Cure Monitoring of Sheet Molding Compound (SMC): The curing behavior of Sheet Molding Compound (SMC) was observed using the LTF-631 High Speed Dielectric Cure Monitor. Bulk Molding Compound (BMC) is the generally the same material as SMC but in bulk form, so the analysis of results apply to BMC as well.

Cure Monitoring of Bulk Molding Compound (BMC):  The curing behavior of Bulk Molding Compound (BMC) was observed using the LTF‑631 High Speed Dielectric Cure Monitor. Bulk Molding Compound is generally the same material as Sheet Molding Compound (SMC) but in bulk form, so the analysis of results can apply to SMC as well. The data from dielectric cure monitoring (DEA) clearly show how Critical Points identify features of the cure and enable quantitative comparison of cures under different process temperatures.

Cure Monitoring of Epoxy Molding Compound (EMC):   Normally available in either B-staged powders or pellets for transfer molding, EMC is essential for electronics packaging and is used to encapsulate billions of integrated circuits each year. Samples of EMC were placed on a reusable 1” Single-Electrode Sensor then compressed and cured for separate runs at 150 °C, 160 °C, 170 °C and 180 °C. The cure time for these samples can be less than three minutes so an LTF‑631 High Speed Dielectric Cure Monitor measured the dielectric properties of each sample.

Cure Monitoring of Urea Molding Compound (UMC): Unlike sheet molding or bulk molding compound, UMC generates conductive volatiles during cure, which must be vented for successful dielectric cure monitoring.

Cure Monitoring of Polyurethane Foam: Manufacturers of polyurethane (PU) foams typically study cure by pouring a large amount—as much as 200 grams or more—of the mixed resin and catalyst into a cup then measuring the rise time. In actual use, however, PU foam adhesives are dispensed as thin bond lines with much lower mass, resulting in very different thermal conditions and therefore very different cure rates compared to the cup test.

Cure Monitoring of Carbon Fiber Sheet Molding Compound (CF-SMC): Carbon fiber sheet molding compound is very similar to standard sheet molding compound but replaces chopped glass fibers with chopped carbon fibers, which are conductive and can short circuit the electrodes of a sensor. The use of filters can prevent conductive fibers from contacting the electrodes and allow resin to reach the sensor, resulting in good measurements for cure studies.

Cure Monitoring of Carbon Fiber Reinforced Prepreg (CFRP):  Carbon fiber reinforced prepreg (CFRP) consists of carbon fiber fabric “pre-impregnated” with an epoxy or other resin system. During processing, heat and pressure bond together multiple layers of CFRP to make a solid part. Heat is usually applied in two ramp-and-hold stages—the first hold step is called “B-Staging,” which partially cures the resin at a lower temperature to increase its viscosity, reducing resin flow during the second ramp-and-hold to the higher, final temperature. For process development and manufacturing, dielectric cure monitoring, also known as dielectric analysis (DEA), gives immediate information and feedback about the viscosity and cure state under actual conditions in a press, autoclave or mold—an advantage not possible with conventional laboratory methods.

Sensors for Cure Monitoring of Carbon Fiber Composites: Testing pure resins or resin-fiberglass composites is generally simple and only requires placing the material on the sensor. With carbon-fiber composites, however, a conductive fiber contacting the sensor will short circuit its electrodes and cause bad, unusable measurements. Despite this problem, cure monitoring of carbon fiber reinforced prepreg (CFRP), carbon fiber sheet molding compound (CF-SMC) and similar composites is possible with filtered or coated sensors.

Carbon+ Sensors for Direct Contact Cure Monitoring of Carbon Fiber Composites: Dielectric sensors normally require filters to block conductive fibers and prevent short circuiting of the electrodes. Filters, however, must be replaced manually after each test and add time, effort and cost, so it is necessary to avoid them in rapid, repetitive operations. For cure monitoring without filters, Carbon+Unitrode sensors from Lambient Technologies have a rugged, insulating coating that allows direct contact with carbon fiber composites. As a result, Carbon+Unitrode sensors can be used in manufacturing to observe the entire cure, and can detect end of cure for opening a press or mold.

Real-Time Monitoring of UV Cured Resin: Quad-Cure 1933 is a urethane acrylate glass-metal bonder that may be cured with UV, visible, LED light and heat. Under UV irradiation, this resin reacts rapidly and exhibits dynamic behavior that would be difficult or impossible to see with differential scanning calorimetry (DSC), the conventional method of studying cure state. In contrast, dielectric cure monitoring (DEA) has the unique ability to measure cure in real-time, which is valuable for studying materials that polymerize in seconds.

Cure Monitoring of Polyurethane: Lambient Technologies studied room temperature cures of a polyurethane resin with three different catalysts. An LT-451 Dielectric Cure Monitor made measurements during each test at excitation frequencies from 0.1 Hz to 100 kHz for 24 to 36 hours.

Cure Index Analysis of Five-Minute Epoxy: Lambient Technologies tested a generic “Five-Minute Epoxy” to observe the effect of different thermal conditions on the progress of cure. For isothermal tests, ion viscosity measurements easily reveal cure state because temperature is not a variable; however, five-minute epoxy can generate a significant exotherm, making the typical reaction non-isothermal.

In this case, because ion viscosity depends on both cure state and temperature, reaction rate and degree of cure are not clear when analyzing ion viscosity alone. With Cure Index analysis, which accounts for the effect of temperature, dielectric measurements clearly show how cure time decreases and how degree of cure increases with greater peak exotherms, as expected for thermally driven reactions.