JP2015134935A - Aqueous ink composition and recorded matter prepared using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silver particle-containing aqueous ink composition which can record an image having excellent metal glossiness when printed on a recording medium.SOLUTION: An aqueous ink composition according to the present invention at least comprises water, silver particles, and a humectant, wherein the humectant is at least one selected from a glycerol, a glycol and a carbohydrate.

Description

  The present invention relates to a water-based ink composition and a recorded matter using the same.

  Conventionally, as a method of forming a coating film having a metallic luster on printed matter, printing ink using gold powder or silver powder made from brass, aluminum fine particles, etc. as a pigment, foil press printing using metal foil, metal foil is used. The thermal transfer method that was used is used.

  In recent years, there have been many examples of application to inkjet in printing, and one of the examples of application is metallic printing, and development of ink having metallic luster is being promoted. For example, Patent Document 1 discloses an aluminum pigment dispersion based on an organic solvent such as alkylene glycol and a non-aqueous ink composition containing the same.

  On the other hand, from the viewpoints of the global environment and the safety to the human body, there is an actual situation that development of a water-based ink composition is desired rather than a non-aqueous ink composition based on an organic solvent. In the case of water-based ink, a moisturizing agent is usually added from the viewpoint of adjusting the viscosity of the water-based ink and preventing drying in a printing machine.

JP 2008-174712 A

  However, in the case of water-based ink containing silver particles as a metal pigment, there has been a problem that the metal glossiness of an image recorded on a recording medium varies greatly depending on the type of humectant added.

  Some embodiments according to the present invention provide a silver particle-containing aqueous ink composition capable of recording an image excellent in metal gloss when printed on a recording medium by solving the above-described problems. Is.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following aspects or application examples.

[Application Example 1]
One aspect of the water-based ink composition according to the present invention is:
A water-based ink composition containing at least water, silver particles, and a humectant,
The humectant is at least one selected from glycerols, glycols and carbohydrates.

  According to the water-based ink composition of Application Example 1, an image having excellent metal glossiness can be recorded when printed on a recording medium.

[Application Example 2]
In application example 1,
The glycerols can be glycerin or trimethylolpropane.

[Application Example 3]
In application example 1 or application example 2,
The glycols can be triethylene glycol, hexylene glycol, propylene glycol, or polyethylene glycol.

[Application Example 4]
In any one of Application Examples 1 to 3,
The content of the humectant may be 5% by mass or more and 20% by mass or less.

[Application Example 5]
In any one of Application Examples 1 to 4,
The average primary particle size of the silver particles may be 10 nm or more and 100 nm or less, and the particle size d90 in the particle size accumulation curve of the silver particles may be 50 nm or more and 1 μm or less.

[Application Example 6]
In application example 5,
Furthermore, the particle diameter d10 in the particle diameter accumulation curve of the silver particles may be 2 nm or more and 20 nm or less.

[Application Example 7]
In any one of Application Examples 1 to 6,
The silver particles may be surface-treated.

[Application Example 8]
In one aspect of the recorded matter according to the present invention, an image is recorded by the water-based ink composition described in any one of Application Examples 1 to 7.

  Hereinafter, preferred embodiments of the present invention will be described. The embodiment described below describes an example of the present invention. In addition, the present invention is not limited to the following embodiments, and includes various modifications that are implemented within a range that does not change the gist of the present invention.

1. Water-based ink composition The water-based ink composition according to an embodiment of the present invention contains water, silver particles, and a humectant. The humectant is at least one selected from glycerols, glycols and carbohydrates.

1.1. Silver particles 1.1.1. Properties of silver particles The water-based ink composition according to the present embodiment contains silver particles. Silver particles are particles mainly composed of silver, and may contain other metal elements, carbon, oxygen, and the like as subcomponents. The purity of silver in the silver particles is preferably 80% or more, more preferably 90% or more. The silver particles may be an alloy of silver and other metals (indium, palladium, platinum, etc.). The silver particles in the water-based ink composition may be present in a colloid (particle colloid) state. When the silver particles are dispersed in a colloidal state, the dispersibility is further improved, and for example, it can contribute to the improvement of the storage stability of the water-based ink composition.

  The average primary particle diameter of silver particles in the water-based ink composition according to the present embodiment is preferably 10 nm or more and 100 nm or less, and more preferably 15 nm or more and 50 nm or less. When the average primary particle size is in the above range, the dispersion stability of silver particles in the water-based ink composition is improved, and the storage stability can be improved.

  The particle diameter d90 in the particle diameter accumulation curve of the silver particles in the aqueous ink composition according to the present embodiment is preferably 50 nm or more and 1 μm or less. Here, the particle size accumulation curve is a statistically processed result obtained by measuring the diameter of the silver particles dispersed in the aqueous ink composition and the number of the particles present. Is a kind of curve obtained. The particle size accumulation curve in this specification is a particle having a small diameter with respect to the particle mass (the product of volume, particle density, and number of particles when the particle is regarded as a sphere) with the diameter of the particle on the horizontal axis. The value (integrated value) integrated from the large to large particles is plotted on the vertical axis. The “particle diameter d90 in the particle diameter accumulation curve” refers to the particle diameter when the cumulative mass% is 90 mass% when the mass is integrated from small particles. In this case, the diameter of the silver particles may be the diameter of the silver particles themselves, or may be the diameter of the particle colloid when the silver particles are dispersed in a colloidal form.

  Furthermore, d10 in the particle size accumulation curve of silver particles in the water-based ink composition according to the present embodiment is more preferably 2 nm or more and 20 nm or less. By doing so, the dispersibility of the silver particles in the water-based ink composition can be made better, so that for example, the storage stability can be further improved. The “particle size d10 in the particle size accumulation curve” refers to the particle size when the cumulative mass% becomes 10 mass% when the mass is integrated from small particles.

  The average primary particle size and particle size accumulation curve of the silver particles in the water-based ink composition according to the present embodiment can be obtained, for example, by using a particle size distribution measuring device based on a dynamic light scattering method. . In the dynamic light scattering method, dispersed silver particles are irradiated with laser light, and the scattered light is observed with a photon detector. Generally, dispersed silver particles usually have a Brownian motion. The speed of movement of silver particles is larger for particles having a larger particle diameter and smaller for particles having a smaller particle diameter. When silver particles that are in Brownian motion are irradiated with laser light, fluctuations corresponding to the Brownian motion of each silver particle are observed in the scattered light. This fluctuation is measured, the autocorrelation function is obtained by the photon correlation method, etc., and the diameter of the silver particles and the frequency (number) of the silver particles corresponding to the diameter can be obtained by using the cumulant method and the histogram method analysis. . The dynamic light scattering method is suitable for a sample containing submicron-sized silver particles such as the aqueous ink composition according to the present embodiment, and the particles can be relatively easily obtained by using the dynamic light scattering method. A diameter accumulation curve can be obtained. Examples of the particle size distribution measuring apparatus based on the dynamic light scattering method include Nanotrac UPA-EX150 (manufactured by Nikkiso Co., Ltd.), ELSZ-2, DLS-8000 (above, manufactured by Otsuka Electronics Co., Ltd.), LB-550 ( Manufactured by HORIBA, Ltd.).

  The silver particle content (solid content) is preferably 0.1% by mass or more and 30% by mass or less, and more preferably 1% by mass or more and 20% by mass or less, with respect to the total mass of the aqueous ink composition. Yes, and particularly preferably 5% by mass or more and 15% by mass or less. When the silver particle content is within the above range, an image having metallic luster can be recorded on the recording medium.

1.1.2. Silver Particle Manufacturing Method The silver particle manufacturing method is not particularly limited, and examples thereof include the following first to third methods. The technique shown below is produced as a colloidal liquid in which silver colloidal particles are dispersed in an aqueous dispersion medium.

1.1.2a. First Method The first method includes a first solution preparation step of preparing a first solution containing at least a polymer of vinylpyrrolidone and a polyhydric alcohol, and a silver precursor that can be reduced to silver (metal). A second solution preparing step of preparing a second solution dissolved in a solvent, a first solution heating step of heating the first solution to a predetermined temperature, and mixing the heated first solution and second solution A mixing step of obtaining, a reaction progressing step of holding the mixed liquid at a predetermined temperature for a certain time, and a dispersion step of taking out silver particles (silver colloidal particles) from the mixed liquid in which the reaction has progressed and dispersing it in an aqueous dispersion medium ing.

<First solution preparation process>
First, a first solution containing at least a vinylpyrrolidone polymer and a polyhydric alcohol is prepared.

  One of the functions of the vinylpyrrolidone polymer contained in the first solution is to prevent the aggregation of silver particles and form silver colloidal particles by adsorbing on the surface of the silver particles produced by the production method of this example. To do.

  The vinyl pyrrolidone polymer used may include a vinyl pyrrolidone homopolymer (polyvinyl pyrrolidone) and a vinyl pyrrolidone copolymer.

  As the copolymer of vinyl pyrrolidone, for example, a copolymer of vinyl pyrrolidone and α-olefin, a copolymer of vinyl pyrrolidone and vinyl acetate, a copolymer of vinyl pyrrolidone and dimethylaminoethyl (meth) acrylate, Copolymer of vinylpyrrolidone and (meth) acrylamidopropyltrimethylammonium chloride, copolymer of vinylpyrrolidone and vinylcaprolactam dimethylaminoethyl (meth) acrylate, copolymer of vinylpyrrolidone and styrene, vinylpyrrolidone and (meta ) A copolymer with acrylic acid.

  When polyvinyl pyrrolidone is used as the polymer of vinyl pyrrolidone, the weight average molecular weight of polyvinyl pyrrolidone is preferably 3000 or more and 60000 or less.

  The polyhydric alcohol is a compound having a function of reducing the silver precursor contained in the second solution to silver (metal).

  Examples of the polyhydric alcohol include ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, 1,3-propanediol, 1,2-butanediol, 2 , 3-butanediol, 1,3-butanediol, 1,4-butanediol, glycerol, trimethylolpropane, pentaerythritol, triethanolamine, trihydroxymethylaminomethane and the like.

  A first solution is prepared by dissolving the polymer of vinylpyrrolidone as described above in the polyhydric alcohol.

  The vinyl pyrrolidone polymer is preferably heated at 70 ° C. or higher and 120 ° C. or lower for the purpose of removing excess moisture or impurities. Moreover, it is preferable that the heating time in this case is 8 hours or more.

  In addition to the polyhydric alcohol, the first solution may contain a reducing agent that reduces the silver precursor in the second solution.

Examples of such a reducing agent include hydrazine and derivatives thereof; hydroxylamine and derivatives thereof; monohydric alcohols such as methanol and ethanol; aldehydes such as formaldehyde, formic acid, acetaldehyde, propionaldehyde and ammonium salts thereof; Phosphate; Sulphite; Tetrahydroborate (eg, Li, Na, K tetrahydroborate); Lithium aluminum hydride (LiAlH ₄ ); Sodium borohydride (NaBH ₄ ); Hydroquinone, alkyl-substituted hydroquinone Polyhydroxybenzenes such as catechol and pyrogallol; phenylenediamines and derivatives thereof; aminophenols and derivatives thereof; carboxylic acids such as ascorbic acid, citric acid and ketal ascorbate and the like Conductor; 3-pyrazolidone and derivatives thereof; hydroxy tetronic acid, hydroxy tetronic acid amides and derivatives thereof; bis-naphthol and derivatives thereof; sulfonamido phenol and derivatives thereof; Li, Na and K, and the like. Among these, it is preferable to use ammonium formate salt, formic acid, formaldehyde, acetaldehyde, propionaldehyde, ascorbic acid, citric acid, sodium borohydride, lithium aluminum hydride, lithium triethylborohydride, and use ammonium formate salt. Is more preferable.

<Second solution preparation step>
Next, a second solution in which a silver precursor that can be reduced to silver is dissolved in a solvent is prepared.

  A silver precursor is a compound which produces | generates silver (metal) by reducing with the polyhydric alcohol mentioned above or a reducing agent.

  Such silver precursors include, for example, silver oxides, hydroxides (including hydrated oxides), nitrates, nitrites, sulfates, halides (eg fluorides, chlorides, bromides and Iodide), carbonate, phosphate, azide, borate (including fluoroborate, pyrazolylborate, etc.), sulfonate, carboxylate (eg, formate, acetate, propionate) Oxalate and citrate), substituted carboxylates (including halogenated carboxylates such as trifluoroacetate, hydroxycarboxylates, aminocarboxylates, etc.), hexachloroplatinates, tetrachlorogolds Examples thereof include silver inorganic and organic acid salts such as acid salts and tungstates, silver alkoxides and silver complexes.

  The solvent is not particularly limited as long as it dissolves the above-described silver precursor. For example, the polyhydric alcohol, aliphatic, alicyclic, and aromatic alcohols described in the first solution preparation step (present) In the specification, when “alcohol” is simply indicated, it means “monohydric alcohol”), ether alcohols, amino alcohols, and the like can be used.

  A second solution is obtained by dissolving the silver precursor as described above in a solvent.

<Mixing process>
Next, the first solution and the second solution are mixed to obtain a mixed solution.

  At this time, the temperature of the first solution is preferably 100 ° C. or higher and 140 ° C. or lower, more preferably 101 ° C. or higher and 130 ° C. or lower, and further preferably 115 ° C. or higher and 125 ° C. or lower. Thereby, the silver precursor in the second solution can be more efficiently reduced, and vinylpyrrolidone can be efficiently adsorbed on the surface of the formed silver particles.

<Reaction progress process>
Next, the liquid mixture obtained by mixing the first solution and the second solution is heated at a predetermined temperature for a predetermined time to advance the reduction reaction of the silver precursor.

  The heating temperature at this time is preferably 100 ° C. or higher and 140 ° C. or lower, more preferably 101 ° C. or higher and 130 ° C. or lower, and further preferably 115 ° C. or higher and 125 ° C. or lower. Thereby, while being able to reduce a silver precursor more efficiently, vinylpyrrolidone can be made to adsorb | suck efficiently to the surface of the silver particle formed.

  The heating time (reaction time) depends on the heating temperature, but is preferably 30 minutes or more and 180 minutes or less, more preferably 30 minutes or more and 120 minutes or less, and 60 minutes or more and 120 minutes or less. More preferably. Thereby, while being able to reduce | restore a silver precursor more reliably, vinylpyrrolidone can be more effectively adsorbed on the surface of the silver particle formed.

<Dispersing process>
Thereafter, if necessary, the formed silver particles (silver colloidal particles) are separated by filtration, centrifugation, or the like, and the separated silver particles are dispersed in an aqueous dispersion medium at a desired concentration. In this way, silver particles, a water-based ink composition, or a silver colloid aqueous dispersion can be obtained.

1.1.2b. Second Method In the second method, first, an aqueous solution in which a dispersant and a reducing agent are dissolved is prepared. Although it does not specifically limit as a dispersing agent, It shall have 3 or more of COOH groups and OH groups, and the number of COOH groups is the same as that of OH groups, or it contains hydroxy acids or its salt more than that. . One of the functions of these dispersants is to form colloidal particles by adsorbing on the surface of the silver particles, and uniformly disperse the silver colloidal particles in the aqueous solution by the electric repulsive force of the COOH groups present in the dispersant. And stabilizing the colloidal solution. By blending the dispersant, the colloidal silver particles can be stably present in the dispersion medium. For example, the dispersion stability can be further increased.

  Examples of such a dispersant include citric acid, malic acid, trisodium citrate, tripotassium citrate, trilithium citrate, triammonium citrate, disodium malate, tannic acid, gallotannic acid, pentaploid tannin and the like. And a combination of one or more of these.

  Further, the dispersant may contain mercapto acid or a salt thereof having two or more COOH groups and SH groups. Since these dispersants have the ability to adsorb to the surface of silver particles of mercapto groups as much as or stronger than hydroxyl groups, colloidal particles are more easily formed, and COOH groups present in the dispersants There is a case where colloidal particles are uniformly dispersed in an aqueous solution by an electric repulsive force to enhance the function of stabilizing the colloidal liquid. Examples of such dispersants include mercaptoacetic acid, mercaptopropionic acid, thiodipropionic acid, mercaptosuccinic acid, thioacetic acid, sodium mercaptoacetate, sodium mercaptopropionate, sodium thiodipropionate, disodium mercaptosuccinate, Examples include potassium mercaptoacetate, potassium mercaptopropionate, potassium thiodipropionate, dipotassium mercaptosuccinate, and the like, and one or a combination of two or more of these may be mentioned.

  As a blending amount of the dispersing agent, it is preferable to blend so that a molar ratio of silver in the silver salt such as silver nitrate as a starting material to the dispersing agent is about 1: 1 to 1: 100. When the molar ratio of the dispersant to the silver salt is increased, the particle size of the silver particles is reduced, and the dispersibility can be further improved.

As one of the functions of the reducing agent, silver nitrate starting material ^- like be by reducing Ag ⁺ ions, such silver salt as produced silver particles (Ag ⁺ NO _3).

  The reducing agent is not particularly limited, and examples thereof include amines such as hydrazine, dimethylaminoethanol, methyldiethanolamine, and triethanolamine; hydrogen compounds such as sodium borohydride, hydrogen gas, and hydrogen iodide; carbon monoxide, Oxide systems such as sulfurous acid hypophosphorous acid, low-valent metal salt systems such as Fe (II) compounds and Sn (II) compounds, sugars such as D-glucose, organic compound systems such as formaldehyde, or hydroxy acids Examples include citric acid, malic acid, and hydroxy acid salts such as trisodium citrate, tripotassium citrate, trilithium citrate, triammonium citrate, disodium malate, and tannic acid. Among these, tannic acid and hydroxy acid can be used more suitably because they function as a reducing agent and at the same time exert an effect as a dispersant. Alternatively, mercaptoacetic acid, mercaptopropionic acid, thiodipropionic acid, mercaptosuccinic acid, mercaptosuccinic acid, sodium mercaptoacetate, which is thioacetic acid or mercaptoate, listed above as a dispersant that forms a stable bond on the silver surface, Sodium mercaptopropionate, sodium thiodipropionate, sodium mercaptosuccinate, potassium mercaptoacetate, potassium mercaptopropionate, potassium thiodipropionate, potassium mercaptosuccinate and the like can be suitably used as the reducing agent.

  Any of these dispersants and reducing agents may be used alone or in combination of two or more. Moreover, when using these dispersing agents and reducing agents, light and heat may be added to promote the reduction reaction.

  The amount of the reducing agent to be blended is sufficient if the starting silver salt can be completely reduced. However, the excess reducing agent remains as an impurity in the silver colloidal liquid and becomes conductive after film formation. Therefore, it is preferable to blend as small an amount as possible. As a specific blending amount, the molar ratio of the silver salt to the reducing agent is preferably about 1: 1 to 1: 3.

  In this example of the production method, it is preferable that the aqueous solution is prepared by dissolving the dispersant and the reducing agent, and then the pH of the aqueous solution is adjusted to 6 or more and 12 or less. This is due to the following reasons. For example, when trisodium citrate, which is a dispersant, and ferrous sulfate, which is a reducing agent, are mixed, the pH is about 4 or more and 5 or less, which is lower than the above pH 6, although it depends on the overall concentration. The hydrogen ions present at this time move the equilibrium of the reaction represented by the following reaction formula (1) to the right side, and the amount of COOH increases. Therefore, thereafter, the electric repulsive force on the surface of the silver particles obtained by dropping the silver salt solution decreases, and the dispersibility of the silver particles (colloid particles) decreases.

^{-COO - + H + ← → -COOH} ... (1)
Therefore, after preparing the aqueous solution by dissolving the dispersant and the reducing agent, an alkaline compound is added to the aqueous solution to reduce the hydrogen ion concentration, thereby suppressing such a decrease in dispersibility. .

  It does not specifically limit as an alkaline compound to add, For example, sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonia water, the alkanolamine mentioned above, etc. can be used. Among these, when alkanolamine is used, the pH can be easily adjusted and the dispersion stability of the formed silver colloidal particles can be further improved.

  If the amount of the alkaline compound added is too large and the pH exceeds 12, it is not preferable because precipitation of remaining reducing agent ions such as iron ions tends to occur.

  Next, in this example of the manufacturing method, an aqueous solution containing a silver salt is dropped into an aqueous solution in which the prepared dispersant and reducing agent are dissolved. The silver salt is not particularly limited, and for example, silver acetate, silver carbonate, silver oxide, silver sulfate, silver nitrite, silver chlorate, silver sulfide, silver chromate, silver nitrate, silver dichromate and the like can be used. . Among these, silver nitrate is particularly preferable because of its high solubility in water.

  The amount of the silver salt is determined in consideration of the content of the target colloidal particles and the ratio reduced by the reducing agent. For example, in the case of silver nitrate, 15 parts by mass with respect to 100 parts by mass of the aqueous solution. The amount is preferably about 70 parts by mass or less.

  The silver salt aqueous solution is prepared by dissolving the silver salt in pure water, and the prepared silver salt aqueous solution is gradually dropped into the aqueous solution in which the dispersing agent and reducing agent described above are dissolved. In this step, the silver salt is reduced to silver particles by a reducing agent, and the dispersant is adsorbed on the surface of the silver particles to form silver colloidal particles. As a result, an aqueous solution in which silver colloidal particles are colloidally dispersed in the aqueous solution is obtained.

  In the obtained solution, in addition to the colloidal particles, a reducing agent residue and a dispersing agent are present, and the ion concentration of the whole liquid is high. In the liquid in such a state, coagulation generally occurs and precipitation is likely to occur. Therefore, it is more desirable to perform washing in order to remove such excessive ions in the aqueous solution and reduce the ion concentration.

  As a washing method, for example, the aqueous solution containing the obtained colloidal particles is allowed to stand for a certain period, and the resulting supernatant liquid is removed, and then pure water is added and stirred again, and further left to stand for a certain period. In addition, a method of repeating the step of removing the supernatant several times, a method of centrifuging instead of the above standing, a method of removing ions by ultrafiltration and the like can be mentioned.

  Alternatively, cleaning may be performed by the following method. After the solution is prepared, the pH of the solution is adjusted to an acidic region of 5 or less, and the electric repulsive force on the surface of the silver particles is reduced by moving the equilibrium of the reaction of the above reaction formula (1) to the right side. It is possible to remove salts and solvents by washing in a state where silver colloidal particles are aggregated. In the case of silver colloid particles having a low molecular weight sulfur compound such as mercapto acid on the particle surface as a dispersant, a stable bond is formed on the metal surface. Therefore, the aggregated silver colloid particles have an alkaline pH of 6 or more. By re-adjusting to this region, it is possible to obtain a metal colloid liquid that is easily redispersed and excellent in dispersion stability.

  In this example of the production method, it is preferable to adjust the final pH to 6 to 11 by adding an aqueous alkali metal hydroxide solution to an aqueous solution in which silver colloidal particles are dispersed as necessary after the above step. In this example of the manufacturing method, since washing is performed after the reduction, the concentration of sodium that is an electrolyte ion may be reduced. In such a state, the solution is represented by the following reaction formula (2). The equilibrium of the reaction will shift to the right side. If this is the case, the electrical repulsive force of the silver colloid may decrease and the dispersibility of the silver particles may decrease. Therefore, by adding an appropriate amount of alkali hydroxide, the equilibrium of the reaction formula (2) is moved to the left side. To stabilize the silver colloid.

_{^{-COO - Na + + H 2 O}} ← → -COOH + Na + + OH - ... (2)
Examples of the alkali metal hydroxide used at this time include the same compounds as those used when the pH is first adjusted. If the pH is less than 6, the equilibrium of the reaction formula (2) shifts to the right side, so that the colloidal particles become unstable. On the other hand, if the pH exceeds 11, hydroxides of remaining ions such as iron ions This is not preferable because precipitation of selenium tends to occur. However, if iron ions or the like are removed in advance, there is no major problem even if the pH exceeds 11.

  Cations such as sodium ions are preferably added in the form of hydroxides. This is because the self-protolysis of water can be used, so that cations such as sodium ions can be added to the aqueous solution most effectively. Moreover, in the said process of adjusting pH to 6-11, you may use an alkanolamine instead of an alkali metal hydroxide aqueous solution.

1.1.2c. Third Method A third method is an oxidation polymer aqueous solution preparation step for preparing an oxidation polymer solution in which an oxidation polymer of a phenol compound is dissolved in a solvent, and a silver compound solution for preparing a silver compound solution in which a silver compound is dissolved. A preparation step, and a mixing / reduction step of mixing an aqueous solution of an oxidized polymer and a silver compound solution to reduce the silver compound to obtain silver fine particles.

<Oxidation polymer solution preparation process>
In this step, an oxidized polymer solution in which an oxidized polymer of a phenol compound is dissolved in a solvent is prepared.

  The oxidation polymer of the phenol compound has a reducing power and can reduce a silver compound described later. Further, those oxidized or excessive by oxidation reaction of an oxidation polymer of a phenol compound can exist on the surface of the generated silver fine particles due to coordination, adsorption, etc. A silver colloid solution in which is dispersed can be obtained.

  As the oxidative polymerization product of a phenol compound, a carbon condensed polycyclic compound formed by combining and polymerizing two or more molecules while oxidizing a part of the phenol compound molecule can be used.

  Specifically, it is preferable to use at least one selected from the following (1) to (4). (1) Dihydroxy-dibenzofuran-dione having two substitution positions of hydroxyl group selected from 1 to 4 positions and two substitution positions of carbonyl group selected from 5 to 8 positions, and derivatives thereof, for example, 1 , 2-dihydroxy-dibenzofuran-7,8-dione, 2,4-dihydroxy-dibenzofuran-5,7-dione, 1,2-dihydroxy-4,5-dicarboxy-dibenzofuran-7,8-dione, etc. 2) Tetrahydroxy-5H-benzo [7] annulen-5-one in which the hydroxyl substitution position is 2 selected from 1 to 3 positions, 1 selected from 4 positions, and 1 selected from 6 and 7 positions And their derivatives, such as 2,3,4,6-tetrahydroxy-5H-benzo [7] annulen-5-one (generic name purpurogallin), etc. (3) 1) or a compound obtained by further oxidative polymerization of the above compound (2), (4) at least one compound selected from the above (1) to (3), a divalent and trivalent phenol compound, and derivatives thereof A compound obtained by oxidative polymerization of at least one compound. Here, the derivative refers to a compound formed by a change in a small portion in the molecule of the oxidation polymer. For example, a hydrogen atom contained in the oxidation polymer is substituted with an alkyl group, a halogen atom, a hydroxyl group, a carboxyl group, or the like. Is.

  The oxidized polymer of a phenol compound can be obtained by oxidizing a phenol compound with an oxidizing agent, and the degree of polymerization can be controlled by the amount of the oxidizing agent added, the oxidation reaction time, and the like. Specifically, the phenol compound and the oxidizing agent are mixed, or the phenol compound is dissolved in an aqueous solvent, an organic solvent such as alcohol, or a mixed solvent of an aqueous solvent and an organic solvent such as alcohol, and then the solution and the oxidizing agent are mixed. It can be obtained by mixing with an agent.

  As the oxidizing agent, for example, an oxidizing gas such as air or oxygen, or a compound such as hydrogen peroxide, permanganic acid, potassium permanganate, or sodium iodate can be used, and it is particularly economical to use air. Advantageous and preferred.

  When an oxidizing gas is used as the oxidizing agent, mixing of a solution in which a phenolic compound is dissolved in a solvent (phenolic compound solution) and an oxidizing gas such as air can be performed by stirring the solution in an open system. You may carry out by bubbling oxidizing gas, such as air.

  As the solvent, it is preferable to use an aqueous solvent from the viewpoint of ease of handling and economy, as in the case of the metal compound solution described later. When the phenol compound is oxidized, the transparent solution turns reddish brown, brownish brown, black brown, etc., and further changes to a darker color as the polymerization proceeds, so that the formation of an oxidized polymer can be confirmed by visual observation. It is preferable to adjust the pH of the phenol compound solution to 6 or more because polymerization is easy to proceed. The range of 6 to 13 is more preferable, and the range of 8 to 11 is more preferable.

  The oxidized polymer is preferably a product obtained by oxidizing and polymerizing a divalent or trivalent phenol compound or a derivative thereof under the above-mentioned conditions. Divalent phenolic compounds include hydroquinone, catechol, resorcinol, etc., trivalent compounds include pyrogallol, phloroglucinol, 1,2,4-trihydroxybenzene, etc. An acid etc. are mentioned, Among these, it can use combining 1 type (s) or 2 or more types. Among those mentioned above, those having three hydroxyl groups are preferred, and pyrogallol, phloroglucinol, and 1,2,4-trihydroxybenzene are more preferred.

  Specifically, the oxidation polymer of pyrogallol includes 1,2-dihydroxy-dibenzofuran-7,8-dione, purpurogallin (2,3,4,6-tetrahydroxy-5H-benzo [7] annulene-5 Carbon condensed polycyclic compounds such as ON). In addition, examples of the oxidation polymer of phloroglucinol include carbon condensed polycyclic compounds such as 2,4-dihydroxy-dibenzofuran-5,7-dione. Examples of the oxidation polymer of 1,2,4-trihydroxybenzene include 1,3-dihydroxy-dibenzofuran-6,8-dione, 1,3,4,7-tetrahydroxy-5H-benzo [7] annulene. Examples thereof include carbon condensed polycyclic compounds such as -5-one.

  Examples of the derivative of the divalent or trivalent phenol compound include, for example, carbon condensation polyvalent compounds such as 1,2-dihydroxy-4,5-dicarboxy-dibenzofuran-7,8-dione, which is an oxidized polymer of gallic acid. A cyclic compound is mentioned.

  Further, an oxidation polymerization of the polycyclic compound or an oxidation polymerization of the polycyclic compound or an oxidation polymer thereof and at least one compound selected from divalent and trivalent phenolic compounds and derivatives thereof. In addition, their derivatives and their derivatives may be prepared and used.

<Silver compound solution preparation process>
On the other hand, a silver compound solution in which a silver compound is dissolved is prepared.

  A silver compound is a compound that becomes silver (metal) when reduced, and is a raw material for producing silver particles.

  As the silver compound, for example, silver chloride, sulfate, nitrate, carbonate, acetate and the like can be used. As the solvent for dissolving the silver compound, water, an organic compound such as alcohol, or a mixture of water and an organic compound such as alcohol can be used, and water is preferably used as the solvent in view of ease of handling and economy. The concentration of the silver compound in the solvent is not particularly limited as long as the silver compound is dissolved, but is preferably 5 mmol / L or more industrially.

<Mixing / reducing process>
Next, the oxidized polymer solution and the silver compound solution as described above are mixed with stirring, and the silver compound is reduced to produce silver particles.

  The amount of the oxidized polymer used is not particularly limited, but is preferably in the range of 0.1 to 10 in terms of the molar ratio of the silver compound based on the simple substance of the phenol compound, and in the range of 0.2 to 5 inclusive. More preferred.

  The reduction temperature can be set as appropriate, but it is preferably performed in the range of about 5 ° C. to 105 ° C., more preferably about 10 ° C. to 80 ° C.

  In addition, you may add another reducing agent, for example, alcohols and amines, auxiliary to the said reduction reaction. In this way, silver particles can be produced, and if necessary, dialysis, solid-liquid separation, and washing can be performed to remove excess components and unnecessary ion components, and further drying can be performed as necessary. .

  Silver particles produced by such a reduction reaction have at least one of an oxidized polymer of the phenol compound and an oxidized form of the oxidized polymer on the surface thereof, and constitute silver colloidal particles. As a result, a silver colloid liquid can be easily obtained by dispersing in, for example, water.

1.2. Humectant The water-based ink composition according to the present embodiment contains a humectant. The water-based ink composition according to the present embodiment contains at least one selected from glycerols, glycols, and carbohydrates as the humectant. By containing such a humectant, an image having excellent metal glossiness can be recorded when printed on a recording medium. In addition, there is an effect of preventing the water-based ink composition from drying and preventing clogging in the ink jet recording head portion.

  Examples of glycerols include glycerin, diglycerin, triglycerin, trimethylolethane, trimethylolpropane, C1-10 alkyl glyceryl ether, C1-10 alkyl diglyceryl ether, C1-10 alkyl triglyceryl ether, and the like. It is done. Among these glycerols, glycerin and trimethylolpropane are preferable because the metal glossiness of the image can be further improved.

  Examples of glycols include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, butylene glycol, 1,2-pentanediol, and 1,2-hexanediol. 1,2-heptanediol, 1,2-octanediol, 1,2,6-hexanetriol, thioglycol, hexylene glycol, polyethylene glycol and the like. Among these glycols, triethylene glycol, hexylene glycol, propylene glycol, and polyethylene glycol are preferable because the metal glossiness of the image can be further improved.

  Sugars include monosaccharides such as glucose, fructose and galactose; disaccharides such as maltose, sucrose, cellobiose, lactose, trehalose, ilmaltose, and gentiose; trisaccharides such as gentianose, raffinose and panose; other polysaccharides; Alcohol etc. are mentioned. As the sugar, a reduced starch saccharified product (a mixture containing a sugar alcohol) such as HS-500 (manufactured by Hayashibara Corporation) may be used.

  The humectants exemplified above may be used alone or in combination of two or more.

  The content of the humectant is preferably 5% by mass or more and 20% by mass or less, and more preferably 10% by mass or more and 15% by mass or less with respect to the total mass of the water-based ink composition. When the content of the humectant is within the above range, an image having excellent metal glossiness can be recorded when printed on a recording medium. When the content of the humectant is less than the above range, the metal glossiness of the image tends to decrease, and even when the content of the humectant exceeds the above range, the metal glossiness of the image tends to decrease.

  As described above, the silver particle-containing aqueous ink composition can control the metal glossiness of an image when printed on a recording medium by appropriately adjusting the type or content of the humectant. According to this technical idea, it is also possible to produce silver particle-containing water-based ink composition sets having different metal glossiness of images when printed on a recording medium.

1.3. Water The water-based ink composition according to the present embodiment contains water. Water is not particularly limited, and pure water or ultrapure water such as ion exchange water, ultrafiltration water, reverse osmosis water, and distilled water can be used. In the water, ions and the like may be present as long as they do not interfere with the dispersion of the silver particles.

1.4. Other Additives The water-based ink composition according to the present embodiment may contain additives such as surfactants, preservatives, pH adjusters, and coloring materials as necessary.

  Examples of the surfactant include acetylene glycol surfactants and polysiloxane surfactants. These surfactants have the effect of improving wettability to the recording surface and improving ink permeability. Examples of acetylene glycol surfactants include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, and 3,5. -Dimethyl-1-hexyn-3-ol, 2,4-dimethyl-5-hexyn-3-ol and the like. Moreover, a commercial item can also be utilized for acetylene glycol type-surfactant, for example, Orphine E1010, STG, Y (above, Nissin Chemical Co., Ltd. product), Surfinol 104, 82, 465, 485, TG (above , Air Products and Chemicals Inc.). Commercially available products can be used as the polysiloxane surfactant, and examples thereof include BYK-347 and BYK-348 (manufactured by Big Chemie Japan Co., Ltd.). Furthermore, you may add other surfactants, such as anionic surfactant, a nonionic surfactant, and an amphoteric surfactant, to the water-based ink composition which concerns on this Embodiment.

  The content of the surfactant is preferably 0.01 to 5% by mass, more preferably 0.1 to 1% by mass with respect to the total mass of the water-based ink composition.

  Examples of the preservative include sodium benzoate, sodium pentachlorophenol, sodium 2-pyridinethiol-1-oxide, sodium sorbate, sodium dehydroacetate, 1,2-dibenzthiazolin-3-one (manufactured by ICI). Proxel CRL, proxel BND, proxel GXL, proxel XL-2, proxel TN) and the like.

  The content of the preservative is preferably 0.1 to 2% by mass and more preferably 0.2 to 1% by mass with respect to the total mass of the water-based ink composition.

  Examples of the pH adjuster include amines such as diethanolamine, triethanolamine, propanolamine, and morpholine, and modified products thereof; inorganic salts such as potassium hydroxide, sodium hydroxide, and lithium hydroxide; ammonium hydroxide, quaternary An ammonium hydroxide (tetramethylammonium etc.) is mentioned.

  Examples of the color material include pigments and dyes, and color materials that can be used for ordinary inks can be used. The color of the color material that can be added to the water-based ink composition according to the present embodiment may be chromatic or achromatic. When a water-based ink composition contains a color material, for example, a glossy color can be imparted to an image recorded on a recording medium together with a metallic luster.

1.5. Uses and Physical Properties of Water-Based Ink Composition The use of the water-based ink composition according to this embodiment is not particularly limited, and can be applied to writing instruments, stamps, recorders, pen plotters, ink jet recording apparatuses, and the like. .

  For example, when the application is printing using an inkjet recording method, the viscosity of the aqueous ink composition at 20 ° C. is preferably 2 mPa · s or more and 10 mPa · s or less, and more preferably 3 mPa · s or more and 5 mPa · s or less. When the viscosity of the aqueous ink composition at 20 ° C. is in the above range, an appropriate amount of the aqueous ink composition is ejected from the nozzle, and the flying bend and scattering of the aqueous ink composition can be further reduced. Can be used for The surface tension of the water-based ink composition is 20 ° C., usually 0.2 to 0.7 mN / cm, preferably 0.25 to 0.6 mN / cm, more preferably 0.3 to 0.4 mN / cm. It is. The viscosity and surface tension of the water-based ink composition can be adjusted by appropriately changing the amount of each component described above.

2. Recorded matter A recorded matter according to an embodiment of the present invention is an image in which an image is recorded on a recording medium by the above-described aqueous ink composition. The water-based ink composition according to the present embodiment contains the silver particles and the humectant described above. Therefore, an image recorded using such an aqueous ink composition has excellent metallic gloss.

  The recording medium may be glossy, matte, or dull. Specific examples of the recording medium include surface-treated paper such as coated paper, art paper, and cast coated paper, and plastic films such as a vinyl chloride sheet and a PET film on which an ink receiving layer is formed.

In addition, the glossiness of the image recorded on the recording medium by the water-based ink composition according to the present embodiment is evaluated according to the method of Japanese Industrial Standard (JIS) Z8741: 1997 “Specular Glossiness—Measurement Method”. Can do. For the glossiness, for example, light is incident on the recorded surface of the image at incident angles of 20 °, 45 °, 60 °, 75 °, and 85 °, and a photodetector is installed in the direction of the reflection angle. Then, it can be calculated based on the result of measuring the light intensity. Examples of the apparatus capable of such measurement include “MULTI GLOSS 268” manufactured by Konica Minolta Co., Ltd., “GlossMeter Model No. VGP5000” manufactured by Nippon Denshoku Industries Co., Ltd.

  In the above glossiness evaluation method, for example, the maximum value of the glossiness at 20 ° is preferably 700 or more, more preferably 800 or more, and particularly preferably 900 or more.

3. EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

3.1. Preparation of water-based ink composition Silver particles, humectant, surfactant, preservative, and ion-exchanged water are mixed and stirred at the blending amounts shown in Table 1, filtered through a metal filter with a pore size of 5 μm, and removed using a vacuum pump. The ink compositions of Examples 1 to 16 and Comparative Example 1 were obtained by performing air treatment. In addition, the unit of the density | concentration described in Examples 1-16 of Table 1 and the comparative example 1 is the mass%, and is solid content conversion density | concentration about silver particle.

  A commercially available product “CSD-29” (manufactured by Cabot Corporation) was used as the silver particles. CSD-29 is a slurry containing silver particles at a solid content concentration of 20%.

  In addition, about the obtained ink composition, the average of silver particle was measured using the particle size distribution measuring apparatus (The Nikkiso Co., Ltd. make, model "Nanotrack UPA-EX-150") which uses a dynamic light scattering method as a measurement principle. When the primary particle size, the particle size d10, and the particle size d90 were determined, the average primary particle size of the silver particles in all the ink compositions was 20 nm, the particle size d10 was 10 nm, and the particle size d90 was 80 nm. It was.

Each component described in Table 1 is as follows.
・ Glycerin (Adeka Clean Aid Co., Ltd., trade name “DG Glycerin”)
・ Trimethylolpropane (Mitsubishi Gas Chemical Co., Ltd., trade name)
・ Triethylene glycol (Mitsubishi Gas Chemical Co., Ltd., trade name)
・ Hexylene glycol (trade name, manufactured by Tokyo Chemical Industry Co., Ltd.)
・ Reduced starch saccharified product (trade name “HS-500” manufactured by Hayashibara Shoji Co., Ltd., a mixture containing sugar alcohol)
・ Propylene glycol (trade name, manufactured by Kanto Chemical Co., Ltd.)
・ Polyethylene glycol (trade name “PEG1000” manufactured by NOF Corporation)
・ Surfactant (manufactured by Nissin Chemical Co., Ltd., trade name "Olfin (R) E1010")
-Preservative (Avicia Co., Ltd., trade name "Proxel (R) XL2")

3.2. Preparation of Evaluation Sample A water-based ink composition containing the silver particles shown in Table 1 was filled in a black ink chamber of a dedicated cartridge of an inkjet printer (manufactured by Seiko Epson Corporation, product name “PX-G930”). The ink cartridge thus produced was attached to the printer. Commercially available ink cartridges other than black were installed. This is used as a dummy and is not used in the evaluation of the present embodiment, so it is not involved in the effect.

Next, printing was performed at a resolution of 1440 × 720 dpi on photographic paper <glossy> (obtained from Seiko Epson Corporation). The printing pattern was a 100% duty solid pattern. “Duty” is a value calculated by the following equation.
duty (%) = number of actual printing dots / (vertical resolution × horizontal resolution) × 100
(Where “number of actual print dots” is the number of actual print dots per unit area, and “vertical resolution” and “horizontal resolution” are resolutions per unit area. 100% duty is a single color for a pixel. Means the maximum ink mass.)

3.3. Glossiness Evaluation Method Each sample obtained in “3.2. Preparation of Evaluation Sample” was evaluated for glossiness.
The glossiness was measured using a “MULTI GLOSS 268 gloss meter” (manufactured by Konica Minolta Co., Ltd.) at an incident angle of 20 ° and 60 °. Table 1 shows measurement results and evaluation results at incident angles of 20 ° and 60 °. The evaluation criteria for glossiness are as follows.
A: Maximum glossiness at an incident angle of 20 ° is 900 or more B: Maximum glossiness at an incident angle of 20 ° is 800 or more and less than 900 C: Maximum glossiness at an incident angle of 20 ° is 700 or more and less than 800 D : Maximum glossiness at an incident angle of 20 ° is less than 700

3.4. Evaluation results The samples using the aqueous ink compositions of Examples 1 to 16 shown in Table 1 all have a glossiness at 20 ° as compared to the sample using the aqueous ink composition of Comparative Example 1 that does not contain a humectant. It was found that the maximum value of rose significantly.

  It was also found that even when the concentration of the humectant was the same, changing the type of humectant changed the maximum glossiness at 20 °. It has been found that when the type of humectant is trimethylolpropane, triethylene glycol, hexylene glycol, sugar alcohol or propylene glycol, the glossiness is particularly good.

  Furthermore, it was found that even when the type of humectant was the same, the maximum glossiness at 20 ° was changed by changing the concentration of the humectant. It was found that when the type of moisturizing agent is trimethylolpropane, tetraethylene glycol, hexylene glycol, sugar alcohol, or propylene glycol, 10% by mass to 15% by mass is the optimum concentration range.

  The present invention is not limited to the embodiments described above, and various modifications are possible. For example, the present invention includes substantially the same configuration (for example, a configuration having the same function, method, and result, or a configuration having the same purpose and effect) as the configuration described in the embodiment. In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that achieves the same effect as the configuration described in the embodiment or a configuration that can achieve the same object. In addition, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

Claims (8)

A water-based ink composition containing at least water, silver particles, and a humectant,
The water-based ink composition, wherein the humectant is at least one selected from glycerols, glycols, and carbohydrates. In claim 1,
The water-based ink composition, wherein the glycerol is glycerin or trimethylolpropane. In claim 1 or claim 2,
The water-based ink composition, wherein the glycol is triethylene glycol, hexylene glycol, propylene glycol, or polyethylene glycol. In any one of Claims 1 to 3,
The water-based ink composition, wherein the content of the humectant is 5% by mass or more and 20% by mass or less. In any one of Claims 1 thru | or 4,
The water-based ink composition wherein the average primary particle size of the silver particles is 10 nm or more and 100 nm or less, and the particle size d90 in the particle size accumulation curve of the silver particles is 50 nm or more and 1 μm or less. In claim 5,
Furthermore, the water-based ink composition whose particle size d10 in the particle size accumulation curve of the said silver particle is 2 nm or more and 20 nm or less. In any one of Claims 1 thru | or 6,
The silver particle is a water-based ink composition which has been surface-treated.   A recorded matter in which an image is recorded with the water-based ink composition according to any one of claims 1 to 7.