JP2001279144A - Aqueous ink composition decolorable with solvent and heating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an aqueous ink composition which gives written or printed characters, wages, or the like, easily decolorable with a solvent and heating. SOLUTION: This ink composition, decolorable with an organic solvent and heating, at least contains (a) water as a solvent, (b) a colorant which contains a leuco dye and a developer, has been kneaded or coated with a water-insoluble resin, and is a fine powder or microcapsules wherein the dye and the developer are in a color-developed state, and (c) a water-soluble decoloring agent which is solid at normal temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for writing implement inks such as ballpoint pens and markers, printing inks, and ink jet inks, and can erase written or printed characters or images by heating with an organic solvent. Water-based ink composition.

[0002]

2. Description of the Related Art In recent years, mass consumption of paper has become a serious problem from the viewpoint of resource conservation. The collection and recycling of used paper has been energetically promoted along with the growing desire to reuse recyclable resources.However, to recycle paper written or printed with conventional water-based inks, A large amount of energy is required to re-fiberize the paper itself or to re-clean the paper. In addition, in order to obtain paper having high whiteness, a large amount of bleaching agent and water are required for the bleaching of the ink, so that the recycling cost is increased and this is a major obstacle from the viewpoint of resource conservation and paper recycling. This is because conventional inks have been developed with an emphasis only on improving light resistance and heat resistance in order to increase the durability of writing lines, so from the viewpoint of recycling paper, The high chemical or physical stability of the ink is an obstacle to regeneration. Therefore, if it is possible to write or print on paper with a writing instrument or printing machine using erasable ink and erase the written or printed characters or images and return it to a blank paper state, Can be reused or reused as it is, and it is considered that the substantial amount of paper used can be reduced.

Conventionally, various types of color erasable inks have been proposed, but a type utilizing an acid-base reaction, a type utilizing an oxidation-reduction reaction, and a type capable of erasing only by heating (Japanese Patent Application Laid-Open No. Hei 9-165538). No., JP-A-10-7
7437, JP-A-10-270881, and JP-A-11-166149), and a type that can be erased only by light (JP-A-6-73319). Ink composition capable of decoloring by solvent and heating (JP-A-10-88046, Japanese Patent Application No. 11-3)
74187) have been proposed, but these ink compositions contain a coloring compound, a developer, a decoloring agent and, if necessary, a resin in the coloring agent. The ratio of the color-forming components (color-forming compound and color developer) in the colorant is naturally low, and the decolorizing agent is also kneaded at the same time when the colorant is prepared. Since the bond between the colorant and the decoloring agent is formed, there is a problem that the color of the colorant is light.

[0004]

The erasable ink according to the above-mentioned technology has only one erasing method, and there are many restrictions on the erasing method. In addition, the erasable ink can be erased by a solvent and can be erased by heating. However, there has been a problem that the color density of the colorant is low. In view of the above, the present invention has been developed in view of the above-mentioned social needs and various problems of the prior art, and has a high coloring density of a colorant and an aqueous solution capable of performing both decoloring by a solvent and decoloring by heating. The purpose is to provide ink.

[0005]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that fine powders or microcapsules comprising at least a leuco dye, a developer and a water-insoluble resin are obtained. As a colorant, at least water as a solvent, by using an aqueous ink composition containing a water-soluble solid decolorant at room temperature, written or printed characters or images and the like by an organic solvent and heating. The inventors have found that the color can be easily erased, and have reached the present invention.

That is, the present invention comprises (1) (a) water as a solvent, and (b) at least a leuco dye and a color developer kneaded with or coated with a water-insoluble resin. A colorant comprising a fine powder or microcapsules in which a leuco dye and a color developer are developed, (c) a water-soluble solid decolorant at room temperature, decolorized by an organic solvent and heating Possible aqueous ink composition, (2)
The aqueous ink composition according to (1), wherein the decoloring agent is a compound that is soluble in water having an amino group and is solid at room temperature.

(3) When the decoloring agent is polyvinylpyrrolidone,
The aqueous ink composition according to (1) or (2), wherein the aqueous ink composition is at least one selected from the group consisting of urea and urea derivatives,
An aqueous ink composition according to any one of (1) to (3), which is preferably volatile and is acidic or neutral with an acidic substance.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention provides a leuco dye, a color developer and a non-aqueous solution in order to prepare an ink which can be decolorized by an organic solvent and decolorized by heating and has a high color density of a colorant. An aqueous ink composition containing a fine powder or microcapsules made of a water-soluble resin as a coloring agent, comprising a water-soluble solid decoloring agent having a decolorizing effect of the coloring agent at room temperature, further comprising the decolorizing agent Preferably, a water-soluble compound having an amino group and solid at room temperature, particularly, polyvinylpyrrolidone, urea and a urea derivative are used, and both the decolorization by an organic solvent and the decolorization by heating are possible and colored. It is intended to provide an ink having a high coloring density of the agent.

The fine powder comprising the leuco dye, the color developer and the water-insoluble resin is preferably prepared by using the leuco dye and the color developer in a molar ratio of 1: 1 to 1: 3. And a temperature of not less than the melting point of the resin, usually 130 to 200 ° C.
The mixture is heated and mixed by using a kneader at a temperature of 4 to obtain a colored pigment mass. The obtained pigment is finely pulverized by a jet mill or the like, and is preferably classified by classification into 0.1 to 15 μm, particularly 0.5 to 10 μm.
An aqueous ink is obtained by using a fine powder pigment having an m particle size and mixing with a decoloring agent and water with a stirrer. In the case of microcapsules, the leuco dye and the developer are melted and mixed according to a conventional coacervation method, and then gradually cooled to obtain a solid. Using a ball mill, this solid is finely pulverized and dispersed in an aqueous gum arabic solution, and then an aqueous gelatin solution, an aqueous acetic acid solution and formalin are added to adjust the pH. The liquid is cooled and left at room temperature to form microcapsules. Hereinafter, the color-developed microcapsules are mixed with water and a decoloring agent to obtain an aqueous ink.

As described above, in the ink composition of the present invention, the color-forming components (leuco dye and color developer) are kneaded in the water-insoluble resin forming the colorant or coated with the water-insoluble resin. In the ink composition, in principle, the color of the ink does not fade due to the effects of water and the decoloring agent dissolved in the ink because it is in a state of being isolated from the decoloring agent. Seem. However, in practice, since the water-insoluble resin forming the colorant itself has some water permeability, water may swell in the colorant and the color of the ink may fade. In order to prevent the color of the ink from fading, by containing an acidic substance in the ink composition,
Since the acidic substance acts as a color developer, even if water swells in the colorant, the color of the ink can be extremely effectively prevented from fading. When the acidic substance is volatile, after the acidic substance is volatilized from written or printed characters or images, the acidic substance no longer functions as a color developer, so that the acidic substance can be erased by an organic solvent. Both color and decoloring by heating are good.

[0011] The mechanism of decoloring of a line drawn or printed with the ink composition of the present invention by an organic solvent is not always clear, but the water-insoluble resin forming the colorant is dissolved by the organic solvent. The color developing components (leuco dye and color developer) dissolve and the bond between the dissolved leuco dye and color developer breaks, forming a strong bond between the color developer and the decolorant. It is considered that the color is erased without coloring. In this case, an excess decoloring agent remains at the erased portion, but when rewriting or reprinting with the ink composition at the erased portion, the color forming component in the ink composition is Since it is in the water-insoluble resin, it does not come into direct contact with the decoloring agent remaining at the erased location, so even if rewriting or reprinting is performed directly on the erased location, the drawing line will not It will not be erased.

Further, although the mechanism of decoloring by heating a drawn or written line using the ink composition of the present invention is not necessarily clear, heating (100 to 25) is also possible.
(About 0 ° C.), the coloring agent and the decoloring compound forming the written or printed characters or images are melted, and the color forming components (leuco dye and developer) are dissolved, and the dissolved leuco is dissolved. It is considered that the bond between the dye and the developer is broken, and the color developer and the decolorant are strongly bonded to each other so that the color is erased without re-coloring. In this case as well, an excess decoloring agent remains at the erased portion.However, when rewriting or reprinting with the ink composition at the erased portion, the color forming component in the ink composition is used. Since is in a water-insoluble resin, it does not come into direct contact with the decoloring agent remaining in the erased area, so even if rewriting or reprinting is performed directly on the erased area, Is not erased.

The leuco dye used in the present invention is, for example, an electron-donating compound having a lactone ring in the molecule, such as triphenylmethanephthalide, spiropyran, diphenylmethane, fluoran, and rhodaminelactam. Yes, one or more of them can be used in combination. Among the leuco dyes used in the present invention, particularly preferred dyes have been found as a result of diligent studies to be effective, although PSD-184 exhibiting black color is effective, but leuco dyes exhibiting other colors, and other Even a leuco dye having a structure can be used without any limitation. Developers that form a leuco dye by forming a pair with the leuco dye include hydroxyacetophenone, hydroxybenzophenone, gallic ester, benzenetriol, benzenediol, bisphenol, triphenol and cresol compounds. The compound preferably has a melting point of 100 to 250 ° C., and one or more of them can be used in combination.

Further, as the decoloring agent which is apparently decolored by being combined with a developer separated from the leuco dye at the time of decoloring, a compound which is soluble in water and has a solid decoloring property at room temperature, For example, polyvinylpyrrolidone, urea and ethylene urea, thiourea, hydantoin, 1-allyl hydantoin, 1-methylhydantoin, 1-isopropylhydantoin, 5,5-dimethylhydantoin, 1-
Urea derivatives such as hydroxymethyl-5,5-dimethylhydantoin, allantoin, biuret and the like, and one or more of them can be used in combination. Furthermore,
In view of the stability on the written paper surface and the stability of the decoloring state, the decoloring agent is preferably a solid compound having a water-soluble amino group at room temperature, and functions as a fixing resin or a humectant. Particularly, polyvinylpyrrolidone, urea, and urea derivatives are preferable since they can be used also. The melting point of the decoloring agent used in the present invention is desirably 30 to 250 ° C. In the present invention, the reason why a solid decolorant at room temperature is used is as follows.
In the written or printed lines, the decoloring agent exists in the state of a liquid with high reaction activity, so the decoloring effect works strongly,
Although the drawing line lacks the aging stability, when a decoloring agent which is solid at normal temperature is used, the erasing agent is fixed in the drawing line and the reaction activity is low, so that the drawing line has high stability over time. (2) In the case of a liquid decoloring agent, no matter how high the decolorizing agent of a high boiling point is used, volatilization of the decoloring agent from the drawing line cannot be completely suppressed, and the decolorizing agent volatilizes and dissipates from the drawing line. With the decolorizing action decreases, eventually decoloring becomes impossible, but if it is a solid decoloring agent, since volatilization can be almost completely suppressed, the decoloring ability can be maintained, It is mentioned.

In the present invention, when a water-soluble resin or a water-based resin emulsion having a film-forming property at room temperature is contained in the ink as a fixing resin for bringing the colorant into close contact with the writing surface or the printing surface, Adhesion to paper or the like is increased, and wear resistance of written or printed characters or images can be improved. However, an aqueous resin emulsion sometimes acts in the same manner as a solvent and may cause the color of the ink to fade, so that care must be taken in combination with a colorant. Here, as the water-soluble resin that can be used as the fixing resin, a water-soluble nylon resin, a water-soluble polyvinyl acetal resin, a water-soluble acrylic resin, a water-soluble polyamide resin, polyethylene oxide, polyvinyl alcohol, polyvinylpyrrolidone, esterified starch, Dextrin, reduced maltose, sugar alcohol and carboxymethylcellulose, preferably polyvinyl alcohol, polyvinylpyrrolidone and dextrin. Examples of the aqueous resin emulsion include ethylene vinyl acetate emulsion, ethylene vinyl acetate vinyl chloride emulsion, ethylene vinyl acetate acrylic emulsion, acrylic emulsion, styrene acrylic emulsion, styrene acrylonitrile emulsion, acrylonitrile butadiene emulsion, acrylic butadiene emulsion, urethane emulsion, and polyethylene imine. It is a derivative emulsion or a polyester emulsion, preferably an ethylene vinyl acetate emulsion or an ethylene vinyl acetate vinyl chloride emulsion, and one or more of them can be used in combination.

Here, when the fixing resin is a compound having a decoloring property, such as polyvinylpyrrolidone, it is not necessary to separately add a decoloring agent in the ink, and the function of the decoloring agent and the fixing resin can be combined. Thus, polyvinylpyrrolidone is particularly preferred from the viewpoints of the ink preparation method and cost.
Also, urea and urea derivatives are known as moisturizing agents that suppress writing inability (called dry-up) due to thickening of the ink due to evaporation of the ink solvent at the pen tip in writing ink. (Japanese Unexamined Patent Publication No. 8-12774
No. 6, Japanese Patent Application No. 11-341865, etc.), urea and urea derivatives can serve both as a decolorizing agent and a humectant. It is excellent as a decoloring agent used for. The water-insoluble resin forming the colorant according to the present invention is a water-insoluble resin having solubility in an organic solvent for decoloring and melting at a temperature for decoloring, and in particular, polystyrene. And styrene resins such as styrene acryl, styrene acrylonitrile, styrene acrylonitrile butadiene and styrene butyl acrylate, and acrylic resins such as copolymers containing polymethyl methacrylate and methyl methacrylate as monomer units.

Further, in view of the object of the present invention, the organic solvent for decoloring may be selected as long as it is capable of dissolving the water-insoluble resin forming the colorant, such as acetone, methyl ethyl ketone, methyl propyl ketone. , Diethyl ketone,
Ethyl propyl ketone, dipropyl ketone, acetylacetone, acetophenone, 3-methyl-2-butanone,
3,3-dimethyl-2-butanone, 2,4-dimethyl-
Ketone solvents such as 3-pentanone and 2,6-dimethyl-4-heptanone, dimethyl ether, diethyl ether, methyl ethyl ether, dipropyl ether, dibutyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, Pyran, furan, methylfuran, tetrahydrofuran, ethylene oxide, propylene oxide, ether solvents such as dioxane, ethyl acetate,
Ester solvents such as butyl acetate and isoamyl acetate;
Glycol ether solvents such as methoxyethanol, 2-ethoxyethanol and 1-methoxy-2-propanol; glycol ether ester solvents such as methyl glycol acetate and ethyl glycol acetate; and aliphatic carbons such as hexane, heptane, cyclohexane and methylcyclohexane. Hydrogen solvents, benzene, toluene, aromatic hydrocarbon solvents such as xylene, methyl chloride, methylene chloride, chloroform, dichloroethane, trichloroethane, tetrachloroethane, perchloroethane, perchloroethylene, halogenated hydrocarbon solvents such as chlorobenzene, A hydrocarbon solvent having a hetero atom such as aniline, toluidine, pyridine, bipyridine, dimethylimidazolidinone, dimethylsulfoxide, etc., and one or more of them. Mixture to be used. Decoloring performance,
Acetone, 1,2-dimethoxyethane, and 1,2-diethoxyethane are particularly preferred from the viewpoints of safety to the human body and drying properties of the solvent. The hetero atom mentioned here is
It does not contain oxygen atoms, especially nitrogen and sulfur atoms.

In the present invention, the composition of the colorant is such that the leuco dye is used in an amount of 2 to 20% by mass, the developer is used in an amount of 1 to 30% by mass, and the resin is used in an amount of 50 to 95% by mass, based on the mass of the colorant. it can. Here, the molar ratio of the leuco dye to the developer is preferably from 1: 1 to 1: 3. In the case of microcapsules, the leuco dye is used in an amount of 30 to 70% by mass and the developer is used in an amount of 30 to 70% by mass, and the molar ratio of the leuco dye to the developer is preferably 1: 1 to 1: 3. Acidic substances for adjusting the ink to acidic or neutral include inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, thiosulfuric acid, chloric acid, chlorous acid and perchloric acid, or formic acid, acetic acid and propion Organic acids such as acid, citric acid, malic acid, oxalic acid, phenol, cresol, acrylic acid, and methacrylic acid, and acetic acid, hydrochloric acid, citric acid, and malic acid are preferable from the viewpoint of safety for the human body. Further, as the volatile acidic substance, formic acid, acetic acid, propionic acid, hydrochloric acid, nitric acid, chloric acid, chlorous acid, perchloric acid, acetic acid is particularly preferred from the viewpoint of safety and volatility for the human body . The pH of the ink is preferably from 4 to 7, more preferably from 4 to 6. Further, the composition of the ink composition in the present invention is such that water is 50 to 90% by mass, a coloring agent is 5 to 35% by mass, and a decoloring agent is 2 to 30% by mass based on the amount of the ink composition substance. Can be used.

The aqueous ink composition according to the present invention is an aqueous dispersion of a colorant, which is a fine powder or microcapsule comprising a leuco dye, a developer and a water-insoluble resin as described above. It is characterized by containing a water-soluble solid decoloring agent at room temperature in a product, and makes it possible to decolor written or printed characters or images by an organic solvent and heating. Other rust inhibitors, preservatives, fungicides, pH adjusters that are commonly used as ink materials,
Additives such as a surface tension modifier, a humectant, a lubricant, a dispersion stabilizer, and a dispersion resin can also be used as needed, but in view of the object of the invention, hinder the color development and decoloration of the ink. must not.

[0020]

The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. (Example 1) (parts by mass) Leuco Dye PSD-184 (trade name, manufactured by Nippon Soda Co., Ltd.) 5.0 Developer 3,5-dihydroacetophenone 3.0 Resin GPPS-673 (A & M styrene ( Polystyrene (trade name), 20.0 [leuco dye: developer = 1: 2 (molar ratio)] was heated and mixed using a kneader to obtain a colored pigment mass.

This pigment is pulverized by a jet mill, and a fine powder pigment of 5 to 10 μm separated by classification is stirred and mixed with a stirrer according to the following composition so that the pH becomes 6.0. It was adjusted with a mass% acetic acid aqueous solution to obtain a black ink for an aqueous marker. (% By mass) Black fine powder 10.0 PVP K-15 (polyvinylpyrrolidone manufactured by ISP, trade name) 10.0 Deltop (manufactured by Takeda Pharmaceutical Co., Ltd., trade name, 2-benzisothiazoline-3-one 10) %, Ethylene glycol 70%) 0.3 ion-exchanged water 79.7 The viscosity of the black ink composition for aqueous marker is 21.6.
mPa · s (25 ° C., 75 s ⁻¹ ).

This ink is made of polypropylene in the same manner as a commercially available normal direct liquid type water-based marker (Zebra Popstar extra fine-trade name-). A stirrer made of stainless steel was put in the tube, and after filling with ink, the tip with a built-in valve was fitted to the narrow side, a chip made of polyester was built in, and the inside of the tube was brought to normal pressure to prepare an aqueous marker pen. In addition,
Immediately before writing, the marker was shaken about 10 times, the ink was sufficiently stirred, the ink was sufficiently impregnated into the chip, and then writing was performed on A4 size copy paper.

(Example 2) (parts by mass) Leuco dye PSD-184 2.5 Developer 2,3,4-trihydroxybenzophenone 2.3 Resin MM-428 (Acrylic resin manufactured by Fujikura Kasei Kogyo Co., Ltd.) 30.0 [Leuco dye: developer = 1: 2 (molar ratio)] was heated and mixed using a kneader to obtain a colored mass pigment.

This pigment is pulverized by a jet mill, and a fine powder pigment of 0.5 to 5 μm separated by classification is used.
The mixture having the following composition was stirred and mixed using a stirrer to adjust the pH to 3.4.
Was adjusted with a 10% by mass aqueous solution of acetic acid to obtain a black ink for an aqueous ballpoint pen. (% By mass) Black fine powder 10.0 Urea 10.0 Deltop 0.3 Emulgen 707 (trade name, nonionic surfactant, polyoxyethylene alcohol ether, manufactured by Kao Corporation) 0.8 Benzotriazole 0 .2 phosphanol (trade name, nonionic surfactant, ether phosphate ester, manufactured by Toho Chemical Industry Co., Ltd.) 0.3 Potassium oleate 0.5 Xanthan gum 0.6 Ion-exchanged water 77.3 The viscosity of the black ink composition for ballpoint pens is 142
mPa · s (25 ° C., 150 s ⁻¹ ).

This ink was prepared by using a commercially available water-based gel-type ballpoint pen (Zebra Hyper Gel-trade name-).
As in the case of the stainless steel chip ball diameter 0.7 mm), after filling the ink into a polypropylene tube, the chip is fitted, an appropriate amount of the ink follower is injected from the tail, and defoamed at 200 G by a centrifuge to create a ballpoint pen. Then, writing was performed on A4 size copy paper.

Example 3 (parts by mass) Leuco Dye Crystal Violet Lactone 6.3 Developing Agent Ethyl Gallate 6.0 Resin GPPS-673 50.0 [Leuco Dye: Developing Agent = 1: 2 (Molar Ratio) )] Was heated and mixed using a kneader to obtain a colored pigment mass.

This pigment is pulverized to a submicron order by a jet mill, and the obtained pigment is stirred and mixed with a stirrer according to the following composition to obtain a 10% by mass aqueous acetic acid solution so that the pH becomes 7.0. And filtered with a 0.22 μm Teflon (registered trademark) filter to obtain a blue ink for an inkjet printer. (% By mass) Blue fine powder 10.0 5,5-dimethylhydantoin 5.0 Diethylene glycol 5.0 Deltop 0.2 Sodium dihydroacetate 0.5 Deionized water 79.3 The viscosity of the blue ink composition for inkjet is 2.4
mPa · s (25 ° C., 75 s ⁻¹ ). This ink was used as an ink for an ink jet printer using a piezo element (PM-700J manufactured by Seiko Epson Corporation-trade name-), and printing was performed on A4 size copy paper.

Example 4 (parts by mass) Leuco dye PSD-V 20.0 Developer Methylenetris-p-cresol 17.0 [Leuco dye: Developer = 1: 1 (molar ratio)] is melted. And then cooled slowly to give a red solid. Using a ball mill, this solid material is 8% by mass of gum arabic
It was pulverized and dispersed in an aqueous solution to the order of 10 μm.
Next, an aqueous gelatin solution was mixed at 40 ° C., and the mixture was stirred for 1 hour, and then water was added dropwise, followed by dilution by stirring. Subsequently, the pH of the solution was adjusted to 3.9 by adding a 10% by mass aqueous acetic acid solution,
Further, 37% formalin was added dropwise to adjust the pH of the solution to 7.0. This liquid was cooled to 5 ° C. and allowed to stand at room temperature for 3 days, and then microcapsules formed in the liquid were separated by a centrifuge to prepare red microcapsules.

Using the obtained microcapsules, the mixture was stirred and mixed with the following composition using a stirrer, and adjusted to a pH of 5.0 with a 10% by mass aqueous acetic acid solution. Obtained. (% By mass) Red microcapsule 15.0 PVP K-15 10.0 Deltop 0.3 Ion-exchanged water 74.7 The viscosity of the aqueous deep pink ink composition is 18.0 mPa ·
s (25 ° C., 75 s ⁻¹ ). This ink was printed on A4 size copy paper by ordinary letterpress printing.

(Comparative Example 1) The pigment obtained in Example 1 was stirred and mixed with the following composition using a stirrer, and adjusted with a 10% by mass aqueous acetic acid solution so as to have a pH of 6.0. And
A black ink for an aqueous marker was obtained. (% By mass) Black fine powder 10.0 N-methyl-2-pyrrolidone 5.0 Deltop 0.3 Kuraray Povar (polyvinyl alcohol manufactured by Kuraray Co., Ltd., trade name) 5.0 Aerosil 200 (Nippon Aerosil Co., Ltd.) 0.5, deionized water 79.2 The above aqueous black ink composition has a viscosity of 19.0 mPa · s.
(25 ° C., 75 s ⁻¹ ). Preparation and writing of a marker pen using this ink were performed in the same manner as in Example 1.

(Comparative Example 2) The pigment obtained in Example 2 was stirred and mixed with the following composition using a stirrer, and adjusted with 28% by mass aqueous ammonia so as to have a pH of 8.5. Thus, a black ink for an aqueous ballpoint pen was obtained. (% By mass) Black fine powder 10.0 Deltop 0.3 Emulgen 707 0.8 PVP K-15 8.0 Benzotriazole 0.2 Potassium oleate 0.5 Xanthan gum 0.6 Ion-exchanged water 79.6 Above aqueous The viscosity of the black ink composition is 171 mPa · s
(25 ° C., 150 s ⁻¹ ). Preparation and writing of a ballpoint pen using this ink were performed in the same manner as in Example 2.

(Test Method) The inks of Examples 1 to 4 and Comparative Examples 1 and 2 were subjected to a storage test in a sample bottle at room temperature, heating of characters or images written or printed by each method, and an organic solvent. (Acetone) was used for the decolorization test. Ink Color Temporal Density Change Test Immediately after the ink was prepared and for 1 month, 3 months, and 6 months, the appearance of the ink stored in a sample bottle at room temperature was visually observed. Decolorization test of written or printed characters or images with acetone (Part 1) Immediately after ink preparation, using each of the above inks, write or print on characters or images written or printed on copy paper 3 minutes after writing or printing A few drops of acetone were dropped, and it was confirmed whether the character or image at the place where the drop was made was erased.

Decolorization test of characters or images written or printed with acetone (No. 2) Immediately after ink preparation, using the above inks, write or print on characters or images written or printed on copy paper. Twenty-four hours later, several drops of acetone were dripped, and it was confirmed whether the character or image at the place where the drops were dropped was erased. Decolorization test by heating Immediately after making ink, using the above-mentioned inks, write or print on characters or images written on copy paper, 3 minutes after writing or printing, press the electric iron heated to about 200 ° C for 5 seconds It was checked whether characters or images were erased.

(Test Results) The test results are shown in Tables 1 and 2.

[0035]

[Table 1]

[Note] ○: sufficiently dark color In the case of black ink (Example 1, Example 2, Comparative Example 1, Comparative Example 2) In the case of blue ink very similar to PANTON 419C (black) (Example 3) ) A color very similar to PANONE 286C (dark blue) In the case of dark pink ink (Example 4) A color very similar to PANONE 226C (dark pink) Δ: In the case of black ink where remarkable fading can be visually confirmed (Comparative Example 2) ) Color very similar to PANTON 416C (dark gray) ×: faded so that it could not be used In the case of black ink (Comparative Example 2) Color very similar to PANTON 401C (grey-brown)-: not performed Here, the value of “PANTONE” is Pantone. Based on company color sample Pantone Color Specifier / coated paper.

[0037]

[Table 2]

As is evident from the test results in Table 1, in Comparative Example 2, the color of the ink faded with time because the ink was basic. However, in Examples 1 to 4 and Comparative Example 1 in which the ink was acidic or neutral, the color of the ink did not change. Also, as is clear from the test results in Table 2,
In Example 2 in which the acidity of the ink was strong and Comparative Example 1 in which the decoloring agent was a liquid, when the color was erased with acetone immediately after writing, the writing line re-colored, but the ink was neutral or In Examples 1, 3, and 4, which were weakly acidic (having a pH of 4 to 7), when the color was erased with acetone immediately after writing or printing, the color could be erased without recurrence. Furthermore,
In Example 2, after the writing line was left for 24 hours after writing and the acidic substance was volatilized, the color was completely erased even when the color was erased only with acetone. However, Comparative Example 1
In addition, N-methyl-2-pyrrolidone as a decolorizing agent volatilized simultaneously with the volatile acidic substance, and neither the decoloring by the organic solvent after standing for 24 hours nor the decoloring by heating could be performed.

[0039]

According to the present invention, there is provided an aqueous ink composition containing a fine powder or a microcapsule comprising a leuco dye, a developer and a water-insoluble resin as a coloring agent, at room temperature which is soluble in water having a decolorizing effect of the coloring agent. By containing a solid decoloring agent, and further using, as the decoloring agent, a compound which is preferably soluble in water having an amino group and is solid at ordinary temperature, in particular, polyvinylpyrrolidone, urea and a urea derivative, an organic solvent is used. Ink that can be erased by heating and can be erased by heating and that has a high coloring density of the colorant can be produced. Further, the decoloring agent remains in the erased portion, but when rewriting or reprinting is performed on the erased portion with the ink composition, the color forming component in the ink composition is insoluble in water. Since it is in the resin, it does not come into direct contact with the decoloring agent remaining at the erased location, so that it is possible to directly rewrite or reprint the erased location.

[Procedure amendment]

[Submission date] May 31, 2000 (2005.3
1)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0003

[Correction method] Change

[Correction contents]

Conventionally, various types of color erasable inks have been proposed, but a type utilizing an acid-base reaction, a type utilizing an oxidation-reduction reaction, and a type capable of erasing only by heating (Japanese Patent Application Laid-Open No. Hei 9-165538). No., JP-A-10-7
7437, JP-A-10-270881, and JP-A-11-166149), and a type that can be erased only by light (JP-A-6-73319). Although an ink composition capable of decoloring by a solvent and heating (Japanese Patent Application Laid-Open No. 10-88046 ) has been proposed, these ink compositions contain a coloring compound, a developer and a decolorizing agent in a coloring agent. Because it contains a colorant and, if necessary, a resin, the ratio of the color-forming components (color-forming compound and color developer) in the colorant is naturally low, and the decolorant is also kneaded at the same time when the colorant is made. Since the bond between the color former and the color developer is broken, and the bond between the color developer and the decolorant is formed, there is a problem that the color of the colorant is light.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shigeo Yoshida 2-9 Higashigokencho, Shinjuku-ku, Tokyo Inside Zebra Co., Ltd. (72) Inventor Koichi Ito 2-9 Higashigokencho, Shinjuku-ku, Tokyo No. F-term in Zebra Co., Ltd. (reference) 2H086 AA32 AA33 AA36 AA46 AA50 BA01 BA58 BA59 BA60 4J039 AD23 BC37 BE02 BE06

Claims (4)

[Claims] (1) water as a solvent, (b) kneaded with a water-insoluble resin or coated with a water-insoluble resin, comprising at least a leuco dye and a developer, wherein the leuco dye and the developer are A colorant consisting of fine powder or microcapsules in a color-developed state, (c) a water-soluble solid decolorant at room temperature,
A water-based ink composition containing at least an organic solvent and decolorable by heating. 2. The water-based ink composition according to claim 1, wherein the decoloring agent is a water-soluble solid compound having an amino group which is soluble at room temperature. 3. The method according to claim 1, wherein the decoloring agent is at least one selected from the group consisting of polyvinylpyrrolidone, urea and urea derivatives.
3. The aqueous ink composition according to claim 1, which is a seed. 4. The aqueous ink composition according to claim 1, wherein the aqueous ink composition is acidic or neutral.