JP2011241239A - Ink composition and recording method - Google Patents

Abstract

An ink composition and a recording method that exhibit a metallic luster with little coloring when printed on a recording medium.
An ink composition according to the present invention includes silver particles, a white pigment, and water, wherein a particle diameter d90 in a particle size accumulation curve of the silver particles is 50 nm to 1 μm, and the silver particles are the water. The white pigment content is 1% or more and 10% or less with respect to the silver particle content.
[Selection figure] None

Description

  The present invention relates to an ink composition and a recording method.

  Conventionally, in order to form a coating film having a metallic luster on printed matter, gold stamping made from brass, aluminum fine particles, etc., printing ink using silver powder as a pigment, foil press printing using metal foil, metal foil The thermal transfer method used is used.

  However, a coating film made of printing ink using gold powder or silver powder has a large average particle diameter of 10 to 30 μm, and a matte metallic luster is obtained, but it is difficult to obtain a mirror gloss. there were. Also, in foil stamping or thermal transfer using metal foil, an adhesive is applied to the print medium, a smooth metal foil is pressed onto the print medium, the recording medium and the metal foil are in close contact and heated, and the metal foil and the recording medium are thermally melted. Take the method of wearing. For this reason, relatively good gloss can be obtained, but since the number of manufacturing processes increases and pressure and heat are applied during the manufacturing processes, there is a limitation that the recording medium is limited to recording media that are resistant to heat and deformation.

  In recent years, many applications of inkjet in printing have been seen, and one of the applications is metallic printing. For example, Patent Document 1 proposes a dispersion containing aluminum particles having a flat plate shape and an ink composition.

JP 2008-174712 A

  However, the metallic luster of metallic printing is obtained by applying a fine metal powder to a recording medium, and thus the action of the powder on light cannot be completely removed. In other words, since the pigment is a powder, the optical properties of the powder may remain after printing. For example, the metallic luster may be colored with black or brown. On the other hand, a silver particle pigment that can be expected to have a metallic luster equivalent to or higher than that of an aluminum pigment is also mixed with the ink as a powder, and thus the color of the powder may also be a problem.

  One of the objects according to some embodiments of the present invention is to provide an ink composition and a recording method that exhibit a metallic luster with little coloring when printed on a recording medium.

  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 ink composition according to the present invention is:
Containing silver particles, white pigment and water,
The particle size d90 in the particle size accumulation curve of the silver particles is 50 nm or more and 1 μm or less,
Including a structure in which the silver particles are dispersed in the water;
The content of the white pigment is 1% or more and 10% or less with respect to the content of the silver particles.

  According to the ink composition of this application example, it is possible to record an image having a good metallic luster with little coloring when printed on a recording medium.

[Application Example 2]
In application example 1,
The particle size d10 in the particle size accumulation curve of the silver particles is 2 nm or more and 20 nm or less,
The silver particles may have a structure dispersed in the water as a dispersed colloid.

  According to the ink composition of this application example, the dispersibility of the silver particles is good, and when the ink composition is attached to the recording medium, it can exhibit a better metallic luster and can improve the storage stability. .

[Application Example 3]
In application example 1 or application example 2,
The particle size d50 in the particle size accumulation curve of the white pigment may be 100 nm or more and 2 μm or less.

  According to the ink composition of this application example, the dispersibility of the white pigment is good, the content of the white pigment can be reduced, and the coloring of the metallic luster when attached to the recording medium is further suppressed. be able to.

[Application Example 4]
In any one of Application Examples 1 to 3,
The water content may be 50% by mass or less and 95% by mass or less.

  According to the ink composition of this application example, the dispersibility of the silver particles and the white pigment becomes better, and the storage stability can be further improved.

[Application Example 5]
One aspect of the recording method according to the present invention is:
A silver particle, a white pigment, and water, wherein the particle size d90 in the particle size accumulation curve of the silver particle is 50 nm or more and 1 μm or less, the silver particle is dispersed in the water, and the white pigment is contained An image is recorded by ejecting an ink composition having an amount of 1% or more and 10% or less with respect to the content of the silver particles by using an ink jet recording apparatus, and depositing the ink composition on a recording medium. To do.

  According to the recording method of this application example, it is possible to record an image having a metallic luster with little coloring on a recording medium.

[Application Example 6]
In application example 5,
The particle size d10 in the particle size accumulation curve of the silver particles is 2 nm or more and 20 nm or less,
The silver particles may have a structure dispersed in the water as a dispersed colloid.

  According to the recording method of this application example, the storage stability of the ink composition can be improved.

[Application Example 7]
In Application Example 5 or Application Example 6,
The recording method according to claim 1, wherein a particle diameter d50 in a particle diameter accumulation curve of the white pigment is 100 nm or more and 2 μm or less.

  According to the recording method of this application example, the content of the white pigment can be reduced, and an image having a metallic luster with little coloring can be recorded on the recording medium.

The plot which shows the duty dependence of the whiteness of the recorded matter of an Example and a comparative example. The plot which shows the duty dependence of 60 degree glossiness of the recorded matter of an Example and a comparative example. The plot which shows the duty dependence of 20 degree glossiness of the recorded matter of an Example and a comparative example.

  Hereinafter, embodiments of the present invention will be described. In addition, the following embodiment demonstrates an example of this invention. Therefore, this invention is not limited to the following embodiment, The various modifications implemented in the range which does not change a summary are also included. Note that not all of the configurations described in the following embodiments are indispensable constituent requirements of the present invention.

1. Ink Composition The ink composition according to this embodiment includes silver particles, a white pigment, and water.

1.1. Silver particles 1.1.1. Properties of Silver Particles Silver particles contained in the ink composition of the present embodiment are particles containing silver as a main component. For example, the silver particles may contain other metals, oxygen, carbon, and the like as subcomponents. The purity of silver in the silver particles can be, for example, 80% or more. The silver particles may be an alloy of silver and another metal. Further, the silver particles in the 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 can contribute to, for example, an improvement in the storage stability of the ink composition.

  The particle size d90 in the particle size accumulation curve of the silver particles is 50 nm or more and 1 μm or less. Here, the particle size accumulation curve is a statistically calculated result obtained by measuring the diameter of a silver particle dispersed in a liquid such as an ink composition and the number of particles present. It is a kind of curve obtained by processing. 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 size d90 is 90% (0.90) when the vertical axis is normalized (the total mass of the measured particles is 1) in the particle size accumulation curve. The value on the horizontal axis, that is, the diameter of the particle. 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.

  The particle size accumulation curve of the silver particles can be obtained, for example, by using a particle size distribution measuring apparatus based on the 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. . In particular, a dynamic light scattering method is suitable for a sample containing submicron-sized silver particles, and a particle size accumulation curve can be obtained relatively easily by the dynamic light scattering method. 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.).

  Further, the particle size accumulation curve of silver particles can be measured also by, for example, electron microscopy in the ink composition containing the silver particle aqueous dispersion of the present embodiment. In this method, the size of silver particles is measured from an electron micrograph, and the particle diameter accumulation curve of silver particles can be obtained by measuring the photograph, for example, by image processing. Specifically, the minor axis diameter and major axis diameter of each silver particle are measured, and a circle diameter (equivalent circle diameter) equal to the area is obtained arithmetically, and 50 or more silver particles are obtained from a certain visual field. There is a method of selecting at random. According to this method, for example, even when particles other than silver particles (for example, white pigment) are contained in the ink composition, the silver particles can be selected on the electron microscope image. A particle size accumulation curve can be obtained. In order to increase the reliability in this measurement, the number of particles to be measured should be increased.

  Further, in the measurement by the above electron microscope method, when particles such as pigments are recognized in the electron microscope image in addition to silver particles, for example, by using an EDX (energy dispersive X-ray analysis) method, Silver particles and other pigments can be distinguished. Furthermore, even when the ink composition of the present embodiment is attached to a recording medium (for example, a printed material), the particle size accumulation curve of silver particles is used in combination with an EDX method if necessary using an electron microscope method. Can be obtained.

Furthermore, in the ink composition containing the silver particle aqueous dispersion and the white pigment according to the present embodiment, as another method for obtaining the particle size accumulation curve of the silver particles, a method using centrifugation (hereinafter referred to as this). May be referred to as a centrifugal method.). As a specific example of the centrifugation method, a 10 cm long centrifuge tube is filled with the ink composition and, for example, centrifuged at 1000 rpm for 5 hours, and then a 1 cm range at the top of the tube and a 1 cm range at the bottom of the tube are collected. . Since the specific gravity of silver is approximately 10.5 g / cm ³ and the specific gravity of titanium dioxide is approximately 3.9 g / cm ³ , the position after centrifugation in the centrifuge tube differs depending on this specific gravity difference. Therefore, for example, silver particles are concentrated in the 1 cm range at the bottom of the tube, and the white pigment is dispersed in the supernatant collected from the 1 cm range at the top of the tube. Therefore, the silver particles in the ink composition containing the silver particle aqueous dispersion and the white pigment are obtained by collecting the dispersion from an appropriate position of the centrifugal tube and measuring the dispersion by the above-described dynamic light scattering method or the like. The particle size accumulation curve of the white pigment and the particle size accumulation curve of the white pigment can be respectively determined.

  The silver particles used in the ink composition of the present embodiment may have a particle size d10 in the particle size accumulation curve of 2 nm or more and 20 nm or less. By doing so, the dispersibility of the silver particles in the ink composition can be made better, and for example, the storage stability can be further improved. The particle diameter d10 is 10% (0.10) when the vertical axis is normalized (the total mass of the measured particles is 1) in the particle size accumulation curve. The value on the horizontal axis, that is, the diameter of the particle.

  The concentration of silver particles in the ink composition of the present embodiment is preferably 0.1% by mass to 30% by mass, more preferably 1% by mass to 20% by mass, with respect to the total mass of the ink composition. Especially preferably, it is 5 mass% or more and 15 mass% or less.

1.1.2. Silver Particle Manufacturing Method The silver particles used in the ink composition of the present embodiment are not limited by the method to be manufactured, but can be manufactured as follows, for example. Below, it illustrates about some of the manufacturing methods of a silver particle and a silver colloid particle dispersion.

1.1.2.1. First Method The silver particle production method exemplified below is a first solution preparation step of preparing a first solution containing at least a vinylpyrrolidone polymer and a polyhydric alcohol, and can be reduced to silver (metal). A second solution preparing step of preparing a second solution in which a silver precursor is dissolved in a solvent, a first solution heating step of heating the first solution to a predetermined temperature, and the heated first solution and second solution. Mixing step of mixing to obtain a mixed solution, a reaction progressing step of holding the mixed solution at a predetermined temperature for a predetermined time, and a dispersion in which silver particles (silver colloidal particles) are taken out from the mixed solution having undergone the reaction and dispersed in an aqueous dispersion medium Process.

(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; Sulfite; 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 3-pyrazolidone and derivatives thereof; hydroxytetronic acid, hydroxytetronic acid amide and derivatives thereof; bis-naphthols and derivatives thereof; sulfonamidophenol 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 process)
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.

(Dispersion 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, an ink composition, or a silver colloid aqueous dispersion can be obtained.

1.1.2.2. Second Method In the silver particle production method exemplified below, 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 dispersing agent include citric acid, malic acid, trisodium citrate, tripotassium citrate, trilithium citrate, triammonium citrate, disodium malate, tannic acid, gallotannic acid, and pentaploid tannin. The thing which combined 1 type (s) or 2 or more types among these can be mentioned.

  Further, the dispersant may contain mercapto acid or a salt thereof having two or more COOH groups and SH groups. These dispersants have the ability to adsorb to the surface of mercapto group silver fine particles, which may be the same as or stronger than the hydroxyl group, so that it is easier to form colloidal particles, and the COOH group present in the dispersant 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 can 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.

One of the functions of the reducing agent is to reduce Ag ⁺ ions in a silver salt such as silver nitrate (Ag ⁺ NO ₃ ⁻ ) which is a starting material to generate silver particles.

  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.

1.1.2.3. Third Method The silver particle production method exemplified below includes an oxidation polymer aqueous solution preparation step of preparing an oxidation polymer solution in which an oxidation polymer of a phenol compound is dissolved in a solvent, and a silver compound solution in which the silver compound is dissolved. A silver compound solution preparation step to be prepared, 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. White Pigment Examples of the white pigment contained in the ink composition of the present embodiment include Group IV element oxides such as titanium dioxide and zirconia dioxide. Other examples of white pigments include calcium carbonate, calcium sulfate, zinc oxide, barium sulfate, barium carbonate, silica, alumina, kaolin, clay, talc, clay, aluminum hydroxide, magnesium carbonate, and white hollow resin emulsion. Preferably, it may be one or a mixture of two or more selected from the group consisting of these.

  The content of the white pigment contained in the ink composition is 1% or more and 10% or less with respect to the content of silver particles. That is, when the silver particle content in the entire ink composition is, for example, 0.1% by mass or more and 30% by mass or less, the white pigment content in the entire ink composition is 0.001% by mass or more and 3% by mass. It is below mass%. Further, from the viewpoint of dispersibility of the white pigment in the water-soluble ink composition, the content of the white pigment is preferably 0.01% by mass or more and 1% by mass or less. Furthermore, from at least one of the viewpoints of increasing whiteness and increasing dispersibility in the water-soluble ink composition, the content of the white pigment is 0.1% by mass or more and 1% by mass or less. preferable.

  The ink composition of the present embodiment can be attached to a recording medium and provide a glossy image, for example, when the application is printing using an inkjet recording method. At this time, the density attached to the recording medium can be defined by, for example, duty.

  “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.)
The ink composition of this embodiment can also improve the balance between whiteness and glossiness in a low-duty image. For example, the content of the white pigment with respect to the content of the silver particles is 1% or more and 4% or less, whereby the balance between whiteness and glossiness in a low duty image can be improved.

  More preferably, the white pigment has a particle size d50 value of 100 nm or more and 2 μm or less in the particle size accumulation curve. When the white pigment is in such a range of the particle diameter d50, for example, the whiteness of printing can be improved. The measurement of the particle size accumulation curve of the white pigment is, for example, at least one of a dynamic light scattering method, an electron microscope method (in combination with an EDX method if necessary), and a centrifugal method, as in the case of the silver particles described above. Can be measured.

1.3. Water The water used in the ink composition of the present embodiment is, for example, pure water such as ion exchange water, ultrafiltration water, reverse osmosis water, distilled water, or ultrapure water. Ions or the like may be present in the water as long as it does not interfere with the dispersion of the silver particles.

  The water content in the ink composition of the present embodiment is not limited as long as the dispersion of silver particles can be maintained, but is more preferably 50% by mass or more and 95% by mass or less with respect to the total amount of the ink composition. When the water content in the ink composition is within this range, the dispersibility of the silver particles and the white pigment becomes better, and the storage stability can be further improved.

  In addition, that content of water is 50 mass% or more and 95 mass% or less has shown that content of components other than water is 5 mass% or more and 50 mass% or less. In the present specification, components other than water may be referred to as solid content, and the content of water is 50% by mass or more and 95% by mass or less means that the concentration of solid content in the ink composition is 5% by mass. % Or more and 50 mass% or less.

1.4. Other Components The ink composition of the present embodiment may contain a surfactant, a polyhydric alcohol, a pH adjuster, resins, a color material, and the like 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 the acetylene glycol surfactant include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 3, Examples include 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, other surfactants such as an anionic surfactant, a nonionic surfactant, and an amphoteric surfactant may be added to the ink composition of the present embodiment.

  Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, propylene glycol, butylene glycol, 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,2-heptanediol, 1,2-octanediol and the like, 1,2-alkanediol having 4 to 8 carbon atoms, 1,2,6-hexanetriol, thioglycol, hexylene glycol, glycerin, trimethylolethane And trimethylolpropane. These polyhydric alcohols are effective in preventing the ink composition from drying and clogging in the ink jet recording head portion when the ink composition of this embodiment is applied to the ink jet recording apparatus.

  Of these, alkanediol is particularly preferable because it has a strong effect of increasing the wettability of the recording surface such as a recording medium to increase the ink permeability. As such alkanediols, 1,2-hexanediol, 1,2-heptanediol, and 1,2-octanediol having 6 to 8 carbon atoms are more preferable because of their particularly high permeability to recording media. .

  The pH adjuster is not particularly limited, and for example, potassium dihydrogen phosphate, disodium hydrogen phosphate, sodium hydroxide, lithium hydroxide, potassium hydroxide, ammonia, diethanolamine, triethanolamine, triisopropanolamine, potassium carbonate Sodium carbonate, sodium hydrogen carbonate and the like.

  Examples of the resins include acrylic acid, acrylic acid ester, methacrylic acid, methacrylic acid ester, acrylonitrile, cyanoacrylate, acrylamide, olefin, styrene, vinyl acetate, vinyl chloride, vinyl alcohol, vinyl ether, vinyl pyrrolidone, vinyl pyridine, vinyl Examples thereof include carbazole, vinylimidazole, vinylidene chloride homopolymer or copolymer, urethane resin, fluororesin, and natural resin. The copolymer can be used in any form of a random copolymer, a block copolymer, an alternating copolymer, and a graft copolymer. These resins can be added to firmly fix the silver particles on the recording medium.

  Examples of the color material include pigments and dyes, and a color material that can be used for ordinary inks can be used without any particular limitation. The color of the color material that can be added to the ink composition of the present embodiment may be a chromatic color or an achromatic color. However, since the ink composition contains a white pigment, it is preferably a chromatic color. . When a color material is included in the ink composition, for example, a glossy color can be imparted to the image formed when applied to the recording medium, along with a metallic luster.

  Examples of dyes that can be used in the ink composition of the present embodiment include direct dyes, acid dyes, food dyes, basic dyes, reactive dyes, disperse dyes, vat dyes, soluble vat dyes, and reactive disperse dyes. Various dyes used for inkjet recording can be used.

  Examples of pigments that can be used in the ink composition of the present embodiment include azo pigments, polycyclic pigments, dye chelates, nitro pigments, and nitroso pigments. Examples of pigment colors include yellow, magenta, and cyan. When the ink composition of the present embodiment contains a color material, it may contain a plurality of color materials. For example, in addition to the basic three colors of yellow, magenta, and cyan, the same series of dark and light colors can be added for each color. That is, in addition to magenta, light color light magenta, dark red and cyan, and light color light cyan and dark blue can be included.

  When the pigment is contained in the ink composition of the present embodiment, the pigment preferably has an average particle diameter in the range of 10 nm to 200 nm, more preferably about 50 nm to 150 nm. When the coloring material is contained in the ink composition of the present embodiment, the amount of the coloring material is preferably in the range of about 0.1% by mass to 25% by mass, more preferably 0.5% by mass to 15% by mass. % Or less.

  In addition, when a pigment is contained in the ink composition, a pigment dispersant for dispersing the pigment may be further added. As a preferable dispersant, a dispersant commonly used for preparing a pigment dispersion, for example, a polymer dispersant can be used. As such a dispersant, any dispersant used in normal ink can be used. The content when the pigment dispersant is contained in the ink composition is 5% by mass or more and 200% by mass or less, preferably 30% by mass or more and 120% by mass or less with respect to the content of the color material in the ink composition. And may be appropriately selected depending on the color material to be dispersed.

  In addition, the ink composition of the present embodiment includes a fixing agent such as a water-soluble rosin, an antifungal / preservative such as sodium benzoate, an antioxidant such as allophanates, a wetting agent, an ultraviolet absorber, a chelating agent, an oxygen Additives such as absorbents, preservatives, and fungicides can be included. These additives can be used individually by 1 type, and can also be used in combination of 2 or more type.

1.5. Uses and Physical Properties of Ink Composition The uses of the ink composition of the present embodiment are 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 use is printing by an inkjet recording method, the viscosity of the ink composition at 20 ° C. is preferably 2 mPa · s or more and 10 mPa · s or less, more preferably 3 mPa · s or more and 5 mPa · s or less. When the viscosity of the ink composition at 20 ° C. is within the above range, an appropriate amount of the ink composition is ejected from the nozzle, and the flying bending and scattering of the ink composition can be further reduced, and thus the ink composition is preferably used for an ink jet recording apparatus. can do.

  The ink composition of the present embodiment can be ejected and applied to a recording medium by an ink jet recording apparatus. And the ink composition of this embodiment contains the above-mentioned silver particle. Therefore, when applied by the ink jet recording method, a good metallic luster can be expressed in the coating film.

  In addition, since the ink composition of the present embodiment has a particle size d90 in a particle size accumulation curve of silver particles contained in the ink composition of 50 nm or more and 1 μm or less, the dispersibility of the silver particles is good and the storage stability is excellent. . Moreover, the ink composition of the present embodiment contains the above-described white pigment. Therefore, when coated by the ink jet recording method, the metallic luster coloring of the coating film can be suppressed. That is, the black or brown hue generated when the silver particles are powder can be suppressed by the white pigment, and a metallic luster having a higher whiteness (less coloring) can be exhibited.

  The glossiness of an image formed on a recording medium with an ink composition can be evaluated according to the method of Japanese Industrial Standard (JIS) Z8741: 1997 “Specular Glossiness—Measurement Method”. The glossiness is, for example, that light is incident at an incident angle of, for example, 20 °, 45 °, 60 °, 75 °, and 85 ° with respect to a surface on which an image is formed, and a photodetector in the direction of the reflection angle. Can be calculated based on the result of measuring the intensity of the light. As an apparatus capable of such measurement, for example, there is MULTI GLOSS 268 manufactured by Konica Minolta Co., Ltd. and GlossMeter model number VGP5000 manufactured by Nippon Denshoku Industries Co., Ltd.

  Further, the whiteness of the image formed on the recording medium by the ink composition can be evaluated using, for example, the L * value of the image. The L * value of the image can be measured using a commercially available spectroscopic device such as “938 Spectrodensitometer” (manufactured by X-rite).

2. Recording Method The recording method of the present embodiment includes discharging the above-described ink composition by an ink jet recording head and attaching the ink composition to a recording medium. Hereinafter, an example of a recording method in which an ink composition is ejected onto a recording medium using an ink jet recording apparatus and adhered onto the recording medium to form a dot group will be described.

2.1. Inkjet recording head As a method of an ink jet recording head, for example, a strong electric field is applied between a nozzle and an acceleration electrode placed in front of the nozzle, and ink is continuously ejected from the nozzle in the form of droplets. A method in which a printing information signal is applied to a polarizing electrode for recording while flying between deflection electrodes, or a method in which ink droplets are ejected in response to a printing information signal without being deflected (electrostatic suction method). Pressure is applied to the liquid, and the nozzle is mechanically vibrated with a crystal oscillator, etc. to forcibly eject ink droplets. The pressure and print information signal are simultaneously applied to the ink liquid using piezoelectric elements, and ink droplets are ejected.・ Recording method (piezo method), ink liquid is heated and foamed with microelectrodes according to the print information signal, and ink droplets are ejected and recorded (thermal jet method) Formula) and the like. Any of the ink jet recording heads described above may be used in the recording method of the present embodiment.

  Examples of the ink jet recording apparatus used in the present embodiment include those provided with the above ink jet recording head, main body, tray, head driving mechanism, carriage, and the like. The ink jet recording head may include an ink cartridge that stores ink sets of at least four colors of cyan, magenta, yellow, and black, and may be configured to perform full color printing. In the present embodiment, at least one of these ink cartridges or a dedicated cartridge is provided and filled with the above-described ink composition. Other cartridges may be filled with normal ink. The ink jet recording apparatus includes a dedicated control board and the like, and can control ink ejection timing of the ink jet recording head and scanning of the head driving mechanism.

2.2. Recording medium The type of the recording medium to which the ink composition is attached in the recording method of the present embodiment is not particularly limited. Examples of the recording medium used in the recording method of the present embodiment include an absorptive recording medium such as paper, porous film, and cloth, and a recording medium having a base material that does not have ink absorptivity such as plastic. It may be.

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

  According to the recording method of the present embodiment, since the above-described ink composition is used, it is possible to record an image having good metallic luster and less coloring (good whiteness) on the recording medium. . In the recording method of the present embodiment, 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 so that the silver particles are dispersed as a dispersed colloid. By doing so, the dispersibility of the silver particles can be further improved, and the metal glossiness of the image can be sufficiently increased. In addition, when the particle size d50 in the particle size accumulation curve of the white pigment contained in the ink composition is 100 nm or more and 2 μm or less, the content of the white pigment can be reduced and the balance between whiteness and metallic luster is excellent. Images can be recorded.

3. Examples and Comparative Examples Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but these do not limit the scope of the present invention.

3.1. Ink composition 3.1.1. Silver Particle Aqueous Dispersion The silver particle aqueous dispersion used in the ink compositions of Examples and Comparative Examples was prepared as follows according to “1.1.2.1. First Method” of the above embodiment. First, polyvinylpyrrolidone was dissolved in propylene glycol to obtain a first solution. Next, silver nitrate as a silver precursor was dissolved in propylene glycol to obtain a second solution. Next, the first solution and the second solution were mixed at 120 ° C. for 90 minutes to reduce the silver precursor, and polyvinyl pyrrolidone was adsorbed on the surface of the generated silver particles. Then, the formed silver particles (silver colloid particles) were separated by centrifugation, and the separated silver particles were dispersed in water so that the solid content concentration was 20% by mass. A silver particle aqueous dispersion was prepared as described above.

  As a result of obtaining the particle size d10, particle size d50 and particle size d90 of the silver particles by a dynamic light scattering method using a model nanotrack UPA-EX-150 type particle size measuring machine manufactured by Nikkiso Co., Ltd., silver particles The particle size d10 of the silver particles in the aqueous dispersion is 10 nm (in the range of 2 nm to 20 nm), the particle size d50 is 20 nm, and the particle size d90 is 80 nm (in the range of 50 nm to 1 μm). there were.

3.1.2. White Pigment The white pigment of each example and each comparative example was NanoTek (registered trademark) Slurry (an aqueous dispersion of titanium dioxide particles having a primary average particle size of 100 nm (solid content concentration: 10) obtained from CI Chemical Co., Ltd. Mass%)). When the particle size d50 of NanoTek (registered trademark) Slurry was confirmed by a dynamic light scattering method, a value of 100 nm was obtained.

3.1.3. Ink Composition The ink composition used in each Example and each Comparative Example was prepared using the above silver particle aqueous dispersion and white pigment slurry. Specifically, the above silver particle aqueous dispersion was prepared, and white pigment slurry, glycerin, 1,2-hexanediol, surfactant (BYK-348: Big Chemie (Japan Co., Ltd.) and ion-exchanged water were mixed and sufficiently stirred. Here, in Table 1, about content of silver particle and titanium dioxide, the quantity of solid content except water was described. Table 1 also shows the ratio (%) of the white pigment content to the silver particle content in the ink compositions of the examples and comparative examples.

  Moreover, the particle diameter accumulation curve of the silver particle in the ink composition of each Example and each comparative example was measured using the electron microscope method. At this time, the EDX method was used in combination to distinguish between silver particles and white pigment. The apparatus used for the electron microscope method and the EDX method is one in which an EDX analyzer (EMAX-W: manufactured by Horiba, Ltd.) is mounted on a scanning electron microscope (S-4700: manufactured by Hitachi, Ltd.). The particle size accumulation curve was obtained by randomly selecting 200 silver particles for each ink composition and subjecting them to image processing. As a result, the particle size d10 was about 10 nm and the particle size d90 was about 80 nm, which agreed well with the particle size d10 and the particle size d90 obtained by the dynamic light scattering method in the silver particle aqueous dispersion.

  Moreover, the particle diameter accumulation curve of the silver particle and the white pigment in the ink composition of each Example and each Comparative Example was also confirmed by a centrifugal method. Specifically, each ink composition was filled in a 10 cm-long centrifuge tube and centrifuged at 1000 rpm for 5 hours, and then a 1 cm range at the top of the tube and a 1 cm range at the bottom of the tube were collected. The collected dispersion was measured by the dynamic light scattering method, and the particle size accumulation curves of the silver particles and the white pigment were obtained. As a result, the particle diameter d10 of the silver particles was about 10 nm, the particle diameter d90 was about 80 nm, and the particle diameter d50 of the white pigment was 100 nm.

3.2. Creation of Evaluation Samples The recorded matter of each Example and each Comparative Example was created using an inkjet printer model PX-G930 (manufactured by Seiko Epson Corporation) as an inkjet recording apparatus. The ink compositions of each Example and each Comparative Example were prepared by filling a black ink chamber of a dedicated cartridge of the printer, and mounting the printer on a printer for printing. The recording medium used was photographic paper <glossy> (obtained from Seiko Epson Corporation).

  In any sample, printing was performed with the paper selection set to photo paper gloss, no color correction, photo-1440 dpi, and unidirectional printing as printing conditions. The image was assumed to have a duty changed by 20% from 20% to 100%, and each example and comparative example could be evaluated at each duty.

3.3. Evaluation Method The glossiness and whiteness were evaluated for the obtained samples of each Example and each Comparative Example.

  The glossiness was measured using an MULTI GLOSS 268 gloss meter manufactured by Konica Minolta, Inc. at an incident angle of 20 ° and 60 °. Table 1 shows the measurement results for 20%, 40%, 60%, 80% and 100% duty at incident angles of 20 ° and 60 °. The glossiness is evaluated as A if the glossiness at an incident angle of 60 ° at a duty of 100% is 500 or more, B if it is 300 or more and less than 500, C if it is 200 or more and less than 300, and less than 200. If present, it is described in Table 1 as D. Further, when the glossiness at an incident angle of 20 ° at a duty of 100% is 700 or more, it is A, when it is 400 or more and less than 700, it is B, when it is 200 or more and less than 400, it is C, and when it is less than 200, it is D. The results are shown in Table 1.

  The whiteness was measured using “938 Spectrodensitometer” (manufactured by X-rite). The light source was D50, and the lightness (L *) at duty 20%, 40%, 60%, 80% and 100% was used as an index of whiteness. The evaluation criteria for whiteness are A when L * at a duty of 100% is 30 or more, B when L * is 20 or more and less than 30, C when L * is 15 or more and less than 20, and L * is 15 Those less than D are listed in Table 1 as D.

  Also, in order to evaluate the balance between whiteness and gloss, at each duty, the product of the increase rate of the L * value and the 60 ° gloss (“L * value increase rate) × (60 ° gloss reduction rate)” The value was determined. As a reference for the increase rate of the L * value and the decrease rate of the 60 ° glossiness, Comparative Example 1 containing no titanium dioxide particles was used. That is, “(L * value increase rate) × (60 ° gloss reduction rate)” indicates the degree of improvement in the balance between whiteness and glossiness when Comparative Example 1 is used as a reference.

  The evaluation criteria of “(L * value increase rate) × (60 ° gloss reduction rate)” is A where the maximum value in each duty is 1.3 or more, and the maximum value in each duty is 1.1 or more 1 A value less than .3 was designated as B, a maximum value in each duty of 1 or more and less than 1.1 was designated as C, and a value less than 1.0 was designated as D.

3.4. Evaluation Results As shown in Table 1, the samples of the respective examples using the ink composition having a titanium dioxide content of 1% to 10% with respect to the silver particle content were excellent in both whiteness and gloss. On the other hand, the sample of Comparative Example 1 containing no white pigment had insufficient whiteness. Further, the sample of Comparative Example 2 using an ink composition having a titanium dioxide content of 35% with respect to the silver particle content had good whiteness, but had insufficient glossiness, whiteness and glossiness. It was inferior in the balance of the degree.

  From these results, it was found that according to the ink composition having a titanium dioxide content with respect to the silver particle content of 1% or more and 10% or less, both glossiness and whiteness can be achieved. That is, it has been found that an ink composition having a titanium dioxide content with respect to the silver particle content of 1% or more and 10% or less can form an image having a metallic luster with little coloring (good whiteness).

  On the other hand, the duty dependency of the L * value in each example and each comparative example was examined. FIG. 1 is a graph in which L * values are plotted with respect to duty in the samples of each example and each comparative example. Referring to FIG. 1, in the ink compositions of Examples 2 and 3, the duty is about 20%, and the whiteness improvement (coloring reduction) effect, which is one of the effects of titanium oxide, is remarkably exhibited. It has been found. In addition, it was found that the whiteness of the ink composition of Example 1 was higher than that of Comparative Example 1 in a wide duty range.

  Furthermore, the duty dependence of 60 ° glossiness in each example and each comparative example was examined. FIG. 2 is a graph in which the 60 ° glossiness is plotted against the duty in the samples of the examples and the comparative examples. As shown in FIG. 2, in the ink compositions of Example 2 and Example 3, it was found that the glossiness, which is one of the effects of silver particles, was remarkably exhibited from the duty of about 20%. The ink composition of Example 1 was found to have a good 60 ° glossiness similar to that of Comparative Example 1.

  Similarly, the duty dependence of the 20 ° glossiness in each example and each comparative example was examined. FIG. 3 is a graph in which the 20 ° glossiness is plotted against the duty in the samples of the examples and the comparative examples. From FIG. 3, it was found that in the ink compositions of Example 2 and Example 3, the glossiness, which is one of the effects of silver particles, is remarkably exhibited from the duty of about 20%. In addition, it was found that the ink composition of Example 1 had a good 20 ° glossiness similar to that of Comparative Example 1.

  Further, (L * value increase rate) × (60 ° gloss reduction rate) shown in Table 1 is based on Comparative Example 1, and Comparative Example 1 and Comparative Example 2 both have a balance between whiteness and gloss. This is an example of insufficient. It can be seen that the ink composition of Example 1 has whiteness and gloss relatively close to those of Comparative Example 1 in the high duty range. It can be seen that the value of (L * value increase rate) × (60 ° gloss reduction rate) is particularly good in the samples of No. 20 and 40%. That is, it has been found that when the content of titanium dioxide with respect to the content of silver particles is about 1%, a remarkable effect is exerted in the balance between whiteness and glossiness at a low duty. It was found that the ink composition of Example 1 was practical and had an excellent effect when forming a low duty image.

  The present invention is not limited to the above-described embodiments, and various modifications can be made. 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 (7)

Containing silver particles, white pigment and water,
The particle size d90 in the particle size accumulation curve of the silver particles is 50 nm or more and 1 μm or less,
Including a structure in which the silver particles are dispersed in the water;
The ink composition according to claim 1, wherein a content of the white pigment is 1% or more and 10% or less with respect to a content of the silver particles. In claim 1,
The particle size d10 in the particle size accumulation curve of the silver particles is 2 nm or more and 20 nm or less,
An ink composition having a structure in which the silver particles are dispersed in the water as a dispersed colloid. In claim 1 or claim 2,
An ink composition having a particle size d50 in a particle size accumulation curve of the white pigment of 100 nm or more and 2 μm or less. In any one of Claims 1 to 3,
An ink composition, wherein the water content is 50% by mass or less and 95% by mass or less.   A silver particle, a white pigment, and water, wherein the particle size d90 in the particle size accumulation curve of the silver particle is 50 nm or more and 1 μm or less, the silver particle is dispersed in the water, and the white pigment is contained An image is recorded by ejecting an ink composition having an amount of 1% or more and 10% or less with respect to the content of the silver particles by using an ink jet recording apparatus, and depositing the ink composition on a recording medium. Recording method. In claim 5,
The particle size d10 in the particle size accumulation curve of the silver particles is 2 nm or more and 20 nm or less,
A recording method comprising a structure in which the silver particles are dispersed in the water as a dispersed colloid. In claim 5 or claim 6,
The recording method according to claim 1, wherein a particle diameter d50 in a particle diameter accumulation curve of the white pigment is 100 nm or more and 2 μm or less.

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