Curing volume resistivity

For polyamine-cured resin, recycle of presoaked epoxy also increased both impact strength and heat deflection temperature. For polyamide-cured resin, recycle also increased volume resistivity. Pre-soaked recycle dramatically increased adhesion to aluminum, especially in the anhydride system. 

Figure 12.5a shows the effect of filler loading on the volume resistivity of MWNTs and CB (CB Ensaco 250G from Timcal) filled composites based on insulating styrene-butadiene rubber. The styrene-butadiene rubber contains 25 w% of styrene units. The microstructure of the butadiene phase is the following 10% cis, 17% trans, 73% 1,2. It was compounded with sulfur (1.1 phr), cyclohexyl benzothiazole sulfenamide (1.3 phr), diphenyl guanidine (1.45 phr), stearic acid (1.1 phr), zinc oxide (1.82 phr) (phr = parts per hundred parts of rubber). The unfilled and filled samples are cured into films (around 200 pm thick) at 170°C during 10 min under a pressure of 150 bar in a standard hot press. 

The properties of polysulphide polymers are summarised in Table 7.2. Cured polysulphide systems possess excellent resistance to most solvents and mild inorganic acids. The solvent resistance depends on the sulphur content of the polymer. Table 7.3 compares the resistance of various liquid polysulphide polymers to a variety of solvents and chemical solutions. However, these data cannot be considered as absolute because the resistance is to some extent dependent on the efficiency of cure. Volume swell values below 40% illustrate excellent resistance. Those between 40% and 90% illustrate fair to good resistance whereas values above 90% may be only fair or even unsatisfactory (Thiokol Chemical Co., 1969). 

Electric resistivity. The electric resistance measurement is the same as discussed below under volume resistivity, to which this measurement is temporary adapted. For flexible materials, special electrode systems are developed to clamp sample and electric wires. The measuring equipment is based on a Wheatstone bridge circuit. The conductivity of metal powder-containing epoxy was measured in special dies equipped with built-in brass electrodes inserted to the die. The material was cured in the die to assure good contact with electrodes. Special sample holders and clamping devices are used for precise determination of rubber compounds containing carbon black. ... 

Volume Resistivity was determined on cured films of the conformal coating in accordance with ASTM D257 and found to be 3.5 x 10 ohm-cm at 23°C and 50% relative humidity. 

DGEBA resin 1 cured with carbon black, %wt. volume resistivity, Ohm.m dielectric constant at 1 kHz. Tg-value, DSC onset, °C... 

These values illustrate the strong influence of the type of curing agent used. The phenomenon studied is clearly present in the first system where the low volume resistivity is accompanied by a high dielectric constant value. This phenomenon is clearly not present in the third, with a cyclo-alifatic amine cured system. The dielectric constant of this system, although increased due to the carbon black addition, is low compared with that of the former system. The resistivity decrease effect is found to some extent present... 

Figure 5.25 shows the AC properties (dielectric constant/ dielectric loss factor) at 23°C as a function of the frequency. The differences found in the volume resistivity of these systems are also reflected in the AC properties. The strong decrease of the dielectric constant as a function of the frequency for the system cured with EPIKURE 160/161 indicates a certain amount of capacitive coupling between the conducting carbon black particles. The dielectric loss factor/frequency relation of this system is nearly linear with a slope of about -l, pointing at a pure resistive behaviour (see equation 5.18). 

The DC properties of anti-static epoxy GFR pipes The use of glass-fibre reinforced (GFR) epoxy resin pipes is, especially in tankers, hampered by the bad electrostatic properties of these pipes. The possibility to decrease the volume resistivity to an acceptable level using only a small amount of carbon black (see 5.3.2) resulted in the development of the WAVIMAR anti-static GFR pipe system by Wavin BV. This pipe system is based on a liquid DGEBA/MDA (100/27) and cured for two hours at 120°C, containing about 1.5 %wt. (on the resin phase) of Ketjen black EC-2000 carbon black. The specific volume resistivity of a sample of such a pipe was measured as a function of the direction, the field strength and the pipe wall thickness. 

To obtain the lowest electrical volume resistivities (in the 10 to 10 ohm-cm range) and the lowest contact resistances, polymer resins must be highly Ailed with 70-80% by weight (25-30% by volume) of metal particles and must be thoroughly cured. Silver and silver alloys are the most widely used fillers but, in specific applications, other metal fillers including gold, copper, nickel, and even carbon are used. Carbon-filled polymers are often used to dissipate static electricity or to protect from electromagnetic interference (EMI). 

Table 2.3 Volume resistivity versus cure conditions for a silver-filled epoxy adhesive ...

The type of lubricant used may have a major effect on the volume resistivity of a cured epoxy. In one example, a conductive epoxy formulated with silver flakes using a thiol lubricant in a proprietary solvent showed consistently higher volume resistivity (4—5 orders of magnitude) than a similar composition where the silver flakes were coated with a fatty acid lubricant. ... 

Product/Supplier Type Viscosity cP (rpm) Cure Schedule Loss 300 °C by TGA Die-Shear Strei th (psi urfaces) Modulus of Elasticity (MPa /psi) 1 2 T ec) Volume Resistivity, ohm-cm Thennal Conductivity (W/m K) Ionic Impurities (ppm)... 

Viscosity (ASTM Volume resistivity Solvent and chemical Exotherm during Hardness Weight loss during cure... 

Table 2.3. Volume Resistivity vs Cure Conditions for a Silver-filled Epoxy Adhesive ...

The type of lubricant used may have a major effect on the volume resistivity of a cured epoxy. In one example, a conductive epoxy formulated with silver... 

Product Name/ Supplier Description Viscosity (cps) Shelf life (-40°C), Pot Life (25 C) Cure Schedule hr °C Hardness (Shore A, unless indicated) NASA Outgassing Test Results (ASTM E 595) Lap- Shear Strength (psi) CTE (ppm/°C) A fC) Volume Resistivity (ohm-cm) Thermal Conductivity (W/m-K)... 

Product/ Supplier Type Shelf Life -40°C/ Pot Life 25°C Cure Schedule % WL Loss at 300°C Bond Strength Al-Al lap shear (psi) Modulus of Elasticity MPa (psi) CTE, ppm/°C T, °C Volume Resistivity, ohm-cm Thermal Conduc- tivity, W/mK Moisture Absorp- tion Ionic Impur- ities (ppm)... 

Product Name/ Supplier Type Viscosity cps Thixo- tropic Index YieU Value (N/m Casson) Shelf life -40°C/ Pot Life 25°C Cure Schedule min Lap- Shear Strength psi CTE ppm/ C T, °C Volume Resistivity ohm-cm Thermal Conductivity W/mK... 

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