Abstract: A selectively activated time-temperature integrating device for providing a visually observable indication of cumulative thermal exposure, in which a viscoelastic material migrates into a diffusely light-reflective porous matrix at a rate which varies with temperature to progressively change the light transmissivity of the porous matrix and thereby provide the visually observable indication. The viscoelastic material can comprise a pressure sensitive adhesive. The visually observable indication can comprise latent indicia which initially are not visible and become visible, obscurable indicia which initially are visible and become obscured, or a combination of both. Various actuating means for selectively switching the indicator from an unactivated state to an activated state are described.

Abstract: A porous material having a top surface and a bottom surface, and a dye applied to the bottom surface of the porous material. The dye is soluble in a volatile imaging liquid contained in a suitable marker, such that when the volatile liquid contacts the top surface of the porous media, the volatile liquid penetrates the porous media, dissolves at least some of the dye to provide a dye solution with at least some of the dye solution migrating to the top surface, and evaporates leaving a permanently visible mark of dye residue on the top surface of the porous material.

Abstract: An article capable of being marked by application of a colored or non-colored fluid thus creating a visible image thereon, said article comprising a substrate bearing a patterned or discontinuous barrier to said fluid.

Abstract: A reusable bingo card comprising an exposed microporous layer having bingo numbers permanently imprinted thereon, and a liquid impervious support sheet bonded to the exposed layer. The support sheet is substantially darker than the background area of the exposed layer. To mark a number on the card a colorless volatile liquid is applied to the exposed layer making the applied area transparent and exposing the support sheet below producing a contrasting indicia that is darker than the background area but lighter than the numbers. Evaporation of the marking liquid restores the bingo card to its original appearance for reuse.

Abstract: Improved imaging device for applying temporary indicia to substrate of the type having a base covered with a relatively light color, opaque, open cell microvoid-containing layer that is rendered translucent when the microvoids are filled with a liquid having a refractive index similar to that of the layer. The improvement in the imaging device involves insuring that the imaging liquid contains no substance having an evaporation rate less than about one-half of the liquid, thereby permitting the imaging device to be repeatedly applied to the same area of the substrate without leaving ghost images.

Abstract: Device which visually indicates exposure to a temperature within a predetermined range for a predetermined length of time. An opaque microporous sheet has a colored stratum on the back and a transparent fusible coating on the face. The coating is a solid solution of amorphous rubbery polymer in crystallizable solvent which, upon melting, gradually penetrates and transparentizes the microporous layer, rendering the colored stratum visible.

Abstract: Re-usable sheet material, having a dark colored base sheet provided on each side with a microvoid layer, temporarily imageable by application of volatile liquids, is treated on the face side with oleophobic (preferably also hydrophobic) fluorochemicals. Surface contamination of the face side with oil, which would cause permanent transparentization and prevent re-use, is readily removed by placing the face side of the sheet material in contact with the back side. One use for the product is as an order blank in the fast food industry.

Abstract: Microvoid-containing sheet material of the type which displays visible indicia when a liquid applied to the surface fills the microvoids. The improvement lies in making the liquid-receiving surface from particles held in pseudo-sintered juxtaposition by a thermoset binder, thereby rendering the structure resistant to inadvertent marking when it is subjected to heat, pressure, or both.