa, and the vacuumizing time is 30 min. After vacuumizing, the temperature of the reaction system is 290 °C, and polyamide 56 melt is obtained.

[0104] (3) Discharge the melt obtained in step (2), and cool and pelletize it by water at 20 °C to obtain polyamide 56 chips.

[0105] (4) Add polyamide 56 chips into the reactor, and add deionized water after anaerobic treatment. The mass ratio of the chips to the deionized water after anaerobic treatment is 1:6; displace the air with nitrogen. The specific operation method is as follows: Use a vacuum pump to evacuate, with a vacuum degree of -0.07 Mpa (relative pressure), maintain for 10 min and then fill with nitrogen, and repeat the displacement 10 times.

[0106] (5) Pass nitrogen into the reactor in step (4) for protection, heat at 96 °C for 46 h, then filter to separate the chips from the water, and then rinse the chips with water at 95 °C and dry them in vacuum at 105 °C for 15 h to obtain polyamide 56 resin.

[0107] Example 3

[0108] (a) Add the polyamide 56 chips prepared in Preparation Example 1 into the reactor, and add deionized water after anaerobic treatment. The mass ratio of the chips to the deionized water after anaerobic treatment is 1:12; displace the air with nitrogen. The specific operation method is as follows: Use a vacuum pump to evacuate, with a vacuum degree of -0.09 Mpa (relative pressure), maintain for 10 min and then fill with nitrogen, and repeat the displacement 10 times.

[0109] (b) Pass nitrogen into the reactor in step (a) for protection, heat and boil at 95 °C for 55 h, then filter to separate the chips from the water, and then rinse the chips with hot water at 95 °C and dry them in vacuum at 105 °C for 15 h to obtain polyamide 56 resin.

[0110] Example 4

[0111] (1) Under nitrogen conditions, mix 1,5-pentanediamine, adipic acid and water evenly. Among them, the molar ratio of 1,5-pentanediamine to adipic acid is 1.05:1 to prepare a 60 wt.% nylon salt solution, and the percentage is the mass percentage of the nylon salt solution; the pH value when the concentration of the nylon salt solution is 10 wt.% is 7.98.

[0112] (2) Add 1200 g of nylon salt solution and 1200 ppm of sodium hypophosphite into the polymerization reactor and heat. The pressure in the reaction system rises to 2.0 Mpa, which takes 1 hour and 30 minutes. Exhaust and maintain pressure. When the pressure maintenance ends, the temperature of the reaction system is 243 °C, and the pressure maintenance takes 3 hours. Then reduce the pressure to make the pressure in the reaction system drop to 0.005 MPa (gauge pressure). After the pressure reduction ends, the temperature of the reaction system is 290 °C, and the pressure reduction takes 1 hour. Evacuate and maintain at -0.08 Mpa. The evacuation time is 30 min. After evacuation, the temperature of the reaction system is 290 °C, and polyamide 56 melt is obtained.

[0113] (3) Discharge the melt obtained in step (2), and carry out water cooling, strand pelletizing at 20 °C.

[0114] (4) Dry in vacuum at 105 °C for 15 h, and polyamide 56 resin is obtained.

[0115] Example 5

[0116] (1) Under nitrogen condition, mix 1,5-pentanediamine, adipic acid and water evenly. Among them, the molar ratio of 1,5-pentanediamine to adipic acid is 1.05:1, and a 60 wt.% nylon salt solution is prepared. The percentage is the mass percentage of the nylon salt solution; the pH value of the nylon salt solution when the concentration is 10 wt.% is 7.98.

[0117] (2) Add 1200 g of nylon salt solution and 2400 ppm of sodium hypophosphite into the polymerization reactor and heat. The pressure in the reaction system rises to 2.0 Mpa, which takes 1 hour and 30 minutes. Exhaust and maintain pressure. When the pressure maintenance ends, the temperature of the reaction system is 243 °C, and the pressure maintenance takes 3 hours. Then reduce the pressure to make the pressure in the reaction system drop to 0.005 MPa (gauge pressure). After the pressure reduction ends, the temperature of the reaction system is 290 °C, and the pressure reduction takes 1 hour. Evacuate and maintain at -0.08 Mpa. The evacuation time is 30 min. After evacuation, the temperature of the reaction system is 290 °C, and polyamide 56 melt is obtained.

[0118] (3) Discharge the melt obtained in step (2), carry out water cooling and strand pelletizing, and the water temperature is 20 °C.

[0119] (4) Dry in vacuum at 105 °C for 15 h, and polyamide 56 resin is obtained.

[0120] Example 6

[0121] (1) Under nitrogen condition, mix 1,5-pentanediamine, adipic acid and water evenly. Among them, the molar ratio of 1,5-pentanediamine to adipic acid is 1.05:1, and a 60 wt.% nylon salt solution is prepared. The percentage is the mass percentage of the nylon salt solution; the pH value of the nylon salt solution when the concentration is 10 wt.% is 7.98.

[0122] (2) Add 1200 g of nylon salt solution and 85 ppm of sodium hypophosphite into the polymerization reactor and heat. The pressure in the reaction system rises to 2.0 Mpa, which takes 1 hour and 30 minutes. Then exhaust the gas and maintain the pressure. When the pressure maintenance ends, the temperature of the reaction system is 243 °C, and the pressure maintenance time is 3 hours. Then reduce the pressure to make the pressure in the reaction system drop to 0.005 MPa (gauge pressure). After the pressure reduction ends, the temperature of the reaction system is 290 °C, and the pressure reduction time is 1 hour. Evacuate and maintain at -0.08 Mpa for 30 min. After evacuation, the temperature of the reaction system is 290 °C, and polyamide 56 melt is obtained.

[0123] (3) Discharge the melt obtained in step (2), cool it by water-cooled strand pelletizing, and the water temperature is 20 °C.

[0124] (4) Dry it in vacuum at 105 °C for 15 h to obtain polyamide 56 resin.

[0125] Test the relative viscosity, water-extractable content, hypophosphite content (converted to P), crystallization temperature, semi-crystallization time, acid resistance, and yellowness index of the polyamide resins in Examples 1 - 6. The test results are shown in Table 1.

[0126] Table 1

[0127]

[0128] Use the polyamide resins, glass fibers, and antioxidants in Examples 1 - 6 as raw materials to prepare polyamide compositions. The formulation of the compositions is shown in Table 2.

[0129] The preparation method of the composition is as follows:

[0130] Use polyamide resin, glass fiber, and antioxidant as raw materials, and use a twin-screw extruder for mixing. Then extrude the strand through the twin-screw extruder, cool the strand below the melting point of polyamide with water as the cooling medium and cut it to obtain a polyamide resin composition. Among them, the twin-screw extruder is in a seven-zone heating mode, and the temperatures of the first zone to the seventh zone are 250 °C, 260 °C, 260 °C, 280 °C, 270 °C, 270 °C, and 270 °C in sequence. The die temperature is 260 °C; the screw speed is 480 r / min; the length-diameter ratio of the twin-screw extruder is 1:40.

[0131] Dry the obtained polyamide resin composition at 110 °C for 5 hours and then injection mold it. The injection molding conditions are: use an injection molding machine to injection mold at a barrel temperature of 280 °C and a mold surface temperature of 110 °C, and the sample thickness is 3 mm. Continuously injection mold 50 molds, observe the scale situation on the high-gloss surface of the mold, and rate the scale situation. 1 point is the worst, with a large amount of scale; 5 points is the best, and no obvious scale is observed. The test results of the injection molded samples are shown in Table 2.

[0132] Table 2

[0133]

[0134]

[0135] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A polyamide resin, characterized in that, The structural units of the polyamide include diamine structural units and diacid structural units. The water extractable content in the polyamide resin is 0.2% or more and 0.7 wt% or less, and the polyamide resin contains hypophosphite, with the content in terms of P being 27 - 200 ppm; the yellowness index of the polyamide resin is less than 5; Among them, more than 90 mol% of the diacid structural units are derived from adipic acid, and more than 90 mol% of the diamine structural units are derived from 1,5 - pentanediamine; the relative viscosity of the polyamide resin is 1.8 - 4.0, and the water extractables include one or both of the following structures: m1 is 4, m2 is 4, and n1 and n2 are integers respectively selected from 1 to 8.

2. The polyamide resin according to claim 1, wherein The hypophosphite includes hypophosphites of alkali metals and hypophosphites of alkaline earth metals; and / or, The content of the water extractables is 0.25% or more; and / or, The yellowness index of the polyamide resin is less than 4.

47.

3. The polyamide resin according to claim 1, characterized in that, The relative viscosity of the polyamide resin is 2.2 - 3.5; and / or, The hypophosphite includes any one or a combination of two or more of sodium hypophosphite, potassium hypophosphite, calcium hypophosphite, and magnesium hypophosphite.

4. The polyamide resin according to claim 1, wherein The relative viscosity of the polyamide resin is 2.4 - 3.

3.

5. A composition containing the polyamide resin according to any one of claims 1 to 4, characterized in that, Comprising the following components in parts by weight: 100 parts of polyamide resin and 10 - 70 parts of glass fiber.

6. The composition according to claim 5, wherein The aspect ratio of the glass fiber is (2 - 800):1; and / or, The length of the glass fiber is 3 - 12 mm; and / or, The composition contains any one or a combination of two or more of antioxidants, nucleating agents, lubricants, flame retardants, coupling agents, heat stabilizers, light stabilizers, antistatic agents, ultraviolet absorbers, and colorants.

7. The composition according to claim 5, characterized in that, The aspect ratio of the glass fiber is (200 - 650):1; and / or, The length of the glass fiber is 3 - 8 mm.

8. A method for preparing a polyamide resin according to any one of claims 1 to 4, characterized in that, The method includes the following steps: S1: Prepare a nylon salt solution under an inert gas atmosphere; S2: Heat the nylon salt solution to raise the pressure of the reaction system of the nylon salt solution to 0.5 - 2.5 MPa, exhaust and maintain the pressure for 0.5 - 4 h, then reduce the pressure to make the pressure in the reaction system drop to 0 - 0.7 MPa, and then evacuate to make the vacuum degree in the reaction system -0.01 - -0.08 MPa to obtain a polyamide melt; S3: Discharge the obtained melt, extrude and pelletize to obtain polyamide pellets.

9. The method according to claim 8, wherein, The molar ratio of 1,5 - pentanediamine to diacid used in step S1 to prepare the nylon salt solution is (1 - 1.1):1; and / or, After the pressure - maintaining process in step S2, the temperature of the reaction system is 232 - 260 °C; and / or, After the pressure - reducing process in step S2, the temperature of the reaction system is 240 - 295 °C; and / or, After evacuation in step S2, the temperature of the reaction system is 250 - 290 °C; and / or, The time for maintaining the vacuum degree after evacuation in step S2 is 11 - 75 min; and / or, The pelletizing in step S3 is carried out in water, and the water temperature is 15 - 50 °C.

10. The method according to claim 8, wherein It further includes the following steps: S4: Mix the polyamide chips with water and place them in a reactor, and displace the air in the reactor with an inert gas; S5: Under an inert gas atmosphere, heat, filter, rinse, and dry to obtain the polyamide resin.

11. The method according to claim 10, wherein in step S4, the reactor is selected from a continuous extraction tower and a batch reactor; and / or, in step S4, the method for displacing the air in the reactor includes evacuating the reactor with a vacuum pump and then filling it with nitrogen or an inert gas; and / or, in step S4, the operation of displacing the air in the reactor is repeated more than twice; and / or, in step S4, the water is deionized water; and / or, in step S4, the mass of the water is more than 1 times the mass of the polyamide chips; and / or, the inert gas in steps S4 and S5 includes one or both of argon and helium.

12. The method according to claim 10, wherein, in step S4, the water is deionized water after deoxygenation treatment; and / or, in step S4, the mass of the water is more than 2 times the mass of the polyamide chips.

13. The method according to claim 10, wherein in step S4, the mass of the water is 1 - 12 times the mass of the polyamide chips.

14. The method according to claim 10, characterized in that, in step S4, the mass of the water is 2 - 10 times the mass of the polyamide chips.

15. The method according to claim 10, characterized in that, in step S4, the mass of the water is 2 - 6 times the mass of the polyamide chips.

16. The method according to claim 10, wherein in step S5, the heating time is 4 - 50 h; and / or, in step S5, the heating temperature is 80 - 140 °C; and / or, in step S5, the rinsing is carried out with hot water at a temperature of 50 °C - 100 °C; and / or, in step S5, the drying is selected from one or more of vacuum drying, freeze drying, fluidized bed drying, microwave drying, infrared drying, and high-frequency drying.

17. The method according to claim 10, wherein in step S5, the heating time is 8 - 45 h; and / or, in step S5, the heating temperature is 85 - 120 °C.

18. The application of the polyamide resin according to any one of claims 1 to 4 or the composition according to any one of claims 5 to 7 in engineering plastics.

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