Ethylene propylene rubber (EPR), including binary ethylene propylene rubber and ternary ethylene propylene rubber (EPDM) two categories, is a saturated rubber, with excellent electrical insulation, moisture, heat, cold and aging resistance, is widely used in the preparation of wires and cables, and has been a comprehensive alternative to the main body of styrene-butadiene rubber as the cable insulation material. With the increasingly high requirements of the laying environment, wire and cable are being developed towards low-smoke halogen-free flame retardant, with the same low-pressure grades of cross-linked polyethylene, EPR also belongs to the flammable materials, its own molecular composition and structure of the flame retardant performance has little effect, only with a considerable amount of flame retardant in order to achieve the purpose of flame retardant, so in order to make low-smoke halogen-free flame-retardant materials can only be added to the halogen-free class of flame retardants. Studies have shown that the electrical properties of EPDM is greatly affected by the flame retardant, just add 80 parts of hydroxide flame retardant will make the rapid decline in electrical resistivity, in order to achieve the IEC 60502 ((rated voltage of 1 ~ 30 kV extruded insulated cables and their accessories) standards in the EPR insulating rubber in the normal operation of the conductor at the highest temperature of the insulation resistance /> 3.67 MΩ -km and volume resistivity ≥ 3.67 MΩ -km and volume resistivity ≥ 3.67 MΩ -km and volume resistivity ≥ 3.67 MΩ -km. km and volume resistivity ≥ 1 × 1012 Ω - cm of the provisions of the standard, and at the same time through the EPR insulation core single vertical combustion test, there is a high degree of difficulty. This has led to the slow development of low-smoke halogen-free flame-retardant EPR insulating rubber over the years, while crowded occasions such as subways and high-rise buildings require the overall flame retardancy of the cable insulation and sheath to improve fire safety. With the surface modification technology of inorganic flame retardants such as aluminum hydroxide and magnesium hydroxide and the research and development of new production methods, it is possible to meet the above requirements.
1 The effect of inorganic flame retardant types on the performance of low-smoke halogen-free flame retardant EPDM insulating rubber material
The tensile strength of EPDM insulating adhesive material with magnesium hydroxide is the largest, mainly due to the fact that
Magnesium hydroxide is needle-like crystalline, particle size less than 2μm, and through the modification of silane coupling agent to enhance the binding force and compatibility of magnesium hydroxide and EPDM. By comparing the oxygen index and vertical combustion grade, it can be seen that the flame retardant effect of magnesium hydroxide is significantly better than that of aluminum hydroxide, this is due to the thermal decomposition temperature of magnesium hydroxide is higher than that of aluminum hydroxide by 140 ℃, which avoids dehydration reaction occurring in advance due to the high temperature of the processing process, moreover magnesium hydroxide will form a layer of oxidized film adsorbed on the surface of the adhesive material after dehydration and promote the formation of charcoal, which will form a layer of hard shell on the surface of the adhesive material In addition, after dehydration, magnesium hydroxide will form a layer of oxidized film adsorbed on the surface of rubber material, and promote the formation of carbon, forming a hard shell on the surface of rubber material, effectively isolating oxygen, thus improving the flame retardant system. Comparison of volume resistivity can be concluded, aluminum hydroxide on the EPDM insulation rubber Ethylene propylene rubber (EPR), including binary ethylene propylene rubber and ternary ethylene propylene rubber (EPDM) two categories, is a saturated rubber, with excellent electrical insulation, moisture, heat, cold and aging resistance, is widely used in the preparation of wires and cables, and has been a comprehensive alternative to the main body of styrene-butadiene rubber as the cable insulation material. With the increasingly high requirements of the laying environment, wire and cable are being developed towards low-smoke halogen-free flame retardant, with the same low-pressure grades of cross-linked polyethylene, EPR also belongs to the flammable materials, its own molecular composition and structure of the flame retardant performance has little effect, only with a considerable amount of flame retardant in order to achieve the purpose of flame retardant, so in order to make low-smoke halogen-free flame-retardant materials can only be added to the halogen-free class of flame retardants. Studies have shown that the electrical properties of EPDM is greatly affected by the flame retardant, just add 80 parts of hydroxide flame retardant will make the rapid decline in electrical resistivity, in order to achieve the IEC 60502 ((rated voltage of 1 ~ 30 kV extruded insulated cables and their accessories) standards in the EPR insulating rubber in the normal operation of the conductor at the highest temperature of the insulation resistance /> 3.67 MΩ -km and volume resistivity ≥ 3.67 MΩ -km and volume resistivity ≥ 3.67 MΩ -km and volume resistivity ≥ 3.67 MΩ -km. km and volume resistivity ≥ 1 × 1012 Ω - cm of the provisions of the standard, and at the same time through the EPR insulation core single vertical combustion test, there is a high degree of difficulty. This has led to the slow development of low-smoke halogen-free flame-retardant EPR insulating rubber over the years, while crowded occasions such as subways and high-rise buildings require the overall flame retardancy of the cable insulation and sheath to improve fire safety. With the surface modification technology of inorganic flame retardants such as aluminum hydroxide and magnesium hydroxide and the research and development of new production methods, it is possible to meet the above requirements.
1. Influence of inorganic flame retardant type on the performance of low smoke halogen-free flame retardant EPDM insulation rubber material
The tensile strength of EPDM insulating adhesive material with magnesium hydroxide is the largest, mainly due to the fact that Magnesium hydroxide is needle-like crystalline, particle size less than 2μm, and through the modification of silane coupling agent to enhance the binding force and compatibility of magnesium hydroxide and EPDM. By comparing the oxygen index and vertical combustion grade, it can be seen that the flame retardant effect of magnesium hydroxide is significantly better than that of aluminum hydroxide, this is due to the thermal decomposition temperature of magnesium hydroxide is higher than that of aluminum hydroxide by 140 ℃, which avoids dehydration reaction occurring in advance due to the high temperature of the processing process, moreover magnesium hydroxide will form a layer of oxidized film adsorbed on the surface of the adhesive material after dehydration and promote the formation of charcoal, which will form a layer of hard shell on the surface of the adhesive material In addition, after dehydration, magnesium hydroxide will form a layer of oxidized film adsorbed on the surface of rubber material, and promote the formation of carbon, forming a hard shell on the surface of rubber material, effectively isolating oxygen, thus improving the flame retardant system. Comparison of volume resistivity can be concluded, aluminum hydroxide on the EPDM insulation rubber material electrical insulation performance of the impact is much smaller than magnesium hydroxide, this is because the ATH 104E conductivity is not more than 60 pS-cm ~; and ordinary magnesium hydroxide, such as varieties of the ore method of production, due to the domestic source of the mine Influence, high impurity content, low purity, in addition to its surface with a positive charge, high polarity, microscopic internal stress, so that the conductivity is up to 250 pS-cm. 1 or more, a large number of magnesium hydroxide added to the EPDM rubber material will make the rubber material's insulating properties decreased significantly, although magnesium hydroxide after a special surface modification treatment can improve the insulating properties of the rubber material, but the results Still not ideal. Considering the same amount of magnesium hydroxide has better flame retardant properties than aluminum hydroxide, we and magnesium hydroxide manufacturers jointly optimize the physical indicators of magnesium hydroxide, the varieties of surface modifiers and production methods, etc., and produce two kinds of magnesium hydroxide suitable for the production of EPDM insulating adhesive material - MH3005 and MH3005 and MH3005Z.
MH3005 and MH3005Z EPDM insulating rubber have high volume resistivity, of which the insulating core made of MH3005Z rubber basically meets the requirements of IEC 60502, but the insulating properties of MH3005 rubber are relatively high. However, the insulation performance of the core made of MH3005 rubber is relatively low, and it is estimated that the surface structure of the core was damaged during the extrusion vulcanization process, and the reason needs to be further explored.
Overall, compared with the EPDM insulation rubber with modified magnesium hydroxide alone and EPDM insulation rubber with aluminum hydroxide alone, the former has good flame retardant property, high tensile strength, and better insulating property after special surface modification, but there is still a risk of degradation of insulating property in the insulating wire core, while the insulating property of aluminum hydroxide is better, and its resistivity can meet the requirements even without modification.
2. The effect of inorganic flame retardants on the performance of low-smoke, halogen-free flame retardant EPDM insulating adhesives
Single use of magnesium hydroxide or aluminum hydroxide inorganic flame retardant can not simultaneously meet the requirements of the electrical properties and flame retardant properties, so the aluminum hydroxide and magnesium hydroxide and its effect on the performance of low-smoke halogen-free flame-retardant EPDM insulating adhesive, ATH 104E and MH3005Z dosage of a total of 120 parts, with the increase in the dosage of MH3005Z, the Menni viscosity and tensile strength of EPDM insulating adhesive increased, flame retardant properties increased, volume resistivity decreased. With the increase of MH3005Z, the Menni viscosity and tensile strength of EPDM insulating adhesive increases, the flame retardant property increases, and the volume resistivity decreases. When the ratio of ATH 104E/MH3005z is 90/30, the insulating and flame retardant properties of EPDM insulating adhesive meets the requirements. Comparison of ATH 104E / MH3005z and the ratio of 110 / 10 and 120 / lo two cases, although the increase of 10 parts of ATH 104E after the EPDM insulation adhesive flame retardant properties have been improved, but the physical properties of the rapid decline. LATH 104E / MH3005Z and the ratio of 70 / 50 and 70 / 40 two cases, reduce 10 parts of MH3005Z although it can improve the insulation properties of the rubber, but the flame retardant properties do not meet the requirements. In order to ensure flame retardant properties, the total amount of flame retardant can not be reduced.
EPDM insulation rubber material flameless smoke density are 355 or so, with the amount of inorganic flame retardant and with no obvious relationship with the ratio, this is because of the formula of all components, the formation of smoke is mainly EPDM, although the inorganic flame retardant can improve the flame retardant properties, and also does not produce smoke, but can not reduce the smoke released by the rubber matrix material combustion.
3. Smoke reducing agent on the performance of low-smoke halogen-free flame-retardant EPDM insulating compound
JB / T 10707 - 2007 "thermoplastic halogen-free low-smoke flame retardant cable materials" requires that the flameless smoke density of the rubber material should not be greater than 250, in order to reduce the smoke density of the rubber material must be added to the smoke suppressant. Montmorillonite contains calcium-based, sodium-based, magnesium-based montmorillonite, after stripping and dispersion, purification and modification, special organic composite, the average thickness of the layer is less than 25 nm. montmorillonite is selected to achieve better smoke effect.
Montmorillonite on the EPDM insulation rubber material smoke density of the impact is very obvious, but also can be a small increase in flame retardant properties, while other properties have less impact; with the increase in the amount of montmorillonite, EPDM insulation rubber material smoke density drop gradually reduced, and tend to be stabilized, taking into account the cost factors, choose the amount of montmorillonite for 5 parts.
4 Conclusion
(1) In the halogen-free low-smoke flame retardant EPDM insulating adhesive, the flame retardant effect of modified magnesium hydroxide with the same dosage is better than that of aluminum hydroxide, but magnesium hydroxide has a greater impact on the electrical insulation properties.
(2) Aluminum hydroxide and magnesium hydroxide and with a ratio of 90 / 30, low smoke and halogen-free flame retardant EPDM insulation adhesive material has good flame retardant properties and insulation properties.
(3) The use of montmorillonite can effectively reduce the smoke density of low-smoke halogen-free flame retardant EPDM insulation adhesive, but with the increase of its dosage, the smoke density of the adhesive decreases slowly, and the best dosage of montmorillonite is 5 parts.
