Use of a compound as color developer, thermosensitive composition and recording material for thermal printing

Abstract

The present invention relates to the use of one or more of compounds of formula (I) wherein R1, R2, R3, R4, R5 and R6 are independent from each other selected from the group consisting of hydrogen, hydroxy, methyl, methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy, tert-butoxy, pentoxy, isopentoxy, and neopentoxy, wherein at least two of R1, R2, R3, R4, R5 and R6 are different from hydrogen, and at least one of R1, R2, R3, R4, R5 and R6 is hydroxy, n is an integer between 1 and 5, and m is an integer between 1 and 5, as a color developer for leuco dyes.

Description

[0001] USE OF A COMPOUND AS COLOR DEVELOPER, THERMOSENSITIVE COMPOSITION AND RECORDING MATERIAL FOR THERMAL PRINTING

[0002] The present invention relates to a new color developer for leuco dyes.

[0003] Thermal imaging technology, a pivotal innovation in the realm of material science and engineering, has revolutionized the way we visualize and interact with thermal energy in our daily lives. Leveraging the principles of thermography, this technology has found a unique and valuable application in the production of thermal papers - a specialized segment of the paper manufacturing industry that caters to a wide array of commercial printing needs. Thermal papers serve as the medium for instant printing processes that are critical for sectors ranging from retail to transportation, offering a rapid and accurate method of capturing and displaying variable information such as transaction records, travel itineraries, product labeling, and other vital data.

[0004] The quintessential element of thermal imaging technology in the context of thermal paper lies in its ingenious use of heat to induce a chemical reaction that results in a visible representation of information. At the heart of this system are the coated layers applied to the paper substrate. Primarily, thermal papers encompass a support layer, for example a paper layer, that is treated with a color- forming layer. This cover-forming layer comprises color former that remain inert until they are activated by thermal energy. These color formers, also known as leuco dyes, belong to a class of dyes capable of switching between two states: a colorless (leuco) form and a colored form. When subjected to the localized heat from a thermal printer's print head, color developers transfer one or more of their hydrogen atoms to the dye, through an acido-basic reaction. This protonation induces a structural change in the leuco dye, activating its chromophoric (color-producing) properties, therefore producing a sharp and durable color change. This eliminates the need for traditional ink-based printing methods and allows for the delivery of high-quality, on-demand printed content.

[0005] Despite the widespread adoption and numerous advantages offered by thermal imaging technology in commercial printing, there exists a growing concern over the material components used in thermal papers. Historically, chemicals like Bisphenol A (BPA) and Bisphenol S (BPS) have been the primary color developers.

[0006]

[0007] Dye (OBD-2) Bisphenol A

[0008] Colored

[0009] However, their use has raised significant health and environmental alarms. These chemicals, part of the endocrine-disrupting class and derived from petroleum sources, have been identified as toxic and potentially harmful following absorption through the skin. The health implications associated with these developers have led to scrutiny and legislative action, as witnessed in the Ell's stringent restrictions on the acceptable levels of BPA content in thermal papers.

[0010] Pergafast® 201 and D-8 are the most well-known non-endocrine active replacements for BPA, BPF, and BPS. However, both are petroleum-based. Additionally, the US Environmental Protection Agency (EPA) has listed Pergafast® 201 as a 'moderate hazard' for repeated exposure.

[0011] The only currently available developer that is both bio-based and non-endocrine active is ascorbic acid, utilized in Alpha® Free Direct Thermal POS Paper technology. However, due to its widespread use in the medical and food industries, it faces competition from these sectors, driving up its cost. US2022184986A1 discloses non-phenolic color developers including 1 ,3-diphenyl urea (DPU) and urea urethane (UU) for thermal recording.

[0012] WO2017178513A1 and WO2021074210A1 disclose a method for preparing monomers and fragments from lignocellulose-containing biomass by aldehyde assisted fractionation, involving the addition of an aldehyde under acidic conditions.

[0013] US4502066 discloses a heat-sensitive recording sheet comprising a base sheet and a color-forming layer including a colorless basic dyestuff and a mono-phenolic 4-hydroxyphenyl compound which is reactive with said dyestuff by heating, wherein said color-forming layer comprises a metal salt of p- alkyl benzoic acid or a metal salt of a specific o-benzoylbenzoic acid.

[0014] JPS60193692 discloses a heat-sensitive recording material with improved sensitivity and storage stability, using a fluoran compound as a basic colorless dye, a monophenol compound as a color developer, and 4,4'-ethylenedioxybisbenzoic acid dibenzyl ester as a stabilizer.

[0015] JPS63216789 discloses a thermosensitive recording medium with enhanced coloring sensitivity and preservability. It combines a fluoran compound as the basic dye with a monophenol compound as the color developer, along with para- and meta-hydroxybenzoic acids to improve compatibility and stability. The effective concentration of these acids ranges from 1 to 40 parts.

[0016] With an ever-expanding market predicted to reach the 6 billion USD mark by the year 2027, the thermal imaging industry is at a crossroads. There is an urgent imperative for innovation in the development of safe, effective, and environmentally friendly color developers ensuring the continued success and responsible evolution of thermal imaging technology in commercial paper applications.

[0017] Therefore, the problem of the present invention is to provide a compound that functions as a color developer while also being safe, efficient, and environmentally friendly.

[0018] The problem is solved by the use of a compound according to claim 1 . Further preferred embodiments are subject of dependent claims 2 to 11 .

[0019] Interestingly, it has been discovered that the compound of formula I has outstanding characteristics as a color developer for leuco dyes. Compound of formula I has the following structure: wherein Ri, R2, R3, R4, Rs and Re are independently from each other selected from the group consisting of hydrogen, hydroxy, methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy, tertbutoxy, pentoxy, isopentoxy, neopentoxy, and methyl, wherein at least two of R1, R2, R3, R4, Rs and Re are different from hydrogen, and at least one of R1, R2, R3, R4, Rs and Re is hydroxy, n is an integer between 1 and 5, and m is an integer between 1 and 5.

[0020] Thus, in the compound of formula (I) at least one of R1, R2, R3, R4, Rs and Re are different from hydrogen, meaning that they are selected from the group consisting of hydroxy, methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy, tert-butoxy, pentoxy, isopentoxy, neopentoxy, and methyl. Further, at least one R1, R2, R3, R4, Rs and Re is a hydroxy group. For example, R2 and Rs can both be hydroxy, with the remaining residues being hydrogen, or R2 can be methoxy while Rs is hydroxy, and the remaining residues are hydrogen.

[0021] This means that at least one hydroxy group is crucial for its role as a color developer in thermal imaging technology. The hydroxy group in the compound of formula I is acidic, which enables it to donate a proton. When the leuco dye, initially colorless, comes into contact with the compound of formula I, the hydroxy groups donate protons to the dye. This protonation induces a structural change in the leuco dye, activating its chromophoric (color-producing) properties and leading to the development of color.

[0022] The compound of the present invention is an optimal color developer for thermal paper imaging, demonstrating outstanding thermal sensitivity for quick and accurate image production. It remains stable under normal conditions (i.e. at temperatures ranging from 15-25°C, for a duration of at least 6 months, even when exposed to natural or artificial light) safeguarding against unwanted color shifts that might affect the print's legibility or accuracy. The compound of the present invention can not only be obtained from bio-based sources, but also demonstrates reduced endocrine activity, offering a safer alternative compared to conventional options. Additionally, the compounds according to the present invention have demonstrated equal or, in some cases, superior effectiveness compared to traditional BPA.

[0023] The compounds of formula I are derived from either p-coumaric acid or ferulic acid. These can easily be obtained from lignin’s or vegetable oils. Of course, they can also be produced petro-based.

[0024] The process of acidic cleavage of lignin, particularly the breakage of the p-O-4 bond, follows two different routes. The first pathway leads to the creation of compounds known as Hibbert's ketones, while the second generates a C2 aldehyde that may manifest as any of the three lignin monomer types, namely H types (having a p-hydroxyphenyl unit), G types (having a guaiacyl unit), or S types (having a syringyl unit), depending on the wood source. Particularly, monomers of types H and G are of special interest for this invention as they can readily be converted into substances like p-coumaric acid and ferulic acid, as well as their corresponding alcohols.

[0025] The compounds according to the present invention exhibit a reduced endocrine activity due to the synergistic integration of two strategic modifications. Firstly, the introduction of substituents on the aromatic ring adjacent to the phenolic hydroxy groups serves to modulate the interaction with endocrine receptors, potentially diminishing their affinity. Secondly, incorporation of the ester group into the bridge that connects both aromatic rings contributes to altering the compound's physicochemical properties, likely diminishing its capability to mimic endogenous hormones. By combining these approaches, the compounds are less bioactive against endocrine systems, thereby reducing potential toxicological impacts.

[0026] Good results can be obtained with a compound of formula I, wherein R1, R2, R3, R4, Rs and Re are independently from each other selected from the group consisting of hydrogen, hydroxy and methoxy, and wherein at least one of R1, R2, R3, R4, Rs and Re is hydroxy and at least one of R1, R2, R3, R4, Rs and Re is methoxy. Preferably, either R2 and / or Rs are hydroxy. Methoxy groups, especially when located at an ortho position to the hydroxy groups (e.g. R1 = methoxy if R2 = hydroxy) are preferred due to their neighboring substituents' ability to influence the interaction with endocrine receptors, which can result in a decreased affinity for these receptors. It is possible that the remaining substituents are methoxy groups. This means that residues Ri, R3, R4, and Re can be methoxy groups. Alternatively, 1 , 2, or 3 of the remaining groups can be methoxy groups, while the other positions would then be hydrogen.

[0027] In a further preferred embodiment of the present invention one or two of R1, R2, R3, R4, Rs and Re are hydroxy. It has been determined that limiting the number of hydroxy groups to one or two yields favorable outcomes.

[0028] A further embodiment of the present invention concerns a compound in which, in addition to at least one hydroxy group, one or two of R1, R2, R3, R4, Rs and Re are methoxy. The presence of the methoxy groups is advantageous because endocrine activity is lowered. These groups are naturally found in biomass in the ortho position relative to the OH group, thereby leveraging this inherent property of wood. In addition, this configuration is advantageous because it enables the fine-tuning of the compound's lipophilic and hydrophilic balance.

[0029] A further embodiment of the present invention relates to the use of a compound, wherein one or two of R1, R2, R3, R4, Rs and Re are independently selected from the group consisting of methyl, ethoxy, propoxy and isopropoxy, and one or two of R1, R2, R3, R4, Rs and Re are hydroxy. It is preferably that the remaining substituents among R1, R2, R3, R4, Rs and Re are hydrogen. Compound 5 is an example of such compounds.

[0030] Especially good results could be obtained by compounds wherein one of R1, R2, R3, R4, Rs and Re is hydroxy and one is selected from the group consisting of methyl, methoxy, ethoxy, propoxy and isopropoxy, preferably isopropoxy. The remainder of the substituents among R1, R2, R3, R4, Rs and Re are hydrogen. Preferably, the hydroxy group is on one aromatic ring, and the alkyl group is on the other aromatic ring.

[0031] A further aspect relates to compounds, wherein n is 2 and m is 3. This arises from the process of depolymerization of lignin. During this process, monomers with a uniform structural trait are obtained, as they each have a residue that includes three carbon atoms. One of these carbon atoms is incorporated into the ester linkage during the condensation process. As a result, a compound according to the present invention derived from lignin is characterized by n being 2, which accounts for the two carbon atoms remaining in the monomer that are not part of the ester linkage. Concurrently, m is identified as 3, representing the original three carbon atoms from the residue of the other monomer. As a consequence of the subsequent condensation reaction, these monomers transform into compounds of formula I. Therefore, depolymerization of lignin may directly yield monomers that, upon condensation, inherently produce compounds of formula I, wherein n is 2 and m is 3. These compounds are renewable, derived from plants, and thus can be produced sustainably and are therefore preferred.

[0032] Especially good results could be obtained with compounds selected from the group consisting of compounds 1 to 19.

[0033] The compounds according to the present invention can be obtained by performing a classical esterification reaction, producing H2O as a side product (Scheme 1): wherein the above scheme Ri, R2, R3, R4, Rs and Re have the same definition as above, and at least one of R1, R2, R3, R4, Rs and Re is a hydroxy group. Alternatively, they can be obtained by replacing the carboxylic acid by its corresponding carboxylate ester, obtaining the same product but with the alcohol as the side product (e.g. methyl ester gives methanol). This is then called trans esterification reaction (Scheme 2). wherein the above scheme Ri, R2, R3, R4, Rs and Re have the same definition as above, and at least one of R1, R2, R3, R4, Rs and Re is a hydroxy group.

[0034] A variety of separation and purification approaches are available for fractions obtained after reductive depolymerisation of lignin, targeting aromatic compounds derived from multiple origins such as biomass, edible seeds, and microbial processes. Examples of these methods include vacuum distillation and the creation of phenolic salts, which can subsequently be precipitated and filtered. By segregating analogous compounds into collective fractions rather than pursuing individual separation of each molecule, distinct batches comprising specific groups of compounds can be obtained, which is cheaper than the separation of every single compound. Thus, one can obtain for example one or more of the following batches: a first batch comprising phenolics with alkyl alcohol side chains, varying in ring substitutions, such as

[0035] - a second batch comprising phenolics with a carboxylate ester side chain, which also exhibit diverse ring substitutions, varying in ring substitutions, such as - and a third batch comprising phenolics with a carboxylic acid side chain, which also exhibit diverse ring substitutions, varying in ring substitutions, which are not volatile and do not distill, but come out of production as a mixture, such as

[0036] Considering the reaction stoichiometry and the compositions specified, the following batches are for example suitable as starting materials:

[0037] - A first batch containing phenolics with alkyl alcohol side chains, varying in ring substitutions, and a second batch containing phenolics with a carboxylate ester side chain, which also exhibit diverse ring substitutions.

[0038] A first batch consisting of phenolics with alkyl alcohol side chains, varying in ring substitutions, alongside a third batch encompassing phenolics with a carboxylic acid side chain, which also exhibit diverse ring substitutions. A method akin to the one outlined for the synthesis of H-ester (Molecule 1) and G-ester (Molecule 2) (as described in the Examples) may be followed, adhering to the general principle that the combination of an aliphatic OH with carboxylic ester or carboxylic acid groups will result in the formation of the corresponding compound of formula I.

[0039] Utilizing such mixtures as starting compounds result in compounds displaying varied substitutions on both aromatic rings, which, in turn, modifies the exact reactivity and endocrine activity. Such variations are dependent on factors like the substituents themselves. When starting from a mixture with a known composition, this aspect can be adjusted or taken into consideration based on the specific needs of the application and / or the particular polarity of the ester developer within the matrix for thermal paper uses. This strategy also enhances economic viability due to the nature of the starting materials.

[0040] A further aspect of the present invention relates to a thermosensitive composition that can be used to coat a support material to obtain thermosensitive recording material. Said thermosensitive composition comprises at least a color former in the form of a leuco dye, a sensitizer, and at least one compound according to the present invention, preferably at least one of compounds 1 to 16. The thermosensitive composition applied to the support material for thermal printing generally includes both solid and liquid components. The liquid component is primarily used during the coating process to ensure an even application of the thermosensitive layer onto the support material. Once the coating is applied, the liquid (typically water) evaporates, leaving behind the solid components that form the thermosensitive layer.

[0041] A further aspect of the present invention relates to a thermosensitive composition comprising two or more of the compounds of formula I. As the monomers can be obtained for lignin after reductive depolymerisation, a mixture of two or more compounds of formula I can be obtained by using distinct batches comprising specific groups of compounds as described above. A thermosensitive composition comprising two or more of the compounds of formula I allows for the derived esters to exhibit diverse substitutions on both aromatic rings. These substitutions can subsequently alter the specific reactivity and endocrine activity of the compounds. The impact of such variations relies on the nature of the substituents. Starting with a mixture whose composition is precisely known affords the opportunity to tailor this aspect to meet the particular demands of the intended application, or to match the desired polarity of the ester developer utilized in the matrix for thermal paper purposes. Adopting this method not only tailors to specific requirements but also improves the economic feasibility given the starting materials' characteristics.

[0042] In one embodiment of the present invention, the thermosensitive composition comprises at least the following ingredients:

[0043] - a color former (leuco dye) in an amount of 1 -15% by weight of the solid components.

[0044] - at least one compound according to the present invention as color developer in an amount of 1-25% by weight of the solid components.

[0045] - At least one compound as sensitizer in an amount of 1 -55% by weight of the solid components. The sensitizer can also act as co-binder.

[0046] Further, the composition can additionally comprise compounds such as binders, fillers, and stabilizers. The binder can be present in an amount of 10-40% by weight of the solid components, and fillers and stabilizers can be present in an amount of 30-50% by weight of the solid components.

[0047] The liquid component typically comprises 50-70% by weight of the total composition during the coating process. Preferred solvents include water or organic solvents such as ethanol, isopropanol, or acetone or mixtures thereof. The solvent facilitates the mixing and application of the solid components onto the support material. After the coating is applied, the solvent evaporates, leaving behind the solid thermosensitive layer.

[0048] The color developer of the present invention is designed for leuco dyes as color formers. When heated, these dyes undergo an acido-basic chemical reaction that alters their molecular structure, allowing them to switch between a colored state and a colorless or differently colored state. This transformation is typically caused by the opening or closing of a molecular ring structure, which in turn changes how the molecule absorbs and reflects light. Preferred color formers in the form of a leuco dye include but are not limited to: 3-diethylamino-6-methylfluoran, 3-dimethylamino-6-methyl-7-anilinofluoran, 3- diethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-(2,4-dimethylanilino) fluoran, 3- diethylamino-6-methyl-7-chlorofluoran, 3-diethylamino-6-methyl-7-(3-trifluoromethylanilino) fluoran, 3- diethylamino-6-methyl-7-(2-chloroanilino) fluoran, 3-diethylamino-6-methyl-7-(4-chloroanilino) fluoran, 3-diethylamino-6-methyl-7-(2-fluoroanilino) fluoran, 3-diethylamino-6-methyl-7-(4-n-octylanilino) fluoran, 3-diethylamino -7-(4-n-octylanilino) fluoran, 3-diethylamino -7-(n-octylamino) fluoran, 3- diethylamino -7-(dibenzylamino) fluoran, 3-diethylamino-6-methyl-7-(dibenzylamino) fluoran, 3- diethylamino-6-chloro-7-methylfluoran, 3-diethylamino-7-t-butylfluoran, 3-diethylamino -7- carboxyethylfluoran, 3-diethylamino-6-chloro-7-anilinofluoran, 3-diethylamino-6-methyl-7-(3- methylanilino) fluoran, 3-diethylamino-6-methyl-7-(4-methylanilino) fluoran, 3-diethylamino-6- ethoxyethyl-7-anilinofluoran, 3-diethylamino-7-methylfluoran, 3-diethylamino-7-chlorofluoran, 3- diethylamino-7-(3-trifluoromethylanilino) fluoran, 3-diethylamino-7-(2-chloroanilino) fluoran, 3- diethylamino-7-(2-fluoroanilino) fluoran, 3-diethylamino-benzo[a] fluoran, 3-diethylamino-benzo[c] fluoran, 3-dibutylamino-7-dibenzylaminofluoran , 3-dibutylamino-7-anilinofluoran , 3-diethylamino-7- anilinofluoran, 3-dibutylamino-6-methyl fluoran, 3-dibutylamino-6-methyl-7-anilinofluoran, 3- dibutylamino-6-methyl-7-(2,4-dimethylanilino) fluoran, 3-dibutylamino-6-methyl-7-(2-chloroanilino) fluoran, 3-dibutylamino-6-methyl-7-(4-chloroanilino) fluoran, 3-dibutylamino-6-methyl-7-(2- fluoroanilino) fluoran, 3-dibutylamino-6-methyl-7-(3-trifluoromethylanilino) fluoran, 3-dibutylamino-6- ethoxyethyl-7-anilinofluoran, 3-dibutylamino-6-chloro-anilinofluoran, 3-dibutylamino-6-methyl-7-(4- methylanilino) fluoran, 3-dibutylamino-7-(2-chloroanilino) fluoran, 3-dibutylamino-7-(2-fluoroanilino) fluoran, 3-dibutylamino-7-(N-methyl-N-formylamino) fluoran, 3-dipentylamino-6-methyl-7- anilinofluoran, 3-dipentylamino-6-methyl-7-(2-chloroanilino) fluoran, 3-dipentylamino-7-(3- trifluoromethylanilino) fluoran, 3-dipentylamino-6-chloro-7-anilinofluoran, 3-dipentylamino-7-(4- chloroanilino) fluoran, 3-pyrrolidino-6-methyl-7-anilinofluoran, 3-piperidino-6-methyl-7-anilinofluoran, 3-(N-methyl-N-propylamino)-6-methyl-7-anilinofluoran, 3-(N-methyl-N-cyclohexylamino)-6-methyl-7- anilinofluoran, 3-(N-ethyl-N-cyclohexylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-p-toluidino)-6- methyl-7-anilinofluoran, 3-(N-ethyl-N-isoamylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N- isoamylamino)-6-chloro-7-anilinofluoran, 3-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7- anilinofluoran, 3-(N-ethyl-N-isobutylamino)-6-methyl-7-anilinofluoran, 3-(N-butyl-N-isoamylamino)-6- methyl-7-anilinofluoran, 3-(N-isopropyl-N-3-pentylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N- ethoxypropylamino)-6-methyl-7-anilinofluoran, 3-cyclohexylamino-6-chlorofluoran, 2-methyl-6-p-(p- dimethylaminophenyl)aminoanilinofluoran, 2-methoxy-6-p-(p-dimethylaminophenyl)- aminoanilinofluoran, 2-chloro-3-methyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran, 2- diethylamino-6-p-(p-dimethylaminophenyl)aminoanilinofluoran, 2-phenyl-6-methyl— 6-p-(p- phenylaminophenyl)aminoanilinofluoran, 2-benzyl-6-p-(p-phenylaminophenyl)amino-anilinofluoran, 3- methyl-6-p-(p-dimethylaminophenyl)aminoanilinofluoran, 3-diethylamino-6-p-(p- diethylaminophenyl)aminoanilinofluoran, 3-diethylamino-6-p-(p-dibutylaminophenyl)- aminoanilinofluoran, 2,4-dimethyl-6-[(4-dimethylamino)-anilino] fluoran, 3-[(4-dimethyl- aminophenyl)amino]-5,7-dimethylfluoran, 3,6,6'-tris(dimethylamino)spiro[fluorene-9,3'-phthalide], 3,6,6'-tris(diethylamino)spiro[fluorene-9,3'-phthalide], 3,3-bis(p-dimethylamino-phenyl)-6- dimethylaminophthalide, 3,3-bis(p-dimethylaminophenyl)phthalide, 3,3-bis-[2-(p- dimethylaminophenyl)-2-(p-methoxyphenyl)ethenyl-4,5,6,7-tetrabromophthalide, 3,3-bis-[2-(p- dimethylaminophenyl)-2-(p-methoxyphenyl)ethenyl-4,5,6,7-tetrachlorophthalide, 3,3-bis[1 ,1 -bis(4- pyrrolidinophenyl)ethylene-2-yl]-4,5,6,7-tetrabromophthalide, 3,3-bis-[1-(4-methoxyphenyl)-1-(4- pyrridinophenyl)ethylene-2-yl]-4,5,6,7-tetrachlorophthalide, 3-(4-diethylamino-2-ethoxyphenyl)-3-(1 - ethyl-2-methylindole-3-yl)-4-azaphthalide, 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-octyl-2- methylindole-3-yl)-4-azaphthalide, 3-(4-cyclohexylethylamino-2-methoxyphenyl)-3-(1-ethyl-2- methyl indole-3-y l)-4-azap hth al ide, 3, 3-bis (1 -ethyl-2-methyli ndole-3-yl) phthalide, 3, 3-bis (1 -octyl-2- methylindole-3-yl) phthalide, , 3-diethylamino-6,8-dimethylfluoran, 3-diethylamino-7,8-benzofluoran, 3-diethyl-aminofluoran-7-carboxylic acid ethyl ester, 3-[N-(4-methylphenyl)-N-ethylamino]-7- methylfluoran, crystal violet and mixtures thereof.

[0049] Representative examples of sensitizer are stearamide, methylol stearamide, benzalphthalide, methylene bis-stearamide, ethylene bis-stearamide, amide waxes, p-benzylbiphenyl, m-terphenyl, benzyl-2-naphthyl ether, 4-methoxybiphenyl, dibenzyl oxalate, di(4-methylbenzyl) oxalate, di(4- chlorobenzyl) oxalate, diphenyl sulfone, dimethyl terephthalate, dibenzyl terephthalate, dibenzyl isophthalate, 1,2-diphenoxyethane, 1 ,2-bis(4-methylphenoxy) ethane, 1 ,2-bis(3-methylphenoxy) ethane, 4,4'-dimethylbiphenyl, phenyl-1-hydroxy-2-naphthoate, 4-methylphenyl biphenyl ether, 1 ,2- bis(3,4-dimethylphenyl) ethane, 2,3,5,6-4'-methyldiphenyl methane, 1 ,4-diethoxynaphthalene, 1 ,4- diacetoxybenzene, 1 ,4-diproprionoxybenzene, o-xylylene-bis(phenyl ether), 4-(m- methylphenoxymethyl) biphenyl, p-hydroxyacetanilide, p-hydroxybutyranilide, p-hydroxynonananilide, p-hydroxylauranilide, p-hydroxyoctadecananilide, N-phenyl-phenylsulphonamide, acetyl biphenyl compounds (e.g. as described in JP2003 063149A2 ) and 2-phenoxyethyl-N-phenylcarbamate.A further aspect of the present invention relates to a recording material for thermal printing comprising a thermosensitive composition including at least one compound according to the present invention as color developer. In this context, the support material refers to the substrate or base material used for printing. This support material includes paper, wood-free paper made from non-chlorine bleached pulp, base paper containing waste paper plastic films, and synthetic paper that can be coated with the thermosensitive formulation.

[0050] The recording material according to the present invention can be prepared by coating a support layer as mentioned above with a thermosensitive composition. This composition generally includes a color former in the form of a leuco dye, a color developer, and other additives to enhance the stability and performance of the thermal paper. The compounds according to the present invention serve as the color developer. When heat is applied to the thermal paper via the thermal print head, the compound according to the present invention reacts with the color former. This chemical reaction results in a visible color change, producing the printed image. During printing, the thermal print head selectively heats specific areas of the paper. The heat causes the color former and the compound according to the present invention to interact, leading to the formation of a colored image.

[0051] The support material must be compatible with the thermal printing process, possessing appropriate thermal sensitivity, durability, and surface properties to ensure high-quality printing. The incorporation of the compound according to the present invention into the thermosensitive composition enhances the paper's ability to produce clear, sharp images when heated.

[0052] Figures:

[0053] Figure 1 shows images alongside color density measurements to illustrate the color change experienced by a mixture containing bisphenol A (BPA), H esters (Molecule 1), and G esters (Molecule 2), in combination with the dye OBD-2, when subjected to a heating-cooling cycle within an octadecanol matrix (100 mg at 100°C). The color density was determined using a colorimeter (CS-10 Colorimeter, CHNSpec, China). It relates to the visual intensity and richness of a color, primarily used in the context of printing, painting, and imaging. The device measures colorimetric coordinates (Y, x, y values), with the Y parameter indicating luminance, ranging from 0 to 100. This Y parameter was then converted into color density (C.D.) using the calculation C.D.=-log(K / 100).

[0054] In the various scenarios: a) The mass ratio of the dye to the developer was maintained at 1 :2 (OBD-2 = 10 mg, Developers = 20 mg), b) the molar ratio between the dye and the developer was kept at a 1 :1 ratio, and c) the molar ratio of the dye to the developer was preserved at 1 :4, which corresponds to a 1 :2 mass ratio equivalent for BPA.

[0055] Figure 2 shows the evolution of coating color density upon heating using benzalphthalide as a sensitizer. Conditions: PVA, OBD-2, CaCOs, Zn Stearate, Developer, benzalphthalide.

[0056] Figure 3 shows the coating stability at room temperature under natural light conditions using benzalphtalide as a sensitizer. Conditions: PVA, OBD-2, CaCO3, Zn Stearate, H or G esters as developer, benzalphtalide as sensitizer.

[0057] Figure 4 shows a demonstration of the lignin-based esters as a color developer in a real-life application.

[0058] Figure 5 shows a ERalpha-CALUX plot of lignin-based H and G esters activity compared to commercial BPA, BPS and estradiol reference.

[0059] Examples

[0060] Preparation of lignin-derived esters a. H-ester (Molecule 1)

[0061] Dihydro-p_'-coumaric acid (1 g, 6.02 mmol, 1.00 eq) was combined with 3-(4-hydroxyphenyl)-1- propanol (0.92 g, 6.02 mmol, 1.00 eq), p-toluenesulfonic acid monohydrate (57 mg, 0.3 mmol, 0.05 eq.) and toluene (60 mL) in a 3-neck 100 mL round-bottom flask of a Dean-Stark set-up. The mixture was heated to 120 °C using an oil bath under N2-flow and with magnetic stirring (400 rpm using a PTFE coated stir-bar) for 6 hours. The reaction progress was followed by Thin Layer Chromatography (50:50 hexane: ethyl acetate). After full conversion, the reaction was stopped and the solvent was removed under reduced pressure. The crude was then diluted with dichloromethane, washed 1x with 0.1 M NaHCOs solution, 1x demineralized water and 1x brine. The organic phase was then concentrated under reduced pressure to yield the H Ester (Molecule 1) product as an off-white solid (96% isolated yield). The purity (>98 wt.%) of the final product was confirmed by quantitative 1 H NMR with 1 ,2,4,5-terachloro-3-nitrobenzene as the internal standard.

[0062] 1 H NMR (400 MHz, DMSO-d6)

[0063] 5 1.82 (2H, quint), 2.51 (2H, t), 2.59 (2H, t), 2.78 (2H, t), 4.00 (2H, t), 6.71 (4H, d), 6.99 (2H, d), 7.05 (2H, d), 9.18 (1 H, s), 9.21 (1 H, s).

[0064] 13C NMR (101 MHz, DMSO-d6)

[0065] 5 172.83 (1 C, s), 156.06 (1 C, s), 155.86 (1C, s), 129.55 (4C,d) , 123.56 (1C,s), 115,51 (4C, d), 63.60 (1 C, 1s), 55.94 (1 C, s), 35.97 (1 C, s), 30.98 (1 C, s), 30.49 (1 C ,s), 30.04 (1 C, s).

[0066] HRMS (ESI / QTOF) m / z: [M + Na]+ Calculated for C18H20NaO4+ 323.1254; Found 323.1261 b. G-ester (Molecule 2)

[0067] Dihydroferulic acid (1 g, 5.10 mmol, 1.00 eq) was combined with dihydroconiferyl alcohol (0.93 g, 5.10 mmol, 1.00 eq), p-toluenesulfonic acid monohydrate (48 mg, 0.25 mmol, 0.05 eq.) and toluene (60 mL) in a 3-neck 100 mL round-bottom flask of a Dean-Stark set-up. The mixture was heated to 120 °C using an oil bath under N2-flow and with magnetic stirring (400 rpm using a PTFE coated stir-bar) for 6 hours. The reaction progress was followed by Thin Layer Chromatography (50:50 hexane: ethyl acetate). After full conversion, the reaction was stopped and the solvent was removed under reduced pressure. The crude was then diluted with dichloromethane, washed 1x with 0.1 M NaHCO3 solution, 1x demineralized water and 1x brine. The organic phase was then concentrated under reduced pressure to yield the G Ester (Molecule 2) product as a viscous yellowish oil (90% isolated yield). The purity of the solid was determined by 1 H-NMR and GC-MS. In order to render to remove trace impurities, the oil got purified by Silica-gel Flash Column Chromatography, yielding the G ester (Molecule 2) as a transparent viscous oil. The purity (>98 wt.%) of the final product was confirmed by quantitative 1 H NMR with 1 ,2,4,5-terachloro-3-nitrobenzene as the internal standard.

[0068] 1 H NMR (400 MHz, DMSO-d6)

[0069] 5 1.82 (2H, quint), 2.50(2H, t), 2.59 (2H, t), 2.77 (2H, t), 3.75 (6H, s), 3.99 (2H, t), 6.56 (1 H, d), 6.61 (1 H, d), 6.69 (2H, d), 6.74 (1 H, s), 6.79 (1 H, s)8.69 (1 H, s), 8.71 (1 H, s)

[0070] 13C NMR (101 MHz, DMSO-d6)

[0071] 5 172.83 (1 C, s), 147.89 (1 C, s), 147.87 (1 C, s), 145.26 (1 C,s), 145.05 (1 C, s), 132.34 (1 C, s), 131 .75 (10, 1s), 120.81 (1 C,s) , 120.73 (1 C,s), 115,78 (10, s), 115.75 (10, s), 112.87 (20, s), 63.67 (10, 1s), 55.94 (20, s), 35.97 (1 C, s), 31.45 (1 C, s), 30.49 (1 C ,s), 30.46 (1 C, s).

[0072] HRMS (ESI / QTOF) m / z: [M + Na]+ Calculated for C20H24NaO6+ 383.1465; Found 383.1468

[0073] Example 2:

[0074] In a rapid screening procedure known as the "octadodecanol test," the dye (OBD-2) and the developer (esters) undergo a temperature change by heating up the sample to 100°C and subsequently cooling it down to room temperature. This process is employed to assess the developer's capacity to interact with the dye and induce a color change, through proton transfer from the developer to the lactone. Surprisingly, H ester (Molecule 1) outperformed the reference sample containing BPA and the G esters (Molecule 2) could reach similar performance when its molar equivalent was increased (Figure 1 ).

[0075] Example 3:

[0076] The static sensitivity of the thermo responsive coating containing H and G ester (Molecule 1 and Molecule 2) as developers were compared to the coating containing BPA as developer. This parameter reflects the initial development temperature needed to generate color, and varies depending on the targeted application. Poly(vinyl alcohol)(PVA) solutions containing developer, dye ODB-2, sensitizers benzalphtalyde, and additives (calcium carbonate and zinc stearate) were coated on white paper (2:1 weight ratio, average coating thickness of 70 pm). To investigate the static sensitivity, the color density (C.D.) was monitored while exposing the paper to increasing temperatures (from room temperature to 140°C, with 20°C incremental, Figure 2) using a temperature-controlled heat gun. Developer “H” ester (Molecule 1) showed comparable performance to commercial BPA at 120°C with an C.D. around 1.6. Nevertheless, the G esters (Molecule 2) showed lower performance at 120°C due to the utilization of less active -OH group per gram. The performance should be able to be increased by increasing the mass of the G ester (molecule 2) in the formulation (see figure 1 c).

[0077] All the solid ingredients (developer, dye, CaCOs, zinc stearate and sensitizer) were individually ground with a mortar for 5 min to decrease particle size to approximately 1000 pm. Then, an aqueous solution of poly vinyl alcohol (PVA) with a solid content of 30 wt% was prepared by dissolving Mowiol(R) 4-88 (Molecular weight « 38,000 Da, 300 mg) in distilled water (700 mg) overnight. In parallel, an aqueous CaCOs solution was prepared by manually mixing CaCOs (80 mg), PVA 30 wt% (75 mg) and distilled water (150 mg) for 20 minutes until a homogeneous white solution was formed. Following these preparative steps, developer (50 mg) was mixed with the aqueous 30 wt% PVA solution (80 mg), followed by the addition of distilled water (152 mg), CaCO3 solution (300 mg), zinc stearate (20 mg), and sensitizer benzalphtalide (50 mg). This formulation was then mixed for another 5 min. Finally, the dye was incorporated (22 mg, dye:developer mass ratio 1 :2) and the total solid content was maintained to 40 wt%. The final solution was applied to white paper using a U-coater, achieving a coating thickness within the range of 70-80 pm. This commercial formulation was also performed with another petroleum-based sensitizer, diphenyl sulphone. Example 4:

[0078] The most effective developers “H ester (Molecule 1)” was selected to illustrate a real-life application. Coatings were formulated using benzalphtalide as sensitizer and “H” ester (Molecule 1) as developer following the recipe of example 2. The EPFL logo was successfully obtained using a poly(methylmetacrylate) mold and a thermal gun heater. Pleasingly, very good contrast was observed (Figure 4).

[0079] Example 5: Toxicity

[0080] The potential agonistic estrogenic activity of the H-ester and G-ester was determined using an estrogen receptor reporter transactivation assay (ERTA) with the human oestrogen receptor (hERa): a human cell line-based assay ERa- Chemical Activated Luciferase gene expression (CALUX®) following ISO 19040-3 (Simon, E. et al, Evaluation of Three ISO Estrogen Receptor Transactivation Assays Applied to 52 Domestic Effluent Samples. Environ. Toxicol. Chem. 2022, 41 (10), 2512-2526).

[0081] In this assay, in short, concentration-effect relationships of compounds are established and compared to the female sex hormone, 17p-estradiol (E2), which serves as the positive control / reference in this assay. From the concentration-effect curves (Figure 5), EC50, PC50, and PC10 values are determined in order to quantify the estrogenic activity of the tested compounds, also compared to the E2 reference (Table 1); EC50: 50% effect concentration, PC50: 50% effect relative to positive control, PC10: 10% effect relative to positive control, see OECD 455 (Performance-Based Test Guideline for Stably Transfected Transactivation In Vitro Assays to Detect Estrogen Receptor Agonists and Antagonists. In OECD Guidelines for the Testing of Chemicals, Section 4; OECD Publishing: Paris, 2021); ISO 23196 (Water Quality - Calculation of Biological Equivalence (BEQ) Concentrations; 2022). Results are shown in Figure 5; Data were normalized to the effect of controls (0%) and the maximum modelled effect of E2 (100%). Experimentally, ERo-CALUX was performed on 96-well plates along ISO 19040-3. E2 (reference compound) and test compounds were dissolved in DMSO and tested, in duplicate, in dilution series with a final DMSO concentration of 0.8% in all wells. 0.8% DMSO served as negative control. Possible cytotoxicity to the mammalian cell was verified under the microscope. Data were fitted using Prism (8.0.1) to establish concentration-effect relationships (Figure 5) and determine EC50 as well as PC50 and PC10 values (Table 1)

[0082] Tests revealed that the esters exhibit much weaker agonistic estrogenic activity, requiring significantly higher concentrations for induction than BPA and showing a reduced response (Figure 5+ Table 1).

[0083] Table 1 : ERo-CALUX® Molar results table. 1Average from eight plates.

[0084] 2Fitted top of the curve.

[0085] 3Highest tested dose was not toxic.

[0086] 4Highest induction seen.

[0087] Figure 5 shows the ERo-CALUX concentration-effect relationships of H-ester and G-ester compared to commercial BPA, BPS and the 17p-oestradiol (E2) reference. Data were normalized to the effect of controls (0%) and the maximum modelled effect of E2 (100%).

Claims

Claims1 . Use of one or more of compounds of formula (I)wherein Ri , R2, R3, R4, Rs and Re are independently from each other selected from the group consisting of hydrogen, hydroxy, methyl, methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy, tert-butoxy, pentoxy, isopentoxy and neopentoxy, wherein at least two of R1, R2, R3, R4, Rs and Re are different from hydrogen, and at least one of R1, R2, R3, R4, Rs and Re is hydroxy, n is an integer between 1 and 5, and m is an integer between 1 and 5, as a color developer for leuco dyes.

2. Use according to claim 1 , wherein R1, R2, R3, R4, Rs and Re are independently from each other selected from the group consisting of hydrogen, hydroxy and methoxy, and wherein at least one of R1, R2, R3, R4, Rs and Re is hydroxy and at least one of R1, R2, R3, R4, Rs and Re is methoxy.

3. Use according to any of the preceding claims, wherein one or two of R1, R2, R3, R4, Rs and Re are hydroxy.

4. Use according to any of the preceding claims, wherein one or two of R1, R2, R3, R4, Rs and Re are methoxy.

5. Use according to claim 1 , wherein one or two of Ri, R2, R3, R4, Rs and Re are independently selected from the group consisting of methyl, and one or two of R1, R2, R3, R4, Rs and Re are hydroxy.

6. Use according to claim 5, wherein one of R1, R2, R3, R4, Rs and Re is hydroxy and one is selected from the group consisting of methyl.

7. Use according to any of the preceding claims, wherein n is 2 and m is 3.

8. Use according to any of the preceding claims, wherein the compound is selected from the group consisting of9. Thermosensitive composition comprising at least a color former in the form of a leuco dye, a sensitizer, and one or more compounds of formula I as defined in any of claims 1 to 8.

10. Thermosensitive composition according to claim 9 comprising two or more compounds of formula I as defined in any of claims 1 to 8.11 . Recording material for thermal printing comprising a composition according to any of claims 9 or 10.

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