Color-change indicator

Claim 2

A color-change indicator comprising: a liquid having a predetermined index of refraction and rate of evaporation; a reservoir for holding said liquid; and an opacifying layer of microporous material having an index of refraction approximately the same as that of the liquid, said opacifying layer overlying the reservoir and having an open-cell network of pores for absorbing the liquid from the reservoir, and said opacifying layer being in a first scattering condition for incident radiation when said liquid occupies said opacifying layer and in a second scattering condition when said liquid is depleted from said opacifying layer.

Claim 3

The indicator of claim 1 in which the opacifying layer is transparent in the first condition and opaque in the second condition due to internal ray scattering of incident radiation.

Claim 4

The indicator of claim 2 further including an image medium which is invisible when the opacifying layer is in the first condition and visible during the second condition.

Claim 5

The indicator of claim 3 in which the image medium includes a message element located in and penetrating through the opacifying layer which remains transparent in the second condition.

Claim 6

The indicator of claim 4 in which the message element is impressed on said opacifying layer.

Claim 7

The indicator of claim 5 in which the impression collapses a sufficient number of pores in the opacifying layer to allow transmission of incident radiation.

Claim 8

The indicator of claim 4 in which the message element is defined by resin having an index of refraction similar to that of the opacifying layer.

Claim 9

The indicator of claim 4 in which the image medium includes a layer of colored pigments beneath the opacifying layer.

Claim 10

The indicator of claim 3 in which the image medium includes: a message element located above the opacifying layer and having colored pigments; and a colored layer beneath the opacifying layer and having colored pigments similar in color to those of the message element.

Claim 11

The indicator of claim 2 further including an image medium which is visible when the opacifying layer is in the first condition and invisible during the second condition.

Claim 12

The indicator of claim 10 in which the image medium includes a message element located above the opacifying layer, having a visual appearance which matches that of the opacifying layer in the second condition such that the message element is visible in the first condition and invisible in the second condition.

Claim 13

The indicator of claim 10 in which the image medium includes a message element located beneath the opacifying layer.

Claim 14

The indicator of claim 12 in which the message element includes pigments in a porous adhesive which bonds the opacifying layer to the medium.

Claim 15

The indicator of claim 1 in which the reservoir includes macroporous absorbent material having pores larger than pores of the opacifying layer.

Claim 16

The indicator of claim 1 in which the liquid is transparent.

Claim 17

The indicator of claim 1 further including at least a second liquid having a different predetermined rate of volatilization.

Claim 18

The indicator of claim 1 in which the opacifying layer has an index of refraction within 0.1 of the index of the liquid.

Claim 19

The indicator of claim 1 in which the opacifying layer is less than 135 microns in thickness.

Claim 20

The indicator of claim 1 in which the opacifying layer has a cross-sectional thickness including at least ten pores.

Claim 21

The indicator of claim 19 in which the average size of the pores is at least as large as the wavelength of incident radiation.

Claim 22

The indicator of claim 1 in which the opacifying layer includes particles having an index of refraction approximately the same as that of the liquid.

Claim 23

The indicator of claim 21 in which the opacifying layer has a cross-sectional thickness including at least ten of said particles.

Claim 24

The indicator of claim 22 in which the average size of the particles is at least as large as the wavelength of incident radiation.

Claim 25

The indicator of claim 1 in which the opacifying layer remains in the first condition until the liquid is depleted from the reservoir and then abruptly changes to the second condition.

Claim 26

The indicator of claim 1 further including a removable barrier, overlying at least a portion of the opacifying layer, for retarding volatilization.

Claim 27

The indicator of claim 1 further including means for mounting the indicator on a product to be monitored.

Claim 28

The indicator of claim 1 in which the opacifying layer covers one portion of the reservoir and a vapor-barrier layer covers the remaining portion.

Claim 29

The indicator of claim 27 in which the reservoir is flattened in shape having the opacifying layer on its upper surface and the barrier layer on its lower surface.

Claim 30

A color-change indicator comprising: a liquid having a predetermined index of refraction and rate of evaporation; a reservoir for holding said liquid; and an opacifying layer of microporous material having an index of refraction similar to that of the liquid, said opacifying layer overlying the reservoir and having an open-cell network of pores for absorbing the liquid from the reservoir and for accomplishing release of said liquid at said rate of evaporation, said opacifying layer being in first scattering condition for incident radiation when said liquid occupies said opacifying layer and in a second scattering condition when said liquid is depleted from said opacifying layer, said opacifying layer remaining in the first condition until the liquid is depleted from the reservoir and then abruptly changing to the second condition within generally ten percent of the evaporative lifetime of said liquid.

Claim 31

A color-change indicator comprising: a liquid having a predetermined index of refraction and rate of evaporation; a reservoir for holding said liquid; and an opacifying layer of microporous material having an index of refraction similar to that of the liquid, said opacifying layer overlying the reservoir and having an open-cell network of pores for absorbing the liquid from the reservoir and for accomplishing release of said liquid at said rate of evaporation, said opacifying layer being in first scattering condition for incident radiation when said liquid occupies said opacifying layer and in a second scattering condition when said liquid is depleted from said opacifying layer, said opacifying layer remaining in the first condition until the liquid is depleted from the reservoir and then abruptly changing to the second condition within generally ten percent of the evaporative lifetime of said liquid.

Claim 32

A color-change indicator comprising: a liquid having a predetermined index of refraction and rate of evaporation; a reservoir for holding said liquid; an opacifying layer of microporous material having an index of refraction similar to that of the liquid, said opacifying layer overlying the reservoir and having an open-cell network of pores for absorbing the liquid from the reservoir and for accomplishing release of said liquid at said rate of evaporation, said opacifyig layer being in a first scattering condition for incident radiation when said liquid occupies said opacifying layer and in a second scattering condition when said liquid is depleted from said opacifying layer; and an image medium which is visible in one of said conditions and invisible in the other of said conditions.

Claim 33

A color-change indicator comprising: a liquid having a predetermined index of refraction and rate of evaporation; a reservoir for holding said liquid; an opacifying layer of microporous material having an index of refraction similar to that of the liquid, said opacifying layer overlying the reservoir and having an open-cell network of pores for absorbing the liquid from the reservoir and for accomplishing release of said liquid at said rate of evaporation, said opacifyig layer being in a first scattering condition for incident radiation when said liquid occupies said opacifying layer and in a second scattering condition when said liquid is depleted from said opacifying layer; and an image medium which is visible in one of said conditions and invisible in the other of said conditions.

Claim 36

The method of claim 31 in which the step of overlying includes laminating a film of microporous material to the reservoir.

Claim 37

The method of claim 31 in which the step of overlying includes coating the reservoir with a mixture of particles in a water-soluble solvent.

Claim 38

The method of claim 31 in which the step of overlying includes coating the reservoir with a solution of a polymer in a water-soluble solvent and immersing the reservoir in water.