The present invention concerns a process for preparing an aqueous gel ink with fixed color comprising the following steps: (i) preparing a gel-based matrix of aqueous ink; (ii) preparing an aqueous suspension of silver nanoparticles with a fixed color by mixing silver salts with: —water, —a mixture of at least an alkali metal or alkaline earth metal salt of citrate, —an oxidizing agent, preferably hydrogen peroxide H.sub.2O.sub.2, —and polyvinylpyrrolidone; (iii) adding under agitation the aqueous suspension of silver nanoparticles obtained in step (ii) to the gel-based matrix of aqueous ink obtained in step (i), to obtain an aqueous gel ink with fixed color with silver nanoparticles dispersed therein.

The present invention concerns a process for preparing an aqueous gel ink with fixed color comprising the following steps: (i) preparing a gel-based matrix of aqueous ink; (ii) preparing an aqueous suspension of silver nanoparticles with fixed color by mixing silver salts with: water, a mixture of at least an alkali metal or alkaline earth metal salt of citrate, preferably an alkali citrate salt and an alkali metal hydride, preferably NaBH4, a further reducing agent, preferably ascorbic acid, and oxidizing agent, preferably hydrogen peroxide H.sub.2O.sub.2 (iii) adding under agitation the aqueous suspension of silver nanoparticles obtained in step (ii) to the gel-based matrix of aqueous ink obtained in step (i), to obtain an aqueous gel ink with fixed color with silver nanoparticles dispersed therein

The present invention concerns a process for preparing in situ an aqueous gel ink with fixed color comprising the following steps: (i) preparing a gel-based matrix of aqueous ink comprising ester(s) of retinol represented by formula (I), and (ii) adding a solution of gold salts (Au3+) to the gel-based matrix of aqueous ink prepared in step (i), to obtain an aqueous gel ink with fixed color with gold nanoparticles dispersed therein. The present invention also relates to an aqueous gel ink with fixed color obtained according to the process of the invention, comprising said ester of retinol represented by formula (I) and gold nanoparticles. The invention finally concerns a writing instrument comprising an aqueous gel ink with fixed color according to the invention.

##STR00001##

The present invention concerns a process for preparing in situ an aqueous gel ink with fixed color comprising the following steps: (i) preparing a gel-based matrix of aqueous ink comprising reducing agent chosen in the group consisting of citric acid and/or derivatives of citric acid, (ii) adding a solution of gold salts, (iii) adding iron powder, (iv) adding polyvinylpyrrolidone to obtain an aqueous gel ink with fixed color, wherein the steps (ii) and (iii) can be interchanged. The present invention also relates to an aqueous gel ink with fixed color obtained according to the process of the invention, comprising citric acid and derivatives, gold nanoparticles, and iron powder. The invention finally concerns a writing instrument comprising an aqueous gel ink with fixed color according to the invention.

The present invention concerns a process for preparing in situ an aqueous gel ink with variable color comprising the following steps: (i) preparing a gel-based matrix of aqueous ink comprising an N-Acyl-aminophenol, wherein said hydroxyl group is preferably in meta or in para position on the benzenic group, and (ii) adding a solution of silver salts to the gel-based matrix of aqueous ink prepared in step (i), to obtain an aqueous gel ink with variable color with silver nanoparticles dispersed therein. The present invention also relates to an aqueous gel ink with variable color obtained according to the process of the invention, comprising an N-Acyl-aminophenol, wherein said hydroxyl group is preferably in meta or in para position on the benzenic group and silver nanoparticles. The invention finally concerns a writing instrument comprising an aqueous gel ink with variable color according to the invention.

The invention relates a process for preparing an aqueous gel ink with fixed color comprising the following steps: (i) preparing a gel-based matrix of aqueous ink; (ii) preparing an aqueous suspension of gold or silver nanoparticles with a fixed color; (iii) adding the aqueous suspension of gold or silver nanoparticles obtained in step (ii) to the gel-based matrix of aqueous ink obtained in step (i).

An object of the present invention is to provide: a developer that can provide a thermosensitive recording material excellent in color development sensitivity and storage stability; and a thermosensitive recording material obtained using the developer. The object is achieved by a developer including a compound represented by the following Formula (1).

##STR00001##

In Formula (1), a, A, and L are as follows: a is an integer selected from 1 to 5, A is each independently a fluoro group or a perfluoroalkyl group, and L is any of functional groups represented by the following Formula (2):

##STR00002##

wherein in Formula (2), R is a C.sub.1-C.sub.4 alkyl group, and * represents a binding site to a sulfur atom in Formula (1).

The present invention concerns a process for preparing in situ an aqueous gel ink with variable color comprising the following steps: (i) preparing a gel-based matrix of aqueous ink comprising 0.005 to 0.1 mol.Math.L.sup.−1 of ester(s) of retinol represented by formula (I), and (ii) adding a solution of 0.002 to 0.05 mol.Math.L.sup.−1 silver salts (Ag.sup.+) to the gel-based matrix of aqueous ink prepared in step (i), to obtain an aqueous gel ink with variable color with silver nanoparticles dispersed therein. The present invention also relates to an aqueous gel ink with variable color obtained according to the process of the invention, comprising said ester of retinol represented by formula (I) and silver nanoparticles. The invention finally concerns a writing instrument comprising an aqueous gel ink with variable color according to the invention

The disclosure provides a microcapsule type thermochromic pigment and a preparation method and use thereof, and a thermochromic ink and use thereof. The microcapsule type thermochromic pigment provided by the disclosure includes a core material and a wall material wrapping the core material, wherein the core material includes the following components: a leuco dye, a developer and stearic acid 2-[4-(phenylmethoxy)phenyl]ethyl ester, and the wall material is self-emulsifying polyurethane or self-emulsifying epoxy resin.

The present disclosure provides an ink composition and a method for preparing an ink composition. The ink composition includes following compositions in parts by weight salt solution in an amount ranging from 500-1000 parts; iron filings in an amount ranging from 20-30 parts; hydrogen chloride in an amount ranging from 2-5 parts; deionized water in an amount ranging from 40-50 parts; monoglyceride stearate in an amount ranging from 1-2 parts; monolauryl phosphate and polydimethylsiloxane in an amount ranging from 5-10 parts; methacrylate in an amount ranging from 5-10 parts; thermoplastic acrylic resin in an amount ranging from 5-10 parts; sodium dioctyl succinate sulfonate in an amount ranging from 2-5 parts; sodium dodecyl benzene sulfonate in an amount ranging from 2-5 parts; polyoxyethylene octyl phenol ether in an amount ranging from 3-8 parts; and isobutyl p-hydroxybenzoate in an amount ranging from 0.5-1 parts.