An antistatic composite filter medium and its preparation method

Abstract

This invention discloses an antistatic composite filter medium and its preparation method. The composite filter medium includes at least one ePTFE membrane layer and at least one substrate support layer, with the ePTFE membrane layer and the substrate support layer arranged alternately. The filtration efficiency of the ePTFE membrane layer is ≥85%. The substrate support layer is a non-woven fiber cloth or a woven fiber cloth, and the raw material of the substrate support layer is selected from one or two of polyolefins, thermoplastic polyesters, and inorganic fibers. The basis weight of the substrate support layer is 65-800 g / m³. 2 The thickness is 0.2-5mm; a conductive ink pattern layer is printed on the surface of the ePTFE membrane layer on the air inlet side, the line width of the conductive ink pattern is 0.5-1.5mm, and the coating area of ​​the conductive ink accounts for 5-48% of the surface area of ​​the ePTFE membrane layer. The composite filter medium of the present invention has excellent filtration performance, antistatic performance, and flame retardant performance.

Description

Technical Field

[0001] This invention relates to the field of air filtration materials technology, specifically to an antistatic composite filter medium and its preparation method. Background Technology

[0002] Polytetrafluoroethylene (PTFE) possesses excellent properties such as high chemical stability, resistance to high and low temperatures, and low surface energy. Expanded PTFE membranes, prepared through extrusion, calendering, and stretching processes, exhibit excellent waterproof and breathable properties, making them ideal surface filters with high filtration efficiency, easy dust removal, and reusability. However, PTFE membranes are insulating and non-conductive. Contact and friction between the filter material and dust can easily generate static electricity, which can easily lead to static charge in dry air. In flammable and explosive environments, this static electricity can generate sparks, potentially causing damage to the filter material or equipment malfunctions, or even dust explosions, posing significant safety hazards. Therefore, filter materials need to possess certain antistatic properties.

[0003] The antistatic performance of filter media mainly depends on two aspects. Firstly, it prevents the generation of static electricity. Since contact, friction, and separation between the filter media and the filtered material are inevitable, static electricity generation is unavoidable. Secondly, it determines the rate of static electricity decay. The main factor determining the rate of static electricity decay is the conductivity of the material. The better the conductivity, i.e., the lower the resistance, the faster the charge decays. Rapid release and dissipation of static charge can prevent accumulation and discharge. Therefore, reducing the resistance of the filter media to a certain level can prevent static electricity phenomena to some extent.

[0004] Currently, antistatic treatment methods for filter media can be summarized into three main types: The first is surface treatment, which involves applying a hygroscopic resin to the fabric surface; the second is adding or mixing hygroscopic materials into the fibers; and the third is weaving conductive yarns into the fabric. The first two methods achieve antistatic effects by absorbing moisture from the air. Moisture absorption enhances conductivity, reducing the material's volume resistivity or surface resistivity, making it a conductor or dissipator of static electricity. However, the antistatic effect is highly dependent on ambient humidity; it loses its antistatic properties under low humidity conditions, and its durability cannot be guaranteed, limiting its application. The third method uses conductive particles or fibers dispersed within the filter material matrix, effectively improving the material's resistivity. The antistatic properties of the fabric are less affected by ambient humidity, and the antistatic effect has good durability. However, conductive fibers are more expensive.

[0005] For example, Chinese patent application publication number CN114434915A discloses an antistatic nanofiltration material and its production method. The material achieves filtration efficiency, antistatic properties, and flame retardant properties through a multi-layer composite of a filter layer (PTFE membrane layer), a conductive layer (conductive fiber), and a support layer (non-woven fabric layer). However, this filter material has a high cost.

[0006] For example, Chinese patent application publication number CN105107267A discloses a fire-retardant and antistatic polytetrafluoroethylene (PTFE) membrane filter material and its preparation method. This filter material has a three-layer structure: the upper layer is an expanded PTFE membrane layer with fire-retardant and antistatic surface filtration functions; the middle layer is an adhesive layer; and the lower layer is a breathable substrate layer with supporting functions. The PTFE membrane is composed of the following components by mass percentage: 60-80% PTFE powder, 15-30% additives, and 5-10% conductive agent. Although it achieves an antistatic effect, the addition of the conductive agent affects the film-forming properties of the PTFE membrane, easily causing leaks and affecting filtration efficiency. Furthermore, the filter material is formed by thermal bonding with an adhesive, which affects its flame-retardant properties.

[0007] For example, Chinese patent application publication number CN115738752A discloses a method for preparing a graphene hybrid PTFE composite membrane and the prepared composite membrane. PTFE dispersion resin, coupling agent / surfactant, extrusion aid, and graphene are mixed uniformly, and a graphene hybrid PTFE multilayer composite membrane is prepared using a biaxial stretching method. Graphene undergoes physical delamination during biaxial stretching, and the delaminated graphene sheets are oriented along the stretching direction. Simultaneously, the graphene sheets interweave with the microfibers in the PTFE membrane, forming a three-dimensional layered composite structure of "microfiber-graphene layer" with cross-linked interlayers, thereby improving the conductivity and mechanical properties of the composite membrane. However, the addition of graphene sheets affects the filtration efficiency of the composite membrane and increases the difficulty of preparing the membrane filtration material, making it difficult to guarantee the consistency of the filtration material's quality.

[0008] Therefore, it is necessary to develop a composite filter material that can meet the requirements of filtration efficiency, antistatic properties, and flame retardancy, while also reducing costs, simplifying production processes, and facilitating mass production. Summary of the Invention

[0009] The purpose of this invention is to address the above-mentioned problems by providing a composite filter medium with excellent filtration effect and antistatic properties, as well as a method for its preparation.

[0010] To achieve its objective, the present invention employs the following technical solution:

[0011] An antistatic composite filter medium includes at least one ePTFE membrane layer and at least one substrate support layer, wherein the ePTFE membrane layer and the substrate support layer are arranged alternately in sequence.

[0012] The filtration efficiency of the ePTFE membrane layer is ≥85%;

[0013] The substrate support layer is made of non-woven or woven fiber fabric. The raw materials for the substrate support layer are selected from one or two of polyolefins, thermoplastic polyesters, and inorganic fibers. The basis weight of the substrate support layer is 65-800 g / m².2 Thickness 0.2-5mm;

[0014] A conductive ink pattern layer is printed on the surface of the ePTFE membrane layer on the air inlet side. The line width of the conductive ink pattern is 0.5-1.5 mm, and the coating area of ​​the conductive ink accounts for 5-48% of the surface area of ​​the ePTFE membrane layer.

[0015] Preferably, the substrate support layer is a flame-retardant material;

[0016] The conductive ink coating area accounts for 5-40%, 5-18%, or 5-15% of the ePTFE film surface area. The line width of the conductive ink pattern is 0.5-0.8 mm or 0.5-0.7 mm, and the ink wetting thickness of the conductive ink pattern is 0.2-1 mm, 0.2-1 mm, 0.2-0.4 mm, or 0.4-1 mm.

[0017] Preferably, the air permeability of the ePTFE membrane layer is 10-300 L / m².s; the basis weight of the substrate support layer is 65-500 g / m². 2 The air permeability is 16-1100L / m2.s, the MD strength is 320-5000N / 5cm, and the TD strength is 195-4800N / 5cm.

[0018] Further preferred values ​​for the ePTFE membrane layer are: air permeability of 40-200 L / m².s, 40-100 L / m².s, or 60-90 L / m².s; and basis weight of the substrate support layer of 100-500 g / m². 2 Or 65-300g / m 2 Or 100-300g / m 2 The air permeability is 16-500L / m2.s, 16-300L / m2.s, 28-300L / m2.s, or 50-300L / m2.s; the MD strength is 320-3500N / 5cm, 320-1200N / 5cm, 320-500N / 5cm, or 320-400N / 5cm; and the TD strength is 195-3300N / 5cm, 280-2000N / 5cm, or 195-400N / 5cm.

[0019] Preferably, the substrate support layer is made of polyolefins including polypropylene, polyethylene or poly-1-butene resin, thermoplastic polyester including PET (polyester resin), and inorganic fiber materials selected from glass fiber, ceramic fiber or basalt fiber.

[0020] Preferably, the substrate support layer is PET fiber cloth, woven fiberglass cloth, or fiberglass paper;

[0021] Preferably, the substrate support layer contains conductive fibers, which are metal, carbon fiber, or chemical fibers mixed with a conductive medium.

[0022] Preferably, the ink pattern of the conductive ink pattern layer is composed of continuous ink lines, and any point in the pattern can extend along the ink lines to the edge of the composite filter medium;

[0023] The preferred conductive ink pattern is a grid pattern, a diagonal pattern, or a curved pattern;

[0024] The conductive ink pattern is preferably a polygonal grid pattern, more preferably a hexagonal grid pattern or a square grid pattern.

[0025] Preferably, in the antistatic composite filter medium, the number of ePTFE membrane layers is 1-2 layers, and the number of substrate support layers is 1-2 layers.

[0026] More preferably, both the ePTFE membrane layer and the substrate support layer are single layers.

[0027] The preparation method of the antistatic composite filter medium according to any one of the above-mentioned methods includes the following steps:

[0028] 1) Composite the ePTFE membrane with the substrate support layer;

[0029] 2) A conductive ink pattern layer is prepared by coating conductive ink using a printing method.

[0030] Preferably, in step 1), the ePTFE membrane and the substrate support layer are thermally bonded or adhesively bonded.

[0031] Preferably, in step 2), the conductive ink comprises conductive filler, binder, solvent and additives, wherein the conductive filler is selected from graphite powder, carbon nanotubes, silver powder, copper powder, aluminum powder, graphene, carbon black, nickel powder and gold powder.

[0032] The printing method is screen printing, letterpress printing, or gravure printing;

[0033] The particle size D50 of the conductive filler is ≤13um, preferably 5-13um, and more preferably 5-7um or 5-10um.

[0034] The antistatic composite filter medium of this invention has a filtration efficiency of 85%-99.99995% and a surface resistivity ≤10. 6 Ω, exhibiting excellent resistance uniformity.

[0035] The beneficial effects of this invention are:

[0036] 1. Performance of ePTFE membrane

[0037] The ePTFE membrane is located on the air inlet side, intercepting dust on this surface. The charge on the dust particles is quickly discharged along with the conductive ink lines, preventing accumulation on the filter media. Dust particles landing on areas without conductive ink coating are attracted by the electrostatic adsorption of the nearby conductive ink, causing the static charge to move across the filter media surface. The shape of the conductive ink pattern affects the release / attenuation rate of the static charge, thus preventing accumulation and discharge, and providing an antistatic effect.

[0038] 2. Support Layer: Provides strength to the filter medium and prevents damage to the ePTFE membrane. It can be processed by pleating, wrapping, sewing, etc. It can be made into filter cartridges, filter bags, and other filter elements. The support layer can be prepared through non-woven processes, such as papermaking, needle punching, hot air bonding, thermal bonding, and ultrasonic bonding, or it can be prepared through weaving processes.

[0039] 3. The composite filter medium of the present invention has excellent filtration performance, antistatic (surface resistivity) performance, and flame retardant performance. Its preparation method simplifies the production process, significantly reduces production costs, and is conducive to mass production. Attached Figure Description

[0040] Figure 1 These are examples of different shapes for conductive ink patterns. Detailed Implementation

[0041] The present invention will be further described below with reference to embodiments, but these embodiments are not intended to limit the scope of the invention.

[0042] Unless otherwise specified, the experimental methods in the following examples are conventional methods; and the materials and chemical reagents used are commercially available conventional materials and chemical reagents.

[0043] 1. The ePTFE membrane uses commercially available standard products with a thickness of 2-30μm.

[0044] 2. The substrate support layer uses commercially available standard products with flame retardant properties. The substrate support layer has a basis weight of 65-800g / m2 and a thickness of 0.2-5mm.

[0045] 3. The conductive ink is a commercially available conventional conductive ink, and the conductive filler particle size D50 ≤ 13um.

[0046] Conductive inks typically consist of four parts: conductive fillers, binders, solvents, and additives. The functions of each component are as follows:

[0047] Conductive fillers: Conductive fillers are the main components in inks that conduct electricity, such as graphite, carbon nanotubes, silver, copper, aluminum, graphene, carbon black, nickel powder, gold powder, etc.

[0048] Binder: The binder mainly plays a binding role and is the main film-forming substance in ink. It is mainly composed of various polymer resins such as synthetic resins and photosensitive resins.

[0049] Solvent: The solvent is mainly used to dissolve the resin so that it can play a binding role and increase the adhesion to the substrate;

[0050] Additives: Additives are used to improve the printability of inks and are selected according to needs. They mainly include dispersants, regulators, surfactants, defoamers, binders, flame retardants, etc.

[0051] Conductive inks are inks capable of conducting electric current and dissipating accumulated static charge. Based on the properties of the binder, conductive inks are classified into water-based inks, solvent-based inks, and oil-based inks. Water-based inks use water as the main binder and are characterized by being non-toxic, environmentally friendly, safe, non-flammable, and low-cost. Solvent-based inks use organic solvents as binders. Oil-based inks use mineral oil as a solvent; because oil has low surface tension, oil-based inks allow for better control of surface tension, absorbency, and wettability.

[0052] The ink materials used in this invention embodiment are sourced from products of Guangdong Shunfeng Ink Co., Ltd. For conductive fillers of graphite powder, the SF-UV7800S series UV inks were used, and experiments were conducted to compare inks with different graphite powder particle sizes (7, 10, 13 μm). For conductive fillers of silver powder, the SFJ001T product was used; for conductive fillers of carbon nanotubes, the SF1001T product was used. For conductive fillers of graphite powder + 3% graphene, the SF-UV7800S UV ink was used, with 3% graphene powder added by mass percentage.

[0053] The method for preparing the antistatic composite filter medium of the present invention includes the following steps:

[0054] 1) The ePTFE membrane is laminated with the substrate support layer by thermal lamination or adhesive lamination.

[0055] 2) A conductive ink pattern layer is prepared by coating conductive ink using a printing method, such as screen printing, letterpress printing, or gravure printing. The conductive ink pattern can be a grid pattern, a diagonal pattern, or a curved pattern. Figure 1 These are examples of different shapes for conductive ink patterns.

[0056] The antistatic composite filter medium of the present invention was prepared using the above method, and the samples shown in Table 1-2 were prepared as follows:

[0057] Table 1

[0058]

[0059]

[0060] Table 2

[0061]

[0062] In Tables 1-2, the antistatic composite filter media of Examples 1-9 and Comparative Examples 1-5 are composed of one ePTFE membrane layer and one substrate support layer; the composite filter media of Example 10 comprises two ePTFE membrane layers and two substrate support layers, which are spaced apart; in the antistatic composite filter media of the present invention, the ePTFE membrane layer is the air inlet surface, and the conductive ink pattern layer is disposed on the outer surface of the ePTFE membrane layer on the air inlet surface.

[0063] The filtration efficiency, air permeability, and surface resistivity of the prepared product were tested.

[0064] 1. Filtration efficiency test method: The filtration efficiency shall be tested in accordance with the method in "QB / T 6165-2021 Performance Test Method for High-Efficiency Air Filters: Efficiency and Resistance".

[0065] 2. Air permeability test method: Tested according to GB / T24218.15-2018 Textiles - Nonwovens - Part 15 - Determination of air permeability.

[0066] 3. Surface resistance test method: The surface resistance tester is Victor VC385. The test method is ASTM standard D-257 parallel electrode sensing method.

[0067] The product performance test results are shown in Table 2. As can be seen from the examples and comparative examples, for filter media products, the smaller the area of ​​the conductive ink pattern layer while still meeting conductivity requirements, the better; the smaller the line width and the greater the wetting thickness of the conductive ink pattern, the better the product performance. Different conductive ink patterns also result in different product performance. For example, compared to Example 1, the hexagonal grid pattern in Example 3 exhibits better conductivity than the square grid pattern. The particle size of the conductive filler also leads to different product performance. For example, compared to Examples 1 and 5, the smaller the particle size of the conductive filler in Example 4, the better the conductivity of the medium.

Claims

1. An anti-static composite filtration media, characterized by: The composite filter medium comprises 1-2 layers of ePTFE film and 1-2 layers of substrate support layer, and the ePTFE film and the substrate support layer are arranged in sequence and spaced apart, The filtration efficiency of the ePTFE film layer is ≥ 85%, and the air permeability is 40-100 L / m 2 s; The substrate support layer is a PET fiber cloth, and the grammage of the substrate support layer is 65-300 g / m 2 , the thickness is 0.2-5 mm, the air permeability is 50-1100 L / m 2 .s, the MD strength is 320-5000 N / 5 cm, and the TD strength is 195-4800 N / 5 cm; the substrate support layer is a flame-retardant material; The surface of the ePTFE film layer of the air inlet face is printed with a conductive ink pattern layer, the ink pattern of the conductive ink pattern layer is composed of continuous ink lines, and any point in the pattern can extend to the edge of the composite filter medium along the ink lines; The conductive ink pattern is a grid pattern, a twill pattern or a curved line pattern; The line width of the conductive ink pattern is 0.5-0.8mm, the ink wet thickness of the conductive ink pattern is 0.2-1mm, and the coating area of the conductive ink accounts for 5-18% of the surface area of the ePTFE film layer.

2. The anti-static composite filter medium according to claim 1, wherein: The coating area of the conductive ink accounts for 5-15% of the surface area of the ePTFE film layer, and the line width of the conductive ink pattern is 0.5-0.7mm.

3. The anti-static composite filter media of claim 1, wherein: The air permeability of the ePTFE film layer is 60-90 L / m 2 The basis weight of the substrate support layer is 100-300 g / m 2 The air permeability is 50-300 L / m 2 The MD strength is 320-3500 N / 5 cm, and the TD strength is 195-3300 N / 5 cm.

4. The anti-static composite filter medium according to claim 1, wherein: The substrate support layer contains conductive fibers, and the conductive fibers are metal, carbon fibers or chemical fibers mixed with conductive medium.

5. The anti-static composite filter medium according to claim 1, wherein: The conductive ink pattern is a polygonal grid pattern.

6. The method of making an anti-static composite filter media according to any one of claims 1 to 5, characterized in that, The method comprises the following steps: 1) composite ePTFE film and substrate support layer; 2) prepare a conductive ink pattern layer by printing conductive ink.

7. The method of claim 6, wherein: In step 1), the ePTFE film and the substrate support layer are hot-composite or glue-composite.

8. The preparation method according to claim 6, wherein: In step 2), the conductive ink comprises conductive fillers, binders, solvents and additives, and the conductive fillers are selected from graphite powder, carbon nanotubes, silver powder, copper powder, aluminum powder, graphene, carbon black, nickel powder and gold powder; The printing method is screen printing, letterpress printing or gravure printing; The particle size D50 of the conductive fillers is ≤13um.

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