Low-resistance thermistor and preparation process thereof

Abstract

The invention relates to the technical field of electronic components, in particular to a low-resistance thermistor and a preparation process thereof, and solves the problem of high resistance change rate of an existing resistor. The thermistor comprises the following components in percentage by weight: 0.1-2.2% of carbon nanotubes, 5.5-12.8% of a polymer matrix and 86.2-94.2% of tungsten carbide particles; at least 30% of the carbon nanotubes also serve as positioning carbon tubes for positioning the tungsten carbide particles, each positioning carbon tube is provided with an adhesion section in contact with the tungsten carbide particles and an embedding section embedded in the polymer matrix, and the preparation process comprises the following steps: a, soaking the carbon nanotubes in a water-based dispersant to form slurry, performing ball-milling and mixing on the slurry and the tungsten carbide particles to obtain a mixture; drying in a drying oven at 120 DEG C to obtain a powder mixture; b, adding the powder mixture and a polymer matrix into an internal mixer, and plastifying at 180 DEG C for 5-10 minutes to form a dispersed mixture; and c, putting the dispersed mixture into an open mill, and extruding the thermistor sheet.

Description

Technical Field

[0001] The invention relates to the technical field of electronic components, in particular to a low-resistance thermistor and a preparation process thereof. Background Art

[0002] In terms of performance, thermistors must first maintain extremely low resistance during normal operation to reduce circuit losses. Second, they must maintain such resistance as much as possible after long-term use to ensure the working stability of the circuit. For example, in the control circuit of new energy vehicles, the electrical performance requirements for thermistors are particularly prominent. Although existing thermistors have achieved low resistance by changing and / or adding conductive fillers, the resistance of the resistors will change during normal operation after long-term hot and cold shocks, and the change range can be as high as 25%, which is equivalent to a decrease in the accuracy of the component, which will eventually lead to a decrease in the control accuracy of the circuit. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a low-resistance thermistor and a preparation process thereof, so that the resistor has a lower resistance change rate and ensures the low resistance and high precision of the resistor.

[0004] The technical solution adopted by the present invention to solve the technical problem is: a low-resistance thermistor, which includes 0.1-2.2% carbon nanotubes, 5.5-12.8% polymer matrix and 86.2-94.2% tungsten carbide particles in a weight ratio; the carbon nanotubes are conductive fillers, at least 30% of the carbon nanotubes also serve as positioning carbon tubes for positioning the tungsten carbide particles, and the positioning carbon tubes have an adhesion section contacting the surface of the tungsten carbide particles and an embedding section embedded in the polymer matrix.

[0005] Specifically, the polymer matrix is ​​polyethylene, such as high-density polyethylene (HDPE).

[0006] Specifically, since the conductivity of tungsten metal powder is 106-110% of tungsten carbide, the resistivity will be lower if tungsten powder is added, but tungsten metal powder itself is easy to oxidize, so the thermistor only includes 0.1-3% by weight of tungsten metal particles.

[0007] Specifically, in order to prevent oxidation of the conductive metal material, the thermistor further includes an antioxidant at a weight ratio of 0.05-1%, such as antioxidant 168 or antioxidant 1010 .

[0008] Specifically, the outer diameter of the carbon nanotube is 1-20 nm, and the carbon nanotube is a single-walled carbon tube or a multi-walled carbon tube.

[0009] The above low resistance thermistor has the following preparation process:

[0010] a. Take 0.1-2.2% carbon nanotubes, 5.5-12.8% polymer matrix and 86.2-94.2% tungsten carbide particles by weight, soak the carbon nanotubes in an aqueous dispersant to form a carbon nanotube slurry, ball-mill the carbon nanotube slurry and tungsten carbide particles, and dry them in an oven at 120°C ± 5°C to form a powder mixture;

[0011] b. Add the powder mixture and the polymer matrix into an internal mixer and plasticize and disperse them at 180°C ± 5°C for 5-10 minutes to form a dispersed mixture;

[0012] c. Put the dispersed mixture into an open mill and extrude thermistor sheets of designed thickness using roller pressure.

[0013] The subsequent process from sheet to finished product is:

[0014] d. Covering the sheet with electrodes on both sides at 180°C ± 5°C using a hot and cold integrated press to produce a semi-finished product;

[0015] e. Processing the semi-finished product into components with positive temperature coefficient function by circuit processing, and then cutting it into finished thermistor monomers.

[0016] Specifically, the polymer matrix in step a is polyethylene.

[0017] Specifically, step a further comprises 0.1-3% by weight of tungsten metal particles, and the tungsten metal particles are ball-milled and mixed with the carbon nanotube slurry and tungsten carbide particles, and then placed in an oven at 120°C±5°C for drying to form a powder mixture.

[0018] Specifically, step a further comprises 0.05-1% by weight of an antioxidant, and the antioxidant is mixed with the carbon nanotube slurry and tungsten carbide particles by ball milling, and then placed in an oven at 120°C±5°C for drying to form a powder mixture.

[0019] Specifically, in step a, the outer diameter of the carbon nanotubes is 1-20 nm.

[0020] The mechanism of the present invention is: by analyzing the reasons why the resistance value of the existing thermistor changes after long-term hot and cold shock, since the metal powder in the resistor material is an inorganic material, the particle size is generally in the micron level, and the crystalline high molecular polymer is an organic material, the two are molecularly combined after being fused, but with the long-term use of the product, the organic material ages and deforms, and the conductive powder particles are displaced, that is, the microscopic structure inside the resistor changes, which leads to changes in the resistance value and reduces the precision of the resistor. The present invention utilizes the metallic and semiconductor properties of carbon nanotubes due to the curling of graphene sheets, and the outer diameter of the carbon nanotubes is nanometer-level and the length is micrometer-level, and adds a small amount of carbon nanotubes to reduce the resistance value. At the same time, the carbon nanotubes can be positioned on the conductive powder particles. However, considering that carbon nanotubes are easily agglomerated due to their hydrophobicity, the carbon nanotubes are first attached to the surface of tungsten carbide through premixing, the dispersion of the carbon nanotubes is increased and their agglomeration is reduced. During the mixing, the temperature and time are precisely controlled to prevent the carbon nanotubes originally attached to the surface of the tungsten carbide particles from being completely reintegrated into the polymer matrix. Of course, another technical path, while considering the electrical properties, is to use a suitable adhesive to appropriately increase the binding force between the carbon nanotubes and the tungsten carbide particles when ball-milling the carbon nanotube slurry and the tungsten carbide particles. This is also a direction that can be studied and implemented.

[0021] The beneficial effects of the present invention are as follows: the low-resistance thermistor of the present invention uses carbon nanotubes and tungsten carbide particles to make the thermistor have an extremely low resistance value, and also allows part of the carbon nanotubes to form a traction position for the tungsten carbide particles. After long-term use, even if the polymer material of the thermistor ages and deforms, it does not affect the relative positions of the tungsten carbide particles, and significantly reduces the resistance change rate of the thermistor after long-term use. The measured resistance change rate of 6.06% is compared with the original 23.33%, and the resistance change rate is reduced to less than one third of the original. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention is further described below in conjunction with the accompanying drawings and implementation modes.

[0023] Figure 1 This is a morphology diagram of carbon nanotubes observed under a microscope;

[0024] Figure 2 This is a morphology diagram of tungsten carbide particles observed under a microscope;

[0025] Figure 3 This is a morphology of a powder mixture formed by ball-milling, mixing and drying carbon nanotube slurry and tungsten carbide particles observed under a microscope;

[0026] Figure 4 This is a partial morphology of the cross section of the extruded sheet observed under a microscope. DETAILED DESCRIPTION

[0027] The present invention will now be described in further detail with reference to the accompanying drawings and preferred embodiments.

[0028] The first is a low-resistance thermistor, which refers to a thermistor chip. The thermistor includes carbon nanotubes, a polymer matrix and tungsten carbide particles. The carbon nanotubes are conductive fillers, and at least 30% of the carbon nanotubes also serve as positioning carbon tubes for positioning the tungsten carbide particles. The positioning carbon tubes have an adhesion section in contact with the surface of the tungsten carbide particles and an embedding section embedded in the polymer matrix. The specific 8 implementation methods and the relative 3 comparative implementation methods are shown in Table 1 below.

[0029] Table 1: Volume resistivity, double 85 (168H) resistivity and resistance change rate of the thermistor group measured in 8 embodiments of the thermistor of the present invention

[0030]

[0031] In Table 1: the method for determining the volume resistivity is to slice the resistor chip material with an area of ​​3*3mm and a thickness of 0.2mm, and calculate the volume resistivity according to the measured resistance value*area / thickness; the method for determining the double 85 (168H) resistivity is to store the product in a constant temperature and humidity chamber at 85°C and 85%RH for 168 hours, and then place it at room temperature for 2 hours to measure the volume resistivity, and the method for calculating the resistance change rate is resistance change rate = [double 85 (168H) resistivity / volume resistivity-1]*100%.

[0032] In Table 1: the amount of HDPE, comparative examples 1 and 2 cannot be bonded and formed because of their too little amount, and the amount of HDPE in the other examples is the minimum amount to ensure that the product can be bonded and formed, and the powder cannot be formed if it is lower than this minimum value.

[0033] Table 1 firstly illustrates that although the amount of carbon nanotubes is small, the effect on the resistance change rate is significant. For example, the resistance change rate of comparative example 3 without using carbon nanotubes is 23.33%, while the resistance change rate is greatly reduced to 9.38% when using 0.3% by weight of carbon nanotubes; secondly, it illustrates that the change in the amount of carbon nanotubes also has a significant effect on the resistance change rate. For example, the resistance change rate of Example 2 using 0.5% by weight of carbon nanotubes is 6.06%, while the resistance change rate of Example 5 using 1% by weight of carbon nanotubes is greatly increased to 14.08%; thirdly, it illustrates that the amount of carbon nanotubes should be appropriate. When comparing Example 1 with Example 2, Example 1 has a small amount, its positioning effect is reduced, and the resistance change rate will increase. However, when the amount is greater than 1%, more HDPE is required for wrapping, which will increase the resistance value of the resistor. Here, the requirement for ultra-low resistance is less than 0.4Ω.cm.

[0034] In addition, the volume resistivity of Comparative Example 3 in Table 1 which does not use carbon nanotubes is 0.030Ω.cm, which is lower than the volume resistivity of Example 1 which uses 0.3% carbon nanotubes, which is 0.032Ω.cm. This is because the resistivity of carbon nanotubes is twice that of tungsten carbide, so the resistance of the batch with added carbon nanotubes will be higher.

[0035] In summary, the data in Table 1 reflect two meanings. One is that a lower volume resistivity can be obtained by using tungsten carbide. The other is that a lower resistance change rate is obtained by using carbon nanotubes that also have the function of positioning tungsten carbide particles.

[0036] The fact that tungsten carbide can achieve a lower volume resistivity can also be verified by the following Table 2, which compares the volume resistivity of tungsten carbide with that of several other common conductive particles. Of course, HDPE is still the minimum amount required to ensure molding.

[0037] Table 2: Comparison of volume resistivity of tungsten carbide particles and other conductive particles

[0038]

[0039] Table 2 illustrates that tungsten carbide can achieve extremely low volume resistivity.

[0040] In view of reducing the resistance of the thermistor, the present invention can also add tungsten metal particles, because the conductivity of tungsten metal powder is 106-110% of tungsten carbide, and the volume resistivity of tungsten powder is lower. However, tungsten metal powder itself is easily oxidized, and the oxidized tungsten metal powder has an adverse effect on the volume resistivity and the resistance change rate. Therefore, the amount of tungsten powder still needs to be verified. The verification results are shown in Table 3 below.

[0041] Table 3: Tungsten powder dosage verification table

[0042]

[0043] Table 3 shows that the use of tungsten powder will affect the volume resistivity and resistance change rate, and the use of 2.0% by weight tungsten metal powder has a better effect.

[0044] The thermistor of the present invention may also include an antioxidant 168 at a weight ratio of 0.05-1% to reduce oxidation of the conductive material. The amount of antioxidant used depends on the amount of tungsten metal powder used. The more tungsten metal powder is used, the more antioxidant 168 is used.

[0045] The carbon nanotubes of the present invention may have an outer diameter of 1-20 nm.

[0046] Secondly, the implementation method of the low-resistance thermistor preparation process. The specific implementation method of the low-resistance thermistor product mentioned above has explained the selection of components and dosages when the product is implemented. In order to avoid repetition of content, only three examples are listed for illustration of the specific method of the process.

[0047] Embodiment 1:

[0048] The preparation process is as follows:

[0049] a. Take 0.1% carbon nanotubes, 12.8% HDPE, 0.1% tungsten metal particles and 87% tungsten carbide particles by weight, soak the carbon nanotubes in an aqueous dispersant to form a carbon nanotube slurry, ball-mill the carbon nanotube slurry, tungsten metal particles and tungsten carbide particles, and dry them in an oven at 120°C ± 5°C to form a powder mixture; Figure 1 is a morphology diagram of carbon nanotubes, attached Figure 2 is the morphology of tungsten carbide particles, attached Figure 3 is the morphology diagram of the powder mixture;

[0050] The water-based dispersant used to immerse the carbon nanotubes is a commercially available product, produced by Jiangsu Xianfeng Nanomaterial Technology Co., Ltd. and Jiaxing Gaozheng Polymer Materials Co., Ltd. The water-based dispersant evaporates during subsequent drying.

[0051] b. Add the powder mixture and HDPE into an internal mixer and plasticize and disperse at 180°C ± 5°C for 5-10 minutes to form a dispersed mixture;

[0052] c. Put the dispersed mixture into an open mill and use roller pressure to extrude thermistor sheets of designed thickness. Figure 4 It is the morphological diagram of the cross section of the sheet;

[0053] d. Covering the thermistor sheet with electrodes on both sides to make a semi-finished product;

[0054] e. Processing the semi-finished product into components with positive temperature coefficient function by circuit processing, and then cutting it into finished thermistor monomers.

[0055] Embodiment 2:

[0056] The preparation process is as follows:

[0057] a. Take 0.25% carbon nanotubes, 5.5% HDPE, 0.05% antioxidant 168 and 94.2% tungsten carbide particles by weight, soak the carbon nanotubes in an aqueous dispersant to form a carbon nanotube slurry, ball-mill the carbon nanotube slurry, antioxidant 168 and tungsten carbide particles, and dry them in an oven at 120°C ± 5°C to form a powder mixture;

[0058] b. Add the powder mixture and HDPE into an internal mixer and plasticize and disperse at 180°C ± 5°C for 5-10 minutes to form a dispersed mixture;

[0059] c. putting the dispersed mixture into an open mill and using roller pressure to extrude thermistor sheets of designed thickness;

[0060] d. Covering the sheet with electrodes on both sides at 180°C ± 5°C using a hot and cold integrated press to produce a semi-finished product;

[0061] e. Processing the semi-finished product into components with positive temperature coefficient function by circuit processing, and then cutting it into finished thermistor monomers.

[0062] Embodiment three:

[0063] The preparation process is as follows:

[0064] a. Take 2.2% carbon nanotubes, 7.6% HDPE, 3% tungsten metal particles, 1% antioxidant 168 and 86.2% tungsten carbide particles by weight, soak the carbon nanotubes in an aqueous dispersant to form a carbon nanotube slurry, ball-mill the carbon nanotube slurry, tungsten metal particles, antioxidant 168 and tungsten carbide particles, and dry them in an oven at 120°C±5°C to form a powder mixture;

[0065] b. Add the powder mixture and HDPE into an internal mixer and plasticize and disperse at 180°C ± 5°C for 5-10 minutes to form a dispersed mixture;

[0066] c. putting the dispersed mixture into an open mill and using roller pressure to extrude thermistor sheets of designed thickness;

[0067] d. Covering the sheet with electrodes on both sides at 180°C ± 5°C using a hot and cold integrated press to produce a semi-finished product;

[0068] e. Processing the semi-finished product into components with PTC function by circuit processing, and then cutting it into finished thermistor monomers.

[0069] The above description only describes the specific implementation mode of the present invention. Various examples do not limit the essential content of the present invention. After reading the description, ordinary technicians in the relevant technical field can modify or deform the specific implementation modes described above without departing from the essence and scope of the invention.

Claims

1. A low resistance thermistor, characterized in that: The thermistor comprises 0.1-2.2% carbon nanotubes, 5.5-12.8% polymer matrix and 86.2-94.2% tungsten carbide particles in a weight ratio; the carbon nanotubes are conductive fillers, and at least 30% of the carbon nanotubes also serve as positioning carbon tubes for positioning the tungsten carbide particles, and the positioning carbon tubes have an adhesion section in contact with the surface of the tungsten carbide particles and an embedding section embedded in the polymer matrix.

2. The low-resistance thermistor according to claim 1, characterized in that: The polymer matrix is ​​polyethylene.

3. The low-resistance thermistor according to claim 1, characterized in that: The thermistor further comprises 0.1-3% by weight of tungsten metal particles.

4. The low-resistance thermistor according to claim 1, characterized in that: The thermistor further comprises an antioxidant in an amount of 0.05-1% by weight.

5. The low-resistance thermistor according to claim 1, characterized in that: The outer diameter of the carbon nanotube is 1-20 nm.

6. The process for preparing a low-resistance thermistor according to claim 1, characterized in that: The preparation process is as follows: a. Take 0.1-2.2% carbon nanotubes, 5.5-12.8% polymer matrix and 86.2-94.2% tungsten carbide particles by weight, soak the carbon nanotubes in an aqueous dispersant to form a carbon nanotube slurry, ball-mill the carbon nanotube slurry and tungsten carbide particles, and dry them in an oven at 120°C ± 5°C to form a powder mixture; b. Add the powder mixture and the polymer matrix into an internal mixer and plasticize and disperse them at 180°C ± 5°C for 5-10 minutes to form a dispersed mixture; c. Put the dispersed mixture into an open mill and extrude thermistor sheets of designed thickness using roller pressure.

7. The process for preparing a low-resistance thermistor according to claim 6, characterized in that: The polymer matrix in step a is polyethylene.

8. The process for preparing a low-resistance thermistor according to claim 6, characterized in that: Step a also includes 0.1-3% by weight of tungsten metal particles, and the tungsten metal particles are ball-milled with the carbon nanotube slurry and tungsten carbide particles, and then placed in an oven at 120°C ± 5°C for drying to form a powder mixture.

9. The process for preparing a low-resistance thermistor according to claim 6, characterized in that: Step a also includes 0.05-1% by weight of an antioxidant, and the antioxidant is mixed with the carbon nanotube slurry and tungsten carbide particles by ball milling, and then placed in an oven at 120°C±5°C for drying to form a powder mixture.

10. The process for preparing a low-resistance thermistor according to claim 6, characterized in that: In step a, the outer diameter of the carbon nanotube is 1-20 nm.

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