WO2000005681A1

WO2000005681A1 - Rewriteable optical-scanner-readable code strip

Info

Publication number: WO2000005681A1
Application number: PCT/IB1999/001399
Authority: WO
Inventors: Steven Blackmore; Stephen Hunt
Original assignee: Datastrip International Limited
Priority date: 1998-07-24
Filing date: 1999-07-23
Publication date: 2000-02-03
Also published as: AU4925599A

Abstract

A rewriteable code strip containing encoded code in distinct bar-space patterns is provided comprising a thermochromic material having two optical states and a plurality of bit areas therein. Each of the bit areas can be in either one of the two optical states to thereby form the distinct bar-space patterns. The optical state of each of the bit areas is switchable thus enabling rewriting of the distinct bar-space patterns.

Description

REWRITEABLE OPTICAL-SCANNER-READABLE CODE STRIP

FIELD OF THE INVENTION

The subject invention broadly relates to bar-code code strips, "Datastrip" code strips, and other optical-scanner-readable code strips containing encoded data in distinct optically-contrasting biphasic, multiareal geometric patterns, and more particularly relates to such optical-scanner-readable code strips which can be repeatedly rewritten to encode changed or new data.

BACKGROUND OF THE INVENTION

Conventional bar-code code strips, Datastrip code strips, and other optical- scanner-readable code strips contain information encoded in a distinct pattern of printed areas and blank spaces. The information encoded by the pattern of presence or absence of printing of such a code strip can be retrieved by optically scanning the code strip with an optical scanner to convert the pattern to an electronic signal which can be decoded digitally. A bar-code code strip consists of a row of essentially parallel rectilinear bars or lines extending perpendicular to the row and spaced and dimensioned to convey encoded information when scanned transversely to the rectilinear areas along the length of the row. Datastrip code strips are two dimensional patterns composed of multiple rows of distinct printed and blank areas capable of encoding thousands of characters or other data in a relatively limited space.

Conventional bar-code code strips and Datastrip code strips are readily printable by customary printing processes or photographic processes. Such bar-code code strips and Datastrip code strips are also easily and accurately readable by standard optical scanners suitably programmed to decode the data encoded by the code strips. As a result of the ease by which bar-code code strips and Datastrip code strips can be printed and read, such code strips have been employed in a wide variety of applications. Bar-code and Datastrip code strips are routinely used, for example, for product identification and pricing, inventory control, the routing and tracking of packages and baggage, employee or visitor identification, and ticketing and access control.

One limitation of conventional bar-code and Datastrip code strips is that, heretofore, the information encoded therein could not be readily modified or changed. For example, once printed, a conventional bar-code code strip cannot be conveniently altered to change its distinctive bar-space pattern so as to change the information encoded in the code strip. Should the information encoded in a bar-code code strip need to be modified or changed, an entirely new bar-code code strip must be printed and the original code strip must be discarded, or masked by the new code strip or otherwise, to prevent the original bar-code code strip from being scanned. Because of the difficulties in changing data encoded by bar-code code strips and Datastrip code strips, such code strips have largely not been employed in applications where data routinely changes or needs to be updated.

Thermochromic materials have been used to produce thermochromic displays which can be repeatedly rewritten by thermal processing. Thermal processing of a thermochromic display provides for writing of text or images in the display by thermally setting the thermochromic material in selected localized regions of the display in one of two optical states stable at ambient temperatures; one state serving as background, the other serving to form the text or image. Moreover, after a region of the thermochromic material has been set to one of the two optical states, it can be reset to the other optical state by thermal processing. Consequently, a thermochromic display displaying given text or image material can be rewritten by thermal processing to display new text or image material. According to a publication by K.M. Moses entitled "TC: The Message Card," in

Card Forum International, Volume , pages 51-55 (19 ) ("the Moses publication") thermochromic technology permits thermochromic displays to be realized on thick plastic cards, thin plastic cards, and paper/carton based material. The Moses publication disclosed thin plastic cards, each having a magnetic stripe and a thermochromic display.

According to the Moses publication, information could be recorded on the magnetic stripe of such a card and the thermochromic display of the card could be used to display the information in visually-readable form for verification by a customer or the issuer of the card, or to display reminders or advertising. The Moses publication disclosed that thermochromic displays could also be used on thick plastic cards having semiconductor chips incorporated in the cards, so that information could be stored in the semiconductor chip of such a card and the thermochromic display could be used to provide a visually- readable message. Both the thick and thin plastic cards described in the Moses publication, however, require information to be read into the card by two separate mechanisms: i.e. , into the magnetic stripe or semiconductor chip of the card by a magnetic or electronic mechanism and separately into the thermochromic display of the card by a thermal printer.

SUMMARY OF THE INVENTION

The subject invention concerns a rewriteable optical-scanner-readable code strip displaying data encoded in an optically-contrasting biphasic, multiareal geometric pattern such as a bar-code code or a Datastrip code. The code strip of the invention comprises a sheet of a thermochromic material having at least a portion divided into a plurality of thermochromic display elements. Each thermochromic display element of the sheet of thermochromic material is stably maintainable at room temperature in one of a first optical state and a second optical state. The first and the second optical state are optically contrasting as detected by the optical scanner. The optical states of each thermochromic display element of the sheet of thermochromic material is repeatedly switchable between the first and the second optical state by means of heating or other thermal treatment carried out on the display element. Collectively, the optically contrasting first and second optical states of the respective thermochromic display elements of the sheet of thermochromic material form an optical-scanner-readable display of an optically-contrasting biphasic, multiareal geometric pattern encoding the data.

In another aspect, the instant invention concerns a method of thermally writing a rewriteable optical-scanner-readable code strip to scanner-readably display data encoded in an optically-contrasting biphasic, multiareal geometric pattern. The code strip includes a sheet of a thermochromic material having at least an encoded-data display portion divided into a plurality of thermochromic display elements. Each thermochromic display element of the sheet of thermochromic material is stably maintainable at room temperature in one of a first optical state and a second optical state, with the first and the second optical state being scanner-detectably optically contrasting. The optical state of each thermochromic display element of the sheet of thermochromic material is repeatedly switchable between the first and the second optical state by means of thermal treatment carried out on the display element. The method of the invention includes the step of thermally treating selected display elements of the encoded-data display portion of the sheet of thermochromic material so that the optically contrasting first and second optical states of the respective thermochromic display elements of the sheet of thermochromic material collectively form an optical-scanner-readable display of an optically-contrasting biphasic, multiareal geometric pattern encoding the data.

In a preferred embodiment of the rewriteable code strip of the invention, the sheet of thermochromic material is mounted on a substrate.

To achieve optical contrast between the first and second optical states in the thermochromic material of preferred embodiments of the invention, the first optical state may be more transparent to light than the second optical state. In certain preferred embodiments, the first optical state is more transparent to infrared light than the second optical state. In such embodiments, it is preferred for the sheet of thermochromic material to be mounted on a substrate and portions of the substrate adjacent to the sheet of thermochromic material to be composed of an infrared light absorbing material. Preferably in such embodiments, the substrate includes a layer of an infrared light absorbing material adjacent to the sheet of thermochromic material.

For certain applications, it is advantageous to provide the rewriteable code strip of the invention with a protective overlayer overlaying the sheet of thermochromic material. The overlayer is preferably substantially transparent to light.

In alternative preferred embodiments of the rewriteable code strip of the invention in which the sheet of thermochromic material is mounted on a substrate, it is preferred for surface portions of the substrate adjacent to the sheet of thermochromic material to reflect light.

In a preferred embodiment of the rewriteable code strip of the invention, the sheet of thermochromic material includes a text-display portion which visibly displays human- readable textual data such as an alphanumeric representation of the data encoded in the optical-scanner-readable geometric pattern on the sheet of thermochromic material.

Because of their ease of use and large data storage capacity, rewriteable Datastrip code strips of the invention are expected to find use in, for example, pre-paid debit or cash cards, telephone cards, multiple- or limited-use transit tickets or passes, hospital charts, driving licenses, health cards, prescription cards, loyalty cards, or membership cards. For example, a driver's license could incorporate a rewriteable Datastrip code strip with encoded data specifying categories of vehicles the driver is permitted to drive, disabilities of the driver, speeding tickets and other offenses, parking violations, and convictions. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In a prefened embodiment of the subject invention, a rewriteable code strip employs a thermochromic material capable of exhibiting either one of two optical states at ambient temperatures as the material on which a distinct geometric code pattern of the code strip is written. Preferred thermochromic materials have two stable optical states at ambient temperatures between which they can be reversibly switched by thermal processing at temperatures greater than ambient temperatures.

The two optical states of a prefened thermochromic material as used in a thermochromic display of a code strip of the invention should be sufficiently different in their interaction with light at wavelengths used by the optical scanner employed to read the code strip to be distinguishable by that particular optical scanner. For example, if the optical scanner detects reflected infrared light, the reflectance of the two optical states of the thermochromic material as used in the code strip with respect to infrared light of the optical scanner should be sufficiently different for the optical scanner to determine effectively whether a display area of a code pattern is written in the code strip in the first or second optical state.

The difference in light reflectance between the two optical states of a sheet of thermochromic material can be increased by selection of an appropriate contrasting background. Preferably, the thermochromic material of a code strip of the invention is layered on a substrate. The substrate may provide a contrasting background to increase the light reflecting disparity between the two optical states of the thermochromic material. For example, the substrate may have a coating of a layer of a contrasting material adjacent to the thermochromic material to provide the contrasting background. The contrasting background may be absorbent or reflective of the light used by the optical scanner.

Presently, typical optical scanners have a peak sensitivity of about 500V/ (L_x s). Particularly prefened thermochromic materials for the invention have one optical state which is substantially opaque, and another optical state which is substantially transparent. In the substantially opaque optical state, such thermochromic material appears white due to light scattering in the material. Providing such a prefened thermochromic material with a black or other light absorbent background to form a thermochromic display enhances the optical contrast between the white appearing, substantially opaque optical state and the transparent optical state which appears dark due to the light absorbing backing.

When a light absorbing background is employed for a sheet of such prefened thermochromic material in a rewriteable code strip of the invention, providing an air gap between the sheet of thermochromic material and the light absorbing background can further enhance the optical contrast between the substantially opaque optical state and the substantially transparent optical state of the thermochromic material. Specifically, light scattering in the opaque state is increased by the air gap because a significant portion of the scattered light is the result of reflections taking place at the side of the thermochromic material layer where two optical media with different refractive indices interface — the thermochromic material and the air. The increase in light scattering in the thermochromic material in the substantially opaque optical state caused by the air gap causes the material in that state to appear whiter than the material would appear were there no air gap. Alternatively, if the thermochromic material is layered on a transparent substrate, an air gap may be provided between a sheet of light-absorbing backing material and the side of the transparent substrate opposing the layer of thermochromic material to enhance the optical contrast between the substantially opaque optical state and the substantially transparent optical state of the thermochromic material.

If a sheet of such a prefened thermochromic material having a substantially opaque optical state and a substantially transparent optical state is provided with a backing of aluminum foil or other light reflective material, an air gap between the thermochromic material and the reflective material provides no substantial enhancement in the apparent whiteness of the substantially opaque optical state, since the reflective backing provides for light reflection at the surface of the thermochromic material facing the backing even without an air gap. It is generally less expensive to provide a sheet of thermochromic material with a backing of a reflective aluminum foil than to provide the thermochromic material with a light absorbent backing material with an air gap interposed between the thermochromic material and the backing material. Because the apparent intensity of light reflected from the reflective backing through a region of the thermochromic material in the substantially transparent optical state can depend on an illumination angle at which the light entered the region and a viewing angle along which the light is viewed, the apparent optical contrast between the substantially opaque optical state and the substantially transparent optical state can depend on the illumination angle and the viewing angle, which can add complications to reading a geometric code displayed on such a reflective-material backed thermochromic display with an optical scanner and offset the economy of manufacture of such reflective-material backed thermochromic displays.

A particularly prefened embodiment of the rewriteable code strip of the invention includes a sheet of thermochromic material with a light absorbing background. In such an embodiment, one of the two optical states of the thermochromic material is more transparent to the scanning light from the optical scanner and the other optical state is more opaque to the scanning light. The light from the optical scanner will therefore more readily pass through the thermochromic material in the more transparent optical state, be absorbed by the light absorbing background and less light will be reflected back to the scanner than from thermochromic material in the more opaque white-appearing optical state. The more transparent optical state is thus the less reflective optical state and the more opaque optical state is the more reflective optical state of the thermochromic material. An infrared light absorbing background is particularly advantageous in this prefened embodiment. In reading such a data strip, an infrared light source and infrared light detectors would be employed by the optical scanner. With the use of infrared light, signal to noise ratios are generally increased, thereby increasing accuracy of reading the encoded data.

Suitable infrared light absorbing background materials employable in the present invention include black paints or black ink.

Reflective background materials prefened for use in code strips of the instant invention include aluminum.

Where the light reflective or absorptive background material is employed in a manner requiring a supportive substrate for the background material, suitable substrates include polyethylene terephthalate ("PET"), paper, card stock, and cardboard.

In embodiments where the light reflective or absorptive background substrate does not also serve as the backing substrate for the thermochromic material, PET, polyvinylchloride, polycarbonate, and paper among other substrates, are suitable for the backing substrate.

Thermochromic material layered onto a reflective background substrate is commercially available. For example, ETIP, GmbH (Erasable Thermographic Imaging

Products), Am Honigbirnbaum 38, D-65812 Bad Soden, Germany ("ETIP"), markets a thermochromic material product under the trade designation "BC550 TC," which consists of a transparent PET substrate onto which in turn a reflective aluminum layer, thermochromic material layer and a protective layer are deposited. ETIP also markets a product under the trade designation "HC 350-NTC" which is a similar product to

"BC550 TC" with a contact adhesive deposited on the opposing side of the PET substrate. ETIP also markets a product under the trade designation "BA 520 TC" which consists of a transparent PET substrate onto which thermochromic material and protective layers are deposited and which allows the user to select the type of contrasting background desired. The aforementioned thermochromic materials available from ETIP, when employed in the present invention, provide for a rewriteable code strip on which data can be encoded in an optical-scanner readable fashion preferably as a bar-code code or a Datastrip code.

The thermochromic material of the ETIP "BA 520 TC" product can assume two stable optical states at room temperature, a more opaque optical state characterized by a milky white color, and a more transparent optical state. When in the more opaque optical state, the thermochromic material obscures the contrasting backing material like a layer of white paint resulting in a white surface appearance. When in the more transparent optical state, the contrasting backing material can be seen through the thermochromic material resulting in a surface appearance conesponding to the color of the contrasting backing material (preferably, black). Thus, a distinct bar-code pattern can be thermally written into the "BA 520 TC" thermochromic display using a black backing material, as essentially black bars on an essentially white background.

With the thermochromic displays noted above available from ETIP, if the thermochromic material is initially in the more opaque optical state, the optical state slowly changes from the more opaque optical state to the more transparent optical state upon heating the material to temperatures from about 87 degrees Centigrade to about 105 degrees Centigrade. If initially in the more transparent optical state, the optical state does not change when the thermochromic material is heated to a temperature in the range of from about 87 to about 105 degrees Centigrade. Heating the thermochromic material to a temperature of from about 105 degrees Centigrade to about 125 degrees Centigrade results in the thermochromic material remaining in, or switching to and stabilizing in, the more transparent optical state. Heating the thermochromic material to a temperature above about 125 degrees Centigrade results in the thermochromic material remaining in, or switching to and stabilizing in, the more opaque optical state. A desired bar-code code pattern or Datastrip code pattern can be written into such a prefened thermochromic display by heating a first group of display areas on the thermochromic display to a temperature in the range of from about 105 to about 125 degrees Centigrade to set the thermochromic material of the first group of display areas into the more opaque optical state and heating a second group of select display areas on the thermochromic display to a temperature greater than about 125 degrees Centigrade to set the thermochromic material of the second group of display areas into the more transparent optical state, with the first and second groups of display areas being selected to define the desired bar-code code or Datastrip code pattern. The process can be repeated on the same thermochromic display to rewrite the display with new or altered bar-code or Datastrip code patterns.

Writing or rewriting bar-code code or Datastrip code patterns in such a prefened thermochromic material can be accomplished through the use of devices using thermal printing technology such as direct thermal printers, thermo transfer printers and thermal sublimation printers. In general, resolution is dependent on printer capabilities.

Resolution values of 200 dots-per-inch are readily achievable, with higher resolutions of 300 dots-per-inch being achievable with cunent state-of-the-art thermal printers.

In addition to an optical-scanner-readable geometric pattern, the code strip of the invention may have human-readable text or symbols accompanying the pattern. Such text or symbols may be printed permanently alongside the rewriteable thermochromic display, if desired.

In an alternative prefened embodiment of the invention, human-readable text or symbols are thermally written in a portion of the thermochromic display separate from the portion of the display on which the optical-scanner readable geometric pattern is written. In such an embodiment, the thermochromic material is divided between two disjoint regions, each containing a plurality of display areas. In the first region, the display areas collectively define at least one optical-scanner-readable pattern by being in either the first or second optical state. In the second region, the display areas collectively define at least one human-readable message by being in either the first or second optical state.

Writing of human-readable text or symbols in the thermochromic material may be performed separately from the writing of the optical-scanner-readable geometric pattern or at the same time, and with the same thermal printer, as the writing of the optical- scanner readable pattern. In such an embodiment, the human-readable text or symbols may be thermally rewritten either separately from, or at the same time, as rewriting of the optical-scanner-readable geometric pattern.

In another prefened embodiment of the invention, an overprint of human- readable text, patterns or solid colors may be printed over the thermochromic display or the optical-scanner readable pattern with an ink that is substantially transparent to infrared light used by the optical scanner to read the code strip. By such an embodiment, information in addition to that encoded in the code strip can be conveyed, or the existence of all or a portion of the optical-scanner-readable pattern can be camouflaged.

It is generally prefened to provide a protective overlay over the thermochromic material to protect it from damage and the environment. Suitable protective overlay for many applications is PET film.

Once written, the code strip of the present invention can be read by readily available optical scanners suitably programmed to read the optical-scanner-readable patterns. Linear scanners, rastering laser scanners, or two-dimensional imaging devices may be selected by one skilled in the art as appropriate to read a particular code strip. Variations and modifications may be made in this invention without departing from its spirit and scope. Accordingly, the foregoing description is to be construed as being illustrative and not limiting.

Claims

WHAT IS CLAIMED IS:

1. A rewriteable optical-scanner-readable code strip scanner-readably displaying data encoded in an optically-contrasting biphasic, multiareal geometric pattern, the code strip comprising a sheet of a thermochromic material having at least an encoded-data-display portion divided into a plurality of thermochromic display elements, each thermochromic display element of the sheet of thermochromic material being stably maintainable at room temperature in one of a first optical state and a second optical state, the first and the second optical state being scanner-detectably optically contrasting, the optical states of each thermochromic display element of the sheet of thermochromic material being repeatedly switchable between the first and the second optical state by means of thermal treatment carried out on the display element, the optically contrasting first and second optical states of the respective thermochromic display elements of the sheet of thermochromic material collectively forming an optical-scanner-readable display of an optically-contrasting biphasic, multiareal geometric pattern encoding the data.

2. The rewriteable code strip of claim 1 wherein the first optical state is more light reflective than the second optical state.

3. The rewriteable code strip of claim 1 in which the sheet of thermochromic material is mounted on a substrate.

4. The rewriteable code strip of claim 3 wherein the first optical state is more transparent to light than the second optical state.

5. The rewriteable code strip of claim 4 wherein the first optical state is more transparent to infrared light than the second optical state.

6. The rewriteable code strip of claim 5 wherein portions of the substrate adjacent to the sheet of thermochromic material are composed of an infrared light absorbing material.

7. The rewriteable code strip of claim 6 wherein the substrate includes a layer of an infrared light absorbing material adjacent to the sheet of thermochromic material.

8. The rewriteable code strip of claim 7 wherein a protective overlayer overlays the sheet of thermochromic material, the overlayer being substantially transparent to infrared light.

9. The rewriteable code strip of claim 4 wherein surface portions of the substrate adjacent to the sheet of thermochromic material reflect light.

10. The rewriteable code strip of claim 4 wherein an air gap is provided between portions of the sheet of thermochromic material and the substrate.

11. The rewriteable code strip of claim 1 wherein the sheet of thermochromic material includes a text-display portion which visibly displays human-readable text.

12. The rewriteable code strip of claim 11 in which the human-readable text visibly displayed in the text-display portion of the sheet of thermochromic material represents the data encoded by the optically-contrasting biphasic, multiareal geometric pattern scanner-readably displayed in the encoded-data-display portion of the sheet of thermochromic material.

13. The rewriteable code strip of claim 1 wherein the geometric pattern encoding the data is a bar-code code or a Datastrip code.

14. A method of thermally writing a rewriteable optical-scanner-readable code strip to scanner-readably display data encoded in an optically-contrasting biphasic, multiareal geometric pattern, the code strip comprising a sheet of a thermochromic material having at least an encoded-data display portion divided into a plurality of thermochromic display elements, each thermochromic display element of the sheet of thermochromic material being stably maintainable at room temperature in one of a first optical state and a second optical state, the first and the second optical state being scanner-detectably optically contrasting, the optical state of each thermochromic display element of the sheet of thermochromic material being repeatedly switchable between the first and the second optical state by means of thermal treatment carried out on the display element, the method including the step of thermally treating selected display elements of the encoded-data display portion of the sheet of thermochromic material so that the optically contrasting first and second optical states of the respective thermochromic display elements of the sheet of thermochromic material collectively form an optical- scanner-readable display of an optically-contrasting biphasic, multiareal geometric pattern encoding the data.

15. The method of claim 14 further including the step of, prior to thermally treating selected thermochromic display elements, thermally treating all of the thermochromic display elements of the encoded-data display portion of the sheet of thermochromic material to place all of the display elements in the first optical state or all of the display elements in the second optical state, thereby erasing data previously encoded by an optically-contrasting biphasic, generally rectangular multiareal geometric pattern in the encoded-data display portion.

16. The method of claim 14 wherein the geometric pattern is a bar-code code or a Datastrip code.