High-temperature-resistant polyamide as well as preparation method and application thereof

Abstract

The invention provides high-temperature-resistant polyamide as well as a preparation method and application thereof. The preparation method of the high-temperature-resistant polyamide comprises the following steps: sequentially carrying out prepolymerization and solid-phase polymerization on polyamide salt; wherein the reaction temperature of the prepolymerization is 180 to 280 DEG C, and the pressure of the prepolymerization is 1.5 to 3.2 MPa; the solid-phase polymerization comprises the following steps: firstly raising the temperature to 100-220 DEG C, then raising the temperature at the temperature raising rate of 1-10 DEG C / min, keeping the temperature for 5-20 minutes when the temperature is raised by 1-10 DEG C until the final temperature is 230-300 DEG C, and continuously reacting for 1-12 hours. The high-temperature-resistant polyamide prepared by the preparation method disclosed by the invention is low in yellowing index, low in gel content and better in mechanical property, and is more beneficial to application in high-temperature-resistant materials.

Description

Technical Field

[0001] The invention belongs to the field of polyamide materials, and in particular relates to a high-temperature resistant polyamide and a preparation method and application thereof. Background Art

[0002] When conventional high temperature and high pressure polymerization is used to prepare high temperature resistant nylon PA5XT in one step, serious gelation, oxidation, decomposition and other phenomena may occur, causing the product to turn yellow, reduce the molecular weight, and further have a negative impact on its mechanical properties. When using the one-step method for direct preparation, higher requirements are placed on the stability of equipment temperature control and long-term durability. If the equipment fails and stops production, it often causes huge losses.

[0003] Patent CN113980266A discloses a low yellow index long-chain polyamide and a preparation method thereof. In this patent, after the reaction is completed, highly polar trifluoroethanol / trifluoroacetic acid or other decolorizing agents are added to dissolve the product, and then the dissolved polyamide solution is added to methanol to precipitate it. The process involves the use of a large amount of solvent, which is costly and polluting to the environment.

[0004] Patent CN112358611A uses a prepolymerization-solid phase thickening method to prepare semi-aromatic high temperature resistant nylon powder. The document does not involve how to solve the problem of reducing the yellowing index and gelation. In addition, the material needs to be crushed into micron-sized powder during the implementation process, and the cost of the crushing equipment is high. At the same time, the powder particles are too small and are easy to block the pipe mouth during solid phase polymerization. Summary of the invention

[0005] The technical problem solved by the present invention is to overcome the problems of high yellowing index and easy gelation of high temperature resistant polyamide in the prior art, and provide a high temperature resistant polyamide and its preparation method and application. The high temperature resistant polyamide prepared by the preparation method of the present invention has low yellowing index and low gel content, better mechanical properties, and is more conducive to application in high temperature resistant materials.

[0006] Through experimental research, the inventors found that by using a specific solid-phase polymerization heating method to process polyamide salt, the final high-temperature resistant polyamide can have a low yellowing index, low gel content, is not easy to decompose, has better mechanical properties, and is more conducive to its application in high-temperature resistant materials.

[0007] The present invention provides a method for preparing high temperature resistant polyamide, which comprises the following steps: sequentially prepolymerizing and solid phase polymerizing a polyamide salt;

[0008] Wherein, the reaction temperature of the prepolymerization is 180-280°C, and the pressure of the prepolymerization is 1.5-3.2MPa;

[0009] The solid phase polymerization comprises: first heating to 100-220° C., then heating at a heating rate of 1-10° C. / min and keeping the temperature for 5-20 minutes every time the temperature is increased by 1-10° C., until the terminal temperature is 230-300° C., and continuing the reaction for 1-12 hours.

[0010] In some specific embodiments, the reaction temperature of the prepolymerization is preferably 220-260° C., such as 240° C. or 250° C. When the reaction temperature of the prepolymerization is within the preferred range, problems such as excessive residual materials in the reaction device and materials blocking the discharge port can be avoided.

[0011] In some specific embodiments, the prepolymerization pressure is preferably 1.6-2.6 MPa, such as 2.0 MPa or 2.2 MPa.

[0012] In some specific embodiments, the prepolymerization time may be 0.5 to 2.5 h, preferably 0.5 to 1.5 h, such as 0.75 h or 1 h.

[0013] In a preferred embodiment, after the prepolymerization is completed, the obtained prepolymer is crushed, and the particle size D of the crushed prepolymer particles is 50 The thickness is 2-10 mm, preferably 3-7 mm, for example 3 mm.

[0014] In a preferred embodiment, after the prepolymerization reaction is completed, the obtained prepolymer is ejected from the reaction device by using the pressure in the reaction device, and then crushed into particles. The reaction device is preferably a reactor. The crushing is performed using a crusher.

[0015] In some specific embodiments, the solid phase polymerization is preferably first heated to 120-220°C, such as 135°C, 140°C, 150°C, 200°C or 220°C, more preferably 200-220°C.

[0016] In some specific embodiments, during the solid phase polymerization, the temperature is first raised to 100-220°C, and the heating rate is not particularly limited and can be adjusted within the heating rate allowed by the equipment. For example, the heating rate can be 1-30°C / min, preferably 1-15°C / min.

[0017] In some specific embodiments, after the temperature is raised to 100-220°C, the temperature is preferably further raised at a rate of 1-5°C / min, for example, 2°C / min; and the temperature is kept warm for 5-20 min for each increase of 1-10°C, for example, 10 min for each increase of 10°C.

[0018] In a preferred embodiment, the solid phase polymerization comprises:

[0019] (1) first heating the temperature to 100-220° C. at a heating rate of 1-30° C. / min, preferably 1-15° C. / min;

[0020] (2) The temperature is then raised at a rate of 1 to 10°C / min, preferably 1 to 5°C / min, and the temperature is kept for 5 to 20 minutes for each 1 to 10°C increase, until the final temperature is 230 to 300°C, and the reaction is continued for 1 to 12 hours.

[0021] In the process of the solid phase polymerization, the step-wise heating and heat preservation method can, on the one hand, make the molecular weight distribution of the polymer narrower and the performance better; on the other hand, it can avoid the phenomenon of powder agglomeration and agglomeration, which is beneficial to the discharge and the obtained polymer has good consistency.

[0022] In some embodiments, the endpoint temperature is preferably 240-300°C, such as 240°C, 250°C or 255°C.

[0023] In some specific embodiments, the reaction time until the terminal temperature reaches 230-300° C. is preferably 6-10 h, such as 6 h, 8 h or 10 h.

[0024] In some specific embodiments, the pressure of the solid phase polymerization may be -0.1 to 0.2 MPa, preferably -0.1 to 0.1 MPa, more preferably -0.1 to -0.05 MPa, such as -0.08 MPa or -0.09 MPa. Under the pressure within the above preferred range, the yellowness index of the obtained polyamide is lower.

[0025] In some embodiments, the pressure of the solid phase polymerization can be controlled by evacuating or introducing a protective gas, for example, evacuating to form a negative pressure or introducing a protective gas to form a positive pressure. The protective gas is a gas that does not react with substances in the solid phase polymerization system, such as nitrogen or an inert gas.

[0026] In some embodiments, the solid phase polymerization is conventionally performed in the presence of a protective gas.

[0027] In a preferred embodiment, before the solid phase polymerization, the protective gas is introduced to replace the air in the reaction system. The number of times of replacement can be conventional in the art, for example, 3-5 times.

[0028] In some specific embodiments, the polyamide salt can be any type of polyamide salt applicable in the art.

[0029] In some specific embodiments, the polyamide salt can be prepared by the following method: subjecting aliphatic diamine, aliphatic dibasic acid and aromatic dibasic acid to a salt-forming reaction.

[0030] The aliphatic diamine may be an aliphatic diamine suitable for preparing polyamide salts in the art, generally one or more aliphatic diamines having 5 to 12 carbon atoms, preferably 1,5-pentanediamine or 1,6-hexanediamine.

[0031] Wherein, the aliphatic dibasic acid can be an aliphatic dibasic acid suitable for preparing polyamide salts in the art, generally one or more of aliphatic dibasic acids with 2 to 18 carbon atoms, preferably one or more of oxalic acid, malonic acid, succinic acid (such as 1,4-succinic acid), glutaric acid, adipic acid (such as 1,6-hexanedioc acid), pimelic acid, suberic acid (such as 1,8-suberic acid), azelaic acid, sebacic acid (such as 1,10-decanedioic acid), undecanedioic acid, dodecanedioic acid (such as 1,12-dodecanedioc acid), tridecanedioic acid, tetradecanedioic acid (such as 1,14-tetradecanedioic acid), pentadecanedioc acid, hexadecanedioic acid (such as 1,16-hexadecanedioic acid), heptadecanedioic acid and octadecanedioc acid (such as 1,18-octadecanedioc acid), for example, adipic acid or dodecanedioic acid.

[0032] Among them, the aromatic dibasic acid can be an aromatic dibasic acid suitable for preparing polyamide salts in the art, generally one or more dibasic acids containing benzene rings with a carbon number of 8 or more, preferably one or more of terephthalic acid, isophthalic acid and phthalic acid, such as terephthalic acid.

[0033] In a preferred embodiment, the polyamide salt is prepared from 1,5-pentanediamine, terephthalic acid and 1,6-hexanedioic acid, or prepared from 1,5-pentanediamine, terephthalic acid and 1,12-dodecanediic acid.

[0034] In a preferred embodiment, the polyamide salt is polyamide 56 / 5T salt or polyamide 512 / 5T salt. The number "5" in the polyamide 56 / 5T salt and the polyamide 512 / 5T salt represents pentamethylenediamine, the number "6" represents adipic acid, the number "12" represents dodecanedioic acid, and the letter "T" represents terephthalic acid.

[0035] In some specific embodiments, the molar ratio of the aliphatic diamine to the "aliphatic dibasic acid and aromatic dibasic acid" is (0.90-1.15):1, preferably (0.95-1.10):1, for example 1.01:1 or 1.02:1. (To be more consistent with the above specific numerical range)

[0036] In some specific embodiments, the molar ratio of the aromatic dibasic acid to the aliphatic dibasic acid may be (0.5-2.5):1, preferably (0.66-2.33):1, more preferably (0.7-2):1, for example 1.15:1, 1.23:1 or 1.62:1.

[0037] According to the conventional art, the polyamide salt is generally prepolymerized and solid-phase polymerized in the form of a polyamide salt solution. The concentration of the polyamide salt solution can be 10wt% to 75wt%, preferably 35wt% to 70wt%, for example 70wt%, where wt% refers to the mass percentage of the polyamide salt in the polyamide salt solution. The solvent of the polyamide salt solution, i.e., the solvent for the salt-forming reaction, can be water or alcohol, wherein the water is preferably deionized water, and the alcohol is preferably ethanol.

[0038] The conditions of the salt-forming reaction may be conventional in the art. The temperature of the salt-forming reaction may be 30 to 100° C., preferably 50 to 90° C., for example 80° C. The time of the salt-forming reaction may be 20 min to 2.5 h, preferably 40 min to 1.5 h, for example 1 h. The salt-forming reaction is generally carried out in a polymerization reactor.

[0039] After the salt-forming reaction, the step of post-treating the obtained salt-forming product is generally included. The post-treatment step can be conventional in the art, generally including adjusting the pH value, ventilation and / or concentration. After the pH value is adjusted, the pH value of the system is generally 7.0 to 9.5, preferably 7.8 to 9.5, for example 8.5 or 8.65. In the process of adjusting the pH value, the pH value of the system is generally adjusted by adding the aliphatic diamine. The ventilation operation can be conventional in the art, for example, the reaction kettle is sealed and the air in the kettle is replaced with nitrogen 3 times. The concentration step can be conventional in the art, for example, the temperature is raised to 120 to 150°C for concentration.

[0040] In a preferred embodiment, the post-treatment comprises the following steps: sealing the reaction kettle, replacing the air in the kettle with nitrogen for 3-5 times, heating to 100-135° C., and further concentrating the system into a 60-70 wt % polyamide salt solution.

[0041] The polyamide salt solution may also contain various applicable additives in the art, such as reducing agents, defoaming agents, coupling agents, antioxidants, chain extenders, heat stabilizers, weathering agents, anti-hydrolysis stabilizers, reinforcing agents, toughening agents, pigments, gloss enhancers, dyes, crystal nucleating agents, matting agents, plasticizers, antistatic agents, dispersants, catalysts, end-capping agents and anti-UV agents, for example, one or more of antioxidants, dispersants and catalysts, preferably antioxidants and dispersants.

[0042] The antioxidant may be a conventional antioxidant in the art, preferably one or more of N,N'-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hexanediamine, triphenyl phosphite, tris[2,4-di-tert-butylphenyl]phosphite, tris[2,4-di-tert-butylphenyl]phosphite, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate and octadecylβ-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, preferably tris[2,4-di-tert-butylphenyl]phosphite.

[0043] The dispersant may be a conventional dispersant in the art, such as one or more of sodium hypophosphite, sodium hypophosphite, sodium tripolyphosphate and trimetaphosphoric acid, preferably sodium hypophosphite.

[0044] The catalyst may be a conventional catalyst in the art, such as one or more of phosphoric acid, phosphorous acid, hypophosphorous acid, phenyl hypophosphorous acid, phosphoric anhydride, tetrapolyphosphoric acid, pyrophosphoric acid, phosphorus pentachloride and ammonium hypophosphite.

[0045] The dosage of the auxiliary agent can be the conventional dosage in the art, preferably 10 to 10000 ppm of the raw material of the polyamide salt solution, more preferably 50 to 6000 ppm, for example 350 ppm or 400 ppm.

[0046] In a preferred embodiment, the auxiliary agent is tris[2,4-di-tert-butylphenyl]phosphite and sodium hypophosphite, and the mass ratio of tris[2,4-di-tert-butylphenyl]phosphite to sodium hypophosphite is 6: 1. Preferably, the dosage of the auxiliary agent is 350 ppm.

[0047] In a preferred embodiment, the auxiliary agent is tris[2,4-di-tert-butylphenyl]phosphite and sodium hypophosphite, and the mass ratio of tris[2,4-di-tert-butylphenyl]phosphite to sodium hypophosphite is 7: 1. Preferably, the dosage of the auxiliary agent is 400 ppm.

[0048] The present invention also provides a high temperature resistant polyamide, which is prepared by the above-mentioned preparation method.

[0049] In some specific embodiments, the melting point of the high temperature resistant polyamide is 285-325°C, preferably 290-310°C, for example 300.6°C, 300.8°C, 301.3°C, 302.7°C, 304.5°C, 304.6°C or 305.1°C.

[0050] In some specific embodiments, the relative viscosity of the high temperature resistant polyamide is 2.0-3.0, preferably 2.0-2.8, for example, 2.16, 2.22, 2.25, 2.42, 2.44, 2.46 or 2.72.

[0051] In some specific embodiments, the tensile strength of the high temperature resistant polyamide is 80-100 MPa, preferably 90-100 MPa, for example 90.5 MPa, 94.5 MPa, 95.1 MPa, 95.8 MPa, 96.9 MPa, 97.5 MPa or 97.6 MPa.

[0052] In some specific embodiments, the elongation at break of the high temperature resistant polyamide is 4-65%, preferably 6-65%, for example 6.3%, 6.4%, 6.5%, 7.8%, 7.9%, 8.6% or 55.9%.

[0053] In some specific embodiments, the flexural strength of the high temperature resistant polyamide is 100-130 MPa, preferably 100-125 MPa, for example, 100.7 MPa, 119.6 MPa, 121.1 MPa, 121.5 MPa, 123.5 MPa, 124.2 MPa or 124.4 MPa.

[0054] In some specific embodiments, the yellowness index of the polyamide is 2-8, preferably 3-5, such as 3.3, 3.7, 4.1, 4.2, 4.5 or 4.7.

[0055] In some specific embodiments, the gel content of the polyamide is 0.005 wt% to 0.03 wt%, preferably 0.005 to 0.02 wt%, for example 0.008 wt%, 0.012 wt%, 0.013 wt%, 0.014 wt%, 0.016 wt% or 0.017 wt%.

[0056] The present invention also provides a high temperature resistant polyamide, which comprises the following polymerization units:

[0057] Polymerization unit A: and

[0058] Polymerization unit B:

[0059] Wherein, m is 0-8, preferably 2-7, such as 2 or 5; the molar ratio of the polymerized unit A to the polymerized unit B is (35-70): (65-30); the relative viscosity of the high temperature resistant polyamide is 2.0-3.0. The high temperature resistant polyamide may also have the aforementioned performance parameters.

[0060] The present invention also provides the use of the above-mentioned high temperature resistant polyamide in the preparation of high temperature resistant materials.

[0061] On the basis of being in accordance with the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0062] The reagents and raw materials used in the present invention are commercially available.

[0063] The positive and progressive effects of the present invention are:

[0064] (1) The high temperature resistant polyamide prepared by the preparation method of the present invention has a low yellowing index (for example, <5), a low gel content (for example, a gel content of only 0.005 to 0.03 wt%), is not easy to decompose, has a narrower molecular weight distribution, good consistency, high whiteness, fewer black spots, and better mechanical properties, and is more conducive to application in high temperature resistant materials.

[0065] (2) The preparation method of the present invention has low polymerization temperature, low energy consumption, simple method and low equipment requirements. DETAILED DESCRIPTION

[0066] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0067] The reagents used in the examples and comparative examples are all commercially available.

[0068] Example 1

[0069] The preparation method of polyamide comprises the following steps:

[0070] (1) Salt formation: 1315 g of 1,5-pentanediamine, diacid (1134 g of terephthalic acid and 864 g of 1,6-hexanedioic acid), 3300 g of deionized water, 0.33 g of sodium hypophosphite, and 1.98 g of tris[2,4-di-tert-butylphenyl]phosphite were added to a polymerization reactor, the molar ratio of 1,5-pentanediamine to diacid was 1.01:1, and the molar ratio of terephthalic acid to 1,6-hexanedioic acid was 1.15:1, and the salt formation reaction was carried out at 80°C for 1 hour. Subsequently, the pH was adjusted to 8.5 by adding 1,5-pentanediamine, the reactor was sealed, and the air in the reactor was replaced with nitrogen three times, the temperature was raised to 135°C, and the system was further concentrated to a 70wt% salt solution.

[0071] (2) Prepolymerization: The reaction temperature is 240°C, the pressure in the kettle is maintained at 2.0 MPa, and the prepolymerization time is 1 hour. The prepolymer is ejected from the kettle using the pressure in the kettle and crushed in a crusher to D 50 =3mm prepolymer particles.

[0072] (3) Solid-phase polymerization: The granular prepolymer was transferred to the polymerization kettle of the solid-phase reaction device, and the air was replaced with nitrogen for 3 times, and the temperature was raised to 220°C at a heating rate of 15°C / min, and then the temperature was raised to the terminal temperature of 250°C at a heating rate of 2°C / min and maintained for 10 minutes every 10°C rise, and the reaction was continued at this temperature for 6 hours, and the pressure was controlled at -0.08MPa by vacuum. After the reaction was completed, the material was discharged to obtain polyamide.

[0073] Example 2

[0074] Except that the reaction time in step (3) was adjusted to 8 h, the remaining operations and conditions were the same as those in Example 1.

[0075] Example 3

[0076] Except that the reaction time in step (3) was adjusted to 10 h, the remaining operations and conditions were the same as those in Example 1.

[0077] Example 4

[0078] The preparation method of polyamide comprises the following steps:

[0079] (1) Salt formation: 1313 g of 1,5-pentanediamine, diacid (1165 g of terephthalic acid and 835 g of 1,6-hexanedioic acid), 3300 g of deionized water, 0.33 g of sodium hypophosphite, and 2.31 g of tris[2,4-di-tert-butylphenyl]phosphite were added to a polymerization reactor, the molar ratio of 1,5-pentanediamine to diacid was 1.01:1, and the molar ratio of terephthalic acid to 1,6-hexanedioic acid was 1.23:1, and the salt formation reaction was carried out at 80°C for 1 hour. Subsequently, the pH was adjusted to 8.65 by adding 1,5-pentanediamine, the reactor was sealed, and the air in the reactor was replaced with nitrogen three times, the temperature was raised to 135°C, and the system was further concentrated to a 70wt% salt solution.

[0080] (2) Prepolymerization: The reaction temperature is 240°C, the pressure in the kettle is maintained at 2.2 MPa, and the prepolymerization time is 1 hour. The prepolymer is ejected from the kettle using the pressure in the kettle and crushed in a crusher to D 50 =3mm prepolymer particles.

[0081] (3) Solid-phase polymerization: The granular prepolymer was transferred to the polymerization kettle of the solid-phase reaction device, and the air was replaced with nitrogen for 3 times, and the temperature was raised to 220°C at a heating rate of 15°C / min, and then the temperature was raised to the terminal temperature of 255°C at a heating rate of 2°C / min and maintained for 10 minutes every 10°C rise. The reaction was continued at this temperature for 6 hours, and the pressure was controlled at -0.08MPa by vacuum. After the reaction was completed, the material was discharged to obtain polyamide.

[0082] Example 5

[0083] Except that the reaction time in step (3) was adjusted to 8 h, the remaining operations and conditions were the same as those in Example 4.

[0084] Example 6

[0085] Except that the reaction time in step (3) was adjusted to 10 h, the remaining operations and conditions were the same as those in Example 4.

[0086] Example 7

[0087] The preparation method of polyamide comprises the following steps:

[0088] (1) Salt formation: The salt formation process is the same as that in Example 1, except that the ratio of diamine to diacid in the raw materials is different. The diamine in this example is 1,5-pentanediamine, and the diacid is 1,12-dodecanediacid and terephthalic acid, wherein the molar ratio of 1,5-pentanediamine to diacid is 1.02:1, and the molar ratio of terephthalic acid to 1,12-dodecanediacid is 1.62:1.

[0089] (2) Prepolymerization: The reaction temperature is 250°C, the pressure in the kettle is maintained at 2.2 MPa, and the prepolymerization time is 45 min. The prepolymer is ejected from the kettle using the pressure in the kettle and crushed in a crusher to D 50 =3mm prepolymer particles.

[0090] (3) Solid-phase polymerization: The granular prepolymer was transferred to the polymerization kettle of the solid-phase reaction device. After replacing the air with nitrogen for 3 times, the temperature of the polymerization kettle was set to 135°C, and the temperature was raised to 200°C at a heating rate of 2°C / min, and then the temperature was raised to 240°C at a heating rate of 2°C / min and maintained for 10 minutes every 10°C rise. The reaction was continued at this temperature for 6 hours, and the pressure was controlled at -0.08MPa by vacuum. After the reaction was completed, the material was discharged to obtain polyamide.

[0091] Comparative Example 1

[0092] The same feeding, salt formation and prepolymerization methods as in Example 1 were adopted, except that, after the prepolymerization, the pressure of the reactor was unloaded to normal pressure after 40 minutes, the prepolymer was not crushed but the reaction temperature was directly raised to 320°C at 30°C / min, and melt polymerization was carried out at a pressure of -0.08MPa for 20 minutes to obtain polyamide.

[0093] Comparative Example 2

[0094] The same feeding, salt formation and prepolymerization methods as in Example 1 were adopted, except that after the prepolymerization, the pressure of the reactor was unloaded to normal pressure after 40 minutes, the prepolymer was not crushed but the reaction temperature was directly raised to 322°C at 30°C / min, and melt polymerization was carried out at a pressure of -0.08MPa for 25 minutes to obtain polyamide.

[0095] Comparative Example 3

[0096] The same feeding, salt formation and prepolymerization methods as in Example 1 were adopted, except that in the (3) solid phase polymerization stage, the temperature was directly increased to the final temperature of 250°C at a heating rate of 50°C / min, and the reaction was continued at this temperature for 6 hours to obtain polyamide.

[0097] Comparative Example 4

[0098] The same feeding, salt formation and prepolymerization methods as in Example 1 were adopted, except that in the (3) solid phase polymerization stage, the polymerization kettle temperature was set at 130°C, and then directly increased to the final temperature of 250°C at a heating rate of 30°C / min, and the reaction was continued at this temperature for 6 hours to obtain polyamide.

[0099] Comparative Example 5

[0100] The same feeding, salt formation and prepolymerization methods as in Example 1 were adopted, except that in the (3) solid phase polymerization stage, the temperature was first raised to 220°C at a heating rate of 30°C / min, and then raised to a terminal temperature of 250°C at a heating rate of 2°C / min with a heating program of 20°C per heating for 2 min, and the reaction was continued at this temperature for 6 h to obtain polyamide.

[0101] Effect Example

[0102] The test objects are the polyamides prepared in Examples 1 to 7 and Comparative Examples 1 to 5. The test results are shown in Table 1 below.

[0103] (1) Relative viscosity test: Using the concentrated sulfuric acid method of the Ubbelohde viscometer, accurately weigh 0.5±0.0002g of the dried polyamide sample, add 50mL of concentrated sulfuric acid (98%) to dissolve, and measure and record the concentrated sulfuric acid flow time t0 and the polyamide resin solution flow time t in a 25°C constant temperature water bath. Relative viscosity calculation formula: relative viscosity ηr = t / t0, where: t: solution flow time; t0: solvent flow time.

[0104] (2) Melting point test according to ISO 11357-3, heating rate: 20°C / min.

[0105] (3) Tensile strength, elongation at break: refer to standard GB / T 1040.2-2006.

[0106] (4) Notched impact strength: refer to standard GB / T 1843-2008.

[0107] (5) Yellow index test reference standard GB / T 39822-2021.

[0108] (6) Gel content: Test method and conditions: Weigh the dried sample (mass m1) and wrap it with filter paper, then put it into a Soxhlet extractor and extract it with trifluoroethanol. The time starts from the first reflux and the reflux is 24 hours. After the reflux is completed, take out the filter paper and dry it, cool it to room temperature in a desiccator, and weigh the mass of the extracted sample (m2). Gel content = ((m1-m2) / m1)*100%.

[0109] Table 1

[0110]

[0111]

[0112] From the data in Table 1 above, it can be seen that the high temperature resistant polyamide prepared by the preparation method of the present invention has a melting point above 300°C, a low yellow index (<5), a low gel content (gel content as low as 0.03wt%), and better mechanical properties. Moreover, the polyamide obtained in Examples 1-7 of the present invention has high whiteness and few black spots when observed from the surface.

[0113] Comparative Example 1-2 uses a direct one-step polymerization method to prepare polyamide, and there is no step of crushing the prepolymer. The yellow index and gel content of the product are much higher than the polyamide prepared by the step-by-step polymerization method in Example 1-7. In addition, the elongation at break of the polyamide prepared in Comparative Example 1-2 is worse than that in Example 1-7.

[0114] In Comparative Example 3, the terminal temperature is reached by directly increasing the temperature in the solid phase reaction stage, and the yellow index and gel content of the obtained polyamide are also higher than those of Examples 1-7. In addition, the melting point and relative viscosity of the polyamide obtained in Comparative Example 3 are lower than those of Examples 1-7, and the tensile strength is worse than that of Examples 1-7.

[0115] Comparative Examples 4 to 5 use a different solid phase heating method from Example 1. The resulting polymers have a higher yellow index and gel content. Due to the rapid heating, local overheating and uneven molecular weight distribution occur, resulting in significantly lower mechanical properties than Example 1.

Claims

1. A method for preparing a high temperature resistant polyamide, characterized in that: The method comprises the following steps: sequentially prepolymerizing and solid phase polymerizing the polyamide salt; Wherein, the reaction temperature of the prepolymerization is 180-280°C, and the pressure of the prepolymerization is 1.5-3.2MPa; The solid phase polymerization comprises: first heating to 100-220° C., then heating at a heating rate of 1-10° C. / min and keeping the temperature for 5-20 minutes every time the temperature is increased by 1-10° C., until the terminal temperature is 230-300° C., and continuing the reaction for 1-12 hours.

2. The method for preparing high temperature resistant polyamide according to claim 1, characterized in that: The prepolymerization satisfies one or more of the following conditions: (1) The reaction temperature of the prepolymerization is 220-260° C.; (2) the prepolymerization pressure is 1.6 to 2.6 MPa; and (3) The prepolymerization time is 0.5 to 2.5 hours, preferably 0.5 to 1.5 hours.

3. The method for preparing high temperature resistant polyamide according to claim 1, characterized in that: After the prepolymerization is completed, the obtained prepolymer is crushed, and the particle size D of the crushed prepolymer is 50 It is 2 to 10 mm, preferably 3 to 7 mm.

4. The method for preparing a high temperature resistant polyamide according to any one of claims 1 to 3, characterized in that: The solid phase polymerization satisfies one or more of the following conditions: (1) The solid phase polymerization is first heated to 120-220° C.; (2) after the temperature is raised to 100 to 220° C., further raising the temperature at a heating rate of 1 to 5° C. / min; (3) The end point temperature is 240-300° C.; (4) the reaction time until the final temperature reaches 230-300° C. is 6-10 hours; and (5) The pressure of the solid phase polymerization is -0.1 to 0.2 MPa, preferably -0.1 to 0.1 MPa, and more preferably -0.1 to -0.05 MPa.

5. The method for preparing high temperature resistant polyamide according to claim 1 or 2, characterized in that: The polyamide salt is polyamide 56 / 5T salt or polyamide 512 / 5T salt; And / or, the polyamide salt is prepared by the following method: subjecting aliphatic diamine, aliphatic dibasic acid and aromatic dibasic acid to a salt-forming reaction.

6. The method for preparing high temperature resistant polyamide according to claim 5, characterized in that: The polyamide salt satisfies one or more of the following conditions: (1) The aliphatic diamine is one or more aliphatic diamines having 5 to 12 carbon atoms, preferably 1,5-pentanediamine or 1,6-hexanediamine; (2) The aliphatic dibasic acid is one or more of an aliphatic dibasic acid having 2 to 18 carbon atoms, preferably one or more of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, tetradecanedioic acid, pentadecanedicarboxylic acid, hexadecanedioic acid, heptadecanedioic acid and octadecanedicarboxylic acid; (3) The aromatic dibasic acid is one or more dibasic acids having 8 or more carbon atoms and containing a benzene ring, preferably one or more of terephthalic acid, isophthalic acid and phthalic acid; (4) the molar ratio of the aliphatic diamine to the "aliphatic dibasic acid and aromatic dibasic acid" is (0.90-1.15):1, preferably (0.95-1.10):1; and (5) The molar ratio of the aromatic dibasic acid to the aliphatic dibasic acid is (0.5-2.5):1, preferably (0.66-2.33):1, and more preferably (0.7-2):

1.

7. A high temperature resistant polyamide, characterized in that: It is prepared by the preparation method described in any one of claims 1 to 6.

8. The high temperature resistant polyamide according to claim 7, characterized in that: The high temperature resistant polyamide meets one or more of the following conditions: (1) The melting point of the high temperature resistant polyamide is 285-325°C, preferably 290-310°C; (2) The relative viscosity of the high temperature resistant polyamide is 2.0 to 3.0, preferably 2.0 to 2.8; (3) The tensile strength of the high temperature resistant polyamide is 80-100 MPa, preferably 90-100 MPa; (4) The elongation at break of the high temperature resistant polyamide is 4-65%, preferably 6-65%; (5) The flexural strength of the high temperature resistant polyamide is 100-130 MPa, preferably 100-125 MPa; (6) The yellowness index of the polyamide is 2 to 8, preferably 3 to 5; and (7) The gel content of the polyamide is 0.005 wt% to 0.03 wt%, preferably 0.005 to 0.02 wt%.

9. A high temperature resistant polyamide, characterized in that: It contains the following aggregate units: Polymerization unit A: and Polymerization unit B: Wherein, m is 0 to 8, preferably 2 to 7; the molar ratio of the polymer unit A to the polymer unit B is (35 to 70): (65 to 30); and the relative viscosity of the high temperature resistant polyamide is 2.0 to 3.

0.

10. Use of the high temperature resistant polyamide according to any one of claims 7 to 9 in the preparation of high temperature resistant materials.

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