PTFE membrane filter material based on pore-forming agent and preparation method of PTFE membrane filter material

Abstract

The invention relates to a PTFE membrane filter material based on a pore-forming agent and a preparation method thereof, and the preparation method comprises the following steps: step 1, preparation of a coating reagent: mixing a PTFE dispersion liquid, the pore-forming agent, a coupling agent and a lubricant to prepare a uniform PTFE-pore-forming agent composite suspension, the composite suspension comprises the following raw materials by mass percentage: 80%-88% of the PTFE dispersion liquid, 5%-15% of the pore-forming agent, 0.5%-2% of the coupling agent, and 0.5%-1% of the lubricant; step 2, pretreatment of the filter material: carrying out dipping treatment on the filter material base material by using PTFE (Polytetrafluoroethylene) emulsion to obtain a pretreated filter material; step 3, coating and hot pressing: uniformly covering the surface of the pretreated filter material with the composite turbid liquid obtained in the step 1 by adopting a spraying or blade coating method; and the pretreated filter material coated with the composite turbid liquid is directly and slowly hot-pressed in a double-roller hot press. According to the invention, the complex process that a PTFE (Polytetrafluoroethylene) film and a filter material need to be additionally purchased for compounding in the traditional technology is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of filter materials, and more particularly to a PTFE-coated filter material based on a pore-forming agent and a preparation method thereof. Background Art

[0002] Common methods for coating PTFE (polytetrafluoroethylene) membrane filter media include gluing and high-temperature hot pressing. The gluing method, which bonds the PTFE film to the filter media substrate with an adhesive, offers the advantages of simplicity and low cost. However, this method can clog micropores with adhesive, leading to reduced air permeability and easy film removal at high temperatures. It is suitable for low- to mid-range or non-high-temperature applications. The high-temperature hot pressing process, on the other hand, directly bonds the PTFE film to the filter media substrate through high-temperature melting, eliminating the need for adhesives. This offers improved air permeability, greater resistance to high temperatures and corrosion, a long lifespan, and is environmentally friendly. However, the process is complex, the film layer is thin, and wear resistance is poor, resulting in high cost. Existing technologies primarily rely on the composite of a finished PTFE microporous membrane and filter media to produce membrane-coated filter media, achieving dust capture through "surface filtration." However, this method presents challenges such as uneven pore distribution, high processing costs, and complex equipment. Summary of the Invention

[0003] The purpose of the present invention is to provide a PTFE-coated filter material based on a pore-forming agent and a preparation method thereof, which can directly form a thin film on the surface of the PTFE filter material, thereby solving the complex process of traditional technology requiring the purchase of a PTFE film and the composite of the filter material.

[0004] In order to achieve the above object, the solution of the present invention is: A PTFE membrane filter material based on a pore-forming agent and a preparation method thereof, comprising the following steps: Step 1, Preparation of coating reagent The PTFE dispersion, pore former, coupling agent and lubricant are mixed to prepare a uniform PTFE-pore former composite suspension. The raw materials of the composite suspension are calculated by mass percentage as follows: 80%-88% PTFE dispersion, 5%-15% pore former, 0.5%-2% coupling agent and 0.5%-1% lubricant. Step 2: Pretreatment of filter media After the filter material base material is impregnated with PTFE emulsion, a pretreated filter material is obtained; Step 3: Coating and hot pressing Coating: The composite suspension prepared in step 1 is evenly coated on the surface of the pretreated filter material by spraying or scraping; Hot pressing: After being coated with the composite suspension, the pretreated filter material is directly and slowly hot pressed on a double-roll hot press. The hot pressing process is divided into three stages: the first stage is the preheating stage, which makes the PTFE initially softened; the second stage is the film-forming stage, which melts the PTFE and decomposes the pore-forming agent; the third stage is the cooling stage, which slowly cools down to ensure that the materials are fully melted and bonded, forming a uniform film on the filter material; After each layer of pre-treated filter material is hot-pressed, it is cooled to room temperature before the next layer is applied, and this process is repeated several times to form a uniform coating layer.

[0005] Furthermore, in step 1, the pore-forming agent is sodium bicarbonate, ammonium carbonate, urea, ammonium nitrate, ammonium oxalate, ammonium citrate, nanobubbles or microspheres.

[0006] Furthermore, in step 1, the coupling agent is a silane coupling agent, a titanate coupling agent or a zirconium aluminate coupling agent.

[0007] Furthermore, in step 1, the lubricant is paraffin or silicone oil.

[0008] Furthermore, in step 1, 1% of a lubricant is added to the PTFE dispersion, and the mixture is maintained at a speed of 1000-2000 rpm in a high-speed shear disperser for 20-30 minutes to ensure that the PTFE particles and the lubricant are evenly dispersed to obtain reagent 1; the coupling agent and the pore-forming agent diluted with water at a ratio of 1:3 are mixed in a ratio of 1:20 to obtain reagent 2; 1% by mass of reagent 2 is added to reagent 1, and the mixture is maintained at a speed of 1000-2000 rpm in a high-speed shear disperser for 10 minutes; after the suspension remains stable, the proportion of the pore-forming agent is slowly and gradually increased, and finally the ratio of reagent 1 to reagent 2 is 8.5:1.5 to form a PTFE-pore-forming agent composite suspension.

[0009] Furthermore, in step 2, the filter material substrate is immersed in the PTFE emulsion at a speed of 3-7 m / min and the drying temperature is 220-320°C.

[0010] Furthermore, in the coating step of step 3, the composite suspension is coated on the surface of the pretreated filter material using a spray gun at a distance of 15-20 cm from the pretreated filter material and a moving speed of 1-3 m / min.

[0011] Furthermore, in the hot pressing step of step 3, in the preheating stage, the pretreated filter material coated with the composite suspension passes through a first double-roll hot press at a temperature of 180-200°C and a pressure of 0.1-0.2 MPa for 10-20 seconds, so that the PTFE in the composite suspension coated on the surface of the pretreated filter material is initially softened; in the film-forming stage, the second double-roll hot press is maintained at a temperature of 280-300°C and a pressure of 0.3-0.5 MPa, and hot pressing is performed for 10-15 seconds to melt the PTFE and decompose the porogen; in the cooling stage, the filter material is maintained at a certain temperature and slowly cooled, and the filter material is placed in the cabin to ensure that the material is fully melted and bonded to form a uniform film; after hot pressing one layer of film, it is cooled to room temperature and then the next layer is coated, and this is repeated 3-5 times, and finally a uniform film layer with a total thickness of 0.5-3 μm is formed on the surface of the filter material.

[0012] A PTFE membrane filter material based on a pore-forming agent is prepared by the above-mentioned preparation method of the PTFE membrane filter material based on a pore-forming agent. The membrane filter material includes a multi-layer membrane layer formed on a pre-treated filter material. The membrane layer is formed by uniformly covering the surface of the pre-treated filter material with a suspension after coating and hot pressing.

[0013] After adopting the above scheme, the present invention adopts adhesive-free hot pressing technology, and the composite suspension formed after the PTFE particles and the blending material are mixed is coated on the surface of the PTFE filter material. Under suitable temperature, pressure and travel speed, the PTFE particles are subjected to high-temperature hot pressing on the surface of the PTFE filter material to form a PTFE film. The pore-forming agent present in the composite suspension can form nanopores during the film formation process, and finally a film with nanopores is obtained, which can ensure the smooth passage of clean gas while intercepting dust. The present invention can regulate the pore size by combining and formulating uniformly dispersed pore-forming agents of different particle sizes and adjusting detailed process parameters. At the same time, multi-layer coating can achieve gradient pore stacking to achieve "surface filtration", and dust cannot penetrate into deep layers, thereby effectively improving filtration efficiency. In addition, the gradient hot pressing process can ensure that the film thickness is uniform, the surface roughness is reduced, and the dust stripping rate is effectively improved. In summary, the present invention forms a thin film directly on the surface of the PTFE filter material through innovation in materials and processes, solving the complex process of traditional technology that requires the purchase of a PTFE film and compounding it with the filter material, and providing a more reliable and efficient solution for high-temperature, high-dust, and corrosive working conditions. DETAILED DESCRIPTION

[0014] The present invention discloses a PTFE membrane filter material based on a pore-forming agent and a preparation method thereof, comprising the following steps: Step 1, Preparation of coating reagent The PTFE dispersion, pore former, coupling agent and lubricant are mixed to prepare a uniform PTFE-pore former composite suspension. The raw materials of the composite suspension are calculated by mass percentage as follows: 80%-88% PTFE dispersion, 5%-15% pore former, 0.5%-2% coupling agent and 0.5%-1% lubricant, and finally a uniform composite suspension is obtained; Step 2: Pretreatment of filter media After the filter material base material is impregnated with PTFE emulsion, a pretreated filter material is obtained; Step 3: Coating and hot pressing Coating: The composite suspension prepared in step 1 is evenly coated on the surface of the pretreated filter material by spraying or scraping; Hot pressing: After being coated with the composite suspension, the pretreated filter material is directly and slowly hot pressed on a double-roll hot press. The hot pressing process is divided into three stages: the first stage is the preheating stage, which initially softens the PTFE; the second stage is the film-forming stage, which melts the PTFE and decomposes the pore-forming agent; the third stage is the cooling stage, during which the filter material after film formation is slowly cooled to ensure that the material is fully melted and bonded, forming a uniform film on the filter material; After each layer of pre-treated filter material is hot-pressed, it is cooled to room temperature before the next layer is coated. This process is repeated several times to form a uniform coating layer, thereby obtaining a PTFE coated filter material.

[0015] In step 1, the pore-forming agent may be sodium bicarbonate, ammonium carbonate, urea, ammonium nitrate, ammonium oxalate, ammonium citrate, nanobubbles or microspheres, etc. The coupling agent may be a silane coupling agent, a titanate coupling agent, a zirconium aluminate coupling agent, etc. The lubricant may be paraffin, silicone oil, etc.

[0016] Among them, the pore-forming agent can produce gas when it decomposes during subsequent hot pressing, thereby forming uniform pores. The pore-forming agent can also reduce the melting and film-forming temperature of PTFE. At the same time, the residue forms a chemical bond with the PTFE surface, promoting intermolecular bonding. The amount of pore-forming agent added can control the pore size of the porous microporous membrane. The chemical bond formed between the coupling agent and the pore-forming agent can enhance the interfacial compatibility and the stability of the dispersion system. For example, the silane coupling agent, the siloxane group in the molecule is bonded to the fluorocarbon chain on the PTFE surface through van der Waals force or hydrogen bond, and the amino or methacryloyl group at the other end reacts with the polar group of the pore-forming agent to form a chemical bond, which can enhance the interfacial compatibility. Lubricants can reduce the mutual adhesion and agglomeration between particles, effectively reduce the melt viscosity of PTFE, and thus obtain a finer microporous structure. At the same time, different pore-forming agent addition ratios can effectively control the surface pore size system of the final membrane-forming filter material, forming a gradient pore structure, and providing different possibilities for the product structure of the filter material.

[0017] In step 1, 1% of the lubricant can be first added to the PTFE dispersion, and the mixture is maintained at a speed of 1000-2000 rpm in a high-speed shear disperser for 20-30 minutes to ensure that the PTFE particles and the lubricant are evenly dispersed to obtain reagent 1; the coupling agent and the pore-forming agent diluted with water at a ratio of 1:3 are mixed in a ratio of 1:20 to obtain reagent 2; 1% by mass of reagent 2 is added to reagent 1, and the mixture is maintained at a speed of 1000-2000 rpm in a high-speed shear disperser for 10 minutes; after the suspension remains stable, the proportion of the pore-forming agent is slowly and gradually increased, and finally the ratio of reagent 1 to reagent 2 is 8.5:1.5 to form a PTFE-pore-forming agent composite suspension.

[0018] In step 2, the filter media substrate, made of felt, is immersed in the PTFE emulsion at a speed of 3-7 m / min and a drying temperature of 220-320°C, resulting in a pretreated PTFE filter media. After surface pretreatment, a layer of PTFE emulsion adheres to the filter media surface, facilitating better adhesion of the subsequent PTFE-containing suspension and enhancing the bond strength between the subsequent coating (composite suspension) and the filter media.

[0019] In the coating step of step 3, the scraping coating can be carried out by compacting the particles with a scraper or a roller, and the spray coating can be carried out by applying the composite suspension on the surface of the pretreated filter material with a spray gun at a distance of 15-20 cm from the pretreated filter material and a moving speed of 1-3 m / min.

[0020] In the hot pressing step of step 3, in the preheating stage, the pretreated filter material coated with the composite suspension is subjected to the first double-roll hot press at a temperature of 180-200°C and a pressure of 0.1-0.2 MPa for 10-20 seconds, so that the PTFE (the active ingredient PTFE in the PTFE dispersion) in the composite suspension coated on the surface of the pretreated filter material is initially softened; in the film-forming stage, the second double-roll hot press is maintained at a temperature of 280-300°C, a pressure of 0.3-0.5 MPa, and hot pressing is performed for 10-15 seconds. The PTFE melts at this stage, and the pore-forming agent decomposes at this stage to form a thin film with micro-nano pores on the surface of the filter material; in the cooling stage, the filter material is kept at a certain temperature and slowly cooled. The filter material can be placed in a cabin to avoid cracking caused by thermal shock, ensuring that the material is fully melted and bonded to form a uniform film.

[0021] After hot pressing a layer of film on the filter material, cool it to room temperature and then apply the next layer. Repeat this process 3-5 times until a uniform film layer with a total thickness of 0.5-3 μm is formed on the surface of the filter material.

[0022] The present invention also discloses a PTFE coated filter material based on a pore-forming agent, which is prepared by the above-mentioned preparation method. The coated filter material includes a multi-layer coating layer formed on a pretreated filter material, and the coating layer is formed by uniformly covering the surface of the pretreated filter material with a suspension after coating and hot pressing.

[0023] In order to further explain the technical solution of the present invention, the present invention is described in detail below through specific embodiments.

[0024] Example 1: Add 1% paraffin to the PTFE dispersion and maintain the speed at 1000-2000rpm in a high-speed shear disperser for 20-30 minutes to ensure that the PTFE particles and paraffin are evenly dispersed to obtain reagent 1. Dilute the silane coupling agent KH-550 with water in a ratio of 1:3 and mix it with ammonium carbonate in a ratio of 1:20 to obtain reagent 2. Add 1% by weight of reagent 2 to reagent 1 and maintain the speed at 1000-2000rpm in a high-speed shear disperser for 10 minutes to observe whether it softens, dissolves, or precipitates. After the suspension remains stable, slowly increase the proportion of the pore-forming agent until the ratio of reagent 1 to reagent 2 is 8.5:1.5, which is the PTFE-ammonium carbonate composite coating suspension (hereinafter referred to as the composite suspension).

[0025] The composite reagent is applied to the surface of a PTFE filter media substrate pre-treated with a silane-containing PTFE emulsion using a spray gun at a distance of 15-20 cm and a speed of 1-3 m / min. The coated filter media then undergoes a three-step hot pressing process. The preheating stage involves pressing the media in a double-roll hot press at 180-200°C and a pressure of 0.1-0.2 MPa for 10-20 seconds to initially soften the PTFE. The film-forming stage involves a second double-roll hot press at 280-300°C and a pressure of 0.3-0.5 MPa for 10-15 seconds to melt the PTFE and decompose the porogen. The cooling stage involves slowly cooling the chamber to prevent cracking caused by thermal shock and ensure full melt adhesion, forming a uniform film. After cooling to room temperature, the next layer of coating is applied. This process is repeated 3-5 times, ultimately forming a uniform film with a total thickness of 0.5-3 μm on the filter media surface, creating a multi-layer PTFE film.

[0026] Compared with the existing technology, in terms of structural design, the existing technology usually adopts a multi-layer composite structure: a middle PTFE base fabric layer + upper and lower fiber layers + an outer microporous film; while this patent uses a coating-hot pressing integrated process to directly form a continuous microporous film on the surface of the PTFE filter material substrate, without the need for an additional coating layer, which simplifies the structure while enhancing the interface bonding strength between the membrane layer and the substrate.

[0027] By adopting the above scheme, the present invention utilizes the film-forming property of PTFE particles under hot pressing, and the pore-forming agent present in the reagent can form nanopores during the film formation process, ultimately obtaining a filter material with a microporous film with a gradient pore size structure attached to the surface. This not only improves the pore uniformity, but also allows the design of a stepped membrane pore structure. The present invention can have the following technical effects: (1) Adjustable pore structure: The combination of multi-layer coating and controllable pore-forming agent addition will bring different pore structures to the PTFE surface membrane. At the same time, multi-layer coating can achieve gradient pore size stacking to achieve "surface filtration", preventing dust from penetrating to deep layers, effectively improving filtration efficiency.

[0028] (2) The composite film pore-forming system of the pore-forming agent and PTFE of the present invention forms a pore structure by decomposing gas and evaporating the pores. The pore size can be controlled in a wider range and the film is directly formed on the surface of the PTFE filter material, which solves the problem of the traditional technology requiring the purchase of a PTFE film and the complex process of compounding the filter material.

[0029] (3) Add coupling agents and lubricants to promote uniform dispersion of the pore-forming agent, improve the density and tensile strength of the membrane layer, make PTFE more fluid during hot pressing, and reduce the risk of pore collapse.

[0030] (4) Gradient hot pressing process parameters are used: staged heating (180°C preheating → 300°C hot pressing) and slow pressurization (0.1MPa → 0.5MPa) to balance pore fixation and surface smoothness; the residence time is precisely controlled to ensure that the pore former is completely decomposed and the pores are stable.

[0031] The above embodiments do not limit the product form and style of the present invention. Any appropriate changes or modifications made by ordinary technicians in the relevant technical field should be deemed to be within the patent scope of the present invention.

Claims

1. A method for preparing a PTFE membrane filter material based on a pore-forming agent, characterized in that: The following steps are involved: Step 1, Preparation of coating reagent The PTFE dispersion, pore former, coupling agent and lubricant are mixed to prepare a uniform PTFE-pore former composite suspension. The raw materials of the composite suspension are calculated by mass percentage as follows: 80%-88% PTFE dispersion, 5%-15% pore former, 0.5%-2% coupling agent and 0.5%-1% lubricant. Step 2: Pretreatment of filter media After the filter material base material is impregnated with PTFE emulsion, a pretreated filter material is obtained; Step 3: Coating and hot pressing Coating: The composite suspension prepared in step 1 is evenly coated on the surface of the pretreated filter material by spraying or scraping; Hot pressing: After being coated with the composite suspension, the pretreated filter material is directly and slowly hot pressed on a double-roll hot press. The hot pressing process is divided into three stages: the first stage is the preheating stage, which makes the PTFE initially softened; the second stage is the film-forming stage, which melts the PTFE and decomposes the pore-forming agent; the third stage is the cooling stage, which slowly cools down to ensure that the materials are fully melted and bonded, forming a uniform film on the filter material; After each layer of pre-treated filter material is hot-pressed, it is cooled to room temperature before the next layer is applied, and this process is repeated several times to form a uniform coating layer.

2. The method for preparing a PTFE membrane filter material based on a pore-forming agent according to claim 1, wherein: In step 1, the pore-forming agent is sodium bicarbonate, ammonium carbonate, urea, ammonium nitrate, ammonium oxalate, ammonium citrate, nanobubbles or microspheres.

3. The method for preparing a PTFE membrane filter material based on a pore-forming agent according to claim 1, wherein: In step 1, the coupling agent is a silane coupling agent, a titanate coupling agent or a zirconium aluminate coupling agent.

4. The method for preparing a PTFE membrane filter material based on a pore-forming agent according to claim 1, wherein: In step 1, paraffin or silicone oil is used as the lubricant.

5. The method for preparing a PTFE membrane filter material based on a pore-forming agent according to claim 1, wherein: In step 1, 1% of the lubricant is added to the PTFE dispersion, and the dispersion is maintained at a speed of 1000-2000 rpm in a high-speed shear disperser for 20-30 minutes to ensure that the PTFE particles and the lubricant are evenly dispersed to obtain reagent 1; the coupling agent and the pore-forming agent diluted with water at a ratio of 1:3 are mixed in a ratio of 1:20 to obtain reagent 2; 1% by mass of reagent 2 is added to reagent 1, and the dispersion is maintained at a speed of 1000-2000 rpm in a high-speed shear disperser for 10 minutes; after the suspension remains stable, the proportion of the pore-forming agent is slowly and gradually increased, and finally the ratio of reagent 1 to reagent 2 is 8.5:1.5 to form a PTFE-pore-forming agent composite suspension.

6. The method for preparing a PTFE membrane filter material based on a pore-forming agent according to claim 1, wherein: In step 2, the filter material substrate is immersed in the PTFE emulsion at a speed of 3-7 m / min and the drying temperature is 220-320°C.

7. The method for preparing a PTFE membrane filter material based on a pore-forming agent according to claim 1, wherein: In the coating step of step 3, the composite suspension is coated on the surface of the pretreated filter material using a spray gun at a distance of 15-20 cm from the pretreated filter material and a moving speed of 1-3 m / min.

8. The method for preparing a PTFE membrane filter material based on a pore-forming agent according to claim 1, wherein: In the hot pressing step of step 3, in the preheating stage, the pretreated filter material coated with the composite suspension passes through a first double-roll hot press at a temperature of 180-200°C and a pressure of 0.1-0.2MPa for 10-20 seconds to initially soften the PTFE in the composite suspension coated on the surface of the pretreated filter material; in the film-forming stage, the second double-roll hot press is maintained at a temperature of 280-300°C and a pressure of 0.3-0.5MPa for 10-15 seconds to melt the PTFE and decompose the porogen; in the cooling stage, the filter material is maintained at a certain temperature and slowly cooled, and the filter material is placed in the cabin to ensure that the material is fully melted and bonded to form a uniform film; after hot pressing one layer of film, it is cooled to room temperature and then the next layer is applied, and this is repeated 3-5 times to finally form a uniform film layer with a total thickness of 0.5-3μm on the surface of the filter material.

9. A PTFE membrane filter material based on a pore former, prepared by the preparation method of a PTFE membrane filter material based on a pore former according to any one of claims 1 to 8, the membrane filter material comprising a multi-layer membrane layer formed on a pre-treated filter material, the membrane layer being formed by uniformly covering the surface of the pre-treated filter material with a suspension after coating and hot pressing.