This invention relates to a recording and erasing system which records
an image on a thermoreversible recording medium and erases such a recorded image
therefrom by controlling a quantity of energy applied thereto.
EP 0 461 606 A2 and EP 0 468 237 A2 refer to a recording and erasing
system for repeatedly recording and erasing an image on and from a thermoreversible
medium by applying a predetermined quantity of energy to desired areas of said
medium via a heating means. Said systems comprise energy varying means so as to
erase an image on the recording medium. The heating means applies a first quantity
of energy to areas where an image is to be erased and a second quantity of energy
to areas where an image is to be formed.
Up to now, efforts have been made to develop recording systems which
can repeatedly record and erase an image on and from a thermoreversible recording
medium which becomes black, or transparent and colorless depending upon quantities
of thermal energy applied thereto.
Japanese patent laid-open publications No. Sho 57-77140 and Hei 2-188294
propose examples of thermographic materials for such a recording medium.
The former publication exemplifies a thermoreversible recording medium
comprising layers of thermoreversible material of a whitening group applied on
the surface of a glass or plastic substrate. This material inserts its state at
two transition temperatures t1 and t2 (t1
When heated above the temperature t2 for a given period of time, the
material becomes white. On the other hand, when heated above t1 but
below t2 for a second given period of time, the material becomes transparent
and colorless. Therefore, heating elements of a thermal head associated with an
image to be recorded are heated above t2, while heating elements associated
with an image to be erased are heated above t1 but under t2.
The latter publication discloses a thermoreversible medium including
a thermoreversible material of a dye group. When the recording medium contains
a dye whose transparency or color changes with temperatures, the medium can be
repeatedly used for recording and erasing images such as letters and symbols thereon
and therefrom, respectively, similarly to the foregoing thermoreversible medium
of the whitening group.
The principle of the recording system will be described hereinafter.
When a first energy (h1) is applied from a dynamic heat source such
as a thermal head, the thermoreversible material is developed to form a first dark
image (in black). The image is maintained as it is in a normal environment (temperature
and humidity), but is erasable when a second energy (h2) is applied
thereto. When the first energy (h1) is applied again, a second image
can be formed. Thus, the recording and erasing can be performed repeatedly.
Fig. 1 of the accompanying drawings is a schematic view showing the
configuration of the foregoing recording medium 1, which comprises a protective
film 14, a recording layer 15 including materials such as a dye, an agent for
making an image visible/invisible and a binder, and a substrate 16. When the first
large energy (h1) of 200 to 300°C is applied onto the recording medium
1 for a short period of time, e.g. 1 to 3 ms, in the direction shown by an arrow
A, a black image is formed on the recording medium 1, for example. Conversely,
when the second small energy (h2) of 80 - 160°C is applied to the recording
medium 1 for a relatively long period of time, e.g. 5 ms to 2 sec, in the direction
of the arrow A, the image is erased from the recording medium.
Specifically, the recording layer 15 includes an agent for making
the image visible/invisible which becomes acid and salt in response to an applied
energy, and a leuco dye whose color changes with variations of acidity. Fig. 2
shows phenyl carbonate and organic amine salt as an example of the agent for making
the image visible/invisible. Fig. 3 (a) shows a colorless leuco compound and Fig.
3 (b) shows a colored leuco compound.
The agent for making the image visible/invisible becomes acid when
it is heated above the temperature t2, so that lactone rings of the
leuco dye are opened. Thus, the leuco dye becomes colored. When heated above the
temperature t1 but under the temperature t2, the agent for
making the image visible/invisible changes to alkaline, so that the opened lactone
rings are closed. Therefore, the leuco dye becomes colorless.
This recording medium has characteristics as shown in Figs. 4 and
5. In Fig. 4, the abscissa represents a period of time for voltage supply, and
the ordinate represents a recording density. From Fig. 4, it can be seen that the
recording medium has the maximum recording density of 1.2 when the recording medium
is applied with a voltage for approximately 3 ms. In Fig. 5, the abscissa denotes
an erasing temperature and the ordinate a recording density after erasure. In
this case, the recording medium is applied with the voltage for 3 ms (i.e. the
state where the recording medium has a recording density of 1.2) and is then heated
by a heat roller, a thermal head or the like. Fig. 5 shows that the recording
medium is completely free from an image near 120°C to 150°C (i.e. the state where
the recording medium is similar to that having the density 0.15 prior to the recording).
The erasing characteristics are also shown in Figs. 6 and 7, which
are obtained in a different manner. Fig. 6 shows a completely black pattern 41
formed by the thermal head on the recording medium 1. Fig. 7 shows the erasing
characteristic of the recording system which erases the black pattern of Fig.
6. An energy of 1.0 mJ/dot and an energy of 0.6 mj/dot are applied to the recording
medium in the direction shown by an arrow B for the recording and erasing, respectively.
Referring to Fig. 7, it can be seen that the erasing is not complete at the beginning
of the erasing process (i.e. about the first to 30th lines in the black image)
and substantially after the 300th and succeeding lines of the black image.
The head portion of the recorded image is not erased because the
thermal head does not reach its effective temperature. This is because heating
elements of the thermal head take a certain period of time to become effective
even when thermal head is left at room temperature (without applying a voltage
thereto for a while) and is heated under such a condition. The thermal head is
not elevated to its effective temperature until the tenth line is being erased.
In other words, the thermal head is unstable in its operation until it is sufficiently
The reason why the image is not erased in a portion following a 300th
line is that the heating elements become too hot in the heated thermal head. Two
kinds of energy are reserved in the thermal head. One is a part of the energy
generated by the heating elements and the other is the energy which is used to
erase a previous line and both energies remain accumulated around the heating elements.
Both of these energies raise the temperature of the heating elements which are
repeatedly heated for every line. Thus, the thermal head becomes too hot to erase
the recorded image.
Fig. 8 shows a comparison of erasing characteristics on a large recording
medium of A4 size and a small recording medium of a card size. In Fig. 8, the ordinate
represents the numerical order of a line to be erased, and the abscissa represents
an erasing temperature. The larger the recording medium, the more incomplete the
The conventional recording and erasing system for the thermoreversible
recording medium adopts a method in which energies are applied to the recorded
image so as to make it invisible. In other words, the recorded image to be erased
is heated at the temperature which is above t1 but under t2
as mentioned above.
As described so far, the thermoreversible recording medium tends
to vary its reflectance and recording density somewhat depending upon its recording
and erasing history. In other words, the recording medium shows different degress
of reflectance and recording densities at the recorded and erased areas and at
the areas which have never been recorded and erased. Therefore, incompletely erased
images sometimes remain vaguely on the recording medium in a manner such that
they are faintly visible. Prior art recording and erasing systems suffer from the
problem that erasure is somewhat incomplete.
Furthermore, there are few recording mediums which are completely
thermoreversible. Usually, the more often they are used, the poorer they become,
and finally they will become unusable. During repeated use, the recording medium
extensively undergoes physical and chemical changes so that it may become worn
out. Furthermore, the recording medium may have its protective film and thermoreversible
film damaged by heat and pressure applied thereto via the thermal head as a heating
means. Therefore, the user has to determine whether or not the recording medium
in use is still usable, and remove the unusable recording medium. If such a unusable
recording medium is continuously used since the user is not aware of its reduced
performance, either recording or erasing cannot be carried out thereon, which will
be inconvenient to the user.
Such determination on the performance of the recording medium will
be troublesome to the user. Sometimes, the user might throw away a still usable
recording medium, or recording might be performed to no avail on an unusable recording
This invention is intended to overcome the foregoing Problems encountered
with prior art systems. It is an object of the invention to provide a recording
and erasing system which can erase a previous image from a recording medium so
that it is remarkably indistinct, and which can identify a used-up recording medium.
This object is achieved by a system having the features mentioned
in claim 1.
The principles of the present invention are shown Figs. 1 to 8.
- Fig. 1 shows the configuration of a thermoreversible recording medium 1 in
- Fig. 2 shows the structure of an agent for making an image visible/invisible
constituting the thermoreversible recording medium.
- Fig. 3 shows the structure of dye used for the recording medium.
- Fig. 4 is a graph showing the relationship between a recording density and
a voltage-supplying period.
- Fig. 5 is a graph similar to Fig. 4.
- Fig. 6 shows an area to be heated for recording and erasing processes on the
- Fig. 7 is a graph showing recording densities of respective lines after the
- Fig. 8 is a graph showing recording densities of respective erased lines.
- Fig. 9 is a schematic view of a recording and erasing system according to an
embodiment of the present invention.
- Fig. 10 shows the configuration of a recording and erasing system according
to another embodiment.
The invention will be described hereinafter with reference to a preferred
embodiment shown in the drawing figures.
The recording and erasing system of the invention has the structure
as shown in Fig. 9. The recording and erasing system is applicable to devices such
as an information display, an electronic board and a message board used in a railway
station. A thermoreversible recording medium 1 is repeatedly used for the recording
and erasing processes, and is in the shape of a film in this embodiment. The recording
medium 1 extends around supports 2 and 4 in a manner such that one image area
thereof is visible in the direction shown by an arrow C. The supports 2 and 4 are
made of material like rubber, and are rotated either clockwise or counterclockwise
by a drive source such as a motor, not shown. A heating means 3 comes into contact
with the support 2 so as to heat the recording medium 1, thereby perform the recording
or erasing thereon. The heating means 3 comprises a thermal head, and has a size
substantially equal to the width of the recording medium 1. For instance, when
a visible area of the recording medium 1 is approximately of A4 size, the heating
means 3 includes approximately 2,500 heating elements (not shown). A control means
62 controls the recording and erasing operations.
In operation, the recording and erasing system records an image based
on data which are read by a word processor, a scanner or the like, and are transferred
to the control means 62.
The invention relates to a device for obscuring a residual image
which is left on the recording medium when the dye in the recording layer is not
Referring to Fig. 12, an image is input from an external data input
unit 61 such as a keyboard. A recording control unit 62 controls a heating unit
63 for heating the heating elements associated with an image to be recorded. In
this case, the recording medium 64 is heated above the temperature t2
(called "high-temperature heating"), and develops the image at the heated portions
thereof. As the recording medium 64 is fed by the roller 65, the heating unit
63 heats heating elements according to the image to be recorded, under control
of the recording control unit 62, so that the image is recorded on the recording
To erase the recorded image, a background pattern of the image is
recorded first of all. Then, the erasing process will be initiated.
The background pattern comprises characters, symbols and so on, which
preferably makes the main images unidentifiable.
First of all, a switch 66 is operated to connect a background pattern
generating unit 67 to the recording control unit 62, which controls the heating
unit 63 according to the background pattern. The heating unit 63 performs the high-temperature
heating so as to record the background pattern over the entire area of the recording
medium 64 which is fed by a roller 5. Thus, the main image which is already present
on the recording medium is merged into the background pattern and becomes indistinct.
This is because the background patterns has substantially the same color and density
as the main image.
Then, the heating unit 63 heats the whole area of the recording medium
64 to the temperature higher than t1 but below t2 (called
"low temperature heating"). Both the main image and the background pattern undergo
the erasing process. The main image and the background patterns are not always
erased completely, and may be vaguely left on the recording medium as mentioned
above. Thus, the residual background pattern makes the main image indistinct. Therefore,
The recording medium of the present invention is applicable as a
parking card, a prepaid card, a commuter ticket and so forth. Repeated use of such
cards is very effective in the conservation of natural resources. Further, contents
of previous recording will not be revealed when the recording medium is reused.