JP7655880B2 - Ink composition and its use - Google Patents

Description

The present invention relates to a metallic luster ink composition for metallically decorating various objects to be decorated, and its uses.

Metallic decoration is needed in a wide range of fields, such as interior and exterior parts of automobiles, emblems, electronic devices, cosmetic containers, and golf club shafts, and a high level of metallic luster comparable to that of metal is required to achieve a sense of luxury. In particular, silver has a high light reflectance and therefore a beautiful metallic luster (metallicity, brilliance, and specularity), and is expected to be a metal suitable for advanced design.

Methods for imparting metallic luster to objects to be decorated include foil stamping, vapor deposition, silver mirror plating using the silver mirror reaction, chrome plating, as well as printing or coating with ink that uses aluminum pigment as a luster pigment or ink that contains metal nanoparticles to form a metallic luster layer on the base material.

Foil stamping, vapor deposition, silver mirror plating, and chrome plating can impart a metallic luster close to that of metal, but the manufacturing process is complicated and specialized equipment is required, making these methods disadvantageous in terms of manufacturing costs. Silver mirror plating also suffers from the whitening, cracks, and uneven coloring that are typical of plating, and has a high defect rate due to areas other than the intended plated being plated. Furthermore, chrome plating places a heavy burden on the environment. In contrast to these techniques, methods such as printing and coating using ink are inexpensive to manufacture and can be applied to a wide range of substrates.

Among inks, the metallic luster layer made from ink containing metal nanoparticles has better metallic luster than ink using aluminum pigment (lustrous pigment).

JP 2009-227736 A (Patent Document 1) describes an ink composition for inkjet printing that contains metal colloid particles formed of metal nanoparticles and a dispersant; and a solvent (B), the dispersant containing an organic compound having a carboxyl group and a polymer dispersant. This document also describes that additives such as binder resins (hydrophilic polymers such as polyvinyl alcohol and polyethylene glycol) may be added.

JP 2017-149942 A (Patent Document 2) discloses an ink composition for printing or marking on a substrate, which contains silver nanoparticles, a dispersant having a carboxyl group or a salt thereof, and an aqueous solvent, and contains, in terms of solid content, 100 parts by mass of silver nanoparticles and 1 to 30 parts by mass of a water-soluble or water-dispersible polymer capable of forming a film.

JP 2018-153965 A (Patent Document 3) discloses an image-formed product having a substrate and a metallic gloss layer formed on the substrate, the metallic gloss layer including metal nanoparticles, a polymeric dispersant adsorbed to the surfaces of the metal nanoparticles, and a binder resin, the polymeric dispersant being a compound having an acid value of 1 or more and 80 or less, and the binder resin being a resin having an SP value of 23.0 or more and 26.0 or less. This document discloses that the binder resin is polyvinyl alcohol having a degree of saponification of 72 or more and 85 or less.

JP 2018-145319 A (Patent Document 4) discloses an ink containing water, a water-soluble organic solvent having a boiling point of 250° C. or less, a glittering pigment, first resin particles containing a vinyl polymer, and second resin particles. This document describes a silver colloid particle dispersion as the glittering pigment.

JP 2019-116522 A (Patent Document 5) discloses an ink containing silver particles having a particle diameter Dav90 of 45 nm or less, a polyol, a silicone-based surfactant, and a resin. This document states that the ink contains a water-soluble resin or a water-dispersible resin.

JP 2017-2219 A (Patent Document 6) discloses a composition liquid for forming a silver mirror film layer, which is made of a dispersion solution of silver nanoparticles obtained by dissolving a polymer dispersant in an alcohol solvent and dispersing at least one silver compound selected from silver oxide and silver carbonate in the alcohol solution, and irradiating the alcohol solution with ultrasonic waves.

JP 2009-227736 A JP 2017-149942 A JP 2018-153965 A JP 2018-145319 A JP 2019-116522 A JP 2017-2219 A

However, the inks using metal nanoparticles disclosed in Patent Documents 1 to 6 did not have sufficient silver luster. Furthermore, in these inks, if the amount of resin such as binder is increased, metallic luster (silver luster) cannot be obtained, so in order to obtain high metallic luster, it was necessary to reduce the amount of resin as much as possible. Reducing the amount of resin reduces adhesion to the substrate and abrasion resistance, so it was necessary to use it in combination with a topcoat layer and an undercoat layer. In other words, there is a trade-off between metallic luster and adhesion, so it was difficult to achieve both properties in a simple manner.

Therefore, the object of the present invention is to provide an ink composition having excellent metallic gloss, such as silver gloss, and uses thereof.

As a result of intensive research into achieving the above object, the inventors discovered that it is possible to improve metallic luster, such as silver luster, by combining composite nanoparticles of a metal (including silver) and a protective colloid, a polyvinyl acetal resin, and a solvent, and thus completed the present invention.

That is, the ink composition of the present invention includes a composite nanoparticle (A) of a metal containing silver and a protective colloid, a resin component (B) containing a polyvinyl acetal resin, and a solvent (C). The polyvinyl acetal resin may be a polyvinyl butyral resin. The resin component (B) may further include a second resin. The second resin may be at least one selected from the group consisting of a (meth)acrylic resin, an alkyd resin, an epoxy resin, and a cellulose resin. The mass ratio of the polyvinyl acetal resin to the second resin may be the former/latter = 99/1 to 5/95. The solvent (C) may include at least one selected from the group consisting of an alkylene glycol monoalkyl ether and a dialkylene glycol monoalkyl ether. The ratio of the resin component (B) may be 3 to 150 parts by mass with respect to 100 parts by mass of the metal containing silver of the composite nanoparticle (A). The composite nanoparticles (A) are particles in which a protective colloid is attached or coordinated to the surface of metal nanoparticles containing silver, the average particle size of the metal nanoparticles is 1 to 100 nm, and the protective colloid may contain a polymer dispersant having a carboxyl group or a salt thereof.

The present invention also includes a method for producing a metallic gloss film, which includes a coating step of coating the ink composition on a substrate, and a drying step of drying the coating film formed from the ink composition to obtain a metallic gloss film.

The present invention also includes a metallic gloss film that contains composite nanoparticles (A) of a metal, including silver, and a protective colloid, and a resin component (B) that contains a polyvinyl acetal resin.

In the present invention, a composite nanoparticle of a metal containing silver and a protective colloid, a polyvinyl acetal resin, and a solvent are combined, so that the metallic luster (particularly the silver luster) can be improved. Furthermore, by distributing the metal containing silver unevenly, the amount of the resin component can be increased while maintaining the metallic luster, so that the metallic luster can be achieved simultaneously with adhesion and abrasion resistance. In detail, a metallic luster film can be formed with high adhesion on the object to be decorated without forming a topcoat layer or an undercoat layer, so that adhesion can be improved by a simple method, and abrasion resistance can also be improved. Furthermore, a dense layer can be formed on the film surface with nanoparticles containing silver, so that the light shielding property (non-transmittance) is high, and the metallic luster (mirror surface) can be improved.

FIG. 1 shows a transmission electron microscope (TEM) image of a cross section of the silver gloss film obtained in Example 7. FIG. 2 is an enlarged image of the TEM image of FIG. FIG. 3 shows a TEM image of a cross section of the silver gloss film obtained in Comparative Example 1. FIG. 4 is an enlarged image of the surface area in the TEM image of FIG. FIG. 5 is an enlarged image of the vicinity of the interface with the substrate in the TEM image of FIG. FIG. 6 is an enlarged image of the vicinity of the center of the film thickness in the TEM image of FIG.

[Ink composition]
The mechanism by which a high level of metallic luster, in particular a silver luster (mirror finish), is expressed by containing a polyvinyl acetal-based resin (in particular a polyvinyl butyral-based resin) as a resin component in the ink (or ink composition) of the present invention can be presumed to be as follows.

First, when the resin component contains only polyvinyl acetal resin, it can be assumed that the molecular structure of the polyvinyl acetal resin has an effect. That is, the polyvinyl acetal resin has a hydrophobic group (acetal group such as butyral group, acetyl group) and a hydrophilic group (hydroxyl group) in the molecular chain. When the resin component is only polyvinyl acetal resin, the composite nanoparticles are unevenly distributed in either the hydrophobic group or the hydrophilic group, and thus, on the molecular chain of the polyvinyl acetal resin, there are parts that contain relatively many composite nanoparticles and parts that contain few. That is, on the molecular chain of the polyvinyl acetal resin, a structure similar to a phase separation structure between a dense phase and a sparse phase of composite nanoparticles is generated. As a result, it can be assumed that the phase that contains relatively many composite nanoparticles (highly shielding phase) plays a role of shielding (not transmitting) light, and a high level of metallic luster is expressed.

On the other hand, when the resin component contains a polyvinyl acetal resin as the first resin and a second resin, it can be assumed that the phase separation structure between the resins is influential. That is, when a polyvinyl acetal resin such as a polyvinyl butyral resin is combined with a second resin such as a (meth)acrylic resin, an alkyd resin, or an epoxy resin, the first resin and the second resin undergo phase separation, and the composite nanoparticles are unevenly distributed in one of the phases. Compared to phase separation on the molecular chain of a polyvinyl acetal resin alone, in phase separation by two types of resins, the size of each phase containing a relatively large amount of composite nanoparticles becomes larger. Therefore, compared to when a polyvinyl acetal resin is used alone, even if the amount of resin relative to metals including silver is increased, a light shielding effect (non-transmittance) is obtained, and a high level of metallic luster is obtained. Therefore, when a first resin and a second resin are combined, a large amount of resin can be blended, and adhesion and abrasion resistance can be further improved.

In contrast, the reason why the conventional ink compositions described in Patent Documents 1 to 6 cannot achieve a high level of metallic luster is presumably because the binder component is a single component and the silver particles are uniformly distributed. Furthermore, in conventional ink compositions, when the proportion of the resin component is small (when the amount of the resin component relative to the silver-containing metal is about 10% by mass or less), the gloss is high but the adhesion and abrasion resistance are low, and an overcoat layer and an undercoat layer are often required. On the other hand, when the proportion of the resin component is large (when the amount of the resin component relative to the silver-containing metal is about 10% by mass or more), the adhesion and abrasion resistance are improved but the gloss is reduced. Therefore, in conventional metallic luster inks, the amount of resin relative to the silver-containing metal needs to be kept small, and the amount of the resin component relative to the silver-containing metal is at most about 10% by mass, and it was not possible to improve adhesion and abrasion resistance with a simple structure.

(A) Composite Nanoparticles The ink composition (metallic ink composition) of the present invention contains composite nanoparticles (A) of a metal including silver and a protective colloid.

In the composite nanoparticles (A), the composite form of the silver-containing metal (silver-containing metal) and the protective colloid is not particularly limited, and may be a composite attached or coordinated to the surface of the silver-containing metal nanoparticles, or a composite that coats the surface of the silver-containing metal nanoparticles. Since the silver-containing metal nanoparticles have a high coordination property with the protective colloid (or dispersant), the protective colloid may be coordinated to the surface of the silver-containing metal nanoparticles to coat the silver-containing metal nanoparticles. When the silver-containing metal nanoparticles are composited with the protective colloid, the dispersion stability of the silver-containing metal nanoparticles can be improved, and the affinity with the resin component can be easily adjusted, forming a phase separation structure.

(Silver-containing metal nanoparticles)
The silver-containing metal nanoparticles are nanometer-sized. The number average particle size (number average primary particle size) of the silver-containing metal nanoparticles is, for example, 1 to 100 nm (e.g., 2 to 80 nm), preferably 3 to 70 nm (e.g., 4 to 50 nm), and more preferably 5 to 40 nm (particularly 10 to 30 nm).

The silver-containing metal nanoparticles have the above average particle size and show a wide particle size distribution in the range of 200 nm or less, but may contain almost no coarse particles exceeding 200 nm. Therefore, the maximum primary particle size of the silver-containing metal nanoparticles is, for example, 200 nm or less, preferably 150 nm or less, and more preferably 100 nm or less.

In silver-containing metal nanoparticles, the proportion of particles with a primary particle diameter of 100 nm or more is, by mass, for example, 10% by mass or less (e.g., 0 to 8% by mass), preferably 5% by mass or less (e.g., 0.01 to 3% by mass), and more preferably 1% by mass or less (e.g., 0.02 to 0.5% by mass).

In this application, the particle size and particle size distribution of silver-containing metal nanoparticles can be measured using a transmission electron microscope, and the average particle size is shown as the average value of any 10 particles.

(Metals including silver)
The metal containing silver (silver-containing metal) may be silver alone or an alloy of silver and other metals. The other metals are not particularly limited as long as they can be alloyed with silver, and examples thereof include Cr, Mo, W, Ni, Pd, Pt, Cu, Au, Zn, In, Sn, and Pb. These other metals can be used alone or in combination of two or more. Among these other metals, Cu is preferred.

The proportion of silver in the silver-containing metal may be 50% by mass or more, for example 90% by mass or more, preferably 95% by mass or more, even more preferably 97% by mass or more, even more preferably 99% by mass or more, and most preferably 100% by mass (silver alone). If the proportion of silver is too low, there is a risk of the metallic gloss decreasing.

When the silver-containing metal is a combination of silver and another metal (especially copper), the ratio of the other metal is, for example, 0.01 to 10 parts by mass, preferably 0.03 to 5 parts by mass, and more preferably 0.05 to 3 parts by mass, per 100 parts by mass of silver.

(Protective colloid)
The protective colloid may be a dispersant, and is often a non-volatile dispersant. In particular, the protective colloid preferably contains a polymer dispersant having a carboxyl group or a derivative group. In this application, the carboxyl group also includes a carboxyl group in the form of an acid anhydride group.

The polymer dispersant (or polymer-type dispersant) may be an amphiphilic polymer dispersant (or oligomer-type dispersant) as long as it has at least a carboxyl group and is capable of dispersing silver-containing metal nanoparticles.

Examples of the polymer dispersant include those that are typically used to disperse colorants in the fields of paints and inks. Representative polymer dispersants (amphiphilic polymer dispersants) include water-soluble or water-dispersible resins that contain hydrophilic units (or hydrophilic blocks) formed from hydrophilic monomers.

Examples of the hydrophilic monomer include addition polymerizable monomers such as carboxyl group-containing monomers (unsaturated polyvalent carboxylic acids such as (meth)acrylic acid, maleic acid, maleic anhydride, or the like, or their acid anhydrides), monomers having a sulfo group (styrene sulfonic acid, etc.), and hydroxyl group-containing monomers (hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, vinylphenol, etc.); and condensation polymerizable monomers such as ethylene oxide. The condensation polymerizable monomers may form hydrophilic units (or blocks) by reacting with active hydrogen such as a hydroxyl group (e.g., the hydroxyl group). The hydrophilic monomers may form hydrophilic units (or blocks) alone or in combination of two or more. Preferred hydrophilic monomers are (meth)acrylic acid, maleic acid, maleic anhydride, and ethylene oxide.

The polymer dispersant only needs to have at least a carboxyl group, and may have a functional group of the hydrophilic monomer, such as an acid group (sulfo group) or a hydroxyl group. These functional groups may be introduced into the polymer dispersant alone or in combination of two or more.

The polymeric dispersant may contain at least a hydrophilic unit (or a hydrophilic block) and may be a homo- or copolymer of a hydrophilic monomer (e.g., polyacrylic acid or a salt thereof) or a copolymer of a hydrophilic monomer and a hydrophobic monomer. Examples of hydrophobic monomers (nonionic monomers) include (meth)acrylic monomers such as (meth)acrylic esters [C 1-20 alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, 2 _- ethylhexyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate, cycloalkyl (meth)acrylates such as cyclohexyl (meth)acrylate, aryl (meth)acrylates such as phenyl (meth)acrylate, and aralkyl (meth)acrylates such as benzyl (meth)acrylate and 2-phenylethyl (meth)acrylate]; styrene-based monomers such as styrene, α-methylstyrene, and vinyltoluene; olefin-based monomers such as α-C _2-20 olefins (ethylene, propylene, 1-butene, isobutylene, 1-hexene, 1-octene, and 1-dodecene); addition-polymerizable monomers such as vinyl carboxylate ester-based monomers such as vinyl acetate and vinyl butyrate; and C monomers such as propylene oxide. Examples of the hydrophobic monomer include condensation polymerizable monomers such as _3-6 alkylene oxide. The hydrophobic monomer may be used alone or in combination of two or more kinds to constitute the hydrophobic unit.

The polymer dispersant of a copolymer (e.g., a copolymer of a hydrophilic monomer and a hydrophobic monomer) may be a random copolymer, an alternating copolymer, a block copolymer (e.g., a copolymer composed of a hydrophilic block composed of a hydrophilic monomer and a hydrophobic block composed of a hydrophobic monomer), a comb copolymer (or a comb graft copolymer), or the like. The structure of the block copolymer is not particularly limited, and may be a diblock structure, a triblock structure (ABA type, BAB type), or the like. In the comb copolymer, the main chain may be formed of the hydrophilic block or the hydrophobic block, or may be formed of a hydrophilic block and a hydrophobic block. A block copolymer of a hydrophilic block and a hydrophobic block can also improve metallic gloss.

As described above, the hydrophilic unit can also be formed of a hydrophilic block (polyalkylene oxide such as polyethylene oxide, etc.). The hydrophilic block (polyalkylene oxide, etc.) and the hydrophobic block (polyolefin block, etc.) may be bonded via a linking group such as an ester bond, an amide bond, an ether bond, or a urethane bond. These bonds may be formed, for example, by modifying the hydrophobic block (polyolefin, etc.) with a modifying agent [unsaturated carboxylic acid or its anhydride (maleic anhydride, etc.), lactam or aminocarboxylic acid, hydroxylamine, diamine, etc.] and then introducing a hydrophilic block. In addition, a comb copolymer (a comb copolymer whose main chain is composed of a hydrophobic block) may be formed by reacting (or bonding) a polymer obtained from a monomer having a hydrophilic group such as a hydroxyl group or a carboxyl group (such as the hydroxyalkyl (meth)acrylate) with the condensation-type hydrophilic monomer (such as ethylene oxide).

Furthermore, the balance between hydrophilicity and hydrophobicity may be adjusted by using a hydrophilic nonionic monomer as a copolymerization component. Examples of such components include monomers or oligomers having an ethyleneoxy unit, such as 2-(2-methoxyethoxy)ethyl (meth)acrylate and polyethylene glycol mono(meth)acrylate (e.g., number average molecular weight 200 to 1,000). The balance between hydrophilicity and hydrophobicity may also be adjusted by modifying (e.g., esterifying) a hydrophilic group (such as a carboxyl group).

In polymeric dispersants having carboxyl groups, the carboxyl groups may be salts or acid anhydride groups. For example, at least some of the carboxyl groups may form salts (salts with amines, metal salts, etc.), but polymeric dispersants in which acid groups such as carboxyl groups do not form salts [i.e., polymeric dispersants having free carboxyl groups] are preferably used.

The acid value of the polymer dispersant having a carboxyl group may be, for example, 1 mgKOH/g or more (e.g., 2 to 100 mgKOH/g), preferably 3 mgKOH/g or more (e.g., 4 to 90 mgKOH/g), more preferably 5 mgKOH/g or more (e.g., 6 to 80 mgKOH/g), and more preferably 7 mgKOH/g or more (e.g., 8 to 50 mgKOH/g), and is usually 3 to 30 mgKOH/g (particularly 5 to 20 mgKOH/g). In addition, in such a polymer dispersant, the amine value may be 0 (or almost 0).

In addition, in the polymer dispersant, the position of the functional group is not particularly limited, and it may be located in the main chain, the side chain, or both the main chain and the side chain. Such a functional group may be, for example, a functional group derived from a hydrophilic monomer or a hydrophilic unit (for example, a functional group introduced by copolymerization of (meth)acrylic acid, maleic anhydride, ethylene oxide, etc.).

The polymer dispersants having carboxyl groups may be used alone or in combination of two or more.

As the polymer dispersant, a polymer dispersant (high molecular weight pigment dispersant) described in JP-A-2004-207558 or the like may be used. The polymer dispersant may be synthesized or a commercially available product may be used. Specific examples of commercially available polymer dispersants (or dispersants composed of at least an amphipathic dispersant) include the Solsperse series (manufactured by Avecia Co., Ltd.) such as Solsperse 13240, Solsperse 13940, Solsperse 32550, Solsperse 31845, Solsperse 24000, Solsperse 26000, Solsperse 27000, Solsperse 28000, and Solsperse 41090; Disperbyk 160, Disperbyk 161, Disperbyk 16 2, Disperbyk series such as Disperbyk 163, Disperbyk 164, Disperbyk 166, Disperbyk 170, Disperbyk 180, Disperbyk 182, Disperbyk 184, Disperbyk 190, Disperbyk 191, Disperbyk 192, Disperbyk 193, Disperbyk 194, Disperbyk 2001, Disperbyk 2015, and Disperbyk 2050 [manufactured by BYK-Chemie Co., Ltd.]; EFKA -46, EFKA-47, EFKA-48, EFKA-49, EFKA-1501, EFKA-1502, EFKA-4540, EFKA-4550, Polymer 100, Polymer 120, Polymer 150, Polymer 400, Polymer 401, Polymer 402, Polymer 403, Polymer 450, Polymer 451, Polymer 452, Polymer 453 [manufactured by EFKA Chemical Co., Ltd.]; Ajisper PB711, Ajisper PAl11, Ajisper PB811, Ajisper PB821, Ajisper Examples of the Ajisper series, such as Spar PW911 (manufactured by Ajinomoto Co., Inc.); the Floren series, such as Floren DOPA-158, Floren DOPA-22, Floren DOPA-17, Floren TG-700, Floren TG-720W, Floren-730W, Floren-740W, and Floren-745W (manufactured by Kyoeisha Chemical Co., Ltd.); and the Joncryl series, such as Joncryl 678, Joncryl 679, and Joncryl 62 (manufactured by Johnson Polymer Co., Ltd.). Representative polymer dispersants include Disperbyk 190, Disperbyk 194, and Disperbyk 2015.

The number average molecular weight of the polymer dispersant, as measured by gel permeation chromatography (GPC), is, in terms of polystyrene, for example, 1,500 to 100,000, preferably 2,000 to 80,000 (e.g., 2,000 to 60,000), more preferably 3,000 to 50,000 (e.g., 5,000 to 30,000), and even more preferably 7,000 to 20,000.

The polymer dispersant having a carboxyl group may be a polymer dispersant that does not have a hydroxyl group.

The proportion of protective colloid is, for example, 0.1 to 100 parts by weight (particularly 1 to 50 parts by weight) relative to 100 parts by weight of silver-containing metal. The proportion of polymer dispersant having carboxyl groups can be selected from the range of, for example, about 0.1 to 60 parts by weight (e.g., 1 to 50 parts by weight) relative to 100 parts by weight of silver-containing metal, and is usually 2 to 40 parts by weight (e.g., 2.5 to 30 parts by weight), more preferably 3 to 25 parts by weight (particularly 5 to 20 parts by weight).

In this application, the proportion of protective colloid in the composite nanoparticle (A) can be measured by a conventional method, for example, thermal analysis (for example, simultaneous thermogravimetry/differential thermal analysis, etc.).

The protective colloid may contain other dispersants, if necessary, which may be inorganic compounds, but are usually organic compounds. Examples of other dispersants include alkanols (C _6-20 alkane monools such as hexanol, octanol, decanol, dodecanol, and octadecanol), aldehydes (C _6-20 aliphatic aldehydes such as caprylaldehyde, laurylaldehyde, and palmitaldehyde), aliphatic hydroxycarboxylic acids, higher fatty acids or salts thereof, and sulfonic acids (arenesulfonic acids such as alkane sulfonic acid, benzene sulfonic acid, and toluene sulfonic acid). These other dispersants may be used alone or in combination of two or more.

The proportion of the other dispersant is, for example, 0.1 to 100 parts by mass, preferably 0.5 to 50 parts by mass, and more preferably 1 to 30 parts by mass, relative to 100 parts by mass of the polymer dispersant.

The method for producing the composite nanoparticles is not particularly limited, and can be a conventional method. For example, when the silver-containing metal is simple silver, the silver nanoparticles can be prepared by reducing a silver compound corresponding to the silver nanoparticles in a solvent in the presence of a protective colloid and a reducing agent. Specific examples of the production method include the methods described in JP-A-2010-80442 and JP-A-2010-229544.

Resin Component (B) The ink composition of the present disclosure contains a resin component containing a polyvinyl acetal resin as a first resin. The resin component (B) may contain only the first resin, or may contain the first resin and the second resin.

(B1) First Resin The first resin, a polyvinyl acetal resin, is obtained by reacting (acetalization reaction) polyvinyl alcohol obtained by saponifying polyvinyl acetate with an aldehyde (particularly, n-butylaldehyde). In the acetalization reaction, polyvinyl alcohol cannot be completely acetalized (particularly butyralized), so hydroxyl groups remain, and a small amount of acetyl groups remain during saponification, so the polyvinyl acetal resin has acetal groups, hydroxyl groups, and acetyl groups in its constituent units.

That is, the polyvinyl acetal resin of the present invention contains, as constituent units, a vinyl acetal unit represented by the following formula (1), a vinyl alcohol unit represented by the following formula (2), and a vinyl ester unit represented by the following formula (3).

(wherein R is a hydrogen atom or a hydrocarbon group).

In the formula (1), the hydrocarbon group represented by R includes an alkyl group, a cycloalkyl group, and an aryl group. Examples of the alkyl group include linear or branched C 1-10 alkyl groups such as a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, a t-butyl group, a hexyl group, a 2-ethyl-butyl group, an octyl group, a 2 _- ethylhexyl group, and a nonyl group. Examples of the cycloalkyl group include a C _5-10 cycloalkyl group such as a hexyl group. Examples of the aryl group include a C _6-10 aryl group such as a phenyl group. As R, these hydrocarbon groups and hydrogen atoms can be used alone or in combination of two or more kinds.

Of these, R is preferably a hydrogen atom or an alkyl group, more preferably a linear or branched _C1-5 alkyl group, even more preferably a linear _C2-4 alkyl group, and most preferably a propyl group. That is, the polyvinyl acetal resin is preferably a polyvinyl butyral resin (butyral resin).

The polyvinyl acetal resin may further contain other structural units in addition to the structural units represented by the formulas (1) to (3). The other structural units may be units derived from copolymerizable monomers having a radical polymerizable group.

Examples of the copolymerizable monomer include C _3-8 alkanoic acid vinyl esters such as vinyl propionate, vinyl butyrate, vinyl pivalate, and vinyl caproate; C 1-6 alkyl vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, and n-butyl vinyl ether; α-C _2-6 olefins such as ethylene, propylene, 1-butene, isobutene, and 1 _- hexene; (meth)acrylic acid and its salts; (meth)acrylic acid C _1-6 alkyl esters such as methyl (meth)acrylate, ethyl (meth)acrylate, and propyl (meth)acrylate; (meth)acrylamide; and unsaturated sulfonic acids such as ethylenesulfonic acid and allylsulfonic acid. These copolymerizable monomers can be used alone or in combination of two or more.

The polyvinyl acetal resin may also be a polyvinyl acetal resin that has been modified or denatured by a conventional method.

The proportion of the units represented by the formula (1) in the polyvinyl acetal resin (acetalization degree) is about 5 to 95 mol% (e.g., 10 to 90 mol%), and may be, for example, 20 to 90 mol%, preferably 30 to 85 mol%, depending on the application, and may be 50 mol% or more (e.g., 50 to 90 mol%), preferably 60 mol% or more (e.g., 60 to 85 mol%), and more preferably 70 mol% or more (e.g., 70 to 80 mol%). The acetalization degree may be, for example, 9 to 98 mass%, preferably 25 to 95 mass%, and more preferably 35 to 90 mass%, and is 55 mass% or more (e.g., 55 to 95 mass%), preferably 65 mass% or more (e.g., 65 to 90 mass%), and more preferably 70 mass% or more (e.g., 70 to 80 mass%). If the degree of acetalization is too low, the metallic gloss may decrease, and if it is too high, it may become difficult to prepare the polyvinyl acetal resin.

The proportion of the units represented by the formula (2) in the polyvinyl acetal resin (units having a hydroxyl group) may be 10 to 50 mol% (e.g., 15 to 40 mol%), preferably 20 to 35 mol%, and more preferably 23 to 27 mol%. The proportion of the units represented by the formula (2) in the polyvinyl acetal resin may be 5 to 40 mass% (e.g., 12 to 30 mass%), preferably 15 to 25 mass%, and more preferably 18 to 23 mass%. If the proportion of the units represented by the formula (2) is too small, there is a risk of a decrease in metallic gloss when the polyvinyl acetal resin is used alone as a resin component, and conversely, if the proportion is too large, the same applies.

The proportion of the units represented by the formula (3) (units having an acetyl group) in the polyvinyl acetal resin is, for example, 15 mol% or less, preferably 10 mol% or less, and more preferably 5 mol% or less. The proportion of the units represented by the formula (3) in the polyvinyl acetal resin is, for example, 20 mass% or less, preferably 10 mass% or less, and more preferably 5 mass% or less. If the proportion of the units represented by the formula (3) is too high, there is a risk of a decrease in metallic gloss.

The total proportion of the structural units represented by the formulas (1) to (3) in the polyvinyl acetal resin is, for example, 80 mol% or more, preferably 90 mol% or more, more preferably 95 mol% or more, and even more preferably 100 mol%.

The proportion of copolymerizable monomers in the polyvinyl acetal resin is, for example, 20 mol% or less, preferably 10 mol% or less, and more preferably 5 mol% or less.

In this application, the degree of acetalization of polyvinyl acetal resins and the proportion of each unit can be measured using conventional methods, such as titration, IR elemental analysis, and NMR. In the case of butyral resins, the degree of acetalization can be measured using a method conforming to JIS K 6728 "Testing methods for polyvinyl butyral."

The weight average molecular weight of the polyvinyl acetal resin (particularly the butyral resin) is, for example, 3,000 to 300,000, preferably 5,000 to 100,000, further preferably 7,000 to 70,000, even more preferably 10,000 to 40,000, and most preferably 12,000 to 20,000. If the molecular weight is too small, the metallic luster and mechanical properties of the metallic luster film may be reduced, and conversely, if it is too high, the film formability may be reduced.

In this application, the weight average molecular weight of the polyvinyl acetal resin is a value calculated based on the molecular weight of standard polystyrene from a chromatogram measured by gel permeation chromatography (GPC) in accordance with the method described in JIS K 0124-2011.

The glass transition temperature of polyvinyl acetal resins (particularly butyral resins) can be selected from the range of about 50 to 130°C, for example 60 to 125°C, preferably 70 to 120°C, further preferably 80 to 115°C, even more preferably 90 to 115°C, and most preferably 100 to 110°C. If the glass transition temperature is too low, the metallic luster and mechanical properties of the metallic luster film may be reduced, and conversely, if it is too high, film formability may be reduced.

In this application, the glass transition temperature of the polyvinyl acetal resin can be measured using a differential scanning calorimeter (DSC).

The viscosity of a 10% by weight solution of polyvinyl acetal resin (particularly butyral resin) (solvent: toluene/ethanol (mass ratio) = 50/50) when measured at a temperature of 20°C using a rotational viscosity type (BM type) can be selected from a range of about 2 to 20,000 mPa·s (particularly 10 to 10,000 mPa·s), and depending on the application, it may be, for example, 5 to 1,000 mPa·s (e.g. 10 to 500 mPa·s), preferably 20 to 400 mPa·s (e.g. 25 to 300 mPa·s), and more preferably 50 to 250 mPa·s (e.g. 70 to 200 mPa·s), or, for example, 3 to 150 mPa·s (e.g. 5 to 100 mPa·s), preferably 10 to 50 mPa·s (especially 10 to 30 mPa·s). If the viscosity is too low, the metallic luster and mechanical properties of the metallic luster film may be reduced, and conversely, if the viscosity is too high, the film-forming properties may be reduced.

(B2) Second Resin The second resin (B2) is not particularly limited as long as it is a resin that can be phase-separated from the first resin, but is preferably at least one selected from the group consisting of (meth)acrylic resins, alkyd resins, epoxy resins, and cellulose resins.

((Meth)acrylic resin)
The (meth)acrylic resin is not particularly limited, and may be, for example, a homopolymer or copolymer of a (meth)acrylic monomer, a (meth)acrylic polyol, or a modified (meth)acrylic resin.

Examples of the (meth)acrylic monomer include (meth)acrylic acid, C 1-20 alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, 2 _- ethylhexyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate, cycloalkyl (meth)acrylates such as cyclohexyl (meth)acrylate, aryl (meth)acrylates such as phenyl (meth)acrylate, aralkyl (meth)acrylates such as benzyl (meth)acrylate and 2-phenylethyl (meth)acrylate, and hydroxy C _1-4 alkyl (meth)acrylates such as hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate. These (meth)acrylic monomers can be used alone or in combination of two or more. Of these, preferred are C _1-4 alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, and butyl (meth)acrylate; and hydroxy C _2-3 alkyl (meth)acrylates such as hydroxyethyl (meth)acrylate.

The (meth)acrylic resin may be a homopolymer of these monomers, but a copolymer is preferred. The copolymer may be a copolymer of two or more of the (meth)acrylic monomers, or may be a copolymer of the (meth)acrylic monomer and a copolymerizable monomer. Examples of the copolymerizable monomer include styrene-based monomers such as styrene, α-methylstyrene, and vinyltoluene; olefin-based monomers such as α-C _2-20 olefins (ethylene, propylene, 1-butene, isobutylene, 1-hexene, 1-octene, 1-dodecene, etc.); and addition-polymerizable monomers such as vinyl carboxylate ester-based monomers such as vinyl acetate and vinyl butyrate. These copolymerizable monomers can be used alone or in combination of two or more. Of these, styrene-based monomers such as styrene are preferred.

When the (meth)acrylic resin is a copolymer of a (meth)acrylic monomer and a styrene monomer (particularly, a copolymer of a methacrylic monomer and a styrene monomer), the molar ratio of the (meth)acrylic monomer to the styrene monomer (former/latter) is 95/5 to 5/95, preferably 90/10 to 10/90, more preferably 80/20 to 20/80, and even more preferably 70/30 to 30/70.

The (meth)acrylic polyol is not particularly limited as long as it is a (meth)acrylic polymer having two or more hydroxyl groups in the molecule, and may be, for example, a (meth)acrylic resin containing a hydroxy C _2-3 alkyl (meth)acrylate as a monomer of the (meth)acrylic resin.

Examples of modified (meth)acrylic resins include polyester-modified (meth)acrylic resins such as polyester (meth)acrylate, polyurethane-modified (meth)acrylic resins such as urethane (meth)acrylate, epoxy-modified (meth)acrylic resins such as epoxy (meth)acrylate, and silicone-modified (meth)acrylic resins such as silicone (meth)acrylate. These modified (meth)acrylic resins can be used alone or in combination of two or more.

These (meth)acrylic resins can be used alone or in combination of two or more. Among these, (meth)acrylic resins having hydroxyl groups are preferred, and (meth)acrylic resins having hydroxyl groups and styrene units (e.g., methyl (meth)acrylate-styrene copolymers, etc.) are particularly preferred, because they have a high affinity for silver-containing metal nanoparticles (especially composite nanoparticles (A)) and are easily cured with a curing agent depending on the application. The position of the hydroxyl group is not particularly limited, and may be in the main chain, in the side chain, or in the main chain and in the side chain.

The hydroxyl value of the (meth)acrylic resin may be, for example, 1 mgKOH/g or more (e.g., 2 to 400 mgKOH/g), preferably 3 mgKOH/g or more (e.g., 4 to 300 mgKOH/g), more preferably 5 mgKOH/g or more (e.g., 6 to 200 mgKOH/g), and more preferably 7 mgKOH/g or more (e.g., 8 to 150 mgKOH/g), and is usually 10 to 150 mgKOH/g (particularly 50 to 100 mgKOH/g). If the hydroxyl value is too low, the metallic gloss and the mechanical properties of the metallic gloss film may decrease, and conversely, if the hydroxyl value is too high, the metallic gloss may decrease.

In this application, the hydroxyl value of the (meth)acrylic resin can be measured by a conventional method, for example, neutralization titration.

The weight average molecular weight of the (meth)acrylic resin is, for example, 1,000 to 100,000, preferably 2,000 to 80,000 (e.g., 3,000 to 50,000), more preferably 5,000 to 30,000 (e.g., 10,000 to 20,000), and even more preferably 12,000 to 16,000. If the molecular weight is too small, the mechanical properties of the metallic gloss film may be reduced, and conversely, if it is too high, the film formability may be reduced.

In this application, the weight average molecular weight of the (meth)acrylic resin is a value calculated from a chromatogram measured by gel permeation chromatography (GPC) based on the molecular weight of standard polystyrene.

The glass transition temperature of the (meth)acrylic resin is, for example, 0 to 120°C, preferably 40 to 110°C, more preferably 50 to 100°C, and most preferably 60 to 90°C. If the glass transition temperature is too low, the mechanical properties of the metallic gloss film may be reduced, and conversely, if it is too high, the film formability may be reduced.

In this application, the glass transition temperature of the (meth)acrylic resin can be measured using a differential scanning calorimeter.

The (meth)acrylic resin may be a (meth)acrylic resin that does not have a carboxyl group or a salt thereof.

The proportion of the (meth)acrylic resin, calculated as solid content, is, for example, 1 to 50 parts by mass, preferably 3 to 40 parts by mass, more preferably 5 to 30 parts by mass, even more preferably 10 to 25 parts by mass, and most preferably 15 to 20 parts by mass, per 100 parts by mass of the silver-containing metal in the composite nanoparticle (A). If the proportion of the (meth)acrylic resin is too low, there is a risk of reduced adhesion and abrasion resistance, and if the proportion is too high, there is a risk of reduced metallic gloss.

(Alkyd resin)
The alkyd resin is a conventional alkyd resin used in the paint field and the like, and may be, for example, a short oil alkyd resin, a long oil alkyd resin, a modified alkyd resin, an isocyanate-cured alkyd resin, an epoxy ester resin (epoxy-modified alkyd resin), an alkyd polyol, an oil-free alkyd resin, or the like.

Specific alkyd resins may be, for example, synthetic resins as defined in JIS K 5500 "Paint Terminology", that is, synthetic resins obtained by condensation polymerization of polybasic acid and oil components with polyols (polyhydric alcohols).

Examples of polybasic acids include aromatic dibasic acids such as phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, and 5-sodium sulfoisophthalic acid; alicyclic dibasic acids such as tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, and 1,4-cyclohexanedicarboxylic acid; aliphatic dibasic acids such as succinic acid, succinic anhydride, alkenylsuccinic acid, alkenylsuccinic anhydride, fumaric acid, maleic acid, maleic anhydride, itaconic acid, adipic acid, sebacic acid, azelaic acid, himic acid, and himic acid anhydride; and trifunctional or higher polybasic acids such as trimellitic acid, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, methylcyclohexene tricarboxylic acid, methylcyclohexene tricarboxylic acid anhydride, and benzophenone tetracarboxylic acid.

These polybasic acids can be used alone or in combination of two or more. Among these, aromatic dicarboxylic acids such as isophthalic acid and terephthalic acid are commonly used.

The oil component (oil and fat component) includes fatty oils (oils and fats) and/or fatty acids.

Examples of fatty oils include vegetable oils such as cottonseed oil, linseed oil, tung oil, castor oil, dehydrated castor oil, safflower oil, soybean oil, rice oil, corn oil, sesame oil, sunflower oil, rice sugar oil, asami oil, rapeseed oil, peanut oil, coconut oil, palm oil, kapok oil, almond oil, olive oil, tall oil, and oyster oil; animal oils such as beef tallow, lard, mutton tallow, goat tallow, horse tallow, chicken tallow, and turkey tallow; fish oils such as herring oil, flounder oil, cod oil, sole oil, halibut oil, carp oil, trout oil, and catfish oil; and hydrogenated oils of these. These oils and fats can be used alone or in combination of two or more.

Examples of fatty acids include linear or branched saturated C _8-24 fatty acids such as caprylic acid, capric acid, pelargonic acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, arachidic acid, and behenic acid; linear or branched unsaturated C _8-24 fatty acids such as myristoleic acid, palmitoleic acid, petroselinic acid, oleic acid, vaccenic acid, linoleic acid, linolenic acid, eleostearic acid, gadoleic acid, arachidonic acid, and erucic acid. These fatty acids may have a substituent such as a hydroxyl group. Examples of fatty acids having a hydroxyl group include ricinoleic acid, savinic acid, and dioxystearic acid, which are the main components of castor oil. The fatty acid may be a fatty acid obtained by saponification of the fatty oil, such as a hygienic fatty acid obtained from dehydrated castor oil, or a fatty acid obtained from linseed oil, tung oil, dehydrated castor oil, soybean oil, safflower oil, etc. (e.g., linseed oil fatty acid, tung oil fatty acid, dehydrated castor oil fatty acid, soybean oil fatty acid, safflower oil fatty acid, etc.) These fatty acids may be used alone or in combination of two or more.

Of these oil components, preferred are vegetable oils such as linseed oil, tung oil, dehydrated castor oil, soybean oil, and safflower oil; fatty acids derived from these vegetable oils; saturated _C10-22 fatty acids such as stearic acid; and unsaturated _C10-22 fatty acids such as oleic acid, linoleic acid, linolenic acid, stearic acid, eleostearic acid, and ricinoleic acid.

Examples of polyols include diols such as ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, 2-methyl-1,8-octanediol, neopentyl glycol, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, tetramethylene glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, hydrogenated bisphenol A, and 2-butyl-2-ethyl-1,3-propanediol; triols such as glycerin, trimethylolpropane, and trimethylolethane; polyols having tetrafunctional or more functional groups such as pentaerythritol, diglycerin, ditrimethylolpropane, ditrimethylolethane, tris(2-hydroxyethyl)isocyanurate, and dipentaerythritol; and polyhydric alcohols that have been used in alkyd resins.

These polyols can be used alone or in combination. Among these, aliphatic polyols such as glycerin, trimethylolpropane, pentaerythritol, and dipentaerythritol are commonly used.

In addition to the oil component and polyol, the alkyd resin may further contain monobasic acids such as benzoic acid, p-t-butylbenzoic acid, abietic acid, and hydrogenated abietic acid.

The hydroxyl value of the alkyd resin is, for example, 5 to 500 mgKOH/g, preferably 10 to 300 mgKOH/g, more preferably 20 to 200 mgKOH/g, and even more preferably 50 to 150 mgKOH/g. If the hydroxyl value is too small, the metallic gloss and the mechanical properties of the metallic gloss film may decrease, and conversely, if the hydroxyl value is too high, the metallic gloss may decrease.

In this application, the hydroxyl value of the alkyd resin can be measured in accordance with ISO 4629 (2).

The acid value of the alkyd resin is, for example, 0.5 to 30 mgKOH/g, preferably 1 to 20 mgKOH/g, more preferably 2 to 15 mgKOH/g, and even more preferably 3 to 8 mgKOH/g. If the acid value is too low, the metallic gloss may decrease, and conversely, if it is too high, the metallic gloss and the mechanical properties of the metallic gloss film may decrease.

In this application, the acid value of the alkyd resin can be measured in accordance with JIS K 5601-1-2.

The weight average molecular weight of the alkyd resin is, for example, 500 to 30,000, preferably 1,000 to 20,000, and more preferably 2,000 to 10,000. If the molecular weight is too small, the mechanical properties of the metallic gloss film may be reduced, and conversely, if it is too high, the film formability may be reduced.

In this application, the weight average molecular weight of the alkyd resin is a value calculated based on the molecular weight of standard polystyrene from a chromatogram measured by gel permeation chromatography (GPC).

(Epoxy resin)
The epoxy resin may be a compound having two or more epoxy groups in the molecule. The epoxy resin includes glycidyl ether type epoxy resin, glycidyl amine type epoxy resin, glycidyl ester type epoxy resin, etc. Among these, glycidyl ether type epoxy resin is widely used.

Examples of glycidyl ether type epoxy resins include bisphenol A type epoxy resins, bisphenol F type epoxy resins, biphenyl type epoxy resins, cresol novolac type epoxy resins, phenol novolac type epoxy resins, bisphenol A novolac type epoxy resins, alcohol ether type epoxy resins, tetrabromobisphenol A type epoxy resins, and naphthalene type epoxy resins.

These epoxy resins can be used alone or in combination. Of these, bisphenol-type epoxy resins such as bisphenol A-type epoxy resins are preferred.

The epoxy equivalent of the epoxy resin is, for example, 100 to 5,000 g/eq, preferably 300 to 3,000 g/eq, more preferably 500 to 1,500 g/eq, and even more preferably 700 to 1,000 g/eq. If the epoxy equivalent of the epoxy resin is too small, the mechanical properties of the metallic gloss film may be reduced, and conversely, if it is too high, the metallic gloss may be reduced.

In this application, epoxy equivalent is defined as "the mass of an epoxy resin containing one equivalent of epoxy groups" and can be measured in accordance with JIS K 7236.

The number average molecular weight of the epoxy resin is, for example, 5,000 to 100,000, preferably 7,000 to 70,000, more preferably 10,000 to 40,000, and even more preferably 12,000 to 20,000. If the molecular weight is too small, the mechanical properties of the metallic gloss film may be reduced, and conversely, if it is too high, the film formability may be reduced.

In this application, the number average molecular weight of the epoxy resin can be measured in accordance with the method described in JIS K 0124-2011, and is a value calculated based on the molecular weight of standard polystyrene from a chromatogram measured by gel permeation chromatography (GPC).

The softening point of the epoxy resin, measured according to a method in accordance with JIS K 7234, is 30 to 150°C, preferably 50 to 130°C, more preferably 70 to 120°C, and even more preferably 90 to 100°C. If the softening point is too low, the mechanical properties of the metallic gloss film may be reduced, and conversely, if it is too high, film formability may be reduced.

In this application, the softening point of the epoxy resin is the temperature measured when the sample encasing the sphere comes into contact with the bottom plate of the ring stand, based on the ring and ball method of JIS K 7234, by filling a specified ring with a sample, supporting it horizontally in a water bath or glycerin bath, placing a specified ball in the center of the sample, and raising the bath temperature at a rate of 5°C per minute.

(Cellulosic resin)
The cellulose-based resin is not particularly limited, but may be, for example, a cellulose derivative such as a cellulose ester.

Examples of cellulose derivatives include cellulose esters, cellulose ethers, and cellulose ether esters. Examples of cellulose esters include inorganic cellulose esters such as nitrocellulose, cellulose sulfate, and cellulose phosphate; organic cellulose esters such as cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, and cellulose acetate propionate butyrate. Examples of cellulose ethers include cellulose alkyl ethers such as methylcellulose and ethylcellulose; carboxyalkyl celluloses such as carboxymethylcellulose; and hydroxyalkyl celluloses such as hydroxymethylcellulose, hydroxyethyl cellulose, and hydroxypropylmethylcellulose. Examples of cellulose ether esters include cellulose ether esters such as carboxymethylcellulose acetate, carboxymethylcellulose propionate, and carboxymethylcellulose butyrate.

These cellulose derivatives can be used alone or in combination. Among these, cellulose organic acid esters are preferred, cellulose acylate is more preferred, cellulose _C2-4 acylate is even more preferred, and cellulose acetate _C3-4 acylate is most preferred. The cellulose organic acid esters may be produced by reacting cellulose with an organic acid and/or an acid anhydride, and in particular, may be produced by triesterifying cellulose with an organic acid and/or an acid anhydride, followed by hydrolysis.

The ester substitution degree of the cellulose acylate is, for example, 30 to 70 mass%, preferably 35 to 60 mass%, further preferably 40 to 55 mass%, and even more preferably 45 to 50 mass%. The acetyl substitution degree of the cellulose acetate C _3-4 acylate is, for example, 0.5 to 30 mass%, preferably 1 to 10 mass%, and the C _3-4 acyl substitution degree is, for example, 15 to 60 mass%, preferably 30 to 50 mass%.

The number average molecular weight of the cellulose resin is, for example, 1,000 to 100,000, preferably 5,000 to 50,000, more preferably 10,000 to 30,000, and even more preferably 15,000 to 25,000. If the molecular weight is too small, the mechanical properties of the metallic gloss film may be reduced, and conversely, if it is too high, the film formability may be reduced.

In this application, the number average molecular weight of the cellulose-based resin is a value calculated based on the molecular weight of standard polystyrene from a chromatogram measured by gel permeation chromatography (GPC).

The glass transition temperature of the cellulose-based resin is, for example, 80 to 180°C, preferably 100 to 160°C, more preferably 120 to 150°C, and most preferably 130 to 140°C. If the glass transition temperature is too low, the mechanical properties of the metallic gloss film may be reduced, and conversely, if it is too high, the film formability may be reduced.

In this application, the glass transition temperature of the cellulose-based resin can be measured using a differential scanning calorimeter.

(Characteristics and Proportions of Second Resin)
Of the second resins, (meth)acrylic resins, alkyd resins and cellulose resins are preferred, with alkyd resins being particularly preferred, in terms of excellent metallic gloss.

The mass ratio of the first resin (polyvinyl acetal resin) to the second resin can be selected from the range of about 100/0 to 5/95 (particularly 99/1 to 5/95) of the former/latter, for example 95/5 to 5/95 (for example 90/10 to 10/90), preferably 80/20 to 20/80, more preferably 70/30 to 30/70, and more preferably 60/40 to 40/60. If the proportion of the second resin is too high, there is a risk of the metallic gloss being reduced. In applications where metallic gloss is important, the first resin/second resin is 99/1 to 50/50, preferably 98/2 to 60/40, more preferably 95/5 to 70/30, more preferably 93/7 to 80/20, and most preferably 92/8 to 85/15.

(Ratio of resin component (B))
The ratio of the resin component (B) can be selected from a range of about 3 to 150 parts by mass (e.g., 5 to 100 parts by mass) relative to 100 parts by mass of the silver-containing metal of the composite nanoparticle (A), for example, 5 to 120 parts by mass (e.g., 10 to 80 parts by mass), preferably 7 to 100 parts by mass (e.g., 7 to 80 parts by mass), more preferably 8 to 60 parts by mass (e.g., 15 to 50 parts by mass), more preferably 10 to 50 parts by mass (e.g., 20 to 40 parts by mass), and most preferably 10 to 30 parts by mass. In applications where metallic gloss is important, the ratio of the resin component (B) is, for example, 6 to 50 parts by mass, preferably 7 to 30 parts by mass, more preferably 8 to 20 parts by mass, and more preferably 9 to 15 parts by mass relative to 100 parts by mass of the silver-containing metal of the composite nanoparticle (A). If the ratio of the resin component (B) is too small, there is a risk that the adhesion and abrasion resistance will decrease, and if it is too large, there is a risk that the metallic gloss will decrease.

The ink composition of the present invention further contains a solvent (C). By blending the solvent (C) with the resin component (B), the film-forming property can be improved, and when the resin component (B) contains a second resin, phase separation due to spinodal decomposition can be promoted.

The solvent (C) preferably contains a polar organic solvent. Examples of the polar organic solvent include alcohols (C _1-4 alkanols such as methanol, ethanol, propanol, and isopropanol), polyhydric alcohols (alkanediols such as ethylene glycol and propylene glycol, alkanetriols such as glycerin and trimethylolpropane, and alkanetetraols such as pentaerythritol), amides (acylamides such as formamide and acetamide, mono- or di-C alkyl amides such as N-methylformamide, N-methylacetamide, N,N-dimethylformamide, and N,N-dimethylacetamide), and the like. _1-4 acylamides, etc.), pyrrolidones (2-pyrrolidone, 3-pyrrolidone, N-methyl-2-pyrrolidone, N-methyl-3-pyrrolidone, etc.), ketones (acetone, diacetone alcohol, methyl ethyl ketone, isophorone, etc.), ethers (dioxane, tetrahydrofuran, etc.), organic carboxylic acids (acetic acid, etc.), esters (acetic acid esters such as methyl acetate, ethyl acetate, isopropyl acetate, butyl acetate, amyl acetate, etc.), alkylene glycol monoalkyl ethers (C _2-6 alkylene glycol mono C 1-4 alkyl ethers such as methyl cellosolve, ethyl cellosolve, propyl cellosolve, butyl cellosolve, propylene glycol methyl ether, 3-methoxy-3-methyl-1-butanol, etc.), dialkylene glycol monoalkyl ethers (di-C _2-6 alkylene glycol mono C _1-4 alkyl ethers such as methyl carbitol, ethyl carbitol, propyl carbitol, butyl carbitol, etc. _1-4 alkyl ether, etc.), cellosolve acetates (C _1-4 alkyl cellosolve acetates such as ethyl cellosolve acetate, etc.), carbitol acetates (C _1-4 alkyl carbitol acetates such as methyl carbitol acetate, butyl carbitol acetate, etc.), dimethyl sulfoxide, etc. These polar organic solvents can be used alone or in combination of two or more kinds.

The proportion of the polar organic solvent in the solvent may be 50% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 100% by mass.

The solvent (C) may further contain a non-polar solvent in addition to the polar solvent. Examples of non-polar solvents include aliphatic hydrocarbons such as hexane, octane, and decane, and alicyclic hydrocarbons such as cyclohexane and tetralin. The ratio of the non-polar organic solvent may be 50 parts by mass or less (e.g., about 0.1 to 50 parts by mass) per 100 parts by mass of the polar organic solvent, preferably 30 parts by mass or less, and more preferably 10 parts by mass or less.

Among these solvents, it is preferable to include at least one selected from alcohols, esters, alkylene glycol monoalkyl ethers, and dialkylene glycol monoalkyl ethers, more preferably at least one selected from esters, alkylene glycol monoalkyl ethers, and dialkylene glycol monoalkyl ethers, and even more preferably at least one selected from alkylene glycol monoalkyl ethers and dialkylene glycol monoalkyl ethers. Among them, it is more preferable to include at least one selected from C _2-6 alkylene glycol mono C _1-6 alkyl ethers and di C _2-6 alkylene glycol mono C _1-6 alkyl ethers, and most preferably at least one selected from C _2-5 alkylene glycol mono C _1-4 alkyl ethers and di C _2-5 alkylene glycol mono C _1-4 alkyl ethers. The dialkylene glycol monoalkyl ether may be a polar solvent derived from a dispersion medium for dispersing silver colloidal particles as a raw material.

The proportion of the solvent (C) is, for example, 50 to 1,000 parts by mass, preferably 100 to 500 parts by mass, more preferably 200 to 450 parts by mass, even more preferably 250 to 400 parts by mass, and most preferably 300 to 350 parts by mass, relative to 100 parts by mass of the silver-containing metal of the composite nanoparticle (A). If the proportion of the solvent is too low, the film-forming properties may decrease, and if a second resin is included, it may be difficult to form a phase-separated structure. Conversely, if the proportion of the solvent is too high, productivity and film-forming properties may decrease.

(D) Curing Agent The ink composition of the present invention may further contain a curing agent (D) in addition to the composite nanoparticles (A), the resin component (B) and the solvent (C). The curing agent (D) may be a conventional curing agent, such as an isocyanate-based curing agent, an amine-based curing agent, an acid anhydride-based curing agent, or an imidazole-based curing agent. Among these, an isocyanate-based curing agent is preferred, and a polyisocyanate is particularly preferred. An isocyanate-based curing agent such as a polyisocyanate is particularly effective when the first resin and the second resin have a functional group (particularly a hydroxyl group).

Examples of polyisocyanates include aliphatic polyisocyanates [diisocyanates such as propylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), trimethylhexamethylene diisocyanate (TMDI), lysine diisocyanate (LDI), etc.; triisocyanates or polyisocyanates such as 1,6,11-undecane triisocyanate methyl octane, 1,3,6-hexamethylene triisocyanate], alicyclic polyisocyanates [cyclohexane 1,4-diisocyanate, isophorone diisocyanate (IPDI), hydrogenated xylylene diisocyanate, etc.], cyanate, diisocyanates such as hydrogenated bis(isocyanatophenyl)methane; tri- or polyisocyanates such as bicycloheptane triisocyanate, etc.], aromatic polyisocyanates [diisocyanates such as phenylene diisocyanate, tolylene diisocyanate (TDI), xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI), naphthalene diisocyanate (NDI), bis(isocyanatophenyl)methane (MDI), toluidine diisocyanate (TODI), 1,3-bis(isocyanatophenyl)propane, etc.; tri- or polyisocyanates], etc.

The polyisocyanate may be a polymer (dimer, trimer, tetramer, etc.), an adduct, a modified product (biuret modified product, allophanate modified product, urea modified product, etc.), or a urethane oligomer having multiple isocyanate groups. Examples of modified products or derivatives of polyisocyanate include an adduct of a polyisocyanate (such as an aliphatic polyisocyanate such as hexamethylene diisocyanate) and a polyhydric alcohol (such as trimethylolpropane or pentaerythritol), a biuret of the polyisocyanate, and a polymer of the polyisocyanate (such as an aliphatic polyisocyanate) (such as a polyisocyanate having an isocyanurate ring, such as a trimer of hexamethylene diisocyanate).

These polyisocyanates can be used alone or in combination of two or more. Among these polyisocyanates, aliphatic polyisocyanates or their derivatives (e.g., HDI or its trimer, etc.), aromatic polyisocyanates (TDI, MDI, etc.), etc. are widely used.

The proportion of the curing agent (D) is, for example, 10 to 200 parts by mass, preferably 20 to 150 parts by mass, and more preferably 25 to 100 parts by mass, per 100 parts by mass of the resin component (B).

(E) Other Metal Nanoparticles The ink composition of the present invention may further contain other metal nanoparticles (E) in addition to the composite nanoparticles (A), the resin component (B) and the solvent (C). The other metal nanoparticles (E) may be, for example, metals of Group 8 of the periodic table (iron, nickel, cobalt, ruthenium, rhodium, palladium, rhenium, iridium, platinum, etc.), metals of Group 1B of the periodic table (copper, gold, etc.), metals of Group 3B of the periodic table (aluminum, gallium, indium, etc.) and metals of Group 4B of the periodic table (germanium, tin, lead, etc.). In addition, the metal (metal atom) is often a metal with high coordination with the protective colloid, such as a metal of Group 8 of the periodic table or a metal of Group 1B of the periodic table. The ratio of the other metal nanoparticles (E) is 100 parts by mass or less, preferably 50 parts by mass or less, more preferably 10 parts by mass or less, relative to 100 parts by mass of the silver-containing metal of the composite nanoparticles (A).

(F) Other Components The ink composition of the present invention may further contain, as other components (F), conventional additives such as plasticizers (or film-forming assistants), gloss-imparting agents, metal corrosion inhibitors (rust inhibitors), stabilizers (antioxidants, UV absorbers, light stabilizers, etc.), surfactants (anionic surfactants, cationic surfactants, nonionic surfactants, amphoteric surfactants, particularly anionic surfactants and/or nonionic surfactants), dispersion stabilizers, thickeners or viscosity adjusters, moisturizers, thixotropic agents, leveling agents, penetrants, defoamers, pH adjusters, chelating agents, surface tension adjusters, colorants (dyes and pigments, etc.), hue improvers, dye fixing agents, bactericides, antifungal agents, preservatives, oxygen absorbers, etc., within the scope of not impairing the effects of the present invention. The surfactants may be acetylene glycol-based surfactants, polysiloxane-based surfactants, fluorine-based surfactants, etc. These additives may be used alone or in combination of two or more. The proportion of the other component (F) is 50 parts by mass or less, preferably 30 parts by mass or less, and more preferably 10 parts by mass or less, per 100 parts by mass of the silver-containing metal of the composite nanoparticle (A).

[Method of preparing ink composition]
The ink composition of the present invention can be prepared by mixing the composite nanoparticles (A), the resin component (B) and the solvent (C) by a conventional method. A conventional stirring device can be used as the mixing method, for example, a stirring and defoaming device can be used. The composite nanoparticles (A) may be mixed with the resin component (B) and the alkylene glycol monoalkyl ether as the solvent (C) in the form of a dispersion in which the composite nanoparticles (A) are dispersed in the dialkylene glycol monoalkyl ether as the solvent (C).

[Metallic gloss film manufacturing method]
The metallic gloss film is obtained through a coating step in which the ink composition is applied onto an object to be decorated (substrate) to form a coating film, and a drying step in which the coating film is dried to obtain the metallic gloss film.

There are no particular limitations on the type of substrate used in the coating process, and resin substrates (films, etc.), metal substrates, glass substrates, ceramic substrates, paper, etc. can be used depending on the application.

The coating method is not particularly limited, and conventional coating methods such as flow coating, dispenser coating, spin coating, spray coating, screen printing, flexographic printing, casting, bar coating, curtain coating, roll coating, gravure coating, dipping, slitting, photolithography, inkjet printing, and offset printing can be used.

The average thickness (dry thickness) of the coating film is, for example, 0.05 to 100 μm, preferably 0.1 to 30 μm, more preferably 0.5 to 10 μm, and even more preferably 1 to 5 μm.

In the present invention, metallic luster, adhesion, and abrasion resistance can be achieved without forming an undercoat layer or a topcoat layer, but an undercoat layer and/or a topcoat layer may be used in combination depending on the application.

In the drying process, the coating is dried to form a metallic gloss film. The coating is preferably dried by heating, and a two-stage heating and drying method that combines a preliminary heating treatment and a main heating treatment is preferred because it is easier to form a phase separation structure.

In the preheating treatment, the preheating temperature is, for example, 40 to 80°C, preferably 45 to 70°C, more preferably 45 to 60°C, and even more preferably 45 to 55°C. The preheating time is, for example, 1 to 100 minutes, preferably 3 to 60 minutes, and even more preferably 5 to 30 minutes.

In this heat treatment, the heating temperature is, for example, 60 to 150°C, preferably 65 to 120°C, more preferably 70 to 90°C, and even more preferably 75 to 85°C. The heating time is, for example, 30 to 240 minutes, preferably 80 to 180 minutes, and even more preferably 100 to 150 minutes.

When the resin component (B) contains a second resin, a metallic gloss film may be formed by phase separation due to spinodal decomposition in the drying process. When the second resin is contained, by drying the coating film, phase separation can be caused by spinodal decomposition as the solvent evaporates into a phase containing a large amount of silver-containing metal and a phase containing a small amount of silver-containing metal.

The metallic gloss film obtained by the above method is formed on a substrate (object to be decorated), and is laminated on the substrate, and contains composite nanoparticles (A) of a metal containing silver and a protective colloid, and a resin component (B) containing a polyvinyl acetal resin. The average thickness of the metallic gloss film is, for example, 0.05 to 100 μm, preferably 0.1 to 30 μm, more preferably 0.3 to 10 μm, even more preferably 0.5 to 5 μm, and most preferably 1 to 3 μm.

In particular, the metallic gloss film formed on the substrate and containing the second resin may have a structure in which an interface layer, an intermediate layer, and a surface layer are laminated in this order on the substrate.

The interface layer is formed from the composite nanoparticles, and the composite nanoparticles are arranged or oriented at the interface with the substrate to form a dense thin film of metal containing silver (silver-containing metal thin film). The formation of such an interface layer at the interface with the substrate can improve the metallic luster from the back surface of a transparent substrate, etc.

The average thickness of the interface layer is, for example, 5 to 300 nm, preferably 10 to 200 nm, more preferably 10 to 100 nm, and even more preferably 20 to 40 nm.

In this application, the average thickness of the interface layer can be measured by observing the cross section of the silver gloss film with a transmission electron microscope (TEM), and in detail, can be measured by the method described in the examples below.

The intermediate layer has a phase separation structure in which a first phase containing the composite nanoparticles and a first resin and a second phase containing the composite nanoparticles and a second resin are separated into phases with different contents of silver-containing metal. By having a phase separation structure with different concentrations of silver-containing metal, the metallic gloss can be improved even if the proportion of the resin component is increased, and metallic gloss can be achieved simultaneously with adhesion and abrasion resistance.

The ratio of the first phase to the second phase (area ratio in the cross section) is first phase/second phase = 90/10 to 10/90, preferably 70/30 to 30/70, more preferably 60/40 to 40/60, and even more preferably 55/45 to 45/55.

In this application, the ratio can be measured based on a transmission electron microscope (TEM) image of a cross section of the silver gloss film, and in detail, can be measured by the method described in the examples below.

The phase separation structure may be a sea-island structure or a co-continuous structure. Of these, a sea-island structure is preferred. When the intermediate layer has a sea-island structure, the continuous phase (matrix phase) constituting the sea portion may be either a first phase or a second phase.

In the sea-island structure, the average diameter of the dispersed phase is, for example, 10 to 3,000 nm, preferably 100 to 1,000 nm, more preferably 150 to 500 nm, and even more preferably 200 to 300 nm.

The average pitch of the dispersed phase (the average value of the distance between the centers of adjacent dispersed phases) is, for example, 10 to 2,000 nm, preferably 100 to 1,000 nm, more preferably 200 to 700 nm, and even more preferably 300 to 500 nm.

The method of observing the cross section of the metallic gloss film is not particularly limited, and any method used in normal structural analysis can be used. Observation methods include morphological and structural observation using a transmission electron microscope (TEM), a scanning electron microscope (SEM), an electron beam microanalyzer (EPMA), a scanning probe microscope (SPM), etc.; and analysis of the constituent elements using fluorescent X-rays, energy dispersive X-ray spectroscopy (EDX), wavelength dispersive X-ray spectroscopy (WDX), electron energy-loss spectroscopy (EELS), etc. Among these, transmission electron microscope (TEM) observation is preferred because it allows observation of even the finest structures. The sample to be observed can be processed appropriately to be suitable for observation and analysis. For example, a thin section sample can be prepared using a microtome, etc.

Therefore, in this application, the structure, size and distribution state of the island structure in the cross section of the metallic gloss film can be observed and measured based on a TEM image of the cross section of the silver gloss film, and the size is the average value of any 10 points. In detail, it can be measured by the method described in the examples below. Furthermore, in the TEM image, the silver-containing metal nanoparticles can be easily confirmed because of their dark color, and in the intermediate layer, the aggregated parts of the silver-containing metal nanoparticles are the dispersed phase.

The average thickness of the intermediate layer is, for example, 0.01 to 100 μm, preferably 0.05 to 30 μm, more preferably 0.1 to 10 μm, and even more preferably 0.2 to 1 μm.

The average thickness of the intermediate layer may be at least twice the average thickness of the surface layer, for example 2 to 1,000 times, preferably 3 to 100 times, more preferably 3.5 to 50 times, and even more preferably 4 to 10 times.

In this application, the average thickness of the intermediate layer can be measured by observing the cross section of the metallic gloss film with a transmission electron microscope (TEM) and is the average value of any three points.

The surface layer is formed from the composite nanoparticles, and the composite nanoparticles are arranged or oriented on the surface of the metallic gloss film, forming a dense thin film (metal thin film) of silver-containing metal. In the present invention, the metallic gloss can be improved by forming such a surface layer on the surface of the metallic gloss film.

The average thickness of the surface layer is, for example, 3 to 300 nm, preferably 5 to 200 nm, more preferably 10 to 150 nm, and even more preferably 30 to 100 nm.

In this application, the average thickness of the surface layer can be measured by observing the cross section of the silver gloss film with a transmission electron microscope (TEM), and more specifically, by the method described in the examples below.

The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples. In the following examples, the preparation method of the ink composition and the measurement method of the evaluation test are shown below.

[Materials used]
(First Resin)
Polyvinyl butyral resin A: "S-LEC KS-10" manufactured by Sekisui Chemical Co., Ltd., degree of acetalization 74 mol% or more, acetyl group 3 mol% or less, hydroxyl group 25 mol%, 10 mass% solution viscosity (temperature 20°C, rotational viscosity type (BM type), solvent = toluene/ethanol = 50/50 (mass ratio)) 10 to 30 mPa·s, glass transition temperature 106°C, weight average molecular weight 17,000
Polyvinyl butyral resin B: "S-LEC SV-12" manufactured by Sekisui Chemical Co., Ltd., hydroxyl group 22 mol%, 10 mass% solution viscosity (temperature 20°C, rotational viscosity type (BM type), solvent = toluene/ethanol = 50/50 (mass ratio)) 70 mPa·s, glass transition temperature 76°C, weight average molecular weight 30,000
Polyvinyl butyral resin C: "S-LEC SV-16" manufactured by Sekisui Chemical Co., Ltd., hydroxyl group 22 mol %, 10 mass % solution viscosity (temperature 20°C, rotational viscosity type (BM type), solvent = toluene/ethanol = 50/50 (mass ratio)) 80 mPa s, glass transition temperature 80°C, weight average molecular weight 100,000.

(Second Resin)
Acrylic resin A: "WXU-880" manufactured by DIC Corporation, isocyanate-curing acrylic resin, non-volatile content 50%, hydroxyl value 10 mgKOH/g, glass transition temperature 90°C
Acrylic resin B: "ARUFON UH2170" manufactured by Toagosei Co., Ltd., styrene acrylic resin, non-volatile content 98% or more, hydroxyl value 88 mg KOH/g, glass transition temperature 60°C
Alkyd resin: "D-128-65BA" manufactured by DIC Corporation, isocyanate-cured alkyd resin, non-volatile content 65%, hydroxyl value 90 mg KOH/g, acid value 5.0 mg KOH/g
Epoxy resin: "jER1055" manufactured by Mitsubishi Chemical Corporation, bisphenol A type epoxy resin, epoxy equivalent 850, softening point 93°C, number average molecular weight 1600
Silicone resin: "KR211" manufactured by Shin-Etsu Chemical Co., Ltd., methylphenyl-based silicone resin. Cellulose-based resin: Cellulose acetate butyrate "CAB-553-0.4" manufactured by Tomoe Engineering Co., Ltd., acetyl group 2%, butyryl group 46%, hydroxyl group 4.8%, falling ball speed 0.30 seconds, glass transition temperature 136°C, number average molecular weight 20,000.

(solvent)
3-Methoxy-3-methyl-1-butanol: manufactured by Tokyo Chemical Industry Co., Ltd., boiling point 174°C
Butyl cellosolve: Fujifilm Wako Pure Chemical Industries, Ltd., boiling point 171°C
Ethyl carbitol: manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., boiling point 202°C.

(Polymer Dispersant)
Polymer dispersant A having a carboxyl group: "Disperbyk 190" manufactured by BYK-Chemie, solution of a high molecular weight block copolymer having a pigment affinity group, solvent: water, non-volatile component 40%, acid value 10 mgKOH/g, amine value 0
Polymer dispersant B having a carboxyl group: "Disperbyk 2015" manufactured by BYK-Chemie, a solution of an acrylic copolymer having a pigment affinity group, solvent: water, non-volatile components 40%, acid value 10 mg KOH/g, amine value 0.

[Glossiness]
The 20° gloss was measured using an appearance analyzer ("Rhopoint IQ-S" manufactured by Konica Minolta Japan, Inc.) and ranked according to the following criteria (A, B, C, D). Note that if the gloss value is 400 or more, the metallic gloss (mirror surface) can be visually confirmed, and therefore ranks A, B, and C were deemed to be acceptable.

Rank A: Glossiness is 600 or more (passed)
Rank B: Glossiness is 400 or more and less than 600 (pass)
Rank C: Glossiness is 300 or more and less than 400 (pass)
Rank D: Glossiness is less than 300 (failure).

[Light non-transmittance]
The visible light transmittance in the wavelength range of 380 to 780 nm was measured using an ultraviolet-visible-near infrared spectrophotometer (Shimadzu Corporation, "UV-3100PC") and an integrating sphere ISR-3100. The integral value of the transmittance relative to the integral value of the blank measurement (air) was determined by integrating the transmittance in the wavelength range of 380 to 780 nm, and was evaluated according to the following criteria. The smaller the integral value of the transmittance relative to the blank measurement, the lower the transmittance of the film and the better it is.

○: The integral value of the transmittance is 1.0% or less (passed)
△: The integral value of the transmittance is 5.0% or less (pass)
×: The integral value of the transmittance is greater than 5.0% (failure).

[Adhesion]
Cellotape (registered trademark) was applied to the cured film and then forcefully peeled off, and the film was evaluated according to the following criteria.

○: No peeling of the film (passed)
△: There is slight peeling on the surface of the film, but the substrate is not visible (passed)
×: The film peeled off (failed).

[Abrasion resistance]
The cured film was subjected to a friction test using a friction and abrasion tester with dry cotton at a load of 500 g and 10 reciprocations. The 20° gloss of the cured film after the friction test was measured, and the reduction rate of gloss before and after the friction test was calculated, and the abrasion resistance was evaluated according to the following criteria.

Good: Gloss reduction rate is less than 20% (passed)
△: The decrease in gloss level is 20% or more and less than 50% (pass)
×: The gloss reduction rate is 50% or more (failure).

[Overall Judgment]
From the results of glossiness, light impermeability, adhesion, and abrasion resistance, a rating of superiority or inferiority was made according to the following criteria, with ratings of A, B, and C being considered as passing.

Grade A: When the gloss level is rank A and the light impermeability, adhesion and abrasion resistance are all good. Grade B: When the gloss level is rank A and the light impermeability, adhesion and abrasion resistance are all pass (including one △), or when the gloss level is rank B and the light impermeability, adhesion and abrasion resistance are pass (○ or △). Grade C: When the gloss level is rank A and the light impermeability, adhesion and abrasion resistance are all pass (including two or more △), or when the gloss level is rank C and the light impermeability, adhesion and abrasion resistance are pass (○ or △). Grade D: When the gloss level is rank D, or any of the light impermeability, adhesion and abrasion resistance is fail.

[Cross-section observation of film]
A sample was cut out from the obtained silver gloss film, embedded in epoxy resin, which is a general-purpose embedding resin, and the cut cross section was exposed with a microtome and observed with a SEM. Furthermore, in order to observe the fine structure, after exposing the cut cross section with a microtome, ultra-thin slices with a thickness of about 100 nm or less were prepared, and TEM observation was performed to measure the size (average diameter and average pitch) of the dispersed phase by the following method.

(Average thickness of surface layer and interface layer)
The thickness of the layer in which the silver nanoparticles were arranged was measured in the enlarged TEM images near the surface and near the interface. The average value of the layer thicknesses measured at three arbitrary points was taken as the average thickness.

(Average diameter of dispersed phase)
The major and minor axes of the dispersed phase (islands) in which silver nanoparticles were aggregated were measured, and the average value was taken as the diameter of the dispersed phase (islands). The average value of the diameters calculated for any 10 dispersed phases (islands) was taken as the average diameter of the dispersed phase.

(Average pitch of dispersed phase)
The intersection of the major axis and minor axis of the dispersed phase was defined as the center of the dispersed phase, and the distance between the centers of adjacent dispersed phases was measured. The average value of the center-to-center distances measured at any 10 points was defined as the average pitch of the dispersed phase.

(Ratio of first and second phases)
The first and second phases were binarized using the image processing software "ImageJ" (available from https://imagej.Nih.gov/ij/) for the cross-sectional TEM image. The areas of the first and second phases were determined from the binarized image processing image, and the ratio of the first and second phases was calculated. In this example, the ratio was calculated without excluding the surface layer and the interface layer, so the ratio of the first phase also includes the areas of the surface layer and the interface layer.

Examples 1 to 31 and Comparative Examples 1 to 7
(Method for preparing silver nanoparticle dispersion A)
66.8 g of silver nitrate and 7.2 g of polymer dispersant A having a carboxyl group were added to 100 g of ion-exchanged water and stirred vigorously to obtain a suspension. 100 g of dimethylaminoethanol (manufactured by Wako Pure Chemical Industries, Ltd.) was gradually added to this suspension so that the water temperature did not exceed 50° C., and the mixture was heated and stirred in a water bath at 50° C. for 4 hours.

An excess amount of methanol was added to the silver nanoparticle dispersion and stirred, then the silver nanoparticles were precipitated by centrifugation, and the supernatant was removed. Methanol was added again and stirred, then the silver nanoparticles were precipitated by centrifugation, and the supernatant was removed. Diethylene glycol monobutyl ether was added to the resulting methanol solution containing the precipitate, and the mixed methanol was removed using an evaporator to obtain a silver nanoparticle (composite nanoparticle) dispersion A with a silver content of 70 mass%. When the particle size of the silver nanoparticles in this dispersion was confirmed using a transmission electron microscope (manufactured by JEOL Ltd.), the number average particle size of the primary particles was approximately 20 nm.

(Method for preparing silver nanoparticle dispersion B)
A silver nanoparticle (composite nanoparticle) dispersion B was prepared in the same manner as silver nanoparticle dispersion A, except that polymer dispersant B having a carboxyl group was used instead of polymer dispersant A having a carboxyl group. When the particle size of the silver nanoparticles in the obtained silver nanoparticle dispersion B was confirmed with a transmission electron microscope (manufactured by JEOL Ltd.), the number average particle size of the primary particles was about 30 nm.

(Method for preparing silver/copper alloy nanoparticle dispersion)
65.58 g of silver nitrate and 7.2 g of polymeric dispersant A having a carboxyl group were added to 100 g of ion-exchanged water and vigorously stirred to obtain suspension A.

1.40 g of copper (II) nitrate trihydrate and 2.93 g of 1 mol/L aqueous nitric acid solution were taken and stirred in a 50°C water bath to dissolve the copper (II) nitrate trihydrate, obtaining aqueous solution B.

The suspension A and the aqueous solution B were mixed while stirring to obtain a mixture of a polymer dispersant having a carboxyl group, silver nitrate, and copper nitrate.

100 g of dimethylaminoethanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was gradually added to this mixture so that the water temperature did not exceed 50°C, and then the mixture was heated and stirred in a water bath at 50°C for 4 hours.

An excess amount of methanol was added to the obtained dispersion containing silver/copper alloy nanoparticles and stirred, and then the silver/copper alloy nanoparticles were precipitated by centrifugation, and the supernatant was removed. Methanol was added again and stirred, and then the silver/copper alloy nanoparticles were precipitated by centrifugation, and the supernatant was removed. Diethylene glycol monobutyl ether was added to the methanol solution containing the obtained precipitate, and the mixed methanol was removed using an evaporator to obtain a silver/copper alloy nanoparticle (composite nanoparticle) dispersion with a ratio of copper to 100 parts by mass of silver and a silver/copper alloy content of 70% by mass. When the particle size of the silver/copper alloy nanoparticles in this dispersion was confirmed using a transmission electron microscope (manufactured by JEOL Ltd.), the number average particle size of the primary particles was about 20 nm.

(Method of preparing metallic ink composition)
The obtained metal nanoparticle dispersion, resin component, and solvent were stirred and mixed in the proportions shown in Tables 1 to 5 using a stirring and degassing device ("Mazerustar" manufactured by Kurabo Industries, Ltd.) to prepare metallic ink compositions. The amount of resin in the tables is the content converted into solid content. The metallic ink composition was applied to a glass substrate (substrate) with an applicator to a thickness of 20 μm. Thereafter, the coating was heated on a hot plate at 50° C. for 10 minutes, and then heated on a hot plate at 80° C. for 120 minutes. The thickness of the obtained metallic gloss film (dry thickness of the coating film) was approximately 2 μm.

The evaluation results of the obtained metallic gloss film are shown in Tables 1 to 5.

The results of verification of the amount and type of resin components are shown in Table 1.

In Examples 1 to 3, in which only polyvinyl butyral resin A was used as the resin component and silver nanoparticles were used as the composite nanoparticles, and the amount of resin relative to the silver was varied to 10 mass%, 30 mass%, and 50 mass%, a metallic gloss film with excellent glossiness, light impermeability, adhesion, and abrasion resistance (overall rating A) was obtained. In Example 4, in which the amount of resin was further increased to 100 mass% relative to the silver, glossiness and light impermeability were slightly reduced, but were still at a practical level (overall rating C).

In Example 5, in which the type of resin component was changed to polyvinyl butyral resin B compared to Example 2, and in Example 6, in which the type was changed to polyvinyl butyral resin C, a metallic gloss film equivalent to that of Example 2 (overall rating A) was obtained.

In Comparative Examples 1 to 5, in which the type of resin component was changed to a resin other than polyvinyl butyral resin compared to Example 2, Comparative Example 1, which used acrylic resin A, and Comparative Example 5, which used silicone resin, failed the gloss level (overall judgement: D). In Comparative Example 2, which used acrylic resin B, Comparative Example 3, which used alkyd resin, and Comparative Example 4, which used epoxy resin, the gloss level was at an acceptable level, but the light impermeability was unacceptable (overall judgement: D).

In addition, in Comparative Example 6, which did not contain any resin components, the gloss and light impermeability were at acceptable levels, but the adhesion and abrasion resistance were unacceptable (overall rating: D).

The verification results for the combination of polyvinyl butyral resin and a second resin (acrylic resin A, acrylic resin B, alkyd resin, epoxy resin, cellulose-based resin) as the resin component are shown in Table 2.

Examples 7 to 9 were prepared by keeping the amount of resin relative to silver at 30% by mass, the mass ratio of polyvinyl butyral resin to second resin in the resin constant at polyvinyl butyral resin:second resin = 50:50, and varying the type of polyvinyl butyral resin. As a result, in Examples 7 to 9, metallic gloss films with excellent gloss, light impermeability, adhesion, and abrasion resistance (overall rating A) were obtained.

Compared to Example 7, Examples 10 to 13, which used a different second resin, produced a metallic gloss film (overall rating of A or B) with excellent gloss, light impermeability, adhesion, and abrasion resistance.

In Comparative Example 7, which combined acrylic resin A with epoxy resin as a combination of two types of resin that did not contain polyvinyl butyral resin, the gloss, adhesion, and abrasion resistance were at acceptable levels, but the light impermeability was unacceptable (overall rating: D).

Compared to Example 2, which used only polyvinyl butyral resin A as the resin component, Table 3 shows the verification results when the mass ratio of polyvinyl butyral resin A to the second resin (acrylic resin A) was changed while keeping the amount of resin to the silver nanoparticles the same (30 mass%).

In the following order, the gloss level tended to decrease, although it was at the pass level (overall judgement A or B), in Example 2 (polyvinyl butyral resin A: acrylic resin A = 100:0) which did not use acrylic resin A, Example 14 (polyvinyl butyral resin A: acrylic resin A = 90:10) which contained a small amount of the second resin, Example 7 (polyvinyl butyral resin A: acrylic resin A = 50:50) which contained equal amounts of both, Example 15 (polyvinyl butyral resin A: acrylic resin A = 20:80) which had a higher ratio of the second resin than Example 7, and Example 16 (polyvinyl butyral resin A: acrylic resin A = 10:90). Furthermore, in Example 17 (polyvinyl butyral resin A: acrylic resin A = 5:95) which had a higher ratio of the second resin, the gloss level and light impermeability were further decreased, but were still at a practical level (overall judgement C). In the aforementioned Comparative Example 1 (Polyvinyl butyral resin A: Acrylic resin A = 0:100), in which polyvinyl butyral resin A was not used and only acrylic resin A was used, the gloss and light impermeability were unsatisfactory (overall rating: D).

Table 4 shows the results of the verification in which the amount of resin relative to the silver nanoparticles was varied in comparison with Example 7, in which polyvinyl butyral resin A and acrylic resin A were used as the resin components and their mass ratio was set to be equal. Note that "amount of resin relative to silver nanoparticles (mass %)" is synonymous with the ratio (parts by mass) of the resin component relative to 100 parts by mass of silver nanoparticles.

All examples were passable (overall rating A to C), but as the amount of resin relative to silver nanoparticles increased, there was a tendency for gloss and light impermeability to decrease, while adhesion and abrasion resistance tended to improve. Example 20 (10% by mass), Example 7 (30% by mass), and Example 21 (50% by mass), in which the amount of resin relative to silver nanoparticles was 10 to 50% by mass, were given an overall rating of A, whereas Example 19, in which the amount of resin was 7% by mass, showed decreased adhesion, and Example 18, in which the amount of resin was 5% by mass, showed decreased adhesion and abrasion resistance. On the other hand, Example 22, in which the amount of resin was 100% by mass, showed decreased gloss and light impermeability, and Example 23, in which the amount of resin was 120% by mass, showed an even further decrease in gloss.

From the above results, it can be said that the amount of resin relative to silver nanoparticles can be practically used in the range of 5 to 120% by mass, with the range of 7 to 100% by mass being the preferred range, and that the range of 10 to 50% by mass is a more suitable range for obtaining a metallic gloss film with an excellent balance of gloss, light impermeability, adhesion, and abrasion resistance.

Table 5 shows the results of the verification when the protective colloid of the silver nanoparticles (composite nanoparticles) was changed, when silver/copper alloy nanoparticles were used as the composite nanoparticles, and when the solvent was changed.

First, the above changes were made to Example 2, which used only polyvinyl butyral resin A as the resin component. In Example 24, where silver nanoparticle dispersion 1 in the composition of Example 2 was changed to silver nanoparticle dispersion 2, which contains a different protective colloid, and in Example 25, where the silver nanoparticle dispersion was changed to a silver/copper alloy nanoparticle dispersion, a metallic gloss film equivalent to that of Example 2 (overall rating A) was obtained. In Example 26, where the solvent in the composition of Example 2 was changed to butyl cellosolve, and in Example 27, where the solvent was changed to ethyl carbitol, a metallic gloss film equivalent to that of Example 2 (overall rating A) was obtained.

Next, the above changes were made to Example 7, which used polyvinyl butyral resin A and acrylic resin A as the resin components (the mass ratios were equal). In Example 28, in which silver nanoparticle dispersion 1 in the composition of Example 7 was changed to silver nanoparticle dispersion 2, which contains a different protective colloid, and in Example 29, in which it was changed to a silver/copper alloy nanoparticle dispersion, a metallic gloss film equivalent to that of Example 7 (overall rating A) was obtained. In Example 30, in which the solvent in the composition of Example 7 was changed to butyl cellosolve, and in Example 31, in which it was changed to ethyl carbitol, a metallic gloss film equivalent to that of Example 7 (overall rating A) was obtained.

Cross-sectional photographs of the metallic gloss film obtained in Example 7 are shown in Figures 1 and 2. Figure 2 is an enlarged TEM image of Figure 1. Note that in Figures 1 and 2, the upper side of the TEM image is the interface layer side with the substrate, and the lower side is the surface layer side.

In the silver gloss film of Example 7, which had a high gloss, the inside of the film (middle layer) was phase-separated into an area where the silver nanoparticles were aggregated (dispersed phase) and an area where the silver nanoparticles were less aggregated (continuous phase). In other words, the silver nanoparticles had a structure in which they were unevenly distributed in the dispersed phase. Furthermore, as is clear from the enlarged image in Figure 2, the silver nanoparticles were aligned on the surface and at the interface with the substrate to form a thin continuous layer (thin layer).

When the average thicknesses of the surface layer and interface layer in Example 7 were measured, the average thickness of the surface layer was 58 nm, and the average thickness of the interface layer was 37 nm. In addition, the average thickness of the intermediate layer was measured and found to be 300 nm. The average thickness of the intermediate layer was 5.2 times that of the surface layer.

Furthermore, the average diameter and average pitch of the dispersed phase (region where silver nanoparticles are aggregated) in the intermediate layer were measured, and the average diameter was 241 nm and the average pitch was 313 nm. The area ratio of the dispersed phase (first phase) to the second phase was measured, and the ratio was first phase/second phase = 51/49.

Cross-sectional photographs of the metallic gloss film obtained in Comparative Example 1 are shown in Figures 3 to 6. As is clear from Figure 3, which shows the overall image, and Figures 4 to 6, which show enlarged images of the inside of the film, in the silver gloss film of Comparative Example 1, which has low gloss, silver nanoparticles were uniformly dispersed throughout the film.

The ink composition of the present invention can be used to improve the decorativeness of various objects (molded objects), for example, in the decoration of interior and exterior parts of automobiles, emblems, mobile phones, notebook computers, golf club shafts, soft packaging and cosmetic containers, as well as for painting and as an ink for inkjet printing.

Claims (10)

An ink composition for improving the decorativeness of an object to be decorated, comprising:
A composite nanoparticle (A) of a metal including silver and a protective colloid, a resin component (B) including a polyvinyl acetal resin, and a solvent (C) ,
The ink composition , wherein the protective colloid contains a polymer dispersant having a carboxyl group or a salt thereof . The ink composition according to claim 1, wherein the polyvinyl acetal resin is a polyvinyl butyral resin. The ink composition according to claim 1 or 2, wherein the resin component (B) further contains a second resin. The ink composition according to claim 3, wherein the second resin is at least one selected from the group consisting of (meth)acrylic resins, alkyd resins, epoxy resins, and cellulose resins. The ink composition according to claim 3 or 4, wherein the mass ratio of the polyvinyl acetal resin to the second resin is the former/the latter = 99/1 to 5/95. The ink composition according to any one of claims 1 to 5, wherein the solvent (C) contains at least one selected from the group consisting of alkylene glycol monoalkyl ethers and dialkylene glycol monoalkyl ethers. The ink composition according to any one of claims 1 to 6, wherein the ratio of the resin component (B) is 3 to 150 parts by mass per 100 parts by mass of the metal containing silver in the composite nanoparticles (A). The ink composition according to any one of claims 1 to 7, wherein the composite nanoparticles (A) are particles in which a protective colloid is attached to or coordinated to the surface of silver-containing metal nanoparticles, and the metal nanoparticles have an average particle size of 1 to 100 nm. A method for producing a metallic gloss film, comprising a coating step of coating a substrate with the ink composition according to any one of claims 1 to 8, and a drying step of drying the coating film formed with the ink composition to obtain a metallic gloss film. A metallic gloss film for improving the decorativeness of a decorated object,
Comprising: (A) composite nanoparticles of a metal including silver and a protective colloid; and (B) a resin component including a polyvinyl acetal resin;
The metallic luster film , wherein the protective colloid contains a polymer dispersant having a carboxyl group or a salt thereof .