JP2002292913A - Image forming method for reversible heat-sensitive recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming method wherein when a reversible heat-sensitive recording medium is irradiated with a laser beam by superposing the irradiation a plurality of times, and a region being adjacent to the heated region is heated right after the heating of the previously heated region to form an image, the image in the section which is heated first does not disappear, and a continuous image can be formed in a plurality of regions, and a bar code including thick lines can be surely printed as well. SOLUTION: A reversible heat-sensitive recording layer is formed of a recording material containing a coloring matter precursor which becomes a coloring matter by discharging electrons, and an electron accepting compound having a long chain alkyl group. After heating a specified region of the reversible heat-sensitive recording layer, the region is cooled at a specified speed to color or decolor the region, and an image is formed by this image forming method for the reversible heat-sensitive recording medium. In such an image forming method, when a linear region 9 being adjacent to the heated linear region 8 is heated right after the heating of the linear region 8, the adjacent linear region 9 is heated while forcibly cooling the previously heated linear region 8 by bringing an air stream at a room temperature or lower into contact with the linear region 8, and thus, the image is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image forming method for a reversible thermosensitive recording medium capable of repeatedly displaying and erasing a visible image.

[0002]

2. Description of the Related Art In general, in the logistics industry for carrying and carrying packages, general-purpose transport containers equipped with labels (tags) displaying information such as destinations and contents of packages are used. When a barcode is printed on the label, the label can be automatically identified by using a barcode reader or a scanner, whereby an efficient distribution line can be formed.

[0003] Labels are attached to these containers in two types: a plug-in type in which a container is provided with a holder, and a seal type in which a label uses an adhesive material. The former comes off during transportation. There is a danger, and the latter takes time to remove the used label.

[0004] Japanese Patent Application Laid-Open No. Hei 9 (1999) discloses a transport container equipped with a rewritable label that does not require peeling of a display label.
Japanese Patent Application Publication No. 188332 discloses that printing can be performed by a laser marker in order to perform non-contact printing on a transport container.

On the other hand, as one of reversible thermosensitive recording media capable of performing printing with a laser marker, a recording material comprising an organic low-molecular compound and a polymer base material and forming an image with a contrast between a transparent area and a cloudy area is used. There is also known a recording medium in which an area is formed or decolored using a leuco dye to form an image.

The latter is a reversible thermosensitive recording material in which a dye precursor which emits electrons to become a dye is combined with an electron-accepting compound, and is described in JP-A-5-124360 and JP-A-6-124360.
JP-A-210954 describes that a compound having a long-chain alkyl group in its molecular structure as an electron-accepting compound has good visibility.

A reversible thermosensitive recording material having a long-chain alkyl group becomes a colored state when rapidly cooled after heating, and becomes a decolored state when gradually cooled after heating, and can form an image at a difference in cooling rate. Incidentally, when the cooling rate is high, the degree of color development is high and the contrast of the image is high, and when the cooling rate is low, the degree of color development is low and the contrast is low.

When non-contact printing is performed on such a reversible thermosensitive recording material by irradiating it with an electron beam using various lasers, the temperature near the center of the laser beam becomes high at the time of irradiation, The temperature gets lower as you go to the section.

That is, as shown in FIG. 3, when a numeral 3 is printed on a reversible thermosensitive recording medium using a laser marker, for example, the central portion of the portion 10 irradiated with the laser beam is heated at a high temperature, The temperature of the peripheral portion 11 becomes lower than that. Due to such a temperature distribution, heat conduction occurs from the portion 10 to which the laser beam is applied to the peripheral portion 11, and the peripheral portion 11 is rapidly cooled to form a color and form an image.

That is, when heating is performed for a very short time using a thermal head, a laser beam, or the like, cooling starts immediately after the heating is completed, so that a colored state can be developed.

On the other hand, when the reversible thermosensitive recording medium is heated for a relatively long period of time, not only the recording layer but also the support and the like are heated, so that the cooling rate is reduced, and the recording medium is erased.

As described above, even if the same heat source is used, a color-developed state or a decolored state can be arbitrarily expressed by controlling the cooling rate according to the heating time or the heating temperature.

In the case of performing heat development by means other than laser light, a thermal head, a heat roll, a heat stamp, high-frequency heating, radiant heat from an electric heater, hot air, or the like can be employed.

[0014]

By the way, a compound having a long-chain alkyl group in its molecular structure as an electron-accepting compound is used as a recording material, and has a thick line and a thin line like a bar code using a laser marker or the like. When forming an image, the thickness of the line that can be formed with a single laser irradiation width is limited, so to form a thick line exceeding the limit, it is necessary to adopt a method of printing two lines next to each other. There is.

However, as shown in the enlarged view of the bar code in FIG. 4, immediately after printing the previously heated linear area 12, the peripheral portion 13 of this line is also warm, so that it is immediately adjacent to the side. When laser light is irradiated to print the linear area 14 to be printed, the cooling rate required for printing cannot be obtained in the previously heated peripheral portion 13 and the peripheral portion 13 is decolored. There is a problem.

For this reason, there has been a problem that a bar code cannot be reliably printed on a reversible thermosensitive recording material using an electron accepting compound having an alkyl group.

Even when an image other than a bar code is formed, for example, when a character or other image formed of a straight line or a curve having a thickness equal to or greater than the thickness of a laser irradiation line is developed, the same problem as described above occurs. Problems arise.

Accordingly, an object of the present invention is to solve the above-mentioned problems and to irradiate a laser beam a plurality of times, for example, when forming a thick line of a bar code, that is, adjacent to a heated area. In a case where an image is formed by heating an area immediately after the heating, a method of forming an almost continuous image in a plurality of areas without erasing an image of a previously heated portion is provided.

[0019]

In order to solve the above-mentioned problems, the present invention relates to a recording material containing a dye precursor which becomes a dye by emitting electrons and an electron-accepting compound having a long-chain alkyl group. An image forming method for a reversible thermosensitive recording medium in which a reversible thermosensitive recording layer is formed, and a predetermined area of the reversible thermosensitive recording layer is heated and then cooled at a predetermined speed to color or decolor the area to form an image. In, heating the area adjacent to the heated area immediately after the heating,
An image forming method for a reversible thermosensitive recording medium is characterized in that an area adjacent to a previously heated area is forcibly cooled while an image is formed by heating the area.

In the image forming method of the present invention configured as described above, when the area adjacent to the heated area is heated immediately after the heating, the previously heated area is forcibly cooled, thereby forcibly cooling the area. Forcibly removes heat from the area, whereby the area heated earlier by the amount of heat applied to the adjacent area does not increase in temperature, that is, does not slow down the cooling rate of the area, and develops color.

As described above, in the image forming method of the present invention, a required cooling rate is obtained for coloring in a previously heated area, and an adjacent (including partially overlapping) heated portion is also provided. By coloring, a continuous image can be formed in a plurality of heated areas.

In order to further ensure the above-mentioned effects, the means for forcibly cooling the previously heated area is provided by contacting the area with an airflow at room temperature or lower. An image forming method is used. More preferably, the heating means is heating by laser beam irradiation.

In this way, when the reversible thermosensitive recording medium is irradiated with the laser light repeatedly in a non-contact state a plurality of times,
The image of the previously heated portion does not disappear, and a continuous image can be formed across a plurality of areas.

In the case of an image forming method for a reversible thermosensitive recording medium in which the image is a barcode image, when forming a thick line larger than a line that can be formed by one movement of the laser, 1
Immediately after printing the first line, the line is forcibly cooled by a stream of air below room temperature. Therefore, two adjacent to the line
When laser light is applied to that part to print the subsequent lines, since the amount of heat has been taken from the periphery of the previously heated line, the cooling rate required for printing can be obtained reliably, Color can also be developed at the boundary between lines or at a portion where lines overlap.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION The basic structure of a reversible thermosensitive recording medium of the present invention is that a recording layer in which various compounds are dispersed in a polymer binder is laminated on a synthetic resin base sheet such as polyethylene terephthalate. Further, it has a laminated structure in which a protective layer is further laminated and integrated.

The reversible thermosensitive recording medium used in the present invention comprises:
Any recording medium having a predetermined heat-sensitive recording layer may be used. Usually, a reversible heat-sensitive recording layer composed of a required support, a binder provided thereon and a composition of a recording material is employed.

The reversible thermosensitive recording layer is formed of a recording material containing a dye precursor which becomes a dye by emitting electrons and an electron-accepting compound having a long-chain alkyl group.

As the electron donating compound (dye precursor), a leuco dye having a lactone ring portion in the molecular structure is used. Specific examples of the electron donating compound (dye precursor) include crystal violet lactone, 3- (4-diethylamino-2-ethoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) -4. Phthalide compounds such as azaphthalide, 3,3-bis (1-ethyl-2-methylindol-3-yl) phthalide, 3-diethylamino-6-methyl-7-anilinofluoran,
-Dibutylamino-6-methyl-7-anilinofluoran, 2- (2-chloroanilino) -6-diethylaminofluoran, 2- (2-chloroanilino) -6-dibutylaminofluoran, 2-anilino-3- Methyl-6-
(N-ethyl isopentylamino) fluoran, 3-cyclohexylmethylamino-6-methyl-7-anilinofluoran, 3-benzylethylamino-6-methyl-
7-anilinofluoran, 3-diethylamino-6-chloro-7-anilinoflurane, 3-methylpropylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-xylidinofluoran And the like.

The electron-accepting compound having a long-chain alkyl group used in the present invention is an organic phosphoric acid compound, an aliphatic carboxylic acid compound or a phenol compound having an aliphatic group having 6 or more carbon atoms. It is a phenolic compound having one or more aliphatic groups.

Specific examples of the electron-accepting compound include dodecylphosphonic acid, tetradecylphosphonic acid, hexadecylphosphonic acid, octadecylphosphonic acid, eicosylphosphonic acid, α-hydroxydecanoic acid, α-hydroxytetradecanoic acid, and α-hydroxytetradecanoic acid. Hydroxyhexadecanoic acid, α-hydroxyoctadecanoic acid, α-hydroxypentadecanoic acid, α-hydroxyeicosanoic acid, α-hydroxydocosanoic acid, α-hydroxytetracosanoic acid, α-hydroxyhexacosanoic acid, α-hydroxyoctacosanoic acid And the like. Examples of the phenolic compound include 4'-hydroxy-4-octadecylbenzanilide, N-octadecyl-4-hydroxybenzamide, N- (4-hydroxyphenyl) -N'-octadecylurea, and 4-hydroxyphenylpropiono-behenylhydrazide. No.

The recording layer made of the recording material as described above
It can be provided by dispersing a dye precursor and an electron-accepting compound in a polymer binder and applying the dispersion to a support such as paper, synthetic paper, or plastic film.

As the polymer binder, a resin having high transparency and film forming properties and high heat resistance is used. For example, polymethacrylic acid ester, polyacrylic acid ester or a copolymer thereof, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinyl acetate-alcohol copolymer Polymer,
Other vinyl acetate compounds, vinyl chloride-based copolymers, polyvinylidene chloride, polyvinylidene chloride-based copolymers, polyvinyl alcohol, polyester, polyamide, polyurethane, polystyrene, acrylonitrile-styrene copolymer, acrylonitrile-butadiene-styrene copolymer Are preferred.

Further, a thermo-crosslinkable resin can be used as the binder. As the thermally crosslinkable resin, any resin having a hydroxyl group, an amino group, a carboxyl group, or the like which is thermally crosslinked with an isocyanate crosslinking agent may be used, but an acrylic polyol, a polyester polyol, and a polyurethane polyol resin are particularly preferable.

As the isocyanate crosslinking agent, hexamethylene diisocyanate and toluene diisocyanate are particularly preferred.

The compounding ratio of the recording material is such that 10 to 100 parts by weight of the electron accepting compound is added to 10 parts by weight of the leuco dye,
Preferably 20 to 50 parts by weight, binder is 10 to 20
0 parts by weight, preferably 20 to 100 parts by weight.

It is preferable to provide a protective layer on the recording layer of the reversible thermosensitive recording medium in order to improve the repetitive durability and the matching property with the thermal head. High heat resistant resins such as terephthalate, polyetherimide, polyetheretherketone, polysulfone, polyphenylenesulfide, polyacrylate, polyethersulfone, polycarbonate, polyethylenenaphthalate, polyimide, acrylic resin, ultraviolet curable resin, and electron beam curable resin Is preferred.

In addition, the recording layer contains a stabilizer, a sensitizer, an ultraviolet absorber, a dispersant, etc. for improving the heat-resistant storage stability and thermal stability of the colored state, preventing discoloration and fading due to light, and improving sensitivity. Can be done.

The reversible thermosensitive recording medium of the present invention is usually a laminate such as a card or label provided with a reversible thermosensitive recording layer on a film or sheet-like support, and an adhesive layer on the back surface. And a card or a label which can be easily attached by means of a holder or the like.

As the heating means in the present invention, any known method can be used as long as it is a non-contact heating (printing) means capable of heating the medium by irradiating an electron beam or the like. Is a carbon dioxide laser,
Examples include a YAG laser, a semiconductor laser, and an infrared laser.

The means for forced cooling of the previously heated area employed in the present invention is a means capable of cooling a reversible thermosensitive recording medium such as a reversible thermosensitive label to a temperature required for color development such as printing. For example, contacting the area with a stream of air below room temperature.

As shown in FIG. 1, in order to forcibly cool the label-like reversible thermosensitive recording medium 3 attached to the side surface of the returnable box 2 transported by the conveyor line 1, the laser marker 4 is used for the reversible thermosensitive recording medium. At the same time as printing the barcode 5 on the thermal recording medium 3 by heating, a cold air generator (a so-called spot cooler can be used) 6 to room temperature (1 to 35 ° C).
The following airflow is blown over the entire label-like reversible thermosensitive recording medium 3 or the portion heated by the laser beam.

The air flow may be air or nitrogen gas such as an air flow at room temperature by a fan, a cool air whose temperature is adjusted to a lower temperature, or an air flow blown out from a gas cylinder containing compressed air. For example, a stream of various gases is blown, the back surface or the periphery of the reversible thermosensitive recording medium 3 is forcibly cooled directly or indirectly with cooling water or other refrigerants, or a cooling means such as a Peltier element-mediated cooling is employed. You can also.

In order to contact a predetermined area of the reversible thermosensitive recording medium 3 with an air stream at room temperature or lower to cool the air stream, the air stream may be constantly blown and contacted, or the air stream may be contacted only during printing. . The contact of the air stream as referred to in the present invention means not only a state in which a cooling air stream is blown against the reversible thermosensitive recording medium 3 from the front of a predetermined area, but also an oblique blow or an air stream substantially parallel to the surface of the predetermined area. And cooling.

Further, it is also possible to provide a nozzle having a narrow air flow outlet and cool only a predetermined portion in accordance with the movement of the laser beam. In that case, as shown in FIG. 1, the returnable box 2 is accurately positioned on the conveyor line 1,
In addition, a computer 7 for line control is provided to adjust the timing of laser light by the laser marker 4 and cooling by the cold air generator 6.

As shown in FIGS. 2 (a) and 2 (b), when forming a bar code on the reversible thermosensitive recording layer, the previously heated linear sections 8 corresponding to the order of printing are kept below room temperature. The linear area 9 adjacent to the linear area 9 is heated by laser light while being forcibly cooled by an air flow, and is bolded (in the enlarged view of FIG. 2b, the parallel linear areas appear to be slightly separated from each other, but to the naked eye, (It is in a state of being substantially adjacent.) In this way, since the heat quantity is quickly conducted and diffused from the previously heated linear section 8 and the surrounding area, the cooling rate required for printing can be reliably obtained, and the adjacent linear section 8 and the adjacent linear section 8 can be cooled. It is also possible to develop a color at a boundary with the linear area 9 and at a portion where these linear sections overlap each other, and a thick line required for a bar code can be printed.

[0046]

Examples and Comparative Examples <Preparation of Reversible Thermosensitive Label> (a) Dye precursor: crystal violet lactone 10 parts by weight (b) Electron accepting compound: hydroxyphenylpropiono-behenyl hydrazide 20 parts by weight (c) Binder: Acrylic polyol (LR-1503: manufactured by Mitsubishi Rayon) 50 parts by weight (d) Solvent: toluene 150 parts by weight After dispersing each material in a solvent for about 2 hours using a paint shaker, add the following isocyanate compound, The mixture was stirred to prepare a coating solution. (E) Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) 5 parts by weight

A 188 μm white polyester film (W400: manufactured by Mitsubishi Chemical Polyester Film Co., Ltd.)
Was coated with a bar coater, dried at 130 ° C., and then aged at 60 ° C. for 48 hours to a thickness of 10 μm.
m recording layers were provided. On top of this, a UV curable resin is applied
μm and cured with ultraviolet light to form a protective layer, thereby producing a reversible thermosensitive recording medium.

A heat-resistant adhesive (double-sided tape 5000N: manufactured by Nitto Denko) was attached to the back of the obtained reversible thermosensitive recording medium to produce a reversible thermosensitive label. The obtained reversible heat-sensitive label attached to a polypropylene container was used in the image forming methods of the following Examples and Comparative Examples.

Example 1 A container to which a reversible thermosensitive label was stuck was supplied from an air compressor to an ambient temperature of 3.
Laser marker (Keyence's CO2 laser: 12W) while blowing in air at 0 ° C at the same temperature
Using alphanumeric characters and barcodes.

The formed prints were visually inspected for print quality and read by a simple bar code reader, and the results were evaluated.

In the evaluation, the print quality was evaluated as good (marked with a circle) and defective (×).
In addition to the two-stage evaluation of (marked), the reading evaluation by the reader was evaluated as two-stage evaluation of good (○) and poor (x), and the results are shown in Table 1 by symbols.

[0052]

[Table 1]

Example 2 An image was formed in exactly the same manner as in Example 1 except that printing was performed while blowing cold air (23 ° C.) using a cooler instead of air, and the formed print was visually observed. The quality of the printing and the reading with a simple barcode reader are performed, and the results are shown in Table 1.
Shown inside.

Comparative Example 1 An image was formed in exactly the same manner as in Example 1 except that printing was performed at an ambient temperature of 30 ° C. without cooling, and the formed print was visually checked for print quality and quality. Reading was performed using a simple barcode reader, and the results are shown in Table 1.

As is clear from the results in Table 1, alphanumeric characters could be printed in both the example and the comparative example. However, the barcode was printed while cooling, although there was no problem. In Comparative Example 1 where there was no bar code, a thick bar could not be printed with a thick line, and was unsuitable for use as a barcode.

Incidentally, as a result of examining the color density while changing the cooling rate variously, the cooling rate required for printing on the reversible thermosensitive recording medium used in Example 1 was 300 ° C./sec or more, The required cooling rate is 50-100 ° C / s
ec. In addition, it was confirmed that printing by the laser instantaneously raised the central portion to several hundred degrees, but also heated the peripheral portion to several tens to 100 ° C. In order to surely print the bar code or the thick line clearly, the cooling temperature of the recording medium is generally 0 to 30.
C., and preferably cooled to room temperature or lower.

[0057]

As described above, according to the present invention, in the method for forming an image on a reversible thermosensitive recording medium, when the area adjacent to the heated area is heated immediately after the heating, the previously heated area is removed. Since an image is formed by heating an area adjacent to the area while forcibly cooling, by forcibly cooling the previously heated area, a required cooling rate for color development can be obtained in this area as well. There is an advantage that a continuous image can be formed over an area.

In the method of forming an image on a reversible thermosensitive recording medium, the heating means is heating by irradiation with a laser beam, and the means for forcibly cooling the previously formed image is blowing cool air onto the image. When the laser beam is irradiated a plurality of times, the image of the previously heated portion does not disappear and a continuous image can be formed over a plurality of areas.

Further, in the case of an image forming method for a reversible thermosensitive recording medium in which the image is a barcode image, a second line can be printed adjacent to the first line immediately after the first line is printed. There is an advantage that a barcode having a line of an arbitrary thickness can be printed.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing an image forming method according to an embodiment.

2A is a plan view showing a barcode printed by the image forming method according to the embodiment; FIG. 2B is an enlarged plan view showing a main part of the barcode shown in FIG. 2A;

3A is a plan view of a character printed using a laser marker. FIG. 3B is an enlarged plan view showing a main part of FIG. 2A.

FIG. 4 is an enlarged plan view of a main part explaining a printing state of a conventional barcode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Conveyor line 2 Returnable box 3 Reversible thermosensitive recording medium 4 Laser marker 5 Bar code 6 Cold air generator 7 Computer 8,12 Linear area heated previously 9,14 Adjacent linear area 10 Part irradiated with laser beam 11 , 13 Peripheral part

Claims (3)

[Claims] 1. A reversible thermosensitive recording layer is formed from a recording material containing a dye precursor which becomes a dye by emitting electrons and an electron-accepting compound having a long-chain alkyl group. In an image forming method for a reversible thermosensitive recording medium, in which an area is heated or cooled at a predetermined speed to form an image by coloring or decoloring the area, an area adjacent to the heated area is heated immediately after the heating. In this case, a method for forming an image on a reversible thermosensitive recording medium is characterized in that an image is formed by heating an area adjacent thereto while forcibly cooling the previously heated area. 2. The method for forming an image on a reversible thermosensitive recording medium according to claim 1, wherein the means for forcibly cooling the previously heated area includes bringing an air flow at room temperature or lower into contact with the area. 3. The method for forming an image on a reversible thermosensitive recording medium according to claim 1, wherein the image is a barcode.