Application Research of the hottest antistatic PC

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Research on the application of antistatic PC

I. overview the high electrical insulation (volume resistivity can be as high as 10 to the 16th power) of PC materials is easy to generate static electricity in the process of transportation, storage, packaging and so on, which limits its application in coal mines, oil fields, oil processing and other fields and other flammable fields. By studying the influence of various antistatic agents on the antistatic properties of PC materials, the author emphatically analyzes the antistatic mechanism and antistatic properties of antistatic PC materials made of conductive carbon black and conductive fiber as antistatic agents. Finally, with the conductive fiber with high conductivity as antistatic agent, using the melt impregnation extrusion process, a specially designed extrusion die is installed on the ordinary extruder, By optimizing the injection molding process parameters and controlling the dispersion degree and aspect ratio of conductive fibers, the antistatic PC material developed can not only have good mechanical properties, but also be endowed with excellent antistatic properties, and its volume resistivity reaches the 6th power Ω of lxlo? cm。

II. Test part

1. Raw material

pc: 141r type, GE company

1 # sample: antistatic agent, atmerl22, ICI company

2 # sample: Antistatic masterbatch. Guangzhou synthetic daily chemical company

3 sample: conductive carbon black, Linzi Huaguang carbon black factory

4 # sample: conductive fiber, commercially available

other additives: commercially available

2. Main equipment and instruments

electrostatic tester: 6517 electrometer, jishili company of the United States

twin screw extruder: TSE 27, leistritz company

scanning electron microscope (SEM): quanta 200, Fei company of the United States

injection molding machine: ba950/500, Battenfield, Austria

electric blast drying oven: wmk-08 type, Shandong electric heating instrument factory

universal testing machine: British instmn company

impact testing machine: xcj-22, xcj-40, Chengde testing machine factory

3. Antistatic PC extrusion process and sample preparation

antistatic PC extrusion process is shown in Figure 1

Figure 1: Antistatic extrusion process flow chart

4. Sex 2. Tensile testing machine. The installation of the testing machine is not level: the mixing level can be tested

antistatic performance is measured by the volume resistivity of the material. The test is carried out according to CB/T 1410-1989. The sample size is a disc with a diameter equal to 10cm and a thickness of 2-3.5mm. See Table 1 for the sample preparation process

the bending strength is tested according to CB/T 9341-2000, the notch impact strength is tested according to GB/T 1043-i993, the sample preparation and size are the same as the bending strength, the tensile strength is tested according to CB/T 1040-1992, and the sample size is type I sample

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III. results and discussion

1. Antistatic mechanical analysis

weigh 1 ~ 3 antistatic agents of the same quality and mix them with the baked PC material respectively, and then blend, extrude and granulate them on the twin-screw extruder. Using the melt impregnation extrusion process, the conductive fibers are introduced at the special die of the twin-screw extruder. By controlling the traction speed and the cutting speed, The length diameter ratio of the conductive fiber in the PC granular towel is controlled to be 500-1000, and the content of the conductive fiber is equivalent to the content of the above three antistatic agents. The sample is tested according to gb/t1410-1989 standard, and the test results are shown in Table 3

as shown in Table 3, among several antistatic agents added to PC materials, conductive fibers have the best antistatic performance

According to the seepage theory; The conductivity of conductive composites consists of three conditions: (a) conductive particles contact each other to form a continuous chain structure. Forming conductive channels; (b) Each conductive particle is independently dispersed in the matrix, and a conductive channel is formed through tunneling effect or electron emission; (c) The intermittent connection of conductive particles is the comprehensive result of chain channel and tunnel effect

the antistatic PC developed by melt impregnation extrusion process has excellent antistatic performance, mainly because the conductive fiber is not sheared by the extruder, and after impregnation and granulation by a special die, the fiber retains a large aspect ratio. It is easy to make conductive fibers lap and wind each other in PC composites to form conductive networks. Obviously, this is the same as the situation described by condition a in percolation theory. The conductive mechanism of conductive carbon black is similar to condition B in percolation theory. In order to achieve the same antistatic property, the spacing of carbon black particles must be reduced and the addition ratio must be greatly increased, but the extrusion process and mechanical properties of PC materials will be greatly affected. The antistatic and mechanical properties of PC materials with different proportions of conductive carbon black are shown in Table 4

as shown in Table 4, when the conductive carbon black is added to 8% to 10%, the volume resistivity of antistatic PC material decreases rapidly, indicating that its percolation threshold is around 8%, while the antistatic PC made of conductive carbon black as antistatic agent, if you want to get better antistatic performance, its originally very excellent impact performance is reduced a lot, only 1/6 of the original resin, and the added PC composite has poor extrusion processability Single material color and other defects

2. The influence of extrusion method on the antistatic property of PC materials

using conductive fiber as antistatic agent, melt impregnation extrusion method (continuous conductive fiber is introduced from the extruder to our customer's special die) and traditional extrusion method (continuous conductive fiber is introduced from the glass fiber inlet of the extruder) are adopted respectively. By adjusting the screw speed of the extruder host, the rotating speed of the feeding screw, the traction speed of conductive fiber and the rotating speed of the pelletizer, To ensure that the addition amount of conductive fiber is the same, the processing process is shown in Figure 1, and the test results are shown in Table 5. Figure 2 and figure 3 are SEM photos of the dispersion of conductive fibers after combustion of the samples injected by two extrusion methods. The length and distribution of conductive fibers can be roughly observed

it can be seen from table 5, figure 2 and figure 3 that the antistatic properties of PC materials are greatly affected by different extrusion methods for conductive fibers with the same amount of addition. PC materials produced by melt impregnation extrusion have excellent antistatic properties, and the retention rate of fiber length in the sample is very high, between 4-7 mm, and they are intertwined and connected with each other. Under the traditional extrusion method, PC samples after granulation and injection have no conductivity: the volume resistivity is the same order of magnitude as the pure resin without conductive fibers. This is mainly because after the conductive fibers are sheared and dispersed by the screw, the fiber length diameter ratio is greatly reduced. It can be seen from Figure 3 that the conductive fibers are kept between 0.1-2mm. They are coated and blocked by PC resin, and their conductive conditions have changed, from condition a described by the percolation theory to condition B. When voltage is applied, the spacing of conductive fibers far exceeds the critical distance of tunneling effect in tunnel transition theory, so PC materials still show insulation characteristics

3. Effect of the amount of antistatic agent added on the antistatic properties of PC materials

the content of conductive fibers was controlled to 1%, 3% and 5% respectively by melt impregnation extrusion,. The influence of its content on the antistatic property of PC material is analyzed. See Table 6 for antistatic performance

from table 6, it can be seen that the antistatic property of PC materials with conductive fibers has no linear relationship with the content of conductive fibers. After the content of conductive fibers increases from 1% to 5%, the volume resistivity of PC materials changes little, and it is in a relatively stable fluctuation state. It can be considered that the percolation threshold in this material system is 1% or less. It shows that the length diameter ratio of conductive fibers can be maintained to the greatest extent by melt impregnation extrusion, and conductive paths can be formed in PC materials with only a small amount of additives. Good antistatic performance is obtained, and the color diversity requirements of the material are guaranteed at the same time

4. The injection molding process also has a prominent impact on the structural contradiction between the product appearance and the anti simultaneous experimental machine product

the injection molding process has a great impact on the product appearance and anti-static performance of this antistatic PC material, which is made by melt impregnation extrusion with conductive fiber as the antistatic agent. Since the conductive fibers are bundled and uniformly wrapped in PC materials, how to adjust the process parameters such as the barrel temperature, screw speed, injection rate and injection pressure of the injection molding machine, so that the PC pellets containing the bundled conductive fibers can be evenly impregnated and dispersed in the barrel, and finally the bundled conductive fibers can be evenly dispersed throughout the sample, so that they form a like structure in the sample or product and avoid their clustering in the sample, Affect the appearance quality of products; Secondly, while ensuring the dispersion efficiency, it is necessary to minimize the damage of conductive fibers, improve the fiber length retention rate, and finally improve the antistatic performance of injection molded products

after repeated trial and error, according to the characteristics of PC material, the author adopts the setting of decreasing temperature from the rear section of the barrel to the front section to reduce the screw pre molding rate, and uses the injection molding process of medium speed and medium pressure to obtain better product appearance and electrostatic performance. Table 7 shows the effects of different injection molding processes on the antistatic properties of PC materials

as shown in Table 7, the ordinary injection process has a poor dispersion effect on the conductive fibers in the PC material system. There is a phenomenon of bunched fiber agglomeration on the surface of the sample, which inhibits the dispersion and expansion of the conductive networks in the material, so the volume resistivity of the material is large. Using the optimized injection molding process, PC material begins to melt in the rear section of the barrel, making the conductive fiber soft, reducing the rigid friction and shear with the screw. At the same time, the low pre molding rate reduces the shear of the conductive fiber in the barrel, prolongs the impregnation and dispersion time, and the medium pressure and medium speed can ensure that PC material can smoothly fill the cavity and reduce the shear of the conductive fiber at the injection nozzle and mold gate. The test results show that the optimized injection molding process can meet the antistatic performance and product appearance quality

5. Main performance and application of antistatic PC

the author uses conductive fiber as antistatic agent, and uses melt impregnation and extrusion process to develop antistatic PC material, which has been applied on the shell of electronic detector. Various performance indexes of antistatic PC material meet its use requirements. See Table 8 for the main performance indexes of antistatic PC material

IV. conclusion

(1) the conductive fiber system shows that the prosperity of the paper industry continues to be depressed in 2019. As an antistatic material, processing equipment and molding technology have an important impact on the antistatic performance of the material

(2) conductive fiber is an excellent antistatic material. Under the condition of maintaining a high aspect ratio, adding a small amount can produce a very good antistatic effect, and the volume resistivity of the material can reach 1 × 10 to the 6th power ω cm, which has been applied to the shell of an electronic detector

reprinted from: plastic industry

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