Low-melting-point PET (Polyethylene Terephthalate) short fiber and production method

Abstract

The invention provides a low-melting-point PET short fiber, and relates to the technical field of fiber production. The low-melting-point PET short fiber comprises a high-strength low-melting-point PET short fiber, the short fiber is of a skin-core composite structure, a skin layer of the skin-core composite structure is modified low-melting-point polyester and is prepared by melt copolymerization of PET, 10-30% of rigid comonomers and 5-15% of flexible chain segments, the melting point is 110-160 DEG C, and the glass-transition temperature (Tg) is larger than or equal to 60 DEG C. The gradient interface enhancement technology is adopted, the PET-g-PE grafting layer is introduced between the skin layer and the core layer, the grafting rate reaches 5-8% through melt blending, a transition layer of 1-3 microns is formed, the peel strength is improved to 1.5 N / cm or above, and the problem of interface stripping of traditional composite fibers is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of fiber production, in particular to a low-melting-point PET staple fiber and a production method thereof. Background Art

[0002] Low-melting-point PET staple fibers are polyester (PET) fibers modified through a special process to achieve a lower melting point than conventional PET fibers (which melt at approximately 250-260°C). Their key characteristic is their ability to melt and bond at relatively low temperatures (typically 110-160°C) while maintaining adequate mechanical properties. They are widely used in nonwovens, clothing accessories, automotive interiors, filter materials, and other applications.

[0003] The existing low melting point PET staple fibers are used in practical applications: Insufficient mechanical properties. Traditional low-melting-point PET fibers destroy the regularity of the molecular chain through copolymerization modification (such as the introduction of isophthalic acid), resulting in a breaking strength generally lower than 2.5 cN / dtex and a decrease in elastic recovery rate. The sheath-core composite fiber is thermodynamically incompatible with the core layer (PET) and the sheath layer (such as polyethylene), and the interfacial peel strength is less than 1.0 N / cm, which seriously limits its application in the field of high-strength non-woven fabrics.

[0004] Conventional low-melting-point PET fibers have poor thermal stability. They can withstand temperatures below 140°C and easily soften and deform in high-temperature environments. For example, in automotive engine compartment interior materials, adhesive failure can occur when used at temperatures above 120°C for extended periods. While copolymerization lowers the melting point, the initial thermal decomposition temperature is often below 250°C, resulting in a narrow processing window.

[0005] There are bottlenecks in technology and environmental protection. Composite spinning requires special equipment and has high investment costs. Fibers containing polyolefin sheaths are difficult to separate during recycling due to their complex components, posing an environmental risk.

[0006] Therefore, in view of this, the existing structure and defects are studied and improved, and a low-melting-point PET staple fiber and a production method are provided. Summary of the Invention

[0007] (1) Technical problems solved:

[0008] In view of the deficiencies in the prior art, the present invention provides a low-melting-point PET staple fiber and a production method to solve the problem.

[0009] (2) Technical solution:

[0010] To achieve the above objectives, the present invention is implemented through the following technical solutions: a low melting point PET staple fiber, its product structure and performance.

[0011] 1. High strength skin-core composite fiber Skin layer: Modified low melting point polyester, made by copolymerizing PET with 10-30% rigid monomer (such as naphthalene dicarboxylic acid) and 5-15% flexible segment (polyethylene glycol), with a melting point of 110-160°C and a glass transition temperature of ≥60°C. 1-3% nano-silica (particle size 20-50nm) is introduced and evenly dispersed, reducing thermal conductivity by 10-20% and surface resistivity ≤10 9 Ω.

[0012] Core layer: high-strength PET, intrinsic viscosity 0.8-1.2dL / g, breaking strength ≥4.0cN / dtex.

[0013] Interface: A gradient transition is formed through the PET-g-PE grafted layer, and the peel strength is ≥1.5N / cm, which is more than 40% higher than that of traditional composite fibers.

[0014] Overall performance: breaking strength ≥3.0cN / dtex, elongation at break 25-40%, thermal shrinkage at 120℃ ≤5%.

[0015] 2. High temperature resistant copolymer modified fiber Copolymer system: 8-15% high temperature resistant component (PBT) and 3-8% surface amino nano-talc powder (particle size 20-50nm) are compounded, and the dispersion is enhanced by grafting with a silane coupling agent (KH-550).

[0016] Thermal stability: melting point 130-160℃, initial thermal decomposition temperature ≥280℃, strength retention rate ≥85% after heat treatment at 150℃ for 2 hours.

[0017] Crystallization characteristics: crystallinity 30-40%, grain size ≤50nm, prepared by twin-screw extruder, spinning temperature 240-260℃.

[0018] Preparation method 1. Copolymerization modification process Raw material ratio: The molar ratio of PTA, EG and the third monomer (isophthalic acid, triethylene glycol) is (70-85): (15-30): (5-15), and titanium catalyst (10-20ppm) and nano zinc oxide (0.01-0.1%) are added.

[0019] Reaction conditions: esterification temperature 230-260℃, reaction time 2-4 hours; polycondensation temperature 270-280℃, vacuum degree ≤100Pa, reaction time 3-5 hours.

[0020] 2. Composite spinning process Melt control: The melt temperature of the skin layer is 10-20℃ lower than that of the core layer, the spinning speed is 1500-3000m / min, the cooling wind speed is 0.5-1.0m / s, and the thickness of the interface diffusion layer is controlled to be 1-3μm.

[0021] Spinneret design: The cortex accounts for 30-70%, and adopts a skin-core structure to promote uniform covering of the cortex.

[0022] 3. Post-processing process Stretching and shaping: two-stage stretching (total stretching ratio 4.5-6.0 times), first-stage temperature 50-70℃, second-stage temperature 90-110℃; wet heat shaping (steam pressure 0.1-0.3MPa, time 1-3min), crystallinity increased by 5-8%.

[0023] Curl cutting: crimp number 8-12 / cm, fiber length 3-6mm.

[0024] (3) Beneficial effects:

[0025] The present invention provides a low-melting-point PET staple fiber and a production method thereof, which has the following beneficial effects: 1. This low-melting-point PET staple fiber and its production method adopt gradient interface enhancement technology to introduce a PET-g-PE graft layer between the skin layer and the core layer. Through melt blending, the grafting rate reaches 5-8%, forming a 1-3μm transition layer, and the peel strength is increased to above 1.5N / cm, solving the interface peeling problem of traditional composite fibers.

[0026] 2. This low-melting-point PET staple fiber and its production method utilize high-temperature-resistant compounding technology to achieve synergistic effects between PBT and nano-talc. The rigid segments of PBT enhance heat resistance, while the nano-talc promotes heterogeneous nucleation, increasing the crystallization rate by 30-50%. The initial thermal decomposition temperature is 30°C higher than that of pure PET.

[0027] 3. This low-melting-point PET staple fiber and its production method uses dynamic cross-linking technology to introduce 0.5-2% isocyanate into the copolymer system. Through ultraviolet light irradiation (wavelength 254nm, dose 5-10kJ / m²), a micro-cross-linked structure is formed, which increases the elastic recovery rate by 15-20% while maintaining hot melt properties. DETAILED DESCRIPTION

[0028] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0029] In the description of the present invention, unless otherwise specified, "plurality" means two or more. Terms such as "upper," "lower," "left," "right," "inner," "outer," "front," "rear," "head," and "tail" indicate positions or locations for the sole purpose of facilitating and simplifying the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and are therefore not to be construed as limiting the present invention. Furthermore, terms such as "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

[0030] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "connected" and "connection" should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integral connection; mechanical connection, electrical connection; direct connection, or indirect connection through an intermediary. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0031] Example 1: High-strength sheath-core composite fiber Raw material preparation Skin layer: PTA 70 mol%, EG 25 mol%, naphthalene dicarboxylic acid 5 mol%, polyethylene glycol (molecular weight 400) 10 wt%, titanium catalyst 15 ppm, nano-silica 1.5 wt%.

[0032] Core layer: high-strength PET with an intrinsic viscosity of 0.9dL / g.

[0033] Preparation steps Copolymerization reaction: put the skin layer raw materials into the reactor, esterify at 240℃ for 3 hours, and condense at 275℃ for 4 hours to obtain low-melting-point copolyester.

[0034] Composite spinning: The skin layer melt temperature is 250℃, the core layer melt temperature is 270℃, and it is extruded through a composite spinneret (the skin layer accounts for 50%), with a spinning speed of 2000m / min and a cooling wind speed of 0.8m / s.

[0035] Post-treatment: The nascent fiber was stretched (total multiple 5.0 times), wet-heat set (0.2 MPa steam treatment for 2 min), crimped and cut to obtain fiber.

[0036] Performance Testing Mechanical properties: breaking strength 3.2 cN / dtex, elongation at break 35%, peel strength 1.6 N / cm.

[0037] Thermal properties: melting point 145℃, thermal shrinkage rate 4.2% at 120℃, initial thermal decomposition temperature 285℃.

[0038] Example 2: High temperature resistant copolymer modified fiber Raw material preparation Comonomer: PTA 80 mol%, EG 15 mol%, PBT 5 mol%, surface amino nano-talc 5 wt%, silane coupling agent KH-550 1 wt%.

[0039] Preparation steps Copolymerization reaction: esterification at 235°C for 2.5 hours and polycondensation at 270°C for 3.5 hours to produce copolyester.

[0040] Spinning molding: melt spinning temperature 250℃, spinning speed 2500m / min, stretching ratio 4.8 times, heat setting temperature 110℃.

[0041] Performance Testing Thermal stability: melting point 150℃, strength retention rate 88% after heat treatment at 150℃ for 2 hours.

[0042] Crystallization characteristics: crystallinity 38%, grain size 45nm.

[0043] Comparative Example 1: Traditional sheath-core composite fiber The fabric uses a PE / PET sheath-core structure, with the sheath accounting for 30% and a spinning speed of 1200 m / min. Test results show: peel strength of 0.9 N / cm, thermal shrinkage of 8.5% at 120°C, and breaking strength of 2.2 cN / dtex.

[0044] Comparative Example 2: Ordinary copolymer modified fiber Only isophthalic acid (10 mol%) was added, without PBT or nano-talc. Test results showed a melting point of 135°C, an initial thermal decomposition temperature of 255°C, and a strength retention of 65% after heat treatment at 150°C.

[0045] Effects of the Invention Breakthrough in mechanical properties: Through gradient interface design and molecular chain reinforcement, the breaking strength is increased by 45% compared to traditional fibers, and the peel strength is increased by 78%, meeting the high-strength application requirements of industrial filtration materials, automotive interiors, etc.

[0046] Thermal stability is significantly improved: the high-temperature resistant components and the nucleating agent work synergistically, the initial thermal decomposition temperature is increased by more than 30°C, and the long-term strength retention rate at 150°C is ≥85%, and it can be used in high-temperature environments (such as kitchen rags and engine compartment sound insulation cotton).

[0047] Process optimization and environmental protection: The composite spinning speed is increased to over 2000m / min, and the production cost is reduced by 15-20%. The detachable structural design is adopted, and the core layer PET and the skin layer materials are efficiently recycled through the pH-responsive skin layer (dissolved in alkali), with a recovery rate of ≥90%.

[0048] Application areas:

[0049] Automotive industry: sound insulation cotton, seat filling materials, mixed with conventional PET fiber (ratio 1:1-3:1), after hot pressing, the tensile strength is ≥8MPa, the sound insulation coefficient (1000Hz) is ≥0.8, and the formaldehyde emission is ≤0.05mg / m³.

[0050] Sanitary materials: The hot air bonding fibers used in diapers and sanitary napkins can reduce water absorption by 60% after being treated with silane coupling agent coating. The bonding strength retention rate can withstand 50 washes at 50°C with a value of ≥90%.

[0051] Smart wearables: Thermosensitive low-melting-point fiber (containing poly (N-isopropyl acrylamide)) achieves adaptive bonding and is suitable for smart adjustment components of wearable devices.

[0052] Future technology directions Smart responsive fiber: Introducing thermosensitive polymers (such as poly (N-isopropylacrylamide)) and using microencapsulation technology to achieve dynamic adjustment of the melting point with the ambient temperature (adjustment range ±10°C).

[0053] Nano-reinforced materials: Carbon nanotubes (CNT) or graphene are evenly dispersed in a low-melting-point PET matrix, increasing strength by 30% and heat resistance by 25°C while retaining hot-melt properties.

[0054] Digital process control: Integrates online viscosity monitoring and infrared spectroscopy real-time analysis systems to precisely control the degree of polymerization and melt state, reducing performance defects caused by process fluctuations.

[0055] The embodiments of the present invention are presented for purposes of illustration and description and are not intended to be exhaustive or to limit the invention to the disclosed forms. Many modifications and variations will be apparent to those skilled in the art. The embodiments are chosen and described in order to better illustrate the principles of the invention and its practical application and to enable those skilled in the art to understand the invention and design various embodiments with various modifications as suited for specific applications.

Claims

1. A low-melting-point PET staple fiber, comprising a high-strength low-melting-point PET staple fiber, wherein the staple fiber is a core-skin composite structure, characterized in that: The skin layer of the core-skin composite structure is a modified low-melting-point polyester, which is prepared by melt copolymerization of PET, 10-30% rigid comonomer and 5-15% flexible segment, with a melting point of 110-160°C and a glass transition temperature (Tg) of ≥60°C. The core layer of the skin-core composite structure is high-strength PET with an intrinsic viscosity of 0.8-1.2dL / g and a breaking strength of ≥4.0cN / dtex; The interface between the skin layer and the core layer is enhanced by the gradient grafting layer, and the peel strength is ≥1.5N / cm; The fiber has an overall breaking strength of ≥3.0 cN / dtex, an elongation at break of 25-40%, and a thermal shrinkage of ≤5%.

2. A low-melting-point PET staple fiber, comprising a high-temperature-resistant low-melting-point PET staple fiber, wherein the staple fiber is made of copolymerized modified PET, and is characterized by: The comonomer of the copolymerized modified PET includes 8-15% of a high temperature resistant component (and 3-8% of a nucleating agent; The copolymer modified PET has a melting point of 130-160°C, an initial thermal decomposition temperature of ≥280°C, and a strength retention rate of ≥85% after heat treatment at 150°C for 2 hours; The copolymer modified PET has a crystallinity of 30-40% and a grain size of ≤50nm, and is prepared by melt spinning through a twin-screw extruder at a spinning temperature of 240-260°C.

3. A low-melting-point PET staple fiber, comprising a method for preparing the low-melting-point PET staple fiber, the method comprising the following steps: Copolymerization modification: PTA, EG and the third monomer are mixed in a molar ratio of 70-85:15-30:5-15, titanium catalyst and nano zinc oxide are added, and esterification reaction is carried out at 230-260°C for 2-4 hours, followed by polycondensation at 270-280°C and vacuum degree ≤100Pa for 3-5 hours to obtain a low melting point copolyester; Composite spinning: The skin layer and the core layer are melted separately and then extruded through a composite spinneret, with a spinning speed of 1500-3000m / min and a cooling air speed of 0.5-1.0m / s; Post-processing: The primary fiber is stretched in two stages, heat-set, curled and cut to obtain the finished product.

4. The low-melting-point PET staple fiber according to claim 1, characterized in that: The skin layer also contains 1-3% nano-silicon dioxide or graphene, which is evenly dispersed in the polyester matrix, reducing the thermal conductivity of the fiber by 10-20% while improving the antistatic performance.

5. A low melting point PET staple fiber according to claim 2, characterized in that: The nucleating agent is nano-talc powder with surface amino modification and a particle size of 20-50 nm. It is grafted with the polyester matrix through a silane coupling agent to promote heterogeneous nucleation and increase the crystallization rate by 30-50%.

6. The method for preparing low-melting-point PET staple fibers according to claim 3, wherein: During the composite spinning process, the melt temperature of the skin layer is 10-20° C. lower than that of the core layer, so as to control the thickness of the interface diffusion layer between the skin layer and the core layer to be 1-3 μm, thereby avoiding excessive mutual dissolution leading to interface weakening.

7. The method for preparing low-melting-point PET staple fibers according to claim 3, wherein: In the post-processing step, heat setting adopts wet heat treatment to increase the crystallinity of the fiber by 5-8%, while reducing internal stress and improving dimensional stability.