Modified polyester and dyeing process thereof

Abstract

The invention relates to the technical field of chemical fiber manufacturing and textile dyeing, and discloses modified polyester which is prepared by copolymerizing raw materials including aromatic dibasic acid or ester thereof, aliphatic dihydric alcohol, a third monomer containing a sulfonic acid group, anti-degradation modified polyethylene glycol and a compatibility regulator, the third monomer containing the sulfonic acid group and the anti-degradation modified polyethylene glycol have a synergistic effect, so that the glass-transition temperature of the modified polyester is reduced to be below 65 DEG C. The modified polyester is prepared by adopting a process of carrying out synergistic copolymerization on the third monomer containing the sulfonic acid group, the anti-degradation modified polyethylene glycol and the compatibility regulator; the glass transition temperature of the modified polyester is reduced to 65 DEG C or below through the synergistic effect, the problems of high energy consumption and strict equipment requirements caused by traditional polyester high-temperature dyeing are solved, the structural stability and dyeing adaptability are better, the fiber breaking strength is reduced, and the damage risk of non-high-temperature-resistant fibers is effectively reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical fiber manufacturing and textile dyeing, and particularly relates to a modified polyester and a dyeing process thereof. BACKGROUND

[0002] Polyester (polyethylene terephthalate fiber) has irreplaceable application value in the fields of textiles, clothing, home textiles, etc. due to its excellent mechanical properties, outstanding dimensional stability and wrinkle resistance, has become the highest yield synthetic fiber in the world, and widely serves multiple scenarios such as civilian clothing and industrial textiles, and plays an important supporting role in promoting the development of the textile industry.

[0003] However, the molecular structure characteristics of conventional polyester make its dyeing process face natural technical bottlenecks. The polyester macromolecular chain is connected by repeated ester bonds, the structure is compact and regular, and there is a lack of polar groups such as hydroxyl and amino groups in the molecular chain which can form effective combination with dyes. In addition, the glass transition temperature of polyester is relatively high, generally about 80℃, and only under high temperature conditions, the molecular chain will move enough to provide a channel for the diffusion of dyes. These two characteristics together cause the difficulty in dyeing conventional polyester. In the existing technology, it is necessary to rely on disperse dyes, and the dyeing is completed under high temperature and high pressure conditions at 120-130℃. In addition, this process requires special high temperature and high pressure dyeing equipment, which not only has high equipment purchase and maintenance costs, but also consumes a large amount of energy, which is contrary to the development needs of energy saving and emission reduction of the current textile industry.

[0004] More importantly, the high temperature and high pressure dyeing process significantly damages the fiber and the blended system. Long-term high temperature can destroy the crystalline structure of polyester itself, resulting in a significant decrease in fiber breaking strength and elongation at break, which directly affects the durability of the final product. Moreover, this process cannot fully adapt to the blending and dyeing needs of spandex, wool and other non-temperature-resistant fibers. High temperature can cause the destruction of the cross-linked structure of spandex molecular chains, significantly reduce the elastic recovery rate, and wool is prone to felting and yellowing at high temperatures, resulting in significant loss of fiber strength. This makes it difficult to achieve integrated dyeing of polyester and functional fiber blended products, and severely limits the functional expansion and application scenarios of polyester blended fabrics.

[0005] In order to break through the limitations of high temperature dyeing of polyester, two paths have been explored in the industry. One is to develop new dyes, but the temperature reduction is limited and the color fastness is easily affected. The second is chemical modification, among which the application of cationic dyeable polyester prepared by introducing isophthalic acid-5-sodium sulfonate is relatively wide. However, the glass transition temperature of traditional cationic dyeable polyester is only reduced to 75-80℃, and still needs to be dyed at about 110℃, which has limited energy saving and emission reduction effect, and the dyeing rate is low, the color depth is insufficient, and it is difficult to meet the deep color demand, and the color fastness also needs to be improved by additional post-treatment. SUMMARY

[0006] The present application aims at the deficiencies in the prior art, and provides a modified polyester and a dyeing process thereof, which cooperates a third monomer containing a sulfonic acid group, polyethylene glycol modified against degradation and a compatibility regulator to reduce the glass transition temperature of the modified polyester to below 65 DEG C, realize low-temperature dyeing below 105 DEG C, and inhibit the degradation of the polyethylene glycol and improve the blending adaptability with non-temperature-resistant fibers.

[0007] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions: A modified polyester is made of raw materials including aromatic dibasic acid or ester thereof, aliphatic dihydric alcohol, third monomer containing a sulfonic acid group, polyethylene glycol modified against degradation and compatibility regulator, the third monomer containing a sulfonic acid group cooperates with the polyethylene glycol modified against degradation to reduce the glass transition temperature of the modified polyester to below 65 DEG C, and the degradation of the polyethylene glycol modified against degradation is inhibited in the high-temperature copolymerization process, and the compatibility regulator is used to improve the interfacial compatibility of the modified polyester with non-temperature-resistant fibers, so that the key performance retention rate of the non-temperature-resistant fibers after low-temperature dyeing of the blending system meets the wearing requirements.

[0008] Preferably, the third monomer containing a sulfonic acid group is sulfonated aromatic dibasic acid or ester thereof.

[0009] Preferably, the modification mode of the polyethylene glycol modified against degradation is end group capping, and the capping agent of the end group capping is aromatic acyl chloride compound.

[0010] Preferably, the compatibility regulator is aliphatic polyester polymer.

[0011] A preparation method of a modified polyester includes the following steps: Esterification or transesterification reaction: aromatic dibasic acid or ester thereof and aliphatic dihydric alcohol are subjected to esterification or transesterification reaction in the presence of a catalyst to generate aromatic dibasic acid bis-hydroxyethyl ester or oligomer thereof; Copolymerization reaction: the product of the esterification or transesterification reaction is added with the third monomer containing a sulfonic acid group, the polyethylene glycol modified against degradation and the compatibility regulator, and then added with a polycondensation catalyst and a stabilizer, and subjected to polycondensation reaction under vacuum condition to obtain a modified copolyester melt; Spinning and post-treatment: the modified copolyester melt is sequentially subjected to melt delivery, metering, spinning, cooling, oiling, drawing, heat setting and winding to prepare a low-temperature deep-dyeing modified polyester fiber.

[0012] Preferably, the catalyst is antimony-based catalyst, the polycondensation catalyst is antimony-based catalyst, and the stabilizer is phosphite compound.

[0013] A dyeing process of a modified polyester includes the following steps: Preparation of dye liquor: add water, leveling agent, pH regulator and cationic dye into the dyeing vat, and stir until uniform; Segmented temperature rising dyeing: put the modified polyester fiber or its fabric into the dyeing vat, first rise the temperature to near the glass transition temperature of the modified polyester at a lower temperature rising rate, then rise the temperature to the target dyeing temperature at a higher temperature rising rate and keep dyeing at the target temperature, the target dyeing temperature is not higher than 105 degrees; Post-treatment: after dyeing, sequentially perform water washing, soaping, warm water washing and drying; during the warm water washing, add a performance restorer to improve the performance of non-temperature-resistant fibers in the blended system.

[0014] Preferably, the dye liquor further comprises a dyeing promoter, which forms a weak interaction with the cationic dye to regulate the dyeing rate of the dye.

[0015] Preferably, the performance restorer is a polyurethane emulsion.

[0016] Compared with the prior art, the present application has the following beneficial effects: In the present application, the modified polyester is made by a process of synergistic copolymerization of a third monomer containing sulfonic acid groups, polyethylene glycol modified against degradation, and a compatibility regulator. The synergistic effect reduces the glass transition temperature of the modified polyester to below 65 degrees, avoids the problems of high energy consumption and strict equipment requirements caused by traditional high-temperature dyeing of polyester, and improves the structural stability and dyeing adaptability. The fiber breaking strength is reduced, and the risk of damage to non-temperature-resistant fibers is effectively reduced. The polyethylene glycol modified by end capping is combined with a stabilizer to copolymerize at high temperature, which effectively reduces the degradation rate of the polyethylene glycol. This combination of raw materials can meet the polyester requirements of different scenarios such as antibiotic carrier fabrics, elastic clothing, and skin-friendly home textiles, reduce performance fluctuations and uneven dyeing caused by high-temperature degradation, and expand the application range. The segmented temperature rising dyeing and warm water washing repair process cover the entire dyeing process, eliminating color bleeding and color floating hazards, and significantly improving the practical value of modified polyester textiles. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed in the embodiments. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0018] Fig. 1 Process flow chart for preparation of modified polyester of the present application; Fig. 2 Process flow chart for dyeing of modified polyester of the present application. DETAILED DESCRIPTION

[0019] The present application will be described in further detail below with reference to the drawings.

[0020] The following description is presented to enable those skilled in the art to make and use the application. Preferred embodiments of the present application are described herein as examples only, and various modifications can be made by those skilled in the art without departing from the spirit and scope of the present application. The present application defined in the claims is not intended to be limited by the description in the following.

[0021] Those skilled in the art will understand that, in the disclosure of the present application, the terms "longitudinal", "transverse", "upper", "lower", "left", "right", "front", "rear", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or position shown in the drawings, which are only for the convenience of the simplified description of the present application, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore the above terms cannot be understood as a limitation of the present application.

[0022] It can be understood that the term "one" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of one element can be one, and in another embodiment, the number of the element can be multiple, and the term "one" cannot be understood as a limitation on the number.

[0023] Embodiment one: Please refer to Figs. 1-2 A modified polyester is prepared by copolymerization of raw materials including aromatic diacid or its ester, aliphatic diol, third monomer containing sulfonic acid group, anti-degradation modified polyethylene glycol and compatibility regulator; Synergistic effect of raw materials: the third monomer containing sulfonic acid group provides cationic dye binding sites, and the anti-degradation modified polyethylene glycol destroys the crystalline regularity of the polyester molecular chain, both of which cooperate to reduce the glass transition temperature of the modified polyester to below 65 degrees, at the same time, the anti-degradation modification can inhibit the degradation of polyethylene glycol during the high-temperature copolymerization process; Compatibility regulator: used to improve the interfacial compatibility of the modified polyester and non-temperature-resistant fibers, such as spandex, wool, cotton, etc., to avoid performance damage caused by stress difference between fibers during dyeing.

[0024] The aromatic diacid or its ester is preferably one or both of terephthalic acid and dimethyl terephthalate, which ensures the mechanical properties of the main structure of the polyester, and the aliphatic diol is preferably ethylene glycol and aromatic diacid to form a PET main chain; The third monomer containing sulfonic acid group is preferably sulfonated aromatic dibasic acid or its ester, specifically one or both of sodium 5-sulfoisophthalate and dimethyl 5-sulfoisophthalate, to balance the dyeing efficiency and fiber mechanical properties; The polyethylene glycol is modified by end capping, and the end capping agent is preferably an aromatic acyl chloride compound, and benzoyl chloride can be used. The compatibility regulator is preferably a fatty polyester polymer, specifically one or both of polycaprolactone and polylactic acid, and the molecular weight can be 4000-6000, which is polar matched with the non-high-temperature-resistant fiber.

[0025] A preparation method of the modified polyester fiber, comprising the following steps: Esterification or transesterification: aromatic dibasic acid or its ester and aliphatic dihydric alcohol are added to an esterification kettle, a catalyst is added, the catalyst can be preferably antimony catalyst such as antimony trioxide, and the reaction is carried out at a temperature of 250-260 degrees and a pressure of 0.2-0.4 MPa until the esterification water rate reaches the required standard, generating aromatic dibasic acid bis-hydroxyethyl ester or its oligomer; Reaction control logic: under this temperature and pressure, it can ensure that the aromatic dibasic acid and ethylene glycol are fully reacted, while avoiding excessive volatilization of ethylene glycol and reducing raw material waste; Copolymerization: the third monomer containing sulfonic acid group, the polyethylene glycol modified against degradation, and the compatibility regulator are added to the esterification or transesterification product, and then a polycondensation catalyst and a stabilizer are added, and the stabilizer can be preferably a phosphite compound such as triphenyl phosphite to inhibit high-temperature oxidative degradation; The system vacuum is gradually reduced to ≤100 Pa, and the temperature is raised to 275-280 degrees for polycondensation reaction until the stirring power reaches the preset value, which indicates that the melt viscosity meets the standard, usually 20-30 Pa per second, and then the modified copolyester melt is obtained, the small molecules of ethylene glycol generated during the reaction are removed through high vacuum, the polycondensation reaction is promoted in the forward direction, and the molecular weight of the copolyester is ensured to meet the standard; Spinning and post-processing: the modified copolyester melt is transported to the spinning box through the melt pipeline, the melt flow is controlled by the metering pump, and the melt is extruded through the spinning assembly, cooled by side blowing, and oiled after uniform cooling and setting of the yarn, and the oil agent can be a polyether type spinning oil agent to reduce yarn friction, and then drawn to improve fiber breaking strength, and then heat set to eliminate internal stress, and the heat setting temperature can be 120-140 degrees, and then the yarn is wound to obtain low-temperature deep-dyeing modified polyester fiber, and the number of spinneret holes of the spinning assembly can be selected according to the fiber specifications, such as 72 holes and 144 holes.

[0026] A dyeing process of the modified polyester fiber, comprising the following steps: Preparation of dyeing solution: Add deionized water to the dyeing vat to avoid water quality impurities affecting dyeing uniformity, and then add leveling agent, pH adjuster, and cationic dye, stir for 10-15 minutes until uniform. The leveling agent can be preferably a cationic surfactant, such as cetyltrimethylammonium chloride, with a dosage of 0.5-2.0 g / L, to prevent dye aggregation. The pH adjuster can be preferably acetic acid, with a dosage of 1.0-3.0 g / L, to adjust the pH of the dyeing solution to 4.0-5.0, suitable for cationic dyeing. The cationic dye can be selected from cationic red GTL and cationic blue X-GRL, with the dosage adjusted according to the color depth requirements.

[0027] Dye solution ratio logic: Cationic leveling agent does not conflict with cationic dye and can delay dyeing rate to avoid color mottle. The pH range of 4.0-5.0 is the optimal pH range for the combination of cationic dye and sulfonic acid group; Segmented temperature rising dyeing: Put the modified polyester fiber or its filament, such as needle filament or machine filament, into the dyeing vat, and control the bath ratio to 1:20-1:30 to ensure that the dyeing solution fully wraps the fiber. First, raise the temperature to near the glass transition temperature of the modified polyester at a lower heating rate, and keep it for 5-10 minutes to allow the dye to be initially absorbed in the amorphous region of the fiber, avoiding surface dyeing. Then, raise the temperature to the target dyeing temperature at a higher heating rate, and keep it for 30-60 minutes. Temperature rising logic: Slow heating in the low glass transition temperature interval to prevent rapid dyeing that leads to internal and external concentration difference. Fast heating in the high glass transition temperature interval to promote deep diffusion of the dye using fast molecular chain movement, balancing dyeing efficiency and uniformity. Post-treatment: After dyeing, cool it down to below 70 degrees, avoiding large temperature difference that causes filament wrinkles, then drain, and then sequentially perform washing, soaping, warm water washing, and drying. Use 70-80 degree hot water for washing, with the washing time determined according to the situation, to remove surface float color. Add soaping agent, which can be preferably a non-ionic soaping agent such as fatty alcohol polyoxyethylene ether, to further remove unbound dye and improve color fastness at 80-85 degrees. Then, use warm water to wash, adding performance repair agent, which can be preferably a polyurethane emulsion such as polyether polyurethane emulsion, to repair the surface damage of the blended fiber. Finally, perform low-temperature drying to avoid thermal shrinkage of non-high-temperature-resistant fibers.

[0028] Preparation of modified polyester: Raw material ratio: terephthalic acid 90%, ethylene glycol 8.3%, m-xylylene sulfonic acid sodium 1.5%, benzoyl chloride-terminated polyethylene glycol 2.0%, and polycaprolactone 0.2%. Esterification reaction: add phthalic acid and ethylene glycol into the esterification kettle, add 0.03% antimony trioxide, and stir under the conditions of the esterification kettle temperature of 255 degrees and the pressure of 0.3 MPa. When the esterification water rate reaches the standard, the bis-hydroxyethyl terephthalate oligomer is generated; Copolymerization reaction: add sodium 5-sulfonate isophthalic acid, benzoyl chloride-terminated polyethylene glycol with a molecular weight of 1500, polycaprolactone with a molecular weight of 5000 into the esterification kettle, and then add 0.02% antimony trioxide and 0.015% triphenyl phosphite. Then gradually reduce the vacuum degree in the kettle to 80 Pa. The high vacuum environment can remove the small molecules of ethylene glycol generated during the polycondensation reaction in time, promoting the reaction to generate high polymers. Then increase the temperature in the kettle to 278 degrees, and start stirring the polycondensation reaction. When the melt viscosity reaches 20-30 Pa s, stop heating, break the vacuum in the kettle, and transport the generated modified copolyester melt through the melt pipeline to the granulator. After water cooling and granulation, the modified copolyester chips are obtained. Spinning post-processing: put the modified copolyester chips into a vacuum drying machine for vacuum drying. The dried chips are sent to a melt spinning machine for melt spinning. The melted melt is transported to the spinning box through the melt pipeline. The melt is extruded from the spinneret, enters the side-blowing cooling device for cooling, and then the cooled yarn is guided to the oil tank, coated with polyether type spinning oil, and then enters the drafting machine for drafting. The drafted yarn enters the heat setting oven to eliminate the internal stress generated during the drafting process and improve the fiber size stability. Finally, it is wound into a bobbin by the winding machine to produce low-temperature deep-dyeing modified polyester filament.

[0029] Example 2: Preparation of modified polyester Raw material ratio: dimethyl terephthalate 88%, ethylene glycol 9.0%, 5-sulfonated isophthalic acid dimethyl ester 4.0%, benzoyl chloride-terminated polyethylene glycol with a molecular weight of 2000 6.0%, and polylactic acid with a molecular weight of 6000 0.5%; Ester exchange reaction: add dimethyl terephthalate and ethylene glycol according to the ratio into the ester exchange kettle, add 0.04% antimony trioxide (ester exchange catalyst) accounting for 0.04% of the total mass of raw materials, and stir under the conditions of the temperature of 190-200 degrees. Stirring reaction and collection of generated methanol, when the amount of collected methanol reaches 95% of the distillation value, stop the ester exchange reaction, and the bis-hydroxyethyl terephthalate oligomer is generated in the system; The copolymerization reaction: to the oligomer in the ester exchange kettle, according to the proportion, add 5-sulfo-m-xylylene dicarboxylic acid dimethyl ester, molecular weight 2000 benzoyl chloride capped polyethylene glycol, molecular weight 6000 polylactic acid, and 0.03% polycondensation catalyst, and 0.02% stabilizer, its polycondensation catalyst is antimony trioxide, and the stabilizer is triphenyl phosphite, then the vacuum degree in the kettle is gradually reduced to 50 Pa, and the temperature is raised to 280 degrees, the polycondensation reaction is started, and after the melt viscosity reaches 20-30 Pa / s, the heating is stopped, the vacuum in the kettle is broken, and the modified copolyester melt is transported to the granulator through the melt pipeline, cooled by water, and granulated to obtain modified copolyester chips, and the vacuum degree is higher than that of comparative example 1, because the residual methyl ester group of dimethyl terephthalate needs stronger vacuum to be completely removed. Spinning after treatment: the modified copolyester chips are vacuum dried, it should be noted that the copolyester with higher molecular weight needs higher temperature drying to avoid residual moisture, then melt spinning, and then side blowing cooling, polyether type spinning oil, traction into yarn, and finally heat setting, and finally winding into a cylinder by the winding machine, to prepare low temperature deep dyeing type modified polyester filament.

[0030] Example 3: dyeing of modified polyester needle filament Yarn preparation: the modified polyester filament prepared in example 1 is taken for dyeing preparation; Dye solution preparation: add deionized water to the stainless steel dye vat, start stirring, and then add cationic leveling agent, pH regulator, and cationic dye in sequence, then keep stirring to mix the components of the dye solution, after a period of stirring, detect the pH value of the dye solution with precision pH test paper or pH meter, and confirm that the pH meets the requirements of cationic dyeing; It is added according to the mass of the filament to be dyed when the proportion is carried out, such as 25L deionized water is added when 1kg of filament is dyed, which can be adjusted according to the liquid absorption of the filament, and it is ensured that the dyeing solution can completely wrap the filament, and when the cationic leveling agent is added, cetyltrimethylammonium chloride can be used, the total amount can be 0.5g-2g / L, when the pH regulator is added, acetic acid can be used, the total amount is 1g-3g / L, and it is added in 2-3 times, 50% of the total amount is added at the first time, and the subsequent is supplemented according to the pH detection result, and finally the pH of the dyeing solution needs to be stabilized at 4.0-5.0, this interval is the best range of pH for the combination of cationic dyes and modified polyester sulfonic groups, pH below 4.0 will lead to dye hydrolysis, and higher than 5.0 will reduce the dyeing rate, when the cationic dye is added, according to the target color depth of the filament, the corresponding cationic dye is weighed, the amount is calculated according to the mass of the filament, 1-4g of dye is added per 100g of filament, such as 1g-2g of dye is added per 100g of filament when the target of dyeing is light color, 2g-3g of dye is added per 100g of filament when the target of dyeing is medium dark color, and 3g-4g of dye is added per 100g of filament when the target of dyeing is dark color, the amount of dye is determined by different color depth requirements to ensure that the filament can present the ideal color effect.

[0031] Segmented temperature rising dyeing: the modified polyester filament after relaxation and setting is slowly put into the stainless steel dyeing vat with prepared dyeing solution, ensuring that the filament is completely immersed in the dyeing solution without local stacking, winding or floating on the liquid surface; Pre-treatment: first stage temperature rising: the temperature is raised from room temperature to 65 degrees at a rate of 1.0 degree / min, and after reaching 65 degrees, it is kept for 8 minutes to allow the dye to be preliminarily adsorbed on the surface of the filament; Second stage temperature rising: the temperature of the dyeing solution is continued to be raised from 65 degrees to 100 degrees at a rate of 2.0 degrees / min, after the temperature of the dyeing solution is stabilized at 100 degrees, the temperature is kept for 45 minutes, by using the characteristics of rapid movement of the molecular chain of the filament at high temperature, the dye is promoted to diffuse deeply into the filament, and the dye is fully combined with the sulfonic acid groups in the filament to achieve the target color depth.

[0032] Post-treatment: the temperature is lowered to 60 degrees at a rate of 1.5 degrees / min, then it is left for a while to make the temperature of the filament uniform, then the water is discharged, 75 degrees hot water is added for cleaning, then soaping is carried out, 85 degrees non-ionic soaping agent is added for cleaning during soaping, then warm water washing is carried out, 45 degrees warm water is added for washing, polyether type polyurethane emulsion can be added to repair the surface damage of the blended fiber, after cleaning, low temperature drying treatment is carried out to complete the dyeing process.

[0033] It will be understood by those skilled in the art that the above description and the examples shown in the drawings of the application are only by way of example and do not limit the application. The object of the application has been fully and effectively achieved. The function and the structural principle of the application have been shown and described in the examples, and the embodiments of the application can have any variation or modification without departing from the principle.

Claims

1. A modified polyester, characterized in that, is prepared from raw materials including aromatic dibasic acid or its ester, aliphatic dihydric alcohol, third monomer containing sulfonic acid group, anti-degradation modified polyethylene glycol and compatibility modifier; the third monomer containing sulfonic acid group and the anti-degradation modified polyethylene glycol synergistically reduce the glass transition temperature of the modified polyester to below 65 degrees, and the degradation of the anti-degradation modified polyethylene glycol is inhibited during the high-temperature copolymerization process; the compatibility modifier is used to improve the interfacial compatibility of the modified polyester with non-temperature-resistant fibers in the blended system, so that the key performance retention rate of the non-temperature-resistant fibers in the blended system after low-temperature dyeing meets the requirements for clothing use.

2. The modified polyester of claim 1, wherein, the third monomer containing sulfonic acid group is sulfonated aromatic dibasic acid or its ester.

3. The modified polyester of claim 1, wherein, the modification method of the anti-degradation modified polyethylene glycol is end group capping, and the end capping agent for the end group capping is an aromatic acyl chloride compound.

4. The modified polyester of claim 1, wherein, the compatibility modifier is an aliphatic polyester polymer.

5. The method for preparing modified polyester according to any one of claims 1-4, characterized in that, comprises the following steps: esterification or transesterification reaction: esterification or transesterification reaction of aromatic dibasic acid or its ester and aliphatic dihydric alcohol in the presence of a catalyst to generate aromatic dibasic acid bis-hydroxyethyl ester or its oligomer; copolymerization reaction: adding the third monomer containing sulfonic acid group, the anti-degradation modified polyethylene glycol and the compatibility modifier to the product of the esterification or transesterification reaction, and then adding a polycondensation catalyst and a stabilizer to perform polycondensation reaction under vacuum to obtain a modified copolyester melt; spinning and post-treatment: the modified copolyester melt is sequentially subjected to melt conveying, metering, spinning, cooling, oiling, drawing, heat setting and winding to obtain low-temperature deep-dyeing modified polyester fibers.

6. The method for preparing modified polyester according to claim 5, characterized in that, the catalyst is an antimony-based catalyst, the polycondensation catalyst is an antimony-based catalyst, and the stabilizer is a phosphite compound.

7. The dyeing process of the modified polyester according to any one of claims 1 to 4, characterized in that, comprises the following steps: preparing a dyeing solution: adding water, leveling agent, pH adjuster and cationic dye to a dyeing vat and stirring until uniform; stepwise temperature rising dyeing: putting the modified polyester fibers or fabrics thereof into the dyeing vat, first rising the temperature to near the glass transition temperature of the modified polyester at a lower temperature rising rate, then rising the temperature to the target dyeing temperature at a higher temperature rising rate and keeping the temperature for dyeing, and the target dyeing temperature is not higher than 105 degrees; post-treatment: after dyeing, sequentially performing water washing, soaping, warm water washing and drying; a performance restorer is added during the warm water washing process to improve the performance of the non-temperature-resistant fibers in the blended system.

8. The dyeing process of modified polyester as claimed in claim 7, wherein, the dyeing solution further comprises a dyeing promoter, and the dyeing promoter forms weak interaction with the cationic dye to regulate the dyeing rate of the dye.

9. The dyeing process of modified polyester as claimed in claim 7, wherein, the performance restorer is a polyurethane emulsion.

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