PVC Cable Formulation Technology And Its Application

PVC Cable Formulation Technology And Its Application

I. Introduction of PVC cable

PVC cable material is based on polyvinyl chloride as the base resin, add stabilizers, dioctyl phthalate, diisodecyl phthalate, dioctyl terephthalate, trioctyl trimellitate and other plasticizers, as well as inorganic fillers such as calcium carbonate, additives and lubricants and other additives, after the mixing and kneading of extrusion and the preparation of particles.

II. PVC cable formulation

III. Analysis of experimental results

Traditional PVC stabilizers contain lead and other heavy metals, although the performance is good but not environmentally friendly, so it is necessary to replace the traditional heavy metal stabilizers with environmentally friendly stabilizers, the current more research and wider application of calcium / zinc composite stabilizers.

Yinsu technicians after a series of studies, with domestic calcium / zinc stabilizers, with the appropriate temperature level of plasticizer, respectively, 70,90,105 ℃ of the environmental protection of PVC sheathing materials, environmental requirements in line with the RoHS regulations, the performance of the performance can meet the requirements of GB/T 8815-2002.

3.1 PVC resin selection

Selection of suitable PVC resin is a crucial step in the design of PVC insulating material formulations with good processing performance and the production of good performance of the cable.The higher the molecular weight of PVC, the higher the tensile strength, impact strength, modulus of elasticity of the product, but the melt fluidity and plasticity decreased, the better the heat and cold resistance, the higher the processing temperature. Tests found that the use of polyvinyl chloride resin with a degree of polymerization of about 1300 is more suitable (i.e., SG-3 type resin).

3.2 Selection of plasticizers

The main role of the plasticizer is to reduce the melt temperature and melt viscosity of the polymer, which in turn reduces the processing temperature of the polymer, giving the polymer products to the softness and low temperature resistance. Through the formulation test, it is found that the volume resistivity of environmentally friendly 70PVCC insulating material at 20 and working temperature is difficult to meet the standard requirements. Therefore, to make the insulating material heat loss and elongation at break and volume resistivity at the same time to meet the standard requirements is the key to the development of the formulation.

PVC resin has good insulating properties, the addition of plasticizers will reduce the insulating properties. Selection of good electrical properties, good thermal stability, volatility is relatively small, good plasticizing effect of plasticizers in order to make the insulating material has a better electrical insulation properties and physical and mechanical properties. Environmentally friendly PVC insulating materials in the more commonly used plasticizers are: dioctyl phthalate vinegar (DOP), dinonyl phthalate vinegar (DINP), diisodecyl phthalate vinegar (DIDP), diisodecyl phthalate vinegar (DUP), bis(tridecyl) phthalate (DTDP), dioctyl phthalate vinegar (DOTP), trimellitate trioctyl (TOTM), and so on.

Picture 1 shows that the volatility and heat resistance of plasticizers in the following order: TOTM > DTDP > DUP > DIDP > DINP > DOTP > DOP o. DOP has excellent overall performance, high plasticizing efficiency, volatility is small, good cold resistance and electrical properties, it is the ideal main plasticizer. But DOP alone is difficult to meet the requirements of electrical insulation properties of insulating materials, DOTP and DOP performance is similar, but cold resistance, thermal stability and electrical insulation are better than DOP (about 18 times higher than DOP). Therefore, DOP and DOTP plasticizers need to be used in conjunction to obtain the required performance of the insulating material.

Picture 1 Thermal weight loss of insulating materials containing different plasticizers

If the volatility of plastic is small, the heat loss of the product will be less, and its aging performance will be good. Its volatility is mainly related to the plasticizer used, the volatility of the plasticizer is related to its flash point, the volatility of the low flash point is larger.

Table 1. Effect of plasticizers on thermal aging properties of materials

Table 1 shows that the heat loss of 13# is larger than that of the other three formulations because of the increase in volatilization of the plasticizer. The heat weight loss is related to the volatilization of plasticizer, the escape of hydrogen chloride, the precipitation of low molecular substances, etc.; the heat weight loss will affect the elongation at break rate of plastic to some extent.

Table 2 Effect of plasticizers on material properties

Table 2 shows that: 10 # formula at 20 and working temperature volume resistivity than 5 # formula, this is because although the two formulations of the total amount of plasticizer is the same, but 10 # formula in the proportion of DOTP more than 5 # formula due to; 2 # formula 20 and working temperature volume resistivity is higher than the 5 # formula, this is because in the same amount of DOTP, 2 # formula DOP added to the same amount of 5 # formula less, insulation resistance with the increase in the amount of plasticizer added and decreased. This is due to the fact that the amount of DOP added in 2# formulation is less than 5# formulation at the same amount of DOTP, and the insulation resistance decreases with the increase of plasticizer addition. In addition, from Table 2, it can also be seen that the low temperature impact test of formula #2 fails, which is due to the fact that the glass transition temperature of the material increases due to the lower amount of plasticizer in formula #2. Therefore, the insulation resistance and low temperature impact performance are a pair of contradictions, in order to make them meet the standard requirements at the same time, it is necessary to choose a suitable plasticizer and control its addition in a suitable range.

Dioctyl phthalate (DOP) and dioctyl terephthalate (CDOTP} were selected as plasticizers for PVC based on various factors. The addition of DOTP is mainly to improve the electrical insulation properties of the plastic, etc.

3.3 Selection of environmentally friendly stabilizers

Environmentally friendly PVC insulation material stabilizers can not contain harmful lead (Pb), pot (Cd), mercury (Hg), arsenic (As), chromium (Cr), selenium (Se), antimony (Sb) and other heavy metal elements, and therefore the selection of non-toxic calcium-zinc composite stabilizers. The thermal stability of calcium-zinc composite stabilizers is close to or exceeds that of some barium/pot stabilizers and lead stabilizers, and has good weather resistance and good transparency. Calcium and zinc composite stabilizers on the thermal stability of the time of Table 3 formula in the filler 25, lubricant 0.6, antioxidant 0.6. Calcium and zinc composite stabilizers to add too little material aging performance is unqualified to add too much cost is too high, generally add 5 or so is more appropriate.

Table 3 Effect of calcium-zinc complex stabilizers on heat stabilization time

3.4 Flame retardant modification

(1) The effect of the amount of plasticizer on the flame retardant properties of PVC cable material added to different plasticizers, the cable material will be different flame retardant and smoke. For the four most commonly used plasticizers in PVC cable materials: dioctyl phthalate, trioctyl trimellitate, trimellitate phosphate and polyester-based plasticizers, which have a great difference in flame retardancy, our technicians have done related research work. In the soft PVC 100 parts added 30 to 60 parts of plasticizers, the study found that when the plasticizer content increases, the oxygen index of PVC decreases. For different plasticizers, the degree of decrease was basically the same. And the PVC containing trimethylphenyl phosphate has the highest oxygen index, which is about 5 higher than that of PVC containing dioctyl phthalate. The study on the amount of fume shows that the amount of fume of PVC containing dioctyl phthalate and trimethylphenyl phosphate increases with the increase of the content of plasticizers. However, PVC containing trioctyl trimellitate and polyester-based plasticizers had the opposite result.

(2) Effect of Flame Retardant Dosage on Flame Retardant Properties

Al(OH)₃, Sb₂O₃, zinc borate (ZB) and other inorganic flame retardants are added to PVC cable materials, and their dosage has a great influence on the flame retardant properties of PVC, and scholars at home and abroad have made a lot of related research. Our technicians have studied the effect of Sb₂O₃ and Sb₂O₃/ZB flame retardant addition on the oxygen index of PVC. They found that with the increase of Sb₂O₃, the limiting oxygen index of PVC cable material showed a linear upward trend, and when the addition of nano-Sb₂O₃ was greater than 1.5 parts, the contribution of nano-Sb₂O₃ to the oxygen index of PVC was greater than that of micron Sb₂O₃. They also studied the oxygen index of PVC at different mass ratios of Sb₂O₃ and ZB, and found that the oxygen index decreased with the increase of the mass ratio. decreases. That is to say, the more Sb₂O₃ is added, the higher the flame retardancy of PVC, but because Sb₂O₃ is expensive, the amount of Sb₂O₃ added is not very high, as long as it can ensure a certain degree of flame retardancy. The added ZB can be used as a smoke suppressant, and the composite use of ZB and Sb₂O₃ will make the PVC cable material have a suitable oxygen index and also have a low amount of smoke. Our technicians, in addition to studying the effect of the addition of ZB and Sb₂O₃ on the flame retardant properties, but also studied the effect of the amount of Al(OH)₃ on the flame retardant properties, as a whole, to get the law: with the increase in the amount of flame retardant, the flame retardant properties of the PVC cable material has been significantly improved.

(3) The effect of the amount of filler on the flame retardant properties in the PVC cable material, usually need to add a certain amount of filler. If we add talc and clay as fillers, the oxygen index increases by 1 to 2 times, but the burning speed of the cable material also doubles, and the maximum extinction coefficient remains unchanged. If we add Al(OH)₃ as a filler, the burning speed increases by 50%, the oxygen index increases, and the maximum extinction coefficient decreases, so it is more effective in suppressing the amount of smoke. CaCO₃ filler is also usually added in PVC, our technicians have found that with the increase of CaCO₃ addition, the oxygen index of PVC cable material decreases, and the maximum extinction coefficient also decreases, so the amount of CaCO₃ added can not be too much, otherwise it will affect the flame retardant smoke suppression effect of the cable material. But CaCO₃ can be used as a trapping agent of HCl gas with very significant effect.

Basic formula

PVC 100%, DOP 30%, chlorinated paraffin 10~25%, stabilizer 3%, CaCO₃ 10~30%

1%~2% of other additives, flame retardant is variable.

Performance testing

Limiting Oxygen Index (L0I) is tested according to the national standard GB /T 2406-2006, the specimen size 100 mmx6.5 mmx3.2 mm.

Mechanical properties according to the national standard GB / T 1040-2006 standards for testing, the specimen for the V-shaped specimen, tensile speed of 250 mm / min .

Results and discussion

Picture 3 shows the ultimate oxygen index of PVC wire and cable materials after adding different amounts of antimony trioxide.As can be seen from the figure, with the increase of antimony trioxide addition, the ultimate oxygen index of PVC cable material is a straight line upward trend, in the nano antimony trioxide addition amount is greater than 1.5 parts of a nano antimony trioxide on the oxygen index of PVC contributes to the large ten micrometer grade antimony trioxide. When the oxygen index is 35%, the additive amount of antimony trioxide can be 20% less than that of micron antimony trioxide. This is because the nanoscale antimony trioxide flame retardant material from ten particle size becomes smaller with special ductility, can be uniformly dispersed in ten polymer materials, the increase in its specific surface area so that in the flame retardant process can be effective in generating SbX3, the use of cohesive phase flame retardant and reduce the chain reaction radicals - OH to achieve flame retardancy, in terms of flame retardant performance than micron antimony trioxide has an order of magnitude increase "z-o. Although the nano antimony trioxide can achieve a relatively high oxygen index at a low addition amount, however, by ten antimony trioxide flame retardant mechanism is gas phase flame retardant and solid phase flame retardant at the same time, so the amount of smoke in the nano antimony trioxide flame retardant PVC cable material is still relatively large, considering the adverse effects of smoke on the escape in the fire, we will have smoke inhibition of the zinc borate introduced into the flame retardant system.

Effect of zinc borate (ZB) and antimony trioxide nanoparticles as flame retardants on the oxygen index of PVC.

Picture 4 shows the limiting oxygen index (LOI) of PVC cable material with the addition of 5 parts of zinc borate and antimony trioxide in different proportions! From the figure, it can be seen that with the increase of antimony trioxide in the composite flame retardant, the LOI of PVC cable material increases. As we all know, antimony trioxide and halogenated flame retardant synergistic effect can be achieved in general flame retardants can not reach the comprehensive performance, however, the current price of antimony trioxide rose again and again, modified plastics, especially PVC, such a relatively low-profit modified materials have been difficult to bear! Zinc borate is inexpensive, and according to previous research can be used as a PVC flame retardant smoke reduction agent. In this study, it was found that the smoke generation of the material was greatly reduced after compounding zinc borate with antimony trioxide, which made the flame retardant have a low smoke generation while achieving a suitable oxygen index.

Effect of zinc borate (ZB) and antimony trioxide nanoparticles as flame retardants on mechanical properties of PVC

The mechanical properties of PV C cable material with different ratios of Sbz03 /ZB are shown in Picture 5. From the figure, it can be seen that with the increase of the proportion of zinc borate, the tensile strength of PVC cable material tends to decrease, and elongation at break

The first has a small increase and then decrease trend, but the reduction of tensile strength and elongation at break are not obvious, the tensile strength is reduced by a maximum of 7. 5 %, and the elongation at break is reduced by a maximum of 9. 47%. This is because the zinc borate used is micron-sized zinc borate with a particle size distribution of 2 a 10 microns, which is not much different from the nano antimony trioxide, and therefore the effect on the mechanical properties is not obvious.

3.5 Conclusion

1) Nano antimony trioxide contributes to the oxygen index of PVC more than ten micron antimony trioxide, when the oxygen index is 35% a, the addition of nano-antimony trioxide can be 20% less than micron antimony trioxide.

2) The oxygen index of the material was reduced after the compounding of nano-antimony trioxide and zinc borate, which indicates that the contribution of zinc borate to the oxygen index is less than ten antimony trioxide, but the amount of smoke generation of the material was greatly reduced after the compounding, and the overall cost of the material was also reduced.

3) With the increase of the proportion of zinc borate in the compound flame retardant, the tensile strength of PVC cable material showed a decreasing trend, and the elongation at break first had a small increase and then a decreasing trend, but the reduction of both tensile strength and elongation at break was not obvious, with a maximum reduction in tensile strength of 7. 5 % and a maximum reduction in elongation at break of 9. 47 %.

VI. Conclusion

With the enhancement of people's awareness of environmental protection and safety, the research and production of flame-retardant and smoke-suppressing PVC cable material has attracted widespread attention around the world. People have been looking for ways to improve the flame retardant properties of PVC cable materials, and made a breakthrough. The amount of plasticizers, flame retardants and fillers added to PVC cable materials can be well controlled, which is a prerequisite for the development of cable materials with excellent performance. And the use of blending and other methods will develop more non-toxic, efficient in one of the new environmentally friendly flame retardant PVC cable materials.

Despite the increasingly stringent environmental protection laws, but the PVC cable material with its excellent performance, low prices and easy to process the characteristics of the cable material still occupies a considerable amount of weight, and this situation in the short term is difficult to have a fundamental change, so the development of environmentally friendly, high-performance PVC cable material in the next period of time is still a hot topic.

With the increasing awareness of environmental protection and safety, the flame retardant and smoke suppressant performance of PVC cable materials has become a hot research topic. In this field, the PVC flame retardant T series of YINSU Flame Retardant Company stands out with its excellent performance. T series belongs to the composite antimony products, which can completely replace the traditional antimony trioxide, and the T30 product can replace 50~60% of antimony trioxide in the PVC formula without antimony trioxide, which provides a new solution for the environmental protection and performance enhancement of the cable materials.