Skin-core type foaming polyester fiber and preparation method thereof

Abstract

The invention relates to the field of polyester, and discloses a skin-core type foaming polyester fiber and a preparation method thereof. The skin-core type foaming polyester fiber comprises a foaming polyester core layer and a polyester skin layer, the foaming polyester core layer is obtained by blending modified foaming polyester, a nucleating agent and a foaming agent and then carrying out melt spinning; the modified foaming polyester is obtained by esterification and polycondensation of terephthalic acid, isophthalic acid, ethylene glycol and pentaerythritol as monomers. The melting point of the foamed polyester is reduced and the melt strength of the foamed polyester is enhanced at the same time by modifying the foamed polyester, and the polyester fiber is designed into a skin-core structure, so that the skin-core type foamed polyester fiber which is complete, good in continuity and excellent in mechanical strength can be successfully prepared.

Description

Technical Field

[0001] The invention relates to the field of polyester, and in particular to a sheath-core foamed polyester fiber and a preparation method thereof. Background Art

[0002] Foam material is a lightweight material with a large number of fine bubbles. The bubbles can be closed or connected, uniform or uneven, single or composite. It is usually made of polymer materials such as plastics and rubber. It forms a porous structure through physical or chemical foaming process. The density is generally 0.01-0.6g / cm 3 It is much lower than that of ordinary polymer materials, thus giving the material the characteristics of lightness, sound absorption, heat insulation, cushioning and shock absorption.

[0003] Among them, polyethylene terephthalate foam materials have gradually attracted attention from the demand side due to their excellent heat resistance, mechanical strength and other advantages. They have broad application prospects in fields such as building construction, automotive interior panels, roof insulation, microwave containers, sports equipment, automobile and aerospace industries.

[0004] At present, foamed polyester is usually processed into products such as plates and films, but it is rarely processed into fiber form. The reason is that the high crystallinity and low melt strength of polyethylene terephthalate itself make it difficult for gas to form closed bubbles in its system, and the pore size is large (the pore size formed by conventional foaming agents is at the level of hundreds of microns), which makes it difficult to ensure the continuous molding of the fiber. Even if it is molded, the strength of the foamed polyester fiber is too low to meet the use requirements. Therefore, the preparation of foamed polyester fiber must not only overcome the foaming difficulties of PET itself, but also consider the complex relationship between the pore structure characteristics and the fiber diameter and mechanical properties, as well as the sequence of the foaming process and the spinning process. However, the relevant process technology is not yet mature.

[0005] Patent CN109852009A discloses a highly thermoplastic foaming polyester, which improves the crystallization performance of thermoplastic polyester, accelerates the crystallization rate, improves its mechanical properties, and effectively improves the stability of the foaming process by adding a needle-shaped structure nucleating agent; the addition of a chain extender and an antioxidant further improves the thermal stability and melt strength of the polyester at high temperatures, and finally a thermoplastic polyester foaming material is prepared by physical foaming. However, in this solution, the diameter of the needle-shaped nucleating agent is 0.1 to 100 μm, and the aspect ratio is 3 to 100, which is too large for the spinning filter assembly, and therefore is not suitable for promotion to foaming fiber production.

[0006] Patent CN1760418A discloses a porous PET foam fiber and a preparation method thereof, wherein conventional or special-shaped PET fibers are placed in a high-pressure container, filled with inert gas, and subjected to gas permeation, pressure release, and heat treatment to obtain foamed fibers. This method uses gas foaming, and the high-pressure conditions involved have high requirements on equipment, making it difficult to mass-produce. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a core-sheath type foamed polyester fiber and a preparation method thereof. The present invention can successfully prepare a core-sheath type foamed polyester fiber with good continuity and excellent mechanical strength by modifying the foamed polyester to reduce its melting point and simultaneously enhance its melt strength, and designing the polyester fiber into a core-sheath structure.

[0008] The specific technical scheme of the present invention is: In a first aspect, the present invention provides a core-shell foamed polyester fiber, comprising a foamed polyester core layer and a polyester skin layer, wherein the foamed polyester core layer is obtained by melt spinning after blending modified foamed polyester with a nucleating agent and a foaming agent; and the modified foamed polyester is obtained by esterification and polycondensation of terephthalic acid, isophthalic acid, ethylene glycol and pentaerythritol as monomers.

[0009] In view of the technical problems that conventional polyester has insufficient melt strength and easily leads to cell collapse during the foaming process, conventional polyester has high spinning temperature and it is difficult to find a suitable chemical foaming agent, and the cell size formed by the conventional foaming agent is large and it is difficult to ensure continuous fiber forming, the present invention provides the following improvement measures: First, the present invention develops a special modified foaming polyester, which is obtained by esterification and polycondensation of terephthalic acid, isophthalic acid, ethylene glycol and pentaerythritol as monomers; an appropriate amount of isophthalic acid can destroy the spatial regularity of polyester macromolecules, reduce its melting point, and also reduce its foaming temperature; and an appropriate amount of pentaerythritol is introduced into the polyester molecular chain to make the polyester have a partial branching structure, enhance the melt strength, and also improve the strength and modulus of the fiber. Therefore, the modified foaming polyester of the present invention has the characteristics of low melting point and high melt strength, and can maintain the pore structure during the foaming process.

[0010] Secondly, the present invention cleverly designs the polyester fiber into a skin-core structure, with the core layer made of foamed polyester and the skin layer made of ordinary polyester; such a design can ensure that the core layer is wrapped by the skin layer polyester when foaming, thereby ensuring the continuous molding of the fiber during the spinning process. Finally, the core layer of the obtained foamed polyester fiber presents a porous structure, and the skin layer serves as the outer wall of the core layer pore structure, which can ensure the integrity and continuity of the fiber structure and provide the fiber with a certain mechanical strength.

[0011] Finally, the present invention adds a nucleating agent while adding a foaming agent to the foamed polyester core layer. The nucleating agent can increase bubble nucleation sites, promote bubble nucleation and stabilization, and facilitate the formation of a uniform and dense pore structure.

[0012] Preferably, the mass ratio of the foamed polyester core layer to the polyester skin layer is 4:6-7:3.

[0013] If the skin layer is too thick and the foam core layer accounts for too small a proportion, the fiber's advantages such as lightweight and warmth retention will not be obvious enough; if the skin layer is too thin and the foam core layer accounts for too large a proportion, the fiber's strength will drop too much, which is not conducive to subsequent weaving and other processing processes.

[0014] Preferably, the foaming agent is selected from one or more of 4,4'-oxybis(benzenesulfonyl semicarbazide), trihydrazino-s-triazine and N-nitroguanidine.

[0015] The reasons for selecting the above-mentioned foaming agent in the present invention are: first, the decomposition temperature of the above-mentioned foaming agent is about 240-250°C, and the higher decomposition temperature is more compatible with the melt spinning temperature of the modified foaming polyester, and the foaming structure can be obtained in situ during the fiber forming process; secondly, the present invention finds that compared with other conventional foaming agents, the above-mentioned types of foaming agents are particularly suitable for the preparation of the foamed polyester fiber of the present invention, and the size of the foam cells finally generated after high-temperature foaming is smaller, which will not significantly affect the strength of the fiber.

[0016] More preferably, the foaming agent accounts for 0.5-2 wt % of the total raw materials of the foamed polyester core layer.

[0017] Preferably, the nucleating agent is selected from one or more of nano-silicon dioxide, nano-titanium dioxide, nano-diatomaceous earth and nano-kaolin.

[0018] The reasons why the present invention selects the above-mentioned foaming agent are: first, the present invention finds that the use of the above-mentioned types of nanoscale inorganic nucleating agents can make the pore size generated by high-temperature foaming of the foaming agent smaller, which will not significantly affect the strength of the fiber; secondly, the above-mentioned nanoscale inorganic nucleating agent itself can improve the mechanical strength of the fiber to a certain extent as a reinforcing material.

[0019] More preferably, the nucleating agent accounts for 0.5-2 wt % of the total raw materials of the foamed polyester core layer.

[0020] Preferably, an antioxidant is added during the formation of the foamed polyester core layer.

[0021] The purpose of adding the antioxidant in the present invention is to reduce the oxidative degradation of the polymer under the heating and shearing action of the screw and the resulting viscosity drop.

[0022] More preferably, the antioxidant is selected from one or more of antioxidant 1024, antioxidant 264, antioxidant 1010 and antioxidant 1076.

[0023] More preferably, the antioxidant accounts for 0.5-2 wt % of the total raw materials of the foamed polyester core layer.

[0024] Preferably, the molar ratio of alkyd to acid in the preparation process of the modified foaming polyester is 1.2-1.4:1.

[0025] Preferably, the isophthalic acid accounts for 10-20 mol% of the total of terephthalic acid and isophthalic acid.

[0026] If the isophthalic acid content is too low, the melting point of the modified polyester will not decrease significantly and cannot match the foaming temperature of the foaming agent; if the isophthalic acid content is too high, the melting point and crystallinity of the modified polyester will decrease significantly, resulting in a decrease in its thermal stability and fiber strength.

[0027] Preferably, the pentaerythritol accounts for 0.02-0.2 mol% of the total of ethylene glycol and pentaerythritol.

[0028] If the pentaerythritol content is too low, the generated branched structure is insufficient, and the melt strength of the modified polyester is insufficiently increased, which is not conducive to supporting the pore structure; if the pentaerythritol content is too high, too many branched structures are generated, and even cross-linking occurs, which is not conducive to subsequent spinning processing.

[0029] In a second aspect, the present invention provides a method for preparing a sheath-core foamed polyester fiber, comprising: 1) Using terephthalic acid, isophthalic acid, ethylene glycol and pentaerythritol as monomers, the modified foaming polyester is obtained through esterification and polycondensation.

[0030] 2) Using modified foamed polyester, foaming agent and nucleating agent as core layer raw materials and polyester as skin layer raw material, during the melt spinning process, on the one hand, the melt is formed into fibers, and on the other hand, the foaming agent foams at high temperature to produce pores, and finally a skin-core foamed polyester fiber is formed.

[0031] Preferably, in step 1), the esterification is carried out under an inert atmosphere at 205-225°C and normal pressure for 30-50 min, and then at 225-255°C and 0.2-0.4 MPa for 90-180 min; the polycondensation is carried out under vacuum at 265-285°C and negative compression for 0.5-2 h.

[0032] Preferably, in step 2), a twin-screw extruder is used for melt blending; wherein the processing temperature of the twin-screw mixing section is 210-230°C, and the twin-screw speed is 100-300r / min.

[0033] Preferably, in step 2), during the melt spinning process, the temperature of the skin layer spinning box is 285-295°C, the temperature of the core layer spinning box is 235-245°C, and the winding speed is 2500-3000m / min.

[0034] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention has developed a special modified foaming polyester, which is obtained by esterification and polycondensation of terephthalic acid, isophthalic acid, ethylene glycol and pentaerythritol as monomers; an appropriate amount of isophthalic acid can destroy the spatial regularity of polyester macromolecules, lower its melting point, and also reduce its foaming temperature; and the introduction of an appropriate amount of pentaerythritol into the polyester molecular chain can make the polyester have a partial branching structure, enhance the melt strength, and also improve the strength and modulus of the fiber. Therefore, the modified foaming polyester of the present invention has the characteristics of low melting point and high melt strength, and can maintain the pore structure during the foaming process.

[0035] (2) The present invention designs the polyester fiber into a skin-core structure, wherein the core layer is made of foamed polyester and the skin layer is made of ordinary polyester; such a design can ensure that the core layer is wrapped by the skin layer polyester during foaming, thereby ensuring the continuous molding of the fiber during the spinning process. Finally, the core layer of the obtained foamed polyester fiber presents a porous structure, and the skin layer serves as the outer wall of the core layer pore structure, which can ensure the integrity and continuity of the fiber structure and provide the fiber with a certain mechanical strength.

[0036] (3) The present invention adds a nucleating agent to the foaming polyester core layer while adding a foaming agent. The nucleating agent can increase the bubble nucleation sites, promote bubble nucleation and stability, and facilitate the formation of a uniform and dense pore structure. Furthermore, the present invention has found that several specific types of nano-scale inorganic nucleating agents can not only make the pore size generated by the high-temperature foaming of the foaming agent smaller, but also will not significantly affect the strength of the fiber; at the same time, they themselves can improve the mechanical strength of the fiber to a certain extent as a reinforcing material.

[0037] (4) The present invention has found a foaming agent that is particularly suitable for the modified foaming polyester of the present invention. On the one hand, its decomposition temperature is more compatible with the melt spinning temperature of the modified foaming polyester, and a foaming structure can be obtained in situ during the fiber forming process; on the other hand, the foaming agent generates a smaller cell size after high-temperature foaming, which will not significantly affect the strength of the fiber.

[0038] (5) The present invention adds the foaming agent to the polymer melt during the melt spinning process. Compared with the method of pre-melting and mixing with the foaming modified polyester, the foaming agent can be prevented from being exposed to high temperature in advance and decomposed. Compared with the method of pre-physical mixing with the foaming modified polyester, the present invention can avoid uneven foaming caused by poor mixing of powder and polyester chips. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is an electron microscope image of the cross section of the foamed polyester fiber core layer of the best embodiment.

[0040] Figure 2 This is an electron microscope image of the cross section of the foamed polyester fiber core layer of Comparative Example 1. DETAILED DESCRIPTION

[0041] The present invention will be further described below in conjunction with the embodiments.

[0042] Overall embodiment A core-skin foamed polyester fiber comprises a foamed polyester core layer and a polyester skin layer, wherein the foamed polyester core layer is obtained by melt spinning after blending modified foamed polyester with a nucleating agent and a foaming agent; and the modified foamed polyester is obtained by esterification and polycondensation of terephthalic acid, isophthalic acid, ethylene glycol and pentaerythritol as monomers.

[0043] In some preferred implementation cases, the mass ratio of the foamed polyester core layer to the polyester skin layer is 4:6-7:3.

[0044] In some preferred implementation cases, the foaming agent is selected from one or more of 4,4'-oxybis(benzenesulfonyl semicarbazide), trihydrazino-s-triazine and N-nitroguanidine. Further preferably, the foaming agent accounts for 0.5-2wt% of the total raw materials of the foaming polyester core layer.

[0045] In some preferred implementation cases, the nucleating agent is selected from one or more of nano-silicon dioxide, nano-titanium dioxide, nano-diatomaceous earth and nano-kaolin. Further preferably, the nucleating agent accounts for 0.5-2wt% of the total raw materials of the foamed polyester core layer.

[0046] In some preferred implementation cases, an antioxidant is also added during the formation of the foamed polyester core layer. Further preferably, the antioxidant is selected from one or more of antioxidant 1024, antioxidant 264, antioxidant 1010 and antioxidant 1076. Further preferably, the antioxidant accounts for 0.5-2wt% of the total raw materials of the foamed polyester core layer.

[0047] In some preferred implementation cases, the molar ratio of alkyd to acid in the preparation process of the modified foaming polyester is 1.2-1.4:1.

[0048] In some preferred implementation cases, the isophthalic acid accounts for 10-20 mol% of the total of terephthalic acid and isophthalic acid; the pentaerythritol accounts for 0.02-0.2 mol% of the total of ethylene glycol and pentaerythritol.

[0049] A method for preparing a core-sheath type foamed polyester fiber, comprising: 1) Using terephthalic acid, isophthalic acid, ethylene glycol and pentaerythritol as monomers, the modified foaming polyester is obtained through esterification and polycondensation.

[0050] In some preferred implementation cases, in step 1), the esterification is carried out under an inert atmosphere, first at 205-225° C. and normal pressure for 30-50 min, and then at 225-255° C. and 0.2-0.4 MPa for 90-180 min; the polycondensation is carried out under vacuum at 265-285° C. and negative compression for 0.5-2 h.

[0051] 2) Using modified foamed polyester, foaming agent and nucleating agent as core layer raw materials and polyester as skin layer raw material, the fibers are melt-spinned to prepare core-skin foamed polyester fibers.

[0052] In some preferred implementation cases, in step 2), a twin-screw extruder is used for melt blending; wherein the processing temperature of the twin-screw mixing section is 210-230° C., and the twin-screw speed is 100-300 r / min.

[0053] In some preferred implementation cases, in step 2), during the melt spinning process, the temperature of the skin layer spinning box is 285-295°C, the temperature of the core layer spinning box is 235-245°C, and the winding speed is 2500-3000m / min.

[0054] Specific Examples and Comparative Examples Best Mode (1) Using 85 mol% terephthalic acid and 15 mol% isophthalic acid, 99.85 mol% ethylene glycol and 0.15 mol% pentaerythritol as polymerization monomers, a low melting point and high melt strength modified foaming polyester is obtained through esterification and polycondensation reaction, and the molar ratio of alcohol to acid is 1.3:1. The specific steps are: 319.18g (5.148mol) of terephthalic acid, 7.08g (0.052mol) of isophthalic acid, 245.52g (3.40mol) of ethylene glycol, 5.45g (0.60mol) of pentaerythritol, 0.35g (400ppm, based on 4mol of PET as the total mass) of ethylene glycol antimony and 0.18g (200ppm, based on 4mol of PET as the total mass) of sodium acetate were added to the polyester polymerization reactor. After nitrogen replacement three times, esterification was first carried out at 215°C under normal pressure for 0.5h, and then at 245°C and 0.30MPa for 2h, and esterification water was separated and condensed in an esterification tower and discharged. Then the polycondensation temperature was adjusted to 278°C, and the low vacuum pre-polycondensation and high vacuum polycondensation reactions were performed for 1.5 hours to make the stirring power reach the expected value. Finally, the melt was released from the bottom of the kettle, and the pellets were cut into pellets after underwater cooling to obtain low melting point and high melt strength modified foamed polyester chips. The polyester product indicators are shown in Table 1.

[0055] (2) The low melting point and high melt strength modified foaming polyester, the nucleating agent nano-silica and the antioxidant 1024 were added into a twin-screw extruder in a mass ratio of 98:1.0:1.0, and the modified polyester for foaming was obtained by blending and granulation under the processing conditions of a processing temperature of 225°C and a twin-screw speed of 200 r / min.

[0056] (3) Through the design of skin-core composite spinning, conventional polyester (polyethylene terephthalate) is added to the screw of the skin component, and modified polyester for foaming and chemical foaming agent (4,4'-oxybis(benzenesulfonylamino urea)) are added to the screw of the core layer, and the chemical foaming agent is added continuously and accurately through a loss-in-weight scale. The skin-core ratio is 4:6, and the feed mass ratio of modified polyester for foaming and chemical foaming agent is 98.5:1.5. During the spinning process, the temperature of the skin spinning box is 285°C, the temperature of the core spinning box is 240°C, and the winding speed is 2800m / min, and the skin-core foamed polyester fiber is obtained in situ. The fiber product indicators are shown in Table 1. Figure 1 This is an electron microscope image of the cross section of the foamed polyester fiber of the best embodiment.

[0057] Example 1 (1) Using 90 mol% terephthalic acid and 10 mol% isophthalic acid, 99.85 mol% ethylene glycol and 0.15 mol% pentaerythritol as polymerization monomers, a low melting point and high melt strength modified foaming polyester is obtained through esterification and polycondensation reaction, and the molar ratio of alcohol to acid is 1.3:1. The specific steps are: 319.18g (5.148mol) of terephthalic acid, 7.08g (0.052mol) of isophthalic acid, 245.52g (3.40mol) of ethylene glycol, 5.45g (0.60mol) of pentaerythritol, 0.35g (400ppm, based on 4mol of PET as the total mass) of ethylene glycol antimony and 0.18g (200ppm, based on 4mol of PET as the total mass) of sodium acetate were added to the polyester polymerization reactor. After nitrogen replacement three times, esterification was first carried out at 215°C under normal pressure for 0.5h, and then at 245°C and 0.32MPa for 2h, and esterification water was separated and condensed in an esterification tower and discharged. Then the polycondensation temperature was adjusted to 275°C, and the low vacuum pre-polycondensation and high vacuum polycondensation reactions were performed for 1.5 hours to make the stirring power reach the expected value. Finally, the melt was released from the bottom of the kettle, and the pellets were cut into pellets after underwater cooling to obtain low melting point and high melt strength modified foamed polyester chips. The polyester product indicators are shown in Table 1.

[0058] (2) The low melting point and high melt strength modified foaming polyester, the nucleating agent nano-silica and the antioxidant 1024 were added into a twin-screw extruder in a mass ratio of 98:1.0:1.0, and the modified polyester for foaming was obtained by blending and granulation under the processing conditions of a processing temperature of 225°C and a twin-screw speed of 200 r / min.

[0059] (3) Through the sheath-core composite spinning design, the screw of the sheath component is added with conventional polyester (polyethylene terephthalate), and the screw of the core layer is added with modified polyester for foaming and chemical foaming agent (4,4'-oxybis(benzenesulfonylamino urea)), wherein the chemical foaming agent is continuously and accurately added through a loss-in-weight scale. The sheath-core ratio is 4:6, and the feed mass ratio of modified polyester for foaming and chemical foaming agent is 98.5:1.5. During the spinning process, the temperature of the sheath spinning box is 285°C, the temperature of the core spinning box is 248°C, and the winding speed is 2800m / min, and the sheath-core foamed polyester fiber is obtained in situ. The fiber product indicators are shown in Table 1.

[0060] Example 2 (1) Using 80 mol% terephthalic acid and 20 mol% isophthalic acid, 99.85 mol% ethylene glycol and 0.15 mol% pentaerythritol as polymerization monomers, a low melting point and high melt strength modified foaming polyester is obtained through esterification and polycondensation reaction, and the molar ratio of alcohol to acid is 1.3:1. The specific steps are: 319.18g (5.148mol) of terephthalic acid, 7.08g (0.052mol) of isophthalic acid, 245.52g (3.40mol) of ethylene glycol, 5.45g (0.60mol) of pentaerythritol, 0.35g (400ppm, based on 4mol of PET as the total mass) of ethylene glycol antimony and 0.18g (200ppm, based on 4mol of PET as the total mass) of sodium acetate were added to the polyester polymerization reactor. After nitrogen replacement three times, esterification was first carried out at 210°C under normal pressure for 0.5h, and then at 250°C and 0.28MPa for 2h, and esterification water was separated and condensed in an esterification tower and discharged. Then the polycondensation temperature was adjusted to 280°C, and the low vacuum pre-polycondensation and high vacuum polycondensation reactions were performed for 1.5 hours to make the stirring power reach the expected value. Finally, the melt was released from the bottom of the kettle, and the pellets were cut into pellets after underwater cooling to obtain low melting point and high melt strength modified foamed polyester chips. The polyester product indicators are shown in Table 1.

[0061] (2) The low melting point and high melt strength modified foaming polyester, the nucleating agent nano titanium dioxide and the antioxidant 1024 were added into a twin-screw extruder in a mass ratio of 98:1.0:1.0, and the modified polyester for foaming was obtained by blending and granulation under the processing conditions of a processing temperature of 225°C and a twin-screw speed of 300 r / min.

[0062] (3) Through the design of skin-core composite spinning, the screw of the skin component is added with conventional polyester (polyethylene terephthalate), and the screw of the core layer is added with modified polyester for foaming and chemical foaming agent (trihydrazino-s-triazine), wherein the chemical foaming agent is added continuously and accurately through a weight loss scale. The skin-core ratio is 4:6, and the feed mass ratio of modified polyester for foaming and chemical foaming agent is 98.5:1.5. During the spinning process, the temperature of the skin spinning box is 285℃, the temperature of the core spinning box is 235℃, and the winding speed is 2700m / min, and the skin-core foamed polyester fiber is obtained in situ. The fiber product indicators are shown in Table 1.

[0063] Example 3 (1) Using 85 mol% terephthalic acid and 15 mol% isophthalic acid, 99.80 mol% ethylene glycol and 0.20 mol% pentaerythritol as polymerization monomers, a low melting point and high melt strength modified foaming polyester is obtained through esterification and polycondensation reaction, and the molar ratio of alcohol to acid is 1.3:1. The specific steps are: 319.18g (5.148mol) of terephthalic acid, 7.08g (0.052mol) of isophthalic acid, 245.52g (3.40mol) of ethylene glycol, 5.45g (0.60mol) of pentaerythritol, 0.35g (400ppm, based on 4mol of PET as the total mass) of ethylene glycol antimony and 0.18g (200ppm, based on 4mol of PET as the total mass) of sodium acetate were added to the polyester polymerization reactor. After nitrogen replacement three times, esterification was first carried out at 215°C under normal pressure for 0.5h, and then at 248°C and 0.28MPa for 1.8h, and the esterified water was separated and condensed in an esterification tower and discharged. Then the polycondensation temperature was adjusted to 280°C, and the low vacuum pre-polycondensation and high vacuum polycondensation reactions were performed for 1.5 hours to make the stirring power reach the expected value. Finally, the melt was released from the bottom of the kettle, and the pellets were cut into pellets after underwater cooling to obtain low melting point and high melt strength modified foamed polyester chips. The polyester product indicators are shown in Table 1.

[0064] (2) The low melting point and high melt strength modified foaming polyester, the nucleating agent nano titanium dioxide and the antioxidant 264 were added into a twin-screw extruder in a mass ratio of 98:1.0:1.0, and the modified polyester for foaming was obtained by blending and granulation under the processing conditions of a processing temperature of 230°C and a twin-screw speed of 200 r / min.

[0065] (3) Through the design of skin-core composite spinning, conventional polyester (polyethylene terephthalate) is added to the screw of the skin component, and modified polyester for foaming and chemical foaming agent (4,4'-oxybis(benzenesulfonylamino urea)) are added to the screw of the core layer, and the chemical foaming agent is added continuously and accurately through a loss-in-weight scale. The skin-core ratio is 4:6, and the feed mass ratio of modified polyester for foaming and chemical foaming agent is 98.5:1.5. During the spinning process, the temperature of the skin spinning box is 285°C, the temperature of the core spinning box is 243°C, and the winding speed is 2800m / min, and the skin-core foamed polyester fiber is obtained in situ. The fiber product indicators are shown in Table 1.

[0066] Example 4 (1) Using 85 mol% terephthalic acid and 15 mol% isophthalic acid, 99.98 mol% ethylene glycol and 0.02 mol% pentaerythritol as polymerization monomers, a low melting point and high melt strength modified foaming polyester is obtained through esterification and polycondensation reaction, and the molar ratio of alcohol to acid is 1.3:1. The specific steps are: 319.18g (5.148mol) of terephthalic acid, 7.08g (0.052mol) of isophthalic acid, 245.52g (3.40mol) of ethylene glycol, 5.45g (0.60mol) of pentaerythritol, 0.35g (400ppm, based on 4mol of PET as the total mass) of ethylene glycol antimony and 0.18g (200ppm, based on 4mol of PET as the total mass) of sodium acetate were added to the polyester polymerization reactor. After nitrogen replacement three times, esterification was first carried out at 215°C under normal pressure for 0.5h, and then at 243°C and 0.34MPa for 2.2h, and the esterified water was separated and condensed in an esterification tower and discharged. Then the polycondensation temperature was adjusted to 279°C, and the low vacuum pre-polycondensation and high vacuum polycondensation reactions were performed for 1.5 hours to make the stirring power reach the expected value. Finally, the melt was released from the bottom of the kettle, and the pellets were cut into pellets after underwater cooling to obtain low melting point and high melt strength modified foamed polyester chips. The polyester product indicators are shown in Table 1.

[0067] (2) The low melting point and high melt strength modified foaming polyester, the nucleating agent nano-silica and the antioxidant 1024 were added into a twin-screw extruder in a mass ratio of 98:1.0:1.0, and the modified polyester for foaming was obtained by blending and granulation under the processing conditions of a processing temperature of 225°C and a twin-screw speed of 200 r / min.

[0068] (3) Through the design of skin-core composite spinning, the screw of the skin component is added with conventional polyester (polyethylene terephthalate), and the screw of the core layer is added with modified polyester for foaming and chemical foaming agent (trihydrazino-s-triazine), wherein the chemical foaming agent is added continuously and accurately through a weight loss scale. The skin-core ratio is 4:6, and the feed mass ratio of modified polyester for foaming and chemical foaming agent is 98.5:1.5. During the spinning process, the temperature of the skin spinning box is 285°C, the temperature of the core spinning box is 238°C, and the winding speed is 2700m / min, and the skin-core foamed polyester fiber is obtained in situ. The fiber product indicators are shown in Table 1.

[0069] Example 5 (1) Using 85 mol% terephthalic acid and 15 mol% isophthalic acid, 99.85 mol% ethylene glycol and 0.15 mol% pentaerythritol as polymerization monomers, a low melting point and high melt strength modified foaming polyester is obtained through esterification and polycondensation reaction, and the molar ratio of alcohol to acid is 1.3:1. The specific steps are: 319.18g (5.148mol) of terephthalic acid, 7.08g (0.052mol) of isophthalic acid, 245.52g (3.40mol) of ethylene glycol, 5.45g (0.60mol) of pentaerythritol, 0.35g (400ppm, based on 4mol of PET as the total mass) of ethylene glycol antimony and 0.18g (200ppm, based on 4mol of PET as the total mass) of sodium acetate were added to the polyester polymerization reactor. After nitrogen replacement three times, esterification was first carried out at 220℃ under normal pressure for 0.5h, and then at 250℃ and 0.31MPa for 2h, and the esterified water was separated and condensed in the esterification tower. Then the polycondensation temperature was adjusted to 277°C, and after low vacuum pre-polycondensation and high vacuum polycondensation reaction for 1.5 hours, the stirring power reached the expected value, and finally the melt was released from the bottom of the kettle, and pelletized by underwater cooling to obtain low melting point and high melt strength modified foamed polyester chips.

[0070] (2) The low melting point and high melt strength modified foaming polyester, the nucleating agent nano-silica and the antioxidant 1010 were added into a twin-screw extruder in a mass ratio of 97:2.0:1.0, and the modified polyester for foaming was obtained by blending and granulation under the processing conditions of a processing temperature of 225°C and a twin-screw speed of 220 r / min.

[0071] (3) Through the design of skin-core composite spinning, conventional polyester (polyethylene terephthalate) is added to the screw of the skin component, and modified polyester for foaming and chemical foaming agent (4,4'-oxybis(benzenesulfonylamino urea)) are added to the screw of the core layer, and the chemical foaming agent is added continuously and accurately through a loss-in-weight scale. The skin-core ratio is 4:6, and the feed mass ratio of modified polyester for foaming and chemical foaming agent is 98.5:1.5. During the spinning process, the temperature of the skin spinning box is 285°C, the temperature of the core spinning box is 240°C, and the winding speed is 2800m / min, and the skin-core foamed polyester fiber is obtained in situ. The fiber product indicators are shown in Table 1.

[0072] Example 6 (1) Using 85 mol% terephthalic acid and 15 mol% isophthalic acid, 99.85 mol% ethylene glycol and 0.15 mol% pentaerythritol as polymerization monomers, a low melting point and high melt strength modified foaming polyester is obtained through esterification and polycondensation reaction, and the molar ratio of alcohol to acid is 1.3:1. The specific steps are: 319.18g (5.148mol) of terephthalic acid, 7.08g (0.052mol) of isophthalic acid, 245.52g (3.40mol) of ethylene glycol, 5.45g (0.60mol) of pentaerythritol, 0.35g (400ppm, based on 4mol of PET as the total mass) of ethylene glycol antimony and 0.18g (200ppm, based on 4mol of PET as the total mass) of sodium acetate were added to the polyester polymerization reactor. After nitrogen replacement three times, esterification was first carried out at 220°C under normal pressure for 0.5h, and then at 251°C and 0.29MPa for 2h, and esterification water was separated and condensed in an esterification tower and discharged. Then the polycondensation temperature was adjusted to 280°C, and after low vacuum pre-polycondensation and high vacuum polycondensation reaction for 1.5 hours, the stirring power reached the expected value, and finally the melt was released from the bottom of the kettle, and pelletized after underwater cooling to obtain low melting point and high melt strength modified foamed polyester chips.

[0073] (2) The low melting point and high melt strength modified foaming polyester, the nucleating agent nano diatomaceous earth and the antioxidant 1024 were added into a twin-screw extruder in a mass ratio of 98.5:0.5:1.0, and the modified polyester for foaming was obtained by blending and granulation under the processing conditions of a processing temperature of 228°C and a twin-screw speed of 200 r / min.

[0074] (3) Through the design of skin-core composite spinning, the screw of the skin component is added with conventional polyester (polyethylene terephthalate), and the screw of the core layer is added with modified polyester for foaming and chemical foaming agent (trihydrazino-s-triazine), wherein the chemical foaming agent is added continuously and accurately through a weight loss scale. The skin-core ratio is 4:6, and the feed mass ratio of modified polyester for foaming and chemical foaming agent is 98.5:1.5. During the spinning process, the temperature of the skin spinning box is 285℃, the temperature of the core spinning box is 240℃, and the winding speed is 2600m / min, and the skin-core foamed polyester fiber is obtained in situ. The fiber product indicators are shown in Table 1.

[0075] Example 7 (1) Using 85 mol% terephthalic acid and 15 mol% isophthalic acid, 99.85 mol% ethylene glycol and 0.15 mol% pentaerythritol as polymerization monomers, a low melting point and high melt strength modified foaming polyester is obtained through esterification and polycondensation reaction, and the molar ratio of alcohol to acid is 1.3:1. The specific steps are: 319.18g (5.148mol) of terephthalic acid, 7.08g (0.052mol) of isophthalic acid, 245.52g (3.40mol) of ethylene glycol, 5.45g (0.60mol) of pentaerythritol, 0.35g (400ppm, based on 4mol of PET as the total mass) of ethylene glycol antimony and 0.18g (200ppm, based on 4mol of PET as the total mass) of sodium acetate were added to the polyester polymerization reactor. After nitrogen replacement three times, esterification was first carried out at 218°C under normal pressure for 0.5h, and then at 248°C and 0.28MPa for 2h, and esterification water was separated and condensed in an esterification tower and discharged. Then the polycondensation temperature was adjusted to 277°C, and after low vacuum pre-polycondensation and high vacuum polycondensation reaction for 1.5 hours, the stirring power reached the expected value, and finally the melt was released from the bottom of the kettle, and pelletized by underwater cooling to obtain low melting point and high melt strength modified foamed polyester chips.

[0076] (2) The low melting point and high melt strength modified foaming polyester, the nucleating agent nano kaolin and the antioxidant 264 were added into a twin-screw extruder in a mass ratio of 98:1.0:1.0, and the modified polyester for foaming was obtained by blending and granulation under the processing conditions of a processing temperature of 225°C and a twin-screw speed of 200 r / min.

[0077] (3) Through the sheath-core composite spinning design, the screw of the sheath component is added with conventional polyester (polyethylene terephthalate), and the screw of the core layer is added with modified polyester for foaming and chemical foaming agent (4,4'-oxybis(benzenesulfonylamino urea)), wherein the chemical foaming agent is continuously and accurately added through a loss-in-weight scale. The sheath-core ratio is 4:6, and the feed mass ratio of modified polyester for foaming and chemical foaming agent is 98:2. During the spinning process, the temperature of the sheath spinning box is 285°C, the temperature of the core spinning box is 242°C, and the winding speed is 2800m / min, and the sheath-core foamed polyester fiber is obtained in situ. The fiber product indicators are shown in Table 1.

[0078] Example 8 (1) Using 85 mol% terephthalic acid and 15 mol% isophthalic acid, 99.85 mol% ethylene glycol and 0.15 mol% pentaerythritol as polymerization monomers, a low melting point and high melt strength modified foaming polyester is obtained through esterification and polycondensation reaction, and the molar ratio of alcohol to acid is 1.3:1. The specific steps are: 319.18g (5.148mol) of terephthalic acid, 7.08g (0.052mol) of isophthalic acid, 245.52g (3.40mol) of ethylene glycol, 5.45g (0.60mol) of pentaerythritol, 0.35g (400ppm, based on 4mol of PET as the total mass) of ethylene glycol antimony and 0.18g (200ppm, based on 4mol of PET as the total mass) of sodium acetate were added to the polyester polymerization reactor. After nitrogen replacement three times, esterification was first carried out at 217°C under normal pressure for 0.5h, and then at 252°C and 0.31 MPa for 2h, and the esterified water was separated and condensed in the esterification tower. Then the polycondensation temperature was adjusted to 278°C, and after low vacuum pre-polycondensation and high vacuum polycondensation reaction for 1.5 hours, the stirring power reached the expected value, and finally the melt was released from the bottom of the kettle, and pelletized by underwater cooling to obtain low melting point and high melt strength modified foamed polyester chips.

[0079] (2) The low melting point and high melt strength modified foaming polyester, the nucleating agent nano-silica and the antioxidant 1010 were added into a twin-screw extruder in a mass ratio of 98:1.0:1.0, and the modified polyester for foaming was obtained by blending and granulation under the processing conditions of a processing temperature of 220°C and a twin-screw speed of 220 r / min.

[0080] (3) Through the design of skin-core composite spinning, the screw of the skin component is added with conventional polyester (polyethylene terephthalate), and the screw of the core layer is added with modified polyester for foaming and chemical foaming agent (N-nitroguanidine), wherein the chemical foaming agent is added continuously and accurately through a weight loss scale. The skin-core ratio is 4:6, and the feed mass ratio of modified polyester for foaming and chemical foaming agent is 99.5:0.5. During the spinning process, the temperature of the skin spinning box is 285°C, the temperature of the core spinning box is 242°C, and the winding speed is 2700m / min, and the skin-core foamed polyester fiber is obtained in situ. The fiber product indicators are shown in Table 1.

[0081] Example 9 (1) Using 85 mol% terephthalic acid and 15 mol% isophthalic acid, 99.85 mol% ethylene glycol and 0.15 mol% pentaerythritol as polymerization monomers, a low melting point and high melt strength modified foaming polyester is obtained through esterification and polycondensation reaction, and the molar ratio of alcohol to acid is 1.3:1. The specific steps are: 319.18g (5.148mol) of terephthalic acid, 7.08g (0.052mol) of isophthalic acid, 245.52g (3.40mol) of ethylene glycol, 5.45g (0.60mol) of pentaerythritol, 0.35g (400ppm, based on 4mol of PET as total mass) of ethylene glycol antimony and 0.18g (200ppm, based on 4mol of PET as total mass) of sodium acetate were added to the polyester polymerization reactor. After nitrogen replacement three times, esterification was first carried out at 218°C under normal pressure for 0.5h, then at 246°C and 0.28MPa for 2h, and esterification water was separated and condensed and discharged through an esterification tower for 1.7h. Then the polycondensation temperature is adjusted to 276°C, and after low vacuum pre-polycondensation and high vacuum polycondensation reactions, the stirring power reaches the expected value. Finally, the melt is released from the bottom of the kettle, and pelletized by underwater cooling to obtain low melting point and high melt strength modified foamed polyester chips.

[0082] (2) The low melting point and high melt strength modified foaming polyester, the nucleating agent nano diatomaceous earth and the antioxidant 1076 were added into a twin-screw extruder in a mass ratio of 98:1.0:1.0, and the modified polyester for foaming was obtained by blending and granulation under the processing conditions of a processing temperature of 225°C and a twin-screw speed of 220 r / min.

[0083] (3) Through the sheath-core composite spinning design, the screw of the sheath component is added with conventional polyester (polyethylene terephthalate), and the screw of the core layer is added with modified polyester for foaming and chemical foaming agent (4,4'-oxybis(benzenesulfonylamino urea)), wherein the chemical foaming agent is added continuously and accurately through a loss-in-weight scale. The sheath-core ratio is 2:8, and the feed mass ratio of modified polyester for foaming and chemical foaming agent is 98.5:1.5. During the spinning process, the temperature of the sheath spinning box is 285°C, the temperature of the core spinning box is 238°C, and the winding speed is 2800m / min, and the sheath-core foamed polyester fiber is obtained in situ. The fiber product indicators are shown in Table 1.

[0084] Example 10 (1) Using 85 mol% terephthalic acid and 15 mol% isophthalic acid, 99.85 mol% ethylene glycol and 0.15 mol% pentaerythritol as polymerization monomers, a low melting point and high melt strength modified foaming polyester is obtained through esterification and polycondensation reaction, and the molar ratio of alcohol to acid is 1.3:1. The specific steps are: 319.18g (5.148mol) of terephthalic acid, 7.08g (0.052mol) of isophthalic acid, 245.52g (3.40mol) of ethylene glycol, 5.45g (0.60mol) of pentaerythritol, 0.35g (400ppm, based on 4mol of PET as the total mass) of ethylene glycol antimony and 0.18g (200ppm, based on 4mol of PET as the total mass) of sodium acetate were added to the polyester polymerization reactor. After nitrogen replacement three times, esterification was first carried out at 218°C under normal pressure for 0.5h, and then at 246°C and 0.30MPa for 2h, and esterification water was separated and condensed in an esterification tower and discharged. Then the polycondensation temperature was adjusted to 276°C, and after low vacuum pre-polycondensation and high vacuum polycondensation reaction for 1.3 hours, the stirring power reached the expected value, and finally the melt was released from the bottom of the kettle, and pelletized after underwater cooling to obtain low melting point and high melt strength modified foamed polyester chips.

[0085] (2) The low melting point and high melt strength modified foaming polyester, the nucleating agent nano kaolin and the antioxidant 1024 were added into a twin-screw extruder in a mass ratio of 98:1.0:1.0, and the modified polyester for foaming was obtained by blending and granulation under the processing conditions of a processing temperature of 228°C and a twin-screw speed of 250 r / min.

[0086] (3) Through the design of skin-core composite spinning, the screw of the skin component is added with conventional polyester (polyethylene terephthalate), and the screw of the core layer is added with modified polyester for foaming and chemical foaming agent (N-nitroguanidine), wherein the chemical foaming agent is added continuously and accurately through a weight loss scale. The skin-core ratio is 8:2, and the feed mass ratio of modified polyester for foaming and chemical foaming agent is 98.5:1.5. During the spinning process, the temperature of the skin spinning box is 285℃, the temperature of the core spinning box is 238℃, and the winding speed is 2700m / min, and the skin-core foamed polyester fiber is obtained in situ. The fiber product indicators are shown in Table 1.

[0087] Comparative Example 1 (1) Conventional PET polyester, nucleating agent nano-silica and antioxidant 1024 were added into a twin-screw extruder in a mass ratio of 98:1.0:1.0, and blended and granulated to obtain foamed polyester under the processing conditions of a processing temperature of 245°C and a twin-screw speed of 300 r / min.

[0088] (2) Through the sheath-core composite spinning design, conventional polyester (polyethylene terephthalate) is added to the screw of the sheath component, and foamed polyester and chemical foaming agent (4,4'-oxybis(benzenesulfonylamino urea)) are added to the screw of the core layer, wherein the chemical foaming agent is continuously and accurately added through a loss-in-weight scale. The sheath-core ratio is 4:6, and the feed mass ratio of foamed polyester and chemical foaming agent is 98.5:1.5. During the spinning process, the temperature of the sheath spinning box is 285°C, the temperature of the core spinning box is 275°C, and the winding speed is 2800m / min, and the sheath-core foamed polyester fiber is obtained in situ. The fiber product indicators are shown in Table 1. Figure 2 This is an electron microscope image of the cross section of the foamed polyester fiber of Comparative Example 1.

[0089] Comparative Example 2 (1) Using 85 mol% terephthalic acid and 15 mol% isophthalic acid, 99.85 mol% ethylene glycol and 0.15 mol% pentaerythritol as polymerization monomers, a low melting point and high melt strength modified foaming polyester is obtained through esterification and polycondensation reaction, and the molar ratio of alcohol to acid is 1.3:1. The specific steps are: 319.18g (5.148mol) of terephthalic acid, 7.08g (0.052mol) of isophthalic acid, 245.52g (3.40mol) of ethylene glycol, 5.45g (0.60mol) of pentaerythritol, 0.35g (400ppm, based on 4mol of PET as the total mass) of ethylene glycol antimony and 0.18g (200ppm, based on 4mol of PET as the total mass) of sodium acetate were added to the polyester polymerization reactor. After nitrogen replacement three times, esterification was first carried out at 215°C under normal pressure for 0.5h, and then at 245°C and 0.30MPa for 2h, and esterification water was separated and condensed in an esterification tower and discharged. Then the polycondensation temperature was adjusted to 278°C, and after low vacuum pre-polycondensation and high vacuum polycondensation reaction for 1.5 hours, the stirring power reached the expected value, and finally the melt was released from the bottom of the kettle, and pelletized by underwater cooling to obtain low melting point and high melt strength modified foamed polyester chips.

[0090] (2) The low melting point and high melt strength modified foaming polyester, the nucleating agent nano-silica and the antioxidant 1024 were added into a twin-screw extruder in a mass ratio of 98:1.0:1.0, and the modified polyester for foaming was obtained by blending and granulation under the processing conditions of a processing temperature of 225°C and a twin-screw speed of 200 r / min.

[0091] (3) Through the sheath-core composite spinning design, the screw of the sheath component is added with modified polyester for foaming, and the screw of the core layer is added with modified polyester for foaming and chemical foaming agent (4,4'-oxybis(benzenesulfonylaminourea)), wherein the chemical foaming agent is continuously and accurately added through a weight loss scale. The sheath-core ratio is 4:6, and the feed mass ratio of modified polyester for foaming and chemical foaming agent is 98.5:1.5. During the spinning process, the temperature of the sheath spinning box is 255°C, the temperature of the core spinning box is 240°C, and the winding speed is 2800m / min, and the sheath-core foamed polyester fiber is obtained in situ. The fiber product indicators are shown in Table 1.

[0092] Comparative Example 3 (1) Using 85 mol% terephthalic acid and 15 mol% isophthalic acid, 99.85 mol% ethylene glycol and 0.15 mol% pentaerythritol as polymerization monomers, a low melting point and high melt strength modified foaming polyester is obtained through esterification and polycondensation reaction, and the molar ratio of alcohol to acid is 1.3:1. The specific steps are: 319.18g (5.148mol) of terephthalic acid, 7.08g (0.052mol) of isophthalic acid, 245.52g (3.40mol) of ethylene glycol, 5.45g (0.60mol) of pentaerythritol, 0.35g (400ppm, based on 4mol of PET as the total mass) of ethylene glycol antimony and 0.18g (200ppm, based on 4mol of PET as the total mass) of sodium acetate were added to the polyester polymerization reactor. After nitrogen replacement three times, esterification was first carried out at 215°C under normal pressure for 0.5h, and then at 245°C and 0.30MPa for 2h, and esterification water was separated and condensed in an esterification tower and discharged. Then the polycondensation temperature was adjusted to 278°C, and the low vacuum pre-polycondensation and high vacuum polycondensation reactions were performed for 1.5 hours to make the stirring power reach the expected value. Finally, the melt was released from the bottom of the kettle, and the pellets were cut into pellets after underwater cooling to obtain low melting point and high melt strength modified foamed polyester chips. The polyester product indicators are shown in Table 1.

[0093] (2) The low melting point and high melt strength modified foaming polyester, the nucleating agent nano-silica and the antioxidant 1024 were added into a twin-screw extruder in a mass ratio of 98:1.0:1.0, and the modified polyester for foaming was obtained by blending and granulation under the processing conditions of a processing temperature of 225°C and a twin-screw speed of 200 r / min.

[0094] (3) Through the design of skin-core composite spinning, the screw of the skin component is added with conventional polyester (polyethylene terephthalate), and the screw of the core layer is added with modified polyester for foaming and chemical foaming agent (azodicarbonamide), wherein the chemical foaming agent is added continuously and accurately through a weight loss scale. The skin-core ratio is 4:6, and the feed mass ratio of modified polyester for foaming and chemical foaming agent is 98.5:1.5. During the spinning process, the temperature of the skin spinning box is 285℃, the temperature of the core spinning box is 240℃, and the winding speed is 2800m / min, and the skin-core foamed polyester fiber is obtained in situ. The fiber product indicators are shown in Table 1.

[0095] Comparative Example 4 (1) Using 85 mol% terephthalic acid and 15 mol% isophthalic acid, 99.85 mol% ethylene glycol and 0.15 mol% pentaerythritol as polymerization monomers, a low melting point and high melt strength modified foaming polyester is obtained through esterification and polycondensation reaction, and the molar ratio of alcohol to acid is 1.3:1. The specific steps are: 319.18g (5.148mol) of terephthalic acid, 7.08g (0.052mol) of isophthalic acid, 245.52g (3.40mol) of ethylene glycol, 5.45g (0.60mol) of pentaerythritol, 0.35g (400ppm, based on 4mol of PET as the total mass) of ethylene glycol antimony and 0.18g (200ppm, based on 4mol of PET as the total mass) of sodium acetate were added to the polyester polymerization reactor. After nitrogen replacement three times, esterification was first carried out at 215°C under normal pressure for 0.5h, and then at 245°C and 0.30MPa for 2h, and esterification water was separated and condensed in an esterification tower and discharged. Then the polycondensation temperature was adjusted to 278°C, and the low vacuum pre-polycondensation and high vacuum polycondensation reactions were performed for 1.5 hours to make the stirring power reach the expected value. Finally, the melt was released from the bottom of the kettle, and the pellets were cut into pellets after underwater cooling to obtain low melting point and high melt strength modified foamed polyester chips. The polyester product indicators are shown in Table 1.

[0096] (2) The low melting point and high melt strength modified foaming polyester, the nucleating agent nano-silica and the antioxidant 1024 were added into a twin-screw extruder in a mass ratio of 98:1.0:1.0, and the modified polyester for foaming was obtained by blending and granulation under the processing conditions of a processing temperature of 225°C and a twin-screw speed of 200 r / min.

[0097] (3) Through the design of skin-core composite spinning, the screw of the skin component is added with conventional polyester (polyethylene terephthalate), and the screw of the core layer is added with modified polyester for foaming and chemical foaming agent (sodium carbonate), wherein the chemical foaming agent is added continuously and accurately through a weight loss scale. The skin-core ratio is 4:6, and the feed mass ratio of modified polyester for foaming and chemical foaming agent is 98.5:1.5. During the spinning process, the temperature of the skin spinning box is 285°C, the temperature of the core spinning box is 240°C, and the winding speed is 2800m / min, and the skin-core foamed polyester fiber is obtained in situ. The fiber product indicators are shown in Table 1.

[0098] Comparative Example 5 (1) Using 85 mol% terephthalic acid and 15 mol% isophthalic acid, 99.85 mol% ethylene glycol and 0.15 mol% pentaerythritol as polymerization monomers, a low melting point and high melt strength modified foaming polyester is obtained through esterification and polycondensation reaction, and the molar ratio of alcohol to acid is 1.3:1. The specific steps are: 319.18g (5.148mol) of terephthalic acid, 7.08g (0.052mol) of isophthalic acid, 245.52g (3.40mol) of ethylene glycol, 5.45g (0.60mol) of pentaerythritol, 0.35g (400ppm, based on 4mol of PET as the total mass) of ethylene glycol antimony and 0.18g (200ppm, based on 4mol of PET as the total mass) of sodium acetate were added to the polyester polymerization reactor. After nitrogen replacement three times, esterification was first carried out at 215°C under normal pressure for 0.5h, and then at 245°C and 0.30MPa for 2h, and esterification water was separated and condensed in an esterification tower and discharged. Then the polycondensation temperature was adjusted to 278°C, and the low vacuum pre-polycondensation and high vacuum polycondensation reactions were performed for 1.5 hours to make the stirring power reach the expected value. Finally, the melt was released from the bottom of the kettle, and the pellets were cut into pellets after underwater cooling to obtain low melting point and high melt strength modified foamed polyester chips. The polyester product indicators are shown in Table 1.

[0099] (2) The low melting point and high melt strength modified foaming polyester, the nucleating agent nano-silica and the antioxidant 1024 were added into a twin-screw extruder in a mass ratio of 98:1.0:1.0, and the modified polyester for foaming was obtained by blending and granulation under the processing conditions of a processing temperature of 225°C and a twin-screw speed of 200 r / min.

[0100] (3) Through the design of skin-core composite spinning, the screw of the skin component is added with conventional polyester (polyethylene terephthalate), and the screw of the core layer is added with modified polyester for foaming and chemical foaming agent (ammonium acetate), wherein the chemical foaming agent is added continuously and accurately through a weight loss scale. The skin-core ratio is 4:6, and the feed mass ratio of modified polyester for foaming and chemical foaming agent is 98.5:1.5. During the spinning process, the temperature of the skin spinning box is 285℃, the temperature of the core spinning box is 240℃, and the winding speed is 2800m / min, and the skin-core foamed polyester fiber is obtained in situ. The fiber product indicators are shown in Table 1.

[0101] Performance Testing The modified foamed polyester slices and foamed polyester fibers of each embodiment and comparative example were tested for performance, and the results are shown in Table 1 and Table 2. The test method is: (1) The intrinsic viscosity and melting point of the foamed polyester chips were evaluated according to the standard "GB / T 14190-2017 Test method for fiber-grade polyester (PET) chips".

[0102] (2) The melt flow rate of the foamed polyester slices was evaluated according to the standard "GB / T 3682-2000 Determination of mass flow rate and volume flow rate of thermoplastic melts".

[0103] (3) After the polyester fiber is stretched and deformed, the tensile strength and elongation at break are evaluated according to the standard "GB / T 14344-2022 Test method for tensile properties of chemical fiber filaments".

[0104] (4) The thermal insulation and heat storage performance of polyester fiber after knitting is evaluated, and the warmth retention rate is assessed with reference to "FZ / T 73022-2019 Knitted Thermal Underwear".

[0105] Table 1: Foamed polyester chips index Table 2: Foamed polyester fiber indicators and properties In Table 1, the basic physical properties of the prepared modified foamed polyester are mainly focused on. The characteristic viscosity mainly examines whether the slices meet the requirements of spinning processing, the melting point mainly examines whether it can match the decomposition and foaming temperature of the foaming agent, and the melt flow rate mainly examines the melt flow performance. Table 2 mainly focuses on the indicators related to the prepared foamed polyester fiber materials and applications. The spinnability mainly examines the breakage of the material during the fiber forming process, the mechanical properties mainly examine the application of the fiber material in the subsequent weaving process, the weight loss rate mainly examines the amount of fiber pore structure formed, and the warmth rate mainly examines the warmth and heat insulation performance of the fabric.

[0106] As can be seen from Table 1-2, the present invention introduces the third component, isophthalic acid, to destroy the regular molecular chain structure of conventional polyester, thereby reducing the melting point of polyester to meet the application temperature of some high decomposition temperature foaming agents; introduces the fourth component, pentaerythritol, to enhance the melt strength and play a role in supporting the pore structure; utilizes the skin-core composite structure design, the skin layer ensures the integrity of the fiber structure and the mechanical properties meet the standards, the core layer undergoes chemical foaming to produce a pore structure, and introduces air to improve the thermal insulation performance. Specifically: By comparing Examples 1 and 2 with the best example, it can be found that the weight loss rate of the foamed fiber prepared by the higher melting point modified foamed polyester (Example 1) decreases. This is because the high melting point modified polyester requires a higher core layer spinning temperature, which causes the foaming agent to decompose faster. More decomposition processes occur before fiber formation, resulting in a reduction in the pore structure in the fiber; however, the foamed fiber prepared by the lower melting point modified foamed polyester (Example 2) has a decrease in fiber mechanical properties due to the formation of more pores.

[0107] By comparing Examples 3 and 4 with the best example, it can be found that when the melt strength is higher (Example 3), the mechanical properties of the fiber are improved, but its melt flow performance is poor, resulting in poor spinnability and easy breakage; when the melt strength is lower (Example 4), the support for the pore structure is weak, so the fiber weight loss rate is reduced.

[0108] By comparing Examples 5 and 6 with the best example, it can be found that more nucleating agents (Example 5) can increase the nucleation density, which is beneficial to the formation of pore structure and thus improves the weight loss rate, but the increased amount of nucleating agents is not conducive to its dispersion in the matrix and can also cause the phenomenon of broken ends during spinning. Less nucleating agents (Example 6) will form fewer pores with larger sizes, and the fiber strength will decrease.

[0109] By comparing Examples 7 and 8 with the best example, it can be found that although adding more foaming agent (Example 7) can increase fiber weight loss, the mechanical properties are significantly reduced; while when less foaming agent is added (Example 8), the fiber weight reduction rate is not high, which leads to a lack of significant improvement in the thermal insulation rate.

[0110] By comparing Examples 9 and 10 with the best example, it can be found that the ratio of the skin and core layer components also needs to comprehensively consider the fiber mechanical indicators and thermal insulation performance. Example 9 has more core layers, and the weight reduction rate and thermal insulation rate are further improved, but the fiber mechanical properties are seriously reduced; Example 10 has fewer core layers, and the fiber mechanical indicators are excellent, but the thermal insulation performance is not good.

[0111] By comparing Comparative Example 1 with the best embodiment, it can be found that when conventional polyester is used as the fiber core material, the spinning temperature is high, the melt strength is insufficient, the foaming agent decomposes early and it is difficult to form stable cells (such as Figure 2 As shown), the weight loss rate and warmth retention rate are both lower.

[0112] By comparing Comparative Example 2 with the best embodiment, it can be found that the modified low-melting-point polyester used as the fiber cortex material has poor fiber mechanical properties.

[0113] The difference between Comparative Examples 3-5 and the optimal embodiment is that conventional chemical foaming agents are used. Due to their low thermal decomposition temperature, they are completely decomposed during the screw mixing stage before fiber formation, and the bubble structure disappears immediately due to shearing after being formed. Therefore, they are not suitable as foaming agents for polyester fibers.

[0114] The raw materials and equipment used in the present invention, unless otherwise specified, are all commonly used raw materials and equipment in the art; the methods used in the present invention, unless otherwise specified, are all conventional methods in the art.

[0115] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A core-sheath foamed polyester fiber, characterized in that: It includes a foamed polyester core layer and a polyester skin layer; The foamed polyester core layer is obtained by blending modified foamed polyester with a nucleating agent and a foaming agent and then melt spinning; The modified foaming polyester is obtained by esterification and polycondensation of terephthalic acid, isophthalic acid, ethylene glycol and pentaerythritol as monomers.

2. The core-sheath type foamed polyester fiber according to claim 1, characterized in that: The mass ratio of the foamed polyester core layer to the polyester skin layer is 4:6-7:

3.

3. The core-sheath type foamed polyester fiber according to claim 1, characterized in that: The foaming agent is selected from one or more of 4,4'-oxybis(benzenesulfonyl semicarbazide), trihydrazino-s-triazine and N-nitroguanidine; The nucleating agent is selected from one or more of nano silicon dioxide, nano titanium dioxide, nano diatomaceous earth and nano kaolin.

4. The core-sheath type foamed polyester fiber according to claim 1 or 3, characterized in that: The foaming agent accounts for 0.5-2wt% of the total raw materials of the foamed polyester core layer; The nucleating agent accounts for 0.5-2wt% of the total raw materials of the foamed polyester core layer.

5. The core-sheath type foamed polyester fiber according to claim 1, characterized in that: Antioxidants are also added during the formation of the foamed polyester core layer.

6. The core-sheath type foamed polyester fiber according to claim 1, characterized in that: The molar ratio of alkyd to acid in the preparation process of the modified foaming polyester is 1.2-1.4:1; The isophthalic acid accounts for 10-20 mol% of the total of terephthalic acid and isophthalic acid; The pentaerythritol accounts for 0.02-0.2 mol% of the total of ethylene glycol and pentaerythritol.

7. A method for preparing the core-sheath foamed polyester fiber according to any one of claims 1 to 6, characterized in that include: 1) Using terephthalic acid, isophthalic acid, ethylene glycol and pentaerythritol as monomers, the modified foaming polyester is obtained through esterification and polycondensation; 2) Using modified foamed polyester, foaming agent and nucleating agent as core layer raw materials and polyester as skin layer raw material, the fibers are melt-spinned to prepare skin-core foamed polyester fibers.

8. The preparation method according to claim 7, characterized in that: In step 1), The esterification is carried out under an inert atmosphere, first at 205-225° C., normal pressure, for 30-50 min, and then at 225-255° C., 0.2-0.4 MPa, under pressure, for 90-180 min; The polycondensation is carried out under vacuum conditions at 265-285° C. for 0.5-2 h.

9. The preparation method according to claim 7, characterized in that: In step 2), a twin-screw extruder is used for melt blending; wherein the processing temperature of the twin-screw mixing section is 210-230° C., and the twin-screw speed is 100-300 r / min.

10. The preparation method according to claim 7, characterized in that: In step 2), during the melt spinning process, the temperature of the skin layer spinning box is 285-295°C, the temperature of the core layer spinning box is 235-245°C, and the winding speed is 2500-3000 m / min.

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