Thermochromic pigment compositions

Abstract

A thermochromic pigment composition including: (A) at least one electron-donor organic dye compound, (B) at least one electron-acceptor compound, and (C) at least one compound corresponding to the following formula (I): in which: X is 0 or a single bond, Z is COO or OCO, R.sub.1 is O-alkyl or (CH.sub.2).sub.mCH.sub.3—R.sub.2 is OCO(CH.sub.2).sub.nCH.sub.3 or H, —y=0-3, —m=12-18; —p=8-18, and on the condition that, when X is 0, y is other than 0. The thermochromic pigment composition are also useable in thermochromic pigment microcapsules ink compositions including the thermochromic pigment microcapsules, and writing instruments including the ink compositions.

Claims

1. A thermochromic pigment composition comprising: (A) at least one electron-donor dye compound, (B) at least one electron-acceptor compound, and (C) at least one compound serving as a reaction medium capable of bringing about a reversible electron-acceptance/donation reaction attributable to compounds (A) and (B), the at least one compound corresponding to the following formula (I): ##STR00010## in which: X represents O or a single bond, Z represents COO or OCO, R.sub.1 represents O-alkyl or (CH.sub.2).sub.mCH.sub.3, R.sub.2 represents OCO(CH.sub.2).sub.nCH.sub.3 or H, y=0-3, m=12-18, n=12-18, p=8-18, and in the condition that when X is O, y does not equal 0, wherein the at least one electron-donor dye compound is present at from 1% to 10% by weight, wherein the at least one electron-acceptor compound is present at from 1% to 10% by weight, and wherein the at least one compound corresponding to the following formula (I) is present at from 70% to 98% by weight based on the total weight of the composition.

2. The thermochromic composition according to claim 1, wherein the at least one compound of the formula (I) corresponds to the following formula (I.sub.a): ##STR00011## in which: X represents O or a single bond, Z represents COO or OCO, R.sub.1 represents O—C.sub.1-6alkyl or (CH.sub.2).sub.mCH.sub.3, y=0-3, m=12-18, and p=8-18.

3. The thermochromic composition according to claim 2, wherein the at least one compound of the formula (I.sub.a) is a compound in which: X represents a single bond, Z represents OCO, R.sub.1 represents (CH.sub.2).sub.mCH.sub.3, y=0, m=12-18, and p=8-18.

4. The thermochromic composition according to claim 1, wherein the compound (A) is selected from the group consisting of 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide (Blue 63), 2′-(dibenzylamino)-6′-(diethylamino)fluorane, N,N-dimethyl-4-[2-[2-(octyloxy)phenyl]-6-phenyl-4-pyridinyl]benzenamine (Yellow CK37), 7-(4-diethylamino-2-hexyloxyphenyl)-7-(1-ethyl-2-methyl-1H-indol-3-yl)-7H-furo[3,4-b]pyridine-5-one (Blue 203), 2-(2,4-dimetylphenylamino)-3-methyl-6-diethylaminofluoran (Black 15), and 3,3-bis-(1-butyl-2-methyl-indol-3-yl)-3H-isobenzofuran-1-one (Red 40).

5. The thermochromic composition according to claim 1, wherein the compound (B) is selected from the group consisting of 2,2-bis(4-hydroxy-3-methylphenyl)propane (Bisphenol C), 4-hexyl-1,3-dihydrxybenzene (4-hexylresorcinol), 4,4′-cyclohexylidene bisphenol (BPZ), 4,4′-(1-phenylethylidene)bisphenol, 2,2′-dihydroxybiphenyl, 4,4′-(1,4-phenylenediisopropylidene)bisphenol, 1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane, 9,9-bis(4-hydroxyphenyl)fluorene, 4,4′-(1,3-phenylenediisopropylidene)bisphenol, 1,1,1-tris(4-hydroxyphenyl)ethan, 4,4′-(2-ethylhexylidene)diphenol, and α,α,α′-tris(4-hydroxyphenyl)-1-ethyl-4-isopropylbenzene.

6. A thermochromic pigment microcapsule containing the thermochromic pigment composition according to claim 1.

7. An ink composition containing a plurality of the thermochromic pigment microcapsule according to claim 6.

8. A writing instrument containing the ink composition according to claim 7.

9. The writing instrument according to claim 8, wherein the writing instrument is a friction erasable ballpoint ink pen.

Description

EXAMPLES

(1) Compounds (1), (2) and (3) of the following formulas:

(2) ##STR00008##
are prepared according to the following protocols:

Synthesis of the Compound (1)

(3) 15.9 of 3-pentadecylphenol (CAS No. 501-24-6) and 5.8 g of triethylamine (CAS No. 121-44-8) are solubilized in 250 mL of tetrahydrofuran (CAS No. 109-99-9). The reactive environment is kept at room temperature and is rendered inert by the addition of nitrogen. 10 g of decanoyl chloride (CAS No. 112-13-0) are added drop by drop for 15 minutes. After this addition, the reactive environment is stirred for 30 minutes at room temperature.

(4) The reactive environment is then extracted with 100 mL of ethyl acetate. The organic phase is recovered and washed with three times 150 mL of water. The organic phase is then dried on sodium sulphate and the solvent is evaporated.

(5) The product is recrystallized twice by ethanol. The analysis by gaseous-phase chromatography (GPC) of the product obtained shows that the product is 98% pure.

Synthesis of the Compound (2)

(6) 11.1 g of 3-pentadecylphenol (CAS No. 501-24-6) and 4.0 g of triethylamine (CAS No. 121-44-8) are solubilized in 150 mL of tetrahydrofuran (CAS No. 109-99-9).

(7) The reactive environment is kept at room temperature and is rendered inert by the addition of nitrogen. 10 g of palmitoyl chloride (CAS No. 112-67-4) are added drop by drop for 15 minutes. At the end of the addition, the reactive environment is stirred for 30 minutes at room temperature.

(8) The reactive environment is then extracted with 100 mL of ethyl acetate. The organic phase is recovered and washed with three times 150 mL of water. The organic phase is then dried on sodium sulphate and the solvent is evaporated.

(9) The product is recrystallized once by ethanol and once by isopropanol. The analysis by gaseous-phase chromatography (GPC) of the product obtained shows that the product is 94% pure.

Synthesis of the Compound (3)

(10) 10.0 g of 3-pentadecylphenol (CAS No. 501-24-6) and 3.7 g of triethylamine (CAS No. 121-44-8) are solubilized in 150 mL of tetrahydrofuran (CAS No. 109-99-9). The reactive environment is kept at 5° C. and is rendered inert by the addition of nitrogen. 10 g of stearoyl chloride (CAS No. 112-76-5) are added drop by drop for 15 minutes. At the end of the addition, the reactive environment is stirred for 30 minutes at room temperature.

(11) The reactive environment is then extracted with 100 mL of ethyl acetate. The organic phase is recovered and washed with three times 150 mL of water. The organic phase is then dried on sodium sulphate and the solvent is evaporated.

(12) The product is recrystallized twice by ethanol. The analysis by gaseous-phase chromatography (GPC) of the product obtained shows that the product is 98% pure.

(13) The condensation temperatures T.sub.FUS of the compounds (1), (2) and (3) obtained are measured by differential scanning calorimetry (DSC) using a device TA Instruments Q20 on a temperature range going from −50 to 100° C., at heating/cooling speeds of +/−20° C./minute. The temperatures measured are indicated in Table 1 below.

(14) TABLE-US-00001 TABLE 1 Formula T.sub.FUS compound (I) (° C.) Compound (1) 30 Compound (2) 47 Compound (3) 48

(15) Preparation of a Thermochromic Pigment Composition:

(16) A thermochromic pigment composition is prepared by mixing 2.2 parts by weight of 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide (compound (A), CAS No.: 69898-40-4), 2.2 parts by weight of 4,4′-(hexafluoroisopropylidene)diphenol (compound (B1) CAS No.: 1478-61-1), 2.2 parts by weight of 2,2-bis(4-hydroxy-3-methylphenyl)propane (compound (B2), CAS No.: 79-97-0), and 93.4 parts by weight of the compound (3) prepared beforehand (compound (C)):

(17) ##STR00009##

(18) The mixture obtained is heated and stirred at a temperature of 110° C. for 45 minutes, until the compounds (A), (B1) and (B2) are fully solubilized in the compound (C).

(19) Preparation of the Thermochromic Pigment Microcapsules:

(20) 7.2 parts by weight of an aqueous solution of an anhydride maleic copolymer and methylvinylether (solution at 33% by weight of copolymer) are neutralized with 8.4 parts by weight of a sodium hydroxide aqueous solution (solution at 1.0 M). This solution is diluted with 42.0 parts by weight of water, and the mixture emulsified with a homogenizer at a speed of at least 15 m.Math.s.sup.−1. 26.0 parts by weight of the previously prepared thermochromic pigment composition are added, and the emulsion obtained is now at a temperature of 85° C. for 30 minutes. 16.4 parts by weight of a pre-polymer melamine-formaldehyde (aqueous solution at 50% by pre-polymer weight) are then added to the mixture drop by drop. The reactive environment is then heated to a temperature of 90° C. and mixed at a speed of at least 15 m.Math.s.sup.−1 for 4 hours.

(21) A slurry formed of microcapsules of thermochromic pigment dispersed in an aqueous solvent is obtained, the microcapsules having a diameter d90 of 4.6 μm, determined using a Zetasizer Nano ZS system by Malvern Instruments with an illumination at 632 nm.

(22) The thermochromic pigment microcapsules obtained change color from blue to colorless above 48° C. with a color hysteresis effect.

(23) TABLE-US-00002 TABLE 2 Transition temperatures of the prepared thermochromic pigment microcapsules Change in color from color to colorless T1 (° C.) T2 (° C.) T3 (° C.) T4 (° C.) T.sub.H (° C.) T.sub.G (° C.) ΔH Thermochromic Blue .fwdarw. colorless 15 20 35 48 17 42 25 pigment microcapsules containing the compound (3)

(24) The transition temperatures measured are the following:

(25) T1: complete recoloration temperature

(26) T2: partial recoloration temperature

(27) T3: partial discoloration temperature

(28) T4: total discoloration temperature

(29) $T_H=\frac{T1+T2}{2},T_S=\frac{T3+T4}{3},$

(30) ΔH=hysteresis range=T.sub.G−T.sub.H