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

Abstract

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.

Claims

1. 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, and an alkali metal hydride, an oxidizing agent, 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.

2. The process according to any of claim 1, wherein the amount of said citrate salts added in step (ii) ranges from 0.001 to 0.08 weight % based on the total weight of the aqueous suspension.

3. The process according to claim 1, wherein the total amount of silver salts added in step (ii) ranges from 0.0005 to 0.006 weight % based on the total weight of the aqueous suspension.

4. The process according to claim 1, wherein the amount of alkali metal hydride added in step (ii) ranges from 0.0005 to 0.005 weight % based on the total weight of the aqueous suspension.

5. The process according to claim 1, wherein the amount of oxidizing agent added in step (ii) ranges from 0.03 to 0.1 weight % based on the total weight of the aqueous suspension.

6. The process according to claim 1, wherein the amount of polyvinylpyrrolidone added in step (ii) ranges from 0.05 to 0.1 weight % based on the total weight of the aqueous suspension.

7. The process according to claim 1, wherein the silver nanoparticles obtained in step (ii) are silver nanoparticles with the shape of spheres.

8. An aqueous suspension of silver nanoparticles with a fixed color obtainable by the process of claim 1, comprising silver nanoparticles and polyvinylpyrrolidone.

9. An aqueous gel ink with fixed color obtainable by the process of claim 1, comprising silver nanoparticles and polyvinylpyrrolidone.

10. The aqueous gel ink according to claim 9, further comprising an alkali metal salt, wherein the amount of alkali metal salt is of at least 0.0003 weight % based on the total weight of the aqueous gel ink.

11. The aqueous gel ink according to claim 9, wherein the silver nanoparticles have an average particle size ranging from 1 to 100 nm.

12. The aqueous gel ink according to claim 9, wherein the amount of silver nanoparticles ranges from 0.0005 to 5 weight % relative to the total weight of the aqueous gel ink.

13. The aqueous gel ink according to claim 9, 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 9, further comprising: a co-solvent, in an amount ranging from 5 to 35% 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; 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 0.08 to 2% 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 9, 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.

16. The aqueous suspension according to claim 8, further comprising an alkali metal salt, wherein the amount of alkali metal salt is of at least 0.0003 weight % based on the total weight of the aqueous suspension.

17. The aqueous suspension according to claim 8, wherein the silver nanoparticles have an average particle size ranging from 1 to 100 nm.

18. The aqueous suspension according to claim 8, wherein the amount of silver nanoparticles ranges from 0.0005 to 5 weight % relative to the total weight of the aqueous suspension.

19. The aqueous suspension according to claim 8, wherein the amount of water ranges from 50 to 95% by weight relative to the total weight of the aqueous suspension.

20. The aqueous gel ink according to claim 10, wherein the silver nanoparticles have an average particle size ranging from 1 to 100 nm.

Description

EXAMPLE 1: PREPARATION OF AN AQUEOUS GEL INK WITH FIXED COLOR ACCORDING TO THE PROCESS OF THE PRESENT INVENTION

[0125] Preparing a Gel-Based Matrix of Aqueous Ink (Step (i))

[0126] In a first step (i), a gel-based matrix of aqueous ink was prepared by mixing 15 g of triethylene glycol (co-solvent), 4 g of polyethylene glycol (co-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.Math.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.Math.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 h30. 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.Math.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.).

[0127] Preparing an Aqueous Suspension of Silver Nanoparticles with Red Color (Step (ii))

[0128] In a second step (ii), an aqueous suspension of silver nanoparticles with a fixed color is prepared by mixing 42.527 mL of distilled water, 0.473 mL of a solution of silver nitrate (10 mM) (9370.1 Cark Roth), 3.68 mL of trisodium citrate (30 mM) (S1804-500G Sigma Aldrich), 3.68 mL of polyvinylpyrrolidone 2% (PVP40-100G Sigma Aldrich) and 120 μL hydrogen peroxide 0% (412071 Carlo Erba), 100 μL of sodium borohydride NaBH.sub.4 (100 mM)(71321-25G Fluka Analytical).

[0129] The mixture was homogenised with a homogenizer mixer at a speed of 400 rpm during 15 to 30 minutes.

[0130] Then, 840 μL of AgNO3 (10 mM) are added to the mixture with a homogenizer mixer at a speed of 400 rpm during 10 min.

[0131] The mixture is heated at 100° C., then 350 μL of NaBH.sub.4 (10 mM) are added. When NaBH.sub.4 is added to the mixture, the resulting solution immediately changed from transparent to colored. This color is due to the plasmonic effect.

[0132] The mixture is stopped when the expected red color is obtained.

[0133] It should be noted that the color of the aqueous suspension of silver nanoparticles depends on the proportion of reducing agent NaBH.sub.4. The resulting composition exhibits a plasmonic effect, which means that its color is due to the plasmon effect i.e. due to the light absorption by the nanoparticles dispersion.

[0134] For example:

[0135] The addition of 200 μL NaBH.sub.4 in the mixture described above ensures a pink suspension of silver nanoparticles (test 1)

[0136] The addition of 250 μL NaBH.sub.4 in the mixture described above ensures a clear purple suspension of silver nanoparticles (test 2).

[0137] The addition of 300 μL NaBH.sub.4 in the mixture described above ensures a purple suspension of silver nanoparticles (test 3).

[0138] The addition of 600 μL NaBH.sub.4 in the mixture described above ensures a blue suspension of silver nanoparticles (test 4).

[0139] The addition of 970 μL NaBH.sub.4 in the mixture described above ensures a red suspension of silver nanoparticles (test 5)

[0140] Preparing the Aqueous Gel Ink with Fixed Color (Step (iii))

[0141] In a third step (iii), 1 mL of the aqueous suspension of silver nanoparticles obtained in step (ii) is added to 1 mL of the gel-based matrix of aqueous ink obtained in step (i) to obtain an aqueous gel ink with fixed color (red color) with silver nanoparticles dispersed therein and stabilized by 0.07% of polyvinylpyrrolidone.

[0142] Test 1: After adding on the gel-based matrix of aqueous ink, the color initially pink appears immediately pink.

[0143] Test 2: After adding on the gel-based matrix of aqueous ink, the color initially clear purple appears immediately clear purple.

[0144] Test 3: After adding on the gel-based matrix of aqueous ink, the color initially purple appears immediately purple

[0145] Test 4: After adding on the gel-based matrix of aqueous ink, the color initially blue appears immediately blue

[0146] Test 5: After adding on the gel-based matrix of aqueous ink, the color initially blue appears immediately red.

[0147] Test 1: When the obtained aqueous gel ink with fixed color was written on cellulosic paper, the color appeared immediately pink and did not change after all.

[0148] Test 2: When the obtained aqueous gel ink with fixed color was written on cellulosic paper, the color appeared immediately clear purple and did not change after all.

[0149] Test 3: When the obtained aqueous gel ink with fixed color was written on cellulosic paper, the color appeared immediately purple and did not change after all.

[0150] Test 4: 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.

[0151] Test 5: When the obtained aqueous gel ink with fixed color was written on cellulosic paper, the color appeared immediately red and did not change after all. Furthermore, a visual assessment of the color of this aqueous gel ink was realized over time (tests 1, 2, 3, 4, 5)

[0152] 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 (Tests 1, 2, 3, 4, 5) over time Time 0 min 2 min 1 hour 1 day 1 week Test 1 Color of the aqueous gel pink pink pink pink pink ink before application on cellulosic paper Color of the aqueous gel Pink pink pink pink pink ink after application on cellulosic paper Test 2 Color of the aqueous gel Clear Clear Clear Clear Clear ink before application on purple purple purple purple purple cellulosic paper Color of the aqueous gel Clear Clear Clear Clear Clear ink after application on purple purple purple purple purple cellulosic paper Test 3 Color of the aqueous gel Purple Purple Purple Purple Purple ink before application on cellulosic paper Color of the aqueous gel Purple Purple Purple Purple Purple ink after application on cellulosic paper Test 4 Color of the aqueous gel Blue Blue Blue Blue Blue ink before application on cellulosic paper Color of the aqueous gel Blue Blue Blue Blue Blue ink after application on cellulosic paper Test 5 Color of the aqueous gel Red Red Red Red Red ink before application on cellulosic paper Color of the aqueous gel Red Red Red Red Red ink after application on cellulosic paper