Information displaying medium

Abstract: An information displaying medium comprises a base member and a writable displaying unit disposed on the base member. The writable displaying unit has a reversible displaying element including a polymer/liquid crystal composite film. A processing means including a control means and an information recording unit is buried in the base member. The processing means comprises a semiconductor device. A communication means is buried in the base member for exchanging signals with an external apparatus.

Description: The present invention relates to an information displaying medium to which information can be repeatedly written. An information displaying medium is a promising information transfer means formed by providing a card, i.e., a base sheet, with a repeatedly writable displaying unit and capable of displaying different pieces of information as occasion demands. The information displaying medium when used, for example, as a customer card, services to the customer can be improved by displaying messages and such on the information displaying medium. Various writable, reversible displaying elements intended for use for forming writable displaying unit have been proposed. Heat, light or magnetism is used for recording information on and erasing recorded information from the reversible displaying element. A reversible displaying element employs a fatty acid dispersed polymer film formed by dispersing a fatty acid that changes its phase between an opaque phase and a transparent phase in a polymer matrix. Another reversible displaying element uses the reversible opening and closing of lactone rings of a leuco dye by a developer/subtracter agent. A third reversible displaying element employs a polymer liquid crystal. A fourth reversible displaying element employs microcapsules containing magnetic powder. The visibility of those known reversible displaying elements will be examined. The reversible displaying element employing a leuco dye indicates blue images on a white background and becomes light blue in an erased state. The reflection densities of the background, the images and the erased state measured by a Macbeth reflection densitometer (RD-918) are about 0.1, about 1.5 and about 0.3, respectively. Although the initial visibility is satisfactory, residual images remain after erasing. The reversible displaying element employing a fatty acid dispersed polymer film indicates white images of 0.4 in reflection density on the background of 1.2 in reflection density having metallic luster and has metallic luster in an erased state of 1.2 in reflection density. White characters displayed on the background having metallic luster is difficult to recognize and the visibility of the reversible displaying element is unsatisfactory. The reversible displaying element employing microcapsules containing magnetic powder displays black images of 1.5 in reflection density on a silvery background of 1.0 in reflection density and becomes silvery in an erased state of 1.0 in reflection density. The visibility of black characters on the silvery background is unsatisfactory. The reversible displaying element employing a polymer/liquid crystal composite film, when used in combination with a black dichroic dye, displays black images of 1.4 in reflection density on a white background of 0.5 in reflection density and becomes white in an erased state of 0.5 in reflection density. Black characters displayed on the white background are easy to recognize, the visibility of the reversible displaying element is excellent and residual images may not remain after erasing. EP-A1-0 752 323, which is a prior art document according to Article 54(3) and (4) EPC, describes a ticket including a substrate and a rewrite display portion using a reversible display element disposed on one of the surfaces of the substrate, made of a liquid crystal/polymer composite film (PDLC film) and requiring both, heat and electric field, for rewriting, and an information recording portion disposed on the other surface of the substrate and made of a magnetic recording layer. JP-A-5-294 092 describes a card permitting rewriting which consists of a composite film layer which is composed of a polymer-liquid crystal material containing a substrate sheet, a polymer material with a film-forming property formed on the surface of the substrate sheet and a liquid crystal material and a protective resin layer which is formed on the surface of the composite film layer. The present invention has been made taking into consideration the foregoing conditions and it is therefore an object of the present invention to provide an information displaying medium to which information can be repeatedly written and information can be displayed in an excellent visibility. According to a first aspect of the present invention, an information displaying medium comprises a base member, a semiconductor information recording device buried in the base member, and a writable displaying unit formed on the base member and permitting repeated recording and erasing of visible information, in which the writable displaying unit is provided with a reversible display element which is changed from either of a recorded state and an erased state to the other by the agency of an electric field and from the latter state to the former state by the agency of heat. According to the first aspect of the present invention, visible information can be repeatedly written to the writable displaying unit provided with the reversible displaying element and, at the same time, pieces of information can be stored on the semiconductor information recording device. Fig. 1 is a block diagram of an information displaying medium in a first embodiment according to the present invention; Fig. 2A is a plan view of the information displaying medium of Fig. 1; Fig. 2B is a sectional view taken on line B-B in Fig. 2A; Fig. 3 is a longitudinal sectional view of a reversible displaying element provided with a PDLC film; Fig. 4 is a diagrammatic view for assistance in explaining a method of erasing information displayed on an writable displaying unit; First Embodiment A first embodiment of the present invention will be described with reference to the accompanying drawings. Figs. 1 to 4 illustrate an information displaying medium 1 in a first embodiment of the present invention. Referring to Fig. 1, the information displaying medium 1 has a card (base member) 1a, a communication unit 2 incorporated into the base member 1a and capable of exchanging information signals by radio with an external device 5, a writable displaying unit 3 on which visible information, such as an image, is made by an external writing device, not shown, and a processing unit 4 connected to the communication unit 2 and capable of processing information signals to be transmitted and those to be received by the communication unit 2 and of controlling the general operations of the information displaying medium 1. The communication unit 2 and the processing unit 4 constitute a non-contact information recording device, and the writable displaying unit 3 serves as a displaying device. The processing unit 4 has a control device 4a, such as a CPU, and a semiconductor storage device 4b for storing control programs and information to be transmitted and received, such as a ROM or an EEPROM. The information displaying medium 1 can be constructed by incorporating the communication unit 2 and the writable displaying unit 3 into a well-known IC card. Figs. 2A and 2B show the information displaying medium 1 in the form of a commuter ticket. The base member 1a is constructed by adhesively joining together an upper base part 51 and a lower base part 52 with an adhesive layer 53. The writable displaying unit 3 provided with a reversible displaying element 30 (Fig. 3) is buried in a recess 8 formed in the central region of the upper surface of the upper base part 51 so that its upper surface is substantially flush with the upper surface of the upper base part 51 or at a height in the range of 0 to 0.5 mm from the upper surface of the upper base part 51. The communication unit 2 provided with an antenna is buried in the central portion of the lower base part 52, and the processing unit 4 including a CPU and a RAM or the like is buried near the communication unit 2 in the lower base part 52. The communication unit 2 and the processing unit 4 are buried in a recess 8 formed in the lower base part 52. Thus the communication unit 2 and the processing unit 4 are buried and concealed in the base member 1a formed by joining together the upper base part 51 and the lower base part 52. Therefore, the writable displaying unit 3 can be positioned at an any suitable position on the base member 1a regardless of the positions of the communication unit 2 and the processing unit 4. The writable displaying unit 3 of the information displaying medium 1 may be formed in a portion of one surface of the base member 1a as shown in Fig. 2A, in the entire area of one surface of the base member 1a or in the both surfaces of the base member 1a. The position of the writable displaying unit 3 on the base member 1a may be determined selectively taking into consideration the purpose of the information displaying medium 1. When issuing the information displaying medium (commuter ticket) 1, initial information is recorded on the information recording device 4b, and required conditions including the user's name, the commutation section and the term of validity are recorded and displayed on the writable displaying unit 3. Characters spelling the user's name and such and graphic information 3a may be displayed on the writable displaying unit 3. Machine-readable information, such as represented by a bar code, may be displayed. When passing a ticket barrier, the user does not need to take out the information displaying medium 1 from a case, not shown; signals are transmitted by radio between the communication unit 2 of the information displaying medium 1 and the external device 5 installed at the ticket barrier to examine the contents of the information displaying medium 1 to examine the validity of the information recorded on the information storage device 4b, such as the commutation section and the term of validity. The information displaying medium 1 whose validity has expired is recovered, initial information is stored again on the information storage device 4b, the information displayed on the writable displaying unit 3 is erased, and new information is written to the writable displaying unit 3 to make the information displaying medium 1 valid again. The writable displaying unit 3 having the reversible displaying element 30 will be described in detail. Referring to Fig. 3, the reversible displaying element 30 has a polymer/liquid crystal composite film (PDLC) 33 requiring both heat and an electric field for writing and erasing. The polymer/liquid crystal composite film 33 is formed by dispersing a smectic liquid crystal in a polymer matrix and is called also a PDLC film (polymer dispersed liquid crystal film). As mentioned above, the reversible displaying element 30 having the PDLC film 33, as compared with other types of reversible displaying elements, is capable of displaying images in an excellent visibility. The visibility can be further improved by using a dichroic dye in combination with the liquid crystal to form the PDLC film 33. The principle of recording visible information on and erasing visible information from the PDLC film 33 uses light scattering and light transmission (change in the light absorptive power of the dichroic dye when the dichroic dye is used in combination with the liquid crystal and guest-host effect is available) due to the orderly change of the orientation state of the liquid crystal molecules caused by heat and an electric field (heat-electric field mode) between a regular orientation state, i.e., a homeotropic orientation or homogeneous orientation state, and an irregular orientation state, i.e., a random orientation state. When an opaque state (light scattering state) is used as a recording state and a transparent state (light transmitting state) is used as an erased state, information can be written to the PDLC film 33 with a thermal head capable of spot-heating and information can be erased by holding the PDLC film 33 between electrodes. When writing information to the reversible displaying element 30 having the PDLC film 33, both an erasing operation and a writing operation are necessary, which needs to use two kinds of external energy. Accordingly, the information written to the reversible displaying element 30 cannot be easily altered dishonestly and does not fade away naturally in the natural environment. Therefore, the reversible displaying element 30 having the PDLC film 33 may be suitable for purposes in which security against the dishonest alteration of the displayed information is important. Other reversible displaying elements on which information can be rewritten only by heat (heat-heat mode), such as those employing a polymer fatty acid dispersed film, a leuco dye or a polymer liquid crystal, and reversible displaying elements to which information can be written only by magnetism, such as those employing microcapsules containing magnetic powder, are readily subject to dishonest alteration and provide low security against the dishonest alteration of information. Since the orderly orientation state of the PDLC film 33 can be quickly established in a time on the order of microseconds by applying an electric field to the PDLC film 33, the reversible displaying element 30 has an excellent ability to enable quick writing and withstands a sufficiently large number of writing cycles. A PDLC film proposed in, for example JP-A No. 4-71899 may be used as the PDLC film 33. A PDLC film employing a microcapsulated liquid crystal has excellent properties such that the liquid crystal does not exude because the liquid crystal is sealed in microcapsules. Films proposed by the applicant of the present patent application in JP-A Nos. 5-301489, 6-33283, 6-44735 and 6-119702 may be used as the PDLC film 33. The polymer matrix binding the liquid crystal dispersed therein to form the PDLC film 33 is, for example, a vinyl chloride resin, a polymethacrylate resin, an acrylic resin, such as an acrylate-methacrylate copolymer, a polyvinyl alcohol resin, a polycarbonate resin, a polyester resin, an epoxy resin, a polyamide resin, a polyurethane resin, a polythiol resin, a radiation-setting resin that sets when exposed to ultraviolet rays or electron rays or a combination thereof. The liquid crystal employed in the PDLC film 33 may be a smectic liquid crystal, a discotic liquid crystal, a nematic liquid crystal, a cholesteric liquid crystal, a polymer liquid crystal or a mixture of some of those liquid crystals. The visibility can be improved by mixing the liquid crystal with an appropriate amount of a dichroic dye to enhance the displaying contrast by the guest-host effect. The liquid crystal can be dispersed in the polymer matrix by any one of a phase separation method, an emulsion method, a microcapsule method, a solvent evaporation method and a suspension polymerization method. Among those methods, a emulsion method and a microcapsule method are most preferable because those methods prevents the liquid crystal from exuding. The microcapsule method improves the durability of the dispersed liquid crystal particles. A microcapsule method using an in situ polymerization process is able to form the PDLC film 33 containing liquid crystal particles of 10 µm or below in particle size, which is suitable for forming the PDLC film 33 in a practically appropriate thickness and for securing a satisfactory display quality. Generally, the thickness of the PDLC film 33 is in the range of about 3 to about 23 µm. The lower limit thickness of the PDLC film 33 is dependent on displaying contrast and the upper limit thickness of the same is dependent on a practical driving voltage necessary for setting the liquid crystal of the PDLC film 33 in a regularly oriented state. The layered structure of the reversible displaying element 33 having the PDLC film 33 comprises at least the PDLC film 33 and an electric field applying device capable of applying an electric field perpendicularly to the PDLC film 33. Although the electric field applying device may be formed of conductive layers formed on the opposite surfaces of the PDLC film 33, an electric field can be applied to an optional portion of the PDLC film 33 when a conductive layer 32 is formed only on the back surface of the PDLC film and the front surface is brought into contact with an external electrode, not shown, or the like. Therefore, the reversible displaying element 30 comprises, at least, a base sheet 31, i.e., a substrate, the conductive layer 32 and the PDLC film 33. A protective layer 35 may be formed on the PDLC film 33 when necessary. The label-shaped reversible displaying element 30 having the PDLC film 33 and provided on its back surface with an adhesive layer will be described in detail with reference to Fig. 3. As shown in Fig. 3, the reversible displaying element 30 has the conductive layer 32, the PDLC film 33, an intermediate layer 34 and the protective layer 35 formed sequentially in that order on the base sheet 31, and a cushion layer 36 and an adhesive layer 37 formed sequentially in that order on the back surface of the base sheet 31. The reversible displaying element 30 is attached adhesively to the base member 1a with the adhesive layer 37 to provide the writable displaying unit 3. Primer layers may be interposed between the layers 31, 32, 33, 34, 35, 36 and 37 to enhance the adhesion between those layers. The reversible displaying element may be formed on the base member 1a by sequentially forming the layers 31 to 37 on the base member 1a by a printing method, such as a silk-screen printing method, a transfer printing method and a coating method instead of attaching a babeling sheet having the reversible displaying element 30 to the base member 1a. When the conductive layer 32 is formed of aluminum, the conductive layer 32 functions as a reflecting layer which improves the visibility of the writable displaying unit 3 comprising the reversible displaying element 30. The base sheet 31 of the reversible displaying element 30 shown in Fig. 3 is a sheet of a polyester resin, such as polyethylene terephthalate, a polyvinyl chloride resin, a polyolefin resin, such as polypropylene, a cellulose resin, an acrylic resin, paper or synthetic paper having a thickness in the range of about 50 to about 1000 µm. A single sheet may be used both as the base sheet 31 and the base member 1a of the information displaying medium 1. Normally, the base sheet 31 is an insulating sheet. When the base member 31 is used independently of the base member 1a, the base sheet 31 may be formed of a material having an appropriate electric conductivity and the conductive layer 32 may be omitted. The conductive layer 32 may be formed of a semiconductor having an electric conductivity that enables the conductive layer 32 to serve as a horizontal electrode to apply an electric field perpendicularly to the PDLC film 33, for example, a semiconductor having a sheet resistivity of 10 12 Ω/sq. or below. However, in view of suppressing voltage loss, it is preferable that the conductive layer 32 has a high electric conductivity. The conductive layer 32 may be, for example, an evaporated metal film or a metal foil of aluminum or the like, a transparent conductive film, such as an ITO film, a conductive paint film containing carbon black, or a layer containing a conductive material dispersed in the layer. The protective layer 35 protects the PDLC film 33 from pressure, external force and the ambient conditions and enhances the heat resistance, abrasion resistance and scratch resistance of the writable displaying element 30 which are important for the writable displaying element 30 to withstand actions exerted thereon by a thermal head and an electrode roller. The protective layer 35 may be a film of a hardenable resin, such as a thermosetting resin or a radiation-setting resin that hardens when exposed to ultraviolet rays or electron rays, having a thickness in the range of about 0.5 to abut 10 µm. The protective layer 35 may be formed so as to coat, not only the surface of the PDLC film 33, the side surfaces of the PDLC film 33, the conductive layer 32 and the entire area of the surface of the base member 1a on which the writable displaying unit 3 is disposed. When the protective layer 35 is formed so as to coat the entire area of the surface of the base member 1a, it is preferable to use a resin film as the protective layer 35. The intermediate layer 34 serves as a barrier layer that prevents the permeation of the solvent contained in the material of the protective layer 35 into the PDLC film 33 and the deterioration of the liquid crystal orienting performance of the PDLC film 33 when forming the protective layer 35. The thickness of the intermediate layer 34 is in the range of about 0.5 to about 10 µm. The intermediate layer 34 is formed by spreading an aqueous solution of a water-soluble resin, such as polyvinyl alcohol, polyvinyl pyrrolidone or carboxymethyl cellulose. The intermediate layer 34 increases the degree of freedom in selecting the material of the protective layer 35. For example, the protective layer 35 of a radiation-setting resin, such as a soft urethane acrylate, is excellent in heat resistance, abrasion resistance, scratch resistance, touch to a thermal head and cushioning performance. The cushion layer 36 formed on the back surface of the base sheet 31 has moderate elasticity and flexibility, and secures satisfactory contact between the reversible displaying element 30 and a thermal head or an electrode. The cushion layer 36 as formed of a heat-insulating material, such as a foam material, prevents the dissipation of thermal energy exerted on the reversible displaying element 30 by a thermal head or the like to heat the reversible displaying element 30 rapidly. The cushion layer 36 may be formed of an elastic resin, such as urethane foam or the like having heat-insulating capability. The thickness of the cushion layer 36 is dependent on the required cushioning and heat-insulating abilities. The adhesive layer 37 is formed of a generally known adhesive, such as a rubberlike resin or an acrylic resin, and has a thickness in the range of about 20 to about 50 µm. The information displaying medium 1 employing the reversible displaying element 30 provided with the PDLC film 33 is capable of displaying images in an excellent visibility, ensures security against dishonest alteration and reliability of the information and is capable of being properly used for various purposes. The large information recording capacity of the information recording device 4b and the signal processing ability of the control device 4a enables the information displaying medium 1 to be properly used for various purposes. The upper base part 51 and the lower base part 52 supporting and storing the reversible displaying element 30, the communication unit 2 including the antenna and the processing unit 4 are sheets, boards or moldings of a resin, such as a vinyl chloride resin or an acrylic resin, or a ceramic material. The shapes of the upper base part 51 and the lower base part 52 are determined according to the purpose and may be that of a card. A method of erasing information recorded on the PDLC film 33 of the writable displaying unit of the information displaying medium 1 by applying an electric field to the PDLC film 33 and a method of recording information on the PDLC film 33 by applying heat to the PDLC film 33 will be described hereinafter. Any one of the electric field applying methods disclosed in, for example, Japanese Patent Application No. 6-103249 of the applicant of the present patent application, Japanese Patent Application No. 6-302701, "Noncontact Method of Orienting the Liquid Crystal of a Liquid Crystal Displaying Medium and Liquid Crystal Orienting Apparatus" (charging system), Japanese Patent Application No. 6-302702, "Method of Orienting the Liquid Crystal of a Liquid Crystal Displaying Medium and Liquid Crystal Orienting Apparatus" (electrode system), and Japanese Patent Application No. 6-333820, "Writing Apparatus for writing Information to Reversible Displaying Medium" (charging system and electrode system) may be used. These previously disclosed electric field applying methods can be classified by various bases of division; the electric field applying methods can be classified into those of a noncontact system and those of a contact system, into those of a charging system and those of an electrode system or into those of a single-electrode system that creates a potential difference across the information displaying medium 1 from one side of the information displaying medium 1 and those of an opposed-electrode system that creates a potential difference across the information displaying medium 1 from the opposite sides of the information displaying medium 1. These electric field applying methods of those systems may be used in combination. An appropriate electric field applying method is selected taking into consideration the shape and the physical properties of the information displaying medium 1. Since the information displaying medium 1 is internally provided with a semiconductor device, an electric field applying method of a single-electrode system that creates a potential difference across the information displaying medium 1 from one side of the information displaying medium 1 is preferable. Fig. 4 shows an electric field applying apparatus 70 that applies an electric field to the information displaying medium 1 by the combination of a charging system (noncontact system) and an electrode system (contact system). Referring to Fig. 4, the electric field applying apparatus 70 has two grounded rollers 72 (electrodes) formed of a conductive rubber, and a charging device 71, such as a corona charger, disposed between the grounded rollers 72, and guide rollers 73 disposed opposite to the grounded rollers 72, respectively. The information displaying unit 3 is disposed under the grounded rollers 72 and the charging device 71 and an electric field is applied perpendicularly to the information displaying unit 3. Different electric field applying methods employ different numbers of charging devices 71 or grounded rollers 72. When the charging device 71 of the electric field applying system shown in Fig. 4 employing the electrodes 72, i.e., grounded rollers, and the charging device 71 is substituted by an electrode which is not grounded and is charged at a potential, a combination of an electrode system, a contact system and a single-electrode system can be constructed. A combination of a charging system, a noncontact system and a single-electrode system can be constructed by substituting the electrodes 72, i.e., grounded rollers, by charging devices. A system employing the electrode 72, i.e., grounded roller, and the charging device 71, a system employing the two electrodes 72, i.e., grounded rollers, and a system employing the two charging devices are possible systems. In any one of those systems, the adjacent electrodes 72 or the adjacent charging devices 71 are charged at different potentials (a ground potential and a positive or negative potential, or a positive potential and a negative potential), respectively. A thermal head like the thermal print head of a thermal transfer printer is used for heating. The information displaying medium 1 (commuter ticket) of the present invention can be applied to various purposes in which the capability of the PDLC film 33 displaying information in a high visibility, security against the dishonest alteration of the displayed information and capability of withstanding the repetition of writing cycles are important. The advantages of the information displaying medium 1 as compared with a conventional magnetic commuter ticket will be explained in detail. Information magnetically recorded on a commuter ticket of a magnetic recording type for use in using transport facilities is read by an automatic ticket examining apparatus as the commuter ticket is passed through the automatic ticket examining apparatus. Therefore, the user needs to carry out a procedure requiring steps of taking out the commuter ticket from the case, inserting the commuter ticket into the automatic ticket examining apparatus, receiving the commuter ticket after the information has been read from and necessary information has been recorded on the commuter ticket by the automatic ticket examining apparatus and returning the commuter ticket into the case. Consequently, the ticket barrier becomes congested when many people use the automatic ticket examining apparatus successively. When the information displaying medium 1 of the present invention having a semiconductor information recording unit from which information is read and to which information is written by radio is used as a commuter ticket, processing operations can be quickly accomplished and the information recorded on the information recording device 4b is transmitted by radio through the communication unit 2 to the external apparatus 5 at the ticket barrier. Therefore, the information displaying medium 1 need not be taken out from and returned into the case. Since the information displaying medium 1 is not brought into mechanical contact with the external apparatus 5, the information displaying medium 1 is scarcely deteriorated and can be used for an extended period of time. Generally, the term of validity of the commuter ticket is far shorter than the life time of the information displaying medium 1, therefore the recovered information displaying medium 1 can be used again to reduce the cost. Generally, the term of validity and the like of the commuter ticket need to be displayed in visible images on the commuter ticket. In the magnetic commuter ticket, the term of validity and the like are recorded on the magnetic recording unit in invisible magnetic data, and conditions of use including the date and time of use and the name of the boarding station are recorded on the magnetic commuter ticket every time the commuter ticket is used. It is convenient for the ticket examiner to examine the commuter ticket when the commuter ticket is not examined by an automatic ticket examining apparatus and for the user to confirm the term of validity of the commuter ticket, when visually recognizable information is displayed on the commuter ticket. Therefore, the currently used magnetic commuter ticket is printed with required conditions including the user's name, the commutation section and the term of validity by thermal transfer printing or the like. Since those printed required conditions cannot be rewritten, the commuter ticket is thrown away after the term of validity has expired, and a new commuter ticket is issued. When using the recovered information displaying medium again after changing the printed information, it is quite troublesome if the display unit needs to be scraped from the information displaying medium and new information needs to be printed on the information displaying medium. Therefore, it is desirable that the information displaying medium is provided with a writable displaying unit that allows repetitive writing. When the information displaying medium is used as a commuter ticket, the information displaying medium must have a function to prevent the dishonest alteration of the recorded information in addition to a function to display the stored information. Therefore, a displaying element that allows repeated information writing and ensures security against the dishonest alteration of the information is desirable. Since the information displaying medium 1 of the present invention has the writable displaying unit 3 provided with the reversible displaying element 30 having the PDLC film 33, security against the dishonest alteration of the information is ensured and new information can be easily written. As is apparent from the foregoing description, the information displaying medium 1 of the present invention has capabilities of ensuring security against the dishonest alteration of the information and enabling repetitive writing in addition to capabilities of displaying information in high visibility, exchanging data in a noncontact mode and recording a large amount of information. The information displaying medium 1 of the present invention is not limited in its practical application to a commuter ticket; the information displaying medium 1 is properly applicable to any purposes requiring capabilities of recording a large amount of information and displaying information in high visibility. The information displaying medium 1 is further effectively applicable to purposes requiring durability and security against the dishonest alteration of information. The advantage of the writable displaying unit is significant because the information displaying medium 1 is provided with an expensive IC module and such and it is desirable to use the information displaying medium 1 repeatedly. Therefore, the information displaying medium 1 is advantageously applicable to purposes in which the information displaying medium 1 is recovered and used repeatedly. Suitable purposes like those mentioned above include membership cards on which important information including the member's name and an ID number assigned to the member is displayed, ski lift ticket on which the term of validity and the like are displayed, and customer cards on which points and the like are displayed every time the customer cards are used. Examples of the present invention will be described hereinafter. Example Referring to Fig. 2B, a recess 8 of 20 mm by 60 mm in area and 0.5 mm in depth was formed in a 1.5 mm thick upper base part 51 of a vinyl chloride resin to bury a writable displaying unit 3 having a reversible displaying element 30 therein. A recess 9 for receiving a communication unit 2 and a processing unit 4 therein was formed in the surface of a 1.5 mm thick lower base part 52 of a vinyl chloride resin, and the processing unit 4 comprising a semiconductor storage device and a CPU, and the communication unit 2 including an antenna were buried in the recess 9. After forming a base member 1a by adhesively joining together the upper base part 51 and the lower base part 52 with an adhesive layer 53, the base part 1a was punched in a size of 60 mm by 90 mm to obtain an information displaying medium 1 (commuter ticket) in accordance with the present invention. The reversible displaying element 30 of the writable displaying unit 3 is provided with a PDLC film 33. A 100 µm thick polyethylene terephthalate film provided with an ITO film on one surface thereof was used as a base sheet 31. The PDLC film 33 was formed in a thickness of 10 µm over the entire surface of the ITO film. An aqueous solution of a polyvinyl alcohol resin was spread over the entire surface of the PDLC film 33 to form a 5 µm thick intermediate layer 34. An ultraviolet-setting resin was spread over the entire surface of the intermediate layer 34 in a film and the film was hardened to form a 5 µm thick protective layer 35. A 1 µm thick anchor layer of a polyester resin was formed on the back surface of the base sheet 31 to enhance the adhesive power of the back surface, a 0.4 mm thick cushion layer 36 of a foam urethane resin was formed over the anchor layer, and then a 20 µm thick adhesive layer 37 of a urethane resin was formed on the cushion layer 36 to complete the reversible displaying element 30 of about 520 µm in thickness. PDLC Film A microcapsulated dispersed coating liquid was prepared by dispersing a liquid crystal (and a dichroic dye) by an in situ polymerizing method using an ultrasonic dispersion process. The liquid crystal is in an irregularly oriented state for a recorded state, and the same is in a regularly (perpendicularly) oriented state for an erased state. The dichroic dye becomes black for a recorded state and becomes transparent for an erased state. Smectic liquid crystal: S-6, Merk Japan Co. Dichroic dye: S-428, Mitsui Toatsu Kagaku K.K. Microcapsules: In situ polymerized methylmethacrylate Protective colloid/polymer matrix: Polyvinyl alcohol KP-06, Nippon Gosei Kagaku Kogyo K.K. Thickener/Matrix: Polyvinyl alcohol KH-20, Nippon Gosei Kagaku Kogyo K.K. Liquid crystal/Matrix Ratio: 1/1 The reversible displaying element thus fabricated is attached adhesively to the bottom surface of the recess 8 of the upper base part 51 to complete an information displaying medium 1 (commuter ticket) in accordance with the present invention. The upper surface of the writable displaying unit 3 extends slightly above a plane including the upper surface of the upper base part 51 or is flush with the upper surface of the upper base part 51 so that the upper surface of the writable displaying unit 3 can be brought into satisfactory contact with a thermal head or the like. Recording Process Desired characters were recorded in black on the writable displaying unit 3 with a thermal head in a resolution of 8 dot/mm at a heating rate of 0.18 mJ/dot. A commuter ticket issuing process is completed by writing desired initial data through the communication unit 2 to the information recording device 4b of the processing unit 4. Writing New Information to Writable Displaying Unit A voltage of 50 V/µm must be applied across the PDLC film 33 to erase information recorded on the writable displaying unit 3. Since the thickness of the PDLC film 33 in this embodiment is 10 µm, an electric field of 500 V or above in field intensity must be applied across the PDLC film 33. Therefore, erasing and dishonest alteration of the information recorded on the writable displaying unit 3 is impossible by the natural environment. When changing the information recorded on the recovered information displaying medium 1 to use the recovered information displaying medium 1 again, a voltage was applied across the information displaying medium 1 by the voltage application system using the corona charger 71 and the two grounded rollers 72 shown in Fig. 4 to erase the information recorded on the information displaying medium 1. The voltage of the corona charger 71 was +5 kV and that of the grounded rollers 72 was 0 V. Comparative Example A commuter ticket the same as the information displaying medium 1 of the present invention was fabricated. The commuter ticket differs from the information displaying medium 1 only in that the reversible displaying element of the writable displaying unit of the commuter ticket was a polymer/fatty acid dispersed film of a material prepared by dispersing stearic acid and dodecanedioic acid in the copolymer of vinyl chloride and vinyl acetate. Desired characters were recorded in black on the writable displaying unit with a thermal head in 8 dot/mm at a heating rate of 0.25 mJ/dot. The characters were erased by heating the commuter ticket with a heat roller of 80°C in surface temperature. Performance Comparison between Example and Comparative Example The contrast between the characters and the background on both Example 1 and the Comparative example 1 was not reduced and the visibility of the characters displayed on Example 1 and the Comparative example 1 was satisfactory after 100 writing cycles. The characters recorded on Comparative example 1 faded away and the information displaying unit of Comparative example 1 became transparent when heat of 80°C was applied to Comparative example 1, and the characters could easily be altered. A high voltage that is unavailable in the natural environment is necessary to erase the characters recorded on Example 1 and the characters written to the PDLC film 33 cannot be erased unless a voltage is applied across the PDLC film 33 by a predetermined method. Since Example 1 needs both heat and an electric field for writing and erasing, the characters are hardly subject to natural fading. Thus, Example 1 is a noncontact information recording/displaying medium capable of ensuring high security against the dishonest alteration of the recorded information. As is apparent from the foregoing description, since the information displaying medium 1 of the present invention has the writable displaying unit provided with the reversible displaying element 30 employing the PDLC film 3, visible information can be written to the writable displaying element 30 in high visibility. A large amount of information can be stored in the semiconductor information recording device 4b and data can be exchanged in a noncontact mode through the communication unit 2 between the information displaying medium 1 and the external apparatus 5. Although data can be exchanged in a contact mode in which the conventional IC card capable of storing a large amount of information exchanges data with an external apparatus, the information displaying medium 1 must be provided with exposed terminals to be brought into contact with the terminals of the external apparatus, and the processing unit 4 is liable to be caused to malfunction by the static charging action of an electric field applying device to be used for changing the information recorded on the writable displaying unit. The information displaying medium 1 of the present invention does not need any exposed terminals and hence the processing unit 4 will not be caused to malfunction due to the aforesaid causes. Since the information displaying medium need not be provided with any external terminals, the size and the position of the writable displaying unit 4 can be determined without paying attention to the positions of terminals. Since the writable displaying unit 3 employs the PDLC film 33, the information displaying medium is excellent in visibility, security of the displayed information, reliability and durability. The information displaying medium having the noncontact data exchanging function is suitable for use as a commuter ticket. The information displaying medium used as a commuter ticket can be recovered and used repeatedly, which reduces the practical costs of the information displaying medium.

Claims: An information displaying medium comprising: a base member; a semiconductor information recording unit buried in the base member; and a writable displaying unit formed on the base member and permitting repeated recording and erasing of visible information; wherein the writable displaying unit is provided with a reversible display element which is changed from either of a recording state and an erased state to the other by the agency of an electric field and from the latter state to the former state by the agency of heat. An information displaying medium according to claim 1, further comprising: a communication means buried in the base member, connected to the semiconductor information recording unit and capable of exchanging signals by radio with an external apparatus. An information displaying medium according to claim 2, wherein the semiconductor information recording unit and the communication means are buried in the base member so that the semiconductor information recording unit and the communication means are not exposed. An information displaying medium according to claim 1, wherein the writable displaying unit is disposed in a recess formed in the base member so that the surface of the writable displaying unit is flush with or lies slightly above the surface of the base member. An information displaying medium according to claim 4, wherein the height of the surface of the writable displaying unit from the surface of the base member is in the range of 0 to 0.5 mm. An information displaying medium according to claim 1, wherein the visible information to be written to the writable displaying unit is characters or patterns. An information displaying medium according to claim 1, wherein the visible information to be written to the writable displaying unit is mechanically readable information. An information displaying medium according to claim 1, wherein the reversible displaying element is changed from a recorded state to a erased state by the agency of an electric field. An information displaying medium according to claim 1, wherein the reversible displaying element includes a polymer/liquid crystal composite film. An information displaying medium according to claim 9, wherein a liquid crystal phase of the polymer/liquid crystal composite film contains a dichroic dye that assumes a displaying state by a guest-host effect. An information displaying medium according to claim 9, wherein the reversible displaying element further comprises a conductive layer formed on an inner side of the polymer/liquid crystal composite film, and a protective layer formed on an outer side of the polymer/liquid crystal composite film.

Inventors: SHIMADA NAOKI, SHIMADA, NAOKI, Shimada, Naoki, c/o Dai Nippon Printing Co., Ltd.
Applicants: DAINIPPON PRINTING CO LTD, DAI NIPPON PRINTING CO., LTD.
Application year: 1996
Main classification: G09F3
IPC codes: G09F3, G06K19, G06K1, G02F1