Production process of multi-layer gradient composite automobile air conditioner filter element

Abstract

The invention relates to the technical field of automobile air conditioner filter elements, in particular to a production process of a multi-layer gradient composite automobile air conditioner filter element, a gradient structure of the multi-layer gradient composite automobile air conditioner filter element realizes active regulation and control on an airflow field and a pollutant capturing path: a loose outer surface serves as a pre-filtering layer to effectively intercept large particles and uniformize airflow; the fiber compactness and the nanopore / adsorption site density which are gradually enhanced inwards are sequentially responsible for fine filtration and efficient adsorption of VOC molecules, so that all functions of a traditional multi-layer structure are realized in a single material system.

Description

Technical Field

[0001] This invention relates to the field of automotive air conditioning filter technology, and in particular to the production process of multi-layer gradient composite automotive air conditioning filters. Background Technology

[0002] Automotive air conditioning filters need to combine particulate matter filtration and volatile organic compound (VOC) adsorption functions. Currently, commonly used filters employ a multi-layered composite structure, integrating functions through the stacking of a pre-filter layer, main filter layer, adsorption layer, and support layer (see Comparative Example 1). While this method can achieve both filtration and adsorption, it has the following significant shortcomings: (1) The preparation process is complicated: each layer needs to be prepared separately and then laminated, hot-pressed or glued together, which involves many steps and low efficiency; (2) Interlayer bonding is prone to failure: Different material layers are prone to peeling under vibration and temperature change environments, affecting the overall structural stability and service life; (3) The gradient function cannot be continuously controlled: Each layer has an independent function, and it is impossible to achieve a continuous gradient change in pore size and chemical properties from the outside to the inside, resulting in uneven airflow distribution and low utilization of dust holding space; To address the aforementioned technical shortcomings, a solution is proposed. Summary of the Invention

[0003] The purpose of this invention is to provide a multi-layer gradient composite automotive air conditioning filter manufacturing process to solve the aforementioned technical defects.

[0004] The objective of this invention can be achieved through the following technical solution: a multi-layer gradient composite automotive air conditioning filter manufacturing process, comprising the following steps: S1. Preparation of spinning solution: Under normal temperature conditions, dissolve the nitrile polymer in a polar organic solvent to prepare a spinning solution containing nitrile polymer, and then subject the spinning solution to static and degassing treatment. S2. Gradient web formation: Under the condition that the nozzle and the receiving device maintain a fixed distance, the spinning solution is continuously formed into a web by adjusting the feeding rate and web formation conditions in stages, so that the resulting fiber web presents a micron-pore gradient structure that is gradually denser from the outside to the inside along the thickness direction. S3. Drying and shaping: The fiber web is dried to reduce the residual solvent content to a predetermined range, thereby obtaining a dried sheet. S4. Unilateral gradient stabilization treatment: The dried sheet is placed in a unilateral heating environment and stabilized in an oxidizing atmosphere, so that the degree of cyclization and crosslinking conversion increases from the outside to the inside along the thickness direction of the sheet. S5. Unilateral gradient carbonization treatment: The sheet after step S4 is subjected to carbonization treatment under an inert atmosphere, so that the degree of carbonization, the proportion of nanopores and the density of adsorption sites of the sheet increase from the outside to the inside along the thickness direction, thereby obtaining a gradient fiber sheet.

[0005] Furthermore, between steps S3 and S4, a crosslinking treatment step is included to form a crosslinked reinforcement structure inside the fiber and at the fiber contact points.

[0006] Furthermore, the crosslinking treatment is electron beam irradiation crosslinking, with an irradiation dose of 20-80 kGy.

[0007] Furthermore, the nitrile-containing polymer mentioned in step S1 is a polyacrylonitrile copolymer.

[0008] Furthermore, the polyacrylonitrile copolymer is copolymerized from acrylonitrile, methyl methacrylate and itaconic acid, wherein the mass ratio of the three is 94:5:1.

[0009] Furthermore, the nitrile-containing polymer mentioned in step S1 is a polyacrylonitrile homopolymer.

[0010] Furthermore, the nitrile-containing polymer mentioned in step S1 is a blend of polyacrylonitrile copolymer and polyacrylonitrile homopolymer, with a mass ratio of 60:40 to 80:20.

[0011] Furthermore, the stabilization treatment temperature in step S4 is 230-255℃, and the holding time is 30-90 min; the carbonization treatment temperature in step S5 is 550-650℃, and the holding time is 20-40 min.

[0012] Furthermore, the gradient fiber sheet has a chemical transformation gradient and pore structure gradient that gradually changes from the outside to the inside along the thickness direction, wherein the degree of cyclization and aromatization of the inner surface is higher than that of the outer surface, and the specific surface area and the proportion of nanopores of the inner surface are higher than those of the outer surface.

[0013] Furthermore, the filter adsorption assembly is formed by bonding two gradient fiber sheets together, with the high-reinforcement ends of the two gradient fiber sheets facing each other, so that both outer surfaces of the filter adsorption assembly are low-reinforcement ends. The two gradient fiber sheets are fixed by perimeter sealing, with a sealing width of 1-5 mm. The filter adsorption assembly is embedded in the embedding groove of the support frame and fixed by hot melting or ultrasonic welding, so that the support frame and the filter adsorption assembly fixed in the support frame constitute an automotive air conditioning filter.

[0014] The beneficial effects of this invention are as follows: This invention utilizes in-situ spinning of nitrile-containing polymers in a single solvent system, and innovatively employs programmed gradient electrospinning and unilateral gradient heat treatment processes. This allows the fiber web to form a physical gradient of sparse outer layers and dense inner layers during the forming stage. Subsequently, in a unilateral programmed temperature rise under an air / nitrogen atmosphere, a continuous gradual change in the degree of cyclization / aromatication is achieved from the outside to the inside. Ultimately, a functional body with a continuous gradient in pore structure and surface chemical properties is constructed within a single sheet material. This "reaction-structure synchronous gradient" process path not only eliminates multiple steps such as separate preparation, lamination, hot pressing, or adhesive bonding of multilayer materials, greatly simplifying the process, improving production efficiency and consistency, but also fundamentally eliminates the risk of interlayer delamination, ensuring the overall reliability of the filter element structure under long-term vibration and humid heat environments.

[0015] This gradient structure enables active control of airflow field and pollutant capture path: the loose outer surface acts as a pre-filter layer, effectively intercepting large particles and uniformly distributing airflow; the progressively increasing fiber density and nanopore / adsorption site density are responsible for fine filtration and efficient adsorption of VOC molecules, thus realizing all the functions of traditional multilayer structures in a single material system. Attached Figure Description

[0016] The invention will now be further described with reference to the accompanying drawings; Figure 1 This is a flowchart of the production process system of the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0018] The basic embodiment of the multi-layer gradient composite automotive air conditioning filter manufacturing process is described in the following steps: S1: Preparation and Defoaming of Stock Solution In an environment with a temperature of 25 degrees Celsius and a relative humidity of no more than 60%, a dimethylformamide spinning solution was prepared with a mass fraction of 12% of a nitrile polymer. The nitrile polymer was added to the dimethylformamide and stirred at 60 degrees Celsius until completely dissolved. After dissolution, the solution was allowed to stand for 30 minutes and then degassed under vacuum for 10 minutes at a pressure of -0.08 MPa to obtain the spinning solution. S2: Three-stage programmatic gradient networking Under continuous web-forming conditions, the distance between the nozzle and the collecting network was set to 25 cm, and the collecting drum rotation speed was set to 30 rpm. A single-sheet gradient fiber web was formed through three stages of continuous deposition: the first stage had a feed rate of 7.0 ml / min, an air pressure of 0.18 MPa, and a deposition time of 4 minutes; the second stage had a feed rate of 6.0 ml / min, an air pressure of 0.22 MPa, and a deposition time of 4 minutes; the third stage had a feed rate of 5.0 ml / min, an air pressure of 0.26 MPa, and a deposition time of 4 minutes. Continuous collection yielded a micron-pore gradient sheet with a loose outer surface and a dense inner surface. S3: Drying and Shaping The S2 sheet was dried for 30 minutes under hot air circulation at 80 degrees Celsius; then vacuum dried for 2 hours at 60 degrees Celsius and -0.08 MPa to ensure that the mass fraction of residual solvent did not exceed 0.5 percent, thus obtaining a dried and shaped sheet. S4: One-sided stabilization or cyclic gradient processing The S3 sheet is placed in a single-sided heating device with the high-reinforcement end (inner surface) facing the heating surface and a heat insulation shield is set on the windward side; air is introduced and the temperature is raised to 240 degrees Celsius at a rate of 2 degrees Celsius per minute, and then kept at that temperature for 60 minutes, so that the degree of cyclization and cross-linking conversion increases along the thickness direction. S5: Unilateral aromatization or char-like gradient treatment Without changing the orientation of S4, switch to nitrogen protection at a flow rate of 10 liters per minute; heat to 600 degrees Celsius at a rate of 5 degrees Celsius per minute and hold for 30 minutes; then cool with the furnace to no more than 80 degrees Celsius and remove from the furnace to obtain a gradient sheet with an increasing degree of carbonization along the thickness direction and an increasing proportion of nanopores and density of adsorption sites along the thickness direction. S6: Double-sided bonding frame fixing and filter element molding Cut the S5 gradient sheet to match the size of the support frame; take two gradient sheets and bond the two high-reinforcement ends (inner surfaces) together so that both outer surfaces of the double-sided assembly are low-reinforcement ends; use peripheral edge sealing for fixation, with an edge sealing width of 3 mm, and the edge sealing method is hot melt sealing or ultrasonic welding; embed the double-sided bonded assembly into the embedding groove of the automotive air conditioning filter support frame, and fix the periphery by hot melt or ultrasonic spot welding to obtain the finished filter; Example 1 The difference from the basic embodiment is that the nitrile-containing polymer in S1 is replaced with a polyacrylonitrile copolymer, wherein the mass ratio of acrylonitrile, methyl methacrylate and itaconic acid is 94:5:1; The heating and holding conditions described in S4 are changed to heating to 230 degrees Celsius at a rate of 2 degrees Celsius per minute and holding for 30 minutes; The heating and holding conditions described in S5 are changed to heating to 550 degrees Celsius at a rate of 5 degrees Celsius per minute and holding for 20 minutes.

[0019] Example 2 The difference from the basic embodiment is that the nitrile-containing polymer in S1 is replaced with a polyacrylonitrile copolymer, wherein the mass ratio of acrylonitrile, methyl methacrylate and itaconic acid is 94:5:1.

[0020] Example 3 The difference from the basic embodiment is that the nitrile-containing polymer in S1 is replaced with a polyacrylonitrile copolymer, wherein the mass ratio of acrylonitrile, methyl methacrylate and itaconic acid is 94:5:1; The heating and holding conditions described in S4 are changed to heating to 255 degrees Celsius at a rate of 2 degrees Celsius per minute and holding for 90 minutes; The heating and holding conditions described in S5 are changed to heating to 650 degrees Celsius at a rate of 5 degrees Celsius per minute and holding for 40 minutes.

[0021] Example 4 The difference from the basic embodiment is that the nitrile-containing polymer in S1 is replaced with a polyacrylonitrile homopolymer, which contains only acrylonitrile repeating units.

[0022] Example 5 The difference from the basic embodiment is that: the nitrile-containing polymer in S1 is replaced by a blend of polyacrylonitrile copolymer and polyacrylonitrile homopolymer, wherein the mass ratio of polyacrylonitrile copolymer to polyacrylonitrile homopolymer is 70 to 30; A new step S3.5 is added between S3 and S4. This step is a crosslinking treatment: the dried and shaped S3 sheet is placed in an electron beam irradiation device for crosslinking, and the irradiation dose is 40 kGry. After irradiation, it is left to stand at 25 degrees Celsius for 30 minutes to allow the crosslinking points to form in situ inside the fiber and at the fiber contact points without forming an independent adhesive layer. Comparative Example 1 (1) The filter material structure is changed to a multi-layer composite structure, including a pre-filtration layer, a main filtration layer, an adsorption layer and a support layer; (2) The preparation process is changed to multi-layer lamination followed by hot pressing or adhesive bonding to form a layered composite, then the pleats are cut and installed into a support frame for fixation. The filtration and adsorption functions are now achieved by stacking multiple layers of materials, rather than by the thickness gradient of a single sheet; traditional production processes involve more steps and are more complex.

[0023] Comparative Example 2 The differences from the basic embodiment are as follows: S1 The nitrile-containing polymer is replaced with a polyacrylonitrile copolymer, wherein the mass ratio of acrylonitrile, methyl methacrylate and itaconic acid is 94:5:1. S4 The single-sided treatment is changed to full-thickness uniform treatment, that is, the windward side heat insulation shield is removed and double-sided or overall uniform heating is adopted, so that it is heated to 240 degrees Celsius at 2 degrees Celsius per minute and kept at that temperature for 60 minutes. The single-sided treatment described in S5 is changed to a full-thickness uniform treatment, that is, heating to 600 degrees Celsius at a rate of 5 degrees Celsius per minute and holding for 30 minutes; only PAN copolymer, without the step of full-thickness uniform treatment with conversion gradient.

[0024] Comparative Example 3 The differences from the basic implementation are as follows: The nitrile-containing polymer in S1 is replaced by a blend of polyacrylonitrile copolymer and polyacrylonitrile homopolymer, wherein the mass ratio of polyacrylonitrile copolymer to polyacrylonitrile homopolymer is 70:30; the crosslinking treatment step S3.5 added in Example 5 is cancelled in the implementation process, that is, electron beam irradiation crosslinking is not performed.

[0025] Comparative Example 4 The differences from the basic embodiment are as follows: the double-sided bonding direction described in S6 is changed to an incorrect bonding direction, that is, the low-reinforcement ends of the two gradient sheets are bonded relative to each other or the high-reinforcement ends of the two gradient sheets are bonded outwards, so that the double-sided assembly does not have a stepwise reinforcement relationship from the two outer surfaces inwards; the PAN copolymer is blended with the PAN homopolymer; it is not cross-linked, which is due to the incorrect double-sided bonding direction and does not satisfy the "stepwise reinforcement from the two outer surfaces inwards".

[0026] test S1: Sampling and Humidity Conditioning Three filter cartridges from Examples 1 to 5 and Comparative Examples 1 to 4 were taken as test samples and conditioned for 24 hours at a temperature of 23 ± 2 degrees Celsius and a relative humidity of 50 ± 10%. S2: Initial Pressure Loss Test Load the sample to be tested into the air duct test bench and set the volumetric flow rate to 150 cubic meters per hour or the rated air volume of the target vehicle model; record the initial pressure loss ΔP0 after the flow rate has stabilized for 5 minutes. S3: Staged Filtration Efficiency Test Under fixed flow conditions, the particle number concentrations at the upstream and downstream ends were determined by particle counting; the efficiency and overall efficiency for particle size segments of 0.3 μm, 1.0 μm, and 2.5 μm were calculated. S4: Dust Holding and Pressure Loss Growth Test Standard test dust was continuously loaded under constant mass concentration conditions; pressure loss ΔPt was recorded every 5 minutes; loading was stopped and the cumulative dust mass was recorded when the pressure loss reached 250 Pa or the vehicle's allowable final resistance; the pressure loss growth rate and dust holding capacity of each sample were compared. S5: VOC Dynamic Penetration Test Toluene was selected as a representative volatile organic compound and the upstream concentration C0 was set to 3 ppm. The downstream concentration C1 was continuously monitored under a fixed flow rate. The breakthrough time when C1 was divided by C0 to reach 5% and 50% was recorded and the dynamic adsorption capacity was calculated. S6: Gradient Validation Test Samples of the outer surface layer, middle layer and inner surface layer of a single gradient sheet were taken along the thickness direction. The cyclization and aromatization indicator parameters, specific surface area and pore size distribution were tested respectively. The ratio of nanopores from the outer surface to the inner surface and the density of adsorption sites were verified to increase stepwise. The double-sided laminated component was verified to have both outer surfaces as low-reinforcement ends and the middle interface as high-reinforcement ends. Test Results Table and Data Analysis Table 1. Validation results of structural gradient Note: For step S6 of the corresponding test, GI: conversion gradient index, the larger the value, the stronger the gradient; SSA ratio: specific surface area ratio, the larger the value, the stronger the inward nanopores and adsorption sites; assembly direction determination: whether the outer side is the low reinforcement end and the center is the high reinforcement end after double-sided bonding.

[0027]

[0028] Table 2 Filtration and Lifetime Performance Results Note: For steps S2–S4 of the corresponding test, ΔP0: initial pressure drop; η0.3, η1.0, η2.5: staged filtration efficiency; HC: dust holding capacity; k: average pressure drop growth rate.

[0029] Table 3. Results of VOC dynamic adsorption and penetration Note: For step S5 of the corresponding test, VOC: toluene; CO = 3 ppm; tB5%: 5% breakthrough time; tB50%: 50% breakthrough time; q: dynamic adsorption capacity.

[0030]

[0031] Data Analysis As shown in Table 1, the gradient sheets prepared by this invention (Examples 1-5) all successfully achieved chemical conversion gradients and pore structure gradients along the thickness direction. Their conversion gradient index (GI) and specific surface area ratio (SSA) were significantly higher than those of Comparative Example 2, which did not undergo gradient treatment. Examples 2-5, in particular, exhibited clear gradient characteristics and correct assembly orientation. In contrast, Comparative Example 4, due to incorrect bonding orientation, although the individual sheet material possessed a gradient, failed to achieve the functional distribution of "low reinforcement on the outer surface and high reinforcement in the center" in the final product configuration, leading to subsequent performance degradation.

[0032] Analysis of the filtration and lifespan performance results in Table 2 shows that the gradient structure design of this invention effectively balances the initial pressure drop ΔP0 and the dust holding life HC. Examples 2 (medium gradient) and 5 (crosslinked) exhibit the best overall performance: while maintaining moderate initial pressure drops (65 Pa and 62 Pa) and good filtration efficiencies (η0.3 reaching 60% and 65%), they achieved the highest dust holding capacity (130 g and 150 g) and the lowest pressure drop growth rate k (1.4 and 1.2 Pa·g). -1 This indicates that its resistance increases more slowly during use, resulting in a longer service life. In contrast, the ungraded comparative example 2 exhibited the highest initial pressure loss (95 Pa), the lowest dust holding capacity (80 g), and the fastest resistance increase (k = 2.5 Pa·g). -1 This demonstrates the crucial role of gradient structures in optimizing flow resistance and lifetime. Comparative Example 4, with its incorrect bonding direction, exhibits high initial efficiency, but its flawed structure results in extremely high flow resistance (ΔP0=110Pa), very poor dust holding capacity (HC=60g), and the shortest lifetime.

[0033] As shown in Table 3, the gradient treatment and correct assembly method of the material significantly improved the dynamic adsorption performance. The breakthrough times tB5% and tB50% of Examples 2–5 were significantly better than those of Comparative Example 2 without gradient, indicating that the gradient structure, through the progressively increasing density of adsorption sites from the outside to the inside, more efficiently utilized the internal space of the material and delayed VOC breakthrough. Example 5 (crosslinked) showed the highest dynamic adsorption capacity q (95 mg·g⁻¹). -1 This even approaches the level of traditional multilayer composite structures (Comparative Example 1), but with simpler process steps. This demonstrates that the monolithic gradient structure design of this invention can achieve VOC adsorption functionality comparable to complex multilayer structures while simplifying the process.

[0034] In summary, the gradient structure design, double-sided bonding assembly method, and optional cross-linking treatment of this invention work synergistically to achieve excellent improvements in filtration efficiency, service life, pressure drop characteristics, and VOC adsorption capacity of the resulting filter element.

[0035] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in the details for the sake of brevity.

[0036] This invention is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A manufacturing process for multi-layer gradient composite automotive air conditioning filters, characterized in that, Includes the following steps: S1. Preparation of spinning solution: Under normal temperature conditions, dissolve the nitrile polymer in a polar organic solvent to prepare a spinning solution containing nitrile polymer, and then subject the spinning solution to static and degassing treatment. S2. Gradient web formation: Under the condition that the nozzle and the receiving device maintain a fixed distance, the spinning solution is continuously formed into a web by adjusting the feeding rate and web formation conditions in stages, so that the resulting fiber web presents a micron-pore gradient structure that is gradually denser from the outside to the inside along the thickness direction. S3. Drying and shaping: The fiber web is dried to reduce the residual solvent content to a predetermined range, thereby obtaining a dried sheet. S4. Unilateral gradient stabilization treatment: The dried sheet is placed in a unilateral heating environment and stabilized in an oxidizing atmosphere, so that the degree of cyclization and crosslinking conversion increases from the outside to the inside along the thickness direction of the sheet. S5. Unilateral gradient carbonization treatment: The sheet after step S4 is subjected to carbonization treatment under an inert atmosphere, so that the degree of carbonization, the proportion of nanopores and the density of adsorption sites of the sheet increase from the outside to the inside along the thickness direction, thereby obtaining a gradient fiber sheet.

2. The manufacturing process for a multi-layer gradient composite automotive air conditioning filter element according to claim 1, characterized in that, Between steps S3 and S4, a crosslinking treatment step is also included, which is used to form a crosslinked reinforcement structure inside the fiber and at the fiber contact points.

3. The manufacturing process for a multi-layer gradient composite automotive air conditioning filter element according to claim 2, characterized in that, The crosslinking treatment is electron beam irradiation crosslinking, with an irradiation dose of 20-80 kGy.

4. The manufacturing process for a multi-layer gradient composite automotive air conditioning filter element according to any one of claims 1-3, characterized in that, The nitrile-containing polymer mentioned in step S1 is a polyacrylonitrile copolymer.

5. The manufacturing process of the multi-layer gradient composite automotive air conditioning filter element according to claim 4, wherein the polyacrylonitrile copolymer is copolymerized from acrylonitrile, methyl methacrylate and itaconic acid, wherein the mass ratio of the three is 94:5:

1.

6. The manufacturing process of the multilayer gradient composite automotive air conditioning filter element according to any one of claims 1-3, wherein the nitrile-containing polymer in step S1 is a polyacrylonitrile homopolymer.

7. The manufacturing process of the multi-layer gradient composite automotive air conditioning filter element according to any one of claims 1-3, wherein the acrylonitrile-containing polymer in step S1 is a blend of polyacrylonitrile copolymer and polyacrylonitrile homopolymer, and the mass ratio of the two is 60:40-80:

20.

8. The manufacturing process for a multi-layer gradient composite automotive air conditioning filter element according to claim 1, characterized in that, The stabilization treatment temperature in step S4 is 230-255℃, and the holding time is 30-90 min. The carbonization treatment temperature in step S5 is 550-650℃, and the holding time is 20-40 min.

9. The manufacturing process for a multi-layer gradient composite automotive air conditioning filter element according to claim 1, characterized in that, The gradient fiber sheet has a chemical transformation gradient and pore structure gradient that gradually changes from the outside to the inside along the thickness direction. The degree of cyclization and aromatization on the inner surface is higher than that on the outer surface, and the specific surface area and the proportion of nanopores on the inner surface are higher than those on the outer surface.

10. The manufacturing process for a multi-layer gradient composite automotive air conditioning filter element according to claim 1, characterized in that, The filter adsorption assembly is formed by bonding two gradient fiber sheets together, with the high-reinforcement ends of the two gradient fiber sheets facing each other, so that both outer surfaces of the filter adsorption assembly are low-reinforcement ends. The two gradient fiber sheets are fixed by perimeter sealing, with a sealing width of 1-5 mm. The filter adsorption assembly is embedded in the embedding groove of the support frame and fixed by hot melting or ultrasonic welding, so that the support frame and the filter adsorption assembly fixed in the support frame constitute an automotive air conditioning filter.

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