JPH08259842A - Coated inorganic powder and its production - Google Patents

Abstract

PURPOSE: To obtain coated inorganic powder by coating the surface of powder of an inorganic substance with an organic thiol compound or a reaction product of the compound and an inorganic substance, hating high dispersibility in a thick film paste, capable of being readily made into a paste, excellent in printability and coating performance. CONSTITUTION: An inorganic substance such as a smoky silver powder produced by a wet method is sufficiently coated with an organic thiol compound such as octadecyl thiol by pouring the organic thiol compound, shaken and stirred for 10 minutes to give a suspension, which is allowed to stand for 8 hours to treat the surface of the inorganic substance. The suspension is decanted to separate and remove the supernatant liquid. The remaining inorganic substance powder is cleaned with hexane, etc., the inorganic substance is settled, the mixture is decanted to separate and remove the remaining organic thiol compound, the inorganic substance is dried to give the objective coated inorganic powder comprising the powder of the inorganic substance whose surface is coated with the organic thiol compound and/or the reaction product of the compound and the inorganic substance, having high dispersibility in a thick film paste, capable of being readily made into a paste.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to high-quality inorganic powder such as metal powder having excellent dispersibility and a method for producing the same. The metal powder of the present invention can be used as a thick film paste of an electrode material for electronic parts, a paste for decoration, and the like.

[0002]

2. Description of the Related Art In manufacturing ceramic electronic parts and electronic circuit parts, a thick film paste is generally used to form a fine, dense and smooth conductor layer and a resistor layer on the surface or inside of a ceramic body. Thick film printing method is used. In the thick film printing method, metal powder such as simple metal, alloy, or metal oxide is dispersed in an organic binder to form a paste, which is printed or applied on an unsintered ceramic green cake or a sintered ceramic. Baking is performed by baking at a high temperature. The paste used here is a paste in which metal powder and an organic binder (organic vehicle) are uniformly mixed and dispersed together with an inorganic binder such as a glass substance and other additives as required. The metal powder blended in the thick film paste is required to form a dense and smooth metal film having no pinholes or protrusions when screen-printed or applied. For this reason, the metal powder must be properly controlled in terms of purity, size, shape, etc. of the metal particles so as to exhibit wettability and dispersibility with respect to other components mixed in the paste.

As such a metal powder, a method of directly reducing a metal oxide powder, an alkali is applied to an aqueous solution of a metal compound to form a hydroxide or an oxide, and then a reducing agent is allowed to act on this product. There is a method of making metal powder. Further, it can also be produced by directly acting a reducing agent on an aqueous solution of a metal compound to reduce and generate metal powder (wet reduction method). As a further alternative, evaporate the molten metal in the gas phase or in an inert gas phase or in a vacuum,
There are a method of condensing and depositing this, a method of decomposing and reducing after evaporating a precursor such as an organometallic compound, and a method of forming fine metal powder by an atomizing method.

The metal powder obtained by such a method is
From a relatively coarse solid powder having a particle size of about 10 μm or more, a powder having a particle size of around 10 μm, a fine powder having a particle size of 10 to 1 μm, and an ultrafine powder of a submicron class.

Further, such a metal powder has a unique characteristic in terms of powder physical properties depending on its manufacturing method. That is, the metal powder produced by the wet reduction method interacts in a complicated manner with respect to the type and form of the starting material, the type of oxidizing agent or reducing agent thereof, the reaction conditions, etc. Controlled by the technology, the cohesiveness is extremely strong and it is difficult to wet the organic medium. For this reason, a metal paste excellent in dispersibility cannot be obtained with conventionally known materials for paste processing.

On the other hand, the atomizing method has a drawback that it is difficult to control the particle size of the metal powder produced. Further, a so-called CV for evaporating the molten metal into a vapor phase and condensing and depositing this
D (Chemical Vapar Deposition) method and PVD (Phisical Vapor Deposition) method
Although vapor deposition methods such as the Vapar Deposition method can produce submicron-sized ultrafine powders, such metal powders have very strong cohesive forces among the powders and have excellent secondary dispersibility. It is difficult to obtain metal powder.

As described above, none of the conventional manufacturing methods has obtained a metal powder having a particle size and a powder morphology suitable as a raw material metal powder for a paste, and having little secondary aggregation and excellent dispersibility.

Further, the surface of the metal powder is chemically and physically more active than the inside of the metal powder. For this reason, the surface of ordinary metal powder is covered with oxide or hydroxide, and usually has hydrophilicity. On the other hand, it is extremely difficult to get wet with an organic solvent or an organic binder. Therefore, conventionally, a thick film paste in which metal powder is sufficiently dispersed at the particle level has not been obtained.

An object of the present invention is to provide a high-quality inorganic substance powder, particularly a metal powder, which has high dispersibility and can be easily formed into a thick film paste or the like, and which has excellent printability and coatability. is there. Another object of the present invention is to provide a method for easily and efficiently producing such an inorganic powder.

[0010]

Means for Solving the Problems As a result of intensive studies on the above problems, the present inventors have found that excellent dispersibility can be obtained by surface-treating an inorganic powder such as a metal powder with an organic thiol compound. The present invention has been completed based on the knowledge obtained.

The present invention provides a coated inorganic powder obtained by coating the surface of a powder of an inorganic substance such as metal with an organic thiol compound. This coating may be a reaction product of the inorganic substance and the organic thiol compound, or may be a mixture of the reaction product and the organic thiol compound. The present invention also provides a method for producing a coated inorganic powder, which comprises treating the inorganic powder with an organic thiol compound. The coated inorganic powder of the present invention comprises an inorganic powder that forms a core and a modified shell layer that modifies its surface properties.

Examples of the above-mentioned inorganic powder include noble metal powders such as gold, silver, palladium, rhodium, iridium, rhenium and ruthenium; base metal powders such as copper, nickel, cobalt, iron, aluminum, molybdenum and tungsten; And a powder of an oxide or the like. Further, other oxide powders such as ordinary oxide ceramic powders such as calcium oxide and barium oxide and non-oxide ceramics such as silicon carbide and aluminum nitride may be used, but metal powders are particularly preferable. If it is a metal powder,
As the powder, any metal powder obtained by a conventionally known chemical or physical method such as a wet method, a reduction method, a wet reduction method, or an atomizing method can be preferably used.

If the particle size of the inorganic powder is too large, problems such as sedimentation in the suspension occur, and if the particle size is too small, aggregates are likely to be formed, and therefore countermeasures are required. Usually, the particle size is preferably 0.01 to 10 μm, and particularly preferably 0.05 to 5 μm, but it may be appropriately selected depending on the application.

The organic thiol compound which is the coating substance is R
(SH) _n (R is a hydrocarbon derivative radical, n = 1 to 3)
It is represented by. Such organic thiol compounds include methylthiol, ethylthiol, propylthiol, butylthiol, heptylthiol, hexylthiol, octylthiol, nonylthiol, decylthiol, undecylthiol, dodecylthiol, tetradecylthiol, octadecylthiol, etc. CnH ₂ n
An aliphatic thiol compound represented by ₊₁ SH, a polyfunctional thiol such as dithiol thereof, thiophenol, toluenethiol, naphthalenethiol, biphenylthiol, aromatic thiol compound such as terphenylthiol, or

Embedded image Examples thereof include thiol terminated oligoimide compounds.

Next, the method for producing the coated inorganic powder of the present invention will be described. In order to produce the coated inorganic powder of the present invention, the powder of the above inorganic substance is treated with an organic thiol compound. In the treatment, the organic thiol compound may be used as it is, or the compound may be dispersed or dissolved in an organic solvent before use. Inorganic powder is dispersed in such an organic thiol compound or a solution or dispersion thereof, and this suspension is left standing or stirred to coat or reactively bond the surface of the inorganic powder with the organic thiol compound.

As the organic solvent, higher hydrocarbon compounds such as hexane, nonanedecane, undecane, dodecane, tetradecane and octadecane are preferably used in the case of high temperature treatment, but hydrocarbons having a relatively low boiling point may be used depending on the treatment temperature. . For such purposes, aliphatic alcohols, aromatic alcohols, ketones, ethers,
There is no particular limitation as long as it is a non-reactive or low-reactive substance such as an ester.

In preparing a suspension of inorganic powder,
Stirring is effective for promoting mixing and dispersion, but stirring may be mechanical or physical as long as particles do not react with each other or cause a sintering phenomenon.

The treatment temperature is appropriately selected in consideration of the treatment time so as to avoid the reaction between the inorganic particles, but it is usually room temperature or higher. Since the treatment efficiency increases as the treatment temperature increases, it is preferable to raise the treatment temperature to a temperature at which the mutual reaction of the inorganic particles does not occur. When the surface treatment is carried out while refluxing at the boiling temperature of the organic solvent, it is easy to control the treatment temperature and the surface treatment concentration in the surface treatment of the inorganic particles. In addition,
It is more preferable to carry out the treatment at a temperature above the boiling temperature of the system, that is, in a high temperature gas phase, because the treatment can proceed uniformly without any influence of the surface tension of the system on the outer shape of the inorganic substance and the details of the internal structure. The inorganic powder thus surface-treated in the suspension is uniformly treated with a surface-treating substance, that is, a thiol compound and / or a reaction product of the thiol compound and the inorganic substance. For this reason, the quality of the inorganic substance powder is extremely high and has high dispersibility.

The surface-coated inorganic powder according to the present invention is, when the powder is a metal substance, estimated by the present inventors to be M ...
It seems that it has a composition of (SH) R or M- (SR).

The coated inorganic powder of the present invention, in the case of metal powder, is kneaded with an organic binder, a solvent and the like by a conventional method, and has excellent quality as an electrode material for electronic materials and other decorative articles. Further, since the metal film after baking is uniform, the quality of the coating film is high and in the case of expensive precious metal powder, the amount of raw material used can be reduced.

Further, according to the present invention, the surface is coated with the organic thiol compound and / or the reaction product of the thiol compound and the metal substance without causing the mutual reaction and sintering phenomenon of the metal powders and the aggregation. it can. Therefore, conventionally,
Problems such as agglomeration of metal powder generated in the process of processing into a thick film paste, metallurgical bonding by fusion, or deformation of the powder shape of the powder caused in the paste processing process can be solved. Therefore, the problem relating to the non-uniform dispersion in the paste, which has been a problem when handling metal powders, can be completely eliminated. The coated inorganic powder of the present invention has good dispersibility as described above, and high-quality surface-treated metal powder can be easily produced.

[0022]

EXAMPLES Next, the present invention will be described more specifically based on examples.

Example 1 To 100 g of smoked silver powder (particle size 1 μm: sedimentation method) produced by a wet method, 50 g of octadecyl thiol was poured to sufficiently cover the silver powder. The mixture was shaken and stirred for 10 minutes to form a suspension, and then left standing for 8 hours to perform surface treatment of silver powder. The suspension was decanted to separate and remove the supernatant. Hexane was further added to the residual silver powder to wash it, and then the silver powder was allowed to settle and similarly decanted to separate and collect the remaining free octadecylthiol. The same washing treatment was repeated 3 times in total, and the obtained silver powder was dried at room temperature for 2 hours to obtain surface-treated smoked silver powder. When the obtained silver powder was observed by SEM, there was no apparent change from the state before the treatment, and no morphology such as a new metallurgical, chemical, or physical bond between the silver powders was observed.

Next, a solution of 15 g of terpineol in which 3 g of ethyl cellulose was dissolved was added to 100 g of the surface-treated silver powder, and the mixture was lightly kneaded with a triple roll for 10 minutes within a range in which the particles of the silver powder were not deformed to form a paste. did. Almost no deformation of the silver powder particles in the obtained paste was observed.

Using the obtained paste, a thick film was formed on a polished alumina substrate (alumina content of 96%) by screen printing.
(Thickness 10 μm) was formed and baked in an air furnace at 650 ° C. to print a silver thick film. The surface roughness of the baked thick silver film is R
The maximum value was 0.5 μm.

Comparative Example 1 In the same manner as in Example 1, except that the surface treatment with octadecylthiol was not performed, a solution of terpineol in which ethyl cellulose was dissolved was added and kneaded to obtain a paste. This paste was rough when judged sensuously and did not show a paste state.
Then, the mixture was further roll-kneaded for 30 minutes to complete the paste. When the obtained paste was observed by SEM, the silver powder particles were flatly deformed. Using this paste, Example 1
A thick silver film was baked on an alumina substrate in the same manner as in. The surface roughness of the thick film was Rmax of 2.5 μm, which was extremely rough, and the surface was markedly roughened.

Example 2 100 g of smoked gold powder (average particle size 1.0 μm: sedimentation method) produced by a wet method was poured with 50 g of octadecylthiol to sufficiently cover the silver powder. The mixture was shaken and stirred for 10 minutes to give a suspension, which was then left to stand for 24 hours for surface treatment of the gold powder. The suspension was decanted to separate and remove the supernatant. Hexane was further added to the remaining gold powder to wash it, and then the gold powder was allowed to settle and similarly decanted to separate and remove the remaining free octadecylthiol. The same washing treatment was repeated a total of three times, and then the obtained gold powder was dried at room temperature for 2 hours to obtain a surface-treated smoked gold powder. When the obtained gold powder was observed by SEM, there was almost no change from the state before the treatment, and no metallurgical binding reaction between the powders was observed at all. Next, to 100 g of the surface-treated gold powder, a solution of 15 g of butyl carbitol in which 3 g of ethyl cellulose was dissolved was added, and the mixture was lightly kneaded with a silicon rubber roll for 10 minutes within a range where the shape of the gold powder particles was not deformed to form a paste. processed. The gold powder in the obtained paste was almost the same as the shape before kneading.

Using the obtained paste, a gold thick film (thickness 5 μm) was baked on a polished alumina substrate in the same manner as in Example 1. The surface roughness of the baked thick silver film is 0.3 at Rmax.
μm.

Comparative Example 2 100 g of gold powder used in Example 2
Without surface treatment with octadecyl thiol,
15 g of terpineol in which 3 g of ethyl cellulose was dissolved
The above solution was added and the mixture was lightly kneaded with a silicon rubber roll for 10 minutes to obtain a paste. The paste was rough and did not give a glossy paste. Therefore, roll kneading was further added for 30 minutes to complete the paste.
SEM observation of the obtained paste revealed that many particles of the smoked gold in the paste were metallurgically fused to each other and were significantly deformed flat. Using this paste, 5 μm was formed on an alumina substrate in the same manner as in Example 2.
A thick film of gold was baked. The surface roughness of the thick film was 2 μm in Rmax, and the surface was remarkably rough and the gloss was inferior.

Example 3 To 100 g of spherical silver powder (average particle size 1.0 μm, observed by SEM) produced by the wet reduction method, 1
Hexane 200 containing 0 g of octadecyl thiol
g solution was poured and refluxed for 4 hours. Next, this suspension was returned to room temperature and then decanted to separate a supernatant liquid to obtain a surface-treated silver powder. Then, an excess amount of hexane was poured into the obtained surface-treated silver powder to wash it, and decantation was performed in the same manner to separate and remove the remaining octadecylthiol. This washing operation was repeated three times in total and then dried at room temperature for 2 hours to obtain a surface-treated silver powder.

The SEM observation of this silver powder showed that the periphery of the spherical silver powder had a contour close to white, suggesting that the surface treatment was performed. Also, when the thermal decomposition behavior was traced by a thermobalance, it was estimated that octadecylthiol was in a chemically bonded state, with a shift to a temperature range of about 30 ° C higher than the thermal decomposition temperature of octadecylthiol alone, and thermal decomposition proceeded slowly. Was done.

Next, 100 g of this surface-treated silver powder
Terpineol 10 in which 3 g of ethyl cellulose was dissolved in
g of the solution was added, and the mixture was lightly kneaded with a triple roll for 10 minutes to form a paste. In the obtained paste, the spherical silver powder particles in the paste showed almost no deformation, and at the SEM observation level, a uniform dispersed state without aggregated powder was formed.
Then, a silver thick film having a thickness of 10 μm was baked using this paste in the same manner as in Example 1. The surface roughness of the thick silver film thus obtained was 1.0 to 1.5 μm in Rmax, and no irregularities were found.

Comparative Example 3 In the same manner as in Example 3, except that the surface treatment with octadecylthiol was not carried out, a solution of terpineol in which ethyl cellulose was dissolved was added, and the mixture was roll-kneaded for 30 minutes under the same conditions as in Example 3. To produce a paste. The silver powder particles in this paste are SEM
Upon observation, metallurgical fusion was generated between the powders, and the deformation was significantly advanced, resulting in a flat shape. Next, using this paste, a silver thick film of 10 μm was formed on the alumina substrate in the same process as in Example 1, and the surface roughness was Rmax of 2.5 to 3 μm, and remarkable unevenness was observed.

[0034]

INDUSTRIAL APPLICABILITY In the coated inorganic powder of the present invention, particles of an inorganic substance such as a metal are chemically and uniformly coated with an organic thiol compound, and they have excellent dispersibility and can be easily made into a paste. The paste of the present invention is suitably used as a thick film paste for electrode materials of electronic parts and a decorative paste. In addition, according to the production method of the present invention, an inorganic powder having excellent dispersibility can be produced extremely easily and efficiently, and it is also excellent in economic efficiency.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H01B 1/00 7244-5L H01B 1/00 A // C09D 11/00 PTF C09D 11/00 PTF ( 72) Inventor Noboru Suzuki 1-2-20 Wakakusa-cho, Utsunomiya City, Tochigi Prefecture

Claims (5)

[Claims] 1. A coated inorganic powder obtained by coating the surface of a powder of an inorganic substance with an organic thiol compound and / or a reaction product of the compound and the inorganic substance. 2. The coated inorganic powder according to claim 1, wherein the inorganic substance is a metal and the organic thiol compound is an aliphatic thiol. 3. A method for producing a coated inorganic powder, which comprises treating the powder of an inorganic substance with an organic thiol compound. 4. The method for producing coated inorganic particles according to claim 3, wherein the treatment with the organic thiol compound is carried out in an organic medium. 5. A paste containing the coated inorganic powder according to claim 1.