System for indicating exposure to preselected temperatures or tampering
AssigneeMinnesota Mining and Manufacturing Company
InventorDaniel B. Pendergrass, Jr.
Life of this patent
Estimating the term…
Abstract
Disclosed is a device for selectively indicating strain comprising a layer of polymeric binder and, distributed in or adjacent to the binder layer, microcapsules containing an indicating means, whereby when the binder is stiff, minor flexure of the device causes rupture of the microcapsules and releases the indicating means. This device has a non-stiff state such that a given strain applied to the binder layer in the non-stiff state will not release the indicating means, and a stiff state such that the same given strain applied to the binder layer in the stiff state will release the indicating means. Also disclosed is a method for determining exposure of an article to a given low temperature.
Claims32
A device for selectively indicating strain, comprising a layer of polymeric binder that is stiff below a preselected stiffening temperature, and distributed in or adjacent to said binder layer, microcapsules containing an indicating means, whereby when the binder is stiff, minor flexure of the device causes rupture of the microcapsules and releases the indicating means, said device having a non-stiff state above the stiffening temperature of the binder such that a given strain applied to the binder layer in the non-stiff state will not release the indicating means and having a stiff state below the stiffening temperature of the binder such that the same given strain applied to the binder layer in the stiff state will release the indicating means, wherein the stiffening temperature of the binder is less than about 110.degree. C.
A device for selectively indicating strain, comprising a layer of polymeric binder that may be made stiff by crosslinking, and distributed in or adjacent to said binder layer, microcapsules containing an indicating means, whereby when the binder is stiff, minor flexure of the device causes rupture of the microcapsules and releases the indicating means, said device having a non-stiff state before crosslinking of the binder wherein a given strain applied to the binder layer will not release the indicating means and a stiff state after crosslinking of the binder wherein the same strain will release the indicating means.
A device for selectively indicating strain, comprising a layer of polymeric binder that may be made stiff by loss of solvent from the binder, and distributed in or adjacent to said binder layer, microcapsules containing an indicating means, whereby when the binder is stiff, minor flexure of the device causes rupture of the microcapsules and releases the indicating means, said device having a non-stiff state before loss of solvent from the binder wherein a given strain applied to the binder layer will not release the indicating means and a stiff state after loss of solvent from the binder wherein the same strain will release the indicating means.
A method for detecting tampering by embrittling and delaminating of a laminated article, comprising including in said article a layer of polymeric binder having a stiffening temperature, and distributed in or adjacent to said binder layer, microcapsules containing an indicating means, whereby when the binder is stiff, minor flexure of the device causes rupture of the microcapsules and releases the indicating means, said device having a non-stiff state above the stiffening temperature of the binder such that a given strain applied to the binder layer in the non-stiff state will not release the indicating means and having a stiff state below the stiffening temperature of the binder such that the same given strain applied to the binder layer in the stiff state will release the indicating means, wherein the stiffening temperature of the binder is less than about 5.degree. C.
Dependencies are inferred from the claim text.