Description

The invention relates to corrosion stabilized copper particles. The invention further relates to a process for preparing the corrosion stabilized copper particles, a conductive powder and a formulation containing such particles as well as the use of such particles. A popular application of conductive powders includes microelectronic applications such as printed circuits or printed circuit boards as used in keyboards or touch screens. For such applications the conductive powder is used as filler in a conductive paste, which serves as ink to be dispersed on a circuit board. Typically, silver particles are used as filler for such formulation. Formulations based on silver particles are for instance described in WO 2010/032795 A1 , JP 2010/135108 A, JP

201 1/241309 A, J P 2010/285678 A, JP201 1017067 A, J P 2012/041592 A and WO

2012/043267 A1. Silver is, however, an expensive raw material. However, other raw materials such as copper are far less expensive than silver leading in the case of copper to its wide com- mercial use. Therefore, there has been considerable effort to develop conductive powders for use in microelectronic applications based on copper.

However, copper oxidizes rapidly in air. Thus, a copper oxide layer is formed on the copper, which acts as insulating layer hampering electrical conductivity. Preventing copper powder from oxidization is a long standing problem in the development of copper powders for microelectronic applications and there has been a considerable effort to improve the conductive behavior of such powders. For this reason, the size of copper powder has been explored for electrical conductivity. In general, copper powder used in such applications is with a median particle size D50<50 μηη) extremely fine. Fine powder provides more inter particle contact and consequently higher electrical conductivity. Furthermore copper flakes have been utilized to improve electrical conductivity. These flakes are said to provide less surface area per unit volume leading to improved particle contact when compared to spherical particles.

One disadvantage is, however, that copper has tendency to oxidize particularly when it is in fine particle form. The copper oxide increases contact resistance and reduces electrical conductivity, making it unsuitable for most microelectronic applications. Although, the surfaces of these copper particles may be cleaned to remove oxides and/or impurities, exposing the particles to air for a short period of time will again result in surface oxidation. Thus compared to silver particles copper particles require special handling to avoid oxidation. For example, typically copper parti- cles are stored in a nitrogen atmosphere and then quickly incorporated into a matrix material to preserve electrical conductivity.

It is known from prior art references to chemically treat copper powder with an anti-oxidizing film to improve electrical conductivity. US 2005/182161 A1 describes a copper powder with substan- tially irregular copper particles. To avoid oxidation the copper particles are coated with an antioxidant coating such as organic acid salts of higher aliphatic amines. The anti-oxidant coating can comprise coupling agents, such as ZB-3, which is the reaction product of peanut oil fatty acids, boric acid, triethanolamine, and treating agents, such as isopropyl-triisostreroyl-titanate, aceoalkoxy-aluminum-diisopropylate, silane, titanate, aluminate and zirconate.

Other prior art references describe preventing oxidation of copper by surface treating copper powder with coupling and treating agents or coating copper powder with silver. US 5,372,749 A describes a method for surface treating conductive copper powder by dispersing the pure cop- per powder or silver-coated copper powder in a solution of a coupling agent selected from the group consisting of silane, titanate, aluminate and zirconate and a ZB-3 treating agent, which is the reaction products of peanut oil fatty acids, boric acid and triethanolamine in a molar ratio of 1 :1 :2 in an organic solvent. US 4,781 ,980 A relates to a copper powder for use in a conductive paste, which comprises a raw material copper powder. The copper powder is coated with an anti-oxidization film formed on the surface of the copper powder comprising an organic acid salt of a higher aliphatic amine and a surface film which comprises a dispersing agent selected from the group consisting of a combination of a boron-containing surfactant and a nitrogen-containing surfactant and at least one coupling agent of the group consisting of isopropyl-triisostearoyl-titanate and acetoalkoxy- aluminum-diisopropylate.

US 2008/0102294 A discloses an electrically conductive paste comprising a paste made of resin material and copper or silver powder particles dispersed in the paste matrix. Here the corro- sion stabilized powder particles each define a dissolved surface layer having reacted with acid solution.

A further problem in conductivity of copper based powders for conductive pastes lies in the anti- oxidization coating itself. In particular, corrosion inhibitors provide a good oxidization protection, but the conductivity drops drastically as the corrosion inhibitor coating is not conductive. Thus coating with corrosion inhibitors act as insulating layer and are therefore thought to be unsuitable for conductive copper particles.

It is an object of the invention to provide corrosion stabilized copper particles, a conductive powder containing such particles and a corresponding process for producing the corrosion stabilized particles that facilitate non-corrosive properties to achieve high conductivity and long- term stability. Furthermore, it is an object of the invention to provide a process, which allows achieving aforementioned goals in a simple, cost-effective and uncomplicated manner. Another object of the invention is to provide microelectronic components including corrosion stabilized copper particles, which requires no further corrosion protection. In this context, one object of the invention is to provide corrosion stabilized copper particles that allows producing microelectronic components without further measures for inhibiting corrosion. These objects are achieved by corrosion stabilized copper particles, wherein the corrosion stabilized particles contain at least one inhibitor, which is a compound with general formula (I),

O R ³

N COOH

R wherein

R ¹ indicates C2 - C28 alkyl, C2 - C28 alkenyl or C2 - C28 alkynyl;

R ² and R ³ independently of each other indicate H, Ci - C6 alkyl, C2

C3 - C7 cycloalkyl or C6 - C12 aryl.

For the purposes of the present invention, -COOH also includes carboxylate which are preferably derivatives of a carboxylic acid function, in particular a metal carboxylate, a carboxylic ester function or a carboxamide function. These include, for example, the esters with Ci-C4-alkanoles such as methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol and tert-butanol.

In the context of the present invention specifications in % by weight (wt.-%) refer to the fraction of the total weight of a composition or mixture unless otherwise specified. Hence the indication wt.-% is based on the total weight of the corresponding composition or mixture.

The invention further relates to a process for producing corrosion stabilized copper particles, wherein the copper particles are treated with at least one inhibitor of formula (I) as specified above. The invention further refers to corrosion stabilized copper particles obtained by aforementioned process, a conductive powder containing such copper particles and a formulation containing such copper particles. Furthermore, the invention pertains uses of such particles and electronic components, in particular microelectronic components, comprising such particles. The following description concerns the products as well as the processes proposed by the invention. In particular, preferred embodiments of the inhibitor, the copper particles and the treatment process apply to the process for producing the corrosion stabilized copper particles and the corrosion stabilized copper particles alike.

The invention provides corrosion stabilized copper particles and a process for producing corrosion stabilized copper particles, which are optimally suited for manufacturing microelectronic components. In particular, the invention provides copper particles and a corresponding process for producing such copper particles that facilitate high corrosion stability. Thus, the corrosion stable copper particles allow manufacturing electronic components with high electrical conductivity and long-term stability. Surprisingly, the inhibitor of formula (I) is found to be not strongly adsorbing on the copper particle's surface and instead being able to desorb, which allows for percolation of the copper particles when added to a vehicle, such as a formulation for printing. Moreover, the corrosion stabilized particles of the present invention are oxidatively stable and require no special handling with regard to corrosion. Owing to the simple and uncomplicated manner of the proposed process, a high batch-to-batch consistency can be achieved, which again allows for reliable production of corrosion stabilized particles for electronic components. Overall, the corrosion stabilized copper particles facilitate to prepare corrosion stabilized pow- der, which is very cost-effective and at the same time results in good conduction characteristics for electronics components.

In one embodiment the corrosion stabilized copper particles comprise copper flakes or copper lamellae. Preferably the corrosion stabilized copper particles are copper flakes. Copper flakes are substantially flat plate-shaped copper particles with a size of a few micrometres and a high aspect ratio. The copper flakes provide interlocking electrical contact points between adjacent particles leading to increased conductivity when used in a formulation for instance for printing. The copper flakes can further be irregular or regular in shape. Preferred is an irregular shape which enhances interlocking electrical contact points between adjacent particles when used in a formulation for instance for printing. In other embodiments the copper particles may also have other shapes known to the person skilled in the art. The shape of the copper particles may, for example, be rod-shaped, needle-shaped, teardrop-shaped, flattened or spherical.

In a further embodiment the corrosion stabilized copper particles have a mean size between 0.5 and 250 μηη, preferably between 2 and 150 μηη, more preferably between 2 and 10 μηη. In terms of the size distribution, the copper flakes can have a mass median parameter D50 of 0.5 to 100 μηη, preferred of 1 to 50 and particularly preferred of 2 to 10 μηη. D10 can lie between 0.01 an 50 μηη, preferred between 0.1 and 10 and particularly preferred between 0.5 and 3 μηη. D90 can lie between 1 and 200 μηη, preferred between 2 and 100 μηη and particularly preferred of 5 and 15 μηη. Here Dx characterizes the size distribution of the particles and is defined by a certain percentage x of the corrosion stabilized particles mass being comprised of particles with a smaller diameter than given by the Dx-parameter. Typical copper particles as utilized herein have for example a size distribution with a D10 of about 2 μηη, a D50 of about 5 μηη and a D90 of about 10 μηη.

In a further embodiment the corrosion stabilized copper particles and in particular the copper flakes have an aspect ratio of 5 to 1 10, preferred 10 to 80 and particularly preferred 15 to 50, for example 30. The aspect ratio enhances adjustment of the copper particles and in particular the copper flakes when used in a formulation for instance for printing and thus enhances interlock- ing electrical contact points between adjacent particles leading to increased conductivity. The specific surface area of the corrosion stabilized copper particles can lie between 1.000 and 30.000 cm ² /g, preferred between 2.000 and 20.000 cm ² /g. The specific surface area of copper particles as utilized herein is for example 10.000 cm ² /g. The tap-density of the corrosion stabilized copper particles can lie between 0.1 and 3 g/cm ³ , for example tap-density can lie around 0.9 g/cm ³ .

The copper flakes can be produced through methods known to the person skilled in the art. The copper flakes may be formed by ball milling having a purity of at least 99.9 %. In one embodiment of the invention, the compound of formula (I) is derived from a fatty acid. In this context, the fatty acid may be saturated or unsaturated, preferably unsaturated. Furthermore, the fatty acid may be chosen from the group consisting of myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid, linoelaidic acid, a- linolenic acid, arachidonic acid, eicosapentaenoic acid, erucic acid, docosahexaenoic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, ricinoleic acid and cerotic acid. Preferred fatty acids are palmitoleic acid, oleic acid, linoleic acid, linoelaidic acid, olinolenic acid, lauric acid, palmitic acid, ricinoleic acid or stearic acid. Particularly preferred fatty acids have 12 to 18 carbon atoms and 1 to 4 double bonds in the fatty acid, such as oleic acid, lauric acid, ricinoleic acid and stearic acid.

A process for producing corrosion stabilized copper particles comprising the following steps:

(A) removing the copper oxide layer from the copper particles, and

(B) treating the copper particles with at least one inhibitor, which is a compound with general formula (I) as defined above.

The treatment with the at least one inhibitor of formula (I) protects the copper particles from cor- rosion, thus providing corrosion stable copper particles. Furthermore, the at least one inhibitor also acts as oxidizer for copper oxide rests and thus further reduces corrosion. Surprisingly, the inhibitor of formula (I) is found to be not strongly adsorbing on the copper particle's surface and instead being able to desorb, which allows for percolation of the copper particles when added to a vehicle, such as a formulation for printing.

In one embodiment the copper particles are treated with an acidic solution to remove the copper oxide layer from the copper particles. The acidic solution can contain various acids dissolving the copper oxide layer from the copper particles. Preferred acids are formic acid or sulphuric acid. The ratio of acidic solution to copper particles can be > 1 , preferred > 2 and particularly preferred >3. Furthermore, the acidic solution may contain at least one surfactant for better dispersion of the copper particles. Suitable surfactants are known to the person skilled in the art. The surfactants may for example contain alkoxylated, predominantly unbranched fatty alcohols, higher alkene oxides and ethylene oxide. For removing the copper oxide layer the copper particles with an oxide layer can be mixed with the acidic solution. The method of mixing these com- ponents is not limited, and the mixing may be effected by a mixer, e.g. stirred tank, planetary mixer, paddle mixer or a kneader. The mixture can be prepared under nitrogen atmosphere. The mixture is preferably stirred to remove the copper oxide layer from the copper particles. Furthermore, the mixture may be heated to elevated temperature > 30 °C, preferred > 50 °C and particularly preferred > 60 °C.

In a further embodiment the acidic solution has an acidic concentration > 5 wt.-%, preferred > 10 wt.-% and particularly preferred > 30 wt.-%. The corresponding pH-value of the solution may be < 1 , preferred < 0.7 and particularly preferred < 0.5. Furthermore, the acidic solution may, depending on the acid used, contain between 10 and 50 wt.-% of acid. For example an acidic solution based on sulphuric acid contains 10 wt.-% of sulphuric acid mixed in water. Such a solution provides a pH-value of around 0.1 . An acidic solution based on formic acid may contain 50 wt.-% of formic acid mixed in water. Such a solution provides a pH-value of around 0.37. In a further embodiment the copper particles are washed with water after treatment with the acidic solution. Thus the acidic solution is removed from the copper particles and pure copper particles substantially clean from any copper oxide on the surface of the copper particles are provided. The amount of copper oxide left on the copper particles may be less than 2 %. It is preferred to remove the oxidized layer on the surface of the copper particles prior to the treatment of the copper particles by dissolving the oxidized layer with an acid, and then wash the copper particles by treating with water until the filtrate is nearly neutral to obtain pure copper particles. In one embodiment the copper particles are washed up to a point at which the filtrate has a pH-value of 1 to 6, preferably of 1 to 5. The pH-value may for example lie around 3.

For treating the copper particles with the at least one inhibitor, the inhibitor may be dissolved in a solvent to form a solution. The solvent content in the solution may amount up to 50 wt.-%. Preferably the solvent content lies between 20 and 5 wt.-%. Suitable solvents are water, acetone, acetic acid, acetone-nitrile, glycerin, hexane, methyl f-butyl ether, propanol, benzene, eth- anol or methanol. Examples of other suitable solvents are aromatic hydrocarbons, such as toluene or xylene; alkyl esters, such as methyl acetate, ethyl acetate, propyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, and 3-methylbutanol; alkoxy alcohols, such as methoxypro- panol, methoxybutanol, ethoxypropanol; alkylbenzenes, such as ethylbenzene, isopropylben- zene; butyl glycol, butyl diglycol, alkyl glycol acetates, such as butyl glycol acetate and butyl diglycol acetate; 2-methoxy-1 -methylethyl acetate, diglycol dialkyl ethers, diglycol monoalkyl ethers, dipropylene glycol dialkyl ethers, dipropylene glycol monoalkyl ethers, diglycol alkyl ether acetates, dipropylene glycol alkyl ether acetates, ethers, such as dioxane and tetrahydro- furan, lactones, such as butyrolactone; ketones, such as acetone, 2-butanone, cyclohexanone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK); methylphenol (ortho-, meta-, or para- cresol), pyrrolidones, such as N-methyl-2-pyrrolidone; dimethylformamide, and also mixtures made of two or more of these solvents.

The solution may be prepared by mixing the at least one first inhibitor with the solvent. The prepared solution may then be mixed with the copper particles. The method of mixing these com- ponents is not limited, and the mixing may be effected by a mixer, e.g. stirred tank, planetary mixer, paddle mixer or a kneader.

In a further embodiment after treatment with the at least one inhibitor of general formula (I), the corrosion stabilized copper particles are washed with a washing agent such as solvent or water. The washing agent for washing the corrosion stabilized copper particles may be chosen depending on the vehicle the corrosion stabilized copper particles may be mixed, such as a formulation for printing. Hence, a solvent may be chosen as washing agent if the vehicle, such as the formulation for printing, is based on a solvent. Preferably the same solvent may be chosen as washing agent as for the vehicle composition. Alternatively, water may be chosen as washing agent if the vehicle, such as the formulation for printing, is based on water.

Suitable solvents are, for example, aliphatic and aromatic hydrocarbons, for example n-octane, cyclohexane, toluene, xylene; alcohols, for example methanol, ethanol, 1 -propanol, 2-propanol, 1 -butanol, 2-butanol, amyl alcohol; polyvalent alcohols such as glycerol, ethylene glycol, propylene glycol, neopentyl glycol; alkyi esters, for example methyl acetate, ethyl acetate, propyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, 3-methyl butanol; alkoxy alcohols, for example methoxypropanol, methoxybutanol, ethoxypropanol; alkyi benzenes, for example ethyl benzene, isopropyl benzene; butyl glycol, dibutyl glycol, alkyi glycol acetates, for example butyl glycol acetate, dibutyl glycol acetate; diacetone alcohol, diglycol dialkyi ethers, diglycol monoalkyi ethers, dipropylene glycol dialkyi ethers, dipropylene glycol monoalkyi ethers, diglycol alkyi ether acetates, dipropylene glycol alkyi ether acetate, propylene glycol alkyi ether acetate, for example propylene glycol monomethyl ether acetate (PGMEA), dioxane, dipropylene glycol and ethers, diethylene glycol and ethers, DBE (dibasic esters); ethers, such as diethyl ether, tetra- hydrofuran, ethylene chloride, ethylene glycol, ethylene glycol acetate, ethylene glycol dimethyl ester, cresol, lactones, such as butyrolactone; ketones, such as acetone, 2-butanone, cyclo- hexanone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK); dimethyl glycol, methylene chloride, methylene glycol, methylene glycol acetate, methyl phenol (ortho-, meta-, para- cresol); pyrrolidones, for example N-methyl-2-pyrrolidone; propylene glycol, propylene carbonate, carbon tetrachloride, toluene, trimethylol propane (TMP), aromatic hydrocarbons and mixtures, aliphatic hydrocarbons and mixtures; alcoholic monoterpenes, such as terpineol; water and mixtures of two or more of these solvents. Preferred solvents are alcohols, for example ethanol, 1 -propanol, 2-propanol, 1 -butanol; alkoxy- alcohols, for example methoxy propanol, ethoxy propanol, butyl glycol, dibutyl glycol; butyrolactone, diglycol dialkyi ethers, diglycol monoalkyi ethers, dipropylene glycol dialkyi ethers, dipropylene glycol monoalkyi ethers; esters, for example ethyl acetate, butyl acetate, butyl glycol acetate, dibutyl glycol acetate, diglycol alkyi ether acetates, dipropylene glycol alkyi ether ace- tates, PGMEA, DBE; ethers, such astetrahydrofuran; polyvalent alcohols such as glycerol, ethylene glycol, propylene glycol, neopentyl glycol; ketones, for example acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone; hydrocarbons, for example cyclohexane, ethyl benzene, toluene, xylene; N-methyl-2-pyrrolidone, water and mixtures thereof. Particularly preferred solvents are alkoxy alcohols, for example ethoxy propanol, butyl glycol, dibutyl glycol and polyvalent alcohols such as glycerol, esters, for example dibutyl glycol acetate, butyl glycol acetate, dipropylene glycol methyl ether acetates, PGMEA; water, cyclohexanone, butyrolactone, N-methyl-pyrrolidone, DBE and mixtures thereof.

After washing the washing agent can at least partially be removed. However, if the washing agent is chosen as set out above depending on the vehicle composition, e.g. a formulation for printing, the washing agent is removed only partially. Thus the corrosion stabilized copper particles may not be completely dried and 10 to 20% of the washing agent can be kept behind to form a slurry containing corrosion stabilized copper particles and washing agent. Via the process described above corrosion stabilized copper particles are obtained that allow for good conducting properties and long-term stability when used in electronic applications such as printing circuits.

The invention further relates to a conductive powder containing the corrosion stabilized copper particles described above. In one embodiment the conductive powder contains at least 90 %, preferred at least 93 % and particularly preferred at least 96% of corrosion stabilized copper particles. Furthermore, the conductive powder may comprise a mixture of corrosion stabilized copper particles and further conductive particles comprising another type of electrically conductive material. Suitable electrically conductive materials are, for example, carbon, for example in the form of carbon black, graphite, or carbon nano tubes, electrically conductive metal complexes, conductive organic compounds or conductive polymers or metals, for example zinc, nickel, tin, cobalt, manganese, iron, magnesium, lead, chromium, bismuth, silver, gold, aluminum, tita- nium, palladium, platinum, tantalum and alloys thereof or metal mixtures which contain at least one of these metals. Suitable alloys are for example CuZn, CuSn, CuNi, SnPb, SnBi, SnCo, NiPb, ZnFe, ZnNi, ZnCo and ZnMn. Silver, aluminum, iron, nickel, zinc, carbon and mixtures thereof are particularly preferred. Furthermore, the conductive powder may contain particles of different shapes and/or sizes.

After treatment of the copper particles a mixture of corrosion stabilized copper particles with other types of conductive particles may be formed. For example the corrosion stabilized corrosion stabilized copper particles may be mixed with conductive particles of silver and/or iron, in particular iron carbonyl particles.

The invention further relates to the use of the corrosion stabilized copper particles described above or obtained by the process as described above in a formulation for circuit printing. For printing the corrosion stabilized copper particles are incorporated into a suitable formulation forming a dispersion. Preferably, the formulation does not interfere with conductivity. Suitable formulations possess good affinity for the corrosion stabilized copper particles and allow the corrosion stabilized copper particles to easily be suspended. Suitable formulations contain for instance a polymer, such as vinyl chloride co- and terpolymers, and a solvent, such as the one listed above, like acetone or polypropylene glycol, or water. In order to be able to apply the formulation containing the corrosion stabilized copper particles onto a support, the solvent content of the formulation may be chosen to adjust the viscosity suitable for respective application methods.

The invention also pertains to an electronic component comprising the corrosion stabilized copper particles as described above or obtained by the process as described above. The corrosion stabilized copper particles according to the process described above and the corrosion stabilized copper particles are particularly suitable for the manufacture of microelectronic components as used in for example touch pads or keyboards. In the following embodiments of the invention are described with respect to the appended drawing, which shows a chart of the process for producing the corrosion stabilized copper particles.

In a first step 10 of the process for producing corrosion stable copper particles the copper parti- cles are treated to remove the copper oxide layer. For removing the copper oxide layer the copper particles with the copper oxide layer are mixed with an acidic solution comprising water and hydrochloric acid (HCOOH) or sulfuric acid (H2SO4) under nitrogen (N2) atmosphere. The mixture is stirred for example with a mechanical stirrer in order to promote dissolving the copper oxide.

After the first step 10 the copper particles mixed in a suspension with Cu+/Cu++ ions and acidic solution. In a second step 12 water and acetone are continuously added to the suspension for washing out the Cu+/Cu++ ions and acidic solution. Thus the Cu+/Cu++ ions and the acidic solution are filtered from the suspension leaving cooper particles without copper oxide layer behind.

In a third step 14 the at least one inhibitor dispersed in a solvent is added to the washed copper particles for surface inhibition. The mixture is stirred for example with a mechanical stirrer for inhibition of the copper particles.

In a fourth step 16 the mixture is filtered by adding a washing agent. The washing agent may be water or a solvent, wherein the washing agent preferably corresponds to a component of a formulation used for printing. If the vehicle formulation is for instance based on acetone, acetone may be used for the filtration in the fourth step 16. The filtration is carried out to keep a wet cake of copper flakes. Thus, the corrosion stable copper particles are not completely dry and 10 to 20% of the washing agent, e.g. acetone, is kept behind to form a slurry containing corrosion stable copper particles and washing agent.

The process thus provides a slurry with corrosion stable copper particles, which may be used for formulations of a conductive paste or ink for circuit printing.

Examples

Example 1

400g of copper flakes (e.g. commercially available under the product specification MP7450 from ECKA Granules Germany GmbH) was dispersed in 2000 g 50 wt.-% formic acid solution using dissolver (4200rpm). 6g of surfactant containing alkoxylated, predominantly unbranched fatty alcohols, higher alkene oxides and ethylene oxide (e.g. commercially available as Plurafac® LF300 from BASF SE) was added for better dispersion of Cu flakes. After CuO removal at 60 °C for 45 min, Cu flakes were collected by vacuum filtration under N2 and rinsed with water and acetone until pH of the filtrate reached 3. The obtained filter cake was divided in two equal mass of 190 g of Cu flakes free of CuO at 95 % in acetone. The first half of the cake was redispersed in 250 g of acetone containing 10 g of Oleoylsarco- sine acid (e. g. commercially available as Sarkosyl® O or Korantin® TC-SH from BASF SE), for 30 min filtered followed by a second dispersion in 500 g acetone and 50 g Oleoylsarcosine acid at 50 °C for 60 min filtered to 95 % copper in 5 % acetone.

In order to prepare a conductive ink, 150 g of the obtained copper flakes was dispersed in a binder solution by classical bowl milling method for 1 hr. The binder solution includes a resin of vinyl chloride-derived copolymers and terpolymers (e. g. commercially available as Vinnol® E15/40) solubilized at 23 wt.-% in acetone at a pigment:polymer (P:P) weight ratio of 3,5:1 . A coated conductive film using a draw-down bar (t = 50 μηη, v = 3m/min) was prepared on a PET plastic polymeric film, dried for 10 min at 100 °C, and then further dried for 1 min at 135 °C. Bulk conductivity of the dried coated film was obtained from the resistivity measurement using four probe method and the thickness of the coated/dried ink. The obtained coated copper film is denoted as 125-1 a.

The second half of the copper cake was subjected to the same procedure in the exact conditions without Oleoylsarcosine acid. The obtained coated copper film is denoted as 125-2a.

Table 1 Conductivity of the coated PET film with Cu-inks

Example 2

400 g of Cu flakes (e. g. commercially available under the product specification MP7450 from ECKA Granules Germany GmbH) was dispersed in 2000 g 50 wt.-% formic acid solution using dissolver (4200rpm). 6 g of surfactant containing alkoxylated, predominantly unbranched fatty alcohols, higher alkene oxides and ethylene oxide (e. g. commercially available as Plurafac® LF300 from BASF SE) was added for better dispersion of Cu flakes. After CuO removal at 60 °C for 45 min, Cu flakes were collected by vacuum filtration under N2 and rinsed with water and acetone until pH of the filtrate reached to 3. The obtained filter cake was divided in two equal mass of 190 g of Cu flakes free of CuO at 95 % in acetone.

The first half of the cake was redispersed in 250 g of acetone containing 10 g of Benzotriazole (BTA), for 30 min filtered followed by a second dispersion in 500 g acetone and 50 g BTA at 50 °C for 60 min filtered to 95 % Copper in 5 % acetone. In order to prepare a conductive ink, 150 g of the obtained copper flakes were dispersed in a binder solution by bowl milling method for 1 hr. The binder solution includes a resin of vinyl chloride-derived copolymers and terpolymers (e. g. commercially available as Vinnol® E15/40) sol- ubilized at 23w% in acetone at a pigment:polymer (P:P) weight ratio of 3,5:1 . A coated conduc- tive film using a draw-down bar (t = 50 micro meter, v = 3m/min) was prepared on a PET plastic polymeric film, dried for 10 min at 100°C, and then further dried for 1 min at 135 ^° C. Bulk conductivity of the dried coated film was obtained from the resistivity measurement using four probe method and the thickness of the coated/dried ink. The obtained coated copper film is denoted as 126-1 a.

The second half of the cake was subjected to the same procedure in the exact conditions without BTA. The obtained coated copper film is denoted as 126-2a.

Table 2 Conductivity of the coated PET film with Cu-inks

Example 3

400 g of Cu flakes (e. g. commercially available under the product specification MP7450 from ECKA Granules Germany GmbH) was dispersed in 2000 g of water solution using dissolver (4200rpm). 6 g of surfactant containing alkoxylated, predominantly unbranched fatty alcohols, higher alkene oxides and ethylene oxide (e. g. commercially available as Plurafac® LF300 from BASF SE) was added for better dispersion of Cu flakes. After CuO removal at 60 °C for 45 min, Cu flakes were collected by vacuum filtration under N2 and rinsed with water and acetone in similar volume as example 1 and 2. The obtained filter cake was divided in two equal mass of 210 g of Cu flakes at 95 % in acetone.

The first half of the cake was redispersed in 250 g of acetone containing 10 g of Oleoylsarco- sine acid, for 30 min filtered followed by a second dispersion in 500 g acetone and 50g

Oleoylsarcosine acid at 50 °C for 60 min filtered to 95 % Copper in 5 % acetone.

In order to prepare an ink, 150 g of the obtained copper flakes was dispersed in a binder solution by bowl milling method for 1 hr. The binder solution includes a resin of vinyl chloride- derived copolymers and terpolymers (e. g. commercially available as Vinnol® E15/40) solubil- ized at 23w% in acetone at a pigment:polymer (P:P) weight ratio of 3,5:1. A coated conductive film using a draw-down bar (t = 50 μηη, v = 3m/min) was prepared on a PET plastic polymeric film, dried for 10 min at 100 °C, and then further dried for 1 min at 135 ^° C. Bulk conductivity of the dried coated film was obtained from the resistivity measurement using four probe method and the thickness of the coated/dried ink. The obtained coated copper film is denoted as 127- 1 a.

The second half of the cake was subjected to the same procedure in the exact conditions without Oleoylsarcosine acid. The obtained coated copper film is denoted as 127-2a.

Table 3 Conductivity of the coated PET film with Cu-inks

Example 4

10 g of Cu flakes (e. g. commercially available under the product specification MP7450 from ECKA Granules Germany GmbH) was dispersed in 40 g 10wt.-% sulfuric acid solution using a magnetic stirrer. 0.1 g of surfactant containing alkoxylated, predominantly unbranched fatty alcohols, higher alkene oxides and ethylene oxide (e. g. commercially available as Plurafac® LF300 from BASF SE) was added for better dispersion of Cu flakes. After Cu-activation at RT for 17 hr, Cu flakes were collected by vacuum filtration under N2 and rinsed with water and ace- tone. The obtained filter cake was rinsed with the solution consisting of 135 g of acetone, 7.5 g of Oleoylsarcosine acid (e. g. commercially available as Sarkosyl® O or Korantin® TC-SH from BASF SE) and 7.5 g of Triethanolamin.

In order to prepare a conductive ink, Cu-flake was dispersed in a binder solution by a ball milling method for 1 hr. The weight ratio between Cu-flake and a binder was fixed as 0.6 to 1. A coated conductive film using a draw-down bar (t = 50 μηη, v = 3m/min) was prepared on a PET plastic polymeric film, dried for 10 min at 100°C, and then further dried for 1 min at 135 ^° C. Conductivity of the dried coating was measured by 4-probe method. Table 4 Conductivity of the coated PET film with Cu-inks

Example 5

200 g of Cu flakes (e. g. commercially available under the product specification MP7450 from ECKA Granules Germany GmbH) was dispersed in 1200 g 50 wt.-% formic acid solution using homogenizer (8000 rpm). 0.5g of surfactant containing alkoxylated, predominantly unbranched fatty alcohols, higher alkene oxides and ethylene oxide (e. g. commercially available as Plu- rafac® LF300 from BASF SE) was added for better dispersion of Cu flakes. After Cu-activation at 40°C for 45 min, Cu flakes were collected by vacuum filtration under N2 and rinsed with water and acetone until pH of the filtrate reached to 3. The obtained filter cake was dispersed in 474g of acetone with 50g of Oleoylsarcosine acid (e. g. commercially available as Sarkosyl® O or Korantin® TC-SH from BASF SE). The mixture was stirred at RT for 60 min, and then filtered by vacuum filtration under N2. The obtained filter cake consisted of 10w% of Cu flakes.

In order to prepare a conductive ink, Cu-flake was dispersed in a binder solution by ball milling method for 1 hr. The weight ratio between Cu-flake and a binder was fixed as 5 to 1 . A conduc- tive film printed on a PET foil using a draw-down bar (t = 50 μηη, v = 3m/min) was dried for 10 min at 100°C, and then further dried for 1 min at 135°C. Conductivity of the dried coating was measured by 4-probe method.

Table 5 Conductivity of the coated PET film with Cu-inks

Temp. μηη ΓΠΩ S/cm

100 12.8 17.00 18093

23w% Vinnol in PGMEA

135 13.1 14.00 21467

100 1 1.8 16.30 20469

23w% Vinnol in Acetone

135 12.5 1 1.50 27388