Dry preparation method of self-heating membrane

Abstract

The invention relates to the technical field of self-heating products, and particularly discloses a dry preparation method of a self-heating diaphragm, which comprises the following steps: mixing a plurality of raw materials to obtain mixed powder; pressing the mixed powder to form a base film; cutting the base membrane to obtain a high-water-absorption self-heating membrane core body; an electrolyte solution is placed on a core body of the high-water-absorption self-heating membrane, the core body of the high-water-absorption self-heating membrane is firstly put into an inner bag made of microporous oxygen-permeable membrane coated non-woven fabric, and then a layer of oxygen-isolation plastic outer bag is externally packaged, so that the self-heating membrane is obtained. According to the dry preparation method of the self-heating membrane, the mixing uniformity of powder is improved, heating generated in the preparation stage due to the existence of water is avoided, the heating performance of the self-heating membrane is enhanced, meanwhile, water is released when the temperature of the self-heating body reaches the body temperature or above through the temperature control water-absorbent resin, the self-heating time is prolonged, and the self-heating effect is improved. The problem that the release of an electrolyte solution is limited due to the fact that the water-retaining property of ordinary water-absorbent resin is too high is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of self-heating products, and in particular relates to a dry preparation method of a self-heating membrane. Background Art

[0002] The principle of self-heating body is to use the reaction of the primary battery to speed up the oxidation reaction, convert chemical energy into heat energy, and use it to keep warm. The raw materials of traditional self-heating products are mainly divided into powder and paste. The production process of powder raw materials is to mix different kinds of powder raw materials, and then wrap the mixed powder with non-woven fabric to make a self-heating sheet. This method has a large difference in the density of powder raw materials, resulting in low mixing uniformity; the production process of paste raw materials is to first mix the powder raw materials with liquid into a paste, and then make the paste into a self-heating sheet and dry it, and then wrap it with non-woven fabric to make a self-heating sheet product.

[0003] At present, most of the self-heating bodies on the market are mainly produced with paste raw materials. For example, in the steps for preparing self-heating materials provided by patent CN112500839B, passivated iron powder, diatomaceous earth, activated carbon, sodium acetate and pure water are first added to a grinder for grinding, and then packaged in a non-woven bag and plastic-sealed under vacuum; for example, in a self-heating sheet and its preparation method disclosed in patent CN115227481B, a paste-like self-heating material is also used, and a water-absorbing material is placed between two layers of paste-like self-heating materials through a sandwich structure to avoid the problem of the air-permeable film being directly covered on the water-absorbing material, causing the air-permeable film to be blocked without heating. However, the paste method used in the above two patents has the problem that the oxidizable metal is very easy to settle and the uniformity is not high due to the large difference in raw material density; and the process cost of drying processing is high, the cycle is long, and the production efficiency is low.

[0004] Therefore, there is an urgent need for a self-heating element with high mixing uniformity in the market. Summary of the invention

[0005] In response to the above problems, the present invention provides a breakthrough dry preparation method for a self-heating membrane, which improves the mixing uniformity of the powder, avoids the heat generated in the preparation stage due to the presence of water, and enhances the heating performance of the self-heating membrane. At the same time, a temperature-controlled water-absorbing resin is used to release water when the temperature of the self-heating body reaches above body temperature, thereby extending the self-heating time and solving the problem of limited release of the electrolyte solution due to the excessive water retention of ordinary water-absorbing resins.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] The present invention provides a dry method for preparing a self-heating membrane, which specifically comprises the following steps:

[0008] S1, mixing active metal powder, conductive agent, binder, temperature control water-absorbing resin and filler to obtain mixed powder;

[0009] S2, conveying the mixed powder of step S1 to a pressing device for pressing to form a base film;

[0010] S3, cutting the base film formed in step S2 according to the size requirements to obtain a highly water-absorbent self-heating film core;

[0011] S4. Put the electrolyte solution on the core of the highly water-absorbent self-heating membrane, first put it into an inner bag made of a non-woven fabric covered with a microporous oxygen-permeable membrane, and then wrap it with an oxygen-isolating plastic outer bag to obtain the self-heating membrane.

[0012] The present invention mixes metal powder with small particle size, uniform particles and easy dispersion, conductive agent, binder and water-absorbing resin as raw materials without adding water to form flocculent powder that can be hot-rolled and made into a cuttable base film. The base film is cut according to the required size, and then electrolyte is added and packaged to obtain a self-heating film. When the self-heating film is used, the plastic outer bag is torn open, and after the non-woven fabric inner bag contacts the air, oxygen enters from the micropores of the non-woven fabric and reacts with the oxidizable metal to generate heat.

[0013] The self-heating diaphragm of the present invention is prepared by a dry method to improve the mixing uniformity of the powder, and also avoid the heat generated in the preparation stage due to the presence of water, thereby enhancing the heating performance of the self-heating diaphragm. Based on the principle of the primary cell reaction of the self-heating body, the reaction requires an electrolyte, and the water-absorbing resin can subsequently absorb the electrolyte to ensure the normal progress of the primary cell reaction. However, the applicant found during the preparation process that the electrolyte solution on the core of the self-heating diaphragm would roll and could not be well absorbed.

[0014] In some embodiments, in step S1, the mixing is divided into four stages, namely, a premixing stage, a fast mixing stage, a slow mixing stage and a mixed discharging stage, and the rotation speeds of the four stages are 600-1200rpm, 1600-2400rpm, 500-1100rpm and 200-700rpm, respectively; the time for the first three stages is 100-500s, 100-1000s and 100-500s, respectively.

[0015] The present application is mixed in four stages, which improves the uniformity of mixing, ensures the performance of the product, and controls the heat generated during the mixing process. Among them, the pre-mixing stage can make the powders fully mixed together; during the fast mixing stage, the binder is fiberized under the high speed shear force, so that each powder is evenly bonded together by the binder to form floccules; the slow mixing stage gradually reduces the speed of the internal powder, and finally keeps the discharge at a relatively low speed.

[0016] In some embodiments, in step S1, based on 100wt%, the mixed powder comprises 20-60wt% active metal powder, 10-40wt% conductive agent, 1-10wt% binder, 1-10wt% temperature-controlled water-absorbing resin and 2-20wt% filler.

[0017] In some embodiments, in step S1, the active metal powder is any one of iron powder, magnesium powder, and aluminum powder, and has a particle size of 100 to 300 meshes.

[0018] The active metal powder of the present invention is preferably iron powder, which can react with oxygen spontaneously and continuously release heat, and the self-heating mechanism of the iron powder can be adjusted by external factors such as temperature, air permeability, etc.

[0019] In some embodiments, in step S1, the conductive agent is carbon powder with a particle size of 100 to 300 meshes.

[0020] Carbon powder has good electrical conductivity and stable chemical properties, which can promote the transmission of electrons and is not easy to react chemically with other materials; at the same time, the light specific gravity of carbon powder can increase the comfort of the product. In addition, the production and use of carbon powder is relatively safe and environmentally friendly, and no harmful substances are produced.

[0021] In some embodiments, in step S1, the binder is any one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid and polytetrafluoroethylene.

[0022] Preferably, the binder is polytetrafluoroethylene.

[0023] The present invention preferably uses polytetrafluoroethylene as a binder, which has the property of being easily fibrous under the action of shear force, and is convenient for forming flocculent powder with other raw materials, which helps to form a self-supporting film, maintain the structural stability of the membrane, and has good combination with active materials and conductive agents, so that the contact between the raw material particles reaches an ideal degree of closeness.

[0024] In some embodiments, in step S1, the preparation steps of the temperature-controlled water-absorbing resin are as follows:

[0025] (1) stirring and dissolving a dispersant, a temperature-sensitive monomer and an alkane to obtain a reaction base liquid;

[0026] (2) stirring acrylic acid and 20-40 wt % sodium hydroxide solution at -5-5° C. until the solution becomes clear, thereby obtaining an acrylic acid neutralization solution;

[0027] (3) mixing 5 to 30 wt % acrylamide solution, 5 to 20 wt % N,N-methylenebisacrylamide solution and 0.1 to 2.0 wt % potassium persulfate solution with the acrylic acid neutralization solution obtained in (2) to obtain an aqueous phase;

[0028] (4) Add the aqueous phase obtained in (3) to the reaction base liquid in (1), stir at 30-60°C for 10-40 minutes, add the PVA solution, and then heat to 60-90°C at a rate of 3-8°C / h, continue stirring for 1-7 hours, wash, and vacuum dry to constant weight to obtain a temperature-controlled water-absorbing resin.

[0029] In some embodiments, in step (1), the dispersant comprises Span 60 and / or Span 85.

[0030] In some embodiments, in step (1), the preparation steps of the temperature-sensitive monomer are as follows: dissolving maleic anhydride in acetone, adding isopropylamine and stirring for 1 to 4 hours, and after the reaction is completed, rotary evaporation and recrystallization are performed to obtain the temperature-sensitive monomer.

[0031] Preferably, the molar ratio of maleic anhydride to isopropylamine is 1:(1.0-1.5).

[0032] In some embodiments, in step (4), the mass ratio of PVA in the PVA solution to acrylic acid in step (2) is (0.05-0.4):1.

[0033] The preparation steps of the water-absorbing resin are combined with the reverse suspension polymerization method and the solution polymerization method. The solution polymerization method is specifically embodied in that the monomer, the initiator and the cross-linking agent are all dissolved in an appropriate solvent. The advantages of this method are that the polymerization system has low viscosity, easy heat transfer and can avoid local overheating; the reverse suspension polymerization method is specifically manifested in that the water phase is dispersed and suspended in the reaction bottom liquid under the action of a dispersant and stirring to carry out polymerization. On the one hand, the problems of low conversion rate, slow polymerization rate and easy formation of block polymers causing discharging difficulties in the solution polymerization method are alleviated; on the other hand, suspended particles with a narrow particle size distribution are obtained, so that the obtained water-absorbing resin has a high degree of mixing uniformity with the remaining raw materials in the mixing stage, can be evenly distributed in the self-heating membrane, and further the electrolyte released by subsequent absorption is evenly distributed.

[0034] The water-absorbent resin molecular chain contains hydrophilic hydroxyl groups, anionic groups and amide groups. These groups tend to interact with water molecules to form hydrogen bonds at room temperature or lower temperatures, showing hydrophilicity. However, once the water-absorbent resin absorbs water and swells to become a hydrogel, it is difficult to separate the water, that is, there is a problem of limited release of the electrolyte solution due to excessive water retention.

[0035] The present invention introduces a hydrophobic isopropyl group through a thermosensitive monomer. When the temperature of the self-heating body reaches above body temperature, the hydrogen bonding effect weakens, and the hydrophobic isopropyl group begins to dominate, causing the polymer chain to tend to aggregate and curl, showing hydrophobicity, that is, releasing water, and prolonging the self-heating time. The water-absorbing resin also neutralizes acrylic acid with a sodium hydroxide solution, so that a large number of sodium carboxylate groups are contained in the molecular network, which provides hydrophilic anionic groups on the one hand; on the other hand, when in contact with the electrolyte, the water molecules in the liquid first gradually penetrate from the surface to the internal cross-linked network through capillary action, and the sodium carboxylate ionizes a large number of Na + , and then the resin reaches its maximum water absorption rate through osmotic pressure, thereby improving the absorption of electrolyte solution.

[0036] In some embodiments, in step S1, the filler is vermiculite with a particle size of 60 to 140 meshes.

[0037] Vermiculite has strong thermal insulation properties, a loose structure, and good air permeability, which can ensure sufficient entry of oxygen to participate in the primary battery reaction.

[0038] In some embodiments, in step S2, the conveying is horizontal belt conveying; the pressing is hot roller pressing, and the roller surface temperature is 40-300°C.

[0039] When the mixed powder is subjected to extrusion force, the tiny fibers in it will be pulled out under the action of the force and cause the resin to agglomerate, which is not conducive to processing. Horizontal belt conveyor can avoid extrusion and collision of the mixed powder as much as possible, reduce agglomeration, and improve the quality and performance of the finished product.

[0040] Hot roll forming can press the diaphragm blank into the required thickness and ensure that the thickness is uniform and flat. The speed difference between the upper and lower pressure rollers can help the diaphragm reach the expected size and shape, and can also improve the brightness of the diaphragm surface. As a continuous production process, it is suitable for large-scale production, which can significantly improve production efficiency, reduce costs, and maintain consistency in product quality.

[0041] In some embodiments, in step S4, the mass ratio of the self-heating membrane core to the electrolyte solution is 1:(0.2-1.0).

[0042] Preferably, the electrolyte solution is a 2-10 wt % sodium chloride solution.

[0043] The sodium chloride solution helps the iron powder and activated carbon to form a primary battery, accelerates the process of iron oxidation corrosion, and thus improves the efficiency of the entire heating process. The present invention controls the concentration of sodium chloride in the electrolyte solution to ensure the osmotic pressure difference between the inside and outside of the molecular network and to avoid the shielding effect of external ions on the charges on the molecular network of the water-absorbing resin, thereby improving the water absorption performance.

[0044] In some embodiments, in step S4, the electrolyte solution further comprises 0.1-2.0 wt % of a foaming agent.

[0045] Preferably, the foaming agent is at least one of dodecyl dimethyl betaine, cocamidopropyl betaine or sodium lauryl polyoxyethylene ether sulfate.

[0046] Further preferably, the foaming agent is dodecyl dimethyl betaine.

[0047] The present invention makes the electrolyte solution into a foam, which solves the problem of poor absorption caused by rolling on the self-heating membrane core, and solves the defoaming problem caused by the sodium chloride solution by using a specifically selected dodecyl dimethyl betaine as a foaming agent, thereby improving the foam stability. However, this brings another problem, that is, the electrolyte solution that penetrates into the membrane core will flow out quickly and cannot stay. The possible reason is that the change in surface tension brought by the foaming agent strengthens the penetration of the electrolyte solution. The applicant accidentally discovered that introducing PVA into the water-absorbing resin can improve this phenomenon. It may be that PVA forms a semi-interpenetrating network structure in the water-absorbing resin, which strengthens the retention of the electrolyte solution.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] 1. The present invention provides a breakthrough dry preparation method for a self-heating membrane. Without adding liquid, metal powder with small particle size, uniform particles, and easy dispersion, conductive agent, binder and water-absorbing resin are mixed as raw materials to form flocculent powder that can be hot-rolled and made into a cuttable base film. The base film is cut to the required size, and then electrolyte is added and packaged to obtain a self-heating membrane. The dry preparation improves the mixing uniformity of the powder, avoids the heat generated in the preparation stage due to the presence of water, and enhances the heating performance of the self-heating membrane.

[0050] 2. The present invention optimizes the reaction process to obtain a water-absorbent resin with small particle size differences, so that it is evenly distributed in the self-heating membrane, and the electrolyte subsequently absorbed and released is also evenly distributed. On this basis, a temperature-sensitive monomer is introduced into the water-absorbent resin to release water when the temperature of the self-heating body reaches above body temperature, thereby extending the self-heating time and solving the problem of limited release of electrolyte solution caused by excessive water retention of ordinary water-absorbent resins.

[0051] 3. The present invention makes the electrolyte solution into a foamy state, thereby solving the problem of poor absorption caused by rolling on the self-heating diaphragm core, and solves the defoaming problem caused by the sodium chloride solution by using specifically selected dodecyl dimethyl betaine as a foaming agent, thereby improving the foam stability; on this basis, the introduction of PVA into the water-absorbing resin improves the phenomenon that the electrolyte solution that has penetrated into the diaphragm core will quickly flow out. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is a picture of a base film product formed after multiple hot rolling in Example 1;

[0053] Figure 2 This is a hollow diagram of the base film product in Example 1;

[0054] Figure 3 This is a scanning electron microscope image of the base film surface after hot roll forming in Example 1. DETAILED DESCRIPTION

[0055] The present invention will be described below in conjunction with specific embodiments. It should be noted that the following embodiments are examples of the present invention and are only used to illustrate the present invention, but not to limit the present invention. Other combinations and various modifications within the concept of the present invention may be performed without departing from the spirit or scope of the present invention.

[0056] In order to facilitate those skilled in the art to implement the present invention, some of the raw materials of the embodiments and comparative examples are described as follows:

[0057] The polytetrafluoroethylene model is PTFE dispersed fine powder resin-JF, which was purchased from Hangzhou Jufu New Material Technology Co., Ltd.

[0058] Preparation Example 1

[0059] The preparation steps of the thermosensitive monomer are as follows:

[0060] Dissolve 1 mol of maleic anhydride in 1 L of acetone, add 1.2 mol of isopropylamine and stir for 3 hours. After the reaction is completed, rotary evaporation and recrystallization with acetone are performed to obtain a thermosensitive monomer.

[0061] Preparation Example 2

[0062] The preparation steps of temperature-controlled water-absorbing resin A are as follows:

[0063] (1) 0.3 mol of Span 60, 0.2 mol of Span 85, and 2 mol of the thermosensitive monomer were stirred and dissolved in 5 L of cyclopentane to obtain a reaction base solution;

[0064] (2) stirring 5 mol of acrylic acid and 30 wt % of sodium hydroxide solution at 0° C. until the solution is clear, to obtain an acrylic acid neutralization solution, wherein the mass ratio of acrylic acid to sodium hydroxide solution is 1:1.8;

[0065] (3) 5 mol of acrylamide, 0.012 mol of N,N-methylenebisacrylamide and 0.012 mol of potassium persulfate are respectively prepared with water to prepare a 20 wt % acrylamide solution, a 10 wt % N,N-methylenebisacrylamide solution and a 1 wt % potassium persulfate solution, and mixed with the acrylic acid neutralization solution obtained in (2) to obtain an aqueous phase;

[0066] (4) adding the aqueous phase obtained in (3) to the reaction base liquid in (1), stirring at 50° C. for 30 min, adding 30 wt % PVA solution, wherein the mass ratio of PVA to the acrylic acid in step (2) is 0.12:1, and then heating to 70° C. at a rate of 5° C. / h, continuing stirring for 6 h, washing with anhydrous ethanol, and vacuum drying at 60° C. to constant weight to obtain temperature-controlled water-absorbing resin A.

[0067] Preparation Example 3

[0068] The preparation steps of temperature-controlled water-absorbing resin B are as follows:

[0069] The difference between this preparation example and preparation example 2 is that:

[0070] (4) The aqueous phase obtained in (3) was added to the reaction liquid in (1), stirred at 50°C for 30 min, then heated to 70°C at a rate of 5°C / h, stirred for 6 h, washed with anhydrous ethanol, and vacuum dried at 60°C to constant weight to obtain temperature-controlled water-absorbing resin B.

[0071] Preparation Example 4

[0072] The preparation steps of water-absorbing resin are as follows:

[0073] The difference between this preparation example and preparation example 2 is that:

[0074] (1) 0.3 mol of Span 60 and 0.2 mol of Span 85 were stirred and dissolved in 5 L of cyclopentane to obtain a reaction base solution.

[0075] Example 1

[0076] A dry method for preparing a self-heating diaphragm specifically comprises the following steps.

[0077] S1, according to 100wt%, 40wt% of iron powder with a particle size of 200 mesh, 30wt% of carbon powder with a particle size of 200 mesh, 5wt% of polytetrafluoroethylene, 5wt% of temperature-controlled water-absorbing resin A and 20wt% of vermiculite with a particle size of 100 mesh are mixed, and the mixing is divided into four stages, namely, a pre-mixing stage, a fast mixing stage, a slow mixing stage and a mixed discharging stage, and the rotating speeds of the four stages are 1000rpm, 2000rpm, 700rpm and 500rpm respectively; the time of the first three stages is 300s, 700s and 300s respectively, to obtain a mixed powder;

[0078] S2, conveying the mixed powder in step S1 horizontally to a hot roller, pressing at 180°C to form a base film, Figure 1 and Figure 2 ;

[0079] S3, cutting the base film formed in step S2 according to the size requirements to obtain a highly water-absorbent self-heating film core;

[0080] S4. Place 0.8 times the mass of electrolyte solution on the core of the highly water-absorbent self-heating membrane, the electrolyte solution containing 7wt% of sodium chloride and 0.3wt% of dodecyl dimethyl betaine, first put it into an inner bag made of non-woven fabric covered with a microporous oxygen-permeable membrane, and then wrap it in an oxygen-isolating plastic outer bag to obtain a self-heating membrane.

[0081] Depend on Figure 1 , Figure 2 It can be seen that the basement membrane can be suspended in the air and maintain a stable shape, indicating that the structure is relatively strong; Figure 3 This is a scanning electron microscope image of the base film, and it can be seen that the materials are mixed evenly.

[0082] Example 2

[0083] A dry method for preparing a self-heating diaphragm specifically comprises the following steps.

[0084] S1, according to 100wt%, 30wt% of iron powder with a particle size of 100 mesh, 35wt% of carbon powder with a particle size of 100 mesh, 10wt% of polytetrafluoroethylene, 10wt% of temperature-controlled water-absorbing resin A and 15wt% of vermiculite with a particle size of 60 mesh are mixed, and the mixing is divided into four stages, namely, a pre-mixing stage, a fast mixing stage, a slow mixing stage and a mixed discharging stage, and the rotating speeds of the four stages are 600rpm, 1600rpm, 500rpm and 200rpm respectively; the time of the first three stages is 500s, 1000s, and 500s respectively, to obtain a mixed powder;

[0085] S2, conveying the mixed powder in step S1 to a hot roller in a horizontal direction, and pressing at 120° C. to form a base film;

[0086] S3, cutting the base film formed in step S2 according to the size requirements to obtain a highly water-absorbent self-heating film core;

[0087] S4. Place 0.4 times the mass of electrolyte solution on the core of the highly water-absorbent self-heating membrane, the electrolyte solution containing 5wt% sodium chloride solution and 0.1wt% dodecyl dimethyl betaine, first put it into an inner bag made of non-woven fabric covered with a microporous oxygen-permeable membrane, and then wrap it in an oxygen-isolating plastic outer bag to obtain a self-heating membrane.

[0088] Example 3

[0089] A dry method for preparing a self-heating diaphragm specifically comprises the following steps.

[0090] S1, according to 100wt%, 50wt% of iron powder with a particle size of 300 mesh, 35wt% of carbon powder with a particle size of 300 mesh, 5wt% of polytetrafluoroethylene, 3wt% of temperature-controlled water-absorbing resin A and 7wt% of vermiculite with a particle size of 140 mesh are mixed, and the mixing is divided into four stages, namely, a pre-mixing stage, a fast mixing stage, a slow mixing stage and a mixed discharging stage, and the rotating speeds of the four stages are 1200rpm, 2400rpm, 1100rpm and 700rpm respectively; the time of the first three stages is 100s, 300s, and 100s respectively, to obtain a mixed powder;

[0091] S2, conveying the mixed powder in step S1 to a hot roller in a horizontal direction, and pressing at 300° C. to form a base film;

[0092] S3, cutting the base film formed in step S2 according to the size requirements to obtain a highly water-absorbent self-heating film core;

[0093] S4. Place 1.0 times the mass of electrolyte solution on the core of the highly water-absorbent self-heating membrane. The electrolyte solution contains 10wt% sodium chloride solution and 1.2wt% dodecyl dimethyl betaine. First put it into an inner bag made of non-woven fabric covered with a microporous oxygen-permeable membrane, and then wrap it in an oxygen-isolating plastic outer bag to obtain a self-heating membrane.

[0094] Example 4

[0095] This embodiment provides a dry method for preparing a self-heating membrane. The specific implementation method is the same as that of Embodiment 1, except that:

[0096] S4. Place 0.8 times the mass of electrolyte solution on the core of the self-heating membrane, the electrolyte solution contains 7wt% of sodium chloride, first put it into an inner bag made of non-woven fabric covered with a microporous oxygen-permeable membrane, and then wrap it with an oxygen-isolating plastic outer bag to obtain a self-heating membrane.

[0097] Example 5

[0098] This embodiment provides a dry method for preparing a self-heating membrane. The specific implementation method is the same as that of Embodiment 1, except that:

[0099] S1. According to 100wt%, 40wt% of iron powder with a particle size of 200 mesh, 30wt% of carbon powder with a particle size of 200 mesh, 5wt% of polytetrafluoroethylene, 5wt% of temperature-controlled water-absorbing resin A and 20wt% of vermiculite with a particle size of 100 mesh are mixed. The mixing is divided into two stages, namely the mixing stage and the mixing and discharging stage. The rotation speeds of the two stages are 2000rpm and 500rpm respectively, and the time of the former is 300s to obtain a mixed powder.

[0100] Example 6

[0101] This embodiment provides a dry method for preparing a self-heating membrane. The specific implementation method is the same as that of Embodiment 1, except that:

[0102] S4. Place 0.1 times the mass of electrolyte solution on the self-heating diaphragm core.

[0103] Example 7

[0104] This embodiment provides a dry method for preparing a self-heating membrane. The specific implementation method is the same as that of Embodiment 1, except that:

[0105] S4. Place 1.3 times the mass of electrolyte solution on the self-heating diaphragm core.

[0106] Example 8

[0107] This embodiment provides a dry method for preparing a self-heating membrane. The specific implementation method is the same as that of Embodiment 1, except that:

[0108] In step S1, the temperature-controlled water-absorbing resin A is replaced by the temperature-controlled water-absorbing resin B in an equal amount.

[0109] Comparative Example 1

[0110] This comparative example provides a dry method for preparing a self-heating membrane. The specific implementation method is the same as that of Example 1, except that in step S1, the temperature-controlled water-absorbing resin is replaced by an equal amount of water-absorbing resin.

[0111] Performance Testing:

[0112] 1. Temperature rise test:

[0113] A thermocouple temperature probe was placed on the self-heating film provided in Examples 1 to 8 and Comparative Example 1 to record the maximum temperature (in integers), the time taken to heat up to the maximum temperature, the duration above 40°C, and the total heating time (with constant temperature as the cutoff point).

[0114] 2. Diaphragm integrity test

[0115] Once the water-absorbent resin absorbs water and swells to become a hydrogel, its volume will expand, affecting the structural stability of the self-heating diaphragm. In this test, the self-heating diaphragms provided by Examples 1 to 7 and Comparative Example 1 were subjected to a drop test (height of 3m) and a vibration test (frequency of 18Hz) to observe the integrity of the diaphragms. A complete diaphragm was recorded as OK, and a broken diaphragm was recorded as NO.

[0116] The results are shown in Table 1.

[0117] Table 1 Performance test results

[0118]

[0119] From the data in Table 1, it can be seen that the heating performance of the self-heating membranes of Examples 1 to 3 is relatively small, with the highest temperature being 43 to 44°C, the time taken to heat up to the highest temperature being 180 to 230 seconds, the duration above 40°C being up to 40 to 50 minutes, and the total heating time being up to 500 minutes. Compared with Example 1, the electrolyte solution used in Example 4 does not contain a foaming agent, which results in the base film's absorption of the electrolyte solution being limited, thereby slowing down the iron oxidation corrosion process and prolonging the time taken to heat up to the highest temperature.

[0120] Compared with Example 1, Example 5 adjusted the raw material mixing process by merging the original three stages of mixing at different speeds into a constant speed mixing, which resulted in breakage in the integrity test. Analysis showed that the premixing time was insufficient, resulting in uneven mixing of the raw materials and the binder, which made it difficult to break up after high-speed mixing, affecting the overall uniformity.

[0121] Compared with Example 1, Examples 6 to 7 add more or less electrolyte solution. The former will affect the iron oxidation corrosion process, resulting in a longer time for heating to the maximum temperature; while the latter will cause the water-absorbing resin to expand too much, destroying the structural stability of the self-heating diaphragm. In addition, excessive electrolyte solution will not only reduce the duration above 40°C when released, but also affect the total heating time of the diaphragm.

[0122] It can be seen from Examples 1 and 8 that the introduction of PVA into the water-absorbing resin can increase the absorption of the electrolyte solution, which means that the time required to heat up to the maximum temperature is reduced. Compared with Example 1, Comparative Example 1 does not adjust the water release of the water-absorbing resin. It can be seen from the temperature increase test data that this is not conducive to increasing the temperature increase rate.

[0123] The embodiments and comparative examples described above do not impose any form of limitation on the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A dry method for preparing a self-heating membrane, characterized in that: The specific steps include: S1, mixing active metal powder, conductive agent, binder, temperature control water-absorbing resin and filler to obtain mixed powder; S2, conveying the mixed powder of step S1 to a pressing device for pressing to form a base film; S3, cutting the base film formed in step S2 according to size requirements to obtain a highly water-absorbent self-heating film core; S4. Put the electrolyte solution on the core of the highly water-absorbent self-heating membrane, first put it into an inner bag made of a non-woven fabric covered with a microporous oxygen-permeable membrane, and then wrap it with an oxygen-isolating plastic outer bag to obtain the self-heating membrane.

2. The dry method for preparing a self-heating film according to claim 1, characterized in that: In step S1, the mixing is divided into four stages, namely, a premixing stage, a fast mixing stage, a slow mixing stage and a mixed discharging stage, and the rotation speeds of the four stages are 600-1200rpm, 1600-2400rpm, 500-1100rpm and 200-700rpm, respectively; the mixing time of the first three stages is 100-500s, 100-1000s and 100-500s, respectively.

3. The dry method for preparing a self-heating membrane according to claim 1, characterized in that: In step S1, based on 100wt%, the mixed powder includes 20-60wt% active metal powder, 10-40wt% conductive agent, 1-10wt% binder, 1-10wt% temperature control water-absorbing resin and 2-20wt% filler.

4. The dry method for preparing a self-heating membrane according to claim 1, characterized in that: The active metal powder is any one of iron powder, magnesium powder and aluminum powder, and the particle size is 100-300 meshes.

5. The dry method for preparing a self-heating membrane according to claim 1, characterized in that: In step S1, the binder is any one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid and polytetrafluoroethylene.

6. The dry method for preparing a self-heating membrane according to claim 1, characterized in that: In step S1, the preparation steps of the temperature-controlled water-absorbing resin are as follows: (1) stirring and dissolving a dispersant, a temperature-sensitive monomer and an alkane to obtain a reaction base liquid; (2) stirring acrylic acid and 20-40 wt % sodium hydroxide solution at -5-5° C. until the solution becomes clear, thereby obtaining an acrylic acid neutralization solution; (3) mixing 5 to 30 wt % acrylamide solution, 5 to 20 wt % N,N-methylenebisacrylamide solution and 0.1 to 2.0 wt % potassium persulfate solution with the acrylic acid neutralization solution obtained in (2) to obtain an aqueous phase; (4) Add the aqueous phase obtained in (3) to the reaction base liquid in (1), stir at 30-60°C for 10-40 minutes, add the PVA solution, and then heat to 60-90°C at a rate of 3-8°C / h, continue stirring for 1-7 hours, wash, and vacuum dry to constant weight to obtain a temperature-controlled water-absorbing resin.

7. The dry method for preparing a self-heating membrane according to claim 6, characterized in that: In step (1), the preparation steps of the temperature-sensitive monomer are as follows: maleic anhydride is dissolved in acetone, isopropylamine is added and stirred for 1 to 4 hours, and after the reaction is completed, rotary evaporation and recrystallization are performed to obtain the temperature-sensitive monomer.

8. The dry method for preparing a self-heating membrane according to claim 1, characterized in that: In step S2, the conveying is horizontal belt conveying; the pressing is hot roller pressing, and the roller surface temperature is 40-300°C.

9. The dry method for preparing a self-heating film according to claim 1, characterized in that: In step S4, the mass ratio of the self-heating membrane core to the electrolyte solution is 1:(0.2-1.0).

10. The dry method for preparing a self-heating film according to claim 1, characterized in that: In step S4, the electrolyte solution further comprises 0.1-2.0 wt % of a foaming agent.

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