Polymer emulsion as binder for conductive composition

Abstract

Provided herein are metal conductive compositions with improved conductivity. The improved conductivity is attributable to the addition of a sintering agent and a polymer emulsion.

Claims

1. A sinterable conductive composition comprising: a metal component having an average particle diameter of greater than about 150 nm to about 100 μm, said metal component being made from or doped with silver, aluminum, gold, germanium or oxides or alloys thereof; a sintering agent; and an emulsion comprising water, and at least one particulate polymer having an average particle diameter wherein a ratio of average metal component particle diameter to average particulate polymer particle diameter is between 1:1 and 10:1.

2. The composition of claim 1, wherein the average particle diameter of the metal component is from about 200 nm to less than about 1 μm.

3. The composition of claim 2, wherein the average particle diameter of the particulate polymer is from about 20 nm to about 1000 nm.

4. The composition of claim 1, wherein the particulate polymer is present in the emulsion in an amount of 0.5 to 80 weight percent.

5. The composition of claim 1, wherein the particulate polymer is a member selected from the group consisting of monomers polymerized or copolymerized from at least one of styrene, butadiene, acrylic and methacrylic esters, chloroprene, vinyl chloride, vinyl acetate, acrylonitrile, acrylamide, ethylene, siloxane, epoxies, and vinyl ether.

6. The composition of claim 1, wherein the particulate polymer is grafted with an organohalogen residue.

7. The composition of claim 1, wherein the particulate polymer is terminated with a diiodomethyl residue.

8. The composition of claim 1, wherein the particulate polymer is present in the emulsion in an amount of up to about 10% by weight.

9. The composition of claim 1, further comprising a surfactant.

10. The composition of claim 9, wherein the surfactant is present in an amount of up to 10% by weight.

11. The composition of claim 1, wherein the sintering agent is an acid.

12. The composition of claim 1, wherein the sintering agent is present in an amount of about 0.01% by weight to about 10% by weight.

13. The composition of claim 1, wherein the sintering agent is selected from phosphoric acid, phosphonic acids, formic acid, acetic acid, hydrogen halides, and halide salts of Group I and II metals.

14. The composition of claim 1, wherein the sintering agent is selected from hydrofluoric acid, hydrochloric acid, hydrobromic acid and hydroiodic acid.

15. The composition of claim 1, further comprising an organohalogen compound.

16. The composition of claim 15, wherein the organohalogen compound is a liquid at room temperature.

17. The composition of claim 15, wherein the halogen of the organohalogen compound is iodine.

18. The composition of claim 15, wherein the organohalogen compound is an alkane halide.

19. The composition of claim 15, wherein the organohalogen compound is represented by halogenated compounds having up to twelve carbon atoms.

20. The composition of claim 15, wherein the organohalogen compound has a boiling point of less than about 150° C.

21. The composition of claim 1, wherein the sintering agent is selected from phosphoric acid, phosphonic acids, formic acid, acetic acid, hydrogen halides, and halide salts of Group I and II metals; and the particulate polymer is grafted with an organohalogen residue.

22. A substrate comprising a composition of claim 1 disposed thereon.

23. A sinterable conductive composition comprising: a metal component made from or doped with silver, aluminum, gold, germanium or oxides or alloys thereof having an average particle diameter of greater than about 150 nm to about 100 μm; a sintering agent selected from phosphoric acid, formic acid, acetic acid, hydrogen halides, and halide salts of Group I and II metals; and an emulsion comprising water, and at least one particulate polymer having an average particle diameter, wherein the particulate polymer is selected from polymethylmethacrylate and polystyrene, and wherein a ratio of average metal component particle diameter to average particulate polymer particle diameter is between 1:1 and 10:1.

24. The composition of claim 23 wherein the metal component is silver, and the sintering agent is selected from phosphoric acid and potassium iodide.

25. A sinterable conductive composition comprising: a metal component having an average particle diameter of greater than about 150 nm to about 100 μm; and an emulsion comprising water, and at least one particulate polymer grafted with an organohalogen residue having an average particle diameter, and wherein a ratio of average metal component particle diameter to average particulate polymer particle diameter is between 1:1 and 10:1.

26. The composition of claim 25, wherein the particulate polymer is terminated with a diiodomethyl residue.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 depicts an SEM image of Control 1 and Sample No. 1, each taken after heating at a temperature of 120° C. for a period of time of 30 minutes. The silver nano particles shown in Control 1 are present in a more granular form, whereas those in Sample No. 1 are shown to have agglomerated into a more three dimensional structure, which has reduced the interstices and therefore the voids therebetween.

DETAILED DESCRIPTION

(2) As noted above, the invention provides a sinterable conductive composition comprising: A metal component having an average particle diameter of greater than about 5 nm to about 100 um; A sintering agent; and An emulsion comprising water, and at least one polymer having an average particle diameter of about 5 nm to 1000 um.

(3) Consistent with the invention a suitable sinterable conductive composition should have a VR of 1×10.sup.−4 or lower.

(4) In a more particular embodiment, the invention provides a sinterable conductive composition comprising: A metal component made from or doped with silver, aluminum, gold, germanium or oxides or alloys thereof having an average particle diameter of greater than about 5 nm to about 100 um; A sintering agent selected from phosphoric acid, phosphonic acids, formic acid, acetic acid, hydrogen halides, and halide salts of Group I and II metals; and An emulsion comprising up to about 95% by weight water, and at least one polymer having an average particle diameter of about 5 nm to 1000 um, which serves as a binder.

(5) In an alternate more particular embodiment, the invention provides a sinterable conductive ink composition comprising: A metal component having an average particle diameter of greater than about 5 nm to about 100 um; and An emulsion comprising water, and at least one of polymer grafted with an organohalogen residue having an average particle diameter of about 5 nm to 1000 um.

(6) In another aspect, the invention provides a method of improving the electrical conductivity of an composition, steps of which comprise: Providing an emulsion comprising water and at least one polymer having an average particle diameter of about 5 nm to 1000 um; Providing to the emulsion a sintering agent; Providing to the emulsion a metal component having an average particle diameter of greater than about 5 nm to about 100 um, to form an ink composition; and Subjecting the composition to a temperature from room temperature to about 200° C. for a time sufficient to sinter the ink composition.

(7) In yet another aspect, the invention provides a substrate on which is disposed the inventive composition.

(8) In still yet another aspect, the invention provides an emulsion comprising water and at least one of polymer grafted with an organohalogen residue.

(9) In the conductive composition, in the various embodiments, the metal component may be chosen from metals made from or doped with silver, aluminum, gold, germanium or oxides or alloys thereof. The average particle diameter of the metal component is from about 20 nm to less than about 1 um, such as from about 200 to about 1000 nm.

(10) When the metal component is silver, the silver may be in any shape that lends itself to the commercial application at hand. For instance, spherical, oblong, powder, and flake shapes of the silver are useful. The silver may be supplied as a dispersion in an appropriate liquid vehicle or as a solid in dry form.

(11) The silver may be sourced from a variety of commercial suppliers, such as Ferro Corporation, Mayfield Heights, Ohio, Inframat Advanced Materials, Manchester, Conn. or Metalor Technologies USA Corporation, North Attleboro, Mass. Mixtures of different size silver flakes, such as a mixture of 11000-25, available from Ferro, and 47MR-23S, commercially available from Inframat, may be used as well.

(12) The silver may be used in the range of about 40 to about 99.5 weight percent of the composition, such as in the range of about 60 to about 98 weight percent of the composition.

(13) The polymer should be selected from those made from monomers polymerized or copolymerized from styrene, butadiene, acrylic and methacrylic esters, chloroprene, vinyl chloride, vinyl acetate, acrylonitrile, acrylamide, ethylene, siloxane, epoxies, vinyl ether and many others. Particularly desirable polymers include polystyrene and polymethylmethacrylate.

(14) The size of the polymer particles in the emulsion was measured with a static light scattering device called HORIBA LA-910, which provides the average particle size and a particle size distribution.

(15) Polymer molecular weights were determined by Gel Permeation Chromatography, Water 1525 Pump, 2414 RI Detector and 2487 UV Detector, 717 Auto Sampler, Empower 3 software. Linear and narrow molecular weight PMMA standards were used for calibration to determine the weight average molecular weight (“Mw”), the number average molecular weight (“Mn”) and the polydispersity (“Mw/Mn”).

(16) In some embodiments, the polymer is grafted with an organohalogen residue.

(17) In some embodiments, the polymer is terminated with a diiodomethyl residue.

(18) The polymer should be present in the emulsion in an amount of 0.5 to 90 weight percent, desirably at about 10 weight percent.

(19) The ratio of the particle size of metal component to polymer should be about 0.02 to about 50, such as about 1.0 to about 0.1.

(20) The emulsion may include water in an amount of up to about 95% by weight, such as up to about 50% by weight, desirably up to about 10% by weight.

(21) The composition may include a sintering agent, which may be an acid or a salt, or may include a polymer onto which is grafted an organohalogen residue, which in part serves as a sintering agent. However, not any acid will suffice. For instance, sulfuric acid will not show improved sintering or volume resistivity. But phosphoric acid, formic acid, acetic acid, and hydrogen halides, such as hydrofluoric acid, hydrochloric acid, hydrobromic acid and hydroiodic acid, will.

(22) Halide salts of Group I and II metals, such as sodium fluoride, sodium chloride, sodium bromide, sodium iodide, potassium fluoride, potassium chloride, potassium bromide, potassium iodide, and the like, may also be used as the sintering agent.

(23) The sintering agent is present in an amount of about 0.01 weight percent to about 10 weight percent.

(24) The sintering aid, when in solid form such as a halide salt, may be added as a solid, or it may be added as a solution in water (up to about 50% by weight) so that the inventive ink has a concentration of sintering aid up to about 0.1 to 5% by weight.

(25) The conductive composition may include a surfactant. Where the surfactant is present, it may be selected from anionic surfactants, which contain anionic functional groups at their head, such as sulfate, sulfonate, phosphate, and carboxylates. Prominent alkyl sulfates include ammonium lauryl sulfate, sodium lauryl sulfate [or, sodium dodecyl sulfate (SDS)] and the related alkyl-ether sulfates, sodium laureth sulfate [or, sodium lauryl ether sulfate (SLES)], and sodium myreth sulfate. Where the surfactant is present, it may be used in an amount of up to 10% by weight.

(26) The conductive composition may also include an organohalogen compound as a conductivity promoter. The organohalogen compound is a liquid at room temperature. The organohalogen compound should have a boiling point of less than about 150° C., such as for instance less than about 120° C., desirable less than about 100° C., and suitably above about 70° C. The organohalogen compound desirably has one or more iodine atoms attached thereto. Desirably, only one iodine atom is attached to the organoiodide compound.

(27) The organo portion of the organohalogen compound may be alkyl or aryl. When it is alkyl, it should be a lower alkyl where the alkyl portion is up to twelve carbon atoms.

(28) Representative examples of the organohalogen compound include 2-iodopropane, 1-iodopropane, 2-iodo-2-methylpropane, 2-iodobutane, 2-fluorobenzotrifluoride, 3-fluorobenzotrifluoride, 4-fluorobenzotrifluoride, fluorobenzene, 2-fluoro ethanol, 1-fluorododecane, 1-fluorohexane, 1-fluoroheptane and trifluoroacetic acid. Of course, mixtures of any two or more of these organohalogen compounds may also be used.

(29) The organohalogen compound should be used in an amount of less than or equal to about 5 percent by weight. Desirably about 0.25 percent by weight has proven to be effective.

(30) Table A provides a list of organohalogen compounds that are useful as conductivity promoters. Organohalogen compounds with boiling points less than about 150° C. encourage a minimum residue in the cured conductive ink.

(31) TABLE-US-00001 TABLE A Name of Boiling Organohalogen Point (° C.) 2-iodopropane 88-90 1-iodopropane 101-102 2-iodo-2-methylpropane  99-100 2-iodobutane 119-120 2-fluorobenzotrifluoride 114-115 3-fluorobenzotrifluoride 101-102 4-fluorobenzotrifluoride 102-105 fluorobenzene 85 2-fluoro ethanol 103 1-fluorododecane 106 1-fluorohexane 92-93 1-fluoroheptane 119 trifluoroacetic acid 72.4

(32) The organohalogen compound is useful to improve the electrical conductivity of the composition and to maintain the electrical conductivity while reducing the loading of the metal component.

(33) In order to render the inventive conductive compositions more readily dispensable it is oftentimes desirable to dilute the composition in an appropriate solvent. The dilution should be about 1 part of the composition to about 5 parts of solvent. Many solvents are suitable for use in the inventive compositions, provided the chosen solvent is compatible with the organohalogen compound.

(34) The inventive conductive compositions are suitable for applications where high electrical conductivity is required on plastic or other substrates, such as PET and PC.

EXAMPLES

Example 1

(35) A composition was prepared by mixing nano-particle silver (7K-35, with a surfactant alcohol solvent, known as DOWANOL, from Ferro Corporation, OH) into a polymethyl methacrylate emulsion (10% PMMA in water, with a PMMA average particle size of 61 nm, from Magsphere Corporation, CA). A sintering aid, H.sub.3PO.sub.4 (10% by weight in water), was added to Sample No. 1 and then mixed at 3000 rpm for 60 seconds. As a control, Control 1, was used to compare performance relative to Sample No. 1. Scanning Electron Microscope (“SEM”) images were acquired using Hitachi field emission SEM model S-4500, and are presented in FIG. 1.

(36) TABLE-US-00002 TABLE 1 Constituents Control 1 Sample No. 1 NP Ag N7k-35 100 62.5 (Ag 86.5%) PMMA Emulsion 0 35.8 (10% solid) 61 nm H.sub.3PO.sub.4 0 1.7

(37) The compositions in Table 1 were each applied to glass slides, and prepared as set forth herein, so that volume resistivity measurements could be made.

(38) The volume resistivity (“VR”) of the prepared composition was measured by a standard strip method. Each specimen for the strip electrical conductive test was prepared by first coating a thin layer onto a glass slide masked with tape. The ink layer was dried at ambient temperature and subsequently cured at a designed temperature over a set period of time. The resistivity was measured with a four-probe ohm meter, and the volume resistivity was calculated from the equation: VR=(M)(T)(W.sub.i)/D, where M is the measured resistivity in mOhms, T is the thickness of the strip in centimeters (cm), W.sub.i is the width of the strip in cm, and D is the distance between the probes (cm).

(39) Table 1A shows volume resistivity (in ohm.Math.cm) measurements for Control 1 and the inventive composition, Sample No. 1, which are each set forth above in Table 1. The compositions were prepared at a temperature of 120° C. for a period of time of 30 minutes.

(40) TABLE-US-00003 TABLE 1A Control 1 Sample No. 1 >2 Million 4.0E−05

(41) Table 1A show that the PMMA emulsion and sintering aid (aqueous H.sub.3PO.sub.4) decreases the volume resistivity (Sample No. 1) while the control (nano silver paste only) had higher volume resistivity after each was heated at a temperature of 120° C. for a period of 30 minutes. The addition of PMMA emulsion and H.sub.3PO.sub.4 improved the electrical conductivity of the silver ink over 10 orders of magnitude.

(42) Considering both the resistivity measurement and the SEM results, one can infer that the addition of a polymer emulsion and sintering aid in the inventive compositions helps nano silver to sinter and form an interconnected network, therefore becoming much more conductive than the control composition.

Example 2

(43) Four compositions were prepared by mixing nano-particle silver (7K-35, from Ferro Corporation, Mayfield Heights, Ohio) into a polystyrene emulsion (10% PSt in water, with a PSt average particle size that varied from 62 nm, 200 nm and 600 nm, from Magsphere Corporation, Pasadena, Calif.). A sintering aid, H.sub.3PO.sub.4 (10% by weight in water), was added to Sample Nos. 3, 4 and 5 and then mixed at 3000 rpm for a period of time of 60 seconds. The so-formed compositions were used for preparing test specimens.

(44) TABLE-US-00004 TABLE 2 Sample No./Amt (wt %) Constituents Control 2 2 3 4 NP Ag N7k-35 64.5 71.4 71.4 71.4 (Ag 86.5%) PSt Emulsion 35.5 27.3 27.3 27.3 (10% solid) (62 nm) (62 nm) (200 nm) (600 nm) H.sub.3PO.sub.4 0   1.3  1.3  1.3

(45) Table 2A shows volume resistivity (in ohm.Math.cm) measurements for Control 2 and three inventive compositions, Sample Nos. 2, 3 and 4, which are each set forth above in Table 2. The compositions were heated at a temperature of 120° C. for a period of time of 30 minutes.

(46) TABLE-US-00005 TABLE 2A Sample No. Control 2 2 3 4 >2 Million 4.6E−05 5.5E−05 2.8E−04

(47) Table 2A shows that the sintering aid (aqueous H.sub.3PO.sub.4) decreases the volume resistivity of silver ink formulated with PSt emulsions (Sample Nos. 2, 3 and 4) while the control (without the sintering aid, H.sub.3PO.sub.4) had higher volume resistivity after curing at a temperature of 120° C. for a period of time of 30 minutes. The addition of sintering aid H.sub.3PO.sub.4 improved the electrical conductivity of the silver ink compositions with each of the PSt emulsions with different particle sizes (i.e., 62 nm, 200 nm, 600 nm). Thus, the inventive compositions have better electrical conductivity performance than the control composition. Within this defined sampling, a smaller particle size of PSt in the emulsion seems to be desirable to achieve excellent volume resistivity performance.

Example 3

(48) Here, two compositions were prepared by mixing nano-particle silver (7K-35, from Ferro Corporation) into a polymethyl methacrylate emulsion (10% PMMA in water, with a PMMA average particle size of 61 nm). Two different sintering aids were chosen—H.sub.3PO.sub.4 and KI (each 10% by weight in water). The sintering aids were added to Sample Nos. 5 and 6 and then mixed at 3000 rpm for 60 seconds. The so-formed compositions were used for preparing test specimens.

(49) TABLE-US-00006 TABLE 3 Sample No./Amt (wt %) Constituents 5 6 NP Ag N7k-35 66.3 67.0 (Ag 86.5%) PMMA Emulsion 33.3 32.8 H.sub.3PO.sub.4 0.4 0 KI 0 0.13

(50) Table 3A shows volume resistivity (in ohm.Math.cm) measurements for two inventive compositions, Sample Nos. 5 and 6, which are each set forth above in Table 3. The compositions were cured at a lower temperature than earlier—a temperature of 80° C. instead of 120° C.—for a period of time of 30 minutes.

(51) TABLE-US-00007 TABLE 3A Sample No. 5 6 1.2E−05 3.1E−05

(52) Table 3A shows that each of the polymer emulsion and sintering aid combinations decreases the volume resistivity of silver nano particle coatings (Sample Nos. 5 and 6), compared to Control 1 (Table 1A).

Example 4

(53) The synthesis of iodine-grafted polymethyl methacrylate is described as is shown in the scheme below, where n is 5 to 10,000.

(54) ##STR00001##

(55) 130 g of D.I. water, of 2.0 g of Brij 98 surfactant [polyoxyethylene oleyl ether, C.sub.18H.sub.35(OCH.sub.2CH.sub.2).sub.20H], and 0.064 g (1 mmol) g of copper powder (<10 micron) were added to a 500-ml four-neck round-bottom flask equipped with a mechanical stirrer. 0.178 g (1 mmol) of Me.sub.6TREN, 0.394 g (1 mmol) of iodoform and 20 g (200 mmol) of methyl methacrylate was added to a 50 milliliter Schlenk tube. Both mixtures were degassed by 6 freeze-pump-thaw cycles under a nitrogen environment. The methyl methacrylate/Me.sub.6TREN/CHI.sub.3 mixture was transferred to the round-bottom flask via a cannula under nitrogen. The polymerization reaction was continued at room temperature for a period of time of 5 hours and stopped with the introduction of air.

(56) Iodine-grafted PMMA had formed and was dried at a temperature of 100° C., resulting in a yield of 47%. By GPC analysis, the weight average molecular weight, M.sub.w, was determined to be about 278,600 and the molecular weight distribution or polydispersity, M.sub.w/M.sub.n, was about 3.3.

(57) The emulsion particle size was measured with a HORIBA LA-910 instrument, and the median size determined to be about 85 nm.

Example 5

(58) The iodine-grafted PMMA from Example 4 was used to prepare a composition with nano-particle silver (7K-35) to form an emulsion. The emulsion contained the iodine-grafted PMMA, in an amount of slightly over 55% by weight of the composition. No additional sintering aid was added; rather, the iodine-grafted PMMA acted both as a binder and as a sintering aid. The composition was mixed at 3000 rpm for a period of time of 60 seconds, and then used to prepare test specimens.

(59) TABLE-US-00008 TABLE 4 Sample No. Sample No./Amt (wt %) Constituents 5 7 NP Ag N7k-35 66.3 56 (Ag 86.5%) PMMA Emulsion 33.3 0 (10% solid) 61 nm H.sub.3PO.sub.4 0.4 0 CHI.sub.2-PMMA-I Emulsion 0 44 (5.8% solid) 85 nm

(60) Table 4A shows volume resistivity measurements (in ohm.Math.cm) for the inventive compositions, Sample Nos. 5 and 7. The compositions were prepared at the different temperatures—room temperature for a period of time of 20 hours and 80° C. for a period of time of 30 minutes.

(61) TABLE-US-00009 TABLE 4A 5 7 1.4E−04 1.4E−04 1.2E−05 3.2E−05

(62) Table 4A shows that the compositions demonstrated a decreased volume resistivity compared to Control 1 (Table 1A), irrespective of the temperature and time used to cure the composition.

Example 6

(63) Two compositions were prepared by mixing nano-particle silver (7K-35, from Ferro Corporation) into a polystyrene emulsion (49% PSt in water, from Arkema Inc., Cary, N.C.). A sintering aid, KI (3.5% by weight in water), was added to Sample No. 8 while to the control 3 was added D.I water instead, and they were mixed at 3000 rpm for 60 seconds. The so-formed compositions were used for preparing test specimens.

(64) TABLE-US-00010 TABLE 5 Sample No./Amt (wt %) Constituents Control 3 8 NP Ag N7k-35 83.8 84.1 (Ag 86.5%) ENCOR 8146 7.9 7.8 (49% solid) KI 0 0.3 D.I. H2O 8.3 7.8

(65) Table 5A shows volume resistivity (in ohm.Math.cm) measurements for two compositions, Control 3 and Sample No. 8, which are each set forth above in Table 5. The compositions were heated at a temperature of 100° C. for a period of time of 30 minutes.

(66) TABLE-US-00011 TABLE 5A Sample No. Control 3 8 >1 Million 7.8E−05

(67) Table 5A shows that the addition of the sintering aid, KI, decreases the volume resistivity of Sample No. 8, compared to Control 3.

Example 7

(68) Two compositions were prepared by mixing nano-particle silver (7K-35, from Ferro Corporation) into a polystyrene emulsion (49% PSt in water, from Arkema Inc.). Sintering aids, 2-iodoethanol (5.0% by weight in water) and iodoacetamide (7.0% by weight in water), were added to Sample Nos. 9 and 10, respectively, and they were mixed at 3000 rpm for 60 seconds. The so-formed compositions were used for preparing test specimens.

(69) TABLE-US-00012 TABLE 6 Sample Nos./Amt(wt %) Constituents 9 10 NP Ag N7k-35 81.3 81.2 (Ag 86.5%) ENCOR 8146 7.2 7.2 (49% solid) 2-Iodoethanol 0.2 0 Iodoacetamide 0 0.3 D.I. H2O 11.3 11.3

(70) Table 6A shows volume resistivity (in ohm.Math.cm) measurements for two compositions, Sample Nos. 9 and 10, which are each set forth above in Table 6. The compositions were heated at a temperature of 80° C. for a period of time of 30 minutes.

(71) TABLE-US-00013 TABLE 6A Sample No. 9 10 5.1E−05 5.8E−05

(72) Table 6A shows that the addition of organo iodide compounds as conductivity promoters decreases the volume resistivity of Sample Nos. 9 and 10, compared to Control 3.