METAL DISPERSION WITH INCREASED STABILITY

Abstract

The invention relates to metal dispersions comprising 50 to 80 wt % of silver nanoparticles, 15 to 45 wt % of water and a dispersant, wherein the dispersant comprises copolymers comprising 1-99 wt % of structural units of formula (1),

##STR00001##

where
R is hydrogen or C.sub.1-C.sub.6 alkyl,
A is C.sub.2-C.sub.4 alkylene group and
B is C.sub.2-C.sub.4 alkylene group with the proviso that A and B are different and
m, n are each independently an integer of 1-200, and
1-99 wt % of structural units of formula (2),

##STR00002##

where
X.sub.a is an aromatic or aliphatic radical having 1 to 30 carbon atoms which optionally comprises one or more, for example 1, 2, or 3, heteroatoms N, O and S,
Z.sub.a is H or (C.sub.1-C.sub.4)-alkyl,
Z.sub.b is H or (C.sub.1-C.sub.4)-alkyl and
Z.sub.c is H or (C.sub.1-C.sub.4)-alkyl.

Claims

1. A metal dispersion comprising 50 to 80 wt % of silver nanoparticles, 15 to 45 wt % of water and a dispersant, wherein the dispersant comprises copolymers having 1-99 wt % of structural units of formula (1), ##STR00005## wherein R is hydrogen or C.sub.1-C.sub.6 alkyl, A is a C.sub.2-C.sub.4 alkylene group and B is a C.sub.2-C.sub.4 alkylene group with the proviso that A and B are different and m, n are each independently an integer of 1-200, and 1-99 wt % of structural units of formula (2), ##STR00006## wherein X.sub.a is an aromatic or aliphatic radical having 1 to 30 carbon atoms, optionally comprising one or more heteroatoms N, O and S, Z.sub.a is H or (C.sub.1-C.sub.4)-alkyl, Z.sub.b is H or (C.sub.1-C.sub.4)-alkyl and Z.sub.c is H or (C.sub.1-C.sub.4)-alkyl.

2. The metal dispersion as claimed in claim 1, wherein A and/or B are an ethylene or propylene group or A is a propylene group and B is an ethylene group or A is a propylene group and B is an ethylene group.

3. The metal dispersion as claimed in claim 1, wherein m=2 to 7 and n=50 to 200.

4. The metal dispersion as claimed in claim 1, further comprising a solvent selected from the group consisting of water-soluble mono-alcohols, water-soluble dialcohols, and ethoxylated monoalcohols.

5. The metal dispersion as claimed in claim 1, wherein the composition of the structural units of formula (1) corresponds to at least one of the following polyglycols: TABLE-US-00007 polyglycol 1 polyalkylene glycol methacrylate (formula (1), m = 2, n = 12-13; (A-O) is [CH.sub.2CH(CH.sub.3)O)]; (B-O) is (CH.sub.2CH.sub.2O)); molar mass about 750 g/mol polyglycol 2 polyalkylene glycol methacrylate (formula (1), m = 2, n = 17-19; (A-O) is [CH.sub.2CH(CH.sub.3)O)]; (B-O) is (CH.sub.2CH.sub.2O)); molar mass about 1000 g/mol polyglycol 3 polyalkylene glycol methacrylate (formula (1), m = 5, n = 38-40; (A-O) is [CH.sub.2CH(CH.sub.3)O)]; (B-O) is (CH.sub.2CH.sub.2O)); molar mass about 2000 g/mol polyglycol 4 polyalkylene glycol methacrylate (formula (1), m = 5, n = 95-105; (A-O) is [CH.sub.2CH(CH.sub.3)O)]; (B-O) is (CH.sub.2CH.sub.2O)); molar mass about 5000 g/mol polyglycol 5 polyalkylene glycol methacrylate (formula (1), m = 5, n = 190-200; (A-O) is [CH.sub.2CH(CH.sub.3)O)]; (B-O) is (CH.sub.2CH.sub.2O)); molar mass about 12 000 g/mol.

6. The metal dispersion as claimed in claim 1, wherein the structural units of formula (2) derive from N-vinylimidazole, N-vinylpyrrolidone, N-vinylcaprolactam, acrylic acid or methacrylic acid.

7. The metal dispersion as claimed in claim 1, wherein the dispersion comprises 1-9 wt % of the dispersant.

8. The metal dispersion as claimed in claim 1, wherein the dispersion comprises additives in an amount of 0.1 to 1.0 wt %.

9. The metal dispersion as claimed in claim 1, wherein the particle size of the silver nanoparticles is between 5 and 100 nm in at least one dimension.

10. The metal dispersion as claimed in claim 1, wherein conductivity values of at least 1.8 E06 S/m are achieved by sintering at temperatures of 90 C.

11. A dispersant for stabilizing metal dispersions comprising 1-99 wt % of structural units of formula (1), ##STR00007## wherein R is hydrogen or C.sub.1-C.sub.6 alkyl, A is a C.sub.2-C.sub.4 alkylene group and B is a C.sub.2-C.sub.4 alkylene group with the proviso that A and B are different and m, n are each independently an integer of 1-200, and 1-99 wt % of structural units of formula (2), ##STR00008## wherein X.sub.a is an aromatic or aliphatic radical having 1 to 30 carbon atoms, optionally comprising one or more heteroatoms N, O and S, Z.sub.a is H or (C.sub.1-C.sub.4)-alkyl, Z.sub.b is H or (C.sub.1-C.sub.4)-alkyl and Z.sub.c is H or (C.sub.1-C.sub.4)-alkyl.

12. A method for producing a composition comprising the step of adding a metal dispersion as claimed in claim 1 to the composition during the manufacture of the composition, wherein the composition is selected from the group consisting of inks, paints, coatings and graphic printed matter.

13. A method for producing an electrically conductive coating comprising the step of adding a metal dispersion as claimed in claim 1 to the electrically conductive coating during the manufacture of the electrically conductive coating.

14. An ink, paint, coating or graphic printed matter comprising a metal dispersion as claimed in claim 1.

15. An electrically conductive coating comprising a metal dispersion as claimed in claim 1.

Description

EXAMPLES

[0046] The synthesis of the copolymers is effected as follows: A flask equipped with a stirrer, reflux cooler, internal thermometer and nitrogen inlet is initially charged, in the weight fractions reported in the following table, with the polyglycol of formula (1) and the acrylic monomer of formula (2) and also a molecular weight regulator in solvent while nitrogen is introduced. The temperature is then brought to 80 C. with stirring and a solution of the initiator is metered in over one hour. The mixture is stirred at this temperature for a further two hours. Further additives may be metered in subsequently. The composition of the copolymers is summarized in the following table.

TABLE-US-00002 TABLE 1 Inventive copolymers example 1 2 3 4 5 6 7 8 9 10 monomer 1 polyglycol 1 (M.sub.w = 750 g/mol) 67.7 67.7 62.5 59.8 polyglycol 2 (M.sub.w = 1000) 62.4 62.4 57.7 59.7 polyglycol 3 (M.sub.w = 2000) 67.7 67.7 polyglycol 4 (M.sub.w = 5000) polyglycol 5 (M.sub.w = 12 000) monomer 2 methacrylic acid 1.9 3.8 6.0 3.9 3.9 1.9 acrylic acid 4.0 4.1 6.0 10 vinylimidazole 1.9 2.0 5.9 vinylpyrrolidone 2.0 1.9 vinylcaprolactam 4.0 4.1 benzyl methacrylate 3.9 isobornyl methacrylate 2-ethylhexyl methacrylate 2.0 phenoxyethyl methacrylate initiator sodium peroxodisulfate 3.1 2.2 2.3 2.3 2.3 2.3 2.6 2.6 2.2 2.2 regulator mercaptopropionic acid 0.4 0.4 0.4 0.4 0.4 0.4 0.5 0.5 0.4 0.4 solvent water 25.0 26.8 26.9 25.8 butyl glycol 24.9 26.85 26.9 29.4 29.4 25.8 additive 1,2-benzisothiazol-3(2H)-one 0.1 0.15

TABLE-US-00003 TABLE 2 Inventive copolymers example 11 12 13 14 15 16 17 18 19 20 monomer 1 polyglycol 1 (M.sub.w = 750 g/mol) polyglycol 2 (M.sub.w = 1000) 4.0 polyglycol 3 (M.sub.w = 2000) 62.7 60.2 polyglycol 4 (M.sub.w = 5000) 65.8 67.7 63.7 63.7 polyglycol 5 (M.sub.w = 12 000) 67.7 62.4 62.6 62.5 monomer 2 methacrylic acid 8 2.9 3.9 3.9 8.0 4.0 acrylic acid 2.9 2.0 4.9 4.0 vinylimidazole 2.1 3.9 vinylpyrrolidone 1.9 vinylcaprolactam 4.0 benzyl methacrylate 4.0 isobornyl methacrylate 4.0 2-ethylhexyl methacrylate 6 phenoxyethyl methacrylate 2.1 initiator sodium peroxodisulfate 2.3 2.4 2.2 2.2 2.2 2.2 2.2 2.3 2.3 2.3 regulator mercaptopropionic acid 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 solvent water 26.6 25.9 25.9 23.6 26.7 butyl glycol 26.9 25.8 24.8 26.9 26.8 additive 1,2-benzisothiazol-3(2H)-one 0.1 0.1

Production of Metal Nanoparticles:

[0047] The nanoscale metal particles were produced in continuous fashion in a microreaction plant as per EP-2010314, paragraphs [0027] to [0056]. The thus obtained metal particle sols were purified by means of membrane filtration and concentrated to a metal content of 50-80 wt %. The dispersant content was determined as 1-9 wt %.

TABLE-US-00004 TABLE 3 Silver content and dispersant content content of silver dispersant and water example based content additive content on copolymer [wt %] [wt %] [wt %] 1 57.8 3.9 38.3 2 58.1 4.0 37.9 3 56.2 3.1 40.7 4 56.4 4.8 38.3 5 53.2 3.2 43.6 6 54.8 3.3 41.9 7 54.1 2.2 43.7 8 58.2 3.0 38.8 9 57.8 3.4 38.8 10 57.0 3.3 39.7 11 78.9 6.8 14.3 12 73.6 6.3 20.1 13 55.3 3.1 41.6 14 58.7 3.8 37.5 15 54.1 5.1 40.8 16 59.8 4.0 36.2 17 67.5 5.1 27.4 18 68.4 5.6 26.0 19 58.2 5.0 36.8 20 56.8 3.8 39.4 comparison 1 16.1 12.5 71.4 (US-2006044384 A) comparison 2 19.2 11.5 69.3 (US-2006044384 G) comparison 3 8 2.3 89.7 (WO-2012/055758) comparison 4 3.1 18.3 78.6 (U.S. Pat. No. 8,227,022)

[0048] For comparison, metal nanoparticles were produced as per US-20060044382 (Lexmark, example A [0019] and example G [0023]), WO-2012/055758 (Bayer Technology Services/BTS, example 1) and U.S. Pat. No. 8,227,022 and included as comparative examples 1, 2, 3 and 4.

Test Results

[0049] The silver sols obtained were stored at room temperature and the solids content of the dispersion (=sum of silver and dispersant content) was determined at intervals of 4, 8 and 16 weeks without stirring of the sample. A reduction in the solids content points to sedimentation of the silver particles and thus to a lower stability of the dispersion.

TABLE-US-00005 TABLE 4 Storability at room temperature solids solids solids content content content Ag sol after 4 weeks after 8 weeks after 16 weeks based on of storage of storage of storage copolymer [wt %] [wt %] [wt %] 1 61.5 61.3 61.6 2 62.0 62.3 61.8 3 59.3 59.0 58.9 4 61.0 61.2 61.0 5 56.5 56.3 56.2 6 57.8 57.9 57.8 7 56.3 56.3 56.1 8 61.0 61.4 61.0 9 60.8 61.0 61.2 10 60.5 60.2 59.8 11 78.6 78.7 78.5 12 73.5 73.7 73.5 13 58.4 58.1 58.0 14 62.3 62.6 62.6 15 59.3 59.3 59.1 16 63.5 63.4 63.3 17 67.2 67.1 66.8 18 68.4 68.2 67.9 19 63.5 63.3 63.2 20 60.1 60.1 59.8 comparison 1 25.2 20.3 12.8 (US-2006044384 A) comparison 2 27.3 22.1 13.1 (US-2006044384 G) comparison 3 7.8 6.5 4.1 (WO-2012055758 1) comparison 4 20.2 19.9 19.3 (U.S. Pat. No. 8,227,022)

[0050] As is apparent from the above table all silver sols based on the inventive polymers exhibit a markedly higher stability at room temperature than the prior art silver sols (comparison 1-4).

[0051] For electrical testing the metal sols obtained were applied by spin-coating to an 1818 mm glass sheet in a layer thickness between 0.1 and 10 m, preferably between 0.5 and 5 m. The glass plate was then subjected to thermal sintering at a defined temperature for 60 minutes in each case and surface resistance was measured by the four point method in [Ohm/square]. After determination of the layer thickness specific conductivity in [S/m] was determined.

TABLE-US-00006 TABLE 5 specific conductivity conductivity conductivity conductivity after after after Ag sol sintering sintering sintering based on at 90 C. at 110 C. at 130 C. copolymer [E06 S/m] [E06 S/m] [E06 S/m] 1 3.5 3.9 5.2 2 3.8 4.1 5.3 3 3.7 4.3 5.6 4 2.5 2.9 6.0 5 2.7 4.0 5.8 6 2.3 4.2 5.5 7 1.8 4.2 5.7 8 2.5 4.4 5.6 9 3.8 6.1 6.3 10 4.2 5.9 6.9 11 6.4 8.3 9.2 12 6.1 8.2 9.0 13 3.7 4.2 7.0 14 5.1 6.9 7.8 15 5.3 6.5 8.0 16 4.9 6.1 7.4 17 5.7 7.6 8.1 18 4.4 7.7 8.0 19 4.3 7.3 7.4 20 4.5 6.9 8.0 comparison 1 0 0 0 (US-2006044384 A) comparison 2 0 0 0 (US-2006044384 G) comparison 3 0 0 4.4 (140 C.) (WO-2012055758 1) comparison 4 2.0 (100 C.) not specified 2.6 (150 C.) (U.S. Pat. No. 8,227,022) comparison 5 not specified not specified 2.3 (210 C.) (Xerox)

[0052] As is apparent from the above table all silver sols produced with the polymers according to the invention exceed the electrical conductivity of the comparative products after thermal sintering both with the absolute value and with the beginning of the sintering temperature. This means that a reduced energy input is required to achieve comparable electrical conductivity in the end product. This also widens the range of thermally sensitive substrates that may be used as printing stock.