Cationic dyeable, non-extracted, spun-dyed nylon-6 and process for the preparation thereof

Abstract

The application discloses cationic dyeing extract-free straight-spun nylon-6 and a preparation method thereof, and comprises the following steps: step 1, adding diamine, monomer containing sulfonic acid group and caprolactam into an opening agent and mixing thoroughly; step 2, performing pre-polymerization on the mixture obtained in step 1; step 3, performing post-polymerization on the product obtained in step 2; step 4, performing tackifying reaction on the product obtained in step 3, and then filling inert gas, extruding, drawing and cooling the melt to obtain the required nylon-6; the nylon-6 is prepared by one-step method, and the step of preparing modified monomer salt and separating and drying in the conventional method is omitted; the three-stage ladder polymerization method of pre-polymerization, post-polymerization and low-vacuum tackifying is adopted, and the reaction condition is stable and controllable; the obtained nylon-6 can obtain high dyeing rate and bright dyeing effect with good color fastness under normal pressure boiling dyeing condition without carrier.

Description

Technical Field

[0001] This invention relates to the field of synthetic fiber materials technology, specifically to an extraction-free direct-spinning nylon-6 dyeable with cationic dyes and its preparation method. Background Technology

[0002] Nylon-6 (polycaprolactam) is widely used in textiles and engineering plastics due to its excellent mechanical properties, abrasion resistance, and chemical resistance. Traditional nylon-6 fibers are primarily dyed with acid dyes, which suffers from limitations such as an incomplete color spectrum and insufficient color vibrancy in some colors. Cationic dyes offer bright colors and high dye uptake, but are generally only suitable for modified polyacrylonitrile fibers with anionic groups such as sulfonic acid groups, exhibiting extremely poor dyeability on conventional nylon-6. To impart dyeability to nylon-6 with cationic dyes, a third monomer containing sulfonic acid groups is typically introduced during polymerization, copolymerizing it with caprolactam to introduce anionic dye sites onto the nylon macromolecular chain. Currently, how to efficiently and stably introduce sulfonic acid groups while ensuring that the polymer's spinnability and mechanical properties remain largely unaffected, and achieving excellent and controllable cationic dyeing effects (such as dye uptake and color fastness), remains a direction for continuous optimization in this field.

[0003] Conventional Nylon-6 synthesis processes are generally characterized by long processes and high energy consumption: the traditional two-step method requires high vacuum and long-term polycondensation, and the resulting chips usually need to be extracted by hydrothermal or organic solvents to remove unreacted monomers and oligomers. This extraction process often takes several hours or even longer, resulting in extended production cycles and high pressure on wastewater treatment. Summary of the Invention

[0004] This invention addresses the problems existing in the prior art by providing an extraction-free, direct-spinning nylon-6 dyeable with cationic dyes and its preparation method.

[0005] The technical solution adopted in this invention is: a method for preparing cationic dyeable, extraction-free, direct-spinning nylon-6, comprising the following steps: Step 1: Add the diamine, the monomer containing the sulfonic acid group, and caprolactam to the ring-opening agent and mix thoroughly; Step 2: The mixture obtained in Step 1 is subjected to a prepolymerization reaction at a temperature of 210–250°C and a pressure of 100–200 kPa. Step 3: The product obtained in Step 2 is subjected to a post-polymerization reaction at a temperature of 250–270°C and a pressure of 40–60 kPa. Step 4: The product obtained in Step 3 is subjected to a thickening reaction at a temperature of 250-270℃ and a pressure of 100 Pa-10 kPa. After the reaction is completed, an inert gas is introduced, and the melt is extruded, stretched, and cooled to obtain the desired Nylon-6.

[0006] Furthermore, the molar ratio of the diamine to the monomer containing the sulfonic acid group is 1:1.0 to 1.1.

[0007] Furthermore, the total mass of the diamine and the monomer containing sulfonic acid groups accounts for 3 wt% to 12 wt% of the mass of caprolactam.

[0008] Furthermore, the diamine is one or more of hexamethylenediamine, butanediamine, ethylenediamine, decanediamine, and long-chain diamines, mixed in any proportion.

[0009] Furthermore, the monomer containing the sulfonic acid group is sodium isophthalic acid-5-sulfonate.

[0010] Furthermore, in step 1, the ring-opening agent is deionized water, and its addition amount is 3 wt% to 6 wt% of the total mass of the diamine, the monomer containing sulfonic acid group, and caprolactam.

[0011] Furthermore, the prepolymerization reaction time in step 2 is 2–8 h.

[0012] Furthermore, the post-polymerization reaction time in step 3 is 2–8 h.

[0013] Furthermore, the thickening reaction time in step 4 is 1 to 8 hours.

[0014] A cationic dyeable, extract-free, direct-spinning nylon-6 is obtained by copolymerization of caprolactam and a modified monomer containing sulfonic acid groups; the modified monomer containing sulfonic acid groups is a salt formed by the monomer containing sulfonic acid groups and a diamine.

[0015] The beneficial effects of this invention are: This invention uses a one-step method to prepare nylon-6, eliminating the steps of pre-preparing modified monomer salts and separating and drying them in conventional methods; it adopts a three-stage step-polymerization method of prepolymerization, postpolymerization and thickening, with stable and controllable reaction conditions, effectively avoiding monomer spraying or burst polymerization. The polymer obtained by this invention has an extremely low water extract content (0.2%–0.4%), achieving an extraction-free process. Compared with the traditional Nylon-6 production process, which requires several hours of hot water or organic solvent extraction, this significantly reduces production time, wastewater discharge, and energy consumption, making it more environmentally friendly. The obtained Nylon-6 polymer melt can be directly spun, eliminating intermediate steps such as slicing, drying, and remelting.

[0016] The polymer molecular chain obtained by this invention introduces stable sodium sulfonate groups, which provide sufficient dyeing sites for cationic dyes, enabling them to achieve high dyeing rates and bright colors under normal pressure boiling dyeing conditions without the need for a carrier, and exhibiting good color fastness. Attached Figure Description

[0017] Figure 1 This is a schematic diagram illustrating the polymer reaction principle of the present invention.

[0018] Figure 2 This is a schematic diagram of the preparation process of the present invention.

[0019] Figure 3 The images show the fibers obtained in Examples 1, 4, 5 and Comparative Example 1 of this invention, as well as the fibers dyed with different concentrations of dyeing agents. a is the fiber obtained in Comparative Example 1, b is the fiber obtained in Example 1, c is the fiber obtained in Example 4, and d is the fiber obtained in Example 5.

[0020] Figure 4 The diagram shows the change in fiber dyeing rate with dye concentration obtained in Examples 1, 4, 5 and Comparative Example 1 of the present invention.

[0021] Figure 5 The diagram shows the change in fiber dyeing rate with dye bath pH in Examples 1, 4, 5 and Comparative Example 1 of the present invention.

[0022] Figure 6 This is a photograph of the fiber obtained in Example 1 of the present invention, showing the changes in dye concentration and dye bath pH.

[0023] Figure 7 The graphs show the changes in tensile strength of fibers before and after dyeing in Examples 1, 4, 5 and Comparative Example 1 of the present invention.

[0024] Figure 8 The graphs show the changes in the breaking elongation before and after fiber dyeing in Examples 1, 4, 5 and Comparative Example 1 of the present invention. Detailed Implementation

[0025] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0026] A method for preparing an extraction-free, direct-spinning nylon-6 dyeable with cationic dyes, such as... Figure 2 The steps shown are as follows: Step 1: Add the diamine, the monomer containing a sulfonic acid group, and caprolactam to the ring-opening agent and mix thoroughly. The molar ratio of the diamine to the monomer containing a sulfonic acid group is 1:1.0–1.1. The total mass of the diamine and the monomer containing a sulfonic acid group accounts for 3 wt%–12 wt% of the mass of caprolactam. The diamine is one or more of hexamethylenediamine, butanediamine, ethylenediamine, decanediamine, or long-chain diamines, mixed in any proportion. The monomer containing a sulfonic acid group is sodium isophthalate-5-sulfonate (5-SSIPA). The ring-opening agent is deionized water, and its addition amount is 3 wt%–6 wt% of the total mass of the diamine, the monomer containing a sulfonic acid group, and caprolactam.

[0027] Step 2: The mixture obtained in Step 1 is subjected to a prepolymerization reaction at a temperature of 210–250°C, a pressure of 100–200 kPa, and a reaction time of 2–8 h, so that the system can initially open the ring and prepolymerize.

[0028] Step 3: The product obtained in Step 2 is subjected to a post-polymerization reaction at a temperature of 250–270°C, a pressure of 40–60 kPa, and a reaction time of 2–8 h to further increase the molecular weight.

[0029] Step 4: The product obtained in Step 3 is subjected to a thickening reaction at a temperature of 250–270℃, a pressure of 100 Pa–10 kPa, and a reaction time of 1–8 h to obtain a modified nylon-6 polymer melt. The polymer viscosity is 2.2–3.3 (relative viscosity, determined using concentrated sulfuric acid as a solvent), and the water extract content is only 0.2 wt%–0.4 wt%. Therefore, no additional extraction process is required, and it can be directly used for the production of direct-spun nylon. This significantly reduces production time, wastewater discharge, and energy conservation and environmental protection.

[0030] An inert gas is introduced into the reactor, and the polymer melt is extruded, stretched, and cooled to obtain the modified nylon-6 polymer that can be dyed with cationic dyes. This eliminates intermediate steps such as slicing, drying, and remelting, further improving production efficiency and energy utilization.

[0031] The process employs a three-stage stepped polymerization process: prepolymerization (medium pressure), postpolymerization (low vacuum), and thickening. This ensures stable and controllable reaction conditions, effectively preventing monomer ejection or explosive polymerization. Compared to traditional high-vacuum processes, it has lower equipment requirements and makes it easier to achieve the target viscosity.

[0032] A cationic dyeable, extract-free, direct-spinning nylon-6 is prepared by copolymerization of caprolactam monomer and a modified monomer containing sulfonic acid groups. The modified monomer containing sulfonic acid groups is a salt formed by sodium isophthalic acid-5-sulfonate (5-SSIPA) and a diamine. The mass percentage of the modified monomer in the polymer is 3.0 wt.% to 12.0 wt.%, preferably 6.0 wt.% to 12.0 wt.%. The reaction mechanism is as follows: Figure 1 As shown, stable sodium sulfonate groups (-SO3Na) are introduced into the polymer molecular chain, providing ample dye sites for cationic dyes. This allows them to achieve high dyeing rates and bright colors under normal pressure boiling conditions without a carrier, while also exhibiting good color fastness.

[0033] Example 1 A method for preparing an extraction-free, direct-spinning nylon-6 dyeable with cationic dyes includes the following steps: Step 1: Add 15.87 g hexamethylenediamine, 17.87 g sodium isophthalic acid-5-sulfonate (5-SSIPA) and 564 g caprolactam to 26.9 g deionized water, add to the reaction vessel, and stir until homogeneous.

[0034] Step 2: Seal the reactor, replace the air with nitrogen three times, turn on the heater, raise the temperature of the material to 220 ℃, the pressure to 150 kPa, and react for 5 h.

[0035] Step 3: Continue heating to 260 ℃, reduce pressure to 50 kPa, and polymerize for 5 h.

[0036] Step 4: Maintain the temperature at 260 ℃, reduce the pressure to 1 kPa, continue polymerization for 3 hours, and take a sample to measure the relative viscosity of the polymer, which is 2.8 and the water extract content is 0.3 wt%.

[0037] After the reaction is complete, nitrogen gas is introduced into the reactor to a slightly positive pressure. The bottom discharge valve is opened to directly transport the polymer melt to the spinning box for melt spinning (direct spinning nylon), or it is cooled and pelletized to obtain chips (no extraction required, no hot water or solvent washing required). The cationic dyeable nylon-6 fiber (i.e., 6SIPA / PA6) is obtained by direct spinning.

[0038] Example 2 The other steps in this embodiment are the same as in Example 1, except that the amount of hexamethylenediamine in step 1 is 6.9 g and the amount of sodium isophthalic acid-5-sulfonate (5-SSIPA) is 10 g.

[0039] The relative viscosity of the polymer melt was tested to be 2.5, and the water extract content was 0.2 wt%. The dyeing uptake rate was approximately 72%, and the mechanical properties remained good.

[0040] Example 3 The other steps in this embodiment are the same as in embodiment 1, except that the pressure in step 4 is 10 kPa and the reaction time is 4 h.

[0041] The polymer tested had a relative viscosity of 2.3 and a water extract content of 0.4 wt%. The dye uptake rate was approximately 80%, and it still exhibited good dyeability.

[0042] Example 4 The other steps in this embodiment are the same as in Example 1, except that the amount of hexamethylenediamine in step 1 is 20.74 g and the amount of sodium isophthalic acid-5-sulfonate (5-SSIPA) is 30.02 g (i.e., 9SIPA / PA6).

[0043] Example 5 The other steps in this embodiment are the same as in Example 1, except that the amount of hexamethylenediamine in step 1 is 27.66 g and the amount of sodium isophthalic acid-5-sulfonate (5-SSIPA) is 40.02 g (i.e., 12SIPA / PA6).

[0044] Example 6 A method for preparing an extraction-free, direct-spinning nylon-6 dyeable with cationic dyes includes the following steps: Step 1: Add 15.87 g butanediamine, 17.87 g sodium isophthalic acid-5-sulfonate (5-SSIPA) and 564 g caprolactam to 17.9 g deionized water, add to the reaction vessel, and stir until homogeneous.

[0045] Step 2: Seal the reactor, replace the air with nitrogen three times, turn on the heater, raise the temperature of the material to 210 ℃, the pressure to 100 kPa, and react for 8 h.

[0046] Step 3: Continue heating to 270 ℃, reduce pressure to 60 kPa, and polymerize for 2 h.

[0047] Step 4: Maintain the temperature at 270 ℃, reduce the pressure to 100 Pa, and continue polymerization for 1 h.

[0048] After the reaction is complete, nitrogen gas is introduced into the reactor to a slightly positive pressure. The bottom discharge valve is opened to directly transport the polymer melt to the spinning box for melt spinning (direct spinning nylon), or it is cooled and pelletized to obtain chips (no extraction required, no hot water or solvent washing required). The cationic dyeable nylon-6 fiber is obtained by direct spinning.

[0049] Example 7 A method for preparing an extraction-free, direct-spinning nylon-6 dyeable with cationic dyes includes the following steps: Step 1: Add 15.87 g of decanediamine, 17.87 g of sodium isophthalic acid-5-sulfonate (5-SSIPA) and 564 g of caprolactam to 35.87 g of deionized water, add to the reaction vessel, and stir until homogeneous.

[0050] Step 2: Seal the reactor, replace the air with nitrogen three times, turn on the heater, raise the temperature of the material to 250 ℃ and the pressure to 200 kPa, and react for 2 h.

[0051] Step 3: Continue heating to 250 ℃, reduce pressure to 40 kPa, and polymerize for 8 h.

[0052] Step 4: Maintain the temperature at 270 ℃, reduce the pressure to 100 Pa, and continue polymerization for 8 h.

[0053] After the reaction is complete, nitrogen gas is introduced into the reactor to a slightly positive pressure. The bottom discharge valve is opened to directly transport the polymer melt to the spinning box for melt spinning (direct spinning nylon), or it is cooled and pelletized to obtain chips (no extraction required, no hot water or solvent washing required). The cationic dyeable nylon-6 fiber is obtained by direct spinning.

[0054] Comparative Example 1 All other steps in this comparative example are the same as in Example 1, except that step 1 does not contain hexamethylenediamine and sodium isophthalate-5-sulfonate (5-SSIPA).

[0055] Tests showed that under the same cationic dye dyeing conditions, the dyeing rate was less than 10%, and it was almost impossible to color the product.

[0056] Comparative Example 2 In this comparative example, nylon-6 was prepared using the conventional high vacuum method. 5-SSIPA-hexanediamine salt was prepared in advance according to conventional methods, and then mixed with caprolactam and water, and polymerized under high temperature and high vacuum (absolute pressure <100 Pa).

[0057] The resulting polymer required hot water extraction for 40 hours to remove oligomers, with a water extract content of 1.2%. Compared to Example 1, the production cycle was significantly longer, and the wastewater discharge was larger.

[0058] The results from the comparative examples and the exemplary examples show that traditional industrial extraction (results from Comparative Example 2) takes approximately 20–48 hours to reduce the caprolactam content to below 0.6 wt.%. However, the exemplary method, involving continued reduced-pressure polymerization for 2–4 hours only in the thickening phase at an absolute pressure of 100 Pa–10 kPa, reduces the caprolactam content to only 0.2–0.4 wt.%.

[0059] The dyeing properties of the fibers obtained from the above-mentioned embodiments and comparative examples were tested using the following methods: Dye: Disperse cationic blue SD-BL, dosage 2.0% owf; Bath ratio: 1:50 pH value: Adjust to 4.5 with acetic acid / sodium acetate. Dyeing process: Start dyeing at 40 ℃, increase the temperature to 95 ℃ at 1.5 ℃ / min, and hold for 90 min.

[0060] The dyeing rate of the fibers obtained in the examples, determined by residual liquor colorimetry, reached over 80%. Washing fastness and rubbing fastness were both grade 4-5. Fiber mechanical properties: Compared to unmodified nylon-6, the strength retention rate was 95%, and the change in elongation at break was within 15%.

[0061] The performance test results of Examples 1-3 and Comparative Examples 1 and 2 are shown in Table 1.

[0062] Table 1. Performance test results of fibers obtained in Examples 1-3 and Comparative Examples 1 and 2

[0063] The dyeing rate of fibers obtained in Examples 1, 4, 5 and Comparative Example 1 was tested as a function of dye concentration. The results are as follows: Figure 4 As shown in the figure, the pH of the dye bath was 5, the dyeing temperature was 95 ℃, and the dyeing time was 120 min. It can be seen from the figure that the dye uptake rate of the fibers obtained in this example was significantly higher than that of Comparative Example 1. The dye uptake rate was >67% (determined by residual liquor colorimetry), significantly higher than that of unmodified nylon-6.

[0064] The dyeing rate of fibers obtained in Examples 1, 4, 5 and Comparative Example 1 was tested as a function of dye bath pH. The results are as follows: Figure 5 As shown, the dye amount was 2.0 owf%, the dyeing temperature was 95 ℃, and the dyeing time was 120 min. It can be seen from the figure that the dye uptake rate of the fibers obtained in this example was significantly higher than that in Comparative Example 1.

[0065] Example 1 shows the actual images of the fibers obtained as a function of dye concentration and dye bath pH. Figure 6 As shown, the left graph shows the results as dye concentration changes, and the right graph shows the results as dye bath pH changes, under the following conditions: Figure 4 and Figure 5 The tests were identical. It can be seen that colorfastness: washing fastness, rubbing fastness, etc., all reach level 4 or above (tested according to national standards).

[0066] The mechanical properties of the fibers obtained in Examples 1, 4, 5 and Comparative Example 1 were tested, and the results are as follows: Figure 7 and Figure 8 As shown in the figure, compared with unmodified Nylon-6, the strength retention rate is >90%, and the change in elongation at break is within 20%, indicating that the modification has little impact on the basic mechanical properties.

[0067] This invention employs a one-step, one-pot polymerization method, eliminating intermediate separation steps. Simultaneously, it combines low-vacuum polymerization and thickening methods to avoid the stringent requirements of high vacuum equipment. By optimizing the polymerization system and monomer ratio, an extraction-free process is achieved, significantly reducing production time (reducing the traditional extraction process of several hours to one without a separate extraction step). Furthermore, it integrates with direct-spinning nylon technology, allowing the polymer melt to be directly spun, significantly improving production efficiency, reducing energy consumption and production costs, while maintaining excellent cationic dyeing properties and mechanical spinnability.

Claims

1. A method for preparing an extraction-free, direct-spinning nylon-6 dyeable with cationic dyes, characterized in that, Includes the following steps: Step 1: Add the diamine, the monomer containing the sulfonic acid group, and caprolactam to the ring-opening agent and mix thoroughly; Step 2: The mixture obtained in Step 1 is subjected to a prepolymerization reaction at a temperature of 210–250°C and a pressure of 100–200 kPa. Step 3: The product obtained in Step 2 is subjected to a post-polymerization reaction at a temperature of 250–270°C and a pressure of 40–60 kPa. Step 4: The product obtained in Step 3 is subjected to a thickening reaction at a temperature of 250-270℃ and a pressure of 100 Pa-10 kPa. After the reaction is completed, an inert gas is introduced, and the melt is extruded, stretched, and cooled to obtain the desired Nylon-6.

2. The method for preparing cationic dyeable, extraction-free, direct-spinning nylon-6 according to claim 1, characterized in that, The molar ratio of the diamine to the monomer containing sulfonic acid groups is 1:1.0 to 1.

1.

3. The method for preparing cationic dyeable, extraction-free, direct-spinning nylon-6 according to claim 1, characterized in that, The total mass of the diamine and the monomer containing sulfonic acid groups accounts for 3 wt% to 12 wt% of the mass of caprolactam.

4. The method for preparing cationic dyeable, extraction-free, direct-spinning nylon-6 according to claim 1, characterized in that, The diamine is one or more of hexamethylenediamine, butanediamine, ethylenediamine, decanediamine, and long-chain diamines, mixed in any proportion.

5. The method for preparing cationic dye-dyeable, extraction-free, direct-spinning nylon-6 according to claim 1, characterized in that, The monomer containing the sulfonic acid group is sodium isophthalic acid-5-sulfonate.

6. The method for preparing cationic dyeable, extraction-free, direct-spinning nylon-6 according to claim 1, characterized in that, In step 1, the ring-opening agent is deionized water, and the amount added is 3 wt% to 6 wt% of the total mass of the diamine, the monomer containing sulfonic acid group and caprolactam.

7. The method for preparing cationic dyeable, extraction-free, direct-spinning nylon-6 according to claim 1, characterized in that, The prepolymerization reaction time in step 2 is 2–8 h.

8. The method for preparing cationic dye-dyeable, extraction-free, direct-spinning nylon-6 according to claim 1, characterized in that, The post-polymerization reaction time in step 3 is 2–8 h.

9. The method for preparing cationic dye-dyeable, extraction-free, direct-spinning nylon-6 according to claim 1, characterized in that, The thickening reaction time in step 4 is 1 to 8 hours.

10. The cationic dye-dyeable, extraction-free, direct-spinning nylon-6 obtained by any one of the preparation methods of claims 1 to 9, characterized in that, Nylon-6 is obtained by copolymerization of caprolactam and a modified monomer containing sulfonic acid groups; the modified monomer containing sulfonic acid groups is a salt formed by the monomer containing sulfonic acid groups and a diamine.

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