Scratch 'N Sniff™ is the trade name for a special kind of perfume or scent saturated printing in which the scent is enclosed in minute capsules, which can be broken open by friction. Individual beads of scented oil too small to be seen with the naked eye are encapsulated in plastic or gelatin, and with specialized printing techniques, the beads are printed on paper. The scent does not leak out until the beads are deliberately broken. Because scratch and sniff patches keep a scent localized—it can be smelled only when some one deliberately scratches and sniffs—scents can be used in printing without overwhelming the surroundings.
Scratch and sniff is popular in children's books, where the reader can scratch and sniff a picture of a cookie to smell the fresh-baked scent, for example. It is also widely used in advertising, where it may capture the scent of a new car or rubber tire, lumber, burnt match, flowers, the smell of a particular detergent or medicine, mush-rooms, ham, ketchup, butter, mildew, or a host of other scents. Micro-encapsulated scent is most prevalent in perfume advertising. A strip of paper printed with micro-encapsulated perfume oil and tacked shut at the border of the advertisement is generally used instead of the open patch of scratch and sniff. The consumer tears open the strip, thus breaking the capsules in two and releasing the scent.
The micro-encapsulation technology that makes scratch and sniff possible was discovered by scientists endeavoring to make carbonless paper. Before the era of the word processor and photocopy machine, typists inserted carbon paper between second and third sheets of white paper to make multiple copies of documents. This could be a messy and aggravating process. In the early 1960s, an organic chemist, Gale Matson, working for 3M (Minnesota Mining and Manufacturing Company) patented a micro-encapsulation process that could be used to make ink copies without carbon paper. The Matson process used a particular plastic called polyoxymethylene urea (PMU). A researcher at National Cash Register came up with a similar micro-encapsulation process using gelatin. Both scientists were thinking only of carbonless paper, but the marketing department at 3M was given the task of finding alternate uses for the technology Matson had patented. It soon became clear that micro-encapsulation could be used for scented oil, and Scratch 'N SniffrM debuted in 1965. The pull-apart perfume strip was introduced in 1981, and has since become the prevalent form of sampling new perfume.
The basic ingredients of scratch and sniff or perfumed strips are water, oil, scent, and either gelatin or a water soluble polymer, usually polyoxymethylene urea. A certain chemical catalyst is used to bring about the reaction. A water-soluble adhesive is needed to affix the material to the paper during printing.
The micro-capsules are subjected to many laboratory tests to determine their strength and longevity under stressful conditions. They may be frozen or subjected to steam, and then examined under magnification. Finished printing for a customer is also checked to make sure the scent released is the correct scent and the correct strength. In the case of perfumed strips, if the scent is too weak or too strong, the printers may adjust the width of the strip, and the adhesion of the strip may be altered by adding or subtracting adhesive to the base coat.
The biggest growth in micro-encapsulating technology has been in perfume strips, possibly because of advancing printing capabilities. Fast, large-scale computer-operated printers with specialized extruder heads are necessary for accurate printing of perfume strips. There have been several new developments in perfume strips in the 1990s, such as pressure sensitive labels and strips that open to reveal tiny pearls of perfume powder that can be applied directly to skin. Future advances seem dependent on the coordination of perfumers, printing technology, and micro-encapsulation technology, in order to make commercially viable products.
Charbonneau, Jack and Keith Relyea. "The Technology Behind On-Page Fragrance Sampling." Drug and Cosmetic Industry, February 1997, pp. 48-52.
— Angela Woodward