A water vapor transfer membrane and a method of making the same

Abstract

The present application belongs to the technical field of membrane materials. The present application provides a kind of water vapor transfer membrane, comprising microporous substrate and selection layer;Microporous substrate is polyolefin microporous membrane;The raw material of selection layer comprises sulfonic acid monomer and bifunctional acrylic monomer with weight ratio of 1-6:4-19.The present application also provides a kind of preparation method of water vapor transfer membrane, which comprises sulfonic acid monomer, bifunctional acrylic monomer and initiator.The surface of microporous substrate is coated with an aqueous solution, and a substantially non-porous selection layer is formed after solidification.The preparation process of the present application has little VOCs pollution, and the prepared water vapor transfer membrane can be washed with water, maintains stable water vapor transfer efficiency after washing, water vapor transmission rate is not less than 12000 GPU, water vapor / carbon dioxide selectivity is greater than 50, and can be applied to enthalpy exchange components of fresh air system.

Description

Technical Field

[0001] This invention relates to the field of membrane materials technology, and in particular to a water vapor transfer membrane and its preparation method. Background Technology

[0002] Good ventilation is essential for maintaining indoor air quality. However, during hot or cold seasons, indoor temperatures are often comfortable due to cooling or heating, leading to significant energy loss during ventilation. Enthalpy exchange components in fresh air systems, which recover the enthalpy between intake and exhaust air and regulate indoor humidity, have become crucial components of these systems.

[0003] In enthalpy exchange components, the material used for enthalpy exchange is a water vapor transfer membrane, which has the following functions: (1) effectively blocking the air (mainly nitrogen, oxygen, carbon dioxide, VOCs, etc.) between the intake and exhaust, avoiding the mixing of intake and exhaust; (2) high water vapor transfer efficiency, realizing latent heat exchange between intake and exhaust; (3) low thickness, improving sensible heat exchange and latent heat exchange between intake and exhaust. In addition, commercially viable water vapor transfer membranes also need to have characteristics such as high strength and low cost in order to further expand customer demand.

[0004] Currently, the water vapor transfer membranes used in fresh air systems are mainly made of specialty paper. After prolonged use, these membranes are prone to fouling, affecting their water vapor transfer efficiency. However, specialty paper cannot be washed with water, necessitating timely replacement of enthalpy exchange components and resulting in high maintenance costs. Therefore, there is a need to develop highly water-resistant, washable polymer water vapor transfer membranes. Unlike single-layer paper water vapor transfer membranes, polymer water vapor transfer membranes typically consist of two layers: a bottom layer of microporous substrate providing support and breathability, and an upper layer of separation material. The microporous substrate can be made of materials with submicron pore sizes and high porosity, such as microfiltration membranes, ultrafiltration membranes, and stretched microporous membranes. The separation layer material is mainly formed using a solvent evaporation process to create a micron-thick hydrophilic polymer layer. Common examples include polyvinyl alcohol-hygroscopic inorganic salt complexes, sulfonated resins (sulfonated polyether ether ketone, sulfonated polystyrene-ethylene-butadiene copolymer, sulfonated perfluoropolyether resin), modified cellulose, and polyethylene oxide copolymers. However, the above materials also have drawbacks. For example, the efficiency of polyvinyl alcohol-hygroscopic inorganic salt composites decreases significantly after washing with water, sulfonated resins are expensive and have high VOC pollution during production, modified cellulose has relatively low performance, and polyethylene oxide copolymers have high VOC pollution during production and their performance deteriorates over time.

[0005] Therefore, in view of the problems of existing water vapor transfer membranes that cannot be washed, which affect water vapor transfer efficiency with long-term use, have low performance of separation layer materials, and have high VOC pollution in the production process, it is of great significance and application value to develop a washable water vapor transfer membrane that can maintain stable water vapor transfer efficiency after washing, so as to better apply it to enthalpy exchange components and reduce the maintenance cost of fresh air systems. Summary of the Invention

[0006] The purpose of this invention is to provide a water vapor transfer membrane and its preparation method to address the shortcomings of existing technologies.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] The present invention provides a water vapor transfer membrane comprising a microporous substrate and a selective layer; the selective layer comprises sulfonic acid monomer and bifunctional acrylic acid monomer in a weight ratio of 1-6:4-19; the selective layer has a thickness of 0.2-5 μm.

[0009] Preferably, the microporous substrate is a polyolefin microporous membrane, wherein the porosity of the polyolefin microporous membrane is 30-60%, the pore size of the polyolefin microporous membrane is 0.02-0.2 μm, and the thickness of the polyolefin microporous membrane is 6-45 μm.

[0010] Preferably, the sulfonic acid monomer is one or more of vinyl sulfonic acid, sodium vinyl sulfonate, p-styrene sulfonic acid, and sodium p-styrene sulfonate.

[0011] Preferably, the bifunctional acrylic monomer is one or more of ethylene glycol diacrylate, diethylene glycol diacrylate, and triethylene glycol diacrylate.

[0012] This invention also provides a method for preparing a water vapor transfer membrane, comprising the following steps:

[0013] After removing air bubbles, the casting solution is applied to the surface of a microporous substrate and then dried and cured sequentially to obtain a water vapor transfer membrane.

[0014] The casting solution contains sulfonic acid monomer, bifunctional acrylic acid monomer, initiator and water.

[0015] Preferably, the initiator is one or more of potassium persulfate, azobisisobutylamidine hydrochloride, azobisisobutylimidazoline hydrochloride, azobiscyanopentanoic acid, and azobisisopropylimidazoline, and the casting solution is obtained by mixing sulfonic acid monomer, bifunctional acrylic acid monomer, initiator, and water, and the mixing temperature is 5-50°C.

[0016] Preferably, the mass fraction of the sulfonic acid monomer and the bifunctional acrylic acid monomer in the casting solution is 2.5-10%, and the mass fraction of the initiator in the casting solution is 0.05-0.5%.

[0017] Preferably, the method for removing bubbles is vacuum degassing or standing; the vacuum degree of vacuum degassing is -0.06 to -0.09 MPa, and the vacuum degassing time is 3 to 10 minutes; the standing time is 20 to 100 minutes.

[0018] Preferably, the coating method is one or more of gravure coating, micro-gravure coating and slot coating, and the coating speed is 5 to 100 m / min.

[0019] Preferably, the drying temperature is 60–80°C, and the drying time is 1–5 hours; the curing method is ultraviolet (UV) curing, the UV curing wavelength is 320–360 nm, and the UV curing power is 50–200 W / m. 2 The UV curing time is 1 to 10 minutes.

[0020] The beneficial effects of this invention include the following:

[0021] 1) The water vapor transfer membrane of the present invention introduces highly hydrophilic sulfonic acid into the separation layer through in-situ polymerization to achieve efficient water vapor transfer; at the same time, it has a cross-linked structure, which can remain stable in high humidity or even liquid water, and has a long-term stable water vapor transfer function.

[0022] 2) Compared with polyvinyl alcohol-hygroscopic inorganic salt composites, the water vapor transfer membrane of the present invention maintains a stable water vapor transfer efficiency after washing; compared with solvent-based polymers such as sulfonated polymers, modified cellulose, and polyethylene oxide copolymers, the preparation method of the present invention is essentially free of VOCs pollution. The water vapor transfer membrane prepared by the present invention is washable and maintains a stable water vapor transfer efficiency after washing, with a water vapor permeability of not less than 12000 GPU and a water vapor / carbon dioxide selectivity greater than 50. It can be applied to enthalpy exchange components of fresh air systems, reducing the maintenance costs of fresh air systems. Detailed Implementation

[0023] The present invention provides a water vapor transfer membrane comprising a microporous substrate and a selective layer; the selective layer comprises sulfonic acid monomer and bifunctional acrylic acid monomer in a weight ratio of 1-6:4-19.

[0024] The preferred weight ratio of the sulfonic acid monomer and the bifunctional acrylic acid monomer in this invention is 2-5:5-17, and more preferably 3-4:7-15.

[0025] The thickness of the selective layer described in this invention is preferably 0.2–5 μm, more preferably 0.5–4 μm, and even more preferably 1.2–3 μm.

[0026] The water vapor transfer efficiency of the selective layer described in this invention is limited by solubility and water vapor diffusion rate. To ensure high water vapor transfer efficiency, the thickness of the selective layer should be minimized. However, the water vapor transfer membrane needs to block the transfer of harmful gases such as carbon dioxide, so the thickness of the selective layer should be increased. To balance the water vapor transfer efficiency and the harmful gas transfer efficiency, this invention controls the thickness of the selective layer to be 0.2–5 μm.

[0027] The microporous substrate of the present invention is preferably a polyolefin microporous membrane, wherein the porosity of the polyolefin microporous membrane is preferably 30-60%, more preferably 35-55%, and more preferably 40-50%; the pore size of the polyolefin microporous membrane is preferably 0.02-0.2 μm, more preferably 0.08-0.17 μm, and more preferably 0.12-0.15 μm; and the thickness of the polyolefin microporous membrane is preferably 6-45 μm, more preferably 15-37 μm, and more preferably 20-30 μm.

[0028] The microporous substrate described in this invention provides support for the selective layer. When the pore size of the microporous substrate is too large, pores are prone to appear in the selective layer, which is not conducive to blocking harmful gases. The higher the porosity and the thinner the thickness of the microporous substrate, the better it is to improve the water vapor transfer efficiency. It is necessary to comprehensively consider factors such as process, water vapor transfer efficiency, and cost to select a suitable material, pore size, porosity, and thickness of the microporous substrate.

[0029] The sulfonic acid monomers described in this invention are preferably one or more of vinyl sulfonic acid, sodium vinyl sulfonate, p-styrene sulfonic acid, and sodium p-styrene sulfonate.

[0030] The sulfonic acid monomer described in this invention has strong hygroscopic properties, which is a key factor in achieving efficient water vapor transfer in the membrane. When the sulfonic acid monomer content is too low, water vapor transfer is hindered; conversely, when the sulfonic acid monomer content is too high, the membrane will absorb moisture and swell, which is detrimental to subsequent processing.

[0031] The bifunctional acrylic monomer of the present invention is preferably one or more of ethylene glycol diacrylate, diethylene glycol diacrylate and triethylene glycol diacrylate.

[0032] The bifunctional acrylic monomer described in this invention is the main component of the selective layer, and its function is to form a substantially non-porous coating on the surface of a microporous substrate. When the bifunctional acrylic monomer is added, the selective layer forms a cross-linked network structure, and the coating is insoluble in water, affecting the water vapor transfer efficiency. Appropriately increasing the amount of sulfonic acid monomer can improve the water vapor transfer efficiency of the water vapor transfer membrane.

[0033] The raw material of the selective layer of the present invention further includes a monofunctional acrylic monomer, which is used to adjust the performance of the selective layer. The monofunctional acrylic monomer is preferably acrylic acid and / or hydroxyethyl acrylate. The weight ratio of the monofunctional acrylic monomer to the difunctional acrylic monomer is preferably 0.01 to 1:1, more preferably 0.2 to 0.6:1, and more preferably 0.3 to 0.5:1.

[0034] This invention also provides a method for preparing a water vapor transfer membrane, comprising the following steps:

[0035] After removing air bubbles, the casting solution is applied to the surface of a microporous substrate and then dried and cured sequentially to obtain a water vapor transfer membrane.

[0036] The casting solution contains sulfonic acid monomer, bifunctional acrylic acid monomer, initiator and water.

[0037] The initiator of the present invention is preferably one or more of potassium persulfate, azobisisobutylamidine hydrochloride, azobisisobutylimidazoline hydrochloride, azodicyanovalerate, and azobisisopropylimidazoline. The casting solution is preferably obtained by mixing sulfonic acid monomer, bifunctional acrylic acid monomer, initiator, and water. The mixing temperature is preferably 5-50°C, more preferably 8-40°C, and even more preferably 10-30°C.

[0038] The mixing of the casting solution described in this invention is preferably carried out under light-protected conditions.

[0039] The casting solution of the present invention further includes additives that facilitate the formation of a uniform and dense selective layer; the additives include one or more of emulsifiers, thickeners, defoamers, light absorbers, and antibacterial agents, and the mass fraction of the additives in the casting solution is preferably 0.1-2%, more preferably 0.5-1%; the emulsifier is preferably alkylphenol polyoxyethylene ether and / or nonylphenol polyoxyethylene ether; the thickener is preferably an alkali-swellable thickener, more preferably a polyacrylate thickener, and more preferably thickener SN-THICKENER-636; the defoamer is preferably a mineral oil defoamer, more preferably defoamer NXZ; the light absorber is preferably 2-phenyl-2-dimethylamino-1-(4-morpholinophenyl)-1-butanone; the antibacterial agent is preferably a cationic antibacterial agent, more preferably... FCG002 Silver Ion Antibacterial Agent.

[0040] The mass fraction of the sulfonic acid monomer and the bifunctional acrylic acid monomer in the casting solution is preferably 2.5-10%, more preferably 3-8%, and even more preferably 4-7%; the mass fraction of the initiator in the casting solution is preferably 0.05-0.5%, more preferably 0.1-0.4%, and even more preferably 0.15-0.3%.

[0041] The preferred method for removing bubbles according to the present invention is vacuum degassing or standing, more preferably vacuum degassing; the vacuum degree of the vacuum degassing is preferably -0.06 to -0.09 MPa, more preferably -0.07 to -0.08 MPa; the vacuum degassing time is preferably 3 to 10 min, more preferably 5 to 8 min, more preferably 6 to 7 min; the standing time is preferably 20 to 100 min, more preferably 30 to 85 min, more preferably 40 to 70 min.

[0042] The coating method described in this invention is preferably one or more of gravure coating, micro-gravure coating, and slot coating. The coating speed is preferably 5 to 100 m / min, more preferably 20 to 80 m / min, and even more preferably 40 to 60 m / min.

[0043] The drying temperature described in this invention is preferably 60–80°C, more preferably 65–75°C; the drying time is preferably 1–5 hours, more preferably 2–4 hours; the curing method is preferably ultraviolet (UV) light curing, the wavelength of which is preferably 320–360 nm, more preferably 330–350 nm; and the UV light curing power is preferably 50–200 W / m. 2 Further preferred is 70–170 W / m 2 More preferably, it is 90–150 W / m 2 The UV curing time is preferably 1 to 10 minutes, more preferably 3 to 8 minutes, and even more preferably 4 to 6 minutes.

[0044] The drying process described in this invention requires maintaining a suitable hot air temperature. Excessively high hot air temperatures will cause the acrylic monomer to volatilize and the initiator to form a large number of free radicals in advance, which is not conducive to the formation of a uniform and dense selective layer.

[0045] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0046] Example 1

[0047] A casting solution was prepared by mixing 1g vinyl sulfonic acid, 19g ethylene glycol diacrylate, 0.15g potassium persulfate, and 180g water at 30°C in the dark. The casting solution was then degassed under vacuum at -0.09MPa for 5 minutes. A 20μm layer of the casting solution was applied to a polypropylene substrate (pore size 0.1μm, thickness 30μm, porosity 45%) using a microgravure coating process at a coating rate of 20m / min. The coated polypropylene substrate was dried at 70°C for 2 hours and then subjected to ultraviolet light (wavelength 320nm, power 100W / m²). 2 The water vapor transfer membrane was obtained by curing for 4 minutes.

[0048] In this embodiment, the selective layer thickness of the water vapor transfer membrane is 2 μm, the water vapor permeability is 13652 GPU, and the water vapor / carbon dioxide selectivity is 54.

[0049] Example 2

[0050] A casting solution was prepared by mixing 12g vinyl sulfonic acid, 8g diethylene glycol diacrylate, 1g azobisisobutylamidine hydrochloride, and 180g water at 30°C in the dark. The casting solution was then degassed under vacuum at -0.09MPa for 5 minutes. A 30μm layer of the casting solution was applied to a polyethylene substrate (pore size 0.08μm, thickness 20μm, porosity 40%) using a microgravure coating process at a coating rate of 20m / min. The polyethylene substrate coated with the casting solution was dried at 80°C for 3 hours and then exposed to ultraviolet light (wavelength 330nm, power 120W / m²). 2 The water vapor transfer membrane was obtained by curing for 5 minutes.

[0051] In this embodiment, the selective layer thickness of the water vapor transfer membrane is 3 μm, the water vapor permeability is 12576 GPU, and the water vapor / carbon dioxide selectivity is 56.

[0052] Example 3

[0053] A casting solution was prepared by mixing 1.5g vinyl sulfonic acid, 2.5g triethylene glycol diacrylate, 0.3g azodicyanovalerate, and 90g water at 20°C in the dark. The casting solution was allowed to stand for 60 minutes to remove air bubbles. A 15μm layer of the casting solution was then coated onto a polypropylene substrate (pore size 0.1μm, thickness 45μm, porosity 60%) using a microgravure coating process at a coating rate of 10m / min. The coated polypropylene substrate was dried at 60°C for 1 hour and then exposed to ultraviolet light (wavelength 320nm, power 80W / m²). 2 The water vapor transfer membrane was obtained by curing for 3 minutes.

[0054] In this embodiment, the selective layer thickness of the water vapor transfer membrane is 0.3 μm, the water vapor permeability is 16430 GPU, and the water vapor / carbon dioxide selectivity is 68.

[0055] Example 4

[0056] A casting solution was prepared by mixing 5g vinyl sulfonic acid, 3g diethylene glycol diacrylate, 2g acrylic acid, 0.1g azobisisopropylimidazoline, and 90g water at 30°C in the dark. The casting solution was then degassed under vacuum at -0.09MPa for 7 minutes. A 50μm layer of the casting solution was applied to a polypropylene substrate (pore size 0.12μm, thickness 35μm, porosity 50%) using a microgravure coating process at a coating rate of 30m / min. The coated polypropylene substrate was dried at 90°C for 4 hours and then subjected to ultraviolet light (wavelength 350nm, power 160W / m²). 2 The water vapor transfer membrane was obtained by curing for 6 minutes.

[0057] In this embodiment, the selective layer thickness of the water vapor transfer membrane is 5 μm, the water vapor permeability is 16790 GPU, and the water vapor / carbon dioxide selectivity is 53.

[0058] Example 5

[0059] A casting solution was prepared by mixing 3g vinyl sulfonic acid, 5g ethylene glycol diacrylate, 2g hydroxyethyl acrylate, 0.3g azobisisobutylamidine hydrochloride, and 90g water at 20°C in the dark. The casting solution was then degassed under vacuum at -0.07MPa for 4 minutes. A 10μm layer of the casting solution was applied to a polyethylene substrate (pore size 0.1μm, thickness 6μm, porosity 35%) using a microgravure coating process at a coating rate of 15m / min. The polyethylene substrate was dried at 50°C for 2 hours and then subjected to ultraviolet light (wavelength 330nm, power 90W / m²). 2 The water vapor transfer membrane was obtained by curing for 2 minutes.

[0060] In this embodiment, the selective layer thickness of the water vapor transfer membrane is 1 μm, the water vapor permeability is 14860 GPU, and the water vapor / carbon dioxide selectivity is 62.

[0061] Example 6

[0062] A casting solution was prepared by mixing 6g vinyl sulfonic acid, 4g ethylene glycol diacrylate, 0.2g azobisisobutylamidine hydrochloride, 0.2g defoamer NXZ, and 90g water at 20°C in the dark. The casting solution was allowed to stand for 40 minutes to remove air bubbles. A 4μm layer of the casting solution was then applied to a polypropylene substrate (pore size 0.05μm, thickness 45μm, porosity 60%) using a slot coating process at a coating rate of 15m / min. The polypropylene substrate coated with the casting solution was dried at 70°C for 2 hours and then exposed to ultraviolet light (wavelength 330nm, power 100W / m²). 2 The water vapor transfer membrane was obtained by curing for 4 minutes.

[0063] In this embodiment, the selective layer thickness of the water vapor transfer membrane is 0.4 μm, the water vapor permeability is 12876 GPU, and the water vapor / carbon dioxide selectivity is 68.

[0064] Example 7

[0065] A casting solution was prepared by mixing 6g sodium vinyl sulfonate, 4g ethylene glycol diacrylate, 0.5g azobisisobutylamidine hydrochloride, and 120g water at 40°C in the dark. The casting solution was then degassed under vacuum at -0.08MPa for 4 minutes. A 10μm layer of the casting solution was applied to a polyethylene substrate (pore size 0.15μm, thickness 12μm, porosity 40%) using a slot coating process at a coating rate of 25m / min. The polyethylene substrate coated with the casting solution was dried at 80°C for 3 hours and then exposed to ultraviolet light (wavelength 350nm, power 180W / m²). 2 The water vapor transfer membrane was obtained by curing for 5 minutes.

[0066] In this embodiment, the selective layer thickness of the water vapor transfer membrane is 5 μm, the water vapor permeability is 15436 GPU, and the water vapor / carbon dioxide selectivity is 52.

[0067] Example 8

[0068] A casting solution was prepared by mixing 7g of p-styrene sulfonic acid, 3g of ethylene glycol diacrylate, 0.3g of azodicyanovalerate, 0.2g of alkylphenol polyoxyethylene ether OP-10, and 90g of water at 40°C in the dark. The casting solution was then degassed under vacuum at -0.07MPa for 3 minutes. A 20μm layer of the casting solution was applied to a polypropylene substrate (pore size 0.1μm, thickness 30μm, porosity 50%) using a slot coating process at a coating rate of 20m / min. The coated polypropylene substrate was dried at 70°C for 3 hours and then subjected to ultraviolet light (wavelength 350nm, power 150W / m²). 2 The water vapor transfer membrane was obtained by curing for 3 minutes.

[0069] In this embodiment, the selective layer thickness of the water vapor transfer membrane is 2 μm, the water vapor permeability is 13657 GPU, and the water vapor / carbon dioxide selectivity is 58.

[0070] Example 9

[0071] A casting solution was prepared by mixing 2g of sodium p-styrene sulfonate, 8g of ethylene glycol diacrylate, 0.1g of azobisisopropylimidazoline, and 90g of water at 30°C in the dark. The casting solution was then degassed under vacuum at -0.08MPa for 4 minutes. A 30μm layer of the casting solution was applied to a polyethylene substrate (pore size 0.15μm, thickness 25μm, porosity 40%) using a slot coating process at a coating rate of 30m / min. The polyethylene substrate coated with the casting solution was dried at 90°C for 5 hours and then exposed to ultraviolet light (wavelength 350nm, power 180W / m²). 2 The water vapor transfer membrane was obtained by curing for 6 minutes.

[0072] In this embodiment, the selective layer thickness of the water vapor transfer membrane is 3 μm, the water vapor permeability is 13272 GPU, and the water vapor / carbon dioxide selectivity is 56.

[0073] Comparative Example 1

[0074] A casting solution was prepared by mixing 1g vinyl sulfonic acid, 19g acrylic acid, 0.1g potassium persulfate, and 180g water at 30°C in the dark. The casting solution was then degassed under vacuum at -0.09MPa for 5 minutes. A 20μm layer of the casting solution was applied to a polypropylene substrate (pore size 0.1μm, thickness 30μm, porosity 45%) using a microgravure coating process at a coating rate of 20m / min. The coated polypropylene substrate was dried at 70°C for 2 hours and then exposed to ultraviolet light (wavelength 320nm, power 100W / m²). 2 The water vapor transfer membrane was obtained by curing for 4 minutes.

[0075] The water vapor transfer membrane in this comparative example is soluble in water, has a selective layer thickness of 2.5 μm, a water vapor permeability of 12942 GPU, and a water vapor / carbon dioxide selectivity of 59.

[0076] Comparative Example 2

[0077] A casting solution was prepared by mixing 1g vinyl sulfonic acid, 9g hydroxyethyl acrylate, 1g azobisisobutylamidine hydrochloride, and 190g water at 30°C in the dark. The casting solution was then degassed under vacuum at -0.09MPa for 4 minutes. A 10μm layer of the casting solution was applied to a polyethylene substrate (pore size 0.1μm, thickness 12μm, porosity 40%) using a microgravure coating process at a coating rate of 10m / min. The polyethylene substrate coated with the casting solution was dried at 70°C for 1 hour and then exposed to ultraviolet light (wavelength 320nm, power 100W / m²). 2 The water vapor transfer membrane was obtained by curing for 5 minutes.

[0078] The water vapor transfer membrane in this comparative example is soluble in water, has a selective layer thickness of 0.1 μm, a water vapor permeability of 13874 GPU, and a water vapor / carbon dioxide selectivity of 45.

[0079] Comparative Example 3

[0080] A casting solution was prepared by mixing 1g vinyl sulfonic acid, 1g ethylene glycol diacrylate, 0.3g azodicyanovalerate, and 98g water at 30°C in the dark. The casting solution was then degassed under vacuum at -0.09MPa for 5 minutes. A 5μm layer of the casting solution was applied to a polypropylene substrate (pore size 0.1μm, thickness 30μm, porosity 50%) using a microgravure coating process at a coating rate of 10m / min. The coated polypropylene substrate was dried at 50°C for 1 hour and then exposed to ultraviolet light (wavelength 320nm, power 100W / m²). 2 The water vapor transfer membrane was obtained by curing for 3 minutes.

[0081] The selective layer thickness of the water vapor transfer membrane in this comparative example is 0.1 μm, the water vapor permeability is 16791 GPU, and the water vapor / carbon dioxide selectivity is 39.

[0082] Compared with the comparative example, the present invention uses a copolymerization method of sulfonic acid monomer and difunctional acrylic acid monomer to form a water vapor transfer membrane on the polymer microporous membrane, which can achieve a water vapor transmission rate of not less than 12000 GPU and a water vapor / carbon dioxide selectivity greater than 50. It is also washable. When used as an enthalpy exchange component in a fresh air system, it not only has high enthalpy exchange efficiency, but is also insoluble in water, and has significant performance and cost advantages.

[0083] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A water vapor transfer membrane characterized in that, Includes a microporous substrate and a selective layer; The raw material of the selective layer comprises sulfonic acid monomer and bifunctional acrylic acid monomer in a weight ratio of 1-6:4-19. The thickness of the selective layer is 0.2–5 μm; The microporous substrate is a polyolefin microporous membrane, the porosity of which is 30-60%, the pore size of which is 0.02-0.2 μm, and the thickness of which is 6-45 μm. The method for preparing the water vapor transfer membrane comprises the following steps: After removing air bubbles, the casting solution is applied to the surface of a microporous substrate and then dried and cured sequentially to obtain a water vapor transfer membrane. The casting solution is composed of sulfonic acid monomer, bifunctional acrylic acid monomer, initiator and water; The sulfonic acid monomer is one or more of vinyl sulfonic acid, sodium vinyl sulfonate, p-styrene sulfonic acid, and sodium p-styrene sulfonate; The bifunctional acrylic monomer is one or more of ethylene glycol diacrylate, diethylene glycol diacrylate, and triethylene glycol diacrylate; The initiator is one or more of potassium persulfate, azobisisobutylamidine hydrochloride, azobisisobutylimidazoline hydrochloride, azobiscyanopentanoic acid, and azobisisopropylimidazoline.

2. The method of claim 1, wherein the water vapor transfer film is prepared by the steps of: It consists of the following steps: After removing air bubbles, the casting solution is applied to the surface of a microporous substrate and then dried and cured sequentially to obtain a water vapor transfer membrane. The casting solution contains sulfonic acid monomer, bifunctional acrylic acid monomer, initiator and water.

3. The preparation method according to claim 2, characterized in that, The casting solution is obtained by mixing sulfonic acid monomer, bifunctional acrylic acid monomer, initiator and water, and the mixing temperature is 5-50°C.

4. The production method according to claim 3, characterized by, The mass fraction of the sulfonic acid monomer and the bifunctional acrylic acid monomer in the casting solution is 2.5-10%, and the mass fraction of the initiator in the casting solution is 0.05-0.5%.

5. The production method according to claim 3 or 4, characterized by, The method for removing bubbles is vacuum degassing or standing; the vacuum degree of vacuum degassing is -0.06 to -0.09 MPa, and the vacuum degassing time is 3 to 10 minutes; the standing time is 20 to 100 minutes.

6. The preparation method according to claim 5, characterized in that, The coating method is one or more of gravure coating, micro-gravure coating and slot coating, and the coating speed is 5 to 100 m / min.

7. The preparation method according to claim 6, characterized in that, The temperature of the drying is 60-80℃, the time of the drying is 1-5h; the mode of the solidifying is ultraviolet light solidifying, the wavelength of the ultraviolet light solidifying is 320-360nm, the power of the ultraviolet light solidifying is 50-200W / m 2 , the time of the ultraviolet light solidifying is 1-10min.