PROCESS OF PREPARATION OF AN AQUEOUS GEL INK WITH FIXED COLOR COMPRISING GOLD NANOPARTICLES

Abstract

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.

Claims

1. 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 chosen from esters, amides and thioesters of citric acid, salts of citric acid or of said derivatives, solvates of citric acid or of said derivatives, such as hydrates, and mixture thereof, (ii) adding a solution of gold salts (Au.sup.3+), (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.

2. The process according to claim 1, wherein said reducing agent is chosen from citric acid and/or esters of citric acid, salts and solvates of citric acid or of said ester derivatives, and mixtures thereof.

3. The process according to claim 1 or claim 2, wherein the concentration of citric acid and derivatives in the gel-based matrix of aqueous ink of step (i) ranges from 0.10 to 0.50 mol.L.sup.−1.

4. The process according to claim 1, wherein the concentration of gold salts in the gel-based matrix of aqueous ink of step (ii) ranges from 0.001 to 0.1 mol. L.sup.−1.

5. The process according to claim 1, wherein the concentration of iron powder in the gel-based matrix of aqueous ink of step (iii) ranges from 0.01 to 0.05 mol.L.sup.−1.

6. The process according to claim 1, wherein the concentration of polyvinylpyrrolidone in the aqueous gel ink of step (iv) ranges from 0.005 to 0.1%.

7. An aqueous gel ink with fixed color obtained according to the process of claim 1, comprising citric acid and derivatives, gold nanoparticles, and iron powder.

8. The aqueous gel ink according to claim 7, wherein the total amount of citric acid and of said citric acid derivatives ranges from 5 to 15% by weight relative to the total weight of the aqueous gel ink.

9. The aqueous gel ink according to claim 7, wherein the gold nanoparticles have an average particle size ranging from 10 to 200 nm.

10. The aqueous gel ink according to claim 7, wherein the gold nanoparticles are gold nanoparticles with the shape of urchins.

11. The aqueous gel ink according to claim 7, wherein the amount of gold nanoparticles ranges from 0.05 to 0.5% by weight relative to the total weight of the aqueous gel ink.

12. The aqueous gel ink according to claim 7, wherein the amount of iron powder ranges from 0.01 to 0.1% by weight relative to the total weight of the aqueous gel ink.

13. The aqueous gel ink according to claim 7, wherein the amount of water ranges from 50 to 95% by weight relative to the total weight of the aqueous gel ink.

14. The aqueous gel ink according to claim 7, further comprising: a solvent; and/or a corrosion inhibitor, in an amount ranging from 0.05 to 1% by weight relative to the total weight of the aqueous gel ink; and/or an antifoam agent, in an amount ranging from 0.05 to 1% by weight relative to the total weight of the aqueous gel ink; and/or a rheology modifier, in an amount ranging from 0.1 to 2% by weight relative to the total weight of the aqueous gel ink; and/or an antimicrobial agent, in an amount ranging from 0.01 to 0.5% by weight relative to the total weight of the aqueous gel ink.

15. A writing instrument comprising: an axial barrel containing an aqueous gel ink with fixed color according to claim 7, and a pen body which delivers the aqueous gel ink stored in the axial barrel, wherein the writing instrument is chosen in the group consisting of gel pens, felt pens, correction fluid, and markers.

Description

EXAMPLES

Example 1

Preparation of an Aqueous Gel Ink with Fixed Color Based on Citric Acid, Gold Nanoparticles, and Iron Powder, According to the Process of the Present Invention

[0089] In a first step (i), a gel-based matrix of aqueous ink was prepared by mixing 15 g of triethylene glycol (solvent), 4 g of polyethylene glycol (solvent), 0.19 g of Acticide® MBS (antimicrobial agent), and 0.1 g of Additin® RC8221 (corrosion inhibitor). The mixture was homogenised with a homogenizer mixer at a speed of 15 m.s.sup.−1 during 15 minutes and heated at a temperature of 35° C. Then, 0.4 g of xanthan gum (rheology modifier) was added to the mixture. The mixture was homogenized with a homogenizing mixer at a speed of 15 m.s.sup.−1 during 15 minutes at a temperature of 35° C. 80.01 g of deionized water was slowly added to the mixture. The mixture was left to stand for 2 h 30. Then, 0.3 g of Moussex® S 9092 (antifoam agent) was added. The mixture was homogenized with a homogenizing mixer at a speed of 15 m.s.sup.−1 during 30 minutes at a temperature of 35° C. The gel-based matrix of aqueous ink obtained was cooled at room temperature (25° C.). Then, 1 mL of the obtained gel-based matrix of aqueous ink was mixed with 0.11 g of citric acid (27491 from Fluka). The mixture was homogenised with a homogenizer mixer at a speed of 400 rpm during 5 minutes.

[0090] In a second step (ii), 50 μL of a solution of gold (III) chloride trihydrate (520918-1G from Sigma-Aldrich) (200 mM) was introduced into the mixture, and homogenised at a speed of 400 rpm during 10 minutes.

[0091] After the addition of the solution of gold (III) chloride trihydrate by continuous injection, the color of the aqueous gel ink was yellow.

[0092] In a third step (iii), 0.01 g of iron powder (spherical iron powder, <10 μm, Reference: 00170, from Alfa Aesar) was added to the dispersion of gold nanoparticles obtained at the end of step (ii). The mixture was homogenized with a homogenizing mixer at a speed of 400 rpm during 5 to 10 minutes.

[0093] After the addition of the solution of silver nitrate by continuous injection, the color of the aqueous gel ink was blue.

[0094] The average particle size of the gold nanoparticles present within the aqueous gel ink is of 50 nm by analysis of 2D images (microscope: JEOL ARM 200), according to the standard ISO9001:2015.

[0095] When the obtained aqueous gel ink with fixed color was written on cellulosic paper, the color appeared immediately blue and did not change after all.

[0096] Thus, the color of the ink is the same before application on cellulosic paper and after application on cellulosic paper.

[0097] Furthermore, a visual assessment of the color of this aqueous gel ink was realized over time. As can be seen from Table 1, the color of the aqueous gel ink did not change over time.

TABLE-US-00001 TABLE 1 Example 1 - Visual assessment of the color of aqueous gel ink over time Time 0 min 2 min 1 hour 1 day 1 week Color of the aqueous blue blue blue blue blue gel ink before application onc cellulosi paper Color of the aqueous blue Blue blue blue blue gel ink after application on cellulosic paper

Comparative Example 1

Preparation of an Aqueous Gel Ink Based on Citric Acid and Gold Nanoparticles, without Iron Powder

[0098] In a first step, a gel-based matrix of aqueous ink was prepared by mixing 15 g of triethylene glycol (solvent), 4 g of polyethylene glycol (solvent), 0.19 g of Acticide® MBS (antimicrobial agent), and 0.1 g of Additin° RC8221 (corrosion inhibitor). The mixture was homogenised with a homogenizer mixer at a speed of 15 m.s.sup.−1 during 15 minutes and heated at a temperature of 35° C. Then, 0.4 g of xanthan gum (rheology modifier) was added to the mixture. The mixture was homogenized with a homogenizing mixer at a speed of 15 m.s.sup.−1 during 15 minutes at a temperature of 35° C. 80.01 g of deionized water was slowly added to the mixture. The mixture was left to stand for 2h30. Then, 0.3 g of Moussex® S 9092 (antifoam agent) was added. The mixture was homogenized with a homogenizing mixer at a speed of 15 m.s.sup.−1 during 30 minutes at a temperature of 35° C. The gel-based matrix of aqueous ink obtained was cooled at room temperature (25° C.). Then, 1 mL of the obtained gel-based matrix of aqueous ink was mixed with 0.11 g of citric acid (27491 from Fluka). The mixture was homogenised with a homogenizer mixer at a speed of 400 rpm during 5 minutes.

[0099] In a second step, 50 μL of a solution of gold (III) chloride trihydrate (520918-1G from Sigma-Aldrich) (200 mM) was introduced into the mixture, and homogenised at a speed of 400 rpm during 10 minutes. After the addition of the solution of gold (III) chloride trihydrate by continuous injection, the color appeared yellow.

[0100] When the obtained aqueous gel ink was written on cellulosic paper, the color did not change and remained yellow.

[0101] Furthermore, a visual assessment of the color of this aqueous gel ink on cellulosic paper was realized over time.

[0102] As can be seen from Table 2, the color of the aqueous gel ink on cellulosic paper appears brown after 1 week.

[0103] Thus, the color of the ink is not the same before application on cellulosic paper and after application on cellulosic paper over time.

TABLE-US-00002 TABLE 2 Comparative example 1- Visual assessment of the color of aqueous gel ink over time Time 0 min 2 min 1 hour 1 day 1 week Color of the aqueous yellow yellow yellow yellow yellow gel ink before application on cellulosic paper Color of the aqueous yellow yellow yellow yellow brown gel ink after application on cellulosic paper