A constant temperature heating diaphragm with enhanced PTC effect reproducibility and a preparation method and application thereof

Abstract

The application discloses a constant temperature heating film piece with enhanced PTC effect reproducibility, and a preparation method and application thereof. The constant temperature heating film piece is composed of two insulating isolation layers, copper electrodes and positive temperature coefficient coating arranged between the insulating isolation layers. The positive temperature coefficient coating comprises the following components: 15-30 wt% thermoplastic polyurethane elastomer, 5-20 wt% secondary phase matrix, 10-40 wt% organic phase change material, 14-25 wt% first conductive filler, 1-5 wt% second conductive filler, 0.1-1 wt% defoaming agent, 0.5-2 wt% thickening agent and 30-50 wt% organic solvent. The first conductive filler has a particle size of 100-300 nm, and the second conductive filler has a particle size of 5-50 um. The constant temperature heating film piece can ensure greater PTC intensity, smaller NTC intensity and softness, and can inhibit the agglomeration of the conductive filler and maintain the reproducibility of the PTC effect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of heat generating materials, and particularly relates to a constant-temperature heating film sheet with enhanced PTC effect reproducibility and a preparation method and application thereof. BACKGROUND

[0002] The heating film with a positive temperature coefficient (PTC) effect is a new type of functional material, which has been widely concerned due to its good processability and excellent conductivity. The heating function can be realized by adding conductive fillers. The PTC material is very sensitive to temperature. When the temperature rises to a specific temperature (Curie temperature point), the resistivity of the material will increase sharply, and at this time, the heating power will rapidly decrease, thereby realizing the functions of temperature control heating or closed circuit. Due to the special properties of the PTC material, it has important application value in the fields of sensors, circuit protection and temperature control heating.

[0003] Chinese patent CN103476158B discloses a PTC composite material heating film and a preparation method and application thereof. The PTC composite material heating film is sequentially laminated by a first high polymer curing sheet, a PTC composite material layer and a second high polymer curing sheet. The first high polymer curing sheet and the second high polymer curing sheet are both epoxy resin, and the PTC composite material layer is composed of 10-80 parts of high polymer, 20-90 parts of conductive particles and 1-10 parts of additives in terms of mass fraction. The high polymer is at least one of polyamide, polyethylene, polypropylene, polyvinylidene fluoride, polytrifluorochloroethylene, epoxy resin and polyimide. The conductive particles are at least one of carbon black, graphite powder, carbon fiber powder, metal powder, carbon nanotube and graphene. The principle of the PTC composite material heating film is that the crystalline or semi-crystalline high polymer is filled with conductive particles, and then the PTC effect is generated to realize intelligent temperature control due to the thermal expansion effect or crystal phase structure conversion effect of the matrix itself. However, the heating film prepared by the technology will only have the PTC effect when reaching the melting point of the polymer, which will cause the polymer to be quickly consumed in the process of multiple uses, and the melting point of the polymer is generally high, so that the Curie temperature point of the PTC composite material is high, which cannot be applied to the low temperature environment.

[0004] Chinese invention patent application CN112770422A discloses a self-control temperature heating film and its preparation method and application. The heating film is composed of an insulating isolation layer, a positive temperature coefficient coating and an insulating protective layer. The insulating isolation layer and the insulating protective layer have the same raw material composition and are both composed of an insulating polymer and a heat insulation nano particle / heat conduction functional nano particle. The positive temperature coefficient coating is composed of 20-40wt% nano conductive filler, 10-30wt% positive temperature coefficient heat sensitive filler, 10-30wt% polymer and the balance phase change material. The nano conductive filler is at least one of graphene, conductive carbon black, carbon nanotube, nano graphite powder, nano metal powder and nano metal wire. The positive temperature coefficient heat sensitive material is at least one of ethylene-vinyl acetate copolymer, positive temperature coefficient ceramic powder, polycaprolactone, biological section paraffin and thermoplastic polyurethane elastomer. The polymer is at least one of silicone rubber, epoxy resin, thermoplastic elastomer, butadiene styrene rubber and polyurethane. The phase change material is at least one of low temperature lubricating oil, low temperature lubricating grease and paraffin. However, the self-control temperature heating film prepared by the technology needs to be improved in application repeatability. The PTC effect in the durability performance curve is only 20 times, which cannot explain that the self-control temperature electric heating film has a good use stability. SUMMARY

[0005] In view of the poor reproducibility of PTC effect of the existing PTC heating film, the primary purpose of the present application is to provide a constant temperature heating film piece with simple and safe preparation process, large PTC strength, small NTC strength and softness, which can significantly enhance the reproducibility of PTC effect and its preparation method.

[0006] Another purpose of the present application is to provide the application of the constant temperature heating film piece with enhanced PTC effect reproducibility in the preparation of temperature control components.

[0007] To achieve the above purpose, the present application adopts the following technical solutions:

[0008] A constant temperature heating film piece with enhanced PTC effect reproducibility is composed of two insulating isolation layers and copper electrodes and a positive temperature coefficient coating arranged between the insulating isolation layers. The lower insulating isolation layer is etched with a copper electrode at the upper end, and the positive temperature coefficient coating is coated on the upper end of the copper electrode. The positive temperature coefficient coating comprises the following components: 15-30wt% thermoplastic polyurethane elastomer, 5-20wt% secondary phase matrix, 10-40wt% organic phase change material, 14-25wt% first conductive filler, 1-5wt% second conductive filler, 0.1-1wt% defoaming agent, 0.5-2wt% thickening agent and 30-50wt% organic solvent. The secondary phase matrix is one of isocyanate, peroxide, polyhydroxy compound and epoxy compound. The particle size of the first conductive filler is 100-300nm, and the particle size of the second conductive filler is 5-50um.

[0009] To further achieve the object of the present application, preferably, the isocyanate is diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI) and hexamethylene diisocyanate (HDI); the peroxide is dibenzoyl peroxide (BPO), diisopropyl peroxide (DCP); the polyhydroxy compound includes glycerol, ethylene glycol and polyethylene glycol (PEG); and the epoxy compound is epoxy resin.

[0010] Preferably, the organic phase change material is at least one of paraffin, fatty acid and polyol.

[0011] Preferably, the fatty acid is stearic acid, palmitic acid, myristic acid, lauric acid; and the polyol is polyethylene glycol and tetradecanol.

[0012] Preferably, the first conductive filler is at least one of conductive carbon black and metal powder; and the second conductive filler is at least one of carbon nanotube, carbon fiber and graphene.

[0013] Preferably, the defoaming agent includes at least one of silicone oil defoaming agent, polyvinyl alcohol defoaming agent or polyester defoaming agent; the thickening agent is at least one of ethyl cellulose, sodium carboxymethyl cellulose, hydroxyethyl cellulose and hydroxypropyl methyl cellulose; and the organic solvent is at least one of toluene, xylene, isophorone, n-hexane and acetone.

[0014] Preferably, both the two insulating isolation layers are polyimide film sheets; the thickness of the insulating isolation layer is 0.5-2mm; the thickness of the positive temperature coefficient coating layer is 0.5-2mm; and the constant temperature heating film sheet with enhanced PTC effect recurrence has a resistivity value of 1-50Ω·cm at room temperature.

[0015] The preparation method of the constant temperature heating film sheet with enhanced PTC effect recurrence includes the following steps:

[0016] S1, adding thermoplastic polyurethane elastomer into an organic solvent and stirring and dispersing to be in a non-particulate state in the solvent;

[0017] S2, adding a secondary phase matrix to the product obtained in step S1, heating and stirring in a water bath for 1-2h for crosslinking reaction;

[0018] S3, adding organic phase change material, first conductive filler and second conductive filler to the product obtained in step S2 and stirring and mixing uniformly;

[0019] S4, adding defoaming agent and thickening agent to the mixed solution in step S3 and stirring and dispersing uniformly;

[0020] S5, using a coating machine to coat the mixed solution obtained in step S4 on the lower layer of insulating isolation layer etched with copper electrode on the upper end, and drying;

[0021] S6, the lower layer of insulating isolation layer and the upper layer of insulating isolation layer are hot-pressed and packaged to obtain a constant-temperature heating film with enhanced PTC effect recurrence.

[0022] Preferably, in steps S1-S4, the stirring is mechanical stirring, the rotating speed is 1000-2400 rmp, and the temperature is 60-90℃; wherein, the stirring time of the solvent in a non-particle state in step S1 is 30-60 min; the stirring time in step S3 is 30-60 min; and the stirring time in step S4 is 20-30 min.

[0023] The temperature of the hot-pressing is 60-100℃, and the pressure is 0.5-1 MPa.

[0024] The constant-temperature heating film with enhanced PTC effect recurrence is applied to the preparation of temperature control components.

[0025] Compared with the prior art, the present application has the following advantages and beneficial technical effects:

[0026] (1) The positive temperature coefficient coating provided by the present application not only forms finer phase regions by adding a secondary phase matrix and using cross-linking, but also dopes conductive fillers of different sizes in the cross-linking process to improve the agglomeration of conductive fillers during cyclic use.

[0027] (2) The present application limits the size of the filler aggregate by constructing a cross-linked phase region with a dual-phase matrix, and uses mixed fillers of different sizes to reduce the contact probability between fillers of the same size, so that the filler agglomeration tendency is inhibited. Under the synergistic action of the dual-phase matrix and the mixed fillers, not only the movement range of the conductive fillers is limited, but also the agglomeration behavior of the same fillers is reduced, further solving the problem of filler migration and agglomeration in the long-term use of PTC heating film.

[0028] (3) The cross-linking process used in the present application is a low-cost chemical cross-linking process performed during preparation, which does not have the disadvantages of high cost and high equipment requirements as in radiation cross-linking and other methods.

[0029] (4) The primary phase matrix used in the present application is a thermoplastic polyurethane elastomer, which has strong flexibility and can be bent at will, and has a wide application prospect.

[0030] (5) The PTC heating film prepared by the present application can be cut to shape according to the application, and can be widely applied to regular and irregular shaped substrates, such as temperature control components for household and industrial electrical appliances, daily indoor and outdoor heat preservation and heating, etc.

[0031] (6) The PTC heating film of the present application has a small room temperature resistivity value, and can reach a balance temperature within 100s under a safe voltage of 6-36V, and has the advantages of fast temperature rise and uniform heating. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 The PTC heating film obtained in Example 1 was subjected to 100 times of power-on and temperature rise curve;

[0033] Figure 2 The PTC heating film obtained in Example 1 was subjected to 100 times of power-on and temperature rise curve;

[0034] Figure 3 The PTC heating film obtained in Example 1 was subjected to 100 times of power-on and temperature rise curve;

[0035] Figure 4 The PTC heating film obtained in Example 1 was subjected to 100 times of power-on and temperature rise curve;

[0036] Figure 5 The PTC heating film obtained in Example 1 was subjected to 100 times of power-on and temperature rise curve.

[0037] Figure 6 The PTC heating film obtained in Example 1 was subjected to 100 times of power-on and temperature rise curve;

[0038] Figure 7 The PTC heating film obtained in Example 1 was subjected to 100 times of power-on and temperature rise curve;

[0039] Figure 8 The PTC heating film obtained in Example 1 was subjected to 100 times of power-on and temperature rise curve;

[0040] Figure 9 The PTC heating film obtained in Example 1 was subjected to 100 times of power-on and temperature rise curve;

[0041] Figure 10 The PTC heating film obtained in Example 1 was subjected to 100 times of power-on and temperature rise curve;

[0042] Figure 11 The PTC heating film obtained in Example 1 was subjected to 100 times of power-on and temperature rise curve; DETAILED DESCRIPTION

[0043] In order to better understand the present application, the present application will be further described below in conjunction with examples, but the embodiments of the present application are not limited thereto.

[0044] In the prior art, conductive particles are usually added to a base resin or a phase change material is added to form an electrothermal paste, which is coated on an insulating layer and connected to electrodes to form a PTC heating film. Such a PTC heating film has a major problem of poor reproducibility of PTC effect, and the repeatability is not high in the application process.

[0045] The reproducibility of PTC effect is based on the complete reversibility of the deconstruction and reconstruction of the conductive network inside the material. However, the incompatibility of the polymer matrix and the conductive filler in thermodynamics makes the conductive filler easily aggregate to form obvious clusters in the molten state. When the aggregates are large, it is difficult to break them, and the conductive network cannot be restored to the original state, resulting in a weak PTC effect of the composite material.

[0046] The present application finds that when the particle size of the first conductive filler is 100-300 nm, the particle size of the second conductive filler is 5-50 um, and the secondary phase matrix includes one of isocyanate, peroxide, polyhydroxy compound and epoxy compound, the thermoplastic polyurethane elastomer can crosslink with the secondary phase matrix to form fine phase regions, and the formation of large aggregates of the conductive filler is inhibited. Specifically, the isocyanate reacts with the amino or hydroxyl groups in the thermoplastic polyurethane elastomer to form urea or carbamate (-NHCOO-) linkages, thereby crosslinking the chains. The peroxide decomposes to generate free radicals at a certain temperature, which can react with monomers or molecules in the thermoplastic polyurethane elastomer chain, resulting in crosslinking between the polymer chains. The hydroxyl groups (-OH) in the polyhydroxy compound react through esterification, the epoxy groups (-C-O-) in the epoxy compound react through addition reaction, and the functional groups (amino, hydroxyl, etc.) in the thermoplastic polyurethane elastomer react to form a crosslinked network structure. Such crosslinked network structure cooperates with the two different sizes of fillers described above to limit the movement range of the two different sizes of fillers, thereby reducing the size of the aggregates. At the same time, the two particle size ranges of fillers can improve the dispersibility and reduce the probability of aggregation of the same filler, and under the synergistic effect of the crosslinked structure and the mixed fillers, the random migration and aggregation of the conductive filler at high temperature are greatly inhibited, the reversibility of the deconstruction and reconstruction of the conductive network is improved, and the cycle life of the PTC heating film is improved. Moreover, the thermoplastic polyurethane elastomer mainly serves as a support material to maintain the flexibility of the whole film, and encapsulates the phase change material and the conductive filler to prevent leakage. The addition of the phase change material in the present application is to achieve the phase change of the positive temperature coefficient coating at a certain temperature, so that the conductive network inside the material breaks and the resistivity increases suddenly, thereby generating PTC effect, which is the core function of general phase change materials. The addition of the defoaming agent in the present application can avoid the bubbles generated during preparation from affecting the film forming effect, which is also the main function of general defoaming agents. The addition of the thickening agent in the present application can improve the viscosity of the mixed solution, so that the composite material remains in a uniform and stable fluid state, and the film forming state is better, which is also the main function of general thickening agents.

[0047] Based on the above findings, the present application develops a constant temperature heating film piece that enhances the reproducibility of PTC effect, which can not only ensure greater PTC intensity, smaller NTC intensity and softness, but also inhibit the agglomeration of conductive fillers to maintain the reproducibility of PTC effect. The core technical measure of the present application is to provide a constant temperature heating film piece that enhances the reproducibility of PTC effect, which is composed of two insulating isolation layers and copper electrodes and positive temperature coefficient coating layers arranged between the insulating isolation layers, the lower insulating isolation layer is etched with copper electrodes at the upper end, and the positive temperature coefficient coating layer is coated on the upper end of the copper electrode; the positive temperature coefficient coating layer comprises the following components: 15-40 wt% thermoplastic polyurethane elastomer, 5-25 wt% secondary phase matrix, 20-50 wt% organic phase change material, 14-25 wt% first conductive filler, 1-5 wt% second conductive filler, 0.1-1 wt% defoaming agent, 0.5-2 wt% thickening agent, and 30-50 wt% organic solvent; the secondary phase matrix is one of isocyanate, peroxide, polyhydroxy compound and epoxy compound; the particle size of the first conductive filler is 100-300 nm, and the particle size of the second conductive filler is 5-50 um.

[0048] It should be noted that the constant temperature heating film piece of the present application is composed of two insulating isolation layers and copper electrodes and positive temperature coefficient coating layers arranged between the insulating isolation layers, the copper electrode etched at the upper end of the lower insulating isolation layer serves as a positive and negative electrode, and the connection of the power supply enables it to be powered and heated; the two insulating isolation layers encapsulate the positive temperature coefficient coating layer and the copper electrode. The constant temperature heating film piece of the present application that enhances the reproducibility of PTC effect can be tailored in shape according to the application, and is widely used in various shaped substrates, such as temperature control components for household and industrial electrical appliances, daily indoor and outdoor heat preservation and heating, etc. Specifically, it is used in a series of heat preservation and heating scenes such as electronic equipment start-up protection components under cold conditions, active thermal control systems of equipment devices, wearable heat preservation fabrics, indoor floor heating, etc.

[0049] In the present application, the test method of the cold and hot impact cycle curve uses the GB / T2423.34-2024 standard for rapid temperature change test. The purpose of this test is to determine the change of PTC effect of the PTC heating film after multiple high and low temperature environmental alternation.

[0050] The test method of the power-on temperature rise curve is based on the GB / T29470-2012 standard for testing. The purpose of this test is to investigate the heating stability and self-adaptive thermal control function of the PTC heating film.

[0051] The film piece uniform heating property is tested according to the GB / T7287-2008 standard, and the test method is to use an infrared thermal imaging camera to observe the surface temperature field of the PTC heating film after reaching the equilibrium state during power-on temperature rise. The purpose of this test is to observe whether the PTC heating film heats uniformly under power-on.

[0052] The test method of resistance-temperature curve is tested according to GB / T29470-2012 standard. The test aims to observe the resistance change and PTC characteristic of the PTC heating film under temperature change, so as to judge the PTC strength.

[0053] Embodiment 1

[0054] A constant temperature heating film piece with enhanced PTC effect reproducibility comprises the following components by mass percentage: thermoplastic polyurethane elastomer 20wt%, secondary phase matrix 10wt%, organic phase change material 20wt%, first conductive filler 17wt%, second conductive filler 1wt%, defoaming agent 0.5wt%, thickening agent 1.5wt%, and organic solvent 30wt%; wherein the secondary phase matrix is glycerol, the phase change material is lauric acid, the first conductive filler is carbon black with a size of 100-200nm, the second conductive filler is carbon nanotube with a size length of 30-50um, the defoaming agent is polydimethylsiloxane, the thickening agent is sodium carboxymethyl cellulose, and the organic solvent is isophorone.

[0055] A preparation method of a constant temperature heating film piece with enhanced PTC effect reproducibility comprises the following steps:

[0056] S1, 16g of thermoplastic polyurethane elastomer is weighed and added into 48ml of isophorone, and mechanically stirred and dispersed into the solvent to be in a non-granular state, with a stirring time of 45min;

[0057] S2, 8g of glycerol is weighed and added, and mechanically stirred under water bath heating to make it fully crosslink with the thermoplastic polyurethane elastomer obtained in step S1, with a reaction time of 1h;

[0058] S3, 16g of lauric acid, 13.6g of carbon black and 0.8g of carbon nanotube are weighed and added to the product obtained in step S2, and are mixed by high-speed mechanical stirring, with a stirring time of 30min;

[0059] S4, 0.4g of polydimethylsiloxane and 1.2g of sodium carboxymethyl cellulose are sequentially added to the mixed solution obtained in step S3, the viscosity of the solution is adjusted to be smooth, and mechanical stirring is performed until it is completely uniform, with a stirring time of 25min;

[0060] S5, the mixed solution obtained in step S4 is coated on a polyimide film piece containing a copper electrode, i.e. the lower layer of the insulating isolation layer, by using a coating machine, to obtain a positive temperature coefficient coating after drying treatment, with a coating thickness of 1mm;

[0061] S6, the lower insulation isolation layer and the upper insulation isolation layer containing the positive temperature coefficient coating are heat pressed and packaged to obtain a PTC heating film; wherein the thickness of the insulation isolation layer is 0.5 mm, and the heat pressing process is as follows: heat pressing temperature is 80℃, and pressure is 1 MPa.

[0062] In the above steps, the rotating speed of mechanical stirring is 1800rmp, the stirring temperature is 70℃, and the viscosity of the solution is adjusted to 1500mPa`s.

[0063] In this embodiment, the thermoplastic polyurethane elastomer contains urethane groups (-NH-COO-), which have strong reactivity. Under heating and stirring, the urethane groups (-NH-COO-) will undergo esterification with the hydroxyl groups (-OH) in glycerol to form new ester bonds (hydroxyformate), while releasing water molecules.

[0064] R-OH+R’-NH-COO-→R-OCO-NH-R’+H2O

[0065] After the esterification reaction occurs, the amino groups in the thermoplastic polyurethane elastomer will be connected with glycerol to form a cross-linked chemical structure. The cross-linked network formed by the two restricts the movement range of carbon black and carbon nanotubes, thereby reducing the size of the aggregates. And because of the existence of two different size fillers, the dispersibility can be improved and the probability of agglomeration of the same filler can be reduced, so under the synergistic effect of cross-linked structure and mixed fillers, the random migration and agglomeration of conductive fillers at high temperature are greatly inhibited, the reversibility of the deconstruction and reconstruction of the conductive network is improved, thereby the cycle life of the PTC heating film is improved.

[0066] The performance of the PTC heating film of Example 1 was tested, and the results are shown in Figures 1-5 .

[0067] Figure 1 The PTC heating film obtained in Example 1 was subjected to 100 times of power-on and temperature rise curves; from Figure 1 it can be seen that after the PTC heating film is subjected to 100 times of power-on and temperature rise cycles, the equilibrium temperature decreases from 41.1℃ to 40.9℃, and the temperature difference is only 0.2℃, which shows that the PTC heating film can still maintain a good heating equilibrium temperature after multiple cycles.

[0068] Figure 2 The PTC heating film obtained in Example 1 was subjected to 100 times of power-on and temperature rise curves; from Figure 2 it can be seen that the surface heating uniformity of the PTC heating film in the 100th cycle is not much different from that in the first cycle.

[0069] Figure 3 The PTC characteristic diagram of the PTC heating film obtained in Example 1 under 700 times of high-low temperature impact cycles is shown inFigure 3 It can be seen that the PTC heating film still has good PTC effect after 700 times of high and low temperature impact cycles.

[0070] Figure 4 Comparison of PTC characteristics of the PTC heating film obtained in Embodiment 1 before and after bending 10 times; from Figure 4 It can be seen that the PTC characteristics of the film are basically unchanged after the PTC heating film is subjected to 10 times of winding behavior, which indicates that the conductive network and structure in the material are not damaged due to mechanical winding, and good flexibility is exhibited.

[0071] Figure 5 Temperature rise curves of the PTC heating film obtained in Embodiment 1 under different voltages. From Figure 5 It can be seen that the PTC heating film has excellent temperature control ability whether under 6V or 24V, and the balance temperature is basically maintained around the phase change temperature of lauric acid, which proves that it has certain self-regulating function.

[0072] It can be seen from the above embodiments that the PTC heating film provided by the present application has good flexibility, excellent PTC effect and repeatability, and the application range of the PTC heating film is widened.

[0073] Embodiment 2

[0074] A constant temperature heating film sheet for enhancing PTC effect repeatability, comprising the following components by mass percentage: thermoplastic polyurethane elastomer 25wt%, secondary phase matrix 5wt%, organic phase change material 20wt%, first conductive filler 13wt%, second conductive filler 5wt%, defoaming agent 0.3wt%, thickening agent 1.7wt%, organic solvent 30wt%; wherein the secondary phase matrix is diphenylmethane diisocyanate, the phase change material is paraffin wax, the first conductive filler is metal powder nickel powder with a size of 200-300nm, the second conductive filler is carbon fiber with a size length of 5-10um, the defoaming agent is polyoxypropylene glycerol ether, the thickening agent is ethyl cellulose, and the organic solvent is isophorone.

[0075] A preparation method of a constant temperature heating film sheet for enhancing PTC effect repeatability, comprising the following steps:

[0076] S1, 15g of thermoplastic polyurethane elastomer is weighed and added into 36ml of isophorone, and mechanically stirred and dispersed into the solvent to be in a non-granular state, and the stirring time is 40min;

[0077] S2, 3g of diphenylmethane diisocyanate is weighed and mechanically stirred under water bath heating to make it and the thermoplastic polyurethane elastomer fully crosslink and react, and the reaction time is 1.5h;

[0078] S3, 12 g of paraffin wax, 7.8 g of granular nickel and 3 g of carbon fiber are weighed and added to S2, and high-speed mechanical stirring is performed for 30 min;

[0079] S4, 0.18 g of polyoxypropylene glycerol ether and 1.02 g of ethyl cellulose are weighed and sequentially added to the mixed solution of S3, the viscosity of the solution is adjusted to a smooth state, and mechanical stirring is performed until it is completely uniform, and the stirring time is 20 min;

[0080] S5, the mixed solution obtained in step S4 is coated on the polyimide film containing the copper electrode, i.e. the lower layer of the insulating isolation layer, by using a coating machine, and after drying treatment, a positive temperature coefficient coating is obtained, and the coating thickness is controlled to be 1.5 mm.

[0081] S6, after the lower layer of the insulating isolation layer containing the positive temperature coefficient coating and the upper layer of the insulating isolation layer are heat pressed and fitted and packaged, a PTC heating film is obtained; wherein the thickness of the single layer of the insulating isolation layer is 1 mm, and the heat pressing process is: heat pressing temperature 80℃, pressure 1MPa.

[0082] In the above steps, the stirring speed of mechanical stirring is 1500rmp, the stirring temperature is 90℃, and the solution viscosity is adjusted to 1500mPa`s.

[0083] In this embodiment, the thermoplastic polyurethane elastomer contains active groups of amino (-NH2) or hydroxyl (-OH), which have strong reactivity. Under heating and stirring, the amino (-NH2) or hydroxyl (-OH) will undergo addition reaction with the isocyanate group (-NCO) of diphenyl methane diisocyanate.

[0084] R-NCO+R’-NH2→R-NH-C(=O)-NH-R’

[0085] R-NCO+R’-OH→R-NH-C(=O)-O-R’

[0086] After the addition reaction occurs, the amino or hydroxyl groups in the thermoplastic polyurethane elastomer are connected with the diphenyl methane diisocyanate, and a cross-linked chemical structure can be formed. Consistent with Example 1, the cross-linked network structure formed by the two-phase matrix limits the size of the aggregates formed, and mixing different sizes of fillers can improve the dispersibility and inhibit the aggregation of the same filler, and the synergistic effect of the two further enhances the reproducibility of the PTC effect of the heating film.

[0087] The PTC heating film of Example 2 was subjected to a cycle performance test, and the results are shown in Figure 6 .

[0088] Figure 6 The PTC characteristic diagram of the PTC heating film obtained in Example 2 under 500 times of high-low temperature impact cycles; from Figure 6It can be seen that the PTC heating film can maintain good PTC effect under 500 times of high and low temperature impact cycle test, and the resistance-temperature curve changes little, showing good PTC effect reproducibility.

[0089] Embodiment 3

[0090] A constant temperature heating film piece with enhanced PTC effect reproducibility comprises the following components by mass percentage: thermoplastic polyurethane elastomer 15wt%, secondary phase matrix 5wt%, organic phase change material 30wt%, first conductive filler 15wt%, second conductive filler 3wt%, defoaming agent 0.5wt%, thickening agent 1.5wt%, and organic solvent 30wt%; wherein the secondary phase matrix is dibenzoyl peroxide, the phase change material is myristic acid, the first conductive filler is carbon black with a size of 100-200nm, the second conductive filler is carbon nanotube with a size length of 30-50um, the defoaming agent is polydimethylsiloxane, the thickening agent is hydroxyethyl cellulose, and the organic solvent is isophorone.

[0091] In the embodiment of the present application, the preparation method of the constant temperature heating film piece with enhanced PTC effect reproducibility comprises the following steps:

[0092] S1, 15g of thermoplastic polyurethane elastomer is weighed and added into 60ml of isophorone, and mechanically stirred and dispersed into the solvent to be in a non-granular state, and the stirring time is 50min;

[0093] S2, 5g of dibenzoyl peroxide is weighed and added, and mechanically stirred under water bath heating to make it and the thermoplastic polyurethane elastomer fully crosslinking reaction, and the reaction time is 1h;

[0094] S3, 30g of myristic acid, 15g of carbon black and 3g of carbon nanotube are weighed and added to S2, and high-speed mechanical stirring is performed for mixing, and the stirring time is 30min;

[0095] S4, 0.5g of polydimethylsiloxane and 1.5g of hydroxyethyl cellulose are weighed and sequentially added to the mixed solution of S3, the viscosity of the solution is adjusted to be smooth, and mechanical stirring is performed for dispersion to be completely uniform, and the stirring time is 25min;

[0096] S5, the mixed solution obtained in step S4 is coated on the polyimide film piece containing copper electrodes, i.e. the lower layer of the insulating isolation layer, by using a coating machine, and a positive temperature coefficient coating is obtained after drying treatment, and the coating thickness is controlled to be 2mm.

[0097] S6, the lower layer of the insulating isolation layer containing the positive temperature coefficient coating and the upper layer of the insulating isolation layer are heat pressed and fitted for packaging to obtain a PTC heating film piece; wherein the thickness of the insulating isolation layer is 2mm, and the heat pressing process is as follows: heat pressing temperature is 90℃, and the pressure is 1MPa.

[0098] The rotation speed of mechanical stirring in the above steps is 2000 rmp, the stirring temperature is 70℃, and the viscosity of the solution is adjusted to 1500 mPa's.

[0099] In this embodiment, the dibenzoyl peroxide decomposes to generate free radicals under heating conditions, and these free radicals can initiate crosslinking of the polymer chains in the TPU. Specifically, the free radicals generated by the decomposition of dibenzoyl peroxide can attack the carbon atoms on the molecular chains of the TPU, initiate free radical chain growth reaction, cause new chemical bonds to form between the polymer chains, and thus achieve crosslinking. Consistent with Embodiment 1, the crosslinked network structure formed by the biphasic matrix limits the size of the aggregates, and mixing fillers of different sizes can improve the dispersibility and inhibit the aggregation of the same filler, and the synergistic effect of the two further enhances the reproducibility of the PTC effect of the heating film.

[0100] The PTC heating film of Embodiment 3 was subjected to a cycle performance test, and the results are shown in Figure 7

[0101] Figure 7 Figure 1 shows the PTC characteristic diagram of the PTC heating film obtained in Embodiment 3 under 500 cycles of high-low temperature impact; it can be seen from Figure 7 that the PTC heating film can still maintain good PTC effect under 500 cycles of high-low temperature impact test, and the resistance-temperature curve changes little, showing good reproducibility of PTC effect.

[0102] Embodiment 4

[0103] A constant temperature heating film piece for enhancing the reproducibility of PTC effect, comprising the following components by mass percentage: thermoplastic polyurethane elastomer 30wt%, secondary phase matrix 10wt%, organic phase change material 15wt%, first conductive filler 12wt%, second conductive filler 2wt%, defoaming agent 0.3wt%, thickening agent 0.7wt%, organic solvent 30wt%; wherein the secondary phase matrix is epoxy resin, the phase change material is lauric acid, the first conductive filler is carbon black with a size of 100-200nm, the second conductive filler is graphene with a size of 5-10um, the defoaming agent is polyoxyethylene oxypropylene glycerol, the thickening agent is sodium carboxymethyl cellulose, and the organic solvent is acetone.

[0104] In the embodiment of the present application, the preparation method of the constant temperature heating film piece for enhancing the reproducibility of PTC effect comprises the following steps: the size of the first conductive filler is preferably 50-400nm, and the size of the second conductive filler is preferably 1-70um

[0105] S1, weigh 15g of thermoplastic polyurethane elastomer and add it into 30ml of acetone, mechanically stir and disperse until it is in a non-particulate state in the solvent, and the stirring time is 60min;

[0106] ​S2, 5 g of epoxy resin is weighed and added to the thermoplastic polyurethane elastomer, and mechanical stirring is performed under water bath heating to fully crosslink the reaction, and the reaction time is 2 h;

[0107] S3, 7.5 g of lauric acid, 6 g of carbon black and 1 g of layered graphene are weighed and added to S2, and high-speed mechanical stirring is performed for mixing, and the stirring time is 45 min;

[0108] S4, 0.15 g of polyoxyethylene oxypropylene glycerol and 0.35 g of sodium carboxymethyl cellulose are weighed and sequentially added to the mixed solution of S3, the viscosity of the solution is adjusted to a smooth state, and mechanical stirring is performed for dispersion until completely uniform, and the stirring time is 20 min;

[0109] S5, the mixed solution obtained in step S4 is coated on the polyimide film containing the copper electrode, i.e. the lower layer of the insulating isolation layer, by using a coating machine, and a positive temperature coefficient coating is obtained after drying treatment, and the coating thickness is controlled to be 0.5 mm.

[0110] S6, the lower layer of the insulating isolation layer containing the positive temperature coefficient coating and the upper layer of the insulating isolation layer are heat pressed and fitted to obtain a PTC heating film; wherein the thickness of the single layer of the insulating isolation layer is 1.5 mm, and the heat pressing process is as follows: heat pressing temperature is 80℃, and pressure is 1 MPa.

[0111] In the above steps, the stirring speed of mechanical stirring is 2000 rmp, the stirring temperature is 80℃, and the solution viscosity is adjusted to 1500 mPa's.

[0112] In this embodiment, the epoxy resin is a high molecular compound composed of an epoxy group (-C-O-C-), which has high reactivity and can react with active groups such as amino groups (-NH2), isocyanate groups (-NCO) or hydroxyl groups (-OH) in the thermoplastic polyurethane elastomer. After the addition reaction occurs, the amino groups in the thermoplastic polyurethane elastomer will form a covalent bond with the epoxy resin to form a crosslinked chemical structure. Consistent with Example 1, the crosslinked network structure formed by the two-phase matrix limits the size of the aggregates, and mixing different sizes of fillers can improve the dispersibility and inhibit the aggregation of the same filler, and the synergistic effect of the two further enhances the reproducibility of the PTC effect of the heating film.

[0113] The PTC heating film of Example 4 was subjected to a cycle performance test, and the results are shown in Figure 8 .

[0114] Figure 8 Figure 4 is a PTC characteristic diagram of the PTC heating film obtained in Example 4 under 500 times high-low temperature impact cycles; from Figure 8It can be seen that the PTC heating film can maintain good PTC effect under 500 times of high and low temperature impact cycle test, and the resistance-temperature curve changes little, showing good PTC effect reproducibility.

[0115] Comparative Example 1

[0116] A constant temperature heating film piece with enhanced PTC effect reproducibility comprises the following components by mass percentage: thermoplastic polyurethane elastomer 30wt%, organic phase change material 20wt%, first conductive filler 17wt%, second conductive filler 1wt%, defoaming agent 0.5wt%, thickening agent 1.5wt%, and organic solvent 30wt%; wherein the phase change material is lauric acid, the first conductive filler is carbon black with a size of 100-200nm, the second conductive filler is carbon nanotube with a size length of 30-50um, the defoaming agent is polydimethylsiloxane, the thickening agent is sodium carboxymethyl cellulose, and the organic solvent is isophorone. The size of the first conductive filler is preferably 50-400nm, and the size of the second conductive filler is preferably 1-70um.

[0117] A preparation method of a constant temperature heating film piece with enhanced PTC effect reproducibility, comprising the following steps:

[0118] S1, 24g of thermoplastic polyurethane elastomer is weighed and added to 48ml of isophorone, and mechanically stirred and dispersed into the solvent to be particle-free, with a stirring time of 45min;

[0119] S2, 16g of lauric acid, 13.6g of carbon black and 0.8g of carbon nanotube are weighed and added to the product obtained in step S1, and high-speed mechanical stirring is performed for mixing, with a stirring time of 30min;

[0120] S3, 0.4g of polydimethylsiloxane and 1.2g of sodium carboxymethyl cellulose are sequentially added to the mixed solution obtained in step S2, the viscosity of the solution is adjusted to be smooth, and mechanical stirring is performed for dispersion until complete uniformity, with a stirring time of 25min;

[0121] S4, the mixed solution obtained in step S3 is coated on the polyimide film piece containing copper electrodes, i.e. the lower layer of the insulating isolation layer, by using a coating machine, and a positive temperature coefficient coating is obtained after drying treatment, with a coating thickness of 1mm;

[0122] S5, the lower layer of the insulating isolation layer containing the positive temperature coefficient coating and the upper layer of the insulating isolation layer are heat-pressed and bonded for packaging to obtain a PTC heating film piece; wherein the thickness of the insulating isolation layer is 0.5mm, and the heat-pressing process is as follows: heat-pressing temperature 80℃, pressure 1MPa.

[0123] In the above steps, the rotating speed of mechanical stirring is 1800rmp, the stirring temperature is 70℃, and the viscosity of the solution is adjusted to be 1500mPa`s.

[0124] The uncrosslinked PTC heating film of Comparative Example 1 was subjected to performance testing, and the results are shown in Table 1. Figures 9-11

[0125] In Table 1, the first column is the number of times of power-on and temperature rise, the second column is the temperature rise, the third column is the temperature difference, and the fourth column is the surface heating uniformity. Figure 9 The 60th power-on and temperature rise curve of the PTC heating film obtained in Comparative Example 1 is shown in FIG. 1. As can be seen from FIG. 1, the equilibrium temperature of the uncrosslinked PTC heating film decreased from 40.3°C to 39.2°C after 60 times of power-on and temperature rise, and the temperature difference was 1.1°C. Figure 9

[0126] The surface heating uniformity of the PTC heating film obtained in Comparative Example 1 after 60 times of power-on and temperature rise is shown in FIG. 2. As can be seen from FIG. 2, the surface heating uniformity of the uncrosslinked PTC heating film in the 60th time was significantly different from that in the first time, and a large area of reduced heating occurred, which was caused by the aggregation of conductive fillers in the large phase area during multiple temperature rise cycles. Figure 10 Figure 10 The SEM comparison of the PTC heating films obtained in Comparative Example 1 and Example 1 is shown in FIG. 3. As can be seen from FIG. 3, compared with the PTC heating film obtained in Comparative Example 1, the PTC heating film obtained in Example 1 has a rich crosslinked network structure and a more fine internal space. Specifically, under the driving force of thermodynamic incompatibility, aggregates are easily formed between the same fillers during the temperature cycle of the PTC heating film, and the large size of the conductive phase can provide a wide space for the conductive fillers, which will lead to the formation of large filler aggregates, and the reproducibility of the PTC effect is negatively affected. Therefore, by selecting hybrid fillers of different sizes, the dispersibility of the fillers can be improved, and the possibility of aggregation of the same fillers can be reduced. Moreover, the smaller size of the conductive phase means that the movement of the conductive fillers in the narrow space is inhibited, which limits the maximum size of the filler aggregates to some extent, and the small aggregates are more easily broken down. In short, the crosslinked structure and the hybrid fillers of different sizes are used to improve the aggregation of the conductive fillers, so as to enhance the reproducibility of the PTC effect.

[0127] Figure 11 Figure 11 Compared with Example 1, the PTC heating film obtained in Comparative Example 1 has a significantly lower heating capacity after multiple power-on uses, and a large area of reduced heating and a continuously expanding temperature difference appear before 100 times of use, which further confirms that the crosslinked structure and the hybrid fillers of different sizes can improve the aggregation phenomenon, ensure the heating stability of the PTC heating film, and prolong the service life of the PTC heating film.

[0128]

[0129] ​​​​In the embodiment, the obtained positive temperature coefficient paste is smooth and has no particle feeling. When the paste is coated on the polyimide film of the copper-clad electrode, the surface of the film is smooth and not rough after drying, and the film has good flexibility and can be bent at will. The PTC film generates heat uniformly, indicating that the PTC heating film has excellent and stable temperature control performance. Since the positive temperature coefficient coating has a rich cross-linked network structure, the PTC film can maintain good PTC effect reproducibility in repeated thermal cycles.

[0130] It should be noted that, for those skilled in the art, some improvements and refinements can be made to the above embodiments without departing from the principles of the present application, and these improvements and refinements should also be considered within the scope of protection of the present application.

Claims

1. A constant temperature heating film with enhanced reproducibility of PTC effect, comprising two insulating isolation layers and copper electrodes and positive temperature coefficient coating layers arranged between the insulating isolation layers, the lower insulating isolation layer being etched at the upper end of the copper electrodes, and the positive temperature coefficient coating layer being coated on the upper end of the copper electrodes; characterized in that, The positive temperature coefficient coating comprises the following components: 15-30wt% thermoplastic polyurethane elastomer, 5-20wt% secondary phase matrix, 10-40wt% organic phase change material, 14-25wt% first conductive filler, 1-5wt% second conductive filler, 0.1-1wt% defoaming agent, 0.5-2wt% thickening agent, 30-50wt% organic solvent; the secondary phase matrix is one of isocyanate, peroxide, polyhydroxy compound and epoxy compound; the first conductive filler has a particle size of 100-300nm, and the second conductive filler has a particle size of 5-50um. ​ 2. The constant temperature heat generating film sheet according to claim 1, wherein The isocyanate is diphenylmethane diisocyanate, toluene diisocyanate and hexamethylene diisocyanate; the peroxide is dibenzoyl peroxide and diisophorone peroxide; the polyhydroxy compound comprises glycerol, ethylene glycol and polyethylene glycol; and the epoxy compound is epoxy resin.

3. The constant temperature heat generating film sheet according to claim 1, wherein The organic phase change material is at least one of paraffin, fatty acid and polyol.

4. The constant temperature heat generating film sheet according to claim 3, wherein The fatty acid is stearic acid, palmitic acid, myristic acid and lauric acid; and the polyol is polyethylene glycol and tetradecanol.

5. The constant temperature heat generating film sheet according to claim 1, wherein The first conductive filler is at least one of conductive carbon black and metal powder; and the second conductive filler is at least one of carbon nanotube, carbon fiber and graphene.

6. The constant temperature heat generating film sheet according to claim 1, wherein The defoaming agent comprises at least one of silicone oil defoaming agent, polyvinyl alcohol defoaming agent and polyester defoaming agent; the thickening agent is at least one of ethyl cellulose, sodium carboxymethyl cellulose, hydroxyethyl cellulose and hydroxypropyl methyl cellulose; and the organic solvent is at least one of toluene, xylene, isophorone, n-hexane and acetone.

7. The constant temperature heat generating film sheet according to claim 1, wherein Both of the two insulation isolation layers are polyimide film sheets; the thickness of the insulation isolation layer is 0.5-2mm; the thickness of the positive temperature coefficient coating is 0.5-2mm; and the enhanced PTC effect recurrence constant temperature heating film has a resistivity value of 1-50Ω·cm at normal temperature.

8. The method of claim 1-7 for producing a constant temperature heat generating film sheet with enhanced reproducibility of PTC effect, characterized in that The method comprises the following steps: S1, adding thermoplastic polyurethane elastomer into organic solvent and stirring and dispersing until the solvent is in a non-particle state; S2, adding secondary phase matrix into the product obtained in step S1, heating and stirring in water bath for 1-2h for cross-linking reaction; S3, adding organic phase change material, first conductive filler and second conductive filler into the product obtained in step S2 and stirring and mixing uniformly; S4, adding defoaming agent and thickening agent into the mixed solution in step S3 and stirring and dispersing uniformly; S5, using a coating machine to coat the mixed solution obtained in step S4 on the lower layer insulation isolation layer etched with copper electrode on the upper end and drying; S6, hot pressing and pasting the lower layer insulation isolation layer and the upper layer insulation isolation layer to obtain the enhanced PTC effect recurrence constant temperature heating film.

9. The production method of the constant temperature heat generating film sheet with enhanced reproducibility of PTC effect according to claim 8, characterized by, In steps S1-S4, the stirring is mechanical stirring, the rotating speed is 1000-2400rmp, and the temperature is 60-90℃; in step S1, the stirring and dispersing time until the solvent is in a non-particle state is 30-60min; in step S3, the stirring time is 30-60min; and in step S4, the stirring time is 20-30min. The temperature of the hot-pressing is 60-100 DEG C, and the pressure is 0.5-1 MPa.

10. The use of the constant temperature heating film with enhanced PTC effect recurrence according to any one of claims 1-7 in the preparation of temperature control components.

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