JPH0532045A - Heat-reversible recording sheet - Google Patents

Abstract

PURPOSE:To provide a heat-reversible recording sheet enhanced in light fastness. CONSTITUTION:In a heat-reversible recording sheet wherein a heat-reversble recording layer based on a microcapsule containing an electron donating color forming org. compound, an electron acceptive compound, a discoloring temp. control compound and a low volatile solvent and a binder is provided on a base material, any part of the heat-reversible recording sheet contains an ultrasonic absorber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoreversible recording sheet which exhibits a color change reversibly in response to a change in temperature. The present invention relates to a recording sheet for a thermal printer, which can be repeatedly used and shows a typical thermal discoloration.

[0002]

2. Description of the Related Art A printing system using a device such as a word processor is widely used in offices and general households. When creating documents, drawings, etc. with this device, usually when printing the screen displayed on the display after input, the text, layout, typographical errors, etc. on the display are not sufficiently confirmed, proofread, and corrected. The work of checking once after printing out is being done. By the way, in general, even if a confirmation work is performed on the display, a work requiring further correction often occurs due to printout. Currently, no special means is used for the prints required for these confirmation, proofing, and correction work.Recently, some of them are printed out on thermal paper for confirmation, proofing, and correction work, and the final print is made. In some cases, thermal transfer printing is performed with an ink ribbon, but in most cases, normal printing is performed for confirmation, calibration, and correction work. Therefore, in a thermal printer using a thermal head, waste of consumables such as paper and ink ribbon is generated.

Japanese Patent Application Laid-Open No. 60-52388 discloses a paper recycling printing method using a thermal printer. This is for the purpose of reusing printing paper. Ag ₂ HgI ₄
When a thermo sheet coated with a reversible heat-sensitive material is used in a low temperature atmosphere as described above, when it is reused, it is cooled to a low temperature, for example, 5 ° C. or lower and used again as a recording medium. However, for the purpose of the present invention, the heat-sensitive material is colored and the contrast is poor (Ag ₂ HgI ₄
Then change from yellow to yellow-orange), and there is a problem that a cooling device is required to erase the print contents for reuse.

A thermoreversible recording sheet for a thermal printer, which is prepared by using the leuco-based heat-coloring type thermoreversible color changing material, which the inventor of the present application has already invented, has a temporary memory function. , Thermal printer documents,
After confirming and correcting the printed contents such as drawings, it can be easily erased by leaving it naturally, so that it can be easily and repeatedly used.

However, when the thermoreversible recording sheet is exposed for a long time under a fluorescent lamp or exposed to sunlight, there is a problem that discoloration of the background portion occurs.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide a thermoreversible recording sheet having improved light resistance.

[0007]

As a result of various investigations in view of the above problems, the present invention provides a substrate with an electron-donating color-forming organic compound, an electron-accepting compound, a color-changing temperature adjusting compound and a low-volatile solvent. A thermoreversible recording sheet having a recording layer in which the encapsulated microcapsules are applied together with a binder, wherein any part of the recording sheet contains an ultraviolet absorber, or further ultraviolet absorption on the recording layer is carried out. It has been found that the light resistance is remarkably improved by providing the protective layer containing the agent, and the present invention has been completed.

That is, according to the present invention, a microcapsule containing an electron-donating color-developing organic compound, an electron-accepting compound, a color-changing temperature adjusting compound and a low-volatile solvent is coated on a substrate together with a binder to prepare a recording medium. A thermoreversible recording sheet for repeated use, in which an image is formed by printing characters or symbols on the recording medium using a thermal head, and the image can be erased again by allowing it to stand naturally. The thermoreversible recording sheet is characterized in that either part contains an ultraviolet absorber or a protective layer containing an ultraviolet absorber is provided on the recording medium. The light resistance of the thermoreversible recording sheet is improved because the ultraviolet absorber prevents photodecomposition of the organic compounds such as leuco dye and binder in the recording layer.

Here, examples of the ultraviolet absorber used in the present invention include 2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone and 2
-Hydroxy-4-n-octoxybenzophenone, 4
-Dodecyloxy-2-hydroxybenzophenone,
2,2'-dihydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2,2 ', 1,4'-tetrahydroxybenzophenone, 2-hydroxy-4-methoxy-2 '
Carboxybenzophenone, 2-hydroxy-4-oxybenzylbenzophenone, 2-hydroxy-4-chlorobenzophenone, 2-hydroxy-5-chlorobenzophenone, 2-hydroxy-4-methoxy-4'-methylbenzophenone, 2-hydroxy-4. -N-heptoxybenzophenone, 2-hydroxy-3,6-dichloro-4-methoxybenzophenone, 2-hydroxy-3,
Benzophenone-based UV absorbers such as 6-dichloro-4-ethoxybenzophenone and 2-hydroxy-4- (2-hydroxy-3-methylacryloxy) propoxybenzophenone, 2- (2'-hydroxy-5'-methylphenyl) Benzotriazole, 2- (2'-hydroxy-3 ', 5'-ditertiarybutylphenyl) benzotriazole, 2- (2'-hydroxy-3'-tert-butyl-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-4'-octoxy) benzotriazole, 2- (2'-hydroxy-
3 ', 5'-ditert-butylphenyl) 5-chlorobenzotriazole, 2- (3'-tert-butyl-2'-hydroxy-5'-methylphenyl) 5-chlorobenzotriazole, 2- (2'- Hydroxy-5
-Methoxyphenyl) benzotriazole, 2- (2 '
-Hydroxy-5-ethoxyphenyl) benzotriazole and other benzotriazole-based UV absorbers, phenyl salicylate, P-octylphenyl salicylate,
P-tert-butylphenyl salicylate, carboxyphenyl salicylate, methylphenyl salicylate, dodecylphenyl salicylate, and other salicylate phenyl ester ultraviolet absorbers, or P-methoxybenzylidene malonic acid dimethyl ester, 2-ethylhexyl-2-cyano-3, 3'diphenyl acrylate, ethyl-2-cyano-3,3'-diphenyl acrylate, 3,5-ditertiary butyl-P-hydroxybenzoic acid, resorcinol monobenzoate to be transformed into benzophenone by ultraviolet light, 2,4-diter Shaributylphenyl, 3,5-ditertiarybutyl-
Examples include 4-hydroxybenzoate, but these examples do not limit the present invention. These may be used alone or in combination of two or more.

As the film-forming resin binder containing the above-mentioned UV absorber to form a protective layer on the recording layer, water-soluble polymers and polymer aqueous emulsions can be used. As specific examples of the water-soluble polymer, for example, polyvinyl alcohol, modified polyvinyl alcohol, starch and its derivatives, cellulose derivatives (methyl cellulose, methoxy cellulose, hydroxyethyl cellulose, etc.), casein, gelatin, polyvinyl pyrrolidone, styrene- Maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, diisobutylene-maleic anhydride copolymer, polyacrylamide, modified polyacrylamide, methyl vinyl ether-
Maleic anhydride copolymer, carboxy-modified polyethylene, polyvinyl alcohol / acrylamide block copolymer, melamine-formaldehyde resin, urea-formaldehyde resin and the like can be mentioned. Examples of the aqueous emulsion include polyvinyl acetate, polyurethane,
Styrene / butadiene copolymer, styrene / butadiene / acrylic copolymer, polyacrylic acid, polyacrylic ester, vinyl chloride, vinyl acetate copolymer, polybutyl methacrylate, ethylene / vinyl acetate copolymer and the like. . These may be used alone or as a mixture, and if necessary, a curing agent may be added to cure the resin.

There is no particular limitation on the coating method and coating amount of the protective layer, but the coating amount is 1 g / m ² or more, more preferably 3 to 15 g, in terms of solid content on the recording medium. / M ²
It is preferable that the coating be performed so that In the thermoreversible recording sheet of the present invention, various additives may be added to the protective layer in order to prevent sticking during recording.

The additives used in the present invention include inorganic and organic fillers such as aluminum hydroxide, heavy and light calcium carbonate, zinc oxide, titanium oxide, barium sulfate, silica gel, activated clay, talc and clay. Examples include satin white, kaolinite, calcined kaolinite, diatomaceous earth, synthetic kaolinite, polyolefin particles, polystyrene particles, urea-formaldehyde resin particles, and examples of lubricants include waxes such as stearic acid amide and stearin. Zinc acid, palmitic acid amide, oleic acid amide, lauric acid amide, ethylenebisstearylamide, methylenebisstearylamide, methylolstearylamide, paraffin wax, higher alcohols, higher fatty acids, higher fatty acid esters, etc. It was added to, may be formed a protective layer.

The electron-donating color-developing organic compound used in the present invention may be used alone or as a mixture of two or more thereof, and is itself a colorless or pale-colored dye precursor, for example, triphenylmethanephthalide system. There are compounds, fluorane compounds, spiropyran compounds, indolinophtalide compounds and the like.

It is preferable to select a material that develops black, blue, green, etc. for the purpose of checking, proofreading, and correcting text, layout, typographical error, etc., which is the object of the present invention, but it is not particularly limited.

Specific examples of the electron-donating color-developing organic compound include the following. 3,3-bis (p-
Dimethylaminophenyl) -phthalide, 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (also known as crystal violet lactone), 3
-Diethylamino-7- (o-chloroanilino) fluorane, 3-dibutylamino-7- (o-chloroanilino) fluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-
7-anilinofluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 3-N-methyl-N-
Isopropylamino-6-methyl-7-anilinofluorane, 3-N-methyl-N-isobutylamino-6-methyl-7-anilinofluorane, 3-N-methyl-N-
Amylamino-6-methyl-7-anilinofluorane,
3-N-methyl-N-isoamylamino-6-methyl-
7-anilinofluorane, 3-N-methyl-N-cyclohexylamino-6-methyl-7-anilinofluorane, 3-Np-tolyl-N-ethylamino-6-methyl-7-anilino Fluoran, 3-diethylamino-6
-Chloro-7-anilinofluorane, 3-diethylamino-5-methyl-7-dibenzylaminofluorane, 3
-N-ethyl-N- (2-ethoxypropyl) amino-
6-methyl-7-anilinofluorane, benzoyl leucomethylel blue, 6'-chloro-8'-methoxybenzoindolino-spiropyran, 3,3-bis (1-ethyl-2-methyl-8-yl) Phthalide, 3-bis (2-
Phenylindol-3-yl) phthalide, 3-diethylamino-6-methyl-7-xylidinofluorane, 3
-Di-n-butylamino-6-methyl-7-xylidinofluorane, 3-pyrrolidino-6-methyl-7-xylidinofluorane, 3- (N-cyclohexyl-N-methyl) amino-6-methyl -7-xylidinofluorane,
3- (NP-Tritolu-N-methyl) amino-6-methyl-7-xylidinofluorane, 3-diallylamino-6-methyl-7-xylidinofluorane, 3- (N-
Ethoxyethyl-N-ethyl) amino-6-methyl-7
-Xylidinofluorane, 3-diethylamino-6-chloro-7-xylidinofluorane, 3-di-n-butylamino-6-chloro-7-xylidinofluorane, 3-
(N-cyclohexyl-N-methyl) amino-6-chloro-7-xylidinofluorane, 3- (N-P-tolyl-N-methyl) amino-6-chloro-7-xylidinofluorane, 3- Diethylamino-6-methyl-7-2 '
-Chloroanilinofluorane, 3- (N-cyclohexyl-N-methyl) amino-6-methyl-7-2'-chloroanilinofluorane, 3- (NP-tolyl-N-methyl) amino- 6-methyl-7-2 ', 4'-dichloroanilinofluorane, 3-diethylamino-6-methyl-7-2', 4'-dichloroanilinofluorane and the like can be mentioned.

Next, the electron-accepting compound used in the present invention for coloring the above-mentioned electron-donating color-developing organic compound by heating can be selected from the color-developing agents generally used for thermal paper. Its selection range is narrower than that of a system that reversibly decolorizes, and particularly preferred electron-accepting compounds include dodecyl gallate, cetyl gallate, gallic acid esters such as stearyl gallate, and methyl parahydroxybenzoate. Examples of the compound include a phenolic hydroxyl group-containing compound such as parahydroxybenzoic acid esters such as ethyl parahydroxybenzoate and propyl parahydroxybenzoate, stearyl protocatechuate, protocatechuic acid esters such as benzyl protocatechuate, and urea.

Examples of the discoloration temperature controlling agent include alcohols, esters, acid amides, carboxylic acids, ethers and ketones having a high boiling point, such as lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol, behenyl alcohol and myristin. Acid stearyl, propyl palmitate, ethyl stearate, butyl stearate, glycerin tristearate, glycerin trimyristate, propylene glycol distearate, glycerin monocetyl ether, myristic acid, palmitic acid, lauric acid, didecyl ether, di Examples include dodecyl ether and stearic acid amide.

The low-volatile solvent used in the present invention is an alkylnaphthalene-based compound, a diarylalkane-based compound, an alkylbiphenyl-based compound, a terphenyl-based compound, a triarylmethane-based compound, and the like, for example, ethylnaphthalene, butylnaphthalene, Hexylnaphthalene,
Dimethylnaphthalene, diethylnaphthalene, dipropylnaphthalene, diisopropylnaphthalene, methylpropylnaphthalene, ethylpropylnaphthalene, methylbutylnaphthalene, dimethylpropylnaphthalene, 1-methyl-1-dimethylphenyl-1-phenylmethane, 1-
There are methyl-1-ethylphenyl-1-phenylmethane, dimethylbiphenyl, diethylbiphenyl, diisopropylbiphenyl, hydrogenated terphenyl, tritoluylmethane and the like.

It is necessary to select an appropriate ratio for the mixing ratio of each component depending on the physical properties of the material to be used, but it is possible to select it in a fairly wide range, and it is possible to select an electron-donating color-forming organic compound: electron-accepting property. The mixing ratio (weight) of compound: discoloration temperature controlling agent is appropriately in the range of 1: 1 to 10: 5 to 50.

The mixing ratio of the low-volatile solvent is 20 to 20 by weight.
The range of 80% is preferable, and if it is too small, the thermal response speed and the color density are not improved much. On the other hand, if the amount is too large, the reversibility of color development and color erasing deteriorates, and especially color erasing cannot be performed sufficiently.

For the purpose of the present invention, in order to avoid color development during handling or storage, and in consideration of thermal response and the like, 40
It is preferably in the range of ℃ to 100 ℃ and is achieved by selecting an appropriate combination and mixing ratio of each component.

In the present invention, the thermoreversible color-changing material having the above constitution is used by being encapsulated in microcapsules. The microencapsulation can be performed in the form of microcapsules having a particle diameter of about 1 to several tens of μm by a known technique such as a coacervation method, an interfacial polymerization method, and an in situ polymerization method.

The thermoreversible recording sheet intended for repeated use according to the present invention can be prepared by dispersing the obtained microcapsules together with a water-soluble polymer binder such as polyvinyl alcohol and coating the dispersion on a substrate.

The substrate may be paper, a plastic sheet, or a composite material thereof, which has been conventionally used for various recording and printing purposes, and is not particularly limited. These substrates may be white or lightly colored for the purpose of identification or the like so as not to interfere with the confirmation work.

[0025]

The present invention will be described in detail below with reference to examples. In addition, all the parts in an Example represent a "weight part."

Example 1 3-Diethylamino-6-methyl-7-xylidinofluorane 1 part Stearyl gallate 5 parts Stearyl alcohol 15 parts Diisopropylnaphthalene (KMC-113 Kureha Chemical Co., Ltd.) 10 parts Thermoreversible discoloration Dissolve the material uniformly at about 100 ° C. Next, while heating 50 parts of a 3% aqueous solution of a styrene-maleic anhydride copolymer adjusted to pH 4.52 to 80 ° C., 25 parts of the thermoreversible color change material dissolved product was dropped.
Using a homomixer, emulsify and disperse into fine droplets of 1 to 8 μm. While stirring the obtained emulsified dispersion liquid, 11.0 g of melamine-formalin prepolymer (Milven SM-700 manufactured by Showa Highpolymer Co., Ltd.) was added and reacted at 70 ° C. for 3 hours to give a micro with a number average particle diameter of 3.7 μm. A capsule dispersion was obtained. To 70 parts of the obtained dispersion liquid, 30 parts of 10% polyvinyl alcohol was added to prepare a coating liquid having a basis weight of 41.
It was applied to a high-quality paper of 4 g / m ² so that the amount of adhesion when dried was 15 g / m ² . Further, the following coating solution for protective layer was applied onto the recording layer so that the amount of adhesion when dried was 5.5 g / m ² , to prepare a thermoreversible recording sheet.

(Protective Layer Coating Liquid) 2,4-Dihydroxybenzophenone 15 parts Light calcium carbonate 20 parts Carboxy group-modified polyvinyl alcohol 10% aqueous solution 50 parts Water 15 parts The protective layer coating liquid is thoroughly pulverized and dispersed by a ball mill. Using.

Example 2 3-diethylamino-5-methyl-7-dibenzylaminofluorane 1 part Stearyl gallate 5 parts Stearyl alcohol 7.5 parts Myristyl alcohol 7.5 parts Diisopropylnaphthalene (KMC-113 manufactured by Kureha Chemical Co., Ltd.) ) Dissolve 10 parts of thermoreversible color change material uniformly at about 100 ° C. 5% gelatin aqueous solution with pH adjusted to 7.0 10
0 part is heated to 80 ° C., 50 parts of the lysate is added dropwise, and the mixture is emulsified and dispersed using a homomixer to form microdroplets of 1 to 8 μm. Next, 5% arabic gum aqueous solution 1 heated to 80 ° C
Add 20 parts, dilute with 220 parts hot water at 70 ° C., gradually add 10% acetic acid with stirring to adjust pH to 4.3 to cause coacervation, then cool to 10 ° C. After gelation, 2 parts of 25% glutaraldehyde was added to adjust pH to 9, and stirring was continued for 1 hour to obtain a microcapsule dispersion liquid having a number average particle diameter of 4.0 μm. 30% of 10% polyvinyl alcohol was added to 300 parts of the obtained dispersion.
Part to make a coating solution, and a coated amount of 15 g / m 2 when dried on a fine blue paper with a basis weight of 81.4 g / m ^2.
The coating was carried out so as to be ² .

Further, the following protective layer coating liquid was applied onto the recording layer so that the amount of adhesion when dried was 4.5 g / m ² , to prepare a thermoreversible recording sheet.

(Protective Layer Coating Liquid) 2- (2′-Hydroxy-5′-methylphenyl) -benzotriazole 16 parts Carboxy group modified polyvinyl alcohol 10% aqueous solution 50 parts Epichlorohydrin / polyamide copolymer 10% aqueous solution 20 parts Carbonic acid Calcium 1 part Water 29 parts Protective layer coating liquid was used after being sufficiently pulverized and dispersed by a ball mill.

Example 3 3-diethylamino-6-methyl-7-xylidinofluorane 1 part Stearyl gallate 5 parts Stearyl alcohol 10 parts Myristyl alcohol 5 parts Diisopropylnaphthalene (KMC-113 manufactured by Kureha Chemical Co., Ltd.) 10 parts The thermoreversible color-changing material was microencapsulated as in Example 1. Next, the microcapsule dispersion liquid was applied in the same manner as in Example 1.

Further, the following coating solution for protective layer was applied on the recording layer so that the amount of adhesion when dried was 5.5 g / m ² , to prepare a thermoreversible recording sheet.

(Protective Layer Coating Liquid) 2-Hydroxy-4-methoxybenzophenone 16 parts Calcium carbonate-coated silica (P-832 manufactured by Mizusawa Chemical Industry Co., Ltd.) 4 parts Carboxy group-modified polyvinyl alcohol 10% aqueous solution 50 parts Stearin Zinc oxide 1 part Water 45 parts The protective layer coating liquid was used after being sufficiently pulverized and dispersed by a ball mill.

Comparative Example 1 A thermoreversible recording sheet of Comparative Example 1 was prepared in the same manner except that the ultraviolet absorber in the protective layer of Example 1 was omitted.

Comparative Example 2 A thermoreversible recording sheet of Comparative Example 2 was prepared in the same manner except that the ultraviolet absorber in the protective layer of Example 2 was omitted.

Comparative Example 3 A thermoreversible recording sheet of Comparative Example 3 was prepared in the same manner except that the protective layer containing the ultraviolet absorber of Example 3 was omitted.

The thermoreversible recording sheet thus prepared for repeated use was recorded with an image using a word processor (Ricoh My Report NL-1), and the following evaluation test was carried out. The results are shown in Table 1. It was shown to.

"Recording Density" Image densities immediately after recording and 10 minutes after recording were measured by a Macbeth densitometer (Macbeth RD-914).
Type).

"Repeatable" word processor (Ricoh
Images were recorded with My Report NL-1) and left for 12 hours after recording, the images disappeared and returned to the original state. This test was repeated 10 times, and the deterioration of the function was visually evaluated.

"Chemical resistance" Ethyl alcohol was attached to the recording sheet, left for 15 minutes at room temperature (24 ° C), and the stability was visually evaluated.

[Water resistance] The recording sheet is immersed in water,
It was left for 12 hours under the condition of room temperature (24 ° C.), and the stability was visually evaluated.

"Sweat resistance" By attaching sweat to the recording sheet,
Stability was visually evaluated by leaving it for one day at room temperature (24 ° C.).

"Abrasion resistance" The rubbing of the thermal head generated when an image was recorded on the recording sheet by using a word processor (Ricoh My Report NL-1) was observed and evaluated by visual observation and a scanning electron microscope.

"Sunlight resistance" The thermoreversible recording sheet was exposed to sunlight for 3 days, and the change in color tone of the sheet at that time was visually observed, and the change in density was measured and evaluated with a Macbeth densitometer RD-914 type.

50 "fluorescent lamp resistant" thermoreversible recording sheets
Macbeth densitometer R was used for 120 hours of exposure under a fluorescent lamp of 00 Lux, and the change in color tone of the sheet at that time was visually observed to determine the change in density.
It was measured and evaluated with a D-914 type.

The evaluation criteria for evaluation tests other than "recording density" are as follows.

[0047] “Evaluation Criteria” ○ −−−−−−− △ −−−−−−− ×               Excellent inferior

[0048]

[Table 1]

[0049]

As shown in Table 1, the thermoreversible recording sheet provided with a protective layer containing an ultraviolet absorber on the recording layer of the present invention does not contain the absorber. The light resistance was remarkably improved as compared with the sheet, and it was extremely useful.

Claims (2)

[Claims] 1. A thermoreversible recording layer comprising, as a main component, a microcapsule containing an electron-donating color-developing organic compound, an electron-accepting compound, a discoloration temperature controlling compound, a low-volatile solvent and a binder. The thermoplastic reversible recording sheet according to claim 1, wherein any part of the thermoreversible recording sheet contains an ultraviolet absorber. 2. The thermoreversible recording sheet according to claim 1, further comprising a protective layer containing an ultraviolet absorber on the thermoreversible recording layer.