JP2020011384A - Inkjet recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inkjet recording method capable of recording an image excellent in gloss while maintaining the water resistance of an aluminum pigment. An inkjet recording method for recording an image by applying a water-based first ink and a water-based second ink to a recording medium, respectively. The first ink contains an aluminum pigment and phosphoric acid or a phosphate, the second ink contains a surfactant, and after applying one of the first ink and the second ink to a recording medium, The other ink is applied to the recording medium so as to come into contact with the applied one ink. [Selection diagram] None

Description

  The present invention relates to an inkjet recording method.

  2. Description of the Related Art Conventionally, in various image recording methods including an ink jet recording method, an ink containing a metal pigment such as an aluminum pigment or a pearl pigment has been used. If an ink containing these metal pigments as a coloring material is used, an image showing metallic luster (metallic color) can be recorded.

  It is known that an aluminum pigment reacts with moisture, generates hydrogen gas, aggregates and blackens. When an ink containing an aluminum pigment in such an aggregated state is used, it is difficult to record an image exhibiting good metallic luster. For this reason, attempts have been made to incorporate various additives into the ink in order to ensure the water resistance of the aluminum pigment in the ink. For example, in order to improve the water resistance of an aluminum pigment, an ink containing phosphoric acid or a phosphoric acid ester has been proposed (Patent Documents 1 and 2).

JP-A-3-074742 JP 2011-508030 A

  The present inventor has studied using an ink containing an aluminum pigment proposed in Patent Documents 1 and 2 to record an image exhibiting metallic luster by an ink jet recording method. As a result, it was found that the metallic gloss of the recorded image was not always good, and there was room for further improvement.

  Accordingly, an object of the present invention is to provide an ink jet recording method capable of recording an image having excellent gloss while maintaining the water resistance of the aluminum pigment.

  That is, according to the present invention, there is provided an ink jet recording method for recording an image by applying a water-based first ink and a water-based second ink to a recording medium, wherein the first ink comprises an aluminum pigment and phosphoric acid. Or containing a phosphate, the second ink contains a surfactant, and after applying one of the first ink and the second ink to the recording medium, the applied one ink An ink jet recording method is provided, wherein the other ink is applied to the recording medium so as to make contact with the recording medium.

  ADVANTAGE OF THE INVENTION According to this invention, the inkjet recording method which can record the image excellent in glossiness, maintaining the water resistance of an aluminum pigment can be provided.

4 is an electron micrograph of an image recorded in Example 1. 5 is an electron micrograph of an image recorded in Comparative Example 1. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram schematically illustrating an example of an inkjet recording apparatus used in an inkjet recording method of the present invention, wherein (a) is a perspective view of a main part of the inkjet recording apparatus, and (b) is a perspective view of a head cartridge.

  Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is dissociated into ions in the ink, but is expressed as "contains a salt" for convenience. Further, the water-based ink for inkjet may be simply described as “ink”. Unless otherwise specified, physical property values are values at normal temperature (25 ° C.) and normal pressure (1 atm).

  The present inventor has studied an ink containing an aluminum pigment and phosphoric acid or phosphate. The phosphoric acid or phosphate ionizes in the ink and binds to the surface of the aluminum pigment, thereby accumulating the aluminum pigment to form an aggregate. When the ink containing the aluminum pigment aggregate is ejected by an inkjet method, an uneven structure derived from the aggregate is easily formed on the applied recording medium, and the glossiness of the recorded image is reduced. It has been found.

  When a shear stress was applied to a portion of the recorded image where the glossiness was reduced, it was found that the glossiness was improved. This is considered to be because the accumulation of the aluminum pigment was eliminated by the applied shear stress, and the flake-shaped aluminum pigment was oriented so as to be substantially parallel to the surface of the recording medium. Therefore, it is possible to improve the glossiness of the image by eliminating the accumulation of the aluminum pigment, orienting the flaky aluminum pigment so as to be substantially parallel to the surface of the recording medium, and reflecting the incident light more strongly. Conceivable.

  By the way, the ink for inkjet usually contains an appropriate amount of a surfactant in consideration of inkjet suitability. It is also speculated that the accumulation of aluminum pigments caused by phosphoric acid or phosphate can be eliminated by coexisting surfactants. However, the coexistence of the aluminum pigment and the surfactant in one ink cannot sufficiently eliminate the accumulation of the aluminum pigment.

  The present inventor observed the process of applying an ink containing an aluminum pigment onto a recording medium by ejecting the ink using an inkjet method from above using an optical microscope. As a result, inside the ink droplet applied to the recording medium, the aluminum pigment migrates from the vicinity of the center of the ink droplet toward the periphery, then turns around at the periphery and moves again to the vicinity of the center (circulation flow). ) Could be confirmed. This circulating flow is considered to be a so-called Marangoni convection generated by a local concentration difference in a dispersion component (aluminum pigment or the like) due to evaporation of water from the ink droplet surface and a surface tension difference caused by the difference. .

  In consideration of the above points, the present inventor generates a circulating flow in ink droplets after applying an ink containing an aluminum pigment to a recording medium, and uses the force of the circulating flow to accumulate the aluminum pigment. Have been found, and the present invention has been completed. That is, in the inkjet recording method of the present invention, an aqueous first ink containing an aluminum pigment and phosphoric acid or a phosphate, and an aqueous second ink containing a surfactant are used. Then, after applying one of the first ink and the second ink to the recording medium, the other ink is applied to the recording medium so as to come into contact with the applied one of the inks, thereby recording an image. More specifically, (i) after the first ink is applied to the recording medium, the first ink and the first ink are applied before the entire state of the applied first ink is absorbed by the recording medium and the liquid state is lost. An image is recorded by applying the second ink so as to make contact. Alternatively, (ii) after applying the second ink to the recording medium, contact the second ink before the entire amount of the applied second ink is absorbed by the recording medium and the liquid state is lost. An image is recorded by applying the first ink.

  With the above configuration, the aluminum pigment dispersed in the first ink is stirred when the inks come into contact with each other, and a strong circulating flow (Marangoni convection) is caused by a locally formed concentration gradient. Occurs. Thereby, the accumulation of the aluminum pigment in the first ink is eliminated, and the flake-shaped aluminum pigment is oriented so as to be substantially parallel to the surface of the recording medium. Therefore, the incident light is more strongly reflected, and the glossiness of the image can be enhanced.

<Inkjet recording method>
The inkjet recording method of the present invention is a method for recording an image by applying a first aqueous ink and a second aqueous ink to a recording medium, respectively. The first ink contains an aluminum pigment and phosphoric acid or phosphate, and the second ink contains a surfactant. Then, after applying one of the first ink and the second ink to the recording medium, the other ink is applied to the recording medium so as to come into contact with the applied one of the inks. Hereinafter, the details of the inkjet recording method of the present invention will be described.

(First ink)
The first ink used in the ink jet recording method of the present invention contains an aluminum pigment and phosphoric acid or phosphate.

[Aluminum pigment]
As the aluminum pigment, a flake-like pigment processed into a size that can be ejected from an ink jet recording head can be used. The average particle size of the aluminum pigment is usually 5 μm or less, preferably 2 μm or less. The average thickness of the aluminum pigment is preferably 5 nm or more and 100 nm or less. The average particle size and average thickness of the aluminum pigment can be measured using an image taken with an electron microscope.

  The content (% by mass) of the aluminum pigment in the first ink is preferably from 0.1% by mass to 10.0% by mass, and more preferably from 1.0% by mass to 7.5% by mass, based on the total mass of the ink. It is more preferable that the content be not more than mass%. If the content of the aluminum pigment in the first ink is too small, the amount of light reflection is likely to be reduced by the aluminum pigment, and the effect of improving the glossiness may be slightly reduced.

  As the aluminum pigment, for example, one prepared by the following procedure can be used. First, a base film having a release layer formed on its surface is prepared, and a thin aluminum film having a desired thickness is formed on the surface of the release layer by a technique such as a vacuum evaporation method. Next, the release layer is dissolved by, for example, dipping the release layer in a dissolvable liquid, and the aluminum thin film is released to obtain a dispersion liquid in which aluminum pieces are dispersed. Thereafter, by crushing the aluminum pieces in the dispersion to a desired size, a flake-like aluminum pigment having a desired particle size and thickness can be obtained.

[Phosphoric acid, phosphate]
The first ink contains phosphoric acid or phosphate. Phosphoric acid and phosphate are components for suppressing the reaction between the aluminum pigment and water to improve the water resistance of the aluminum pigment. The content (% by mass) of phosphoric acid or phosphate in the first ink is preferably 0.1% by mass or more and 20.0% by mass or less based on the total mass of the ink, and is 1.0% by mass or less. More preferably, the content is at least 10.0 mass%. If the content of the phosphoric acid or phosphate in the first ink is too small, the water resistance of the aluminum pigment tends to decrease, and the aluminum pigment which reacts with water and has a reduced glossiness is partially contained. , The glossiness of the image may be slightly reduced.

  Phosphates include sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, calcium monohydrogen phosphate, dihydrogen phosphate Examples include calcium, tricalcium phosphate, zirconium phosphate, aluminum phosphate, and sodium pyrophosphate. These phosphates can be used alone or in combination of two or more.

[Aqueous medium]
The first ink is an aqueous ink containing water as an aqueous medium. As the water, it is preferable to use deionized water (ion exchange water). The content (% by mass) of water in the first ink is preferably from 10.0% by mass to 90.0% by mass, and more preferably from 50.0% by mass to 90.0% by mass, based on the total mass of the ink. % Is more preferable.

  The aqueous medium may further contain a water-soluble organic solvent. The type of the water-soluble organic solvent is not particularly limited as long as it is water-soluble. The content of the water-soluble organic solvent in the first ink is preferably 0.1% by mass or more and 5.0% by mass or less based on the total mass of the ink.

  By using a glycol ether among the water-soluble organic solvents, the dispersion state of the aluminum pigment can be further improved. As the glycol ether, ethylene glycol monoallyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monohexyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether, propylene glycol monopropyl ether, etc. Can be mentioned. These glycol ethers can be used alone or in combination of two or more.

[Surfactant]
The first ink may contain a surfactant. As the surfactant, an anionic surfactant, a cationic surfactant, a nonionic surfactant, an amphoteric surfactant, a silicone-based surfactant, a fluorine-based surfactant, and the like are blended in an inkjet ink. Known surfactants can be used. Among them, it is preferable to use a nonionic surfactant. Examples of the nonionic surfactant include a polyoxyethylene alkyl ether-based surfactant, a polyoxyethylene alkyl phenyl ether-based surfactant, and an acetylene glycol-based surfactant.

  The content (% by mass) of the surfactant in the first ink is preferably 0.1% by mass or more and 5.0% by mass or less based on the total mass of the ink.

[Other ingredients]
In addition to the above components, the first ink may be a water-soluble organic solid that is solid at room temperature, such as polyhydric alcohols such as trimethylolpropane and trimethylolethane, and urea derivatives such as urea and ethylene urea. It may contain a compound. Further, the first ink may contain various additives such as a pH adjuster, a rust inhibitor, a preservative, a fungicide, an antioxidant, an antioxidant, a reduction inhibitor, an evaporation accelerator, a chelating agent, and a resin, as necessary. An agent may be contained.

[Physical properties]
The viscosity of the first ink at 25 ° C. is preferably from 1.0 mPa · s to 10.0 mPa · s, and more preferably from 1.0 mPa · s to 5.0 mPa · s.

(Second ink)
The second ink used in the inkjet recording method of the present invention contains a surfactant.

[Surfactant]
As the surfactant, an anionic surfactant, a cationic surfactant, a nonionic surfactant, an amphoteric surfactant, a silicone-based surfactant, a fluorine-based surfactant, and the like are blended in an inkjet ink. Known surfactants can be used. Among them, it is preferable to use a nonionic surfactant. Examples of the nonionic surfactant include a polyoxyethylene alkyl ether-based surfactant, a polyoxyethylene alkyl phenyl ether-based surfactant, and an acetylene glycol-based surfactant. When a surfactant is contained in the first ink, the surfactant contained in the second ink is preferably of the same type as the surfactant contained in the first ink. The content (% by mass) of the surfactant in the second ink is preferably from 0.1% by mass to 10.0% by mass, and more preferably from 1.0% by mass to 5.0% by mass, based on the total mass of the ink. More preferably, it is 0% by mass or less.

  It is preferable that the first ink contains a surfactant and the content (% by mass) of the surfactant in the second ink is larger than the content (% by mass) of the surfactant in the first ink. . If the content of the surfactant in the second ink is equal to or less than the content of the surfactant in the first ink, even if the second ink comes into contact with the first ink, the local concentration A circulating flow due to the difference is less likely to occur, and the effect of improving glossiness may be slightly reduced.

[Aqueous medium]
The second ink is an aqueous ink containing water as an aqueous medium. As the water, it is preferable to use deionized water (ion exchange water). The content (% by mass) of water in the second ink is preferably from 10.0% by mass to 90.0% by mass, and more preferably from 50.0% by mass to 90.0% by mass, based on the total mass of the ink. % Is more preferable.

  The aqueous medium may further contain a water-soluble organic solvent. The type of the water-soluble organic solvent is not particularly limited as long as it is water-soluble, and the same water-soluble organic solvent as that contained in the first ink can be used. The content of the water-soluble organic solvent in the second ink is preferably 0.1% by mass or more and 5.0% by mass or less based on the total mass of the ink.

[Other ingredients]
Other components can be contained in the second ink, as in the first ink. The types, properties, contents, and the like of these components are the same as the other components contained in the first ink, including the preferred types and ranges.

[Physical properties]
The viscosity of the second ink at 25 ° C. is preferably from 1.0 mPa · s to 10.0 mPa · s, more preferably from 1.0 mPa · s to 5.0 mPa · s.

(recoding media)
It is preferable to use an absorptive recording medium as the recording medium. Whether the recording medium is absorptive or non-absorbable can be determined by the Bristow method described below. First, J.I. TAPPI paper pulp test method No. The liquid absorptivity is measured by the Bristow method according to 51-87, and the Ka value for water is calculated. A recording medium having a water Ka value of 0.35 mL · m ⁻² · msec ^−1/2 or more can be determined to be an “absorbent recording medium”. On the other hand, a “non-absorbable recording medium” is a recording medium that does not absorb water. Therefore, when the above-described liquid absorbency measurement is performed, the calculated Ka value is less than 0.35 mL · m ⁻² · msec ^-1/2 . Examples of the non-absorbable recording medium include a plastic film such as a vinyl chloride sheet, a polyethylene terephthalate film, and an acrylic resin film.

  Examples of the absorbent recording medium include uncoated paper having no coat layer such as plain paper; and coated paper having a coat layer such as matte paper and glossy paper. Among them, coated paper having glossiness can be preferably used. Since the coated paper has a high surface smoothness, when an aluminum pigment is applied, light incident on the surface of the aluminum pigment is easily reflected in a certain direction, so that an image with more excellent gloss can be recorded. .

(Inkjet recording method)
In the inkjet recording method of the present invention, after applying one of the first ink and the second ink (for example, the first ink) to the recording medium, the other ink (for example, the first ink and the second ink) is brought into contact with the applied one ink. , Second ink) to the recording medium. The applied amount (μg / inch ² ) of each ink (first ink and second ink) per unit area of the recording medium is preferably 25 μg or more and 45 μg or less, more preferably 30 μg or more and 40 μg or less.

  The ratio of the applied amount of the second ink per unit area of the recording medium to the applied amount of the first ink per unit area of the recording medium is preferably more than 0.5 times and not more than 1.0 times, More preferably, it is set to 0.6 times or more and 1.0 times or less. By setting the ratio (second / first) of the applied amount of the second ink to the applied amount of the first ink within the above range, a circulating flow with sufficient strength can be generated, and the accumulation of aluminum pigments Is eliminated, and an image with more excellent gloss can be recorded.

  It is preferable to apply the second ink to the recording medium within 500 milliseconds after applying the first ink to the recording medium. When the application of the second ink to the recording medium exceeds 500 milliseconds after the application of the first ink to the recording medium, the first ink applied first maintains a liquid state due to absorption into the recording medium. It becomes difficult. For this reason, even if the first ink contacts the second ink, a sufficient circulation flow cannot be generated, and the effect of improving the glossiness of the image may be slightly reduced.

(Inkjet recording device)
The inkjet recording method of the present invention is a method of ejecting the above-described first ink and second ink from an inkjet type recording head and applying them to a recording medium to record an image. Examples of the method of ejecting ink include a method of applying mechanical energy to the ink and a method of applying thermal energy to the ink. In the present invention, it is particularly preferable to employ a method of applying thermal energy to the ink to eject the ink.

  FIGS. 3A and 3B are diagrams schematically showing an example of an ink jet recording apparatus used in the ink jet recording method of the present invention, wherein FIG. 3A is a perspective view of a main part of the ink jet recording apparatus, and FIG. 3B is a perspective view of a head cartridge. It is. The inkjet recording apparatus includes a transport unit (not shown) for transporting the recording medium 32 and a carriage shaft 34. A head cartridge 36 can be mounted on the carriage shaft 34. The head cartridge 36 includes recording heads 38 and 40, and is configured so that the ink cartridge 42 is set. While the head cartridge 36 is conveyed in the main scanning direction along the carriage shaft 34, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32. Then, the image is recorded on the recording medium 32 by being conveyed in the sub-scanning direction by the conveying means (not shown).

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the following Examples unless it exceeds the gist thereof. Components described as "parts" and "%" are based on mass unless otherwise specified.

<Preparation of aluminum dispersion>
As a substrate film, a film made of polyethylene terephthalate having a surface roughness Ra of 0.1 μm or less was prepared. After a 5% aqueous solution of polyvinyl alcohol was uniformly applied onto the substrate film, it was dried to form a release layer having a thickness of 10 to 50 μm. Aluminum was formed as a thin film having a thickness of 50 μm on the formed release layer by a vacuum evaporation method. The film on which aluminum was formed on the thin film was immersed in an aqueous solution containing 5.0% of diethylene glycol monomethyl ether, 10.0% of disodium hydrogen phosphate, and 85.0% of ion-exchanged water, and irradiated with ultrasonic waves. The release layer (polyvinyl alcohol) was dissolved by the irradiation of ultrasonic waves, and an aluminum dispersion in which aluminum pieces were dispersed was obtained.

  The particle size of the aluminum pieces in the aluminum dispersion was measured using a liquid flow type particle size analyzer (trade name “FPIA3000”, manufactured by Malvern). As a result, the integrated frequency of particles having an equivalent circle diameter of 1 μm or less was 95% or more. The thickness of the aluminum piece measured using a field emission scanning electron microscope (trade name “SU-8040”, manufactured by Hitachi High-Technologies Corporation) was 50 nm. Further, an aluminum piece was fractionated from the obtained aluminum dispersion and used as an aluminum pigment.

<Preparation of ink>
Each component (unit:%) shown in Tables 1 and 2 was mixed and sufficiently stirred, and then subjected to pressure filtration with a micro filter having a pore size of 3.0 μm (manufactured by FUJIFILM Corporation) to prepare each ink. In Tables 1 and 2, "acetylenol E100" is a trade name of a nonionic surfactant (ethylene oxide adduct of acetylene glycol) manufactured by Kawaken Fine Chemicals.

  When the content of disodium hydrogen phosphate is less than 0.1%, the water resistance of the aluminum pigment is reduced, and the aluminum pigment reacts with water to generate hydrogen gas, and may coagulate and blacken. is there. For this reason, subsequent evaluations could not be performed for inks having a disodium hydrogen phosphate content of less than 0.1%.

<Evaluation>
The cartridge filled with the prepared ink was set in an ink jet recording apparatus (PIXUS MG5730, manufactured by Canon) which discharges the ink by thermal energy. In the present embodiment, the recording duty of a solid image recorded under the condition of applying 20 pL of ink to a unit area of 1/1200 inch × 1/1200 inch is defined as 100%. Under the evaluation conditions of this embodiment, if the print duty is 125%, the coverage of the print medium with the ink is 100%. An image was recorded on glossy paper (trade name "Canon Photo Paper / Glossy Gold GL-101", manufactured by Canon) under the evaluation conditions shown in Table 3 with ink applied. Specifically, a circular pattern having a diameter of 10 mm is formed with “ink applied first”, and within 500 ms, “ink applied later” is formed in a circular shape so as to overlap the circular pattern formed earlier. The image was recorded with the application. Using a gloss meter (trade name "VG7000", manufactured by Nippon Denshoku Industries Co., Ltd.), the 20-degree specular gloss of the recorded circular image was measured in accordance with JIS Z8741: 1997, and the evaluation criteria shown below were used. Therefore, the glossiness of the image was evaluated. In the present invention, “A”, “B”, “C”, “D”, and “E” are set to preferable levels, and “F” is set to an unacceptable level in the following evaluation criteria. Table 3 shows the evaluation results.
A: The difference in glossiness from the control glossiness F was 300 or more.
B: The difference in gloss from the control gloss F was 100 or more and less than 300.
C: Difference in glossiness from control glossiness F was less than 100.
D: The difference in glossiness from the control glossiness F was 100 or more and less than 300, but the amount of aluminum constituting the image was smaller than that in rank B.
E: The difference in glossiness from the control glossiness F was less than 100, but the amount of aluminum constituting the image was smaller than that in rank C.
F: The gloss was set to “control gloss F” of less than 100 (the second ink was not used).

  The images recorded in Example 1 and Comparative Example 1 were observed using a field emission scanning electron microscope (trade name “SU-8040”, manufactured by Hitachi High-Technologies Corporation). FIG. 1 is an electron micrograph of the image recorded in Example 1. FIG. 2 is an electron micrograph of the image recorded in Comparative Example 1. As shown in FIG. 1, in the image recorded in Example 1, the flaky aluminum pigment is fixed in a state of being oriented substantially parallel to the plane of the recording medium. Light incident on the aluminum pigment oriented in this manner is appropriately reflected, and exhibits good gloss. On the other hand, as shown in FIG. 2, in the image recorded in Comparative Example 1, it can be seen that the flaky aluminum pigment is fixed in a partially accumulated state and in a state of rising on the surface of the recording medium. . The light incident on the aluminum pigment arranged in this manner is scattered in all directions, so that the glossiness of the image is low.

Claims (6)

An ink jet recording method for recording an image by applying an aqueous first ink and an aqueous second ink to a recording medium, respectively,
The first ink contains an aluminum pigment, and phosphoric acid or phosphate,
The second ink contains a surfactant,
An ink jet method comprising: applying one of the first ink and the second ink to the recording medium, and then applying the other ink to the recording medium so as to come into contact with the applied one ink. Recording method.   The inkjet recording method according to claim 1, wherein the content (% by mass) of the aluminum pigment in the first ink is 0.1% by mass or more and 10.0% by mass or less based on the total mass of the ink.   3. The method according to claim 1, wherein a content (% by mass) of the phosphoric acid or the phosphate in the first ink is 1.0% by mass or more and 20.0% by mass or less based on the total mass of the ink. The ink-jet recording method as described above. The first ink further contains the surfactant,
The content (mass%) of the surfactant in the second ink is higher than the content (mass%) of the surfactant in the first ink. The ink-jet recording method as described above.   The ratio of the applied amount of the second ink per unit area of the recording medium to the applied amount of the first ink per unit area of the recording medium is more than 0.5 times and not more than 1.0 times. The inkjet recording method according to claim 1.   The ink jet recording method according to any one of claims 1 to 5, wherein the second ink is applied to the recording medium within 500 milliseconds after applying the first ink to the recording medium.