JPH0624129A - Erasing method of image - Google Patents

Abstract

PURPOSE:To erase an image formed onto a heat-reversible recording medium having a heat-sensitive layer, transparency of which reversibly changes by heat, on a support uniformly in a short heating time at a low temperature. CONSTITUTION:Both sides of a recording medium M are provided with erasing heating means 1, 2, and the recording medium is heated so that different phase or periods are obtained on the support side and heat-sensitive layer side of the recording medium M. A hot plate, a heating roller, a hot air type heater, etc., are used as the erasing heating means 1, 2. Accordingly, the recording medium is heated uniformly, thus allowing equal erasing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for erasing an image formed on a thermoreversible recording medium whose transparency reversibly changes due to heat.

[0002]

2. Description of the Related Art Recently, in recent years,
BACKGROUND OF THE INVENTION Reversible recording materials, which enable temporary image formation and can erase the image when it is no longer needed, are used everywhere. As a typical example thereof, there is known a reversible thermosensitive recording material having a thermosensitive layer in which an organic low molecular weight substance such as a higher fatty acid is dispersed in a resin matrix such as a vinyl chloride resin (Japanese Patent Laid-Open No. Sho 61-206). 54-119
377, JP-A-55-154198 and the like).
However, these have a narrow temperature range of 2 to 4 ° C. for making the opaque portion transparent, so that the recording material which is partially opaque is made entirely transparent, or a transparent image is formed on the recording material which is totally opaque. It was difficult to control the temperature.

On the other hand, the present inventors have previously proposed a reversible thermosensitive recording material which makes it possible to widen the temperature range for making the opaque part transparent by using a specific material (Japanese Patent Laid-Open No. 2004-242242). JP-A-63-39378, JP-A-63-178
No. 079 and Japanese Patent Laid-Open No. 63-14754). According to these proposed reversible thermosensitive recording materials, although the intended purpose can be achieved, uniform transparency is not necessarily obtained when the speed of a heat roller or the like is increased and the heating temperature is shortened to make the material transparent. There was a tendency that it was not always obtained.

Various methods of erasing by heating from only one side of the thermoreversible recording medium have been proposed so far, and are roughly classified into two methods: a method of heating from the heat sensitive layer side and a method of heating from the support side. In the case of heating from the heat sensitive layer side, if the time required for erasing is shortened, there is a drawback that it is not heated uniformly and it becomes difficult to erase, and when heating from the support side, it can be erased uniformly in a short heating time. However, since it is heated through the support, it must be heated at a considerably higher temperature than when it is heated from the heat-sensitive layer side, the temperature of other parts of the device becomes high, and polychlorinated as a medium support. There is a drawback that the material is deformed when a material weak to heat such as vinyl is used.

The present invention solves the above problems and provides an image erasing method capable of obtaining a uniform erasing state even at a low temperature for a short heating time.

[0006]

In order to achieve the above object, the present invention erases an image formed on a thermoreversible recording medium having a thermosensitive layer whose transparency reversibly changes by heat on a support. In the method described above, a means for heating the recording medium from both sides is provided, and the recording medium is heated so that the support side and the heat-sensitive layer side have different phases or cycles.

In the present invention, since the support side and the heat sensitive layer side of the recording medium are heated at different phases or cycles, the temperature of the recording medium becomes uniform and the image can be erased uniformly.

The present invention will be described in detail below. The present invention is
The present invention relates to a method for erasing an image formed on a thermoreversible recording medium having a heat-sensitive layer whose transparency reversibly changes on heat on a support. Basically, a heating device for heating the recording medium from both sides is provided. The recording medium is heated so that the support side and the thermosensitive layer side of the recording medium have different phases or periods. Here, the heating phase will be described with reference to the drawings. FIG. 1 shows the temperature change of the heating device over time. During heating at t _{12, the} temperature rises at this time. At t _13, the heating is stopped, and the time t ₁ from the time when the heating is started to the time when the next heating is started is one cycle. FIG. 1A shows a case where the period t ₁ of the temperature (solid line) of the heating device on the heat sensitive layer side of the recording medium and the period t ₂ of the temperature (broken line) of the heating device on the support side are the same and the phases are different. There is. FIG.1 (b) has shown the case where the period of the temperature of both heating devices differs. As shown in FIG. 1A, when the cycle is the same and the phase is different, the medium temperature is uniform. 1 (b)
When the cycle is different, as in
The temperature change is gentle, and the occurrence of swell does not pose a problem. On the other hand, when the cycle and the phase are the same, the temperature change is large, and the temperature changes in the same screen, making it difficult to erase uniformly.

As the heating device, there are two types of heating devices, that is, a self-controlled heating device and a heating device provided with a means for detecting a heating temperature and a means for controlling the heating temperature.
The self-temperature control type heating device uses a coloring material having a characteristic that the electric resistance of the heating element itself increases as the temperature rises. Examples of this type of material include certain types of conductive ceramics and conductive resin compositions. The heating device using this material has a characteristic that the temperature can be controlled with high accuracy despite the simple structure. However, this type of heating device has a problem when the temperature is arbitrarily changed. On the other hand, the latter type of heating device has an advantage that the temperature can be easily changed.

Specific examples of the heating means include a hot plate, a heat roller, and warm air. FIG. 2 shows an example thereof. Figure (a) is a hot plate, (b) is a heat roller, (c)
Is an example of warm air, M in these figures is a recording medium, P is a hot plate, R is a heat roller, and B is a warm air generator. Although the same heating device is used for the upper and lower parts here, different heating devices may be combined for the upper and lower parts.

FIG. 3 shows the overall construction of an example of an image erasing apparatus to which the method of the present invention is applied. This apparatus is provided with heating devices 1 and 2 composed of heating plates above and below a conveyance path of a recording medium M. The image erasing device further controls the erasing heating device control circuits 3 and 4, the controller 5 and C for controlling the overall operation.
It has a PU 11 and a temperature detecting means 12 for detecting the ambient temperature. The temperature detecting means 12 comprises a thermistor or the like,
The environmental temperature is detected and taken into the CPU 11. At this time, C
In the PU 11, the relationship between the environmental temperature and the heating temperature, the heating time, the medium transport speed, and the like is stored in advance, and an appropriate condition is determined according to the input environmental temperature. Based on the signal determined thereby, the controller 5 determines the erasing conditions such as the heating temperature, the heating time, and the transport speed. Usually, when the environmental temperature is low, the heating temperature is increased in order to keep the temperature of the medium constant, the heating time is long, and the transport speed is slow. As a result, even if the environment temperature becomes low and it becomes difficult to erase under the conditions that have been set so far, the conditions are changed to appropriate conditions and uniform erasing becomes possible.

Among such image erasing devices, an example of a practical device for a card is a heating plate as a heating means. The feature of the hot plate is that compared to a heat roller, it can erase only an arbitrary area in the display medium, and the time required for the entire erasing device is limited to maximize the heating time of the display medium. It is possible to take. Another drawback is that it becomes difficult to keep the temperature uniform in a large area. Due to such characteristics, a hot plate is currently most suitable as a high-speed erasing device for a display medium having a small area and being thin and soft, for example.

Further, in a device such as a heating plate or a heat roller which directly erases a medium by bringing a heating device into contact with the medium, a layer of a cushioning material such as rubber is provided in the heating device to uniformly heat the medium to improve the uniformity of erasing. be able to. As the rubber used for the cushioning material, silicone-based or fluorine-based materials are preferably used.

According to the present invention, the image forming and erasing apparatus can be constructed by combining the image erasing means and the image forming means as described above. In this way, it is possible to rewrite a desired image after the previously formed image is erased. A particularly preferable image forming means is a thermal head, and any type such as a thin film type, a thick film type, an end face type, an edge type, a flat type, and a partial grace type can be used. Of course, other image forming means may be used. As shown in FIG. 4, an image forming unit (thermal head) 8 is arranged immediately downstream of the heating devices (heat rollers) 6 and 7 in the transport direction of the recording medium M, and the medium M is heated during image formation. When the image is formed by the image forming means 8 in the above, it is possible to form an image even with a low printing energy, and there are effects such as reduction of printing scratches and improvement of repeated printing durability of the medium. In the figure, 9 is a platen roller, and 10 is a thermal head control circuit.

As the thermoreversible recording medium used in the present invention,
Any material can be used as long as the transparency reversibly changes by heat. For example, a mixture of two or more polymers, which changes to transparent or cloudy depending on the difference in compatibility state (JP-A-61-161).
No. 258853), which utilizes a phase change of a liquid crystal polymer (Japanese Patent Laid-Open No. 62-66990), a first color state is obtained at a first specific temperature higher than normal temperature, and a first color temperature higher than the first specific temperature. The second color may be obtained by heating after cooling at the second specific temperature and then cooling. In particular, the one whose color state changes between the first specific temperature and the second specific temperature is preferably used. Examples of these are those that become transparent at the first specified temperature and become cloudy at the second specified temperature (Japanese Patent Laid-Open No. 55-154198), color develops at the second specified temperature, and the first specified temperature. Decolored by temperature (Japanese Patent Application No. 2-4
No. 14438), a white turbid state at a first specific temperature, and a transparent state at a second specific temperature (JP-A-3-169).
590), develops black, red, blue, etc. at the first specific temperature,
What is decolored at a second specific temperature (Japanese Patent Laid-Open No. 18829/1990)
No. 3, JP-A-2-188294) and the like.

In particular, a dispersion of an organic low molecular weight substance in a resin, which becomes transparent at the first specific temperature and becomes cloudy at the second specific temperature, is preferably used in terms of sensitivity and durability (special characteristics JP-A-63-39378, JP-A-63-1
30380, JP-A-2-1363, Japanese Patent Application No. 63-1
4754, Japanese Patent Application No. 1-140109, JP-A 64-140
14079, JP-A-3-7377, JP-A-63-2
21087, JP-A-63-317385, JP-A-2
-566, JP-A-4-85077, JP-A-1-13
No. 3781, Japanese Utility Model Laid-Open No. 2-3876, JP-A-3-130
188).

[0017]

EXAMPLES Next, examples of the present invention will be described. All parts in the examples are specified by weight. Apply a liquid consisting of the following composition to a 188 μm thick polyester film.
After drying, a thermosensitive recording layer made of a reversible thermosensitive recording material was provided. Behenic acid (BA2225 manufactured by NOF CORPORATION) 7 parts Eicosane diacid (SL-20 manufactured by Okamura Oil) 3 parts Diisodecyl phthalate 2 parts Vinyl chloride / vinyl acetate copolymer resin (VYHH manufactured by UCC) 40 parts THF 150 parts Toluene 15 Department

Next, a protective layer made of a UV curable resin is provided on the heat-sensitive recording layer, and it becomes cloudy at a second specific temperature of about 100 ° C. or higher, and the first specific temperature region is about 70 ° C.
A thermoreversible recording medium having a characteristic of becoming transparent at temperatures up to 100 ° C. was prepared.

The thermoreversible recording medium prepared above was made cloudy with a thermal head in advance using a heat roller as shown in FIG. 4, and then 120 mm / mm from both sides at the timing shown in FIG. 1 (a). The results when heated at a high speed of s are shown in FIG. In addition, an example of heating from only the heat sensitive layer side and heating from only the support side is shown in FIG.
Shown in. As is clear from this figure, when heated from both sides, the transparent temperature range is wider than when heated from only the heat sensitive layer side, and the temperature is lower than when heated from only the support side. Similar results were obtained by repeating image formation and erasing with a thermal head 100 times. On the other hand, when the support side and the heat sensitive layer side were heated at the same phase and at the same cycle with respect to the above heat-departable recording medium, a part which could not be completely erased occurred.

The thickness of the support of this thermoreversible recording medium is 50
When a new thermoreversible recording medium was made by sticking the one with a thickness of μm and the one with a black print on 1 mm thick polyvinyl chloride and conducting the same test, similar results were obtained for the degree of transparency. However, when heated from the side of the support, the polyvinyl chloride was deformed after the image formation and erasing were repeated 50 times.

When the apparatus of FIG. 4 was used to perform printing at 0.5 mJ / dot by lowering the energy immediately after heat erasing, there was no change in the surface properties even after repeating 100 times. When printing was performed after the medium was cooled, clear printing could not be performed unless the energy was raised to 0.8 mJ / dot, and after repeating 100 times, small irregularities were generated on the surface.

[0022]

As described in detail above, according to the present invention, means for heating both sides of a thermoreversible recording medium having a heat-sensitive layer whose transparency is reversibly changed by heat is provided on a support. Since the image formed on the recording medium is erased by heating so that the support side and the heat-sensitive layer side of the recording medium have different phases or periods, the temperature of the recording medium becomes uniform and a uniform image is obtained. It can be erased. Also,
Deformation does not occur even when an image is erased on a recording medium using a heat-sensitive support such as polyvinyl chloride. Further, by detecting the environmental temperature and controlling the erasing conditions such as the heating time and the heating temperature by the heating means according to the detection result, it becomes possible to perform the erasing uniformly even when the environmental temperature becomes low.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a heating phase and a heating cycle.

FIG. 2 is a diagram showing an example of heating means.

FIG. 3 is a diagram illustrating an overall configuration of an example of an image erasing device.

FIG. 4 is a diagram showing an example of an image forming / erasing apparatus having a combination of image erasing means and image forming means.

FIG. 5 is a diagram showing an erase heating result of an example.

[Explanation of symbols]

1, 2 heating device (hot plate) 3, 4 erasing heating device control circuit 5 controller 6, 7 heating device (heat roller) 8 thermal head 9 platen roller 10 thermal head control circuit 11 CPU 12 temperature detection means M recording medium P heat Plate R Heat roller B Warm air generator

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location B41J 29/36 8804-2C B41M 5/36 C09D 11/02 PSW 7415-4J H04N 1/23 102 Z 9186-5C B41J 3/20 114 Z 8305-2H B41M 5/26 102

Claims (2)

[Claims] 1. A method for erasing an image formed on a thermoreversible recording medium having a thermosensitive layer whose transparency is reversibly changed by heat on a support, wherein a means for heating the recording medium from both sides is provided. An image erasing method, characterized in that heating is performed so that the support side and the heat sensitive layer side of the recording medium have different phases or periods. 2. The method according to claim 1, wherein the environmental temperature is detected, and the erasing conditions such as the heating time and the heating temperature by the heating means are controlled according to the detection result.