High temperature resistant low melting point polyester, its preparation method and application on fiber

Abstract

This invention relates to a high-temperature resistant, low-melting-point polyester, its preparation method, and its application in fibers. The high-temperature resistant, low-melting-point polyester is prepared by polycondensation reaction of esterified A, esterified B, and zinc acetate as a coordinating agent. Esterified A is obtained by esterification reaction of terephthalic acid, isophthalic acid, and ethylene glycol. Esterified B is obtained by esterification reaction of isophthalic acid, isosorbide, and hexanediol. The mass ratio of esterified A to esterified B is 70–75:25–30. The obtained high-temperature resistant, low-melting-point polyester has a glass transition temperature of 90–95°C and a melting point of 190–200°C. A high-temperature resistant, low-melting-point polyester fiber is provided, using the aforementioned high-temperature resistant, low-melting-point polyester as a sheath and PCTG as a core layer, with a sheath-to-core ratio of 45–55:55–45. The high-temperature resistant, low-melting-point polyester fiber of this invention has good heat resistance and a melting point that meets the requirements of its application, and has significant practical implications.

Description

Technical Field

[0001] This invention belongs to the field of polyester fiber technology, and relates to a high-temperature resistant, low-melting-point polyester, its preparation method, and its application in fibers. Background Technology

[0002] Thermal bonding low-melting-point fibers are one of the important raw materials for nonwoven fabrics, accounting for approximately 28% of the total fiber usage in nonwoven fabrics. In the rapidly developing nonwoven fabric industry, thermal bonding has been prioritized due to its simple processing method using fiber-based adhesives, resulting in environmentally friendly products. For the polyester nonwoven fabric industry, there is a need for a polymer with a lower melting point than conventional polyester fibers and good compatibility with conventional polyesters as a thermal bonding fiber.

[0003] With the rapid development of electronic and electrical integration, miniaturization, automotive lightweighting, the replacement of steel with plastics, LEDs, and industrial manufacturing, there are increasingly higher requirements for the heat resistance, strength, and other properties of materials. Automotive engines require sound and heat insulation. Existing sound and heat insulation pads, while thick, do not provide satisfactory sound and heat insulation. To address the problems of existing technologies, a material with better high-temperature resistance, shock absorption, sound insulation, and heat insulation is needed.

[0004] The difference between low-melting-point polyester fiber and ordinary polyester fiber lies in its core-shell structure. The outer layer has a melting point of approximately 110–130°C, while the core layer is made of ordinary polyester fiber. A major drawback of low-melting-point polyester fiber is its poor heat resistance. The glass transition temperature of conventional low-melting-point polyester fibers is mostly around 60–65°C. This lack of heat resistance limits its application in high-temperature fields, particularly in the automotive industry. (Glass transition temperature T) g The glass transition temperature is a crucial characteristic parameter of a material, as many of its properties change dramatically around this temperature. Therefore, the glass transition temperature determines the upper limit of a material's usability.

[0005] The heat resistance of low-melting-point polyester fibers is improved by increasing the glass transition temperature of the copolyester. Increasing the glass transition temperature generally falls into two categories: one is adding acids to the polyester raw material, such as introducing rigid diacids into the macromolecular chain, like naphthalenecarboxylic acid and biphenyl diacid; the other is adding alcohols to the polyester raw material, specifically rigid diols, such as 1,4-cyclohexyldiethanol and isosorbide. Both rigid diacids and diols present two problems: firstly, increased synthesis difficulty, resulting in lower molecular weights; and secondly, a higher melting point along with a higher glass transition temperature. To meet the requirements of its applications, low-melting-point polyester fibers typically have melting points below 200℃.

[0006] Therefore, developing a low-melting-point polyester fiber with good heat resistance and a melting point that meets the requirements of its application is of great practical significance. Summary of the Invention

[0007] The purpose of this invention is to solve the above-mentioned problems existing in the prior art, and to provide a high-temperature resistant, low-melting-point polyester, its preparation method, and its application in fibers.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing a high-temperature resistant, low-melting-point polyester involves mixing ester A and ester B with a ligand and then carrying out a polycondensation reaction to obtain the high-temperature resistant, low-melting-point polyester.

[0010] Ester A is obtained by esterification reaction using terephthalic acid, isophthalic acid and ethylene glycol as raw materials;

[0011] Ester B is obtained by esterification reaction using isophthalic acid, isosorbide and hexanediol as raw materials.

[0012] The mass ratio of ester A to ester B is 70–75:25–30; the ligand is zinc acetate, and the amount of zinc acetate added is 2.5–3.0% of the total mass of terephthalic acid and isophthalic acid.

[0013] The transition temperature and melting point of copolyester are the combined result of the influence of terephthalic acid, isophthalic acid, ethylene glycol, hexanediol, isosorbide, and the coordination of zinc ions. The disruption of the regularity of the PET molecular chain by isophthalic acid, hexanediol, and isosorbide makes the low-melting-point polyester an amorphous copolyester, which is beneficial to the melting, flow, and adhesion of the low-melting-point polyester.

[0014] During the synthesis process, the hydroxyl group on isosorbide is a secondary alcohol, and the reactivity of secondary alcohols in esterification reactions is lower than that of primary alcohols. Furthermore, isosorbide's unique V-shaped spatial structure causes significant steric hindrance, resulting in a low esterification reaction rate. Therefore, the proposed synthetic route involves using isophthalic acid, isosorbide, and hexanediol as raw materials, and terephthalic acid, isophthalic acid, and ethylene glycol as raw materials, to prepare two esterified products through esterification. Then, the two esterified products undergo polycondensation. Because isosorbide has lower reactivity than ethylene glycol, a higher temperature is required during esterification. Separate esterification ensures a high esterification rate for isosorbide, thus ensuring that the isosorbide content in the polyester is close to the feed ratio and reducing isosorbide loss. The hydroxyl group on isosorbide is a secondary alcohol, and the reactivity of secondary alcohols in esterification reactions is lower than that of primary alcohols. Additionally, isosorbide's unique V-shaped spatial structure causes significant steric hindrance, leading to a low esterification or transesterification reaction rate. In this invention, isophthalic acid, isosorbide, and hexanediol are used together for esterification. This has two main advantages: First, due to the conjugation effect of carboxylic acids, isophthalic acid has a higher carboxylic acid activity than terephthalic acid, which is beneficial to increasing the esterification rate. Second, the addition of hexanediol, which has a flexible chain, reduces viscosity during esterification and increases the activity of isosorbide, which is beneficial to the esterification process. At the same time, the movement of hexanediol chain segments also facilitates polycondensation.

[0015] As a preferred technical solution:

[0016] The specific steps of the preparation method of the high-temperature resistant, low-melting-point polyester described above are as follows:

[0017] (1) After preparing terephthalic acid, isophthalic acid and ethylene glycol into a slurry, react them at a temperature of 230-250℃ until the water distillation reaches more than 95% of the theoretical value to obtain ester A.

[0018] (2) After preparing a slurry from isophthalic acid, isosorbide and hexanediol, react it at a temperature of 250-260°C until the water distillation reaches more than 95% of the theoretical value to obtain ester B.

[0019] (3) The esterified A obtained in step (1) and the esterified B obtained in step (2) are thoroughly mixed and a catalyst, a coordinating agent and a stabilizer are added. The mixture is reacted for 30 to 50 minutes at a temperature of 260 to 270°C and a pressure less than or equal to 500 Pa absolute pressure. Then the mixture is reacted for 70 to 90 minutes at a temperature of 275 to 280°C and a pressure less than or equal to 100 Pa absolute pressure to obtain a high-temperature resistant, low-melting-point polyester.

[0020] In the above-described method for preparing a high-temperature resistant, low-melting-point polyester, the molar ratio of terephthalic acid, isophthalic acid, and ethylene glycol in step (1) is 1:0.70-0.75:2.2-2.6.

[0021] In step (2), the molar ratio of phthalic acid, isosorbide and hexanediol is 1:1.2-1.4:0.08-0.10;

[0022] In step (3), the amount of catalyst added is 0.01 to 0.03% of the total mass of terephthalic acid and isophthalic acid, and the amount of stabilizer added is 0.01 to 0.05% of the total mass of terephthalic acid and isophthalic acid.

[0023] In the preparation method of the high-temperature resistant, low-melting-point polyester described above, the catalyst is n-butyl titanate, and the stabilizer is triphenyl phosphate, trimethyl phosphate, or trimethyl phosphite.

[0024] This invention also provides a high-temperature resistant, low-melting-point polyester prepared by the method described above, wherein the O atoms on the carbonyl groups of terephthalic acid and isophthalic acid, and the O atoms in isosorbide, are combined with Zn in the macromolecular chain of the polyester. 2+ Perform coordination;

[0025] The high-temperature resistant, low-melting-point polyester has a glass transition temperature of 90–95°C and a melting point of 190–200°C.

[0026] This invention also provides a high-temperature resistant, low-melting-point polyester fiber, which has a core-sheath structure. The sheath material is the high-temperature resistant, low-melting-point polyester as described above, and the core material is PCTG. PCTG is a copolyester of 1,4-cyclohexanediol terephthalate and ethylene glycol terephthalate. It is a high-temperature resistant, semi-crystalline thermoplastic copolyester with a glass transition temperature mostly above 90°C. It has good processability, meets the heat resistance requirements of low-melting-point polyester fibers, and its crystallinity ensures the dimensional stability of the low-melting-point polyester fiber during application and processing.

[0027] As a preferred technical solution:

[0028] The high-temperature resistant, low-melting-point polyester fiber described above has a core-sheath ratio of 45–55:55–45.

[0029] The high-temperature resistant, low-melting-point polyester fiber described above has a spinning process that includes a crimping step and a subsequent spinning process using a drawing process, wherein the drawing process is an oil bath drawing process.

[0030] The main process parameters for spinning are: spinning temperature 285~290℃, spinning speed 500~800m / min, ring blower temperature 20~25℃, ring blower speed 0.5~0.8m / s; oil bath temperature 90~100℃, draw ratio 2.7~3.0, crimping temperature 60~70℃, crimping main pressure 0.4~0.6MPa, crimping back pressure 0.2~0.4MPa.

[0031] The high-temperature resistant, low-melting-point polyester fiber described above has a length of 51 mm, a single filament fineness of 3.0–5.0 dtex, a breaking strength ≥3.50 cN / dtex, a breaking elongation of 50–60%, a crimp number of 8–12 / 25 mm, and a crimp degree of 12–14%.

[0032] The principle of this invention is as follows:

[0033] When polymers undergo a glass transition, many physical properties, especially mechanical properties, change drastically, which affects the material's performance. The glass transition temperature is the upper limit for the use of low-melting-point polyester fibers; therefore, the glass transition temperature is a very important property of low-melting-point polyester fibers. g The T is the transition temperature of a polymer chain segment from freezing to movement (or vice versa). This segment movement is achieved through internal rotation of single bonds within the main chain. Therefore, any factor that affects the flexibility of the polymer chain will affect the T. g Yes, factors that increase the rigidity of polymer chains will affect T. g rise.

[0034] Isosorbide (IS) is a cyclic diol with a unique spatial structure (the two-membered ring has a V-shaped structure). As a bio-based diol with a unique spatial structure, compared with aliphatic diols, isosorbide's unique spatial structure results in greater internal rotational hindrance and fewer conformations, leading to rigid polymer molecular chain segments. This can significantly increase the glass transition temperature of copolyester materials, thereby improving their heat resistance. However, to meet the heat resistance requirements, the amount of isosorbide added is very large, around 35-45% in molar ratio. When too much isosorbide is introduced, the molecular weight (intrinsic viscosity [η], weight-average molecular weight Mw) of the modified polyester is significantly smaller than that of the unmodified polyester. This is mainly because, compared with α,ω-aliphatic diols, the hydroxyl group on isosorbide is a secondary alcohol, and the activity of secondary alcohols in esterification reactions is lower than that of primary alcohols. Additionally, the unique V-shaped spatial structure of isosorbide results in greater steric hindrance, leading to a lower rate of esterification or transesterification reactions. Therefore, increasing the glass transition temperature of copolyester by adding a high content of isosorbide results in a low molecular weight of copolyester, which cannot meet the requirements for processing and application of low melting point fibers.

[0035] This invention introduces a certain amount of zinc ions into the copolyester, thereby achieving a significant increase in the glass transition temperature of the copolyester material while substantially reducing the isosorbide content, resulting in unexpected technical effects.

[0036] Metallic zinc has an atomic number of 30 and is a transition element in Group HB, Period 4. Its valence electron configuration is 3d.10 4s 2 Electronic configuration. When metallic zinc loses its outermost two electrons, it becomes a colorless zinc ion. The zinc ion has only one valence state (+2), an ionic radius of 0.74 Å, and a stable d-valence electron configuration. 10 Due to its electronic configuration, zinc ions are relatively stable and not easily reduced, making them strong Lewis acids. As zinc is a transition element, zinc ions have a small ionic radius, a large effective nuclear charge, and empty 4s and 4p valence electron orbitals that can accept lone pairs of electrons from foreign ligands. Therefore, zinc ions have a strong attraction to ligands, meaning their structural characteristics give them a strong tendency to form complexes.

[0037] The O atoms with lone pairs of electrons in terephthalic acid, isophthalic acid, and isosorbide in the copolyester macromolecular chain can coordinate with zinc ions, and the coordination mode is flexible and varied, which can generate complexes with coordination numbers of 3, 4, 5 and 6.

[0038] In practical applications, polyester molecules, due to their linear arrangement and the lack of strong cross-linking nodes for support, often suffer unavoidable mechanical property degradation when heated. Cross-linking points can be chemical or physical. Chemical cross-linking structures form stable intramolecular chemical bonds, while physical cross-linking structures include hydrogen bonds, ionic bonds, and coordination bonds. The Zn of this invention... 2+ The formation of coordinate bonds between the O atoms with lone pairs of electrons in the copolyester macromolecular chain, along with the enhanced physical crosslinking points and intermolecular interactions, restricts chain segment movement. This makes inter-chain slippage difficult, and requires more energy for chain segments to change their conformation through movement. This, to some extent, increases the Tg of the copolyester. g , making T g Increase to above 90℃.

[0039] Metal-ligand coordination interactions enhance molecular interactions within macromolecular chain segments while simultaneously forming physical crosslinking points, hindering polymer chain movement. In zinc-doped polyesters, Zn... 2+ A single core can contain two isosorbides, and the coordination structure between the two isosorbides tends to promote polymer chain aggregation. Metal coordination bonds, as a supramolecular force, exhibit excellent dynamics. The bond energy of metal coordination bonds is approximately 50–200 kJ / mol, stronger than hydrogen bonds (4–120 kJ / mol) and second only to covalent bonds, and is considered one of the strongest supramolecular interactions.

[0040] In this invention, after zinc ions form coordination bonds with isosorbide, the crosslinking points of the polymer increase, and the macromolecular interactions are enhanced. Zinc ions form chelates with two isosorbide molecules, each with a five-membered ring structure. Chelates are cyclic complexes obtained through the chelation of two or more ligands with the same metal ion to form chelate rings. The interaction between zinc ions and isosorbide enhances the molecular interactions of the macromolecular chain segments, hindering polymer chain movement. Therefore, the formation of metal-ligand coordination interactions strengthens intermolecular interactions, further increasing the glass transition temperature of the polymer with zinc ions.

[0041] In metal-ligand coordination, chelates with five- or six-membered ring structures are the most stable and have the most significant impact on the thermal properties of materials. However, terephthalic acid and isophthalic acid in polyesters cannot form five- or six-membered ring chelates with zinc ions. Although terephthalic acid, isophthalic acid, and isosorbide all contain lone-paired oxygen atoms, theoretically, coordination without isosorbide could increase thermal glycemic index (Tg), but the desired effect would not be achieved.

[0042] The main functions of isosorbide in this invention are: (1) the unique spatial structure of isosorbide results in high internal rotational resistance and a small number of conformations, thus making the polymer molecular chain segments rigid; (2) isosorbide contains four oxygen atoms, which can form more hydrogen bonds and chelates with zinc ions to form five-membered and six-membered ring structures, which can significantly increase the glass transition temperature of the copolyester material. However, if the amount of isosorbide added is too small, the amount of hydrogen bonds formed and the amount of coordination are insufficient to raise the glass transition temperature of the polyester to above 90°C. The molar content of isosorbide in the polyester of this invention is about 25%, and with the coordination with zinc ions, the glass transition temperature of the polyester can be raised to above 90°C.

[0043] To meet the processing requirements of low-melting-point fibers, their melting point must be below 200℃, mainly for molding and shaping. If the melting point of low-melting-point fibers is above 200℃, the high molding and shaping temperatures will cause significant deformation of other materials, resulting in a decline in product quality.

[0044] The introduction of isophthalic acid (IPA) disrupts the regularity of the PET molecular chains, reducing the intermolecular forces and facilitating chain mobility. Simultaneously, steric hindrance hinders internal rotation of the chains, resulting in minimal change in the sample's crystal lattice (Tg). Furthermore, the steric hindrance of IPA makes it difficult for the chains to enter the crystal lattice. With increasing IPA content, the crystalline structure is largely disrupted, the cold crystallization peak disappears on the DSC chart, and the temperature (Tm) decreases.

[0045] Hexanediol belongs to the aliphatic flexible chain segment family. When introduced, it facilitates the movement of molecular chain segments, reducing the ordered length of PET chain segments and decreasing the number of segments entering the crystal lattice, thus lowering the Tm (transformation meter). Simultaneously, due to the unique spatial structure of isosorbide, the movement of hexanediol chain segments also helps to increase the molecular weight of the copolyester.

[0046] Beneficial effects:

[0047] (1) In this invention, isosorbide is introduced into the molecular chain as a glass transition temperature regulator, and zinc ions (Zn) are introduced on this basis. 2+ The formation of coordinate bonds with the O atoms with lone pairs of electrons in the copolyester macromolecular chain enhances the physical crosslinking points and intermolecular interactions in the copolyester, thereby increasing the Tg of the copolyester to a certain extent and significantly reducing the amount of isosorbide added, which is beneficial to increasing the molecular weight of the copolyester.

[0048] (2) In this invention, isophthalic acid and hexanediol are introduced into the copolyester molecular chain as melting point regulators, so that the low melting point polyester is an amorphous copolyester, which is beneficial to the melting, flow and adhesion of the low melting point polyester.

[0049] (3) In this invention, the glass transition temperature of the high temperature resistant low melting point polyester in the skin layer is 90-95℃ and the melting point is 190-200℃; the glass transition temperature of the PCTG core layer is ≥90℃, the glass transition temperature is high, and it has excellent processability. Detailed Implementation

[0050] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0051] Example 1

[0052] A method for preparing a high-temperature resistant, low-melting-point polyester, comprising the following specific steps:

[0053] (1) Terephthalic acid, isophthalic acid and ethylene glycol are mixed in a molar ratio of 1:0.7:2.2 to form a slurry, and then reacted at a temperature of 230°C until the water distillation reaches 96% of the theoretical value to obtain ester A.

[0054] (2) After preparing a slurry by mixing isophthalic acid, isosorbide and hexanediol in a molar ratio of 1:1.2:0.08, the mixture was reacted at a temperature of 250°C until the water distillation reached 96% of the theoretical value, and esterified compound B was obtained.

[0055] (3) The esterified compound A obtained in step (1) and the esterified compound B obtained in step (2) are thoroughly mixed at a mass ratio of 70:30 and 0.01% of tetrabutyl titanate, 2.5% of zinc acetate, and 0.01% of triphenyl phosphate relative to the total mass of terephthalic acid and isophthalic acid are added. The mixture is reacted at a temperature of 260°C and a pressure of 480 Pa for 50 min, and then reacted at a temperature of 275°C and a pressure of 95 Pa for 90 min to obtain a high-temperature resistant low-melting-point polyester.

[0056] In the macromolecular chain of the obtained high-temperature resistant, low-melting-point polyester, the O atoms on the carbonyl groups of terephthalic acid and isophthalic acid, as well as the O atoms in isosorbide, are related to Zn. 2+ Coordination is carried out; the glass transition temperature of the high-temperature resistant, low-melting-point polyester is 95℃, and the melting point is 200℃.

[0057] Example 2

[0058] A method for preparing a high-temperature resistant, low-melting-point polyester, comprising the following specific steps:

[0059] (1) Terephthalic acid, isophthalic acid and ethylene glycol are mixed in a molar ratio of 1:0.72:2.2 to form a slurry, and then reacted at a temperature of 235℃ until the water distillation reaches 98% of the theoretical value to obtain ester A.

[0060] (2) After preparing a slurry by mixing isophthalic acid, isosorbide and hexanediol in a molar ratio of 1:1.2:0.1, the mixture was reacted at a temperature of 255℃ until the water distillation reached 97% of the theoretical value, and esterified compound B was obtained.

[0061] (3) The esterified compound A obtained in step (1) and the esterified compound B obtained in step (2) are thoroughly mixed at a mass ratio of 70:30 and 0.02% of tetrabutyl titanate, 2.6% of zinc acetate, and 0.02% of triphenyl phosphate relative to the total mass of terephthalic acid and isophthalic acid are added. The mixture is reacted at a temperature of 262°C and a pressure of 460 Pa for 45 min, and then reacted at a temperature of 277°C and a pressure of 92 Pa for 82 min to obtain a high-temperature resistant low-melting-point polyester.

[0062] In the macromolecular chain of the obtained high-temperature resistant, low-melting-point polyester, the O atoms on the carbonyl groups of terephthalic acid and isophthalic acid, as well as the O atoms in isosorbide, are related to Zn. 2+ Coordination is carried out; the glass transition temperature of the high-temperature resistant, low-melting-point polyester is 94℃, and the melting point is 190℃.

[0063] Example 3

[0064] A method for preparing a high-temperature resistant, low-melting-point polyester, comprising the following specific steps:

[0065] (1) Terephthalic acid, isophthalic acid and ethylene glycol are mixed in a molar ratio of 1:0.75:2.4 to form a slurry, and then reacted at a temperature of 245℃ until the water distillation reaches 98% of the theoretical value to obtain ester A.

[0066] (2) After preparing a slurry by mixing isophthalic acid, isosorbide and hexanediol in a molar ratio of 1:1.3:0.08, the mixture was reacted at a temperature of 255℃ until the water distillation reached 98% of the theoretical value, and esterified compound B was obtained.

[0067] (3) The esterified compound A obtained in step (1) and the esterified compound B obtained in step (2) are thoroughly mixed at a mass ratio of 72:28 and 0.02% of tetrabutyl titanate, 2.8% of zinc acetate, and 0.03% of trimethyl phosphate relative to the total mass of terephthalic acid and isophthalic acid are added. The mixture is reacted at a temperature of 268°C and a pressure of 450 Pa for 42 min, and then reacted at a temperature of 278°C and a pressure of 90 Pa for 75 min to obtain a high-temperature resistant low-melting-point polyester.

[0068] In the macromolecular chain of the obtained high-temperature resistant, low-melting-point polyester, the O atoms on the carbonyl groups of terephthalic acid and isophthalic acid, as well as the O atoms in isosorbide, are related to Zn. 2+ Coordination is carried out; the glass transition temperature of the high-temperature resistant, low-melting-point polyester is 90℃, and the melting point is 193℃.

[0069] Example 4

[0070] A method for preparing a high-temperature resistant, low-melting-point polyester, comprising the following specific steps:

[0071] (1) Terephthalic acid, isophthalic acid and ethylene glycol are mixed in a molar ratio of 1:0.7:2.6 to form a slurry, and then reacted at a temperature of 250°C until the water distillation reaches 97% of the theoretical value to obtain ester A.

[0072] (2) After preparing a slurry by mixing isophthalic acid, isosorbide and hexanediol in a molar ratio of 1:1.4:0.1, the mixture was reacted at a temperature of 260°C until the water distillation reached 98% of the theoretical value, and esterified compound B was obtained.

[0073] (3) The esterified compound A obtained in step (1) and the esterified compound B obtained in step (2) are thoroughly mixed at a mass ratio of 75:25 and 0.03% of tetrabutyl titanate, 3% of zinc acetate, and 0.05% of trimethyl phosphite relative to the total mass of terephthalic acid and isophthalic acid are added. The mixture is reacted at a temperature of 270°C and a pressure of 420 Pa for 30 min, and then reacted at a temperature of 280°C and a pressure of 85 Pa for 70 min to obtain a high-temperature resistant low-melting-point polyester.

[0074] In the macromolecular chain of the obtained high-temperature resistant, low-melting-point polyester, the O atoms on the carbonyl groups of terephthalic acid and isophthalic acid, as well as the O atoms in isosorbide, are related to Zn. 2+ Coordination is carried out; the glass transition temperature of the high-temperature resistant, low-melting-point polyester is 93℃, and the melting point is 198℃.

[0075] Example 5

[0076] A method for preparing high-temperature resistant, low-melting-point polyester fiber, wherein the high-temperature resistant, low-melting-point polyester fiber has a core-sheath structure with a core-sheath ratio of 45:55. The sheath material is the high-temperature resistant, low-melting-point polyester of Example 1, and the core material is PCTG. PCTG is a copolyester of terephthalic acid, 1,4-cyclohexanediol ester and ethylene glycol terephthalate, with a glass transition temperature of 95°C. The spinning process of the high-temperature resistant, low-melting-point polyester fiber includes a crimping step and a subsequent spinning process using a drawing process, with oil bath drawing. The spinning process parameters are: spinning temperature 285°C, spinning speed 500 m / min, ring blower temperature 20°C, ring blower speed 0.5 m / s; oil bath temperature 90°C, drawing ratio 2.7, crimping temperature 60°C, crimping main pressure 0.4 MPa, and crimping back pressure 0.2 MPa.

[0077] The obtained high-temperature resistant, low-melting-point polyester fiber has a length of 51 mm, a single filament fineness of 3.0 dtex, a breaking strength of 3.8 cN / dtex, a breaking elongation of 50%, a crimp number of 10 / 25 mm, and a crimp degree of 13%.

[0078] Example 6

[0079] A method for preparing high-temperature resistant, low-melting-point polyester fiber, wherein the high-temperature resistant, low-melting-point polyester fiber has a core-sheath structure with a core-sheath ratio of 50:50. The sheath material is the high-temperature resistant, low-melting-point polyester of Example 2, and the core material is PCTG. PCTG is a copolyester of terephthalic acid, 1,4-cyclohexanediol ester and ethylene glycol terephthalate, with a glass transition temperature of 98°C. The spinning process of the high-temperature resistant, low-melting-point polyester fiber includes a crimping step and a subsequent spinning process using a drawing process, with oil bath drawing. The spinning process parameters are: spinning temperature 287°C, spinning speed 620 m / min, ring blower temperature 22°C, ring blower speed 0.6 m / s; oil bath temperature 92°C, drawing ratio 2.7, crimping temperature 60°C, crimping main pressure 0.4 MPa, and crimping back pressure 0.2 MPa.

[0080] The obtained high-temperature resistant, low-melting-point polyester fiber has a length of 51 mm, a single filament fineness of 4.0 dtex, a breaking strength of 3.7 cN / dtex, a breaking elongation of 57%, a crimp number of 8 / 25 mm, and a crimp degree of 12%.

[0081] Example 7

[0082] A method for preparing high-temperature resistant, low-melting-point polyester fiber, wherein the high-temperature resistant, low-melting-point polyester fiber has a core-sheath structure with a core-sheath ratio of 50:50. The sheath material is the high-temperature resistant, low-melting-point polyester of Example 3, and the core material is PCTG. PCTG is a copolyester of terephthalic acid, 1,4-cyclohexanediol ester and ethylene glycol terephthalate, with a glass transition temperature of 92°C. The spinning process of the high-temperature resistant, low-melting-point polyester fiber includes a crimping step and a subsequent spinning process using a drawing process, with oil bath drawing. The spinning process parameters are: spinning temperature 288°C, spinning speed 750 m / min, ring blower temperature 25°C, ring blower speed 0.8 m / s; oil bath temperature 95°C, drawing ratio 2.9, crimping temperature 65°C, crimping main pressure 0.5 MPa, and crimping back pressure 0.3 MPa.

[0083] The obtained high-temperature resistant, low-melting-point polyester fiber has a length of 51 mm, a single filament fineness of 5.0 dtex, a breaking strength of 3.5 cN / dtex, a breaking elongation of 52%, a crimp number of 12 / 25 mm, and a crimp degree of 14%.

[0084] Example 8

[0085] A method for preparing high-temperature resistant, low-melting-point polyester fiber, wherein the high-temperature resistant, low-melting-point polyester fiber has a core-sheath structure with a core-sheath ratio of 55:45. The sheath material is the high-temperature resistant, low-melting-point polyester of Example 4, and the core material is PCTG. PCTG is a copolyester of terephthalic acid, 1,4-cyclohexanediol ester and ethylene glycol terephthalate, with a glass transition temperature of 90°C. The spinning process of the high-temperature resistant, low-melting-point polyester fiber includes a crimping step and a subsequent spinning process using a drawing process, with oil bath drawing. The spinning process parameters are: spinning temperature 290°C, spinning speed 800 m / min, ring blower temperature 25°C, ring blower speed 0.8 m / s; oil bath temperature 100°C, drawing ratio 3, crimping temperature 70°C, crimping main pressure 0.6 MPa, and crimping back pressure 0.4 MPa.

[0086] The obtained high-temperature resistant, low-melting-point polyester fiber has a length of 51 mm, a single filament fineness of 4.5 dtex, a breaking strength of 3.7 cN / dtex, a breaking elongation of 60%, a crimp number of 12 / 25 mm, and a crimp degree of 13%.

Claims

1. A process for the preparation of a high temperature resistant low melting point polyester, characterized by: A high-temperature resistant, low-melting-point polyester was prepared by mixing ester A and ester B with a ligand and then carrying out a polycondensation reaction. Ester A is obtained by esterification reaction using terephthalic acid, isophthalic acid and ethylene glycol as raw materials; Ester B is obtained by esterification reaction using isophthalic acid, isosorbide and hexanediol as raw materials. The mass ratio of ester A to ester B is 70~75:25~30; the complexing agent is zinc acetate, and the amount of zinc acetate added is 2.5~3.0% of the total mass of terephthalic acid and isophthalic acid; The molar ratio of terephthalic acid, isophthalic acid, and ethylene glycol is 1:0.70~0.75:2.2~2.

6. The molar ratio of isophthalic acid, isosorbide, and hexanediol is 1:1.2~1.4:0.08~0.10; In the macromolecular chain of the obtained high-temperature resistant low-melting-point polyester, the O atoms on the carbonyl groups of terephthalic acid and isophthalic acid, as well as the O atoms in isosorbide, coordinate with Zn2+. The high-temperature resistant, low-melting-point polyester has a glass transition temperature of 90-95℃ and a melting point of 190-200℃.

2. The method for preparing a high-temperature resistant, low-melting-point polyester according to claim 1, characterized in that, The specific steps are as follows: (1) After preparing terephthalic acid, isophthalic acid and ethylene glycol into a slurry, react them at a temperature of 230~250℃ until the water distillation reaches more than 95% of the theoretical value to obtain ester A; (2) After preparing a slurry from isophthalic acid, isosorbide and hexanediol, react it at a temperature of 250~260℃ until the water distillation reaches more than 95% of the theoretical value to obtain ester B. (3) The esterified A obtained in step (1) and the esterified B obtained in step (2) are thoroughly mixed and a catalyst, a coordinating agent and a stabilizer are added. The mixture is reacted for 30 to 50 minutes at a temperature of 260 to 270°C and a pressure less than or equal to 500 Pa absolute pressure. Then it is reacted for 70 to 90 minutes at a temperature of 275 to 280°C and a pressure less than or equal to 100 Pa absolute pressure to obtain a high-temperature resistant, low-melting-point polyester.

3. The method for preparing a high-temperature resistant, low-melting-point polyester according to claim 2, characterized in that, In step (3), the amount of catalyst added is 0.01~0.03% of the total mass of terephthalic acid and isophthalic acid, and the amount of stabilizer added is 0.01~0.05% of the total mass of terephthalic acid and isophthalic acid.

4. The method for preparing a high-temperature resistant, low-melting-point polyester according to claim 3, characterized in that, The catalyst is tetrabutyl titanate, and the stabilizer is triphenyl phosphate, trimethyl phosphate, or trimethyl phosphite.

5. A high-temperature resistant, low-melting-point polyester fiber, characterized in that: The high-temperature resistant, low-melting-point polyester fiber has a core-sheath structure, with the sheath material being the high-temperature resistant, low-melting-point polyester described in claim 1, and the core material being PCTG.

6. The high-temperature resistant, low-melting-point polyester fiber according to claim 5, characterized in that, The core-skin ratio of the core-skin structure is 45~55:55~45.

7. The high-temperature resistant, low-melting-point polyester fiber according to claim 6, characterized in that, The spinning process of high-temperature resistant, low-melting-point polyester fiber includes a crimping process and a subsequent spinning process using a drawing process, with oil bath drawing used. The main process parameters for spinning are: spinning temperature 285~290℃, spinning speed 500~800m / min, ring blower temperature 20~25℃, ring blower speed 0.5~0.8m / s; oil bath temperature 90~100℃, draw ratio 2.7~3.0, crimping temperature 60~70℃, crimping main pressure 0.4~0.6MPa, crimping back pressure 0.2~0.4MPa.

8. The high-temperature resistant, low-melting-point polyester fiber according to claim 7, characterized in that, The high-temperature resistant, low-melting-point polyester fiber has a length of 51 mm, a single filament fineness of 3.0~5.0 dtex, a breaking strength ≥3.50 cN / dtex, a breaking elongation of 50~60%, a crimp number of 8~12 / 25 mm, and a crimp degree of 12~14%.