Composite ptfegasket and method of making

Abstract

The application relates to the technical field of composite diaphragm materials for diaphragm valves, in particular to a composite PTFE diaphragm and a preparation method thereof. The preparation method comprises the following steps: obtaining a calendered sheet after die pressing, sintering, preheating turning, cutting, low-temperature flat setting, and hot calendering of modified PTFE resin powder; performing oxygen plasma treatment on the back adhesive side of the calendered sheet and contacting the back adhesive side with a glue joint liquid to form an adhesion-increasing layer on the back adhesive side; performing oxygen plasma treatment on the medium contact surface of the calendered sheet, and sequentially contacting the medium contact surface with a primer liquid and a surface treatment liquid to form a PDA primer layer and an anti-fouling functional layer; subsequently, coating a polyurethane adhesive on the surface of the adhesion-increasing layer on the back adhesive side, and hot-pressing the polyurethane adhesive with an EPDM support layer to obtain a composite PTFE diaphragm after cooling and die cutting. The diaphragm obtained by the application has good interlayer bonding performance and anti-fouling performance of the medium contact surface.

Description

Technical Field

[0001] This invention relates to the field of composite diaphragm materials for diaphragm valves, and particularly to a composite PTFE diaphragm sheet and its preparation method. Background Technology

[0002] PTFE possesses excellent corrosion resistance, chemical resistance, and low surface energy, making it widely used as a media contact layer in pumps, valves, diaphragm valves, and high-purity fluid control components. Existing products also include solutions for forming pump diaphragms by combining a PTFE layer with a thermoplastic elastomer layer containing EPDM and PP. The PTFE layer can be dense PTFE or in the form of skived PTFE. These disclosures also explicitly mention achieving the composite of the PTFE layer and the support layer through adhesives and hot pressing.

[0003] On the other hand, regarding the PTFE diaphragm sheet body, existing technologies have disclosed various basic preparation routes for PTFE sheets or diaphragms. For example, existing patents disclose a process of sieving PTFE resin powder through a 10-mesh sieve, followed by molding, sintering, and turning to obtain a turned film; other disclosures indicate that the turned film can be further subjected to hot stretching or heat treatment to improve flexural fatigue performance. Therefore, the "sieving-molding-sintering-turning" process itself is a well-known basic process for PTFE sheet preparation.

[0004] Furthermore, addressing the issue of PTFE's strong surface inertness and difficulty in further functionalization, existing technologies have publicly disclosed a route of depositing a PDA layer after plasma pretreatment. Publicly available research shows that PTFE can form a more stable PDA layer after plasma pretreatment. Meanwhile, reviews on PTFE plasma modification indicate that although gas plasma modification is widely used to improve PTFE surface wettability and adhesion, the surface state varies greatly under different treatment conditions, and hydrophobic recovery occurs. Other studies have shown that the water contact angle of untreated PTFE can be quite high, reaching as high as 141.9° for some film-like PTFEs. While simple plasma treatment can reduce the contact angle, its stability is not necessarily reliable.

[0005] Furthermore, zwitterionic polymers, especially those containing phosphorylcholine or betaine structures, are widely considered an effective route for limiting non-specific protein adsorption due to their ability to form a strong hydration layer on the surface. Public reviews indicate that zwitterionic coatings are generally superior to traditional approaches in limiting protein adsorption; published literature also points out that MPC-type surfaces have a highly hydration structure, which helps to inhibit the adsorption of protein and lipid molecules.

[0006] However, existing technologies still lack a comprehensive technical solution for composite PTFE membrane sheets: on the basis of ensuring good thickness consistency and subsequent compatibility of PTFE sheets, different functional surface layers are constructed on both sides of the same PTFE sheet, so that the non-medium contact surface is suitable for composite with the support layer, while the medium contact surface has a stable anti-fouling surface layer, thereby taking into account both the interlayer bonding ability and the low residue requirement on the medium side. Summary of the Invention

[0007] The purpose of this invention is to provide a composite PTFE membrane sheet and its preparation method, so as to solve the problem that existing PTFE membrane sheets are difficult to simultaneously achieve both back-side compatibility and media contact surface anti-fouling performance.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for preparing a composite PTFE membrane sheet, comprising the following steps: Step (1) After sieving the modified PTFE resin powder, add it into the hollow cylindrical mold, and after pressurization, degassing, pressure holding and demolding, obtain the pressed blank of the hollow cylinder; Step (2) involves sintering, holding, cooling and sintering the pressed billet in stages to obtain a sintered billet; Step (3) After preheating the sintered billet, it is machined to obtain continuous PTFE machined sheets; Step (4) Trim the PTFE machined sheet according to the target diaphragm sheet size and cut it into square sheets; Step (5) The square sheet is subjected to low-temperature thermal relaxation and flattening under restricted flat pressure, and then cooled and dried to obtain the shaped sheet; Step (6) Hot-calender the shaped sheet to make the PTFE sheet thickness reach the target PTFE functional layer thickness, and obtain the calendered sheet; Step (7) The calender sheet is masked on one side, exposing only the adhesive side. Then, the adhesive side is treated with oxygen plasma and contacted with adhesive liquid to form an tackifying layer on the adhesive side. Then, the calender sheet is flipped over and masked on one side, exposing only the medium contact surface. Then, the medium contact surface is treated with oxygen plasma and contacted with primer and surface treatment liquid in sequence to form a PDA primer and anti-fouling functional layer on the medium contact surface to obtain an anti-fouling sheet. Step (8) Coat the surface of the tackifying layer on the adhesive side of the antifouling sheet with polyurethane adhesive, and then laminate it with the EPDM support layer by hot pressing. After cooling, it is die-cut to obtain a composite PTFE diaphragm sheet.

[0009] Preferably, the modified PTFE resin powder is unfilled modified PTFE molding powder.

[0010] More preferably, the modified PTFE resin powder is TFM1610.

[0011] Preferably, the preparation method of the surface treatment liquid includes the following steps: S1: 4-Vinylpyridine was dissolved in anhydrous acetonitrile, and 1,3-propanesulfonic acid lactone was added under an inert atmosphere to carry out a ring-opening quaternization reaction. After the reaction was completed, the betaine monomer was obtained by separation, washing and drying. In the above process, the pyridine nitrogen atom in 4-vinylpyridine undergoes a ring-opening quaternization reaction with 1,3-propanesulfonic acid lactone to obtain a zwitterionic monomer containing a betaine structure, which can be used to prepare antifouling polymers in the future.

[0012] S2: Betaine monomer, glycidyl methacrylate and free radical initiator are added to a mixed solvent of methanol and water, and a polymerization reaction is carried out under an inert atmosphere. After the reaction is completed, the polymer is obtained by precipitation, washing and drying. In the above process, the antifouling polymer contains zwitterionic structural units and reactive epoxy groups, which is beneficial for the subsequent formation of a stable functional layer on the surface of the base coating.

[0013] S3: Disperse the antifouling polymer in a mixed solvent of ethanol and Tris buffer to obtain a surface treatment solution.

[0014] Preferably, in S1, the molar ratio of 4-vinylpyridine to 1,3-propanesulfonic acid lactone is 1:0.9-1.1, the reaction temperature is 40-50°C, the reaction time is 10-14 h, the drying temperature is 40-50°C, and the drying time is 8-12 h.

[0015] Preferably, in step S2, the mass ratio of betaine monomer to glycidyl methacrylate is 70:30 to 90:10, the free radical initiator is azobisisobutyronitrile, the volume ratio of methanol to water is 6:4 to 8:2, the polymerization temperature is 60 to 70°C, and the polymerization time is 4 to 8 hours.

[0016] Preferably, in step S3, the mass concentration of the antifouling polymer in the surface treatment solution is 1-10 wt%, the mass ratio of ethanol to Tris buffer is 4:6-8:2, and the pH of the Tris buffer is 8.0-8.5.

[0017] Preferably, the preparation method of the primer is as follows: dopamine hydrochloride is dissolved in Tris buffer solution, the pH is adjusted to weakly alkaline, and the solution is stirred and dissolved under an oxygen atmosphere to obtain the primer.

[0018] In the above process, the primer is used to form a PDA primer layer on the medium contact surface to improve the stability of the subsequent antifouling functional layer construction.

[0019] Preferably, the concentration of dopamine hydrochloride in the primer is 1-5 g / L, the concentration of Tris buffer is 5-50 mmol / L, and the pH is 8.3-8.8; the treatment temperature of the primer used to form the PDA primer layer is 20-30°C, and the treatment time is 2-12 h.

[0020] Preferably, the adhesive liquid is an adhesive liquid containing a prepolymer, which is prepared by free radical solution polymerization of acrylamide, glycidyl methacrylate and 2-hydroxyethyl methacrylate; the obtained prepolymer is dissolved or uniformly dispersed in an organic solvent to obtain the adhesive liquid.

[0021] In the above process, the acrylamide structural unit provides amide polar sites, the 2-hydroxyethyl methacrylate structural unit provides hydroxyl sites, and the glycidyl methacrylate structural unit provides epoxy sites in the prepolymer, thus giving the resulting prepolymer both certain polarity and interfacial reactivity. After oxygen plasma treatment, the polarity and wettability of the PTFE adhesive-side surface are improved. The prepolymer in the adhesive solution is more easily spread, adsorbed, and dried to form a tackifying layer on the adhesive-side surface. This tackifying layer enhances the interfacial interaction between the prepolymer and the subsequent polyurethane adhesive and EPDM support layer, thereby improving the composite bonding strength between the PTFE functional layer and the EPDM support layer.

[0022] Preferably, the mass ratio of acrylamide, glycidyl methacrylate, and 2-hydroxyethyl methacrylate is 45–70:15–35:10–25; the free radical initiator is preferably azobisisobutyronitrile (AIB), and its amount is 0.2–2.0 wt% of the total monomer mass; the solution polymerization is preferably carried out under an inert atmosphere, and the polymerization solvent is preferably one of 1,4-dioxane, N,N-dimethylformamide, and dimethyl sulfoxide, or a mixed solvent composed of 1,4-dioxane and at least one of ethanol, N,N-dimethylformamide, and dimethyl sulfoxide; the polymerization temperature is preferably 60–70°C, and the polymerization time is preferably 4–8 h.

[0023] Preferably, after polymerization, the reaction solution is added to a precipitant to precipitate the prepolymer, which is then washed and dried to obtain the prepolymer. The prepolymer is then dissolved or uniformly dispersed in an organic solvent to obtain a bonding solution. Preferably, the mass concentration of the prepolymer in the bonding solution is 2–15 wt%.

[0024] Preferably, after the adhesive liquid comes into contact with the backing adhesive side treated with oxygen plasma, it is dried and fixed at 70-90°C to form an tackifying layer; if necessary, it can be further post-treated at 80-100°C for 0.5-2 hours to improve the stability of the tackifying layer.

[0025] Preferably, in step (1), after the modified PTFE resin powder is sieved through a 10-mesh sieve, it is first pressurized to 5MPa at a downward speed of 10-30mm / min at 23-26℃ and then depressurized and vented once. Then, the pressure is further increased to 20-35MPa and held for 10-20min to obtain a pressed blank.

[0026] Preferably, in step (2), sintering includes heating to 280-300°C at 2-4°C / min and holding for 5-20 min, then heating to 375-380°C at 0.5-1.5°C / min and holding for 6-10 h, followed by cooling to 280-300°C at 0.5-1.5°C / min and then naturally cooling.

[0027] Preferably, in step (3), the preheating temperature before turning is 80-120°C and the preheating time is 1-3 hours.

[0028] Preferably, in step (5), the temperature for low-temperature leveling and shaping is 53-75℃, the pressure is 0.3-0.8MPa, the time is 6-10min, and the cooling medium is deaerated deionized water at 5-15℃.

[0029] Preferably, in step (6), the hot rolling temperature is 200-240℃, the linear pressure is 20-60kN / m, the rolling speed is 0.5-1.5m / min, the number of rolling passes is 1-3, and the thickness of the rolled sheet is 0.5-2.0mm.

[0030] Preferably, the oxygen plasma treatment in step (7) is radio frequency oxygen plasma treatment, with a treatment frequency of 13.56MHz, a cavity pressure of 10-30Pa, an oxygen flow rate of 20-50sccm, a treatment power of 30-120W, and a treatment time of 20-180s.

[0031] Preferably, in step (7), the treatment of the adhesive side and the medium contact surface is carried out by single-sided shielding. When treating one side, the other side is physically shielded or prevented from contacting the treatment liquid to reduce mutual interference between the two interface layers.

[0032] Preferably, in step (8), the coating amount of polyurethane adhesive is 5-20 g / m². 2 The hot-pressing temperature is 175–190℃, the hot-pressing pressure is 10–30MPa, and the hot-pressing time is 5–15min.

[0033] The present invention also provides a composite PTFE diaphragm sheet, which is prepared by the above method. The composite PTFE diaphragm sheet includes a PTFE functional layer, an tackifying layer located on the adhesive side of the PTFE functional layer, a PDA undercoating layer and an anti-fouling functional layer located on the medium contact surface side of the PTFE functional layer, and a polyurethane adhesive layer and an EPDM support layer located on the side of the tackifying layer away from the PTFE functional layer; the side of the tackifying layer away from the PTFE functional layer is compositely connected to the EPDM support layer through the polyurethane adhesive layer.

[0034] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. This invention constructs an tackifying layer, a PDA undercoat layer, and an anti-fouling functional layer on both sides of the same PTFE sheet. Through this structural arrangement, the adhesive side and the medium contact surface each undertake different interface functions, thereby simultaneously ensuring interlayer bonding performance and medium surface anti-fouling performance.

[0035] 2. Before the double-sided differential surface treatment, the PTFE machined sheet is first subjected to low-temperature flattening and hot calendering. This process arrangement improves the flatness and thickness consistency of the sheet, thereby enhancing the stability of subsequent surface treatment and hot-pressing lamination.

[0036] 3. This invention employs a sequential construction method of oxygen plasma treatment, PDA undercoat, and antifouling functional layer at the media contact surface. This structural arrangement improves the stability of the antifouling functional layer on the PTFE surface, thereby reducing contaminant adhesion and residue after cleaning. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a schematic diagram of the cross-sectional structure of the composite PTFE diaphragm sheet of the present invention.

[0039] Figure 2 This is a physical image of the composite PTFE diaphragm sheet of the present invention.

[0040] Figure 3 This is a bar chart showing the water contact angle of the composite PTFE diaphragm sheet of the present invention.

[0041] Figure 4 This is a line graph showing the BSA adsorption capacity and residual amount after cleaning of the composite PTFE membrane sheet of the present invention. Detailed Implementation

[0042] 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.

[0043] like Figure 1 As shown, the composite PTFE membrane sheet includes a PTFE functional layer, an adhesive layer on the backing side of the PTFE functional layer, a PDA base coating and an anti-fouling functional layer sequentially disposed on the media contact surface of the PTFE functional layer, and the side of the adhesive layer away from the PTFE functional layer is compositely connected to the EPDM support layer through a polyurethane adhesive layer.

[0044] In this invention, the treatment of the adhesive side and the medium contact surface is preferably carried out by a single-sided shielding method, that is, when treating one side, the other side is physically shielded or prevented from contacting the treatment liquid, so as to reduce cross-contamination on both sides and thus form different interface layers on both sides respectively.

[0045] The modified PTFE resin used in this embodiment is preferably modified PTFE molding powder. The support layer is preferably a sheet-like EPDM support layer. The monomers used in the surface treatment solution include 4-vinylpyridine and 1,3-propanesulfonic acid lactone, the raw materials used in the primer solution include dopamine hydrochloride and Tris buffer, and the raw materials used in the adhesive solution include acrylamide, glycidyl methacrylate, and 2-hydroxyethyl methacrylate. Unless otherwise specified, all reagents used in this embodiment can be commercially available raw materials of conventional purity grades in the art.

[0046] Preparation Example 1 This preparation example discloses a method for preparing a surface treatment liquid, including the following steps: S1: Dissolve 79g of 4-vinylpyridine in 300mL of anhydrous acetonitrile and stir until completely dissolved under nitrogen protection. Then add 92g of 1,3-propanesulfonic acid lactone in portions and react at 45℃ for 12h. After the reaction is complete, cool to room temperature, filter the precipitated solid, wash the obtained solid with anhydrous acetonitrile and diethyl ether 2-3 times in sequence, and dry under vacuum at 45℃ for 10h to obtain betaine monomer.

[0047] S2: Add 80g of the betaine monomer and 20g of glycidyl methacrylate to a mixed solvent of 400mL methanol and deionized water, then add 1.0g of azobisisobutyronitrile. After purging with nitrogen for 30min, react at 65℃ for 6h. After the reaction is complete, slowly add the reaction solution dropwise to 2L of acetone to precipitate the precipitate. Filter the precipitate, wash it with acetone 2-3 times, and dry it under vacuum at 40℃ for 12h to obtain the antifouling polymer. The volume ratio of methanol to deionized water is 7:3.

[0048] S3: Add 5g of the antifouling polymer to a mixed solvent of 95g ethanol and 10mmol / L Tris buffer, and stir at room temperature for 30min to uniformly disperse the antifouling polymer and obtain the surface treatment solution.

[0049] The pH of the Tris buffer solution is 8.0–8.5, and the mass ratio of ethanol to Tris buffer solution is 6:4.

[0050] Preparation Example 2 This preparation example discloses a method for preparing a primer, including the following steps: Dissolve 2.0 g of dopamine hydrochloride in 1 L of 10 mmol / L Tris buffer, adjust the pH to 8.5 with sodium hydroxide, and stir in the dark under air until completely dissolved to obtain the primer solution, which should be prepared and used immediately.

[0051] Preparation Example 3 This preparation example discloses an adhesive prepolymer and a method for preparing the adhesive, including the following steps: P1: Add 60g of acrylamide to a four-necked flask equipped with a stirrer, thermometer, condenser and nitrogen inlet device, add 200mL of N,N-dimethylformamide, and stir at room temperature until the acrylamide dissolves; then add 25g of glycidyl methacrylate, 15g of 2-hydroxyethyl methacrylate and 200mL of anhydrous 1,4-dioxane, and continue stirring until a clear solution is formed to obtain a monomer mixture; then add 1.0g of azobisisobutyronitrile as a free radical initiator.

[0052] P2: Continue stirring for 30 minutes under nitrogen protection to remove dissolved oxygen from the system, then raise the temperature to 65°C and keep it at that temperature for 6 hours to carry out free radical solution polymerization. After the reaction is completed, cool to room temperature.

[0053] P3: Slowly pour the reaction solution into 2L of acetone to precipitate the precipitate, filter and collect the precipitate, and wash it three times with acetone to remove unreacted monomers and low molecular weight substances; then dry it under vacuum at 40℃ for 11h to obtain the adhesive prepolymer.

[0054] P4: Weigh 8g of the above prepolymer and add it to a mixed solvent of 92g ethanol and 1,4-dioxane. Stir at room temperature for 45min to dissolve or uniformly disperse it to obtain the adhesive solution.

[0055] The mass ratio of ethanol to 1,4-dioxane is 1:1; the mass concentration of the prepolymer in the adhesive solution is 8 wt%. Example 1

[0056] This embodiment discloses a method for preparing a composite PTFE membrane sheet, including the following steps: Step (1) 100 parts by weight of modified polytetrafluoroethylene TFM1610 resin were sieved through a 10-mesh sieve and then evenly added into a hollow cylindrical mold. At 25°C, the pressure was increased to 5MPa at a downward speed of 20mm / min. The pressure was released once after 4s of depressurization. Then the pressure was increased to 25MPa at the same rate and held for 15min. The molded blank was then demolded to obtain the pressed blank.

[0057] Step (2) Place the pressed blank in a sintering furnace, raise the temperature to 290°C at a heating rate of 3°C / min and hold for 10 min, raise the temperature to 380°C at a heating rate of 1°C / min and hold for 8 h, then lower the temperature to 290°C at a cooling rate of 1°C / min and then cool naturally to room temperature to obtain the sintered blank.

[0058] Step (3) After the sintered billet is kept at 100℃ for 2 hours, it is turned to obtain a continuous sheet with a thickness of 1.7mm, which is called a turned sheet. The turned thickness is slightly larger than the thickness of the final product to leave machining allowance for subsequent low-temperature flattening, hot rolling and composite die cutting.

[0059] Step (4) Trim the edge of the machined sheet according to the maximum diameter of the target film and cut it into a square sheet with a side length of 20-40 mm plus the target diameter to obtain a square sheet.

[0060] Step (5) The square sheet is placed between two mirror-polished stainless steel plates, and a release PTFE film is placed between the sheet and the stainless steel plates. Then, it is kept at 65°C for 8 minutes and a flat pressure of 0.5MPa is applied to allow the sheet to undergo low-temperature thermal relaxation and flattening under restricted conditions. After the heat preservation is completed, the sheet and the clamping plates are transferred to 10°C deaerated deionized water for cooling. After the sheet temperature is below 50°C, it is taken out and dried to obtain the shaped sheet.

[0061] Step (6) The shaped sheet is fed into the hot calendering device and hot calendered at 220°C. The calendering roll gap is pre-calibrated according to the target PTFE functional layer thickness and sheet springback, so that the PTFE sheet thickness after calendering reaches the target value. The sheet thickness after calendering is controlled at 1.5mm, the linear pressure is controlled at 40kN / m, the calendering speed is controlled at 1m / min, and calendering is performed continuously for 2 passes to obtain the calendered sheet.

[0062] Step (7-1) First, the calender sheet is shielded on one side with the adhesive side facing outward, exposing only the adhesive side. While keeping the opposite side surface shielded, the exposed adhesive side is subjected to O2 radio frequency plasma treatment with a treatment power of 50W and a treatment time of 60s. Then, without removing the shield, the adhesive side of the plasma-treated calender sheet is brought into contact with the adhesive liquid obtained in Preparation Example 3, so that the adhesive liquid covers the exposed adhesive side surface. After removing the excess adhesive liquid, it is dried and fixed at 80°C for 3h, followed by post-treatment at 90°C for 1h. After the treatment is completed, it is taken out and the shield is removed to obtain the tackified sheet with an tackifying layer formed on the adhesive side.

[0063] The plasma treatment uses 13.56MHz radio frequency oxygen plasma conditions, with a chamber pressure of 20Pa and an oxygen flow rate of 35sccm.

[0064] Step (7-2): Flip the tackifying sheet over and re-mask it with the dielectric contact surface facing outwards, exposing only the dielectric contact surface. While keeping the opposite side surfaces masked, perform O2 radio frequency plasma treatment on the exposed surface at a power of 50W for 60s. Then, without removing the mask, immerse the sheet in the primer solution obtained in Preparation Example 2 and react at 25°C for 6 hours to deposit a PDA primer coating on the exposed surface. Remove the sheet, rinse with deionized water, and dry to obtain the primer sheet. Then, while keeping the sheet masked on one side, immerse it in the surface treatment solution obtained in Preparation Example 1 and react at 50°C for 2 hours, followed by drying at 80°C for 1 hour. After the reaction, wash, dry, and remove the mask to obtain a sheet with single-sided anti-fouling treatment, i.e., an anti-fouling sheet.

[0065] Step (8) Apply polyurethane adhesive evenly to the tackifying layer surface on the adhesive side of the anti-fouling sheet, with an adhesive application rate of 15 g / m². 2 The adhesive-coated tackifying layer is then stacked with the EPDM support layer and hot-pressed at 180°C and 25MPa for 10 minutes. After cooling, the film is demolded to obtain a composite sheet. The film is then die-cut to the target size to obtain the finished film. Example 2

[0066] This embodiment is the same as Embodiment 1 except for the following conditions: In step (1), the final molding pressure is 20 MPa, and the pressure is held for 10 minutes; In step (2), the heat preservation time at 380℃ is 6 hours; In step (5), the low-temperature leveling and shaping temperature is 55℃, the pressure is 0.3MPa, and the time is 6min; In step (6), the hot rolling temperature is 205℃, the linear pressure is 20kN / m, and the rolling is done in one pass. In step (7-1), the adhesive solution treatment temperature is 75℃ and the time is 2 hours; In step (7-2), the primer application time is 4 hours, the surface treatment liquid temperature is 40℃, and the time is 1.5 hours. Example 3

[0067] This embodiment is the same as Embodiment 1 except for the following conditions: In step (1), the final molding pressure is 35 MPa, and the pressure is held for 20 minutes; In step (2), the heat preservation time at 380℃ is 10 hours; In step (5), the low-temperature leveling and shaping temperature is 72℃, the pressure is 0.7MPa, and the time is 10min; In step (6), the hot rolling temperature is 235℃, the linear pressure is 50kN / m, and the rolling is done in 2 passes. In step (7-1), the adhesive solution treatment temperature is 90℃ and the time is 4 hours; In step (7-2), the primer application time is 8 hours, the surface treatment liquid temperature is 55℃, and the time is 3 hours. Example 4

[0068] This embodiment is the same as Embodiment 1 except for the following conditions: In Preparation Example 1, the mass ratio of betaine monomer to glycidyl methacrylate was adjusted to 70:30; In Preparation Example 3, the mass ratio of acrylamide, glycidyl methacrylate, and 2-hydroxyethyl methacrylate was adjusted to 45:35:20. In step (7-2), the mass concentration of the antifouling polymer in the surface treatment solution is adjusted to 3 wt%.

[0069] Comparative Example 1 Compared with Example 1, Comparative Example 1 omits step (7), and the rest is the same as Example 1. That is, after calendering, no adhesive-backing treatment is performed, nor is PDA base coating and anti-fouling treatment performed on the dielectric surface. Instead, polyurethane adhesive is directly coated on the adhesive-backing side of the calender and hot-pressed with the EPDM support layer.

[0070] Comparative Example 2 Compared with Example 1, Comparative Example 2 only retains step (7-1) and omits step (7-2), while the rest is the same as Example 1. That is, only the adhesive side is treated with oxygen plasma and comes into contact with the adhesive liquid to form an tackifying layer, while the media side is not treated with PDA primer and anti-fouling layer.

[0071] Comparative Example 3 Compared with Example 1, Comparative Example 3 only retains step (7-2) and omits step (7-1), and the rest is the same as Example 1. That is, only the medium contact surface is treated with oxygen plasma, primer, and surface treatment liquid, while no tackifying layer is constructed on the adhesive side.

[0072] Comparative Example 4 Compared with Example 1, Comparative Example 4 omits the primer treatment in step (7-2), and the rest is the same as Example 1. That is, the medium contact surface is directly in contact with the surface treatment liquid after oxygen plasma treatment, without first forming a PDA primer coating.

[0073] Test methods The samples obtained in Examples 1-4 and Comparative Examples 1-4 were subjected to tests on the water contact angle of the medium contact surface, the water contact angle of the adhesive side, the 180° peel strength of the PTFE / EPDM interlayer, the protein adsorption amount, and the residual amount after washing.

[0074] The water contact angle of the media contact surface was tested using the media contact surface of the composite PTFE diaphragm sheet; the water contact angle of the adhesive side was tested using the adhesive side of the same batch of PTFE sheets that had undergone adhesive side treatment but had not yet been coated with polyurethane adhesive and the composite EPDM support layer. The water contact angle was tested using the static contact angle method at a temperature of 25±2℃ and a drop volume of 2μL. Five locations were randomly tested for each sample, and the average value was taken. The 180° peel strength between the PTFE / EPDM layers was tested using an electronic tensile testing machine with a sample width of 15mm and a peel speed of 100mm / min. Five parallel samples were tested in each group, and the average value was taken. In the protein adsorption test, a 1.0mg / mL BSA solution was used as the simulated contaminant, and adsorption was performed at 25℃ for 2 hours. After adsorption, the media contact surface of the sample was rinsed with deionized water, and the adsorption amount per unit area was calculated using a protein quantification method. In the residual amount test after cleaning, after the sample was contaminated with BSA, the sample medium contact surface was rinsed three times with deionized water for 30 seconds each time; then the amount of residual protein on the sample medium contact surface was measured and converted into residual amount per unit area.

[0075] The test results are shown in Table 1: Table 1

[0076] According to Table 1 and the test results of Examples 1-4 and Comparative Examples 1-4, the composite PTFE membrane prepared in Example 1 of the present invention has a low water contact angle on the medium surface, a low amount of BSA adsorption and residual amount after cleaning, and a high interlayer peel strength of PTFE and EPDM, indicating that it has both good compatibility of the adhesive side and anti-fouling performance on the medium contact surface. The comparison between Comparative Example 1 and Example 1 shows that the lack of double-sided differential surface treatment leads to a decrease in interlayer bonding performance, as well as a deterioration in the wettability and antifouling properties of the medium surface. The comparison between Comparative Example 2 and Example 1 shows that while adhesive-side tackification treatment alone can improve interlayer bonding performance, it cannot effectively reduce contaminant adhesion and residue after cleaning. The comparison between Comparative Example 3 and Example 1 shows that while antifouling treatment alone can improve the wettability and antifouling properties of the medium surface, the compatibility of the adhesive-side bonding is insufficient. The comparison between Comparative Example 4 and Example 1 shows that the lack of a PDA undercoat in the medium surface treatment weakens the construction effect of the antifouling functional layer, thereby increasing the contact angle of the medium surface, the amount of protein adsorption, and the amount of residue after cleaning.

[0077] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. All equivalent substitutions, modifications, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a composite PTFE diaphragm sheet, characterized in that, Includes the following steps: Step (1) After sieving the modified PTFE resin powder, add it into the hollow cylindrical mold, and after pressurization, degassing, pressure holding and demolding, obtain the pressed blank of the hollow cylinder; Step (2) involves sintering, holding, cooling and sintering the pressed billet in stages to obtain a sintered billet; Step (3) After preheating the sintered billet, it is machined to obtain continuous PTFE machined sheets; Step (4) Trim the PTFE machined sheet according to the target diaphragm sheet size and cut it into square sheets; Step (5) The square sheet is subjected to low-temperature thermal relaxation and flattening under restricted flat pressure, and then cooled and dried to obtain the shaped sheet; Step (6) Hot-calender the shaped sheet to make the PTFE sheet thickness reach the target PTFE functional layer thickness, and obtain the calendered sheet; Step (7) The calender sheet is masked on one side, exposing only the adhesive side. Then, the adhesive side is treated with oxygen plasma and contacted with adhesive liquid to form an tackifying layer on the adhesive side. Then, the calender sheet is flipped over and masked on one side, exposing only the medium contact surface. Then, the medium contact surface is treated with oxygen plasma and contacted with primer and surface treatment liquid in sequence to form a PDA primer and anti-fouling functional layer on the medium contact surface to obtain an anti-fouling sheet. Step (8) Coat the surface of the tackifying layer on the adhesive side of the antifouling sheet with polyurethane adhesive, and then laminate it with the EPDM support layer by hot pressing. After cooling, it is die-cut to obtain a composite PTFE diaphragm sheet.

2. The preparation method according to claim 1, characterized in that, The preparation method of the surface treatment liquid includes the following steps: S1: 4-Vinylpyridine was dissolved in anhydrous acetonitrile, and 1,3-propanesulfonic acid lactone was added under an inert atmosphere to carry out a ring-opening quaternization reaction. After the reaction was completed, the betaine monomer was obtained by separation, washing and drying. S2: The betaine monomer, glycidyl methacrylate and free radical initiator are added to a mixed solvent of methanol and water, and a polymerization reaction is carried out under an inert atmosphere. After the reaction is completed, the polymer is obtained by precipitation, washing and drying. S3: Disperse the antifouling polymer in a mixed solvent of ethanol and Tris buffer to obtain a surface treatment solution.

3. The preparation method according to claim 2, characterized in that, In step S1, the molar ratio of 4-vinylpyridine to 1,3-propanesulfonic acid lactone is 1:0.9–1.1, the reaction temperature is 40–50°C, the reaction time is 10–14 h, the drying temperature is 40–50°C, and the drying time is 8–12 h. In step S2, the mass ratio of betaine monomer to glycidyl methacrylate is 70:30–90:10, the free radical initiator is azobisisobutyronitrile, the volume ratio of methanol to water is 6:4–8:2, the polymerization temperature is 60–70°C, and the polymerization time is 4–8 h. In step S3, the mass concentration of the antifouling polymer in the surface treatment solution is 1–10 wt%, the mass ratio of ethanol to Tris buffer is 4:6–8:2, and the pH of the Tris buffer is 8.0–8.

5.

4. The preparation method according to claim 1, characterized in that, The preparation method of the primer liquid includes the following steps: Dopamine hydrochloride was dissolved in Tris buffer, the pH was adjusted to weakly alkaline, and the solution was stirred and dissolved under an oxygen atmosphere to obtain the primer.

5. The preparation method according to claim 4, characterized in that, The concentration of dopamine hydrochloride in the primer solution is 1–5 g / L, the concentration of the Tris buffer solution is 5–50 mmol / L, and the pH is 8.3–8.8; the treatment temperature of the primer solution used to form the PDA primer layer is 20–30 °C, and the treatment time is 2–12 h.

6. The preparation method according to claim 1, characterized in that, The adhesive liquid is an adhesive liquid containing a prepolymer, which is obtained by solution polymerization of acrylamide, glycidyl methacrylate and 2-hydroxyethyl methacrylate under the action of a free radical initiator; the obtained prepolymer is dissolved or uniformly dispersed in an organic solvent to obtain the adhesive liquid.

7. The preparation method according to claim 6, characterized in that, The mass ratio of acrylamide, glycidyl methacrylate, and 2-hydroxyethyl methacrylate is 45–70:15–35:10–25; the free radical initiator is azobisisobutyronitrile (AIB), and its dosage is 0.2–2.0 wt% of the total monomer mass; the solution polymerization is carried out under an inert atmosphere, and the polymerization solvent is one of 1,4-dioxane, N,N-dimethylformamide, and dimethyl sulfoxide, or a mixed solvent composed of 1,4-dioxane and at least one of ethanol, N,N-dimethylformamide, and dimethyl sulfoxide; the polymerization temperature is 60–70°C, and the polymerization time is 4–8 h; after polymerization, the prepolymer is obtained by precipitation, washing, and drying; the mass concentration of the prepolymer in the adhesive solution is 2–15 wt%; after the adhesive solution comes into contact with the backing adhesive side treated with oxygen plasma, it is dried and fixed at 70–90°C to form an tackifying layer.

8. The preparation method according to claim 1, characterized in that, In step (1), the modified PTFE resin powder is sieved through a 10-mesh sieve, and then pressurized to 5MPa at a downward speed of 10-30mm / min at 23-26℃, followed by depressurization and gas release once, and then pressurized to 20-35MPa and held for 10-20min to obtain a pressed blank; in step (2), sintering includes heating to 280-300℃ at 2-4℃ / min and holding for 5-20min, then heating to 375-380℃ at 0.5-1.5℃ / min and holding for 6-10h, and then cooling to 280-300℃ at 0.5-1.5℃ / min and then naturally cooling; in step (3), the preheating temperature before turning is 80-120℃ and the preheating time is 1-3h.

9. The preparation method according to claim 1, characterized in that, In step (5), the temperature for low-temperature leveling and shaping is 53-75℃, the pressure is 0.3-0.8MPa, the time is 6-10min, and the cooling medium is deaerated deionized water at 5-15℃; in step (6), the temperature for hot calendering is 200-240℃, the linear pressure is 20-60kN / m, the calendering speed is 0.5-1.5m / min, the number of calendering passes is 1-3, and the thickness of the calendered sheet is 0.5-2.0mm.

10. A composite PTFE diaphragm sheet, characterized in that, It includes a PTFE functional layer, with an adhesive layer on the backing side of the PTFE functional layer, and a PDA base coating and an anti-fouling functional layer sequentially disposed on the media contact surface of the PTFE functional layer. The side of the adhesive layer away from the PTFE functional layer is compositely connected to the EPDM support layer through a polyurethane adhesive layer.

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