CN100472674C - overcurrent protection element - Google Patents

Abstract

The present invention discloses an overcurrent protection element, which comprises two metal foils and a positive temperature coefficient (PTC) material layer. The PTC material layer is between the two metal foils and comprises a plurality of crystalline polymers, a conductive ceramic filler and a non-conductive filler. The particle size of the conductive filler has a specific size distribution and the volume resistance value of the PTC material layer is less than 0.1Ω-cm.

Description

overcurrent protection element

technical field

The present invention relates to an overcurrent protection element, more specifically, an overcurrent protection element with a PTC conductive composite material, the overcurrent protection element has a preferred volume resistance value and resistance reproducibility, and is especially suitable for mobile Power supply protection for communication equipment.

Background technique

Since the resistance of conductive composite materials with positive temperature coefficient (Positive Temperature Coefficient; PTC) characteristics has the characteristics of sensitive response to temperature changes, it can be used as a material for current sensing elements, and has been widely used in overcurrent protection elements or circuits. component. Because the resistance of the PTC conductive composite material can maintain an extremely low value at normal temperature, the circuit or battery can operate normally. However, when an over-current or over-temperature phenomenon occurs in a circuit or battery, its resistance value will instantly increase to a high resistance state (at least 10 ⁴ ohms or more), and the excessive current will be Reverse offset to achieve the purpose of protecting the battery or circuit components.

Generally speaking, the PTC conductive composite material is composed of one or more crystalline polymers and conductive fillers, and the conductive fillers are uniformly dispersed in the polymers. The polymer is generally a polyolefin polymer, such as polyethylene. The conductive filler is generally carbon black, metal particles or oxygen-free ceramic powder, such as titanium carbide or tungsten carbide.

The conductivity of the conductive composite material depends on the type and content of the conductive filler. Generally speaking, due to the concave-convex surface of carbon black, it has good adhesion to polyolefin polymers, so it has good resistance reproducibility. However, the electrical conductivity that carbon black can provide is lower than that of metal particles, while metal particles have a larger specific gravity, are less uniformly dispersed and are easily oxidized, resulting in increased resistance. In order to effectively reduce the resistance value of overcurrent protection components and avoid oxidation, ceramic powders are gradually used as conductive fillers for low-resistance conductive composite materials. However, since ceramic powder does not have a concave-convex surface like carbon black, and its adhesion to polymers such as polyolefins is worse than that of carbon black, its resistance reproducibility is also difficult to control. In order to increase the adhesion between polyolefin polymers and metal particles, a conventional conductive composite material using ceramic powder as a conductive filler will add a coupling agent, such as: anhydride compounds or silane compounds, to strengthen the polyolefin. Adhesion between polymer-like particles and metal particles, but the addition of coupling agent cannot effectively reduce the overall resistance value.

At present, the PTC conductive composite material with low resistance (about 20mΩ) on the market uses nickel (Ni) as the conductive filler, and its withstand voltage is only 6V. Among them, if nickel is not tightly protected and insulated from the air, it is easily oxidized after a period of time, resulting in an increase in resistance. In addition, after the conductive composite material is tripped, its resistance reproducibility is not good.

Contents of the invention

The main purpose of the present invention is to provide an overcurrent protection element, which has excellent performance by adding a conductive filler with a specific particle size distribution and at least one crystalline high molecular polymer with a low melting point. Low resistance value, low temperature quick trip (trip) protection function, withstand voltage characteristics and resistance reproducibility.

In order to achieve the above purpose, the present invention discloses an overcurrent protection element, which includes two metal foils and a PTC material layer. The metal foil has a nodule protruding rough surface and is in direct physical contact with the PTC material layer. The PTC material layer is between the two metal foils and includes a plurality of crystalline polymers, an oxygen-free conductive ceramic powder (ie, conductive filler) and a non-conductive filler. The particle size of the oxygen-free conductive ceramic powder is between 0.01 μm and 30 μm, preferably the particle size is between 0.1 μm and 10 μm, the volume resistance of the oxygen-free conductive ceramic powder is less than 500 μΩ-cm, and uniformly dispersed among the plurality of crystalline polymers. The plurality of crystalline polymers may be selected from high density polyethylene, low density polyethylene, polypropylene, polyvinyl fluoride and copolymers thereof. In order to achieve the protective function of rapid tripping at low temperature, the PTC material layer contains at least one crystalline polymer with a melting point lower than 115°C.

In order to protect the safety of overcharging of lithium-ion batteries, the over-current protection components used in lithium-ion batteries must be able to generate a trigger (trip) reaction at a relatively low temperature, so the PTC material layer uses a polymer material with a lower melting point: such as low-density polymer Ethylene, and one or more polymer materials can be selected, but the minimum melting point of each polymer must be lower than 115°C. The low-density polyethylene can be polymerized with traditional Ziegler-Natta catalysts or with Metallocene catalysts, and can also be polymerized through ethylene monomers and other monomers (for example: butene (butene), hexene (hexene), octene (octene) , acrylic acid (acrylic acid) or vinyl acetate (vinyl acetate)) copolymerization.

The oxygen-free conductive ceramic powder used in the present invention is selected from (1) metal carbides (for example: titanium carbide (TiC), tungsten carbide (WC), vanadium carbide (VC), zirconium carbide (ZrC), niobium carbide (NbC) , tantalum carbide (TaC), molybdenum carbide (MoC) and hafnium carbide (HfC)); (2) metal borides (for example: titanium boride (TiB ₂ ), vanadium boride (VB ₂ ), zirconium boride (ZrB ₂ ), niobium boride (NbB ₂ ), molybdenum boride (MoB ₂ ) and hafnium boride (HfB ₂ )); or (3) metal nitrides (eg zirconium nitride (ZrN)).

The shape of the oxygen-free conductive ceramic powder used in the present invention can present various types of particles, such as: spherical, cubic, flake, polygonal or columnar. Generally speaking, because the hardness of conductive ceramic powder is quite high, the manufacturing method is different from carbon black or metal powder, so that its shape is also different from carbon black or some high structure metal powder. The shape of oxygen-free conductive ceramic powder particles is mainly low structure type, with a particle size of less than 10 μm and an aspect ratio of less than 10.

The non-conductive filler used in the present invention is selected from inorganic compounds with flame-retardant effect or anti-arc effect, for example: zinc oxide, antimony oxide, aluminum oxide, silicon oxide, calcium carbonate, magnesium sulfate, barium sulfate and containing hydroxyl ( OH) compounds (for example: magnesium hydroxide, aluminum hydroxide, calcium hydroxide, barium hydroxide, etc.). The particle size of the non-conductive filler is mainly between 0.05 μm and 50 μm, and its weight ratio is between 1% and 20%.

Since the volume resistance of the oxygen-free conductive ceramic powder is very low (less than 500 μΩ-cm), the mixed PTC material can achieve a volume resistance value lower than 0.5 Ω-cm. Generally speaking, it is difficult for PTC materials to achieve a volume resistance value lower than 0.1Ω-cm. Even when the PTC material can achieve a volume resistance value lower than 0.1Ω-cm, it often loses the characteristics of withstand voltage because the resistance value is too low. However, the PTC material layer in the overcurrent protection element of the present invention can reach less than 0.1Ω-cm and can withstand a voltage of 12V to 40V and a current of less than or equal to 50 amperes.

Generally speaking, when the PTC material reaches a volume resistance value lower than 0.1Ω-cm, it is often unable to withstand a voltage higher than 12V. Therefore, in order to improve the voltage resistance in the present invention, a non-conductive filler is added to the PTC material, mainly containing hydrogen Oxygen (OH) is the main inorganic compound, and the thickness of the PTC material layer is controlled to be greater than 0.2mm, so that the low-resistance PTC material can greatly increase the withstand voltage. The non-conductive filler of the inorganic compound also has the function of controlling the resistance reproducibility, and usually can control the resistance reproducibility ratio (trip jump) R ₁ /R _i to be less than 3. Among them, R _i is the initial resistance value, and R ₁ is the resistance value measured after returning to room temperature for one hour after being triggered once.

Because the PTC material layer has a relatively low volume resistance value, the area of the PTC chip (that is, the required PTC material layer of the overcurrent protection element of the present invention) can be reduced to less than 50mm ² , and the low resistance of the element can still be achieved. The purpose is to finally produce more PTC chips from each PTC material layer of the same area, so as to reduce the production cost.

In the overcurrent protection device of the present invention, the two metal foils can be combined with the other two metal nickel sheets (that is, metal electrode sheets) by reflow soldering or spot welding with solder paste. Assembly (assembly), usually an axial-leaded, radial-leaded, terminal or surface mount component. In the overcurrent protection device of the present invention, wherein the upper and lower metal foils can be connected to a power supply to form a conductive circuit (in another embodiment, it can be formed by connecting the two metal electrode sheets to a power supply) A conductive circuit), the PTC material layer operates under the condition of overcurrent, and achieves the function of protecting the circuit.

Description of drawings

Figure 1 illustrates an overcurrent protection element of the present invention; and

FIG. 2 illustrates another embodiment of the overcurrent protection element of the present invention.

Detailed ways

The two components (Example 1 and Example 2) and the manufacturing process of the overcurrent protection device of the present invention are described below.

The composition and weight (unit: gram) of the PTC material layer used in the overcurrent protection element of the present invention are shown in Table 1.

Table I

LDPE-1 HDPE-1 HDPE-2 Mg(OH)₂ TiC Embodiment one 12.66 0.50 ---- 5.04 92.60 Embodiment two 11.20 ---- ---- 5.04 93.60 comparative example ---- 3.16 12.65 4.20 90.90

Among them, LDPE-1 is low-density crystalline polyethylene (density: 0.924g/cm ³ , melting point: 113°C); HDPE-1 is high-density crystalline polyethylene (density: 0.943g/cm ³ , melting point: 125°C) ; HDPE-2 is high-density crystalline polyethylene (density: 0.962g/cm ³ , melting point: 131°C); Mg(OH) ₂ is magnesium hydroxide with 96.9wt% purity and contains 0.50% CaO, 0.85% SO _3. Trace compounds such as 0.13% SiO ₂ , 0.03% Fe ₂ O ₃ , 0.06% Al ₂ O ₃ and titanium carbide (TiC) conductive filler. The average particle size of titanium carbide (TiC) is 3 μm, and the particle size aspect ratio (aspect ratio) is less than 10.

The production process is as follows: set the feed temperature of the batch mixer (Hakke-600) at 160°C, the feed time is 2 minutes, and the feed program is to add a quantitative amount of crystalline polymer polymer according to the weight shown in Table 1. Stir for a few seconds, then add oxygen-free conductive ceramic powder (titanium carbide, the particle size is between 0.1 μm and 10 μm) and non-conductive filler. The rotational speed of the mixer rotation was 40 rpm. After 3 minutes, the rotating speed was increased to 70 rpm, and the kneading was continued for 7 minutes before feeding to form a conductive composite material with PTC characteristics.

Put the above-mentioned conductive composite material into a mold whose outer layer is a steel plate and the middle thickness is 0.35mm in a symmetrical manner up and down. Put a layer of Teflon release cloth on the upper and lower sides of the mold, pre-press for 3 minutes, and the pre-press operating pressure is 50kg/ cm ² at a temperature of 180°C. Pressing is carried out after exhausting, the pressing time is 3 minutes, the pressing pressure is controlled at 100kg/cm ² , the temperature is 180°C, and then the pressing action is repeated again, the pressing time is 3 minutes, and the pressing pressure is controlled at 150kg /cm ² , the temperature is 180°C, and then a PTC material layer 11 is formed (see FIG. 1 ). The thickness of the PTC material layer 11 is 0.35mm or 0.45mm.

The PTC material layer 11 is cut into a square of 20 x 20 cm ² , and then two metal foils 12 are directly physically contacted on the upper and lower surfaces of the PTC material layer 11 by pressing, which is on the upper and lower surfaces of the PTC material layer. The surface of 11 is sequentially covered with metal foil 12 in a vertically symmetrical manner. The metal foil 12 has a nodule protruding rough surface and is in direct physical contact with the PTC material layer 11 . Press special buffer material, Teflon release cloth and steel plate to form a multi-layer structure. The multi-layer structure is then pressed, and the pressing time is 3 minutes, the operating pressure is 70kg/cm ² , and the temperature is 180°C. Afterwards, a chip-shaped overcurrent protection element 10 of 3.4mm x 4.1mm or 3.5mm x 6.5mm is punched out with a mold, and then two metal electrode pieces 22 are connected up and down with solder paste by means of reflow. A shaft-shaped current protection element 20 is formed on the two metal foils 12 (see FIG. 2 ).

In addition, the volume resistance value (ρ) of the PTC material layer 11 can be calculated according to formula (1):

$\mathrm{<span\; class="notranslate">\; \&rho;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; A</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Where R is the resistance value (Ω) of the PTC material layer 11 , A is the area (cm ² ) of the PTC material layer 11 , and L is the thickness (cm) of the PTC material layer 11 . Substitute R in formula (1) with the Ri(Ω) value (0.0069Ω) in Table 2, substitute A with 6.5 x 3.5mm ² (=6.5 x 3.5 x 10 ^-2 cm ² ), and L with 0.45mm (= 0.045cm) is substituted, and ρ=0.0349Ω-cm can be obtained, which is obviously smaller than 0.1Ω-cm.

The shaft-shaped current protection element 20 is placed at an ambient temperature of 80°C, and tested at a voltage and current of 6V/0.8A to simulate the situation when the battery temperature rises to 80°C under an overcharged environment of 6V/0.8A. The shaft-shaped current protection element 20 must be able to be triggered in order to cut off the current, so as to achieve the purpose of protecting the battery.

Table 2 shows that both Example 1 and Example 2 can be triggered, and the purpose of protecting the battery can be achieved; however, the comparative example cannot be triggered, and thus the purpose of protecting the battery cannot be achieved. In addition, the surface temperature of the shaft-shaped current protection element 20 triggered under the voltages of 6V, 12V and 16V (ie, in the overcurrent protection triggering state) is also shown in Table 2. Wherein, the surface temperature of the comparative example exceeds 100° C., which is at least 10° C. higher than that of the second example (the surface temperatures of the second example are all lower than 100° C.). Therefore, the overcurrent protection element in the second embodiment can be triggered at a lower temperature, and the response to temperature is faster than that in the comparative example, and the initial resistance (R _i ) is less than 0.010Ω due to the use of conductive ceramic powder.

Table II

The overcurrent protection element of the present invention, by adding a conductive filler with a specific particle size distribution and at least one crystalline polymer with a low melting point (below 115 ° C), the results in Table 2 show that the overcurrent protection of the present invention The protection element can indeed achieve the expected purpose of having excellent initial resistance value (R _i is less than 20mΩ), low temperature (80°C) rapid trigger protection function, withstand voltage characteristics and resistance reproducibility.

The technical content and technical features of the present invention have been disclosed above, but those skilled in the art may still make various substitutions and amendments based on the teaching and disclosure of the present invention without departing from the spirit of the present invention. Therefore, the protection scope of the present invention should not be limited to the contents disclosed in the embodiments, but should include various substitutions and modifications that do not depart from the present invention, and are covered by the above claims.

Claims (17)

1. An overcurrent protection element, characterized in that it comprises: two metal foils; and A PTC material layer, which is stacked between the two metal foils and has a volume resistance value of less than 0.1Ω-cm, comprising: (i) a plurality of crystalline polymers, including at least one crystalline polymer with a melting point lower than 115°C; (ii) an oxygen-free conductive ceramic powder, the particle size of which is between 0.1 μm and 10 μm, the volume resistance value is less than 500 μΩ-cm, and is dispersed in the crystalline polymer; and (iii) A non-conductive filler. 2. The overcurrent protection element according to claim 1, characterized in that the thickness of the PTC material layer is greater than 0.2mm. 3. The overcurrent protection element according to claim 1, characterized in that the initial resistance value of the PTC material layer is less than 20mΩ. 4 . The overcurrent protection element according to claim 1 , wherein the withstand voltage of the PTC material layer is less than or equal to 40 volts. 5. The overcurrent protection element according to claim 1, characterized in that the area of the PTC material layer is less than 50 mm ² . 6. The overcurrent protection element according to claim 1, characterized in that its surface temperature is lower than 100°C when the overcurrent protection is triggered. 7. The overcurrent protection element according to claim 1, characterized in that the resistance reproducibility ratio is less than 3. 8. The overcurrent protection element according to claim 1, characterized in that the oxygen-free conductive ceramic powder is titanium carbide. 9 . The overcurrent protection device according to claim 1 , wherein the crystalline polymer having a melting point lower than 115° C. is a low-density polyethylene. 10. The overcurrent protection element according to claim 9, characterized in that the low density polyethylene is polymerized by a catalyst. 11. The overcurrent protection device according to claim 1, wherein the non-conductive filler is an inorganic compound containing hydroxyl groups (OH). 12. The overcurrent protection element according to claim 11, characterized in that the inorganic compound is magnesium hydroxide. 13 . The overcurrent protection device according to claim 1 , wherein the two metal foils have bumpy rough surfaces and are in direct physical contact with the PTC material layer. 14 . 14 . The overcurrent protection device according to claim 1 , further comprising two metal electrode sheets, which are joined with the two metal foil sheets to form an assembly. 15. The overcurrent protection device according to claim 1, wherein the two metal foils can be connected to a power source to form a conductive loop. 16. The overcurrent protection device according to claim 14, wherein the two metal electrode pieces can be connected to a power source to form a conductive loop. 17. The overcurrent protection device according to claim 1, characterized in that the withstand current is less than or equal to 50 amperes.

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