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 responding to the following formula (I), in which: R.sub.1 is H or a phenyl group, —R.sub.2 is H or a phenyl group, and -n=1-8. The thermochromic pigment composition includes thermochromic pigment microcapsules ink compositions including such thermochromic pigment microcapsules, and writing instruments including such ink compositions.

Claims

1. A thermochromic pigment composition comprising: (A) at least one electron-donor organic dye compound, (B) at least one electron-acceptor compound, and (C) at least one compound responding to the following formula (I): ##STR00009## wherein: R.sub.1 represents H or a phenyl group, R.sub.2 represents H or a phenyl group, and n=1-8.

2. The thermochromic pigment composition according to claim 1, wherein the compound (C) responds to the following formula (I.sub.a): ##STR00010## wherein n=1-8.

3. The thermochromic pigment composition according to claim 1, wherein the compound (C) responds to the following formula (I.sub.b): ##STR00011## wherein n=1-8.

4. The thermochromic pigment composition according to claim 1, wherein 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, CAS no.: 69898-40-4), 2′-(dibenzylamino)-6′-(diethylamino)fluorane (CAS no.: 34372-72-0), N,N-dimethyl-4-[2-[2-(octyloxy)phenyl]-6-phenyl-4-pyridinyl]benzenamine (Yellow CK37, CAS no.: 144190-25-0), 7-(4-diethylamino-2-hexyloxyphenyl)-7-(1-ethyl-2-methyl-1H-indol-3-yl)-7H-furo[3,4-b]pyridine-5-one (Blue 203, CAS no.: 98660-18-5), 2-(2,4-dimethylphenylamino)-3-methyl-6-diethylaminofluoran (Black 15, CAS no.: 36431-22-8) and 3,3,-bis-(1-butyl-2-methyl-indol-3-yl)-3H-isobenzofuran-1-one (Red 40, CAS no.: 50292-91-6).

5. The thermochromic pigment 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, CAS no.: 79-97-0), 4-hexyl-1,3-dihydroxybenzene (4-hexylresorcinol, CAS no.: 136-77-6), 4,4′-cyclohexylidenebisphenol (BPZ, CAS no.: 843-55-0), 4,4′-(hexafluoroisopropylidene)diphenol (Bisphenol AF, CAS no.: 1478-61-1), 4,4′-(1-phenylethylidene)bisphenol (CAS no.: 1571-75-1), 2,2′-dihydroxybiphenyl (CAS no.: 1806-29-7), 4,4′-(1,4-phenylenediisopropylidene)bisphenol (CAS no.: 2167-51-3), 1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane (CAS no.: 2362-14-3), 9,9-bis(4-hydroxyphenyl)fluorine (CAS no.: 3236-71-3), 4,4′-(1,3-phenylenediisopropylidene)bisphenol (CAS no.: 13595-25-0), 1,1,1-tris(4-hydroxyphenyl)ethane (CAS no.: 27955-94-8), 4,4′-(2-ethylhexylidene)diphenol (CAS no.: 74462-02-5), and α,α,α′-tris(4-hydroxyphenyl)-1-ethyl-4-isopropylbenzene (CAS no.: 110726-28-8).

6. A thermochromic pigment microcapsule comprising a composition according to claim 1.

7. An ink composition comprising thermochromic pigment microcapsules according to claim 6.

8. A writing instrument comprising an ink composition according to claim 7.

9. The writing instrument according to claim 8 chosen from among friction-erasable ink pens.

Description

EXAMPLES

[0090] The compounds (1) and (2) of the following formulas:

##STR00007##

are prepared according to the following protocols:

Synthesis of Compound (1)

[0091] 10 g of 1,10-decanediol (CAS no.: 112-47-0), 52 g of 3,3-diphenylpropionic acid (CAS no.: 606-83-7), and 200 mg of p-toluenesulfonic acid (PTSA) monohydrate (CAS no.: 6192-52-5) are mixed and headed to 140° C. for 6 hours, under reduced pressure (400 mbar).

[0092] The reaction medium is then made soluble in 150 ml of ethyl acetate. The organic phase is recovered and washed three times with 150 ml of water. The organic phase is then dried on sodium sulfate and the solvent is evaporated.

[0093] The product is recrystallized once using isopropanol and once using ethanol. The gaseous phase chromatography (GPC) analysis of the product obtained reveals that the product is pure at 95%.

Synthesis of Compound (2)

[0094] 10 g of 1,10-decanediol (CAS no.: 112-47-0), 34.2 g of 3-phenylpropionic acid (CAS no.: 501-52-0), and 200 mg of p-toluenesulfonic acid (PTSA) monohydrate (CAS no.: 6192-52-5) are mixed and headed to 160° C. for 6 hours, under reduced pressure (400 mbar).

[0095] The reaction medium is then made soluble in 150 ml of ethyl acetate. The organic phase is recovered and washed three times with 150 ml of water. The organic phase is then dried on sodium sulfate and the solvent is evaporated.

[0096] The product is recrystallized once using isopropanol and once using ethanol. The gaseous phase chromatography (GPC) analysis of the product obtained reveals that the product is pure at 95%.

[0097] The fusion temperatures TFUS of the compounds (1) and (2) obtained are measured using differential scanning calorimetry (DSC) with a TA Instruments Q20 device, for a temperature range from −50 to 100° C., at cooling/heating speeds of +/−20° C./minute. The temperatures measured are indicated in Table 1 below.

TABLE-US-00001 TABLE 1 Compound of formula (I) T.sub.FUS (° C.) Compound (1) 71 Compound (2) 35

Preparation of a Thermochromic Pigment Composition

[0098] A thermochromic pigment composition is prepared by mixing 1.9 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), 2.1 parts by weight of 4,4′-(hexafluoroisopropylidene)diphenol (compound (B1) CAS no.: 1478-61-1), 2.1 parts by weight of 2,2-bis(4-hydroxy-3-methylphenyl)propane (compound (B2), CAS no.: 79-97-0) and 93.9 parts by weight of a compound of formula (I) according to the disclosure (compound (1)) (compound (C)):

##STR00008##

[0099] The mixture obtained is heated, under agitation, to a temperature of 110° C. for 45 minutes, until the compounds (A), (B1) and (B2) have been completely solubilized into the compound (C).

Preparation of Thermochromic Pigment Microencapsules

[0100] 7.7 parts by weight of an aqueous solution of a copolymer of a maleic anhydride and methyl vinyl ether (33% solution by weight of the copolymer) are neutralized with 10.5 parts by weight of an aqueous solution of sodium hydroxide (1.0 M solution). This solution is diluted with 39.5 parts by weight of water, and the mixture emulsified with a homogenizer at a speed of at least 15 m.Math.s.sup.−1.Math.25.3 parts by weight of the thermochromic pigment composition prepared before are added, and the emulsion obtained is kept at a temperature of 90° C. for 30 minutes. 17.0 parts by weight of a melamine-formaldehyde pre-polymer (50% aqueous solution by weight of the pre-polymer) are then added dropwise to the mixture. The reaction medium 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.

[0101] A slurry made up of thermochromic pigment microcapsules dispersed in an aqueous solvent is obtained, the microcapsules having a D90 diameter of 3.8 μm, determined using a Malvern Zetasizer Nano ZS system with an illumination of 632 nm.

[0102] The thermochromic pigment microcapsules obtained have the property of changing colors from blue to colorless beyond 71° C. with a color hysteresis effect.

Determination of the Decoloration and Recoloration Temperatures of the Thermochromic Pigment Microcapsules Prepared

[0103] The transition temperatures of the thermochromic pigment microcapsules obtained are measured using differential scanning calorimetry (DSC) with a TA Instruments Q20 device, for a temperature range from −50 to 100° C., at cooling/heating speeds of +/−20° C./minute. The temperatures measured are indicated in Table 2 below.

TABLE-US-00002 TABLE 1 Transition temperatures of the thermochromic pigment microcapsules Color change colored T1 T2 T3 T4 T.sub.H T.sub.G Δ .Math. colorless (° C.) (° C.) (° C.) (° C.) (° C.) (° C.) H Prepared blue .Math. −24 −10 40 71 −17 55 72 thermo- colorless chromic pigment micro- capsules
The transition temperatures measured are as follows:
T1: complete recoloration temperature,
T2: partial recoloration temperature,
T3: partial decoloration temperature,
T4: complete decoloration temperature,

[00001]$T_H=\frac{\left(T.Math.1+T.Math.2\right)}{2}$$T_G=\frac{\left(T.Math.3+T.Math.4\right)}{2}$

ΔH=hysteresis range=T.sub.G−T.sub.H