JPH01215905A - coated copper powder - Google Patents

Abstract

PURPOSE:To manufacture coated copper powder having excellent storing stability and environmental resistance without deteriorating electric conductivity and electromagnetic shield effect by coating the surface of Cu powder with phosphoric ester series surface active agent and aminoether ester series surface active agent. CONSTITUTION:The Cu powder is added and dispersed into dispersion medium of water, alcohol, toluene, hexane, etc., and in this, the mixed material of 10-150wt. parts of the aminoether ester series surface active agent containing at least one functional group shown in the generate formula III of triethanol amin, etc., in one molecule to 100wt. parts of the phosphoric ester series surface active agent shown in the general formula I or the general formula II of lauryl alcohol tridecyl alcohol, etc., is added and coated on the surface of Cu powder at 0.1-10wt.% to the Cu powder. The coated Cu powder having excellent characteristic as raw material for forming the electromagnetic shield material is manufactured at low cost.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to copper powder surface treatment technology, and more specifically, to impart rust prevention properties to copper powder itself and to improve the storage stability of paints obtained from copper powder. This invention relates to coated copper powder with improved properties.

[Conventional technology]

As an electromagnetic wave shielding material that protects electronic devices from electromagnetic interference, there are conventionally conductive paints that are made by mixing conductive fillers such as nickel powder, silver powder, copper powder, and carbon powder with various binder resins. Apply paint to the surface of plastic molded products by spraying or brushing to shield electromagnetic waves. Among various conductive paints, copper-based conductive paints are cheaper than paints using silver powder or nickel powder, and have excellent shielding effects.

However, with copper-based conductive paints, copper powder aggregates in the paint, making it difficult to obtain a good dispersion state, resulting in poor storage stability.Moreover, it is easily oxidized in environments such as heat and humidity, and therefore has poor durability. There is a problem that environmental properties and conductivity are likely to deteriorate (attenuation of shielding effect). Various proposals have been made in the past to solve this problem. For example, JP-A-6
0-35405, JP 57-113505, JP 60-258273, JP 60-3
0200, JP 60-243277, JP 59-174661, JP 59-1796
It is described in Publication No. 71.

Conductive paints obtained from these copper powders can improve storage stability and environmental resistance to some extent without reducing the conductivity and electromagnetic shielding effect of the copper powder.

[Invention or problem to be solved]

However, among the conventional copper powders, chemical substitution method, CV
Metals and coalescence of silver, nickel, zinc, soot, and solder produced by the D method, mechanical bonding method, etc. 3-Gold-coated copper powder has significantly higher production costs and has the unique conductivity of copper powder. It is difficult to fully bring out the characteristics of Also,
Copper powder coated with metal-organic compounds such as titanium and silicon is expensive to produce and is by no means cheap. Furthermore, conventionally known benzotriazole, tolyltriazole,
Copper powder coated with silicates, chromates, and similar organic substances significantly reduces the electrical conductivity characteristic of copper powder.

Further, the copper powder itself and the paint do not necessarily exhibit excellent storage stability and environmental resistance.

This invention has been made based on the above-mentioned background, and its purpose is to eliminate the drawbacks of the conventional coated copper powder and conductive paint obtained therefrom, and to improve the conductivity of copper powder and electromagnetic shielding. The purpose of the present invention is to provide a coated copper powder that improves the storage stability and environmental resistance of the copper powder itself and the paint without reducing its effectiveness.

[Means to solve the problem]

As a result of conducting various tests and studies on coated copper powder, the present inventor has achieved the object of the present invention by coating the surface of copper powder with a mixture of a phosphate ester surfactant and an aminoether ester surfactant. This invention was completed based on the knowledge that it is effective for the following purposes.

That is, the coated copper powder of the present invention is characterized in that the surface of the copper powder is coated with a phosphate ester surfactant and an aminoether ester surfactant.

In a preferred embodiment of this invention, the phosphate ester surfactant is of the following general formula I and/or I
A compound represented by I can be used.

(In the formula, R1 is an alkyl group or alkenyl group having 8 to 22 carbon atoms, R is an OH group or R10 group, R3
is a higher alcohol having an alkyl group or alkenyl group having 8 to 22 carbon atoms or an alkylphenol having an alkyl group having 1 to 12 carbon atoms to 1 to 10 mol of ethylene oxide or/and propylene oxide.
The residue obtained by adding 0 moles, R4, is an OH group or an R30 group) In a preferred embodiment of the present invention, the aminoether ester surfactant has at least one of the following functional groups in one molecule. things can be used.

(In the formula, R5 is an alkyl group having 7 to 2 carbon atoms, R6 is an ethylene group or a propylene group, and n is 1 to 5 carbon atoms.
In a preferred embodiment of the present invention, the mixing ratio of the phosphoric acid ester surfactant and the aminoether ester surfactant is set to 100 parts by weight of the phosphoric acid ester surfactant. Activator 10-500
It can be parts by weight.

In a preferred embodiment of the present invention, the amount of the mixture of the phosphate ester surfactant and the aminoether ester surfactant coated on the copper powder can be 0.1 to 10% by weight.

This invention will be explained in more detail below.

Solution U The shape of the copper powder used in this invention can be obtained by electrolytic method, reduction method,
There are dendritic, granular, and spherical shapes obtained by the atomization method.
Furthermore, there are flakes obtained by mechanically processing these materials using a ball mill or the like.

Further, dendritic copper powder, flaky copper powder, granular copper powder, and spherical copper powder can be mixed and used using a V-type mixer or the like.

Further, as the raw material copper powder that can be used in this invention, metals such as silver, nickel, zinc, platinum, and palladium, alloys such as solder, metal organic compounds such as organosilicon compounds, organotitanium compounds, and organoaluminum compounds, It may be coated with a surfactant, an amino acid, an amine, a carboxylic acid, a derivative thereof, or the like.

The raw material copper powder is pretreated to remove oxidation coating from the surface of the copper powder using reagents such as inorganic acids, organic acids, various reducing agents, and reducing gases such as ammonia gas and hydrogen gas as necessary. It is preferable that the Additionally, the copper powder to be treated can be dried as a pretreatment.

Phosphate ester surfactant One of the components coated on the copper powder is a phosphate ester surfactant.

As the phosphate ester surfactant used in this invention, compounds represented by the following general formulas I and/or II can be used.

In the above formulas I and 2, R1 is an alkyl group or alkenyl group having 8 to 22 carbon atoms, R2 is an OH group or RO
The group R3 is a higher alcohol having an alkyl group or an alkenyl group having 8 to 22 carbon atoms or a carbon number 1 to 12
A residue obtained by adding 1 to 100 moles of ethylene oxide or/and propylene oxide to 1 mole of alkylphenol having an alkyl group of R4 is OH
group or R30 group.

This phosphate ester surfactant is, for example, decyl alcohol, lauryl alcohol, tridecyl alcohol, myristyl alcohol, stearyl alcohol, cetyl alcohol, oleyl alcohol, a mixed alcohol having 11 to 15 carbon atoms from the oxo method, or a carbon number 12 Ethylene oxide or/and
and nonionic surfactants with 1 to 100 moles of propylene oxide added, butylphenol, octylphenol, nonylphenol, dodecylphenol,
Using a nonionic surfactant such as a nonionic surfactant in which 1 to 100 moles of ethylene oxide and/or propylene oxide are added by a known method to 1 mole of alkylphenol such as dinonylphenol, phosphorus oxychloride is added to 1 mole of these raw materials. , is obtained by reacting a phosphorus compound such as phosphorus pentoxide, preferably 0.2 to 1.0 mol of phosphorus pentoxide, by a known method, and is usually obtained as a reaction mixture of a monoester and a diester. .

Among the above phosphoric acid ester surfactants, preferred are lauryl alcohol, tridecyl alcohol, oleyl alcohol, a mixed alcohol having 11 to 15 carbon atoms from the oxo method, octylphenol or nonylphenol, and a method known in the art. The raw material is a nonionic surfactant to which 5 to 15 moles of ethylene oxide and/or propylene oxide are added.

The separation and purification of the synthesized phosphate ester surfactant is
This can be done by methods such as distillation, extraction, recrystallization, and column chromatography.

Aminoetherester surfactant Specifically, the aminoetherester surfactant used in the present invention has at least the following functional groups in one molecule.

In the above formula, R5 is an alkyl group having 7 to 21 carbon atoms or an alkelni group, R6 is an ethylene group or a propylene group, and n is 1 to 50.

Specific examples of such include triethanolamine, triisopropanolamine, and polyalkylene polyamines such as ethylenediamine, propylenediamine, triethylenetetramine, diethylenetriamine, tetraethylenepentamine, aminoethyleneaminopropylamine, decylamine, dodecylamine, etc. Alkylamines such as amines, myristylamine, palmitylamine, oleylamine, cetylamine, stearylamine, alkyl polyalkylene polyamines such as dodecylaminoethylamine, tallow aminopropylamine, dodecylaminopropylamine, dodecyldiethylenetriamine, tetradecyldiethylenetriamine, laurylamide Ethylene oxide or/and propylene oxide is added per amino group to fatty acid amite amines such as ethylamine, stearylamide ethyl ethylenediamine, and alkylimidacillin derivatives such as N-laurylhydroxyethylimidacillin and N-oleylaminoethyl imidacillin. After adding ~50 mol by a known method, lauric acid, stearic acid, oleic acid, isostearic acid,
It can be obtained by reacting fatty acids having 8 to 22 carbon atoms such as palmitic acid, myristic acid, and linoleic acid by a known method so that each molecule has at least one R5Co (OR6) N group.

Preferred in this invention are oleic acid adducts of 5 to 20 moles of ethylene oxide such as triethanolamine, ethylenediamine, and triethylenetetramine;
Isostearic acid, lauric acid monoester; Oleic acid, an adduct of 5 to 20 moles of ethylene oxide such as decylamine, dodecylamine, myristylamine, palmitylamine, oleylamine, cetylamine, stearylamine, tallow aminopropylamine, dodecylaminopropylamine; It is preferable to use mono- or diesterized isostearic acid or lauric acid.

The synthesized aminoether ester surfactant can be separated and purified by methods such as distillation, extraction, recrystallization, and column chromatography.

In this invention, the mixing ratio of the phosphoric acid ester surfactant and the aminoether ester surfactant detailed above is, for example, the mixing ratio of the aminoether ester surfactant to 100 parts by weight of the phosphoric acid ester surfactant. Activator 10
~500 parts by weight.

In terms of properties, it is preferable to mix the surfactant so that the acid value equivalent of the phosphate ester surfactant and the amine value equivalent of the aminoether ester surfactant are neutralized. Specifically, the amount of the aminoether ester surfactant is 30 to 200 parts by weight per 100 parts by weight of the phosphate ester surfactant.

Method for producing coated copper powder The method for producing coated copper powder according to the present invention includes adding a dispersion bath of copper powder to a dispersion bath of copper powder.
A mixture of a phosphate ester surfactant and an aminoether ester surfactant is added to form a film of the phosphate ester surfactant and aminoether ester surfactant on the surface of the copper powder. The method includes removing the dispersion medium accordingly to obtain coated copper powder.

The copper powder dispersion bath used in this production method is one in which the copper powder to be coated is well dispersed by the dispersion medium, and examples of the dispersion medium used here include water, alcohol, toluene, There are organic solvents such as hexane.

Preferred dispersion media include water, methyl alcohol, ethyl alcohol, toluene, and hexane. The amount of the dispersion medium is the amount necessary to form a good dispersion state of the copper powder, and is preferably set to the minimum amount possible.

This is because as the amount of dispersion medium increases, the reaction rate between the mixture of phosphate ester surfactant and aminoether ester surfactant and the surface of copper powder decreases, making it difficult to obtain the desired copper powder. This is because it becomes difficult.

The mixture of the phosphate ester surfactant and the aminoether ester surfactant to be added can be obtained by mixing predetermined amounts of each of the phosphate ester surfactant and the aminoether ester surfactant. .

The mixing ratio of the phosphate ester surfactant and the aminoether ester surfactant in this mixture is, as described above, 10 parts by weight of the aminoether ester surfactant to 100 parts by weight of the phosphate ester surfactant. ~500 parts by weight, preferably 30 to 200 parts by weight of the aminoether ester surfactant.

For example, a mixture of a phosphate ester surfactant and an aminoether ester surfactant can be made into a fabric using an organic solvent. Organic solvents that can be used here include preferably non-polar solvents such as toluene and hexane, as well as polar solvents such as alcohol and acetone.

The amount of the mixture of phosphate ester surfactant and aminoether ester surfactant treated with respect to copper powder is 0.05 to 15% by weight, preferably 0.1% by weight based on the weight of copper powder.
~10% by weight. This means that at less than 0.1% by weight,
The occurrence of patina, discoloration, and agglomeration of copper powder become more likely.
If the amount is less than 0.05% by weight, this tendency becomes significant. On the other hand, if it exceeds 10% by weight, an excessive hydrophobic film will be formed on the surface of the copper powder, making it impossible to obtain good conductivity, and if it exceeds 15% by weight, this tendency will become significant.

The mixture of phosphate ester surfactant and aminoether ester surfactant can be added to the copper powder dispersion bath, for example, by adding it directly in small amounts to the dispersion bath, or by adding it directly to the dispersion bath in small amounts, or by adding it to the dispersion bath using an organic solvent, water, etc. Dilute and add. Operational parameters such as addition rate and stirring time after addition are determined by the surface condition of the copper powder,
That is, it is desirable to select the material appropriately depending on the amount of adsorbed water, specific surface area, shape, etc.

After forming a film of phosphate ester surfactant and aminoether ester surfactant, if necessary,
Remove the dispersion medium. This is because, in some cases, if drying is insufficient, the copper powder may oxidize, making it impossible to obtain good conductivity or shielding effects, and there is a risk of patina or discoloration. .

Conductive Coating Composition The obtained copper powder of the present invention can be mixed with a binder resin and a solvent and used as a conductive coating composition.

Furthermore, a mixture of a phosphate ester surfactant and an aminoether ester surfactant can be added to a mixed system of copper powder, binder resin, and solvent to be used as a conductive coating composition.

Binder resins that can be used in this invention include:
There are thermoplastic resins and thermosetting resins that have good adhesion to the plastics commonly used in electronic devices. For example, for electronic device housing plastics such as ABS, polystyrene, PPO, and polycarbonate,
Acrylic resin, polyurethane resin, polyester resin, styrene resin, phenol resin, epoxy resin, etc. can be used.

Further, as the solvent that can be used in this invention, an organic solvent that dissolves additives such as a binder resin and has low reactivity is preferable. For example, hydrocarbons such as toluene, hexane, and xylene; alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, and butyl alcohol; ketones such as methyl ethyl ketone and methyl isobutyl ketone; esters such as ethyl acetate and butyl acetate; One or a mixture of two or more organic solvents such as ethers such as methyl calpitol, ethyl calpitol, methyl cellosolve, and ethyl cellosolve are preferred.

In addition to the above components, various additives can be included depending on the purpose. Such agents include reducing agents, surfactants, antisettling agents, antifoaming agents, thickening agents, thixotropic agents, rust preventives, and flame retardants.

In the above-mentioned specification, although copper powder was explained, it can also be applied to other metal powders, and it can be expected to obtain the same effect as copper powder.

[For production]

In this invention and preferred embodiments having the above configuration,
It works as follows.

In this invention, the surface of the copper powder is modified by coating the surface of the copper powder with a mixture of a phosphate ester surfactant and an aminoether ester surfactant.

Specifically, phosphate ester surfactants and aminoether ester surfactants have a hydrophilic part and a lipophilic part, so the hydrophilic part reacts with adsorbed water on the copper powder surface or coating. and bond to the surface of the copper powder, while the lipophilic portions are oriented on the outside of the copper powder. The film of this lipophilic part acts as a hydrophobic film on the surface of the copper powder, and furthermore, this lipophilic part acts as a hydrophobic film on the surface of the copper powder. The copper powder is skillfully intertwined with the bonds, and forms a good dispersion state of copper powder in paints and coatings by stirring, shear stress during the cross-wire process, etc.

〔Effect of the invention〕

In the copper powder according to claim 1, which has the following effects according to the present invention, since the copper powder is coated with a mixture of a phosphate ester surfactant and an aminoether ester surfactant, the adsorbed water on the copper powder surface or coating is A strong film that does not impair conductivity can be formed by reacting with Therefore, the copper powder itself has good rust prevention properties and dispersibility.

Since the conductive paint composition using the coated copper powder of claim 1 contains the coated copper powder of claim 1, the conductivity, environmental resistance, and storage stability of the paint are improved, and the coating composition is improved. The chemical and physical strength of the membrane is improved.

〔Example〕

The invention will be illustrated by the following example.

Experimental material a, Phosphate ester surfactant The phosphate ester surfactant used in this example was obtained by reacting the following number of moles of phosphorus pentoxide with 1 mole of the starting materials shown in Table 1. Prepared.

= 20 - Table 1 Phosphoric ester Phosphorus pentoxide surfactant NO Starting material Mol number 1-1
Nonylphenol 8EOO,41-2 Lauryl alcohol 0,51-3 Lauryl alcohol 3
20 0.41-4 Oleyl alcohol 5E
0 0.41-5 Tridecyl alcohol 7E
0 0.31-6 Octylphenol 2POO
, 51-7 nonylphenol GEOO, 4 1-8 dopanol 23.8EOO, 351-9 stearyl alcohol GP02EOO, 4 notes) EO: ethylene oxide, PO: propylene oxide b, aminoether ester surfactant Starting shown in Table 2 The raw materials and fatty acids were mixed and reacted to prepare aminoether ester surfactants 2-1 to 2-9 used in this example.

Niece 00, (g) Oi OiΔ , , , , r+.

Medium - prisoner one - (g) (g) + r + ji de eight JL/, \ t
ry Ii's Hachi II
) % Tom, -hen [F] ■0 0111111 l11 Z To CS3 To (G) I1 (G) To To (G) C, Phosphate ester surfactant and aminoether ester interface Mixture with Active Agents (Invention) A mixture 3- according to the invention is prepared by combining the phosphate ester surfactant shown in Table 1 and the aminoether ester surfactant shown in Table 2 in combination and composition shown in Table 3. 1 to 18 were prepared.

Table 3 No. Phosphate ester Aminoether varnish surfactant Chill surfactant 3-1 1-1 100g 2-1 70gB-2
1-2100g 2-232-23O1-3100
g 2-3 60g3-4 1. -4 100g
2-4 30g3-5 1-5 100g 2
-5 40g3-6. 1-6 100g 2-6
82-68O1-7100g 2-7 120g3
-8 1-8 100g, 2-8 40g3-9
1-9 1.00g '2-9 50g3-10
1-5 100g, 2-2 9.0g3-II
1-5. 100g 2. -7 180 g3
-121-6100g 2-3 60g3-1
j 1. , -6 1010g 275 40
g3-14 ,i-7,”,',I C1,,9,,
-”) 2. ”, 2. 8', 01 g3-1
5"', i-7kawa""":)2-8. ''',3'O
gB-16-, 1,778" 100g: , 2'f
212'0',',g3-17 1. '78"109.
jg 2-4 35. g3-181-8100g
2-550gd Comparative Surfactant ゛For comparison, the surfactants shown in Table 4 below were used.

Table 4 Steel-based surfactant (No. 1-1.) Triethanol' amine salt 4-2..., phosphoric acid, ster-based surfactant (No.
', 1-1)・iN'th salt - 4-3,... Aminomotyl dried ester surfactant (No. 2 '-', 1) alone ・4-4. Phosphorus ester surfactant ('No, 1', -5)
Monoethanol' amine salt' 4-5... Phosphoric ester surfactant (No. 1-
7) Potassium salt 4-6...aminoether ester surfactant (N
o, 2=8) alone e, copper powder A dendritic electrolytic copper powder (manufactured by Mitsui Mining & Smelting Co., Ltd., MF-D2) shown in Table 5 was used.

Table 5 Apparent Density 0.8-1. 1g/cm3 Specific surface area 0.40i/g Purity 99.2% or more HNO3 insoluble matter Less than 0.03% Reduction loss Less than 0.80% Average particle size 8.0μm Experimental example 1 Rust prevention effect Oxide film was removed. The copper powder shown in Table 5 was stirred and dispersed in a hexane solvent, and the surfactants shown in Tables 3 and 4 were added little by little into the copper powder dispersion bath to treat the copper powder. After drying the copper powder, a temperature of 85°C, 40'
Heat resistance and humidity resistance tests were conducted by leaving the product for 1350 hours in a high humidity environment of C/95% RH. In addition, the amount of surfactant treated with respect to copper powder was 0.05.0. ], 0.5, ], 0
．． It was 5.0.10.0.10.5% by weight.

As a result, the copper powder of the present invention treated with Mixture Nos. 3-1 to 3-18 according to the present invention and treated in an amount of 0.1 to 10% by weight did not discolor at all and did not develop patina.

It should be noted that when the treatment amount was 0.05% by weight, some discoloration to brownish brown and occurrence of greenish blue were observed.

On the other hand, in the copper powders treated with the comparative samples N014-1 to N014-6, significant discoloration and patina occurred.

From the results of this experimental example, it was found that the copper powder according to the present invention exhibits excellent environmental resistance and mackerel-proofing effect at high temperatures and high humidity.

Experimental Example 2 Volume resistivity (conductivity) The copper powder treated in Experimental Example 1 was added to the copper powder in an amount of 45% by weight based on the copper powder.
A conductive paint was prepared using an acrylic resin solution (solid content: 60% by weight) and a solvent (toluene) by stirring with a homomixer for 10 minutes.

A circuit was formed on an acrylic plate using the obtained conductive paint using a screen printer, and after drying at 40'C in the air for 30 minutes, the volume resistivity of this circuit was measured.

As a result, the circuit obtained from the conductive paint obtained from the copper powder according to this invention is approximately 8X10'~2X], O-3Ω
・It had a volume resistivity of cm.

After leaving the same conductive paint in an environment of 20-25°C/60-7o% RH for 3 months, a circuit was formed using the same operation,
The volume resistivity of the circuit was measured.

The circuit obtained from the conductive paint according to this invention is approximately 8×1
It had a volume resistivity of 0 to 2×10 ”Ω·cm.

On the other hand, the circuit obtained from the conductive paint according to the comparative sample had a volume resistivity of about 5 x 10 to IX], O-2 Ω·cm.

From the results of Experimental Example 2, it was found that the conductive paint using the copper powder of the present invention has excellent dispersibility (storage stability) and good conductivity.

Experimental Example 3 Dispersibility of Copper Powder Regarding the coating film applied to the acrylic plate of Experimental Example 2 described above, the dispersion state of the copper powder was observed.

An electron micrograph of a cross section of the coating film according to the present invention is shown in FIG. This photo shows the good dispersion of the copper powder in the resin binder and the strong adhesion between the acrylic base material and the resin binder.

An electron micrograph of a cross section of a comparative coating film is shown in FIG. This photo shows the poor dispersion state of copper powder in the resin binder.
It is observed that the copper powder has a poor adhesion with the resin binder and the profit due to the 8-position of the copper powder.

[Brief explanation of the drawing]

Figure 1 is a 700x scanning electron micrograph showing the structure of copper powder particles in a cross section of a coating film of the paint according to the present invention, and Figure 2 shows the structure of copper powder particles in a cross section of a coating film of a comparative paint. This is a scanning electron micrograph at 700x magnification. Figure 1 Figure 2

Claims (1)

[Claims] 1. Copper powder coated with a mixture of a phosphate ester surfactant and an aminoether ester surfactant. 2. The copper powder according to claim 1, wherein the phosphate ester surfactant comprises a compound represented by the following general formula I and/or II. ▲There are mathematical formulas, chemical formulas, tables, etc.▼...I ▲There are mathematical formulas, chemical formulas, tables, etc.▼...II (In the formula, R^1 is an alkyl group or alkenyl group having 8 to 22 carbon atoms, R ^2 is an OH group or R^1O group, R
^3 is 1 to 1 mole of ethylene oxide or/and propylene oxide to 1 mole of a higher alcohol having an alkyl group or alkenyl group having 8 to 22 carbon atoms or an alkylphenol having an alkyl group having 1 to 12 carbon atoms.
The residue obtained by adding 100 moles, R^4, is an OH group or R^3O group) 3. The aminoether ester surfactant has at least one of the following functional groups in one molecule, Copper powder according to claim 1 or 2. R^5CO(OR^6)_nN group (in the formula, R^5 is an alkyl group having 7 to 21 carbon atoms or an alkelni group, R^6 is an ethylene group or a propylene group, and n is 1 to 50) 4. A claim in which the mixing ratio of the phosphate ester surfactant and the aminoether ester surfactant is 10 to 500 parts by weight of the aminoether ester surfactant per 100 parts by weight of the phosphate ester surfactant. Copper powder according to 1, 2 or 3. 5. The amount of coating of the mixture of phosphate ester surfactant and aminoether ester surfactant on copper powder is
The copper powder according to any one of claims 1 to 4, which contains 0.1 to 10% by weight.