Effect of Coupling Agent on the Performance of Positive Temperature Coefficient Polymer Materials

The phenomenon of the positive temperature coefficient of resistance (PTC) of the composite material formed by adding conductive carbon black to the polymer matrix as the matrix was first discovered by Frydman in 1945. In recent years, polymer PTC materials are widely used in the preparation of self-controlled temperature heating cables, over-current protection devices, and other temperature sensing devices. However, PTC conductive materials and devices have negative temperature coefficient (NTC) effect of resistance during use, and the resistance stability is poor, which seriously hinders its popularization and use.

In this paper, surface treatment of carbon black is performed by using different coupling agents to find a coupling agent that has a good dispersion effect on carbon black, so that the carbon black is uniformly dispersed and has a higher PTC strength and a smaller NTC strength, thereby improving Polymer PTC material properties. In addition, the effect of irradiation cross-linking on the properties of PTC materials was studied.

1 Experimental section 1.1 The basic system of raw materials is high-density polyethylene/carbon black (HDPE/CB). Among them, HDPE melt index MI is 0.90g/10min, density is 0.954g/cm3; carbon black is acetylene carbon black, particle size is 35~宄 center, professor, doctoral tutor.

Fund Project: Natural Science Foundation of Shaanxi Province (98C21).

45nm; DBP oil absorption value is 4.40cm3/g, specific surface area is 800m2/g; coupling agent 12, 3 and lubricant zinc stearate are industrial products, 12 is titanate coupling agent, 3 is silicone Coupling agents.

1.2 Sample preparation Weigh a certain amount of HDPE resin, carbon black and other auxiliaries according to the proportion, mix in a two-roll mill at a certain temperature, mix evenly, and put it into a special mold to cure the plate. The machine was heated and pressed to form a flat specimen with two parallel tinned copper strands. The distance between the two copper wires was 8.0 mm, the thickness of the specimen was 1 mm, and the length was cut as required.

The liquids, respectively, were mixed with 100 g of carbon black, ball milled for 4 h, the solvent was removed and dried, and samples were mixed with HDPE to prepare samples labeled 12 and 3 with 2 g of zinc stearate together with 100 g of carbon black not treated with a coupling agent, and HDPE open blending, the prepared sample was marked as 4 pairs of samples were cross-linked with 200kGyCo-Y irradiation to make a cross-linked sample.

1.3 Sample Test Place the prepared sample in an oven and use the two wires in the sample as electrodes, and lead the oven with a high-temperature wire. During the test, when each temperature point is stable for 20 minutes and the resistance is less than 2X107n, it is measured with a digital multimeter; when the resistance is greater than 2X and 107n, it is measured with a ZC36 ultra high resistance meter, and the measurement result is converted into volume resistivity.

In order to characterize the PTC effect, the ratio (Pmax/P25) of the volume resistivity peak Pmax and the room temperature (25 C) volume resistivity P25 on the volume resistivity P versus temperature T curve is generally defined as the PTC intensity. Here, the ratio (Pmax/Pl60) of the volume resistivity P60 at the volume resistivity peak Pmax to 160C is similarly defined as the NTC strength.

2 Results and discussion 2.1 Effects of coupling agents on the dispersibility of carbon black in composite systems PTC materials for HDPE/CB were prepared using carbon black treated with coupling agents 1, 2, and 3 and carbon black added with zinc stearate. The resistance-temperature curve of the sample is shown in Table 1. It can be seen that the room temperature volume resistivity, the maximum volume resistivity, and the volume resistivity at 160°C of the 3 samples are the largest, indicating that the coupling agent 3 pairs. Carbon black has the best dispersion effect, so that carbon black is uniformly dispersed in HDPE, and the volume resistivity of the sample is the largest. In addition, the use of zinc stearate as a lubricant also has a better dispersion effect, but the relative data of the non-cross-linked sample of the coupling agent is larger than that of the related sample, and the strength of the NTC of the 3 sample is small. It shows that the PTC material prepared from the carbon black treated by the coupling agent 3 has high PTC strength and small NTC strength. Special attention should be paid to the fact that the samples with zinc stearate also had PTC strength equivalent to that of the 1 to 3 samples, but the NTC strength was large.

For silicones, coupling agent 3 has the best high temperature resistance. Since the dispersion of the coupling agents 1 and 2 decreases at high temperatures, the dispersion effect is reduced. Coupling agent 3 is not affected by high temperature or has little effect. Therefore, the composite system of carbon black treated by coupling agent 3 has higher PTC strength, lower NTC strength, and best performance.

2.2 The effect of the coupling agent on the stability of the composite system The sample was subjected to three heating-cooling cycles. During the heating process, the volume resistivity was measured. The results of the test are shown in Table 3. The PTC materials prepared by these four methods can be found to be stable. The properties are good, but the stability of the coupling agent 3 at 20 ~ 120C is obviously worse than 1,2. Through analysis, 1, 2 is more polar than 3, so it has better stability to the dispersion of carbon black. At high temperatures, the dispersion effects of 1, 2 decrease, and 3 due to the high temperature resistance, so the dispersion effect changes little. In a word, the dispersion of 1,2 is better than 3 in the medium and low temperature, and worse than 3 in the high temperature; conversely, the dispersion of 3 is similar to the difference of 2 in the dispersion of the similar agent. Good at high temperatures.

Then the test was carried out and the results were seen. By ~ visible, the PTC intensity after composite irradiation was significantly increased compared to that before irradiation, and the NTC strength was significantly reduced. At high temperatures, PE softens, the movement of polymer segments increases, and the binding force to carbon black weakens, resulting in carbon black forming more conductive chains, lowering the resistivity of the sample, thereby reducing the PTC strength of the sample. Irradiation cross-linking limits the self-aggregation tendency of carbon black at high temperatures, and increases the volume resistivity at high temperatures, so that the PTC intensity of the sample after irradiation cross-linking increases and the NTC strength decreases. Irradiation cross-linking increases the volume resistivity of the sample at low to high temperatures, but the amplitude is not large.

2.3 The effect of irradiation cross-linking on the performance of the composite system 442V4 true benefits (3) Pang! Radiation exposure continuum, MshingHoufe: From 0, Table 2 shows that in the 1 to 4 samples after irradiation cross-linking, the PTC intensity of the 3 samples treated with the coupling agent 3 is the highest, close to 107, and the NTC strength is the smallest , less than 1005, overall performance over other specimens.

Table 21 4 Relevant data of cross-linked specimens Specimen 3 Conclusion Through the study, it was found that in the PTC materials prepared with the carbon blacks treated with the coupling agents 1, 2, and 3, the carbon black can be uniformly dispersed and has a good uniformity. Stability.

Since the polarity of the coupling agent 12 is stronger than 3, it has a good dispersion effect at a medium and low temperature, and 3 to 12 has a better high temperature resistance, so that the dispersion of the carbon black at a high temperature is better than 1 and 2.

(3) Through irradiation cross-linking, it was found that all of the 1 ~ 4 samples can increase their PTC strength and reduce their NTC strength, especially the 3 samples have the best improvement effect.

01-4 Cross-linked sample lgP-r curve Thanks to Professor Liu Fuyi's support for this subject, and the help of Cui Xiufang teacher and An Chunying teacher, thank you for this.