WRITING AND/OR DRAWING SYSTEM COMPRISING PH SENSITIVE DYE AND METHOD THEREOF

Abstract

The invention refers to a writing and/or drawing system comprising a pH sensitive dye and a writing material having a pH configured to provide a change in the colour of said dye on said surface of the support, as well as to a method to write and/or draw on the system with the writing material.

Claims

1) A writing and/or drawing system comprising a support having a surface and a device that includes a writing and/or drawing material suitable to write and/or draw on said support, characterised in that said support comprises a dye, said dye being pH-sensitive, whereby the colour of said dye is modified by a change of the pH on said support; said writing and/or drawing material having a pH configured to provide a change in the colour of said dye on said surface of the support.

2) The writing system according to claim 1, further including at least a second device including a further writing and/or drawing material having a pH suitable to bring the pH of the areas of said support at least to its initial value and to return the initial colour to said dye, whereby the applied writing is removed.

3) The writing system according to claim 1 or 2, wherein said support includes a fabric, preferably a woven fabric, and said dye is applied to said fabric.

4) The writing system according to claim 3, wherein said fabric includes cellulosic fibers.

5) The writing system according to any previous claim, wherein said support is one of a canvas, notepad, billboard and publicity poster.

6) The writing system according to claim 5, wherein said support is a canvas, preferably an un-primed canvas.

7) The writing system according to any previous claim, wherein said dye is selected from: 1-(2-pyridylazo)-2-naphtol (PAN); Alizarin Red S (3,4-Dihydroxy-9,10-dioxo-2-anthracenesulfonic acid sodium salt); Bromocresol green (3′,3″,5′,5″-Tetrabromo-m-cresolsulfonephthalein); Bromocresol purple (5,5′-Dibromo-o-cresolsulfonephthalein); Bromophenol blue (3′,3″-Dibromothymolsulfonephthalein); Indigo Carmine GR (Indigo-5,5′-disulfonic acid disodium salt); Methyl Blue (Aniline blue water soluble); Thymol Blue (Thymolsulfonphthalein); and mixtures thereof.

8) The writing system according to any previous claims 1 to 6, wherein said dye is selected from: Benzopurpurine 4; Congo Red; Eriochrome Black T; Iodine; Methyl Orange (4-[4-(Dimethylamino)phenylazo]benzenesulfonic acid sodium salt); Xylenol Orange tetrasodium salt (3,3′-Bis[N,N-bis(carboxymethyl)aminomethyl]-o-cresol sulfonephthalein tetrasodium salt); and mixtures thereof.

9) The writing system according to any previous claims 1 to 6, wherein said dye is selected from: Phenolphthalein (3,3-Bis(4-hydroxyphenyl)-1(3H)-isobenzofuranone); Thymolphthalein (5′,5″-Diisopropyl-2′,2″-dimethylphenolphthalein) and mixtures thereof.

10) The writing system according to any previous claims 1 to 9, wherein the writing material is an aqueous basic solution or an aqueous acid solution.

11) A writing and/or drawing support having a surface, characterised in that said support comprises a dye, said dye being pH-sensitive, whereby the colour of said dye is modified by a change of the pH on said support.

12) The writing support of claim 11, wherein said support is as disclosed in any one of claims 3 to 6.

13) A method for writing and/or drawing on a support comprising the following steps: a) providing a support having a surface and a writing and/or drawing material suitable to write and/or draw on said support, applying a dye to said support; b) applying said writing and/or drawing material to said support, whereby a writing and/or drawing on said support is obtained; characterized in that the support comprises a dye, said dye being pH-sensitive, whereby the colour of said dye is modified by a change of the pH on said support; said writing and/or drawing material having a pH configured to provide a change in the colour of said dye on said surface of the support.

14) The method of claim 13, wherein step c) is further comprised: c) applying a further writing and/or drawing material having a pH suitable to bring the pH of the areas of said support at least to its initial value and to return the initial colour to said dye.

15) The method of claim 13 or 14, further comprising before step b) the additional steps of: a′) drying the support; and a″) fixing the dye on said support.

16) The method of any one of claims 13 to 15, wherein said support includes a fabric, preferably a woven fabric, and said dye is applied to said fabric fibers.

17) The method of any one of claims 13 to 16, wherein said support is one of canvas, notepad, billboard and publicity poster.

18) The method of any one of claims 13 to 17, wherein said dye is selected from the dyes of claim 7, or of claim 8, or of claim 9.

Description

DESCRIPTION OF THE FIGURE

[0061] FIG. 1 is a scheme representing embodiments of the method of the invention.

DETAILED DESCRIPTION OF THE FIGURE AND EXPERIMENTAL SECTION

[0062] The invention will be further illustrated by means of FIG. 1 and of examples that are provided for illustrative purposes only and do not aim to limit the scope of the invention.

Example 1—Preparation of the Support by Drop-Casting

[0063] A pH sensitive board including cotton fabric is prepared as follows. A 5 g/l solution of Alizarin Red S is prepared by dissolving 5 g of Alizarin Red S (3,4-Dihydroxy-9,10-dioxo-2-anthracenesulfonic acid sodium salt) in 1 l of distilled water in volumetric flask and by stirring for 5 minutes. The cotton fabric 100 is dyed by drop-casting using the Alizarin Red S solution. The board is dried at 100° C. for 1 min and then dye is fixed at 110° C. for 1 min. The cotton fabric 101 so-obtained has a brick red colour.

Example 2—Preparation of the Support by Pad-Batch Dyeing

[0064] A pH sensitive fabric is prepared as follows. A 5 g/l solution of Alizarin Red S is prepared as for Example 1. The fabric 100 is dyed with the Alizarin Red S solution using a pad-batch dyeing machine. The pad-batch dyeing is carried out with a pressure of the cylinders of 2 bar and a speed of 2 m/min. The fabric is dried at 100° C. for 1 min and then is fixed at 110° C. for 1 min. The fabric 101 so-obtained has a brick red colour.

Example 3—Writing and/or Drawing Tests

[0065] A solution of 1.0 M sodium hydroxide prepared by dilution of 47° Be NaOH with deionized water is used as basic writing material for the present test. A solution of 1.0 M hydrochloric acid prepared by dilution of 37% concentrated HCl solution with deionized water is used as acidic writing material for the present test. According to the embodiment on the right branch of the scheme of FIG. 1, drops of HCl solution is applied to the brick-red coloured fabric 101 obtained as for Example 1 or Example 2. The areas of the fabric 101 where the HCl solution is applied change colour from brick red to yellow, and a fabric 103 having yellow areas (i.e. yellow writings/drawings) is obtained. The application of the writing material can also be made for example by means of a paintbrush. Afterwards, drops of the NaOH solution are applied to the yellow-coloured areas of the fabric 103, and the colours of these areas change from yellow to purple, thus obtaining a fabric 102 having purple areas (i.e. purple writings/drawings). In order to erase the purple coloured areas and to obtain the original fabric 101, the pH of the purple coloured areas of fabric 102 has to be brought to the operational range pH of the dye, which is about pH 4.6-6.0 for Alizarin Red S; accordingly, to return to the original red-brick colour, the pH has to be adjusted to about 5-5.5, which can be made by preparing a writing material, i.e. an aqueous solution, having suitable pH and by applying it to the purple coloured areas. According to the embodiment on the left branch of the scheme of FIG. 1, the same test as above is also carried out by applying first the NaOH solution to the dyed fabric 101 obtained as for Example 1 or Example 2, providing a fabric 102 having purple coloured areas. Afterwards, the HCl solution is applied to the purple areas of fabric 102, providing a fabric 103 having yellow coloured areas.

[0066] These yellow coloured areas can be returned to the original red-brick colour by using a solution having an appropriate pH.