Nylon 6-66 copolymer and preparation method thereof

Abstract

The invention relates to a nylon 6-66 copolymer and a preparation method thereof, and relates to the technical field of copolymerization modification of nylon 6, the preparation method adopts an in-situ copolymerization method, and the preparation method comprises the following steps: obtaining a mixture containing nylon 66 salt, caprolactam and a catalyst; and sequentially carrying out a salt solution polymerization reaction stage, a first melt polymerization reaction stage and a second melt polymerization reaction stage on the mixture in an inert gas atmosphere in a gradient pressure reduction manner to obtain the nylon 6-66 copolymer. According to the preparation method, an in-situ copolymerization method and mixed monomer one-step feeding are utilized, a multi-stage gradient pressure reduction method is combined for copolymerization, and stage polymerization is performed by gradient control of reaction pressure in a reaction system, so that the uniformity of copolyamide bonds and the size stability of the copolymer are improved, and the molecular weight of the copolymer is controlled within a specific value; the mechanical properties of the copolymer are controlled by adjusting the molecular chain sequence distribution of the copolymer, so that the comprehensive properties of the nylon 6-66 copolymer are improved.

Description

Technical Field

[0001] The present application relates to the technical field of copolymerization modification of nylon 6, and in particular to a nylon 6-66 copolymer and a preparation method thereof. Background Art

[0002] Polyamide 6, commonly known as nylon 6 (PA6), is a crystalline polymer with good comprehensive properties and is one of the most widely used varieties of engineering plastics. Nylon 6 chips, also known as nylon 6 chips, are the second largest chemical fiber of synthetic fibers and play an important role in industrial use. They have excellent properties such as high heat resistance, wear resistance, self-lubrication, and chemical corrosion resistance. However, nylon 6 has the disadvantages of low impact strength in dry state or at low temperature, poor transparency, high melting point, and poor softness at low temperature, which limit its application.

[0003] At present, in order to expand the application scope of nylon 6 and meet the actual use needs in more fields, people mostly use copolymerization to modify nylon 6. Chinese invention patent CN106519218A discloses a continuous polymerization process of PA6-66 copolymer and PA6-66 copolymer, which adopts a combination of solid nylon 66 salt and nylon 66 salt solution to produce PA6-66 copolymer with high randomness and high PA66 content, ensuring the stability and uniformity of the product. However, the production of dimers cannot be avoided during the preparation process; although the prepared PA6-66 copolymer has good tensile strength, its impact strength and transparency have not been improved, resulting in a relatively single field of use. Therefore, the comprehensive performance of existing nylon 6-66 copolymers is poor and cannot meet the use needs of PA6 in multiple fields in the prior art. Summary of the invention

[0004] The present application provides a nylon 6-66 copolymer and a preparation method thereof, in order to solve the technical problem that the existing nylon 6-66 copolymer cannot meet the requirements of the prior art for the use of PA6 in multiple fields due to poor comprehensive performance.

[0005] In a first aspect, the present application provides a method for preparing a nylon 6-66 copolymer, wherein the preparation method adopts an in-situ copolymerization method and comprises the following steps:

[0006] A mixture containing nylon 66 salt, caprolactam and a catalyst is obtained;

[0007] In an inert gas atmosphere, the mixture is subjected to a salt solution polymerization reaction stage, a first melt polymerization reaction stage, and a second melt polymerization reaction stage in sequence by a gradient pressure reduction method to obtain a nylon 6-66 copolymer;

[0008] The reaction pressure of the first melt polymerization reaction stage is 0.10 MPa to 0.15 MPa.

[0009] Furthermore, the weight ratio of the caprolactam, the nylon 66 salt and the catalyst is 1:(0.01-0.4):(0.001-0.05).

[0010] Furthermore, the working parameters of the salt solution polymerization reaction stage include: a first reaction temperature of 200° C. to 270° C., a first reaction pressure of 1.0 MPa to 5.0 MPa, and a first reaction time of 0.5 to 5 h.

[0011] Furthermore, the working parameters of the first melt polymerization reaction stage include: a second reaction temperature of 230° C. to 285° C., a second reaction pressure of 0.1 MPa, and a second reaction time of 0.5 h to 5 h.

[0012] Furthermore, the working parameters of the first melt polymerization reaction stage include: a second reaction temperature of 240° C. to 272° C., a second reaction pressure of 0.1 MPa, and a second reaction time of 1 h to 3 h.

[0013] Furthermore, the operating parameters of the second melt polymerization reaction stage include: a third reaction temperature of 230° C. to 285° C., a third reaction pressure of 0.0001 MPa to 0.1 MPa, and a third reaction time of 0.5 h to 4 h.

[0014] Furthermore, the operating parameters of the second melt polymerization reaction stage include: a third reaction temperature of 240° C. to 270° C., a third reaction pressure of 0.0005 MPa to 0.02 MPa, and a third reaction time of 0.5 h to 2.5 h.

[0015] Furthermore, the catalyst is at least one of phosphoric acid, phosphate, phosphite and hypophosphite.

[0016] Furthermore, the step of obtaining a mixture containing nylon 66 salt, caprolactam and a catalyst comprises:

[0017] The hexamethylenediamine solution and the adipic acid solution are mixed and then concentrated to obtain nylon 66 salt with a mass percentage concentration of 30% to 90%;

[0018] The nylon 66 salt, caprolactam and catalyst are heated and stirred to obtain the mixture containing nylon 66 salt, caprolactam and catalyst.

[0019] Furthermore, the gradient pressure reduction method includes:

[0020] The reaction pressure of the salt solution polymerization reaction stage is uniformly reduced at a first pressure reduction rate of 0.05Mpa / min to 0.5Mpa / min to the reaction pressure of the first melt polymerization reaction stage, and then uniformly reduced at a second pressure reduction rate of 0.001Mpa / min to 0.025Mpa / min to the reaction pressure of the second melt polymerization reaction stage.

[0021] In a second aspect, the present application provides a nylon 6-66 copolymer, wherein the nylon 6-66 copolymer is prepared by the preparation method described in any one of the first aspects.

[0022] Furthermore, the physical parameters of the nylon 6-66 copolymer include: number average molecular weight>18000 g / mol, melting point between 187° C. and 235° C., and relative viscosity between 2.6 and 3.9.

[0023] Furthermore, the performance parameters of the nylon 6-66 copolymer include: tensile strength 89 to 177 MPa; impact strength 71 to 142 kJ / m 2 ; Heat-resistant temperature 410℃~435℃; Water absorption 0.32%~0.63%; Transparency 59%~87%.

[0024] In a third aspect, the present application provides a multi-stage polymerization reaction system for realizing the method for preparing nylon 6-66 copolymer according to any one of the embodiments of the first aspect, wherein the multi-stage polymerization reaction system comprises a multi-stage series polymerization reaction device;

[0025] The multi-stage series polymerization reaction device comprises a first stage reactor, a second stage reactor and a third stage reactor which are sequentially connected in series, and are used to sequentially realize the salt solution polymerization reaction stage, the first melt polymerization reaction stage and the second melt polymerization reaction stage respectively;

[0026] The first stage reactor is provided with a feed port for feeding a mixture containing nylon 66 salt, caprolactam and a catalyst;

[0027] The third stage reactor is provided with a discharge port for discharging the nylon 6-66 copolymer;

[0028] The first stage reactor is provided with a first exhaust port, and the second stage reactor is provided with a second exhaust port, so as to realize the reaction under an inert gas atmosphere and control the pressure in the reaction system.

[0029] In a fourth aspect, the present application provides an intermittent polymerization reaction device for realizing the preparation method of nylon 6-66 copolymer described in any one of the embodiments of the first aspect, wherein the intermittent polymerization reaction device comprises a high-pressure reactor;

[0030] The high-pressure reactor is provided with an external circulation heating system and a thermocouple to control the temperature inside the high-pressure reactor;

[0031] The high-pressure reactor is provided with a pressure gauge and a bursting disc on the outside, and the high-pressure reactor is connected to a vacuum regulating system and a pressure relief water tank through a vacuum pipeline to control the pressure inside the high-pressure reactor;

[0032] The high-pressure reactor is provided with a stirring device inside to achieve stirring and mixing of materials;

[0033] The upper part of the high-pressure reactor is provided with a gas input port and a feeding port, which are used to respectively realize the reaction under an inert gas atmosphere and to feed a mixture containing nylon 66 salt, caprolactam and a catalyst;

[0034] The upper part of the high-pressure reactor is provided with a discharge port for discharging the nylon 6-66 copolymer.

[0035] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0036] The embodiment of the present application provides a method for preparing a nylon 6-66 copolymer, which utilizes an in-situ copolymerization method, mixes monomers and feeds them in one step, and combines a multi-stage gradient pressure reduction method for copolymerization, thereby reducing the number of operation steps, and gradiently controls the reaction pressure in the reaction system (especially controlling the reaction pressure in the first melt polymerization reaction stage to be 0.10Mpa to 0.15Mpa) to perform staged polymerization, thereby increasing the uniformity of the copolyamide bonds, increasing the dimensional stability of the polymer, and controlling the molecular weight of the copolymer to be within a specific value, thereby achieving control of the mechanical properties of the copolymer by adjusting the molecular chain sequence distribution of the copolymer, thereby improving the comprehensive properties of the nylon 6-66 copolymer, especially the super mechanical properties, heat resistance and ultra-low water absorption properties, and improving the added value of the nylon 6-66 copolymer product, and effectively solving the technical problem that the existing nylon 6-66 copolymer cannot meet the use requirements of PA6 in multiple fields in the prior art due to poor comprehensive properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0038] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0039] Figure 1A schematic flow chart of a method for preparing a nylon 6-66 copolymer provided in an embodiment of the present application;

[0040] Figure 2 A schematic diagram of the structure of a multi-stage polymerization reaction system provided in an embodiment of the present application;

[0041] Figure 3 A schematic structural diagram of a batch polymerization reaction device provided in an embodiment of the present application;

[0042] Figure 4 Polarized light microscope images of the nylon 6 raw material provided in this application and the nylon 6 / 66 copolymer prepared in Examples 3-5;

[0043] Figure 5 This is a schematic diagram of the electron microscope structure of the nylon 6 / 66 copolymer prepared in Example 3 of the present application;

[0044] Figure 6 Melting point analysis diagram of nylon 6 raw material of the present application and nylon 6 / 66 copolymer prepared in Examples 3-5;

[0045] Figure 7 The wide-angle X-ray diffractometer analysis diagram of the nylon 6 raw material of the present application and the nylon 6 / 66 copolymer prepared in Examples 3-5;

[0046] Figure 8 (a) melting curve and (b) crystallization curve of nylon 6 raw material of the present application and nylon 6 / 66 copolymer prepared in Examples 3-5;

[0047] Among them, 100-multi-stage series polymerization reaction device; 110-first stage reactor; 120-second stage reactor; 130-third stage reactor; 140-feed port; 150-discharge port; 160-first exhaust port; 170-second exhaust port; 200-intermittent polymerization reaction device; 210-high-pressure reactor; 220-stirring device; 230-thermocouple; 240-pressure relief tank; 250-feeding port; 260-gas input port; 270-pressure gauge; 280-bursting disc; 290-discharge port. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0049] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0050] In the first aspect, the present application provides a method for preparing a nylon 6-66 copolymer, such as Figure 1 As shown, the preparation method adopts an in-situ copolymerization method, comprising the following steps:

[0051] A mixture containing nylon 66 salt, caprolactam and a catalyst is obtained;

[0052] In an inert gas atmosphere, the mixture is subjected to a salt solution polymerization reaction stage, a first melt polymerization reaction stage, and a second melt polymerization reaction stage in sequence by a gradient pressure reduction method to obtain a nylon 6-66 copolymer;

[0053] The reaction pressure of the first melt polymerization reaction stage is 0.10 MPa to 0.15 MPa.

[0054] The embodiment of the present application provides a method for preparing a nylon 6-66 copolymer, which utilizes an in-situ copolymerization method, mixes monomers and feeds them in one step, and combines a multi-stage gradient pressure reduction method for copolymerization, thereby reducing the number of operation steps, and gradiently controls the reaction pressure in the reaction system (especially controlling the reaction pressure in the first melt polymerization reaction stage to be 0.10Mpa to 0.15Mpa) to perform staged polymerization, thereby increasing the uniformity of the copolyamide bonds, increasing the dimensional stability of the polymer, and controlling the molecular weight of the copolymer to be within a specific value, thereby achieving control of the mechanical properties of the copolymer by adjusting the molecular chain sequence distribution of the copolymer, thereby improving the comprehensive properties of the nylon 6-66 copolymer, especially the super mechanical properties, heat resistance and ultra-low water absorption properties, and improving the added value of the nylon 6-66 copolymer product, and effectively solving the technical problem that the existing nylon 6-66 copolymer cannot meet the use requirements of PA6 in multiple fields in the prior art due to poor comprehensive properties.

[0055] The above reaction mechanism includes:

[0056] The repeating unit of PA6 is [NH(CH2)5CO], which has an amino group and a carboxyl group at each chain end. The repeating unit of PA66 is [NH(CH2)6NHCO(CH2)4CO], which includes a mixture of molecular chains containing only amino groups / only carboxyl groups or both carboxyl groups and amino groups. PA6 and PA66 have significant differences in melting point / glass transition temperature and crystal structure. However, the introduction of PA66 into PA6 does not change the crystal structure of PA6. That is, the crystal structure is a monoclinic structure, and PA6 in the PA6 / 66 copolymer still maintains its crystal structure. Therefore, the copolymer can maintain the characteristics of PA6 and improve the physical properties of PA6 through PA66. The present invention prepares a high-performance nylon 6 / 66 copolymer by in-situ copolymerization and modification of PA6 and PA66, thereby broadening the application scope of PA6. In the prior art, nylon 66 salt synthesized by solvent crystallization method using hexamethylenediamine and adipic acid as raw materials is used as copolymerization modifier, and then mixed with caprolactam and synthesized by melt copolymerization method to synthesize nylon 6 / 66 copolymer. The copolymer synthesized by this method can regulate the sequence structure distribution and improve the uniformity of the block of the copolymer structure. However, the nylon 6 / 66 copolymer prepared by this method has the same disadvantage of single performance as the copolymer prepared by other methods, which limits its application in the technical field.

[0057] The present invention optimizes the process on the basis of the prior art, and obtains a nylon 6 / 66 copolymer with high comprehensive performance, which has a higher molecular weight, a higher glass transition temperature than conventional nylon 6, and a lower melting point than conventional nylon 6. The introduction of PA66 salt into PA6 does not change the crystal form of PA6, so that PA6 can maintain its own excellent performance. On the other hand, PA6 is modified by introducing PA66 to reduce the melting point of the polymer, and the molecular weight of the copolymer is controlled by precisely controlling the reaction conditions, so that the PA6 / 66 copolymer has higher hydrophobicity and dimensional stability than conventional nylon 6, and has excellent toughness and wear resistance, thereby improving the comprehensive performance of the nylon 6-66 copolymer.

[0058] In some specific embodiments, the reaction pressure of the first melt polymerization reaction stage of the present application may be 0.10 MPa, 0.11 MPa, 0.12 MPa, 0.13 MPa, 0.14 MPa, 0.15 MPa, etc.

[0059] In some specific embodiments, the inert gas may be one of nitrogen, helium, neon, and argon, or a mixture of several of them.

[0060] As an implementation method of an example of the present application, the weight ratio of the caprolactam, the nylon 66 salt and the catalyst is 1:(0.01-0.4):(0.001-0.05).

[0061] The purpose of controlling the weight ratio of the caprolactam, the nylon 66 salt and the catalyst to be 1:(0.01-0.4):(0.001-0.05) in the present application is to adjust the chain length and molecular weight distribution of the polymer, control the crystallization behavior and improve the product quality.

[0062] The above-mentioned "the weight ratio of the caprolactam, the nylon 66 salt and the catalyst is 1: (0.01-0.4): (0.001-0.05)" in the present application can also be expressed as "based on the amount of caprolactam, the amount of the nylon 66 salt added is 1wt%-40wt% of the amount of the caprolactam monomer, and the amount of the catalyst added is 0.1wt%-5wt% of the caprolactam monomer". If the amount of the nylon 66 salt added is too much or too little, the adverse effects are: too much addition will lead to unstable molecular weight and a decrease in overall quality; too little addition will lead to instability of the reaction system, too fast or too slow polymerization speed, thereby affecting the quality and performance of the polymer; if the amount of the catalyst added is too much or too little, the adverse effects are: too much addition will slightly increase the polymerization conversion rate, but the molecular weight is difficult to control; too little addition will lead to insufficient reaction activity and increase the reaction time.

[0063] In some specific embodiments, based on the amount of caprolactam used, the amount of nylon 66 salt added is preferably 2.5wt% to 25wt% of the amount of caprolactam monomer used, specifically 2.5wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt% and the like; more preferably 5wt% to 15wt%; most preferably 10wt%.

[0064] In some specific embodiments, based on the amount of caprolactam used, the amount of the catalyst added is preferably 0.5wt% to 2.5wt% of the caprolactam monomer, specifically 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2.0wt%, 2.1wt%, 2.2wt%, 2.3wt%, 2.4wt%, 2.5wt% and the like; more preferably 1.0wt% to 2.0wt%; most preferably 1.5wt%.

[0065] As an implementation method of an embodiment of the present application, the working parameters of the salt solution polymerization reaction stage include: a first reaction temperature of 200°C to 270°C, a first reaction pressure of 1.0Mpa to 5.0Mpa, and a first reaction time of 0.5 to 5h.

[0066] The purpose of controlling the first reaction temperature of the salt solution polymerization reaction stage (high temperature and high pressure reaction stage) to be 200°C to 270°C, the first reaction pressure to be 1.0Mpa to 5.0Mpa, and the first reaction time to be 0.5 to 5h in this application is to make the reaction proceed faster, reduce the occurrence of side reactions, and improve the polymerization conversion rate. If the first reaction temperature of the salt solution polymerization reaction stage is too high or too low, the adverse effects are: too high temperature will lead to an increase in side reactions; too low temperature will lead to a slow polymerization rate and affect production efficiency; the adverse effects of too high or too low first reaction pressure are: too high pressure will lead to too violent reaction and poor heat transfer in the system; too low pressure will make low-pressure polymerization unable to play an initiating role; the adverse effects of too long or too short first reaction time are: too long reaction time will lead to an increase in side reactions and increased energy consumption; too short reaction time will lead to low conversion rate and incomplete reaction.

[0067] In some specific embodiments, the first reaction temperature may be 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, etc.

[0068] In some specific embodiments, the first reaction pressure may be 1.0 MPa, 1.1 MPa, 1.2 MPa, 1.3 MPa, 1.4 MPa, 1.5 MPa, 1.6 MPa, 1.7 MPa, 1.8 MPa, 1.9 MPa, 2.0 MPa, 2.1 MPa, 2.2 MPa, 2.3 MPa, 2.4 MPa, 2.5 MPa, 2.6 MPa, 2.7 MPa, 2.8 MPa, 2. 9Mpa, 3.0Mpa, 3.1Mpa, 3.2Mpa, 3.3Mpa, 3.4Mpa, 3.5Mpa, 3.6Mpa, 3.7Mpa, 3.8Mpa, 3.9Mpa, 4.0Mpa, 4.1Mpa, 4.2Mpa, 4.3Mpa, 4.4Mpa, 4.5Mpa, 4.6Mpa, 4.7Mpa, 4.8Mpa, 4.9Mpa, 5.0Mpa, etc.

[0069] In some specific embodiments, the first reaction time may be 0.5 h, 1.0 h, 1.5 h, 2.0 h, 2.5 h, 3.0 h, 3.5 h, 4.0 h, 4.5 h, 5 h, etc.

[0070] As an implementation method of an embodiment of the present application, the operating parameters of the first melt polymerization reaction stage include: the second reaction temperature is 230°C to 285°C, the second reaction pressure is 0.1 MPa, and the second reaction time is 0.5h to 5h.

[0071] The purpose of controlling the second reaction temperature of the first melt polymerization reaction stage (high temperature and normal pressure reaction stage) to be 230°C to 285°C, the second reaction pressure to be 0.1Mpa, and the second reaction time to be 0.5h to 5h in this application is to make the reaction proceed faster, reduce the occurrence of side reactions, and improve the polymerization conversion rate. If the second reaction temperature is too high or too low, the adverse effects are: too high temperature will lead to an increase in side reactions; too low temperature will lead to a slow polymerization rate and affect production efficiency; the adverse effects of too high or too low second reaction pressure are: too high pressure will lead to too violent reaction and poor heat transfer in the system; too low pressure will make low-pressure polymerization unable to play an initiating role; the adverse effects of too long or too long second reaction time are: too long reaction time will lead to an increase in side reactions and increased energy consumption; too short reaction time will lead to low conversion rate and incomplete reaction.

[0072] In some specific embodiments, the first reaction temperature is preferably 240°C to 272°C, specifically 240°C, 241°C, 242°C, 243°C, 244°C, 245°C, 246°C, 247°C, 248°C, 249°C, 250°C, 251°C, 252°C, 253°C, 254°C, 255°C, 256°C, 257°C, 258°C, 259°C, 260°C, 261°C, 262°C, 263°C, 264°C, 265°C, 266°C, 267°C, 268°C, 269°C, 270°C, 271°C, 272°C, etc.; more preferably 245°C to 265°C, and most preferably 250°C.

[0073] In some specific embodiments, the second reaction time is preferably 1 h to 3 h, and can be 1.0 h, 1.5 h, 2.0 h, 2.5 h, 3.0 h, etc.

[0074] As an implementation method of an embodiment of the present application, the operating parameters of the second melt polymerization reaction stage include: the third reaction temperature is 230°C to 285°C, the third reaction pressure is 0.0001Mpa to 0.1Mpa, and the third reaction time is 0.5h to 4h.

[0075] The third reaction temperature of the second melt polymerization reaction stage (high temperature negative pressure reaction stage) controlled by the present application is 230°C to 285°C, the third reaction pressure is 0.0001Mpa to 0.1Mpa, and the third reaction time is 0.5h to 4h, so as to make the reaction proceed faster, reduce the occurrence of side reactions, and improve the polymerization conversion rate. If the third reaction temperature is too high or too low, the adverse effects are: too high temperature will lead to an increase in side reactions; too low temperature will lead to a slow polymerization rate and affect production efficiency; the adverse effects of too high or too low third reaction pressure are: too high pressure will lead to too violent reaction and poor heat transfer of the system; too low pressure will make low-pressure polymerization unable to play an initiating role; the adverse effects of too long or too long third reaction time are: too long reaction time will lead to an increase in side reactions and increased energy consumption; too short reaction time will lead to low conversion rate and incomplete reaction.

[0076] In some specific embodiments, the third reaction temperature is preferably 240°C to 270°C, and can be 240°C, 250°C, 260°C, 270°C, etc.; more preferably 250°C to 265°C, and most preferably 260°C.

[0077] In some specific embodiments, the third reaction pressure is preferably 0.0005 MPa to 0.02 MPa, more preferably 0.001 MPa to 0.015 MPa, and most preferably 0.01 MPa.

[0078] In some specific embodiments, the third reaction time is preferably 0.5h to 2.5h, which can be 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h, 2.0h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, etc., and the most preferred is 1.5h.

[0079] As an implementation of an example of the present application, the catalyst is at least one of phosphoric acid, phosphate, phosphite and hypophosphite.

[0080] The present application selects at least one of phosphoric acid, phosphate, phosphite and hypophosphite as the catalyst to act as an acid intermediary in the reaction, adsorb and transition products, thereby reducing the generation of side reaction products and improving the polymer yield. In some specific embodiments, the catalyst includes but is not limited to phosphoric acid, sodium phosphate, potassium phosphate, sodium phosphite, potassium phosphite, sodium hypophosphite, potassium hypophosphite, ammonium phosphate, ammonium phosphite, ammonium hypophosphite, etc.

[0081] As an implementation method of the present application, the step of obtaining a mixture containing nylon 66 salt, caprolactam and a catalyst comprises:

[0082] The hexamethylenediamine solution and the adipic acid solution are mixed and then concentrated to obtain nylon 66 salt with a mass percentage concentration of 30% to 90%;

[0083] The nylon 66 salt, caprolactam and catalyst are heated and stirred to obtain the mixture containing nylon 66 salt, caprolactam and catalyst.

[0084] In some specific embodiments, the mass percentage concentration of the concentrated nylon 66 salt can be 30%, 40%, 50%, 60%, 70%, 80%, 90%, etc.; the temperature for heating and stirring the nylon 66 salt, caprolactam and catalyst can be 150°C to 200°C.

[0085] It should be noted that, in the above “the weight ratio of the caprolactam, the nylon 66 salt and the catalyst is 1:(0.01-0.4):(0.001-0.05)”, the “nylon 66 salt” is calculated based on the amount of nylon 66 salt in the nylon 66 salt concentrate.

[0086] As an implementation of the embodiment of the present application, the gradient pressure reduction method includes:

[0087] The reaction pressure of the salt solution polymerization reaction stage is uniformly reduced at a first pressure reduction rate of 0.05Mpa / min to 0.5Mpa / min to the reaction pressure of the first melt polymerization reaction stage, and then uniformly reduced at a second pressure reduction rate of 0.001Mpa / min to 0.025Mpa / min to the reaction pressure of the second melt polymerization reaction stage.

[0088] The gradient pressure reduction described in the present application refers to reducing the pressure in the polymerization reaction system in two steps by a steady program pressure relief method; the first step of the pressure reduction gradient includes uniformly reducing the high temperature and high pressure conditions (salt solution polymerization reaction stage) to the temperature and normal pressure conditions (first melt polymerization reaction stage), and the pressure reduction rate is 0.05-0.5MPa / min; the second step of the pressure reduction gradient includes uniformly reducing the temperature and normal pressure conditions (first melt polymerization reaction stage) to the high temperature negative pressure conditions (second melt polymerization reaction stage), and the pressure reduction rate is 0.001-0.025MPa / min.

[0089] In a second aspect, based on a general inventive concept, the present application provides a nylon 6-66 copolymer, wherein the nylon 6-66 copolymer is prepared by the preparation method described in any one of the first aspects.

[0090] The nylon 6-66 copolymer provided in the present application is realized based on the preparation method described in any one of the first aspects above, and therefore has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be described one by one here.

[0091] As an implementation of an embodiment of the present application, the physical parameters of the nylon 6-66 copolymer include: number average molecular weight>18000 g / mol, melting point between 187°C and 235°C, and relative viscosity between 2.6 and 3.9.

[0092] The number average molecular weight of the nylon 6-66 copolymer provided in the present application is greater than 18000 g / mol (the number average molecular weight can reach up to 120000 g / mol), and has a higher molecular weight, indicating that it has higher strength and rigidity and can withstand heavier loads; the melting point is between 155°C and 205°C, and has a lower melting point, indicating that the monomer units in the PA6-66 copolymer have better random distribution; the relative viscosity is between 2.6 and 3.9, indicating that the product has a higher molecular weight and a narrower molecular weight distribution.

[0093] As an implementation of the present application, the performance parameters of the nylon 6-66 copolymer include: tensile strength 89 to 177 MPa; impact strength 71 to 142 kJ / m 2 ; Heat-resistant temperature 410℃~435℃; Water absorption 0.32%~0.63%; Transparency 59%~87%.

[0094] The nylon 6-66 copolymer provided in the present application has excellent comprehensive properties, especially super strong mechanical properties, good heat resistance, good transparency and ultra-low water absorption, has higher product added value, and can meet the existing technology for the use of PA6 in multiple fields.

[0095] Thirdly, Figure 2 As shown, based on a general inventive concept, the present application provides a multi-stage polymerization reaction system for realizing the preparation method of nylon 6-66 copolymer described in any one of the embodiments of the first aspect, wherein the multi-stage polymerization reaction system comprises a multi-stage series polymerization reaction device 100;

[0096] The multi-stage series polymerization reaction device 100 comprises a first stage reactor 110, a second stage reactor 120 and a third stage reactor 130 which are sequentially connected in series, and are used to sequentially realize the salt solution polymerization reaction stage, the first melt polymerization reaction stage and the second melt polymerization reaction stage respectively;

[0097] The first stage reactor 110 is provided with a feed port 140 for feeding a mixture containing nylon 66 salt, caprolactam and a catalyst;

[0098] The third stage reactor 130 is provided with a discharge port 150 for discharging the nylon 6-66 copolymer;

[0099] The first stage reactor 110 is provided with a first exhaust port 160 , and the second stage reactor 120 is provided with a second exhaust port 170 , so as to realize the reaction under an inert gas atmosphere and control the pressure in the reaction system.

[0100] The preparation method of nylon 6-66 copolymer provided in the first aspect of the present application can be carried out step by step in the multi-stage polymerization reaction system provided in the third aspect in a continuous operation mode: a mixture containing nylon 66 salt, caprolactam and a catalyst is continuously added to the first stage reactor 110 of the multi-stage series polymerization reaction system, and the reaction is carried out in the first stage reactor 110, the second stage reactor 120 and the third stage reactor 130 in sequence; the salt solution polymerization reaction under high temperature and high pressure conditions is carried out in the first stage reactor 110; the first melt polymerization reaction stage under high temperature and normal pressure conditions and the second melt polymerization reaction stage under high temperature and negative pressure conditions are carried out in the second stage reactor 120 and the third stage reactor 130 in sequence, and the obtained nylon 6-66 copolymer is discharged through the discharge port 150.

[0101] It should be noted that the first stage reactor, the second stage reactor, the third stage reactor and other equipment and components involved in the multi-stage polymerization reaction system of the present application, if there are no special limitations and requirements, can adopt existing equipment such as conventional polymerization reactors in the field and connect according to existing process design methods, and will not be described one by one here.

[0102] Fourthly, Figure 3 As shown, based on a general inventive concept, the present application provides an intermittent polymerization reaction device for realizing the preparation method of nylon 6-66 copolymer described in any one of the embodiments of the first aspect, wherein the intermittent polymerization reaction device 200 comprises a high-pressure reactor 210;

[0103] The high-pressure reactor 210 is provided with an external circulation heating system and a thermocouple 230 to control the temperature inside the high-pressure reactor;

[0104] The high-pressure reactor 210 is provided with a pressure gauge 270 and a bursting disc 280 outside, and the high-pressure reactor is connected to a vacuum regulating system and a pressure relief water tank 240 through a vacuum pipeline to control the pressure inside the high-pressure reactor;

[0105] The high pressure reactor 210 is provided with a stirring device 220 for stirring and mixing the materials;

[0106] The upper portion of the high-pressure reactor 210 is provided with a gas input port 260 and a feed port 250 for respectively realizing the reaction under an inert gas atmosphere and feeding a mixture containing nylon 66 salt, caprolactam and a catalyst;

[0107] The upper portion of the high-pressure reactor 210 is provided with a discharge port 290 for discharging the nylon 6-66 copolymer.

[0108] The preparation method of the nylon 6-66 copolymer provided in the first aspect of the present application can be gradually carried out in the intermittent polymerization reaction device provided in the fourth aspect through an intermittent operation mode: the mixture containing nylon 66 salt, caprolactam and catalyst is added to the intermittent polymerization reaction device at one time, the temperature and pressure in the high-pressure reactor 210 are controlled, and the salt solution polymerization reaction stage, the first melt polymerization reaction stage and the second melt polymerization reaction stage are carried out in sequence. After the reaction is completed, the nylon 6 / 66 copolymer is discharged from the outlet of the polymerization reactor.

[0109] It should be noted that the external circulation heating system, thermocouple, vacuum pipeline connected vacuum adjustment system and pressure relief water tank and other equipment and components involved in the intermittent polymerization reaction device of the present application, if there are no special restrictions and requirements, can adopt conventional existing equipment in the field and be connected according to existing process design methods, and will not be described one by one here.

[0110] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are intended only to illustrate the present application and are not intended to limit the scope of the present application. The experimental methods for which specific conditions are not specified in the following examples are usually measured according to national standards. If there is no corresponding national standard, then the conditions recommended by the manufacturer are followed.

[0111] Example 1

[0112] This embodiment provides a multi-stage polymerization reaction system, such as Figure 2 As shown, the multi-stage polymerization reaction system includes a multi-stage series polymerization reaction device 100;

[0113] The multi-stage series polymerization reaction device 100 comprises a first stage reactor 110, a second stage reactor 120 and a third stage reactor 130 which are sequentially connected in series, and are used to sequentially realize the salt solution polymerization reaction stage, the first melt polymerization reaction stage and the second melt polymerization reaction stage respectively;

[0114] The first stage reactor 110 is provided with a feed port 140 for feeding a mixture containing nylon 66 salt, caprolactam and a catalyst;

[0115] The third stage reactor 130 is provided with a discharge port 150 for discharging the nylon 6-66 copolymer;

[0116] The first stage reactor 110 is provided with a first exhaust port 160 , and the second stage reactor 120 is provided with a second exhaust port 170 , so as to realize the reaction under an inert gas atmosphere and control the pressure in the reaction system.

[0117] Example 2-30 provides a method for preparing a nylon 6-66 copolymer, wherein the preparation method adopts an in-situ copolymerization method and comprises the following steps:

[0118] Dissolve equimolar amounts of adipic acid (ADA) and hexamethylenediamine (HMDA) powders in anhydrous ethanol, heat to 60° C., and continue stirring until the hexamethylenediamine solid is completely dissolved to obtain a hexamethylenediamine solution;

[0119] The adipic acid solution is heated to 75° C., and then the hexamethylenediamine solution is added and stirred continuously, and then concentrated to obtain nylon 66 salt with a mass percentage concentration of 30% to 90%;

[0120] The nylon 66 salt, caprolactam and catalyst are heated and stirred to obtain the mixture containing nylon 66 salt, caprolactam and catalyst;

[0121] In an inert gas atmosphere, the mixture is subjected to a salt solution polymerization reaction stage, a first melt polymerization reaction stage, and a second melt polymerization reaction stage in sequence by a gradient pressure reduction method to obtain a nylon 6-66 copolymer;

[0122] Wherein, based on the amount of caprolactam used, the amount of nylon 66 salt added is 1wt% to 40wt% of the amount of caprolactam monomer used, and the amount of the catalyst added is 0.1wt% to 5wt% of the caprolactam monomer;

[0123] The working parameters of the salt solution polymerization reaction stage include: a first reaction temperature of 200° C. to 270° C., a first reaction pressure of 1.0 MPa to 5.0 MPa, and a first reaction time of 0.5 to 5 h;

[0124] The working parameters of the first melt polymerization reaction stage include: a second reaction temperature of 230°C to 285°C, a second reaction pressure of 0.10Mpa to 0.15Mpa, and a second reaction time of 0.5h to 5h;

[0125] The working parameters of the second melt polymerization reaction stage include: a third reaction temperature of 230° C. to 285° C., a third reaction pressure of 0.0001 MPa to 0.1 MPa, and a third reaction time of 0.5 h to 4 h;

[0126] The catalyst comprises at least one of phosphoric acid, sodium phosphate, potassium phosphate, sodium phosphite, potassium phosphite, sodium hypophosphite, potassium hypophosphite, ammonium phosphate, ammonium phosphite and ammonium hypophosphite;

[0127] The gradient pressure reduction method includes:

[0128] The reaction pressure of the salt solution polymerization reaction stage is uniformly reduced at a first pressure reduction rate of 0.05Mpa / min to 0.5Mpa / min to the reaction pressure of the first melt polymerization reaction stage, and then uniformly reduced at a second pressure reduction rate of 0.001Mpa / min to 0.025Mpa / min to the reaction pressure of the second melt polymerization reaction stage.

[0129] The preparation method of the nylon 6-66 copolymer provided in Examples 2-30 can be carried out step by step in the multi-stage polymerization reaction system provided in Example 1 in a continuous operation mode: a mixture containing nylon 66 salt, caprolactam and a catalyst is continuously added to the first reactor 110 of the multi-stage series polymerization reaction system, and the reaction is carried out in the first reactor 110, the second reactor 120 and the third reactor 130 in sequence; the salt solution polymerization reaction under high temperature and high pressure conditions is carried out in the first reactor 110; the first melt polymerization reaction stage under high temperature and normal pressure conditions and the second melt polymerization reaction stage under high temperature and negative pressure conditions are carried out in the second reactor 120 and the third reactor 130 in sequence, and the obtained nylon 6-66 copolymer is discharged through the discharge port 150, and the product of the obtained nylon 6-66 copolymer is analyzed.

[0130] Test method for number average molecular weight: The number average molecular weight (Mn) is determined by titrating the concentrations of the terminal carboxyl group and terminal amino group of nylon 6 / 66 copolymer with potassium hydroxide ethanol solution and hydrochloric acid solution respectively, and then according to the formula Mn = 2 (C -NH2 +C -COOH ) to determine.

[0131] Melting point test method: Differential scanning calorimetry (DSC) was used to test the melting point, and DiamondDSC (PerkinElmer) was used to analyze the isothermal and non-isothermal crystallization behavior of PA6 / 66 copolymers. The melting point and the melting enthalpy of high-purity indium metal were used to calibrate the temperature range and power response of the DSC analysis. All DSC analyses were performed under a nitrogen atmosphere. In order to analyze the crystallization and melting behavior, 5-10 mg of the sample was heated to 250°C at a rate of 10°C / min and kept constant for 10 minutes. Then, the sample was cooled to 50°C at a rate of 5°C / min. The crystallization exotherm was recorded and the corresponding crystallization start temperature (T0), crystallization temperature (Tp) and crystallization termination temperature (Tf) were read. Finally, the sample was heated to 250°C at a rate of 10°C / min, the melting curve was recorded and the corresponding melting point (Tm) was read.

[0132] Relative viscosity test method: Refer to the relative viscosity test method of nylon 6 chips in GB / T38138-2019, use 50ml of concentrated sulfuric acid with a mass fraction of (96.0±0.1)% as the solvent, accurately weigh 0.5000g of the dried polymer sample, and prepare a 0.010g / mL solution. Test at a temperature of (25.00±0.02)℃, and the capillary diameter of the Ubbelohde viscometer is 1.03mm. The ratio of the residence time t of the sample solution through the viscometer to the residence time t0 of the pure solvent is the relative viscosity η of the sample. r =t / t0.

[0133] Test method for impact strength: refer to GB / T 1043-1993 impact test method for hard plastics, after pressing the sample, measure the width and thickness of the middle part of the sample, accurate to 0.02mm. The residual thickness at the notch should be measured for the notch sample, and the measurement should be done once at both ends of the notch, and the arithmetic mean should be taken; select the pendulum according to the energy required for sample destruction, so that the energy consumed is within the range of 10% to 85% of the total energy of the pendulum; adjust the zero point of the energy dial pointer so that it contacts the active needle when the pendulum is in the starting position, and conduct an empty strike test; lift and lock the pendulum, place the sample on the two support blocks as required, with the sample support surface close to the support block, align the impact blade with the center of the sample, and the notch sample blade with the back center position; release the pendulum steadily, and read the impact energy absorbed by the sample from the dial.

[0134] Test method for water absorption performance: Refer to the water absorption test method for evaluating materials in GB / T 1034-2008 standard, place the sample in a 50.0℃±2.0℃ oven and dry it for about 24 hours, then cool it to room temperature in a dryer, weigh each sample to an accuracy of 0.1 mg (mass m1); place the sample in a container filled with distilled water, and control the water temperature at 23.0℃±1.0℃; after soaking for 24h±1h, take out the sample, quickly wipe off all moisture on the surface of the sample with clean filter paper, and weigh each sample again to an accuracy of 0.1 mg (mass m2). After the sample is taken out of the water, the weighing should be completed within 1 minute, and the test result of each sample in the test is the average of at least 3 samples. The final water absorption mass fraction of the sample can be expressed as c is the mass fraction of the sample, and the value is expressed in %.

[0135] Test method for heat resistance: Using TGA analysis, place an appropriate amount of sample in a crucible, raise the temperature to 600°C at 10°C / min under a nitrogen atmosphere, record the curve, and measure the temperature corresponding to 5% thermal decomposition.

[0136] Dynamic mechanical thermal analysis (DMA): The extracted polymer particles were injection molded into specimens with a size of 35×12×2 mm3 using an injection molding machine (HAAKE MiniJet-557-2270). Dynamic mechanical properties were measured in tensile mode using a DMAQ800 (TA Instruments, America) equipped with a liquid nitrogen cooling system. The test temperature range was -100 to 150 °C, the heating rate was 5 °C / min, and the test frequency was 1 Hz.

[0137] Test method for oligomer content: First, use a Soxhlet extractor to extract the residual caprolactam and cyclic dimer in all samples. The specific operation is as follows: put 0.5g of polymer sample into the filter cartridge to load the extractor, add 200ml of anhydrous methanol as the extractant, extract at 200℃ for 24h, collect the extract and dilute to 250ml for analysis. The extracted polymer particles are vacuum dried at 80℃ for 24h before analysis; water and methanol are used as two mobile phases, and high performance liquid chromatography (HPLC) is used to analyze the oligomer content in the extract. The content of caprolactam and cyclic dimer in the liquid sample is analyzed by external standard method.

[0138] Examples 2-7 investigate the effect of the amount of nylon 66 salt added on the preparation of nylon 6-66 copolymer.

[0139] The specific amount of nylon 66 salt in Examples 2-7 (measured in terms of the amount of nylon 66 salt in the nylon 66 salt concentrate) is shown in Table 2, and the remaining parameters are: the concentration of nylon 66 salt after concentration is 50wt%; the amount of caprolactam is 1kg; the catalyst is phosphoric acid, and the amount of added is 0.1wt% of the caprolactam monomer; the operating parameters of the salt solution polymerization reaction stage include: the first reaction temperature is 200°C, the first reaction pressure is 1.0Mpa, and the first reaction time is 1h; the operating parameters of the first melt polymerization reaction stage include: the second reaction temperature is 230°C, the second reaction pressure is 0.10Mpa, and the second reaction time is 2h; the working parameters of the second melt polymerization reaction stage include: the third reaction temperature is 230°C, the third reaction pressure is 0.005Mpa, and the third reaction time is 1h; the reaction pressure of the salt solution polymerization reaction stage is uniformly reduced at a first pressure reduction rate of 0.02Mpa / min to the reaction pressure of the first melt polymerization reaction stage, and then uniformly reduced at a second pressure reduction rate of 0.015Mpa / min to the reaction pressure of the second melt polymerization reaction stage.

[0140] Table 2 Example 2-7 Influence of the amount of nylon 66 salt added on the preparation of nylon 6-66 copolymer

[0141]

[0142] Examples 8-9 investigate the effect of the concentration of concentrated nylon 66 salt on the preparation of nylon 6-66 copolymer.

[0143] Based on Example 6, Examples 8-9 only adjust the concentration of nylon 66 salt after concentration. The specific concentrations of nylon 66 salt after concentration in Examples 8-9 are shown in Table 3.

[0144] Table 3 Example 8-9 Influence of the concentration of nylon 66 salt after concentration on the preparation of nylon 6-66 copolymer

[0145]

[0146] Examples 10-15 investigate the effects of the operating parameters in the salt solution polymerization stage on the preparation of nylon 6-66 copolymer.

[0147] On the basis of Example 6, Examples 10-15 only adjust the working parameters of the salt solution polymerization reaction stage. The specific working parameters of the salt solution polymerization reaction stage in Examples 10-15 are shown in Table 4. The test analysis results of the obtained nylon 6-66 copolymer are shown in Table 5.

[0148] Table 4 Influence of working parameters in salt solution polymerization stage on preparation of nylon 6-66 copolymer in Examples 10-15

[0149]

[0150] Table 5 Test and analysis results of nylon 6-66 copolymer obtained in Examples 10-15

[0151]

[0152]

[0153] Examples 16-21 investigate the effects of the operating parameters of the first melt polymerization stage on the preparation of nylon 6-66 copolymer.

[0154] Based on Example 12, Examples 16-21 only adjusted the operating parameters of the first melt polymerization reaction stage. The specific operating parameters of the first melt polymerization reaction stage in Examples 16-21 are shown in Table 6. The test analysis results of the obtained nylon 6-66 copolymer are shown in Table 7.

[0155] Table 6: Effect of the working parameters of the first melt polymerization reaction stage on the preparation of nylon 6-66 copolymers in Examples 16-21

[0156]

[0157] Table 7 Test and analysis results of nylon 6-66 copolymers obtained in Examples 16-21

[0158]

[0159]

[0160] Examples 22-30 investigate the effects of the operating parameters of the second melt polymerization stage on the preparation of nylon 6-66 copolymer.

[0161] Based on Example 18, Examples 22-30 only adjust the operating parameters of the second melt polymerization reaction stage. The specific operating parameters of the second melt polymerization reaction stage in Examples 22-30 are shown in Table 8, and the test analysis results of the obtained nylon 6-66 copolymer are shown in Table 9.

[0162] Table 8: Effect of working parameters of the second melt polymerization reaction stage on the preparation of nylon 6-66 copolymer in Examples 22-30

[0163]

[0164] Table 9 Test and analysis results of nylon 6-66 copolymer obtained in Examples 22-30

[0165]

[0166] Examples 28-30 investigate the effect of catalyst type on the preparation of nylon 6-66 copolymer.

[0167] Based on Example 25, Examples 28-30 only adjusted the catalyst type. The catalyst types in Examples 28-30 are shown in Table 10.

[0168] Table 10: Effect of catalyst type on the preparation of nylon 6-66 copolymers in Examples 28-30

[0169]

[0170] Embodiment 31

[0171] This embodiment provides a batch polymerization reaction device, such as Figure 3 As shown, the intermittent polymerization reaction device 200 includes a high-pressure reactor 210;

[0172] The high-pressure reactor 210 is provided with an external circulation heating system (temperature is regulated by circulating heat medium such as heat transfer oil) and a thermocouple 230 to control the temperature inside the high-pressure reactor;

[0173] The high-pressure reactor 210 is provided with a pressure gauge 270 and a bursting disc 280 outside, and the high-pressure reactor is connected to a vacuum regulating system and a pressure relief water tank 240 through a vacuum pipeline to control the pressure inside the high-pressure reactor;

[0174] The high pressure reactor 210 is provided with a stirring device 220 for stirring and mixing the materials;

[0175] The upper portion of the high-pressure reactor 210 is provided with a gas input port 260 and a feed port 250 for respectively realizing the reaction under an inert gas atmosphere and feeding a mixture containing nylon 66 salt, caprolactam and a catalyst;

[0176] The upper portion of the high-pressure reactor 210 is provided with a discharge port 290 for discharging the nylon 6-66 copolymer.

[0177] The preparation method of the nylon 6-66 copolymer provided in Examples 2-30 of the present application can be gradually carried out in an intermittent polymerization reaction device provided in Example 28 by an intermittent operation mode: the mixture containing nylon 66 salt, caprolactam and catalyst is added to the intermittent polymerization reaction device at one time, the temperature and pressure in the high-pressure reactor 210 are controlled, and the salt solution polymerization reaction stage, the first melt polymerization reaction stage and the second melt polymerization reaction stage are carried out in sequence. After the reaction is completed, the nylon 6 / 66 copolymer is discharged from the outlet of the polymerization reactor.

[0178] Also, see Figure 4 and Figure 5 When the morphological changes of the crystallization process of PA6 and PA6 / 66 copolymer were analyzed by polarizing microscope and electron microscope, it was shown that the crystallization ability of PA6 was stronger than that of PA6 / 66 copolymer. Figure 4 Figure a) and Example 3 ( Figure 4 (b), Example 4 ( Figure 4 Figure c), Example 5 ( Figure 4 The corresponding crystallization completion times of Figure d are 2.2 min, 2.5 min, 7.8 min and 9.5 min, respectively, which indicates that within a certain range, the crystallization rate decreases with the increase of nylon 66 salt content, the randomness of the chain segments of PA6 / 66 copolymer increases with the feeding ratio of nylon 66 salt, and the growth of spherulites is restricted due to the deterioration of the regularity of molecular chain arrangement, thereby reducing the crystallization ability.

[0179] Figure 7The WAXD analysis of PA6 and PA6 / 66 copolymers by wide angle X-ray diffractometer. The spectrum of the PA6 / 66 polymer samples of Examples 3-5 shows two strong diffraction peaks corresponding to the characteristic structure of α-type crystals at 2θ=20° and 2θ=23.7°, and another strong diffraction peak corresponding to the characteristic structure of γ-type crystals at 2θ=21.3°, which is similar to the spectrum of PA6, further proving that the PA6 / 66 copolymer prepared by the technical solution of Examples 3-5 has the same crystal structure as PA6. Furthermore, as the salt content of PA66 increases, its intensity gradually increases.

[0180] See also Figure 6 and Figure 8 The melting curves of PA6 raw material and PA6 / 66 copolymer both have two melting peaks, which further proves that the addition of PA66 does not change the crystal form of PA6. The melting point, crystallization starting temperature, crystallization temperature and crystallization termination temperature of PA6 / 66 copolymer in Examples 3-5 are all lower than those of PA6, and decrease with the increase of nylon 66 salt content, indicating that with the increase of the addition amount of nylon 66 salt, the number of copolyamide bonds in the molecular chain gradually increases, the degree of destruction of the segment regularity increases, the polymer melting point decreases, and the crystallization ability decreases. On the other hand, the peak width of the crystallization curve also increases with the increase of nylon 66 salt content, which indicates that the difference in the degree of crystal perfection in the polymer system increases with the deterioration of segment regularity.

[0181] In summary, the present invention utilizes an in-situ copolymerization method, mixes monomers and feeds them in one step, and combines a multi-stage gradient pressure reduction method to carry out copolymerization, gradient controls the reaction pressure and other parameters in the reaction system to carry out staged polymerization, increases the uniformity of the copolymer amide bonds and the dimensional stability of the polymer, controls the molecular weight of the copolymer to be within a specific value, and realizes the control of the mechanical properties of the copolymer by adjusting the molecular chain sequence distribution of the copolymer, thereby improving the comprehensive performance and added value of the nylon 6-66 copolymer.

[0182] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0183] In the present application, in the absence of any contrary description, the directional words used, such as "upper" and "lower", are specifically the directions of the drawings in the accompanying drawings. In addition, in the description of the present specification, the terms "including", "comprising", etc. refer to "including but not limited to". In this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of the associated objects, indicating that there may be three relationships, for example, A and / or B, which can represent: A exists alone, A and B exist at the same time, and B exists alone. Wherein A, B can be singular or plural. In this article, "at least one" refers to one or more, and "plural" refers to two or more. "At least one", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of singular or plural items. For example, "at least one of a, b, or c", or "at least one of a, b and c", can both mean: a, b, c, ab (i.e. a and b), ac, bc or abc, where a, b, c can be single or plural, respectively.

[0184] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. A method for preparing a nylon 6-66 copolymer, characterized in that: The preparation method adopts an in-situ copolymerization method, comprising the following steps: A mixture containing nylon 66 salt, caprolactam and a catalyst is obtained; In an inert gas atmosphere, the mixture is subjected to a salt solution polymerization reaction stage, a first melt polymerization reaction stage, and a second melt polymerization reaction stage in sequence by a gradient pressure reduction method to obtain a nylon 6-66 copolymer; The reaction pressure of the first melt polymerization reaction stage is 0.10 MPa to 0.15 MPa.

2. The preparation method according to claim 1, characterized in that: The weight ratio of the caprolactam, the nylon 66 salt and the catalyst is 1:(0.01-0.4):(0.001-0.05).

3. The preparation method according to claim 1, characterized in that: The working parameters of the salt solution polymerization reaction stage include: a first reaction temperature of 200° C. to 270° C., a first reaction pressure of 1.0 MPa to 5.0 MPa, and a first reaction time of 0.5 to 5 h.

4. The preparation method according to claim 1, characterized in that: The working parameters of the first melt polymerization reaction stage include: a second reaction temperature of 230° C. to 285° C., a second reaction pressure of 0.1 MPa, and a second reaction time of 0.5 h to 5 h.

5. The preparation method according to claim 1, characterized in that: The working parameters of the second melt polymerization reaction stage include: a third reaction temperature of 230° C. to 285° C., a third reaction pressure of 0.0001 MPa to 0.1 MPa, and a third reaction time of 0.5 h to 4 h.

6. The preparation method according to claim 1, characterized in that: The catalyst is at least one of phosphoric acid, phosphate, phosphite and hypophosphite.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The step of obtaining a mixture containing nylon 66 salt, caprolactam and a catalyst comprises: The hexamethylenediamine solution and the adipic acid solution are mixed and then concentrated to obtain nylon 66 salt with a mass percentage concentration of 30% to 90%; The nylon 66 salt, caprolactam and catalyst are heated and stirred to obtain the mixture containing nylon 66 salt, caprolactam and catalyst.

8. The preparation method according to claim 7, characterized in that: The gradient pressure reduction method includes: The reaction pressure of the salt solution polymerization reaction stage is uniformly reduced at a first pressure reduction rate of 0.05Mpa / min to 0.5Mpa / min to the reaction pressure of the first melt polymerization reaction stage, and then uniformly reduced at a second pressure reduction rate of 0.001Mpa / min to 0.025Mpa / min to the reaction pressure of the second melt polymerization reaction stage.

9. A nylon 6-66 copolymer, characterized in that: The nylon 6-66 copolymer is prepared by the preparation method described in any one of items 1 to 8.

10. The nylon 6-66 copolymer according to claim 9, characterized in that The physical parameters of the nylon 6-66 copolymer include: number average molecular weight>18000g / mol, melting point of 187°C to 235°C, relative viscosity of 2.6 to 4.0, tensile strength of 89 to 177MPa, impact strength of 71 to 150kJ / m 2 , heat-resistant temperature 410℃~435℃, water absorption 0.32%~0.63%; transparency 59%~87%.

11. A multi-stage polymerization reaction system used in conjunction with the preparation method according to any one of claims 1 to 8, characterized in that: The multi-stage polymerization reaction system comprises a multi-stage series polymerization reaction device; The multi-stage series polymerization reaction device comprises a first stage reactor, a second stage reactor and a third stage reactor which are sequentially connected in series, and are used to sequentially realize the salt solution polymerization reaction stage, the first melt polymerization reaction stage and the second melt polymerization reaction stage respectively; The first stage reactor is provided with a feed port for feeding a mixture containing nylon 66 salt, caprolactam and a catalyst; The third stage reactor is provided with a discharge port for discharging the nylon 6-66 copolymer; The second stage reactor and the third stage reactor are both provided with an inert gas input port, the first stage reactor is provided with a first exhaust port, and the second stage reactor is provided with a second exhaust port, so as to realize the reaction under an inert gas atmosphere and control the pressure in the reaction system.

12. A batch polymerization reaction device used in conjunction with the preparation method according to any one of claims 1 to 8, characterized in that: The intermittent polymerization reaction device comprises a high-pressure reactor; The high-pressure reactor is provided with an external circulation heating system and a thermocouple to control the temperature inside the high-pressure reactor; The high-pressure reactor is provided with a pressure gauge and a bursting disc on the outside, and the high-pressure reactor is connected to a vacuum regulating system and a pressure relief water tank through a vacuum pipeline to control the pressure inside the high-pressure reactor; The high-pressure reactor is provided with a stirring device inside to achieve stirring and mixing of materials; The upper part of the high-pressure reactor is provided with a gas input port and a feeding port, which are used to respectively realize the reaction under an inert gas atmosphere and to feed a mixture containing nylon 66 salt, caprolactam and a catalyst; The upper part of the high-pressure reactor is provided with a discharge port for discharging the nylon 6-66 copolymer.

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