AQUEOUS LASER-SENSITIVE COMPOSITION FOR MARKING SUBSTRATES

1 . An aqueous composition comprising a colour former, a developer, and a binder, wherein

(a) the weight ratio between the developer and the colour former is in the range of from 1 to 5;

(b) the binder comprises an acrylate binder, comprising acrylic acid and styrene, and at least one additional monomer selected from the group consisting of α-methyl styrene, ethyl acrylate and 2-ethylhexyl acrylate; and

(c) the colour former and/or the developer are present in an un-encapsulated form.

2 . Composition according to claim 1 , wherein the colour former is a fluoran.

3 . Composition according to claim 2 , wherein the fluoran is at least one selected from the group consisting of 3-dibutylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isoamylamino)-6-methyl-7-anilinofluoran, 3-dipentylamino-6-methyl-7-anilinofluoran, and 3-(N-ethyl-N-p-tolylamino)-6-methyl-7-anilinofluoran.

4 . Composition according claim 1 , wherein the developer is selected from the group consisting of sulfonylurea derivatives, 4,4′-bis(p-toluenesulphonylaminocarbonylamino)diphenylmethane), 4,4′-bisphenol sulfone, 2,4′-dihydroxydiphenylsulfone, 4-hydroxy-4′-isopropoxydiphenylsulfone, 4-hydroxybenzoate derivative of a polypentaerythritol compound with CAS number 378244-93-0; phenol, 4,4′-sulfonylbis-polymer with 1,1′-oxobis(2-chloroethane); N,N′-[sulfonylbis[4,1-phenylene iminocarbonylimino(methylphenylene)]]bis-, C,C′-diphenyl ester; ZnCl 2 , octylammonium stearate and ammonium stearate.

5 . Composition according to claim 4 , wherein the developer is N-(p-toluenesulfonyl)-N′-3-(ptoluenesulfonyloxyphenyl)urea or phenol, 4,4′-sulfonylbis-polymer with 1,1′-oxobis(2-chloroethane).

6 . Composition according claim 1 , wherein the weight ratio between the developer and the colour forming compound is in the range of from 1.5 to 3.

7 . A process for preparing the composition of claim 1 , which comprises the step of mixing a colour former and a developer in a weight ratio in the range of from 1 to 5; a binder comprising an acrylate binder, comprising acrylic acid and styrene, and at least one additional monomer selected from the group consisting of α-methyl styrene, ethyl acrylate and 2-ethylhexyl acrylate; and wherein the colour former and/or the developer are present in an un-encapsulated form.

8 . A substrate coated with the composition of claim 1 .

9 . A process for preparing a coated substrate, which comprises the step of coating a substrate with the composition of claim 1 .

10 . A process for preparing a marked substrate, which comprises the steps of i) coating a substrate with the composition of claim 1 , and ii) exposing those parts of the coated substrate, where a marking is intended, to energy in order to generate a marking.

11 . The process of claim 10 , wherein the energy is selected from the group consisting of UV, IR, visible and microwave irradiation.

12 . A marked substrate, which is obtained by the process of claim 10 .

13 . A substrate coated with the composition of claim 2 .

14 . A process for preparing a coated substrate, which comprises the step of coating a substrate with the composition of claim 2 .

15 . A process for preparing a marked substrate, which comprises the steps of i) coating a substrate with the composition of claim 2 , and ii) exposing those parts of the coated substrate, where a marking is intended, to energy in order to generate a marking.