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 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

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 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, a further reducing agent, and oxidizing agent, (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 claim 1, wherein step ii) comprises: a first step ii.a) of mixing said alkali metal or alkaline earth metal salt of citrate salts with said alkali metal hydride, and with said oxidizing agent followed by a second step ii.b) comprising the addition of said further reducing agent, and followed by a third step ii.c) comprising a further addition of silver salt.

3. The process according to claim 1, wherein the total amount of said citrate salts added in step (ii) ranges from 0.02 to 0.1 weight % based on the total weight of the aqueous suspension.

4. The process according to claim 1, wherein the total amount of silver salts added in step (ii) ranges from 0.0001 to 5 weight % based on the total weight of the aqueous suspension.

5. The process according to claim 1, wherein the amount of alkali metal hydride added in step (ii) ranges from 0.0005 to 0.002 weight % based on the total weight of the aqueous suspension.

6. The process according to claim 1, wherein the amount of oxidizing agent added in step (ii) ranges from 0.001 to 0.005 weight % based on the total weight of the aqueous suspension.

7. The process according to claim 1, wherein said further reducing agent is ascorbic acid and/or the amount of the further reducing agent added in step (ii) ranges from 0.002 to 0.01 weight % based on the total weight of the aqueous suspension.

8. An aqueous suspension of silver nanoparticles with fixed color obtainable by the process of any claim 1, comprising silver nanoparticles dispersed therein.

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

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 0.002 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 200 nm.

12. The aqueous gel ink according to claim 9, wherein the amount of silver nanoparticles ranges from 0.0001 to 3% by weight relative to the total weight of the aqueous gel ink.

13. The aqueous gel ink according to 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 any of claims 9 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 0.002 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 200 nm.

18. The aqueous suspension according to claim 8, wherein the amount of silver nanoparticles ranges from 0.0001 to 3% by 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. 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 citrate salt and sodium borohydride NaBH.sub.4, ascorbic acid, 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.

Description

EXAMPLE 1

Preparation of an Aqueous Gel Ink with Fixed Color According to the Process of the Present Invention

[0134] Preparing a Gel-Based Matrix of Aqueous Ink (Step (i))

[0135] 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 Additie RC8221 (corrosion inhibitor). The mixture was homogenised with a homogenizer mixer at a speed of 15 m.5.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.5.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.5.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.).

[0136] Preparing an Aqueous Suspension of Silver Nanoparticles with Fixed Color (Step (ii))

[0137] In a second step (ii), an aqueous suspension of silver nanoparticles with a fixed color is prepared by mixing 39.3 mL of distilled water, 2 mL of trisodium citrate (75 mM) (S1804-500G Sigma Aldrich), 186 μL of a solution of silver nitrate (10 mM) (9370.1 Cark Roth) and 256 μL hydrogen peroxide 0.6% (412071 Carlo Erba) with a homogenizer mixer at a speed of 400 rpm during 5 minutes,

[0138] Then 192 μL of sodium borohydride (100 mM) (71321-25G Fluka Analytical) was rapidly added to initiate reduction, and the solution immediately changed from transparent to a pale yellow color (nucleation step).

[0139] The solution was stored overnight at room temperature.

[0140] Then 200 μL of L-ascorbic acid (5 mM) (A92902-100G Sigma Aldrich) was added to this mixture, followed by addition of silver nitrate (10 mM) dropwise until the desired solution color was reached.

[0141] It should be noted that the color of the aqueous suspension of silver nanoparticles depends on the amount of silver nitrate added at this stage of the process (growing step).

[0142] 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.

[0143] The addition of 2 drops (100 μL by drop) of silver nitrate AgNO.sub.3 at this step lets to obtain a yellow suspension (test 1).

[0144] The addition of 4 drops (100 μL by drop) of silver nitrate AgNO.sub.3 at this step lets to obtain an orange suspension (test 2).

[0145] The additions of 7 drops (100 μL by drop) of silver nitrate AgNO.sub.3 at this step lets to obtain a red suspension (test 3).

[0146] Preparing the Aqueous Gel Ink with Fixed Color (Step (iii))

[0147] In a third step (iii), 1 mL of the aqueous suspension of silver nanoparticles obtained in step (ii) is added to 1mL of 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.

[0148] Test 1: After adding on the gel-based matrix of aqueous ink, the color initially yellow appears immediately pink.

[0149] Test 2: After adding on the gel-based matrix of aqueous ink, the color initially orange appears immediately blue.

[0150] Test 3: After adding on the gel-based matrix of aqueous ink, the color initially red appears immediately black.

[0151] 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.

[0152] Test 2: 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.

[0153] Test 3: When the obtained aqueous gel ink with fixed color was written on cellulosic paper, the color appeared immediately black and did not change after all.

[0154] Furthermore, a visual assessment of the color of this aqueous gel inks was realized over time (tests 1, 2, and 3).

[0155] 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 (Test 1, 2, 3) over time Time 0 min 2 min 1 hour 1 day 1 week Test 1 Color of the pink pink pink pink pink aqueous gel ink before application on cellulosic paper Color of the pink pink pink pink pink aqueous gel ink after application on cellulosic paper Test 2 Color of the blue blue blue blue blue aqueous gel ink before application on cellulosic paper Color of the blue blue blue blue blue aqueous gel ink after application on cellulosic paper Test 3 Color of the black black black black black aqueous gel ink before application on cellulosic paper Color of the black black black black black aqueous gel ink after application on cellulosic paper