Microstructured time dependent indicators

Horology: time measuring systems or devices – Miscellaneous

Reexamination Certificate

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Details

C368S089000, C116S220000, C116S308000, C374S102000

Reexamination Certificate

active

06741523

ABSTRACT:

FIELD OF THE INVENTION
The present invention provides time dependent indicators including but not limited to timers and time/temperature indicators that preferably have a high level of accuracy and are easy to read. The invention also provides indicators that have uses as greeting cards, calendars, announcements, game pieces, novelty items, etc.
BACKGROUND OF THE INVENTION
Applications for time indicators may be divided into two broad categories. The first category requires time indicators that measure not only time but take into account the actual cumulative thermal exposure of the product. This objective is accomplished by having the rate of change of the indicator increase with temperature according to a desired function. Some such indicators exhibit a threshold temperature, below which the indicator does not change. Others respond more continuously to changes in temperature. This type of time indicator is typically referred to as a “time-temperature indicator”.
The second category of applications requires time indicators in which the thermal sensitivity is minimized. Thus, in this application the time indicators work much like a timepiece, giving a visual indication of time elapsed. This type of time indicator is frequently referred to as a “timer”.
Timers and time-temperature indicators are known which operate by chemical reaction mechanisms, diffusion mechanisms, and capillary driven fluid wicking mechanisms. For a discussion of several types of indicators, reference is made to Dee Lynn Johnson, Indicating Devices, in
The Wiley Encyclopedia of Packaging Technology,
400-406 (John Wiley & Sons, 1986).
A selectively activated time-temperature integrating device providing a visually observable indication of cumulative thermal exposure is disclosed in U.S. Pat. No. 5,667,303 (Arens, et al.). In this device a viscoelastic material migrates into a porous matrix at a rate varying with temperature and progressively changes the transmissivity of light through the porous film to provide a visually observable indication. The viscoelastic material can comprise a pressure sensititve adhesive. The visually observable indication comprises latent indicia which are not initially visible later and become visible. The device is activated by lamination of a front and back part.
A time-temperature indicator that operates on diffusion properties and provides a visual indication by means of a chemical reaction is disclosed in U.S. Pat. No. 5,053,339 (Patel). This patent discloses a color changing device for monitoring the time-temperature history of perishable products containing an activator tape and an indicating tape. The activator tape contains an activator composition matrix that includes an activating composition such as an organic acid. The indicating tape includes an indicating composition matrix that includes an indicating composition such as an acid-base dye indicator. One or both of the matrices is a pressure sensitive adhesive. The indicator produces a color change as the activating composition diffuses out of the activator matrix and into the indicator matrix and chemically reacts with the indicating composition in the indicating matrix. The color intensifies with time and temperature as more activator composition diffuses into the indicator matrix and reacts.
Another type of indicator is disclosed in U.S. Pat. No. 3,954,011 (Manske). This patent discloses an indicator including a porous fluid carrying pad, a saturant material, a wick material for the saturant, and an indicator means whereby the progress of the saturant from the porous carrying pad along the wick material can be visibly indicated and used to measure the passage of time, the exposure to a given minimum temperature, or a time-temperature relationship. When the saturant is chosen so as to be in a liquid state at the intended storage temperature, the indicator indicates the passage of a time interval as the liquid progresses along the wick. The saturant may instead be selected so as to be solid at desired storage temperatures at which frozen foods are stored and to become liquid at temperatures at which the food is thawed. The saturant will remain solid while the indicator is at the desired storage temperature. The saturant will melt to a penetrating state and then progress along the wick while the indicator is above the predetermined temperature, thereby indicating the passage of time above the predetermined temperature. A plurality of saturant materials having varying freezing points, each having its own wicking path, can be used to indicate time of exposure to discrete predetermined temperature ranges.
Another indicator is disclosed in U.S. Pat. No. 4,428,321 (Arens). This patent discloses a device which provides a visual indication that permissible time within a predetermined temperature range has been exceeded. The device includes an opaque microporous sheet with a colored stratum on its back and a transparent fusible coating bonded to its face. The fusible coating is a solid solution of an amorphous rubbery polymer dissolved in a crystallizable solvent such as wax. The solvent has a melting point below the lower end of the predetermined temperature range and the polymer has a glass transition temperature below the lower end of the predetermined temperature range. Below the melting temperature of the solvent, the composition is a non-penetrating solid. When the indicator is heated to a predetermined temperature, the solid wax solvent melts and dissolves the rubbery polymer, resulting in a liquid penetrating state which gradually penetrates the microporous layer. The refractive index of the polymer and wax composition is essentially the same as that of the solid component of the microporous layer, rendering the microporous layer gradually transparent.
U.S. Pat. No. 4,154,107 (Giezen et al.) describes a time temperature indicating device having an indicator layer and a signaling component in a reservoir which migrates to the indicating layer and causes the indicator layer to undergo a visually perceptible change.
U.S. Pat. No. 2,896,568 (Pryor et al.) discloses a temperature indicating device comprising substances introduced in liquid form into a plurality of wells and frozen in situ, which substances melt and migrate out of the wells as a result of gravity or capillary attraction or both and the migration may be detected by observation.
U.S. Pat. No. 3,999,946 (Patel et al.) describes a time-temperature history indicator, which contains compositions containing at least two conjugated acetylene groups which exhibit sequences of irreversible color changes at combinations of time and temperature. The device may be supported on the surface of a product or on a substrate.
Other types of known time indicators, which are generally short-term time indicators, are based on the gradual diffusion or migration of a substance such as an ink from one substrate through another substrate, i.e. in a path perpendicular to the surface of the substrate. After the ink or other substance migrates through the substrate(s) it is viewed on a display surface to thereby indicate that the predetermined time period has elapsed.
U.S. Pat. No. 4,903,254 (Haas) describes a time indicator comprising a number of layers that are adhered together. The indicator has a front part and a rear part. The rear part comprises an ink pattern layer upon rear support member and the front part comprises a transparent support member and an opaque adhesive layer. The adhesive layer is capable of dissolving the ink pattern and has a front ink display surface. Contacting the front part and rear part activates the dissolution and migration of ink from the ink pattern layer to the front ink display surface.
U.S. Pat. No. 5,364,132 (Haas et al) describes a reusable self-expiring security identification badge including a base substrate having a void indicia area, an ink substrate having an expired indicia area of a soluble ink and an adhesive surface and an overlay substrate having an ink dissolver and a display surface. When the badge is issued, the inked substrate

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