Compound for use in colour change compositions

Novel reaction media for electron donating and electron accepting components in colour-change compositions are described. The compound is of formula (VI); R1, and R2 are independently selected from an optionally substituted linear or branched alkyl group, alkenyl group, alkoxy group, aryl group and an alkylene aryl group having from 5 to 22 carbon atoms; X1 and X2 are independently selected from —OC(O)—, —CO2— and O; Y1, and Y2 are independently selected from hydrogen, halogen, R1, —OR1; y is independently 0 or 1; and suitably the groups R1X1— and —X2R2 are independently in the ortho or meta position. The compounds are useful in ink compositions, writing implements containing the compound and medical and industrial applications in which temperature sensitive colour change may be required.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a U.S. National Stage of International PCT Application No. PCT/EP2016/070838, filed Sep. 5, 2016 and claims the benefit of priority to Great Britain Application No. 1515610.2, filed Sep. 3, 2015, the disclosures of which are hereby incorporated by reference in their entireties.

FIELD OF THE INVENTION

This invention relates to a compound for use in a colour-change composition, preferably a thermochromic composition, a microencapsulated colour material, such as a pigment comprising the colour-change composition and an article comprising the said composition or microencapsulated pigment.

Colour change compositions are widely known and change between a discoloured state and coloured state colour or between a first and second coloured state. Colour-change compositions may change colour upon the application of energy for example with a change in temperature or with a change in pressure. Colour-change compositions which change colour with a change in temperature are widely known as thermochromic compositions. Colour-change compositions may also be referred to as colour memory compositions.

In this specification, reference will be made to change between a discoloured and coloured state for convenience but this also encompasses a change between a first coloured state and a second coloured state. Colour-change compositions typically comprise an electron-donating colour-developing organic compound or leuco dye, an electron-accepting compound or colour developer and a compound acting as a reaction medium for reversible electron exchange between the electron-accepting and electron-donating compounds or colour change temperature regulator. The components of the composition are typically micronized or enclosed in microcapsules and may be formulated to produce an ink composition. The composition may be employed in any applications in which temperature dependent colour-change is required or desirable for example in toys, printed materials, decoration, writing instruments, temperature indicators in packaging of medical products such as vaccines and in a wide range of industrial applications such as in curing or bonding processes, pipes, measurement of surface temperature, indication of overheating for example of machinery, plant or the like.

Thermochromic compositions reversibly change colour or change between a coloured and discoloured state when subjected to a change in temperature of a sufficient magnitude. Typically, an increase in temperature will lead to the ink having a discoloured state while cooling will lead to reappearance of colour. As temperature increases, the thermochromic composition will retain colour until the temperature reaches a maximum temperature for retention of the complete coloured state, known as the “maximum colour-retaining temperature” or T3as shown inFIG.1of the accompanying drawings. The composition will then become progressively discoloured as the temperature increases until it reaches a completely discoloured state at a temperature known as the “complete discolouring temperature” or T4, the minimum temperature for achieving the completely discoloured state. The mean temperature between T3and T4is known as TG.

As the thermochromic composition cools from a discoloured state, the composition remains discoloured until a temperature is reached below which colour reappears, known as the “minimum discoloured state retaining temperature) or T2as the temperature decreases, colour reappears fully at a temperature known as the “complete colouring temperature” or T1. The mean temperature between T1and T2is referred to as TH. The thermochromic composition has a hysteresis width, known as ΔH which is the temperature difference between THand TG.

As the composition is subject to heating or cooling, the coloured state or discoloured state of the thermochromic composition may be retained after removal of the source of heat or cold required for respectively discoloration or coloration. Depending on whether the composition approaches a particular temperature from a lower or higher temperature, the composition may be coloured or discoloured at that particular temperature.

Where the thermochromic composition is heated above a certain temperature, in the discoloured state, the coloured state may not reappear on cooling the composition until temperature T1is reached. This may be referred to as the “locking temperature” This provides a means of determining whether the composition has been subjected to the locking temperature which may be beneficial especially in medical applications or other applications where health or safety considerations are important. The hysteresis width, locking temperature and the minimum temperature at which colour reappears are dependent on the components of the composition.

BACKGROUND ART

U.S. Pat. No. 7,494,537 B2 describes thermochromic colouring colour-memory compositions comprising an electron donative colouring organic compound (A), an electron accepting colouring organic compound (B) to form the thermochromic and (C) a reaction medium of formula I, II or III below:

The components of the composition may be selected to achieve a desired colour memory effect and hysteresis width and T4 temperature dependent on the intended use.

There remains a need for Colour-change compositions and especially thermochromic compositions which provide good thermal and chemical stability and a large hysteresis width. We have now found that novel compounds of a certain structure provide an excellent combination of characteristics suitable for use in a colour-change composition including compatibility with a wide range of electron accepting and electron donating components and enabling control of the colour and discolour characteristics of the composition, stability and which may be tailored to provide desired hysteresis characteristics and flexibility in formulating the colour-change composition.

SUMMARY OF THE INVENTION

In a first aspect, the invention provides a compound (VI):

wherein R1, and R2are independently selected from an optionally substituted linear or branched alkyl group, alkenyl group, alkoxy group, aryl group and an alkylene aryl group; preferably having from 5 to 22 or 6 to 22 carbon atoms, preferably C5-22alkyl or C1-12alkylene or aryl, especially C9to C17alkyl for example C6alkyl, C10alkyl, C12alkyl, C14alkyl, C16alkyl, C1-4alkylene and phenyl;X1and X2are independently selected from —OC(O)—, —CO2— and O;Y1and Y2are independently selected from hydrogen, halogen, R3, and —OR3wherein R3is selected from hydrogen and an optionally substituted linear or branched hydrocarbyl group, preferably alkyl group, cycloalkyl group, alkenyl group and alkoxy group; especially hydrogen, C1-10alkyl, more preferably hydrogen and C1-4alkyl, for example methyl; andy is 0 or 1

provided that where R1X1— and/or —X2R2is in the para position, X1and X2are is independently selected from —OC(O)— and —CO2— and where Y1and/or Y2is in the para position Y1and Y2are not OR3.

We have found that a compound which conformationally is not planar provides an excellent hysteresis width whereas corresponding compounds which are planar do not provide as beneficial hysteresis characteristics. The compound is preferably non planar.

Preferably the compound has a hysteresis width of at least 10 degrees, more preferably at least 20 degrees and desirably at least 30 degrees, for example 40 degrees or more.

Accordingly, the groups R1X1— and —X2R2, where present, are independently in the ortho or meta position to provide a non-planar compound. Corresponding compounds in which the R1X1— and —X2R2are in a para position provide much less advantageous hysteresis characteristics. Preferably both groups R1X1— and —X2R2are in the ortho position.

In a preferred embodiment, when Y1and/or Y2are in the para position Y1and Y2are independently selected from hydrogen, halogen and R3, and more preferably hydrogen and C1-4alkyl, for example methyl.

In a preferred embodiment, compound (VI) is selected from:

and Compound VIb:

wherein R1and R2, are independently selected from aryl for example phenyl, C5-22alkyl, preferably C7-22alkyl, especially C9or C10to C18alkyl for example C14alkyl and alkylene aryl of formula —[CH2]zAr where z is from 1 to 6 and Ar is optionally substituted phenyl, for example —[CH2]2C6H5.

In another preferred embodiment the compound of formula (VIa) is a compound of the following formula (VIa1), (VIa2) or (VIa3):

The term “optionally substituted” as employed herein means that the group or moiety may be substituted with one or more substituents but preferably is unsubstituted. If a substituent is present, it may be selected a group containing a heteroatom but is preferably a hydrocarbyl group containing only hydrogen and carbon atoms. Examples of substituents include nitro, chloro, fluoro, bromo, nitrile, hydroxyl, thiol, a carboxylic acid group, a carboxylic ester group, C1-22-alkoxy, C1-22-alkyl, C1-22-alkenyl, C1-14aryl or C1-6alkaryl, amino, amino C1-22-alkyl and amino di (C1-22-alkyl).

The term aryl refers to a five or six membered cyclic, 8-10 membered bicyclic or 10-14 membered tricyclic group with aromatic character and includes groups which contain only hydrogen and carbon atoms and also heteroaromatic groups which contain hydrogen, carbon and one or more heteroatoms, for example, N, O or S. Examples of suitable aryl groups include phenyl, pyridinyl and furanyl. Where the term “alkylaryl” is employed herein, the immediately preceding carbon atom range refers to the alkyl substituent only and does not include any aryl carbon atoms. Examples of alkaryl groups include benzyl, phenylethyl and pyridylmethyl. Advantageously the aryl group is a phenyl group.

In preferred embodiments, optional substituents are selected from halogen, for example chlorine, halo alkyl, for example C1-6halo alkyl and C1-4alkoxy, for example methoxy

The phenyl moieties of compound (VI) may independently be unsubstituted where Y1and Y2are hydrogen or substituted by one or more groups of Y1and Y2other than hydrogen.

Each aryl ring of compound (VI), may have 2 or more Y1and Y2substituents respectively. Where one or more aryl ring has 2 or more substituents, the substituents are suitably selected from hydroxyl and C1-4alkyl, preferably methyl.

The compounds of formula (VI) as defined above are particularly useful as components of a colour change, preferably thermochromic, composition. The invention provides for use of a compound of of formula (VI) as defined above in a colour-change composition, preferably thermochromic composition.

The invention provides in a further aspect a colour change, preferably thermochromic, composition comprising: A) an electron donating organic colouring compound, B) an electron accepting compound and C) a compound of formula (VI) as defined above

Compositions and pigments according to the invention provide a wide hysteresis and a tuneable hysteresis. By varying the colour-change composition formulation the width of the hysteresis may be varied and the complete decolouring temperature T4 may be varied, allowing excellent flexibility in the design of the colour-change microcapsule pigment.

Any suitable known or future electron donating colouring compounds, component A) of the composition and conventionally known as a colour former, may be employed. Examples of suitable classes of compounds include indolyles, phthalides, azaphthalides, fluorans, styrylquinoline and diazarhodamine lactones.

Advantageously, component A) is selected from the group consisting of 3-(4-diethylamino-2-hexyloxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide, 2′-chloro-6′-diethylaminofluoran, 6′-(diethylamino)-2′-(phenylamino)-3H-spiro[2-benzofuran-1,9′-xanthen]-3-one, 3,3-bis(1-n-butyl-2-methylindol-3-yl)phthalide and 2-(2-chloroanilino)-6-di-n-butylaminofluoran.

Any suitable known or future electron accepting group component B) of the composition may be employed. Examples of suitable classes of compounds include compounds having labile or active protons, pseudo-acidic compounds, or electron voids. Examples of classes of compounds having active protons include compounds having a phenolic group such as mono- and poly-phenols bearing substituents known in the art and their metal salts.

Examples of suitable component B) compounds include:

Advantageously component B) can be a mixture of at least two of the above-mentioned component. Advantageously component B) is selected from the group consisting of 2,2-bis(4′-hydroxyphenyl)hexafluoropropane, 1,1-bis(4′-hydroxyphenyl)-2-methylpropane and mixture thereof, more advantageously it is a mixture of 2,2-bis(4′-hydroxyphenyl)hexafluoropropane and 1,1-bis(4′-hydroxyphenyl)-2-methylpropane

Suitably, the ratio of components B) to C) In parts by weights is in the range 0.5 to 40 and preferably within 1 to 20. The ratio of components A) to C) In parts by weights is suitably in the range 0.5 to 30 and preferably within 1 to 20.

Each component may comprise 2 or more components. Conventional additives for example emulsifiers, antioxidants, UV absorbers, metal chelates may also be included in the composition.

We have found that by including a non-ionic surfactant in the composition, improved stability against colour change when the composition is subjected to pressure in the clear state may be secured.

The invention provides in a further aspect for the use of a non-ionic surfactant in a colour-change composition or a colour change microencapsulated pigment, preferably according to the invention, which has a coloured state and a clear state to provide increased stability or resistance to colour-change when subjected to pressure, particularly when the composition is in a clear or colourless state.

The term “surfactant” refers to a compound which has a hydrophilic group or region and a hydrophobic group or region. The non-ionic surfactant is preferably an alkoxylate which has a hydrophobic terminal group.

The hydrophobic terminal group is suitably a hydrocarbyl and preferably an alkyl, group. The alkyl group is preferably a C1to C22group, more preferably C7to C22especially a C9to C15group for example a mixed C9/C11group and a mixed C13/C15group. The alkyl group is suitably derived from an alcohol or an amine, preferably a primary amine.

The alkoxylate is suitably based on multiple units of alkylene oxide and is preferably an ethoxylate, a propoxylate, a butoxylate or a mixture of two or more alkoxylates. Preferably the alkoxylate is an ethoxylate. The mixture may be a random or block arrangement of the different alkoxylates. The alkoxylate preferably comprises from 2 to 30, more preferably 2 to 15 and desirably 3 to 12 alkylene oxide units.

Suitably the non-ionic surfactant has a formula Q:
R′[Het][(CH2)qO]rR″  (Q)

wherein R′ is a hydrocarboyl, for example an alkyl group, alkenyl group, aryl group and alkylaryl group having from 1 to 22 carbon atoms, more preferably a C1to C22group, more preferably a C7to C22and especially a C9to C15alkyl, alkenyl or alkylaryl group; Het is O, S or NH or NR′; g is 2 to 4, preferably 2; r is 2 to 30, preferably 3 to 12; and R″ is selected from R′ and H.

The non-ionic surfactant may be “end-capped” which refers to the case where R″ is selected from the substituents defining R′. The terminal groups R′ and R″ may be the same or different.

Suitably, the non-ionic surfactant has a molecular weight from 300 to 1500, preferably 500 to 1000. Preferably the non-ionic surfactant comprises an alcohol alkoxylate.

Examples of suitable non-ionic surfactants include those available under the BIOSOFT trade name from Stepan, the LUTENSOL trade name from BASF, the EMULSOGEN and GENAPOL trade names from Clariant and products available under the EMPILAN, HYDRAPOL, SURFONIC, BIONIC and TERIC trade names from Huntsman.

FIG.1of the accompanying drawings shows a typical hysteresis profile for a reversible colour-change composition. Colour density is plotted against temperature. The colour density advancement due to temperature change on heating and cooling cycles is illustrated and progresses in the direction of the arrow. Point A at T4 is the fully decolourised state (herein will be called fully decolorized temperature); point B at T3 is the point at which the composition is in a fully coloured state during heating. Point C shows the last point at which the composition is fully discoloured during cooling at T2; Point D is the point at which the composition is in a fully coloured state during cooling at T1 ((herein will be called fully coloured temperature). It will be apparent that the thermochromic composition may be in fully coloured state or a fully discoloured state at a said temperature between T2 and T3 depending on whether the composition is being heated from a lower temperature or cooled form a higher temperature. The difference between temperatures T3 and T2 (ΔHT3-T2) is the practical value for hysteresis (herein will be called practical hysteresis).

The difference between T1 and T2 (ΔHT2-T1) is related to the sensitivity of the colour change mechanism. The lower the value of ΔHT2-T1, the sharper the transition between the last point of the fully coloured state and the fully discoloured state and also the sharper the transition between last point of the fully discoloured state and the fully coloured state. Colour density difference or colour contrast is measured by the difference of colour between E and F as shown inFIG.1.

The components A), B) and C) of the composition may be selected and the relative amounts employed to tailor properties of the composition to the desired use. The component is suitably selected to provide the desired practical hysteresis and the sensitivity of the colour change, as well as the temperature T1 and T4.

Suitably, the practical hysteresis range may be from 10 to 80° C. and preferably is at least 50° C. The fully coloured temperature T4 is suitably higher than ambient temperature, preferably higher than 50° C. The fully decolorized temperature T1 is suitably lower than 20° C., preferably lower than 0° C.

The composition of the invention suitably comprises a homogeneous solubilised mixture of the components A), B) and C) of the composition. Preferably, components A) and B) are dissolved in component C) to produce the composition.

Component C is suitably synthesised by stirring a mixture of 1 mole of biphenol and 2.5 moles of triethyl amine in acetone and cooling to 5° C. 2.2 moles of acid chloride is added gradually so that temperature does not rise above 35° C. during the addition. After the addition is complete the reaction is brought to room temperature and stirred for 24-48 hours. The resulting reaction medium is then poured into 7% aqueous ice cold HCI. The precipitate is filtered off and washed with water and saturated sodium bicarbonate solution. The solid precipitate is crystallised from isopropanol. Suitably, the relative quantities of biphenol/acid chloride/triethylamine are 1/2.2/2.5 moles. Biphenol is available from Chemos (Germany).

US 644124881 and Wiley Organics “Preparation of biphenols by oxidative coupling of alkylphenols using copper catalyst” describe the synthesis of biphenols.

Suitably, the colour-change composition is microencapsulated to provide a colour-change microcapsule pigment by a known method.

The invention further provides a colour-change microencapsulated pigment comprising a composition according to the invention which is microencapsulated. Suitably, the composition is homogeneous. Preferably the composition comprises components A), B), C) and a non-ionic surfactant to provide improved stability or resistance to colour-change in the clear state as described above.

The microcapsules suitably have a particle size from 0.5 to 50 microns, preferably 1 to 20 microns so as to provide suitable dispersion stability and processing characteristics whilst providing high density colour.

Unless otherwise stated, all particle sizes referred to herein are measured by volume using a Coulter particle size analyser by laser diffraction, All figures given for particle size represents the 90% fraction of particles showing diameter no larger than the specified size.

The composition may be microencapsulated by any known method, for example by using isocyanate interfacial polymerisation, melamine or urea formaldehyde interfacial polymerisation, free radical interfacial polymerisation, polycondensation of epoxy or complex coacervation.

Microencapsulation allows the colour-change composition to retain its composition when in contact with chemicals or heat. Chemicals are blocked by the microcapsule walls and the formulation of the composition is retained. The microencapsulation may also have a practical benefit on the way the colour-change composition performs.

The microencapsulated pigment enables the colour-change colour memory composition to be used in paint, coating and plastic vehicle either as water based pigment dispersion or a pigment powder. The composition or microencapsulated pigment may be employed in any applications in which temperature dependent colour-change is required or desirable for example in toys, printed materials, decoration, writing instruments, temperature indicators in packaging of medical products such as vaccines and in a wide range of industrial applications such as in curing or bonding processes, pipes, measurement of surface temperature, indication of overheating for example of machinery, plant or the like.

As further examples, the compositions and pigments of the present invention may be employed in inks for multiple printing mode offset, flexo, gravure, screen, 3D printing, pad printing, spray coating and other coating modes and ink jet. The compositions and pigments may be provided as an ink composition for use in writing implements such as ball point pen, marking pen, fountain pen, gel pen, roller ball pen and other inks vehicles.

In a further aspect of the invention, there is provided an ink composition for a writing implement which comprises a colour-change microencapsulated pigment according to the invention.

Advantageously, the ink composition may contain also a carrier, such as a solvent for example an aqueous or organic solvent, advantageously an aqueous solvent. The ink composition may also contain other additives known to one skilled in the art to be useful for preparing an ink composition for example a dispersing agent, an emulsifying agent, a surface-tension modifier, a surfactant, an humectant, a resin, a biocide and the like.

The invention further provides a writing implement comprising a writing implement containing an ink composition according to the invention.

In particular the writing implement may be a ball point pen, a marking pen, a fountain pen, a gel pen or a roller ball pen.

Advantageously the writing implement contains a means for erasing the ink composition.

In a further aspect, the invention provides in combination, a writing implement adapted to receive an ink composition according to the invention and an ink composition for charging to the writing implement.

The colour-change composition or pigment may be used in vehicles such as wax, polymer resins, thermosetting resins where the melt blending of the colour-change colour memory pigment allows manufacturing of pellet, powder of moulded or injected articles such as toys.

The present memory colour-change composition pigment can give memory colour change property to a variety of different substrates and materials: gel, inks, paper, synthetic paper, coated paper, fiber, plastics, glass metal ceramic, wood, stone, plastics, concrete, synthetic glass.

Colour-change compositions of the invention are especially useful in the production of printing inks for preparation of labels to provide a temperature indicator. Prior art with conventional colour-change compositions typically indicate when a particular temperature is reached without any further indication.

A colour-change composition or pigment of this invention provides an indication of when temperature T4 is exceeded by remaining colourless, until the composition is subjected to temperature T1 and regaining colour at this point.

The invention provides a colour-change composition or pigment where component C) is such that the composition or pigment temperature has a T2 temperature at a first temperature, for example 0° C. and a T3 temperature above a second temperature, for example 50° C.

A composition with these characteristics allows the design of an indicator which provides an indication of whether the indicator has been subjected to a particular temperature.

The invention further provides an indicator comprising a first portion of a colour-change composition in its coloured state and a second portion of the same colour-change composition in its discoloured state wherein the composition is according to the present invention.

Suitably, the indicator is printed with a memory composition pigment, preferably converted into printed ink, heated to temperature exceeding temperature T4 prior to the printing process. A second sample of the composition is then suitably cooled to below temperature T1 and printed on the indicator, suitably next to the first print of the thermochromic composition. The printed label is allowed to dry at temperature not exceeding temperature T3 and not below temperature T2.

In a further aspect, the invention provides a process for producing an indicator comprising providing a support with a first portion of the colour-change composition, pigment or ink having colour change temperatures T1, T2, T3 and T4, heating the first portion of the colour-change composition, pigment or ink to a temperature exceeding T4, cooling a second portion of the colour-change composition, pigment or ink composition to a temperature below T1, applying the said second portion to the support and drying the colour-change composition, pigment or ink composition at temperature not exceeding temperature T3 and not below temperature T2.

The colour-change composition is preferably a thermochromic composition.

The combination on the label is now suitable for indication of temperature below T2. By tuning the temperature T2 to 0° C., the indicator may be employed to provide a visual or readable indication of when the indicator and any article or material to which it is applied has been subjected to a temperature of less than 0° C. In this way, the indicator may act as a “freeze indicator”.

By way of illustration, in the initial state at ambient temperature above T2 and below T3 is represented inFIG.2a. As the temperature drops below the temperature T2, and is kept below T4 at all times, the state of the indicator changes to that shown inFIG.2b. By raising the temperature to greater than T3 the indicator provides two colourless compositions as shown inFIG.2c).

The indicator may also be configured so it may not be reset and provides a single use indicator.

The invention provides for a single use indicator comprising a first portion of a colour-change composition in its coloured state and a second portion of the same colour-change composition in its discoloured state wherein the composition is according to the present invention.

Suitably, the indicator has a thermochromic composition or pigment according to the invention suitably in the form of a printable ink applied to it and heated to a temperature exceeding T4 prior to application to the indicator, for example in a printing process. An ink showing permanent colour change at a desired temperature, for example 50° C. is applied to the indicator, for example printed next to the memory composition pigment converted into printed ink. Any known permanent colour change ink may be employed and a preferred example is available from TMC Hallcrest, under the brand name Kromagen. The printed label is allowed to dry at temperature not exceeding T3 or 50° C. and preferably not below T2. The combination on the label is now suitable for indication of temperature below zero, of what can be cold a “freeze indicator”. The indicator used a single time.

By way of illustration,FIGS.3a,3band3cillustrate the various forms of the indicator where the indicator comprises a composition according to the invention comprising Kromagen ink.FIG.3ashows the initial state at ambient temperature above T2 and below the temperature of colour transition of Kromagen.FIG.3bshows the indicator as the temperature drops below T2 and below the temperature at which Kromagen changes colour andFIG.3cshows the indicator as it appears after heating above T4.

The invention is now illustrated by the following non-limiting examples in which parts are by weight unless otherwise stated.

A thermochromic colour memory composition was obtained by homogeneously compatibilizing:

4 parts of 3-(4-diethylamino-2-hexyloxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide (electron donating compound) available from Yamada Chemicals and 6 parts 2,2-bis(4′-hydroxyphenyl)hexafluoropropane and 6 parts of 1,1-bis(4′-hydroxyphenyl)-2-methylpropane (both electron accepting compounds) available from Sigma Aldrich and 84 parts of compound (VIa1) 2,2′ biphenyl bistetradecanoate ester as shown below:

Component VIa1 is suitably synthesised by stirring a mixture of 1 mole of 2,2′-Dihydroxybiphenyl, which is available from Sigma Aldrich or may be prepared using the method described by B. Schmidt, M. Riemer, and M. Karras (J. Org. Chem.,2013, 78 (17), pp 8680-8688), and 2.5 moles of triethyl amine in acetone and cooling to 5° C. 2.2 moles of acid chloride is added gradually so that temperature does not rise above 35° C. during the addition. After the addition is complete the reaction is brought to room temperature and stirred for 24-48 hours. The resulting reaction medium is then poured into 7% aqueous ice cold HCI. The precipitate is filtered off and washed with water and saturated sodium bicarbonate solution. The solid precipitate is crystallised from isopropanol. The relative quantities of biphenol/acid chloride/triethylamine are 1/2.2/2.5 moles.

The resulting memory composition changed colour form blue to colourless. The thermochromic colour memory composition was heated above T4. 100 parts of the hot thermochromic colour memory composition was then dispersed into 100 parts of a 10% solution of methyl vinyl ether-maleic anhydride copolymerized resin neutralised with sodium hydroxide to pH 4 by means of a high speed homogeniser. The resulting emulsion was maintained at temperature above T4 and slowly added 25 parts of a solution of melamine formaldehyde resin. The resulting emulsion was stirred and heated to a temperature of 80° C. for 6 hours. Some of the resulting dispersion was then drum dried and the pigment was isolated in encapsulated form, the thermochromic colour memory pigment having a particle size of 1.5 microns changed colour from blue to colourless.

4.1 parts of 3-(4-diethylamino-2-hexyloxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide (electron donating compound) available from Yamada Chemicals and 4.85 parts 2,2-bis(4′-hydroxyphenyl)hexafluoropropane and 4.85 parts of 1,1-bis(4′-hydroxyphenyl)-2-methylpropane (both electron accepting compounds) available from Sigma Aldrich and 86.2 parts of compound (VIa2) 2,2′ biphenyl bisoctadecanoate ester as shown below:

Component VIa2 is suitably synthesised by stirring a mixture of 1 mole of 2,2′-Dihydroxybiphenyl, which is available from Sigma Aldrich or may be prepared using the method described by B. Schmidt, M. Riemer, and M. Karras (J. Org. Chem.,2013, 78 (17), pp 8680-8688), and 2.5 moles of triethyl amine in acetone and cooling to 5° C. 2.2 moles of octadecanoyl chloride is added gradually so that temperature does not rise above 35° C. during the addition. After the addition is complete the reaction is brought to room temperature and stirred for 24-48 hours. The resulting reaction medium is then poured into 7% aqueous ice cold HCI. The precipitate is filtered off and washed with water and saturated sodium bicarbonate solution. The solid precipitate is crystallised from isopropanol. The relative quantities of biphenol/acid chloride/triethylamine are 1/2.2/2.5 moles.

The resulting memory composition changed colour form blue to colourless. The thermochromic colour memory composition was heated above 100° C. 100 parts of the hot thermochromic colour memory composition was then dispersed into 100 parts of a 10% solution of methyl vinyl ether-maleic anhydride copolymerized resin neutralised with sodium hydroxide to pH 4 by means of a high speed homogeniser. The resulting emulsion was maintained at temperature above 80° C. and slowly added 25 parts of a solution of melamine formaldehyde resin. The resulting emulsion was stirred and heated to a temperature of 80° C. for 6 hours. Some of the resulting dispersion was then drum dried and the pigment was isolated in encapsulated form, the thermochromic colour memory pigment having a particle size of 2.1 microns changed colour from blue to colourless.

4.1 parts of 3-(4-diethylamino-2-hexyloxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide (electron donating compound) available from Yamada Chemicals and 4.85 parts 2,2-bis(4′-hydroxyphenyl)hexafluoropropane and 4.85 parts of 1,1-bis(4′-hydroxyphenyl)-2-methylpropane (both electron accepting compounds) available from Sigma Aldrich and 86.2 parts of compound (VIa3) 2,2′ biphenyl bishexadecanoate ester as shown below:

Component VIa3 is suitably synthesised by stirring a mixture of 1 mole of 2,2′-Dihydroxybiphenyl, which is available from Sigma Aldrich or may be prepared using the method described by B. Schmidt, M. Riemer, and M. Karras (J. Org. Chem.,2013, 78 (17), pp 8680-8688), and 2.5 moles of triethyl amine in acetone and cooling to 5° C. 2.2 moles of hexadecanoyl chloride is added gradually so that temperature does not rise above 35° C. during the addition. After the addition is complete the reaction is brought to room temperature and stirred for 24-48 hours. The resulting reaction medium is then poured into 7% aqueous ice cold HCI. The precipitate is filtered off and washed with water and saturated sodium bicarbonate solution. The solid precipitate is crystallised from isopropanol. The relative quantities of biphenol/acid chloride/triethylamine are 1/2.2/2.5 moles.

The resulting memory composition changed colour form blue to colourless. The thermochromic colour memory composition was heated above 100° C. 100 parts of the hot thermochromic colour memory composition was then dispersed into 100 parts of a 10% solution of methyl vinyl ether-maleic anhydride copolymerized resin neutralised with sodium hydroxide to pH 4 by means of a high speed homogeniser. The resulting emulsion was maintained at temperature above 80° C. and slowly added 25 parts of a solution of melamine formaldehyde resin. The resulting emulsion was stirred and heated to a temperature of 80° C. for 6 hours. Some of the resulting dispersion was then drum dried and the pigment was isolated in encapsulated form, the thermochromic colour memory pigment having a particle size of 2.5 microns changed colour from blue to colourless.

Preparation of the Measuring Samples

10 parts of the thermochromic colour memory composition of the water dispersion obtained in Example 1 in encapsulated form were dispersed in 10 parts of a polyvinyl alcohol solution was screen printed onto sheet of copy paper, thereby obtaining a test sample.

The same method has been carried out in order to obtain a test sample for the thermochromic colour memory composition of Examples 2 to 13 in encapsulated form. Each of the test samples was heated and cooled by the below described method, The measuring sample thus prepared was set on a predetermined position of a Linkam (manufactured by linkam, UK) and the colour density at each temperature was measured by heating and cooling at a rate of 5° C./min with a temperature width of 100° C.

For example, in the case of Example 1, the sample was heated up to 100° C. at a rate of 5° C./min from a measurement starting temperature of 0° C., and then cooled to −20° C. at a rate of 5° C./min. The brightness of the colour displayed at each temperature was plotted on a graph to prepare the colour density-temperature curve as illustrated inFIG.1, and each of T1, T2, T3, T4, and ΔH was obtained.

The results of the temperature analysis in ° C. of the microcapsules is reported below as per their temperature of full clearing (T4) and temperature of full colour return (T1) as well as practical hysteresis ΔH. The results are reported below for the Components C) with different R1groups as shown in the formula below.