A method for inhibiting the formation of polyamide 6 non-melting cyclic dimers and its application

Abstract

The present invention belongs to the technical field of polyamide 6 synthesis, and relates to a method for inhibiting the formation of infusible cyclic dimers of polyamide 6 and an application thereof. A method for inhibiting the formation of infusible cyclic dimers of polyamide 6 is to add an amino acid in the ring opening stage and the polycondensation stage respectively during the process of synthesizing polyamide 6 from caprolactam by hydrolysis, wherein the amino acid is an amino acid other than aminocaproic acid. An application is to synthesize a polyamide 6 by adopting the method for inhibiting the formation of infusible cyclic dimers of polyamide 6. The present invention reduces the proportion of original infusible cyclic dimers at thermodynamic equilibrium by adding an amino acid at different stages, thereby improving the melt quality, avoiding the influence of infusible cyclic dimers on the melt spinning process, and meeting the processing requirements of direct high-speed spinning.

Description

Technical Field

[0001] The invention belongs to the technical field of polyamide 6 synthesis, and relates to a method for inhibiting the generation of polyamide 6 infusible cyclic dimers and an application thereof. Background Art

[0002] Polyamide 6 (PA6) has excellent physical and mechanical properties and textile processing properties, and is widely used in the field of plastic fibers. Its supply and demand are both on the rise. In particular, polyamide 6 fiber has the characteristics of high breaking strength, good abrasion resistance, good moisture absorption, excellent elastic recovery rate and fatigue resistance, and good dyeability. It can be used in clothing, tire cord fabrics, filter materials, carpet bulked yarns and other fields.

[0003] At present, one of the main methods for synthesizing polyamide 6 is to use caprolactam as raw material for hydrolysis ring-opening polymerization. Due to thermodynamic equilibrium limitations, the conversion rate of caprolactam hydrolysis ring-opening polymerization is generally around 90%, which means that about 10wt% of impurities such as caprolactam monomers and oligomers remain in the polyamide 6 polymer (monomers account for about 75wt% of impurities, and oligomers account for about 25wt% of impurities). The oligomers are mainly infusible cyclic dimers. The formation principle of infusible cyclic dimers is as follows Figure 1 As shown in the figure, the melting point of these infusible cyclic dimers is 348°C. They are unstable in the melt and easily aggregated, which can cause single-filament breakage, hard-headed yarns and other defects during spinning, affecting the performance of multifilaments. In order to avoid the influence of impurities such as infusible cyclic dimers on fiber quality, the spinning of polyamide 6 fiber requires a two-step (slice method) spinning process, but the two-step spinning process affects the production efficiency of polyamide 6 fiber.

[0004] In order to improve the production efficiency of polyamide 6 fibers, the spinning process of polyamide 6 is also continuously developing towards melt direct spinning. For example, CN105669969A and CN104480561A disclose the melt direct spinning synthesis preparation process of polyamide 6 based on dynamic devolatilization. Compared with the two-step spinning, melt direct spinning can simplify the production process and improve the unit production efficiency. For example, CN112566764A and CN111253566A disclose a polyamide 6 melt direct spinning device matched with dynamic devolatilization, which has a shorter process and higher efficiency, reduces infrastructure investment, and further reduces the production cost of polyamide 6 fibers.

[0005] However, these oligomers are products of thermodynamic equilibrium and cannot be completely removed. In addition, the melting point of the infusible cyclic dimers is 348°C. They are insoluble and non-meltable in the polyamide 6 melt and are not easily volatile, resulting in the infusible cyclic dimer content of polyamide 6 being 0.4-0.5wt%. These infusible cyclic dimers are also difficult to effectively remove by dynamic (negative pressure devolatilization) means, which has an adverse effect on the melt spinning process.

[0006] Therefore, in order to reduce the impact of these infusible cyclic dimers on melt spinning processing and improve fiber quality, it is necessary to develop a method for inhibiting the formation of infusible cyclic dimers of polyamide 6. Summary of the invention

[0007] The purpose of the present invention is to solve the problems existing in the prior art and to provide a method for inhibiting the formation of infusible cyclic dimers of polyamide 6 and its application.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] A method for inhibiting the formation of infusible cyclic dimers of polyamide 6 is provided. In the process of synthesizing polyamide 6 from caprolactam by hydrolysis, an amino acid is added in the ring opening stage and the polycondensation stage respectively. The amino acid is an amino acid other than aminocaproic acid.

[0010] In the process of polyamide 6 synthesis, the infusible cyclic dimer (bisaminocaproic acid, melting point is 348℃, which is much higher than the synthesis temperature of polyamide 6, and has extremely strong hydrogen bonding inside. It is difficult to open the ring again after it is generated, and it will eventually become a solid infusible substance in the polyamide 6 melt) is mainly generated in two stages. The first stage is the ring opening stage, in which caprolactam opens the ring to generate aminocaproic acid, and aminocaproic acid reacts with aminocaproic acid to generate bisaminocaproic acid. The second stage is the polycondensation stage, in which the terminal amino group of the polyamide 6 prepolymer molecular chain attacks the second carbonyl group closest to it to generate bisaminocaproic acid.

[0011] The present invention suppresses the generation of diaminocaproic acid during the synthesis of polyamide 6 by adding amino acids (amino acids other than aminocaproic acid) in the ring-opening stage and the polycondensation stage, thereby reducing its content in polyamide 6. The specific principle is as follows:

[0012] Studies have shown that the melting point and ring-opening temperature of the unstable cyclic dimer generated by the reaction of amino acid and aminocaproic acid are lower than the melting polymerization temperature of polyamide 6, so it can be opened again after melting to participate in the amide exchange reaction, and will not become a solid infusible substance like diaminocaproic acid.

[0013] In the ring-opening stage, the stability of the unstable cyclic dimer generated by the reaction of amino acid and aminocaproic acid is significantly lower than that of the infusible cyclic dimer generated by the reaction of aminocaproic acid and aminocaproic acid. From the perspective of organic synthesis, the energy required for the generation of unstable substances and the energy of destruction are lower than those of stable substances. Therefore, unstable substances will be generated first during the synthesis process. After the addition of amino acid, the amino acid reacts with aminocaproic acid first (the total amount of dimers generated after reaching reaction equilibrium is certain), so this inhibits the reaction of aminocaproic acid and aminocaproic acid to a certain extent, reducing the amount of diaminocaproic acid generated;

[0014] During the polycondensation stage, since the amino acid is a small molecule, it is easier to undergo thermal motion and is more likely to contact the terminal amino group of the polyamide 6 prepolymer molecular chain to undergo an amidation reaction, forming an unstable cyclic dimer. This, to a certain extent, inhibits the terminal amino group of the polyamide 6 prepolymer molecular chain from attacking the second carbonyl group closest to it (reducing the back-biting reaction of the terminal amino group) and reduces the amount of diaminocaproic acid produced.

[0015] The reason why the present invention adds an amino acid in the ring-opening stage and the polycondensation stage respectively, rather than adding a large amount of an amino acid in the ring-opening stage at one time, is that in the polycondensation stage, since thermodynamic equilibrium always exists, the amino acid added in the ring-opening stage will inevitably react with the chain in the chain due to chain exchange, so the amino acid must be added again in the polycondensation stage.

[0016] As the preferred technical solution:

[0017] In the method for inhibiting the formation of infusible cyclic dimers of polyamide 6 as described above, the mass of an amino acid added in the ring-opening stage is 1-3wt% of the mass of caprolactam, and the mass of an amino acid added in the polycondensation stage is 1-3wt% of the mass of caprolactam; in the present invention, one end of the amino acid is an amino group and the other end is a carboxyl group, which has no effect on the reaction process of polyamide 6, and at the same time, a trace amount of addition has limited effect on the macromolecular chain structure of polyamide 6, and currently industrial polyamide 6 production also requires the addition of 0.1-0.5wt% of terephthalic acid as a molecular weight regulator, so the physical and chemical properties and application characteristics of polyamide 6 are still maintained after a trace amount of amino acid is added.

[0018] The above-mentioned method for inhibiting the formation of infusible cyclic dimers of polyamide 6, wherein the amino acid is phenylalanine, p-aminobenzoic acid and the structural formula is One or more of the amino acids, n=1-4, or n=6-10.

[0019] The present invention also provides a method for synthesizing polyamide 6 using the method for inhibiting the formation of polyamide 6 infusible cyclic dimers as described in any one of the above items, comprising the following steps:

[0020] (1) caprolactam, water and amino acid are mixed and subjected to a ring-opening reaction to obtain a polyamide 6 prepolymer;

[0021] (2) mixing the polyamide 6 prepolymer and an amino acid, and performing a polycondensation reaction to obtain polyamide 6;

[0022] The structural formula is amino acid Taking amino acids as an example, the reaction equation for synthesizing polyamide 6 is as follows Figure 2 shown.

[0023] As the preferred technical solution:

[0024] In the above-mentioned method for synthesizing polyamide 6, in step (1), the mass of water is 1-3wt% of the mass of caprolactam; the temperature of the ring-opening reaction is 220-250°C, the pressure is 0.4-0.6MPa, and the time is 1-3h.

[0025] In the above-mentioned method for synthesizing polyamide 6, in step (2), the temperature of the polycondensation reaction is 250-270°C, the vacuum degree is ≤300Pa, and the time is 3-5h; the relative viscosity of polyamide 6 is 2.4-3.6, the melting point is 220-230°C, and the number average molecular weight is 16000-30000g / mol.

[0026] In the above-mentioned method for synthesizing polyamide 6, in step (2), the oligomer content of polyamide 6 is 0.5-2wt%, and the infusible cyclic dimer content is 0.05-0.1wt%, which can meet the processing requirements of direct high-speed spinning.

[0027] Beneficial effects:

[0028] (1) The amino acid added in the present invention has the same heterocyclic structure as that of caprolactam after hydrolysis and ring opening, and will not affect the polymerization process of synthesizing polyamide 6. In the ring opening stage, the amino acid directly reacts with the caprolactam that has just opened its ring to form an unstable cyclic dimer (taking the amino acid as 11-aminoundecanoic acid and 4-aminobutyric acid as an example, the reaction equation is as follows: Figure 3 As shown), the proportion of infusible cyclic dimers can be reduced; in the polycondensation stage, the carboxyl end of an amino acid reacts with the active end amino group of the polyamide 6 prepolymer to form an unstable cyclic dimer (with an amino acid as the structural formula Take amino acids as an example, the reaction equation is as follows Figure 3 The above two stages can reduce the content of infusible cyclic dimers in the polyamide 6 melt at thermodynamic equilibrium, which has a long-term control effect on infusible cyclic dimers and prevents infusible cyclic dimers from affecting melt spinning processing.

[0029] (2) The method for inhibiting the formation of infusible cyclic dimers of polyamide 6 of the present invention is achieved by adding an amino acid. The operation process is simple and can be carried out on existing polymerization production equipment. It is low in cost and easy to promote. It can be widely used in the fiber field. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the principle of producing an infusible cyclic dimer when synthesizing polyamide 6 by ring-opening polymerization using caprolactam as a raw material in the prior art;

[0031] Figure 2 This is a schematic diagram of the reaction of adding amino acid to synthesize polyamide 6 according to the present invention;

[0032] Figure 3 It is a schematic diagram of the principle of generating unstable cyclic dimers according to the present invention. DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0034] The following are the test methods for the relevant performance indicators in each embodiment and comparative example:

[0035] (1) Test method for relative viscosity of polyamide 6: Referring to the test method of China Textile Industry Standard FZ / T 51004-2011, the sample was dissolved in 96wt% concentrated sulfuric acid (solvent is water) to prepare a test solution with a concentration of 0.01g / mL, and the test was carried out using an Ubbelohde viscometer (capillary diameter is 1.03mm) in a constant temperature water bath at a water temperature of 25±0.1℃. The test was repeated 5 times and the average value was taken. The calculation is performed according to the following formula:

[0036] ;

[0037] Wherein, t is the outflow time (s) of the test solution with a concentration of 0.01 g / mL, and t0 is the outflow time (s) of concentrated sulfuric acid with a concentration of 96 wt%.

[0038] (2) Testing method for melting point of polyamide 6: The crystallization and melting behavior of the sample were tested using a TA-Q20 differential scanning calorimeter. About 5 mg of dry sample was heated and cooled at a rate of 10°C / min in a nitrogen atmosphere. The scanning results of the first cooling and second heating were selected to obtain the melting point data.

[0039] (3) Test method for number average molecular weight of polyamide 6: First, dry the sample and then dissolve it in hexafluoroisopropanol to prepare a solution with a concentration of 1.0 mg / mL. Then, use the GPC-50 gel permeation chromatograph of PL Company of the United Kingdom to test the number average molecular weight of the sample. During the test, use 1,1,1,3,3,3-hexafluoro-2-propanol as the eluent and set its flow rate to 1 mL / min. When the temperature of the chromatographic column is stabilized at 40±1°C, inject the prepared solution into the chromatograph to perform the test and record the data.

[0040] (4) Test method for oligomer content in polyamide 6: According to the test method of China Textile Industry Standard FZ / T 51004-2011, the sample is placed in a vacuum oven at 105°C and dried for 24 hours until constant weight is reached, and then a certain mass (recorded as , unit g) of the sample, add water according to the weight ratio of water to sample 20:1, use Soxhlet extractor to extract the sample in boiling water (water bath temperature ≥ 98℃) for 8h, take out the sample and put it into a vacuum oven at 105℃ to dry for 24h and weigh it, record the mass (recorded as , unit g), calculated by the following formula :

[0041] ×100%;

[0042] That is the content of oligomers in polyamide 6.

[0043] (5) Test method for the content of infusible cyclic dimer in polyamide 6: Take a certain mass of sample (denoted as , unit mg), water was added at a weight ratio of 20:1 between water and sample, and the extraction was carried out in an environment of ≥95°C for 8 hours to obtain an extract. The extraction was repeated three times. Since the infusible cyclic dimer is slightly soluble in water, the infusible cyclic dimer will be transferred to water along the concentration gradient. The three extracts were then combined as the test solution (denoted as V, unit mL), and the test solution was then subjected to liquid chromatography test; the liquid chromatography test was performed using Shimadzu's WondaSil The determination was carried out using a C18-WR chromatographic column (the length of the chromatographic column was 200 mm, the inner diameter of the chromatographic column was 4.6 mm, and the particle size of the filling particles was 5 μm) and an LC-16 high performance liquid chromatograph (HPLC) with an ultraviolet detector; wherein the detection wavelength was 210 nm and the detection temperature was 40°C; mobile phase: mobile phase A was methanol, and mobile phase B was water, and the binary gradient method was used for testing, and the injection volume was 10 μL; the infusible cyclic dimer was prepared into standard aqueous solutions with concentrations of 0.0375 mg / mL, 0.075 mg / mL, 0.15 mg / mL, 0.3 mg / mL, and 0.6 mg / mL, respectively, and was fitted into a standard curve using the external standard method, and the infusible cyclic dimer concentration of the test solution (denoted as C, in mg / mL) was calculated according to the chromatographic results of the test solution and the standard curve, and according to the formula ×100% to calculate the content of the infusible cyclic dimer in the sample.

[0044] Example 1

[0045] The polyamide 6 synthesis method using the polyamide 6 infusible cyclic dimer generation inhibition method has the following specific steps:

[0046] (1) Raw material preparation;

[0047] Caprolactam: CAS No. 105-60-2, manufactured by BASF;

[0048] Amino acid: aminoacetic acid, CAS No. 56-40-6, manufactured by Wuhan Baixing Biological;

[0049] water;

[0050] (2) Open-loop stage;

[0051] After caprolactam, water and amino acid are mixed, a ring-opening reaction is carried out to obtain a polyamide 6 prepolymer. The amino acid directly reacts with the caprolactam that has just been ring-opened to generate an unstable cyclic dimer, which can reduce the generation ratio of infusible cyclic dimers. The mass of the amino acid added in the ring-opening stage is 3wt% of the mass of caprolactam; the mass of water is 3wt% of the mass of caprolactam; the temperature of the ring-opening reaction is 250°C, the pressure is 0.6MPa, and the time is 1h.

[0052] (3) Polycondensation stage;

[0053] After mixing an amino acid and the polyamide 6 prepolymer obtained in step (2), a polycondensation reaction is carried out to obtain polyamide 6. The carboxyl end of the amino acid reacts with the active end amino group of the polyamide 6 prepolymer to reduce the generation ratio of the infusible cyclic dimer. The mass of the amino acid added in the polycondensation stage is 1wt% of the mass of the caprolactam in step (2). The temperature of the polycondensation reaction is 250°C, the vacuum degree is 200Pa, and the time is 3h.

[0054] The final polyamide 6 has a relative viscosity of 2.9, a melting point of 224° C., a number average molecular weight of 22000 g / mol, an oligomer content of 1 wt %, and a non-melting cyclic dimer content of 0.08 wt %.

[0055] The prepared polyamide 6 is directly spun at high speed according to the FDY process, the spinning temperature is 265°C, the specifications of the spinneret are 0.3mm (aperture) × 36f (number of holes), the spinning speed is 4000m / min, the drafting multiple is 1.2, the drafting hot roller temperature is 60°C, the drafting hot plate temperature is 120°C, there is no single filament breakage, no hard head wire (hard head wire means: the wire has a bulging appearance after winding), which meets the requirements of direct high-speed spinning.

[0056] Comparative Example 1

[0057] A method for synthesizing polyamide 6 is basically the same as that of Example 1, except that no amino acid is added in the ring-opening stage and the polycondensation stage.

[0058] The final polyamide 6 has a relative viscosity of 3.0, a melting point of 225° C., a number average molecular weight of 23000 g / mol, an oligomer content of 2.3 wt %, and a non-melting cyclic dimer content of 0.35 wt %.

[0059] When the prepared polyamide 6 is directly spun at high speed according to the FDY process (spinning process parameters are the same as in Example 1), hard-end yarns, broken yarns and floating yarns appear, and the spinning stability is poor, which cannot meet the requirements of stable direct high-speed spinning. This is because the content of infusible cyclic dimers is too high, which will be further enriched during the drawing process. The infusible cyclic dimers will be wrapped in the polyamide 6 fibers to produce hard-end yarns, which will also cause stress concentration and brittle fracture, resulting in broken yarns and floating yarns.

[0060] Comparative Example 2

[0061] A method for synthesizing polyamide 6 is basically the same as that in Example 1, except that amino acid is replaced by aminocaproic acid.

[0062] The final polyamide 6 has a relative viscosity of 2.9, a melting point of 224° C., a number average molecular weight of 22000 g / mol, an oligomer content of 2.2 wt %, and a non-melting cyclic dimer content of 0.32 wt %.

[0063] When the prepared polyamide 6 is used for high-speed spinning of a certain diameter (spinning process parameters are the same as those in Example 1), hard-end yarns, broken yarns and floating yarns appear, and the fiber spinning stability is poor, which cannot meet the requirements of stable diameter high-speed spinning. This is because the structure of caprolactam after hydrolysis and ring opening is aminocaproic acid, and the main type of cyclic dimer generated is still an infusible cyclic dimer formed by two aminocaproic acids, which is insoluble and infusible in the polyamide 6 melt. The infusible cyclic dimer content in the polyamide 6 melt is too high, and it will also be further enriched during the drawing process, resulting in hard-end yarns in the polyamide 6 fiber, which will also cause stress concentration and brittle fracture, resulting in broken yarns and floating yarns.

[0064] Example 2

[0065] The polyamide 6 synthesis method using the polyamide 6 infusible cyclic dimer generation inhibition method has the following specific steps:

[0066] (1) Raw material preparation;

[0067] Caprolactam: CAS No. 105-60-2, manufactured by BASF;

[0068] Amino acid: 3-aminopropionic acid, CAS No. 107-95-9, manufactured by Titan Technology;

[0069] water;

[0070] (2) Open-loop stage;

[0071] After caprolactam, water and amino acid are mixed, a ring-opening reaction is carried out to obtain a polyamide 6 prepolymer. The amino acid directly reacts with the caprolactam that has just been ring-opened to generate an unstable cyclic dimer, which can reduce the generation ratio of infusible cyclic dimers. The mass of the amino acid added in the ring-opening stage is 2.5wt% of the mass of caprolactam; the mass of water is 2wt% of the mass of caprolactam; the temperature of the ring-opening reaction is 250°C, the pressure is 0.6MPa, and the time is 1.5h;

[0072] (3) Polycondensation stage;

[0073] After mixing an amino acid and the polyamide 6 prepolymer obtained in step (2), a polycondensation reaction is carried out to obtain polyamide 6. The carboxyl end of the amino acid reacts with the active end amino group of the polyamide 6 prepolymer to form a ring, which can reduce the generation ratio of infusible cyclic dimers. The mass of the amino acid added in the polycondensation stage is 3wt% of the mass of the caprolactam in step (2). The temperature of the polycondensation reaction is 250°C, the vacuum degree is 200Pa, and the time is 3h.

[0074] The final polyamide 6 has a relative viscosity of 2.4, a melting point of 220° C., a number average molecular weight of 16000 g / mol, an oligomer content of 1.5 wt %, and a non-melting cyclic dimer content of 0.05 wt %.

[0075] The prepared polyamide 6 is directly subjected to high-speed spinning according to the FDY process. The spinning temperature is 265°C, the specification of the spinneret is 0.3mm×36f, the spinning speed is 3800m / min, the drafting multiple is 1.4, the drafting hot roller temperature is 60°C, the drafting hot plate temperature is 120°C, there is no single filament breakage, no hard head filament, and the requirements of direct high-speed spinning are met.

[0076] Example 3

[0077] The polyamide 6 synthesis method using the polyamide 6 infusible cyclic dimer generation inhibition method has the following specific steps:

[0078] (1) Raw material preparation;

[0079] Caprolactam: CAS No. 105-60-2, manufactured by BASF;

[0080] Amino acid: 4-aminobutyric acid, CAS No. 56-12-2, manufactured by Guangzhou Guangyu Biological;

[0081] water;

[0082] (2) Open-loop stage;

[0083] After caprolactam, water and amino acid are mixed, a ring-opening reaction is carried out to obtain a polyamide 6 prepolymer. The amino acid directly reacts with the caprolactam that has just been ring-opened to generate an unstable cyclic dimer, which can reduce the generation ratio of infusible cyclic dimers. The mass of the amino acid added in the ring-opening stage is 2.5wt% of the mass of caprolactam; the mass of water is 2wt% of the mass of caprolactam; the temperature of the ring-opening reaction is 240°C, the pressure is 0.5MPa, and the time is 2h;

[0084] (3) Polycondensation stage;

[0085] After mixing an amino acid and the polyamide 6 prepolymer obtained in step (2), a polycondensation reaction is carried out to obtain polyamide 6. The carboxyl end of the amino acid reacts with the active end amino group of the polyamide 6 prepolymer to form a ring, which can reduce the generation ratio of infusible cyclic dimers. The mass of the amino acid added in the polycondensation stage is 2wt% of the mass of the caprolactam in step (2). The temperature of the polycondensation reaction is 260°C, the vacuum degree is 300Pa, and the time is 3.5h.

[0086] The final polyamide 6 has a relative viscosity of 2.6, a melting point of 223° C., a number average molecular weight of 18,000 g / mol, an oligomer content of 2 wt %, and a non-melting cyclic dimer content of 0.06 wt %.

[0087] The prepared polyamide 6 is directly subjected to high-speed spinning according to the FDY process. The spinning temperature is 265°C, the specification of the spinneret is 0.3mm×36f, the spinning speed is 3600m / min, the drafting multiple is 1.6, the drafting hot roller temperature is 60°C, the drafting hot plate temperature is 120°C, there is no single filament breakage, no hard head filament, and the requirements of direct high-speed spinning are met.

[0088] Example 4

[0089] The polyamide 6 synthesis method using the polyamide 6 infusible cyclic dimer generation inhibition method has the following specific steps:

[0090] (1) Raw material preparation;

[0091] Caprolactam: CAS No. 105-60-2, manufactured by BASF;

[0092] Amino acid: 5-aminovaleric acid, CAS No. 660-88-8, manufactured by Titan Technology;

[0093] water;

[0094] (2) Open-loop stage;

[0095] After caprolactam, water and amino acid are mixed, a ring-opening reaction is carried out to obtain a polyamide 6 prepolymer. The amino acid directly reacts with the caprolactam that has just been ring-opened to generate an unstable cyclic dimer, which can reduce the generation ratio of infusible cyclic dimers. The mass of the amino acid added in the ring-opening stage is 2wt% of the mass of caprolactam; the mass of water is 2wt% of the mass of caprolactam; the temperature of the ring-opening reaction is 240°C, the pressure is 0.5MPa, and the time is 2h;

[0096] (3) Polycondensation stage;

[0097] After mixing an amino acid and the polyamide 6 prepolymer obtained in step (2), a polycondensation reaction is carried out to obtain polyamide 6. The carboxyl end of the amino acid reacts with the active end amino group of the polyamide 6 prepolymer to form a ring, which can reduce the generation ratio of infusible cyclic dimers. The mass of the amino acid added in the polycondensation stage is 1wt% of the mass of the caprolactam in step (2). The temperature of the polycondensation reaction is 260°C, the vacuum degree is 200Pa, and the time is 3.5h.

[0098] The final polyamide 6 has a relative viscosity of 3.3, a melting point of 228° C., a number average molecular weight of 26000 g / mol, an oligomer content of 1.2 wt %, and a non-melting cyclic dimer content of 0.08 wt %.

[0099] The prepared polyamide 6 is directly subjected to high-speed spinning according to the FDY process. The spinning temperature is 265°C, the specification of the spinneret is 0.3mm×36f, the spinning speed is 4100m / min, the drafting multiple is 1.2, the drafting hot roller temperature is 60°C, the drafting hot plate temperature is 120°C, there is no single filament breakage, no hard head filament, and the requirements of direct high-speed spinning are met.

[0100] Example 5

[0101] The polyamide 6 synthesis method using the polyamide 6 infusible cyclic dimer generation inhibition method has the following specific steps:

[0102] (1) Raw material preparation;

[0103] Caprolactam: CAS No. 105-60-2, manufactured by Sinopec;

[0104] Amino acid: 7-aminoheptanoic acid, CAS No. 929-17-9, manufactured by Titan Technology;

[0105] water;

[0106] (2) Open-loop stage;

[0107] After caprolactam, water and amino acid are mixed, a ring-opening reaction is carried out to obtain a polyamide 6 prepolymer. The amino acid directly reacts with the caprolactam that has just been ring-opened to generate an unstable cyclic dimer, which can reduce the generation ratio of infusible cyclic dimers. The mass of the amino acid added in the ring-opening stage is 2wt% of the mass of caprolactam; the mass of water is 1wt% of the mass of caprolactam; the temperature of the ring-opening reaction is 220°C, the pressure is 0.4MPa, and the time is 3h;

[0108] (3) Polycondensation stage;

[0109] After mixing an amino acid and the polyamide 6 prepolymer obtained in step (2), a polycondensation reaction is carried out to obtain polyamide 6. The carboxyl end of the amino acid reacts with the active end amino group of the polyamide 6 prepolymer to form a ring, which can reduce the generation ratio of infusible cyclic dimers. The mass of the amino acid added in the polycondensation stage is 2wt% of the mass of the caprolactam in step (2). The temperature of the polycondensation reaction is 260°C, the vacuum degree is 300Pa, and the time is 4h.

[0110] The final polyamide 6 has a relative viscosity of 3.0, a melting point of 225° C., a number average molecular weight of 23000 g / mol, an oligomer content of 1.3 wt %, and a non-melting cyclic dimer content of 0.09 wt %.

[0111] The prepared polyamide 6 is directly subjected to high-speed spinning according to the FDY process. The spinning temperature is 265°C, the specification of the spinneret is 0.3mm×36f, the spinning speed is 4300m / min, the drafting multiple is 1.2, the drafting hot roller temperature is 60°C, the drafting hot plate temperature is 120°C, there is no single filament breakage, no hard head filament, and the requirements of direct high-speed spinning are met.

[0112] Example 6

[0113] The polyamide 6 synthesis method using the polyamide 6 infusible cyclic dimer generation inhibition method has the following specific steps:

[0114] (1) Raw material preparation;

[0115] Caprolactam: CAS No. 105-60-2, manufactured by Sinopec;

[0116] Amino acid: 11-aminoundecanoic acid, CAS No. 2432-99-7, manufactured by Titan Technology;

[0117] water;

[0118] (2) Open-loop stage;

[0119] After caprolactam, water and amino acid are mixed, a ring-opening reaction is carried out to obtain a polyamide 6 prepolymer. The amino acid directly reacts with the caprolactam that has just been ring-opened to generate an unstable cyclic dimer, which can reduce the generation ratio of infusible cyclic dimers. The mass of the amino acid added in the ring-opening stage is 1wt% of the mass of caprolactam; the mass of water is 1wt% of the mass of caprolactam; the temperature of the ring-opening reaction is 220°C, the pressure is 0.4MPa, and the time is 3h;

[0120] (3) Polycondensation stage;

[0121] After mixing an amino acid and the polyamide 6 prepolymer obtained in step (2), a polycondensation reaction is carried out to obtain polyamide 6. The carboxyl end of the amino acid reacts with the active end amino group of the polyamide 6 prepolymer to form a ring, which can reduce the generation ratio of infusible cyclic dimers. The mass of the amino acid added in the polycondensation stage is 1wt% of the mass of the caprolactam in step (2). The temperature of the polycondensation reaction is 270°C, the vacuum degree is 200Pa, and the time is 5h.

[0122] The final polyamide 6 has a relative viscosity of 3.6, a melting point of 230° C., a number average molecular weight of 30,000 g / mol, an oligomer content of 1.1 wt %, and a non-melting cyclic dimer content of 0.1 wt %.

[0123] The prepared polyamide 6 is directly subjected to high-speed spinning according to the FDY process. The spinning temperature is 265°C, the specification of the spinneret is 0.3mm×36f, the spinning speed is 3700m / min, the drafting multiple is 1.6, the drafting hot roller temperature is 60°C, the drafting hot plate temperature is 120°C, there is no single filament breakage, no hard head filament, and the requirements of direct high-speed spinning are met.

[0124] Example 7

[0125] The polyamide 6 synthesis method using the polyamide 6 infusible cyclic dimer generation inhibition method has the following specific steps:

[0126] (1) Raw material preparation;

[0127] Caprolactam: CAS No. 105-60-2, manufactured by Sinopec;

[0128] Amino acid: DL-phenylalanine, CAS No. 150-30-1, manufactured by Titan Technology;

[0129] water;

[0130] (2) Open-loop stage;

[0131] After caprolactam, water and amino acid are mixed, a ring-opening reaction is carried out to obtain a polyamide 6 prepolymer. The amino acid directly reacts with the caprolactam that has just been ring-opened to generate an unstable cyclic dimer, which can reduce the generation ratio of infusible cyclic dimers. The mass of the amino acid added in the ring-opening stage is 1.5wt% of the mass of caprolactam; the mass of water is 2wt% of the mass of caprolactam; the temperature of the ring-opening reaction is 230°C, the pressure is 0.45MPa, and the time is 2.5h;

[0132] (3) Polycondensation stage;

[0133] After mixing an amino acid and the polyamide 6 prepolymer obtained in step (2), a polycondensation reaction is carried out to obtain polyamide 6. The carboxyl end of the amino acid reacts with the active end amino group of the polyamide 6 prepolymer to form a ring, which can reduce the generation ratio of infusible cyclic dimers. The mass of the amino acid added in the polycondensation stage is 3wt% of the mass of the caprolactam in step (2). The temperature of the polycondensation reaction is 255°C, the vacuum degree is 100Pa, and the time is 4.5h.

[0134] The final polyamide 6 has a relative viscosity of 2.7, a melting point of 223° C., a number average molecular weight of 19500 g / mol, an oligomer content of 0.7 wt %, and a non-melting cyclic dimer content of 0.07 wt %.

[0135] The prepared polyamide 6 is directly subjected to high-speed spinning according to the FDY process. The spinning temperature is 265°C, the specification of the spinneret is 0.3mm×36f, the spinning speed is 3900m / min, the drafting multiple is 1.4, the drafting hot roller temperature is 60°C, the drafting hot plate temperature is 120°C, there is no single filament breakage, no hard head filament, and the requirements of direct high-speed spinning are met.

[0136] Example 8

[0137] The polyamide 6 synthesis method using the polyamide 6 infusible cyclic dimer generation inhibition method has the following specific steps:

[0138] (1) Raw material preparation;

[0139] Caprolactam: CAS No. 105-60-2, manufactured by Sinopec;

[0140] Amino acid: p-aminobenzoic acid, CAS No. 150-13-0, manufactured by Titan Technology;

[0141] water;

[0142] (2) Open-loop stage;

[0143] After caprolactam, water and amino acid are mixed, a ring-opening reaction is carried out to obtain a polyamide 6 prepolymer. The amino acid directly reacts with the caprolactam that has just been ring-opened to generate an unstable cyclic dimer, which can reduce the generation ratio of infusible cyclic dimers. The mass of the amino acid added in the ring-opening stage is 1.5wt% of the mass of caprolactam; the mass of water is 2wt% of the mass of caprolactam; the temperature of the ring-opening reaction is 230°C, the pressure is 0.45MPa, and the time is 2.5h;

[0144] (3) Polycondensation stage;

[0145] After mixing an amino acid and the polyamide 6 prepolymer obtained in step (2), a polycondensation reaction is carried out to obtain polyamide 6. The carboxyl end of the amino acid reacts with the active end amino group of the polyamide 6 prepolymer to form a ring, which can reduce the generation ratio of infusible cyclic dimers. The mass of the amino acid added in the polycondensation stage is 2wt% of the mass of the caprolactam in step (2). The temperature of the polycondensation reaction is 255°C, the vacuum degree is 100Pa, and the time is 4h.

[0146] The final polyamide 6 has a relative viscosity of 3.2, a melting point of 227° C., a number average molecular weight of 25000 g / mol, an oligomer content of 0.5 wt %, and a non-melting cyclic dimer content of 0.07 wt %.

[0147] The prepared polyamide 6 is directly subjected to high-speed spinning according to the FDY process. The spinning temperature is 265°C, the specification of the spinneret is 0.3mm×36f, the spinning speed is 4000m / min, the drafting multiple is 1.4, the drafting hot roller temperature is 60°C, the drafting hot plate temperature is 120°C, there is no single filament breakage, no hard head filament, and the requirements of direct high-speed spinning are met.

Claims

1. A method for inhibiting the formation of infusible cyclic dimers of polyamide 6, characterized in that: In the process of synthesizing polyamide 6 from caprolactam by hydrolysis, an amino acid is added in the ring opening stage and the polycondensation stage, wherein the amino acid is phenylalanine, p-aminobenzoic acid and a structural formula is One or more of the amino acids, n=1-4, or n=6-10.

2. A method for inhibiting the formation of infusible cyclic dimers of polyamide 6 according to claim 1, characterized in that: The mass of the amino acid added in the ring-opening stage is 1-3wt% of the mass of caprolactam, and the mass of the amino acid added in the polycondensation stage is 1-3wt% of the mass of caprolactam.

3. A method for synthesizing polyamide 6 using the method for inhibiting the formation of infusible cyclic dimers of polyamide 6 as described in any one of claims 1 to 2, characterized in that: The following steps are involved: (1) mixing caprolactam, water and amino acid, and performing a ring-opening reaction to obtain a polyamide 6 prepolymer; (2) After mixing the polyamide 6 prepolymer and an amino acid, a polycondensation reaction is carried out to obtain polyamide 6.

4. A polyamide 6 synthesis method according to claim 3, characterized in that: In step (1), the mass of water is 1-3wt% of the mass of caprolactam; the temperature of the ring-opening reaction is 220-250°C, the pressure is 0.4-0.6MPa, and the time is 1-3h.

5. A polyamide 6 synthesis method according to claim 3, characterized in that: In step (2), the temperature of the polycondensation reaction is 250-270° C., the vacuum degree is ≤300 Pa, and the time is 3-5 hours; the relative viscosity of polyamide 6 is 2.4-3.6, the melting point is 220-230° C., and the number average molecular weight is 16000-30000 g / mol.

6. A polyamide 6 synthesis method according to claim 3, characterized in that: In step (2), the oligomer content of polyamide 6 is 0.5-2wt%, and the infusible cyclic dimer content of polyamide 6 is 0.05-0.1wt%.

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