JP3792497B2 - Reversible thermochromic stamp ink composition - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a reversible thermochromic stamp ink composition. More specifically, the present invention relates to a reversible thermochromic stamp ink composition that exhibits good performance without losing the initial thermochromic function and stamp function over time.
[0002]
[Prior art]
Conventionally, dyes or pigments have been used as the colorant of the stamp ink composition, but no colorant exhibiting reversible thermal discoloration has been found.
Further, as the colorant exhibiting reversible thermochromic property, (a) an electron donating color-forming organic compound, (b) an electron-accepting compound, and (c) a reaction medium that determines the temperature at which the color reaction of both occurs is determined. A reversible thermochromic capsule pigment containing a reversible thermochromic composition containing the pigment can be exemplified, but the pigment generally has a large particle size. This is due to the relatively low color density at the time of color development of the reversible thermochromic composition contained therein. However, when the pigment having a large particle diameter is used for the stamping ink, the pigment is difficult to be led out from the gap of the stamp pad, and thus the image formed by imprinting on a support such as paper is faded. It causes a defect.
Further, when the printed image is discolored, the image may be peeled off by rubbing with a finger or the like.
Even if an attempt is made to reduce the particle diameter of the capsule pigment in order to solve the above-mentioned problems, the wall film also becomes thinner when the particle diameter is reduced, so that the water-soluble organic solvent having a low vapor pressure such as glycol or glycerin is used. It becomes poor in solvent resistance and tends to impair the reversible thermochromic function.
Further, the specific gravity of the capsule pigment is approximately 0.85 to 1.15, which is light in specific gravity compared with the water-soluble organic solvent and various additives contained in the vehicle, and thus stable in the ink. It is difficult to disperse, and the pigment is unevenly distributed over time, and the density of the printed image may vary.
[0003]
[Problems to be solved by the invention]
The present applicant intends to solve the above-mentioned problems. That is, the present applicant forms a clear image having excellent solvent resistance of the pigment and having a good thermal discoloration function and abrasion resistance. It is an object of the present invention to provide a reversible thermochromic stamp ink composition.
[0004]
[Means for Solving the Problems]
The present invention is an ink composition for a reversible thermochromic stamp comprising at least a reversible thermochromic microcapsule pigment, a water-soluble organic solvent, and water, wherein the reversible thermochromic microcapsule pigment comprises: An average particle diameter [(()) containing a reversible thermochromic composition containing a donating color-forming organic compound, (b) an electron-accepting compound, and (c) a reaction medium that determines the temperature at which the color reaction of the both occurs. (Major axis + minor axis) / 2] is 0.1 to 15 μm, reversible thermochromic composition / wall film = 7/1 to 1/1 (weight ratio), and the ink viscosity is 1000. An ink composition for a reversible thermochromic stamp exhibiting 10000 mPa · s is a requirement. Furthermore, it is a requirement that the reversible thermochromic microcapsule pigment has a non-circular cross-sectional shape having depressions.
[0005]
The reversible thermochromic microcapsule pigment is a conventionally known (a) electron-donating color-forming organic compound, (b) an electron-accepting compound, and (c) a reaction that determines the temperature at which the color reaction of both occurs. A medium in which a reversible thermochromic composition containing three essential components of a medium is encapsulated in a microcapsule is effective. Specifically, Japanese Patent Publication No. 51-44706, Japanese Patent Publication No. Sho, proposed by the present applicant. Those described in Japanese Patent Publication No. 51-44707, Japanese Patent Publication No. 1-29398, and the like can be used. The above color changes before and after a predetermined temperature (discoloration point), exhibits a decolored state at a temperature range above the discoloration point, and develops a color state at a temperature range below the discoloration point. Only one of the states can exist. That is, the other state is maintained while the heat or cold necessary to develop the state is applied, but when the heat or cold is not applied, the state returns to the state exhibited in the normal temperature range. _A heat decoloring type having a relatively small width (ΔH _A = 1 to 5 ° C.) can be exemplified, and a system in which ΔH _A is 3 ° C. or less [shown in Japanese Examined Patent Publication No. 1-29398 / In a system in which a fatty acid ester exhibiting a ΔT value (melting point-cloud point) is applied as a color-changing temperature adjusting compound], it is sensitive to temperature change at the color-changing point and exhibits high-sensitivity heat decoloring property, [Delta] H _a is after discoloration at 4 to 5 ° C. about the system, slowly return to the original aspect, it is possible to enhance the visibility effect.
In addition, the large hysteresis characteristics (ΔH described in Japanese Patent Publication No. 4-17154, Japanese Patent Application Laid-Open No. 7-179777, Japanese Patent Application Laid-Open No. 7-33997, Japanese Patent Application Laid-Open No. 8-39936, etc. proposed by the present applicant. _B = 5 to 50 ° C.), that is, the shape of the curve plotting the change in color density due to the temperature change is higher than the color change temperature range, contrary to the case where the temperature is raised from the lower temperature side than the color change temperature range. The color changes by following a path that differs greatly from the case of lowering from the low temperature side, the color development state in the low temperature range below the low temperature side discoloration point (t ₁ ), or the color disappearance in the high temperature range above the high temperature side color change point (t ₄ ). A color memory retention type thermochromic composition capable of storing and maintaining a color state in a specific temperature range [temperature range between t _{2 and} t ₃ (substantially two-phase retention temperature range)] is also applicable.
Further, as a heat-colorable composition, a specific color having a linear or side chain alkyl group having 3 to 18 carbon atoms as an electron-accepting compound proposed by the present applicant, which develops color when heated from a decolored state. A system to which an alkoxyphenol compound is applied (Japanese Patent Application Laid-Open Nos. 11-129623 and 11-5973) or a system to which a specific hydroxybenzoic acid ester is applied (Japanese Patent Application No. 11-286202) can also be mentioned. .
In the microcapsule, a non-thermochromic colorant is integrally encapsulated with the reversible thermochromic composition so as to exhibit a tautomeric color change from colored (1) to colored (2). You may have done.
[0006]
The reversible thermochromic microcapsule pigment applied to the present invention preferably has a non-circular cross-sectional shape, particularly a cross-sectional shape having a depression (see FIGS. 1 to 3). The specific-shaped pigment passes smoothly from the stamp pad, and can form a good thermochromic image on a support such as paper.
Furthermore, the printed image formed by the stamping has the above-mentioned microcapsule pigment closely oriented and fixed on the long diameter side (maximum outer diameter side) with respect to the support, and exhibits high color development. Even for applications where the thermochromic image is heated and discolored by applying an external force such as friction or scratching, the capsule pigment is slightly elastically deformed into a shape that relaxes the external force, and the destruction of the capsule wall film is suppressed. It can be expressed effectively without impairing the thermochromic function.
Here, the capsule pigment having a non-circular cross-sectional shape has an average particle diameter [(major axis + minor axis) / 2] of 0.1 to 15 μm, and a reversible thermochromic composition / wall film = 7/1 to 1/1 /. Must meet the range of 1 (weight ratio).
If the capsule pigment has an average particle diameter of more than 15 μm, the flowability from the stamp pad is lowered and it becomes difficult to form a desired image. Further, in a system of 0.1 μm or less, it is difficult to show a high density of color developability.
If the ratio of the reversible thermochromic composition to the wall film is larger than the above range, the thickness of the wall film becomes too thin, resulting in a decrease in resistance to solvent, pressure or heat, and conversely, the reversible heat of the wall film. When the ratio to the color changing composition is larger than the above range, the color density and sharpness during color development are inevitably lowered, and preferably the reversible thermochromic composition / wall film = 6/1 to 1/1 (weight) Ratio).
The ink can be mixed with a non-thermochromic dye or pigment so that a thermochromic image exhibiting tautomerism from colored (1) to colored (2) can be formed by temperature change. .
[0007]
For the microencapsulation of the reversible thermochromic composition, known means such as an interfacial polymerization method, an interfacial polycondensation method, an in situ polymerization method, and a coacervate method can be applied, but the particle size range satisfying the above-described requirements of the present invention. In order to obtain a capsule pigment having a non-circular cross-sectional shape, it is effective to apply an interfacial polymerization method or an interfacial polycondensation method that hardly causes aggregation and coalescence.
[0008]
Examples of water-soluble organic solvents include glycols such as glycerin, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, 1,3-butylene glycol, ethylene glycol monomethyl ether, and their lower alkyl ethers, 2-pyrrolidone, N-vinyl. Appropriate amounts of pyrrolidone, urea and the like can be blended.
[0009]
The reversible thermochromic stamp ink composition has an ink viscosity adjusted to 1000 to 10,000 mPa · s, preferably 1000 to 5000 mPa · s, and more preferably 1000 to 3000 mPa · s. Below 1000 mPa · s, the capsule pigment is difficult to stably disperse in the vehicle, and the capsule pigment is unevenly distributed over time, and the density of the print image tends to vary.
Also, if it exceeds 10,000 mPa · s, the ink supply through the stamp pad becomes insufficient, and the penetrating and drying properties of the ink on the paper surface also become poor. Ink is transferred to the image portion and the image looks worse.
[0010]
An appropriate amount of a binder resin is added to adjust the image fixing property and viscosity. The binder resin is selected from a resin emulsion, an alkali-soluble resin, and a water-soluble resin.
Examples of the resin emulsion include polyacrylic acid ester, styrene-acrylic acid copolymer, polyvinyl acetate, ethylene-vinyl acetate copolymer, ethylene-vinyl chloride copolymer, methacrylic acid-maleic acid copolymer, ethylene- Examples include aqueous dispersions such as methacrylic acid copolymers, α-olefin-maleic acid copolymers, polyesters, and polyurethanes. Examples of the alkali-soluble resins include styrene-maleic acid copolymers and ethylene-maleic acid copolymers. , Styrene-acrylic acid copolymer, and the like. Examples of the water-soluble resin include polyvinyl alcohol and polyvinyl butyral, and one or a mixture of two or more can be used.
[0011]
Also, xanthan gum, welan gum, succinoglycan (average molecular weight about 1 to 8 million) whose constituent monosaccharide is organic acid-modified heteropolysaccharide of glucose and galactose, guar gum, locust bean gum and its derivatives, hydroxyethyl cellulose, alginic acid alkyl ester , Polymers having an alkyl ester of methacrylic acid as the main component and a molecular weight of 100,000 to 150,000, glycomannan, thickening polysaccharides having gelling ability extracted from seaweeds such as agar and carrageenan, benzylidene sorbitol and benzylidene xylitol Or derivatives thereof, crosslinkable acrylic acid polymer, inorganic fine particles, polyglycerin fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyethylene glycol fatty acid ester, polyoxyethylene castor oil, poly Nonionic surfactants having an HLB value of 8 to 12, such as oxyethylene lanolin, lanolin alcohol, beeswax derivatives, polyoxyethylene alkyl ether, polyoxypropylene alkyl ether, polyoxyethylene alkyl phenyl ether, fatty acid amide, dialkyl or dialkenyl Examples thereof include salts of sulfosuccinic acid, which can be used alone or in combination.
Furthermore, it is also possible to add a compound exhibiting shear thinning, such as a mixture of N-alkyl-2-pyrrolidone and an anionic surfactant, a mixture of polyvinyl alcohol and an acrylic resin, to adjust the fixing property and viscosity of the image. it can.
[0012]
In addition, a pH adjuster, an antiseptic, or an antifungal agent can be added as necessary.
Examples of the pH adjuster include inorganic basic salts such as ammonia, sodium carbonate, sodium phosphate, sodium hydroxide and sodium acetate, and organic basic compounds such as water-soluble amine compounds such as triethanolamine and diethanolamine.
Examples of the preservative or antifungal agent include carboxylic acid, sodium salt of 1,2-benzisothiazolin-3-one, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl paraoxybenzoate, 2, 3, 5, 6 -Tetrachloro-4- (methylsulfonyl) pyridine and the like.
In addition, an antifoaming agent such as a fluorine-based surfactant that improves the permeability of the solvent, a nonion, an anion, a cationic surfactant, or dimethylpolysiloxane may be added.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
A reversible thermochromic stamp ink composition is added by adding various additives to a dispersed ink consisting of a microcapsule pigment encapsulating a reversible thermochromic composition, a water-soluble organic solvent, and water as necessary. obtain.
The ink composition may be impregnated in a stamp pad to supply ink to a stamp surface to be contacted, or may be contained in a stamp having a structure in which ink is directly supplied to a stamp surface having open cells. Can also be used.
[0014]
【Example】
Examples are shown below, but the present invention is not limited to these examples. Moreover, the form of the reversible thermochromic microcapsule pigment can be arbitrarily applied with the non-circular cross-sectional shape pigments illustrated in FIGS. 1 to 3 and may be a mixture of these forms of pigments. In addition, the part in an Example is a weight part.
[0015]
Example 1
2- (2-Chloroanilino) -6-di-n-butylaminofluorane 3 parts, 1,1-bis- (4-hydroxyphenyl) -2-ethylhexane 6 parts, cetyl caprate 25 parts, butyl stearate 25 parts of the reversible thermochromic composition was heated and dissolved, and 30 parts of an aromatic isocyanate prepolymer / ethyl acetate solution (prepolymer: 75% by weight) was added as a wall film material to add a uniformly dissolved solution. A stock solution of a microcapsule pigment containing a reversible thermochromic composition is obtained by adding it to 100 parts of a warm 15% by weight gelatin aqueous solution with stirring and emulsifying it into fine droplets, followed by further heating and reaction. It was. Subsequently, the stock solution was centrifuged to obtain a reversible thermochromic micro-capsule pigment [average particle size 1.5 μm, reversible thermochromic composition / wall film = 2.6 / 1.0].
25 parts of the reversible thermochromic microcapsule pigment is dispersed in a mixed solution consisting of 7 parts of water, 50 parts of glycerin and 10 parts of propylene glycol, and further 7 parts of oleic acid diethanolamide, 0.5 part of antifoaming agent, A reversible thermochromic stamp ink composition was obtained by adding 0.5 parts of a preservative and 1.0 part of a penetrant.
The viscosity of the ink composition measured at 25 ° C. using a B-type viscometer was 2000 mPa · s.
[0016]
A stamp pad was prepared by impregnating the ink composition with a sponge having open cells set on a substrate.
The stamp surface (made of rubber) was brought into contact with the sponge to deposit ink, and then pressed onto fine paper to form a printed image.
The image was colorless at room temperature (25 ° C.), but turned black when cooled to 15 ° C. or lower, and became colorless again when heated to 18 ° C. Note that the above-described change in appearance could be repeatedly performed due to a change in temperature.
Furthermore, even when the print image was repeatedly formed using the stamp, a print image that always showed a clear and good thermochromic function was obtained.
Even when the stamp pad was allowed to stand at 50 ° C. for 2 weeks, the thermal discoloration function and color density of the formed printed image were equivalent to the initial values.
[0017]
Example 2
Warming a reversible thermochromic composition comprising 3 parts of 1,3-dimethyl-6-diethylaminofluorane, 6 parts of 1,1-bis- (4-hydroxyphenyl) -2-ethylhexane and 70 parts of neopentyl stearate Dissolve and add 30 parts of an aromatic isocyanate prepolymer / ethyl acetate solution (prepolymer: 75% by weight) as a wall film material and stir the solution uniformly in 100 parts of a warmed 15% by weight gelatin aqueous solution. Then, the mixture was emulsified into fine droplets, and further heated and reacted to obtain a stock solution of a microcapsule pigment containing a reversible thermochromic composition. Subsequently, the stock solution was centrifuged to obtain a reversible thermochromic micro-capsule pigment [average particle size 4 μm, reversible thermochromic composition / wall film = 3.5 / 1].
15 parts of the reversible thermochromic microcapsule pigment is dispersed in a mixed solution consisting of 17 parts of water, 50 parts of glycerin and 10 parts of propylene glycol, and further 7 parts of oleic acid diethanolamide, 0.5 part of antifoaming agent, A reversible thermochromic stamp ink composition was obtained by adding 0.5 parts of a preservative and 1.0 part of a penetrant.
The viscosity of the ink composition measured at 25 ° C. using a B-type viscometer was 3000 mPa · s.
[0018]
A stamp pad was prepared by impregnating the ink composition with a sponge having open cells set on a substrate.
The stamp surface (made of rubber) was brought into contact with the sponge to deposit ink, and then pressed onto fine paper to form a printed image.
When the image was cooled to 15 ° C. or lower, it turned orange, and this state was stored and retained at room temperature (25 ° C.). Further, when it is heated to 32 ° C., it becomes colorless, and this state is stored and retained at room temperature (25 ° C.). When it was cooled again to 15 ° C., it turned orange, and this change in appearance could be repeated due to a change in temperature.
Furthermore, even when the print image was repeatedly formed using the stamp, a print image that always showed a clear and good thermochromic function was obtained.
Even when the stamp pad was allowed to stand at 50 ° C. for 2 weeks, the thermal discoloration function and color density of the formed printed image were equivalent to the initial values.
[0019]
Comparative Example 1
Using the reversible thermochromic composition of Example 1, a reversible thermochromic stamp ink composition was obtained by the same method except that the average particle size of the microcapsules was 20 μm.
The ink composition is impregnated into a sponge having open cells set on a base material to create a stamp pad, and the stamp surface (made of rubber) is brought into contact with the sponge so that the ink adheres thereto, and then is applied onto a high-quality paper. Press to form an image.
The initial image formed as described above had the same thermal discoloration function and color density as in Example 1. However, when the image was repeatedly formed using the stamp, an image with a low color density was obtained. Came to be formed. This is presumably because the capsules were clogged in the sponge and did not adhere to the marking surface because the microcapsules had a large particle size.
[0020]
Comparative Example 2
Using the reversible thermochromic composition of Example 1, the reversible thermochromic microcapsule pigment was prepared in the same manner except that the aromatic isocyanate prepolymer / ethyl acetate solution (prepolymer: 75% by weight) was 10 parts. An average particle size of 4 μm, a reversible thermochromic composition / wall film = 7.8 / 1] was obtained.
Using the reversible thermochromic microcapsule pigment, a reversible thermochromic stamp ink composition was obtained in the same manner as in Example 1.
The ink composition is impregnated into a sponge having open cells set on a base material to create a stamp pad, and the stamp surface (made of rubber) is brought into contact with the sponge so that the ink adheres thereto, and then is applied onto a high-quality paper. Press to form an image.
The initial image formed as described above had the same thermochromic function and color density as in Example 1. However, after the stamp pad was left at 50 ° C. for 2 weeks, the image formed in the same manner was used. The image did not color when cooled to below 15 ° C. This is because the ratio of the wall film of the microcapsule was less than that of the encapsulated thermochromic composition, the wall film strength was weak, and the discoloring function of the thermochromic composition was inhibited by glycerin or the like in the vehicle. Inferred.
[0021]
Comparative Example 3
Using the reversible thermochromic microcapsule pigment of Example 2, a reversible thermochromic stamp ink composition was obtained in the same manner except that 7 parts of oleic acid diethanolamide was replaced with water.
When the viscosity of the ink composition was measured at 25 ° C. using a B-type viscometer, it was 500 mPa · s.
The ink composition is impregnated into a sponge having open cells set on a base material to create a stamp pad, and the stamp surface (made of rubber) is brought into contact with the sponge so that the ink adheres thereto, and then is applied onto a high-quality paper. Press to form an image.
The initial image formed as described above had the same thermal discoloration function and color density as in Example 2. However, after the stamp pad was allowed to stand at 50 ° C. for 2 weeks, the image formed in the same manner was used. The image was not clear and faded.
This is because the viscosity of the ink is low, the capsule and the vehicle are separated in the sponge, the microcapsules with low specific gravity are unevenly distributed on the upper part of the sponge, and the vehicle is unevenly distributed on the lower part of the sponge, so that the ink does not adhere to the printing surface. Inferred.
[0022]
【The invention's effect】
INDUSTRIAL APPLICABILITY The present invention can provide an ink composition for a reversible thermochromic stamp that is excellent in the solvent resistance of a microcapsule pigment and that has a good thermochromic function and resistance to scratching and can form a clear image. .
In addition, since the reversible thermochromic microcapsule pigment has a non-circular cross-sectional shape having depressions, the printed image is closely fixed with the major axis side oriented on the paper surface, and a high density of clear thermochromic pigment. A sex image can be formed. Furthermore, when heat discoloration is caused by rubbing or rubbing the thermochromic image, the capsule wall film is durable against this type of external pressure.
[Brief description of the drawings]
FIG. 1 is an enlarged explanatory view of (a) appearance and (b) cross section showing an example of a reversible thermochromic microcapsule pigment applied to the reversible thermochromic aqueous ink composition of the present invention.
FIG. 2 is an enlarged explanatory view of (a) the appearance and (b) the cross section showing another example of the reversible thermochromic microcapsule pigment applied to the reversible thermochromic aqueous ink composition of the present invention.
FIG. 3 is an enlarged explanatory view of (a) the appearance and (b) the cross section showing another example of the reversible thermochromic microcapsule pigment applied to the reversible thermochromic aqueous ink composition of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Microcapsule pigment 11 Thermochromic composition 12 Wall film 13 Dimple

Claims (2)

An ink composition for a reversible thermochromic stamp comprising at least a reversible thermochromic microcapsule pigment, a water-soluble organic solvent, and water, wherein the reversible thermochromic microcapsule pigment comprises (a) an electron-donating color. Average particle diameter [(major axis + minor axis) encapsulating a reversible thermochromic composition containing a reactive organic compound, (b) an electron accepting compound, and (c) a reaction medium that determines the temperature at which the color reaction of both occurs. ) / 2] is 0.1 to 15 μm, reversible thermochromic composition / wall film = 7/1 to 1/1 (weight ratio), and the ink viscosity is 1000 to 10,000 mPa · s. An ink composition for a reversible thermochromic stamp. The ink composition for a reversible thermochromic stamp according to claim 1, wherein the reversible thermochromic microcapsule pigment has a noncircular cross-sectional shape having a depression.

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