Polypropylene hydrophilic welding method for bag type filter

Abstract

The invention belongs to the field of bag type filter processing, and particularly relates to a polypropylene hydrophilic welding method for a bag type filter. The method comprises the following steps: (1) carrying out plasma treatment on a polypropylene component for the bag type filter to obtain a plasma modified polypropylene component; (2) mixing ovalbumin and tannic acid, and adding a pH regulator to obtain a mixed solution; (3) immersing the plasma modified polypropylene component into the mixed solution for reaction, and taking out and drying after the reaction is completed, so as to obtain a hydrophilic modified polypropylene component; and (4) melting the hydrophilic modified polypropylene component, and integrally welding the hydrophilic modified polypropylene component with the polyethersulfone membrane to form a complete bag type filter assembly. Plasma destroys chemical bonds on the surface of polypropylene to form polar groups, and the mixed solution and the polar groups are crosslinked to form a stable hydrophilic layer. Good wetting can be achieved without pressurization, the performance of a polypropylene body is reserved, the process is simple, and the method is suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of capsule filter processing, and specifically relates to a hydrophilic welding method for polypropylene used in capsule filters. Background Technology

[0002] Encapsulated filters, as a type of high-efficiency and precision filtration equipment, are widely used in pharmaceuticals, bioengineering, food and beverage, and water treatment. Their core function is to trap particles and impurities in fluids through a filter membrane. The welding quality between the filter membrane and the end cap directly determines the filter's filtration performance, wetting efficiency, and service life. In current encapsulated filter production, the filter membrane is mostly made of hydrophilic polyethersulfone (PES), which has advantages such as uniform pore size, high filtration accuracy, and good chemical stability. However, during the high-temperature hot-melt welding process, the polar groups (such as hydroxyl groups and ether bonds) in the PES membrane's molecular chain are prone to breakage, leading to a significant decrease in the hydrophilicity and an increase in the hydrophobicity of the membrane at the weld joint.

[0003] Meanwhile, the filter's flat cap, outlet cap, and other components are all made of polypropylene. Polypropylene is a typical non-polar polymer material with low surface energy and a lack of active functional groups on its molecular chains. Water has a contact angle of nearly 90° on its surface, exhibiting extremely strong hydrophobicity, making it difficult for water droplets to spread and wet the surface. In traditional processes, polypropylene is directly melted and welded to a polyethersulfone membrane. The hydrophobicity of the molten polypropylene further exacerbates the insufficient hydrophilicity of the welded area, resulting in the filter requiring forced wetting with 1-2 bar pressure from imported pressurization equipment before use to achieve ideal initial filtration conditions.

[0004] This forced wetting method has many drawbacks: on the one hand, it adds extra production processes, equipment investment, and energy consumption, increasing the production cost of the filter and reducing production efficiency; on the other hand, the welded joints of some complex filter structures may not be sufficiently wetting under pressure, leaving residual air or forming "dry areas," which affects the filtration accuracy and may even lead to filtrate contamination; in addition, long-term reliance on pressure wetting will increase the operational complexity of the filter during use and limit its application in scenarios where pressure is not required (such as low-pressure fluid filtration).

[0005] Currently, the main methods for hydrophilic modification of polypropylene in the industry include chemical grafting modification and surface coating modification. However, chemical grafting modification requires the use of strong oxidants or initiators, which can easily damage the mechanical properties, temperature resistance, and other key indicators of the polypropylene matrix. Surface coating modification suffers from problems such as poor adhesion between the coating and the polypropylene substrate, easy peeling after long-term use, and insufficient solvent resistance, making it difficult to meet the requirements of capsule filters under harsh operating conditions. Therefore, developing a polypropylene hydrophilic modification and welding method that does not change the properties of the polypropylene matrix, has a simple and controllable process, provides stable hydrophilic modification effects, and is compatible with existing welding processes has become a key requirement for solving the pain points of existing capsule filter technology.

[0006] Therefore, based on this, the technical solution of the present invention is proposed. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention improves the hydrophilicity of the polypropylene surface through surface modification technology without changing the properties of the main polypropylene material. This solves the problem of strong hydrophobicity and difficulty in wetting at the weld joint after welding with polyethersulfone membrane, and simplifies the wetting process of the capsule filter.

[0008] This invention provides a hydrophilic welding method for polypropylene used in capsule filters, the hydrophilic welding method for polypropylene comprising the following steps:

[0009] (1) Plasma treatment is performed on the polypropylene components used in the capsule filter to obtain plasma-modified polypropylene components; (2) Mix ovalbumin and tannic acid, and add a pH adjuster to obtain a mixed solution; (3) The plasma-modified polypropylene component is immersed in the mixed solution for reaction, and after completion, it is taken out and dried to obtain the hydrophilic modified polypropylene component; (4) Melt the hydrophilic modified polypropylene component and weld it to the polyethersulfone membrane to form a complete capsule filter assembly.

[0010] To facilitate understanding of this invention, the principles of this invention are described below: First, this invention utilizes nitrogen gas ejected from a direct-injection plasma treatment machine to bombard the surface of polypropylene. High-energy particles disrupt the original chemical bonds on the polypropylene surface, generating numerous polar molecular chains (such as molecular structures containing polar functional groups like hydroxyl and carboxyl groups), providing reaction sites for subsequent hydrophilic modification. Second, the mixed solution of ovalbumin and tannic acid contains a large number of hydrophilic functional groups (amino, carboxyl, hydroxyl, and phenolic hydroxyl groups). Under alkaline conditions, these groups can introduce negative charges into the solution, accelerating the cross-linking reaction between the hydrophilic functional groups and the polar molecular chains generated on the polypropylene surface. Finally, the modification only acts on the polypropylene surface, without altering its overall melting characteristics. During high-temperature welding, the surface-modified polypropylene retains its hydrophilicity after melting. When combined with a polyethersulfone film, the overall hydrophilicity of the weld joint is consistent, avoiding the problem of increased hydrophobicity after melting of unmodified polypropylene.

[0011] Preferably, in step (1), the polypropylene component is a polypropylene end cap and a polypropylene liquid outlet.

[0012] Preferably, in step (1), the plasma treatment is performed by connecting a direct-injection plasma treatment machine to a nitrogen tank and spraying nitrogen under pressure to bombard the surface of the polypropylene component for treatment.

[0013] Preferably, the pressure is 0.4-0.6 MPa and the processing time is 10-15 seconds.

[0014] Preferably, in step (2): The mass ratio of ovalbumin to tannic acid is 2-3:1; And / or, in the mixed solution, the total mass fraction of ovalbumin and tannic acid is 1-2%.

[0015] Preferably, in step (2), the pH adjuster is a NaOH solution with a concentration of 0.5-1 mol / L.

[0016] Preferably, in step (3), the reaction temperature is 60-70℃ and the reaction time is 30-40min.

[0017] Preferably, in step (3), the drying temperature is 50-60°C.

[0018] Preferably, in step (4), the melting temperature is 630-650°C.

[0019] The beneficial effects of this invention are as follows: This invention utilizes a composite modification process involving plasma treatment and crosslinking with a hydrophilic mixed solution to form a stable hydrophilic layer on the polypropylene surface. After welding with a polyethersulfone membrane, rapid and uniform wetting can be achieved without applying 1-2 bar of imported pressure, completely solving the core problem of strong hydrophobicity and difficult wetting at the weld joint in traditional processes, thus improving the ease of use of the filter. Secondly, the modification process only acts on the surface of the polypropylene, without damaging the internal molecular structure of the substrate. The original mechanical strength, temperature resistance, and chemical corrosion resistance of the polypropylene remain unchanged, fully meeting the requirements of capsule filters for end cap materials. Finally, the mixed solution of ovalbumin and tannic acid forms covalent crosslinks with the polar groups on the polypropylene surface through functional groups such as amino, carboxyl, and hydroxyl groups, resulting in strong bonding. After drying and curing, the hydrophilic layer does not decompose or fall off during subsequent hot-melt welding, and it maintains good hydrophilicity even after long-term immersion in water or common filtrates, resulting in a long service life. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0021] Example 1 This embodiment provides a hydrophilic welding method for polypropylene used in capsule filters, the hydrophilic welding method for polypropylene includes the following steps: (1) Pretreatment of polypropylene components: Gently wipe the surface of the polypropylene components (polypropylene end caps and polypropylene liquid outlets) with a lint-free cloth soaked in anhydrous ethanol, focusing on removing dust and other impurities. After wiping, place the end caps on a clean workbench and let them air dry for 5 minutes. This removes surface contaminants, prevents impurities from obstructing the contact between the plasma and the polypropylene surface, and also prevents impurities from affecting the bonding force between the hydrophilic layer and the substrate, ensuring the uniformity and stability of subsequent modification treatment.

[0022] (2) Plasma treatment equipment commissioning: Connect the direct-injection plasma treatment machine to the nitrogen tank via a high-pressure resistant pipeline. Seal the connection with sealing tape. Open the nitrogen tank valve and check for leaks in the pipeline (by applying soapy water to the connection and observing whether bubbles appear). Start the plasma treatment machine and adjust the output pressure to 0.4 MPa. Keep the equipment running unloaded for a period of time to stabilize the nitrogen pressure and the equipment's operating status. Ensure that the nitrogen pressure remains constant during the plasma treatment process to avoid pressure fluctuations that could lead to uneven formation of polar groups on the polypropylene surface. Investigate pipeline leaks to prevent gas waste and safety hazards, and improve process reliability.

[0023] (3) Plasma treatment: After air-drying, the polypropylene parts are evenly placed on the worktable. The nozzle axis of the direct-injection plasma treatment machine is adjusted to be perpendicular to the surface of the polypropylene parts to be treated. The plasma spray switch is turned on, and the nozzle is moved at a uniform speed to perform a comprehensive direct-injection treatment on the surface to be treated. The treatment time for each area is 10 seconds. After the treatment is completed, the equipment is turned off, and the polypropylene parts are transferred to a clean container for later use. Plasma has high energy. When bombarding the surface of polypropylene, it can break the non-polar chemical bonds in its molecular chain, so that polar functional groups such as hydroxyl and carboxyl groups are generated on the surface. This provides sufficient active sites for the subsequent cross-linking reaction with the hydrophilic mixed solution. The uniform movement of the nozzle can ensure the uniformity of the treatment area.

[0024] (4) Preparation of hydrophilic mixed solution: (4-1) Weigh 2.000g of ovalbumin and 1.000g of tannic acid accurately using an electronic balance, and put them into a 500mL beaker. Add 297.0mL of deionized water to the beaker, place the beaker on a magnetic stirrer, set the stirring speed to 300r / min, and stir continuously for 15 minutes until the ovalbumin and tannic acid are completely dissolved, and an initial mixture without obvious precipitation is obtained.

[0025] (4-2) Take 0.5 mol / L NaOH solution and place it in a burette. Slowly add it to the initial mixture at a rate of 1 drop / second. Keep the stirring speed constant (300 r / min) during the addition process. At the same time, use a precision pH meter to monitor the pH value of the solution in real time. When the pH meter shows a stable value of 10.00, stop adding NaOH solution.

[0026] (4-3) Transfer the beaker containing the mixed solution to a constant temperature water bath. Set the water bath temperature to 65°C and turn on the water bath. After the solution temperature rises to 65°C, maintain the constant temperature for 5 minutes to ensure that the solution temperature is uniform and stable.

[0027] The amino, carboxyl, hydroxyl, and phenolic hydroxyl groups contained in ovalbumin and tannic acid have extremely strong hydrophilicity. The alkaline environment of pH 10 adjusted by NaOH solution can ionize the functional groups in the mixed solution to generate negative charges, thereby accelerating the cross-linking reaction rate with the polar groups on the polypropylene surface. The constant temperature of 65℃ can maintain the stability of the solution system, avoid the reaction rate being too slow due to excessively low temperature, and prevent high temperature from damaging the hydrophilic functional groups.

[0028] (5) Hydrophilic crosslinking immersion treatment: The polypropylene parts that have undergone plasma treatment are quickly placed into the above-mentioned hydrophilic mixed solution at a constant temperature of 65°C, ensuring that the parts are completely submerged. The water bath temperature is kept constant at 65°C, and the immersion time is 30 minutes. During the immersion process, the solution is gently stirred with a glass rod for 1 minute every 10 minutes to ensure that the surface of the parts is in full contact with the solution. The polar functional groups on the surface of polypropylene undergo crosslinking reactions with the amino and phenolic hydroxyl groups in the mixed solution. Under alkaline conditions, the reaction rate is significantly increased, and a uniform preliminary hydrophilic layer can be formed in 30 minutes. Regularly stirring the solution can prevent the local solution concentration on the end cap surface from decreasing, ensuring that the thickness of the hydrophilic layer is uniform.

[0029] (6) Drying and curing of modified end caps: After the soaking time is over, use tweezers to remove the polypropylene end caps from the mixed solution, gently absorb the excess solution adhering to the surface with clean filter paper, place the parts in an electric thermostatic drying oven, set the drying temperature to 50℃, close the oven door and start the drying program, and dry for 1 hour; after drying, open the drying oven door and allow it to cool naturally to room temperature (about 20 minutes) to obtain the surface-modified polypropylene parts. Low-temperature drying at 50℃ can slowly remove the moisture on the surface of the end caps, avoiding the decomposition of the hydrophilic layer or deformation of the polypropylene substrate caused by high-temperature drying; during the drying process, the hydrophilic cross-linked structure is further cured to form a dense and firm hydrophilic layer, which improves its stability in subsequent welding and use.

[0030] (7) Welding: Start the hot melt welding machine, set the welding temperature to 650℃, and wait for the equipment temperature display to stabilize at 650℃ (hold for 3 minutes). Then, put the polypropylene component and filter membrane into the welding machine for welding. After welding, turn off the heating device and remove the components after natural cooling. The high temperature of 650℃ melts the welding area of ​​the modified polypropylene end cap. The hydrophilic layer in the molten polypropylene is not destroyed and forms a tight bond with the polar surface of the polyethersulfone membrane, which not only ensures the welding strength but also solves the problem of increased hydrophobicity in traditional welding.

[0031] Example 2 This embodiment provides a hydrophilic welding method for polypropylene used in capsule filters, which is basically the same as the operation steps in Embodiment 1. The hydrophilic welding method for polypropylene includes the following brief steps: (1) Place the polypropylene end cap (flat seal cap) and the liquid outlet end cap on the workbench and prepare the direct injection plasma treatment machine; connect the direct injection plasma treatment machine to the nitrogen tank and spray nitrogen at a pressure of 0.6 MPa to bombard the surface of the polypropylene end cap in a directional manner. The treatment time is strictly controlled to 15 seconds. (2) Mix ovalbumin and tannic acid at a mass ratio of 3:1 to prepare a mixed solution with a total concentration of 1%. Then slowly add 1 mol / L NaOH solution to the solution to adjust the pH value of the system to 10. After stirring evenly, heat the solution in a water bath to 70°C and keep the temperature stable. (3) Place the polypropylene component after plasma treatment into the above-mentioned hydrophilic mixed solution at 70°C and soak for 40 minutes to ensure that the surface polar chains and hydrophilic functional groups react fully. Take out the soaked polypropylene component and dry it in an environment at 60°C for 1 hour to form a stable hydrophilic layer on the surface. (4) The modified polypropylene is melted at 630℃ and welded to the polyethersulfone membrane to form a complete filter core component.

[0032] Example 3 This embodiment provides a hydrophilic welding method for polypropylene used in capsule filters, which is basically the same as the operation steps in Embodiment 1. The hydrophilic welding method for polypropylene includes the following brief steps: (1) Place the polypropylene end cap (flat seal cap) and the liquid outlet end cap on the workbench and prepare the direct injection plasma treatment machine; connect the direct injection plasma treatment machine to the nitrogen tank and spray nitrogen at a pressure of 0.5 MPa to bombard the surface of the polypropylene end cap in a directional manner. The treatment time is strictly controlled to 12 seconds. (2) Mix ovalbumin and tannic acid at a mass ratio of 2.5:1 to prepare a mixed solution with a total concentration of 1.5%. Then slowly add 0.8 mol / L NaOH solution to the solution to adjust the pH value of the system to 10. After stirring evenly, heat the solution in a water bath to 60°C and keep the temperature stable. (3) Place the polypropylene component after plasma treatment into the above-mentioned hydrophilic mixed solution at 60°C and soak for 35 minutes to ensure that the surface polar chains and hydrophilic functional groups react fully. Take out the soaked polypropylene component and dry it in an environment at 55°C for 1 hour to form a stable hydrophilic layer on the surface. (4) The modified polypropylene is melted at 640℃ and welded to the polyethersulfone membrane to form a complete filter core component.

[0033] Detection example The water contact angle of the original unmodified polypropylene and the modified polypropylene obtained in Examples 1-3 were tested using the seat drop method. The results are shown in Table 1.

[0034] Table 1

[0035] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A hydrophilic welding method for polypropylene used in capsule filters, characterized in that, The polypropylene hydrophilic welding method includes the following steps: (1) Plasma treatment is performed on the polypropylene components used in the capsule filter to obtain plasma-modified polypropylene components; (2) Mix ovalbumin and tannic acid, and add a pH adjuster to obtain a mixed solution; (3) The plasma-modified polypropylene component is immersed in the mixed solution for reaction, and after completion, it is taken out and dried to obtain the hydrophilic modified polypropylene component; (4) Melt the hydrophilic modified polypropylene component and weld it to the polyethersulfone membrane to form a complete capsule filter assembly.

2. The polypropylene hydrophilic welding method for the capsule filter according to claim 1, characterized in that, In step (1), the polypropylene components are a polypropylene end cap and a polypropylene liquid outlet.

3. The polypropylene hydrophilic welding method for the capsule filter according to claim 1, characterized in that, In step (1), the plasma treatment method is as follows: connect the direct injection plasma treatment machine to the nitrogen tank, spray nitrogen under pressure, and bombard the surface of the polypropylene component for treatment.

4. The polypropylene hydrophilic welding method for the capsule filter according to claim 3, characterized in that, The pressure is 0.4-0.6 MPa, and the processing time is 10-15 seconds.

5. The polypropylene hydrophilic welding method for the capsule filter according to claim 1, characterized in that, In step (2): The mass ratio of ovalbumin to tannic acid is 2-3:1; And / or, in the mixed solution, the total mass fraction of ovalbumin and tannic acid is 1-2%.

6. The polypropylene hydrophilic welding method for the capsule filter according to claim 1, characterized in that, In step (2), the pH adjuster is a NaOH solution with a concentration of 0.5-1 mol / L.

7. The polypropylene hydrophilic welding method for the capsule filter according to claim 1, characterized in that, In step (3), the reaction temperature is 60-70℃ and the reaction time is 30-40min.

8. The polypropylene hydrophilic welding method for the capsule filter according to claim 1, characterized in that, In step (3), the drying temperature is 50-60℃.

9. The polypropylene hydrophilic welding method for the capsule filter according to claim 1, characterized in that, In step (4), the melting temperature is 630-650℃.

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