JP5686502B2 - Thermal decolorizable ink composition - Google Patents

Description

  The present invention relates to a thermosensitive decolorable ink composition that utilizes the color developing and decoloring mechanism of a leuco dye, and more specifically, without using microcapsules, can be easily decolored by simple heating such as rubbing. The present invention relates to a thermally decolorable ink composition which does not recur even when stored at a low temperature (−50 ° C. or lower), has excellent temporal stability, and has a vivid hue density.

Conventionally, many heat-decolorable ink compositions using a leuco dye developing and decoloring mechanism are known.
For example, a colorant used in a solvent or a water-based ink that can be erased by heating, and a fine powder comprising at least a leuco dye, a color developer, a color eraser, and a resin is used as the colorant, and the resin has a glass transition temperature or Vicat. Among the softening temperatures, the lower one of the softening temperatures is higher than 50 ° C., and the colorant for water-based ink made of a resin having a melting point or moldable temperature of 230 ° C. or lower (for example, see Patent Document 1), or resin-made spherical fine particles There is known a decolorable or discolorable water-based ink (for example, see Patent Document 2) characterized by containing a colorant formed by coloring a colorant selected from leuco dyes.

  However, the water-based inks of Patent Documents 1 and 2 described above solve the problem of fading of the colorant over time, and write or print letters or images with a solvent such as acetone or heating at 200 ° C. (in the examples) Since it is decolored by ironing, it cannot be easily decolored by heating by rubbing or the like, and there are problems in terms of usability and versatility.

  On the other hand, examples of the heat-decolorable ink composition using a leuco dye that can be decolored by heating by rubbing or the like include (a) an electron-donating color-forming organic compound (leuco dye, the same shall apply hereinafter), and (b) an electron. Homogeneity containing three components, ie, specific esters that control the color reaction of (b) and (b) above, and specific arylalkyl ketones, as essential components. Thermosensitive color-changing color memory that constitutes a compatible solution and exhibits a large hysteresis width (ΔH) of 8 ° C. to 30 ° C. and 8 ° C. to 80 ° C. with respect to the color density-temperature curve and exhibits quasi-reversible thermochromic characteristics Microcapsule pigments (see, for example, Patent Documents 3 and 4) are known.

  Examples of the heat erasable writing instrument using these microcapsule pigments include (a) an electron donating color-forming organic compound, (b) an electron accepting compound, (c) the above (a), (b) ) At least a microcapsule pigment containing a temperature-sensitive color-changing color memory composition comprising a homogeneous solution of a reaction medium for controlling the color reaction, a solvent, and a resin. -Shows a hysteresis width (ΔH) of 40 ° C. to 70 ° C. with respect to the temperature curve, complete decolorization temperature (T4) is 45 to 95 ° C., and color development start temperature (T2) is 0 ° C. or less. A heat-erasable writing instrument filled with a temperature-sensitive color-changing color-memory ink composition (for example, see Patent Document 5), (a) an electron-donating color-forming organic compound, and (b) an electron-accepting property. Compound, (c) Before A reversible thermochromic microcapsule pigment encapsulating a reversible thermochromic composition comprising a reaction medium that determines the temperature at which the color reaction of both occurs, and the reversible thermochromic microcapsule pigment comprising at least water The water-based reversible thermochromic writing instrument is characterized in that the average particle diameter is 2.5 to 4.0 [mu] m and particles of 2.0 [mu] m or less are 30% by volume or less in the total microcapsule pigment. The ink composition and the reversible thermochromic microcapsule pigment have a complete color development temperature (t1) of −30 to 0 ° C. and a complete decolorization temperature (t4) of 50 to 95 ° C. with respect to the color density-temperature curve. A ballpoint pen-shaped writing instrument (for example, see Patent Document 6) containing a water-based ink composition for a reversible thermochromic writing instrument is known.

The thermosensitive decolorizable ink composition described in Patent Documents 3 to 6 includes a leuco dye that is an electron-donating color-forming organic compound, a developer that is an electron-accepting compound, and a crystalline substance in a microcapsule. Etc. are included. In this decoloring mechanism, first, a leuco dye and a developer are dissolved in a molten crystalline substance, and the crystalline substance is crystallized by cooling to precipitate a leuco dye and a developer. The leuco dye and the developer that are no longer in a dissolved state interact (neutralize) with each other, and the lactone ring of the leuco dye is opened to develop a color, resulting in a developed toner. The toner in this developer state is heated by rubbing or the like, so that the crystalline substance melts and redissolves the leuco dye and the developer, so that the leuco dye and developer cannot interact with each other. It becomes a state.
When heating due to rubbing or the like is stopped, the toner is cooled to room temperature, the crystalline substance is crystallized, and the leuco dye and the developer are precipitated again and interact to form a re-developed state. In order to prevent this, a substance that causes thermal hysteresis is mixed with a crystalline substance to inhibit recrystallization at room temperature. The melting point of the crystalline substance in the heat-sensitive toner is not less than room temperature (for example, 60 ° C.), but the freezing point of recrystallization after melting is not more than room temperature (for example, −10 ° C.). Re-coloring is prevented.

  Therefore, the leuco dyes described in Patent Documents 3 to 6 are in a decolored state when the crystalline material is melted and in a developed state when solidified, so that the crystalline material is melted and solidified. It is a conventional technique to control the color erasing and developing state by controlling (thermal hysteresis).

However, in conventional heat-sensitive decoloring ink compositions, etc., the mechanism for controlling decoloration color development is to widen the thermal hysteresis of the crystalline substance, so that the decolored drawn line stored below the re-freezing point temperature of the crystalline substance Has a problem of recoloring.
In addition, it is possible to suppress recurrent color by widening the range of thermal hysteresis, but the current state where no effective substance has been found and the crystalline substance will eventually crystallize. There is a problem that cannot be prevented.

  Furthermore, in order to impart the thermal hysteresis to the crystalline substance, it is necessary to prevent the contamination of impurities, and it is essential to encapsulate. Currently, microencapsulation is difficult to achieve with an average particle size of 20 μm or less, or even if an average particle size of 20 μm or less can be produced as microencapsulation, the production efficiency is low. If a microcapsule having a large average particle size is used, the hue density is low, and the amount of crystalline material to be melted to erase the drawn lines increases, so more energy is required for decoloring. It has a problem of becoming.

JP 2001-271011 A (Claims, Examples, etc.) JP 2002-294104 A (Claims, Examples, etc.) JP-A-7-33997 (Claims, Examples, etc.) JP-A-8-39936 (Claims, Examples, etc.) JP 2006-63238 A (Claims, Examples, etc.) JP 2008-280440 A (Claims, Examples, etc.)

  The present invention has been made in view of the above-described problems of the prior art and the current situation, and is intended to solve this problem. It can be easily discolored by simple heating such as rubbing without using microcapsules, and can be made extremely low temperature (−50 It is an object of the present invention to provide a heat-sensitive decolorable ink composition that does not recur even when stored at a temperature of not more than 0 ° C., has excellent temporal stability, and has a vivid hue density.

  As a result of intensive studies in view of the above-described conventional problems, the present inventors have further developed a thermal ink composition containing, as a colorant, at least developer particles composed of at least a leuco dye, a developer, and a crystalline substance. The inventors have found that the above-described heat-sensitive decoloring ink composition can be obtained by containing a specific decoloring agent, and have completed the present invention.

That is, the present invention resides in the following (1) to (12).
(1) A thermal ink composition containing, as a colorant, at least developer particles comprising a leuco dye, a developer, and a crystalline substance, and further comprising a decolorizer comprising a cholesterol derivative. A heat-sensitive decolorizable ink composition.
(2) The thermosensitive decolorizable ink composition according to (1), wherein the cholesterol derivative is an alkyl ester of cholic acid.
(3) The heat-decolorable ink composition according to (1) or (2), wherein the decolorizer has a melting point of 30 to 190 ° C.
(4) The heat-decolorable ink composition according to any one of (1) to (3), wherein the color erasing agent comprises fine particles having an average particle diameter of 10 to 2000 nm.
(5) The decolorizer is contained in the ink in a crystalline state, and its melting point is 40 to 150 ° C. The heat-sensitive eraser according to any one of the above (1) to (4), Color ink composition.
(6) The heat erasing agent according to any one of the above (1) to (5), wherein the color erasing agent is blended in the ink in a crystalline state and has a heat capacity of 10 J / g or more. Color ink composition.
(7) The thermal decoloring property as described in any one of (1) to (6) above, wherein the content of the decolorizer is 5 to 30% by mass with respect to the total amount of the ink composition. Ink composition.
(8) The thermosensitive decolorization according to any one of the above (1) to (7), wherein the developer particles are contained in the ink in a crystalline state and have a melting point of 40 to 150 ° C. Ink composition.
(9) The thermosensitive decolorization according to any one of (1) to (8) above, wherein the developer particles are contained in the ink in a crystalline state, and the heat capacity thereof is 10 J / g or more. Ink composition.
(10) A thermal decolorizable ink composition in which the thermal decolorable ink composition according to any one of (1) to (9) is mounted on a writing instrument.
(11) A writing instrument, wherein the heat-decolorable ink composition according to any one of (1) to (10) is mounted on a writing instrument.
(12) The writing instrument as described in (11) above, wherein the writing instrument is a ballpoint pen or a marking pen.

  According to the present invention, the color can be easily erased by simple heating such as by rubbing without using microcapsules, and even when stored at a very low temperature (−50 ° C. or lower), it does not recur and is stable over time. A thermosensitive decolorizable ink composition suitable for a writing instrument having an excellent property and a vivid hue density, and a writing instrument equipped with the ink composition are provided.

Hereinafter, embodiments of the present invention will be described in detail.
The heat-sensitive decoloring ink composition of the present invention is a heat-sensitive ink composition containing, as a colorant, color developing particles comprising at least a leuco dye, a developer, and a crystalline substance, and further comprises a color erasing comprising a cholesterol derivative. It is characterized by containing an agent.

The colorant used in the present invention is composed of developer particles composed of at least a leuco dye, a developer, and a crystalline substance.
The leuco dye used in the present invention is not particularly limited as long as it is an electron donating dye and functions as a color former. Specifically, for example, 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 3- (4-diethylaminophenyl) -3- (1) from the viewpoint of obtaining an ink having excellent color development characteristics. -Ethyl-2-methylindol-3-yl) phthalide, 3- (4-diethylamino-2-ethoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) -4-azaphthalide, 1, 3-dimethyl-6-diethylaminofluorane, 2-chloro-3-methyl-6-dimethylaminofluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7 -Anilinofluorane, 3-diethylamino-6-methyl-7-xylidinofluorane, 2- (2-chloroanilino) -6-dibutylaminofluor Lan, 3,6-dimethoxyfluorane, 3,6-di-n-butoxyfluorane, 1,2-benz-6-diethylaminofluorane, 1,2-benz-6-dibutylaminofluorane, 1,2 -Benz-6-ethylisoamylaminofluorane, 2-methyl-6- (Np-tolyl-N-ethylamino) fluorane, 2- (N-phenyl-N-methylamino) -6- (N- p-tolyl-N-ethylamino) fluorane, 2- (3′-trifluoromethylanilino) -6-diethylaminofluorane, 3-chloro-6-cyclohexylaminofluorane, 2-methyl-6-cyclohexylaminofluor Oran, 3-methoxy-4-dodecoxystylinoquinoline, and the like, which are used alone (one kind) or a mixture of two or more kinds (hereinafter simply referred to as “small amount”). Can be used).
Furthermore, a pyridine compound, a quinazoline compound, a bisquinazoline compound, or the like that develops yellow to red coloring can also be used.
These leuco dyes have a lactone skeleton, a pyridine skeleton, a quinazoline skeleton, a bisquinazoline skeleton, etc., and develop color when these skeletons (rings) are opened.

  The developer used in the present invention develops a leuco dye, and is, for example, o-cresol, tertiary butylcatechol, nonylphenol, n-octylphenol, n-dodecylphenol, from the viewpoint of obtaining an ink having excellent color development characteristics. n-stearylphenol, p-chlorophenol, p-bromophenol, o-phenylphenol, hexafluorobisphenol, n-butyl p-hydroxybenzoate, n-octyl p-hydroxybenzoate, resorcin, dodecyl gallate, 2, 2-bis (4′-hydroxyphenyl) propane, 4,4-dihydroxydiphenylsulfone, 1,1-bis (4′-hydroxyphenyl) ethane, 2,2-bis (4′-hydroxy-3-methylphenyl) Propane, bis (4-hydroxyphenyl) Sulfide, 1-phenyl-1,1-bis (4′-hydroxyphenyl) ethane, 1,1-bis (4′-hydroxyphenyl) -3-methylbutane, 1,1-bis (4′-hydroxyphenyl)- 2-methylpropane, 1,1-bis (4′-hydroxyphenyl) n-hexane, 1,1-bis (4′-hydroxyphenyl) n-heptane, 1,1-bis (4′-hydroxyphenyl) n -Octane, 1,1-bis (4'-hydroxyphenyl) n-nonane, 1,1-bis (4'-hydroxyphenyl) n-decane, 1,1-bis (4'-hydroxyphenyl) n-dodecane 2,2-bis (4′-hydroxyphenyl) butane, 2,2-bis (4′-hydroxyphenyl) ethyl propionate, 2,2-bis (4′-hydroxyphenyl) -4-methylpentane, 2,2-bis (4'-hydroxyphenyl) hexafluoropropane, 2,2-bis (4'-hydroxyphenyl) n-heptane, 2,2-bis (4'-hydroxyphenyl) n-nonane etc. are mentioned, These can be used at least 1 sort (s).

The crystalline substance used in the present invention dissolves the leuco dye and the developer in a molten state, and the crystalline substance is crystallized by cooling (for example, 5 to 20 ° C.) to cause crystallization of the leuco dye and developer. The leuco dye and developer are dissolved in the leuco dye and developer by heating (for example, 60 to 80 ° C.) by rubbing or the like to cause the crystalline substance to melt and re-dissolve the leuco dye and developer. The dye and the developer can no longer interact with each other and function as a decolored state. When heating by rubbing or the like is stopped, the dye is cooled to room temperature, the crystalline substance is crystallized, and the leuco dye and the developer are again formed. It precipitates, interacts, and functions as a re-developed state.
The crystalline substance that can be used is not particularly limited as long as it has the above-described functions. For example, a compound having at least one polar group such as a hydroxyl group, an ester bond, an ether bond, and an amide bond, specifically Are saturated fatty acids such as decanoic acid, dodecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, nonadecanoic acid, icosanoic acid, docosanoic acid, tetradocosanoic acid, hexadocosanoic acid, octadocosanoic acid, capryl alcohol, lauryl alcohol Higher alcohols such as myristyl alcohol, cetyl alcohol, stearyl alcohol, behenyl alcohol, isostearyl alcohol, palmitoleyl alcohol, the fatty acid and amine amides, the fatty acid and alcohol esters, and the like Examples include ethers of secondary alcohols with glycerin, propylene glycol, ethylene glycol, and diphenylpropanedione, dibendioxybenzene, diphenoxybenzene, diisopropylnaphthalene, benzylbiphenyl, benzylnaphthyl ether, dibenzyl sulfoxide, dimethyl Aromatic compounds such as terephthalate, diphenyl carbonate, diphenylsulfone, fluoranthene, fluorene, methylhydroxynaphthalate, phenylhydroxynaphthalate, and stearanilide are exemplified, and at least one of them can be used.

Preferably, it is desirable to use a crystalline substance having a melting point of 40 to 90 ° C. from the viewpoint of further enhancing the stability in the drawn state before rubbing and in the ink state, and more preferably, stable color developing fine particles From the viewpoint of obtaining the above, it is preferably a chain molecule having 13 to 20 carbon atoms and having at least one polar group such as a hydroxyl group, an ester bond, an ether bond, and an amide bond.
Preferred examples of the crystalline substance of the developer particles include stearic acid (melting point: about 70 ° C.), palmitic acid (melting point: 63 ° C.), stearamide (melting point: 104 ° C.), behenyl alcohol (melting point: 60 ° C.), zinc stearate ( In addition to crystalline substances having a polar group such as a melting point of 130 ° C., paraffin wax, microcrystalline wax, polyethylene wax, polypropylene wax [melting point depends on the molecular weight and can be used (for decolorizers). ) As a crystalline substance, it has a melting point of 30 to 150 ° C.].

The colorant of the present invention uses at least developer particles composed of the above leuco dye, developer, and crystalline substance, and the preparation method thereof can be prepared by using a melt emulsification method, for example, A leuco dye, a developer, a crystalline substance, an emulsifier, water (ion exchange water, etc.) is mixed and heated, and then stirred at 60-95 ° C. with a kneader such as a high-speed homogenizer, and then cooled (for example, Developer particles can be prepared by cooling with ice.
The content of these leuco dye, developer, and crystalline substance is 0.8 to 3 developer and 1 to 5 crystalline substance by mass ratio with respect to leuco dye 1.
In the colorant of the present invention, the coloration temperature and decoloration temperature can be arbitrarily set by suitably combining the above-described types, amounts, and the like of the leuco dye, the developer, and the crystalline substance.

Further, the average particle diameter of the obtained developer particles is preferably from 10 to 2000 nm, more preferably from 80 to 300 nm, from the viewpoint of colorability, color developability and easy decolorization.
The “average particle size” defined in the present invention (including examples and the like) is a value obtained by measuring the average particle size with a particle size distribution measuring apparatus [Unimodal measurement (average particle size measurement)].
In addition, the developer particles composed of the leuco dye, the developer, and the crystalline substance preferably have a melting point of 40 to 150 ° C. from the viewpoint of thermal stability with ink and easy decolorization. It is preferable that the temperature is 60 to 130 ° C.
Further, the heat capacity of the developer particles is preferably 10 J / g or more, particularly preferably 10 J / g or more to 500 J / g or less. When the heat capacity of the developer particles is lower than 10 J / g, a decoloring action may be manifested by a slight temperature change in the environment. On the other hand, when the heat capacity is higher than 500 J / g, too much energy is required for the color erasing. Thus, there is a problem that the color cannot be erased unless the rubbing is repeated for a long time.
The “melting point” of the above leuco dye, developer, developer particles composed of a crystalline substance, decolored particles described later, and the like specified in the present invention (including examples and the like) refers to developer toner (emulsified liquid), The drying residue of the decolorizing liquid was measured under the condition of increasing the temperature at a rate of 10 ° C / min using a differential scanning calorimeter (Rigaku Denki Co., Ltd .: DSC8230L), and the top temperature of the endothermic peak was defined as “melting point”. The endothermic peak area is a value measured as “heat capacity”.

In the present invention, the content of the colorant (developed particles) is preferably 5 to 30% by mass, and more preferably 10 to 20% by mass with respect to the total amount of the ink composition.
When the content of the colorant (developed particles) is less than 5% by mass, the coloring power and the color developability become insufficient. On the other hand, when the content exceeds 30% by mass, the necessary amount of the decolorizer corresponding thereto increases. , The viscosity of the ink increases and the writing property decreases, which is not preferable.

  The decolorizer used in the present invention is composed of a cholesterol derivative. The decoloring action of the color erasing agent by this cholesterol derivative is such that when the drawn line [colorant in the developed state (developed particle)] is rubbed by writing, etc., the erasing agent itself is melted by heating by rubbing. Amorphization occurs by incorporating a leuco dye and a developer dissolved in the molten crystalline material. Since the decolorizer becomes amorphous by incorporating the leuco dye and the developer, the interaction between the leuco dye and the developer is prevented and the decolored state is maintained even after cooling.

The cholesterol derivative that can be used is not particularly limited as long as it is a cholesterol derivative capable of exhibiting the above-mentioned functions. Preferably, the cholesterol derivative is a cholic acid derivative from the viewpoint that an ink having a suitable decoloring ability can be obtained. Those that are alkyl esters are preferred.
In the present invention, the melting point of the color erasing agent is 30 to 190 ° C., preferably 30 to 170 ° C., more preferably 60 from the viewpoint that the drawn line before rubbing and the stability in the ink state can be further enhanced. What is set to -150 degreeC is desirable.
Specific examples of cholesterol derivatives that can be used include methyl cholate (melting point 150 ° C.), testosterone (melting point approximately 160 ° C.), methyl testosterone (melting point approximately 160 ° C.), lithocholic acid (melting point approximately 190 ° C.). ), Cholic acid (melting point: about 190 ° C.), cholesterol (melting point: about 150 ° C.), lanosterol (melting point: about 140 ° C.), and the like.

The decolorizer of the present invention uses at least the above-mentioned cholesterol derivative, preferably at least decolored particles comprising the above-mentioned cholesterol derivative and a crystalline substance, and the preparation method thereof is by using a melt emulsification method. For example, a cholesterol derivative, a crystalline substance, an emulsifier, water (ion-exchanged water, etc.) is blended, heated, stirred at 60-95 ° C. with a kneader such as a high-speed homogenizer, and then cooled (for example, The color-erasable particles can be prepared by cooling with ice.
The average particle size of the color erasing agent is 10 to 2000 nm, particularly preferably 80 to 300 nm from the viewpoint that it is possible to prevent sedimentation of the color erasing agent and to further improve the stability during storage over time. It is desirable to use something.

Further, the decolorizable particles (decolorant) composed of at least the cholesterol derivative and the crystalline substance are contained in the ink in a crystalline state, and are preferably from the viewpoint of thermal stability and easy decolorization in the ink. The melting point is preferably 40 to 150 ° C, and more preferably 60 to 130 ° C.
Further, the heat capacity of the decoloring particles (decoloring agent) is preferably 10 J / g or more, and particularly preferably 10 J / g or more and 500 J / g or less. When the heat capacity of the decolorized particles is lower than 10 J / g, the decoloring action may be manifested by a slight temperature change in the environment. On the other hand, when the heat capacity is higher than 500 J / g, too much energy is required for decoloring. Thus, there is a problem that the color cannot be erased unless the rubbing is repeated for a long time.

The content of these decolorizers is preferably 5 to 30% by mass, more preferably 10 to 20% by mass, based on the total amount of the ink composition.
If the content of the decolorizer is less than 5% by mass, the decoloring property becomes insufficient. On the other hand, if the content exceeds 30% by mass, the viscosity of the ink increases and the writing property decreases, which is not preferable. .

In the heat-sensitive decoloring ink composition of the present invention, in addition to the above leuco dye, color developer, color developing particles composed of a crystalline substance, color erasing agent, and within the range that does not impair the effects of the present invention, From the viewpoint of improvement, a fixing agent, a wetting agent and the like can be appropriately contained.
The heat-sensitive decoloring ink composition of the present invention can be prepared by stirring the colorant, the decolorant, the optional component, etc. with a kneader or the like.

The heat-decolorable ink composition of the present invention configured as described above essentially comprises two components, a colorant (developed particles) and a decolorizer. The developer particles contain at least a crystalline substance, a leuco dye, and a developer, and the leuco dye and the developer interact with each other when the crystalline substance is crystallized, as in the prior art described above. It is in a developed state. As in the prior art, the crystalline substance is melted by heating by rubbing, and the leuco dye and the developer are dissolved therein, and a decolored state is obtained. However, since the crystalline substance of the developer particles of the present invention does not contain a material that develops thermal hysteresis, when the heating by rubbing stops, it is cooled to room temperature and re-solidified at the same temperature as the melting point. And recolored.
In the thermosensitive decolorizable ink composition of the present invention, a component that is essential for maintaining the decolored state is a decolorizing agent. The action of the color erasing agent of the present invention is such that when the drawn line (colorant in the developed state (developed particles)) is rubbed by writing or the like, the color erasing agent itself is melted by heating by rubbing, and the fused crystals It becomes amorphous by incorporating a leuco dye and a developer dissolved in the active substance. Since the decolorizer becomes amorphous by incorporating the leuco dye and the developer, the interaction between the leuco dye and the developer is prevented and the decolored state is maintained even after cooling. Specifically, the above-mentioned cholesterol derivative alone or composite particles are used as a color erasing agent.

The decoloring mechanism of the present invention does not rely on the thermal hysteresis of the crystalline material, but the decolorizing agent becomes amorphous and decolored by incorporating the leuco dye and / or the developer from the crystalline material. is there. In the decoloring mechanism of the present invention, the decolorizing agent that incorporates the leuco dye and / or the developer (compatible) does not crystallize even when cooled, and therefore it is possible to prevent recurrent coloration at extremely low temperatures.
Further, in the present invention, both the developer particles and the decolorizer fine particles (because it is not necessary to protect them with microcapsules), it is possible to make fine particles, a higher hue concentration, and a less sensitive decolorization energy. A decolorizable ink composition can be prepared.
Therefore, in the present invention, the color can be easily erased by a simple heating such as rubbing without using microcapsules, and even when stored at a very low temperature (−50 ° C. or lower), the color does not recur and is stable over time. A heat-sensitive decoloring ink composition having excellent properties and a vivid hue density can be obtained.

The heat-sensitive decolorizable ink composition of the present invention configured and exerted in this way is preferably mounted on a writing instrument such as a water-based ballpoint pen, gel ink ballpoint pen, or marking pen, and is drawn on a writing surface such as paper. The writing lines can be easily erased by rubbing heat (for example, 60 ° C. or higher) with a eraser provided at the rear end of the writing instrument body.
The writing instrument of the present invention is equipped with the heat-sensitive decoloring ink composition, and can be suitably used as a water-based ballpoint pen, gel ink ballpoint pen, marking pen, writing pen, and the like.

  EXAMPLES Next, although an Example and a comparative example demonstrate this invention still in detail, this invention is not limited to the following Example etc.

[Examples 1-5 and Comparative Examples 1-5]
<Example 1>
Colorant liquid 1 was prepared by the following method.
CVL (crystal violet lactone, leuco dye, manufactured by Yamada Chemical Co., Ltd.) 1 part by mass Hexafluorobisphenol A (developer, melting point about 130 ° C., heat capacity 60 J / g, manufactured by Tokyo Chemical Industry Co., Ltd.) 1 part by mass Behenyl alcohol 80 (crystalline substance) 8 parts by weight sodium dodecyl sulfate (emulsifier, Wako Pure Chemical Industries, Ltd.) 1 part by weight ion-exchanged water 89 parts by weight The above colorant solution was heated at 80 ° C. for 2 hours. .

Next, after stirring at 15,000 rpm for 10 minutes at 80 ° C. with a high-speed homogenizer, the mixture was immediately cooled with ice to prepare Colorant Liquid 1 (average particle size 130 nm).
The developer particles in the colorant liquid 1 had a melting point of 70 ° C. and a heat capacity of 31 J / g.

Next, the decoloring liquid 1 was prepared by the following method.
Methyl cholate (cholesterol derivative, manufactured by Wako Pure Chemical Industries, Ltd.) 2 parts by mass Behenyl alcohol 80 (crystalline substance, manufactured by Nikko Chemical Co., Ltd.) 8 parts by mass Sodium dodecyl sulfate (emulsifier, manufactured by Wako Pure Chemical Industries, Ltd.) 1 part by mass Ion exchange 89 parts by weight of water The decolorizing liquid having the above composition was heated at 80 ° C. for 2 hours.
Next, the mixture was rapidly stirred at 15,000 rpm for 10 minutes with a high-speed homogenizer under the conditions of 80 ° C., and then immediately cooled with ice to prepare a decoloring solution 1 (average particle size 150 nm).
The decolorizing particles in the decoloring liquid 1 had a melting point of 68 ° C. and a heat capacity of 35 J / g.

A heat-sensitive decolorable ink composition 1 was prepared by the following method using the colorant liquid 1 and the color erasing liquid 1.
Colorant liquid 1 50 parts by mass Decoloring liquid 1 40 parts by mass Jonkrill 61J (sticking agent, manufactured by BASF Japan) 10 parts by mass

<Example 2>
Colorant liquid 2 was prepared by the following method.
RED-500 (leuco dye, manufactured by Yamada Chemical Co., Ltd.) 1 part by mass Hexafluorobisphenol A (developer, manufactured by Tokyo Chemical Industry Co., Ltd.) 1 part by mass Behenyl alcohol 80 (crystalline substance, manufactured by Nikko Chemical Co., Ltd.) 8 parts by mass Sodium dodecyl sulfate (Emulsifier, manufactured by Wako Pure Chemical Industries, Ltd.) 1 part by mass Ion-exchanged water 89 parts by mass The colorant solution having the above composition was heated at 80 ° C. for 2 hours.
Next, after stirring at 15,000 rpm for 10 minutes at 80 ° C. with a high-speed homogenizer, the mixture was immediately cooled with ice to prepare a colorant solution 2 (average particle size 140 nm).
The developer particles in the colorant liquid 2 had a melting point of 70 ° C. and a heat capacity of 33 J / g.

Using the colorant liquid 2 and the decolorizing liquid 1 of Example 1, a thermosensitive decolorable ink composition 2 was prepared by the following method.
Colorant liquid 2 50 parts by mass Decoloring liquid 1 40 parts by mass Jonkrill 61J (sticking agent, manufactured by BASF Japan) 10 parts by mass

<Example 3>
Colorant liquid 3 was prepared by the following method.
BLACK-202 (leuco dye, manufactured by Yamada Chemical Co., Ltd.) 1 part by mass Hexafluorobisphenol A (developer, manufactured by Tokyo Chemical Industry Co., Ltd.) 1 part by mass Behenyl alcohol 80 (crystalline substance, manufactured by Nikko Chemical Co., Ltd.) 8 parts by mass Sodium dodecyl sulfate (Emulsifier, manufactured by Wako Pure Chemical Industries, Ltd.) 1 part by mass Ion-exchanged water 89 parts by mass The colorant solution having the above composition was heated at 80 ° C. for 2 hours.
Next, after stirring at 15,000 rpm for 10 minutes at 80 ° C. with a high-speed homogenizer, the mixture was immediately cooled on ice to prepare Colorant Liquid 3 (average particle size 140 nm).
The developer particles in the colorant liquid 3 had a melting point of 70 ° C. and a heat capacity of 30 J / g.

Using the colorant liquid 3 and the decoloring liquid 1 of Example 1, a heat-sensitive decoloring ink composition 2 was prepared by the following method.
Colorant liquid 3 50 parts by mass Decoloring liquid 1 40 parts by mass Jonkrill 61J (sticking agent, manufactured by BASF Japan) 10 parts by mass

<Example 4>
A thermal decolorizable ink 4 was prepared using the colorant liquid 1 of Example 1 and the decolorizing liquid 2 prepared by the following method.
The decoloring liquid 2 was prepared by the following method.
Testosterone (cholesterol derivative, manufactured by Tokyo Chemical Industry Co., Ltd.) 2 parts by mass Behenyl alcohol 80 (crystalline material, manufactured by Nikko Chemical Co., Ltd.) 8 parts by mass Sodium dodecyl sulfate (emulsifier, manufactured by Wako Pure Chemical Industries, Ltd.) 1 part by mass Ion-exchanged water 89 parts by mass Part The decolorizing solution having the above composition was heated at 80 ° C. for 2 hours.
Next, after stirring at 15,000 rpm for 10 minutes with a high-speed homogenizer under the condition of 80 ° C., the mixture was immediately cooled with ice to prepare a decoloring solution 2 (average particle size 160 nm).
The decoloring particles in the decoloring liquid 2 had a melting point of 69 ° C. and a heat capacity of 41 J / g.

Using the colorant liquid 1 of Example 1 and the decoloring liquid 2 described above, a thermosensitive decolorable ink composition 4 was prepared by the following method.
Colorant liquid 1 50 parts by mass Decoloring liquid 2 40 parts by mass Jonkrill 61J (sticking agent, manufactured by BASF Japan) 10 parts by mass

<Example 5>
A heat-decolorable ink 4 was prepared using the colorant liquid 2 of Example 2 and the decolorizing liquid 3 prepared by the following method.
The decoloring liquid 3 was prepared by the following method.
Methyltestosterone (cholesterol derivative, manufactured by Tokyo Chemical Industry Co., Ltd.) 2 parts by mass Behenyl alcohol 80 (crystalline substance, manufactured by Nikko Chemical Co., Ltd.) 8 parts by mass Sodium dodecyl sulfate (emulsifier, manufactured by Wako Pure Chemical Industries, Ltd.) 1 part by mass Ion-exchanged water 89 Part by mass The decolorizing liquid having the above composition was heated at 80 ° C. for 2 hours.
Next, after stirring at 15,000 rpm for 10 minutes at 80 ° C. with a high-speed homogenizer, the mixture was immediately cooled with ice to prepare a decoloring solution 1 (average particle size 160 nm).
The decoloring particles in the decoloring liquid 3 had a melting point of 68 ° C. and a heat capacity of 33 J / g.

Using the colorant liquid 2 of Example 2 and the decoloring liquid 3 described above, a thermosensitive decolorable ink composition 4 was prepared by the following method.
Colorant liquid 2 50 parts by mass Decoloring liquid 3 40 parts by mass Jonkrill 61J (sticking agent, manufactured by BASF Japan) 10 parts by mass

<Comparative Examples 1-3>
Only the colorant liquids 1 to 3 of Examples 1 to 3 above were used alone as inks to obtain heat-sensitive decoloring inks 6 to 8.

<Comparative example 4>
The heat-sensitive decolorizable ink 9 was obtained by the following method.
The ink was taken out from the refill of “Friction Ball Black” manufactured by Pilot, and diluted to 50% with purified water to reduce the viscosity, thereby preparing a heat-sensitive decolorable ink 9.

<Comparative Example 5>
The thermosensitive decolorizable ink 10 was obtained by the following method.
The ink was taken out from a pad of “Friction Line Blue” manufactured by Pilot Co.

Writing instruments using the heat-sensitive decoloring inks 1 to 5 of Examples 1 to 5 and the heat decoloring inks 6 to 10 of Comparative Examples 1 to 5 obtained above (collector-type water-based ballpoint pen (UB -150, product name UNIBALL EYE)], and evaluation of color developability, stability over time, color erasability, and restoration resistance of color erasing lines was performed by the following evaluation methods.
These results are shown in Table 1 below.

[Evaluation method of color development]
The writing instrument was handwritten on plain paper, and the hue of the writing line was visually evaluated according to the following evaluation criteria.
Evaluation criteria:
○: Writing is possible without fading. Hue density is also high.
Δ: Scratch There is a part that is partially erased.
X: Writing is impossible.

[Evaluation method of stability over time]
The writing lines were stored for one week under the condition of 40 ° C., and the hues of the writing lines were visually evaluated according to the following evaluation criteria.
Evaluation criteria:
○: No change in hue Δ: Partially decolored. Or the hue is reduced overall.
X: Decoloring. Unable to recognize strokes.

[Evaluation method of decolorization by heating with rubbing with eraser and re-restorability at −50 ° C.]
The writing lines were rubbed with an eraser prepared by the following production method and evaluated according to the following evaluation criteria. Moreover, the paper surface containing the location erase | eliminated with this eraser was preserve | saved for 3 hours in a -50 degreeC freezer, and the subsequent re-restorability was evaluated by the following evaluation criteria.
(Production method of eraser)
25 parts by mass of a polypropylene resin (J-728, manufactured by Mitsui Chemicals) and 75 parts by mass of a thermoplastic elastomer (Actimar, LQA9770N, manufactured by Riken Technos) were heated and melted and sufficiently kneaded with a kneader, and then cooled and pulverized. What was melt-extruded by an extrusion molding machine and cooled was cut to obtain an eraser (size: 12 × 5 × 20 mm).

Evaluation criteria for decolorization by heating:
○: The color can be erased and the drawn line is not recognized.
Δ: Partially not decolored. Or the hue remains thin as a whole.
X: Discoloration is impossible. No change in strokes.
Evaluation criteria for restoration resistance of decolored drawn lines at −50 ° C .:
○: No change in the decolored stroke. Do not restore.
Δ: There is a part of restoration. Or, the hue is restored thinly as a whole.
X: The drawn line is restored. Written strokes can be recognized.
-: Since the color was not erased by heating, the restoration resistance of the decolored drawn line was not evaluated.

As is clear from the results in Table 1 above, the writing lines of the inks of Examples 1 to 5 were immediately discolored by rubbing with the eraser and stored in a freezer at −50 ° C. for 3 hours. It was found that there was no re-coloring and excellent color development and stability over time.
On the other hand, it was found that the writing lines of the inks of Comparative Examples 1 to 3 were discolored for a moment by rubbing with the eraser, but immediately reappeared when the rubbing was stopped.
In Comparative Examples 4 and 5, there was no problem with color developability, stability over time, and color erasability, but the hue of the drawn line was erased by storing in a refrigerator at -50 ° C for 3 hours. Since it was found to be restored, there was a problem in the stability of the decolored stroke.
From the above, the thermosensitive decolorizable ink according to the present invention can decolor the writing lines by the heat of rubbing, and it does not recur even when stored at an extremely low temperature, and also develops color and stability over time. I found it excellent.

  A heat-decolorable ink composition that can be suitably mounted on a writing instrument such as a ballpoint pen or a marking pen is obtained.

Claims (10)

A thermal ink composition containing, as a colorant, at least a leuco dye, a developer, and a crystalline material comprising a crystalline substance selected from the following group A compounds , and further comprising a cholesterol derivative together with the colorant A color erasing agent comprising a crystalline substance selected from an agent or a cholesterol derivative and a compound of the following group A , and the developer particles and the color erasing agent are in a crystalline state without using a microcapsule. A heat-sensitive decolorizable ink composition for writing instruments, wherein the melting point is 40 to 150 ° C.
Group A: A chain molecule having 13 to 20 carbon atoms, a compound having at least one polar group of a hydroxyl group, an ester bond, an ether bond and an amide bond, paraffin wax, microcrystalline wax, polyethylene wax, polypropylene wax, behenyl alcohol The thermosensitive decolorizable ink composition for a writing instrument according to claim 1, wherein the cholesterol derivative is an alkyl ester of cholic acid. The heat-decolorable ink composition for a writing instrument according to claim 1 or 2 , wherein the decolorizer comprises fine particles having an average particle size of 10 to 2000 nm. Decolorizer is contained in the ink in the crystalline state, the thermal capacity, for writing instruments sensitive decolorable ink composition according to any one of claims 1-3, characterized in that at 10J / g or more object. The thermosensitive decolorizable ink composition for a writing instrument according to any one of claims 1 to 4 , wherein the content of the decolorizer is 5 to 30% by mass based on the total amount of the ink composition. . The heat-decolorable ink composition for a writing instrument according to any one of claims 1 to 5, wherein the developer particles are fine particles having an average particle diameter of 10 to 2000 nm. The heat-decolorable ink composition for a writing instrument according to any one of claims 1 to 6 , wherein the developer particles are contained in the ink in a crystalline state, and the heat capacity thereof is 10 J / g or more. object. The thermosensitive decolorizable ink composition for writing instruments according to any one of claims 1 to 7, wherein the content of the developer particles is 5 to 30% by mass with respect to the total amount of the ink composition. . A writing instrument, wherein the thermosensitive decolorizable ink composition for a writing instrument according to any one of claims 1 to 8 is mounted on the writing instrument. The writing instrument according to claim 9 , wherein the writing instrument is a ballpoint pen or a marking pen.