Method for making a laser recordable wallet-size plastic card

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TECHNICAL FIELD

The invention relates to optical information storage.

BACKGROUND ART

Dil, in U.S. Pat. No. 4,209,804, teaches a reflective information recording structure which contains prepressed V-shaped grooves in which data may be recorded by local melting of the reflective metal coating by a laser. The data on the media is read by means of optical phase shift effects. Since the preformed grooves are at an optical phase depth of 95.degree. to 140.degree., the reading laser must be of the precise wavelength corresponding to the groove depth. The information area has a width of approximately 0.6 microns, so a thick protective substrate, usually 1200 microns deep is used to ensure that one micron surface dust particles are out-of-focus for the read beam.

Such thick protective materials cannot be used for wallet cards which have a total thickness of only 800 microns under ISO (International Standards Organization) standards and further it would be uncomfortable to carry a rigid card in trouser pockets or wallets. Also, it is difficult to bond a phase sensitive recording/reading surface to a protective laminating material with an adhesive without introducing a varying phase shift across the surface. It is also impractical to melt large holes since a large lip would be formed around the hole causing a great distortion of the phase shift. Edge transition of the hole is the phase shift which is measured, and since the height of the lip is directly proportional to the square root of the hole diameter, phase shift reading is only practical for small holes. For example, a 25 micron diameter hole creates a lip with one micron height, which is much larger than the wavelength of the reading beam. Thus for large holes and bonded protective materials it is desirable to have a recording/reading structure that does not rely on phase shifts.

Lahr in U.S. Pat. No. 3,873,813 teaches a debit card in which use is indicated by alteration of a spot of heat sensitive coating in a selected area thereby permanently changing the reflective characteristics of that area. A reflective heat sensitive material becomes transparent on heating, thereby exposing an underlying strip of black paper which then absorbs the light energy. Recording requires exposure to a high intensity light beam for 0.7 second to raise the temperature of the material to 175.degree. F. and an additional 5 milliseconds above 175.degree. F. This type of credit card system permits recording of less than two data bits per second. Because of the retained, diffused liquid, the sizes of the data spots are large and difficult to regulate. This card requires a blue read beam, therefore scratches and surface dust will cause a large number of data errors unless very large data spots are used that reduce capacity to under 10,000 bits. While this data capacity is satisfactory for some debit and credit cards, it is unsuitable for detailed recording of financial, insurance, medical and personal records. Also, the recording rate of less than two bits per second would make it unacceptable for use in most applications. Another disadvantage of this card is that all of the data is destroyed if its temperature reaches 175.degree. C., for example on the dashboard of a car or if passed through a household washer and dryer.

Nagata in U.S. Pat. No. 4,197,986, Girard in U.S. Pat. No. 4,224,666 and Atalla in U.S. Pat. No. 4,304,990 teach updating of data cards. Nagata teaches the updating of maximum limits and balance on a card in which the complete data file is in an auxiliary memory circuit such as a magnetic disc or drum. A sales slip containing the transaction is recorded separately from the card. Giraud teaches a data-processing machine-access card containing an integrated circuit chip with a memory bank. The memory stores predetermined items of confidential data intended to authorize or prevent access to the machine. Only the balance is updated.

Atalla teaches a card in which only the balance is recorded and updated. This card can only be used where the transaction system is connected to a central computer. None of these cards has the memory storage capacity needed to accumulate records of past transactions.

Various recording media have been developed for use on a rotating disc format. Because the disc is spinning rapidly, short laser pulse times (on the order of 500 nanoseconds) are necessary to confine the heating to small spots. The media have been developed to increase the sensitivity to the beam by varying the parameter of media absorptivity. Spong in U.S. Pat. Nos. 4,190,843 and 4,305,081 puts an absorptive dye layer over a reflective aluminum layer. Spots are recorded by ablation of the dye layer exposing the underlying reflective layer. Bell in U.S. Pat. No. 4,300,143, teaches a similar technique. Bartolini in U.S. Pat. No. 4,313,188 adds a protective layer between the dye layer and the reflective layer. Wilkinson in U.S. Pat. No. 4,345,261 uses a light absorptive silica dielectric layer in place of the dye layer. Terao teaches an inorganic absorptive layer over an organic recording film layer. Holes are formed in the film layer by heat generated in the absorptive layer. Suzuki in U.S. Pat. No. 4,202,491 uses a fluorescent ink layer on which data spots emit infrared radiation. Improved sensitivity is obtained in these media at the expense of extra layers which increase complexity and cost. This increased sensitivity is not necessary for a card format.

DISCLOSURE OF INVENTION

It is the object of the present invention to devise a wallet-size plastic data card containing a laser recordable strip and a system for sequential recording transaction data on the data card with a laser where the data on the card optically contrasts with the surrounding unrecorded field. It is also an object of the invention to perform related sequential laser recording of transactions and events related to the fields of insurance, personal medical records, personal information, banking and related data records.

It is a further object of the invention to devise a wallet-size card, containing a laser recordable strip, that meets the ISO dimensions for plastic credit cards, has a capacity of at least 250,000 bits, can record data at thousands of bits per second and contains prerecorded information such as reference position on the strip, and would not degrade at temperatures of 175.degree. F. or higher.

These objects were met with a wallet-size sealed plastic card only 800 microns thick containing a laser recordable strip using data spots up to 25 microns in size to minimize reading errors and which also contains prerecorded information on the strip such as reference position information. The data system of the present invention relies on reading of optical contrast ratios. The card is formed by first prerecording information on the strip, adhering the strip on the card base, bonding protective, transparent material over the strip and then recording transaction information with a laser. The prerecording can be done by photolithography, laser recording or surface molding.

One of the chief advantages of the present invention is the high information capacity of laser recording media strips. Typically, high resolution laser recording materials record spots of altered reflectivity optically contrasting with the surrounding reflective field and having dimensions less than 25 microns. A high capacity laser recording material strip enables a credit card to carry the equivalent of scores of pages of text, more than ample for most applications. The transaction card of the present invention is suitable for accumulating sequentially recorded data involving financial transactions, insurance transactions, medical information and events, and personal information and identification.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view of one side of a data card in accord with the present invention.

FIG. 2 is a partial side sectional view taken along lines 2--2 in FIG. 1.

FIG. 3 is a detail of laser writing on a portion of the laser recording strip illustrated by dashed lines in FIG. 1.

FIG. 4 is a plan view of an apparatus for reading and writing on the optical recording media strip illustrated in FIG. 1.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to FIGS. 1 and 2, a data card 11 is illustrated having a size common to most credit cards. The width dimension of such a card is approximately 54 mm and the length dimension is approximately 85 mm. These dimensions are not critical, but preferred because such a size easily fits into a wallet and has historically been adopted as a convenient size for automatic teller machines and the like. The card's base 13 is a dielectric, usually a plastic material such as polyvinyl chloride or similar material. Polycarbonate plastic is preferred. The surface finish of the base should have low specular reflectivity, preferably less than 10%. Base 13 carries strip 15. The strip is about 15 millimeters wide and extends the length of the card. Alternatively, the strip may have other sizes and orientations. The strip is relatively thin, approximately 100-500 microns, although this is not critical. The strip may be applied to the card by any convenient method which achieves flatness. The strip is adhered to the card with an adhesive and covered by a transparent laminating sheet 19 which serves to keep strip 15 flat, as well as protecting the strip from dust and scratches. Sheet 19 is a thin, transparent plastic sheet laminating material or a coating, such as a transparent lacquer. The material is preferably made of polycarbonate plastic.

The opposite side of base 13 may have user identification indicia embossed on the surface of the card. Other indicia such as card expiration data, card number and the like may be optionally provided.

The high resolution laser recording material which forms strip 15 may be any of the reflective recording material which have been developed for use as direct read-after-write (DRAW) optical disks, so long as the materials can be formed on thin substrates. An advantage of reflective materials over transmissive materials is that the read/write equipment is all on one side of the card and automatic focus is easier. For example, the high resolution material described in U.S. Pat. No. 4,230,939 issued to de Bont, et al. teaches a thin metallic recording layer of reflective metals such as Bi, Te, Ind, Sn, Cu, Al, Pt, Au, Rh, As, Sb, Ge, Se, Ga. Materials which are preferred are those having high reflectivity and low melting point, particularly Cd, Sn, Tl, Ind, Bi and amalgams. Suspensions of reflective metal particles in organic colloids also form low melting temperature laser recording media. Silver is one such metal. Typical recording media are described in U.S. Pat. Nos. 4,314,260, 4,298,684, 4,278,758, 4,278,758, 4,278,756 and 4,269,917, all assigned to the assignee of the present invention. The laser recording material which is selected should be compatible with the laser which is used for writing on it. Some materials are more sensitive than others at certain wavelengths. Good sensitivity to infrared light is preferred because infrared is affected least by scratches and dirt on the transparent laminating sheet. The selected recording material should have a favorable signal-to-noise ratio and form chigh contrast data bits with the read/write system with which it is used. The material should not lose data when subjected to temperatures of about 175.degree. F. (79.degree. C.) for long periods. The material should also be capable of recording at speeds of at least several thousand bits/sec. This generally precludes the use of materials that require long heating times or that rely on slow chemical reactions in the presence of heat, which may permit recording of only a few bits/sec. A large number of highly reflective laser recording materials have been used for optical data disk applications. Data is recorded by forming spots in the surrounding field of the reflective layer itself, thereby altering the reflectivity in the data spot. Data is read by detecting the optical reflective contrast between the surrounding reflective field of unrecorded areas and the recorded spots. Spot reflectivity of less than half the reflectivity of the surrounding field produces a contrast ratio of at least two to one, which is sufficient contrast for reading. Greater contrast is preferred. Reflectivity of the strip field of about 50% is preferred with reflectivity of a spot in the reflective field being less than 10%, thus creating a contrast ratio of greater than five to one. Alternatively, data may also be recorded by increasing the reflectivity of the strip. For example, the recording laser can melt a field of dull microscopic spikes on the strip to create flat shiny spots. This method is described in SPIE, Vol. 329, Optical Disk Technology (1982), p. 202. A spot reflectivity of more than twice the surrounding spiked field reflectivity produces a contrast ratio of at least two to one, which is sufficient contrast for reading.

With reference to FIG. 3, a magnified view of laser writing on the laser recording material strip 15 may be seen. The dashed line 33, corresponds to the dashed line 33 in FIG. 1. The oblong spots 35 are aligned in a path and have generally similar dimensions. The spots are generally circular or oval in shape with the axis of the oval perpendicular to the lengthwise dimension of the strip. A second group of spots 37 is shown aligned in a second path. The spots 37 have similar dimensions to the spots 35. The spacing between paths is not critical, except that the optics of the readback system should be able to easily distinguish between paths.

Presently, in optical disk technology, tracks which are separated by only a few microns may be resolved. The spacing and pattern of the spots along each path is selected for easy decoding. For example, oval spots of the type