JP2006056740A - Method for preparing silver oxide fine particle, method for preparing conductive composition or conductive image by using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for preparing a silver oxide fine particle suitable for obtaining a conductive composition by heating at a relatively low temperature or by laser irradiation through a simple process without using a complicate apparatus. <P>SOLUTION: The method for preparing the silver oxide fine particle having good settling property permitting easy desalting work comprises reacting a silver ion and an alkali in an aqueous solution in the presence of dextrin where the used amounts of the dextrin and the alkali to the silver ion are confined each to a specified ratio. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for easily producing fine particles of silver oxide. The fine particles are suitable for obtaining a conductive composition or a conductive image by heating.

  Silver is a material widely used in highly conductive materials, recording materials, surface coatings, printing plates and the like. A silver image formed with silver can be used in a specific manner, even when used as a highly conductive material, such as a printed circuit board, a light-transmitting electromagnetic wave shielding material, an IC card and tag antenna coil, and a flat panel display. For example. Silver image preparation methods include wet plating methods that chemically deposit silver, methods that remove non-image parts by etching from silver films obtained by directly melting, adhering, or vapor-depositing metallic silver, and small silver particles. There are many methods, such as a method of forming a pattern by printing after processing into a paste, a method of drawing an image by inkjet using a dispersion of silver fine particles, and a method of photoreducing silver halide.

  In particular, a method of forming a conductive composition or a conductive image by pasting or forming silver fine particles into a paste has attracted attention, and many methods for producing silver fine particles have been proposed. Examples thereof include a mechanical pulverization method, an atomization method, a gas phase reduction method, a gas evaporation method, an electrolytic deposition method, a chemical reduction method, and the like (for example, see Patent Document 1).

  The mechanical pulverization method is a method in which force is applied to metal particles to further pulverize them. However, metals generally have extensibility, and when pulverized to a certain extent, it is difficult to further pulverize, or There are drawbacks such as secondary agglomeration and the like, and it is not suitable for the production of fine particles having a particle diameter of 1 μm or less.

  Other methods can be used to produce relatively small particles, but the atomization method, gas phase reduction method, gas evaporation method, and electrolytic deposition method require complicated equipment or are not problematic at the experimental level, but are industrial. There are problems such as difficulty in scaling up at the level, and it is difficult to say that this is an industrially simple method.

  In contrast to these methods, metal fine particles are produced by applying a reducing agent to an aqueous solution of a metal compound, or hydroxide particles or oxide fine particles are produced by allowing a base to act to produce metal fine particles. The chemical reduction method has the advantage of simple equipment and relatively easy scale-up. In particular, in the case of silver, silver nitrate is highly water-soluble and may be easily reduced, which is suitable for fine particle production by a chemical reduction method.

  However, in this method, the fine particles are obtained in the form of a suspension, but the components that were counter ions of the metal ions are mixed as a water-soluble salt. If the salt is not removed, there are disadvantages such as reduced conductivity.

  Methods for removing water-soluble salts include sedimenting particles and decanting, separating particles and liquid by centrifugation, collecting only particles by filtration, and concentrating particles by ultrafiltration. However, in each method, the smaller the particle size, the more difficult it is to settle or the filter is clogged, resulting in increased labor for solving the problem.

  Among them, the silver colloid preparation method known as the Carey Lea method is an excellent method in which the particle diameter obtained is extremely small, secondary aggregation of the particles is small, and desalting is relatively easy. . In this method, silver ions in an aqueous silver nitrate solution are reduced with excess dextrin and sodium hydroxide to produce silver fine particles using dextrin as a protective colloid. These silver fine particles show good dispersion stability with respect to water, but they settle by addition of methanol and can be easily desalted by decantation.

  However, the silver fine particles obtained by this method also have drawbacks when used as a conductive material. That is, since the particle surface is covered with the protective colloid, the protective colloid acts as an insulator, so that no current flows between the particles. The protective colloid can be thermally decomposed and removed by heating to 300 ° C. or higher, and conduction can be obtained by advancing the adhesion between the particles and further fusing. For this reason, support for placing silver fine particles as a conductive material The body is limited to those with high heat resistance.

Since silver oxide is easily reduced to silver by heat, a method using silver oxide fine particles has also been proposed (see, for example, Patent Documents 2 and 3). However, even the methods shown in these documents have the disadvantage that it is difficult to make fine particles having a particle diameter of less than 100 nm, or that even if they are made, the desalting treatment is not easy, and they cannot be said to be complete. Met.
Japanese Patent Laid-Open No. 10-317022 JP 2003-308730 A JP 2004-203696 A

  An object of the present invention is to obtain silver oxide fine particles suitable for obtaining a conductive composition by heating at a relatively low temperature or laser irradiation, without using a complicated apparatus, by a simple method.

  As a result of conducting research to solve this problem, the present inventor has improved the Curry-Lee method and solved the problem by suppressing the amount of base and dextrin used relative to silver nitrate, thereby completing the present invention. It came.

  As an example of the method for preparing silver fine particles by the Curry-Lee method, 1.7 mol of sodium hydroxide is mixed with 1 mol of silver ions, and dextrin is mixed at a ratio of 1.4 with respect to 1 mass of silver ions. Then, silver ions are reduced with excess sodium hydroxide and dextrin to produce silver fine particles using dextrin as a protective colloid. Since silver oxide can be formed from equimolar silver ions and sodium hydroxide, reducing the amount of sodium hydroxide and dextrin in the Curry-Lee formulation reduces the reduction of silver ions and oxidizes instead of silver. Silver fine particles are produced.

  Specifically, a reaction in an aqueous solution in which 0.5 to 1.5 mol of a base is added to 1 mol of silver ions to produce silver oxide particles, and dextrin has a mass of 0.1 to 1 of silver ion mass. A silver oxide fine particle suspension is prepared by carrying out under the condition of a ratio of 0.5. When a water-soluble organic solvent, specifically methanol, is added to this suspension, the fine particles settle on standing, and salt can be easily removed by decantation.

  The silver oxide fine particles obtained by the above means do not require a complicated apparatus for production, and can be obtained with a very small particle diameter while being relatively easy to desalinate and recover. The obtained fine particles have a small particle diameter and are coated with a protective colloid having a reducibility to silver oxide, and thus have high reactivity and are reduced to silver by heating at a relatively low temperature. The composition containing the fine particles can easily obtain a conductive composition in which particles are fused by heating, and is particularly suitable as a material for obtaining a conductive image with near-red laser light.

  Silver oxide fine particles are produced by reacting silver ions and a base in the presence of dextrin. Silver ions can be obtained by dissolving a water-soluble silver salt in water. Specific examples of the water-soluble silver salt include silver nitrate, silver perchlorate, and silver azide. Silver nitrate is particularly preferable because it is highly water-soluble, relatively stable, and highly safe. Although there is no restriction | limiting in particular also about a base, As a specific example, sodium hydroxide, potassium hydroxide, an organic amine, etc. are mentioned.

  The ratio of the base is 0.5 to 1.5 mol per mol of silver ions, and the dextrin is preferably 0.1 to 0.5 mass per mass of silver ions. The most preferred amount of base is equimolar to silver ion. If the base is less than 0.5 mol, a large amount of unreacted silver ions are generated and the efficiency is poor. If the base exceeds 1.5 mol, the efficiency is not only poor with the unreacted base, but also silver oxide. There is a possibility that fine particles are reduced to produce silver fine particles. As for dextrin, when the addition amount is less than 0.1, the dispersibility is poor and the silver oxide particle size becomes large. Conversely, when it exceeds 0.5, the silver oxide particles are reduced to form silver particles. End up. The ratio of silver ion, base, and dextrin is limited by the above conditions, but the concentration in the aqueous solution is not particularly limited and may be within a common sense range. When actually reacting, an aqueous base solution may be added to a mixed aqueous solution of silver salt and dextrin. A part of the dextrin may be added to the base aqueous solution. The addition is basically performed little by little while stirring, but there is no particular limitation on the degree of stirring and the speed of addition, and this may be performed within a common sense range.

  The silver oxide suspension thus obtained contains water-soluble salts derived from counterions of silver ions and bases in addition to silver oxide fine particles using dextrin as a protective colloid. . The silver oxide fine particles are settled by standing or centrifuging, but the water-soluble organic solvent increases the sedimentation rate and facilitates desalting.

  The water-soluble organic solvent to be used is not particularly limited, and a solvent that improves the sedimentation property of the particles may be appropriately used. Specific examples include methanol, ethanol, isopropyl alcohol, and acetone. The amount added to the silver oxide particle suspension is not particularly limited, but is preferably about 1/2 to 3 times the amount of the suspension.

  By adding a water-soluble organic solvent, the silver oxide fine particles easily settle and settle upon standing for 12 to 24 hours. At this stage, the supernatant is discarded by decantation, and the water-soluble salt is removed from the suspension by adding a water-soluble organic solvent or a mixture of water and a water-soluble organic solvent again and repeating the standing and decantation. It will be written. Desalting by decantation is time consuming and has the disadvantages of requiring a large amount of solvent, but has the advantage of being easy to redisperse in water because the equipment is simple and the agglomeration of fine particles does not easily occur. Centrifugation can also be used as a method for efficiently separating particles and liquid. Also in this case, the number of rotations and time of centrifugation can be suppressed by adding a water-soluble organic solvent.

  The desalted silver oxide fine particles obtained in this way are used for actual use as a composition containing them. Specifically, it may be used as a coating liquid while suspended in water or the like, or it may be used as a paste by adding a small amount of solvent or binder to the sediment obtained by centrifugation. . The obtained fine particles may be once dried and powdered, and then processed into a state where it is easy to use, such as a coating liquid or a paste. In drying, it is preferable to avoid aggregation during drying by a method such as freeze drying or spray drying.

  Various additives can be contained in the composition containing silver oxide fine particles. Examples include solvents, polyvinyl alcohol as a binder, polymer compounds such as acrylic resin, epoxy resin, phenolic resin, surfactants for improving dispersibility and defoaming agents, thickeners for improving liquid properties, pH Examples thereof include adjusting agents, coupling agents, sensitizing dyes, and near-infrared laser absorbing dyes. Examples of the solvent include water, acetone, methyl ethyl ketone, cyclohexanone, ethyl acetate, toluene, xylene, methanol, ethylene glycol, diethylene glycol, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, α-terpineol, and the like. In order to improve conductivity, it is coated with various conductive metal powders represented by silver, copper, tin, lead, nickel, gold, platinum, palladium and their alloys, and compounds containing conductive metals, or these conductive metals. It is also possible to add a small amount of conductive fine particles.

  Moreover, a reducing agent can also be added as an additive. The term “reducing agent” as used herein does not generally mean a chemical having a reducing action, but when mixed and heated with silver oxide, the temperature at which silver oxide is reduced to metallic silver is lowered, that is, the reducing action of silver oxide is promoted. It means that the drug is. Therefore, what does not normally have a reducing action and what is not called a reducing agent are referred to here as reducing agents, focusing only on the action on silver oxide.

  There are many types that can be used as reducing agents. Examples include those having at least one of a cyclic amine, a hydroxyl group, an oxyalkylene group, an epoxy group, a carboxyl group, and a carboxyl group metal salt as described in JP-A No. 2004-058466, for example. Examples thereof include epoxy compounds and acrylic compounds as described in JP-A No. 139754 and glycerin and reducing sugars described in JP-A No. 2004-176079. Specific examples include the following, but are not limited thereto.

  1,3-di-4-piperidylpropane, 4-piperidinopiperidine, 1,3-di-4-pyridylpropane, 1,3,5-triazine, 2-aminopyridine, 3-aminopyridine, 4-amino Pyridine, 2,4-lutidine, 2,6-lutidine, 1,2,4,5-tetrazine, β-cyclodextrin, chitin, chitosan, amylose, carboxymethylcellulose, alginic acid, polyethylene glycol, polypropylene glycol, polyvinyl alcohol, phenyl iso Butyric acid or silver salt thereof, abietic acid or silver salt thereof, 2,4-diethylglutaric acid or silver salt thereof, behenic acid, silver behenate, glycerin, glyceraldehyde, threose, ribose, xylose, altrose, glucose, mannose , Galactose, xylulose, Rukutosu, lactose, maltose and the like.

  The functions of these additives such as reducing agents are not limited to a single one, and there is no problem even if they have a plurality of functions at the same time. Alternatively, a plurality of types of chemicals having similar functions can be used in combination.

  There is no particular limitation on the method for producing a coating liquid or paste containing silver oxide fine particles. What is necessary is just to mix | blend and disperse | distribute a required component uniformly using a propeller stirrer, a homogenizer, a paint conditioner, a dyno mill, a raking machine, a kneader, a three roll, a rotation revolution mixer.

  There is no particular limitation on how to use the composition containing silver oxide fine particles thus obtained. Basically, after attaching and applying to the place where conductivity is desired, the silver oxide is reduced by heating and converted to silver. The heating temperature is preferably 100 to 200 ° C. Alternatively, a conductive image can be produced by processing a composition containing silver oxide fine particles into a film and partially heating the composition.

  There is no particular limitation on the method for processing the composition containing silver oxide fine particles into a film. It may be prepared by applying a coating liquid composition to a support, or may be printed with a paste-like composition. The film may be formed over the entire surface of the support, or a fine image may be formed by laser irradiation or the like after coating the image roughly on the support by a printing method or the like. There is no restriction | limiting in particular in the support body for forming a silver oxide film. Specific examples include paper, metal plates such as aluminum plates and copper plates, polymer films such as PET films, glass, ceramics, and stone plates.

  In order to produce a conductive image from a film-like composition containing silver oxide fine particles, a method of partially heating the film-like composition includes a method of stamping a heated metal lump and a method of using a thermal head of a thermal printer. And a method of irradiating with laser light. In particular, a method of irradiating near-red laser light having a wavelength in the range of 750 to 900 nm is preferable because a high-definition image can be efficiently produced.

  The energy applied to the silver oxide fine particle film by irradiation with near-red laser light is determined by the laser output, the laser beam diameter, the irradiation time, and the like. The energy to be irradiated may be sufficient as long as the silver oxide fine particles in the irradiated portion are reduced to become silver. It is preferable to remove the non-irradiated portion remaining as silver oxide by washing with water or acid treatment, since the image becomes clearer and falsification is prevented. Also, by reducing silver oxide explosively by irradiation with higher energy than just reducing silver oxide to silver, it is possible to blow off silver oxide fine particles in the irradiated area by ablation and form an image. is there. At this time, the laser beam may be blown only by irradiation, the laser beam irradiation may be limited to extremely weaken the film strength, and the film may be removed by blowing air or washing.

  Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited to these examples. In addition, the number of parts and percentage in an Example are based on mass.

  100 parts of a 10% silver nitrate aqueous solution and 16 parts of a 10% dextrin aqueous solution were mixed. The mass ratio of silver ions to dextrin is approximately 1: 0.25. While stirring with a homomixer, 24 parts of a 10% sodium hydroxide aqueous solution was slowly added so that sodium hydroxide was equivalent to silver ions to prepare a silver oxide fine particle suspension. When 140 parts of methanol was added thereto and allowed to stand overnight, the particles settled and the supernatant was transparent. The supernatant was removed by decantation. Further, 100 parts of a 1: 1 mixed solvent of methanol and water was added and the operation of standing and decantation was repeated 5 times. Finally, water was added to make 40 parts to obtain a dispersion of silver oxide fine particles. The size of the silver oxide fine particles was observed with a scanning electron microscope (SEM). The size of the primary particles was about 100 nm.

  The silver oxide fine particle dispersion thus obtained was applied to a slide glass and air-dried. The continuity was checked with a tester, but no continuity was found. After conducting heat treatment for 30 minutes in a blow dryer set at 150 ° C., the continuity was examined again. As a result, continuity occurred over the entire surface.

The silver oxide fine particle dispersion obtained in Example 1 was applied to white PET (Lumirror E-22 manufactured by Panac Co., Ltd., thickness 188 μm) and air-dried. Using a semiconductor laser with a wavelength of 830 nm (maximum output 600 mW, beam diameter 25 μm), the laser output and the drawing speed were adjusted so that the applied energy was 250 mJ / cm ² , and drawing on the silver oxide film was performed. When examined with a tester, it was confirmed that conduction occurred in the drawing portion.

  100 parts of 10% aqueous silver nitrate solution and 19 parts of 10% aqueous dextrin solution were mixed. The mass ratio of silver ions to dextrin is approximately 1: 0.3. While stirring with a homomixer, 24 parts of a 10% sodium hydroxide aqueous solution was slowly added so that sodium hydroxide was equivalent to silver ions to prepare a silver oxide fine particle suspension. 140 parts of methanol was added to this, and after standing overnight, the supernatant was discarded by decantation. Further, 100 parts of a 1: 1 mixed solvent of methanol and water was added and centrifuged at 4000 rpm for 10 minutes. All particles settled and the supernatant was clear. Discard the supernatant, add a small amount of 8% polyvinyl alcohol aqueous solution to the remaining sedimented particles, and use a rotating / revolving mixer (product name: Shintaro Awatori, model AR-250, manufactured by Shinkey Co., Ltd.) The mixture was mixed for 3 minutes under the conditions of revolution 2000 rpm and rotation 800 rpm to form a paste.

  A circuit pattern was printed on a glass plate by screen printing using the silver oxide paste thus obtained. When the glass plate on which the paste was printed was subjected to heat treatment for 30 minutes in a blower dryer set at 200 ° C. and then tested for continuity with a tester, continuity occurred in the circuit pattern.

(Comparative Example 1)
[Preparation of silver fine particles by the Curry-Lee method]
A silver fine particle suspension was prepared in exactly the same manner as in Example 1, except that the dextrin aqueous solution of Example 1 was changed to 140 parts and the sodium hydroxide aqueous solution was changed to 40 parts. At this time, the mass ratio of silver ions to dextrin is 1: 2.2, and the molar ratio of silver ions to sodium hydroxide is 1: 1.7. When methanol was added in the same manner as in Example 1 and allowed to stand overnight, the particles settled and the supernatant was transparent. Decantation and addition of the solvent were repeated in the same manner as in Example 1, and then water was added to make a total of 40 parts to obtain a dispersion of silver fine particles.

  The silver fine particle dispersion thus obtained was applied to a slide glass and air-dried. The continuity was checked with a tester, but no continuity was found. After conducting heat treatment for 30 minutes in a blower dryer set at 200 ° C., the conduction was examined again. As a result, only a part of the conduction occurred, and a portion where no conduction was observed remained. In addition, as with Example 2, the application onto white PET was drawn with a laser, but no change was observed in the laser irradiation part, and no conduction occurred in the drawing part.

(Comparative Example 2)
A silver fine particle suspension was prepared in exactly the same manner as in Example 1 except that 50 parts of the dextrin aqueous solution of Example 1 and 40 parts of the sodium hydroxide aqueous solution were changed. At this time, the mass ratio of silver ions to dextrin is 1: 0.8, and the molar ratio of silver ions to sodium hydroxide is 1: 1.7. When methanol was added in the same manner as in Example 1 and allowed to stand overnight, the particles settled and the supernatant was transparent. Decantation and addition of the solvent were repeated in the same manner as in Example 1, and then water was added to make a total of 40 parts to obtain a dispersion of silver fine particles. Using this dispersion, a heating test using a blower / air dryer and a drawing test using a laser were conducted in the same manner as in Comparative Example 1, and the results were also the same as in Comparative Example 1.

(Comparative Example 3)
A silver fine particle suspension was prepared in the same manner as in Example 1 except that 16 parts of the dextrin aqueous solution in Example 1 was changed to 140 parts. When methanol was added in the same manner as in Example 1 and allowed to stand overnight, the particles settled and the supernatant was transparent. Decantation and addition of the solvent were repeated in the same manner as in Example 1, and then water was added to make a total of 40 parts to obtain a dispersion of silver fine particles. Using this dispersion, a heating test using a blower / air dryer and a drawing test using a laser were conducted in the same manner as in Comparative Example 1, and the results were also the same as in Comparative Example 1.

(Comparative Example 4)
A silver oxide fine particle suspension was prepared in exactly the same manner as in Example 1 except that the 10% dextrin aqueous solution in Example 1 was changed to 140 parts of a 2% polyvinyl alcohol aqueous solution. When methanol was added in the same manner as in Example 1 and allowed to stand overnight, some of the particles settled, but turbidity was observed in the supernatant. Therefore, the mixture was centrifuged at 4000 rpm for 10 minutes. However, the sedimentation of the particles was still not complete, and turbidity remained in the supernatant. The supernatant finally became transparent by setting the centrifugation conditions at 18000 rpm for 15 minutes. The size of the silver oxide fine particles was observed with an SEM. The primary particles were about 100 nm in size.

(Comparative Example 5)
A silver oxide fine particle suspension was prepared in exactly the same manner as in Example 1, except that 16 parts of the 10% dextrin aqueous solution of Example 1 was changed to 50 parts of 5% hydroxypropylcellulose. When methanol was added in the same manner as in Example 1 and allowed to stand overnight, the particles settled and the supernatant was transparent. Decantation and addition of the solvent were repeated in the same manner as in Example 1, and then water was added to make a total of 40 parts to obtain a dispersion of silver oxide fine particles. The size of the silver oxide fine particles was observed with an SEM. The primary particles were about 300 nm in size. Using this dispersion, a heating test using a blower dryer and a drawing test using a laser were performed in the same manner as in Comparative Example 1. As a result, conduction was obtained on the entire surface at 200 ° C. in the heat treatment of the blower dryer, but drawing with a laser at an applied energy of 250 mJ / cm ² did not lead to conduction.

  In addition to being used as a conductive material as described in the text, the present invention can also be used as a recording material such as a lithographic printing plate, a decoration, and a craft.

Claims (5)

  A reaction in an aqueous solution in which 0.5 to 1.5 mol of a base is added to 1 mol of silver ions to produce silver oxide particles, and dextrin has a mass of 0.1 to 0.5 with respect to 1 mass of silver ions. A method for producing silver oxide fine particles, which is carried out under conditions that exist in an aqueous solution at a ratio.   A method for producing silver oxide fine particles, comprising adding a water-soluble organic solvent to a suspension of silver oxide fine particles produced by the method according to claim 1, thereby precipitating the fine particles to remove water-soluble salt.   A method for producing a conductive composition, comprising heating a composition containing silver oxide fine particles produced by at least the method according to claim 1 or 2 to 100 to 200 ° C.   A method for producing a conductive image comprising processing a composition containing silver oxide fine particles prepared by at least the method according to claim 1 or 2 into a film shape and partially heating the composition.   The method for producing a conductive image according to claim 4, wherein the method of partially heating the film-shaped composition is irradiation with near-red laser light having a wavelength in the range of 750 to 900 nm.