Anyone who has been X-rayed at the dentist's office knows the routine: Hold perfectly still with the edges of the film packet pressed tightly to your gums as the technician clicks the button of the camera in the next room.
Eastman Kodak Dental Products Business in Rochester, N.Y., has tried to take the discomfort out of the process by developing an oral X-ray film called SureSoft, with a delicate bead of flexible vinyl compound to cushion its edge. The 1.1-millimeter-diameter vinyl bead presented Kodak with some tough challenges in robotics, injection molding, and adhesion.
Kodak manufactures its dental X-ray products in a sandwich construction of X-ray film, paper, and foil between outer layers of plasticized, or flexible, polyvinyl chloride film, coated black on one side to protect the enclosed X-ray film from accidental exposure. A proprietary machine brings together the various layers, seals them around the perimeter, and die-cuts them into packets.
Michael McGovern, a Kodak K&D plastics engineer, said the company tweaked the basic packet, which it has made for decades, to accommodate the delicate vinyl compound comfort cushion. Teknor Apex Co. of Pawtucket, R.I., supplies the PVC-based flexible vinyl compound, Apex 3208-80-NT.
Kodak had been concerned over adhesion. It didn't want the bead falling off" in the patient's mouth. In researching materials, Kodak found that the 80 Shore A durometer grade adhered best.
Kodak added an insert injection molding step to place the vinyl compound comfort bead around the edge of the packet after die cutting. The vinyl cushion has a shot size of just 0.27 gram. To improve adhesion, the company's engineers substituted the bottom layer of plasticized PVC film with one of rigid PVC, which provides a better backing for the soft vinyl bead. Although the vinyl bead is gated in only one spot to fill the mold cavity, adhesion is sufficient along all four sides, McGovern said.
He said that the die cutting consistently provides a sufficient edge of rigid PVC outside the seal on which to mold the vinyl bead. Kodak had to make sure its robotic handling equipment, which places the packets inside the mold, is accurate enough to maintain tight molding tolerances and avoid damage to the X-ray film, he said.