JP2003231355A - Reversible thermal recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reversible thermal recording medium which uses paper as a support, has at least a recording layer using the coloring reaction between an electron donating coloring compound and an electron accepting compound and a substrate, and is free from color nonuniformity on the back and residual elimination during printing/elimination. <P>SOLUTION: The reversible thermal recording medium comprises at least the recording layer using the coloring reaction between the electron donating coloring compound and the electron accepting compound and the support. The paper support provided with coated paper 45 g/m<SP>2</SP>or below in water absorbency by a water absorbency testing method (cup method) for paper of JIS P 8140 and cardboard or an under layer is used as the support. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible thermosensitive recording medium and an erasing method utilizing a color forming reaction between an electron-donating color-forming compound and an electron-accepting compound.

[0002]

2. Description of the Related Art Heretofore, a heat-sensitive recording medium utilizing a color-forming reaction between an electron-donating color-forming compound (hereinafter also referred to as a color-developing agent) and an electron-accepting compound (hereinafter also referred to as a color-developing agent) has been widely known. It has been widely applied to the output of electronic computers, facsimiles, automatic ticket vending machines, printers of scientific measuring machines, printers for CRT medical measurement, and the like. However, all the conventional products have irreversible color development, and it is not possible to repeat the color development and the color erasing alternately. On the other hand, according to the patent publication, some thermosensitive recording media that utilize the color-forming reaction between a color-forming agent and a color-developing agent to reversibly perform color-development and decolorization are proposed. For example, JP-A-60
According to Japanese Patent Laid-Open No. 193691, a developer using a combination of gallic acid and phloroglucinol is shown. The color-developing material obtained by thermally coloring this material is decolorized with water or steam. However, in the case of this heat-sensitive recording medium, there is a problem in that it is difficult to make it water resistant, and there is a problem in recording storability, and there is a problem that the erasing device for erasing the color developing body becomes large.

Japanese Patent Laid-Open No. 61-237684 discloses a rewritable optical recording medium using a compound such as phenolphthalene, thymolphthalene or bisphenol as a developer. This product forms a color-developing substance by heating and gradually cooling it, while it can be decolored by heating the color-developing substance to a temperature just higher than the coloring temperature and then rapidly cooling it. However, in the case of this recording medium, the process of coloring and erasing is complicated, and some color is still seen in the erasable body obtained by erasing the chromophore, so that a colored image with good contrast can be obtained. I can't.

JP-A-62-140881, JP-A-62-138568 and JP-A-62-13855.
Japanese Patent No. 6 discloses a homogeneous compatible solution of a color former, a color developer and a carboxylic acid ester. This product shows a completely colored state at a low temperature and a completely decolored state at a high temperature, and can keep the colored or decolored state at an intermediate temperature between them, and by printing with a thermal head on this medium, the colored background White characters (decolored body) can be recorded on (colored body). Therefore, in the case of this recording medium, the image to be recorded is a negative image, so that its use is limited, and it is necessary to keep the image within a specific temperature range for storing the recorded image.

JP-A-2-188294 and JP-A-2-188293 disclose a salt of gallic acid and a higher aliphatic amine that reversibly perform a color developing action and a color reducing action, respectively, and The use of a salt of bis (hydroxyphenyl) acetic acid or butyric acid and a higher aliphatic amine is shown. This product can be thermally colored in a specific temperature range and decolorized by heating at a higher temperature than that, but since its color developing action and color reducing action occur competitively, these actions are thermally suppressed. It is difficult to control and it is difficult to obtain good image contrast. As described above, the conventional reversible thermosensitive recording medium utilizing the reaction between the color former and the color developer has various problems and is still unsatisfactory. Therefore, the present inventors proposed a reversible thermosensitive recording medium using a long-chain alkyl type color developer in JP-A-5-124360, JP-A-10-95175, etc., and relatively simple heat control. We have proposed a recording medium that can develop and erase colors. These reversible heat-sensitive recording media are used as point cards for displaying digital information recorded on a magnetic layer or the like so that a person can see the contents.
It is commercialized with ET film and vinyl chloride resin as a support.

On the other hand, in the office, the amount of paper used in the office continues to increase as a large amount of information and high speed processing become possible due to the development and popularization of computer and network technology. Although most information is now digitized and processed electronically, it is often the case that viewing it on a display is not enough for people to think about it. It is printed on paper using a printer. Paper is indispensable as a thinking environment because it is easy to read without eye strain, easy to handle anywhere without a power supply, and lightweight, and has a list that allows you to see as much information as you want. It has become a thing. However, on the other hand, the large consumption of paper causes environmental problems such as depletion of forest resources and social problems such as the large amount of paper waste. Recycling to collect and recycle used paper is in progress, but even recycled paper requires the same amount of electricity and water as the paper made from new pulp.
This alone cannot solve the problem. As a method for solving these problems, it is possible to use a reversible thermosensitive recording medium of this kind for general documents for office and repeatedly use it. However, general documents have various requirements different from card applications. For example, since it has a large area such as A4 size, the recording medium itself needs to be elastic even if it is thin, and it is relatively light when multiple sheets are stacked. A recording medium is required.

On the other hand, this type of reversible thermosensitive recording medium is
From the viewpoint of repeated durability, it is preferable to use a solvent-based resin and a crosslinking agent thereof in the recording layer, the protective layer, and the like. For example, as described in JP-A-10-230680, a solvent-based resin having a hydroxyl group is used. Isocyanate crosslinking agents and the like are preferably used. However, when a solvent-based coating liquid is applied onto a normal paper support, there are problems that color unevenness occurs on the back surface or unerased residue occurs during erasing.

[0008]

SUMMARY OF THE INVENTION The present invention uses paper as a support and has at least a recording layer and a substrate utilizing a color-forming reaction between an electron-donating color-forming compound and an electron-accepting compound. It is an object of the present invention to provide a reversible thermosensitive recording medium having no color unevenness on the back surface and an unerased residue during printing / erasing.

[0009]

[Means for Solving the Problems] As a result of various studies on the above-mentioned problems, as a result, color unevenness and erasing defects on the back surface of a reversible thermosensitive recording medium utilizing a color-forming reaction between a color-developing agent and a color-developing agent. It was found that the problem of (1) was largely due to the penetration of the recording layer into the support. In particular, when the recording layer was applied directly to the paper support, it was found that the leuco dye dissolved in the solvent would stain the support, causing color unevenness on the back side and unerased residue during erasing. It became clear that these problems can be solved by preventing the.

Based on the above findings, according to the present invention, in a reversible thermosensitive recording medium utilizing a color-forming reaction between a color-developing agent and a color-developing agent, JIS P 81 is used as a support.
40 By using coated paper having a water absorption of 45 g / m ² or less according to the water absorption test method (cup method) of paper and board,
Color unevenness on the back side and erasing defects can be improved. Also, by providing an under layer on the paper support, the water absorption of which is 45 g / m ² or less according to the water absorption test method (cup method) of JIS P 8140 paper and paperboard, penetration into the inside of the support is eliminated, There will be no color unevenness on the back side and no erasure residue when printing / erasing. Furthermore, since the resin of the under layer is in a crosslinked state, the repeated durability is further improved. The water absorption can be adjusted, for example, by changing the configuration of the undercoat layer made of a pigment and a resin.

The coated paper used in the present invention is a paper having a base paper coated with a coating material of about 10 g / m ² or more per side. The paint contains a pigment and a binder as main components. As the pigment, kaolin, aluminum hydroxide, calcium carbonate, titanium dioxide, silica, zinc oxide, barium sulfate, plastic pigment, etc. are used, and as the binder, water-soluble resin such as polyvinyl alcohol, starch, casein and latex resin, etc. An aqueous emulsion resin or the like is preferably used. Further, in the present invention, the under layer coated on the base paper may be the same pigment or binder resin as that used for the coating layer of the coated paper, and may also be a solvent-based resin. As the solvent-based resin, a crosslinkable resin is preferably used from the viewpoint of repeated durability, and examples thereof include an ultraviolet curable resin, an electron beam curable resin, and a thermosetting resin. Among them, a thermosetting resin is preferable. preferable. As the thermosetting resin, for example, a resin obtained by curing a resin having a hydroxyl group with an isocyanate crosslinking agent is particularly preferable.

Examples of the resin used in the present invention include olefin polymers such as polyethylene, polybutadiene, polypropylene, polyisoprene and hydrogenated polybutadiene; polymethyl acrylate, polyethyl acrylate, poly (n-butyl acrylate), poly ( Isobornyl acrylate), poly (2-hydroxyethyl acrylate), poly (2-hydroxypropyl acrylate), poly (2-hydroxybutyl acrylate),
Polymethylmethacrylate, polyethylmethacrylate, poly (n-butylmethacrylate), poly (isobutylmethacrylate), poly (sec-butylmethacrylate), poly (tert-butylmethacrylate),
Poly (isobornyl methacrylate), poly (benzyl methacrylate), poly (2-ethylhexyl methacrylate), polycyclohexyl methacrylate, poly (2-hydroxyethyl methacrylate, poly (2-hydroxypropyl methacrylate), poly (2-hydroxybutyl methacrylate) ), Acrylic polymers such as polyacrylic acid, polymethacrylic acid and copolymers thereof; polystyrene, poly (α-methylstyrene),
Styrenic polymers such as poly (4-methylstyrene), poly (4-methoxystyrene), styrene-acrylonitrile copolymers, styrene-butadiene copolymers;
Polyvinyl chloride, polyvinyl acetate, polyvinyl butyral, polyvinyl acetal, polyvinyl formal, vinyl alcohol-vinyl butyral copolymer, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride- Vinyl-based polymers such as vinyl acetate-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer, poly (2-vinylpyridine), poly (4-vinylpyridine), poly (N-vinylcarbazole); polytetra Fluoro-based polymers such as fluoroethylene, polytrifluoroethylene, polyvinylidene fluoride; nitrocellulose, cellulose acetate, cellulose triacetate, cellulose acetate butyrate, cellulose acetate propionate,
Cellulosic polymers such as ethyl cellulose and methyl cellulose; polytetrahydrofuran; isobutylene-maleic anhydride copolymers; polyisobutyl ether;
Polycarbonate, polyarylate, polysulfone, poly (2,6-dimethyl-p-phenylene oxide),
Engineering plastics such as polyimide polyamide imide and polyether imide; polyurethane;
Polyamide resins such as nylon 6 and nylon 66;
Examples thereof include rubber-based polymers such as natural rubber, styrene-butadiene rubber, and acrylonitrile-butadiene rubber, and if necessary, two or more kinds may be used in combination.
In addition, a resin having a group reactive with a cross-linking agent such as an acrylic polyol resin, a polyester polyol resin, a polyurethane polyol resin, a polyvinyl butyral resin, a cellulose acetate propionate, or a cellulose acetate butyrate, or a monomer having a group reactive with a cross-linking agent. Resins obtained by copolymerizing other monomers may also be used.

The coated paper and the base paper having the under layer used in the present invention have a thickness of 70 μm to 150 μm.
It is preferably about 90 m from the viewpoint of repeated durability and easy handling as a document.
Those having a thickness of about 0 μm are particularly preferably used.

A typical example of the developer for the recording layer is as follows.
For example, JP-A-5-124360 and JP-A-6-2
It is a developer used in the recording layer described in JP-A-10954 and JP-A-10-95175. The developer used here has a structure capable of developing a leuco dye in the molecule, such as a phenolic hydroxyl group, a carboxylic acid group, a phosphoric acid group, and a structure for controlling the cohesive force between molecules,
For example, it is a compound having one or more structures in which long-chain hydrocarbon groups are linked. A divalent or higher valent linking group containing a hetero atom may be interposed in the connecting portion of the structure having the color-developing ability and the structure controlling the cohesive force between molecules, and the structure controlling the cohesive force between molecules. The long-chain hydrocarbon group may also contain a divalent or higher valent linking group containing a hetero atom and / or an aromatic group. Specific examples of such a reversible color developer are, in addition to the above-mentioned publication, for example, JP-A-9-290563, JP-A-11-188969, and JP-A-11-9.
No. 9749, etc. As the developer, it is particularly preferable to use a phenolic compound having an alkyl chain having 8 or more carbon atoms. By using such a compound, a recording medium having a high color density and excellent high-speed erasability can be obtained. In addition to these color developers, for example, JP-A-4
It is also possible to use a salt compound of an acidic substance and a basic substance as described in JP-A-50289.

The leuco dye used in the present invention includes:
Examples thereof include phthalide compounds, azaphthalide compounds, fluorane compounds, and the like. Examples of these compounds include:
JP-A-5-124360 and JP-A-6-21095
No. 4, JP-A-10-230680, and other leuco dyes. Among them, particularly preferable examples of the black dye include 2-anilino-3-methyl-6-diethylaminofluorane and 2-anilino-3-methyl-
6-di (n-butylamino) fluorane, 2-anilino-3-methyl-6- (Nn-propyl-N-methylamino) fluorane, 2-anilino-3-methyl-6-
(N-isopropyl-N-methylamino) fluorane,
2-anilino-3-methyl-6- (N-isobutyl-N
-Methylamino) fluorane, 2-anilino-3-methyl-6- (Nn-amyl-N-methylamino) fluorane, 2-anilino-3-methyl-6- (N-ethyl-
p-toluidino) fluorane, 3- (1-ethyl-2-)
Methylindol-3-yl) -3- (2-ethoxy-
4-diethylaminophenyl) -4-azaphthalide, 3
-(1-Ethyl-2-methylindol-3-yl)-
3- (2-ethoxy-4-diethylaminophenyl)-
7-azaphthalide and the like can be mentioned.

The recording layer is coated with a binder resin together with these color developer and leuco dye. As the binder resin, the above-mentioned resins are used alone or as a mixture. The resin used for the recording layer is preferably a crosslinkable resin from the viewpoint of durability, and among them, a thermally crosslinkable resin is particularly preferably used. Further, the recording layer may contain various additives used in this type of recording medium.

The reversible recording layer using these leuco dye and long-chain alkyl developer develops and decolors by the process shown in FIG. When the initial decolored state (A) is heated, the leuco dye and the color developer are melt-mixed at the temperature T1 or higher to develop a color (B), and when this state is rapidly cooled, the colored state is fixed.
When this color-developed state (C) is heated, the color is erased at a temperature T2 lower than the color-developing temperature, and when cooled, the color-erased state is the same as the initial state. In this way, the recording layer can be erased by controlling the heating temperature and the cooling rate after heating. Printing with this recording layer provides high contrast and excellent image quality. Further, it is excellent in storage stability and durability against repeated printing and erasing, and is particularly suitable as the rewritable recording medium for documents of the present invention. Printing on a reversible recording medium using this recording layer can be performed by a thermal head as in the case of normal thermal recording, and erasing can be performed by a temperature-controlled heat roller, a heating element such as a ceramic heater, or a thermal head. Can be used with a small and simple rewrite device.

Further, in the present invention, one or more protective layers may be provided on the recording layer, if desired.
For example, the ultraviolet absorbing layer, the head matching layer, the barrier layer and the like may be provided individually or in combination. In addition, a back layer may be provided to prevent curling and improve transportability. Any conventionally known material can be used for these protective layer and back layer.

The recording medium of the present invention can be combined with the recording layer and an IC chip or a magnetic recording layer according to the application, and can be printed on the entire surface or a part thereof. Further, it is used after being processed into a card shape, a sheet shape, or a roll shape as required.

[0020]

The present invention will be described in more detail with reference to the following examples. In the examples, "parts" and "%" are based on weight.

[0021] Example 1 [Creation of recording layer]   1) 2-anilino-3-methyl-6 dibutylaminofluorane 2 parts   2) 8 parts of developer having the structure of the following formula (1)

[Chemical 1] 3) 2 parts of coloring / decoloring control agent having the structure of the following formula (2)

[Chemical 2] 4) Acrylic polyol resin (LR503 manufactured by Mitsubishi Rayon Co., Ltd.) 15 parts 5) MEK 130 parts

The above composition was pulverized and dispersed using a ball mill to an average particle size of about 1 μm. 20 parts of Coronate HL (75% ethyl acetate solution of adduct-type hexamethylene diisocyanate) manufactured by Nippon Polyurethane Industry Co., Ltd. was added to the obtained dispersion liquid and well stirred to prepare a recording layer coating liquid. The recording layer coating liquid having the above composition is coated on a coated paper (thickness 90 μm) having a water absorption of 27.5 g / m ² (contact time 60 seconds) by the water absorption test method described in JIS P8140 using a wire bar, After drying at 100 ° C. for 2 minutes, it was heated at 60 ° C. for 24 hours to form a recording layer having a film thickness of about 8.0 μm. [Creation of protective layer] 1) Acrylic polyol resin (LR503 manufactured by Mitsubishi Rayon Co., Ltd.) 10 parts 2) Silica (P-832 manufactured by Mizusawa Chemical Co., Ltd.) 4 parts 3) MEK 50 parts

The above composition was pulverized and dispersed by a ball mill to an average particle size of about 0.5 μm. To the obtained dispersion liquid, 4 parts of Coronate HX manufactured by Nippon Polyurethane Co., Ltd. was added and well stirred to prepare a protective layer coating liquid. The protective layer coating solution,
Coating on the recording layer with a wire bar at 100 ° C 2
After drying for 5 minutes, it is heated at 60 ° C. for 24 hours to obtain a film thickness of about 3.
A reversible recording medium of the present invention was prepared by providing a 0 μm recording layer.

Example 2 Instead of the coated paper used in Example 1, the water absorption was 30.0.
g / m ² (contact time 60 seconds) coated paper (thickness 90μ
A recording medium was produced in the same manner as in Example 1 except that m) was used.

Example 3 Instead of the coated paper used in Example 1, a water absorption of 42.5
g / m ² (contact time 60 seconds) coated paper (thickness 110μ
A recording medium was produced in the same manner as in Example 1 except that m) was used.

Example 4 A recording medium was prepared in the same manner as in Example 1 except that the following underlayer coated paper was used in place of the coated paper used in Example 1. [Preparation of Under Layer] 1) Acrylic polyol resin (LR503 manufactured by Mitsubishi Rayon Co., Ltd.) 10 parts 2) Silica (P-526 manufactured by Mizusawa Chemical Co., Ltd.) 3 parts 3) MEK 20 parts

The above composition was pulverized and dispersed using a ball mill to an average particle size of about 0.5 μm. 4 parts of Coronate HL manufactured by Nippon Polyurethane Industry Co., Ltd. was added to the obtained dispersion and well stirred to prepare an underlayer coating solution. The underlayer coating solution is applied to a quality paper having a thickness of 110 μm using a wire bar, dried at 100 ° C. for 2 minutes, and then heated at 60 ° C. for 24 hours to provide an underlayer having a thickness of about 3.0 μm. , The under layer coated paper. The water absorption of the underlayer-coated paper was 0.5 g / m ² (contact time 60 seconds).

Comparative Example 1 Instead of the coated paper used in Example 1, the water absorption rate was 46.5.
g / m ² (contact time 60 seconds) coated paper (thickness 110μ
A recording medium was produced in the same manner as in Example 1 except that m) was used. The recording medium produced as described above was subjected to a thermal printing device manufactured by Okura Electric Co., Ltd., voltage 13.3V, pulse width 1.2 ms.
When printed with ec, all developed high density. Using the heat roller erasing device,
The erasability was evaluated by erasing under the condition of 50 ° C. and 30 mm / s. Also, the color unevenness on the back surface was visually evaluated. The above results are shown in Table 1.

[0029]

[Table 1] * 1) ○: It has been completely erased. X: Partially erased residue is seen. * 2) O: No color unevenness is observed. X: Color unevenness is seen. As is clear from the above results, the reversible thermosensitive recording medium of the present invention is excellent without erasing failure due to penetration and color unevenness on the back surface.

[0030]

According to the present invention, at least a recording layer and a substrate utilizing a color-forming reaction between an electron-donating color-forming compound and an electron-accepting compound without defective erasure due to penetration and color unevenness on the back surface are provided. Provided is a reversible thermosensitive recording medium.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kyoji Tsutsui             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh F term (reference) 2H026 AA07 AA09 BB01 BB25 DD03                       DD43 DD57 EE03 GG00

Claims (6)

[Claims] 1. A reversible thermosensitive composition containing a reversible thermosensitive composition, which comprises an electron-donating color-forming compound and an electron-accepting compound on a support, and can develop and decolor by changing heating and cooling conditions. In a reversible thermosensitive recording medium provided with a thermal recording layer, the water absorption of the paper and board of JIS P 8140 as a support has a water absorption of 45 g / m according to the water absorption test method (cup method).
A reversible thermosensitive recording medium characterized by using coated paper of ² or less. 2. A reversible thermosensitive recording medium comprising at least a recording layer utilizing a color reaction between an electron-donating color-forming compound and an electron-accepting compound and a paper support, which is a paper support. The water absorption of the paper and board according to JIS P 8140 is 45 g / m ² according to the water absorption test method (cup method).
A reversible thermosensitive recording medium comprising the following under layer. 3. The reversible thermosensitive recording medium according to claim 2, wherein the resin of the under layer is in a crosslinked state. 4. A coloring state (B) is formed by heating the initial decoloring state (A) to cause color development, and the coloring state (B) is fixed by rapid cooling of the coloring state (B). C) is formed, the colored state (C) is heated to form a decolored state (D) at a temperature lower than the coloring temperature, and when the colored state (C) is cooled, an initial decolored state (A) is formed. The reversible thermosensitive recording medium according to any one of claims 1 to 3, wherein color development and color erasing can be performed reversibly in each of the processes. 5. The reversible thermosensitive recording medium according to claim 1, wherein the electron-accepting compound used in the reversible recording layer is a phenolic compound having a hydrocarbon group having 8 or more carbon atoms. 6. The reversible thermosensitive recording medium according to claim 1, which has a thermoreversible recording section and an information storage section.