Playtex Heat Therapy patches, a new product to ease the discomfort of menstrual cramps, last up to 12 hours, according to executives. The barely-there thin patches are different from Procter & Gamble’s recently launched ThermaCare heat wraps for menstrual pain, and are positioned on shelves next to tampons with a smaller price tag. ThermaCare is sold near oral analgesics with an emphasis on back pain....