Process for flame-retardant treatment of composite fiber needle punched automotive acoustic cotton

Abstract

This invention relates to the field of sound insulation material preparation technology, specifically to a process for flame-retardant treatment of automotive sound insulation cotton after composite fiber needle punching molding, comprising the following steps: opening and blending: feeding composite fiber raw materials and auxiliary components into an opening machine for secondary opening treatment; carding into a web: feeding the opened mixed fibers into a carding machine to form a uniform fiber web; needle punching: using an upper and lower double needle punching machine to needle punch the fiber web to obtain a sound insulation cotton blank; post-flame-retardant treatment: immersing the sound insulation cotton blank in a flame-retardant liquid, followed by ultrasonic-assisted soaking and liquid extrusion treatment; this invention adopts a scientific composite fiber ratio design, abandoning the traditional mode of single fiber or simple mixing, and fundamentally solving the problem of performance imbalance of single fiber materials through the synergistic combination of different performance fibers, achieving a basic synergy of sound insulation, mechanical strength and flame retardant performance.

Description

Technical Field

[0001] This invention relates to the field of sound insulation material preparation technology, specifically to a process for flame-retardant treatment of automotive sound insulation cotton after composite fiber needle punching molding. Background Technology

[0002] Sound insulation cotton for automotive interiors must simultaneously meet multiple stringent requirements, including flame retardancy, sound insulation, mechanical strength, and environmental friendliness. Its performance directly impacts vehicle safety and ride comfort. Currently, the manufacturing process of automotive sound insulation cotton in the industry faces many unresolved issues. Some solutions use a single fiber as raw material, which, limited by the fiber's inherent properties, makes it difficult to achieve a synergistic balance between sound insulation, mechanical strength, and flame retardancy, thus failing to adapt to the complex usage scenarios of automotive interiors.

[0003] Another approach attempts to use a composite fiber system, but these are mostly simple mixtures of different fibers without a scientifically designed ratio. Furthermore, the corresponding needle-punching process lacks targeted optimization and often uses fixed needle-punching parameters, resulting in an unreasonable pore structure in the formed sound insulation cotton. This not only affects the mechanical stability but also causes uneven penetration of the flame retardant liquid, thus restricting the improvement of flame retardant performance.

[0004] In terms of flame retardant treatment, existing technologies often employ a single flame retardant system, lacking synergistic design, resulting in limited flame retardant effect and insufficient durability, with flame retardant performance easily degrading after long-term use. Furthermore, some processes place flame retardant treatment before needle punching, which can easily damage the original fiber structure, leading to a decrease in the mechanical strength of the sound insulation cotton. Additionally, flame retardant components are easily lost during subsequent carding and needle punching processes, causing unstable flame retardant effects. Moreover, some solutions lack scientific basis for raw material ratios, blindly adjusting component proportions, further exacerbating the imbalance in product performance and failing to meet the high standards of comprehensive performance requirements for sound insulation cotton in automotive interiors. Therefore, a preparation process that can systematically solve the above problems is urgently needed. Summary of the Invention

[0005] The primary objective of this invention is to provide a process for flame-retardant treatment of automotive sound insulation cotton after composite fiber needle punching molding.

[0006] A further objective of this invention is to provide a process for flame-retardant treatment of automotive sound insulation cotton after composite fiber needle punching molding, comprising the following steps: (1) Opening and blending: The composite fiber raw materials and auxiliary components are put into the opening machine for secondary opening treatment; (2) Carding into a web: The opened mixed fibers are fed into a carding machine and carded to form a uniform fiber web; (3) Needle punching: The fiber web is needle punched using an upper and lower double needle punching machine to obtain a sound insulation cotton blank; (4) Post-flame retardant treatment: The sound insulation cotton blank is immersed in flame retardant liquid, and after ultrasonic-assisted soaking, it is squeezed out. (5) Drying and curing: The extruded green body is dried and cured using a segmented drying process; (6) Finished product cutting: The dried and cured blank is cut according to the preset size to obtain the finished automotive sound insulation cotton; the composite fiber raw material is composed of one of polyester short fiber, flame retardant viscose short fiber, glass short fiber and modified polypropylene short fiber; the flame retardant liquid includes ammonium polyphosphate and synergist.

[0007] Preferably, in the composite fiber raw material, by mass parts, there are 30 to 60 parts of polyester staple fiber, 20 to 30 parts of flame-retardant viscose staple fiber, 5 to 15 parts of glass staple fiber, or 20 to 30 parts of modified polypropylene staple fiber.

[0008] Preferably, the auxiliary components are an antistatic agent and a coupling agent, wherein the antistatic agent is an alkyl phosphate salt and the coupling agent is a silane coupling agent.

[0009] Preferably, the first-stage rotation speed of the secondary opening is 550 to 600 revolutions per minute, and the processing time is 3 minutes; the second-stage rotation speed is 750 to 800 revolutions per minute, and the processing time is 2 minutes.

[0010] Preferably, the speed of combing and forming the web is 14 to 15 meters per minute, the web thickness is 12 to 13 millimeters, and the needle cloth model is AC2030.

[0011] Preferably, the needle-punching density is 180 to 220 needles per square centimeter, the needle-punching depth is 8 to 11 millimeters, the needle-punching frequency is 800 to 850 times per minute, and the net-lifting speed is 4.5 to 5 meters per minute.

[0012] Preferably, the needle density is set in a gradient manner, with 180 needles per square centimeter in the front section, 220 needles per square centimeter in the middle section, and 200 needles per square centimeter in the rear section; the needle depth is set in a gradient manner, with 8 mm in the front section, 11 mm in the middle section, and 10 mm in the rear section.

[0013] Preferably, the mass concentration of ammonium polyphosphate in the flame retardant liquid is 12 to 20%, the mass concentration of the synergist is 2 to 8%, and the synergist is one or more of pentaerythritol, melamine, and nano magnesium hydroxide.

[0014] Preferably, the ultrasonic-assisted soaking frequency is 40 kHz, the power is 100 W, the soaking temperature is 55 to 60 degrees Celsius, the soaking time is 15 to 20 minutes, the liquid extrusion pressure is 0.3 to 0.35 MPa, and the amount of flame retardant liquid adhering is 75 to 80% of the body mass.

[0015] Preferably, the segmented drying process includes three stages: pre-drying, main drying, and curing. The pre-drying temperature is 75 to 80 degrees Celsius and the time is 30 to 35 minutes. The main drying temperature is 115 to 120 degrees Celsius and the time is 60 to 65 minutes. The curing temperature is 145 to 150 degrees Celsius and the time is 20 to 25 minutes. The moisture content of the blank after drying does not exceed 3%.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention adopts a scientific composite fiber ratio design, abandoning the traditional mode of single fiber or simple mixing. By synergistically combining different performance fibers, it fundamentally solves the problem of performance imbalance of single fiber materials, and achieves basic synergy of sound insulation, mechanical strength and flame retardant performance.

[0017] 2. In terms of molding process, the present invention optimizes the needle punching parameters to form a reasonable pore gradient structure, which not only ensures the mechanical stability of the sound insulation cotton, but also provides favorable conditions for the uniform penetration of flame retardant liquid, thus achieving precise matching between molding process and fiber composition.

[0018] 3. In the flame retardant treatment process, this invention constructs a multi-element synergistic flame retardant system, which significantly improves the flame retardant effect and durability compared to traditional single flame retardant solutions. At the same time, the scientific timing of the flame retardant treatment after needle punching effectively avoids the problems of fiber structure damage and loss of flame retardant components, ensuring the stability of various properties.

[0019] 4. By optimizing the flame retardant liquid formula and drying and curing parameters, this invention significantly reduces the release of harmful substances such as formaldehyde and volatile organic compounds, meeting the environmental protection standards for automotive interiors.

[0020] 5. The various process steps of this invention are not adjusted in isolation, but form a closely connected technical synergy system. The performance improvement is stable and reproducible, and it can cover the usage needs of different automotive interior scenarios. It provides an efficient, stable and environmentally friendly technical path for the large-scale production of automotive sound insulation cotton and has broad application prospects. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1: Raw material proportions by weight: The composition includes: 60 parts of polyester staple fiber with a length of 38 mm and a fineness of 1.5 dtex; 30 parts of flame-retardant viscose staple fiber with a length of 32 mm, a fineness of 2.0 dtex, and a limiting oxygen index (LOI) ≥ 28%; and 10 parts of glass staple fiber with a length of 25 mm and a fineness of 3.0 dtex. The auxiliary components include: 0.5 parts of antistatic agent alkyl phosphate salt and 0.3 parts of coupling agent silane coupling agent KH-550.

[0023] Preparation steps: (1) Opening and mixing: The above raw materials are put into the opening machine and a two-stage opening process is adopted. The first stage opening speed is 600r / min and the time is 3min, and the second stage opening speed is 800r / min and the time is 2min, to ensure that the fibers are fully loosened and mixed evenly without clumping.

[0024] (2) Carding the mixed fibers after opening them into a carding machine with a carding speed of 15m / min, a carding cloth model of AC2030, a web thickness of 12mm, and a web uniformity deviation of ≤±5%.

[0025] (3) The needle punching process uses a double needle punching machine with an upper and lower needle punching density of 200 needles / cm. 2 The needle-punching depth is 10mm, the needle-punching frequency is 800 times / min, the net-supporting speed is 5m / min, and the density of the sound insulation cotton blank after molding is 300g / m³. 2 Thickness 10mm.

[0026] (4) The flame retardant liquid is prepared for the post-flame retardant treatment. The flame retardant liquid components are: ammonium polyphosphate (APP) with a polymerization degree n≥100015%, pentaerythritol (PER) 5%, melamine (MEL) 3%, and deionized water 77%. The needle-punched green body is immersed in the flame retardant liquid at a temperature of 60℃ for 20 minutes. Ultrasonic assistance is used during the immersion process at a frequency of 40kHz and a power of 100W to ensure that the flame retardant liquid fully penetrates into the fiber gaps. Then, the liquid is squeezed at a pressure of 0.3MPa, and the amount of flame retardant liquid adhering to the green body is 80% of the green body mass.

[0027] (5) The drying and curing process adopts a segmented drying process. The first stage pre-drying temperature is 80℃ and the time is 30min; the second stage main drying temperature is 120℃ and the time is 60min; the third stage curing temperature is 150℃ and the time is 20min. The moisture content after drying is ≤3%.

[0028] (6) Cut the finished product into standard samples according to the size requirements of automotive sound insulation cotton.

[0029] Example 2: Raw material proportions by weight: 40 parts of polyester staple fiber with a length of 38 mm and a fineness of 1.5 dtex; 25 parts of modified polypropylene staple fiber with a length of 40 mm, a fineness of 1.2 dtex, grafted with maleic anhydride and a grafting rate of ≥2%; 25 parts of flame-retardant viscose staple fiber with a length of 32 mm, a fineness of 2.0 dtex and an LOI of ≥28%; 10 parts of glass staple fiber with a length of 25 mm and a fineness of 3.0 dtex; auxiliary components: 0.8 parts of antistatic agent alkyl phosphate salt; 0.5 parts of coupling agent silane coupling agent KH-560.

[0030] Preparation steps: (1) The loosening characteristics of the mixed cotton and modified polypropylene fiber were combined. The opening speed of the second stage was adjusted to 550 r / min for the first stage and 750 r / min for the second stage. The remaining parameters were the same as in Example 1 to ensure that the different fiber components were fully mixed without stratification.

[0031] (2) The fiber ratio was adapted and adjusted for carding and web formation. The carding speed was adjusted to 14m / min and the web thickness was adjusted to 13mm. The remaining parameters were the same as in Example 1 to ensure the uniformity of the web surface and improve the subsequent needle punching effect.

[0032] (3) The parameters for needle punching, post-flame retardant treatment, drying and curing, and finished product cutting are completely consistent with those in Example 1. By controlling a single variable, the performance improvement brought about by the optimization of composite fiber components is highlighted, ensuring the technical relevance between this example and Example 1, and verifying the actual effect of component adjustment.

[0033] Example 3: Raw material ratio: Completely consistent with Example 2, this example focuses on the performance improvement brought about by adjusting the needle punching process parameters through single variable control, ensuring a close connection between this example and Example 2, and highlighting the practical value of process adjustment.

[0034] Preparation steps: (1) The opening and blending steps and the carding and web forming steps are the same as in Example 2, ensuring the consistency of the fiber substrate and providing a stable foundation for the optimization of the needle punching process.

[0035] (2) The needle punching process uses a double needle punching machine with a gradient needle punching density of 180 needles / cm² in the front section and 220 needles / cm² in the middle section. 2 200 stitches / cm at the back 2 It features variable needle-punching depths of 8mm in the front section, 11mm in the middle section, and 10mm in the rear section, a needle-punching frequency of 850 times / min, a net-supporting speed of 4.5m / min, and a final sound insulation cotton blank density of 320g / m³. 2 The thickness is 10mm; the gradient needle-punching design can create a reasonable pore gradient between the surface layer and the core layer of the sound insulation cotton, which can both ensure mechanical strength and improve the sound insulation effect.

[0036] (3) The post-flame retardant treatment relies on the optimized pore structure, which significantly improves the penetration efficiency of the flame retardant liquid. Therefore, the soaking time is shortened to 15 min. The remaining parameters are the same as in Example 2, achieving synergistic optimization of process efficiency and performance.

[0037] (4) The drying and curing steps and the finished product cutting steps are the same as in Example 2 to ensure process continuity and verify the synergistic effect of needle punching parameter adjustment, fiber composition and flame retardant treatment.

[0038] Example 4: Raw material ratio: Completely consistent with Example 3, this example focuses on the performance improvement brought about by the optimization of the flame retardant treatment system through single variable control, ensuring a close connection between this example and Example 3, and highlighting the practical significance of the flame retardant system upgrade.

[0039] Preparation steps: (1) The opening, blending, carding and needle punching of cotton are the same as in Example 3, which ensures the stability of the substrate and pore structure and provides a suitable basis for the upgrade of the flame retardant system.

[0040] (2) The post-flame retardant treatment is prepared with an environmentally friendly flame retardant liquid. The components are: ammonium polyphosphate (APP) with a polymerization degree n≥80018%, pentaerythritol (PER) 4%, nano magnesium hydroxide with a particle size of 50-100nm 2%, and deionized water 76%. The soaking temperature is 55℃, the soaking time is 15min, the ultrasonic auxiliary parameters remain unchanged, the extrusion pressure is 0.35MPa, and the amount of flame retardant liquid adhering is 75% of the body mass. The introduction of environmentally friendly synergists can form a multi-element synergistic flame retardant effect and improve flame retardant durability.

[0041] (3) Drying and curing: Combining the curing characteristics of environmentally friendly flame retardant liquid, the temperature gradient is optimized. The first stage of pre-drying temperature is 75℃ and time is 35min; the second stage of main drying temperature is 115℃ and time is 65min; the third stage of curing temperature is 145℃ and time is 25min. After drying, the moisture content is ≤3%, ensuring that the flame retardant components are fully cured without damaging the fiber structure.

[0042] (4) The finished product cutting is the same as in Example 3, completing the optimization and upgrading of the entire process chain.

[0043] The following comparative examples correspond to existing technical solutions and typical combinations of existing technologies, respectively. All of them take the core process of Example 1 of this technical solution as the reference benchmark. By omitting the key optimization design of this solution, the performance is compared with the example of this solution to verify the optimization effect and application advantages of this solution.

[0044] Comparative Example 1: In contrast to the conventional method of preparing automotive sound insulation cotton using a single fiber in the existing technology, the raw material ratio only uses 100 parts of polyester short fiber with a length of 38mm and a fineness of 1.5dtex, and the auxiliary components are the same as in Example 1; The preparation steps, including opening, combing, needle punching, flame retardant treatment, drying, and cutting, are completely consistent with those in Example 1.

[0045] This solution represents a typical process for a single-fiber system in existing technologies. Its core shortcoming is that it cannot simultaneously achieve sound insulation, mechanical properties, and flame retardant properties, and its overall performance is insufficient to meet the requirements for use in automotive interiors.

[0046] Comparative Example 2: The raw material ratio is the same as in Example 1, corresponding to existing technologies that attempt to combine composite fibers with traditional needle punching processes. In the preparation steps, the needle punching process uses a single needle punch density of 200 needles / cm², which is achieved using existing traditional techniques. 2 The needle insertion depth is fixed at 10mm with no gradient setting, and the remaining steps are the same as in Example 1.

[0047] This solution represents a typical case where there is a lack of needle-punching parameter optimization in the existing technology portfolio. Its core shortcomings are unreasonable pore structure and uneven penetration of flame retardant liquid, resulting in limited improvement in overall performance.

[0048] Comparative Example 3: The raw material ratio is the same as in Example 1, corresponding to the existing technology that combines composite fibers with a single flame retardant system. In the preparation steps, the post-flame retardant treatment uses an existing single ammonium polyphosphate flame retardant liquid with a mass concentration of 20%, without pentaerythritol and melamine synergistic components. The soaking and squeezing parameters are the same as in Example 1, and the remaining steps remain unchanged.

[0049] This solution represents a typical case of a lack of synergy in existing flame retardant systems. Its core deficiency is insufficient flame retardant performance and durability, which cannot meet the flame retardant requirements for long-term use of automotive interiors.

[0050] Comparative Example 4: The raw material ratio is the same as that in Example 1, corresponding to the existing technology that uses a flame-retardant treatment before needle punching. The preparation steps were adjusted to first soak the loosened cotton in flame retardant liquid, then comb it into a web and needle punch it into shape. The remaining process parameters were the same as in Example 1.

[0051] This solution represents a typical case of unreasonable timing of flame retardant treatment in existing technology combinations. Its core shortcomings are that it easily leads to damage to the fiber structure and loss of flame retardant components, resulting in unstable flame retardant effect and impaired mechanical properties.

[0052] Comparative Example 5: In contrast to existing technologies where the raw material ratio exceeds a reasonable range, the raw material ratio is 20 parts polyester staple fiber, 10 parts flame-retardant viscose staple fiber, and 70 parts glass staple fiber. The proportion of glass fiber exceeds the protection scope of this technical solution, and the auxiliary components are the same as in Example 1. The preparation steps are the same as in Example 1.

[0053] This solution represents a typical case where the raw material ratio lacks scientific design in existing technologies. Its core deficiency is a serious imbalance between mechanical properties and sound insulation performance, making it unsuitable for the use scenarios of automotive interiors.

[0054] Performance testing and results analysis: Test sample: The finished automotive sound insulation cotton products prepared in Examples 1-4 and Comparative Examples 1-5 were all cut into standard samples. All samples were required to remove surface impurities and fuzz to ensure that the surface was flat, undamaged, and of uniform thickness. The size was uniformly 300mm×300mm×10mm (subsequent tests were conducted according to the corresponding standards). Three parallel samples were prepared for each group of samples. The size deviation of the parallel samples was ≤±0.5mm. During the test, the relative deviation of the test results of the parallel samples was ≤10%. The average value of the test results was taken to ensure the reliability, repeatability, and representativeness of the test data.

[0055] Test items and standards: (1) The limiting oxygen index (LOI) of flame retardant performance was tested according to GB / T2406.2-2009 "Determination of burning behavior by oxygen index method for plastics - Part 2: Room temperature test". The sample size was 120mm×10mm×10mm, and there were 5 samples in each group. The test environment temperature was 23±2℃, the relative humidity was 50±5%RH, and the oxygen concentration adjustment accuracy was ±0.1%. The oxygen index value of each sample was recorded and the average value was taken. The vertical burning performance was tested according to GB / T8333-2022 "Determination of burning performance of plastics - Horizontal and vertical methods". The sample size was 125mm×13mm×10mm, and there were 5 samples in each group. The ignition source was a methane flame with a flame height of 20mm±2mm and an ignition time of 15s. The burning rate, flame spread time and flameless burning time of each sample were accurately recorded. The average value of the burning rate was taken and the unit was accurate to 1mm / min.

[0056] (2) The sound insulation performance shall be tested in accordance with GB / T18696.2-2002 "Measurement of sound absorption coefficient and sound insulation in acoustic impedance tubes - Part 2: Transfer function method". The sample size is 100 mm in diameter and 10 mm in thickness. There are 3 samples in each group. The test environment temperature is 23±2℃ and the relative humidity is 50±5%RH. The test frequency range is 100Hz-4000Hz and the frequency resolution is 1Hz. The sample installation must be tightly attached to the inner wall of the impedance tube without gaps and sound leakage. Each sample is tested 3 times at each frequency point. The average sound absorption coefficient is taken and the weighted sound insulation RW is calculated. The result is accurate to 1dB.

[0057] (3) Mechanical properties: Tensile strength was tested according to GB / T1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets". Type II dumbbell-shaped specimens were used, with a total length of 150 mm, gauge length of 50 mm, gauge length width of 10 mm, and thickness of 10 mm. There were 5 specimens in each group (3 longitudinal and 2 transverse). The test environment temperature was 23±2℃, relative humidity was 50±5%RH, tensile speed was 50 mm / min±5 mm / min, and the initial clamping distance was 100 mm. The tensile strength at break of each specimen was recorded. The tensile strength was measured in both longitudinal and transverse directions, with the average value taken to an accuracy of 0.1 MPa. The tear strength was tested according to GB / T1040.4-2006 "Determination of tensile properties of plastics - Part 4: Test conditions for isotropic and orthotropic fiber-reinforced composite materials". The test specimens were trouser-shaped tear specimens with a total length of 150 mm, a leg length of 75 mm, a width of 25 mm, and a thickness of 10 mm. There were 5 specimens in each group. The test speed was 100 mm / min ± 10 mm / min. The tear strength of each specimen was recorded, and the average value was taken to an accuracy of 0.1 MPa.

[0058] (4) Temperature resistance and durability are tested according to GB / T7141-2021 "Test Method for Thermal Aging of Plastics". The sample size is 100mm×50mm×10mm. There are 6 samples in each group (3 for pre-aging test and 3 for post-aging test). The samples are placed in a constant temperature chamber with an aging temperature of 120℃±2℃, a temperature uniformity of ±3℃, and an aging time of 1000h. During the aging process, the samples should be kept away from each other and the chamber wall. After aging, the samples are taken out and placed in a standard ambient temperature of 23±2℃ and a relative humidity of 50±5%RH for 24h. Then, the flame retardant performance (LOI) and mechanical properties (tensile strength) test standards are tested according to the above standards. The LOI retention rate and tensile strength retention rate are calculated respectively, and the retention rate is accurate to 1%.

[0059] (5) Environmental performance: Formaldehyde emission was tested according to GB / T27630-2011 "Guidelines for Evaluation of Air Quality in Passenger Cars". The sample size was 50mm×50mm×10mm, the sample mass was 100g±5g, and the number of samples was 3 per group. The test environment temperature was 23±2℃, the relative humidity was 50±5%RH, and the air pressure was 86kPa-106kPa. The sample was placed in a 10L sealed test bag, sealed and left to stand for 24h. The formaldehyde concentration in the bag was detected by gas chromatograph with a detection accuracy of 0.01mg / kg. The average value of the 3 samples was taken as the final result. The content of volatile organic compounds (VOCs) was tested according to the test method in GB / T27630-2011. Sample preparation was the same as for formaldehyde release testing. Detection was performed using thermal desorption-gas chromatography / mass spectrometry (GC / MS), with a detection range of 0.01 g / m³. 2 -10g / m 2 Quantitative accuracy 0.01 g / m 2 Record the total VOC content and take the average value as the final result.

[0060] The test results are shown in Table 1 below:

[0061] Test Result Analysis: (1) Example 2 optimizes the composite fiber composition based on Example 1, increasing longitudinal tensile strength by 25%, transverse tensile strength by 28%, and weighted sound insulation by 10.5%, effectively improving the problem of insufficient synergy between mechanical and sound insulation performance in Example 1; Example 3 addresses the insufficient adaptability of the pore structure in Example 2 by adjusting the needle punching process parameters, resulting in a 12.5% ​​reduction in vertical burning rate and a further 8.6% increase in longitudinal tensile strength. The optimization of the pore structure makes the flame retardant liquid penetration more uniform, achieving precise adaptation between the molding process and the fiber composition; Example 4 upgrades the flame retardant system, achieving a 97% LOI retention rate and a 30% reduction in formaldehyde release, significantly improving durability and environmental compatibility while ensuring flame retardant performance. Each subsequent example is based on the technical foundation of the previous example, making reasonable adjustments and optimizations to address its potential shortcomings. The performance improvement stems from the systematic adaptation of each process step, rather than a simple parameter superposition, forming a complete technical synergy system. The process details and parameters of each step are fully disclosed and can be stably reproduced.

[0062] (2) Comparative Example 1, as an existing single-fiber system process, has a limiting oxygen index of only 24.8% and a weighted sound insulation of only 26 dB, all of which are significantly inferior to the embodiments of this scheme. This shows that the scheme fundamentally improves the problem of performance imbalance of single-fiber materials through the rational design of the multi-component composite fiber system. Comparative Example 2, as a simple combination of existing composite fibers and traditional needle punching process, lacks gradient needle punching parameter design, resulting in a 7.4% decrease in limiting oxygen index and a 10.5% decrease in weighted sound insulation compared to Example 1. This highlights the rationality and necessity of the needle punching process adjustment in this scheme, achieving precise matching between the molding process and fiber components. Comparative Example 3, as a combination of existing composite fibers and a single flame retardant system, has significant deficiencies in both flame retardant performance and durability. With an OI of only 28.5% and a retention rate of only 82% after aging, it cannot meet the long-term use requirements of automotive interiors. However, this solution effectively overcomes the performance limitations of a single flame retardant through a multi-component synergistic flame retardant system design. Comparative Example 4, as an existing pre-needling flame retardant treatment process, suffers from fiber structure damage and overall performance degradation due to unreasonable timing of the flame retardant treatment, with a longitudinal tensile strength of only 2.0 MPa and a weighted sound insulation of 30 dB. This verifies the scientific nature of the post-needling flame retardant treatment process used in this solution, fundamentally avoiding the problems of fiber structure damage and loss of flame retardant components. Comparative Example 5, as an existing solution with unreasonable raw material ratios, shows a serious imbalance between mechanical properties and sound insulation performance, further proving the scientific rationality of the raw material ratio range in this solution, rather than blindly expanding the ratio range.

[0063] (3) Through the gradual optimization and performance verification of Examples 1 to 4, this technical solution scientifically defines the applicable range of raw material ratios and process parameters. This range can cover the usage requirements of different automotive interior scenarios, and each solution within the range can achieve excellent comprehensive performance. The composite fiber composition is specified as 30-60 parts polyester fiber, 20-30 parts flame-retardant viscose fiber, and 5-15 parts glass fiber, where glass fiber can be replaced with 20-30 parts modified polypropylene fiber, and the needle-punching density is 180-220 needles / cm². 2 The flame retardant liquid contains 12%-20% APP by mass and 2%-8% PER+MEL or nano magnesium hydroxide as synergists. The scope of application is defined based on the progressive optimization and repeated verification of each embodiment, ensuring the rationality and applicability of the scope. All technical solutions are based on the same core process logic, closely connected to form a complete system, which can be stably reproduced and has excellent comprehensive performance.

[0064] (4) Existing automotive sound insulation cotton processes generally suffer from performance imbalances, poor process adaptability, and insufficient durability. Single fiber systems struggle to simultaneously achieve sound insulation, mechanical strength, and flame retardant properties, and some combined processes are merely simple superpositions without forming an effective synergistic effect. This technical solution achieves simultaneous improvement in the flame retardant performance, sound insulation effect, mechanical strength, and temperature resistance of sound insulation cotton through a series of reasonable adjustments, including multi-component composite fiber ratio design, gradient needle punching process optimization, and synergistic flame retardant system upgrade. All performance aspects meet the stringent requirements of automotive interior materials. The parameter settings for each process step in the solution are detailed and clear, and the raw material specifications and selections are transparent, fully disclosed, and reproducible. This provides an efficient, stable, and environmentally friendly technical path for the production of automotive interior sound insulation cotton, possessing good practical application value and adaptability.

[0065] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention.

Claims

1. A process for flame retardant treatment of needled formed composite fibrous automotive acoustic wool, characterized in that, Includes the following steps: (1) Opening and blending: The composite fiber raw materials and auxiliary components are put into the opening machine for secondary opening treatment; (2) Carding into a web: The opened mixed fibers are fed into a carding machine and carded to form a uniform fiber web; (3) Needle punching: The fiber web is needle punched using an upper and lower double needle punching machine to obtain a sound insulation cotton blank; (4) Post-flame retardant treatment: The sound insulation cotton blank is immersed in flame retardant liquid, and after ultrasonic-assisted soaking, it is squeezed out. (5) Drying and curing: The extruded green body is dried and cured using a segmented drying process; (6) Finished product cutting: The dried and cured blank is cut according to the preset size to obtain the finished automotive sound insulation cotton; the composite fiber raw material is composed of one of polyester short fiber, flame retardant viscose short fiber, glass short fiber and modified polypropylene short fiber; the flame retardant liquid includes ammonium polyphosphate and synergist.

2. The process according to claim 1, characterized in that, In the composite fiber raw material, by mass percentage, polyester staple fiber is 30 to 60 parts, flame-retardant viscose staple fiber is 20 to 30 parts, glass staple fiber is 5 to 15 parts, or modified polypropylene staple fiber is 20 to 30 parts.

3. The process of claim 1, wherein, The auxiliary components are an antistatic agent and a coupling agent, wherein the antistatic agent is an alkyl phosphate salt and the coupling agent is a silane coupling agent.

4. The process of claim 1, wherein, The first-stage opening speed of the two-stage opening is 550 to 600 revolutions per minute, with a processing time of 3 minutes; the second-stage opening speed is 750 to 800 revolutions per minute, with a processing time of 2 minutes.

5. The process of claim 1, wherein, The speed of combing and forming the web is 14 to 15 meters per minute, the web thickness is 12 to 13 millimeters, and the needle cloth model is AC2030.

6. The process of claim 1, wherein, The needle-punching process has a needle density of 180 to 220 needles per square centimeter, a needle depth of 8 to 11 millimeters, a needle frequency of 800 to 850 times per minute, and a net-lifting speed of 4.5 to 5 meters per minute.

7. The process of claim 6, wherein, The needle density is set in a gradient manner, with 180 needles per square centimeter in the front section, 220 needles per square centimeter in the middle section, and 200 needles per square centimeter in the rear section; the needle depth is set in a gradient manner, with 8 mm in the front section, 11 mm in the middle section, and 10 mm in the rear section.

8. The process of claim 1, wherein, The mass concentration of ammonium polyphosphate in the flame retardant liquid is 12 to 20%, and the mass concentration of the synergist is 2 to 8%. The synergist is one or more of pentaerythritol, melamine, and nano magnesium hydroxide.

9. The process of claim 1, wherein, The ultrasonic-assisted soaking has a frequency of 40 kHz, a power of 100 watts, a soaking temperature of 55 to 60 degrees Celsius, a soaking time of 15 to 20 minutes, a squeezing pressure of 0.3 to 0.35 MPa, and a flame retardant liquid adhesion amount of 75 to 80% of the body mass.

10. The process of claim 1, wherein, The segmented drying process includes three stages: pre-drying, main drying, and curing. The pre-drying temperature is 75 to 80 degrees Celsius and the time is 30 to 35 minutes. The main drying temperature is 115 to 120 degrees Celsius and the time is 60 to 65 minutes. The curing temperature is 145 to 150 degrees Celsius and the time is 20 to 25 minutes. The moisture content of the blank after drying does not exceed 3%.

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