A stepwise slow-release stress dyeing method for a multi-layer knitted fabric

Abstract

This invention provides a step-by-step stress-relieving dyeing and finishing method for multi-layer knitted fabrics, relating to the field of knitted fabric dyeing and finishing technology. The method includes steps such as ring drying pretreatment, pre-setting, flat-width hot water pre-shrinking, low-liquor-ratio overflow dyeing, and finishing. By sequentially incorporating ring drying pretreatment, pre-setting, and flat-width hot water pre-shrinking during the dyeing process of multi-layer knitted fabrics, and combining a U-shaped buffer guide tube, high initial dyeing water level, low-tension fabric movement, and a specific heat-preservation relaxation process during the overflow dyeing stage, this invention allows the internal stress of the weaving and the wet-heat shrinkage stress to be released in stages before and during dyeing. Furthermore, after disperse dyeing, intermediate pre-setting can further fix the loop shape of the chemical fiber layers. This achieves a transformation in the shrinkage process of multi-layer knitted fabrics from concentrated, rapid release within the dyeing vat to a multi-step, slow release. Simultaneously, it reduces compression and folding during the rope-like movement process, which helps improve quality issues such as creases, worm marks, and fabric shrinkage.

Description

Technical Field

[0001] This invention relates to the field of dyeing and finishing technology for knitted fabrics, and in particular to a stepwise stress-relieving dyeing and finishing method for multi-layer knitted fabrics. Background Technology

[0002] Multi-layer knitted fabrics typically employ a double-knitted structure, with one side composed of cellulose fibers such as cotton, lyocell, and modal, and the other side composed of polyester chemical fibers. A connecting yarn forms the middle layer, and some fabrics also incorporate spandex. Due to differences in the shrinkage characteristics, elastic recovery properties, and heat-setting properties of different fibers under humid and hot conditions, coupled with the accumulation of internal stress during the weaving process due to the stretching, bending, and compression of the loops, these multi-layer knitted fabrics are prone to concentrated humid and hot shrinkage when entering the rope-like overflow dyeing process, under the combined influence of moisture, temperature, and mechanical action. This is especially true for multi-layer knitted fabrics with higher weight, thicker weaves, or those containing spandex. During the rope-like circulation within the dyeing vat, the fabric is further subjected to self-accumulation, tube folding, fabric lifting, and jetting effects, easily leading to the superposition of localized shrinkage and mechanical compression. This results in fabric defects such as creases, worm marks, and claw marks, and may cause significant width shrinkage, decreased warp and weft dimensional stability, loop shape instability, and reduced dyeing uniformity.

[0003] Existing technologies have been improved in terms of pre-shrinking before dyeing, dyeing operating parameters, and dyeing equipment structure. For example, invention patent CN 111088713 A discloses a dyeing method for TR air-layer fabrics, which employs flat-width horizontal straightening and hot water treatment before dyeing, combined with high-temperature setting, to reduce fabric shrinkage and reduce creases during wet processing; this solution mainly relies on flat-width wet heat treatment and setting to stabilize the coil structure before dyeing. Invention patent CN107254751 A discloses a method for eliminating wrinkles during low-liquor-ratio airflow dyeing of rayon-spandex Roma fabrics. This method involves pre-shrinking the fabric width and setting operating parameters such as the fan, fabric lifting speed, and main pump of the airflow dyeing machine to maintain low tension and change the stacking state of the fabric within the dyeing machine, thereby reducing the possibility of wrinkles. The utility model patent with publication number CN206256265 U discloses a fabric feeding tube for a jet dyeing machine. It adopts a U-shaped fabric feeding tube and puts the fabric in a relaxed floating state in the dye liquor, so as to reduce the running tension of the fabric and promote the release of internal stress.

[0004] However, the above technologies typically focus on one aspect of pre-shrinking or setting before dyeing, control of dyeing machine operating parameters, and improvement of the fabric tube structure. For multi-layered knitted fabrics composed of different fiber layers and connecting yarns, the internal stress of weaving and the stress from wet and heat shrinkage often persist through multiple stages, including pre-dyeing treatment, dyeing in the dyeing vat, high-temperature dyeing, and finishing. Simply relying on one pre-shrinking, one setting, or reducing the tension during dyeing is still insufficient to gradually release the internal stress of the fabric according to the processing stages. Especially during the sensitive stage of wet and heat shrinkage after the fabric enters the dyeing vat, if the remaining internal stress is released in a concentrated manner during the heating process, and the fabric is in a state of rope folding, accumulation, or local compression, permanent creases that are difficult to eliminate through subsequent setting may still form. The above problems are even more pronounced for multi-layered knitted fabrics containing spandex, with high basis weight, and with significant differences in wet and heat shrinkage between the fibers on both sides.

[0005] Therefore, it is necessary to provide a method that can simultaneously solve the problems of insufficient stress release before dyeing, excessive shrinkage in the dyeing vat, and local compression and folding during fabric operation, while ensuring the normal progress of dyeing processing and improving the fabric surface quality and dimensional stability of multi-layer knitted fabrics. Summary of the Invention

[0006] In view of this, the present invention provides a step-by-step stress-relieving dyeing and finishing method for multi-layer knitted fabrics. This invention, through sequentially setting ring drying pretreatment, pre-forming, and hot water pre-shrinking during the dyeing process of multi-layer knitted fabrics, and combining a U-shaped buffer guide pipe, high initial dyeing water level, low tension fabric movement, and a heat-preserving relaxation process at 90-110℃ during the overflow dyeing stage, allows the internal stress of weaving and the wet-heat shrinkage stress to be released in stages before and during dyeing. Furthermore, after disperse dyeing, intermediate pre-setting can further fix the loop shape of the chemical fiber layers. This achieves a transformation in the shrinkage process of multi-layer knitted fabrics from concentrated, rapid release within the dyeing vat to a multi-step, slow release. Simultaneously, it reduces compression and folding during rope-like movement, which is beneficial for improving quality problems such as creases, worm marks, and fabric shrinkage, and has good prospects for industrial application.

[0007] The stepwise stress-relieving dyeing and finishing method for multi-layer knitted fabrics of the present invention includes the following steps: S1. Circular drying pretreatment: The fabric is subjected to circulating hot air drying to release the internal stress of the weaving loops; S2, Pre-set type: High-temperature pre-setting of the pre-fabricated fabric after ring drying to fix the basic coil structure; S3, Flat-width hot water pre-shrinking: The fabric after pre-setting is continuously passed through a hot water tank in a flat, non-compression state for the first wet heat pre-shrinking. The greige fabric is first subjected to ring drying to release the internal stress generated during weaving, and then pre-shrinked in hot water at the fixed width and flat width to distribute the total shrinkage of the fabric, avoid the shrinkage from being concentrated in the dyeing vat, and release some of the internal stress. S4. Low liquor ratio overflow dyeing: An overflow dyeing machine equipped with a U-shaped buffer guide tube is used to raise the starting water level so that the fabric is fully immersed and wetted throughout the process; after the fabric enters the vat, the temperature is raised to 90~110℃ and kept at that temperature for 10~20 minutes, maintaining a constant temperature for relaxation in the range where fiber shrinkage is most likely; the nozzle spray pressure and the speed of the cloth roller are matched to keep the rope-like fabric in a relaxed and unstretched state between the pipe and the roller; the dyeing process sequentially involves dyeing the polyester fiber layer with disperse dye, reduction cleaning, and over-dyeing the cellulose fiber layer with reactive dye; U-shaped buffer guide tubes are used instead of L-shaped straight guide tubes. The bottom of the U-shaped buffer guide tube accumulates dye liquor to form a buffer layer, which allows the fabric to be briefly suspended and relaxed when passing through, and changes the rope-like folding shape. In contrast, the L-shaped straight tubes do not have the above buffering, and the fabric is easily squeezed and folded when it slides down quickly. Raise the dyeing water level to completely immerse the fabric in the dye solution to avoid localized dry rubbing and pressing. This step can release some internal stress. After the dyeing tank is filled, a heat preservation relaxation section of 90~110℃ is set before high-temperature dyeing. The temperature is kept for 10~20 minutes, and the nozzle spray pressure is 0.1~0.35 MPa, so as to slowly release the internal stress of humid heat and stabilize the width. S5. Finishing: After dyeing, dehydration, fabric removal, drying and finishing are carried out in sequence; The multi-layered knitted fabric has a cellulose fiber layer on one side and a chemical fiber layer on the other side, with connecting yarn in the middle.

[0008] Preferably, the multi-layer knitted fabric is a five-layer, six-layer, or seven-layer double-sided weave; the cellulose fiber layer includes at least one of cotton, lyocell, and modal; the chemical fiber layer is polyester; the connecting yarn is a composite yarn of chemical fiber and spandex or spandex; and the cellulose fiber layer and / or chemical fiber layer are interwoven with spandex.

[0009] Preferably, the temperature of the annular hot air in step S1 is 75~85℃.

[0010] Preferably, the embryo fixation temperature in step S2 is 190~200℃.

[0011] Preferably, the water temperature in the hot water tank in step S3 is 85~95℃.

[0012] Preferably, the overflow dyeing bath ratio in step S4 is 1:4 to 1:6; the bottom of the U-shaped buffer guide tube accumulates dye liquor to form a buffer layer, so that the fabric is in a suspended and relaxed state when passing through the tube and changes the rope-like folding shape; the heat preservation temperature after heating is 100 to 105°C, and the heat preservation time is 12 to 18 minutes; the nozzle spray pressure is 0.1 to 0.35 MPa, and the speed of the cloth wheel is adjusted to 200 to 280 rpm, so that the nozzle spray pressure matches the speed of the cloth wheel, so that the rope-like fabric is kept in a relaxed and untensioned state, and the "relaxed and untensioned state" means that the sample fabric is in a relaxed state in the cylinder.

[0013] Preferably, the disperse dyeing step S4 is as follows: dyeing with disperse dye at a temperature of 90~130℃ for 20~45 min; the disperse dye, calculated by fabric weight, includes at least one of 0.12~4% disperse blue, 0.05~3.5% disperse yellow, and 0.15~5% disperse red.

[0014] Preferably, the reactive dyeing step S4 is as follows: dyeing with reactive dye at a temperature of 60~90℃ for 15~45 min; the reactive dye, calculated by fabric weight, includes at least one of 0.001~2.8% reactive red, 0.015~3% reactive blue, and 0.16%~3.5% reactive yellow.

[0015] Preferably, the final product setting temperature in step S5 is 130°C.

[0016] Preferably, after the disperse dyeing is completed and before the reduction cleaning, the fabric is taken out of the vat for intermediate preforming to fix the shape of the chemical fiber loops, and then reduced cleaning and reactive dyeing are performed. The temperature of the intermediate preforming is 180~195℃ and the speed is 15~35 m / min.

[0017] The U-shaped buffer guide tube of the present invention has an outlet pipe at its lowest point, and a three-way valve at the bottom end of the outlet pipe. The other two ports of the three-way valve are respectively provided with a connecting pipe and a discharge pipe. The valve core of the three-way valve can be switched manually or electrically and has the following two working states: First, the connected state (working position): the first port of the three-way valve is connected to the outlet pipe, the second port of the three-way valve is connected to the connecting pipe, and the third port is cut off from the discharge pipe. At this time, the residual dye liquor at the bottom of the U-shaped guide tube enters the connecting pipe through the outlet pipe and the three-way valve, and the interior of the U-shaped guide tube and the interior of the connecting pipe form a communicating vessel; Second, the empty state (slag discharge position): the third port of the three-way valve is connected to the discharge pipe, and the second port is cut off from the connecting pipe.

[0018] Compared with the prior art, the beneficial technical effects of the present invention are as follows: This invention first uses hot air to relax the greige fabric through ring drying, releasing some of the internal stress accumulated during weaving before it enters the high-temperature setting and dyeing processes. Then, the basic loop structure is fixed through pre-setting, and the fabric undergoes wet-heat shrinkage under a rope-free compression state using flat-width hot water pre-shrinkage. This distributes the shrinkage that would otherwise occur concentrated in the dyeing vat to different processes in advance, reducing loop deformation, local congestion, and crease formation caused by instantaneous shrinkage after the fabric enters the vat. The aforementioned ring drying, pre-setting, and flat-width hot water pre-shrinkage are not simply repeated shrinkage treatments, but rather respectively undertake the functions of internal stress relaxation, initial loop stabilization, and wet-heat pre-shrinkage, thus forming a preliminary, step-by-step stress-relieving process.

[0019] Based on this, the present invention employs a U-shaped buffer guide tube during the overflow dyeing process, forming a buffer zone with the accumulated dye liquor at its bottom. As the fabric passes through this zone, it experiences brief suspension and relaxation, changing the continuous folded state of the rope-like fabric. Simultaneously, by raising the initial dyeing water level, the fabric remains fully saturated, and the nozzle spray pressure and the operating state of the conveyor rollers are matched, ensuring the fabric remains relaxed rather than overly taut between the pipes and the conveyor rollers. This reduces fixed creases caused by dry rubbing, dry pressing, and rapid slippage and compression of the rope-like fabric. A heat-preserving relaxation section of 90-110°C is set before high-temperature dyeing, allowing the fabric sufficient time for wet-heat relaxation before reaching the high-temperature dyeing temperature, further reducing fabric deformation caused by the concentrated release of residual shrinkage stress.

[0020] For multi-layer knitted fabrics including chemical fiber layers and cellulose fiber layers, this invention can also perform intermediate preforming after the disperse dye has finished dyeing the chemical fiber layers, thereby fixing the shape of the chemical fiber loops that have already undergone high-temperature and humid heat treatment, before reduction cleaning and reactive dye over-dyeing. This reduces the likelihood of significant changes to the loop structure already formed during subsequent wet processing. By combining pre-release, in-dye release, and necessary intermediate structure fixation, this invention can control the shrinkage and deformation of multi-layer knitted fabrics from both the stress release timing and the fabric running state.

[0021] In summary, this invention, through process combination and adaptive improvements to the dyeing machine guide tube in existing dyeing and finishing production processes, enables phased control of weaving internal stress and dyeing wet-heat shrinkage stress without altering the basic weaving structure of multi-layer knitted fabrics. It also considers low tension, sufficient wetting, and rope-like folding adjustments during the dyeing process, which helps improve the fabric smoothness, width, and warp and weft dimensional stability after dyeing, reducing the probability of rework due to defects such as creases and worm marks. Furthermore, this method can be implemented using existing dyeing and finishing production lines combined with local structural modifications such as the guide tube, demonstrating good process adaptability to multi-layer knitted structures such as five-layer, six-layer, and seven-layer knitted fabrics, as well as high-shrinkage fabrics containing spandex. Therefore, it has good prospects for large-scale production and widespread application. Attached Figure Description

[0022] The present invention will be further described below with reference to the accompanying drawings.

[0023] Figure 1 This is a front view of the U-shaped buffer guide tube device used in this invention.

[0024] Explanation of reference numerals in the attached drawings: 1. U-shaped guide pipe; 2. Outlet pipe; 3. Three-way valve; 4. Connecting pipe; 5. Overflow sleeve; 501. Rack; 6. Support shell; 14. Discharge pipe; 16. Overflow recovery pipe. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] Unless otherwise specified, all experiments were repeated three times, and the results are expressed as averages.

[0027] Example 1: Seven-layer knitted fabric Fabric structure: The outer layer is cotton fiber, the bottom layer is polyester, the connecting yarn in the middle is polyester, and the outer and bottom layers are interwoven with spandex. The weight is 320 g / m². 2 ; Circular drying: 80℃ circulating hot air is used for circular drying, and the vehicle speed is 30 m / min; Embryo setting: The setting temperature is 195℃, and the machine speed is 25 m / min; Flat-width hot water pre-shrinking: The fabric is continuously passed through a 90℃ flat-width hot water bath, allowing the fabric surface to shrink freely; Overflow dyeing: Low liquor ratio overflow dyeing is performed using a Danley water flow tank, and a system such as... is installed in the fabric circulation channel. Figure 1 The U-shaped buffer guide tube shown has a liquor ratio of 1:5, raising the dyeing water level to completely submerge the fabric; after the fabric enters the dyeing tank, it is heated to 100℃ and kept at that temperature for 15 minutes; the water flow cylinder nozzle spray pressure is 0.25 MPa, and the cloth wheel speed is 240 rpm, matching the nozzle spray pressure to keep the rope-like fabric relaxed. The disperse dyeing steps are as follows: dyeing is carried out at a temperature of 130°C for 30 minutes; the disperse dye composition, calculated by fabric weight, is as follows: 2% disperse blue, 1.7% disperse yellow, and 2.5% disperse red. Intermediate embryologization: After disperse staining, intermediate embryologization is performed at a temperature of 190℃ and a speed of 20 m / min. The process then proceeds sequentially with reduction cleaning, reactive dye over-dyeing, dehydration, and drying. The reduction cleaning process parameters are 85℃×20 min; the reactive dye over-dyeing process parameters are 80℃×20 min. The reactive dye composition, calculated by fabric weight, is as follows: 1.5% reactive red, 1.5% reactive blue, and 2% reactive yellow. Finished product shaping: The finished product shaping temperature is 130℃.

[0028] Shrinkage test method: GB / T8629-2017, 4N, 3 wash and hang dry; Test results: No creases or worm marks on the fabric surface; warp shrinkage was 2.2%, weft shrinkage was 1.7%, and the fabric width was stable; the one-time dyeing pass rate was 96%.

[0029] Comparative Example 1 The difference from Example 1 is as follows: the ring drying, flat-width hot water pre-shrinking, and intermediate pre-setting processes after exiting the dyeing vat are cancelled; the fabric is directly pre-set at 195°C with a machine speed of 25 m / min; after pre-setting, it directly enters the U-shaped tube overflow dyeing process with a liquor ratio of 1:5, the starting water level is raised, and after entering the vat, it is kept at 100°C for 15 min with a nozzle spray pressure of 0.25 MPa; dispersion dyeing is performed at 130°C and kept at 130°C for 30 min, followed by reduction washing and reactive dyeing; dehydration, drying, and final setting are the same as in Example 1, with the final setting temperature at 130°C.

[0030] Test results: The fabric surface showed localized striped worm marks and multiple intermittent creases; warp shrinkage was 5.7%, weft shrinkage was 5%, and the width deviation was 4.5±0.5 cm; the one-time dyeing pass rate was 65%.

[0031] This comparative example lacks two pre-treatment slow-release processes: ring drying to release internal stress during weaving and step-by-step hot water pre-shrinking. The shrinkage occurs concentrated in the dyeing vat, and relying solely on U-tube buffering cannot achieve the dimensional stability and fabric quality of Example 1.

[0032] Comparative Example 2 The difference from Example 1 is as follows: the ring drying, embryo fixation, and flat-width hot water pre-shrinking are retained, and the U-shaped buffer guide tube is replaced with a traditional L-shaped straight guide tube; the ring drying temperature is 80℃ and the machine speed is 30 m / min; the embryo fixation temperature is 195℃ and the machine speed is 25 m / min; the flat-width hot water bath temperature is 90℃; the overflow dyeing bath ratio of the L-shaped straight tube is 1:5, the water level is raised, the temperature in the tank is raised to 100℃ and kept at that temperature for 15 min, followed by disperse dyeing, intermediate embryo fixation, reduction cleaning, and reactive dyeing; the dehydration, drying, and finished product setting are the same as in Example 1, and the finished product setting temperature is 130℃.

[0033] Test results: Fixed hard creases were found in the rope-shaped running position, and the fabric surface was covered with tiny chicken claw prints; the warp shrinkage was 3.9%, the weft shrinkage was 3.2%, and the width fluctuation was obvious; the first-pass yield was 72%.

[0034] The pre-shrinking process can release some stress, but the L-shaped pipeline has no dye buffer layer, and the fabric is continuously squeezed and folded when it slips off, forming permanent creases during operation, which is more defective than in Example 1.

[0035] Comparative Example 3 The difference from Example 1 is as follows: the complete pre-process and U-tube overflow dyeing are retained, but the 90~110℃ heat preservation and relaxation section is cancelled; the ring drying temperature is 80℃ and the machine speed is 30 m / min; the pre-setting temperature is 195℃ and the machine speed is 25 m / min; the flat-width hot water bath temperature is 90℃; the U-tube overflow dyeing bath ratio is 1:5, the water level is raised, and the fabric is directly heated to 130℃ for disperse dyeing after entering the dyeing tank, without the 100℃, 15 min heat preservation and relaxation; then intermediate pre-setting, reduction cleaning and reactive dyeing are performed; dehydration, drying and finished product setting are the same as in Example 1, and the finished product setting temperature is 130℃.

[0036] Test results: Wavy creases and localized worm marks were found in the middle section of the fabric; warp shrinkage was 4.5%, weft shrinkage was 4%, and the width of the fabric varied from front to back; the first-pass yield rate was 78%.

[0037] Without this constant temperature slow release stage, the fabric will experience instantaneous and violent shrinkage and compression when it directly enters the high-temperature dyeing stage, increasing the likelihood of abnormalities in the finished product's size and appearance.

[0038] Table 1 Comparison results of Example 1 and Comparative Examples 1-3

[0039] Example 2: Spandex-containing multilayer knitted fabric of polyester / modal The difference from Example 1 is that: the top layer is modal, the bottom layer is polyester, and the connecting yarn in the middle is spandex; the pre-shrinking temperature of the flat-width hot water is 90℃; in the U-tube overflow dyeing, it is kept at 105℃ for 12 min. The process sequence is: ring drying → pre-setting → 90℃ flat-width hot water pre-shrinking → U-tube overflow dyeing and keeping at 105℃ for 12 min → dispersion dyeing → intermediate pre-setting after leaving the dye bath → reduction washing → reactive over-dyeing → dehydration, drying, and final product setting.

[0040] Test results: No chicken claw marks, no longitudinal earthworm marks; warp shrinkage is 2.7%, weft shrinkage is 2%; no segmented color difference.

[0041] Comparative Example 4 The difference from Example 1 is as follows: the ring drying pretreatment step is cancelled, the greige fabric is directly fixed without being ring dried with 80°C circulating hot air, the fixing temperature is 195°C, and the machine speed is 25 m / min; after fixing, it is pre-shrinked with 90°C flat-width hot water; then overflow dyeing is carried out using a U-shaped tube with a liquor ratio of 1:5, the dyeing water level is raised to fully immerse the fabric, after the fabric enters the dyeing tank, the temperature is raised to 100°C and held for 15 min, the nozzle spray pressure is 0.25 MPa, and the speed of the fabric roller is matched with the nozzle spray pressure to keep the rope-like fabric loose; then disperse dyeing is carried out at 130°C and held for 30 min, after disperse dyeing, intermediate fixing is carried out, followed by reduction washing, reactive dye over-dyeing, dehydration, drying and finishing in sequence, the finishing temperature is 130°C, and the remaining process conditions are the same as in Example 1.

[0042] Test results: The fabric defects were worm marks; warp shrinkage was 4.1%, weft shrinkage was 3.5%, and the width deviation was 3.5 ± 0.3 cm; the one-time dyeing pass rate was 80%.

[0043] Comparative Example 5 The difference from Example 1 is that the flat-width hot water pre-shrinking step is omitted. The greige fabric is dried in an 80°C circulating hot air bath at a speed of 30 m / min, followed by pre-setting at 195°C at a speed of 25 m / min. After pre-setting, instead of pre-shrinking in a 90°C flat-width hot water bath, overflow dyeing is performed directly using a U-shaped tube with a liquor ratio of 1:5. The starting water level is raised to ensure the fabric is fully submerged. After the fabric enters the dyeing bath, the temperature is raised to 100°C and held for 15 minutes. The nozzle spray pressure is 0.25 MPa, and the speed of the fabric roller is matched with the nozzle spray pressure to keep the rope-like fabric loose. Then, disperse dyeing is performed at 130°C and held for 30 minutes. After disperse dyeing, intermediate pre-setting is performed, followed by reduction washing, reactive dye over-dyeing, dehydration, drying, and final setting. The final setting temperature is 130°C, and the remaining process conditions are the same as in Example 1.

[0044] Test results: The fabric defects were intermittent creases; warp shrinkage was 3.8%, weft shrinkage was 3.6%, and the width deviation was 4.5±0.2 cm; the pass rate for one-time dyeing was 82%.

[0045] Comparative Example 6 The difference from Example 1 is that the order of pre-setting and hot water pre-shrinking is adjusted. The greige fabric is first dried in an 80°C circulating hot air bath at a speed of 30 m / min. After the drying, the fabric is continuously passed through a 90°C hot water bath for hot water pre-shrinking, followed by pre-setting at 195°C at a speed of 25 m / min. After pre-setting, overflow dyeing is performed using a U-tube at a liquor ratio of 1:5. The dyeing water level is raised to fully immerse the fabric. After the fabric enters the dye bath, the temperature is raised to 100°C and held for 15 minutes. The nozzle spray pressure is 0.25 MPa, and the speed of the fabric roller is matched with the nozzle spray pressure to keep the rope-like fabric relaxed. Then, disperse dyeing is performed at 130°C and held for 30 minutes. After disperse dyeing, intermediate pre-setting is performed, followed by reduction washing, reactive dye over-dyeing, dehydration, drying, and final setting. The final setting temperature is 130°C, and the remaining process conditions are the same as in Example 1.

[0046] Test results: The fabric defects were scattered chicken claw marks; the warp shrinkage was 2.8%, the weft shrinkage was 3.1%, and the width deviation was 2.2±0.2 cm; the one-time dyeing pass rate was 90%.

[0047] Comparative Example 7 The difference from Example 1 is that the intermediate pre-setting step after disperse dyeing is omitted. The greige fabric is dried with circulating hot air at 80°C at a speed of 30 m / min; then pre-setting is performed at a temperature of 195°C at a speed of 25 m / min; the pre-set fabric is continuously passed through a 90°C flat-width hot water bath for flat-width hot water pre-shrinking; overflow dyeing is performed using a U-shaped tube with a liquor ratio of 1:5, raising the starting water level to fully immerse the fabric, and after the fabric enters the bath, the temperature is raised to 100°C and held for 15 min, the nozzle spray pressure is 0.25 MPa, and the speed of the fabric roller is matched with the nozzle spray pressure to keep the rope-like fabric loose; then disperse dyeing is performed at 130°C and held for 30 min; after disperse dyeing, the fabric is not removed from the bath for intermediate pre-setting, and then directly subjected to reduction washing and reactive dye over-dyeing, followed by dehydration, drying, and final setting at 130°C. The remaining process conditions are the same as in Example 1.

[0048] Test results: Fabric defects included worm marks and hard creases; warp shrinkage was 3.5%, weft shrinkage was 3.8%, and width deviation was 3.5 ± 0.5 cm; the one-time dyeing pass rate was 85%.

[0049] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A stepwise stress-relieving dyeing and finishing method for multi-layer knitted fabrics, characterized in that, The multi-layer knitted fabric has a cellulose fiber layer on one side and a chemical fiber layer on the other side, with connecting yarns in the middle; the dyeing and finishing method includes the following steps: S1. Circular drying pretreatment: The fabric is subjected to circulating hot air drying to release the internal stress of the weaving loops; S2, Pre-setting: High-temperature pre-setting of the fabric after ring drying to fix the basic coil structure; S3, Flat-width hot water pre-shrinking: The pre-shaped fabric is continuously passed through a hot water bath in a flat-width state for wet heat pre-shrinking. S4. Low liquor ratio overflow dyeing: An overflow dyeing machine equipped with a U-shaped buffer guide tube is used, where dye liquor accumulates at the bottom of the U-shaped buffer guide tube to form a buffer layer; the starting water level is raised to immerse and wet the fabric, and after the fabric enters the dyeing tank, the temperature is raised to 90~110℃ and kept at that temperature for 10~20 minutes; the nozzle spray pressure and the speed of the belt roller are adjusted to keep the rope-like fabric in a relaxed state during operation; then, disperse dyes are used to dye the chemical fiber layer, reduction cleaning is performed, and reactive dyes are used to over-dye the cellulose fiber layer; S5. Finishing: After dyeing, the following steps are performed in sequence: dehydration, fabric removal, drying, and final shaping.

2. The stepwise stress-relieving dyeing and finishing method for multi-layer knitted fabrics according to claim 1, characterized in that, The multi-layer knitted fabric is a five-layer, six-layer, or seven-layer double-sided weave; the cellulose fiber layer includes at least one of cotton, lyocell, and modal; the chemical fiber layer is polyester; the connecting yarn is a composite yarn of chemical fiber and spandex or spandex; and the cellulose fiber layer and / or the chemical fiber layer are interwoven with spandex.

3. The stepwise stress-relieving dyeing and finishing method for multi-layer knitted fabrics according to claim 1, characterized in that, In step S1, the temperature of the hot air in the circulating hot air drying process is 75~85℃.

4. The stepwise stress-relieving dyeing and finishing method for multi-layer knitted fabrics according to claim 1, characterized in that, In step S2, the temperature of the pre-formed sample is 190~200℃.

5. The stepwise stress-relieving dyeing and finishing method for multi-layer knitted fabrics according to claim 1, characterized in that, In step S3, the water temperature in the hot water tank is 85~95℃.

6. The stepwise stress-relieving dyeing and finishing method for multi-layer knitted fabrics according to claim 1, characterized in that, In step S4, the bath ratio for overflow dyeing is 1:4 to 1:6, and the nozzle spray pressure is 0.1 to 0.35 MPa.

7. The stepwise stress-relieving dyeing and finishing method for multi-layer knitted fabrics according to claim 1, characterized in that, In step S4, the heat preservation temperature after the fabric enters the cylinder is 100~105℃, and the heat preservation time is 12~18 min.

8. The stepwise stress-relieving dyeing and finishing method for multi-layer knitted fabrics according to claim 1, characterized in that, After the chemical fiber layer is dyed with disperse dyes and before reduction cleaning, the fabric is removed from the dyeing vat for intermediate pre-setting, followed by reduction cleaning and reactive dye over-dyeing.

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