GB2345348A - Reversible thermosenstive recording medium - Google Patents

Abstract

A reversible thermosensitive recording medium comprising a thermosensitive layer 13 provided on a substrate 11, changing transparency or color tone reversibly with temperature, in which the reversible thermosensitive recording medium has a change in deferred transparentization initiation temperature of at most 5{ C, or a rate of the change in transparentization temperature width of at least 90%. The layer includes a matrix resin in which is dispersed a low molecular weight organic material, the matrix resin is either a cross-linked mixture of a hydroxyl group containing thermoplastic resin, a linear isocyanate compound, and a cyclic isocyanate compound; or a cross-linked polycarbonate-based urethane resin. The substrate of the recording medium may be utilized as a reversible thermosensitive recording label. This label can be provided on the surface of a disk cartridge, a rewritable or write-once disk, and a cassette of a magnetic tape, thereby being capable of displaying at least a part of information stored in the information storage disk or magnetic tape. There is preferably a reflective Al layer 12, below layer 13, and a protective layer 14 over layer 14, and a magnetic layer 16 on the back of the substrate 11.

Description

1 1 2345348 REVERSIBLE THERMOSENSITIVE RECORDING MEDIUM AND THE USE IN

DISPLAYING UNIT FOR INFORMATION DATA STORAGE

BACKGROUND

Field

The present invention relates generally to a reversible recording medium, and more particularly to a reversible thermosensitive recording medium capable of repeatedly forming and erasing images by utilizing a reversible change in transparency or in color of a thermosensitive layer with temperature, having a high image contrast and improved erasability.

Discussion of Backqround A variety of information recording media have been developed to comply with the demands for expanding and diversifying the volume of the information. A reversible thermosensitive recording medium, which is capable of changing transparency or color tone reversibly with temperature on demand, has been attracting much attention recently. In addition, The image forming and erasing are achieved at relatively low cost without complicated developing steps.

As an illustrative example of the reversible thermal recording media, there is known recording media including low molecular weight organic materials such as higher fatty acids dispersed in matrix resins such as vinyl chloridevinyl acetate copolymers (Japanese LaidOpen Patent Application No. 55- 154198).

For this recording medium, however, a temperature range in which the recording medium is transparent (or transparentization temperature range) is as narrow as from 20 to 40 C. This is not satisfactory for controlling the temperature to achieve image recordings utilizing the above-mentioned reversibility.

In view of the above problem, some of the present inventors have proposed several recording materials in Japanese LaidOpen Patent Application Nos. 2-1363 and 3-2089. They disclose that, with the use of higher fatty acids, aliphatic dicarboxylic acids and the combination thereof as a mixture, the transparentization temperature range is extended to about 200 C and image erasure can be achieved with relative ease.

Also, methods and apparatuses have been investigated to realize more miniaturized and less expensive apparatuses, in that both the formation and erasure of the images can be carried out with a single thermal printhead without any additional erasing unit.

2 However, when a heating time is decreased during the study to, for example, as short as several milliseconds, such as the case of the thermal printhead, there have been encountered shortcomings. Namely, after heated for such a short heating 5 time and after a prolonged storage at temperature higher than room temperature, known material systems of the recording medium have difficulties such as the reduction in the erasability (or transparentization capability) and insufficient image contrast.

Referring to FIG. 1, the reduction in the erasability and image contrast is described hereinbelow.

As long as the erasure of formed images are made not long after the heating, for example, within several tens of minutes, images-can be erased upto a base transparency even when the heating time with a thermal printhead is reduced to several milliseconds. Also in this case, since the energy range for achieving the base transparency is relatively broad as shown in FIG. 1, the transparentization (or erasure) can be satisfactorily carried out with a sufficient margin, even when the erasing conditions change such as, for example, the ambient temperature and when a concomitant change in necessary input energy is caused.

In contrast, when the erasure of formed images are made after a prolonged period of time under the same erasure conditions as immediately after the heating, the erasure can neither attain the base transparency, nor retain the previous 3 broad energy range for achieving the satisfactory transparency. The above reduction in the erasability is considered due to the change in materials properties of the matrix resin included in the reversible thermosensitive recording layer.

When a polymer material is quenched after being heated above its glass transition temperature, it is generally known that the polymer material cannot return to its characteristic or stable state and, at temperatures lower than the glass transition temperature, can return to the stable state only after a long period of time.

This is known as the enthalpy relaxation. Examples of such change in the materials properties are known to include the increase in glass transition temperatures and in specific densities. In the above cases of the reduction in the erasability is thus considered due to the increase in glass transition temperatures of the matrix resin.

In order to prevent the reduction in the erasability, there are proposed a method of admixing a specific radiation curing resin (Japanese Laid- Open Patent Application No. 8-72416) and another method of including a reacting polymer species in a reversible thermosensitive recording layer (Japanese Laid- Open Patent Application No. 10-100547). Although the erasability are improved to some extent by these methods, these improvements are not sufficient enough to comply with ever increasing data processing speed and the concomitant decrease in heating time of a thermal printhead, thereby causing 4 unsatisfactory erasability and image contrast.

In addition, since the radiation curable resin is only mixed with a matrix resin but not cross-linked therebetween in the above method disclosed in the Application '416, there still 5 persist a difficulty of decreasing erasability in repeated use.

Further, when the resin is cured by ultraviolet light irradiation in the method disclosed in the Application '547, only the portion of the radiation curing resin is cross-linked. The erasability is again decreased in repeated use. In addition, although a more improved erasability is achieved by a electron beam irradiation method, there are disadvantages in this method, such as a large-scaled and costly apparatus.

Still further, there proposed is another method of preventing the reduction in the erasability in repeated use, in which a vinyl chloride-vinyl acetate-vinyl alcohol copolymer is cross- linked with an isocyanate compound in a matrix resin (Japanese Laid-Open Patent Application No. 3-227688). Since a rather rigid chain structure in the isocyanate compound is utilized in this method, the durability is found improved.

However, the difficulties remain, in which the erasability decreases immediately after the image formation and after a prolonged storage as well.

Also, there disclosed is the use of polyurethane resin as a matrix resin, having a glass transition temperature of equal to or more than 35 C. This method has difficulties, however, such as a relative large reduction in the erasability after prolonged storage and unsatisfactory durability in repeated use (Japanese Laid-Open Patent Application No. 632053).

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an improved reversible thermosensitive recording material, having most, if not all, of the advantages and features of similar employed materials, while eliminating many of the aforementioned disadvantages.

A further object of the present invention is to provide a reversible thermosensitive recording material, having an improved erasability and image contrast even in a decreased heating time of a thermal printhead to be capable of complying with ever increasing data processing speed. In addition, the reversible thermosensitive recording material is preferably prepared without a large-scaled and costly apparatus, and still having a satisfactory durability in repeated use.

To achieve the foregoing and other objects, the invention in a first aspect provides a reversible thermosensitive recording medium comprising a thermosensitive layer provided on a supporting substrate, the thermosensitive layer changing transparency or color tone reversibly with temperature, in which the reversible thermosensitive recording medium has a 6 change in deferred transparentization initiation temperature of at most 5 C, more pref erably at most 2 C.

According to alternative embodiment, another reversible thermosensitive recording medium is provided, having a change in deferred transparentization initiation temperature of at most 50 C, or a rate of the change in transparent i zati on temperature width of at least 90%.

In another embodiment, a reversible thermosensitive recording medium is provided, comprising a thermosensitive layer provided on a supporting substrate and including, as main ingredients, a matrix resin and a low molecular weight organic material dispersed in the matrix resin, the thermosensitive layer changing transparency or color tone reversibly with temperature, in which the matrix resin comprises either a cross-linked mixture of a hydroxyl group containing thermoplastic resin, a linear isocyanate compound, and a cyclic isocyanate compound; or a cross-linked polycarbonate-based urethane resin. In addition, the cyclic isocyanate compound has a molecular weight in terms of an isocyanate group of at least 250. Further, the matrix resin has a glass transition temperature of at least 40' C and at most 1200 C.

In yet another embodiment, the low molecular weight organic material dispersed in the matrix resin comprises a mixture of at least one low melting point low molecular weight organic material with at least one high melting point low 7 molecular weight organic material, in which the difference in melting point between the low melting point low molecular weight organic material and high melting point low molecular weight organic material is at least 300 C. In addition, the low molecular weight organic material comprises a mixture of at least a linear hydrocarbon containing compound having a melting point of at least 130" C, which include at least one of amide, urea and sulfonyl bonds and a carboxyl radical, with at least a linear hydrocarbon containing compound having a melting point higher by at least 300 C than the linear hydrocarbon containing compound.

In another embodiment, a reversible thermosensitive recording medium has an uppermost transparentization temperature of at least 1250 C, the difference between the uppermost transparentization temperature and the lowermost white opaque temperature of at most 200 C, and a transparetization temperature width of at least 300 C.

In another embodiment, a layer of an adhesive or pres sure- sensitive adhesive is further provided on the side of the supporting substrate opposite to the thermosensitive recording layer to form a reversible thermosensitive recording label. In addition, the supporting substrate may be of a card type.

In another embodiment, the supporting substrate further comprises an information recording section, which may include 8 at least one of a magnetic recording layer, an IC and an optical memory, and a printed display portion may also provided on reversible thermosensitive recording medium.

In another embodiment, the supporting substrate may be one of the surfaces of a disk cartridge, in which a rewritable memory disk is housed; a rewritable or write-once disk; and a cassette of a magnetic tape.

In a further aspect, the invention provides a disk cartridge capable of displaying at least a part of information stored in a rewritable information storage disk, comprising the rewritable information storage disk and a reversible thermosensitive recording label provided on at least one of the surfaces of the disk cartridge, in which the rewritable information storage disk is housed.

In another embodiment, a rewritable information storage disk is provided being capable of displaying at least a part of information stored in the rewritable information storage disk, comprising the rewritable information storage disk and a reversible thermosensitive recording label provided on at least one of the surfaces of the rewritable information storage disk.

In yet another embodiment, a magnetic tape cassette is provided being capable of displaying at least a part of information stored in a magnetic tape, comprising the magnetic 25 tape cassette and a reversible thermosensitive recording label provided on at least one of the surfaces of the magnetic tape 9 cassette, in which the magnetic tape is housed.

In yet further aspect, the invention provides a method of forming and erasing an image in reversible thermosensitive recording medium. The reversible thermosensitive recording medium may be selected from the group consisting of:

the reversible thermosensitive recording medium comprising a thermosensitive layer provided on a supporting substrate, in which the reversible thermosensitive recording medium has a change in deferred transparentization of at most 5" C, the reversible thermosensitive recording medium being further included in a reversible thermosensitive recording label, which further comprises a layer of an adhesive or pressure-sensitive adhesive provided on a side of the supporting substrate opposite to the thermosensitive recording layer; the reversible thermosensitive recording medium being further provided on at least one of the surfaces of a rewritable information storage disk; the reversible thermosensitive recording medium being further provided on at least one of the surfaces of a disk cartridge, in which a rewritable information storage disk is housed; and the reversible thermosensitive recording medium being further provided on at least one of the surfaces of a cassette of a magnetic tape, wherein the method is carried out by heating.

In another embodiment, the method of forming and erasing an image may also be carried out either a thermal printhead or a ceramic heater. In addition, the method may be carried out with a thermal printhead to conform the overwrite method, in which writing new images is made imagewise right after erasing the old images with varying heating power for each image.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described hereinbelow with reference to the drawings wherein:

FIG. 1 is a diagram illustrating the change in reflection density with heating energy input of a thermosensitive recording medium according to the present invention; FIG. 2 is a diagram illustrating the change in transparency with temperature of a thermosensitive recording medium according to the present invention; FIG. 3 is a diagram illustrating the change in reflection density with temperature and representing various characteristic parameters of a thermosensitive recording medium according to the present invention; FIG. 4 illustrates a thermosensitive recording label provided on a disk cartridge; FIG. 5 illustrates a thermosensitive recording label provided on a CD-RW disk; FIG. 6 illustrates a layered structure of an optical information storage medium according to one embodiment; FIG. 7 illustrates a thermosensitive recording label provided on a video cassette; FIGS. 8A through 8C illustrate a variety of structures thermosensitive recording media according to the present invention; FIGS. 9A and 9B show a further embodiment of a thermosensitive recording medium formed of a card type; FIG. 10A shows a still further embodiment of a thermosensitive recording medium formed of a card type, further provided with a concave portion for a wafer substrate be fixed thereto; FIG. 10B shows the wafer of FIG. 10A, with integrated circuits fabricated thereon and electrical contact terminals interconnected thereto; FIG. 11A contains a schematic diagram of the integrated circuits of FIG. 1OB; FIG. 11B contains a table illustrating memory locations in RAM of FIG. 11A; FIGS. 12A and 12B illustrate recording apparatuses for the reversible thermosensitive recording medium of the present invention; FIG. 13 is a diagram illustrating the change in reflection density with temperature and representing various characteristic parameters of a thermosensitive recording 12 medium according to the present invention; FIG. 14 is a diagram illustrating the change in reflection density with temperature of the thermosensitive recording medium obtained in Example 1; 5 FIG. 15 is a diagram illustrating the change in reflection density with temperature of the thermosensitive recording medium obtained in Example 4; FIG. 16 is a diagram illustrating the change in reflection density with temperature of the thermosensitive recording medium obtained in Example 5; FIG. 17 is a diagram illustrating the change in reflection density with temperature of the thermosensitive recording medium obtained in Example 6; FIG. 18 is a diagram illustrating the change in reflection density with temperature of the thermosensitive recording medium obtained in Example 7; FIG. 19 is a diagram illustrating the change in reflection density with temperature of the thermosensitive recording medium obtained in Example 8; 20 FIG. 20 is a diagram illustrating the change in reflection density with temperature of the thermosensitive recording medium obtained in Example 9; FIG. 21 is a diagram illustrating the change in reflection density with temperature of the thermosensitive recording medium obtained in Example 10; FIG. 22 is a diagram illustrating the change in reflection 13 density with temperature of the thermosensitive recording medium obtained in Comparative Example 1; FIG. 23 is a diagram illustrating the change in reflection density with temperature of the thermosensitive recording 5 medium obtained in Comparative Example 2; and FIG. 24 is a diagram illustrating the change in reflection density with temperature of the thermosensitive recording medium obtained in Comparative Example 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the detailed description which follows, specific embodiments of the invention particularly usef ul in the image recording applications are described. It is understood, however, that the invention is not limited to these embodiments.

For example, it is appreciated that the recording media and methods of the invention are adaptable to any form of reversible recording media. Other embodiments will be apparent to those skilled in the art upon reading the following description.

A reversible thermosensitive recording medium of the present invention comprises a layer of thermosensitive recording material capable of exhibiting the change in transparency or in color with temperature of the recording material. In the present invention, attention will be focused primarily on the former, in which the medium exhibits the change in transparency (that is, between transparent and white opaque 14 states). The mechanism of this change of the reversible thermosensitive recording material between transparency and white opaqueness is considered as follows. 5 The mechanism is based on the facts that (1) in the transparent state, particles of the low molecular weight organic material dispersed in the resin matrix are in close contact with a matrix resin without any space therebetween and without any space within the particles either, so that incident light from one side can be transmitted to the other side without appreciable scattering, thereby exhibiting transparency and (2) in white opaque state, the particles of the low molecular weight organic material are now formed of numerous minute crystals, and also formed are interstices at the interface between the minute crystals and the matrix resin, so that incident light from one side is reflected or scattered on the interfaces, thereby exhibiting white opaqueness.

Referring to FIG. 2, showing the change in transparency by heating, a thermosensitive layer comprising a matrix resin and a low molecular weight organic material dispersed in the matrix resin is at a white opaque state at an ambient temperature To or below.

Upon being heated, the thermosensitive layer at a temperature T1 begins gradually becoming transparent and becomes completely transparent in a temperature range T2 to T3. When this layer is cooled to ambient temperature below TO, the layer remains transparent.

The above phenomenon is explained as follows. As the temperature is increased to T 1, the resin begins softening. As this softening proceeds, the resin fills the space between the resin and the particles of the low molecular weight organic material and between adjacent particles, to thereby the transparency increases. At a temperature ranging from T2 to T3, the low molecular weight organic material partly melts so that the remaining space is filled therewith, whereby the layer becomes transparent. When the layer is cooled as mentioned above, the low molecular weight organic material is crystallized at a relatively high temperature because of the presence of seed crystals. In this case, since the resin still remains in a softened state, the resin can follow the volume change caused by the crystallization of the low molecular weight organic material, so that no space is formed. That is, the layer is maintained transparent upon cooling.

By contrast, when heated to a temperature T4 or higher, the layer becomes translucent between the maximum transparency and the opaqueness. When the temperature is subsequently lowered, the layer returns to the original white opaque state rather than the transparent state.

This may be explained as follows. At a temperature of T4 or higher, the low molecular weight material completely melts.

When the temperature is then lowered, the low molecular weight material becomes super-cooled and crystallizes at a temperature 16 a little higher than To. In this case, the matrix resin which already started to solidify and which is no longer in the softened state, cannot follow the volume change caused by the crystallization of the low molecular weight organic material, resulting in the formation of space and thereby the opaque state, as mentioned earlier.

It may be noted that, although transparency versus temperature curve in FIG.1 illustrates a typical example, the transparency characteristics will vary when the materials used are changed.

At this point, two parameters are defined, such as the change in transparentization initiation temperature and the rate of change in transparentization temperature width.

First, by gradually heating a white opaque sample, a temperature is measured, at which a white opaque sample becomes transparent. Sepcifically, the heating is carried out using a thermal gradient tester (HG-100, TOYO SEIKI Co), for a heating period of 0.1 second, with a heating block of the tester in contact with the sample at a pressure of 1. 0 kg/ CM2, such that the sample temperature is increased at a equal step of 2" C, from a low temperature, at which the white opaqueness of the sample does not change, to a temperature at which the transparency is achieved. Subsequently, the temperature is again increased at equal steps of f rom 20 C to 5 C, f rom a low temperature, at which the transparency of the sample is attained, to a temperature at which a white opaqueness is sufficiently obtained.

17 In order to prevent for the medium sample to be adhered to the heating block during the heating, a thin film, which is composed of polyimide or polyamide, having a thickness of 10 microns or less with a satisfactory heat resistance, may be 5 interposed therebetween.

After heating in the manner described above, the sample is cooled to room temperature, and subjected to measurements of optical reflection densities at respective positions heated at respective temperatures, using a MacBeth reflection densitometer RD-914. The measured density values are plotted with the selected temperature of the thermal gradient tester as the abscissa and the reflection density as the ordinate.

When the support underlying the reversible recording layer is transparent, reflection density values can be measured with, for example, a sheet or a layer of aluminum, which is attached on the backside of the recording layer, such that the sheet or layer can either absorb light or provide the regular reflection.

After plotting the density values at respective temperatures, a graph is completed by connecting pairs of adjacent plotted points with straight lines. The data curve in the graph is obtained generally in the trapezoid shape such as shown in FIG. 13.

The observed values are af f ected by several parameters such as, for example, the total thickness of the recording layer together with the substrate and the kind of the material used. Since there is observed no appreciable effect of thickness for 18 the range of the recording layer thickness of at most about 300 microns, reproducible results can be obtained for this range.

In contrast, when the thickness exceeds the above range, density values may be affected by the thickness and reliable values can be obtained after adjusting the effect of the thickness. This is carried out either by removing rear portions of the recording layer to decrease the thickness to at most about 300 microns, or by converting the observed values through calculation against the thickness. In addition, when the recording layer is composed primarily of polymer materials, no appreciable ef f ect arises; whereas, when the layer is primarily composed of metals, calculation for the conversion similar to that mentioned above becomes necessary.

Characteristic parameters, such as a dynamic transparentization initiation temperature and a dynamic transparentization termination temperature are obtained from the thus prepared graph.

Referring to FIG. 13, the maximum reflection density is obtained from the graph. A straight line representing y=0.7x (themaximum reflection density) is subsequently drawn. A plurality of data points are selected in the area above the thus drawn straight line, to thereby find preferably 5 to 20 points inside this area. The number of the points less than the above number may cause some ambiguity in the results obtained by the succeeding calculations. Therefore, when the 19 number is found less than the above range, it is necessary to increase the number of the points by decreasing the heating time interval during the aforementioned heat treatment using the thermal gradient tester.

After excluding the same number of both higher and lower density points among the thus selected points, density values for remaining points are obtained. This is followed by averaging these values, to thereby result in an average transparentization density (Dtavd) The ratio of the number of the above-mentioned excluded points to the total selected points is preferably 10% to 30%, more preferably 15% to 25%. By excluding the higher and lower density points as above, reliable transparentization density values can be obtained.

Next, the lowermost dynamic transparentIzation density (Dt1d) is calculated by the following equation:

Dt1d = Dtavd - 0.2X (Dtavd - D,) (1), where D, is the maximum opaque density which is obtained among the density values when the white opaqueness is visually confirmed. Therefore, the lowermost dynamic transparentization density (Dt1d) is obtained as the density, above which the sample is visually recognized as nearly transparent.

In addition, after drawing a straight line representing y=Dtld,, the temperatures at the intersection between the thus drawn straight line and the data curve are obtained. Between the temperatures, the lower temperature is defined as the dynamic transparentization initiation temperature (Ttsd). while the higher temperature is defined as the dynamic transparentization termination temperature (Tted). The transparentization temperature width (dTwd) is subsequently given by the following equation.

dTwd = Tted - Ttsd (2).

White opaque images can be f ormed, f or example, by pressing the thermosensitive medium for about 10 seconds against a hot plate which is heated to a temperature high enough for achieving the white opaqueness and by cooling thereafter to room temperature. When the thus prepared white opaque images are heat treated with the heat gradient tester and subjected to the optical density measurements within several tens of minutes, the thus obtained Ttsd value is a dynamic transparentization initiation temperature (Ttsd) immediate after the image formation and, in a similarmanner, the obtained dTwd value is a dynamic transparentization temperature width (dTwd) immediate after the image formation. 20 Next, other two parameters are described, such as the dynamic transparentization initiation temperature and dynamic transparentization temperature width, both after prolonged storage. In this case, white opaque images in the thermosensitive medium are stored for one week at 35C. The thermosensitive 21 medium with the white opaque images is subsequently heated under similar conditions to the aforementioned measurements of the transparentization initiation temperature, in which the heating is made by increasing temperature at equal steps using 5 the heat gradient tester.

After drawing a straight line representing y=Dt1d. temperatures at the intersection between the thus drawn straight line and the data curve are obtained. Between these temperatures, the lower temperature is defined as the dynamic transparentization initiation temperature after a prolonged storage (Ttsd') t whereas the higher temperature is taken as the dynamic transparentization termination temperature after a prolonged storage (Tted '). The transparentization temperature width after a prolonged storage (dTwd f) is subsequently given by the following equation.

dTwd ' = Tted ' - Ttsd (3) Therefore, the thus obtained Ttsd' is the dynamic transparentization initiation temperature (Ttsd) after a prolonged storage, and dTwdr is the transparentization temperature width (dTwd) after a prolonged storage.

Subsequently, a deferred change in transparentization initiation temperature (dTt,) and a rate of the change in transparentization temperature width (dTw) are given by the following equations.

dTt, = Ttsd Ttsd (4) 22 dTw (dTWd dTWd) X 100 (5) The deferred change in transparentization initiation temperature (dTt,) is preferably at most WC, more preferably at most 2C. The deferred change larger than the above range cause a difficulty in erasing images. Also, this change (dTt,) is pref erably at least -W C, more pref erably at least 2" C. The deferred change smaller than the above range cause a difficulty such as for images to be erased easily during the storage at high temperatures.

The deferred change in transparentization temperature width (dTw) is preferably required to be at least 90%, more preferably at least 95%. The change smaller than the above range causes a difficulty in erasing image with relatively short heating time using a thermal printhead. Also, this change (dTw) is at least 120%, pref erably at most 115%, more preferably at most 110%, and most preferably at most 105%. The change larger than the above range causes a dif f iculty such as changing density of images formed using a thermal printhead.

The aforementioned two parameters, the deferred change 20 in transparentization initiation temperature (dTt.,) and rate of the change in transparentization temperature width (dTw), may also be considered as the parameters which elucidate, from a different viewpoint, the change in materials properties of the matrix resin in the thermosensitive layers.

Namely, as described earlier, the change in the 23 erasability is considered due to the change in glass transition temperatures of the matrix resin. Although, the glass transition temperatures are measured, in general, with a measurement apparatus such as DSC or DMS, it is difficult to obtain reliable results f rom the measurements with a sample such as a thermosensitive layer coated on a substrate, as is the case often carried out. In the present measurements for the reversible recording layer, the temperature T, represents a glass temperature, which is a temperature to correspond to the transparentization initiation as shown in the transparency versus temperature relationship shown in FIG. 2.

Therefore, the dynamic transparentization initiation temperature (Ttsd). which is obtained thorough heat treatments using the heat gradient tester, corresponds to the glass transition temperature. Accordingly, the deferred transparentization initiation temperature (dTts) is considered to represent the change in the glass transition temperature with time.

In addition, the dynamic transaprentization termination temperature (Tted) r that is, the temperature at which the shift is initiated from the transparent state caused by the heating using the heat gradient tester to the white opaque state, represent the temperature at which high melting point long chain low molecular weight molecules start to melt. In a similar manner, the transparentization temperature width represents the temperature width from the glass temperature of the resin 24 to the melting point of the high melting point long chain low molecular weight molecules. Further, the rate of the change in transparentization temperature width (dTw) represents the change in the temperature width from the glass temperature to the melting point of the high melting point long chain low molecular weight molecules.

One of the points for achieving the reversible thermosensitive recording medium having improved capabilities in the above-mentioned deferred transparentization initiation temperature and rate of the change in transparentization temperature width is, among others, to incorporate a flexible structure of the molecule into the resin matrix.

Specif ically, this can be accomplished by selecting either an appropriate combination of a resin material and a crosslinking agent having a flexible structure or a resin material having a flexible structure. By thus incorporating a flexible structure in the resin matrix, there can be attained several effects such as preventing the aggregation of the molecules for a prolonged period of storage, and decreasing the enthalpy relaxation in the molecular system. As a result, the reduction of the rate of the change in glass transition temperature and the change in the above-mentioned parameters with time can be prevented.

In addition, the durability in repeated use can also be improved by forming the matrix resin in the reversible recording medium through a crosslinking reaction using a thermoplastic resin having a functional group which is capable of reacting the crosslinking agent.

As to a method for crosslinking the resin contained in the reversible thermosensitive layer, heating, ultraviolet (UV) irradiation or electron beam (EB) irradiation may be adopted. Since the EB irradiation necessitates a rather costly apparatus, the heating or UV irradiation method is preferred. The heating method is more preferable, since this method employs in general less expensive apparatus and the crosslikng reaction may proceed thermally even at relative low temperature during prolonged storage for the period of, for example, 1 week or 1 month.

Examples of such desirable combination of the resin material and crosslinking agent typically incliide, but are not limited to, (1) a thermoplastic resin having a hydroxyl group and an isocyanate compound and (2) a thermoplastic resin having an acryloyl or methacryloyl group and an acrylic or methacrylic monomer.

In the former combination of the hydroxyl group containing thermoplastic resin and an isocyanate compound, the mixture of linear and cyclic isocyanate compounds may preferably be used as the isocyanate compound.

When only linear isocyanete compounds are used, resultant crosslinked resin has a flexible structure and the erasability is improved. However, a too flexible structure causes difficulties such as the decrease in durability for the repeated 26 use and heat resistance of formed images.

In contrast, when only cyclic isocyanete compounds are used, resultant crosslinked resin has a rather rigid structure. Although the durability for the repeated use and heat resistance of formed images are improved in this case, erasability is found decreased. By using the mixture of linear and cyclic isocyanate compounds, erasability, durability and heat resistance can therefore be improved simultaneously.

The weight ratio of the linear isocyanate compound to the cyclic isocyanate compound is preferably 90:10 to 10:90, more preferably 90: 10 to 30: 70, and most preferably 80:20 to 30: 70. With the increase in the linear isocyanate compound, erasability and maximum erase gradient may increase to thereby result in the improvement in image contrast.

The linear isocyanate compound used in the present invention may be obtained by either reacting a linear isocyanate compound having a hydroxy group such as triol directly with an aliphatic isocyanate such as hexamethylene diisocyanate, or reacting these compounds under the existence of at least an ethylene oxide or propylene oxide.

The molecular weight of the linear isocyanate compound is preferably at least 500, more preferably at least 700, and most preferably at least 1000. Also, the above molecular weight is preferably at most 5000, more preferably at most 4000, and most preferably at most 3000.

Too small the molecular weight of the linear isocyanate 27 compound causes the decrease in the flexibility in crosslinked resin structure, thereby reducing erasability, whereas too large the molecular weight thereof causes the reduction of the degree of crosslinking due to the difficulty in the movement of the molecules, thereby resulting in the reduction in the durability.

The molecular weight in terms of an isocyanate group is pref erably at least 2 5 0, more pref erably at least 3 0 0, and most preferably at least 400. Also, the above molecular weight is preferably at most 2000, more preferably at most 1500, and most preferably at most 1000.

Too small the molecular weight in terms of an isocyanate group mentioned above causes the decrease in the flexibility in crosslinked resin structure, thereby reducing erasability, whereas too large molecular weight thereof causes the reduction of the degree of crosslinking due to the difficulty in the movement of the molecules, thereby resulting in the reduction in the durability.

Specific examples of the linear isocyanate compound include, but are not limited to, 0 0 H 11 11 1 CH20-1----12)s-O-IL--C-N -(C H2)6-14 C 0 0 0 H CH3CH,C CH-,0-[-C-(CH,)s-0-1m-C-N-(CH-,)6-NCO 0 0 H C1-12C)-1-L--h,)s-O-In-C-N-(CH2)6-NCO (1,m,n: 1-10).

28 WN-W-O-CONH-R-NHCO-W'-NCO (11) (R,Rl,W': alkylene,(CH2CH30)n-r or (CH2CH3CH2-0)m; m,n: 1-10).

The cyclic isocyanate compounds disclosed herein represent isocyanate compounds which have a benzene ring or an isocyanurate ring. Of these compounds, ones having an isocyanurate ring are preferably used for their capability of preventing yellowing. It is also preferable for these isocyanate compounds to incorporate a linear structure such as a alkylene chain in addition to the ring structure.

The molecular weight of the cyclic isocyanate compound is preferably at least 100, more preferably at least 200, and most preferably at least 300. Also, the above molecular weight is preferably at most 1000, more preferably at most 700.

Too small the molecular weight of the cyalic isocyanate compound causes insufficient crorsslinking due to the evaporation of the compound with heating during the coating process steps to thereby result in the decrease in the durability. In contrast, too large the molecular weight thereof results in the reduction in also the durability due to the insufficient formation of the rigid molecular structure.

Specific examples of the cyclic isocyanate compound include, but are not limited to, 29 OCN 0 NCO R R N N 1 1 (M) /,'(- -, N _ L\\ 0 1 0 R 1 NCO (R: alkylene) The mixture of the linear and cyclic isocyanate compounds may be obtained either by mixing the aforementioned compounds or as a commercially available mixture. Examples of such mixture include., but are not limited to, Coronate 2298-90T (from Nippon Polyurethane Industry Co) having a ratio of the compound (1) to the compound (U) of 7/3.

The glass transition temperature of the above-mentioned thermoplastic resin, having hydroxyl groups and being used with an isocyanate compound, is preferably at least 400 C, more preferably at least 500 C, and most preferably at least 601> C. Also, the glass transition temperature is preferably at most 1200 C, more preferably at most 1000 C. Too low the glass transition temperature of the thermoplastic resin causes the decrease in the heat resistance of formed images, whereas too high the temperature thereof causes a decreased erasability.

Illustrative examples of the thermoplastic resin useful in the present invention include, but are not limited to, polyvinyl chloride resins, polycar-bonate resins, polyurethane resins and copolymers thereof.

Specific examples of the thermoplastic resin include vinyl chloride-vinyl acetate-vinyl alcohol copolymers, vinyl chloride-acrylatevinyl alcohol copolymers, and vinyl 5 chloride-vinyl acetate-hydroxyalkyl acrylate copolymers.

Furthermore, vinyl chloride resins having a sulphonic acid group in addition to the hydroxyl group may also be used. As specific materials suitably used in the invention include MR-110, MR-104, MR-112 and MR-113, which are each available 10 commercially from Nippon Zeon Co. In particular, the resins which incorporate a highly polar functional group such as sulphonic group is preferably used for its capability of improving image contrast.

The amount by weight of the isocyanate compound to be added to 100 by weight of resin is preferably at least 1 (one), more preferably at least 3. Also, the amount is preferably at most 50, more preferably at most 40.

Too small the amount of the isocyanate compound causes the decrease in the durability, whereas too large the amount thereof causes the decrease in transparency.

The equivalent of the isocyanate group in the isocyanate compound in terms of a hydroxyl group in the resin is preferably at least 0. 05, more preferably at least 0. 1, and most preferably at least 0.2. Also, the equivalent is preferably at most 2, more preferably at most 1 (one).

Too small the equivalent of the isocyanate group causes 31 the decrease in the durability, whereas too high the equivalent thereof causes the decrease in transparency.

As crosslinking methods disclosed herein which can be carried out in the combination of a thermoplastic resin having an acryloyl or methacryloyl group, and an acrylic or methacrylic monomer, there may be utilized herein two methods, among others.

The one is through the crosslinking reaction between an acryloyl or methacryloyl group in the resin and the monomer, assisted by radicals which are generated by heating with organic peroxides admixed therein. The other is the crosslinking reaction assisted by radicals which are generated by ultraviolet light irradiation with photopolymerization initiators added therein, in place of the radicals by heating mentioned above.

Of these methods, the former is preferable due to easier access than the latter, in that the crosslinking reaction in the former can be achieved by heating using organic peroxides, without a rather costly apparatus such as necessitated in the latter.

The examples of the acrylic or methacrylic monomers suitable for the present invention include functional monomers and oligomers, which are generally used for forming ultraviolet or electron beam hardening resins. Of these compounds, those having more flexible structure are preferably used, as exemplified by aliphatic compounds and aromatic compounds accompanying linear chain structure. In a similar manner, 32 mono- or bi-functional monomers are preferred over multi functional (that is, trior higher-) monomers.

Specific examples of these monomers include, but are not limited to:

monofunctional monomers methacrylic acid (MAA) hydroxyethyl methacrylate (HEMA) hydroxypropyl methacrylate (HPMA) dimethylaminoethyl methacrylate (DMMA) chloride salt of dimethylaminoethyl methacrylate (DMCMA) diethylaminoethyl methacrylate (DEMA) glycidyl methacrylate (GMA) tetrahydrofurfuryl methacrylate (THFMA) allyl methacrylate (AMA) ethylene glycol dimethacrylate (EDMA) triethyleneglycol dimethacrylate (3EDMA) tetraethylene glycol dimethacrylate (4EDMA) 1,3-butylene glycol dimethacrylate (BDMA) 1,6-hexanediole dimethacrylate (HXMA) trimethylolpropane trimethacrylate (TMPMA) 2-ethoxyethyl methacrylate (ETMA) 2-ethylhexyl acrylate phenoxyethyl acrylate 2-ethoxyethyl acrylate 2-ethoxyethoxyethyl acrylate 33 2-hydroxyethyl acrylate 2-hydroxypropyl acrylate dicyclopentenyloxyethyl acrylate N-vinylpyrolidone vinylacetate bifunctional monomez-s 1,4-butanediol acrylate 1,6-hexanediol diacrylate 1,9-nonanediol diacrylate neopentyl glycol diacrylate tetraethylene glycol diacrylate tripropylene glycol diacrylate polypropylene glycol diacrylate (adduct of bisphenol A with ethylene oxide) diacrylate gluycerol methacrylate acrylate (adduct of neopenty1glycol with 2 mols of propylene oxide) diacrylate diethylene glycol diacrylate polypropylene glycol (400) diacrylate neopentyl glycol hydroxypivarate diacrylate 2,2-bis(4-acryloxydiethyoxyphenyl) propane neopentyl glycol adipate diacrylate (adduct of neopentyl glycol hydroxypivarate with e caprolactone) diacrylate 2-(2-hydroxy-l,l-dimethylethyl)5-hydroxymethyl-534 ethyl-1,3dioxane diacrylate tricyclodecane dimethylol diacrylate (adduct of tricyclodecane dimethylol with E- caprolactone) diacrylate 1,6-hexamethylene diglycidylether diacrylate trimethylolpropane triacrylate pentaerythritol triacrylate (adduct of glycerol with polyethylene oxide) triacrylate trisacryloyloxyethyl phosphate pentaerythritol tetraacrylate (adduct of trimethylolpropane with 3 mols of propyleneoxide) triacrylate glycerol propoxy triacrylate dipentaerythritol polyacrylate (adduct of dipentaerythritol with E-caprolactone) polyacrylate dipentaerythritol propionate triacrylate (hydroxypivalic aldehyde modified dimethylol propyne) triacrylate dipentaerythritol propionate tetraacrylate dimethylol propane tetraacrylate dipentaerythritol propionate pentaacrylate dipentaerythritol hexaacrylate (DPHA) adduct of dipentaerythritol hexaacrylate with e- caprolactone The amount of an acrylic or methacrylic monomer to be added to a thermoplastic resin is preferably at least 1 (one) part by weight, more preferably at least 3 parts by weight, and most preferably at least 5 parts by weight, per 100 parts by weight 5 of the resin. Also, the amount thereof is preferably at most 70 parts by weight, more preferably at most 50 parts by weight.

Too small the amount of the monomer causes a difficulty of reducing the durability in repeated use, whereas too large the amount thereof causes a degradation of transparency.

In addition, the equivalent of the acrylic or methacrylic group in the acrylic or methacrylic monomer in terms of a acryloyl or methacryloyl group is preferably at least 0. 02, more preferably at least 0.05. In addition, the equivalent is preferably at most 2, more preferably at most 1 (one), and most preferably at most O.B.

Too small the equivalent of the monomer causes a dif f iculty of reducing the durability in reversible capability, whereas too large the equivalent thereof causes a degradation of transparency.

Glass transition temperature of the thermoplastic resin having an acryloyl or methacryloyl group is preferably at least 400 C, more preferably at least 50' C, and most preferably at least 600 C. In addition, the glass transition temperature is preferably at most 120 C, more preferably at most 1000 C.

Too low the glass transition temperature of the 36 thermoplastic resin causes a difficulty of reducing heat resistance of formed images, whereas too high the glass transition temperature thereof causes a deduction of erasability. 5 Illustrative examples of the thermoplastic resin having an acryloyl or methacryloyl group include, but are not limited to, polyvinyl chloride resins, polycarbonate resins, polyurethane resins and copolymers thereof. Specific compounds of the thermoplastic resin having an acryloyl or methacryloyl group are exemplified by graft copolymers which may be obtained through the reaction of the hydroxyl group of the aforementioned thermoplastic resin having a hydroxyl group with the isocyanate group of the isocyanate compound having a methacryloyl or acryloyl group. 15 Examples of the thermoplastic resin having an acryloyl or methacryloyl group disclosed herein include vinyl chloride-vinyl acetatevinyl alcohol copolymers, vinyl chloride-acrylate- vinyl alcohol copolymers, and vinyl chloride-vinyl acetate-hydroxyalkyl acrylate copolymers. 20 In addition, examples of the isocyanate compound having a methacryloyl or acryloyl group include, but are not limited to, methacryloyloxyethyl isocyanate. Examples of the organic peroxides suitably used in the present invention include ketone peroxide, peroxyketal, hydroperoxide, dialkylperoxide, diacylperoxide, peroxyester, peroxydicarbonate.

37 The photopolymerization initiator is selected from those generally used in hardening resins with UV irradiation and these initiators are used individually or as a mixture of two or more.

The amount of the photopolymerization initiators to be added is preferably 0. 005 to 1. 0 part by weight, more preferably 0. 01 to 0. 5 part by weight, per part by weight of the crosslinking agent.

In addition, a photopolymerization accelerator such as aromatic tertiary amines or aliphatic amines may be added.

These accelerators are used individually or as a mixture of two or more. The amount of the photopolymerization acccelerator is preferably 0. 1 to 5 parts by weight, more preferably 0. 3 to 3 parts by weight, per part by weight of the photopolymerization initiators.

Illustrative examples of the aforementioned resin suitably used in the present invention having a flexible structure include, but are not limited to, polycarbonate-based urethane resins. Specific examples of the base polycarbonate include, but are not limited to, HO- [ -R-0-C-0-] m-R'-OH (IV) 0 (R,R': methylene or aromatic group; m=110).

As the polycarbonate-based urethane resins, there may also be available as, but are not limited to, NIPPOLAN 3151 from Nippon Polyurethane Industry Co.

Another point for attaining the reversible 38 thermosensitive recording medium having improved capabilities in the erasability and maximum erasure gradient is the use of a plurality of compounds having different melting points in combination.

Among the compounds, the difference in melting point between the lowest and highest melting point compounds is at least 30' C, preferably at least 400 C, more preferably at least 50' C, and most preferably at least 60 C. The larger the difference, the more improvement in the erasability.

It is preferred that the properties of reversible thermosensitive recording medium in the present invention satisfies the following three conditions: (1) The uppermost transparentization temperature is at least 1250 C, (2) the difference between the uppermost transparentization temperature and the lowermost white opaque temperature is at most 200 C and (3) the temperature range for transparetization is at least 30 C.

In the present invention, characteristic temperatures may be determined as follows for the reversible thermosensitive recording medium, such as the uppermost transparentization temperature (Tt,), lowermost white opaque temperature (Tj) the difference between the uppermost transparentization temperature and lowermost white opaque temperature (Tt,), a transparentization initiation temperature (Tta), and a temperature range for transparentization (ATw).

39 First, a sample piece of white opaque reversible thermosensitive recording medium is prepared. Either transparent or premature white opaque piece can be used after attaining the white opaqueness with heating by pressing to, for example, a hot plate. In order to find whether the heating temperature previously chosen is high enough to achieve the white opaqueness, the sample piece can be brought to a second heating, in which the temperature is higher by 100 C, for example.

When the same degree of the white opaqueness is found after the second heating, it is indicated that the previous temperature is high enough for achieving the white opaque. Otherwise, the previous temperature is not high enough for obtaining the white opaqueness. Therefore, when a higher degree of the white opaqueness is found after the secondheating, a second heating at a s lightly higher temperature can be adopted. This procedure may be repeated successively until the white opaqueness is achieved.

The thus prepared white opaque sample of the reversible thermosensitive recording medium is subsequently subjected to heating at different temperatures to find transparentization temperatures.

The heating is carried out with the thermal gradient tester (HG-100, TOYO SEIKI Co). This tester is equipped with five heating blocks, each of which can be controlled individually at a different temperature, heating period and pressure, to thereby be able to heat simultaneously five locations on the sample at five respective temperatures using this tester.

Specifically, the heating is carried out for 1 second in contact with the heating block at 2. 5 kg/ CM2 pressure, such that the temperature is increased at equal steps of P C to 5 C, from a low temperature, at which the transparency of the sample does not change, to a temperature at which the white opaqueness is certainly achieved. In order to prevent for the medium sample to be adhered to the heating block during the heating, a thin film, which is composed of polyimide or polyamide, having a thickness of 10 microns or less with a satisfactory heat resistance, may be interposed therebetween.

After heating in the manner described above, the sample is cooled to room temperature, and subjected to measurements of optical reflection densities at positions heated at respective temperatures, using a MacBeth reflection densitometer RD-914. The measured values are plotted as shown in FIG - 3, with the selected temperature of the thermal gradient tester as the abscissa and the reflection density as the ordinate.

When the support underlying the reversible recording layer is transparent, density values can be measured with a sheet attached in the rear of the recording layer, such that the sheet can either absorb light or provide the regular reflection.

After plotting the density values at respective 41 temperatures, a graph is completed by connecting pairs of adjacent plotted points with straight lines. The data curve in the graph is obtained generally in the trapezoid shape such as shown in FIG. 2.

The observed data are affected by several parameters such as, for example, the total thickness of the recording layer together with the substrate and the kind of the material used.

Since there is observed no appreciable effect of thickness for the range of the recording layer thickness of at most about 300 microns, reproducible results can be obtained for this range.

In contrast, when the thickness exceeds the above value, density values may be affected by the thickness and reliable values can be obtained after adjusting the effect of the thickness. This is carried out either by removing rear portions of the recording layer to decrease the thickness to at most about 300 microns, or by converting the observed values through calculation against the thickness. In addition, when the recording layer is composed primarily of polymer materials, no appreciable effect arises; whereas calculation for the conversion similar to that mentioned above becomes necessary, when the layer is primarily composed of metals.

The aforementioned characteristic temperatures, such as uppermost transparent i zation temperature and lowermost white opaque temperature, will be obtained from the thus prepared graph.

Referring to FIG. 3, the maximum reflection density (D,,,,,x) 42 is first obtained from the graph. A straight line representing y=0.7xD,,,, ,, is then drawn. A plurality of data points are subsequently selected in the area above the 0.7xD,,, straight line, to thereby find preferably 5 to 20 points insidethisarea.

The number of the points less than the above number may cause someambiguity in the results obtained by the succeeding calculations. Therefore, when the number is found less, it is necessary to increase the number of the points by decreasing the heating time interval during the aforementioned heat treatment using the thermal gradient tester.

After excluding the same number of both higher and lower density points among the thus selected points, density values for remaining points are obtained. This is followed by averaging these values, to thereby result in an average transparent density (Dt,,) The ratio of the number of the above-mentioned excluded points to the total selected points is preferably 10% to 30%, more preferably 15% to 25%. By excluding the higher and lower density points as above, reliable transparentization values can be obtained.

Next, the lowermost transparentization density (Dt,,) is calculated by the following equation:

Dt, = Dtav- 0.2x (D a. - D,i,) (6), where D,j, is the maximum opaque density which is obtained by averaging density values for three neighboring points, when the difference in density between these three values reaches at most 43 0.3. Further, the value Dt. corresponds approximately to the density value, above which the recording layer can be found visually transparent.

After drawing a straight line representing y=0.7xDtm, temperature readings at the intersections between the thus drawn straight line and the data curve are obtained. The temperatures for the higher and lower readings are regarded as lowermost (Ttl) and uppermost transparentization temperatures (Tt,), respectively.

The transparentization temperature width (ATw) is obtained by the following equation:

&Tw = Tt, - Ttj (7).

In addition, the uppermost white opaque density (D,) is calculated by the following equation:

D, = Dmin + 0. 1 X (Dtav - Dmi,) After drawing a straight line representing y=D,, the lowermost transparentization temperature is read as the temperature corresponding to the intersection between the thus drawn straight line and the data curve.

The temperature difference (ATt,) between the uppermost transparentization temperature and uppermost white opaque temperature is obtained by the following equation:

ATt, = Ts, - Tt, (9).

The transparentization initiation density (Dt,) is calculated by the following equation:

44 Dt, = D,in + 0.25x (Dtav - D,in) (10).

As shown in FIG. 3, the transparentization initiation temperature (Tta) is then read as the temperature corresponding to the intersection between the straight line representing 5 y=Dts and the data curve.

In the present invention, the uppermost transparent i z at ion temperatures (Tt,) is preferably at least 125 C. By increasing Tt,, the transparentization temperature width (ATw) can be widened without degrading durability of formed images. In addition, the uppermost transparentization temperatures (Tt,) is preferably at least 130' C, more preferably at least 135' C, and most preferably at least 140' C.

The higher the Tt, temperature, the more sensitive the recording medium becomes in the image recording. Also, the T t u temperature is preferably at most 190 C, more preferably at most 18 0' C, and most preferably at most 17 00 C. Within the range, the lower the Tt,, temperature, the more sensitive the recording medium.

The temperature difference (ATt,) between the uppermost transparentization temperature and uppermost white opaque temperature is preferably at most 20' C. The difference ATt, of larger than 200 C causes difficulties, in which a larger amount of energy is required for the formation of white opaque images due to the above-mentioned white opaque temperature higher than usual, to thereby possibly result in the damage on the surface of, and/or degraded white opaque density of the recordinglayer. The difference ATt. is more preferably at most 5 20 C, and most preferably at most 10' C.

The transparentization initiation temperature (Tt,) is preferably at most 95 C, more preferably at most 90' C, and most preferably at most 850 C. Also, the temperature Tta is preferably at least 700 C, more preferably at least 75" C. With the decrease in this temperature, the image erasability increases; whereas the durability increases with the increases in this temperature.

The transparentization temperature width (ATw) is preferably at least 300 C. The difference ATw smaller than 30' C causes the decrease in erasability. The difference ATw is preferably at least 4C C, more preferably at least 451 C, and most preferably at least 500 C. The larger the difference, the higher erasability. Also, the difference is preferably at most 100' C, more preferably at most 900 C, and most preferably at most 800 C. In particular, a larger difference in the transparentization temperature width results in an advantage such that constant erasing results can be achieved even at higher processing speed during erasing operation. In such cases, the difference ATw is preferably at least 600 C, more 46 preferably at least 70' C.

In order to form desirable reversible thermosensitive recording medium as mentioned above, one of the points is the selection of low molecular weight organic materials to be used in the present invention. Namely, this is achieved by finding suitable combinations of linear hydrocarbon containing compounds (A) and (B), in which the compound (A) has a melting point of at least 130 C and the compound (B) has a melting point higher than the compound (A) by at least 300 C.

The melting point of the linear hydrocarbon containing compound (A) is preferably at least 1350 C, more preferably at least 14C. Also, the melting point is preferably at most 2000 C, more preferably at most 19C C, and most preferably at most 1700 C.

The lower limit of the dif f erence in melting point between the compounds (A) and (B) is preferably at least 30' C, more preferably at least 40 C, most preferably at least 500 C. The image erasability increases with the increase in the lower limit of the difference in melting point. Further, the upper limit of the dif f erence is pref erably at most 10 011 C, more pref erably at most 90', and most preferably at most 80' C. The heat sensitivity increases with the increase in the upper limit of the difference.

The lower limit of the melting point of the linear 47 hydrocarbon containing compound (A) is preferably at least 50 C, more preferably at least 600, and most preferably at least 700 C. The higher the melting point, the more improved the heat resistance.

In addition, these compounds (A) and (B) may be admixed further with linear hydrocarbon containing compounds (C) which have melting points by at least 10' C higher than the compounds (B) and by at least 1C C lower than the compounds (A). By the addition of the compounds (C), image contrast can be improved.

The melting point of the linear hydrocarbon containing compound (C) is preferably at least 800 C, more preferably at least 9011 C, and most preferably at least 100 C. Also, the melting point is preferably at most 150' C, more preferably at most 1400 C, and most preferably at most 130' C.

These linear hydrocarbon containing compounds (A), (B) and (C) may be used in the present invention individually or incombination. They preferably include along chain structure, having carbon atoms of preferably at least 4, more preferably at least 6, most preferably at least 8. With the increase in 20 the carbon number, the durability is improved in repeated use.

The number of the long chain structure included in the linear compound may be equal to one or more. Incidentally, the above carbon number represents the total of the carbon number in the long chains included in the linear compound. When two 48 long chain structures are included in a linaer compound, each having six carbon atoms, the linear compound is referered to have a long chain structure of 12 carbon atoms.

In the case of the compounds (A) and (B) admixed, the weight ratio of the compound (A) to the total weight of the low molecular weight organic compounds, that is, to the weight of the compounds (A) and (B) combined, is preferably at least 3%, more preferably at least 5%, and most preferably at least 10%. The larger the weight ratio, more improved the erasability. The weight ratio is also preferably at most 50%, more preferably at most 40%, and most preferably at most 30%. The smaller the weight ratio, the higher the transparency.

In a similar manner, the weight ratio of the compound (B) to the total weight of the low molecular weight organic compounds is preferably at least 30%, more preferably at least 50%, most preferably at least 60%. The smaller the weight ratio, the more improved the erasability. The weight ratio is also preferably at most 95%, more preferably at most 90%, and most preferably at most 8 5%. The larger the weight ratio, the higher the transparency after erasure.

In the case of the linear hydrocarbon containing compound (C) admixed further, the weight ratio of the compound (C) to the total weight of the low molecular weight organic compounds is preferably at least 3%, more preferably at least 5%, and most preferably at least 10%. The larger the weight ratio, more improved the transparency. The weight ratio is also preferably 49 at most 50%, more preferably at most 40%, and most preferably at most 30%. The smaller the weight ratio, the higher the erasability.

The low molecular weight organic material of the reversible thermosensitive recording medium suitably used in the present invention may preferably include the mixture of at least one kind of the linear hydrocarbon containing compound (A), having melting points of at least 130' C, which include at least one of amide, urea and sulfonyl bonds and at least one carboxyl radical, with at least one kind of the linear hydrocarbon containing compound (B) which has a melting point higher by at least 300 C than the compound (A).

In the above low molecular weight organic material, the amide, urea and sulfonyl bonds may be included at most one of the respective bonds or at least one of these bonds. Also, these bonds may also be included either at the end or at the middle of the molecular chain. In addition, any number of the carboxyl radicals may be included, being bonded either at the end of the molecular chain or in one of side chains.

The linear hydrocarbon containing compound (A) may preferably include, but is not limited to, both of an amide bond and carboxyl radical. In addition, a plurality of at least either one the amide bond and carboxyl radical may preferably be included in the low molecular weight organic material.

Further, it is more preferable for both of the amide bond and so carboxyl radical to be included therein.

The linear hydrocarbon containing compound (A) including the amide bond and carboxyl radical is expressed by, but is not limited to, the following general formula:

HOOC-(CH2)nX-(CH2)m-y-(CH2)n-COOH (IV) 1 where 26k nk 1, 26-::tmk 1, with X and Y being one of the groups of CONH and NHCO, but not same simultaneously. The number 2n+m is preferably at least 6, more preferably at least 8, and most preferably at least 10.

The linear hydrocarbon containing compound (A) may preferably include both of a urea bond and carboxyl radical.

Also, the compound (A) may preferably include both of a sulf onyl bond and carboxyl radical.

The linear hydrocarbon containing compound (A) including the urea bond and carboxyl radical, as well as the sulfonyl bond and carboxyl radical, is expressed by, but is not limited to, the following general formula:

CH3-(CH2)nZ-(CH2)m-COOH (V), where 25k nk' 0, 26k mk 1, with Z being either NHCONH or S02.

The number n+m is preferably at least 6, more preferably at least 8, and most preferably at least 10.

The melting point of the compound expressed by the formula (M) is preferably at least 130 C, more preferably at least 0 135. and most pref erably at least 1400 C. The image erasability increases with the increase in the melting point. Also, the 51 melting point is at most 2000 C, preferably at most 180', more preferably at most 1700, and most preferably at most 1600 C.

The heat sensitivity increases with the increase in the melting point.

In addition, the melting point of the compound expressed by the f ormula (V) is pref erably at least 135> C, more pref erably at least 140. The image erasability increases with the increase in the melting point. Also, the melting point is preferably at most 190', more preferably at most 17C, and most preferably at most 15C C. The heat sensitivity increases with the increase in the melting point.

Specif ic examples of the compound described above include, but are not limited to, as follows.

TABLE 1

M.P. CC) (1) HOOC-CH2-NHCO-(CH2)1o-CONH-CH2-COOH 198 (2) HOOC-(CH2)2-NHCO-(CH2)4-CONH-(CH2)2-COOH 197 (3) HOOC-(CH2)2-NHCO-(CH2)8-CONH-(CH2)2-COOH 198 (4) HOOC(CH2)2-NHCO-(CH2)10-CONH-(CH2)3-COOH 187 (5) HOOC-(CH2)3-NHCO-(CH2)4-CONH-(CH2)3-COOH 139 (6) HOOC-(CH2)3-NHCO-(CH2)6-CONH(CH2)3-COOH 144 (7) HOOC-(CH2)3-NHCO-(CH2)8-CONH(CH2)3-COOH 148 (8) HOOC-(CH2)3-NHCO-(CH2)1o-CONH-(CH2)3-COOH 150 (9) HOOC-(CH2)3-NHCO-(CH2)12-CONH-(CH2)3COOH 156 52 (10) HOOC-(CH2)3-NHCO(CH2)18-CONH(CH2)3COOH 151 (11) HOOC(CH2)s-NHCO-(CH2)2-CONH-(CH2)s-COOH 168 (12) HOOC- (CH2).s-NHCO (CH2) 4-CONH- (CH2) s-COOH 146 (13) HOOC- (CH2) -5-NHCO- (CH2) 6-CONH- (CH2) sCOOH 138 (14) HOOC- (CH2) s-NHCO- (CH2) 8CONH- (CH2) 5-COOH 146 (15) HOOC- (CH2) s-NHCO- (CH2) 10CONH- (CH2) s-COOH 145 (16) HOOC- (CH2) sNHCO(CH2) 12-CONH- (CH2) s-COOH 145 (17) HOOC- (CH2) 11 -NHCO- (CH 2) 2 -CONH(CH 2) 11 -COOH 144 (18) HOOC (CH2) 11 -NHCO- (CH2) 4 -CONH- (CH 2) 11 -COOH 155 (19) HOOC- (CH2) I l -NHCO (CH2) 6-CONH- (CH2) 11-COOH 135 (20) HOOC- (CH2) liNHCO (CH2) 8-CONH- (CH2) 11-COOH 144 (21) HOOC- (CH2) ii-NHCO- (CH2) lo-CONH- (CH2) ii-COOH 148 (22) HOOC- (CH2) ii-NHCO- (CH2) 12-CONH (CH2) ii-COOH 145 (23) HOOC- (CH2) 2-CONH- (CH2) 12-NHCO (CH2) 2-COOH 181 (24) HOOC- (CH2) 4CONH- (CH2) lo-NHCO- (CH2) 4-COOH 158 (25) HOOC- (CH2) 4-CONH- (CH2) 12-NHCO (CH2) 4COOH 159 (26) HOOC- (CH2) s-CONH(CH2) 8-NHCO (CH2) s-COOH 143 (27) HOOC- (CH2) 7CONH- (CH2) 6-NHCO- (CH2) 7-COOH 164 (28) HOOC- (CH2) loCONH- (CH2) 4-NHCO- (CH2) loCOOH 168 TABLE 2 m. P. (0 C) (29) CH3-(CH2)17-NHCONH-CH2-COOH 143 (30) CH3(CH2)17-NHCONH-(C12)2COOH 140 53 (31) CH3-(CH2)17-NHCONH-(CH2)3-COOH 130 (32) CH3-(CH2)13-NHCONH(CH2)2-COOH 136 (33) CH3-(CH2)17-SO2(CH2)2-COOH 136 The linear hydrocarbon containing compounds (B) may preferably be those having melting points such as tabulated above and also having a linear chain structure. The linear chain structure preferably has at least 8 carbon atoms, more preferably at least 10 carbon atoms, most preferably at least 12 carbon atoms. Also, the linear chain structure preferably has at most 50 carbon atoms, more preferably at most 40 carbon atoms, and most preferably at most 30 carbon atoms.

Examples of the linear hydrocarbon containing compounds (B) useful in the present invention include, but not limited to, alkanols; alkane dioles; halogenated alkanols or halogenated alkane diols; alkylamines; alkanes; alkenes; alkynes; halogenated alkanes; halogenated alkenes; halogenated alkynes; cycloalkanes; cycloalkenes; cycloalkynes; esters of saturated or unsaturated monocarboxylic acids, or saturated or unsaturated dicarboxylic acids, or esters, amides and ammonium salts thereof; saturated or unsaturated halogenated fatty acids, and esters, amides and ammonium salts thereof; arylcarboxylic acids, and esters, amides and ammonium salts thereof; halogenated arylcarboxylic acids, and esters, amides and ammonium salts thereof; 54 thioalcohols; thiocarboxylic acids, and esters, amides and ammonium salts thereof; and carboxylic acid esters of thioalcohol.

These compounds may be used individually or in combination.

These compounds have 10 to 60 carbon atoms, preferably 10 to 38 carbon atoms, more preferably 10 to 30 carbon atoms. Alcohol groups in these esters may be saturated, unsaturated or halogenated. It is preferred that the low molecular weight organic compounds have at least one of oxygen, nitrogen, sulfur and halogen in its molecule, such as, for example, -OH, -COOH, -CONH, - COOR, -NH-, -NH2, S-, -S-S-, 0, or halogen.

Specific examples of these compounds includes, but not limited to, a monocarboxylic fatty acid, a dicarboxylic fatty acid, a fatty acid ester, a ketone having higher alkyl groups, an ester of dibasic acid, a polyhydric alcohol difatty acid ester, a fatty acid monoamide, a compound expressed by the general formula (VI), and a compound expressed by the general formula (Vff).

CH3-(CH2)n_X(CH2),COOH (VI) where the melting point of the compound expressed by the formula (V1) is lower than 1300 C, and where 26kn--0, 26'-z=mkO, n+m 10, with Z being one of NHCONH, S02, CONH or NHCO.

HOOC-(CH2),-NHCO(CH2)m-COOH M) 1 where the melting point of the compound expressed by the formula (V9) is lower than 1301 C, and where 26 k n ---h 0, 2 6 m k 0 and n+m 10.

Examples of the linear hydrocarbon containing compounds useful in the present invention are further provided, including but not limited to, the following compounds.

Illustrative examples of the monocarboxylic fatty acid include lauric acid, tridecyl acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, nonadecylic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, montanic acid, and melissic acid.

Illustrative examples of the dicarboxylic fatty acid include succinic acid, glutaric acid, adipic acid, pimeric acid, suberic acid, azelaic acid, sebasic acid, undecanedionic acid, dodecanedionic acid, tetradecanedionic acid, pentadecanedionic acid, hexadecanedionic acid.

heptadecanedionic acid, octadecanedionic acid, nonadecanedionic acid, eicosanedionic acid, heneicosanedionic acid, and docosanedionic acid.

Specific examples of the fatty acid esters for use in the present invention include octadecyl laurate, dococyl laurate, dococyl myristate, dodecyl palmitate, tetradecyl palmitate, pentadecyl palmitate, hexadecyl palmitate, octadecyl palmitate, triacontyl palmitate, dococyl palmitate, vinyl stearate, propyl stearate, isopropyl stearate, butyl stearate, amyl stearate, octyl stearate, tetradecyl stearate, hexadecyl stearate, heptadecyl stearate, octadecyl stearate, dococyl 56 stearate, hexacocyl stearate, triacontyl stearate, dodecyl behenate, octadecyl behenate, dococyl behenate, tetracocyl lignocerate, and melissyl myristate.

Illustrative examples of the ketone having higher alkyl 5 groups include 8pentadecanone, 9-heptadecanone, 10-nonadecanone, 11-henicosanone, 12-tricosanone, 14-heptacosanone, 16-hentriacontanone, 18-entatriacontanone, 22- tritetracontanone, 2pentadecanone, 2-hexadecanone, 2-hepatadecanone, 2-octadecanone, and 2-nonadecanone.

The dibasic acid esters may possibly be either monoester ordiester, which is expressedbythe following general formula, ROOC- (CH2) n - COOR 1 (ME) 1 where R and R'are constituted by hydrogen atom or alkyl radical of carbon atoms of 1 to 30, and R and R' are either the same or different each other, in exclusive of being hydrogen at the same time and also the number n is an integer of 0 to 40.

In the dibasic acid ester, expressed by the general formula (V1) above, the carbon numbers of the alkyl radicals R and R' are preferably 1 to 22 and also the number n is an integer of 1 to 30, more preferably 2 to 20. The melting temperature of the ester is preferably at least 400C.

The specific examples of the dibasic acid ester include succinic acid diester, adipic acid diester, sebatic acid diester, and 1(18-)octadecamethylene dicarboxylic acid ester.

The polyhydric alcohol difatty acid ester useful in the 57 present invention are expressed by the following general formula, CH 3 (CH 2) m-2C00 (CH 2) n OOC (CH 2) rn-2 CH 3 (IX) where the number n is an integer of 2 to 40, preferably 3 to 30, and more preferably 4 to 22; and the number m is an integer of 2 to 40, preferably 3 to 30, more preferably 4 to 22.

The specific examples of the esters include 1,3propanediole dialkanate, 1, 6-hexanediole dialkanate, 1,10decanediole dialkanate, and 1,18octadecanediole dialkanate.

The a fatty acid monoamide suitable for the present invention is expressed by the following general formula, R' -CONH-R 2 (X) 1 where R' is a linear hydrocarbon group containing at most 25 carbon atoms; R 2 is selected from hydrogen, a linear hydrocarbon group containing at most 26 carbon atoms, and a methylol group; and at least one of R' and R 2 is a linear hydrocarbon group containing at most 10 carbon atoms.

Specific examples of the monoamide include nonanamide, decanamide, undecanamide, dodecanamide, tridecanmide, tetradecanamide, haxadecanamide, ocatadecanamide, eicosanamide, docosanamide, tricosanamide, hexacosanamide, and octacosanamide.

Illustrative examples of the compounds expressed by the general relation formulae (VI) and (A) are shown in Tables 3 and 4, respectively.

TABLE 3

58 M. P. ( 0 C (34) CH3(CH2)13NHCOM-(CH2)s-COOH 117 (35) CH3 (CH2) 13-NHCONH- (CH2) 7-COOH 118 (36) CH3 (CH2) 17NHCOM- (CH2) 5-COOH 119 (37) CH 3 (CH 2) 13 -NHCONH- (CH 2) 7 -COOH 120 (38) CH 3 (CH 2) 13 -NHCONH(CH 2) 1 o -COOH 122 (39) CH3 (CH2)17-SO2-CH2-COOH 118 (40) CH3 (CH2) 19-SO2CH2COOH 120 (41) CH3 (CH2) 16-CONHCH2-COOH 122 (42) CH3 (CH2) 16-CONH (CH2) 2-COOH 120 (43) CH3 (CH2) 2o-CONH-CH2-COOH 125 (44) CH3 (CH2) ll-NHCO- (CH2) 4-COOH 109 (45) CH3 (CH2) 17NHCO (CH2) 4-COOH 108 TABLE 4

M. P. (OC) (46) HOOC-(CH2)11NHCO-(CH2)2COOH 127 (47) HOOC-(CH2)11-NHCO(CH2)4-COOH 123 In addition to the aforementioned linear hydrocarbon containing compounds (A) and (B), at least one kind of the low molecular weight organic material may also be included, which is characterized to have a melting point higher by at least 1011 C than the compound (B) and lower by at least by 101> C than the 59 compound (A). These compounds may suitably be selected from the aforementioned compounds (B).

The thermosensitive recording layer in the present invention preferably has a thickness of 1 to 30 microns, more preferably 2 to 20 microns, and most preferably 4 to 15 microns.

Too large a thickness of the recording layer causes a dif f iculty in uniformly transparentizing the recording layer, since a temperature variation occurs in the layer. Too small thickness of the recording layer, on the other hand, causes a reduction of the white opaqueness and the contrast. By increasing the amount of the aliphatic acids and/or crosslinking resin materials in the recording layer, the white opaqueness can be increased.

The weight ratio of the low molecular weight organic materials to the crosslinked resin materials is 2:1 to 1:16, preferably 1:2 to 1:8, more preferably 1:2 to 1:5, further preferably 1:2 to 1:4, and most preferably 1:2.5 to 1:4.

A proportion of the resin below the above range causes a dif f iculty in f orming a f ilm in which the low molecular weight organic material is retained in the resin. An amount of the resin above the above range also causes a difficulty in achieving the white opaqueness because the amount of the low molecular weight organic material is small.

A protective layer may f urther be provided on the recording layer to protect the same from damage or deterioration. Suitable materials for the protective layer having a thickness of 0. 1 to 5 microns include silicone rubber or silicone resin (Japanese Laid-Open Patent Application No. 63-221087), polysiloxane graft polymer (Japanese Laid-Open Patent Application No. 63-317385), and ultraviolet radiation curable 5 resin or electron beam curable resin (Japanese Laid-Open Patent Application No. 2566) In addition, organic or inorganic filler materials may further be included, where relevant.

In addition, an intermediate layer may be interposed between the protective layer and the recording layer to protect the recording layer f rom solvents or monomer components in layer formation liquid for forming the protective layer, as disclosed in Japanese Laid-Open Patent Application No. 1-133781.

As the materials for the intermediate layer, the following thermosetting resins and thermoplastic resins -may be used in addition to the aforementioned resin materials for forming the recording layer. Examples of the suitable materials include polyethylene, polypropylene, polystyrene, polyvinyl alcohol, polyvinyl butyral, polyurethane, saturated polyester, unsaturated polyester, epoxy resin, phenolic resin, polycarbonate, and polyamide. The thickness of the intermediate layer is preferably 0. 1 to 2 microns. A thickness of below the above range of the intermediate layer causes a difficulty in protecting the recording layer, whereas an amount thereof above the above range causes a reduction of the heat sensitivity.

The reversible thermosensitive recording medium of the 61 present invention may be utilized effectively together with another data storage medium. Namely, this will be accomplished by providing both of these media on, for example, a memory card; storing (or transferring) various information, which is frequently rewritten, from the data storage medium into the reversible thermosensitive recording medium; and subsequently rendering the information in the reversible thermosensitive recording medium visually recognizable. With this configuration of the media and information data handling, the card owner can have an immediately access visually to necessary data out of the whole stored data even without any other read out gadget, to thereby be able to enhance the convenience for users considerably.

The data storage medium mentioned above suitably used in the present invention may be any of data storage medium, and preferably be the storage medium such as, for example, magnetic recording, integrated circuit (IC), non-contact type IC and optical memory. As to magnetic layers for forming the magnetic recording medium include those of iron oxides and barium ferrites which are formed on a substrate either by coating a coating composition admixed with urethane or nylon resins, or by depositing without resins by, for example, vacuum evaporation or sputtering method.

The portions of the magnetic recording medium may be provided (1) on the side of the substrate opposite to the reversible thermosensitive recording layer, (2) between the 62 substrate and the reversible thermosensitive recording layer or (3) on the portions of the reversible thermosensitive recording layer.

The reversible thermosensitive recording medium may also serve as a portion of the data storage medium by fabricating in the form of a bar code or two-dimensional code. Of these storage media, magnetic recording and IC memories may preferably be used in the present invention.

A layer of an adhesive or pres sure- sensitive adhesive may further be provided on the backside of the substrate to a form a reversible thermosensitive recording label. Any materials generally used as adhesive or pres, sure- sensitive adhesive may also be used in the present invention.

Examples of materials of the adhesive layer include, but are not limited to, urea resins, melamine resins, phenol resins, epoxy resins, vinyl acetate resins, vinyl acetateacrylic copolymers, ethylene- vinyl acetate copolymers, acrylic resins, polyvinyl ether resins, vinyl chloride-vinyl acetate copolymers, polystyrene resins, polyester resins, polyurethane resins, polyamide resins, chlorinated polyolef in resins, polyvinyl butyral resins, acrylate copolymers, methacrylate copolymers, natural rubbers, cyanoacrylate resins and silicone resins. The adhesive layer can be composed of a hot-melt material. When a label is used, one either with of without a released paper may be employed.

By additionally using the thus prepared adhesive or 63 pressure-sensitive adhesive layer, a reversible thermosensitive recording label can be formed. With the adhesive layer, the reversible thermosensitive recording material can therefore be provided even on the areas such as, for example, the entire surface or the portions of relatively thick substrate ofpolyvinyl chloride card having magnetic stripes thereon, where the coating of the recording material is generally hard to be achieved. Therefore, portions of the information data previously stored in the magnetic data storage medium can thus become visually recognizable on the reversible thermosensitive recording layer, to thereby be able to enhance the convenience for users considerably.

In addition to the above polyvinyl chloride card having magnetic stripes thereon, the reversible thermosensitive recording label provided with the adhesive layer may also be used with relatively thick memory cards such as IC or optical memory cards.

Also, the reversible thermosensitive recording label may also be used as a display label on the surface of a disk cartridge in which a rewritable memory disk such as a floppy disk, MD or DVD-RAM is housed therein. FIG. 4 is included to illustrate the reversible thermosensitive recording label placed on the front surface of a MD disk cartridge.

Further, in case of a CD-RW disk, for example, for which no disk cartridge is generally used, a reversible thermosensitive recording label is placed directly onto the 64 face of the disk. Therefore, the recording label may be used appropriately in a variety of ways such that the display content thereof can be made to change (or rewritten) automatically in accordance with the change in the original content of the data storage medium. FIG. 5 illustrates a reversible thermosensitive recording label placed directly onto the front face of a CD-RW disk.

Still further, a reversible thermosensitive recording label is placed directly onto the face of a rewritable optical disk such as a CD-R disk, in which the portions of information data originally stored into the CD-R disk is transferred to the label, to be subsequently displayed thereon.

FIG. 6 illustrates an embodiment of a reversible thermo6ensitive recording label placed on an optical information storage medium (CD-RW) using an AgInSbTe phasetransition type of the recording material.

The storage medium has a basic configuration including, a substrate having a guide groove, with the following contiguous layers formed thereon in the order recited: A first dielectric layer, an optical data storage layer, a second dielectric layer, a reflecting/heat-dissipating layer, an intermediate layer, and a hard coat layer on the back side of the substrate. In addition, a reversible thermosensitive recording label is placed on the intermediate layer. The dielectric layers are not necessary provided on the both sides of the data storage layer. Also, the first dielectric layer is preferably provided in the case where the substrate is formed of resin materials having relatively low melting points, such as polycarbonate resin, for example.

* Further, a reversible thermosensitive recording label is also provided on the face of a video cassette as illustrated in FIG. 7.

In addition to the above-mentioned method of providing the reversible thermosensitive material as the from of a label on a relatively thick disk, the thermosentive material can also be coated directly, or transferred from another support, which previously carry the thermosensitive material, to the surface of the disk cartridge or disk itself. As to the above transfer method, a hot-melt type adhesive or pressure sensitive adhesive layer may appropriately be used by placing on the thermosensitive layer. When the thermosensitive layer or the label thereof is provided on a rigid surface of card, disk, disk cartridge or tape cassette, for example, a cushion sheet or layer may preferably be interposed between the rigid substrate to achieve satisfactory contact with a thermal printhead. This makes it feasible to maintain satisfactory constant conditions throughout the image formation processes.

When the image formed on the reversible thermosensitive recording layer is used together with a bar code, it is preferred that a light reflection layer be provided behind the recording layer. The reflection layer can increase the white opaque density on the white opaque portions of the recording layer, 66 and also the contrast. This enables the increase in the accuracy of read out data. The reflection layer may be formed as a thin film or an evaporated layer of metal such as, for example, Al.

When the reversible thermosensitive recording medium is provided with both (1) rewritable bar code portions usually recognized by a reading unit and (2) other portions recognized visually by human eyes, including both images and alphanumerics, these two portions are preferably formed as at least two different portions having respective reflectivity.

Namely, it is preferable that, on the back of the bar code portions, a light reflection layer is provided, whereas a light absorbing or colored layer be provided on the back of the visually recognizable portions. This is -considered as follows.

When the latter portions are visually recognized, the eyes can generally perceive the dif f erence in color, as well as that in intensity of reflected light, between white opaque imaged portions and colored nonimaged portions. In addition, by providing the color layer, excessively intense glare from reflection can be suppressed at certain viewing angle to thereby facilitate to observe images formed in the reversible recording layer.

In contrast, when the same images are read by a reading unit such as, for example, a reflection spectrometer or bar-code.reader, of which sensing unit is generally positioned normal 67 to the surface of the recording layer with the incoming light beams incident obliquely. It is matter of course that this configuration results undue observed values of the image contrast, which are decreased by the light absorption caused 5 by the color layer.

Accordingly, it is highly desirable that the reversible thermosensitive recording medium of the present invention is formed to include at least two portions which are preferably formed having respective reflectivity, such that a light reflection layer is formed on the back of the bar code portions and that a light absorbing or colored layer is formed on the back of the visually recognizable portions. With this configuration, the images formed in the reversible thermosensitive recording medium is not only ob; erved visually with high contrast, but also measured with the reading unit with sufficient accuracy.

Referring to FIG. 8A, the reversible thermosensitive recording medium of the present invention may preferably be formed as a film, including a substrate 11 with a reversible thermosensitive recording layer 13 formed thereon, and a protective layer 14 formed further thereon.

Alternately, as shown in FIG. 8B, the reversible thermosensitive recording medium may preferably be formed as a film, including a substrate 11 with a reflection layer 12 of Al formed thereon, a reversible thermosensitive recording layer 13 formed thereon, and a protective layer 14 formed further 68 thereon.

Further, the reversible thermosensitive recording medium may also be formed as a film, as shown in FIG. 8C, including a substrate 11 with a reflection layer 12 of Al formed thereon, a reversible thermosensitive recording layer 13 formed thereon, and a protective layer 14 formed further thereon, with a magnetic recording layer 16 further formed on the backside of the substrate.

In addition, these films 22 may each be provided on the face on a card 21 which also include a printed display portion 23 thereon.

Still further, the reversible thermosensitive recording medium may also be formed as a card, as illustrated in FIG. 9A, including a substrate 11 with a reversible thermosensitive recording layer 13 formed thereon, and a protective layer 14 formed further thereon. This film is then shaped to be of a card type, having further a concave portion 23 thereon to accommodate an IC chip, for example.

In the present embodiment, a rewritable memory portion 24 serves as a label, and a concave portion 23 is formed in a predetermined portion on the backside of the card for a wafer substrate 231 such as shown in FIG. 10B to be fixed. On the wafer substrate 231, integrated circuits 233 are fabricated. A plurality of electrical contact terminals 234 are interconnected thereto, and these terminals 234 are exposed to the back face of the wafer 232 to be electrically interconnected 69 for retrieving and rewriting relevant information data by means of an exclusive printer or reader/writer.

Operation characteristics of the reversible thermosensitive recording card will be exemplified hereinbelow with the reference to FIGS. 11A and 11B.

FIG. 11A is a block diagram illustrating the construction of the IC circuit 233 and FIG. 11B is a block diagram illustrating the structure of memory data in a RAM.

The IC circuit is composed of an LSI, for example. There included in the LSI are a CPU 235 for enabling the execution of controlling steps in a predetermined order, ROM 236 for storing program data for the CPU operation, and RAM 237 for read/write operations of requisite data. In addition, the IC circuit 233 include an 1/0 interface 238 for inputting/outputting data signals in response to input/output signals, respectively, and other circuits (not shown) such as, a power-on reset circuit, clock signal generating circuit, pulse dividing circuit (or interrupt signal generating circuit) and address decoding circuit.

The CPU 235 is enabled to execute interrupt control routines in response to interrupt signals which are fed into periodically. The address decoding circuit decodes address data are outputted from the CPU 235 and subsequently feed necessary signals to the ROM 236, RAM 237 and 1/0 interface 238, respectively.

Through a plurality of the contact terminals (i.e., 8 terminals shown in FIG. 11A) interconnected to the 10 interface 238, requisite data outputted from the printer (or reader/writer) are fed to the CPU 235.

The CPU 235 then carries out predetermined processing steps in response to inputted signals and/or program data previously stored in the ROM 236, and subsequently outputs necessary data and signals to the printer though the 10 interface 238.

The RAM 237 includes a plurality of memory regions 239 as shown 239a through 239f in FIG. 11B. There stored are, respectively, a card number in the region 239a; name, address, phone number and other information of the card owner in the region 239b; the current balance and other data of the valuable asset for the card owner in the region 239c; and sales record of the'valuables by the card owner in the regions 239d, 239e, 239f and 239g.

The methods of writing and erasing images suitable in the reversible thermosensitive recording medium of the present invention are carried out as follows.

The writing of the images is achieved by a heating means such as, for example, a thermal printhead or laser, which is capable of heating the partial portions of already existing images. The erasure of the images is carried out with various means including a hot stamp, ceramic heater, heat roller, flow of hot air, thermal printhead and laser. Of these means, a ceramic heater is preferably used, which ensures stable erasure and high contrast images with a miniature apparatus. The 71 temperature suitable for the heating the ceramic unit is preferably at least 1100 C, more preferably at least 112' C, and most preferably at least 1150 C.

With the use of a thermal printhead, the erasure apparatus may further be miniaturized, the electrical power consumption by the apparatus can be further reduced, which makes a portable erasure apparatus feasible, being powered by batteries, for example.

When both writing and erasing images are carried out with a single thermal printhead, this is made by either (1) writing new images after erasing the entire old images or (2) writing new images right after erasing imagewise the old images with varying heating power for each image, which is generally called the overwrite method. Therefore, the total writing and erasure time can be decreased in this overwrite method to thereby be able to achieve faster data processing.

In addition, the reversible thermosensitive recording medium of the present invention is further provided other data storage medium, as aforementioned, to thereby for the portion of information in the other data storage medium can be transferred and subsequently rendered visually recognizable in the reversible thermosensitive recording medium. This can be achieved by additionally providing both reading and rewriting capabilities in the above-mentioned heating means.

Referring to FIGS. 12A and 12B, recording apparatuses are 72 described, which are suitably used for the reversible thermosensitive recording medium of the present invention.

In the apparatus outlined in FIG. 12A, a ceramic heater is used as an image forming (or writing) means, while a thermal printhead is used as an erasing means. Referring again to FIG.

12A, information data previously recorded in a magnetic recording layer is first read with a magnetic head, old image data in the reversible thermosensitive recording medium is then heated to be erased, and new image data, which are updated based on the current data read by the magnetic head, are recorded in the reversible thermosensitive recording medium with the thermal printhead. Subsequently, image data in the a magnetic recording layer are also updated.

In the present embodiment, a reversible thermosensitive recording medium is used, which is provided with a magnetic recording layer formed on the backside of the medium from a reversible thermosensitive layer.

In FIG. 12A, the reversible thermosensitive recording medium 1 may be displaced either to the first direction (e.g., rightward) or to the second or opposite direction (e.g., leftward) through a conveying path represented by a double arrow. Along the conveying path, the apparatus is conf igured for the reversible thermosensitive recording medium 1 be processed as f ollows: (1) The data in the magnetic recording layer is magnetically updated (i.e., recorded and/or erased) during the passage between a magnetic head 34 and a platen roller 40, (2) 73 the image data in the reversible medium are heated/erased during the passage between a ceramic heater 38 and a roller 40, and (3) image data in the reversible medium are rewr i tten /updated during the passage between a thermal printhead 53 and a roller 47. Thereafter, the reversible thermosensitive recording medium is released from the apparatus.

As described earlier, the temperature suitable for the heating the ceramic unit 38 is preferably at least 1100 C, more preferably at least 112 C, and most preferably at least 1150 C.

It may be noted that the data updating steps for magnetic recording layer may be carried out either prior to or following the erasure of image data with the ceramic heater. When relevant, the reversible thermosensitive recording medium may alternately be displaced in the reverse direction right after the passage either between the ceramic heater 38 and roller 40 or between the thermal printhead 53 and roller 47, to thereby be able to be processed again with the ceramic heater 38 or thermal printhead 53, respectively. 20 In alternate embodiment as illustrated in FIG. 12B, a reversible thermosensitive recording medium 1 is displaced inside the apparatus along a path 50 represented by a dotted line in either forward or backward direction. After being fed from a feeding slot 30, the reversible thermosensitive recording medium 1 is conveyed through the 74 inside of the apparatus by a conveying roller 31 and a guide roller 32. Upon arriving at a predetermined position along the path 50, the recording medium 1 is sensed by a sensor 33 and a controlling unit 34C, data in a magnetic recording layer is magnetically updated (i.e., recorded and/or erased) during the passage between a magnetic head 34 and a platen roller 35.

Subsequently, the recording medium is further displaced through a guide roller 36 and another conveying roller 40, and passes between a guide roller 39 and conveying roller 40 up to a point where the recording medium is detected by a sensor 43. At this point, the sensor 43 together with a controlling unit activates operations to heating by the ceramic heating to thereby carry out heating/erasing steps for the medium during the passage between a ceramic heater 38 and a-roller 44.

The recording medium is further displaced through conveying rollers 45,46,47, along the path 50, until being detected by another sensor 51 at another predetermined point. At this point, the operation for the image data in the reversible medium to be rewr i tten /updated is activated during the passage between a thermal printhead 53 and a platen roller 52.

Thereafter, the reversible thermosensitive recording medium is released from the apparatus along a conveying path 56a thorough a conveying roller 59, guide roller 60, and an exit slot 61.

The temperature suitable for the heating the ceramic unit 38 is preferably at least 1100 C, more preferably at least 112" C, and most preferably at least 115' C, as described earlier.

In addition, when relevant, the reversible thermosensitive recording medium may alternately be processed again with the thermal printhead 53. This is achieved (1) first by feeding the recording medium to an alternate path 56b by switching by a conveying path switching means 55a, (2) the recording medium is then displaced in the reversed direction on a conveying belt 58 which advances to the reversed direction after being switched by a limiting switch 57a activated by pressure by the weight of the recording medium, (3) data are processed between the thermal printhead 53 and platen roller 52, upon the arrival of the medium, (4) displaced to the forward direction along a conveying path 49b which is formed by activating a path switching means 55b, (5) then returning along the conveying belt 48 after activating a limiting switch 57b, and (6) subsequently released from the apparatus after passing along the path 56a through the guide roller and an exit slot 61.

The above-mentioned divided conveying paths and conveying path switching means, which is capable of selecting one among the plurality of the divided paths, is alternately provided on either side of the ceramic heater 38. In this case, a sensor is preferably provided between the platen roller 44 and conveying roller 45.

Having generally described this invention, a further 76 understanding can be obtained by reference to certain specific examples which are provided herein for purposes of illustration only and are not intended to be limiting. In the description in the following examples, numerals are parts by weight unless 5 otherwise indicated.

EXAMPLES

EXAMPLE 1

A reversible thermosensitive recording medium of the present invention was fabricated in accordance with steps and apparatus which follow.

A sheet of a magnetic raw roll was used as a supporting substrate, which was composed of a film of polyethylene terephthalate coated with a magnetic recording layer and a self 15 cleaning layer formed further thereon, available as Memorydick DS-1711- 1040 from Dainippon Ink and Chemicals Inc.

A layer of aluminum was deposited on the polyethylene terephthalate film of the substrate to form a light reflection layer having a thickness of 400 A using a vacuum evaporation apparatus. A coating composition for forming an adhesive layer was then prepared by mixing the following components.

Vinyl chloride-vinyl acetate-phosphoric ester copolymer (Denka-Vinyl #1000P from Denki Kagaku Kogyo Co) 10 parts Methyl ethyl ketone 45 parts Toluene 45 parts 77 The thus prepared coating composition was coated on the Al light reflection layer, and dried to form an adhesive layer having a thickness of 0.5 micron.

A disperse solution A was then prepared as follows. Into 50 parts of a tetrahydrofuran solution containing 15% of solid portion of polyvinyl chloride copolymers (MR110 from Nippon Zeon Co), 1. 5 part of HOOC- (CH2) 5-NHCO- (CH2) 4-CONH- (CH2) 5-COOH was added. The thus prepared mixture was further mixed by stirring for 4 8 hours in a glass bottle with also contained glass beads of about 2 millimeter in diameter using a paint shaker (from Asada Tekko Co).

A dissolving liquid B was prepared by mixing the following components.

Behenic acid R95 from Miyoshi Oil and Fat Co) 1.1 part Eicosanedioic acid (SL-20-90 from Okamura Oil Co) 0.25part Vinyl chloride copolymer (MR110 from Nippon Zeon Co) 3.0 parts Tetrahydrofuran 17.0 parts o-Xylene 6.0 parts Subsequently, a coating composition for forming a thermosensitive recording layer was prepared by mixing the following solutions and component.

Disperse solution A 7.8 parts Dissolving liquid B 27.0 parts 78 Isocyanate compound (Nippon Polyurethane Industry Co) 0.6 parts The thus prepared coating composition was coated on the adhesive layer which was previously formed as described above with the underlying magnetic recording with the polyethylene terephthalate substrate, and dried to form a thermosensitive layer having a thickness of about 11 microns. The thermosensitive layer was further hardened by standing at 600 C for 72 hours.

Another coating composition was prepared by mixing the following components.

75% solution of urethane acrylate-based UV hardening resin (Unidec C7-157 from - Dainippon Ink and Chemicals Inc) in butyl acetate 10 parts Isopropyl alcohol 10 parts.

The thus prepared coating composition was coated with a wire bar on the recording layer, dried, and irradiated with ultraviolet radiation f rom a high pressure mercury lamp of about 80 W/cm to form an overcoat layer having a thickness of about 3 microns.

Subsequently, the thus formed recording medium was brought to white opaque state by heating at 1500 C for 10 seconds on ahotplate, then transparenti zed by heating at 9 0 0 C forlminute in a constant temperature oven, whereby a reversible thermosensitive recording medium was fabricated.

79 EXAMPLE 2

A further reversible thermosensitive recording medium of the present invention was fabricated in accordance with steps 5 and apparatus which follow.

A layer of aluminum was deposited on a film of polyester to form a light reflection layer. The film of polyester was used as the supporting substrate for the recording medium, and was available from Toray Co (Lumilar #125, having a thickness of about 125 microns).

A coating composition for forming an adhesive layer was prepared by mixing the following components.

Vinyl chloride-vinyl acetate-phosphoric ester copolymer (Denka-vynyl #1000P from Denki Kagaku Kogyo Co) 10 parts Methyl ethyl ketone 45'parts Toluene 45 parts The thus prepared coating composition was coated on the Al light reflection layer, and dried to form an adhesive layer having a thickness of 0.5 micron. Subsequently, also in a similar manner to Example 1, a thermosensitive recording layer was formed thereon, and an overcoat layer was formed further thereon, whereby a reversible thermosensitive recording medium was fabricated. Further, the thus formed recording medium was heat treated, in a similar manner to Example 1, to thereby bring to white opaque state and then transparentized.

The reversible thermosensitive recording medium of the present invention was thus fabricated.

Further, a layer of an adhesive composed of acrylic resin was provided having a thickness of about 5 microns on the backside of the recording medium, whereby a reversible thermosensitive recording label was formed. Subsequently, the recording label was applied to the surface of a CDRW disk, whereby an optical data storage medium was fabricated incorporating reversible displaying capabilities.

The thus fabricated optical data storage medium was subjected to a test as follows.

Information data such as dates and times were first stored in the CD-RW disk by a WRW drive (MP 6200S from Ricoh Co).

The portions of this information were then transferred into the reversible thermosensitive recording layer, using a writing/ recording device (a thermal printhead) and an erasing device (a ceramic heater), while adjusting each recording energy of the thermal printhead depending on the recording temperature of the recording medium. As a result, the transferred information data were successfully displayed and recognized visually on the reversible thermosensitive recording label.

In addition, after the previous information data in the CD-RW disk were rewritten and the old displayed data in the recording label were erased with the erasing device, a new set 81 of information data were rewritten into the recording label with the thermal printhead. The newly written information data were successfully displayed again on the reversible thermosensitive recording label. This procedure was subsequently repeated up to 50 times, to find the writing and erasure results satisfactory.

EXAMPLE 3

A reversible thermosensitive recording label was formed in a similar manner to Example 2.

The reversible thermosensitive recording label was subsequently applied to the surface of an MD disk cartridge, whereby a data storage medium was fabricated incorporating reversible displaying capabilities.

Information data such as dates and music titles were already stored in the MD disk. The portions of this information were then transferred into the reversible thermosensitive recording layer, using a writing/recording device (a thermal printhead) and an erasing device (a ceramic heater), while adjusting each recording energy of the thermal printhead depending on the recording temperature of the recording medium.

As a result, the transferred information data were successfully displayed and recognized visually on the reversible thermosensitive recording label.

In addition, after the old displayed data in the recording 82 label were erased with the erasing device, a new set of information data were rewritten into the recording label with the thermal printhead. The newly written information data were successfully displayed again on the reversible thermosensitive recording label. This procedure was subsequently repeated 50 times, to find the writing and erasure results satisfactory.

COMPARATIVE EXAMPLE 1 A further reversible thermosensitive recording medium of the present invention was fabricated in accordance with the following steps.

In a similar manner to Example 1, and a light reflection layer and an adhesive layer were formed on the surface of the polyethylene terephthalate film of the magnetic raw roll.

A coating composition for forming a thermosensitive recording layer was then prepared by mixing the following components.

Hexadecanedionic acid (from Tokyo Kasei Co) 1 part Stearyl behenate (from Sigma Co) 5 parts Vinyl chloride-vinyl acetate copolymer (VMCH from Union Carbide Co) 12 parts 1,9-nonanediol diacrylate 4 parts Photopolymerization initiator (Irgacure 184 from Ciba-Geigy Co) 0.2 part 83 Photo-curing resin (S-2040 from Toa Gosei Co) 26.7 parts Tetrahydrofuran 140 parts The thus prepared coating composition was coated on the adhesive layer, dried, and irradiated with ultraviolet radiation from a high pressure mercury lamp of about 80 W/cm to form a thermosensitive layer having a thickness of about 11 microns.

A coating layer was subsequently formed on the thermosensitive layer in a similar manner to Example 1, whereby a reversible thermosensitive recording medium was fabricated.

COMPARATIVE EXAMPLE 2 A reversible thermosensitive recording medium of the present invention was fabricated in accordance with the following steps.

In a similar manner to Example 1, and a light reflection layer and an adhesive layer were formed on the surface of the polyethylene terephthalate film of the magnetic raw roll.

A coating composition for forming a thermosensitive recording layer was then prepared by mixing the following components.

1,18-octadeca-dicarboxylic acid dodecyl (Miyoshi Oil and Fat Co) 2.4 parts Eicosanedioic acid (SL-20-99 from Okamura Oil Co) 2.6 parts 84 Vinylchloride-vinyl acetate copolymer (M2018 with 80% of vinyl chloride, 20% of vinyl acetate and an average degree of polymerization of 1800 from Kaneka Co) 14.0 parts Reacting polymer species (NK polymer B-3015H from Shin Nakamura Kagaku Co) 2.4 part Photopolymerization initiator (Irgacure 184 from Ciba-Geigy Co) 0.1 part Tetrahydrofuran 108 parts Amyl alcohol 12 parts The thus prepared coating composition was coated on the adhesive layer, dried, and irradiated with ultraviolet radiation from a high pressure mercury lamp of about 80 W/cm to form a thermosensitive layer having a thickness of about 11 microns.

A coating layer was subsequently formed on the thermosensitive layer in a similar manner to Example 1, whereby a reversible thermosensitive recording medium was fabricated.

EXAMPLE 4

A reversible thermosensitive recording medium of the present invention was fabricated in accordance with the following steps.

In a similar manner to Example 1, and a light reflection layer and an adhesive layer were formed on the surface of the polyethylene terephthalate film of the magnetic raw roll.

A disperse solution B was prepared as follows. Into 50 parts of a tetrahydrofuran solution containing 15% of solid portion of urethane resin (Nipporan 3151 with 35% of solid portion from Nippon Polyurethane Industry Co), 1. 5 part of HOOC- (CH2) 5-NHCO- (CH2) 4CONH- (CH2) 5-COOH was added. The thus prepared mixture was further mixed by stirring for 48 hours in a glass bottle with also contained glass beads of about 2 millimeter in diameter using a paint shaker (from Asada Tekko Co).

A dissolving liquid C was prepared by mixing the following components.

Behenic acid (#95 from Miyoshi Oil and Fat Co.) 1.1 parts Eicosanedioic acid (SL-20-99 from Okamura Oil Co) 0.25 parts Polyurethane resin (Nipporan 3151 with 35% of solid portion from Nippon Polyurethane Industry Co) 15.6 parts Tetrahydrofuran 17.1 parts o-Xylene 4.43 parts Subsequently, a coating composition for forming a thermosensitive recording layer was prepared by mixing the following solutions and component.

86 Disperse solution B 2.2 parts Dissolving liquid C 26.6 parts Isocyanate compound (Coronate HK from Nippon Polyurethane Industry Co) 0.25 part The thus prepared coating composition was coated on the adhesive layer which was previously formed as described above with the underlying magnetic recording with the polyethylene terephthalate substrate, and dried to form a thermosensitive layer having a thickness of about 11 microns, in a similar manner to Example 1. Further, an overcoat layer was formed thereon having a thickness of about 3 microns in a similar manner to Example 1.

Subsequently, the thus formed recording medium was heat treated in a similar manner to Example 1. Namely, the medium brought to white opaque state by heating at 15 0 0 C for 10 seconds on a hot plate, then transparentized by heating at 900 C for 1 minute in a constant temperature oven, whereby a reversible thermosensitive recording medium was fabricated.

EXAMPLE 5

A reversible thermosensitive recording medium of the present invention was fabricated in accordance with the following steps.

In a similar manner to Example 1, and a light reflection layer and an adhesive layer were formed on the surface of the 87 polyethylene terephthalate film of the magnetic raw roll.

As a disperse solution, a disperse solution A prepared in a similar manner to Example 1 was also used. In addition, a dissolving liquid D was prepared by mixing the following 5 components.

Behenic acid (#95 from Miyoshi Oil and Fat Co.) 1.1 part Eicosanedioic acid (SL-20-99 from Okamura Oil Co) 0.25 part Vinyl chloride copolymer (MR110 from Nippon Zeon Co.) 2.81 parts Tetrahydrofuran 18.6 parts o -Xylene 4. 0 parts Subsequently, a coating composition for forming a thermosensitive recording layer was prepared by mixing the following solutions and component.

Disperse solution A 6.18 parts Dissolving liquid D 20.4 parts Isocyanate compound (Coronate 2298-90T from Nippon Polyurethane Industry Co) 0.45 part The thus prepared coating composition was coated on the adhesive layer which was previously formed as described above with the underlying magnetic layer with the polyethylene terephthalate substrate, and dried to form a thermosensitive layer having a thickness of about 11 microns, in a similar manner 88 to Example 1. Further, an overcoat layer was formed thereon having a thickness of about 3 microns in a similar manner to Example 1.

Subsequently, the thus formed recording medium was heat treated in a similar manner to Example 1 to bring about white opaque state by heating at 1500 C for 10 seconds on a hot plate, then to transparentize by heating at 900 C for 1 minute in a constant temperature oven. The reversible thermosensitive recording medium was thus fabricated.

EXAMPLE 6

A reversible thermosensitive recording medium of the present invention was fabricated in accordance with the following steps.

In a similar manner to Example 1, and a light reflection layer and an adhesive layer were formed on the surface of the polyethylene terephthalate film of the magnetic raw roll.

As a disperse solution, a disperse solution A prepared in a similar manner to Example 1 was also used. In addition, a dissolving liquid E was prepared by mixing the following components.

Behenic acid (#95 from Miyoshi Oil and Fat Co.) 1.1 part Eicosanedioic acid (SL-20-99 from Okamura Oil Co) 0.25 part 89 Vinyl chloride copolymer (MR110 from Nippon Zeon Co.) 2.81 parts Tetrahydrofuran 18.6 parts o-Xylene 4.0 parts Subsequently, a coating composition for forming a thermosensitive recording layer was prepared by mixing the following solutions and component.

Disperse solution A 6.18 parts Dissolving liquid E 20.4 parts Isocyanate compound (Coronate 2298-90T from Nippon Polyurethane Industry Co) 0.61 part The thus prepared coating composition was coated on the adhesive layer which was previously formed as described above with the underlying magnetic layer with the polyethylene terephthalate substrate, and dried to form a thermosensitive layer having a thickness of about 11 microns, in a similar manner to Example 1. Further, an overcoat layer was formed thereon having a thickness of about 3 microns in similar manner to Example 1.

Subsequently, the thus formed recording medium was heat treated in a similar manner to Example 1 to bring about white opaque state by heating at 1501 C for 10 seconds on a hot plate, then to transparentize by heating at 900 C for 1 minute in a constant temperature oven. The reversible thermosensitive recording medium was thus fabricated.

EXAMPLE 7 A reversible thermosensitive recording medium of the present invention was fabricated in accordance with the following steps. 5 In a similar manner to Example 1, and a light reflection layer and an adhesive layer were formed on the surface of the polyethylene terephthalate film of the magnetic raw roll. A coating composition for forming a thermosensitive recording layer was then prepared by mixing the following components.

Behenic acid (#95 from Miyoshi Oil and Fat Co.) 0.8 part Eicosanedioic acid (SL-20-99 from Okamura Oil Co) 0.8 part Vinyl chloride copolymer (MR110 from Nippon Zeon Co.) 4.2 parts Tetrahydrofuran 25.7 parts o-Xylene 4.5 parts Isocyanate compound (229890T from Nippon Polyurethane Industry Co) 0.66 part The thus prepared coating composition was coated on the adhesive layer which was previously formed as described above with the underlying magnetic layer with the polyethylene terephthalate substrate, and dried to form a thermosensitive layer having a thickness of about 11 microns, in a similar manner 91 to Example 1. Further, an overcoat layer was formed thereon having a thickness of about 3 microns in a similar manner to Example 1. The reversible thermosensitive recording medium was thus fabricated.

EXAMPLE 8

A reversible thermosensitive recording medium of the present invention was fabricated in accordance with the following steps.

In a similar manner to Example 1, and a light reflection layer and an adhesive layer were formed on the surface of the polyethylene terephthalate film of the magnetic raw roll.

As a disperse solution, a disperse solution A prepared in a similar manner to Example 1 was also used. in addition, a dissolving liquid F was prepared by mixing the following components.

12-Tricosanone (from Tokyo Kasei Co) 0.82 part 14-Heptacosanone (from Tokyo Kasei Co) 0.28 part Eicosanedioic acid (SL-20-99 from Okamura Oil Co) 0.25 part Vinyl chloride copolymer (MR110 from Nippon Zeon Co.) 2.81 parts Tetrahydrofuran 18.6 parts o-Xylene 4.0 parts Subsequently, a coating composition for forminga thermosensitive recording layer was prepared by mixing the 92 following solutions and component.

Disperse solution A 6.18 parts Dissolving liquid F 20.8 parts Isocyanate compound (Coronate 2298-90T from Nippon Polyurethane Industry Co) 0.5 part The thus prepared coating composition was coated on the adhesive layer which was previously formed as described above with the underlying magnetic layer with the polyethylene terephthalate substrate, and dried to form a thermosensitive layer having a thickness of about 11 microns, in a similar manner to Example 1. Further, an overcoat layer was formed thereon having a thickness of about 3 microns in a similar manner to Example 1.

Subsequently, the thus formed recording medium was heat treated in a similar manner to Example 1 to bring about white opaque state by heating at 1500 C for 10 seconds on a hot plate, then to transparentize by heating at 901 C for I minute in a constant temperature oven. The reversible thermosensitive recording medium was thus fabricated.

EXAMPLE 9

A reversible thermosensitive recording medium of the present invention was fabricated in accordance with the following steps.

93 j In a similar manner to Example 1, and a light reflection layer and an adhesive layer were formed on the surface of the polyethylene terephthalate film of the magnetic raw roll.

As a disperse solution, a disperse solution A prepared in a similar manner to Example 1 was also used. In addition, a dissolving liquid G was prepared by mixing the following components.

Diphenyl behenate (from Sigma Co) 1.1 part Eicosanedioic acid (SL-20-99 from Okamura Oil Co) 0.25 part Vinyl chloride copolymer (MR110 from Nippon Zeon Co.) 2.81 parts Tetrahydrofuran 18.6 parts o-Xylene 4.0 parts Subsequently, a coating composition for forming a thermosensitive recording layer was prepared by mixing the following solutions and component.

Disperse solution A 6.18 parts Dissolving liquid G 20.8 parts Isocyanate compound (Coronate 2298-90T from Nippon Polyurethane Industry Co) 0.5 part The thus prepared coating composition was coated on the adhesive layer which was previously formed as described above with the underlying magnetic layer with the polyethylene terephthalate substrate, and dried to form a thermosensitive 94 layer having a thickness of about 11 microns, in a similar manner to Example 1. Further, an overcoat layer was formed thereon having a thickness of about 3 microns in a similar manner to Example 1.

Subsequently, the thus formed recording medium was heat treated in a similar manner to Example 1 to bring about white opaque state by heating at 1500 C for 10 seconds on a hot plate, then to transparentize by heating at 901 C for 1 minute in a constant temperature oven. The reversible thermosensitive recording medium was thus fabricated.

EXAMPLE 10

A reversible thermosensitive recording medium of the present invention was fabricated in accordance with the following steps.

In a similar manner to Example 1, and a light reflection layer and an adhesive layer were formed on the surface of the polyethylene terephthalate film of the magnetic raw roll.

A coating composition for forming a thermosensitive 20 recording layer was then prepared by mixing the following components.

Behenic acid (#95 from Miyoshi Oil and Fat Co.) 0.8 part CH3(CH2)17-SO2-(CH2)2-COOH 0.8 part Vinyl chloride copolymer (MR110 from Nippon Zeon Co.) 4.2 parts Tetrahydrofuran 25.7 parts o-Xylene 4.5 parts Isocyanate compound (Coronate 2298-90T from Nippon Polyurethane Industry Co) 0.66 parts The thus prepared coating composition was coated on the adhesive layer which was previously formed as described above with the underlying magnetic layer with the polyethylene terephthalate substrate, and dried to form a thermosensitive layer having a thickness of about 11 microns, in a similar manner to Example 1. Further, an overcoat layer was formed thereon having a thickness of about 3 microns in a similar manner to Example 1. The reversible thermosensitive recording medium was thus fabricated.

COMPARATIVE EXAMPLE 3 A reversible thermosensitive recording medium of the present invention was fabricated in accordance with the following steps.

In a similar manner to Example 1, and a light reflection layer and an adhesive layer were formed on the surface of the polyethylene terephthalate film of the magnetic raw roll (Memorydick DS-1711-1040 f rom Dainippon Ink and Chemicals Inc) A coating composition for forming a thermosensitive 96 recording layer was then prepared by mixing the following components.

Behenic acid (#95 from Miyoshi Oil and Fat Co.) 0.5 part Eicosanedioic acid (SL-20-99 from Okamura Oil Co) 0.5 part Vinyl chloride-vinyl acetate-vinyl alcohol copolymer (VAGH from Union Carbide Co) 3 parts Tetrahydrofuran 15.0 parts Isocyanate compound (Coronate L from Nippon Polyurethane Industry Co) 0.5 part The thus prepared coating composition was coated on the adhesive layer which was previously formed as described above with the underlying magnetic layer with the polyethylene terephthalate substrate, and dried to form a thermosensitive layer having a thickness of about 11 microns, in a similar manner to Example 1. Further, an overcoat layer was formed thereon having a thickness of about 3 microns in a similar manner to Example 1. The reversible thermosensitive recording medium was thus fabricated.

COMPARATIVE EXAMPLE 4 A reversible thermosensitive recording medium of the present invention was fabricated in accordance with the following steps.

97 In a similar manner to Example 1, and a light reflection layer and an adhesive layer were formed on the surface of the polyethylene terephthalate film of the magnetic raw roll (Memorydick DS-1711-1040 from Dainippon Ink and Chemicals Inc) A coating composition for forming a thermosensitive recording layer was then prepared by mixing the following components.

Behenic acid (#95 from Miyoshi Oil and Fat Co.) 1.0 part Vinyl chloride-vinyl acetate-vinyl alcohol copolymer (VAGH from Union Carbide Co) 3.0 parts Tetrahydrofuran 15.0 parts Isocyanate compound (Coronate L from Nippon Polyurethane Industry Co) 0.5 part The thus prepared coating composition was coated on the adhesive layer which was previously formed as described above with the underlying magnetic layer with the polyethylene terephthalate substrate, and dried to form a thermosensitive layer having a thickness of about 11 microns, in a similar manner to Example 1. Further, an overcoat layer was formed thereon having a thickness of about 3 microns in a similar manner to Example 1. The reversible thermosensitive recording medium was thus fabricated.

The plurality of the reversible thermosensitive recording 98 media thus prepared in Examples 1, 4, 5, 6, 7, 8 and Comparative Examples 1 through 4 were each subjected to the measurements to determine characteristic parameters. These parameters are the change in elapsed transparentization initiation temperature and the rate of the change in transparentization temperature width.

Measurement Conditions using Hgat Gradation Tester Sample pieces of white opaque reversible thermosensitive recording medium were first prepared by heating the medium to temperatures high enough to achieve the white opaqueness, as described earlier.

The thus prepared white opaque samples were subsequently heated'. The heating was carried out with the thermal gradient tester (HG-100, TOYO SEIKI Co) with a heating time of 0. 1 second and at a pressure of 1 kg/ CM2 The temperature was increased at an equal step of 2' C from 72 C to 165 C, at which the transparentization was possibly initiated, and at an equal step of 5 C for the temperature range, at which the transparentization was possibly terminated, respectively. The samples were then cooled to room temperature, and subjected to measurements of optical densities, using a MacBeth reflection densitometer RD-914.

Another set of measurements were subsequently carried out for the white opaque samples, which were prepared in a similar 99 manner as above and left for one week at 35'C. These samples were then subjected to the similar heat treatment and optical measurements as described above. From the measurements at respective temperatures, the change in the deferred transparentization initiation temperature and the rate of the change in transparent i z ation temperature width were obtained, respectively.

The results from the measurements are shown in FIG. 14 for the results obtained from the measurements in Example 1. In a similar manner, there shown are the results, respectively, in FIG. 15 for Example 4, FIG. 16 for Example 5, FIG. 17 for Example 6, FIG. 18 for Example 7, FIG. 19 for Example 8, FIG. 20 for Example 9, FIG. 21 for Example 10, FIG. 22 for Comparative Example 1, FIG. 23 for Comparative Example 2, and FIG. 24 for Comparative Example 3.

Also, the calculated results of the change in the deferred transparentization initiation temperature and the rate of the change in transparent i zat ion temperature width are summarized in Table 5.

Further, a lowermost and an uppermost transparentization temperatures, and transparentization temperature width were obtained in a similar manner as described above.

Namely, sample pieces of white opaque reversible thermosensitive recording medium were f irst prepared by heating the medium to temperatures high enough to achieve the white opaqueness. The thus prepared white opaque samples were subsequently heated, using the thermal gradient tester (HG100, TOYO SEIKI Co), with a heating time of 1 second and at a pressure of 2.5 kg/ CM2. The temperature was increased, at an equal step of ranging f rom 1 0 C to 5 0 C, f rom a temperature low enough for maintaining the white opaqueness to a temperature high enough for achieving a satisfactory transparency. The samples were then cooled to room temperature, and subjected to measurements of optical densities, using the MacBeth reflection densitometer RD-914.

From the measurements at respective temperatures, a lowermost and an uppermost transparentization temperatures, and transparentization temperature width were obtained as shown in Table 6.

In addition, the plurality of the reversible thermosensitive recording media prepared in Examples 1, 4, 5, 6, 7, 8 and Comparative Examples 1 through 4 were each subjected to measurements of erasability. The measurements were carried out using a printing tester from Yashiro Denki Co. equipped with a edge type thermal 20 printhead EUX-ET8A9AS1, having a resistance of 1152a, from Matsushita Electronic Device Co. Erability Measurement Conditions (1) Printing conditions with the thermal printhead were 25 adjusted to a pulse width of 2. 0 msec, line period of 2. 86 msec, 101 printing speed of 43. 10 mm/sec, lateral scanning density of 8 dot/mm, and platen roll pressure of 3 kgf.

The transparent reversible thermosensitive recording media were then heated by applying various amount of energy, by varying applied voltage potential, ranging from 0.176 to 0. 527 mj /dot, to thereby obtain energy values required to bring the respective media to saturated white opaque density.

The results were obtained as 0.414 mj /dot for Examples 1, 4, 5, 6, 8, 9 and 10; and 0.339 mj/dot for Example 7, and Comparative Examples 1, 2, 3 and 4.

Subsequently, after white opaque images were printed on respective media with the abovementioned printing energy, printing steps on the white opaque image portions were carried out with the same printing conditions as above. During the printing, the printing energy values were adjusted ranging from 0.09 to 0. 363 mj/dot by varying applied voltage potential, to thereby erasability for respective media at respective energy values were obtained.

Further, after white opaque images were printed on respective media with the above-mentioned printing energy, these media were left for one week at 35'C. The thus prepared media were printed under the same conditions as above, to thereby erasability for respective media after prolonged storage at respective energy values were obtained.

Erability MeasuremQnt Conditions (II) 102 In order to measure erasability for shorter printing time, additional measurements were carried out. Namely, printing conditions with the thermal printhead were adjusted to a pulse width of 1. 62 msec, line period of 1. 8 msec, printing speed of 69.44 mm/sec, lateral scanning density of 8 dot/mm, and platen roll pressure of 3 kgf.

After white opaque images were printed on respective media with the above conditions, printing steps on the white opaque image portions were carried out with the printing energy values ranging f rom 0. 084 to 0. 297 mj /dot by varying applied voltage potential. Erasability for respective media at respective energy values were thus obtained.

Further, after white opaque images were printed on respective media with the above-mentioned printing energy, these media were left for one week at 350C. The thus prepared media were printed under the same conditions as above, to thereby erasability for respective media after prolonged storage at respective energy values were obtained.

There summarized in Table 7 are the aforementioned values, obtained from the measurements using the gradation heating tester, such as average transparent density, lowermost transparentization density, uppermost transparentization density, and the change in deferred transparentization temperature; and also the other aforementioned values, obtained from the erasure under the conditions (I) using the thermal printhead, such as initial maximum erasure density, and 103 deferred maximum erasure density.

In a similar manner, there summarized in Table 8 are the aforementioned values, obtained from the measurements using the gradation heating tester, such as average transparent density, lowermost transparentization density, uppermost transparentization density, and the deferred change in transparentization temperature; and also the other aforementioned values, obtained from the erasure under the conditions (II) using the thermal printhead, such as initial maximum erasure density, and deferred maximum erasure density.

The results shown in the Tables 5 through 8 clearly indicate that, regarding the erasability using the thermal printhead under the conditions (I), respective media in the Examples each have higher maximum erasure density than Dtm, for both initial and deferred states of the media. This indicates the erasure is sufficiently completed.

In contrast, some of the media in the Comparative Examples sometimes have lower maximum erasure density than Dtm, thereby indicating the erasability not completely satisfied. Namely, the difference between the initial and deferred erasure densities for the media of Example 5 is higher than those in other Examples, although the maximum easure density of higher than Dtm is found for the medium which has a deferred transparentization initiation temperature of -2.0C as in the recording medium in Example 5.

TABLE 5

104 Example Ttsd Ttsd dTt, dTWd dTWd dTw (0 C) (%) 1 89.0 90.8 1.8 67.0 65.2 97.3 4 89.5 89.5 0.0 51.7 58.4 113.

92.1 96.6 4.5 64.4 59.4 92.2 6 89.5 90.8 1.3 66.6 65.3 98.0 7 100.3 97.6 -2.7 29.2 31.9 109.2 8 80.0 81.7 1.7 68.8 67.1 97.5 9 82.6 84.0 1.4 61.7 58.0 94.0 92.1 93.9 1.8 44.1 46.8 106.1 COMP.1 89.9 96.7 6.8 53.6 47.2 88.1 Comp.2 96.7 105.7 9.0 41.1 34.4 83.7 Comp.3 97.6 100.2 12.6 31.9 19.3 60.1 Comp.4 Not measured or not transparentized Dynamic transparentization characteristics measured (The heat gradation tester: 0.1 second and at a pressure of 1 kg/ CM2).

Ttsd Dynamic transparentization initiation temperature immediately after medium fabrication Ttsd': Dynamic transparentization initiation temperature after prolonged storage of the medium dTWd: Dynamic transparentization temperature width immediately after image formation dTWd': Dynamic transparentization temperature width after prolonged storage of the medium dTts The deferred change in transparentization initiation temperature dTw The rate of the change in transparentization temperature width TABLE 6

Example Dmax Dt,, Dtm Tt, Tt, ATw 1 1.25 1.15 0.96 84.0 138.0 54.0 4 1.1 1.04 0.90 84.0 133.9 49.9 1.13 1.07 0.89 87.1 137.5 50.4 6 1.35 1.18 0.98 84.0 137.1 50.1 7 0.97 0.92 0.79 94.5 117.4 22.9 8 1.38 1.34 0.12 75.4 136.0 60.6 9 0.96 0.90 0.79 81.0 132.1 51.1 1.28 1.14 0.94 88.0 125.4 37.4 COMP.1 0.94 0.87 0.75 84.5 129.5 45.

Comp.2 0.96 0.92 0.79 91.7 123.1 31.4 Comp.3 0.97 0.92 0.80 94.5 118.3 23.8 Comp.4 0.64 Transparentization characteristics (The heat gradation tester: 1 second and at a pressure of 2.5 kg/ CM2) TABLE 7

106 Dtav Dt, d T t., Conditions I Rating (OC) Initial Deferred maximum maximum erasure erasure density density 1 1.15 0.96 1.8 1.24 1.20 0 4 1.04 0.90 0.0 0.97 0.95 0 1.07 0.89 4.5 1.23 1.20 0 6 1.18 0.98 1.3 1.26 1.25 0 7 0.92 0.79 -2.7 0.96 0.90 0 8 1.34 0.12 1.7 1.27 1.25 0 9 0.90 0.79 1.4 0.87 0.85 0 1.14 0.94 1.8 1.14 1.11 0 COMP.1 0.87 0.75 6.8 0.71 0.70 X Comp.2 0.92 0.79 9.0 0.90 0.65 X Comp.3 0.92 0.80 12.6 0.74 0.50 X ---o-mp4 -- - - 0.42 0.40 X Transparentization characteritics and erasability using thermal printhead (Conditions I) TABLE 8 107 Dtav Dt, dTts Conditions II Rating PC) Initial Deferred maximum maximum erasure erasure density density 1 1.15 0.96 1.8 1.22 1.18 0 4 1.04 0.90 0.0 0.97 0.96 0 1.07 0.89 4.5 1.21 1.08 6 1.18 0.98 1.3 1.25 1.20 0 7 0.92 0.79 -2.7 0.95 0.90 0 8 1.34 0.12 1.7 1.25 1.23 0 9 0.90 0.79 1.4 0.86 0.84 0 1.14 0.94 1.8 1.11 1.10 0 COMP.1 0.87 0.75 6.8 0.70 0.67 X Comp.2 0.92 0.79 9.0 0.87 0.60 X Comp.3 0.92 0.80 12.6 0.53 0.43 X Comp.4 - - - 0.35 0.30 X - 1 L Transparentization characteritics and erasability using thermal printhead (Conditions II) As will be apparent from the above description including the examples, the reversible thermosensitive recording medium

108 of the present invention has an improved erasability and image contrast even in a decreased heating time of a thermal printhead to be capable of complying with ever increasing data processing speed.

In addition, the reversible thermosensitive recording medium of the present invention may be of a card-type to be used as a reversible thermosensitive recording label. This label can be provided on the surface of a disk cartridge, a rewritable or write-once disk, and a cassette of a magnetic tape, thereby being capable of displaying at least a part of information stored in the information storage disk or magnetic tape.

This document claims priority and contains subject matter related to Japanese Patent Application 10-316542, filed with the Japanese Patent Office on November 6, 1998, the entire contents of which are hereby incorporated by reference.

Additional modifications and variations of the embodiments disclosed herein are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, these embodiments may be practiced otherwise than as specifically described herein.

109

Claims (22)

WHAT IS CLAIMED IS:

1 A reversible thermosensitive recording medium comprising:

a supporting substrate; and a thermosensitive layer provided on said supporting substrate, said thermosensitive layer changing transparency or color tone reversibly with temperature, wherein said reversible thermosensitive recording medium has a change in deferred transparentization initiation temperature of at most 50 C.

2. A reversible thermosensitive recording medium according to claim 1, wherein said reversible thermosensitive recording medium has a change in deferred transparentization initiation temperature of at most 20 C.

3. A reversible thermosensitive recording medium according to claim 1, wherein said reversible thermosensitive recording medium has a rate of the change in transparentization temperature width of at least 90%.

4. A reversible thermosensitive recording medium according to claim 1, 2 or 3, wherein said reversible thermosensitive recording medium has a change in deferred transparentization initiation temperature of at most 5 C and a rate of the change in transparentization temperature width of at least 90%.

5. A reversible thermosensitive recording medium comprising:

a supporting substrate; and a thermosensitive layer provided on said supporting substrate and including, as main ingredients, a matrix resin and a low molecular weight organic material dispersed in said matrix resin, said thermosensitive layer changing transparency or color tone reversibly with temperature, wherein said matrix resin comprises a cross-linked mixture of a hydroxyl group containing thermoplastic resin, a linear isocyanate compound, and a cyclic isocyanate compound.

6. A reversible thermosensitive recording medium according to claim 5, wherein said cyclic isocyanate compound has a molecular weight in terms of an isocyanate group of at least 250.

7. A reversible thermosensitive recording medium comprising:

a supporting substrate; and a thermosensitive layer provided on said supporting substrate and including, as main ingredients, a matrix resin and a low molecular weight organic material dispersed in said matrix resin, said thermosensitive layer changes transparency or color tone reversibly with temperature, wherein said matrix resin comprises a cross-linked polycarbonate-based urethane resin.

8. A reversible thermosensitive recording medium according to claim 5, 6 or 7, wherein said low molecular weight organic material comprises a mixture of at least one low melting point low molecular weight organic material with at least one high melf-ing point low molecular weight organic material, the difference in melting point between said low melting point low molecular weight organic material and said high melting point low molecular weight organic material being at least 300 C.

9. A reversible thermosensitive recording medium according to claim 5, 6, 7, or 8, wherein said matrix resin has a glass transition temperature of at least 400 C and at most 120' C.

10. A reversible thermosensitive recording medium 112 according to claim 1, 2, 3, 4, 5, 6, 7, 8 or 9, wherein said reversible thermosensitive recording medium has an uppermost transparentization temperature of at least 125 C, the difference between the uppermost transparentization 5 temperature and a lowermost white opaque temperature of at most C, and a transparetization temperature width of at least C.

11. A reversible thermosensitive recording medium jo according to 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, wherein said low molecular weight organic material comprises a mixture of at least a linear hydrocarbon containing compound having a melting point of at least 130 C, which i-nclude at least one of amide, urea and sulfonyl bonds and a carboxyl radical, with at least a linear hydrocarbon containing compound having a melting point higher by at least 300 C than said linear hydrocarbon containing compound.

12. A reversible thermosensitive recording medium according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or 11, further comprising a layer of an adhesive or pressuresensitive adhesive provided on a side of said supporting substrate opposite to said thermosensitive recording layer to form a reversible thermosensitive recording label.

113

13. A reversible thermosensitive recording medium according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or 11, wherein said supporting substrate is of a card type, further comprising an information recording section.

14. A reversible thermosensitive recording medium according to claim 12, wherein said supporting substrate is of a card type, being further comprised of an information recording section.

15. A reversible thermosensitive recording medium according to claim 13 or 14, wherein said information recording section includes at least one of a magnetic recording layer, an IC and an optical memory.

16. A reversible thermosensitive recording medium according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or 11, wherein said supporting substrate is one of a disk cartridge, in which a rewritable memory disk is housed; a rewritable or write-once disk; and a cassette of a magnetic tape.

17. A disk cartridge capable of displaying at least a part of information stored in a rewritable information storage disk comprising 114 said rewritable information storage disk; and a reversible thermosensitive recording label provided on at least one of the surfaces of said disk cartridge.

18. A rewritable information storage disk capable of displaying at least a part of information stored in said rewritable information storage disk comprising said rewritable information storage disk; and a reversible thermosensitive recording label provided on at least one of the surfaces of said rewritable information storage disk.

19. A magnetic tape cassette capable of displaying at least a part of information stored in a magnetic tape comprising said magnetic tape cassette; and a reversible thermosensitive recording label provided on at least one of the surfaces of said magnetic tape cassette.

20. A reversible thermosensitive recording medium according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 or 19, further comprising a printed display portion provided on reversible thermosensitive recording medium.

21. A method of forming and erasing an image in I reversible thermosensitive recording medium, said reversible thermosensitive recording medium being selected from the group consisting of: said reversible thermosensitive recording medium comprising a thermosensitive layer provided on a supporting substrate, said thermosensitive layer changing transparency or color tone reversibly with temperature, in which said reversible thermosensitive recording medium has a change in deferred transparentization of at most 5' C; said reversible thermosensitive recording medium being further included in a reversible thermosensitive recording label, further comprising a layer of an adhesive or pressure-sensitive adhesive provided on a side of said supporting substrate opposite to said thermosensitive recording layer; said reversible thermosensitive recording medium being further provided on at least one of the surfaces of a rewritable information storage disk; said reversible thermosensitive recording medium being further provided on at least one of the surfaces of a disk cartridge, in which a rewritable information storage disk is housed; and said reversible thermosensitive recording medium being further provided on at least one of the surfaces of a cassette of a magnetic tape, 116 wherein said method is carried out by heating.

22. A method of forming and erasing an image according to claim 21, wherein said method is carried out with a thermal 5 printhead.

3 22. A method of forming and erasing an image according to claim 21, wherein said method is carried out with a thermal printhead to conform the overwrite method, in that said writing new images is made imagewise right after erasing the old images with varying heating power for each image.

It 22. A method of forming and erasing an image according to claim 23, wherein said erasing is carried out with a ceramic 15 heater.

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