A dry method for preparing a self-heating membrane

Abstract

The present application relates to the technical field of self-heating product, and specifically discloses a dry preparation method of self-heating film, 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 film to obtain a high water-absorption self-heating film core; placing an electrolyte solution on the high water-absorption self-heating film core, first into an inner bag made of a microporous oxygen-permeable film covered with non-woven fabric, and then wrapping an outer bag of oxygen-blocking plastic, thereby obtaining the self-heating film. The dry preparation method of the self-heating film improves the uniformity of the mixed powder, avoids the generation of heat during the preparation stage due to the presence of water, enhances the heating performance of the self-heating film, and uses temperature-controlled water-absorption resin to release water when the temperature of the self-heating body reaches above body temperature, thereby prolonging the self-heating time and solving the problem of limited release of the electrolyte solution caused by the high water-retention of ordinary water-absorption resin.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of self-heating products, and particularly relates to a dry method for preparing a self-heating film. BACKGROUND

[0002] The principle of the self-heating body is to use the original battery reaction to accelerate the oxidation reaction speed, convert chemical energy into heat energy, and be used for warmth. The raw material form of the traditional self-heating product is mainly divided into powder and paste, wherein the production process of the powder raw material is to mix different kinds of powder raw materials, and then the mixed powder is wrapped by non-woven fabric to form a self-heating sheet. This method causes that the mixed uniformity is not high due to the large difference in density of the powder raw materials. The production process of the paste raw material is to mix the powder raw material with a liquid into a paste, and then the paste is dried after being made into a self-heating sheet, and then the self-heating sheet product is wrapped by non-woven fabric.

[0003] At present, the self-heating body on the market is mainly produced by using paste raw materials. For example, in the step of preparing the self-heating material provided in the patent CN112500839B, the passivated iron powder, diatomite, activated carbon, sodium acetate and pure water are added to a grinding machine for grinding, and then are packaged in a non-woven fabric bag and subjected to plastic packaging under vacuum. For another example, in the self-heating sheet and the preparation method thereof disclosed in the patent CN115227481B, a paste self-heating material is also used, and a water-absorbing material is placed between two layers of the paste self-heating material through a sandwich structure to avoid the problem that the air-permeable film is directly covered on the water-absorbing material to cause the air-permeable film to be blocked and not to generate heat. However, the paste method used in the above two patents has the problems that the oxidizable metal is prone to sedimentation due to the large difference in density of the raw materials, and the uniformity is not high. Moreover, the process cost of the drying process is high, the cycle is long, and the production efficiency is low.

[0004] Therefore, there is an urgent need for a self-heating body with high mixing uniformity on the market. SUMMARY

[0005] In view of the above problems, the application provides a dry method for preparing a self-heating film, which improves the mixing uniformity of the powder, avoids the generation of heat in the preparation stage due to the presence of water, enhances the heating performance of the self-heating film, and releases water when the temperature of the self-heating body reaches the body temperature by using the temperature-controlled water-absorbing resin, thereby prolonging the self-heating time and solving the problem of limited release of the electrolyte solution caused by the high water-retention property of the ordinary water-absorbing resin.

[0006] To achieve the above purpose, the technical scheme adopted by the application is as follows:

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

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

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

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

[0011] S4, placing an electrolyte solution on the high water-absorbing self-heating film piece core, first into an inner bag made of a microporous oxygen-permeable film covered non-woven fabric, and then wrapping an outer bag of oxygen-separating plastic, to obtain a self-heating film piece.

[0012] The application mixes metal powder, conductive agent, binder and water-absorbing resin as raw materials under the condition of no water, forms flocculent powder that can be hot-rolled and makes it into a cuttable base film, cuts the base film according to the required size, adds electrolyte and packages to obtain a self-heating film piece. When the self-heating film piece is used, the plastic outer bag is torn open, the non-woven fabric inner bag contacts air, oxygen enters from the micropores of the non-woven fabric and reacts with oxidizable metal to generate heat.

[0013] The self-heating film piece of the application is prepared by dry method, which improves the uniformity of the mixed powder, avoids heat generation during preparation due to the presence of water, and enhances the heating performance of the self-heating film piece. Based on the principle of the primary cell reaction of the self-heating body, the reaction requires electrolyte, and the water-absorbing resin can absorb the electrolyte later to ensure the normal operation of the primary cell reaction. However, the applicant found that the electrolyte solution on the self-heating film piece core would roll during preparation and could not be well absorbed.

[0014] In some embodiments, in step S1, the mixing is divided into four stages, namely pre-mixing stage, rapid mixing stage, slow mixing stage and mixing discharge stage, and the rotation speeds of the four stages are 600-1200 rpm, 1600-2400 rpm, 500-1100 rpm and 200-700 rpm, respectively; the times of the first three stages are 100-500 s, 100-1000 s and 100-500 s, respectively.

[0015] The application mixes according to four stages, which improves the uniformity of the mixing, ensures the performance of the product, and controls the heat generated during the mixing process. Among them, the pre-mixing stage can mix the powders together; in the rapid mixing stage, the binder is fibrillated under high shear force, so that the powders are uniformly bonded together by the binder to form flocculation; the rotation speed of the internal powder is gradually reduced in the slow mixing stage, and finally the discharge is kept at a low speed.

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

[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 100-300 mesh.

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

[0019] In some embodiments, in step S1, the conductive agent is carbon powder, and has a particle size of 100-300 mesh.

[0020] The carbon powder has good electrical conductivity and stable chemical properties, can promote the transmission of electrons, and is not prone to chemical reactions with other materials; at the same time, the light specific gravity of the carbon powder can increase the comfort of the product. In addition, the production and use process of the carbon powder is relatively safe and environmentally friendly, and will not produce harmful substances.

[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 application preferably uses polytetrafluoroethylene as the binder, which has the characteristic of being easily fibrous under the action of shear force, facilitating the formation of flocculent powder with the remaining raw materials, helping to form a self-supporting film, maintaining the structural stability of the film, and combining well with the active material and the conductive agent, so that the contact between the particles of the raw materials reaches the ideal tightness.

[0024] In some embodiments, in step S1, the temperature-controlled water-absorbing resin is prepared as follows:

[0025] (1) The dispersant, temperature-sensitive monomer, and alkane are stirred and dissolved to obtain a reaction bottom solution;

[0026] (2) The acrylic acid and 20-40 wt% sodium hydroxide solution are stirred at -5-5°C until the solution is clear to obtain an acrylic acid neutralization solution;

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

[0028] (4) adding the water phase obtained in (3) into the reaction bottom solution in (1), stirring at 30-60°C for 10-40 min, adding PVA solution, then increasing the temperature to 60-90°C at a rate of 3-8°C / h, continuing to stir for 1-7 h, washing, and vacuum drying to constant weight to obtain the temperature-controlled water-absorbing resin.

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

[0030] In some embodiments, in step (1), the temperature-sensitive monomer is prepared by dissolving maleic anhydride in acetone, adding isopropylamine, stirring for 1-4 h, and then rotary evaporation and recrystallization after the reaction 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 combine inverse suspension polymerization and solution polymerization. The solution polymerization is specifically reflected in that the monomer, initiator, and crosslinking agent are all dissolved in a suitable solvent. This method has the advantages of low polymerization system viscosity, easy heat transfer, and avoidance of local overheating. The inverse suspension polymerization is specifically reflected in that the water phase is dispersed and suspended in the reaction bottom solution under the action of the dispersing agent and stirring for polymerization. On the one hand, this method alleviates the problems of low conversion rate, slow polymerization rate, and easy formation of block-shaped polymers that cause difficulty in discharging in solution polymerization. On the other hand, it obtains suspended particles with narrow particle size distribution, so that the obtained water-absorbing resin has high uniformity in mixing with the remaining raw materials in the mixing stage, can be uniformly distributed in the self-heating membrane, and further makes the subsequent absorbed electrolyte uniformly distributed.

[0034] The molecular chain of the water-absorbing resin 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-absorbing resin swells into a hydrogel after absorbing water, it is difficult to separate the water, i.e., there is a problem of limited release of electrolyte solution due to high water retention.

[0035] The present application introduces hydrophobic isopropyl by temperature-sensitive monomer, when the temperature of the self-heating body reaches above body temperature, the hydrogen bond is weakened, the hydrophobic isopropyl starts to dominate, the polymer chain tends to gather and curl, and the hydrophobicity is exhibited, that is, water is released, and the self-heating time is prolonged. The water-absorbing resin also neutralizes the acrylic acid by sodium hydroxide solution, so that a large number of sodium carboxylate groups are contained in the molecular network, on the one hand, providing hydrophilic anion groups; on the other hand, when in contact with the electrolyte solution, the water molecules in the liquid first penetrate into the internal crosslinked network from the surface through capillary action, and a large number of Na + , and then the resin reaches its maximum water absorption by osmotic pressure, thereby improving the absorption of the electrolyte solution.

[0036] In some embodiments, in step S1, the filler is vermiculite, and the particle size is 60-140 mesh.

[0037] Vermiculite has strong heat preservation and insulation performance, loose structure, and good air permeability, which can ensure sufficient oxygen to enter and participate in the primary cell reaction.

[0038] In some embodiments, in step S2, the conveying is horizontal belt conveying, and the pressing is hot roller pressing, with the surface temperature of the roller being 40-300℃.

[0039] When the mixed powder is subjected to extrusion force, the tiny fibers in the powder can be pulled out under the action of the force, causing the resin to form clumps, which is not conducive to processing. Horizontal belt conveying can minimize the extrusion and collision of the mixed powder to reduce clumping and improve the quality and performance of the finished product.

[0040] Hot roller pressing can press the membrane blank to the desired thickness and ensure uniform and flat thickness. The speed difference between the upper and lower pressing rollers helps the membrane to reach the expected size and shape, and also improves the surface brightness of the membrane. As a continuous production process, hot roller pressing is suitable for large-scale production, which can significantly improve production efficiency, reduce costs, and maintain product quality consistency.

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

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

[0043] The sodium chloride solution helps the iron powder and activated carbon to form a primary cell and accelerates the process of iron oxidation and corrosion, thereby improving the efficiency of the entire heating process. By controlling the concentration of sodium chloride in the electrolyte solution, the present application ensures the osmotic pressure difference between the inside and outside of the molecular network and avoids the shielding effect of external ions on the charges on the water-absorbing resin molecular network, 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 application makes the electrolyte solution into a foam shape, solves the problem of poor absorption caused by rolling of the electrolyte solution on the self-heating membrane core, and solves the defoaming problem caused by sodium chloride solution by specifically selecting dodecyl dimethyl betaine as a foaming agent, thereby improving the stability of the foam. However, this brings another problem, that is, the electrolyte solution that penetrates into the membrane core will flow out quickly and cannot stay, and the possible reason is that the change of surface tension caused by the foaming agent strengthens the penetration of the electrolyte solution. The applicant accidentally found that introducing PVA into the water absorbing resin can improve this phenomenon, which may be because the PVA forms a semi-interpenetrating network structure in the water absorbing resin, thereby strengthening the retention of the electrolyte solution.

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

[0049] 1. The present application provides a dry method for preparing a self-heating membrane, which breaks through the prior art and mixes metal powder, conductive agent, binder and water absorbing resin as raw materials to form flocculent powder that can be hot-rolled and made into a base film that can be cut, and then the base film is cut according to the required size, electrolyte is added and packaged to obtain a self-heating membrane. The dry preparation improves the uniformity of the powder mixture, avoids the generation of heat during the preparation stage due to the presence of water, and enhances the heating performance of the self-heating membrane.

[0050] 2. The present application optimizes the reaction process to obtain water absorbing resin with small particle size difference, so that it is uniformly distributed in the self-heating membrane, and then the electrolyte solution is also uniformly distributed during subsequent absorption and release. On this basis, a temperature-sensitive monomer is introduced into the water absorbing resin to release water when the temperature of the self-heating body reaches body temperature or above, thereby prolonging the self-heating time and solving the problem of limited release of electrolyte solution caused by the high water retention of ordinary water absorbing resin.

[0051] 3. The present application makes the electrolyte solution into a foam shape, solves the problem of poor absorption caused by rolling of the electrolyte solution on the self-heating membrane core, and solves the defoaming problem caused by sodium chloride solution by specifically selecting dodecyl dimethyl betaine as a foaming agent, thereby improving the stability of the foam. On this basis, introducing PVA into the water absorbing resin improves the phenomenon that the electrolyte solution that penetrates into the membrane core will flow out quickly. Attached Figure Description

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

[0053] Figure 2 This is a hollow image 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 Implementation

[0055] The present invention will be described below with reference to specific embodiments. It should be noted that the following embodiments are examples of the present invention and are used only to illustrate the invention, not to limit it. Other combinations and various modifications within the scope of the present invention can be made without departing from its spirit or scope.

[0056] To facilitate implementation of this invention by those skilled in the art, some of the raw materials used in the embodiments and comparative examples are described below:

[0057] The polytetrafluoroethylene (PTFE) product, designated as PTFE dispersion fine powder resin-JF, was purchased from Hangzhou Jufu New Material Technology Co., Ltd.

[0058] Preparation Example 1

[0059] The preparation steps of the temperature-sensitive 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 h. After the reaction is complete, rotary evaporate and recrystallize from acetone to obtain the temperature-sensitive monomer.

[0061] Preparation Example 2

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

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

[0064] (2) At 0℃, 5 mol of acrylic acid and 30 wt% sodium hydroxide solution were stirred until the solution became clear to obtain a neutralized acrylic acid solution, wherein the mass ratio of acrylic acid to sodium hydroxide solution was 1:1.8.

[0065] (3) 5 mol of acrylamide, 0.012 mol of N,N-methylenebisacrylamide and 0.012 mol of potassium persulfate were respectively configured into 20 wt% acrylamide solution, 10 wt% N,N-methylenebisacrylamide solution and 1 wt% potassium persulfate solution with water, and mixed with the neutralized acrylate solution obtained in (2) to obtain an aqueous phase;

[0066] (4) The aqueous phase obtained in (3) was added to the reaction bottom solution in (1), stirred at 50°C for 30 min, 30 wt% PVA solution was added, the mass ratio of PVA to acrylate in step (2) was 0.12:1, then the temperature was raised to 70°C at a rate of 5°C / h, and stirring was continued for 6 h, washed with anhydrous ethanol, and dried at 60°C under vacuum to constant weight to obtain temperature-controlled water-absorbing resin A.

[0067] Preparation Example 3

[0068] The preparation steps of the 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 bottom solution in (1), stirred at 50°C for 30 min, then the temperature was raised to 70°C at a rate of 5°C / h, and stirring was continued for 6 h, washed with anhydrous ethanol, and dried at 60°C under vacuum to constant weight to obtain temperature-controlled water-absorbing resin B.

[0071] Preparation Example 4

[0072] The preparation steps of the 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, 0.2 mol of Span 85 and 5 L of cyclopentane were stirred and dissolved to obtain a reaction bottom solution.

[0075] Example 1

[0076] A dry method for preparing a self-heating film, specifically comprising the following steps.

[0077] S1, 40wt% iron powder with particle size of 200 mesh, 30wt% carbon powder with particle size of 200 mesh, 5wt% polytetrafluoroethylene, 5wt% temperature control water absorbing resin A and 20wt% vermiculite with particle size of 100 mesh are mixed according to 100wt%, the mixing is divided into four stages, which are pre-mixing stage, fast mixing stage, slow mixing stage and mixing discharge stage, 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, and the mixed powder is obtained;

[0078] S2, the mixed powder of step S1 is horizontally conveyed to hot rolling, and the base film is formed by pressing at 180℃, see Figure 1 and Figure 2 ;

[0079] S3, the base film formed in step S2 is cut according to the size requirement, and the high water absorbing self-heating film piece core is obtained;

[0080] S4, 0.8 mass times of electrolyte solution is placed on the high water absorbing self-heating film piece core, the electrolyte solution contains 7wt% sodium chloride and 0.3wt% dodecyl dimethyl betaine, and then the inner bag made of microporous oxygen permeable film covered non-woven fabric is filled, and then the outer bag is packaged with oxygen barrier plastic, and the self-heating film piece is obtained.

[0081] As Figure 1 , Figure 2 can be known, the base film can be suspended in the air and keep stable shape, which shows that the structure is relatively firm; Figure 3 is the scanning electron microscope graph of the base film, and it can be seen that the material is uniformly mixed.

[0082] Example 2

[0083] A dry process for preparing a self-heating film piece, specifically comprising the following steps.

[0084] S1, 30wt% iron powder with particle size of 100 mesh, 35wt% carbon powder with particle size of 100 mesh, 10wt% polytetrafluoroethylene, 10wt% temperature control water absorbing resin A and 15wt% vermiculite with particle size of 60 mesh are mixed according to 100wt%, the mixing is divided into four stages, which are pre-mixing stage, fast mixing stage, slow mixing stage and mixing discharge stage, 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, and the mixed powder is obtained;

[0085] S2, the mixed powder of step S1 is horizontally conveyed to hot rolling, and the base film is formed by pressing at 120℃;

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

[0087] S4, placing 0.4 mass times of an electrolyte solution on the high water-absorption self-heating film piece core, the electrolyte solution containing 5wt% of sodium chloride solution and 0.1wt% of dodecyl dimethyl betaine, first loading into an inner bag made of a microporous oxygen-permeable film covered non-woven fabric, and then wrapping with an oxygen barrier plastic outer bag, to obtain a self-heating film piece.

[0088] Example 3

[0089] A dry process for preparing a self-heating film piece, specifically comprising the following steps.

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

[0091] S2, horizontally conveying the mixed powder of step S1 to a hot roller for pressing at 300℃ to form a base film;

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

[0093] S4, placing 1.0 mass times of an electrolyte solution on the high water-absorption self-heating film piece core, the electrolyte solution containing 10wt% of sodium chloride solution and 1.2wt% of dodecyl dimethyl betaine, first loading into an inner bag made of a microporous oxygen-permeable film covered non-woven fabric, and then wrapping with an oxygen barrier plastic outer bag, to obtain a self-heating film piece.

[0094] Example 4

[0095] The embodiment provides a dry process for preparing a self-heating film piece, and the specific implementation manner is the same as that in embodiment 1, and the difference lies in that:

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

[0097] Example 5

[0098] The embodiment provides a dry method for preparing a self-heating film, and the specific implementation manner is the same as that in Embodiment 1, and the difference lies in 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 control 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 a mixing stage and a mixing discharge stage, the rotation speeds of the two stages are 2000rpm and 500rpm respectively, the time of the former is 300s, and the mixed powder is obtained.

[0100] Example 6

[0101] The embodiment provides a dry method for preparing a self-heating film, and the specific implementation manner is the same as that in Embodiment 1, and the difference lies in that:

[0102] S4, put 0.1 mass times of electrolyte solution on the self-heating film core.

[0103] Example 7

[0104] The embodiment provides a dry method for preparing a self-heating film, and the specific implementation manner is the same as that in Embodiment 1, and the difference lies in that:

[0105] S4, put 1.3 mass times of electrolyte solution on the self-heating film core.

[0106] Example 8

[0107] The embodiment provides a dry method for preparing a self-heating film, and the specific implementation manner is the same as that in Embodiment 1, and the difference lies in that:

[0108] In step S1, the temperature control water absorbing resin A is replaced by the same amount of temperature control water absorbing resin B.

[0109] Comparative Example 1

[0110] The comparative example provides a dry method for preparing a self-heating film, and the specific implementation manner is the same as that in Embodiment 1, and the difference lies in that: in step S1, the temperature control water absorbing resin is replaced by the same amount of water absorbing resin.

[0111] Performance test:

[0112] 1. Temperature rise test:

[0113] A thermocouple temperature probe was placed on the self-heating film provided in Examples 1-8 and Comparative Example 1, and the highest temperature (in integer), the time taken to rise to the highest temperature, the duration above 40°C, and the total heating time (with temperature constant as the cut-off point) were recorded.

[0114] 2. Film integrity test

[0115] Once the water-absorbing resin swells into a hydrogel, the volume expands, affecting the structural stability of the self-heating film. In this test, the self-heating films provided in Examples 1-7 and Comparative Example 1 were subjected to drop test (height of 3 m) and vibration test (frequency of 18 Hz) to observe the film integrity. OK was recorded for intact, and NO for broken.

[0116] The results are shown in Table 1.

[0117] Table 1 Performance test results

[0118]

[0119] As shown in Table 1, the heating performance of the self-heating films of Examples 1-3 had little difference, with the highest temperature of 43-44°C, the time taken to rise to the highest temperature of 180-230s, the duration above 40°C of 40-50min, and the total heating time of 500min. Compared with Example 1, the electrolyte solution used in Example 4 did not contain a foaming agent, which limited the absorption of the electrolyte solution by the base film, thereby slowing down the iron oxidation and corrosion process, resulting in a longer time taken to rise to the highest temperature.

[0120] Compared with Example 1, Example 5 adjusted the raw material mixing process by combining the original three-stage speed mixing into one constant speed mixing, which resulted in damage in the integrity test. Analysis showed that the insufficient premixing time caused uneven mixing of the raw materials and the binder, which was not easy to disperse after high-speed mixing, affecting the overall uniformity.

[0121] Compared with Example 1, Examples 6-7 added more or less electrolyte solution. The former affected the iron oxidation and corrosion process, resulting in a longer time taken to rise to the highest temperature, while the latter caused the swelling volume of the water-absorbing resin to be too large, damaging the structural stability of the self-heating film, and the excessive electrolyte solution not only reduced the duration above 40°C, but also affected the total heating time of the film.

[0122] From Example 1 and Example 8, it can be seen that the introduction of PVA into the water-absorbing resin can increase the absorption amount of the electrolyte solution, which means that the time for heating to the maximum temperature is reduced. Comparative Example 1 does not adjust the water release of the water-absorbing resin compared to Example 1, and from the heating test data, it can be seen that this is not conducive to improving the heating speed.

[0123] The above examples and comparative examples do not limit the present application in any form, although the present application has been disclosed as above with preferred embodiments, however, not intended to limit the present application, any skilled person in the art, without departing from the technical solution of the present application, can make some changes or modifications to the above disclosed technical content as equivalent embodiments, but as long as it does not deviate from the technical solution of the present application, any simple modification, equivalent change and modification made to the above examples according to the technical essence of the present application, still belongs to the scope of the technical solution of the present application.

Claims

1. A dry method of preparing a self-heating patch, characterized in that, Specifically comprising the following steps: S1, mixing active metal powder, conductive agent, binder, temperature-controlled 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 high water-absorbing self-heating film piece core; S4, placing an electrolyte solution on the high water-absorbing self-heating film piece core, first into an inner bag made of a microporous oxygen-permeable film covered non-woven fabric, and then wrapping it with an oxygen-sealed plastic outer bag, to obtain a self-heating film piece; In step S1, the preparation steps of the temperature-controlled water-absorbing resin are as follows: (1) stirring and dissolving the dispersant, temperature-sensitive monomer and alkane to obtain a reaction bottom solution; (2) stirring acrylic acid and 20-40wt% sodium hydroxide solution at -5-5℃ until the solution is clear to obtain an acrylic acid neutralization solution; (3) mixing 5-30wt% acrylamide solution, 5-20wt% N,N-methylene bisacrylamide solution and 0.1-2.0wt% potassium persulfate solution with the acrylic acid neutralization solution obtained in (2) to obtain an aqueous phase; (4) adding the aqueous phase obtained in (3) to the reaction bottom solution in (1), stirring at 30-60℃ for 10-40min, adding PVA solution, then increasing the temperature to 60-90℃ at a rate of 3-8℃ / h, continuing to stir for 1-7h, washing, and vacuum drying to constant weight to obtain the temperature-controlled water-absorbing resin; In step (1), the preparation steps of the temperature-sensitive monomer are as follows: dissolving maleic anhydride in acetone, adding isopropylamine and stirring for 1-4h, then rotary evaporation and recrystallization after the reaction is completed to obtain the temperature-sensitive monomer.

2. The dry process for the preparation of a self-heating patch according to claim 1, characterized in that, In step S1, the mixing is divided into four stages: pre-mixing stage, fast mixing stage, slow mixing stage and mixing discharge stage, and the rotation speeds of the four stages are 600-1200rpm, 1600-2400rpm, 500-1100rpm and 200-700rpm, respectively; the mixing times of the first three stages are 100-500s, 100-1000s and 100-500s, respectively.

3. The dry process for the preparation of a self-heating patch according to claim 1, characterized in that, In step S1, the mixed powder contains 20-60wt% active metal powder, 10-40wt% conductive agent, 1-10wt% binder, 1-10wt% temperature-controlled water-absorbing resin and 2-20wt% filler, based on 100wt%.

4. The dry process for the preparation of a self-heating patch 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 mesh.

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

6. The dry process for the preparation of a self-heating patch 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℃.

7. The dry process for the preparation of a self-heating patch according to claim 1, characterized in that, In step S4, the mass ratio of the self-heating film piece core to the electrolyte solution is 1:(0.2-1.0).

8. The dry process for the preparation of a self-heating patch according to claim 1, characterized in that, In step S4, the electrolyte solution further contains 0.1-2.0wt% foaming agent.

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