JP7229707B2 - Inkjet recording method - Google Patents

Description

The present invention relates to an inkjet recording method.

Inks containing metal particles have been used to form electric circuits by utilizing the characteristics of the metal particles used, but in recent years, they have also been used for applications such as Christmas cards that express a metallic effect. It has become to. In such applications, it is desired to record a highly decorative metallic color image (hereinafter referred to as a "color metallic image") instead of the conductivity required for electric circuits. In order to record a color metallic image, an ink set of an oil-based ink containing flat aluminum particles and an oil-based ink containing a dye has been proposed (see Patent Document 1). Furthermore, an inkjet recording method has been proposed in which a water-based ink containing a dye and a water-based ink containing silver particles are sequentially discharged onto a region of a matte paper to which a processing agent containing inorganic particles has been applied (Patent Document 2).

JP 2016-14141 A JP 2015-193127 A

Since the oil-based ink described in Patent Document 1 requires countermeasures against the odor of the volatilized organic solvent, the present inventors assumed the use of water-based ink instead of oil-based ink. In order to suppress the deterioration of the image recorded on the recording medium, recording is performed using a recording medium having a transparent base material instead of using matte paper as described in Patent Document 2. There is a method of observing an image from the surface opposite to the recording surface of the medium. Even when this method is used, it is required to record a color metallic image. A water-based ink containing silver particles and a water-based ink containing a dye were applied to a recording medium having a transparent substrate, and the image was observed from the side opposite to the side on which the ink was applied. However, it was found that glossiness could not be obtained in some cases.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an ink jet recording method capable of producing images with excellent glossiness and color development.

The above objects are achieved by the present invention described below. That is, in the present invention, a first ink and a second ink are at least partially overlapped on the surface having the ink-receiving layer of a recording medium having a transparent substrate and an ink-receiving layer on one side of the transparent substrate. , wherein the first ink is aqueous ink containing silver particles, and the second ink is aqueous ink containing dye. and the ink-jet recording method characterized in that the volume-based cumulative 50% particle size (nm) of the silver particles is larger than the average pore size (nm) of the ink-receiving layer.

According to the present invention, it is possible to provide an ink jet recording method that provides an image with excellent glossiness and color development.

Hereinafter, embodiments of the present invention will be described in detail. In the present invention, hereinafter, water-based ink may be referred to as "ink". Various physical property values are values at a temperature of 25° C. unless otherwise specified. In the present invention, the glossiness and color development of the image are the effects obtained when the image is observed from the side of the recording medium opposite to the side having the ink-receiving layer. Further, a color-developing image is an image having the color tone of the dye used instead of silver.

First, when an image was recorded on a recording medium using an aqueous ink containing flat aluminum particles (described in Patent Document 1) and an aqueous ink containing a dye, the image was not glossy. When the reason for this is investigated, it has been found that the use of ink containing aluminum particles (described in Patent Document 1) increases the number of gaps in the metallic layer formed on the recording medium. Therefore, it has been found that the use of an ink containing silver particles instead of an ink containing aluminum particles makes it possible to obtain a glossy image. Furthermore, it was found that the volume-based cumulative 50% particle size of the silver particles should be larger than the average pore size of the ink-receiving layer in order to improve the glossiness of the image. The reason is presumed as follows.

In general, particles used in water-based ink for inkjet have a particle size of several to several tens of nm in consideration of ejection stability. The melting point of metal particles depends on the type of metal and the size of the particles. In the case of silver particles composed of silver atoms, the smaller the particle size, the lower the melting point. Compared to silver particles with a large particle size, silver particles with a small particle size have a higher ratio of silver atoms existing on the surface of the silver particles to the total number of silver atoms. Compared to the silver atoms inside the silver particles, which are difficult to move due to metal bonds with the surrounding silver atoms, the silver atoms existing on the surface of the silver particles are more mobile, so they are present on the surface of the nearby silver particles. It fuses by metallic bonding with existing silver atoms. Thus, silver particles with a small particle size tend to fuse with nearby silver particles. Therefore, by forming a silver layer with few gaps on the recording medium, the glossiness of the image is exhibited.

On the other hand, in the case of aluminum particles, fusion of particles like silver particles is less likely to occur. Therefore, even if an image is recorded using an ink containing aluminum particles, since the aluminum particles do not fuse, the metallic layer formed on the recording medium has many gaps. As a result, the amount of light reflected in a certain direction is reduced, and the glossiness of the image cannot be obtained.

By using the ink containing the silver particles in this way, the silver particles are fused to form a silver layer with few gaps on the recording medium, and the glossiness of the image is exhibited. However, even if the first ink containing silver particles is applied to the surface having the ink-receiving layer of a recording medium having a transparent base material and an ink-receiving layer on one side of the transparent base material, the glossiness of the image does not improve. It turned out that the levels were still insufficient in some cases. As a result of investigations, the present inventors found that the penetration of the silver particles into the pores of the ink-receiving layer makes it difficult for the silver particles to come close to each other. I assumed that the level was insufficient.

Therefore, the present inventors believe that it is important for silver particles to be difficult to enter the pores of the ink-receiving layer in order to improve the glossiness of the image. It was found that the pore size should be larger than the average pore size of the ink-receiving layer. Hereinafter, the volume-based cumulative 50% particle size of silver particles may be abbreviated as " _D50 particle size of silver particles" and the average pore size of the ink receiving layer as "pore size of the ink receiving layer". be. The particle size of silver particles is determined using a dynamic light scattering method. The pore size of the ink-receiving layer is determined using a pore-size distribution measuring device based on the gas permeation method.

Here, the cumulative 50% particle size is the diameter of particles that is integrated from the small particle size side to 50% of the total volume of the measured silver particles in the particle size integration curve. Furthermore, the pore size of the ink-receiving layer is the diameter of the pores. As a result of studies by the present inventors, it was found that there is a correlation between the volume-based cumulative 50% particle size of silver particles and the average pore size of the ink-receiving layer.

Since the _D50 particle size of the silver particles is larger than the pore size of the ink-receiving layer, the silver particles are less likely to enter the pores of the ink-receiving layer. Therefore, silver particles are fused with nearby silver particles to form a silver layer with fewer gaps on the recording medium, thereby obtaining a glossy image.

Furthermore, in order to obtain the color development property of the image, it is necessary to apply the second ink containing the dye in addition to the first ink containing the silver particles so that at least a part thereof overlaps to record the image. When the dye-containing ink is applied, the dye permeates the ink-receiving layer together with the liquid component in the ink. Since the highly transparent dye is present in the ink-receiving layer, it does not block the glossiness of the silver layer formed on the ink-receiving layer. Become.

Even if an ink containing a pigment instead of a dye is applied as a coloring material, it is not possible to obtain the glossiness and coloring of the image. When the ink containing the silver particles is applied after the ink containing the pigment is applied, since the pigment does not have transparency, the glossiness of the silver layer formed in the ink receiving layer is blocked, and the glossiness of the image is reduced. I can't get it. When the ink containing the pigment is applied after the ink containing the silver particles is applied, the pigment adheres to the formed silver layer. Since the image has a color tone of , the image color development property cannot be obtained.

<Inkjet recording method>
In the inkjet recording method of the present invention, at least a part of the first ink and the second ink is applied to the surface having the ink-receiving layer of a recording medium having a transparent substrate and an ink-receiving layer on one side of the transparent substrate. It has a recording step of recording an image by applying so as to overlap.

In the recording step, it is preferable to record an image by ejecting ink from an inkjet recording head. Methods for ejecting ink include a method in which mechanical energy is applied to ink and a method in which thermal energy is applied to ink. In the present invention, it is preferable to adopt a method of applying thermal energy to the ink to eject the ink.

After applying the first ink containing the silver particles, the second ink containing the dye may be applied so as to at least partially overlap the area to which the first ink has been applied. Alternatively, after applying the second ink containing the dye, the first ink containing the silver particles may be applied so that at least a part of the area to which the second ink is applied overlaps. In either case, the glossiness and color development of the image can be obtained. In particular, after applying the second ink containing the dye, it is preferable to apply the first ink containing silver particles so that at least a part of the area to which the second ink is applied overlaps.

The inkjet recording method of the present invention preferably does not have a step of applying a liquid other than the first ink and the second ink before applying the first ink and the second ink to the recording medium. Compared to the case where the liquid is not applied before applying the first ink and the second ink, the amount of liquid applied to the recording medium is increased when the liquid is applied before applying the first ink and the second ink. Therefore, it may not be possible to sufficiently suppress image bleeding. The inkjet recording method of the present invention preferably has a step of applying the first ink or the second ink.

<First ink>
The first ink is an aqueous ink containing silver particles. The components constituting the first ink will be described below.

(silver particles)
Silver particles are composed of silver atoms. The silver particles may contain other metal atoms, oxygen atoms, sulfur atoms, carbon atoms, etc. in addition to silver atoms. It is preferably 0% by mass or more.

Methods for producing silver particles include, for example, a method of pulverizing silver lumps with a pulverizer such as a ball mill or a jet mill (pulverization method), and a method of reducing and aggregating silver ions or silver complexes with a reducing agent (reduction method). etc. In the present invention, it is preferable to produce silver particles by a reduction method from the viewpoints of ease of controlling the particle size of silver particles and dispersion stability of silver particles.

[Roundness of silver particles]
The degree of roundness of the silver particles is determined using the long and short diameters measured from projections observed using a scanning electron microscope (SEM) or transmission electron microscope (TEM). Specifically, the degree of roundness of silver particles is specified for convenience by a value calculated from (major axis+minor axis)/(2×minor axis). The silver particles preferably satisfy the following formula (1).
1.0≦(major axis + minor axis)/(2×minor axis)≦1.3 Formula (1)
When formula (1) is satisfied, the silver particles are nearly spherical. When metal particles that are not spherical but have uneven or pointed portions are used, light incident on the uneven or pointed portions is scattered, so the amount of light reflected in a certain direction is reduced. Therefore, sufficient glossiness of the image may not be obtained. In particular, when flat aluminum particles such as those described in Patent Document 1 are used, the particles do not fuse and there are many gaps in the formed metallic layer. Furthermore, flat aluminum particles tend to have sharp portions because they are produced by miniaturizing the aluminum deposited layer. As a result, the light incident on the sharp portion is scattered, so that the amount of light reflected in a certain direction is reduced. As a result, sufficient glossiness of the image may not be obtained. In particular, the silver particles are preferably nearly spherical.

The long and short diameters of silver particles can be measured using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). 100 silver particles are observed and the length and breadth values are measured. The average length of 100 silver particles is calculated, and the calculated value is defined as the average length of the silver particles. Similarly, the average value of short diameters of 100 silver particles is calculated, and the calculated value is defined as the average short diameter of the silver particles. This average major axis and average minor axis are the "major axis" and "minor axis" in the formula (1).

[Volume-Based Cumulative 50% Particle Size ( _D50 ) of Silver Particles]
The volume-based cumulative 50% particle size of the silver particles is the particle size that is integrated from the small particle size side to 50% of the total volume of the measured silver particles in the particle size accumulation curve. The volume-based cumulative 50% particle size (nm) of the silver particles is preferably 10 nm or more and 150 nm or less. _D50 can be measured by dynamic light scattering.

[Volume-Based Cumulative 90% Particle Size ( _D90 ) of Silver Particles]
The volume-based cumulative 90% particle size of silver particles is the particle size that is integrated from the small particle size side to 90% of the total volume of the measured silver particles in the particle size accumulation curve. The volume-based cumulative 90% particle size (nm) of the silver particles is preferably 200 nm or less. The larger the particle size of the silver particles, the easier it is to settle. In order to suppress sedimentation of silver particles, it is necessary to use an indicator that includes silver particles having a large particle size as an indicator of the particle size of silver particles. For this reason, attention was paid to the cumulative 90% particle size, which is the particle diameter that is 90% when integrated from the small particle size side. It should be noted that the silver particles having a particle size of 10% on the larger side in the cumulative distribution can be ignored because the particle size is large but the frequency is low. By reducing the volume-based cumulative 90% particle size to 200 nm or less, the silver particles are less likely to settle and the storage stability of the ink is improved. Furthermore, silver particles with a small particle size are more likely to fuse together than silver particles with a large particle size. By reducing the volume-based cumulative 90% particle diameter to 200 nm or less, a uniform silver layer can be easily formed, and the glossiness of the image can be improved. _D90 is preferably 10 nm or more. _D90 can be measured by dynamic light scattering.

[Method of Dispersing Silver Particles]
Methods for dispersing the silver particles include a surfactant dispersion type using a surfactant as a dispersant and a resin dispersion type using a resin as a dispersant. Of course, in the first ink, it is also possible to use silver particles with different dispersion methods.

An anionic surfactant, a nonionic surfactant, a cationic surfactant, an amphoteric surfactant and the like can be used as a surfactant used as a dispersant in the surfactant dispersion type. Examples of anionic surfactants include fatty acid salts, alkyl sulfates, alkylarylsulfonates, alkyldiaryletherdisulfonates, dialkylsulfosuccinates, alkylphosphates, naphthalenesulfonate formalin condensates, polyoxyethylene alkyl Ether sulfates, polyoxyethylene alkyl phosphate salts, glycerol borate fatty acid esters, and the like. Nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethyleneoxypropylene block copolymers, sorbitan fatty acid esters, glycerin fatty acid esters, polyoxyethylene fatty acid esters, polyoxyethylene alkylamines, fluorine compounds, silicone compounds, etc. is mentioned. Cationic surfactants include alkylamine salts, quaternary ammonium salts, alkylpyridinium salts, alkylimidazolium salts and the like. Amphoteric surfactants include alkylamine oxides and phosphatidylcholines.

Among them, as the surfactant, it is preferable to use at least one selected from anionic surfactants and nonionic surfactants. The anionic surfactant is preferably a polyoxyethylene alkyl ether sulfate, and the nonionic surfactant is preferably a polyoxyethylene alkyl ether.

It is preferable that the resin used as a dispersing agent in the resin dispersion type has both a hydrophilic portion and a hydrophobic portion. Examples of resins include polyvinyl resins, polyester resins, amino resins, acrylic resins, epoxy resins, urethane resins, polyether resins, polyamide resins, unsaturated polyester resins, phenol resins, and silicone resins. , fluorine-based polymer compounds, and the like.

The polystyrene equivalent weight average molecular weight (Mw) obtained by gel permeation chromatography (GPC) of the resin is preferably 1,000 or more and 100,000 or less, and is preferably 3,000 or more and 50,000 or less. More preferred.

The content (% by mass) of the dispersant in the first ink is preferably 1.0 times or less as a mass ratio (times) to the content (% by mass) of the silver particles. If the ratio exceeds 1.0 times, the amount of the dispersing agent is too large relative to the silver particles, making it difficult for the silver particles to come close to each other, making it difficult for the silver particles to fuse together. As a result, sufficient glossiness of the image may not be obtained.

When the dispersant is a surfactant, the ratio is more preferably 0.02 times or more. When the dispersant is a resin, the ratio is more preferably 0.05 times or more. When the dispersant is a surfactant, if the ratio is less than 0.02 times, the amount of the dispersant is too small for the silver particles in the first ink, so the silver particles are stably dispersed in the first ink. difficult to do. As a result, sufficient ink ejection stability may not be obtained. When the dispersant is a resin, if the ratio is less than 0.05 times, the ink ejection stability may not be sufficiently obtained for the same reason as described above.

The content (% by mass) of silver particles in the first ink is preferably 2.0% by mass or more and 15.0% by mass or less based on the total mass of the first ink. If the content is less than 2.0% by mass, the amount of silver particles is too small, making it difficult for the silver particles to come close to each other. This makes it difficult for the silver particles to fuse with each other, so that the image may not have sufficient glossiness. If the content exceeds 15.0% by mass, the amount of silver particles is too large, which may increase the viscosity of the ink and may not provide sufficient ink ejection stability. More preferably, the content (% by mass) of the silver particles in the first ink is 2.0% by mass or more and 8.0% by mass or less based on the total mass of the first ink.

(Surfactant)
The first ink preferably contains a surfactant in addition to the surfactant that can be used as a dispersing agent for silver particles. Surfactants that can be used include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants. Among them, the surfactant is preferably a nonionic surfactant. Examples of nonionic surfactants include ethylene oxide adducts of acetylene glycol. Among them, the nonionic surfactant preferably has an HLB value of 10 or more according to the Griffin method. If the HLB value is less than 10, the hydrophobicity is high, and it becomes difficult to dissolve in the first ink. Here, the HLB value according to the Griffin method is obtained from the formula weight of the ethylene oxide group of the surfactant and the molecular weight of the surfactant, HLB value = 20 × (formula weight of the ethylene oxide group of the surfactant) / (surfactant (molecular weight of). The HLB value indicates the degree of hydrophilicity or lipophilicity of a surfactant (compound) in a range of 0 to 20. A lower HLB value indicates a higher lipophilicity (hydrophobicity) of the compound. On the other hand, the higher the HLB value, the higher the hydrophilicity of the compound.

The content (% by mass) of the surfactant used as a dispersing agent for the silver particles in the first ink is preferably 0.1% by mass or more and 3.0% by mass or less. The content (% by mass) of the surfactant other than the surfactant used as the dispersing agent for the silver particles in the first ink is preferably 0.1% by mass or more and 2.0% by mass or less.

(aqueous medium)
The first ink contains water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. It is preferable to use deionized water (ion-exchanged water) as water. The water-soluble organic solvent is not particularly limited, and alcohols, glycols, glycol ethers, nitrogen-containing compounds, and the like, which can be used for inkjet inks, can all be used. Also, one or more of these water-soluble organic solvents can be contained in the ink.

The water content (% by mass) in the first ink is preferably 50.0% by mass or more and 95.0% by mass or less based on the total mass of the ink. Also, the content (% by mass) of the water-soluble organic solvent in the first ink is preferably 3.0% by mass or more and 50.0% by mass or less based on the total mass of the first ink. If the content of the water-soluble organic solvent is less than 3.0% by mass, reliability such as adhesion resistance may not be sufficiently obtained when the first ink is used in an inkjet recording apparatus. Moreover, when the content of the water-soluble organic solvent exceeds 50.0% by mass, the viscosity of the ink increases, which may cause ink supply failure.

(other ingredients)
In addition to the above components, the first ink may contain water-soluble organic compounds that are solid at a temperature of 25° C., such as urea and its derivatives, trimethylolpropane, and trimethylolethane. In addition, the ink of the present invention may optionally contain various additives such as pH adjusters, antifoaming agents, rust inhibitors, preservatives, antifungal agents, antioxidants, anti-reduction agents, and chelating agents. may be included.

(Physical properties of the first ink)
The viscosity (mPa·s) of the first ink at a temperature of 25° C. is preferably from 1 mPa·s to 5 mPa·s, more preferably from 1 mPa·s to 3 mPa·s. In addition, the surface tension (mN/m) of the ink at a temperature of 25° C. is preferably 10 mN/m or more and 60 mN/m or less, more preferably 20 mN/m or more and 60 mN/m or less, and 30 mN/m or more. It is more preferably 40 mN/m or less. The surface tension of the ink can be adjusted by appropriately determining the type and content of the surfactant in the ink.

<Second ink>
The second ink is a water-based ink containing a dye. The components constituting the second ink will be described below.

(dye)
The dye is not particularly limited as long as it is an anionic dye that can be used as a coloring material for general inkjet inks. Among them, the dye is preferably a compound having at least one selected from the group consisting of an azo skeleton, a phthalocyanine skeleton, an anthrapyridone skeleton, and a xanthene skeleton.

The content (% by mass) of the dye in the second ink is preferably 1.0% by mass or more and 10.0% by mass or less, more preferably 2.0% by mass or more and 8.0% by mass or less. preferable.

(aqueous medium)
The second ink contains water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. It is preferable to use deionized water (ion-exchanged water) as water. The water-soluble organic solvent is not particularly limited, and alcohols, glycols, glycol ethers, nitrogen-containing compounds, and the like, which can be used for inkjet inks, can all be used. Also, one or more of these water-soluble organic solvents can be contained in the ink.

The content (% by mass) of water in the second ink is preferably 50.0% by mass or more and 95.0% by mass or less based on the total mass of the ink. The content (% by mass) of the water-soluble organic solvent in the second ink is preferably 3.0% by mass or more and 50.0% by mass or less based on the total mass of the second ink. If the content of the water-soluble organic solvent is less than 3.0% by mass, reliability such as adhesion resistance may not be obtained when the ink is used in an inkjet recording apparatus. Moreover, when the content of the water-soluble organic solvent exceeds 50.0% by mass, there are cases where ink supply failure occurs.

(other ingredients)
In addition to the above components, the second ink may contain water-soluble organic compounds that are solid at room temperature (25° C.), such as urea and its derivatives, trimethylolpropane, and trimethylolethane. In addition, the ink of the present invention may optionally contain surfactants, resins, pH adjusters, antifoaming agents, rust inhibitors, preservatives, anti-mold agents, antioxidants, anti-reduction agents, and chelating agents. You may contain various additives, such as.

(Physical properties of the second ink)
The viscosity (mPa·s) of the second ink at a temperature of 25° C. is preferably from 1 mPa·s to 5 mPa·s, more preferably from 1 mPa·s to 3 mPa·s. Further, the surface tension (mN/m) of the second ink at a temperature of 25° C. is preferably 10 mN/m or more and 60 mN/m or less, more preferably 20 mN/m or more and 60 mN/m or less, and 30 mN/m. It is more preferable to be m or more and 40 mN/m or less. The surface tension of the second ink can be adjusted by appropriately determining the type and content of the surfactant in the second ink.

<Recording medium>
The recording medium has a transparent substrate and an ink-receiving layer on one side of the transparent substrate. The transparent substrate and the ink-receiving layer that constitute the recording medium are described below.

(Transparent substrate)
A transparent base material means that at least part of visible light is transmitted through the base material when visible light is incident on the base material. Transmitting indicates that more light is transmitted through the substrate than is reflected from the substrate. For example, glass is colorless and transparent because it transmits almost all visible light, and colored glass is transparent but colored because it transmits only a part of visible light. Among them, the transparent base material is preferably a colorless and transparent base material.

Examples of transparent substrates include polyester resins such as polyethylene terephthalate and polyethylene naphthalate, acetate resins such as diacetate and triacetate, polystyrene resins, polyolefin resins such as polyethylene and polypropylene, polycarbonate resins, and polymethacrylates such as polymethyl methacrylate. Resins, plastic films such as cellophane, celluloid, polyvinyl chloride resins, and polyimide resins, plastic plates, glass plates, and the like. Among them, the transparent substrate is preferably a polyester resin, a polyolefin resin, or a polyvinyl chloride resin, and more preferably a polyethylene terephthalate film, a polyethylene film, or a polyvinyl chloride film. Since the transparent base material only needs to transmit at least part of visible light, it is possible to impart a pattern or gloss to the recording medium. The thickness (μm) of the substrate is preferably 1 μm or more and 5,000 μm or less, more preferably 3 μm or more and 1,000 μm or less, and even more preferably 5 μm or more and 500 μm or less.

(Ink receiving layer)
When an image is observed from the opposite side of the transparent substrate to the side having the ink-receiving layer, the ink-receiving layer preferably has transparency so that the recorded image can be observed. The ink-receiving layer may be a single layer or a multi-layer of two or more layers. The coating amount (g/m ² ) of the ink receiving layer is preferably 5.0 g/m ² or more and 30.0 g/m ² or less. The thickness (μm) of the ink-receiving layer is preferably 5.0 μm or more, more preferably 5.2 μm or more, and even more preferably 5.5 μm or more. When the thickness is less than 5.5 μm, the ink-receiving layer is thin, and thus the ink absorbability is lowered, and bleeding of the recorded image may not be sufficiently suppressed. The thickness (μm) of the ink receiving layer is preferably 30.0 μm or less.

Furthermore, the ink absorption amount (mL/m ² ) of the ink receiving layer is preferably 0.4 mL/m ² or more. When the ink absorption amount is less than 0.4 mL/m ² , the ink absorption amount is so small that the ink absorbability is lowered, and bleeding of the recorded image may not be sufficiently suppressed. The ink absorption amount is preferably 2.0 mL/m ² or less.

The average pore size (nm) of the ink-receiving layer is preferably 40 nm or less. If the pore size exceeds 40 nm, the silver particles tend to enter the pores, which may result in insufficient glossiness of the image. The average pore size (nm) of the ink-receiving layer is preferably 10 nm or more and 30 nm or less.

[Inorganic particles]
The ink-receiving layer preferably contains inorganic particles. The average primary particle size of the inorganic particles is preferably 150 nm or less, more preferably 1 nm or more and 100 nm or less, and even more preferably 3 nm or more and 30 nm or less. The average primary particle size of the inorganic particles is the number average particle size of the diameter of a circle having an area equal to the projected area of the primary particles of the inorganic particles when observed with an electron microscope. At this time, the measurement is performed at 100 points or more.

The inorganic particles are preferably used in the ink-receiving layer coating liquid in a state of being dispersed with a dispersant. The secondary average particle diameter of the inorganic particles in a dispersed state is preferably 0.1 nm or more and 500 nm or less, more preferably 1 nm or more and 300 nm or less, and even more preferably 10 nm or more and 250 nm or less. The secondary average particle size of inorganic particles in a dispersed state can be measured by a dynamic light scattering method.

The content (% by mass) of the inorganic particles in the ink-receiving layer is preferably 50.0% by mass or more and 98.0% by mass or less, preferably 70.0% by mass or more and 96% by mass, based on the total mass of the ink-receiving layer. 0% by mass or less is more preferable.

The coating amount (g/m ² ) of the inorganic particles applied when forming the ink-receiving layer is preferably 8 g/m ² or more and 45 g/m ² or less. Within the above range, the thickness of the ink-receiving layer tends to be preferable.

Inorganic particles include alumina hydrate, alumina, silica, colloidal silica, titanium dioxide, and the like. One or more of these inorganic particles can be used as necessary. Among these inorganic particles, it is preferable to use alumina hydrate, alumina, and silica, which can form a porous structure with high ink absorption.

Boehmite-type alumina hydrate or amorphous alumina hydrate is preferable as the alumina hydrate. As the alumina, gas-phase alumina is preferable. Examples of vapor phase alumina include γ-alumina, α-alumina, δ-alumina, θ-alumina, χ-alumina and the like. Among them, it is preferable to use γ-alumina as the vapor-phase method alumina from the viewpoint of the optical density of the image and the ink absorbability.

Alumina hydrate and alumina are preferably mixed in the ink-receiving layer coating liquid as an aqueous dispersion, and an acid is preferably used as a dispersing agent. As the acid, it is preferable to use a compound represented by R--SO ₃ H since it has the effect of suppressing bleeding of the image. In the formula, R represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or an alkenyl group having 1 to 4 carbon atoms. R may be substituted with an oxo group, a halogen atom, an alkoxy group, and an acyl group.

The content of the acid is preferably 1.0% by mass or more and 2.0% by mass or less, based on the total content of alumina hydrate and alumina, and 1.3% by mass or more and 1.6% by mass. % or less.

Silica used for the ink-receiving layer is roughly classified into a wet method and a dry method (vapor phase method) depending on the manufacturing method. As a wet method, a method is known in which hydrous silica is obtained by producing active silica by acid decomposition of silicate, appropriately polymerizing it, and coagulating and sedimenting it. On the other hand, as a dry method (gas phase method), there is a method by high-temperature gas phase hydrolysis of silicon halide (flame hydrolysis method), and silica sand and coke are heat-reduced and vaporized by an arc in an electric furnace. is known to obtain anhydrous silica by air oxidation (arc method). Silica obtained by a dry method (vapor phase method) (hereinafter also referred to as “vapor phase silica”) is preferably used. Vapor-phase method silica has a particularly large specific surface area, so that it has a particularly high ink absorbability, and since it has a low refractive index, it can impart transparency to the ink-receiving layer.

Alumina hydrate, alumina, and silica may be used in combination. Specifically, there is a method of mixing and dispersing at least two kinds selected from alumina hydrate, alumina, and silica in a powder state to form a dispersion liquid. In the present invention, both alumina hydrate and vapor phase alumina are preferably used as the inorganic particles.

[binder]
The ink receiving layer preferably contains a binder. A binder means a material capable of binding inorganic particles and forming a film.

The content (% by mass) of the binder in the ink-receiving layer is preferably 0.50 times or less as a mass ratio (times) to the content (% by mass) of the inorganic particles. If the ratio exceeds 0.50 times, the amount of the binder is too large relative to the inorganic particles, resulting in a decrease in ink absorbability, and bleeding of the recorded image may not be sufficiently suppressed. More preferably, the ratio is 0.30 times or less. From the viewpoint of the binding property of the ink-receiving layer, the ratio is preferably 0.05 times or more, more preferably 0.08 times or more.

Examples of binders include starch derivatives such as oxidized starch, etherified starch and phosphate esterified starch; cellulose derivatives such as carboxymethyl cellulose and hydroxyethyl cellulose; casein, gelatin, soybean protein, polyvinyl alcohol, and derivatives thereof; Conjugated polymer latex such as polyvinylpyrrolidone, maleic anhydride polymer, styrene-butadiene copolymer, methyl methacrylate-butadiene copolymer; acrylic polymer latex such as acrylic acid ester and methacrylic acid ester polymer; Vinyl polymer latex such as vinyl acetate copolymer; cationized polymer with cationic groups; cationized polymer surface with cationic surfactant; cationic polyvinyl A product obtained by polymerizing the monomers constituting the above polymer in the presence of alcohol and adsorbing polyvinyl alcohol on the surface of the polymer; , Polymers with cationic colloidal particles adsorbed on their surfaces; Aqueous binders such as thermosetting resins such as melamine resins and urea resins; (Co)polymers of acrylic acid esters and methacrylic acid esters such as polymethyl methacrylate Synthetic resins such as One or more of these binders may be used as necessary.

Among the above binders, polyvinyl alcohol and polyvinyl alcohol derivatives are preferably used. Examples of polyvinyl alcohol derivatives include cation-modified polyvinyl alcohol, anion-modified polyvinyl alcohol, silanol-modified polyvinyl alcohol, and polyvinyl acetal.

When preparing the coating solution for the ink-receiving layer, it is preferable to use polyvinyl alcohol or a polyvinyl alcohol derivative as an aqueous solution. In this case, the solid content of the polyvinyl alcohol and polyvinyl alcohol derivative in the aqueous solution is preferably 3.0% by mass or more and 20.0% by mass or less based on the total mass of the ink-receiving layer coating liquid.

[Crosslinking agent]
The ink-receiving layer preferably further contains a cross-linking agent. Examples of cross-linking agents include zirconium-based compounds, amide-based compounds, aluminum-based compounds, boric acid, borate salts, and the like. One or more of these cross-linking agents can be used as necessary. Particularly when polyvinyl alcohol or a polyvinyl alcohol derivative is used as the binder, it is preferable to use boric acid or a borate among the above-described cross-linking agents.

Boric acid includes orthoboric acid (H ₃ BO ₃ ), metaboric acid, hypoboric acid, and the like. The borate is preferably a water-soluble salt of boric acid. Examples thereof include alkali metal salts of boric acid such as sodium boric acid and potassium boric acid; alkaline earth metal salts of boric acid such as magnesium boric acid and calcium boric acid; and ammonium boric acid. Among these, it is preferable to use orthoboric acid from the viewpoint of the effect of suppressing the generation of cracks and the stability of the coating solution over time.

The amount of the cross-linking agent used can be appropriately adjusted according to the production conditions and the like. The content of the cross-linking agent in the ink-receiving layer is preferably 1.0% by mass or more and 50.0% by mass or less, and 5.0% by mass or more and 40.0% by mass or less, based on the binder content. is more preferable.

When the binder is polyvinyl alcohol and the cross-linking agent is at least one selected from boric acid and borate salts, the total content of the cross-linking agent in the ink-receiving layer is 5% based on the content of the binder. 0% by mass or more and 30.0% by mass or less.

[Other additives]
The ink-receiving layer may contain other additives than those mentioned so far. Specific examples include pH adjusters, thickeners, release agents, fluorescent whitening agents, ultraviolet absorbers, antioxidants, preservatives, antifungal agents, waterproofing agents, curing agents, and the like.

The haze (%) of the recording medium is preferably 60% or less, more preferably 30% or less. Let T _t be the transmittance of all light transmitted through the recording medium, and T _d be the transmittance of diffused light among all the light transmitted through the recording medium. Haze (%) is expressed by (T _d /T _t )×100 and is an index showing the transparency of a recording medium. The closer the haze is to 0%, the lower the transmittance of diffused light and the higher the transparency of the recording medium. Haze (%) can be measured using a haze meter according to JIS K 7105 and JIS K 7136.

[Method for producing recording medium]
A method for producing a recording medium is preferably a method for producing a recording medium comprising a step of preparing an ink-receiving layer coating liquid and a step of applying the ink-receiving layer coating liquid to a transparent substrate. A method for manufacturing the recording medium will be described below.

Examples of the method for forming the ink-receiving layer on the transparent substrate include the following methods. First, an ink-receiving layer coating solution is prepared. Then, the above coating solution is applied to the transparent substrate and dried. Thereby, a recording medium can be obtained. As a method for applying the coating liquid, a curtain coater, a coater using an extrusion method, a coater using a slide hopper method, or the like can be used. The coating liquid may be heated during coating. In addition, drying methods after coating include methods using hot air dryers such as straight tunnel dryers, arch dryers, air loop dryers, sine curve air float dryers, and dryers using infrared rays, heating dryers, microwaves, etc. and the like.

EXAMPLES The present invention will be described in more detail below with reference to examples , comparative examples , and reference examples , but the present invention is not limited by the following examples as long as it does not exceed the scope of the invention. "Parts" and "%" regarding component amounts are based on mass unless otherwise specified.

<Preparation of inorganic particle dispersion>
(Inorganic particle dispersion liquid 1)
40.0 g of powdered alumina hydrate (DISPERAL HP14, manufactured by Sasol) and 0.6 g of methanesulfonic acid were added to 160.0 g of pure water. After that, the mixture was stirred for 30 minutes with a mixer to prepare an inorganic particle dispersion liquid 1 containing 20.0% of alumina hydrate as inorganic particles.

(Preparation of inorganic particle dispersion liquid 2)
Inorganic particle dispersion liquid 2 was prepared in the same manner as inorganic particle dispersion liquid 1, except that the type of inorganic particles was changed to powdery alumina hydrate (DISPERAL HP22, manufactured by Sasol).

(Preparation of inorganic particle dispersion liquid 3)
Inorganic Particle Dispersion 3 was prepared in the same manner as Inorganic Particle Dispersion 1, except that the type of inorganic particles was changed to powdery alumina hydrate (DISPERAL HP30, manufactured by Sasol).

(Preparation of inorganic particle dispersion liquid 4)
To 160.0 g of pure water were added 40.0 g of powdery vapor-phase silica (AEROSIL 50, manufactured by EVONIK) and 2.0 g of Charol DC-902 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.). After that, the mixture was stirred for 30 minutes with a mixer to prepare an inorganic particle dispersion liquid 4 containing 20.0% silica as inorganic particles.

<Preparation of coating solution>
Polyvinyl alcohol (PVA235 manufactured by Kuraray, degree of polymerization: 3500, degree of saponification: 88%) as a binder was dissolved in ion-exchanged water to obtain an aqueous solution of polyvinyl alcohol with a solid content of 8.0%. Then, the polyvinyl alcohol aqueous solution obtained in the inorganic particle dispersion described in Table 1 is converted to the solid content of the polyvinyl alcohol aqueous solution ((binder) / (inorganic particles)) with respect to the solid content of the inorganic particle dispersion. Mixed to the values described in 1. Next, a 3.0% boric acid aqueous solution was mixed so as to have a boric acid solid content of 1.0% based on the solid content of the inorganic particles, to obtain a coating liquid.

<Production of Recording Medium>
As shown in Table 2, the prepared coating solution was applied to a transparent substrate having a thickness of 100 μm so that the dry coating amount (g/m ² ) was the value shown in Table 2, and the temperature was 90. C. to obtain a recording medium. Table 2 also describes the haze, the average pore size of the ink-receiving layer, the ink absorption amount of the ink-receiving layer, and the thickness of the ink-receiving layer. A measuring method will be described later. In Table 2, PET is polyethylene terephthalate, PE is polyethylene, and PVC is polyvinyl chloride.

[Method for measuring haze]
The haze (%) of the recording medium was measured according to JIS K 7105 and JIS K 7136 using a haze meter (NDH4000, manufactured by Nippon Denshoku Industries).

[Method for measuring average pore size]
The pore size of the ink-receiving layer was measured using a pore size distribution measuring device (POROMETER 3Gz, manufactured by Quantachrome Instruments) using a gas permeation method. 100 pore sizes were randomly selected, and the average value of the 100 pore sizes was used as the average pore size of the ink-receiving layer.

[Method for measuring ink absorption]
As a method for evaluating the absorption characteristics of the ink (solvent) to the recording medium, JAPAN TAPPI paper pulp test method No. 51, "Test Method for Liquid Absorbency of Paper and Paperboard", the Bristow method. Using this Bristow method, ink absorption was measured.

A certain amount of ink (solvent) was injected into a holding container having an opening slit of a predetermined size, and brought into contact with a recording medium processed into a strip and wound around a disc through the slit. Then, while the position of the holding container was fixed, the disk was rotated, and the area (length) of the ink band transferred to the recording medium was measured. A transfer amount (ml/m ² ) per unit area can be calculated from the area of the ink band, and this transfer amount (ml/m ² ) indicates the amount of ink absorbed by the recording medium in a predetermined time. Here, the predetermined time is defined as transition time. The transition time (millisecond ^1/2 ) corresponds to the contact time between the slit and the recording medium, and is converted from the speed of the disk and the width of the opening slit. The ink absorption amount of the recording medium in the present invention represents the ink transfer amount at ^1/2 of 10 milliseconds.

<Preparation of silver particle dispersion>
Silver particle dispersions 1 to 3 (silver particle content: 20.0%, resin content: 2.0%) according to the preparation method described in Example 2 of WO 2008/049519. got Varying the stirring speed during preparation varied the value of _D50 . Furthermore, according to the preparation method described in Example 2-2 of JP-A-2004-285106, silver particle dispersion 4 (silver particle content: 20.0%, surfactant content: 2.0%) was prepared. 0%) was obtained. The _D50 of the silver particles was determined by dynamic light scattering and is listed in Table 3.

<Preparation of aluminum particle dispersion>
Aluminum particle dispersions 1 and 2 (aluminum particle content: 20.0%) were obtained according to the method for preparing a metallic pigment dispersion in Examples of JP-A-2010-18651. Changing the dispersing conditions changed the _D50 values. The _D50 of the aluminum particles was determined by dynamic light scattering and is listed in Table 3.

[Method for measuring _D50 ]
The D ₅₀ of silver particles and aluminum particles was measured using a particle size distribution meter (Nanotrac UPA-EX150, manufactured by Nikkiso) using a dynamic light scattering method. The measurement conditions are SetZero: 30 seconds, number of measurements: 3 times, measurement time: 180 seconds, shape: spherical, refractive index: 1.6.

<Preparation of first ink>
After mixing each component shown in Table 4 and sufficiently stirring, pressure filtration was performed with a filter having a pore size of 1.2 μm to obtain a first ink. Acetylenol E100 is a nonionic surfactant manufactured by Kawaken Fine Chemicals. Acetylenol E100 has an HLB value of 13 determined by the Griffin method. Compound 1 was obtained from C.I. I. Acid Blue 9.

<Preparation of second ink>
(Preparation of dye)
The following compounds were prepared. Although the structural formula of compound 3 is shown in the free acid form, it was used as the potassium salt.
Compound 1: C.I. I. acid blue 9
Compound 2: C.I. I. acid red 249
Compound 3: A compound represented by the following formula (2), synthesized according to the description of the synthesis method of JP-A-2016-108545.

(Preparation of pigment dispersion)
A styrene-ethyl acrylate-acrylic acid copolymer (resin dispersant) having an acid value of 150 mgKOH/g and a weight average molecular weight of 8,000 was prepared. 20.0 parts of this copolymer is neutralized with potassium hydroxide having an equimolar acid value, an appropriate amount of pure water is added, and a resin dispersant having a resin (solid content) content of 20.0% is obtained. was prepared. 20.0 parts of a pigment (Monac 1100, manufactured by Cabot Corporation), 10.0 parts of an aqueous solution of a resin dispersant, and 75.0 parts of pure water were mixed. This mixture and 200 parts of zirconia beads having a diameter of 0.3 mm were placed in a batch-type vertical sand mill (manufactured by Imex) and dispersed for 5 hours while cooling with water. After that, centrifugal separation is performed to remove coarse particles, and pressure filtration is performed through a cellulose acetate filter (manufactured by Advantech) with a pore size of 3.0 μm to obtain a pigment content of 20.0% and a resin dispersant content of 2.0%. A .0% pigment dispersion was prepared.

(second ink)
After mixing each component shown in Table 5 and sufficiently stirring, pressure filtration was performed with a filter having a pore size of 1.2 μm to obtain a second ink. Acetylenol E100 is a nonionic surfactant manufactured by Kawaken Fine Chemicals.

(Processing agent)
A treatment agent containing 15 parts of powdered vapor-phase silica (CAB-O-SPERSE PG002, manufactured by Cabot), 5 parts of urethane resin (Yucoat UWS-145, manufactured by Sanyo Chemical Industries), and 80 parts of ion-exchanged water was prepared. .

<Evaluation>
Each of the first ink and the second ink shown in Table 6 was filled in an ink cartridge, and set in an inkjet recording apparatus (PIXUS MG3630, manufactured by Canon Inc.) equipped with a recording head that ejects ink by thermal energy. In this embodiment, the first ink and the second ink are used to print an image under the condition that one ink droplet of about 11.2 pL is applied to a unit area of 1/1200 inch×1/1200 inch, and the printing duty is 100. %. In Examples 1 to 7, 9 to 14, 15 and 16, and Comparative Examples 1 to 5 and 7 , the inkjet recording apparatus was used to apply the second ink to the recording medium shown in Table 6 at a recording duty of 100%. Granted. After that, the first ink was applied at a recording duty of 100% so that at least a part of the area to which the second ink was applied overlapped . In Comparative Example 6, the inkjet recording apparatus was used to apply the first ink to the recording medium shown in Table 6 at a recording duty of 100%. After that, the second ink was applied at a recording duty of 100% so that at least a part of the area to which the first ink was applied overlapped. In Reference Example 1, after the processing agent was applied to the recording medium with a roller, the second ink was applied at a recording duty of 100%. The amount of the processing agent applied per unit area (g/m ² ) to the recording medium was 1 g/m ² . After that, the first ink was applied at a recording duty of 100% so that at least a part of the area to which the second ink was applied overlapped. The glossy paper used in Comparative Example 1 was Canon photo paper (Gloss Pro Platinum Grade, manufactured by Canon). In the present invention, according to the following evaluation criteria, A or B was defined as an acceptable level, and C was defined as an unacceptable level. Evaluation results are shown in Table 6.

(Image Glossiness)
For the obtained image, using a goniospectrophotometer (GSP-2, manufactured by Murakami Shiki), sharpness = L / w (L is the highest lightness measured at the light receiving part of the spectrophotometer As the lightness value, w is the width of the light-receiving angle at two points representing the half value of L (L/2). When the definition value is 0.2 or more, when the image is visually observed, the brightness changes depending on the observation angle, so that the image can be recognized as having glossiness.
A: Clarity was 4.0 or more B: Clarity was 3.0 or more and less than 4.0 C: Clarity was less than 3.0.

(Image color development)
Using an integrating sphere type colorimeter CM-2600d (manufactured by Konica Minolta) in SCI mode, measurements were made as follows to evaluate color development. a ₀ ^* and b ₀ ^* of an image recorded at a recording duty of 100% using only the first ink containing silver particles, and each ink using an ink containing silver particles and an ink containing a dye at a recording duty of 100%. The a ₁ ^* and b ₁ ^* of the images recorded in % were measured. Using these values, ΔE _ab was calculated from the formula: color difference ΔE _ab ={(a ₁ ^* −a ^* ₀ ) ² +(b ₁ ^* −b ^* ₀ ) ² } ^1/2 . a ^* and b ^* are the values of the L ^* a ^* b ^* system defined by the CIE (International Commission on Illumination). When ΔE _ab is 2.0 or more, an image is obtained in which the color tone of the dye used is recognizable instead of silver. When the value of ΔE _ab is large, an image is obtained in which the color tone of the dye used is well recognized.
A: ΔE _ab was 6.0 or more B: ΔE _ab was 2.0 or more and less than 6.0 C: ΔE _ab was less than 2.0.

(Image bleeding)
In the obtained image, the evaluation was made by visually observing the regions to which both the first ink and the second ink were applied.
A: There was no bleeding in the image. B: There was bleeding in the image.

Claims (18)

A recording medium having a transparent substrate and an ink-receiving layer on one side of the transparent substrate is coated with a first ink and a second ink so that at least a part thereof overlaps with the surface having the ink-receiving layer . An inkjet recording method having a recording step of recording a metallic image,
the first ink is an aqueous ink containing silver particles;
the second ink is an aqueous ink containing a dye,
An inkjet recording method, wherein a volume-based cumulative 50% particle diameter (nm) of the silver particles is larger than an average pore size (nm) of the ink-receiving layer. The inkjet recording method according to Claim 1, wherein the ink absorption amount (mL/ ^m2 ) of the ink receiving layer is 0.4 mL/ ^m2 or more. Ink absorption amount of the ink receiving layer (mL/m ² ) is 2.0 mL/m ² 3. The inkjet recording method according to claim 2, wherein: 4. The inkjet recording method according to any one of claims 1 to 3, wherein the average pore size (nm) of the ink receiving layer is 40 nm or less. 4. The inkjet recording method according to any one of claims 1 to 3, wherein the average pore diameter (nm) of the ink receiving layer is 10 nm or more and 30 nm or less. 6. The ink jet recording method according to any one of claims 1 to 5 , wherein the ink receiving layer has a thickness ([mu]m) of 5.5 [mu]m or more. 7. The ink jet recording method according to claim 6, wherein the thickness ([mu]m) of the ink receiving layer is 30.0 [mu]m or less. 1 to 1, wherein the content (% by mass) of the binder in the ink-receiving layer is 0.50 times or less as a mass ratio (fold) with respect to the content (% by mass) of the inorganic particles in the ink-receiving layer. 8. The inkjet recording method according to any one of 7 . 9. The method according to claim 8, wherein the content (% by mass) of the binder in the ink-receiving layer is 0.05 times or more as a mass ratio (fold) to the content (% by mass) of the inorganic particles in the ink-receiving layer. The ink jet recording method described. 10. The inkjet recording method according to any one of claims 1 to 9, wherein the transparent substrate is polyester resin, polyolefin resin, or polyvinyl chloride resin. The inkjet recording method according to any one of claims 1 to 10, wherein the thickness of the transparent base material is 1 µm or more and 5,000 µm or less. 12. Any one of claims 1 to 11, wherein the content (% by mass) of the silver particles in the first ink is 2.0% by mass or more and 15.0% by mass or less based on the total mass of the first ink. The ink jet recording method according to the item. The inkjet recording method according to any one of claims 1 to 12, wherein the volume-based cumulative 50% particle size (nm) of the silver particles in the first ink is 10 nm or more and 150 nm or less. 14. The inkjet recording method according to any one of claims 1 to 13, wherein the volume-based cumulative 90% particle diameter (nm) of the silver particles in the first ink is 10 nm or more and 200 nm or less. 15. The content (% by mass) of the dye in the second ink is 1.0% by mass or more and 10.0% by mass or less based on the total mass of the second ink. The inkjet recording method described in . 16. The recording medium according to any one of claims 1 to 15, wherein after applying the second ink, the first ink is applied so that at least a part of the area to which the second ink is applied overlaps. Inkjet recording method. 17. The inkjet recording method according to any one of Claims 1 to 16, wherein the image is observed from the side of the recording medium opposite to the side having the ink-receiving layer. 18. The inkjet according to any one of claims 1 to 17, wherein in the recording medium on which the image is recorded, the dye contained in the second ink is present in the ink receiving layer of the recording medium. Recording method.