CN110898689B

CN110898689B - Flat membrane with nano porous structure and preparation method thereof

Info

Publication number: CN110898689B
Application number: CN201911262130.1A
Authority: CN
Inventors: 刘爱林
Original assignee: Shanghai Xidian New Material Technology Co ltd
Current assignee: Shanghai Xidian New Material Technology Co ltd
Priority date: 2019-09-26
Filing date: 2019-12-10
Publication date: 2021-11-16
Anticipated expiration: 2039-12-10
Also published as: CN110938271B; CN110894167A; CN110951106A; CN110898688B; CN110898688A; CN110898681A; CN110898689A; CN110938271A; CN110804205A; CN110898681B; CN110804205B; CN110951106B

Abstract

The invention discloses a flat membrane with a nano porous structure and a preparation method thereof. The preparation method of the resin flat membrane with the nano porous structure comprises the steps of uniformly coating a solvent type resin sol raw material on a supporting layer to form a coating with the solvent content of 5-50 wt%; heating the coating to melt the solvent-evaporated resin and maintain its form; and then swelling to reach the required porosity, thus obtaining the resin flat membrane with the nano porous structure.

Description

Flat membrane with nano porous structure and preparation method thereof

Technical Field

The invention belongs to the field of processing and application of membrane materials, and mainly relates to a resin organic membrane with a nano porous structure and a preparation method thereof.

Background

The microporous filtration technology is widely applied to the fields of food, beverage, medicine, chemical industry, electric power and the like due to the advantages of simplicity, rapidness, high efficiency, energy conservation and the like. In recent decades, microporous filtration membranes have gradually replaced or popularized many conventional filtration processes in their application, such as clarification and filtration of matured beer, rather than the original cardboard fine filter, thereby improving the whiteness of matured beer; such as replacing raw cotton and activated carbon filled air filtration. As a unique separation technology, the method has become one of the most important and indispensable means for ensuring the product quality in the fields of electronics, biopharmaceuticals, scientific research, quality detection and the like. Thus, the microfiltration membrane product occupies the largest share in the overall composition of the national membrane market.

When the preparation method is provided by the patent CN108043234A, polyether sulfone is added into a solvent at 70-80 ℃, the solution is stirred for the first time until the solution is clear, then an interoperable pore-forming agent and an inorganic additive are added, the solution is stirred again at 50-60 ℃ until a homogeneous solution is formed, the homogeneous solution is subjected to vacuum defoaming treatment to obtain a membrane casting solution, the membrane casting solution and non-woven fabrics are made into a membrane piece, and the membrane piece is subjected to standing in an air environment, solidification in a deionized water coagulation bath, deionized water soaking and airing treatment in sequence to obtain the ultrafiltration membrane. CN108043246A proposes that a modified organic membrane is obtained by grafting polymethacrylic acid macromolecules on the surface of a complementary micro-nano structure of the organic membrane. It is proposed by CN109862959A to obtain a filtration membrane by coating a copolymer solution on a porous support layer to form a polymer layer thereon, solidifying the polymer layer on top of the porous support layer to obtain a thin film composite membrane, and immersing the thin film composite membrane in a water bath.

The preparation of the existing membrane material is improved aiming at the preparation process of the membrane material, the preparation process is complex, innovation is not provided on a drying method, and the inventor actively researches and innovates the existing membrane material on the basis of long-term practical experience and abundant professional knowledge, and finally invents a method for preparing an organic membrane material by solvent type resin high-temperature puffing, so as to solve the defects in the prior art.

Disclosure of Invention

The biggest problem faced in the existing membrane preparation process is drying at the later stage of membrane formation, and the collapse of a membrane pore structure can be caused by the evaporation of water in the drying process, so that the pore diameter of the membrane is reduced and the porosity is reduced. The properties of the resulting film are difficult to ensure due to improper evaporation of water. In order to solve the problems, the invention provides a resin flat membrane with a nano porous structure and a preparation method thereof.

In a first aspect, the invention provides a preparation method of a resin flat membrane with a nano-porous (hole) structure, wherein a solvent type resin sol raw material is uniformly coated on a support layer to form a coating with the solvent content of 5-50 wt%; heating the coating to melt the solvent-evaporated resin and maintain its form; and then swelling to reach the required porosity, thus obtaining the resin flat membrane with the nano porous structure.

According to the scheme disclosed by the invention, the solvent content of the coating is controlled to be 5-50 wt%, then the solvent is vaporized under the action of high temperature, and is released in a gas form, so that the phenomena of collapse and shrinkage caused by the surface tension effect of a pore structure in the traditional drying method (such as supercritical drying, freeze drying, normal-pressure drying and the like) in the traditional ultrafiltration membrane preparation process are avoided.

By controlling the content of the solvent in the coating layer within the above range, not only can the adhesion of the coating layer on the support layer be enhanced, but also the pore size and the pore size distribution uniformity of the resin flat sheet membrane can be favorably controlled. Too high solvent content easily causes too large pore diameter or uneven pore diameter distribution, and too low solvent content easily causes insufficient puffing degree or unsuccessful puffing, so that the control of the solvent content in a certain range is beneficial to the uniform distribution of the pore diameter of the material and the control of the pore diameter size of the material.

The solvent content of the coating is controlled to be 5-50 wt%, and the method comprises the steps of coating a sol raw material with high solvent content on a flat supporting layer, and heating the coating to control the solvent content of the coating within a proper range. More preferably, the content of the coating solvent is controlled to be 10-30 wt%. The heating temperature can be 25-200 ℃. The heating manner and apparatus are not limited as long as the content of the solvent is reduced to a desired content. The rate of solvent reduction is slower at lower heating temperatures, but the heating temperature is not too high to avoid premature vaporization. In the stage of reducing the solvent content by heating, the heating temperature should be lower than the curing temperature of the resin to avoid premature curing of the resin, and the cured resin does not have fluidity even if heated.

In the present disclosure, a coating layer having a specified solvent content is heated to melt the solvent-vaporized resin and maintain its morphology, and then expanded to a desired porosity, resulting in a resin flat membrane having a nanoporous structure. When the solvent vaporized resin is melted, the volume of the material is kept unchanged, namely, the material is not expanded, and the pore size distribution can be controlled to be uniform. By maintaining its morphology is meant that the solvent is vaporized but not expanded. The shape can be maintained by controlling the volume to be constant.

In the process of heating a coating layer having a prescribed solvent content to melt the solvent-vaporized resin and maintain its form, the heating temperature is preferably in excess of the boiling point of the solvent and in excess of the glass transition temperature and the curing temperature of the solvent-based resin. The heating temperature range of the water-soluble resin is 140-400 ℃. For solvent type resins, the boiling point of some organic solvents is only tens of degrees, and the heating temperature range is 100 to 400 ℃. It will be appreciated that during heating (prior to expansion), the solvent is ensured to be vaporized at this point in time to facilitate the formation of a nanoporous ultrafiltration membrane having a uniform pore size distribution after the coating material is expanded into an ultrafiltration membrane at a later stage. The heating time can be reduced when the heating temperature is high. It will be appreciated that during heating (before expansion), it is ensured that the resin melts whilst the solvent vaporises.

Preferably, the material of the support layer is at least one selected from glass fiber, ceramic fiber, metal fiber felt made of metal fiber, inorganic fiber felt made of inorganic fiber, inorganic fiber cloth and metal fiber net.

In a preferable scheme, the coating weight of the coating is 10-60 g/m². Too thick coating easily results in low filtration efficiency of the membrane material, and too thin coating easily results in poor membrane material strength. The coating amount should be controlled within a suitable range to give the membrane material better filtration efficiency and better strength. It will be appreciated that different viscosity ranges of the solution are required for different substrates and that the appropriate viscosity needs to be selected to achieve the desired coating weight. For exampleThe viscosity of the support layer is preferably not too high for the less strong support layer to avoid damage to the support layer during the coating process. For example, the viscosity of the support layer should not be too low to prevent the sol from penetrating the support layer. The viscosity of the sol is required to be different depending on the coating method, and it is preferable that the required coating amount can be achieved.

Preferably, the coating having a defined solvent content is heated to vaporize the solvent and maintain its morphology while being pressurized at a pressure higher than the saturated vapor pressure of the solvent under the heating conditions. The pressure of the pressurization is adjusted according to the content of the solvent in the coating, the temperature of heating, and the desired pore size. The solvent is vaporized by heating and pressurizing, and the volume of the material is kept constant. The range of pressurization is preferably higher than the saturated vapor pressure of the solvent used for the resin sol under the heating condition. Preferably, the pressurizing pressure is 0.01-10 MPa; more preferably 0.01 to 5 MPa.

Then puffing, namely relieving pressure (reducing pressure), and puffing to reach the specified porosity. The pressure relief process is controlled pressure relief. The time of depressurization should be controlled to achieve the desired expansion and to achieve the desired porosity, pore size and pore size distribution. Too rapid a pressure reduction tends to result in too large a pore size and a non-uniform pore size distribution. Too slow a pressure reduction tends to result in expansion failure or too low porosity. In addition, the air permeability of the substrate (support layer) itself has an effect on the swelling of the membrane. If the substrate itself has a certain pore structure, water or solvent that is vaporized during expansion (pressure relief) can escape through the substrate. Therefore, under the same conditions, the higher the air permeability of the substrate, the smaller the pore diameter of the expanded membrane. The decompression time is preferably 0.4 to 5 seconds. In the swelling (pressure relief) process, because the solvent is vaporized and the resin is in a molten state, the film layer swells and forms pores (holes) under the action of the solvent gas after pressure relief. As the pressure release is complete, the material cools and sets.

"solvent-type resin" refers to a resin that is soluble in organic solvents or water. The resin may be a thermosetting resin, a thermoplastic resin, a natural polymer material, rubber, or the like. The invention can select proper solvent according to different requirements and resin types. The solvent can completely dissolve the resin and vaporize at a certain temperature. The resin may be dissolved in a solvent in an amount of 1 to 5 times the weight of the resin. The large amount of solvent allows the resin to dissolve relatively quickly and uniformly, and then the solvent is reduced to a gel-like form suitable for film formation. Preferably, the resin gel with the solvent content of 30-70 wt% of the total amount is easier to form a film. After film forming, the content of the film layer solvent is reduced to the amount suitable for later heating, vaporization and expansion. The amount of solvent required will vary from resin to resin.

"Water-soluble resin" refers to a resin that is water-soluble. The water-soluble resin is at least one of water-soluble phenolic resin, water-soluble epoxy resin, water-soluble melamine formaldehyde resin, water-soluble urea formaldehyde resin, water-soluble unsaturated polyester resin, water-soluble polyurethane resin solution, water-soluble acrylic resin solution, polyvinyl alcohol, polyacrylamide, sodium polyacrylate, polyethylene glycol, polyvinyl alcohol, polymaleic anhydride, polyethyleneimine, polyethylene oxide, polyvinyl chloride, starch, water-soluble natural gum, methyl cellulose, hydroxyethyl cellulose and sodium carboxymethyl cellulose.

When the resin is a water-soluble resin, the solvent is water. Preferably, the water-soluble resin sol raw material also comprises a curing agent accounting for 10-60 wt% of the total weight of the raw materials. Preferably, the water-soluble resin is dissolved by water, and then is uniformly mixed with the curing agent in a certain proportion to obtain a solution in which the water and the curing agent are uniformly dispersed in the water-soluble resin; finally, the water content of the solution is reduced until the water content reaches the required content. The curing agent can increase the strength of the expanded material and the water resistance of the material. The control of the addition amount of the curing agent and the water content of the coating can ensure that the resin gel coating can better keep the skeleton structure in the process of heating to vaporize water and the later-stage puffing process, so as to prevent the influence on the pore diameter and the pore diameter distribution due to better fluidity after puffing, and ensure that the coating begins to be cured after puffing. Furthermore, for different resins, to accommodate the substrate, the sol viscosity can also be adjusted by adding a curing agent to facilitate coating.

In a preferred embodiment, the swelling temperature of the film layer including the curing agent is higher than the curing temperature of the water-soluble resin under the curing agent. Thus, after the swelling is finished, the curing agent and the resin are subjected to chemical reaction, and the curing agent can cure the resin, so that the formation of a polymer framework is promoted, the strength of the resin is improved, and the heat resistance, the water resistance and the corrosion resistance of the resin are enhanced.

In a preferred embodiment, the coating layer (in this case, the coating layer refers to the coating layer adhered to the support layer, that is, the support layer and the coating layer) is fed into a preparation system comprising hot press rolls at a predetermined speed to be heated to vaporize the solvent in the resin sol coating layer, the resin sol coating layer is heated between the two rolls to vaporize the solvent therein and to be subjected to a certain amount of extrusion, and the form of the resin sol coating layer is maintained between the two rolls until the coating layer is separated from the gap between the two rolls and expanded. The material is squeezed between the two rolls while contacting the two rolls without puffing (equivalent to puffing in a closed space) and then exits the rolls with a slow pressure release. The time for evaporation of the solvent as the material is heated in the nip between the rolls can be controlled by controlling the roll speed, and the rate at which the material exits the rolls (i.e. controlling the puffing process) can also be controlled. The material is preferably sandwiched between release papers and then fed into the twin rolls. The temperature of the double-roller hot press is preferably 150-300 ℃; the speed of the double rollers is preferably 0.4-10 m/min; more preferably 0.4 to 5 m/min. The twin roll gap is preferably 0.2 to 2mm (in the case where no particular description is given, the twin roll gap means the minimum distance between the twin rolls). The twin roll gap is related to the thickness of the substrate. Alternatively, the material may be sandwiched between protective layers and then fed into the twin rolls. The thickness of the material comprising the coating layer and the supporting layer (the release paper and/or the protective layer when the release paper and/or the protective layer is/are included) is preferably 1-50% higher than the gap between the two rollers; more preferably 5-20% so that the material is somewhat squeezed as it enters between the rollers. The protective layer may be, for example, an iron sheet having an appropriate thickness. The temperature of the double-roller hot press is higher under the condition that a protective layer is arranged, and preferably 200-300 ℃; the twin roll gap may then be up to 5mm or even larger. In the case of a protective layer, it is preferable that the material be squeezed as it enters between the rollers, so as to control the pore size and avoid local macro-porosity (holes) or uneven pore size distribution. It will be appreciated that the temperature, speed and gap of the hot press can be affected for substrates of different materials or thicknesses, and that the solvent of the film layer can be vaporized to achieve the desired pore size and porosity.

The present invention can control the pore size, pore size distribution (uniform pore size), and porosity of the product film layer by controlling at least one of the coating solvent content, the heating temperature and time to vaporize the solvent, and the rate of expansion (time to relieve pressure). And preparing the ultrafiltration membrane filtering material with the porosity of 60-95% by adopting a high-temperature puffing and drying technology. The flat membrane filter material prepared by the method has a porous polymer skeleton formed by taking solvent type resin as a raw material, and nano-scale pores (holes) are uniformly distributed in the porous polymer skeleton. The pore size distribution is adjustable within 10-1000 nm. Other physical properties: burst index of 2-3 kPa g/m²A tensile index of 10 to 30 N.g/m²And the tearability is 800-1500 mN. For films with a substrate, the burst index and tensile strength of the film also depend on the substrate.

Compared with the membrane filter material prepared by the existing sol-gel method, the method of the invention has the following advantages:

1. the method of the invention is that after the solvent of the solution is evaporated to 5-50% of the solvent content, the solvent is vaporized by the action of high temperature, and the vaporized solvent is released in the form of gas by expansion. Therefore, the phenomena of large material solvent content, difficult drying and collapse and shrinkage caused by the surface tension of a pore structure in the middle of the drying process in the traditional sol-gel method are avoided. Therefore, the invention greatly improves the drying speed and the drying efficiency and greatly reduces the manufacturing cost of the ultrafiltration membrane.

2. The invention adopts high-temperature puffing and drying technology to prepare the membrane filter material with smaller aperture ratio and higher porosity ratio, and can adopt inorganic fiber sticky felt, inorganic fiber cloth and metal fiber net which are prepared by glass fiber, ceramic fiber and metal fiber as supporting materials to prepare the resin ultrafiltration membrane filter material with a flexible structure. The method overcomes the defects that the traditional resin ultrafiltration membrane filtering material is brittle and difficult to process, enables the traditional membrane filtering material to be applied to the application range of the traditional organic membrane filtering material, and greatly widens the application range and the application field of the resin ultrafiltration membrane.

3. The invention adopts high-temperature bulking technology, and controls the size of the pore structure of the formed material and the amount of the porosity by controlling at least one of the solvent content, the heating temperature and the bulking speed, so as to prepare the membrane filter material with higher porosity and smaller pore diameter structure. The pore-forming mode is completely different from the mode of preparing the membrane filtering material by the traditional sol-gel method, and is a gas phase pore-forming mode.

Drawings

FIG. 1 is a photograph of a film material obtained in example 1 of the present invention;

FIG. 2 is a photograph of a film material obtained in example 2 of the present invention;

FIG. 3 is a photograph of a film material obtained in comparative example 1 of the present invention;

FIG. 4 is a photograph of a film material obtained in comparative example 2 of the present invention;

FIG. 5 is a photograph of a film material obtained in comparative example 3 of the present invention;

FIG. 6 is a photograph of a film material obtained in comparative example 4 of the present invention;

FIG. 7 is a photograph of a film material obtained in comparative example 5 of the present invention;

FIG. 8 is a photograph of a film material obtained in comparative example 6 of the present invention;

FIG. 9 is a thermogravimetric analysis chart of the membrane material obtained in example 14 of the present invention;

FIG. 10 is a photograph of a film material obtained in example 14 of the present invention;

FIG. 11 is a pressure-flow graph of example 1.

Detailed Description

The present invention is further illustrated by the following examples, which are to be understood as merely illustrative and not restrictive.

The following shows a method for preparing the resin flat membrane with a nanoporous structure according to the present invention.

First, a resin sol coating is prepared. A resin sol coating may be applied to the flat sheet membrane support layer. The coating method is not limited, and usable coating apparatuses include a brush coater, an air knife coater, a blade coater, a roll coater, a spray coater, a curtain coater, a slit coater, and the like. The source of the resin sol is not limited, and commercially available sol can be used, or the resin sol can be self-prepared by the existing method.

In the present disclosure, "solvent-type resin" refers to a resin that can be dissolved with an organic solvent or water. The resin may be a thermosetting resin, a thermoplastic resin, a natural polymer material, rubber, or the like.

The thermosetting resin mainly comprises phenolic resin, urea resin, melamine formaldehyde resin, epoxy resin, unsaturated resin, polyurethane, polyimide and the like.

The thermoplastic resin mainly comprises polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyamide, polyformaldehyde, polycarbonate, polyphenyl ether, polysulfone, rubber and the like.

The solvent-type resin includes, but is not limited to, one or more of phenolic resin, melamine formaldehyde resin, silicone resin, epoxy resin, acrylic resin, polyamide resin, polycarbonate, thermoplastic polyester, polyether plastic, polysulfone plastic, polyurethane, natural gum, cellulose derivative, rosin, asphalt, camphor, polyethylene, polyvinyl chloride, polystyrene resin, polypropylene, polyisobutylene, fluoroplastic, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, natural rubber, butadiene rubber, styrene rubber, fluororubber, and ethylene propylene rubber.

"Water-soluble resin" refers to a resin that is water-soluble. The resin is selected from water-soluble phenolic resin, water-soluble epoxy resin, water-soluble melamine formaldehyde resin, water-soluble urea formaldehyde resin, water-soluble unsaturated polyester resin, water-soluble polyurethane resin, water-soluble acrylic resin, polyacrylamide, sodium polyacrylate, polyethylene glycol, polyvinyl alcohol, polymaleic anhydride, polyethyleneimine, polyethylene oxide, polyvinyl chloride, starch, water-soluble natural gum, methyl cellulose, hydroxyethyl cellulose and sodium carboxymethyl cellulose.

The invention can select proper curing agent according to different requirements and resin types. In some embodiments, suitable curing agents for the water-soluble phenolic resin can be inorganic and organic medium-strong acids, and can also be sodium carbonate, sodium bicarbonate, paraformaldehyde, hexamethylenetetramine, isocyanate, propylene carbonate, methyl methacrylate, vinyl acetate, triethanolamine, butyl acrylate, ammonium chloride, petroleum ether, trimethyl phosphate, benzenesulfonic acid, and the like; suitable curing agents for water-soluble epoxy resins include aliphatic diamines, aliphatic polyamines, aromatic polyamines, nitrogen-containing compounds, modified aliphatic amines, organic acids, acid anhydrides, boron trifluoride and complexes thereof; suitable curing agents for the water-soluble melamine-formaldehyde resin include sulfuric acid, hydrochloric acid, formic acid, ammonium chloride, ammonium sulfate, and the like; suitable curing agents for the water-soluble urea-formaldehyde resin include sulfuric acid, hydrochloric acid, formic acid, ammonium chloride, ammonium sulfate, and the like; suitable curing agents for the water-soluble unsaturated polyester resin include cyclohexanone peroxide, dibenzoyl peroxide, methyl ethyl ketone peroxide, and the like; suitable curing agents for the water-soluble polyurethane resin include toluene diisocyanate, trimethylolpropane, biuret polyisocyanate, and the like; suitable curing agents for water-soluble acrylic resins include isocyanates, pyridine, amino resins, resins with epoxy groups, titanium tetraisopropoxide, and the like.

Regarding the preparation of the coating layer, in one embodiment, a resin sol is coated on a flat membrane support layer to obtain a coating layer. In another embodiment, the preparation of the coating may comprise the following two steps: (1) coating the resin sol with higher solvent content on a flat membrane supporting layer to form a coating; (2) the solvent content in the coating is reduced to 5-50%. The solvent content of the coating can be reduced by utilizing a natural airing mode. The solvent in the coating can also be reduced to the desired level under heating. The resin sol with high solvent content is coated on the flat membrane supporting layer and then the solvent content is reduced, so that the resin sol with high solvent content has good fluidity and is easy to coat on the flat membrane supporting layer for membrane formation. The content of the resin sol solvent used for film formation in the step (1) can be 30-70 wt%, then the solvent is reduced to a proper amount, and the proper amount of the solvent is maintained to be vaporized in a later heating process and then expanded to form nano pores (holes). The resin sol has higher solvent content, so that the raw materials can be uniformly dispersed in the solvent, and the uniformity of the post-expansion pore size distribution is facilitated. Moreover, the direct drying and shaping of the coating with high solvent content in the existing preparation method can affect the pore size of the material, or the pore size is difficult to control. The method comprises the steps of heating the material (the supporting layer and the coating) with a certain solvent content, controlling the solvent content in the coating to be 5-50%, controlling the subsequent heating vaporization temperature and the speed of pressure release in the subsequent puffing process to regulate the aperture and porosity of the material.

In the step (2) of the preparation of the coating layer, in one embodiment, the solvent content in the coating layer may be reduced by applying a certain temperature to the coating layer. The temperature setting is such that the solvent in the material is partially evaporated (vaporized) to reach a specific solvent content range. The heating temperature can be adjusted at 25-200 ℃ according to different solvent contents. More preferably 40 to 120 ℃. The step is to reduce the content of the solvent, the boiling points of the solvents are different, the boiling points of some organic solvents are only dozens of degrees, the boiling point of water is 100 degrees, but as long as the time is short enough, the solvent can not be completely evaporated, and the specific solvent content range can be reached. The heating temperature is too low, the solvent is slowly reduced, and the industrial chain time is prolonged; if the solvent is heated too high, the solvent is reduced too fast, and the solvent is vaporized in advance and bulked, the pore diameter of the product cannot be controlled, and the pore diameter distribution is not uniform.

In the step (2) of the preparation of the above-mentioned coating, any apparatus capable of reducing the solvent content to effect drying may be used. In another embodiment, the solvent of the resulting solution can be reduced by an instrument with high temperature functionality. The apparatus used for controlling the solvent content may be an open mill, drying cabinet, microwave oven, freeze dryer, pressure sprayer, or impinging stream dryer. Methods used to reduce solvent content include, but are not limited to, atmospheric drying, reduced pressure drying, spray drying, fluidized drying, freeze drying, infrared drying, microwave drying, moisture absorption drying, impingement drying, sonic drying, displacement drying, steam drying, ice slurry drying, airless drying, pulse combustion drying, and the like. The industrial mass production can be realized by using the instrument, so that the limitation of the production quantity is avoided.

Then, the coating is subjected to a porosification treatment to obtain a resin flat membrane having a nanoporous (hole) structure. The voiding treatment is a treatment in which the solvent-vaporized resin is melted to generate voids in the film layer. Specifically, the coating is heated to melt the solvent vaporized resin and keep the volume or the shape of the resin unchanged, then the pressure is released through expansion until the required porosity is reached, and the resin flat membrane filter material with the nano porous structure is obtained after cooling and shaping.

The coating is heated, during which time sufficient time is ensured to evaporate the solvent in the coating and to maintain the volume of the material constant. Controlled pressure relief, i.e., pressure reduction (including solvent vaporization-induced pressure and externally applied pressure), is then performed to puff the material to a specified porosity. And naturally cooling to keep the structure stable, and preparing the resin flat membrane with the nano porous structure.

The temperature at which the coating is heated during the porosification treatment (solvent vaporization and material expansion) can be selected according to the kind of the resin sol. In a preferred embodiment, the temperature of heating should exceed the boiling point of the solvent. If the temperature is too low, this can result in too low a material expansion; if the temperature is too high, the pore size of the material is too large, thereby affecting the filtering performance of the material. For water-soluble resins, in some embodiments, the heating temperature ranges from 140 to 400 ℃. For solvent type resins, the boiling point of some organic solvents is only tens of degrees, and the heating temperature range is 100 to 400 ℃.

The heating time of the coating porosification treatment is preferably controlled so that the solvent is vaporized at the heating temperature. The lower the solvent content and the higher the temperature, the shorter the heating time. In addition, although the solvent may be completely vaporized in this heating process, a small amount of solvent may remain as long as it does not affect the filtration performance of the material.

In some embodiments, the coating may be heated to vaporize the solvent while simultaneously applying pressure. The solvent is vaporized by heating and pressurizing, and the shape volume of the material is kept unchanged to regulate the pore structure, such as uniform pore distribution and pore size. The pressure can be controlled to be higher than the saturated vapor pressure of the solvent at this time temperature and the volume of the material is made constant. Then the subsequent pressure release is carried out to realize the expansion. In some embodiments, the pressurization pressure is 0.01 to 10 MPa. Preferably, the pressurization pressure is 0.01 to 5 MPa.

After the solvent is vaporized, the solvent is released in a controlled manner, namely, the solvent is expanded to form holes, so that the pores reach the specified porosity. The pressure during puffing is slowly reduced from 10-0 MPa. In the pressure relief process, the material is not heated continuously, the temperature is slowly reduced, the pressure is gradually released in a controlled manner, and the temperature of the material is gradually reduced, belonging to a natural cooling process. In the pressure relief process, the solvent is in a gas state at this time, and the material still has certain fluidity, so that the pressure formed by vaporization of the solvent promotes the material to expand. For the pressure relief time, it is desirable to complete the expansion and to provide a suitable porosity and uniform pore size distribution. The rate of pressure reduction should be such that material expansion is achieved and the desired porosity is achieved. In some embodiments the time for pressure release is not less than 0.4 seconds and not more than 10 seconds. Too rapid a pressure reduction tends to result in too large a pore size and a non-uniform pore size distribution. But too slow a pressure reduction tends to cause puffing failure or too low a porosity.

The present invention can control the pore structure, such as the pore size and/or the uniformity of the pore size distribution, by controlling at least one of the solvent content, the heating temperature, the pressure of the pressurization, the rate of expansion (time of pressure release).

In some embodiments, the coating (which in this case refers to the coating being attached to a flat support layer, i.e., the support layer in combination with the coating) is fed to a two-roll hot press for porosification.

In one embodiment, a manufacturing system including heated press rolls is used to effect the vaporization and expansion of the solvent in the coating by heating it. The thickness of the material comprising the coating layer and the support layer is preferably 5 to 20% greater than the gap between the two rolls (without any special indication, the minimum distance between the two rolls). Since the coating thickness is higher than the twin roll gap, the coating is subjected to temperature and twin roll squeezing (i.e., heat and pressure) as it is fed into the twin roll press until it exits the twin roll gap (i.e., the minimum distance between the rolls) causing the solvent to vaporize. And after the coating exits the nip, the material expands as the pressure is released as the distance between the rolls increases (i.e., slowly decreases). A single roller or a twin roller may be used. When the twin rolls are used, the pressurizing pressure can be controlled by controlling the gap between the twin rolls, and the pressure reduction speed and the shape of the nano-pores (holes) can be controlled by controlling the rotating speed of the twin rolls, thereby controlling the size of the pores and the uniformity of the pore size distribution. With a single roll, the application and release of pressure can be controlled by controlling the gap between the material and the roll to vary gradually. Wherein, the slow pressure relief is realized by the gradual increase of the gap between the material and the roller, and the pressure is reduced as the gap is increased. It will be appreciated that the higher the solvent content and the higher the temperature, the lower the rotation speed of the rolls. Since the higher the temperature, the higher the solvent content and the higher the flowability of the material, the lower the roll speed, the formation of large bubbles (large holes) in the resin film can be avoided. In a specific embodiment, the temperature of the double-roller hot press is 150-300 ℃; the speed of the double rollers is 0.7-3.5 m/min; the gap between the two rollers is 0.2-2 mm (in the case of no specific description, the gap between the two rollers is the minimum distance between the two rollers).

In one embodiment, a flat plate hot press is used, and the temperature is 120-200 ℃; the pressure is 0.5-5 MPa, the pressure is maintained for 10-40 s, and the membrane is preferably prepared within 10s from the beginning to the completion of pressure relief.

In one embodiment, a flat vulcanizing machine is used, and the temperature is 150-250 ℃; the pressure is 0.6-7 MPa; and maintaining the pressure for 10-40 s, and preferably performing membrane making within 10s from the beginning of pressure relief to the completion of pressure relief.

Porosity in the present invention is tested by the following method: p ═ V₀-V)/V₀*100％＝(1-ρ₀ρ) × 100%, wherein: p-porosity of material,%; v₀Volume or apparent volume, cm, of material in its natural state³Or m³；ρ₀Bulk density of the material, g/cm³Or kg/m³(ii) a Absolute dense body of V-materialVolume, cm³Or m³(ii) a Rho-material density, g/cm³Or kg/m³。

In some embodiments, the resin flat sheet membrane has a density of 0.004 to 0.5g/cm³. The density in the present invention is measured by the following method: p is m/abt 10⁴Rho-density, kg/m³(ii) a m-dry mass of sample, g; a is the length of the sample, mm; b-width of the sample, mm; t-thickness of the pattern, mm.

In some embodiments, the specific surface area of the resin flat sheet membrane is 100 to 2000m²(ii) in terms of/g. The specific surface area of the invention is obtained by testing the specific surface area of V-Sorb 2800P and a pore size analyzer.

The average pore size test method adopts a liquid flow rate method. According to the Hagen-Poiseuille law, if the pore size of the filtering membrane is the same and is vertical to the surface of the filtering membrane, the pure water flux of the filtering membrane is measured under certain pressure and time, and the average pore size of the filtering membrane can be calculated by using a formula.

In the formula: r-mean pore diameter, μm;

P_R-porosity,%;

l is the thickness of the film, m;

eta-viscosity of pure water under test conditions, Pa · s;

q-pure water flux, m³；

A-effective filtration area, m²；

Δ P-differential pressure, Pa;

t-filtration time, s.

The pore size distribution test method comprises the following steps: bubble point method (pore diameter testing range 20nm-500um)

The pore size analyzer is obtained by testing with a bubble pressure method, and the testing principle is as follows: when the channels are blocked with the liquid wetting agent, a certain pressure is applied to the gas if the holes are opened by the gas due to the surface tension of the wetting agent, and the pressure required for opening the holes is larger as the holes are smaller. The pore size distribution of the sample can be obtained by comparing the relation curve between the pressure and the gas flow of the porous material in the dry and wet states and calculating according to a certain mathematical model.

The burst index is determined by measuring the burst strength and calculating according to the following formula: burst strength (kPa) ═ burst index (kpa.m)²Gram weight (g/m) of film and substrate²). The burst strength of the present disclosure is measured by placing the sample in the middle of a burst tester chuck and clamping the sample with a clamping force of not less than 690 kPa. The tester was started and gradually pressurized at a rate of (170. + -. 15) m/min, and when the specimen broke, the value indicated on the pressure gauge was read. Ten samples are taken during the test, five times are respectively measured on the front side and the back side, and the average value of 10 times is taken. The test specimens must be pretreated in accordance with the provisions of GB 10739-89. The unit of the value read by the test instrument is kgf/cm²Then converted into kPa or kPa.m²(ii) in terms of/g. The conversion formula is as follows: 1kgf/cm²＝ 98.1kPa，1kPa＝0.011223kgf/cm²。

And (3) testing the tensile index: the tensile index is a tensile strength of a film expressed in n.m/g in terms of a unit width and a unit weight of a sample, and is calculated as follows: x is F × W₀×b₀Div (W × b); in the formula: x-tensile index (N.m/g); f-tensile (N); w-sample quantitative (g/m)²)；W₀One l00/m²(ii) a b-sample width (15 mm); b₀One 100 mm.

The tear strength Ta is calculated as follows: ta is F/d; in the formula: ta-tear strength, kN/m; f is the median of the stress when the sample is torn, N; d is the median thickness of the sample, mm.

Pure water flux: the pure water flux refers to the pure water flux of a certain area of the membrane in corresponding time under corresponding temperature and pressure conditions, and the unit is L/(m)²H). The expression method is as the formula:

in formula II, the J-membrane permeation, L/(m)²H); v-total liquid transmission, L; a-effective area of the film, m²(ii) a t-the time of filtration,h。

retention rate: the retention rate refers to the mass of solute retained by a membrane in the solution after the solution is processed by the membrane, and the mass of the solute is the percentage of the total mass of the solute in the solution, and the specific determination method is as follows: (1) and preparing bovine serum albumin solution required by the experiment. (2) Preparing a Coomassie brilliant blue G-250 solution. (3) According to different bovine serum albumin solutions and different Coomassie G-250 dye reaction conditions, and measuring A in different solution states₅₉₅The values of (A) and (B) are summarized and analyzed, and finally the linear regression line equation y of the linear regression line equation is 0.0192x²+0.0499. x is the concentration of bovine serum albumin solution and y is the value of the concentration under 595nm ultraviolet light. (4) And adding a bovine serum albumin solution into the interception device, placing the prepared membrane at a right position, taking the intercepted solution after a period of time as a test sample for sample measurement, and calculating the concentration and the interception rate of the bovine serum albumin solution.

Average pore diameter: in the experiment, a liquid flow velocity method is adopted, according to the Hagen-Poiseuille law, if the pore size of the ultrafiltration membrane is the same and is vertical to the surface of the membrane, the pure water flux of the ultrafiltration membrane is measured under certain pressure and time, and the average pore size of the ultrafiltration membrane can be calculated by using a formula:

in formula III: r-mean pore size, μm; p^R-porosity,%; l-thickness of the film, m; eta-viscosity of pure water under test conditions, Pa · s; q-pure water flux, m³(ii) a A-effective filtration area, m²(ii) a Δ P-differential pressure, Pa; t-filtration time, s. From formula iii, the average pore size can be calculated by combining the flux and porosity. Flux analysis was performed using the organic membrane prepared in example 14 described below.

Table 1 table of flux analysis of the films obtained in example 14 under different pressures

The data in table 1 above show that the flux of the membrane increases with increasing pressure and eventually stabilizes. The increase in pressure causes the pore size to become larger or the incompletely opened pores to be opened and the pore size to become larger, thereby progressing to a larger flux. As the pressure increases, the flux of the membrane increases first. When the pressure exceeds a certain value, the change of the membrane flux along with the pressure tends to be flat.

Thermogravimetric analysis of the thin film. Referring to the thermogravimetric analysis chart shown in fig. 9, from the TG analysis chart of the organic nylon (polyamide) membrane, we can conclude that at the first peak 75.75 ℃, it is the residual formic acid of the nylon membrane that volatilizes and that a process of vaporization, which is a change in mass by 5.74% within 180 ℃, should be the change produced by the combustion of paper and the evolution of formic acid. The second process is 180-380 deg.c, the whole mass change is about 50%, the peak value of the process is 343.24 deg.c, the process is one of nylon melting, sublimation and vaporization, the mass change is great, the third process is 380-500 deg.c, and the reaction process is the vitrification process after nylon melting, sublimation and vaporization, so the mass change is 20.10%. The final residual mass, as ash remaining from the wisdom combustion, and the crystals produced by melting, subliming, vaporizing, vitrifying nylon, or materials requiring higher temperatures to decompose.

The present invention will be described in detail by way of examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in light of the above teachings. The specific process parameters and the like of the following examples are also only one example of suitable ranges, i.e., those skilled in the art can select the appropriate ranges through the description herein, and are not limited to the specific values exemplified below. In the case where the present invention is not specifically described, the addition amount or the content refers to the mass percentage content.

The phenolic resin (analytically pure) in this example was purchased from north Hebei Zetian chemical Co., Ltd; polyurethane (analytical grade), available from Shanghai Michelin Biochemical technology, Inc.; acrylic emulsion (analytically pure) purchased from Jitian chemical Co., Ltd, Shenzhen, etc.; propylene carbonate (analytically pure) available from Shandong Depu chemical Co., Ltd; epoxy resins (analytical grade) available from chemical resins ltd, dennauery; polyamide (analytically pure) available from yilong new materials, inc, guangzhou; triisopropanol tert-amine titanate (analytically pure) purchased from Tianjingdong chemical Co., Ltd; formic acid (analytically pure), purchased from chemical reagents, ltd, national pharmaceutical group; sodium fluorosilicate (analytically pure) purchased from Shanghai Michelin Biotech, Inc.; all the reagents are analytically pure, and are directly purchased and used without further purification; a precision type double-roller open mill, a department of technical and technical subsidiary of the institutional mechanical and electrical engineering, Dongguan city; electric heating constant temperature blast box DHG-9070A, Shanghai sperm macro experimental facilities Co.

Example 1

Black A4 paper (thickness 0.08mm) is used as a base material, and water-soluble phenolic resin (purity 98% and solid content 82.5%) is used as a raw material. 5g of water-soluble phenolic resin is weighed and coated on paper by a coater, and the coating weight is 45g/m²The coating thickness is 0.05 mm. After coating, the mixture is placed in an oven at 50 ℃ to bake the water content of the water-soluble phenolic resin to 15 percent. The twin-roll temperature was set at 180 ℃ and the gap was 0.25mm, the speed was 2.5m/min, a piece of polytetrafluoroethylene release paper (thickness 0.14mm) was placed on each side of the membrane, and the photograph of the resulting membrane material is shown in FIG. 1, and the thickness of the membrane after swelling was 0.12 mm. The pore size distribution data of the membrane material obtained by the bubble point method test are shown in table 3, and a pressure-flow graph is prepared as shown in fig. 11.

Example 2

Black A4 paper (thickness 0.08mm) is used as a base material, and water-soluble phenolic resin (purity 98% and solid content 82.5%) is used as a raw material. Weighing 20g of water-soluble phenolic resin, adding 2g of water, uniformly stirring, and coating a small amount of the water-soluble phenolic resin on paper, wherein the coating amount is 28.9g/m²The coating thickness is 0.03 mm. After coating, the mixture is placed in an oven at 50 ℃ to bake the water content of the water-soluble phenolic resin to 23.5 percent. The twin-roll temperature was set at 180 ℃ and the gap was 0.2mm, the speed was 2.5m/min, a piece of polytetrafluoroethylene release paper (thickness 0.14mm) was placed on each side of the membrane, and the photograph of the resulting membrane material is shown in FIG. 2, and the thickness of the membrane after swelling was 0.09 mm. Compared with example 1 in waterThe phenolic resin is added with a small amount of water, so that the coating is easier.

Comparative example 1

Black A4 paper (thickness 0.08mm) is used as a base material, and water-soluble phenolic resin (purity 98% and solid content 82.5%) is used as a raw material. 20g of water-soluble phenolic resin is weighed, 2g of water is added, a small amount of the water-soluble phenolic resin is uniformly stirred and coated on paper, the coating weight is 25.8g/m2, and the coating thickness is 0.02 mm. After coating, the mixture is placed in an oven at 50 ℃ to bake the water content of the water-soluble phenolic resin to 22.3 percent. The temperature of the twin rolls was set at 350 deg.C, the gap was 0.2mm, the rotation speed was 2.5m/min, a piece of polytetrafluoroethylene release paper (thickness 0.14mm) was placed on each side of the membrane, and the photograph of the resulting membrane material is shown in FIG. 3, and the thickness of the membrane after swelling was 0.11 mm. Due to the higher temperature, the aperture of the expanded phenolic resin film is larger.

Comparative example 2

Black A4 paper (thickness 0.08mm) is used as a base material, and water-soluble phenolic resin (purity 98% and solid content 82.5%) is used as a raw material. Weighing 20g of water-soluble phenolic resin, adding 2g of water, uniformly stirring, and coating a small amount of the water-soluble phenolic resin on paper, wherein the coating amount is 27.5g/m²The coating thickness is 0.03 mm. After coating, the mixture is placed in an oven at 50 ℃ to bake the water content of the water-soluble phenolic resin to 21.9 percent. The twin-roll temperature was set at 180 ℃ and the gap was 0.2mm, the speed was 11.5m/min, a piece of polytetrafluoroethylene release paper (thickness 0.14mm) was placed on each side of the membrane, and the photograph of the resulting membrane material is shown in FIG. 4, and the thickness of the expanded membrane was 0.04 mm. Because the rotating speed is too fast, the heat transfer is not enough, the phenolic resin film is heated unevenly, and the surface of the phenolic resin film is provided with expanded macropores and is distributed unevenly.

Comparative example 3

Black A4 paper (thickness 0.08mm) is used as a base material, and water-soluble phenolic resin (purity 98% and solid content 82.5%) is used as a raw material. Weighing 20g of water-soluble phenolic resin, adding 2g of water, uniformly stirring, and coating a small amount of the water-soluble phenolic resin on paper, wherein the coating amount is 23.9/m²The coating thickness is 0.02 mm. After coating, the mixture is placed in an oven at 50 ℃ to bake the water content of the water-soluble phenolic resin to 19.9 percent. The temperature of the two rollers is set at 180 deg.C, the gap is 0.1mm, the rotation speed is 2.5m/min, two pieces of polytetrafluoroethylene release paper (thickness is 0.14mm) are respectively placed on two sides of the membrane, and the obtained membrane material is expanded as shown in FIG. 5The film thickness after the formation is 0.03 mm. The gap is too small and the phenolic resin has almost solidified in the middle of the twin rolls, resulting in no or little expansion.

Examples 3 to 6

A4 paper (thickness 0.08mm) was used as a base material, and an aqueous polyurethane solution (solid content 43%) was used as a raw material. Coating a small amount of polyurethane aqueous solution on paper, wherein the coating amount is 23.9/m²The coating thickness is 0.02 mm. After coating, the mixture is placed in an oven at the temperature of 80 ℃ to bake the water content of the water-soluble phenolic resin to 25.6 percent. Four sets of experiments are set, the temperature of the double rollers is respectively set to be 150 ℃, 170 ℃, 190 ℃ and 210 ℃, the gap is 0.2mm, the rotating speed is 2.5m/min, two pieces of polytetrafluoroethylene release paper (the thickness is 0.14mm) are respectively placed on the two surfaces of the membrane, and the membrane thickness after the expansion is respectively 0.03mm, 0.05mm, 0.07mm and 0.11 mm. When the conditions such as the water content, the gap, the rotating speed and the like are the same, the higher the temperature is, the higher the expanded porosity of the polyurethane film is, and the larger the pore diameter is.

Examples 7 to 11

A4 paper (thickness 0.08mm) is used as a base material, and acrylic emulsion (solid content 40%) is used as a raw material. Coating a small amount of acrylic emulsion on paper, wherein the coating weight is 33.9/m²The coating thickness is 0.02 mm. After coating, the mixture is placed in an oven at the temperature of 80 ℃ to bake the water content of the water-soluble phenolic resin to 19.8 percent. Five groups of experiments are set, the temperature of the double rollers is set to be 250 ℃, the gap is 0.2mm, the rotating speed is respectively set to be 0.5m/min, 1.5m/min, 3.5m/min, 5.5m/min and 6.5m/min, two surfaces of the membrane are respectively provided with a piece of polytetrafluoroethylene release paper (the thickness is 0.14mm), and the membrane thickness after the expansion is respectively 0.04mm, 0.06mm, 0.07mm, 0.12mm and 0.14 mm. When the conditions such as temperature, clearance, water content and the like are the same, and the temperature is high enough and the heat transfer is enough, the higher the rotating speed is, the higher the porosity of the membrane expansion is, and the pore diameter is also larger.

Example 12

A4 paper (thickness 0.08mm) is used as a base material, and water-soluble phenolic resin (purity 98% and solid content 82.5%) is used as a raw material. Weighing 20g of water-soluble phenolic resin, adding 2g of water, adding 1g of curing agent propylene carbonate, uniformly stirring, and coating a small amount of the mixture on paper, wherein the coating weight is 35.5g/m²The coating thickness is 0.03 mm. After coating, the mixture is placed in an oven at 50 DEG CAnd (3) drying the water content of the water-soluble phenolic resin to 13.8%. The temperature of the double rollers is set to 190 ℃, the gap is 0.22mm, the rotating speed is 1.7m/min, two pieces of polytetrafluoroethylene release paper (the thickness is 0.14mm) are respectively placed on the two surfaces of the membrane, and the thickness of the membrane after expansion is 0.09 mm.

Example 13

A4 paper (thickness 0.08mm) is used as a base material, and water-soluble epoxy resin is used as a raw material. Weighing 20g of water-soluble phenolic resin, adding 5g of water, adding 3g of curing agent triisopropanol tertiary amine titanate, uniformly stirring, taking a small amount of the obtained product, and coating the obtained product on paper, wherein the coating amount is 41.1g/m²The coating thickness was 0.04 mm. After coating, the mixture is placed in an oven at 50 ℃ to bake the water content of the water-soluble phenolic resin to 17.8 percent. The temperature of the double rollers is set to be 200 ℃, the gap is 0.23mm, the rotating speed is 1.9m/min, two pieces of polytetrafluoroethylene release paper (the thickness is 0.14mm) are respectively placed on the two surfaces of the membrane, and the thickness of the membrane after expansion is 0.11 mm.

Example 14

White A4 paper (thickness 0.08mm) was used as a base material, polyamide (solid powder) was used as a raw material, and formic acid (mass fraction 88%) was used as a solvent. Weighing 20g of polyamide, weighing 40g of formic acid, pouring into the polyamide, stirring until the polyamide is completely dissolved, and coating a small amount of the polyamide on paper, wherein the coating amount is 25.6g/m²The coating thickness is 0.01 mm. After coating, the polyamide is placed in an oven at 40 ℃ to reduce the content of formic acid in the polyamide to 20 percent. The temperature of the twin rolls was set at 180 ℃ and the gap was 0.2mm, the rotation speed was 1.7m/min, a piece of polytetrafluoroethylene release paper (thickness 0.14mm) was placed on each side of the membrane, and the photograph of the resulting membrane material is shown in FIG. 10, and the thickness of the membrane after swelling was 0.08 mm.

TABLE 2 data of membrane materials prepared in part of examples and comparative examples

Table 3 average pore size and pore size distribution data for membrane material prepared in example 1

Comparative example 4

White A4 paper (thickness 0.08mm) was used as a base material, polyamide (solid powder) was used as a raw material, and formic acid (mass fraction 88%) was used as a solvent. Weighing 20g of polyamide, weighing 40g of formic acid, pouring into the polyamide, stirring until the polyamide is completely dissolved, coating a small amount of the polyamide on paper, wherein the coating amount is 21.3g/m²The coating thickness is 0.01 mm. After coating, the polyamide is placed in an oven at 50 ℃ to reduce the content of formic acid in the polyamide to 20 percent. The twin-roll temperature was set at 350 ℃ and the gap was 0.2mm, the rotation speed was 1.7m/min, and a piece of polytetrafluoroethylene release paper (thickness: 0.14mm) was placed on each side of the film, and a photograph of the resulting film material is shown in FIG. 6. Due to the over-high temperature, the polyamide membrane has obvious macropores after being expanded. The thickness of the expanded membrane is 0.1 mm.

Comparative example 5

White A4 paper (thickness 0.08mm) was used as a base material, polyamide (solid powder) was used as a raw material, and formic acid (mass fraction 88%) was used as a solvent. Weighing 20g of polyamide, weighing 40g of formic acid, pouring into the polyamide, stirring until the polyamide is completely dissolved, and coating a small amount of the polyamide on paper, wherein the coating amount is 24.7g/m²The coating thickness is 0.01 mm. After coating, the polyamide is placed in an oven at 50 ℃ to reduce the content of formic acid in the polyamide to 20 percent. The twin-roll temperature was set at 180 ℃ and the gap was 0.2mm, the rotation speed was 10.5m/min, and a piece of polytetrafluoroethylene release paper (thickness: 0.14mm) was placed on each side of the membrane, and a photograph of the resulting membrane material is shown in FIG. 7. Because the rotating speed is too fast and the heat transfer is not enough, the polyamide film has insufficient expansion degree and low porosity, and the thickness of the expanded film is 0.02 mm.

Comparative example 6

White A4 paper (thickness 0.08mm) was used as a base material, polyamide (solid powder) was used as a raw material, and formic acid (mass fraction 88%) was used as a solvent. Weighing 20g of polyamide, weighing 40g of formic acid, pouring into the polyamide, stirring until the polyamide is completely dissolved, and coating a small amount of the polyamide on paper, wherein the coating amount is 24.7g/m²The coating thickness is 0.01 mm. After coating, the polyamide is placed in an oven at 50 ℃ to reduce the content of formic acid in the polyamide to 20 percent. The temperature of the double rollers is set to be 180 ℃, the gap is 0.1mm, the rotating speed is 1.7m/min, and two surfaces of the film are respectively put one sheet to gatherTetrafluoroethylene release paper (thickness 0.14mm), and the photograph of the resulting film material is shown in FIG. 8. Because the gap between the two rollers is too small, part of the polyamide penetrates into the paper, and the space is too small, so that the puffing degree of the polyamide is not high, the porosity is lower, and the thickness of the puffed film is 0.02 mm.

Claims

1. A preparation method of a resin flat membrane with a nano porous structure is characterized in that a solvent type resin sol raw material is uniformly coated on a supporting layer to form a coating with the solvent content of 5-50 wt%; the solvent is an organic solvent; the solvent type resin is a resin soluble with an organic solvent; heating the coating to melt the solvent-evaporated resin and maintain its form; the material volume is kept unchanged and no expansion occurs when the solvent vaporized resin is melted; heating the coating to melt the solvent vaporized resin at a heating temperature of 100-400 ℃; heating the coating to vaporize the solvent and simultaneously pressurizing, wherein the pressurizing pressure is 0.01-10 MPa; then swelling to reach the required porosity to obtain the resin flat membrane with the nano porous structure; said expansion is controlled pressure relief, wherein the time of pressure relief is not less than 0.4 seconds and not more than 10 seconds; the preparation method controls the pore diameter and porosity of the film layer by controlling at least one of the content of a coating solvent, the heating temperature and the bulking speed; the resin flat membrane with the nano porous structure has the porosity of 60-95% and the pore size distribution is adjustable within 10-1000 nm.

2. The method according to claim 1, wherein the coating is applied in an amount of 10 to 60g/m²。

3. The method according to claim 1, wherein the solvent-type resin is one or more of phenol resin, melamine-formaldehyde resin, silicone resin, epoxy resin, acrylic resin, polyamide resin, polycarbonate, thermoplastic polyester, polyether plastic, polysulfone plastic, polyurethane, natural gum, cellulose derivative, rosin, asphalt, camphor, polyethylene, polyvinyl chloride, polystyrene resin, polypropylene, polyisobutylene, fluoroplastic, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, natural rubber, butadiene-based rubber, styrene-based rubber, fluororubber, and ethylene-propylene rubber.

4. The preparation method according to claim 1, wherein the material of the support layer is at least one selected from glass fibers, ceramic fibers, metal fiber mats made of metal fibers, inorganic fiber mats made of inorganic fibers, inorganic fiber cloth, and metal fiber nets.

5. The production method according to claim 1, wherein the pressure of the pressurization is higher than the saturated vapor pressure of the solvent under the heating condition.

6. The method of claim 1, wherein the resin is dissolved in a solvent in an amount of 1 to 5 times the weight of the resin, and the solvent content is reduced to 30 to 70 wt% of the total amount of the resin gel to form the coating layer on the support layer.