JP7644509B2 - Method for producing silver chloride particles - Google Patents

Description

The present invention relates to a silver chloride-containing paste used to form conductors such as electrodes and wiring, and to silver chloride particles that are the raw material for this silver chloride-containing paste.

A paste containing silver chloride particles (also referred to as "silver chloride-containing paste" in this specification) is used as a raw material for forming electrodes and wiring, for example, a bioelectrode. For example, Patent Document 1 discloses a conductive composition containing an elastomer, silver powder, and silver chloride particles, in which the silver powder is surface-treated, the silver powder has an average primary particle size of 1.0 μm or less, an apparent porosity of 50 to 95%, and the cumulative 95% particle size (D95 particle size) in the particle size distribution of the secondary particles of the silver powder and silver chloride particles in the conductive composition is 3.0 to 25.0 μm.

The silver chloride-containing paste can be used in a wide range of fields, including medicine, as a photocatalyst, due to the excellent photochemical properties of silver chloride and silver (see, for example, Patent Document 2). Patent Document 2 discloses a method for producing nanoaggregates in which the shape and structure of the nanoaggregates formed are changed by the reaction molar ratio of silver nitrate and hydrochloric acid, and that when the reaction molar ratio of silver nitrate and hydrochloric acid is 1:2-1:30, silver chloride nanocubes with sizes of 50-2000 nm are formed.

JP 2020-55918 A Korean Patent No. 10-1209175

From the viewpoint of stabilizing the characteristics of the component using the silver chloride-containing paste, such as an electrode, it is preferable that the silver chloride particles contained therein are dispersed as uniformly as possible. For this reason, it has been thought that it is preferable to reduce the primary particle size of the silver chloride particles contained in the silver chloride-containing paste.

The present invention aims to provide a method for producing silver chloride particles that are used, for example, to prepare a silver chloride-containing paste that is a raw material for electrodes and wiring, and that have good dispersibility when made into a silver chloride-containing paste. The present invention also aims to provide silver chloride particles that have good dispersibility when made into a silver chloride-containing paste, and a silver chloride-containing paste that contains such silver chloride particles.

The method for producing silver chloride particles according to one embodiment of the present invention, which is provided to solve such problems, is a method for producing silver chloride particles that includes precipitating silver chloride particles by a liquid reaction between a silver ammine complex and chloride ions, and is characterized in that a dispersant is added before or after the precipitation of the silver chloride particles, or both.

By adopting this manufacturing method, it is possible to obtain silver chloride particles that have a relatively large primary particle size and that are less prone to agglomeration.

In the above manufacturing method, the silver ammine complex may be produced by reacting silver nitrate with ammonia.

In the above manufacturing method, the dispersant is preferably an anionic surfactant.

In the above manufacturing method, it may be preferable that the chlorine source that provides chloride ions contains hydrochloric acid.

In another aspect, the present invention provides silver chloride particles characterized in that the cumulative 50% particle diameter D50 in the cumulative particle size distribution from the small particle size side (in this specification, "cumulative particle size distribution" is used in this sense unless otherwise specified) in the volumetric particle size distribution obtained by wet measurement using a laser diffraction/scattering method (in this specification, "cumulative particle size distribution" is used in this sense unless otherwise specified) is 8 μm or more and 25 μm or less.

Since such silver chloride particles have a small primary particle size and a small proportion of silver chloride particles with high cohesive power, they are less likely to aggregate, and as a result, coarse particles are less likely to be generated.

In the above silver chloride particles, it may be preferable that the cumulative 10% particle diameter D10, the cumulative 90% particle diameter D90, and the cumulative 50% particle diameter D50 in the cumulative particle size distribution satisfy the following formula (1).
(D90-D10)/D50≦2.2 (1)

In the above silver chloride particles, it may be preferable that the most frequent particle size Dm of the volume-based particle size distribution is 10 μm or more.

In the above silver chloride particles, it is sometimes preferable that the cumulative 50% particle diameter D50 and the most frequent particle diameter Dm in the volume-based particle diameter distribution satisfy the following formula (2).
Dm/D50≦1.7 (2)

In the volume-based particle size distribution of the silver chloride particles, the frequency distribution value Ps of a sub-peak, which is a peak located on the smaller particle size side than the most frequent particle size Dm, satisfies the following formula (3) together with the frequency distribution value Pm at the most frequent particle size Dm: Ps≦Pm×0.6 (3)

The method for producing the silver chloride particles may be for producing the silver chloride particles.

In another aspect, the present invention provides a silver chloride-containing paste comprising the above-mentioned silver chloride particles and a vehicle. This silver chloride-containing paste may further contain conductive particles, and the conductive particles may contain silver powder.

The present invention provides a method for producing silver chloride particles that is less likely to produce silver chloride particles with excessively large secondary particle sizes. The present invention also provides silver chloride particles that exhibit good dispersibility when made into a silver chloride-containing paste, and a silver chloride-containing paste that contains such silver chloride particles.

1 is a graph showing the volume-based particle size distribution of silver chloride particles of Example 1 and Comparative Example 1. 1 is a graph showing the volume-based cumulative particle size distribution of silver chloride particles of Example 1 and Comparative Example 1. FIG. 2 is a diagram showing an observation image (magnification: 500 times) of the silver chloride particles of Example 1. FIG. 2 is a diagram showing an observation image (2000x) of the silver chloride particles of Example 1. FIG. 2 is a diagram showing an observation image (10,000 times) of the silver chloride particles of Example 1. FIG. 2 is a diagram showing an observed image (magnification: 500 times) of silver chloride particles in Comparative Example 1. FIG. 2 is a diagram showing an observed image (2000x) of silver chloride particles in Comparative Example 1. FIG. 2 is a diagram showing an observed image (10,000 times) of silver chloride particles in Comparative Example 1. 2 is a graph showing the volume-based particle size distribution of the silver chloride particles of Example 22. 2 is a graph showing the cumulative particle size distribution by volume for the silver chloride particles of Example 22. FIG. 13 is a diagram showing an observation image (10,000 times) of silver chloride particles of Example 22. 1A and 1B are diagrams showing measurement results of the shape of a wiring pattern (wiring pattern 1, measurement point 2) based on Example 1. FIG. 23 is a diagram showing the measurement results of the shape of a wiring pattern (wiring pattern 1, measurement point 2) based on Example 21. FIG. 13 is a diagram showing the measurement results of the shape of a wiring pattern (wiring pattern 2, measurement location 1) based on Comparative Example 1. 11 is a diagram showing the measurement results of the shape of a wiring pattern (wiring pattern 2, measurement point 4) based on Example 1. FIG. FIG. 23 is a diagram showing the measurement results of the shape of a wiring pattern (wiring pattern 1, measurement point 4) based on Example 21. FIG. 13 is a diagram showing the measurement results of the shape of a wiring pattern (wiring pattern 1, measurement point 5) based on Comparative Example 1.

The following describes an embodiment of the present invention. In the volume-based particle size distribution obtained by wet measurement using a laser diffraction/scattering method, the silver chloride particles according to one embodiment of the present invention have a cumulative 50% particle diameter D50 of 8 μm or more and 25 μm or less in the cumulative particle size distribution from the small particle size side. By having a cumulative 50% particle diameter D50 of 8 μm or more and 25 μm or less, the proportion of silver chloride particles with small primary particle diameters and high cohesive force is reduced, and as a result, coarse secondary particles are less likely to be generated. From the viewpoint of more stably reducing the proportion of silver chloride particles with small primary particle diameters, it may be more preferable that the cumulative 50% particle diameter D50 is 20 μm or less.

In the silver chloride particles according to this embodiment, it may be preferable that the cumulative 10% particle diameter D10, the cumulative 90% particle diameter D90, and the cumulative 50% particle diameter D50 in the cumulative particle size distribution satisfy the following formula (1).
(D90-D10)/D50≦2.2 (1)

The left side of the above formula (1) indicates the degree of steepness of the rise of the cumulative particle size distribution; the smaller the value on the left side, the steeper the rise and the narrower the distribution width of the particle size distribution. Since it may be preferable for the distribution of silver chloride particles to be as narrow as possible from the viewpoint of the quality stability of the silver chloride-containing paste (prevention of coarse secondary particles), it may be more preferable for the left side of the above formula (1) to be 2.0 or less, and particularly preferably 1.5 or less.

The silver chloride particles according to this embodiment may preferably have a modal particle diameter Dm of 10 μm or more. When the modal particle diameter Dm is 10 μm or more, the amount of silver chloride having a small primary particle diameter is relatively small, and the quality stability of the silver chloride-containing paste is excellent. There is no particular upper limit to the cumulative modal particle diameter Dm, but it may be preferable for it to be 35 μm or less, and it may be more preferable for it to be 30 μm or less.

The cumulative 50% particle diameter D50 and the most frequent particle diameter Dm of the volume-based particle diameter distribution may satisfy the following formula (1).
1.0<Dm/D50≦1.7 (1)

The cumulative 50% particle diameter D50 is the particle diameter at which the cumulative value from the small diameter side of the particle volume is equal to the cumulative value from the large diameter side in the volume-based particle diameter distribution. On the other hand, the most frequent particle diameter Dm is the particle diameter at which the maximum peak of the volume-based particle size distribution is located.

When the particle size ratio (Dm/D50) is 1.7 or less, the sub-peak located on the smaller diameter side of the maximum peak is less likely to become apparent, and the proportion of silver particles with small primary particle sizes is small. Therefore, large secondary particles are less likely to be generated in a silver chloride-containing paste that contains such silver chloride particles. From this perspective, Dm/D50 may be preferably 1.6 or less, more preferably 1.5 or less, even more preferably 1.4 or less, and particularly preferably 1.3 or less.

The lower limit of Dm/D50 is not particularly limited. Dm/D50 being less than 1.0 means that the most frequent particle diameter Dm is smaller than the cumulative 50% particle diameter D50. Therefore, from the viewpoint of more stably reducing the proportion of silver chloride particles having a small primary particle diameter, Dm/D50 may be preferably 0.5 or more, more preferably 0.6 or more, even more preferably 0.7 or more, and particularly preferably 0.8 or more.

In the silver chloride particles according to this embodiment, in a volume-based particle size distribution, it may be preferable that a frequency distribution value Ps of a sub-peak, which is a peak located on the smaller particle size side than the most frequent particle diameter Dm, and a frequency distribution value Pm at the most frequent particle diameter Dm satisfy the following formula (3):
Ps≦Pm×0.6 (3)

As shown in the examples described later, silver chloride particles having a primary particle size of about 10 μm or more are unlikely to form coarse secondary particles when made into a silver chloride-containing paste, but silver chloride particles having a primary particle size of 6 μm or less are likely to form coarse secondary particles. Therefore, silver chloride particles having a particle size distribution in which the most frequent particle size Dm is 10 μm or more are preferable as a raw material for a silver chloride-containing paste, but depending on the manufacturing method of silver chloride particles, silver chloride particles having a most frequent particle size Dm of 10 μm or more but a double-peak type particle size distribution having a sub-peak on the smaller diameter side than the most frequent particle size Dm may be obtained, rather than a single-peak type particle size distribution in which only the most frequent particle size Dm is a peak. Even in such a case, it is preferable that the frequency distribution value Ps of the sub-peak is sufficiently lower than the frequency distribution value Pm of the peak (main peak) that gives the most frequent particle size Dm, and specifically, as shown in the above formula (3), Ps/Pm is preferably 0.6 or less.

As a simple measure for controlling the proportion of silver chloride particles having a primary particle size of 6 μm or less, the ratio (P10/P3) of the frequency distribution value P3 having a particle size of about 3 μm to the frequency distribution value P10 having a particle size of about 10 μm in the volume-based particle size distribution can be mentioned. From the viewpoint of reducing the proportion of silver chloride particles having a primary particle size of 6 μm or less, this ratio (P10/P3) is preferably 3 or more, more preferably 5 or more, even more preferably 6 or more, and particularly preferably 7 or more.

The silver chloride particles according to this embodiment have a relatively large primary particle size, so when the powder state is observed under a scanning electron microscope at 10,000x magnification with a field of view of 9 μm × 13 μm, there tend to be fewer than 10 silver chloride particles that can be observed in their entirety without overlapping.

Next, a method for producing silver chloride particles according to one embodiment of the present invention will be described. The silver chloride particles produced by the production method according to this embodiment may have the characteristics of the silver chloride particles according to this embodiment described above, and are less likely to produce coarse secondary particles, so that a silver chloride-containing paste containing such silver chloride particles has excellent quality.

The manufacturing method according to this embodiment involves precipitating silver chloride particles by a liquid reaction between a silver ammine complex and chloride ions. The solvent for the reaction liquid is typically water, but is not limited to this. The silver ammine complex can be prepared by any method. As a non-limiting example, a silver ammine complex can be produced by a reaction between silver nitrate and ammonia.

There is no limitation on the substance that supplies chloride ions to the reaction solution, i.e., the chlorine source. Examples of chlorine sources include hydrochloric acid and chlorides, such as sodium chloride and potassium chloride. When the chlorine source is hydrochloric acid, it does not contain alkali metal ions such as sodium and potassium, and is therefore suitable for use in electronic materials.

The reaction in the liquid between the silver ammine complex and chloride ions may occur by supplying chloride ions (chlorine source) to a liquid containing the silver ammine complex, or the silver ammine complex may be supplied to a liquid containing chloride ions. The supply form is not limited. For example, when the chlorine source is hydrochloric acid, a liquid containing hydrochloric acid may be supplied to the liquid containing the silver ammine complex. For example, when sodium chloride is the chlorine source, sodium chloride may be supplied as a solid or as a sodium chloride solution to the liquid containing the silver ammine complex.

The quantitative relationship between the silver ammine complex and the chloride ions is not limited. It is preferable to supply a molar amount of chloride ions equal to or greater than the molar amount of silver so that the total amount of silver becomes silver chloride. When generating a silver ammine complex from a silver salt such as silver nitrate and ammonia, it is preferable to supply a molar amount of ammonia at least twice the molar amount of silver so that the total amount of silver becomes an ammine complex.

In the manufacturing method according to this embodiment, a dispersant is added before or after precipitation of silver chloride particles, or both. Adding a dispersant makes it difficult for primary particles to aggregate. Here, "before precipitation of silver chloride particles" refers to the stage before the in-liquid reaction between the silver ammine complex and chloride ions begins, and the dispersant may be present in the liquid containing the silver ammine complex before chloride ions are supplied, or the dispersant may be present in the liquid containing chloride ions before the silver ammine complex is supplied.

A surfactant may be used as the dispersant, and the dispersant is preferably an anionic surfactant. Specific examples of anionic surfactants include fatty acid surfactants based on higher fatty acids having 6 or more carbon atoms; linear alkylbenzene surfactants such as linear alkylbenzene sulfonates; higher alcohol surfactants such as alkyl sulfates and alkyl ether sulfates based on higher alcohols having 12 or more carbon atoms; paraffin surfactants such as sodium alkylsulfonate; and polycarboxylic acid surfactants based on polyacrylic acid, acrylic acid-phthalic acid copolymers, and acrylic acid-sulfonic acid monomer copolymers. Of these, for polycarboxylic acid surfactants, it may be preferable to use a weight average molecular weight in the range of 5,000 to 500,000, and it may be more preferable to use a weight average molecular weight in the range of 10,000 to 200,000.

The amount of dispersant supplied is not particularly limited. It may be supplied in the range of 0.1 to 10% based on the mass of the silver chloride particles produced, and it may be preferable to supply it in the range of 0.5 to 5%.

From the viewpoint of properly fulfilling the function of the dispersant (preventing the generation of coarse particles), it is preferable to supply the dispersant before and after the precipitation of silver chloride. In this case, the supply balance is arbitrary, and one specific example is to supply an equal amount before and after precipitation.

By adopting the manufacturing method according to this embodiment, it may be easier to obtain the silver chloride particles according to this embodiment.

The silver chloride thus obtained is filtered and washed, and the filtered product is dried to obtain the desired silver chloride particles. The silver chloride particles obtained by drying the filtered product may be pulverized to improve handling. Even if this pulverization is performed, it does not affect the quality stability of the silver chloride-containing paste, since silver chloride particles with large particle diameters are formed at the primary particle level.

Next, a silver chloride-containing paste according to one embodiment of the present invention will be described. The silver chloride-containing paste according to this embodiment contains the silver chloride particles according to the embodiment described above or silver chloride particles produced by the method for producing silver chloride particles according to the embodiment described above, and further contains a vehicle.

The type of vehicle contained in the silver chloride-containing paste according to this embodiment is not particularly limited, and various solvents known in the field of paste compositions can be suitably used.

Specific examples of the glycol ethers include diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether; acetate esters of these glycol ethers (a specific example of which is 2-(2-butoxyethoxy)ethyl acetate); esters such as dibasic acid esters (DBE), 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, and 2,2,4-trimethyl-1,3-pentanediol diisobutyrate; ketones such as cyclohexanone and isophorone; monoterpene alcohols such as terpineol and hydrogenated terpineol; acetate esters of these monoterpene alcohols; γ-butyrolactone; limonene; and the like. Only one of these substances may be used, or two or more of them may be used in appropriate combination.

When the silver chloride-containing paste according to this embodiment is used for creating a pattern by screen printing, the vehicle preferably contains a substance whose boiling point is 200°C or higher. It is preferable that the vehicle is a high-boiling point solvent. Although there is no particular limitation on such high-boiling point solvents, specific examples include diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, and terpineol. Only one of these substances may be used, or two or more types may be used in appropriate combination.

The silver chloride-containing paste according to this embodiment may further contain conductive particles. Examples of conductive particles include metal particles such as silver powder, copper powder, and silver-coated copper powder, and carbon particles such as acetylene black, graphite powder, and Ketchan black. When used as a bioelectrode, the conductive particles are preferably silver powder or silver-coated copper powder.

The size of the conductive particles is not particularly limited, but from the viewpoint of shape stability of the pattern (e.g., printed pattern) created from the paste, it may be preferable that the cumulative 50% particle diameter D50 is 15 μm or less. The shape of the conductive particles is not limited, and may be spherical, scaly, or irregular, or the conductive particles may be a mixture of these.

The silver chloride-containing paste according to this embodiment may further contain a binder resin. The binder resin may be required to have heat resistance, i.e., to be a heat-resistant resin. Specific examples of heat-resistant resins include cellulose-based resins, fluororesins, polyimide resins, polyamideimide resins, polyesterimide resins, polyester resins, polyethersulfone resins, polyetherketone resins, polyetheretherketone resins, polybenzimidazole resins, polybenzoxazole resins, polyphenylene sulfide resins, bismaleimide resins, epoxy resins, phenolic resins, and phenoxy resins. Only one type of these heat-resistant resins may be used, or two or more types may be used in appropriate combination.

The silver chloride-containing paste according to this embodiment may further contain a curable component. An example of such a curable component is an epoxy resin. Specific examples of epoxy resins include bisphenol-type epoxy resins (A type, F type, AD type, etc.), phenol and cresol-type epoxy resins (novolac type, etc.), polyol glycidyl ether-type epoxy resins, polyacid glycidyl ester-type epoxy resins, polyamine glycidyl amine-type epoxy resins, alicyclic epoxy resins, and heterocyclic epoxy resins. Only one type of these epoxy resins may be used, or two or more types may be used in appropriate combination.

When the silver chloride-containing paste according to this embodiment contains a curable component, it is preferable that a curing agent is further contained. Specific examples of the curing agent when the silver chloride-containing paste according to this embodiment contains an epoxy resin as a curable component include acid anhydrides such as phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, maleic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, and succinic anhydride; imidazoles such as imidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1-benzyl-2-methylimidazole, 2-phenyl-4-methylimidazole, 1-cyanoethyl-2-methylimidazole, 1-aminoethyl-2-methylimidazole, 1-methylimidazole, and 2-ethylimidazole; dimethyloctylamine, dimethyldecylamine, dimethyl Tertiary amines such as laurylamine, dimethylmyristylamine, dimethylpalmitylamine, dimethylstearylamine, dimethylbehenylamine, dilaurylmonoethylamine, methyldideethyamine, methyldioleylamine, triallylamine, triisopropanolamine, triethylamine, 3-(dibutylamino)propylamine, tri-n-octylamine, 2,4,6-trisdimethylaminomethylphenol, triethanolamine, methyldiethanolamine, and diazabicycloundecene; Lewis acids containing boron fluoride such as boron trifluoride ethyl ether, boron trifluoride phenol, boron trifluoride piperidine, boron trifluoride acetate, boron trifluoride monoethylamine, boron trifluoride triethanolamine, and boron trifluoride monoethanolamine, or compounds thereof. These compounds may be used alone or in combination of two or more.

The silver chloride-containing paste according to this embodiment may further contain various additives known in the field of paste compositions. Specific examples of such additives include antioxidants, ultraviolet absorbers, colorants, defoamers, and viscosity adjusters. The amounts of these additives added are appropriately set within a range in which the silver chloride-containing paste according to this embodiment can perform its inherent functions.

The above-described embodiments are described to facilitate understanding of the present invention, and are not described to limit the present invention. Therefore, each element disclosed in the above embodiments is intended to include all design modifications and equivalents that fall within the technical scope of the present invention.

For example, the silver particles according to this embodiment may be produced without employing the production method according to this embodiment. As a specific example of such a production method, silver chloride particles that satisfy the above conditions may be obtained by using a particle size selection means such as classification for silver chloride particles produced by a very common production method for silver chloride particles (for example, neutralization of silver nitrate with hydrochloric acid). When using a particle size selection means, it may be preferable to select silver chloride particles with a particle size of about 6 μm or more as a rough guideline.

The effects of the present invention will be explained below based on examples, but the present invention is not limited to these.

Example 1
20.0 g of silver nitrate crystals were dissolved in 23 g of pure water, and 18.0 g of 25% ammonia water was added to obtain a solution containing a silver ammine complex (silver-containing solution). 1.27 g of a dispersant made of polyacrylic acid (weight average molecular weight 25,000) was added to the silver-containing solution, and then 41.5 g of 12% hydrochloric acid was added to perform a neutralization reaction and a precipitation reaction of silver chloride to obtain a silver chloride-containing liquid. 1.27 g of polyacrylic acid (weight average molecular weight 25,000) was added to the silver chloride-containing liquid, and then the liquid was filtered, and the filtered product was washed with 400 g of pure water, and then 40 g of ethanol was added to replace the pure water contained in the filtered product. The filtered product was dried at a drying temperature of 60° C. for 14 hours to obtain silver chloride particles.

The resulting silver chloride particles were measured in a wet state using a laser diffraction/scattering method (equipment used: Shimadzu Corporation's "SALD-7100") to obtain a volume-based particle size distribution. In addition, the dried silver chloride particles were observed using a scanning electron microscope (JEOL Ltd.'s "JCM-5700").

A silver chloride-containing paste was prepared by mixing 2.0 g of the above silver chloride particles, 2.0 g of spherical silver powder ("KT058" manufactured by Toyo Kagaku Co., Ltd., cumulative 50% particle diameter D50: 2.1 μm), and 1.5 g of a mixture of 95% 2-(2-butoxyethoxy)ethyl acetate and 5% ethyl cellulose (100 cps) as a vehicle. A pattern with a width of 1 mm was printed using the obtained silver chloride-containing paste. The shape of the created pattern was measured using a surface roughness shape measuring device ("SURFCOM TOUCH 50" manufactured by Tokyo Seimitsu Co., Ltd.).

The details of the pattern shape measurement were as follows: Four grooves measuring 4 cm in length and 1 mm in width were printed on a glass substrate using tape or stickers, and a paste containing silver chloride was applied to each groove, which was then flattened with a spatula to create four wiring patterns. The substrate was then heated in a dryer at 150°C for at least one hour.

Of the four wiring patterns obtained, two were randomly selected that had no fading (wiring pattern 1, wiring pattern 2). Each wiring pattern was visually inspected and the three locations with the greatest irregularities were selected as measurement points 1 to 3. Two locations on the same pattern that were visually flat were also selected as measurement points 4 and 5. Surface roughness was measured in the short direction (cross-sectional direction) of the wiring pattern for these five measurement points, and the arithmetic mean height Pa and maximum cross-sectional height Pt were calculated from the resulting cross-sectional curve.

(Comparative Example 1)
Silver chloride particles were obtained in the same manner as in Example 1, except that the silver-containing solution was prepared without adding aqueous ammonia. The obtained silver chloride particles were subjected to the same measurements and observations as in Example 1. In addition, a silver chloride-containing paste was prepared in the same manner as in Example 1, and a wiring pattern having a width of 1 mm was created by printing using this paste, and the shape of the wiring pattern was measured in the same manner as in Example 1.

(Examples 2 to 22)
From the viewpoint of confirming the reproducibility of the production method, silver chloride particles were produced by the same production method as in Example 1, and measurements and observations were performed in the same manner as in Example 1. In Examples 10 to 22, silver chloride particles were produced on a scale 1000 times or more larger than that of Example 1. Of these, a silver chloride-containing paste was prepared using the silver chloride particles of Example 21 in the same manner as in Example 1, and the shape of the wiring pattern was measured.

(Particle size distribution)
The volume-based particle size distribution and cumulative particle size distribution of the silver chloride particles of Example 1 are shown in Table 1. In Table 1, silver chloride particles having a particle size in the range of more than 0 μm and less than 0.064 μm were not measured, so they are omitted. The same applies to particles having a particle size in the range of more than 57.648 μm and less than 300 μm.

The volume-based particle size distribution and cumulative particle size distribution of the silver chloride particles of Comparative Example 1 are shown in Table 2. In Table 2, "Omitted" is used in the same sense as in Table 1.

Figures 1 and 2 are graphs of the distributions in Tables 1 and 2.

As shown in FIG. 1, the volume-based particle size distribution of the silver chloride particles in Example 1 and the volume-based particle size distribution of the silver chloride particles in Comparative Example 1 had fundamentally different trends. The silver chloride particles in Example 1 had a single-peak distribution with a peak at approximately 10 μm.

Regarding the particle size distribution of the silver chloride particles in Example 1, the ratio (P10/P3) of the frequency distribution value P3 for a particle size of about 3 μm to the frequency distribution value P10 for a particle size of about 10 μm was calculated as follows. In Table 1, the frequency distribution value for a particle size of 10 μm was not measured, so the average value of the frequency distribution value (P9) for a particle size of 9 μm and the frequency distribution value (P11) for a particle size of 11 μm was taken as P10. The P10/P3 calculated in this way was 6.4 (= (7.984 + 9.562) / 5.605), which is greater than 6.

On the other hand, the silver chloride particles of Comparative Example 1 had a double-peak distribution with a main peak at just over 10 μm and a sub-peak with a peak on the smaller diameter side of the main peak. From Table 2, the particle size at which the main peak was located (most frequent particle size Dm) was 13.614 μm, and the frequency distribution value Pm at this time was 10.179%. The particle size at which the sub-peak was located was 3.215 μm, and the frequency distribution value Ps at this time was 5.065%. Therefore, Ps/Pm was 0.50, which did not satisfy the above formula (3). When P10/P3 was also calculated in the same manner as in Example 1, it was 2.2, which was less than 3.

Reflecting this difference in the basic tendency of particle size distribution, the cumulative particle size distribution of the silver chloride particles in Comparative Example 1 had a more gradual rise than that of the silver chloride particles in Example 1.

To further quantitatively evaluate the tendency of particle size distribution, the cumulative 10% particle diameter D10, cumulative 90% particle diameter D90, cumulative 50% particle diameter D50, and most frequent particle diameter Dm were determined for the silver chloride particles of Examples 1 to 22 and Comparative Example 1, and (D90-D10)/D50 and Dm/D50 were calculated from these, and the results are shown in Table 3.

As shown in Table 3, the silver chloride particles of Examples 1 to 22 satisfied both the above formula (1) and the above formula (2), but the silver chloride particles of Comparative Example 1 did not satisfy either the above formula (1) or the above formula (2).

Figures 3 to 5 show images (500x, 2000x, 10000x) of the silver chloride particles of Example 1. Figures 6 to 8 show images (500x, 2000x, 10000x) of the silver chloride particles of Comparative Example 1. By comparing these images, it was confirmed that the silver chloride particles of Example 1 have a larger primary particle size than the silver chloride particles of Comparative Example 1. In particular, Figures 6 and 7 show that the silver chloride particles of Comparative Example 1 contain secondary particles having a size of 50 μm or more, which are formed by agglomeration of primary particles. These coarse secondary particles remain even when the silver chloride particles are made into a paste, reducing the quality stability of the silver chloride-containing paste.

The silver chloride particles of Example 22 are a scaled-up version of Example 1. Figure 9 is a graph showing the volumetric particle size distribution of the silver chloride particles of Example 22, Figure 10 is a graph showing the volumetric cumulative particle size distribution of the silver chloride particles of Example 22, and Figure 11 is a diagram showing an observation image (10,000 times) of the silver chloride particles of Example 22. As shown in Figure 11, the silver chloride particles of Example 22 have a primary particle size equal to or greater than that of the silver chloride particles of Example 1, and as shown in Figures 9 and 10, they have a sharper (narrower) distribution than those of Example 1. This point can also be confirmed by comparing (D90-D10)/D50 in Table 3. That is, (D90-D10)/D50 in Example 1 was 1.96, which was almost 2, but in Example 22 it was 1.2, which shows that the uniformity of the particle size of the silver chloride particles is improved.

The measurement results of the shape of the wiring pattern are shown in Tables 4 and 5. Table 4 shows the arithmetic mean height Pa of the cross-sectional curve (JIS B0601:2001), and Table 5 shows the maximum cross-sectional height Pt of the cross-sectional curve (JIS B0601:2001). The units of the numbers showing the measurement results in the tables are all μm. For both the arithmetic mean height Pa and the maximum cross-sectional height Pt, the average values were Comparative Example 1 > Example 1 > Example 21. This tendency was also observed for the average values of measurement points 1 to 3, which had large irregularities, and the average values of measurement points 4 and 5, which were flat and had little irregularities.

Specific examples of the measurement results of the wiring pattern are shown in Figures 12A to 13C. Figures 12A to 12C show the measurement results of a measurement point with large unevenness, and Figures 13A to 13C show the measurement results of a flat measurement point with small unevenness. As shown in Tables 4 and 5 and Figures 12A to 13C, the wiring pattern formed from the silver chloride-containing paste using the silver chloride particles of Comparative Example 1 had higher average values of the cross-sectional curve parameters (arithmetic mean height Pa) and (maximum cross-sectional height Pt) than the wiring patterns formed from the silver chloride-containing paste using the silver chloride particles of Example 1 and the silver chloride particles of Example 21 (about 1.5 to 2 times). The reason why the numerical values of the shape parameters of the wiring pattern of Comparative Example 1 were larger is thought to be because the silver chloride-containing paste prepared using the silver chloride particles of Comparative Example 1 contained a relatively large number of coarse particles.

(Examples 23 to 24, Comparative Example 2)
Silver chloride particles were produced in the same manner as in Example 1, except that the conditions for adding the dispersant were changed as follows.
Example 23: No dispersant added to silver-containing solution. Example 24: No dispersant added to silver chloride-containing liquid. Comparative Example 2: No dispersant added to silver-containing solution, and no dispersant added to silver chloride-containing liquid.

The appearance of the obtained silver chloride particles was visually confirmed. In Examples 23 and 24, the amount of coarse secondary particles increased compared to the silver chloride particles of Example 1, but by crushing, the particles became equivalent to those of Example 1. In contrast, in Comparative Example 2, the obtained silver chloride was substantially clump-like rather than particulate, and even after crushing, it still contained coarser particles than the silver chloride particles of Examples 23 and 24.

(Examples 25 to 27)
Silver chloride particles were produced in the same manner as in Example 1, except that the type of dispersant was changed as follows.
Example 25: Polyoxyethylene sorbitan monolaurate (Tokyo Chemical Industry Co., Ltd. "Twin 20")
Example 26: Benzethonium chloride Example 27: Stearic acid

The appearance of the obtained silver chloride particles was visually confirmed. In Examples 25 and 26, the amount of coarse secondary particles increased compared to the silver chloride particles of Example 1, but the particles became equivalent to those of Example 1 by crushing. The silver chloride particles of Example 27 were in a powder form, and the cumulative 50% particle diameter D50 was 5.8 μm.

Claims (7)

1. A method for producing silver chloride particles, comprising: precipitating silver chloride particles by reacting a silver ammine complex with chloride ions in a liquid,
reacting silver nitrate with ammonia to produce an ammine complex of said silver to obtain a silver-containing solution;
adding an anionic surfactant as a dispersant to the silver-containing solution, and then precipitating the silver chloride particles;
(excluding the case where the pH of the silver-containing solution before adding the chloride ions is 7.5 or less). The method for producing silver chloride particles according to claim 1, wherein the chlorine source that provides the chloride ions includes hydrochloric acid. 2. The method for producing silver chloride particles for forming a conductor according to claim 1, wherein the cumulative 50% particle diameter D50 in the cumulative particle size distribution from the small particle diameter side in the volume-based particle size distribution obtained by wet measurement using a laser diffraction/scattering method is 8 μm or more and 25 μm or less. 4. The method for producing silver chloride particles for forming an electric conductor according to claim 1, wherein a cumulative 10% particle diameter D10, a cumulative 90% particle diameter D90 , and a cumulative 50% particle diameter D50 in the cumulative particle size distribution satisfy the following formula (1):
(D90-D10)/D50≦2.2 (1) 4. The method for producing silver chloride particles for forming an electric conductor according to claim 1, wherein the most frequent particle diameter Dm of the volume-based particle diameter distribution is 10 μm or more. 4. The method for producing silver chloride particles for forming an electric conductor according to claim 1, wherein the cumulative 50% particle diameter D50 and the most frequent particle diameter Dm of the volume-based particle diameter distribution satisfy the following formula (2):
Dm/D50≦1.7 (2) 4. The method for producing silver chloride particles for forming an electric conductor according to claim 1, wherein in the volume-based particle size distribution, a frequency distribution value Ps of a sub-peak, which is a peak located on the smaller particle size side than the most frequent particle diameter Dm, and a frequency distribution value Pm at the most frequent particle diameter Dm satisfy the following formula (3) :
Ps≦Pm×0.6 (3)