阅读说明：本技术 一种改善插件型pptc成品阻值下降的方法 (Method for improving resistance reduction of plug-in type PPTC (polyphenylene terephthalate) finished product ) 是由 胡元希 于 2021-08-18 设计创作，主要内容包括：本发明公开了一种改善插件型PPTC成品阻值下降的方法。即将包封好的产品放入密闭环境中,使所述密闭环境内的温度降温至90℃以下时保温至少5分钟,再从所述密闭环境中取出产品即可。该方法可以有效的替代冷热冲击或其它设备来降低或消除阻值下降的问题。(The invention discloses a method for improving the resistance reduction of a plug-in type PPTC finished product. Putting the encapsulated product into a closed environment, keeping the temperature for at least 5 minutes when the temperature in the closed environment is reduced to below 90 ℃, and taking out the product from the closed environment. The method can effectively replace cold and hot impact or other devices to reduce or eliminate the problem of resistance reduction.)

1. A method for improving the resistance reduction of an insert type PPTC finished product is characterized in that the encapsulated product is placed in a closed environment, the temperature in the closed environment is reduced to be below 90 ℃, the temperature is kept for at least 5 minutes, and then the product is taken out from the closed environment.

2. The method for improving the resistance drop of an insert-type PPTC finished product as claimed in claim 1, further comprising the step of removing said finished product from said closed environment and allowing said finished product to cool naturally.

3. The method for improving the resistance drop of the insert-type PPTC finished product as claimed in claim 2, wherein said product is naturally cooled at room temperature after being taken out.

4. The method for improving the resistance drop of the insert-type PPTC finished product as claimed in any one of claims 1 to 3, wherein the closed environment is a hot air circulation oven or a curing oven.

5. The method for improving the resistance drop of the insert-type PPTC product according to any one of claims 1 to 3, wherein the cooling rate in the closed environment is controlled within 0.8 ℃/Min.

6. The method for improving the resistance drop of the plug-in type PPTC finished product according to claim 5, wherein the cooling rate in the closed environment is controlled to be 0.4-0.8 ℃/Min.

7. A method for improving the resistance drop of an insert-type PPTC final product as claimed in any one of claims 1 to 3, wherein said at least 5 minutes means 5-10 minutes.

8. The method for improving the resistance drop of a finished insert-type PPTC according to any one of claims 1 to 3, wherein after the encapsulated product is placed in a closed environment, the closed environment is first heated to cure the product, and then the temperature in the closed environment is reduced to below 90 ℃.

9. The method for improving the resistance drop of the finished insert-type PPTC as claimed in claim 8, wherein the heating and cooling processes are performed in the same hot air circulation oven.

10. The method for improving the resistance drop of the finished insert-type PPTC as claimed in claim 8, wherein the temperature rise process is carried out in a tunnel oven, and the temperature drop process is carried out in a curing oven.

Technical Field

The invention relates to the field of polymer processes, in particular to a method for improving the resistance reduction of a plug-in type PPTC finished product.

Background

The polymer Positive Temperature Coefficient thermistor device (PPTC) is prepared by mixing polymer and conductive substance and assembling. At normal temperature, the conductor is dispersed in the polymer, and the conductor forms a conductive path in the polymer. Under the condition of normal current, the heat generated by the PPTC with low resistance value is less than the dissipated heat, so that the temperature of the polymer is lower than a certain value. When abnormal strong current passes through or the temperature of the external environment rises, the heat generated by the PPTC is larger than the dissipated heat, the temperature of the element rises due to the accumulation of the heat, when the temperature exceeds the softening temperature of the polymer, the polymer expands to disconnect the formed conductive channel, and the impedance of the element is rapidly increased, so that the protection circuit is realized.

In the actual production process, the general plug-in type PPTC is subjected to banburying granulation, film covering and core material forming, irradiation, die cutting to prepare chips, chip assembly, encapsulation, solidification, cold and hot impact, resistance test and packaging to complete the production from raw materials to finished products, wherein the processes involving high temperature include: banburying granulation, film covering and core material molding, chip assembly, encapsulation and curing. The curing is the last high-temperature process before the finished product is produced, and mainly comprises the following steps: and (3) putting the encapsulated material into an oven, curing for a set time, and opening a door after the curing time is up to take out the product for subsequent cold and hot impact. Because the polymer is in a molten state at high temperature, the product is cooled from high temperature to room temperature after baking and the cooling rate is different, so that a large amount of residual stress exists in the material, the residual stress is different, and meanwhile, because the conductive substance is frozen down without fully adjusting the state in the polymer, the produced conductive network is unstable, and the problem that the resistance value of the product is reduced along with the change of time (namely, relaxation effect) occurs. According to experimental research results, the resistance value is stable after 20-30 days, and the stable resistance value is reduced by about 9-14% on the basis of the original resistance value. It is now common practice to eliminate this effect by cold and hot shock. The cold and hot impact is adopted to increase the working procedures and the cost, and the time of the cold and hot impact is generally 2 to 8 hours, thereby increasing the production time of the product.

Disclosure of Invention

The invention aims to provide a method for effectively replacing cold and hot shock to reduce or eliminate the problem of resistance reduction.

In order to achieve the purpose, the invention provides a method for improving the resistance reduction of a finished product of an insert type PPTC, which comprises the steps of putting the encapsulated product into a closed environment, keeping the temperature for at least 5 minutes when the temperature in the closed environment is reduced to be below 90 ℃, and taking out the product from the closed environment.

Further, the method also comprises the step of taking the product out of the closed environment and naturally cooling the product; preferably, it is allowed to cool naturally at room temperature.

Further, the closed environment is a hot air circulation oven or a curing box.

Further, the cooling rate in the closed environment is controlled within 0.8 ℃/Min.

Further, the cooling rate in the closed environment is controlled to be 0.4-0.8 ℃/Min.

Further, the at least 5 minutes means 5 to 10 minutes.

Further, after the encapsulated product is placed in a closed environment, the closed environment is heated first, the product is solidified, and then the temperature in the closed environment is reduced to below 90 ℃.

Furthermore, the heating and cooling processes are carried out in the same hot air circulation oven.

Furthermore, the temperature rise process is carried out in a tunnel type oven, and the temperature reduction process is carried out in a curing box.

The invention provides a method for improving the reduction of the resistance of a finished product of an insert type PPTC (polyphenylene sulfide) product, which can replace cold and hot shock to solve the problem of the reduction of the resistance of the finished product of the insert type PPTC (polyphenylene sulfide) (see figure 1).

The invention adopts the closed environment to cool. The closed environment can be an independent hot air circulation oven or other closed equipment capable of adjusting the temperature and the cooling rate. The purpose of the closed environment is to eliminate the interference of room temperature or other temperatures so as to achieve relatively uniform cooling rates of all materials. The effect of equivalent cold and hot impact is achieved by combining the control of the cooling rate.

The cooling rate of the invention in the oven, such as a hot air circulation oven, is controlled at 0.8 ℃/Min, preferably 0.4-0.8 ℃/Min. The same effect can be produced when the temperature reduction rate is lower than 0.4 ℃/Min, but the time for producing the product can be greatly increased when the temperature reduction rate is lower than 0.4 ℃/Min, and the improvement on the reduction of the product resistance value is not greatly different from the set condition. The temperature decrease rate is higher than 0.8 ℃/Min, and the desired improvement cannot be achieved or the improvement effect is impaired. According to experimental data, when the cooling rate is 1.0 ℃/Min, the product shows that the resistance of the sample is increased (the comparison cooling rate is 0.8 ℃/Min), and the resistance is reduced by more than 3% after the product is placed for a period of time (more than 30 days) due to the high cooling rate.

The invention reduces the temperature to 90 ℃ and below 90 ℃ and keeps the temperature for at least 5 minutes, preferably 5 to 10 minutes. When the temperature is lower than 5 minutes, the product temperature cannot be guaranteed to be not higher than 90 ℃, unnecessary production time waste can be generated when the temperature exceeds 10 minutes, the product temperature can be fully guaranteed to meet the requirement in 5-10 minutes, the waste of the production time can be effectively avoided, and the production time is saved.

Compared with the method of cooling the product to below 90 ℃ and the product to 90 ℃, the method has little difference in improvement on the reduction of the resistance value of the product. The cooling to the temperature includes any temperature from room temperature to 90 ℃. Preferably 90 ℃, can effectively reduce the working time: the common cold and hot impact operation time is 2-8 hours, and the time for cooling the product to 90 ℃ by adopting the method of the invention is less than or equal to 2 hours.

And for the baked products with the baking temperature lower than 90 ℃, the temperature is reduced to room temperature in an independent hot air circulation oven, the door is opened, and the cooling rate is also controlled to be 0.4-0.8 ℃/min.

If the tunnel type drying oven is used, the temperature rising section, the baking section and the temperature reduction section of the tunnel type drying oven run at the same speed, and the baking time of the temperature rising section and the baking section can be influenced by adjusting the temperature reduction speed, so that the change of production parameters can be caused. The tunnel type oven is adjusted to achieve the effect. The specific embodiment is as follows: the baking time of the product can be divided, the tunnel type oven is used for primary baking for the first time, and then the closed curing box is used for secondary curing (the effect of two operations is equal to that of a hot air circulation oven). Although the operation mode of the tunnel type oven is different from that of the hot air circulation oven, a unified theoretical basis is adopted: the control of the cooling rate can be summarized as the same method. The effect of curing the epoxy resin encapsulating material of the product is achieved through secondary baking. And cooling the product to 90 ℃ after secondary curing, and controlling the cooling speed to be 0.4-0.8 ℃/Min. Although this invention results in splitting the baking operation into two operations, the overall operation time is not increased too much. Meanwhile, an independent hot air circulation oven or other similar closed equipment is added, but the cold and hot impact process is replaced by the invention. The improvement obtained is very clear.

Before cold and hot impact is not adopted, the resistance value of the product is reduced by 9-14 percent; the resistance value can be reduced to be within 3% by adopting a cold and hot impact mode; the resistance value can be reduced to be within 3% by adopting the invention. That is to say, the method of the invention can replace the cold and hot impact process to achieve the effect similar to the cold and hot impact.

The invention relates to a method for improving the stability of a product, which is characterized in that high-temperature and low-temperature extreme speed change (usually-20-110 ℃ or higher) is adopted in cold and hot impact, and the stress in the product caused by a high-temperature process is released through multiple times of high and low temperature impact to achieve the aim of stabilizing the product.

The method of the invention saves the cost: the invention can be simply transformed based on the existing curing equipment or added with a hot air circulation oven with the cost far lower than that of cold and hot impact equipment.

Drawings

Figure 1 is a schematic diagram of the production process of a PPTC plug-in product adopting the invention.

FIG. 2 is a graph of the temperature profile of the surface of a material during the curing of an epoxy resin using the method of the present invention.

FIG. 3 is a graphical representation of the temperature profile of the surface of a material during the curing of an epoxy resin using the method of the present invention.

Figure 4 is a schematic diagram of a general production flow of a PPTC insert type product.

FIG. 5 is a graph showing the results of the surface temperature profile of the material in the epoxy resin curing process of comparative example 1.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention. The examples do not specify particular techniques or conditions, and are performed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.

Example 1: preparation of plug-in type PPTC semi-finished product

S1: mixing 60 wt% of high-density polyethylene and 40 wt% of carbon black, adding the mixture into an internal mixer for internal mixing and plasticizing for 15-18 minutes, controlling the highest temperature of equipment to be not more than 280 ℃, and then adding the plasticized mixture into an extrusion granulator for granulation to prepare cylindrical particles with the diameter of 2.5mm and the length of 3-5 mm. The step is not only suitable for the raw material ratio of the product in the embodiment, but also suitable for the raw material ratio of any plug-in type PPTC.

And S2, extruding the formed granular material to form a film, rolling and coating the nickel-plated copper foil electrode to form a core material.

S3, the core material is punched into a Φ 0.4 disc using a 45T punch. This procedure is applicable not only to the product size in this example, but also to any insert type PPTC size.

S4, irradiating the core material with high-energy particle beams, wherein the irradiation dose is 100 KGY. After 50kgy of single side is completed, the material is irradiated in a reverse side.

S5, in this example, the core material was assembled using a tin-plated copper wire, and the core material and the copper wire were welded using a SnAgCu tin bar.

S6, in this embodiment, the encapsulation is performed by using an epoxy resin encapsulation material, and the encapsulation is performed by immersing the preheated product in powder for 2 times, and the rear end of the encapsulation device has a semi-curing process with a set value of about 100 degrees.

Example 2: resistance reduction of plug-in type PPTC finished product is improved

The semi-product from example 1 was cured with an epoxy encapsulant using a separate heated air circulation oven. Specifically, the semi-finished product obtained in example 1 is placed in a hot air circulation oven, the temperature of the oven is set to be 160 ℃, the temperature is raised to 160 ℃, the time is kept for 90 minutes (after the time of 90 minutes is over, the equipment stops heating, but the actual temperature in the oven can be read and displayed normally), the temperature of the oven is set to be 90 ℃, the temperature is lowered to 90 ℃, the temperature is kept for 5 minutes, the door is opened, the product is taken out, and then the plug-in type PPTC semi-finished product is obtained (see the flow chart of fig. 1).

Or a tunnel type oven is adopted, the temperature in the oven is raised to 160 ℃, the temperature is kept for 90 minutes, then the product is taken out from the oven and placed into a closed curing box, the temperature of the curing box is reduced to 90 ℃, the temperature is kept for 5 minutes, and the product is taken out from the curing box, so that the plug-in type PPTC semi-finished product is obtained.

And naturally cooling the plug-in type PPTC semi-finished product in a room temperature environment after being taken out. After cooling to room temperature for more than 2 hours, the resistance of the product was measured.

The resistance value measurement method is defined by UL-1434 or IEC-62319, and is measured by using a HIOKI 3541 resistance meter, and the meter is reset to zero before measurement. The measuring environment is carried out in an environment of 25 +/-3 ℃. Measuring 16ea sample resistance value data R_Initial. The sample was left at room temperature for 30 days, and the resistance R after 30 days was measured_{Finally, the product is processed}. The resistance value reduction proportion calculation formula is as follows: [ solution ] [ R ]_{Finally, the product is processed}-R_Initial)|/R_Initial100%. The results are shown in Table 1.

Table 1 data table of experimental results of example 2

During the test, the independent hot air circulation or the cooling rate of the curing box is controlled to be 0.4-0.8 ℃/Min. The results are shown in FIGS. 2 and 3. FIG. 2 is a graph of the temperature profile of the surface of a material during the curing of an epoxy resin using the method of the present invention. FIG. 3 is a graphical representation of the temperature profile of the surface of a material during the curing of an epoxy resin using the method of the present invention. FIG. 2 is a graph showing the results of the surface temperature curve of the epoxy resin cured product and the product of this embodiment, which is cooled to 90 ℃ at a temperature of 0.4-0.8 ℃/Min, with the abscissa representing time and the ordinate representing temperature. It can be seen that the temperature point 4 is lowered to 90 c, after which it is naturally cooled to room temperature. And part of the closed oven without temperature reduction rate control can control the temperature reduction rate through the condition air extraction rate. From fig. 2-3, it can be seen that the product is cooled in the closed hot air box after being baked, and the slope of the temperature curve of the product is slower (between the temperature point 2 and the temperature point 4), i.e. the cooling speed of the product is slow. The stress in the product caused by the high-temperature process is released through slow cooling so as to achieve the aim of stabilizing the product. Based on the fact that in the prior art, the product is always at a high temperature (90 ℃) in the cooling process, the product body expands, and the carbon black particles move slightly in the Brownian mode to overcome the constraint rearrangement of the high-density polyethylene in the molten or softened state of the high-density polyethylene, so that the conductive network is complete. This principle is described in chapter 8, section 4 of "polymer composite materials conducting electricity" of beam base. (Polymer composite material for electricity conduction, beam-based literature, Guangdong science and technology Press, 8.8.2019, 1 st edition, ISBN 978-7-5359-.

Example 3: resistance reduction of plug-in type PPTC finished product is improved

And (3) putting the semi-product obtained in the example 1 into a closed hot air circulation oven, controlling the cooling rate in the oven to be 0.4-0.8 ℃/Min, keeping the temperature for 8 minutes when the temperature in the oven is reduced to 70 ℃, and taking the product out of the oven to naturally cool the product at room temperature. After cooling to room temperature for more than 2 hours, the resistance of the product was measured.

Example 4: resistance reduction of plug-in type PPTC finished product is improved

And (2) putting the semi-product obtained in the example 1 into a closed hot air circulation oven, controlling the cooling rate in the oven to be 0.4-0.8 ℃/Min, keeping the temperature for 10 minutes when the temperature in the oven is reduced to 80 ℃, and taking the product out of the oven to naturally cool the product at room temperature. After cooling to room temperature for more than 2 hours, the resistance of the product was measured. Resistance measurement method and method reference example 2. The temperature of the product leaving the oven was below 90 ℃ and the stress had been fully released.

The data of the 16ea sample shows that the resistance value data R after 30 days is traced after the product is finished in example 4_{Finally, the product is processed}Comparison of resistance R_InitialThe decrease of the resistance value is controlled within 3 percent. The results are shown in Table 2.

Table 2 data table of experimental results of example 4

Comparative example 1: (prior art solution)

The semi-product from example 1 was cured with an epoxy encapsulant using a separate heated air circulation oven. The temperature of the equipment is set to be 160 ℃, and the equipment is kept for 90 minutes at 160 ℃. Then the material is subjected to cold and hot impact. The cold and hot impact enables the product to be released through the temperature conversion from low temperature of-20 ℃ to 110 ℃, and the specific implementation process is as follows:

1. the product is placed in a cold and hot impact test box at room temperature, and the temperature in the cold and hot impact test box is raised to 110 ℃.

2. The cold and hot impact test chamber is kept at the temperature of 110 ℃ for a certain time. This time is defined by the process and may vary from vendor to vendor.

3. The temperature in the cold-hot impact test box body is reduced from 110 ℃ to-20 ℃.

4. The cold-hot impact test box is kept at the temperature of minus 20 ℃ for a certain time. This time is defined by the process and may vary from vendor to vendor.

5. And when the temperature of the cold and hot impact test box rises to the room temperature, the cold and hot impact test box starts defrosting, and the product and the water vapor in the box body are removed. The temperature from room temperature to 110 ℃ to-20 ℃ and then to room temperature is called a cycle, different cycle numbers are defined according to the product resistance value and the product resistance value specification, and the cycle number is generally 1-6 cycles.

And obtaining the final product through a product cold and hot impact process. And measuring the resistance value of the product. FIG. 4 shows the steps of the comparative example. FIG. 5 is a graph showing the temperature profile of the surface of the material during the curing of the epoxy resin when this comparative example was used. Temperature test methods used: the temperature recorder is used for checking the temperature in the validity period by using a K-type temperature measuring line. And placing a temperature sensing head of the temperature sensing line on the surface of the sample, and fixing the temperature sensing line. The sample on which the temperature measuring wire is placed is baked together with the product. The sample surface temperature was read. It can be seen from fig. 5 that the product is cooled in the air (temperature point 2 to temperature point 3) after being baked, and has a large temperature difference with the baking temperature of 160 ℃ of the product due to the room temperature of about 25 ℃. When the hot product is in a room temperature environment, the heat of the product is diffused into the air at a high speed, and the temperature of the product is reduced at a high speed. The concrete characteristics are that the slope of the temperature curve of the product is large,i.e. the product is cooled quickly. The very rapid cooling results in incomplete release of stresses within the product due to the high temperature process. Stress is slowly released when a subsequent product is placed in the environment, and the release of the stress causes the constraint rearrangement of the high-density polyethylene, so that the conductive network is perfect, and the resistance value is gradually stable. Tracking resistance data R after 30 days_{Finally, the product is processed}The 25% sample will have a resistance value that drops more than 3% from R initially.

Comparative example 2: (the cooling rate is higher than 0.8 ℃/Min when the method is adopted)

And (2) putting the semi-product obtained in the example 1 into a closed hot air circulation oven, controlling the cooling rate in the oven to be 1.0 ℃/Min, keeping the temperature for 8 minutes when the temperature in the oven is reduced to 90 ℃, and taking out the product from the oven to naturally cool the product at room temperature. After cooling to room temperature for more than 2 hours, the resistance of the product was measured. Resistance measurement method and method reference example 2. Tracking resistance data R after 30 days_{Finally, the product is processed}Resistance ratio R of 25% sample_InitialThe reduction will exceed 3%. The results are shown in Table 3.

Table 3 data table of experimental results of comparative example 2

Comparative example 3: (the temperature after cooling is higher than 90 ℃ when the method is adopted.)

And (2) putting the semi-product obtained in the example 1 into a closed hot air circulation oven, controlling the cooling rate in the oven to be 0.6 ℃/Min, keeping the temperature for 8 minutes when the temperature in the oven is reduced to 100 ℃, and taking out the product from the oven to naturally cool the product at room temperature. After cooling to room temperature for more than 2 hours, the resistance of the product was measured. Resistance measurement method and method reference example 2. Tracking resistance data R after 30 days_{Finally, the product is processed}Resistance ratio R of 37.5% sample_InitialThe reduction will exceed 3%. The results are shown in Table 4.

Table 4 data table of experimental results of comparative example 3

Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made in the above embodiments by those of ordinary skill in the art without departing from the principle and spirit of the present invention.