JP2007265801A - Conductive powder and forming method of conductive powder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conductive powder superior especially in conductivity when made in a conductive paste, since a lubricant made of fatty acid is bonded strongly to the metal surface and remains on the surface of the conductive powder obtained making difficult further improvement in conductivity, although the lubricant such as fatty acid is used in order to prevent condensation of conductive particles in the flaking process of the conductive powder. <P>SOLUTION: The conductive powder including a conductive particle and a fatty acid ester compound and its manufacturing method are provided. In the manufacturing method of the conductive powder, a fatty acid ester compound is used in the flaking process of the conductive particles. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a conductive powder and a method for producing a conductive powder.

Conductive paste in which conductive powder is dispersed in an organic binder is used to form electrodes and circuits for electronic components, through-hole connection of printed circuit boards, wiring crossover, bonding of semiconductor elements, bonding of heat dissipation members such as heat sinks In addition, it is used in a wide variety of applications such as electromagnetic shielding. The conductive powder used in such a conductive paste is obtained by pulverizing conductive particles obtained by a chemical reduction method, an electrolytic method, an atomizing method, etc. using a pulverizer such as a stamp mill, an attritor, or a ball mill (flakes). In general). Here, in the flaking process, fatty acids, fatty acid salts, higher aliphatic alcohols, esters of higher aliphatic alcohols, higher aliphatic amines, higher aliphatic amides, polyethylene wax, etc. are used as lubricants for the purpose of preventing aggregation of the conductive particles. (See, for example, Patent Documents 1 to 3). Moreover, in order to ensure electroconductivity, the lubricant is removed after the flaking process. (For example, see Patent Document 3)
In recent years, the demand for conductive pastes has become more stringent. In particular, better electrical conductivity is required than ever, due to solder replacement, electrode miniaturization, circuit miniaturization, etc., as a lead-free product for the environment. However, conventionally used lubricants such as fatty acids remain on the surface of the conductive powder obtained by being firmly bonded to the metal surface, making it difficult to further improve the conductivity.

JP 2000-080409 A JP 2001-303111 A JP 2003-268402 A

  The present invention provides a conductive powder capable of exhibiting good conductivity when used as a conductive paste, and a method for manufacturing the same.

Such an object is achieved by the present invention described in the following [1] to [8].
[1] A conductive powder comprising conductive particles and a fatty acid ester compound.
[2] The conductive powder according to item [1], wherein the fatty acid ester compound is an alkyl ester compound of a fatty acid having 10 to 30 carbon atoms.
[3] The conductive powder according to item [1] or [2], wherein the fatty acid ester compound is a fatty acid methyl ester compound.
[4] The conductive powder according to any one of [1] to [3], wherein the fatty acid ester compound is an ester compound of an unsaturated fatty acid.
[5] The conductive powder according to any one of [1] to [4], wherein the conductive particles are silver.
[6] The conductive powder according to any one of [1] to [5], wherein a weight reduction rate measured by a suggested thermobalance (TGA) is 0.05% by weight or more and 2% by weight or less.
[7] The conductive powder according to any one of [1] to [6], wherein the 50% average particle size by laser diffraction method is 1 μm or more and 50 μm or less.
[8] A method for producing a conductive powder according to any one of items [1] to [7], wherein a fatty acid ester compound is used in the flaking step of the conductive particles. Powder production method.

  When the conductive powder of the present invention is used in a conductive paste, a conductive powder that exhibits better conductivity than ever can be obtained.

The conductive powder of the present invention is a conductive powder containing conductive particles and a fatty acid ester compound, and a conductive paste using the obtained conductive powder exhibits particularly good conductivity.
Hereinafter, the present invention will be described in detail.

The conductive particles used in the present invention can be used as long as they have conductivity, but metal particles are preferred. Preferred metal particles include noble metal particles such as silver, gold, platinum, and palladium, and non-noble metal particles such as copper, copper alloy, and nickel, with silver being particularly preferred. Here, silver is pure silver or a silver alloy. Examples of the silver alloy include silver-copper alloy, silver-palladium alloy, silver-tin alloy, silver-zinc alloy, silver-magnesium alloy, silver-nickel alloy containing 50% by weight or more, preferably 70% by weight or more of silver. Can be mentioned. Silver is preferable because it has good electrical conductivity and thermal conductivity, and is difficult to be oxidized and has excellent workability.
The average particle diameter of the conductive particles is preferably from 0.5 μm to 30 μm, and the more preferable average particle diameter is from 0.5 μm to 10 μm. Within this range, aggregation is unlikely to occur and the conductivity is good.

  The fatty acid ester compound used in the present invention is used as a lubricant for flaking conductive particles. This is for showing favorable electroconductivity, when the electroconductive powder obtained compared with the case where the fatty acid generally used is used is evaluated as an electroconductive paste. The fatty acid ester compound is preferably an alkyl ester compound of a fatty acid having 10 to 30 carbon atoms. More preferred are alkyl ester compounds of fatty acids having 14 to 20 carbon atoms. This is because if it is less than the upper limit value, it volatilizes in the drying step after the flaking process and causes aggregation, and if it exceeds the lower limit value, the dispersion during the flaking process is poor and the flakes cannot be effectively flaked.

  Examples of such compounds include saturated fatty acid alkyl ester compounds such as methyl caprate, ethyl caprate, butyl caprate, other alkyl esters of capric acid, methyl laurate, ethyl laurate, butyl laurate, and lauric acid. Other alkyl esters, methyl myristate, ethyl myristate, butyl myristate, other alkyl esters of myristic acid, methyl pentadecylate, ethyl pentadecylate, butyl pentadecylate, other alkyl esters of pentadecyl acid, methyl palmitate, ethyl palmitate , Butyl palmitate, other alkyl esters of palmitic acid, methyl margarate, ethyl margarate, butyl margarate, other alkyl esters of margaric acid, stearin Methyl, ethyl stearate, butyl stearate, other alkyl esters of stearic acid, methyl arachidate, ethyl arachidate, butyl arachidate, other alkyl esters of arachidic acid, methyl behenate, ethyl behenate, butyl behenate, behenic acid Other alkyl esters, methyl lignocerate, ethyl lignocerate, butyl lignocerate, other alkyl esters of lignoceric acid, methyl serotic acid, ethyl serotic acid, butyl serotic acid, other alkyl esters of serotic acid, methyl montanate, ethyl montanate , Butyl montanate, other alkyl esters of montanic acid, methyl melicinate, ethyl melicinate, butyl melicinate, other alkyl esters of melicic acid, etc. As the alkyl ester of acid, methyl myristoleate, ethyl myristoleate, butyl myristoleate, other alkyl esters of myristoleic acid, methyl palmitoleate, ethyl palmitoleate, butyl palmitoleate, other alkyl esters of palmitoleic acid, oleic acid Methyl, ethyl oleate, butyl oleate, other alkyl esters of oleic acid, methyl elaidate, ethyl elaidate, butyl elaidate, other alkyl esters of elaidic acid, methyl vaccenate, ethyl vaccenate, butyl vacceate, vaccenic acid Other alkyl esters such as methyl gadrate, ethyl gadrate, butyl gadrate, other alkyl esters of gadrate, methyl erucate, ethyl erucate, Butyl lucate, other alkyl esters of erucic acid, methyl nervonic acid, ethyl nervonic acid, butyl nervonic acid, other alkyl esters of nervonic acid, methyl linoleate, ethyl linoleate, butyl linoleate, other alkyl esters of linoleic acid, linolenic Methyl acid, ethyl linolenate, butyl linolenate, other alkyl esters of linolenic acid, methyl eleostearate, ethyl eleostearate, butyl eleostearate, other alkyl esters of eleostearic acid, methyl stearidonic acid, stearidone Ethyl ester, butyl stearidonic acid, other alkyl esters of stearidonic acid, methyl arachidonic acid, ethyl arachidonic acid, butyl arachidonic acid, other alkyl esters of arachidonic acid, eicosapentaenoic acid , Ethyl eicosapentaenoate, butyl eicosapentaenoate, other alkyl esters of eicosapentaenoic acid, methyl sardate, ethyl sardate, butyl sardate, other alkyl esters of sardate, methyl docosahexaenoate, ethyl docosahexaenoate, butyl docosahexaenoate And other alkyl esters of docosahexaenoic acid, and these may be used alone or in combination.

  Preferred is a methyl ester compound of a fatty acid, at least one selected from methyl palmitate, methyl palmitate and methyl oleate, and selected from methyl palmitate, methyl palmitate and methyl oleate In combination with at least one selected from the above and other saturated fatty acid methyl ester compounds. More preferably, it is at least one selected from methyl palmitate and methyl oleate which are methyl ester compounds of unsaturated fatty acids, and saturated with at least one selected from methyl palmitate and methyl oleate. It is a combined use with a fatty acid methyl ester compound. Further, fatty acids, fatty acid salts, higher aliphatic alcohols, esters of higher aliphatic alcohols, higher aliphatic amines, higher aliphatic amides, polyethylene wax and the like can be used in combination.

The method for producing the conductive powder containing the conductive particles and the fatty acid ester compound is obtained by using a mechanical milling method, a chemical reduction method, an electrolytic method, an atomizing method, etc. The fatty acid ester compound is used as a lubricant in the flaking process for pulverizing (flaking) using a pulverizer.
Conductive particles can be obtained by mechanical pulverization, etc., but there may be problems such as the target particle size not being obtained depending on the type of conductive particles, chemical reduction method, electrolytic method It is preferably obtained by any of the atomizing methods.
In particular, when silver particles smaller than 10 μm are required, a water atomization method in which molten metal is sprayed into water or a chemical reduction method in which a silver nitrate solution is reduced with a reducing agent is suitable.

The fatty acid ester compound is preferably used in an amount of 0.005 g to 0.5 g per 1 m ² of the surface area of the obtained conductive powder. Within this range, aggregation does not occur during the flaking process, and good conductivity can be obtained. If it is less than this, agglomeration is likely to occur during the flaking process, and if it is more than this, the amount of fatty acid ester compound remaining in the obtained conductive powder becomes too much, which may lead to deterioration in conductivity when a conductive paste is obtained. Because.
Flaking can be done either dry or wet, but it is preferable to carry out flaking from the viewpoint of quality stability. Solvents used in the wet process include methanol, ethanol, propanol, butanol, pentanol, dimethyl ketone, diethyl ketone, dimethyl ether, diethyl ether, diphenyl ether, toluene, and xylene. These may be used alone or in combination. Absent.

A conductive powder can be obtained by removing the aggregates and coarse particles by filtration after flaking and then drying. The obtained conductive powder has a weight reduction rate of 0.05% by weight after being heated at room temperature and from room temperature to 500 ° C. and held at 500 ° C. for 1 hour in a nitrogen atmosphere by a suggestive thermobalance (TGA). The content is preferably 2% by weight or less. A more preferable weight loss rate is 0.05% by weight or more and 1% by weight or less. If the amount is less than the lower limit value, aggregation may proceed gradually after drying. If the amount is more than the upper limit value, the amount of the remaining lubricant may increase so much that the conductive paste may be deteriorated. The obtained conductive powder preferably has a 50% average particle diameter of 1 μm or more and 50 μm or less by a laser diffraction method. A more preferable 50% average particle diameter is 1 μm or more and 15 μm or less, and further preferably 3 μm or more and 10 μm or less. If it is smaller than the lower limit, the viscosity becomes too high when it is made into a conductive paste, and it becomes impossible to mix conductive powder sufficient to obtain sufficient conductivity, and if it is larger than the upper limit, fine processing becomes impossible when it is made into a conductive paste. is there.
EXAMPLES The present invention will be specifically described below using examples, but is not limited thereto.

[Example 1]
A stirring ball mill provided with a cylindrical container having a radius of 15 cm and a height of 30 cm and a stirring blade (radius 14 cm) disposed in the cylindrical container was prepared.
10 kg of reduced silver particles having an average particle diameter of about 5 μm and a specific surface area of 0.2 m ² / g obtained by chemical reduction of silver nitrate and 30 kg of titanium balls (0.8 mm in diameter) are charged into a cylindrical container of a stirring ball mill. Further, 8 kg of ethanol, 0.1 kg of methyl oleate and 0.1 kg of methyl palmitate were added. The rotation speed of the stirring blade was set to 500 rpm, the stirring ball mill was started, and flaking was started. After the stirring ball mill was operated for 2 hours, the rotation was stopped. Thereafter, the contents of the cylindrical container were filtered and the filtrate was dried to obtain a conductive powder.
Table 1 shows characteristic values evaluated by the following methods.

-Tap density: It calculated by reading the capacity | capacitance after putting 100 g of electroconductive powders into a measuring cylinder, adding shake.
Specific surface area: measured by the BET method.
-50% average particle diameter: Measured with a laser diffraction particle size measuring apparatus (SALD-3000J, manufactured by Shimadzu Corporation). A sample having a 50% average particle diameter of 1 μm or more and 50 μm or less was regarded as acceptable.
Weight reduction rate: Weight reduction rate after setting 50 mg of conductive powder on a suggestive thermobalance (TGA), raising the temperature from room temperature to room temperature in a nitrogen atmosphere and holding at 500 ° C. for 1 hour. Was measured. A weight reduction rate of 0.05% to 2% by weight was regarded as acceptable.
Conductivity: Raw materials are prepared at a blending ratio shown in Table 2, these raw materials are blended so that the amount is 15% by weight, and the conductive powder is 85% by weight, kneaded using three rolls, and defoamed. As a result, a conductive paste was obtained. The conductive paste was printed on a glass plate so as to have a width of 4 mm, a length of about 50 mm, and a thickness of 0.04 mm, and cured at 175 ° C. for 60 minutes. After curing, the resistance value in the length direction of 40 mm was measured and the volume resistivity was calculated. A sample having a volume resistivity of 5 × 10 ⁻⁵ Ω · cm or less was accepted.

[Example 2]
Conductive powder was produced in the same manner as in Example 1 and evaluated in the same manner as in Example 1. In Example 2, 0.2 kg of methyl palmitate was added instead of 0.1 kg of methyl oleate and 0.1 kg of methyl palmitate.

[Comparative Examples 1 and 2]
Conductive powder was produced in the same manner as in Example 1 and evaluated in the same manner as in Example 1. In Comparative Example 1, 0.1 kg of methyl oleate and 0.2 kg of palmitic acid instead of 0.1 kg of methyl palmitate were added, and in Comparative Example 2, 0.15 kg of oleic acid and 0.05 kg of N, N-dimethylstearylamide were added. did.

  Since the conductive powder of the present invention is particularly excellent in conductivity when a conductive paste is used, it can be suitably used as a conductive material.

Claims (8)

A conductive powder comprising conductive particles and a fatty acid ester compound. The conductive powder according to claim 1, wherein the fatty acid ester compound is an alkyl ester compound of a fatty acid having 10 to 30 carbon atoms. The conductive powder according to claim 1, wherein the fatty acid ester compound is a fatty acid methyl ester compound. The conductive powder according to claim 1, wherein the fatty acid ester compound is an ester compound of an unsaturated fatty acid. The conductive powder according to claim 1, wherein the conductive particles are silver. The conductive powder according to any one of claims 1 to 5, wherein a weight reduction rate measured by a suggestive thermobalance (TGA) is 0.05% by weight or more and 2% by weight or less. The conductive powder according to any one of claims 1 to 6, wherein a 50% average particle diameter measured by a laser diffraction method is from 1 µm to 50 µm. It is a manufacturing method of the electroconductive powder of any one of Claims 1-7, Comprising: A fatty acid ester compound is used in the flaking process of electroconductive particle, The manufacturing method of the electroconductive powder characterized by the above-mentioned.