Alkali-resistant modified fiber and its pretreatment-dyeing one-bath low-water dyeing method

Abstract

This invention discloses an alkali-resistant modified fiber and its pretreatment-dyeing method using a low-water-content bath, belonging to the field of synthetic fiber modification technology. The alkali-resistant modified fiber has a core-sheath composite structure: the sheath layer is copolymerized from terephthalic acid, ethylene glycol, sodium isophthalate-5-sulfonate, and CHDM, with the addition of end-capping agents and halloysite nanotubes; the core layer is copolymerized from terephthalic acid, ethylene glycol, and sodium isophthalate-5-sulfonate. The method involves: mixing the fabric with the dye bath, heating to 70-85℃ and holding, then heating to 130℃ and holding for dyeing, followed by cooling, draining the bath, and washing with warm water before removing the fabric. This invention utilizes a core-sheath gradient structure to achieve a synergistic balance between high binding sites and alkali resistance in the sheath layer, and high crystallinity in the core layer to ensure mechanical properties, solving the technical problem of existing homogeneous modified fibers being unable to simultaneously achieve alkali resistance and dyeability; and constructing a negatively charged enrichment region to achieve deep dye penetration, solving the problem of insufficient wet fastness for medium and dark colors.

Description

Technical Field

[0001] This invention relates to the field of synthetic fiber modification technology, specifically to an alkali-resistant modified fiber and its pretreatment-dyeing method using a low-water-temperature bath. Background Technology

[0002] Polyester fiber (polyester) has become the world's largest-produced synthetic fiber due to its excellent mechanical properties, dimensional stability, and chemical resistance. However, the highly regular molecular chains and high crystallinity of polyester fibers, coupled with the lack of polar groups that can form chemical bonds with dyes, result in low affinity for conventional dyes. Dyeing can only be completed under high temperature and high pressure conditions using disperse dyes, and the color fastness, especially wet fastness, is difficult to improve further.

[0003] Traditional dyeing and finishing processes for polyester fabrics typically include alkali reduction pretreatment, acid neutralization, multiple washes, high-temperature and high-pressure dyeing (pH 4.5-5.5), reduction washing, and multiple washes. The alkali reduction pretreatment requires strongly alkaline and high-temperature conditions, while traditional disperse dyes are not alkali-resistant and dyeing must be completed under weakly acidic conditions. These two processes have diametrically opposed conditions and must be implemented step-by-step, requiring multiple washes in between. This traditional process is lengthy, consuming 80-120 tons of water per ton of polyester fabric, and the reduction washing process uses sodium hydrosulfite, generating sulfur-containing wastewater, which poses a significant environmental burden.

[0004] To address the aforementioned issues, recent improvements in this field have primarily focused on two directions: first, developing alkali-resistant disperse dyes, modifying their molecular structure to ensure stable color development under alkaline conditions, thus enabling simultaneous pretreatment and dyeing in the same bath; second, copolymerizing polyester fibers by introducing a third monomer containing sulfonic acid groups, giving the fibers anionic dye sites and improving colorfastness. Based on these improvements, some studies have attempted to combine polyester alkali reduction and dyeing into a one-bath, one-step process, while others have developed degreasing and leveling auxiliary agent systems for simultaneous scouring and dyeing of polyester.

[0005] However, the existing technologies still have the following shortcomings: First, the relationship between alkali-resistant disperse dyes and polyester fibers is still mainly based on physical adsorption, lacking chemical bonding anchors, making it difficult to meet the requirements for wet fastness of medium and dark-colored products; Second, existing fiber copolymerization modifications are mostly homogeneous modifications, with the modified components evenly distributed throughout the fiber cross-section. While introducing hydrophilic groups and a loose structure, this inevitably leads to a decrease in the overall strength of the fiber and an increase in moisture absorption. Under low liquor ratio dyeing conditions, the effective concentration of the dye bath is easily reduced due to fiber water absorption, and sulfonic acid-containing fibers are easily hydrolyzed under strongly alkaline conditions, making it impossible to carry out the process in the same bath as the pretreatment; Third, existing one-bath processes mostly rely on the optimization of the auxiliary agent system, failing to address the contradiction between alkali resistance and easy dyeing from the structural design of the fiber material itself.

[0006] To address the above problems, this invention provides an alkali-resistant modified fiber and a pretreatment-dyeing method using a low-water bath. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides an alkali-resistant modified fiber and a method for pretreatment-dyeing in a single bath with low water content.

[0008] The technical solutions provided by the embodiments of the present invention are as follows:

[0009] An alkali-resistant modified fiber, comprising a sheath and a core layer, is prepared by the following steps:

[0010] S1. Preparation of cortical and core slices:

[0011] The cortex slices are copolymerized from terephthalic acid, an ethylene glycol suspension containing acid-treated halloysite nanotubes, sodium isophthalate-5-sulfonate, and 1,4-cyclohexanediethanol, with carbodiimide end-capping agent added; the core slices are copolymerized from terephthalic acid, ethylene glycol, and sodium isophthalate-5-sulfonate.

[0012] During the esterification stage, terephthalic acid and ethylene glycol undergo an esterification reaction at 220-240℃ and 0.25-0.35 MPa to produce diethyl terephthalate and aqueous byproducts. In the skin chip polymerization, sodium isophthalate-5-sulfonate is used instead of terephthalic acid, reacting with alcohol to generate esters containing sulfonic acid groups. These sulfonic acid groups (-SO3Na) are inert under the reaction conditions and do not participate in esterification and polycondensation reactions. They are suspended on the polyester molecular chain as side groups and ionize into sulfonate anions (-SO3Na) in an alkaline dye bath. - ); 1,4-Cyclohexanediethanol (CHDM) is a diol component. Its molecular structure contains a saturated six-membered ring. During the esterification stage, it reacts with the carboxyl group together with ethylene glycol to generate an ester with an alicyclic structure, which is randomly embedded in the polyester molecular chain.

[0013] Halloysite nanotubes, after acid activation treatment, are rich in silanol groups on their surface. Before esterification, they are mixed with ethylene glycol and ultrasonically dispersed to form a uniform suspension. This suspension is then added to the reactor along with all monomers. After esterification, the process enters the polycondensation stage. Diethyl terephthalate and its copolyesters continuously remove ethylene glycol through transesterification, achieving molecular chain growth. During this process, the -Si-OH groups on the surface of the halloysite nanotubes can undergo a condensation reaction with the carboxyl groups at the ends of the polyester molecular chains to form -Si-O-CO covalent bonds, chemically anchoring the halloysite nanotubes to the polyester molecular chains. The reaction formula is as follows:

[0014]

[0015] When the temperature is lowered to 230-240℃ at the end of the polycondensation process, a carbodiimide end-capping agent is added. The accumulated double bond in the functional group of the carbodiimide end-capping agent has high reactivity, and its central carbon atom is electrophilic and easily attacked by nucleophiles. Some residual carboxyl groups at the ends of the polyester molecular chains act as nucleophiles, initiating nucleophilic addition to the central carbon of the accumulated double bond of the carbodiimide, generating an O-acylisourea intermediate. This intermediate is unstable and rapidly undergoes intramolecular rearrangement, with the acyl group migrating from the oxygen atom to the adjacent nitrogen atom, generating an N-acylurea structure. The terminal carboxyl group of the polyester is converted into an acylurea structure, eliminating the active initiation site of the hydrolytic chain reaction at the terminal carboxyl group. The relevant mechanism reaction formula is as follows:

[0016]

[0017] S2, spinning:

[0018] The dermal and core slices are melt-extruded through a dermal-core composite spinning assembly, and then cooled and wound to obtain nascent fibers.

[0019] The cortex and core chips differ in thermodynamic properties: cortex chips, containing CHDM, have a glass transition temperature (Tg) of 50-60℃ and a melting point of approximately 245-250℃; core chips, lacking 1,4-cyclohexanediethanol, have a Tg of approximately 75-78℃ and a melting point of approximately 255-260℃. Both types of chips are melted separately in independent screw extruders of a cortex-core composite spinning assembly. The extrusion temperature of the cortex chips is 270-280℃, and that of the core chips is 285-290℃, both approximately 20-30℃ higher than their respective melting points. The melts exhibit good fluidity. The cortex and core melts separate on the composite spinneret. The core melt and the outer layer melt converge in the molten metal, and are extruded together from the spinneret. After extrusion, the fine stream of melt enters the 18-25℃ side-blowing cooling zone. Due to its lower Tg, the outer layer slice undergoes a phase transition from the molten state to the glassy state before the core layer and solidifies and sets first. The core layer continues to cool inside the outer layer, and its shrinkage is constrained by the solidified outer layer, generating radial compressive stress at the interface. After cooling, the outer layer is in a compressive stress state, while the core layer is in a tensile stress state. This stress distribution reduces the tendency of microcracks to form in the outer layer and further improves the orientation and crystallinity of the core layer molecular chains. The outer layer maintains a low crystallinity structure due to the presence of 1,4-cyclohexanediethanol.

[0020] Halloysite nanotubes dispersed in the cortex are subjected to shear and tensile flow fields during melt flow and stretching. The axial direction of the tubes is aligned with the axis of the alkali-resistant modified fiber, and the channels formed are conducive to the diffusion of dye molecules. The winding speed of 800-1200 m / min imparts a certain molecular orientation to the nascent fiber. The sulfonic acid groups, halloysite nanotubes and carbodiimide end-capped products in the cortex are not affected during the spinning process, and their chemical structure remains unchanged.

[0021] S3, Post-processing:

[0022] Nascent fibers are stretched and heat-set to obtain alkali-resistant modified fibers, with the sheath thickness accounting for 20-40% of the radius of the alkali-resistant modified fiber and the core layer accounting for 60-80%.

[0023] After the nascent fiber is drawn, the cortex molecular chains and halloysite nanotubes are aligned along the axis of the alkali-resistant modified fiber. However, the orientation may loosen due to thermal shrinkage during subsequent use and needs to be fixed by heat setting. The drawn alkali-resistant modified fiber is heat-set at 180-200℃, which is between the glass transition temperatures of the cortex and the core. The cortex molecular chains can undergo segment rearrangement to eliminate the internal stress of the drawing process and form a thermodynamically stable low-crystallinity structure. This allows the sulfonate groups suspended in the cortex to be evenly distributed at the alkali-resistant modified fiber-water interface. At the same time, the dispersed halloysite nanotube cavities remain structurally intact and do not collapse at this temperature, maintaining unobstructed diffusion channels. At this temperature, the movement of the molecular chain segments in the core is restricted, and the orientation and crystallization induced by the drawing process are locked.

[0024] A pretreatment-dyeing method using the above-mentioned alkali-resistant modified fibers with a low-water bath includes the following steps:

[0025] T1, Fabric preparation solution:

[0026] Fabrics knitted from alkali-resistant modified fibers are placed in a dyeing vat at 25-30℃. Alkali-resistant disperse dyes are dispersed in water and filtered through a 200-mesh filter to obtain a dye pre-dispersion solution. Alkali-resistant degreasing scouring agent, alkali-resistant dispersing and leveling agent, chelating dispersant, penetrant, and non-silicone defoamer are dissolved in water, and then the dye pre-dispersion solution and sodium hydroxide are added. The temperature of the mixture is controlled to be ≤35℃. The mixture is pumped into the dyeing equipment at a bath ratio of 1:(5-10) and circulated for 5-10 minutes.

[0027] The fabric is placed in the dye bath at 25-30℃, a temperature lower than the glass transition temperature of disperse dyes and the Tg of alkali-resistant modified fibers. This ensures the dye particles remain stably suspended and dispersed in the dye bath, preventing significant dye uptake or aggregation. Alkali-resistant disperse dyes are insoluble in water, dispersing as crystalline particles. The hydrophobic interactions between dye molecules are weaker at low temperatures, making particle aggregation less likely and contributing to the stability of the subsequent dye pre-dispersion solution. A 200-mesh filter can trap undispersed dye agglomerates and mechanical impurities larger than 75μm, preventing defects such as color spots and stains during subsequent dyeing. It also ensures that the dye particle size distribution is within the range that allows for effective dye uptake during subsequent high-temperature, high-pressure dyeing. Alkali-resistant degreasing and scouring agents, alkali-resistant dispersing and leveling agents, chelating dispersants, penetrants, and non-silicone defoamers are molecularly dispersed in water, maintaining their functional activity and not interacting with the dye. Sodium hydroxide ionizes to Na+ at low temperatures. + and OH - OH -The nucleophilic attack rate on polyester bonds is extremely low at 25-35℃, and the cortex will not undergo hydrolysis. The sodium hydroxide added at this stage is only used to establish an initial alkaline environment, ensuring that the pH of the dye bath is 9.0-10.5. The sodium hydroxide is added in stages, with 70% of the total amount added first to avoid local OH-. - Excessive concentration caused abrupt changes in the surface charge state of dye particles, leading to aggregation. After 10 minutes of homogenization, OH... - Add the remaining 30% to precisely stabilize the pH to the target value, avoiding dye aggregation in areas of excessive concentration.

[0028] The temperature of the mixed liquor is controlled below 35℃. At this temperature range, the thermal activity of the dye particles is low, making it less prone to irreversible aggregation and preventing the dye crystal structure from changing due to excessively high temperatures, thus altering the dyeing performance. At the same time, the auxiliaries and sodium hydroxide are evenly dispersed at low temperatures without reacting, ensuring the stability and consistency of the initial state of the dye liquor. The mixture is circulated and mixed for 5-10 minutes to ensure uniform concentration of each component in the dye liquor. This process also ensures that the fabric is completely soaked in the dye liquor, the surface of the alkali-resistant modified fiber is fully wetted, and air bubbles at the interface between the alkali-resistant modified fiber and the dye liquor are eliminated. The air on the surface of the alkali-resistant modified fiber is completely replaced by the dye liquor, and the liquid phase continuously covers the surface of the alkali-resistant modified fiber. A liquor ratio of 1:(5-10) ensures a high concentration of each component in the dye liquor, maintaining a sufficient chemical concentration gradient in a limited amount of water, providing ample power for subsequent short-process dyeing.

[0029] T2, Pre-bathing treatment:

[0030] Increase the temperature to 70-85℃ at a rate of 1.5-2.0℃ / min, and hold for 15-25 min;

[0031] Reference Figure 1 The pretreatment-dyeing bath process curve shows that in the above stage, the temperature is increased to 70-85℃ at a rate of 1.5-2.0℃ / min and held for 15-25 minutes. The cortex Tg is 50-60℃. At this temperature, the molecular chain segment movement in the cortex is enhanced, the dye liquor permeability is improved, and the degreasing and scouring agent emulsifies and removes the surface oil and sizing agent of the alkali-resistant modified fiber, achieving a desizing rate of over 85%. Suspended sulfonate ions (-SO3) in the cortex... - The molecular chain segments move uniformly at the alkali-resistant modified fiber-water interface, forming a negatively charged enrichment region. The core layer Tg is about 75-78℃, the glass transition is not fully achieved, the molecular chain segments move, and the diffusion of dye into the core layer is hindered. At this temperature, sodium hydroxide has a low nucleophilic attack rate on the ester bond of the cortex, resulting in a low weight reduction rate.

[0032] T3, high temperature dyeing:

[0033] Continue heating to 130℃ at a rate of 1.0-1.2℃ / min, and hold for 30-45 min;

[0034] During the high-temperature dyeing stage, the temperature is further increased to 130℃ at a rate of 1.0-1.2℃ / min and held for 30-45 minutes. After reaching 130℃, the disperse dye gains sufficient kinetic energy and diffuses into the interior of the alkali-resistant modified fiber in a single-molecule state. The molecular chain segments in the cortex are highly mobile, and the frequency and pore size of instantaneous vacancies in the amorphous region increase. Halloysite nanotubes provide rigid diffusion channels for dye molecules. Suspended sulfonate ions and ester bond breakage in the cortex generate carboxylate anions, forming a negatively charged enrichment region at the alkali-resistant modified fiber-water interface. Although the alkali-resistant disperse dye does not carry a positive charge, the polar groups (-NO2, -CN, -Cl, etc.) in its molecular structure have molecular dipole moments. When they approach the surface of the alkali-resistant modified fiber, they undergo ion-dipole interactions with the negatively charged centers of sulfonate ions.

[0035] Incubate for 30-45 minutes to allow the dye to fully diffuse into the deep cortex, reaching dyeing equilibrium. In the cortex, the CHDM cyclohexane ring forms a steric barrier outside the ester bonds. The carbodiimide end-capping agent has converted the terminal carboxyl groups into inert acylurea structures. Together, they control the cortex alkali reduction to 5.0-8.0%, providing additional binding sites for nascent carboxylate groups while preventing excessive hydrolysis of the cortex. The core layer, lacking CHDM and having higher crystallinity, [continues to maintain its OH content]. - Less penetration, a small amount of dye anchored and diffused to this area by sulfonic acid groups;

[0036] T4. Post-cooling treatment:

[0037] Cool the fabric to 50-60℃ at a rate of 1.5-2.0℃ / min, drain the liquid, wash once with warm water at 50-60℃ for 10-15 minutes, and then remove the fabric.

[0038] In the post-cooling treatment stage, the temperature is lowered to 50-60℃ at a rate of 1.5-2.0℃ / min. After draining the liquid, the fiber is washed once with warm water. At this time, the movement of the molecular chain segments in the cortex is slow, and the dye that has diffused into the cortex is physically sealed inside the alkali-resistant modified fiber. When the cooling rate exceeds 2℃ / min, the thermal shrinkage coefficients of the cortex and the core are different, which may cause interfacial slippage or micro-cracks in the cortex, affecting the color fastness. The warm water wash removes the floating color and residual auxiliaries on the surface of the alkali-resistant modified fiber, and no reduction cleaning is required. The dye that has entered the cortex is physically encapsulated due to the freezing of the molecular chain segments. At the same time, the ion-dipole interaction in the negatively charged enrichment region continues to anchor the dye. The required color fastness can be achieved with a single water wash.

[0039] Preferably, the dermal slice preparation process is as follows:

[0040] Terephthalic acid, ethylene glycol, sodium isophthalate-5-sulfonate, and 1,4-cyclohexanediethanol were esterified in a molar ratio of 1:(1.2-1.5):(0.06-0.08):(0.06-0.10) for 120-180 min at a temperature of 220-240℃ and a pressure of 0.25-0.35 MPa.

[0041] Polycondensation was carried out at a temperature of 270-280℃ and a vacuum degree of ≤100 Pa for 180-240 min. At the end of the polycondensation, the temperature was lowered to 230-240℃ and carbodiimide end-capping agent was added. The mixture was stirred for 20-30 min. The amount of carbodiimide end-capping agent was 0.8-1.2 wt% of the total mass of the cortex slices, and the amount of halloysite nanotubes added was 1.0-3.0 wt% of the total mass of the cortex slices.

[0042] Preferably, the core layer slicing preparation process is as follows:

[0043] Terephthalic acid, ethylene glycol, and sodium isophthalate-5-sulfonate were esterified in a molar ratio of 1:(1.2-1.5):(0.015-0.025) at a temperature of 220-235℃ and a pressure of 0.25-0.35 MPa for 120-180 min.

[0044] Polycondensation was carried out at a temperature of 275-285℃ and a vacuum degree of ≤100 Pa for 180-240 min.

[0045] Preferably, the core-sheath composite spinning process is as follows:

[0046] The extrusion temperature of the outer layer is 270-280℃, the extrusion temperature of the core layer is 285-290℃, the temperature of the spinning box is 275-280℃, the side blowing temperature is 18-25℃, the wind speed is 0.5-0.8 m / s, and the winding speed is 800-1200 m / min.

[0047] The stretching and heat setting process is as follows: two-stage heat stretching, the first stage at 80-90℃ and 1.2-1.5 times, the second stage at 120-140℃ and 2.0-3.0 times, the total stretching ratio is 2.5-3.5 times, and the heat setting is carried out at 180-200℃ for 30-60 seconds.

[0048] Preferably, the carbodiimide end-capping agent is N,N'-bis(2,6-diisopropylphenyl)carbodiimide.

[0049] Preferably, the mixture formulation is as follows:

[0050] Alkali-resistant disperse dyes 1.0-8.0% owf;

[0051] Sodium hydroxide 0.5-2.0 g / L;

[0052] Alkali-resistant degreasing and refining agent: 0.5-1.2 g / L;

[0053] Alkali-resistant dispersing leveling agent: 0.5-1.2 g / L;

[0054] Chelating dispersant 0.3-0.8 g / L;

[0055] Penetrant 0.2-0.5 g / L;

[0056] Non-silicone defoamer 0.05-0.1 g / L; sodium hydroxide added in stages: first add 70% of the total amount, circulate for 10 min, measure the pH, and then add the remaining 30% to bring the pH to 9.0-10.5.

[0057] Compared with the prior art, the beneficial effects of the present invention are:

[0058] (1) This invention adopts a core-sheath gradient structure for alkali-resistant modified fibers. The sheath layer has concentrated sulfonic acid anion binding sites and CHDM cyclohexane structures, which are combined with carbodiimide end-capping agents to eliminate terminal carboxyl hydrolysis active sites, achieving a synergistic unity of high-density binding sites and alkali resistance in the sheath layer. The core layer maintains a high crystallinity structure to ensure the overall mechanical properties of the alkali-resistant modified fiber. This scheme starts from the fiber cross-section partitioning, concentrating the alkali resistance and dyeing function in the sheath layer and retaining the mechanical properties in the core layer, solving the technical problem that existing homogeneous modified fibers cannot simultaneously achieve alkali resistance and dyeability.

[0059] (2) This invention utilizes the confined and controllable hydrolysis of cortical ester bonds under alkaline bath conditions. The newly formed carboxylate ions, in conjunction with the existing sulfonate ions, construct a high-density negatively charged enrichment region at the alkali-resistant modified fiber-water interface. Through ion-dipole interactions, the adsorption affinity of the polar groups of disperse dyes on the surface of the alkali-resistant modified fiber is enhanced. Simultaneously, the cortical layer's Tg decreases to 50-60℃ and its crystallinity decreases due to CHDM copolymerization. Combined with the rigid tubular channels of halloysite nanotubes, this achieves rapid deep penetration and uniform distribution of dye molecules. This scheme transforms the unfavorable side reaction of fiber hydrolysis in traditional alkaline dyeing into a controllable dyeing enhancement method. It simultaneously solves the dual problems of insufficient wet fastness for medium and dark colors due to the lack of chemical anchoring points for disperse dyes and the dependence on toxic carriers for low-temperature diffusion. This results in improved dyeing depth and rubbing fastness.

[0060] (3) After dyeing, the present invention can remove the surface floating color with a single warm water wash, without the need for sodium hydrosulfite reduction cleaning and multiple water washes. The total water consumption is about 36 tons / ton of fabric, which saves about 60% of water compared with the traditional process. This solution reduces the generation and adhesion of floating color from the structural design of alkali-resistant modified fiber materials and the dye binding mechanism, reduces the intensity of post-treatment washing, and solves the technical problems of traditional processes such as lengthy process, high water and energy consumption, and sulfur-containing wastewater pollution caused by multiple water washes and reduction cleaning. Attached Figure Description

[0061] Figure 1 This is the pretreatment-staining process curve of the present invention. Detailed Implementation

[0062] The technical solutions of this invention are described below. It should also be noted that, to make the embodiments more detailed, the following embodiments are the best and preferred embodiments; those skilled in the art can also use other alternative methods to implement some well-known technologies.

[0063] Example 1: Pretreatment-dyeing method for alkali-resistant modified fibers using a single bath with low water content.

[0064] (a) Raw material preparation

[0065] Halloysite nanotubes were placed in 1 mol / L hydrochloric acid and stirred at 60°C for 4 h. They were then washed with deionized water until the pH reached 6.5, dried at 100°C for 12 h, and ground through an 800-mesh sieve to obtain acid-activated halloysite nanotubes.

[0066] (II) Preparation of dermal sections

[0067] The acid-activated halloysite nanotubes were mixed with ethylene glycol and ultrasonically dispersed for 30 min to form a uniform suspension.

[0068] Terephthalic acid, an ethylene glycol suspension containing acid-treated halloysite nanotubes, sodium isophthalate-5-sulfonate, and 1,4-cyclohexanediethanol were added to an esterification reactor in a molar ratio of 1:1.3:0.07:0.08. The suspension was based on the molar amount of ethylene glycol. The amount of halloysite nanotubes added was 2.0% of the total mass of the skin slices. Under nitrogen protection, the mixture was heated to 230°C, maintained at a pressure of 0.30 MPa, and stirred for 150 min to carry out the esterification reaction. The water generated during the esterification process was continuously discharged through a distillation column.

[0069] After esterification, the esterification product was transferred to a polycondensation reactor, and 0.035% (by weight of terephthalic acid) of antimony trioxide catalyst and 0.030% (by weight of trimethyl phosphate heat stabilizer) of trimethyl phosphate were added. The temperature was gradually raised to 275℃, and the vacuum was drawn to ≤100 Pa. The polycondensation reaction was carried out for 210 min. At the end of the polycondensation, the temperature was lowered to 235℃, and 1.0 wt% (by weight of total weight of the skin chips) of carbodiimide end-capping agent (N,N'-bis(2,6-diisopropylphenyl)carbodiimide) was added. The mixture was stirred for another 25 min, discharged under nitrogen pressure, water-cooled and pelletized, and vacuum dried at 130℃ for 7 h to obtain skin chips.

[0070] (III) Preparation of core slices

[0071] Terephthalic acid, ethylene glycol, and sodium isophthalate-5-sulfonate were added to an esterification reactor in a molar ratio of 1:1.3:0.02. The reactor was heated to 225°C under nitrogen protection and maintained at a pressure of 0.30 MPa. The mixture was stirred for 140 min to carry out the esterification reaction. After esterification, the mixture was transferred to a polycondensation reactor. 0.035 wt% of antimony trioxide catalyst and 0.030 wt% of trimethyl phosphate heat stabilizer were added to the reactor. The temperature was gradually increased to 280°C, and the reactor was evacuated to a vacuum degree of ≤100 Pa. The polycondensation reaction was carried out for 200 min. The mixture was then discharged under nitrogen pressure, water-cooled and pelletized, and vacuum-dried at 130°C for 7 h to obtain core layer chips.

[0072] (iv) Spinning and post-processing

[0073] The sheath and core layers are separately fed into two independent screw extruders of the sheath-core composite spinning assembly for melting. The sheath extrusion temperature is 275℃, the core layer extrusion temperature is 288℃, and the spinning box temperature is 278℃. The sheath melt and core melt converge in the distribution plate of the composite spinneret, with the sheath melt enveloping the core melt. The core melt is then extruded through the sheath-core composite spinneret, with the sheath / core thickness ratio controlled at 20 / 80. The extruded melt stream enters the side-blowing cooling zone at a temperature of 20℃ and a wind speed of 0.6 m / s. After cooling and solidification, the melt is wound at a speed of 1000 m / min to obtain nascent fibers.

[0074] The nascent fibers undergo two stages of hot stretching on a stretching machine: the first stretching temperature is 85℃ and the stretching ratio is 1.4; the second stretching temperature is 130℃ and the stretching ratio is 2.1. After stretching, the fibers are heat-set at 190℃ for 45 seconds and wound into a cylinder to obtain alkali-resistant modified fibers.

[0075] (v) Pretreatment - Staining in a bath with little water

[0076] Fabric: Fabric knitted from the above-mentioned alkali-resistant modified fibers

[0077] Dye prescription:

[0078] Alkali-resistant Dispersible Red HA-G: 2.0% owf

[0079] Sodium hydroxide: 1.0 g / L

[0080] Alkali-resistant degreasing and refining agent: 0.8 g / L

[0081] Alkali-resistant dispersing leveling agent: 0.8 g / L

[0082] Chelating dispersant: 0.5 g / L

[0083] Penetrant: 0.3 g / L

[0084] Non-silicone defoamer: 0.08 g / L

[0085] Operating steps:

[0086] (1) Fabric preparation: The fabric is put into the dyeing tank at 28°C. The alkali-resistant dispersible red HA-G is slurried and stirred with 45°C warm water for 15 min. After filtration through a 200-mesh filter, the dye pre-dispersion liquid is obtained. The alkali-resistant degreasing scouring agent, alkali-resistant dispersing and leveling agent, chelating dispersant, penetrant, and non-silicone defoamer are diluted with water and then added to the dye pre-dispersion liquid. Sodium hydroxide is added in stages: 70% of the total amount is added first, and the pH is measured after circulating for 10 min. Then the remaining 30% is added to bring the pH to 10.0. The temperature of the mixed liquid is controlled to be ≤35°C. The mixture is pumped into the dyeing equipment at a bath ratio of 1:7 and circulated and mixed for 8 min.

[0087] (2) Pre-bath treatment: Heat to 80℃ at 1.8℃ / min, keep warm for 20 min, pH 10.0 throughout, and do not drain.

[0088] (3) High temperature staining: continue to heat to 130℃ at 1.1℃ / min, keep warm for 40 min, keep pH 10.0 throughout the process, do not drain or adjust pH.

[0089] (4) Cooling and post-treatment: Cool down to 55℃ at 1.8℃ / min, drain the liquid, wash once with 55℃ warm water for 12 min, and then remove the fabric.

[0090] Example 2: Pretreatment-dyeing method for alkali-resistant modified fibers using a single bath with low water content:

[0091] (a) Raw material preparation

[0092] Halloysite nanotubes were placed in 1 mol / L hydrochloric acid and stirred at 60°C for 4 h. They were then washed with deionized water until the pH reached 6.5, dried at 100°C for 12 h, and ground through an 800-mesh sieve to obtain acid-activated halloysite nanotubes.

[0093] (II) Preparation of dermal sections

[0094] The acid-activated halloysite nanotubes were mixed with ethylene glycol and ultrasonically dispersed for 30 min to form a uniform suspension.

[0095] Terephthalic acid, an ethylene glycol suspension containing acid-treated halloysite nanotubes, sodium isophthalate-5-sulfonate, and 1,4-cyclohexanediethanol were added to an esterification reactor in a molar ratio of 1:1.3:0.07:0.08. The suspension was based on the molar amount of ethylene glycol. The amount of halloysite nanotubes added was 2.0% of the total mass of the skin slices. Under nitrogen protection, the mixture was heated to 230°C, maintained at a pressure of 0.30 MPa, and stirred for 150 min to carry out the esterification reaction. The water generated during the esterification process was continuously discharged through a distillation column.

[0096] After esterification, the esterification product was transferred to a polycondensation reactor, and 0.035% (by weight of terephthalic acid) of antimony trioxide catalyst and 0.030% (by weight of trimethyl phosphate heat stabilizer) of trimethyl phosphate were added. The temperature was gradually raised to 275℃, and the vacuum was drawn to ≤100 Pa. The polycondensation reaction was carried out for 210 min. At the end of the polycondensation, the temperature was lowered to 235℃, and 1.0 wt% (by weight of total weight of the skin chips) of carbodiimide end-capping agent (N,N'-bis(2,6-diisopropylphenyl)carbodiimide) was added. The mixture was stirred for another 25 min, discharged under nitrogen pressure, water-cooled and pelletized, and vacuum dried at 130℃ for 7 h to obtain skin chips.

[0097] (III) Preparation of core slices

[0098] Terephthalic acid, ethylene glycol, and sodium isophthalate-5-sulfonate were added to an esterification reactor in a molar ratio of 1:1.3:0.02. The reactor was heated to 225°C under nitrogen protection and maintained at a pressure of 0.30 MPa. The mixture was stirred for 140 min to carry out the esterification reaction. After esterification, the mixture was transferred to a polycondensation reactor. 0.035 wt% of antimony trioxide catalyst and 0.030 wt% of trimethyl phosphate heat stabilizer were added to the reactor. The temperature was gradually increased to 280°C, and the reactor was evacuated to a vacuum degree of ≤100 Pa. The polycondensation reaction was carried out for 200 min. The mixture was then discharged under nitrogen pressure, water-cooled and pelletized, and vacuum-dried at 130°C for 7 h to obtain core layer chips.

[0099] (iv) Spinning and post-processing

[0100] The sheath and core layers are separately fed into two independent screw extruders of the sheath-core composite spinning assembly for melting. The sheath extrusion temperature is 275℃, the core layer extrusion temperature is 288℃, and the spinning box temperature is 278℃. The sheath melt and core melt converge in the distribution plate of the composite spinneret, with the sheath melt enveloping the core melt. The core melt is then extruded through the sheath-core composite spinneret, with the sheath / core thickness ratio controlled at 30 / 70. The extruded melt stream enters the side-blowing cooling zone at a temperature of 20℃ and a wind speed of 0.6 m / s. After cooling and solidification, the melt is wound at a speed of 1000 m / min to obtain nascent fibers.

[0101] The nascent fibers undergo two stages of hot stretching on a stretching machine: the first stretching temperature is 85℃ and the stretching ratio is 1.4; the second stretching temperature is 130℃ and the stretching ratio is 2.1. After stretching, the fibers are heat-set at 190℃ for 45 seconds and wound into a cylinder to obtain alkali-resistant modified fibers.

[0102] (v) Pretreatment - Staining in a bath with little water

[0103] Fabric: Fabric knitted from the above-mentioned alkali-resistant modified fibers

[0104] Dye prescription:

[0105] Alkali-resistant Dispersible Red HA-G: 2.0% owf

[0106] Sodium hydroxide: 1.0 g / L

[0107] Alkali-resistant degreasing and refining agent: 0.8 g / L

[0108] Alkali-resistant dispersing leveling agent: 0.8 g / L

[0109] Chelating dispersant: 0.5 g / L

[0110] Penetrant: 0.3 g / L

[0111] Non-silicone defoamer: 0.08 g / L

[0112] Operating steps:

[0113] (1) Fabric preparation: The fabric is put into the dyeing tank at 28°C. The alkali-resistant dispersible red HA-G is slurried and stirred with 45°C warm water for 15 min. After filtration through a 200-mesh filter, the dye pre-dispersion liquid is obtained. The alkali-resistant degreasing scouring agent, alkali-resistant dispersing and leveling agent, chelating dispersant, penetrant, and non-silicone defoamer are diluted with water and then added to the dye pre-dispersion liquid. Sodium hydroxide is added in stages: 70% of the total amount is added first, and the pH is measured after circulating for 10 min. Then the remaining 30% is added to bring the pH to 10.0. The temperature of the mixed liquid is controlled to be ≤35°C. The mixture is pumped into the dyeing equipment at a bath ratio of 1:7 and circulated and mixed for 8 min.

[0114] (2) Pre-bath treatment: Heat to 80℃ at 1.8℃ / min, keep warm for 20 min, pH 10.0 throughout, and do not drain.

[0115] (3) High temperature staining: continue to heat to 130℃ at 1.1℃ / min, keep warm for 40 min, keep pH 10.0 throughout the process, do not drain or adjust pH.

[0116] (4) Cooling and post-treatment: Cool down to 55℃ at 1.8℃ / min, drain the liquid, wash once with 55℃ warm water for 12 min, and then remove the fabric.

[0117] Example 3: Pretreatment-dyeing method for alkali-resistant modified fibers using a single bath with low water content.

[0118] (a) Raw material preparation

[0119] Halloysite nanotubes were placed in 1 mol / L hydrochloric acid and stirred at 60°C for 4 h. They were then washed with deionized water until the pH reached 6.5, dried at 100°C for 12 h, and ground through an 800-mesh sieve to obtain acid-activated halloysite nanotubes.

[0120] (II) Preparation of dermal sections

[0121] The acid-activated halloysite nanotubes were mixed with ethylene glycol and ultrasonically dispersed for 30 min to form a uniform suspension.

[0122] Terephthalic acid, an ethylene glycol suspension containing acid-treated halloysite nanotubes, sodium isophthalate-5-sulfonate, and 1,4-cyclohexanediethanol were added to an esterification reactor in a molar ratio of 1:1.3:0.07:0.08. The suspension was based on the molar amount of ethylene glycol. The amount of halloysite nanotubes added was 2.0% of the total mass of the skin slices. Under nitrogen protection, the mixture was heated to 230°C, maintained at a pressure of 0.30 MPa, and stirred for 150 min to carry out the esterification reaction. The water generated during the esterification process was continuously discharged through a distillation column.

[0123] After esterification, the esterification product was transferred to a polycondensation reactor, and 0.035% (by weight of terephthalic acid) of antimony trioxide catalyst and 0.030% (by weight of trimethyl phosphate heat stabilizer) of trimethyl phosphate were added. The temperature was gradually raised to 275℃, and the vacuum was drawn to ≤100 Pa. The polycondensation reaction was carried out for 210 min. At the end of the polycondensation, the temperature was lowered to 235℃, and 1.0 wt% (by weight of total weight of the skin chips) of carbodiimide end-capping agent (N,N'-bis(2,6-diisopropylphenyl)carbodiimide) was added. The mixture was stirred for another 25 min, discharged under nitrogen pressure, water-cooled and pelletized, and vacuum dried at 130℃ for 7 h to obtain skin chips.

[0124] (III) Preparation of core slices

[0125] Terephthalic acid, ethylene glycol, and sodium isophthalate-5-sulfonate were added to an esterification reactor in a molar ratio of 1:1.3:0.02. The reactor was heated to 225°C under nitrogen protection and maintained at a pressure of 0.30 MPa. The mixture was stirred for 140 min to carry out the esterification reaction. After esterification, the mixture was transferred to a polycondensation reactor. 0.035 wt% of antimony trioxide catalyst and 0.030 wt% of trimethyl phosphate heat stabilizer were added to the reactor. The temperature was gradually increased to 280°C, and the reactor was evacuated to a vacuum degree of ≤100 Pa. The polycondensation reaction was carried out for 200 min. The mixture was then discharged under nitrogen pressure, water-cooled and pelletized, and vacuum-dried at 130°C for 7 h to obtain core layer chips.

[0126] (iv) Spinning and post-processing

[0127] The cortex and core layers are fed into two independent screw extruders of the cortex-core composite spinning assembly for melting. The cortex extrusion temperature is 275℃, the core layer extrusion temperature is 288℃, and the spinning box temperature is 278℃. The cortex melt and core melt converge in the distribution plate of the composite spinneret, and the cortex melt wraps around the core melt. The core melt is then extruded through the cortex-core composite spinneret. The cortex / core thickness ratio is controlled at 40 / 60. The extruded melt stream enters the side-blowing cooling zone with a side-blowing temperature of 20℃ and a wind speed of 0.6m / s. After cooling and solidification, the melt is wound at a speed of 1000m / min to obtain nascent fibers.

[0128] The nascent fibers undergo two stages of hot stretching on a stretching machine: the first stretching temperature is 85℃ and the stretching ratio is 1.4; the second stretching temperature is 130℃ and the stretching ratio is 2.1. After stretching, the fibers are heat-set at 190℃ for 45 seconds and wound into a cylinder to obtain alkali-resistant modified fibers.

[0129] (v) Pretreatment - Staining in a bath with little water

[0130] Fabric: Fabric knitted from the above-mentioned alkali-resistant modified fibers

[0131] Dye prescription:

[0132] Alkali-resistant Dispersible Red HA-G: 2.0% owf

[0133] Sodium hydroxide: 1.0 g / L

[0134] Alkali-resistant degreasing and refining agent: 0.8 g / L

[0135] Alkali-resistant dispersing leveling agent: 0.8 g / L

[0136] Chelating dispersant: 0.5 g / L

[0137] Penetrant: 0.3 g / L

[0138] Non-silicone defoamer: 0.08 g / L

[0139] Operating steps:

[0140] (1) Fabric preparation: The fabric is put into the dyeing tank at 28°C. The alkali-resistant dispersible red HA-G is slurried and stirred with 45°C warm water for 15 min. After filtration through a 200-mesh filter, the dye pre-dispersion liquid is obtained. The alkali-resistant degreasing scouring agent, alkali-resistant dispersing and leveling agent, chelating dispersant, penetrant, and non-silicone defoamer are diluted with water and then added to the dye pre-dispersion liquid. Sodium hydroxide is added in stages: 70% of the total amount is added first, and the pH is measured after circulating for 10 min. Then the remaining 30% is added to bring the pH to 10.0. The temperature of the mixed liquid is controlled to be ≤35°C. The mixture is pumped into the dyeing equipment at a bath ratio of 1:7 and circulated and mixed for 8 min.

[0141] (2) Pre-bath treatment: Heat to 80℃ at 1.8℃ / min, keep warm for 20 min, pH 10.0 throughout, and do not drain.

[0142] (3) High temperature staining: continue to heat to 130℃ at 1.1℃ / min, keep warm for 40 min, keep pH 10.0 throughout the process, do not drain or adjust pH.

[0143] (4) Cooling and post-treatment: Cool down to 55℃ at 1.8℃ / min, drain the liquid, wash once with 55℃ warm water for 12 min, and then remove the fabric.

[0144] Comparative Example 1:

[0145] Compared with Example 2, Comparative Example 1 did not add acid-activated halloysite nanotubes, while other conditions remained unchanged.

[0146] Comparative Example 2:

[0147] Compared with Example 2, sodium isophthalic acid-5-sulfonate was not added in Comparative Example 2, and other conditions remained unchanged.

[0148] Comparative Example 3:

[0149] Compared with Example 2, Comparative Example 3 did not use a core-sheath composite structure, but used homogeneous fibers. The sheath slices were directly stretched to form homogeneous fibers, and the spinning step was conventional melt spinning. All other conditions remained unchanged.

[0150] Comparative Example 4:

[0151] Compared with Example 2, no carbodiimide end-capping agent was added in Comparative Example 4, while other conditions remained unchanged.

[0152] Comparative Example 5:

[0153] Compared with Example 2, Comparative Example 5 used the traditional two-bath method, namely alkali reduction (NaOH 10 g / L, 130℃, 50 min) → water washing → staining (pH 4.5, 130℃, 40 min) → reduction cleaning → water washing, with other conditions unchanged.

[0154] Performance testing:

[0155] (1) Color fastness to washing

[0156] National Standard: GB / T 3921-2008 "Textiles - Tests for color fastness - Color fastness to washing with soap"

[0157] Test principle: The sample is sewn together with a standard lining fabric and placed in soap solution and sodium carbonate solution. It is mechanically stirred and washed under specified temperature and time conditions. After drying, the color change of the sample and the staining grade of the lining fabric are evaluated using a gray scale.

[0158] (2) Color fastness to rubbing

[0159] National Standard: GB / T 3920-2008 "Textiles - Tests for color fastness - Color fastness to rubbing"

[0160] Test principle: The textile sample is rubbed with dry and wet friction cloth respectively, and the degree of staining of the friction cloth is evaluated. The gray scale is used for rating (1-5, with 5 being the best).

[0161] (3) Breaking through strong force

[0162] National Standard: GB / T 19976-2005 Determination of Bursting Strength of Textiles – Steel Ball Method

[0163] Test principle: The bursting strength of the fabric is determined by using a ball-shaped push rod. The sample is clamped on the holder and bursts at a constant speed. The maximum bursting force value is recorded.

[0164] (4) Fiber alkali reduction rate

[0165] Test method:

[0166] The fiber sample was dried in an oven at 105℃ to constant weight (m0), then treated with alkali and dried again at 105℃ to constant weight (m1). The weight loss rate was calculated using the following formula:

[0167]

[0168] In the formula: m0 is the dry weight of the fiber before treatment (g), and m1 is the dry weight of the fiber after treatment (g).

[0169] Test conditions: The fiber sample was placed in a NaOH solution at pH 10.0 and 130℃ for 40 min, then washed thoroughly with water until neutral, dried at 105℃ to constant weight, and weighed.

[0170] (5) Staining depth (K / S value)

[0171] Test method:

[0172] Using a spectrophotometer, at D 65 Under light source and 10° field of view conditions, the K / S value of the dyed fabric at the wavelength of maximum absorption was measured. The fabric was folded into 4 layers, and measurements were taken at least 10 points at different locations, with the average value taken.

[0173] Test conditions: The dyed fabric was tested after being washed with warm water and dried.

[0174] (6) Percentage of staining

[0175] Test method:

[0176] Using a UV-Vis spectrophotometer, measure the absorbance A0 of the original dye solution (dye solution before dyeing) and the absorbance A1 of the residual dye solution (dye solution discharged after dyeing) at the maximum absorption wavelength of the dye. Calculate the dyeing percentage using the following formula:

[0177]

[0178] Test conditions: Both the original dye solution and the residual solution must be diluted with acetone and water at a volume ratio of 1:4 before measurement to eliminate the interference of disperse dye suspended particles on the absorbance measurement.

[0179] (7) Water consumption

[0180] Water consumption is calculated as follows: The actual total water consumption (in liters) of the entire dyeing process (fabric feeding and solution preparation, pretreatment in the same bath, high-temperature dyeing, post-treatment after cooling, and warm water washing) is divided by the mass of the processed fabric (in kilograms) to convert it into water consumption per ton of fabric (tons / ton of fabric).

[0181] The performance test data of the above embodiments and comparative examples are shown in Table 1.

[0182] Table 1. Performance test data for both the examples and the comparative examples.

[0183]

[0184] As can be seen from the data comparison in Table 1, in Examples 1 to 3, as the proportion of the cortex increased from 20% to 40%, the increased cortex thickness led to more dye-accommodating space and binding sites, resulting in a K / S value increase from 20.8 to 24.0 and a dye uptake rate increase from 86.1% to 89.6%. Both the wash fastness and rubbing fastness remained at grade 4 or above, indicating that thicker cortex is beneficial for improving dyeing performance. However, the alkali reduction rate increased from 5.2% to 8.1%, and the bursting strength decreased from 741N to 688N, indicating that while thicker cortex improves dyeing performance, it also comes at the cost of increased cortex hydrolysis and decreased mechanical properties. The cortex-core ratio needs to be balanced according to actual application requirements, taking into account both dyeing depth and the strength of alkali-resistant modified fibers.

[0185] In Comparative Example 1, after removing halloysite nanotubes, the alkali reduction rate increased from 6.5% in Example 2 to 7.8%, the K / S value decreased from 22.6 to 19.4, the dye uptake decreased from 88.6% to 82.8%, and the wet fastness to rubbing decreased from grade 4 to grade 3-4. The removal of halloysite nanotubes reduced the rigid channels for dye diffusion in the cortex, shortened the path for dye molecules to enter the cortex, and simultaneously increased the cortex's alkali resistance, leading to intensified surface hydrolysis. Some of the already dyed dye was shed with the hydrolysis products, indicating that halloysite nanotubes in the cortex possess both physical dyeing channels and alkali-resistant barrier functions. In Comparative Example 2, without the addition of sodium isophthalic acid-5-sulfonate, the K / S value was only 8.7, the dyeing rate was only 52.6%, and the wash fastness dropped to grade 2-3. This indicates that when there are no sulfonate groups in the cortex and core, the alkali-resistant modified fiber-water interface lacks a negatively charged enrichment region, the ion-dipole interaction disappears, and the dye can only rely on hydrophobic interactions and van der Waals forces for dyeing, resulting in a severe decrease in dyeing ability and color fastness. However, the alkali reduction rate was only 3.7%, lower than the 6.5% in Example 2, confirming that the hydrophilicity of sulfonate groups does indeed accelerate the penetration of alkali solution into the interior of the alkali-resistant modified fiber. That is, the sulfonate groups provide a dye seat and promote hydrolysis, which are two sides of the same coin.

[0186] Comparative Example 3, using homogeneous fibers, showed an alkali reduction rate as high as 14.2%, and a bursting strength of only 532 N, far lower than the 715 N of Example 2. This indicates that when 1,4-cyclohexanediethanol and homogeneous fibers are evenly distributed throughout the fiber cross-section, the overall crystallinity is significantly reduced. Under alkaline conditions, the simultaneous hydrolysis of the skin and core layers leads to a severe loss of mechanical properties. This proves that the skin-core composite structure, which confines the functional components to the skin layer and maintains high crystallinity in the core layer, is the key to maintaining the overall strength of the alkali-resistant modified fiber. In Comparative Example 4, without the addition of the end-capping agent, the alkali reduction rate increased from 6.5% to 10.6%, the bursting strength decreased from 715N to 618N, and the color fastness to washing and rubbing decreased to grades 3-4 and 3-4 / 3, respectively. This indicates that the carboxyl groups at the ends of the uncapped polyester molecular chains initiate a hydrolytic chain reaction under alkaline conditions and continue to expand, resulting in a greater degree of cortex hydrolysis. The surface structure of the alkali-resistant modified fiber is damaged, causing the dyed dye to fall off with the hydrolysis products of the cortex. The end-capping agent makes an important contribution to the stability of the cortex structure and color fastness.

[0187] Comparative Example 5, using the traditional two-bath method, showed slightly higher dyeing depth and dyeing rate than Example 2, with similar color fastness, but consumed as much as 92 tons of water per ton of fabric, approximately 2.6 times that of the single-bath process of this invention. The traditional two-bath method involves multiple drainage steps, including alkali reduction followed by draining and washing, acid neutralization followed by draining and washing, dyeing followed by draining, and reduction cleaning followed by draining and washing, leading to a significant increase in water consumption. This invention combines pretreatment and dyeing in the same dye bath, without draining or pH adjustment throughout the process, only requiring a final warm water wash and drainage step, resulting in excellent water conservation. In summary, the synergistic effect of the four technical features—the sheath-core gradient structure, sulfonate groups, halloysite nanotubes, and carbodiimide end-capping agent—enables alkali-resistant modified fibers to achieve a balance between low crystallinity and rich dyeing function in the sheath and high crystallinity and high strength in the core layer under weakly alkaline single-bath conditions. Compared to the traditional two-bath method, this invention saves approximately 60% of water while maintaining similar dyeing quality.

[0188] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An alkali-resistant modified fiber, comprising a sheath layer and a core layer, characterized in that, It is prepared by the following steps: S1. Preparation of cortical and core slices: The cortex slices are copolymerized from terephthalic acid, an ethylene glycol suspension containing acid-treated halloysite nanotubes, sodium isophthalate-5-sulfonate, and 1,4-cyclohexanediethanol, with carbodiimide end-capping agent added; the core slices are copolymerized from terephthalic acid, ethylene glycol, and sodium isophthalate-5-sulfonate. S2, spinning: The dermal and core slices are melt-extruded through a dermal-core composite spinning process, and then cooled and wound to obtain nascent fibers. S3, Post-processing: Nascent fibers are stretched and heat-set to obtain alkali-resistant modified fibers, in which the sheath thickness accounts for 20-40% of the radius of the alkali-resistant modified fiber, and the core layer accounts for 60-80%.

2. The alkali-resistant modified fiber according to claim 1, characterized in that, The process for preparing the dermal slices is as follows: Terephthalic acid, ethylene glycol, sodium isophthalate-5-sulfonate, and 1,4-cyclohexanediethanol were esterified for 120-180 min at a molar ratio of 1:(1.2-1.5):(0.06-0.08):(0.06-0.10) under a temperature of 220-240℃ and a pressure of 0.25-0.35 MPa. Polycondensation was then carried out for 180-240 min at a temperature of 270-280℃ and a vacuum degree ≤100 Pa. At the end of the polycondensation, the temperature was lowered to 230-240℃, and carbodiimide end-capping agent was added. The mixture was stirred for 20-30 min. The amount of carbodiimide end-capping agent was 0.8-1.2 wt% of the total mass of the cortical slices. During the polycondensation stage, antimony trioxide catalyst (0.03-0.05% by mass of terephthalic acid) and trimethyl phosphate heat stabilizer (0.02-0.04% by mass) are added. The amount of acid-treated halloysite nanotubes added is 1.0-3.0 wt% of the total mass of the cortical slices. They are mixed with ethylene glycol before the esterification reaction and then ultrasonically dispersed to form a uniform ethylene glycol suspension.

3. The alkali-resistant modified fiber according to claim 1, characterized in that, The core layer slice preparation process is as follows: Terephthalic acid, ethylene glycol, and sodium isophthalate-5-sulfonate were esterified in a molar ratio of 1:(1.2-1.5):(0.015-0.025) at a temperature of 220-235℃ and a pressure of 0.25-0.35 MPa for 120-180 min. Polycondensation was carried out at a temperature of 275-285℃ and a vacuum degree of ≤100 Pa for 180-240 min, and antimony trioxide catalyst (0.03-0.05% by mass of terephthalic acid) and trimethyl phosphate heat stabilizer (0.02-0.04% by mass of terephthalic acid) were added during the polycondensation stage.

4. The alkali-resistant modified fiber according to claim 1, characterized in that, The carbodiimide end-capping agent is N,N'-bis(2,6-diisopropylphenyl)carbodiimide.

5. The alkali-resistant modified fiber according to claim 1, characterized in that, The core-sheath composite spinning process is as follows: The extrusion temperature of the outer layer is 270-280℃, the extrusion temperature of the core layer is 285-290℃, the temperature of the spinning box is 275-280℃, the side blowing temperature is 18-25℃, the wind speed is 0.5-0.8 m / s, and the winding speed is 800-1200 m / min.

6. The alkali-resistant modified fiber according to claim 1, characterized in that, The stretching and heat setting parameters are: Two-stage heat drawing: the first stage at 80-90℃, 1.2-1.5 times the original length; the second stage at 120-140℃, 2.0-3.0 times the original length; and heat setting at 180-200℃ for 30-60 seconds.

7. A method for pretreatment-dyeing with a low-water bath using alkali-resistant modified fibers as described in claims 1-6, characterized in that, Includes the following steps: T1, Fabric preparation solution: Fabrics knitted from alkali-resistant modified fibers are placed in a dyeing vat at 25-30℃. Alkali-resistant disperse dyes are dispersed in water and filtered through a 200-mesh filter to obtain a dye pre-dispersion solution. Alkali-resistant degreasing scouring agent, alkali-resistant dispersing and leveling agent, chelating dispersant, penetrant, and non-silicone defoamer are dissolved in water and then added to the dye pre-dispersion solution and sodium hydroxide. The temperature of the mixture is controlled to be ≤35℃. The mixture is pumped into the dyeing equipment at a bath ratio of 1:(5-10) and circulated for 5-10 minutes to mix thoroughly. T2, Pre-bathing treatment: Increase the temperature to 70-85℃ at a rate of 1.5-2.0℃ / min, and hold for 15-25 min; T3, high temperature dyeing: Continue heating to 130℃ at a rate of 1.0-1.2℃ / min, and hold for 30-45 min; T4. Post-cooling treatment: Cool the fabric to 50-60℃ at a rate of 1.5-2.0℃ / min, drain the liquid, wash once with warm water at 50-60℃ for 10-15 minutes, and then remove the fabric.

8. The pretreatment-staining method with low water content in a single bath according to claim 7, characterized in that, The formula for the mixture is as follows: Alkali-resistant disperse dyes 1.0-8.0% owf; Sodium hydroxide 0.5-2.0 g / L; Alkali-resistant degreasing and refining agent: 0.5-1.2 g / L; Alkali-resistant dispersing leveling agent: 0.5-1.2 g / L; Chelating dispersant 0.3-0.8 g / L; Penetrant 0.2-0.5 g / L; Non-silicone defoamer 0.05-0.1 g / L; sodium hydroxide added in stages: first add 70% of the total amount, circulate for 10 min, measure the pH, and then add the remaining 30% to bring the pH to 9.0-10.5.

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