Fireproof, temperature-sensitive and color-changing silica gel heating sheet with flexible PTC (Positive Temperature Coefficient) effect

Abstract

The invention provides a fireproof, temperature-sensitive and color-changing silica gel heating sheet with a flexible PTC (Positive Temperature Coefficient) effect, and belongs to the technical field of heating products. The silica gel heating sheet comprises a PTC heating layer, an electrode layer, an insulating layer and a temperature-sensitive color-changing layer; wherein the PTC heating layer is made of a silicone rubber-based PTC material, and comprises 50-60 parts of organic silicone rubber, 10-20 parts of a halogen-free phosphorus-nitrogen flame retardant, 25-35 parts of spherical graphite powder, 0.1-0.5 part of carbon nanotubes, 5-10 parts of fumed silica, 1-5 parts of a heat-conducting filler, and 0.5-2 parts of a silane coupling agent and a platinum vulcanizing agent. The carbon nanotubes and the graphite form a stable double network, the flame retardant and the reinforcing filler synergistically improve the mechanical and fireproof performance, and the obtained silica gel heating sheet has the functions of fire prevention, cold resistance, high temperature resistance, automatic constant temperature and temperature monitoring, and can be widely applied to multiple fields such as heating of wearable clothes, heating of physical therapy articles and heating of household articles.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heating products, in particular to a flexible PTC effect silica gel heating sheet with fireproof and temperature-sensitive discoloration. BACKGROUND

[0002] Traditional flexible heating materials (such as carbon fiber heating wire, metal alloy wire, etc.) are widely used in the fields of human wear type clothing heating and food temperature preservation, but there are significant safety hazards. For example, when the heating sheet is folded, overlapped or externally covered, causing poor heat dissipation, the local temperature will rise sharply. If the user forgets to turn off the heating switch after taking off the clothes, the material will overheat, burn out or even catch fire. The existing heating clothes rely on external temperature control switches (mechanical or NTC electronic) to achieve overheat protection. Once the switch fails, the system will lose temperature protection capability, and there is a serious safety blind area. Moreover, the user cannot directly perceive the surface temperature state of the heating sheet, and it is difficult to discover abnormal temperature rise in time, further amplifying the safety risk. Therefore, self-limiting PTC (positive temperature coefficient) material is considered as an ideal solution because its resistance increases automatically with temperature rise, thereby inhibiting power output and achieving intrinsic safety. However, the existing silica gel based PTC material still has obvious limitations. For example, pure reliance on conductive fillers (such as carbon black) easily leads to high material hardness and poor flexibility, which is difficult to meet the comfort requirement of wearing. At the same time, conventional silicone rubber is flammable and cannot resist fire in extreme overheating scenarios. It also cannot directly see the temperature warning function, and the application range is limited.

[0003] Therefore, it is urgent to develop a PTC heating material and device with flexibility, safety, fireproofness and real-time temperature visualization, so as to realize multiple safety protection and solve the temperature out of control and fire hazard. SUMMARY

[0004] In view of the defects of the prior art, the present application prepares a flexible silica gel heating sheet which not only has good flame retardance, but also has PTC effect and realizes temperature monitoring through color-changing ink, thereby improving the safety of the heating sheet.

[0005] In order to achieve the above purpose, the technical problem of the present application is solved by adopting the following technical scheme: A silicone rubber based PTC material, by mass fraction, includes 50-60 parts of silicone rubber, 10-20 parts of flame retardant, 25-35 parts of conductive spherical graphite powder, 5-10 parts of fumed silica, 3-8 parts of silicone oil, 1-5 parts of thermal conductive filler, 0.1-0.5 parts of carbon nanotube, 0.1-0.3 parts of platinum gold vulcanizing agent, and 0.5-2 parts of silane coupling agent.

[0006] Further, the above-mentioned one kind of silicone rubber-based PTC material, by mass parts, including 55 parts of vinyl silicone rubber, 15 parts of flame retardant, 30 parts of conductive spherical graphite powder, 7 parts of fumed silica, 5 parts of silicone oil, 3 parts of aluminum nitride heat-conducting filler, 0.3 parts of carbon nanotube, 0.2 parts of platinum gold vulcanizing agent, 1 part of silane coupling agent.

[0007] Further, the above-mentioned one kind of silicone rubber-based PTC material, the spherical diameter of the conductive spherical graphite powder is 8-25 μm.

[0008] Further, the above-mentioned one kind of silicone rubber-based PTC material, the flame retardant is halogen-free phosphorus-nitrogen flame retardant.

[0009] Further, the above-mentioned one kind of silicone rubber-based PTC material, the halogen-free phosphorus-nitrogen flame retardant is composed of aluminum diethyl hypophosphite, melamine and ammonium polyphosphate in a mass ratio of (1-3):3:1.

[0010] The application also discloses a flexible PTC effect silicone heating sheet with fireproof and temperature-sensitive color change.

[0011] Further, the above-mentioned flexible PTC effect silicone heating sheet with fireproof and temperature-sensitive color change, the preparation of the PTC heating layer comprises the following steps: The preparation of the PTC heating layer comprises the following steps: S0. Pretreatment: the conductive spherical graphite powder, fumed silica, heat-conducting filler, carbon nanotube and silane coupling agent are uniformly mixed, 20%-50% of the total amount of silicone oil is added as a dispersion medium, and ultrasonic treatment is carried out at 60-80 DEG C for 20-40 minutes to perform surface modification and dispersion; S1. Mixing: the silicone rubber, the mixture after the step S0 treatment, the flame retardant and the remaining silicone oil are mixed at room temperature, and are pressed and rolled repeatedly for 6-12 times; and then the platinum gold vulcanizing agent is added to perform mixing to obtain raw silicone rubber; S1a. Curing: the raw silicone rubber after mixing is placed in an environment at 25-35 DEG C for curing for 12-24 hours; S2. Vulcanization and shaping: the raw silicone rubber after curing is placed in a mold, and high-temperature vulcanization is carried out at 180-200 DEG C for 1-3 minutes to perform pressure shaping to obtain a sheet with a thickness of 1mm-1.5mm, namely the PTC heating layer.

[0012] Further, the above-mentioned flexible PTC effect silicone heating sheet with fireproof and temperature-sensitive color change, the heating sheet further comprises an electrode layer, an insulation layer, a wire and a temperature-sensitive color change layer; wherein the PTC heating layer is located at the bottom layer, the electrode layer is arranged on the PTC heating layer, and the temperature-sensitive color change layer is arranged on the upper portion of the electrode layer.

[0013] Further, the flexible PTC effect silica gel heating sheet with fireproof and temperature-sensitive discoloration, the electrode layer comprises a positive electrode strip, a negative electrode strip, a positive electrode lead and a negative electrode lead; the positive electrode strip, the negative electrode strip, the positive electrode lead and the negative electrode lead are all made of conductive material.

[0014] Further, the flexible PTC effect silica gel heating sheet with fireproof and temperature-sensitive discoloration, the temperature-sensitive discoloring layer is made of microencapsulated temperature-sensitive discoloring colorless ink at 10-20 g / m 2 Printed on the surface of the insulating cloth.

[0015] Compared with the prior art, the present application has the following beneficial effects: The present application provides a kind of silica rubber-based PTC material, spherical graphite is used as conductor, compared with ordinary flake graphite, its PTC effect is better, and there is no need to use expensive BaTiO3 Ceramics as raw material, reduce the composition, it is conducive to large-scale industrial production, synergistic effect with carbon nanotube, makes resistance fluctuation extremely low in cold and hot cycle, solve the problem of resistance drift of traditional PTC material, at the same time, pretreatment process using silane coupling agent significantly improves the dispersion of filler, combined with fumed silica reinforcement and silicone oil plasticization, the material has high tensile strength and superior bending durability.

[0016] The present application provides a kind of silica rubber-based PTC material, spherical graphite is used as conductor, compared with ordinary flake graphite, its PTC effect is better, and there is no need to use expensive BaTiO3 Ceramics as raw material, reduce the composition, it is conducive to large-scale industrial production, synergistic effect with carbon nanotube, makes resistance fluctuation extremely low in cold and hot cycle, solve the problem of resistance drift of traditional PTC material, at the same time, pretreatment process using silane coupling agent significantly improves the dispersion of filler, combined with fumed silica reinforcement and silicone oil plasticization, the material has high tensile strength and superior bending durability.

[0017] Other features and advantages of the present application will be described in the following specification. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creating laborious work.

[0019] Figure 1 It is a side view of the silica gel heating sheet in the embodiment of the present application.

[0020] Figure 2 It is a structure schematic view of the silica gel heating sheet in the embodiment of the present application.

[0021] Figure 3 is the electron micrograph of the spherical graphite electric mirror in the embodiment of the present application, in which: (1) is the electron micrograph of the silica gel heating sheet at normal temperature environment 26℃; (2) is the electron micrograph of the silica gel heating sheet after heating at 100℃.

[0022] Figure 4 is the actual shot of the silica gel heating sheet in the embodiment of the present application, in which: the light-colored surface is the temperature-sensitive color-changing layer of the heating sheet, and the temperature change can be directly observed; the dark-colored surface is the PTC heating layer of the heating sheet.

[0023] Figure 5 is the test result graph of the silica gel heating sheet in the embodiment of the present application.

[0024] Figure 6 is the color development graph of the silica gel heating sheet when the temperature is < 35℃.

[0025] Figure 7 is the color development graph of the silica gel heating sheet when the temperature is 35℃≤temperature<40℃.

[0026] Figure 8 is the color development graph of the silica gel heating sheet when the temperature is 40℃≤temperature≤60℃.

[0027] Figure 9 is the color development graph of the silica gel heating sheet when the temperature is > 60℃.

[0028] Explanation of reference signs: 1, PTC heating layer 1; 2, electrode layer; 3, insulation layer; 4, wire; 5, temperature-sensitive color-changing layer; 21, positive electrode strip; 22, negative electrode strip; 23, positive electrode lead; 24, negative electrode lead; 31, positive electrode insulation layer; 32, negative electrode insulation layer; 41, positive electrode wire; 42, negative electrode wire. DETAILED DESCRIPTION

[0029] In the prior art, the heating sheet is a sheet-shaped electric appliance element specially converting electric energy into heat energy, which has wide application in the fields of home heating, energy and the like. However, the heating sheet has certain safety hazards, such as easy over-temperature or excessive dependence on temperature control switch, and the temperature of the heating sheet may be out of control when a fault occurs.

[0030] The present application provides a flexible PTC effect silica gel heating sheet with fireproof and temperature-sensitive color change, which not only has PTC effect and can automatically maintain temperature, but also can monitor temperature, and has functions of fireproof, cold-resistant and high-temperature-resistant.

[0031] The embodiments of the present application will be described below in conjunction with the drawings, but it should be understood that these descriptions are only some of the embodiments of the present application, not all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of the present application.

[0032] In the present application, the terms "upper", "lower" and the like indicate the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application, and do not require the present application to be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0033] In the present application, the description of the terms "one embodiment", "another embodiment" and the like means that the specific features, structures, materials or characteristics described in conjunction with the embodiments are included in at least one embodiment of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine the different embodiments or examples described in the present specification and the features of the different embodiments or examples, without contradiction. In addition, it should be noted that in the present specification, the terms "first", "second" are for descriptive purposes only, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features.

[0034] In the present application, the test methods used are conventional methods unless otherwise specified; the materials, reagents, etc. used are commercially available reagents and materials unless otherwise specified.

[0035] The remaining raw materials are shown in the following Table 1 Raw Material Table: Table 1 Raw Material Parameter Table In the present application, the term "temperature-sensitive heat-variable colorless ink" is prepared from an electron transfer type organic compound system. The electron transfer type organic compound is a class of organic color systems with special chemical structure. At a certain temperature, the molecular structure of the organic compound changes due to electron transfer, thereby realizing color change. Such color-changing substances not only have bright colors, but also can realize color change from "colored - colorless" state.

[0036] In the present application, the diameter of the conductive spherical graphite ball is 8-25 μm.

[0037] According to the embodiments disclosed in the present application, as Figure 1 , 2As shown, a fireproof and temperature-sensitive color-changing flexible PTC effect silica gel heating sheet comprises a PTC heating layer 1, an electrode layer 2, an insulating layer 3, a wire 4 and a temperature-sensitive color-changing layer 5. The PTC heating layer 1 is located at the bottom layer, and the upper surface of the PTC heating layer 1 is provided with the electrode layer 2, the upper part of the electrode layer 2 is provided with the temperature-sensitive color-changing layer 5, and the temperature-sensitive color-changing layer 5 is away from the electrode layer 2.

[0038] The electrode layer 2 comprises a positive electrode strip 21, a negative electrode strip 22, a positive electrode lead 23 and a negative electrode lead 24, the insulating layer 3 comprises a positive electrode insulating layer 31 and a negative electrode insulating layer 32, and the wire 4 comprises a positive electrode wire 41 and a negative electrode wire 42; the positive electrode strip 21 is connected with the positive electrode wire 41 through the positive electrode lead 23, and the positive electrode lead 23 is provided with the positive electrode insulating layer 31 between the positive electrode lead 23 and the PTC heating layer 1; the negative electrode strip 22 is connected with the negative electrode wire 42 through the negative electrode lead 24, and the negative electrode lead 24 is provided with the negative electrode insulating layer 32 between the negative electrode lead 24 and the PTC heating layer 1.

[0039] The PTC effect realization principle of the silica gel heating sheet is that spherical graphite is adopted, and the spherical graphite is tightly arranged to form a graphite conductive chain under the force of the molecular chain of silica gel. Figure 3 As shown, when the heating sheet is not powered, the internal temperature of the silica gel heating sheet is the same as the ambient temperature and is in a low-temperature state, the spherical graphite conductive chain is arranged very tightly, the on-resistance (square resistance) is very small, and at this time, the power of the heating sheet is P=U 2 / R (min), when the heating sheet is powered, the temperature of the heating sheet starts to rise, the heating sheet will expand when hot and contract when cold, because the difference between the thermal expansion coefficient of the spherical graphite and the thermal expansion coefficient of the organic silica gel is large (the thermal expansion coefficient of the spherical graphite is about 3.5-5 ppm / ℃, and the thermal expansion coefficient of the organic silica gel is about 30-100 ppm / ℃), the thermal expansion coefficient of the spherical graphite powder is small, the size is stable when the temperature rises, and the thermal expansion of the organic silica gel is large, the size becomes large when the temperature rises, so the gap between the originally tightly arranged spherical graphite powders starts to become large, the arrangement density also becomes large, the resistance of the spherical graphite conductive chain also becomes large, and then the total power of the heating sheet starts to decrease, that is, the higher the temperature, the lower the heating power, until the resistance of the heating sheet stops decreasing when the temperature no longer rises, and at this time, the power is P=U 2 / R (max), so as to achieve the PCT effect of automatic temperature reduction.

[0040] According to the embodiment disclosed by the application, the PTC heating layer 1 is made of a heating material, and the thickness is 1mm-1.5mm.

[0041] According to the disclosed embodiment of the present application, the electrode layer 2 comprises positive electrode strips 21 and negative electrode strips 22, each having a thickness of 0.5 mm and a width of 10 mm; the electrode layer 2 further comprises positive electrode lead poles 23 (10x50 mm) and negative electrode lead poles 24 (10x50 mm), each having a thickness of 0.3 mm. The positive electrode strips 21, the negative electrode strips 22, the positive electrode lead poles 23 and the negative electrode lead poles 24 are made of conductive copper.

[0042] According to the disclosed embodiment of the present application, the insulating layer 3 is made of polyimide, a high-temperature-resistant material, and has a thickness of 0.2 mm.

[0043] According to the disclosed embodiment of the present application, the temperature-sensitive color-changing layer 5 is made by uniformly printing microencapsulated temperature-sensitive heat-variable colorless ink (from Shenzhen Fantasy Color-Changing Technology Co., Ltd.) on the upper surface of an insulating cloth (aluminum silicate ceramic fiber cloth, 0.5 mm thick).

[0044] The temperature-sensitive color-changing colors are colorless-to-turquoise green ink 1, colorless-to-orange ink 2 and colorless-to-magenta ink 3, respectively; the printing amount of each ink is 15 g / m 2 Wet weight.

[0045] Preparation Example 1 Preparation of the PTC heating layer 1: 1. First, the raw materials are weighed according to the following mass parts: vinyl silicone rubber 55 parts, halogen-free phosphorus-nitrogen flame retardant 15 parts (aluminum diethylphosphinate: melamine: ammonium polyphosphate = 2:3:1), conductive spherical graphite powder 30 parts, fumed silica 7 parts, methyl silicone oil 5 parts, aluminum nitride 3 parts, multi-walled carbon nanotubes 0.3 parts, platinum gold vulcanizing agent 0.2 parts, silane coupling agent 1 part 2. Pretreatment: The conductive spherical graphite powder, fumed silica, aluminum nitride, carbon nanotubes and silane coupling agent are put into a high-speed mixer, 2 parts of silicone oil (total amount 40%) are added, and ultrasonic treatment is carried out at 70°C for 30 minutes (power 800W) to obtain a modified filler mixture.

[0046] 3. Mixing: The vinyl silicone rubber, modified filler mixture, flame retardant and the remaining 3 parts of silicone oil are added to an internal mixer, and repeated 12 times under normal temperature by flattening and plying. The platinum gold vulcanizing agent is mixed for 5 minutes to obtain gray-black raw silicone rubber.

[0047] 4. Curing: The raw silicone rubber is placed in a constant humidity box at 30°C for 18 hours.

[0048] 5. Vulcanization and shaping: The cured rubber is placed in a mold and vulcanized at 180°C for 2 minutes (pressure 100 tons) to obtain a 1.2 mm thick PTC heating layer with a smooth surface and no bubbles.

[0049] Preparation Example 2 Preparation of PTC heating layer 1: 1. First, the raw materials were weighed as follows: Vinyl silicone rubber 58 parts, halogen-free phosphorus-nitrogen flame retardant 20 parts (aluminum diethyl phosphinate: melamine: ammonium polyphosphate = 1:3:1), conductive spherical graphite powder 25 parts, fumed silica 5 parts, phenyl silicone oil 3 parts, alumina 1 part, multi-walled carbon nanotubes 0.1 part, platinum gold vulcanizing agent 0.3 part, silane coupling agent 0.5 part 2. Pretreatment: The conductive spherical graphite powder, fumed silica, alumina, carbon nanotubes, and silane coupling agent were mixed, and 1.2 parts of silicone oil (total amount 40%) was added, and ultrasonic treatment was performed at 65°C for 25 minutes (power 600W).

[0050] 3. Mixing: The vinyl silicone rubber, pretreatment mixture, flame retardant, and remaining 1.8 parts of silicone oil were mixed, and the mixture was repeatedly pressed and rolled for 10 times, and vulcanizing agent was added and mixed for 4 minutes.

[0051] 4. Curing: The raw rubber was cured at 25°C for 24 hours.

[0052] 5. Vulcanization and shaping: Vulcanization was performed at 190°C for 1.5 minutes (pressure 100 tons) in a mold, and a 1.0 mm thick PTC heating layer was obtained.

[0053] Preparation Example 3 Preparation of PTC heating layer 1: 1. First, the raw materials were weighed as follows: Vinyl silicone rubber 52 parts, halogen-free phosphorus-nitrogen flame retardant 10 parts (aluminum diethyl phosphinate: melamine: ammonium polyphosphate = 3:3:1), conductive spherical graphite powder 35 parts, fumed silica 10 parts, dimethyl silicone oil 8 parts, boron nitride 5 parts, multi-walled carbon nanotubes 0.5 parts, platinum gold vulcanizing agent 0.1 part, silane coupling agent 2 parts 2. Pretreatment: The filler was mixed with the silane coupling agent and 3.2 parts of silicone oil (total amount 40%), and ultrasonic treatment was performed at 80°C for 40 minutes (power 1000W).

[0054] 3. Mixing: The base rubber, pretreatment, flame retardant, and remaining 4.8 parts of silicone oil were mixed, and the mixture was repeatedly pressed and rolled for 8 times, and vulcanizing agent was added and mixed for 3 minutes.

[0055] 4. Curing: Curing was performed at 35°C for 12 hours.

[0056] 5. Vulcanization and shaping: Vulcanization at 200°C for 1 minute (pressure 100 tons) to produce a PTC heating layer 1 of 1.5 mm thickness.

[0057] Test Example 1 I. Conductive network stability test Test method Sample: The PTC heating layer 1 prepared in Preparation Examples 1-3 was assembled into a silica gel heating sheet, and named as No. 1, No. 2 and No. 3, respectively. A commercially available ordinary graphite-filled silica gel heating sheet (control group) was used for comparison. (The product has a voltage of 5V, a power of 5W, and a temperature of 30-100°C. The base material is silica gel + nanocarbon black / graphene mixture without carbon nanotube addition).

[0058] Test conditions: Temperature cycle range: -30°C → 100°C (simulating extreme use environment); Cycle number: 100 times (each time the temperature was raised / dropped at a rate of 10°C / min, and the constant temperature was maintained for 30 min); Measurement: After every 10 cycles, the resistance value R was measured at 25°C n ; Calculate the resistance fluctuation rate: δ = |R n -R0| / R0 x 100% (R0 is the initial resistance) Table 2. Results of conductive network stability test As shown in Table 2, the carbon nanotubes (0.1-0.5 parts) can form a synergistic effect with the spherical graphite under the action of the silane coupling agent, significantly inhibiting the breakage of the conductive path caused by thermal expansion. The silica gel heating sheet assembled with the PTC heating layer 1 prepared in Preparation Example 3 showed the best performance due to the high filler content of graphite and carbon nanotubes, and the resistance fluctuation rate was only 1 / 5 of that of the control group, indicating the synergistic effect of carbon nanotubes and spherical graphite, ensuring the stability of the conductive network under temperature alternation, and overcoming the defect of large resistance drift of traditional PTC materials.

[0059] II. Test the effect of low-temperature curing process on the performance of silica gel heating sheet Test method Sample comparison: Group A: The silica gel heating sheet assembled with the PTC heating layer 1 prepared in Preparation Example 1 (containing 24 hours of curing); Group B: The silica gel heating sheet assembled with the PTC heating layer 1 prepared without curing (direct vulcanization after mixing).

[0060] Test items: Vulcanization defect rate: the proportion of surface bubbles / cracks observed under a microscope; Bending durability: curvature radius R = 5mm, resistance change rate after 5000 times of dynamic bending; PTC response speed: time required for recording from 25℃ to 100℃.

[0061] Table 3 Test results of different curing processes As shown in Table 3, the low-temperature curing process can effectively eliminate internal stress during mixing and avoid vulcanization bubbles. At the same time, it promotes the directional arrangement of fillers, improves the flexibility and durability, and proves that the low-temperature curing can effectively reduce the defect rate of vulcanization bubbles and has a faster PTC response speed.

[0062] Test Example 2 I. PTC test PTC property refers to the property that the resistivity of the material increases linearly with the increase of the temperature of the material itself, that is, when the temperature of the PTC material increases, the resistivity also increases. When the resistivity increases, the current and power decrease with the same voltage, and the temperature rise rate decreases.

[0063] The silicone heating sheet assembled with the PTC heating layer prepared in Preparation Example 1 was subjected to an electric heating test. Before the test, the silicone heating sheet was as shown in Figure 4 The light-colored side is the temperature-sensitive color-changing layer of the heating sheet, and the temperature change can be directly observed; the dark-colored side is the PTC heating layer of the heating sheet.

[0064] No power: temperature 34℃, voltage 12V, current 0A, power 0W; initial data after power-on: temperature 34℃, voltage 12V, current 1.69A, power 20.28W.

[0065] As shown in Figure 5 At 39 minutes after power-on, the temperature was 98℃, the voltage was 12V, the current was 0.99A, and the power was 11.88W, indicating that the heating sheet of the present application has a PTC effect, and the working temperature affects the working resistance, thereby affecting the heating power. The PTC heating layer prepared in Preparation Example 2 and Preparation Example 3 is the same as the PTC heating layer prepared in Preparation Example 1, and will not be described here.

[0066] At the same time, as shown in Figures 6-9 The silicone heating sheet changes color with temperature change, the color change of the silicone heating sheet is weak when the temperature is <35℃, the silicone heating sheet is turquoise when the temperature is 35℃≤temperature<40℃, the silicone heating sheet is orange when the temperature is 40℃≤temperature<60℃, and the silicone heating sheet is magenta when the temperature is >60℃, indicating that the silicone heating sheet of the present application has a certain safety, and the temperature change can be judged by color change, thereby enhancing the safety, beauty and practicality of the product.

[0067] II. Flame Retardant Test According to the limiting oxygen index test standard (GB / T 2406.12008), the flame retardancy of the heating sheet was tested.

[0068] III. Temperature Test The silica gel heating sheet was placed in a thermostat for temperature test, and was placed at each temperature for one month to resist low temperature (-55℃) and high temperature (200℃). A commercially available graphene heating sheet with temperature control switch was set as a control group (Model: XFHMB-3, manufacturer: Jiangsu Xianfeng Nanometer Material Technology Co., Ltd.).

[0069] IV. Tensile property of the heating sheet was tested according to GB / T 528-2009 "Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber".

[0070] Table 4. Results of flame retardant test of silica gel heating sheet Note: "Examples 1-3" in the table are silica gel heating sheets assembled by PTC heating layers prepared in Preparation Examples 1-3, respectively.

[0071] As shown in Table 4, the limiting oxygen index of Examples 1-3 is basically higher than that of the control group, indicating that the heating sheet of the application has good flame retardant and fireproof performance, and the heating sheet of the application has PTC effect, does not need to rely on temperature control switch, improves the safety during use of the heating sheet, and the heating sheet also has low and high temperature resistance, prolongs the service life of the heating sheet, and when the heating sheet is stretched by external force, it can withstand a large tensile force without breaking and can be bent within a certain range.

[0072] In summary, the application provides a silica rubber-based PTC material, which, through the synergistic effect of spherical graphite and carbon nanotubes, has very low resistance fluctuation in cold and heat cycles, solves the problems of resistance drift of traditional PTC materials, and significantly improves the dispersibility of fillers by using a silane coupling agent pretreatment process, and combines fumed silica reinforcement and silicone oil plasticization to make the material have high tensile strength and superior bending durability; and the application uses a low-temperature curing process to prepare the PTC heating layer, which can effectively eliminate internal stress and improve product yield and PTC response speed.

[0073] The application also provides a PTC heating layer made of the silica rubber-based PTC material, which is assembled with an electrode layer, an insulating layer, a wire, and a temperature-sensitive color-changing layer to form a silica gel heating sheet, which not only has fireproof and PTC properties, but also is flexible and bendable, waterproof and washable, and changes color with temperature change, facilitating monitoring of the heating state of the clothes and avoiding over-heating, thereby ensuring the safety of the heating material; and has wide applicability, fireproof, cold-resistant, high-temperature-resistant, automatic constant-temperature, and temperature monitoring functions, and can be widely applied in heating of wearable clothes, heating of physiotherapy products, and heating of home products, etc.

[0074] Furthermore, it should be understood that although the specification is described in terms of embodiments, not every embodiment includes only one independent technical solution, and the specification is described in this way only for the sake of clarity, and those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that those skilled in the art can understand.

Claims

1. A silicone rubber based PTC material, characterized by, By mass fraction, including 50-60 parts of silicone rubber, 10-20 parts of flame retardant, 25-35 parts of conductive spherical graphite powder, 5-10 parts of fumed silica, 3-8 parts of silicone oil, 1-5 parts of thermal conductive filler, 0.1-0.5 parts of carbon nanotube, 0.1-0.3 parts of platinum gold vulcanizing agent, 0.5-2 parts of silane coupling agent.

2. The silicone rubber based PTC material according to claim 1, characterized in that, By mass fraction, including 55 parts of vinyl silicone rubber, 15 parts of flame retardant, 30 parts of conductive spherical graphite powder, 7 parts of fumed silica, 5 parts of silicone oil, 3 parts of aluminum nitride thermal conductive filler, 0.3 parts of carbon nanotube, 0.2 parts of platinum gold vulcanizing agent, 1 part of silane coupling agent.

3. The silicone rubber based PTC material according to claim 1 or 2, characterized in that, The spherical diameter of the conductive spherical graphite powder is 8-25 μm.

4. The silicone rubber based PTC material according to claim 1 or 2, characterized in that, The flame retardant is a halogen-free phosphorus-nitrogen flame retardant.

5. The silicone rubber based PTC material according to claim 4, characterized in that, The halogen-free phosphorus-nitrogen flame retardant is composed of aluminum diethyl phosphinate, melamine, and ammonium polyphosphate in a mass ratio of (1-3):3:

1.

6. A flexible PTC effect silicone heating sheet which is fireproof and changes color in response to temperature, characterized in that, The heating sheet includes a PTC heating layer made of the silicone rubber-based PTC material according to any one of claims 1-5.

7. The fireproof and temperature-sensitive color-changing flexible PTC effect silicone heating sheet according to claim 6, characterized in that, The preparation of the PTC heating layer includes the following steps: (1) uniformly mix the conductive spherical graphite powder, fumed silica, thermal conductive filler, carbon nanotube, and silane coupling agent, add 20%-50% of the total amount of silicone oil as a dispersion medium, and ultrasonically treat at 60-80°C for 20-40 minutes for surface modification and dispersion; (2) mix the silicone rubber, the mixture after step S0 treatment, the flame retardant, and the remaining silicone oil at room temperature, flatten and roll into a strip, repeat 6-12 times, and then add the platinum gold vulcanizing agent for mixing to obtain raw silicone rubber; (3) place the mixed raw silicone rubber in an environment of 25-35°C for 12-24 hours for curing; (4) place the cured raw silicone rubber in a mold, vulcanize at 180-200°C for 1-3 minutes, and press to shape to obtain a sheet with a thickness of 1 mm-1.5 mm, which is the PTC heating layer.

8. The fireproof and temperature-sensitive color-changing flexible PTC effect silicone heating sheet according to claim 6, characterized in that, The heating sheet further includes an electrode layer, an insulating layer, a wire, and a temperature-sensitive color-changing layer; wherein the PTC heating layer is located at the bottom layer, and the electrode layer is arranged thereon, and the temperature-sensitive color-changing layer is arranged on the upper part of the electrode layer.

9. The fireproof and temperature-sensitive color-changing flexible PTC effect silicone heating sheet according to claim 8, characterized in that, The electrode layer includes a positive electrode strip, a negative electrode strip, a positive electrode lead, and a negative electrode lead; the positive electrode strip, the negative electrode strip, the positive electrode lead, and the negative electrode lead are all made of conductive material.

10. The fireproof and temperature-sensitive color-changing flexible PTC effect silicone heating sheet according to claim 8, characterized in that, The temperature-sensitive color-changing layer is made of microencapsulated temperature-sensitive thermochromic colorless ink at 10-20 g / m 2 Printed on the surface of the insulating cloth.

Images