WO2020203088A1 - Image recording method and ink set - Google Patents

Abstract

Provided is an image recording method by which an image excelling in concealability and having suppressed roughness can be recorded on an impermeable base material, the image recording method also excelling in the speed of image recording. Also provided is an ink set that is suitable for the image recording method. The image recording method and ink set of the present invention are such that a white ink A is discharged from an inkjet head A and applied onto the impermeable base material, and a white ink B having a smaller dynamic surface tension at 10 ms than the white ink A is discharged from an inkjet head B and applied to a region at which the white ink A was applied, whereby an ink dot A and an ink dot B having a portion at which at least a part of the ink dot A and a part of the ink dot B overlap are formed. Moreover, a time from when the droplet A lands until when the droplet B lands is 20-10,000 ms.

Description

Image recording method and ink set

This disclosure relates to an image recording method and an ink set.

Conventionally, studies have been made on white ink.
For example, Patent Document 1 describes at least a colorant as an ink set for an inkjet that can obtain a high-definition image having good visibility even on a transparent recording medium having no ink absorption or a recording medium having low brightness. In an inkjet ink set composed of a color ink and a white ink containing the above, an inkjet ink set characterized in that the surface tension of the white ink is lower than the surface tension of the color ink is disclosed.
In Patent Document 2, as a printing device capable of flattening the base layer with white ink, the first white ink and the second white ink are used by switching between the injection of the first white ink and the injection of the second white ink. A head for ejecting and a control unit for controlling the head so that the first white ink is ejected to land the first white ink on the medium and then the second white ink is ejected onto the first white ink. A printing apparatus is disclosed, wherein the surface tension of the second white ink is smaller than the surface tension of the first white ink.

Japanese Patent No. 4877224 Japanese Unexamined Patent Publication No. 2013-215917

By the way, the image recorded by the white ink may be required to have low light transmission (also referred to as “concealment”).
Specifically, by forming a concealing image on the character image and / or the base material, the character image and / or the base material can be obscured, and the color of the character image and / or the base material can be visually recognized. It may be required to eliminate it.

As a method of recording an image having excellent concealing property using white ink, first, a first drop of white ink is landed on a substrate, and then a second drop of white ink is landed. Therefore, a method of recording an image by forming ink dots having portions overlapping with each other can be considered. According to this method, the coverage of the image on the base material can be improved, so that the concealment of the image can be improved.
However, in this method, when a non-permeable base material is used as the base material and the landing interval between the first drop and the second drop is shortened from the viewpoint of the speed of image recording, the graininess of the image is reduced. ) May occur.
The reason for this is that a non-permeable base material is used as the base material and the landing interval between the first and second drops is shortened, so that the ink dots due to the first drop are not sufficiently dried. It is considered that the second drop is landed, and as a result, landing interference is likely to occur between the first drop and the second drop.
In Patent Documents 1 and 2, no attention is paid to the above problem when the landing interval between the first drop and the second drop is shortened.

The subject of the present disclosure is an image recording method capable of recording an image having excellent concealing property and suppressed roughness on a non-penetrating base material and having an excellent image recording speed, and is suitable for this image recording method. Is to provide a good inkjet.

Specific means for solving the problem include the following aspects.
<1> A step of preparing a non-permeable base material, a white ink A, and a white ink B having a smaller dynamic surface tension at 10 ms than the white ink A, respectively.
White ink A is ejected from the inkjet head A onto the impermeable substrate, and white ink B is ejected from the inkjet head B to the region to which the white ink A is imparted on the impermeable substrate. Including the step of recording an image by giving,
In the step of recording an image, a droplet A of white ink A is landed on a non-permeable substrate, and then a droplet B of white ink B is landed, and ink dots A and ink dots having overlapping portions are landed. An image recording method that includes forming B and that the time from the impact of the droplet A to the impact of the droplet B is 20 ms to 10000 ms.
<2> The time from the landing of the droplet A to the landing of the droplet B is Tms, the dynamic surface tension of the white ink A at Tms is γ _A (T), and the time of 10 ms of the white ink B. The image recording according to <1>, wherein the absolute value of the difference between γ _A (T) and γ _B (10) is 3.0 mN / m or less when the dynamic surface tension is γ _B (10). Method.
<3> The value obtained by subtracting the dynamic surface tension of the white ink B at 10 ms from the dynamic surface tension of the white ink A at 10 ms is 1.0 mN / m to 7.0 mN / m <1> or < The image recording method according to 2>.
<4> The image recording method according to any one of <1> to <3>, wherein the dynamic surface tension of the white ink B at 10 ms is 25.0 mN / m to 40.0 mN / m.
<5> In the step of recording an image, a transport mechanism for transporting a non-permeable base material, an inkjet head A, and an inkjet head B arranged on the downstream side of the non-permeable base material in the transport direction with respect to the inkjet head A. A non-penetrating base material is conveyed by a conveying mechanism using an image recording device equipped with the above, and white ink A is ejected from the inkjet head A onto the conveyed non-penetrating base material to apply the non-penetrating base material. The image recording method according to any one of <1> to <4>, wherein the white ink B is ejected from the inkjet head B to the region on the sex substrate to which the white ink A is applied.
<6> The white ink A does not contain an organic solvent having a boiling point of 270 ° C. or higher, or when it is contained, the content of the organic solvent having a boiling point of 270 ° C. or higher is 5% by mass or less based on the total amount of the white ink A. Yes,
The white ink B does not contain an organic solvent having a boiling point of 270 ° C. or higher, or when it does, the organic solvent having a boiling point of 270 ° C. or higher is 5% by mass or less based on the total amount of the white ink B <1> to < The image recording method according to any one of 5>.
<7> The white ink A contains a white pigment, and the content of the white pigment is 6% by mass to 20% by mass with respect to the total amount of the white ink A.
The image recording method according to any one of <1> to <6>, wherein the white ink B contains a white pigment, and the content of the white pigment with respect to the total amount of the white ink A is 6% by mass to 20% by mass.
<8> White ink A contains water and
The image recording method according to any one of <1> to <7>, wherein the white ink B contains water.
<9> The white ink A does not contain the polymerizable compound, or when it contains the polymerizable compound, the content of the polymerizable compound with respect to the total amount of the white ink A is less than 1% by mass.
The white ink B does not contain the polymerizable compound, or if it does, the content of the polymerizable compound with respect to the total amount of the white ink B is less than 1% by mass, any one of <1> to <8>. The image recording method according to one.
<10> White ink A and
An ink set including white ink B having a smaller dynamic surface tension at 10 ms than white ink A.
<11> The white ink A does not contain an organic solvent having a boiling point of 270 ° C. or higher, or when it is contained, the content of the organic solvent having a boiling point of 270 ° C. or higher is 5% by mass or less based on the total amount of the white ink A. Yes,
Described in <10>, wherein the white ink B does not contain an organic solvent having a boiling point of 270 ° C. or higher, or when it is contained, the organic solvent having a boiling point of 270 ° C. or higher is 5% by mass or less based on the total amount of the white ink B. Ink set.

According to the present disclosure, an image recording method capable of recording an image having excellent concealing property and suppressed roughness on a non-penetrating base material and having an excellent image recording speed, and suitable for this image recording method. Inkjet is provided.

It is a schematic cross-sectional view which shows an example of two adjacent ink dots A and ink dots B in a preferable aspect of the present disclosure. It is a schematic block diagram which shows an example of the image recording apparatus suitable for the image recording method of this disclosure. It is a black character image used for evaluation of the concealment property of an image in an Example.

In the present disclosure, the numerical range represented by using "-" means a range including the numerical values before and after "-" as the lower limit value and the upper limit value.
In the numerical range described stepwise in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of another numerical range described stepwise.
In the numerical range described in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the examples.
In the present disclosure, the amount of each component in the composition means the total amount of the plurality of substances present in the composition when a plurality of substances corresponding to each component are present in the composition, unless otherwise specified. To do.
In the present disclosure, "recording an image" means drawing an image on a substrate using ink and fixing the drawn image. The "image" may be an image recorded by ink, and includes characters, a solid film, and the like.
In the present disclosure, the term "process" is included in the term not only in an independent process but also in the case where the intended purpose of the process is achieved even if it cannot be clearly distinguished from other processes.
In the present disclosure, "(meth) acrylic" means at least one of acrylic and methacrylic, and "(meth) acrylate" means at least one of acrylate and methacrylate.

[Image recording method]
The image recording method of the present disclosure is
A step of preparing a non-permeable substrate, a white ink A, and a white ink B having a smaller dynamic surface tension at 10 ms than the white ink A (hereinafter, also referred to as a “preparation step”).
White ink A is ejected from the inkjet head A onto the impermeable substrate, and white ink B is ejected from the inkjet head B to the region to which the white ink A is imparted on the impermeable substrate. Including a step of recording an image (hereinafter, also referred to as an “image recording step”) by adding the ink.
In the image recording step, a droplet A of white ink A is landed on a non-permeable substrate, and then a droplet B of white ink B is landed to form ink dots A and ink dots B having overlapping portions. The time from the impact of the droplet A to the impact of the droplet B is 20 ms to 10000 ms, which includes the formation.

In the present disclosure, the dynamic surface tension at 10 ms (milliseconds) means the dynamic surface tension at 10 ms measured by the maximum foam pressure method in an environment of 23 ° C. and 55% RH.
The dynamic surface tension at T (landing interval) ms, which will be described later, means the dynamic surface tension at Tms measured by the maximum foam pressure method in an environment of 23 ° C. and 55% RH.
Each of the dynamic surface tension at 10 ms and the dynamic surface tension at T ms is measured using, for example, a maximum foam pressure method dynamic surface tension meter BP100 (manufactured by KRUSS).

According to the image recording method of the present disclosure, an image having excellent concealing property and suppressed roughness can be efficiently recorded on a non-penetrating base material.
The reason why such an effect is achieved is presumed as follows.

In the image recording method of the present disclosure, a droplet A of white ink A (hereinafter, also referred to as “white ink A”) is landed on a non-permeable substrate, and then white ink B (hereinafter, “white ink B”) is landed. The droplet B (also referred to as) is landed to form ink dots A and ink dots B having portions that overlap each other. Here, the ink dot A is an ink dot formed by landing the droplet A, and the ink dot B is an ink dot formed by landing the droplet B.
As a result, the area that cannot be completely covered by the ink dots A can be covered by the ink dots B, so that an image having excellent concealing property can be obtained as compared with the case where the image is recorded only by the droplets A.
Further, in the image recording method of the present disclosure, the white ink A and the white ink B are ejected from separate inkjet heads (that is, the inkjet head A and the inkjet head B), so that the droplet A is landed and then the droplet A is ejected. It is realized that the time until the B lands (hereinafter, also referred to as “the landing interval T between the droplet A and the droplet B” or simply “the landing interval T”) is limited to 10000 ms or less. This improves the speed of image recording.

On the other hand, according to the study by the present inventors, the same white ink is used as the white ink A and the white ink B, and the same white ink is ejected from each of the inkjet head A and the inkjet head B to eject the droplet A (first It was recorded when the droplet) and the droplet B (the next droplet) were sequentially landed on the impermeable substrate and the landing interval T between the droplet A and the droplet B was set to 10000 ms or less. It has been found that the image may be grainy.
The reason for this is that when a non-permeable substrate is used and the landing interval T between the droplet A and the droplet B is 10000 ms or less, the liquid before the ink dot A by the droplet A is completely dried. It is considered that the drop B is likely to land, and as a result, landing interference (droplet interference) is likely to occur between the droplet A and the droplet B.
More specifically, the surface tension (dynamic surface tension) of the ink A (droplet A) ejected from the inkjet head A begins to decrease from the moment of ejection, decreases even after landing, and eventually. It converges to the value of the static surface tension of ink A. The rate of decrease in surface tension is greatest immediately after ejection, and gradually decreases as time elapses after ejection (that is, the decrease in surface tension gradually slows down).
Therefore, when the white ink A (that is, the droplet A) and the white ink B (that is, the droplet B) are landed in sequence, the movement of the white ink A (that is, the ink dot A) has already occurred at the time when the droplet B lands. It is considered that the target surface tension is lower than the dynamic surface tension at the time of landing as the droplet A. Therefore, at the time when the droplet B lands, the surface tension of the ink dot A is lower than the surface tension of the droplet B, and it is considered that the landing interference occurs due to the difference in the surface tension. .. Specifically, it is considered that the ink dots A having a relatively low surface tension are attracted to the droplets B having a relatively high surface tension, so that the thickness of the image varies. It is considered that the image becomes grainy due to this variation in thickness.

Regarding the above-mentioned problems, in the image recording method of the present disclosure, the same white ink is not used as the white ink A and the white ink B, but the dynamic surface tension at 10 ms is smaller than that of the white ink A and the white ink A. White ink B and is used.
Here, the dynamic surface tension at 10 ms is the dynamic surface tension at the moment when the white ink droplets land on the impermeable substrate, among the dynamic surface tensions that can be actually and reliably measured by the current technology. Is the closest value to. The dynamic surface tension at 10 ms roughly corresponds to the dynamic surface tension at the time when the white ink droplets land on the impermeable substrate.
In the image recording method of the present disclosure, the white ink is in anticipation of a decrease in the dynamic surface tension of the white ink A applied first by the time the white ink B (droplet B) applied later is landed. The dynamic surface tension of A at 10 ms is made higher than the dynamic surface tension of white ink B at 10 ms.
As a result, when the white ink B (droplet B) lands, the surface tension of the white ink A (ink dot A) that has already been applied and the surface tension of the landed white ink B (droplet B) become Is close to the value, and as a result, the above-mentioned landing interference is suppressed, and it is considered that the graininess of the image due to the landing interference is suppressed.

As described above, in the image recording method of the present disclosure, in the image recording step, white ink A and white ink B are ejected from separate heads (injection head A and inkjet head B) and sequentially applied onto the impermeable substrate. At this time, the landing interval between the droplet A and the droplet B is set to 10000 ms or less. As a result, high-speed image recording is realized.
The image recording method of the present disclosure is an image recording method of such an embodiment for suppressing image roughness caused by landing interference, which is a problem peculiar to image recording on a non-penetrating substrate.
In these respects, the image recording method of the present disclosure is completely different from the image recording method of Patent Document 2 (Japanese Unexamined Patent Publication No. 2013-215917) described above, which ejects two types of ink from the same inkjet head.

Hereinafter, each step of the image recording method of the present disclosure will be described.

<Preparation process>
The preparation step is a step of preparing a non-permeable base material, a white ink A, and a white ink B having a smaller dynamic surface tension at 10 ms than the white ink A, respectively.
In the preparatory step, the impermeable substrate, the white ink A, and the white ink B, which are each manufactured in advance, may be simply prepared for carrying out the image recording step described later. However, it may be a step of producing at least one of the impermeable substrate, the white ink A, and the white ink B.
Further, it may be a step of adjusting the dynamic surface tension of at least one of the white ink A and the white ink B.

(Non-penetrating base material)
In the present disclosure, the non-permeable base material refers to a base material having a water absorption rate (mass%, 24 hr.) Of less than 0.2 in ASTM D570 of the ASTM test method.
The non-permeable base material is not particularly limited, but a resin base material is preferable.
The resin base material is not particularly limited, and examples thereof include a base material made of a thermoplastic resin.
Examples of the resin base material include a base material obtained by molding a thermoplastic resin into a sheet or a film.
As the resin base material, a base material containing polypropylene, polyethylene terephthalate, nylon, polyethylene, or polyimide is preferable.

The resin base material may be a transparent resin base material or a colored resin base material.
Here, "transparency" means that the transmittance of visible light having a wavelength of 400 nm to 700 nm is 80% or more (preferably 90% or more).

The shape of the resin base material is not particularly limited, but it is preferably a sheet-shaped resin base material, and from the viewpoint of productivity of the recording medium, it is a sheet-shaped resin base material capable of forming a roll by winding. Is more preferable.
The thickness of the resin base material is preferably 10 μm to 200 μm, more preferably 10 μm to 100 μm.

The resin base material may be surface-treated from the viewpoint of improving the surface energy.
Examples of the surface treatment include, but are not limited to, corona treatment, plasma treatment, frame treatment, heat treatment, abrasion treatment, light irradiation treatment (UV treatment), and flame treatment.

(White ink A)
The white ink A preferably contains at least one white pigment.

-White pigment-
The white pigment is not particularly limited, and a known white pigment is used. For example, titanium dioxide particles (TiO ₂ ), zinc oxide particles, barium sulfate particles, silicon oxide particles, aluminum oxide particles, magnesium oxide particles, and calcium silicate are used. Examples thereof include inorganic pigment particles such as particles, calcium carbonate particles, kaolin particles, talc particles, and colloidal silica particles. Further, as the white pigment, hollow resin particles can also be mentioned.

It is particularly preferable that the white pigment contains titanium dioxide particles from the viewpoint of image hiding property.
Since the titanium dioxide particles are particles having a large refractive index, when the white pigment contains the titanium dioxide particles, the hiding property of the image is further improved.
Examples of the titanium dioxide particles include anatase-type titanium dioxide particles, rutile-type titanium dioxide particles, and brookite-type titanium dioxide particles, but rutile-type titanium dioxide particles are preferable from the viewpoint of refractive index. Further, the rutile-type titanium dioxide particles have a weaker photocatalytic action than the anatase-type titanium dioxide particles and the brookite-type titanium dioxide particles, and therefore have an advantage that the influence on the resin, the resin base material, etc. in the white ink A is small. is there.

When the white pigment contains titanium dioxide particles, the white pigment may contain a white pigment (for example, inorganic pigment particles) other than the titanium dioxide particles.
When the white pigment contains titanium dioxide particles, the ratio of the titanium dioxide particles to the total amount of the white pigment is preferably 20% by mass or more, more preferably 50% by mass or more, and more preferably 80% by mass or more. Is more preferable. The upper limit of the ratio of titanium dioxide particles to the total amount of the white pigment is not particularly limited, and may be 100% by mass or less.

The average primary particle size of the white pigment is preferably 100 nm or more, more preferably 150 nm or more, still more preferably 200 nm or more, from the viewpoint of further improving the concealing property of the image.
The average primary particle size of the white pigment is preferably 400 nm or less, preferably 300 nm or less, from the viewpoint of ink dispersion stability (for example, ejection stability when ink is used as ink). More preferred.

The average primary particle size of the white pigment in the present disclosure is a value measured using a transmission electron microscope (TEM). A transmission electron microscope 1200EX manufactured by JEOL Ltd. can be used for the measurement.
Specifically, from an image magnified 100,000 times by TEM after dropping 1,000-fold diluted ink onto a Cu200 mesh (manufactured by JEOL Ltd.) to which a carbon film is attached and drying it. The equivalent circle diameters of 300 independent particles that do not overlap are measured, and the measured values are averaged to obtain the average particle size.

Further, from the viewpoint of image hiding property, the refractive index of the white pigment is preferably 2.0 or more.
In the present disclosure, "refractive index" means a value measured by ellipsometry with visible light having a wavelength of 550 nm at a temperature of 23 ° C., unless otherwise specified.

The content of the white pigment in the white ink A is preferably 1% by mass to 20% by mass, more preferably 6% by mass to 20% by mass, and 7% by mass with respect to the total amount of the white ink A. It is more preferably from 20% by mass, and most preferably from 7% by mass to 15% by mass.
When the content of the white pigment in the white ink A is 1% by mass or more with respect to the total amount of the white ink A, the concealing property of the image is further improved.
When the content of the white pigment in the white ink A is 20% by mass or less with respect to the total amount of the white ink A, the ejection property of the white ink A is further improved.

-Other color materials-
The white ink A may further contain a coloring material other than the white pigment.
Examples of other coloring materials include organic pigment particles and inorganic pigment particles, and the pigment particles described in paragraphs 0029 to 0041 of JP2011-94112A are preferably mentioned.
When the white ink A contains a coloring material other than white, a slight chromatic tint may be added to the white ink A, but even in this case, the brightness specified in JIS Z 8721: 1993 is If it is 9 or more, it is regarded as "white ink" in this disclosure.

The proportion of the white pigment in the entire color material contained in the white ink A is preferably 50% by mass or more, more preferably 80% by mass or more, and further preferably 90% by mass or more.
The ratio of the white pigment to the entire color material contained in the specific ink may be 100% by mass.

-water-
The white ink A preferably contains water.
The water content is preferably 30% by mass or more, more preferably 40% by mass or more, based on the total amount of the white ink A.
The upper limit of the water content depends on the amount of other components. Examples of the upper limit of the water content with respect to the total amount of the white ink A include 90% by mass, 80% by mass, and the like.

-Organic solvent with a boiling point of 270 ° C or higher-
The content of the organic solvent having a boiling point of 270 ° C. or higher with respect to the total amount of the white ink A is preferably 5% by mass or less, more preferably 2% by mass or less, and most preferably not contained.
In short, it is preferable that the white ink A does not substantially contain an organic solvent having a boiling point of 270 ° C. or higher.
This improves the speed of image recording. In addition, the stickiness of the image is further suppressed.

Further, when the white ink A does not substantially contain an organic solvent having a boiling point of 270 ° C. or higher, the dynamic surface tension at 10 ms immediately after the white ink A is ejected may be more likely to decrease. Therefore, when the white ink A does not substantially contain an organic solvent having a boiling point of 270 ° C. or higher, it may be a condition in which landing interference is likely to occur.
However, in the image recording method of the present disclosure, even when the white ink A does not substantially contain an organic solvent having a boiling point of 270 ° C. or higher, the dynamic surface tension of the white ink A at 10 ms is applied to the white ink B. By making it larger than the dynamic surface tension at 10 ms, it is possible to effectively suppress the landing interference and the roughness of the image caused by the landing interference.
Therefore, when the white ink A does not substantially contain an organic solvent having a boiling point of 270 ° C. or higher, the white ink A substantially does not contain an organic solvent having a boiling point of 270 ° C. or higher. The range of improvement (width of suppressing graininess of the image) by making the dynamic surface tension at 10 ms larger than the dynamic surface tension at 10 ms of the white ink B is larger.

In the present disclosure, the boiling point means the boiling point under 1 atm (101325 Pa).
The boiling point is a value measured by a boiling point meter, and can be measured using, for example, DosaTherm 300 manufactured by Titan Technologies Co., Ltd.

Examples of the organic solvent having a boiling point of 270 ° C. or higher include glycerin (boiling point: 290 ° C.), tripropylene glycol (boiling point: 273 ° C.), triethylene glycol monobutyl ether (boiling point: 276 ° C.), and sulfolane (boiling point: 285 ° C.). ), Thiodiglycol (boiling point: 282 ° C.) and the like.

-Organic solvent with a boiling point of 120 ° C or higher and lower than 270 ° C-
The white ink A can contain at least one low boiling point organic solvent selected from organic solvents having a boiling point of 120 ° C. or higher and lower than 270 ° C.
This improves the speed of image recording. In addition, the stickiness of the image is further suppressed.

Examples of the organic solvent having a boiling point of 120 ° C. or higher and lower than 270 ° C. include polyhydric alcohols, polyhydric alcohol alkyl ethers, nitrogen-containing heterocyclic compounds, amide compounds, amine compounds, and sulfur-containing compounds.

Examples of the polyhydric alcohol having a boiling point of 120 ° C. or higher and lower than 270 ° C. include propylene glycol (boiling point: 188 ° C.), 1,3-propanediol (boiling point: 210 ° C.), and 1,3-butanediol (boiling point: 203 ° C.). , 1,4-Butanediol (boiling point: 230 ° C), 1,5-pentanediol (boiling point: 242 ° C), ethylene glycol (boiling point: 197 ° C), diethylene glycol (boiling point: 244 ° C), dipropylene glycol (boiling point: 242 ° C) 232 ° C.), 1,3-propanediol (boiling point: 210 ° C.), 1,3-butanediol (boiling point: 203 ° C.), 2-methyl-2,4-pentanediol (boiling point: 196 ° C.), 1,2 -Hexanediol (boiling point: 223 ° C), 1,6-hexanediol (boiling point: 250 ° C), 1,2,6-hexanetriol (boiling point: 178 ° C), 1,2,4-butanetriol (boiling point: 190 ° C) ℃), 1,2,3-butanetriol (boiling point: 175 ° C.), petriol (boiling point: 216 ° C.) and the like.

Examples of the polyhydric alcohol alkyl ether having a boiling point of 120 ° C. or higher and lower than 270 ° C. include ethylene glycol monoethyl ether (boiling point: 135 ° C.), ethylene glycol monobutyl ether (boiling point: 171 ° C.), and diethylene glycol monomethyl ether (boiling point: 194 ° C.). , Diethylene glycol monoethyl ether (boiling point: 202 ° C.), diethylene glycol monobutyl ether (also known as butyl carbitol) (boiling point: 230 ° C.), dipropylene glycol monobutyl ether (boiling point: 227 ° C.), triethylene glycol monomethyl ether (boiling point: 122 ° C.) ℃), Triethylene glycol monoisobutyl ether (boiling point: 160 ℃), tripropylene glycol monomethyl ether (boiling point 243 ℃), tetraethylene glycol monomethyl ether (boiling point: 158 ℃), propylene glycol monoethyl ether (boiling point: 133 ℃) And so on.

Examples of the amide compound having a boiling point of 120 ° C. or higher and lower than 270 ° C. include formamide (boiling point: 210 ° C.), N-methylformamide (boiling point: 199 ° C.), N, N-dimethylformamide (boiling point: 153 ° C.) and the like. ..

Examples of the amine compound having a boiling point of 120 ° C. or higher and lower than 270 ° C. include monoethanolamine (boiling point: 170 ° C.), diethanolamine (boiling point: 217 ° C.), triethanolamine (boiling point: 208 ° C.), and the like.

Examples of the nitrogen-containing heterocyclic compound having a boiling point of 120 ° C. or higher and lower than 270 ° C. include N-methyl-2-pyrrolidone (boiling point: 202 ° C.), 2-pyrrolidone (boiling point: 245 ° C.), and 1,3-dimethyl-2-. Examples thereof include imidazolidinone (boiling point: 220 ° C.) and ε-caprolactam (boiling point: 136 ° C.).

Examples of the sulfur-containing compound having a boiling point of 120 ° C. or higher and lower than 270 ° C. include dimethyl sulfoxide (boiling point: 189 ° C.).

Low boiling point organic solvents having a boiling point of 120 ° C. or higher and lower than 270 ° C. include polyhydric alcohols having a boiling point of 120 ° C. or higher and lower than 270 ° C. and a boiling point of 120 ° C. or higher and 270 ° C. in terms of dryness of the image portion after recording. It preferably contains a low boiling organic solvent selected from the group consisting of polyhydric alcohol alkyl ethers below ° C.

The content of the low boiling point organic solvent is preferably in the range of 4% by mass or more and 35% by mass or less, and more preferably in the range of 10% by mass or more and 35% by mass or less with respect to the total amount of the white ink A. It is preferably in the range of 15% by mass or more and 30% by mass or less.
When the content of the low boiling point organic solvent is 4% by mass or more, the dispersibility of the white inorganic pigment can be well maintained. Further, when the content of the low boiling point organic solvent is 35% by mass or less, the drying property after recording becomes better.

-resin-
The white ink A preferably contains at least one resin.
The resin referred to here means all the resin components contained in the white ink A.
Specific forms of the resin contained in the white ink A include resin particles which are particles made of resin; a resin dispersant for coating at least a part of the pigment and dispersing the pigment; and the like.

-Resin particles-
The resin particles preferably have a solid shape.
In the present disclosure, the solid shape is a term used as a synonym for the hollow shape.
Specifically, the void ratio of the resin particles is preferably less than 10%, more preferably 5% or less.
When the resin particles have voids, the void ratio can be calculated by the following formula.
When the resin particles do not have voids, the void ratio is 0%.
Void ratio (%) = (radius of voids of resin particles / radius of resin particles) ³ × 100
Also, if the resin particles have multiple voids instead of one,
Void ratio (%) = Σ (radius of voids of resin particles) ³ / (radius of resin particles (1/2 of particle size) ³ × 100.
The radius of the resin particles and the radius of the voids of the resin particles can be determined by observing the resin particles with a transmission electron microscope. The arithmetic mean value of the void ratio obtained for 100 resin particles is defined as the void ratio of the resin particles.

The glass transition temperature (Tg) of the resin particles is not particularly limited.
From the viewpoint of further improving the adhesion of the image, the glass transition temperature (Tg) of the resin particles is preferably 0 ° C. or higher, more preferably 40 ° C. or higher, still more preferably 80 ° C. or higher, still more preferable. Is 120 ° C. or higher, more preferably 140 ° C. or higher.
The upper limit of the Tg of the resin particles is not particularly limited, but the Tg of the resin particles is preferably 300 ° C. or lower, more preferably 200 ° C. or lower, and further preferably 180 ° C. or lower.

In the present disclosure, the measured Tg obtained by actual measurement is applied as the glass transition temperature (Tg).
Specifically, the measured Tg means a value measured under normal measurement conditions using a differential scanning calorimeter (DSC) EXSTAR6220 manufactured by Hitachi High-Tech Science Corporation. However, if measurement is difficult due to decomposition of the resin or the like, the calculated Tg calculated by the following formula is applied. The calculation Tg is calculated by the following formula (1).
1 / Tg = Σ (Xi / Tgi) ... (1)
Here, it is assumed that the resin to be calculated is copolymerized with n kinds of monomer components from i = 1 to n. Xi is the weight fraction of the i-th monomer (ΣXi = 1), and Tgi is the glass transition temperature (absolute temperature) of the homopolymer of the i-th monomer. However, Σ is the sum of i = 1 to n. As the value (Tgi) of the homopolymer glass transition temperature of each monomer, the value of Polymer Handbook (3rd Edition) (J. Brandrup, E. H. Immunogut (Wiley-Interscience, 1989)) is adopted. The value of the homopolymer glass transition temperature of the monomer not described in the above document is obtained as a measurement Tg by the above-mentioned measuring method after preparing the homopolymer of the monomer. At this time, by setting the weight average molecular weight of the homopolymer to 10,000 or more, the influence of the weight average molecular weight on Tg of the polymer can be ignored.

The glass transition temperature of the resin particles can be appropriately controlled by a commonly used method. For example, the glass transition temperature of the resin particles can be controlled within a desired range by appropriately selecting the type of the monomer (polymerizable compound) constituting the resin particles, the composition ratio thereof, the molecular weight of the resin constituting the resin particles, and the like. Can be done.

Examples of the resin in the resin particles include acrylic resin, epoxy resin, polyether resin, polyamide resin, unsaturated polyester resin, phenol resin, silicone resin, fluororesin, and polyvinyl resin (eg, vinyl chloride, vinyl acetate, polyvinyl alcohol, etc.). Alternatively, polyvinyl butyral, etc.), alkyd resin, polyester resin (eg, phthalic acid resin, etc.), amino material (eg, melamine resin, melamine formaldehyde resin, aminoalkide cocondensation resin, urea resin, urea resin, etc.) and the like can be mentioned.

As the resin particles, acrylic resin, polyether resin, polyester resin, or polyolefin resin particles are preferable, and acrylic resin particles are more preferable.

In the present disclosure, the acrylic resin means a resin containing a structural unit derived from (meth) acrylic acid or a (meth) acrylate compound. The acrylic resin may contain a structural unit other than the structural unit derived from the (meth) acrylic acid or the (meth) acrylate compound.

Further, the resin forming the resin particles may be a copolymer containing two or more kinds of constituent units constituting the resin exemplified above, or may be a mixture of two or more kinds of resins. Further, the resin particles themselves may be not only those composed of a mixture of two or more kinds of resins, but also composite resin particles in which two or more kinds of resins are laminated like a core / shell.

The resin particles are preferably resin particles obtained by a phase inversion emulsification method, and more preferably self-dispersible resin particles (self-dispersive resin particles).
Here, the self-dispersible resin is a self-dispersible resin due to a functional group (particularly an acidic group such as a carboxy group or a salt thereof) possessed by the resin itself when it is dispersed by a phase inversion emulsification method in the absence of a surfactant. A water-insoluble resin that can be dispersed in an aqueous medium.
Here, the dispersed state is an emulsified state (emulsion) in which a water-insoluble resin is dispersed in a liquid state in an aqueous medium, and a dispersed state (suspension) in which a water-insoluble resin is dispersed in a solid state in an aqueous medium. It includes both states.
Further, "water insoluble" means that the amount dissolved in 100 parts by mass (25 ° C.) of water is less than 5.0 parts by mass (preferably less than 1.0 part by mass).

As a phase inversion emulsification method, for example, a resin is dissolved or dispersed in a solvent (for example, a water-soluble solvent, etc.) and then put into water as it is without adding a surfactant, and a salt-forming group (salt-forming group) contained in the resin (for example). For example, there is a method of obtaining an aqueous dispersion in an emulsified or dispersed state after stirring and mixing in a neutralized state (an acidic group such as a carboxy group) to remove a solvent.

The self-dispersible resin particles are selected from the self-dispersible resin particles described in paragraphs 0090 to 0121 of JP2010-64480 or paragraphs 0130 to 0167 of JP2011-068085. be able to.

As the self-dispersing resin particles, self-dispersing resin particles having a carboxy group are preferable.
A more preferred form of the self-dispersing resin particles having a carboxy group is a form composed of a resin containing a structural unit derived from an unsaturated carboxylic acid (preferably (meth) acrylic acid).

A more preferred form of the self-dispersing resin particles having a carboxy group is
A building block having an alicyclic group and
A structural unit having an alkyl group and
Constituent units derived from unsaturated carboxylic acids (preferably (meth) acrylic acids)
It is a form made of a resin containing.
The content of the structural unit having an alicyclic group in the resin (total content when two or more kinds are present) is preferably 3% by mass to 95% by mass, preferably 5% by mass, based on the total amount of the resin. It is more preferably from 75% by mass, further preferably from 10% by mass to 50% by mass.
The content of the structural unit having an alkyl group (total content when two or more kinds are present) in the above resin is preferably 5% by mass to 90% by mass and 10% by mass to 85% with respect to the total amount of the resin. By mass% is more preferable, 20% by mass to 80% by mass is further preferable, 30% by mass to 75% by mass is further preferable, and 40% by mass to 75% by mass is further preferable.
The content of the structural unit derived from the unsaturated carboxylic acid (preferably (meth) acrylic acid) in the resin (the total content when two or more kinds are present) is from 2% by mass to the total amount of the resin. It is preferably 30% by mass, more preferably 5% by mass to 20% by mass, still more preferably 5% by mass to 15% by mass.

Further, as the form of the self-dispersible resin particle having a carboxy group, in the above-mentioned "more preferable form of the self-dispersible resin particle having a carboxy group", the structural unit having an alicyclic group group has an aromatic group. A form changed to a structural unit, or a form containing a structural unit having an aromatic group in addition to the structural unit having an alicyclic group is also preferable.
In any form, the total content of the structural unit having an alicyclic group and the structural unit having an aromatic group is preferably 3% by mass to 95% by mass and 5% by mass to 75% by mass with respect to the total amount of the resin. % Is more preferable, and 10% by mass to 50% by mass is further preferable.

The structural unit having the alicyclic group is preferably a structural unit derived from an alicyclic (meth) acrylate.
Examples of the alicyclic (meth) acrylate include a monocyclic (meth) acrylate, a bicyclic (meth) acrylate, and a tricyclic (meth) acrylate.
Examples of the monocyclic (meth) acrylate include cyclopropyl (meth) acrylate, cyclobutyl (meth) acrylate, cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, cycloheptyl (meth) acrylate, cyclooctyl (meth) acrylate, and cyclononyl. Examples thereof include cycloalkyl (meth) acrylates having 3 to 10 carbon atoms in the cycloalkyl group such as (meth) acrylate and cyclodecyl (meth) acrylate.
Examples of the bicyclic (meth) acrylate include isobornyl (meth) acrylate and norbornyl (meth) acrylate.
Examples of the tricyclic (meth) acrylate include adamantyl (meth) acrylate, dicyclopentanyl (meth) acrylate, and dicyclopentenyloxyethyl (meth) acrylate.
These can be used alone or in combination of two or more.
Of these, bicyclic (meth) acrylates or tricyclic (meth) acrylates of three or more rings are preferred, and isobornyl (isobornyl), from the viewpoint of fixability, blocking resistance, and dispersion stability of self-dispersible resin particles. More preferred are meta) acrylates, adamantyl (meth) acrylates, or dicyclopentanyl (meth) acrylates.

The structural unit having an aromatic group is preferably a structural unit derived from an aromatic group-containing monomer.
Examples of the aromatic group-containing monomer include an aromatic group-containing (meth) acrylate monomer (for example, phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, phenyl (meth) acrylate, etc.), a styrene compound, and the like. ..
Among them, an aromatic group-containing (meth) acrylate monomer is preferable from the viewpoint of the balance between hydrophilicity and hydrophobicity of the resin chain and ink fixability, and phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, or phenyl (meth). Acrylate is more preferred, and phenoxyethyl (meth) acrylate or benzyl (meth) acrylate is even more preferred.

The structural unit having an alkyl group is preferably a structural unit derived from an alkyl group-containing monomer.
Examples of the alkyl group-containing monomer include methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, and t. -Alkyl (meth) acrylates such as butyl (meth) acrylate, hexyl (meth) acrylate, ethylhexyl (meth) acrylate; hydroxymethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate. , 4-Hydroxybutyl (meth) acrylate, hydroxypentyl (meth) acrylate, hydroxyhexyl (meth) acrylate and other ethylenically unsaturated monomers; dialkylaminoalkyl (meth) acrylate such as dimethylaminoethyl (meth) acrylate N-hydroxyalkyl (meth) acrylamide such as N-hydroxymethyl (meth) acrylamide, N-hydroxyethyl (meth) acrylamide, N-hydroxybutyl (meth) acrylamide; N-methoxymethyl (meth) acrylamide, N-ethoxy Methyl (meth) acrylamide, N- (n-, iso) butoxymethyl (meth) acrylamide, N-methoxyethyl (meth) acrylamide, N-ethoxyethyl (meth) acrylamide, N- (n-, iso) butoxyethyl ( Examples thereof include (meth) acrylamide such as N-alkoxyalkyl (meth) acrylamide such as meta) acrylamide.
Of these, alkyl (meth) acrylate is preferable, and alkyl (meth) acrylate having an alkyl group having 1 to 4 carbon atoms is more preferable, and methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, or butyl. (Meta) acrylate is more preferable, and methyl (meth) acrylate is further preferable.

The weight average molecular weight of the resin constituting the resin particles (preferably self-dispersing resin particles; the same applies hereinafter) is preferably 3,000 to 200,000, more preferably 5,000 to 150,000, and 10,000 to 100,000. Is more preferable.
When the weight average molecular weight is 3000 or more, the amount of the water-soluble component can be effectively suppressed. Further, by setting the weight average molecular weight to 200,000 or less, the self-dispersion stability can be improved.

The weight average molecular weight of the resin constituting the resin particles means a value measured by gel permeation chromatography (GPC).
For measurement by gel permeation chromatography (GPC), HLC (registered trademark) -8020 GPC (Tosoh Co., Ltd.) is used as a measuring device, and TSKgel (registered trademark) Super Multipore HZ-H (4.6 mm ID ×) is used as a column. Use 3 bottles of 15 cm, Toso Co., Ltd., and use THF (tetrahydrofuran) as the eluent. The measurement conditions are a sample concentration of 0.45% by mass, a flow rate of 0.35 ml / min, a sample injection amount of 10 μl, a measurement temperature of 40 ° C., and a differential refractive index (RI) detector. ..
The calibration curve is "Standard sample TSK standard, polystyrene": "F-40", "F-20", "F-4", "F-1", "A-5000", "A" of Tosoh Corporation. It is made from 8 samples of "-2500", "A-1000", and "n-propylbenzene".

The resin constituting the resin particles is preferably a resin having an acid value of 100 mgKOH / g or less, and an acid value of 25 mgKOH / g to 100 mgKOH / g, from the viewpoint of self-dispersion and the aggregation rate when the treatment liquid comes into contact with each other. The resin of g is more preferable.

The volume average particle diameter of the resin particles is preferably in the range of 1 nm to 200 nm, more preferably in the range of 1 nm to 150 nm, further preferably in the range of 1 nm to 100 nm, and particularly preferably in the range of 1 nm to 10 nm. When the volume average particle size is 1 nm or more, the manufacturing suitability is improved. Further, when the volume average particle size is 200 nm or less, the storage stability is improved. The particle size distribution of the resin particles A is not particularly limited, and may be either one having a wide particle size distribution or one having a monodisperse particle size distribution.
The volume average particle size of the resin particles is measured by a particle size distribution measuring device using light scattering (for example, Microtrac UPA (registered trademark) EX150 manufactured by Nikkiso Co., Ltd.).

From the viewpoint of improving the hiding property, the refractive index of the resin particles is preferably 1.0 to 1.7.

One type of resin particles may be used alone, or two or more types may be used in combination.
The content of the resin particles (preferably self-dispersing resin particles) in the ink (the total content when there are two or more types) is not particularly limited, but is 0.5% by mass or more based on the total amount of the ink. 11% by mass is preferable, 0.5% by mass to 9% by mass is more preferable, 2% by mass to 9% by mass is further preferable, and 2% by mass to 7% by mass is further preferable.
When the content is 0.5% by mass or more, the adhesion of the image is further improved.
When the content is 11% by mass or less, the dispersion stability of the ink can be further improved. Therefore, for example, when ink is used as ink, the ejection stability from the inkjet head (hereinafter, also simply referred to as “ejection stability”) can be further improved.

Specific examples of the resin particles will be given below, but the present disclosure is not limited thereto. The numbers in parentheses represent the mass ratio of the copolymerization components.
-Methyl methacrylate / isobornyl methacrylate / methacrylic acid / sodium methacrylate copolymer (70/20/5/5), Tg: 150 ° C.
-Joncryl (registered trademark) JDX-C3080 (manufactured by Johnson Polymer), Tg: 130 ° C.
・ Trepearl (registered trademark) EP, manufactured by Toray Industries, Inc., Tg: 190 ° C
-Trepearl (registered trademark) PES, manufactured by Toray Industries, Inc., Tg: 225 ° C

-Resin dispersant-
The white ink A may contain, as a resin, a resin dispersant for coating at least a part of the pigment and dispersing the pigment.
The pigment referred to here means a pigment contained in the white ink A, which is typified by a white pigment described later.

Acrylic resin is preferable as the resin dispersant.
As the resin dispersant, for example, the dispersants described in paragraphs 0080 to 096 of JP-A-2016-145312 are preferably mentioned.

The content of the dispersant with respect to the content of all the pigments contained in the white ink A is preferably 3% by mass to 20% by mass, more preferably 4% by mass to 18% by mass, and 5% by mass. It is more preferably% to 15% by mass.
The content of the dispersant (z mass% described later) with respect to the total amount of the white ink A is preferably 0.1% by mass to 2.4% by mass, and is 0.5% by mass to 2.0% by mass. Is more preferable, and 0.8% by mass to 1.5% by mass is further preferable.

-Preferable content of resin-
The content of the resin (for example, resin particles and the resin dispersant) in the white ink A (for example, the total content of the resin particles and the resin dispersant) is 1% by mass to 12% by mass with respect to the total amount of the white ink A. Is preferable, 1% by mass to 10% by mass is more preferable, 3% by mass to 10% by mass is further preferable, and 3% by mass to 8% by mass is further preferable.

-Surfactant-
The white ink A may contain at least one type of surfactant.
Examples of the surfactant include nonionic surfactants, cationic surfactants, anionic surfactants, betaine surfactants and the like.
Among them, anionic surfactants or nonionic surfactants are preferable, and nonionic surfactants are more preferable.

Examples of the surfactant include pages 37 to 38 of JP-A-59-157636 and Research Disclosure No. Also included are compounds listed as surfactants in 308119 (1989). Further, the fluorine (alkyl fluoride-based) surfactants and silicone-based surfactants described in JP-A-2003-322926, JP-A-2004-325707, and JP-A-2004-309806 are also mentioned.

As the nonionic surfactant, an acetylene glycol-based surfactant is particularly preferable.
Examples of the acetylene glycol-based surfactant include 2,4,7,9-tetramethyl-5-decine-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 2,5. Examples thereof include alkylene oxide adducts (preferably ethylene oxide adducts) such as 8,11-tetramethyl-6-dodecine-5,8-diol and 2,5-dimethyl-3-hexyne-2,5-diol. In particular, ethylene oxide adducts of 2,4,7,9-tetramethyl-5-decine-4,7-diol (3 ≦ x + y ≦ 30, more preferably 5 ≦ x + y ≦ 30) are preferable.

As the acetylene glycol-based surfactant, a commercially available product on the market may be used.
Commercially available products of acetylene glycol-based surfactants include the Surfinol series manufactured by Air Products & Chemicals or Nisshin Kagaku Kogyo Co., Ltd. (for example, Surfinol 420, Surfinol 440, Surfinol 465, Surfinol 485, Orfin. Examples thereof include a series (for example, Orfin E1010, Orfin E1020), a Dynol series (for example, Dynol 604), and acetylenol manufactured by Kawaken Fine Chemicals Co., Ltd.

The dynamic surface tensions of the white ink A and the white ink B at 10 ms can be adjusted by adjusting the type and / or content of the surfactant, respectively.
The dynamic surface tension of white ink A and white ink B at 10 ms may be adjusted by adjusting the type and / or content of other components such as an organic solvent, but the type of surfactant and / Or when adjusted according to the content, the difference in viscosity between the white ink A and the white ink B can be further reduced.

The surfactant can also be used as an antifoaming agent.
As the surfactant, a fluorine-based compound, a silicone-based compound, a chelating agent typified by ethylenediaminetetraacetic acid (EDTA), and the like can also be used.

The content of the surfactant is preferably 0.01% by mass to 10% by mass, 0.1% by mass to 5% by mass, and more preferably 0.3% by mass to the total amount of the white ink A. It is 3% by mass.

-Other additives-
The white ink A may contain other components other than the above components.
Other ingredients include, for example, colloidal silica, inorganic salts, solid wetting agents (urea, etc.), anti-fading agents, emulsion stabilizers, penetration promoters, UV absorbers, preservatives, fungicides, pH regulators, defoamers. Known additives such as foaming agents, viscosity regulators, dispersion stabilizers, rust preventives, chelating agents, and water-soluble polymer compounds can be mentioned.

The content of the polymerizable compound (for example, (meth) acrylate compound, etc.) in the white ink A with respect to the total amount of the white ink A is preferably less than 1% by mass, and most preferably not contained in the white ink A. , It is not necessary to contain substantially a polymerizable compound.
When the white ink A does not substantially contain a polymerizable compound, the ink dots cannot be positively cured by pinning exposure or the like. Therefore, the condition is such that landing interference is likely to occur.
However, in the image recording method of the present disclosure, even when the white ink A does not substantially contain the polymerizable compound, the dynamic surface tension of the white ink A at 10 ms and the motion of the white ink B at 10 ms By making it larger than the target surface tension, it is possible to effectively suppress the landing interference and the graininess of the image caused by the landing interference.
Therefore, when the white ink A does not substantially contain the polymerizable compound, the dynamic surface tension of the white ink A at 10 ms is increased as compared with the case where the white ink A substantially contains the polymerizable compound. The width of improvement (width of suppressing roughness of the image) due to being larger than the dynamic surface tension of the white ink B at 10 ms is larger.

-Dynamic surface tension at -10 ms-
The dynamic surface tension of the white ink A at 10 ms may be larger than the dynamic surface tension of the white ink B at 10 ms, and there are no other restrictions.
The method for measuring the dynamic surface tension at 10 ms is as described above.
The dynamic surface tension of the white ink A at 10 ms is, for example, 10.0 mN / m to 60.0 mN / m, preferably 20.0 mN / m to 50.0 mN / m, and more preferably 25. It is 0 mN / m to 50.0 mN / m, more preferably 25.0 mN / m to 40.0 mN / m.

-viscosity-
The viscosity of the white ink A is not particularly limited, but is preferably 1.2 mPa · s to 15 mPa · s, more preferably 2 mPa · s to 13 mPa · s, and even more preferably 2.5 mPa · s to 10 mPa · s.
The viscosity in the present disclosure is a value measured at 25 ° C.
As the viscometer, for example, a VISCOMETER TV-22 type viscometer (manufactured by Toki Sangyo Co., Ltd.) is used.

-PH-
The pH of the white ink A is not particularly limited, but is preferably pH 6 to 11, more preferably pH 7 to 10, and even more preferably pH 7 to 9.
The pH in the present disclosure is a value measured at 25 ° C.
The pH is measured using a commercially available pH meter.

(White ink B)
The dynamic surface tension of the white ink B at 10 ms may be smaller than the dynamic surface tension of the white ink A at 10 ms, and there are no other restrictions.
The preferred embodiment of the white ink B is the same as the preferred embodiment of the white ink A as long as the dynamic surface tension at 10 ms is smaller than the dynamic surface tension of the white ink A at 10 ms.
From the viewpoint of more effectively suppressing the graininess of the image caused by the impact interference, the composition of the white ink B is preferably the same as that of the white ink A except for the type and content of the surfactant.
Further, as for the preferable physical properties of the white ink B (dynamic surface tension at 10 ms, static surface tension, viscosity, pH, etc.), the dynamic surface tension of the white ink B at 10 ms is dynamic at 10 ms of the white ink A. It is the same as the preferable physical properties of the white ink A except that it is smaller than the surface tension.

For example, the white ink B preferably contains a white pigment.
The preferable range of the content of the white pigment with respect to the total amount of the white ink B is the same as the preferable range of the content of the white pigment with respect to the total amount of the white ink A.
Further, the white ink B preferably contains water.
The preferable range of the water content with respect to the total amount of the white ink B is the same as the preferable range of the water content with respect to the total amount of the white ink A.
The content of the organic solvent having a boiling point of 270 ° C. or higher with respect to the total amount of the white ink B is preferably 5% by mass or less, more preferably 2% by mass or less, and most preferably not contained.
Further, the white ink B preferably contains less than 1% by mass of the polymerizable compound with respect to the total amount of the white ink B, and most preferably does not contain it.

The difference between the viscosity of the white ink A and the viscosity of the white ink B (hereinafter, also referred to as viscosity difference | AB |) is preferably 2.0 mPa · s or less.
When the viscosity difference | AB | is 2.0 mPa · s or less, the roughness of the image due to the impact interference is further suppressed.
The viscosity difference | AB | is preferably 1.0 mPa · s or less, and more preferably 0.5 mPa · s or less. The viscosity difference | AB | is ideally 0 mPa · s.

The dynamic surface tension of the white ink B at 10 ms is preferably 20.0 mN / m to 50.0 mN / m, more preferably 25.0 mN / m to 50.0 mN / m, and even more preferably 25. It is 0.0 mN / m to 40.0 mN / m.
When the dynamic surface tension of the white ink B at 10 ms is 50.0 mN / m or less, the roughness of the image due to the impact interference is further suppressed.
When the dynamic surface tension of the white ink B at 10 ms is 20.0 mN / m or more, the ejection property of the white ink B is more excellent.

From the dynamic surface tension of the white ink A at 10 ms (hereinafter, also referred to as “γ _A (10)”) to the dynamic surface tension of the white ink B at 10 ms (hereinafter, also referred to as “γ _B (10)”). The subtracted value (hereinafter, also referred to as “γ _A (10) −γ _B (10)”) is more than 0 mN / m.
As a result, the effect of suppressing the graininess of the image due to the impact interference can be obtained.
γ _A (10) -γ _B (10) is preferably 0.5 mN / m to 8.0 mN / m, more preferably 1.0 mN / m to 7.0 mN / m, and even more preferably 1. It is 0.0 mN / m to 5.0 mN / m, more preferably 1.0 mN / m to 3.0 mN / m.
When γ _A (10) −γ _B (10) is in the above preferable range, the roughness of the image due to the impact interference is further suppressed.

<Image recording process>
In the image recording step, the white ink A is ejected from the inkjet head A (hereinafter, also referred to as “head A”) onto the impermeable substrate, and the white ink A on the impermeable substrate is imparted. This is a step of recording an image by ejecting white ink B from an inkjet head B (hereinafter, also referred to as “head B”) and applying the white ink B to the region.
In this image recording step, the droplet A of the white ink A is landed on the impermeable substrate, and then the droplet B of the white ink B is landed on the ink dots A and the ink dots having overlapping portions. Includes forming B.
At this time, the time from the impact of the droplet A to the impact of the droplet B (landing interval T) is 20 ms to 10000 ms.

In the image recording step, the “region to which the white ink A is applied” on the impermeable substrate means the region where the ink dots A are formed.
When a plurality of ink dots A are formed in halftone dots in the image recording process, the “region to which the white ink A is applied on the impermeable substrate” is defined as the plurality of ink dots A formed in halftone dots. It means the entire region (that is, the entire region including a plurality of ink dots A and a place where the ink dots A are not formed). In this case, the white ink B can be applied to any part of the entire region in which the plurality of ink dots A are formed in a halftone dot shape, as long as the ink dots A and the ink dots B having overlapping portions are formed. Good. For example, as long as it is within this region, the ink dots A may be applied to places where they are not formed.

(Landing interval T)
In the image recording step, the time from the impact of the droplet A to the impact of the droplet B (landing interval T) is 20 ms to 10000 ms.
When the landing interval T is 20 ms or more, the ease and stability of image recording are ensured.
Further, when the landing interval T is 20 ms or more, a difference in surface tension between the ink dot A and the landing droplet B at the time when the droplet B lands can occur. In this case, γ _A ( 10) -γ _B (10) (that is, the value obtained by subtracting the dynamic surface tension of white ink B at 10 ms from the dynamic surface tension of white ink A at 10 ms) is more than 0 mN / m. It is effectively demonstrated.
From these viewpoints, the landing interval T may be 20 ms or more, preferably 30 ms or more, and more preferably 50 ms.

When the landing interval T is 10000 ms or less, high-speed image recording is realized.
Further, when the landing interval T is 10000 ms or less, the problem of image roughness due to landing interference may occur. In this case, γ _A (10) -γ _B (10) (that is, white ink A). The effect of setting the value obtained by subtracting the dynamic surface tension of the white ink B at 10 ms from the dynamic surface tension at 10 ms) of more than 0 mN / m is effectively exhibited.
From these viewpoints, the landing interval T may be 10,000 ms or less, preferably 1000 ms or less, more preferably 150 ms or less, still more preferably 120 ms or less.

In this disclosure, the landing interval T is NIP25: International Conference on Digital Printing Technologies and Digital Fabrication 2009, September 20, 2009, p. Refers to the value measured by strobe photography in accordance with the method of "Velocity of Drops in Full flight" described in 71-74.

(Preferable aspect of dynamic surface tension)
In the image recording step, as described above, the surface tension of the white ink A (ink dot A) already applied when the white ink B (droplet B) lands and the white ink B (liquid) at the time of landing The surface tension of the droplet B) becomes close to a value, and as a result, the impact interference is suppressed, and the graininess of the image due to the impact interference is suppressed.
The surface tension of the white ink A (ink dot A) already applied at the time when the white ink B (droplet B) lands is, in other words, the movement of the white ink A at the landing interval Tms (T milliseconds). Target surface tension (hereinafter, also referred to as “γ _A (T)”).
On the other hand, the surface tension of the white ink B (droplet B) at the time of landing roughly corresponds to the dynamic surface tension of the white ink B at 10 ms (that is, γ _B (10)) as described above. ..
Therefore, from the viewpoint of suppressing image roughness caused by landing interference, the absolute value of the difference between γ _A (T) and γ _B (10) in the image forming step (hereinafter, “| γ _A (T) −γ _B ”). (10) | ”) is preferably small.

In the present disclosure, | γ _A (T) -γ _B (10) | is preferably 4.5 mN / m or less, more preferably 3.0 mN / m or less, still more preferably 2.5 mN / m. It is less than or equal to, more preferably 2.0 mN / m or less.
When | γ _A (T) −γ _B (10) | is 4.5 mN / m or less, the graininess of the image due to landing interference is further suppressed.
| Γ _A (T) -γ _B (10) | may be 0 mN / m.

(Ink dot A and ink dot B)
In the image recording step, the droplet A of the white ink A ejected from the head A is landed on the impermeable substrate to form the ink dot A, and the droplet B of the white ink B ejected from the head B is formed. Is landed on a non-permeable substrate to form ink dots B.
At this time, the droplet A and the droplet B are landed so that the formed ink dots A and ink dots B have portions that overlap each other, respectively.
By forming ink dots A and ink dots B having overlapping portions on the impermeable substrate, the regions on the impermeable substrate that could not be covered by the ink dots A alone are formed by the ink dots B. It is covered, and as a result, an image having excellent hiding power is recorded. From the viewpoint of more effectively obtaining such an effect, it is preferable that a part of the ink dots A and the ink dots B overlap each other.
The ink dots A and the ink dots B may be united after the ink dots B are formed.

The image recording step preferably includes forming two adjacent ink dots A among the plurality of ink dots A and an ink dot B straddling between the two adjacent ink dots A.
According to this aspect, the hiding rate of the image is further improved.
Further, according to this aspect, γ _A (10) −γ _B (10) (that is, the value obtained by subtracting the dynamic surface tension of the white ink B at 10 ms from the dynamic surface tension of the white ink A at 10 ms). The effect of setting the value to more than 0 mN / m is more effectively exhibited.

In the above preferred embodiment, more preferably, the distance between the center XA between the centers of two adjacent ink dots A and the center XB of the ink dots B is the distance D between the centers of the two adjacent ink dots A. It is 1/4 or less of.

FIG. 1 is a schematic cross-sectional view showing an example of two adjacent ink dots A and ink dots B in the above preferred embodiment of the present disclosure.
As shown in FIG. 1, in this example, two dot IDAs as two adjacent ink dots A and a dot IDB as ink dots B straddling between the two dot IDAs are formed.
In this example, the midpoint XA between the center XA1 and the center XA2, which are the centers of the two dot IDAs, and the center XB of the dot IDB overlap. That is, the distance between the midpoint XA and the center XB is 0. As in this example, the distance between the midpoint XA and the center XB is preferably (1/4) D or less.
However, needless to say, the image recording method of the present disclosure is not limited to the above example.
Further, the combination of the two dot IDAs and the dot IDBs in this example may be a part of the entire formed image. For example, dot IDAs and dot IDBs may be arranged alternately to form a continuous image.

The two dot IDAs and dot IDBs in the above example can be suitably formed by using the head A which is a full line head and the head B which is a full line head in a specific example of an image recording device described later. In this case, the two dot IDAs correspond to two of the plurality of ink dots A formed by the white ink A ejected from the head A, and the dot IDBs correspond to the white ink B ejected from the head B. Corresponds to one of the plurality of ink dots B formed.

(Head A, Head B, etc.)
The method of ejecting the white ink A from the head A and the method of ejecting the white ink B from the head B are known methods, for example, a charge control method for ejecting ink by using an electrostatic attraction force. Drop-on-demand method (pressure pulse method) that uses the vibration pressure of the piezo element, acoustic inkjet method that converts an electric signal into an acoustic beam and irradiates the ink to eject the ink using radiation pressure, and heating the ink A thermal inkjet (bubble jet (registered trademark)) method or the like that forms bubbles and utilizes the generated pressure can be applied.
Further, for example, described in JP-A-54-59936, a method in which an ink subjected to the action of thermal energy causes a sudden volume change, and the ink is ejected from a nozzle by the acting force due to this state change; JP-A-2003. -The method described in paragraphs 093 to 0105 of JP-A-306623; and the like may be used.

The head A and head B methods include a shuttle method in which a short serial head is scanned in the width direction of the base material for recording, and recording elements are arranged corresponding to the entire area of one side of the base material. There is a line method using a line head.
In the line method, image recording can be performed on the entire surface of the base material by scanning the base material in a direction intersecting the arrangement direction of the recording elements. The line system eliminates the need for a transport system such as a carriage that scans a short head in the shuttle system. Further, in the line method, as compared with the shuttle method, the movement of the carriage and the complicated scanning control with the base material are not required, and only the base material moves. Therefore, according to the line method, the speed of image recording can be increased as compared with the shuttle method.

The amount of droplets of white ink A ejected from the nozzle of head A and the amount of droplets of white ink B ejected from the nozzle of head B are preferably, for example, 1 pL (picolitre) to 10 pL, respectively. More preferably, 5 pL to 6 pL.
Further, from the viewpoint of improving the unevenness of the image and the connection of continuous gradation, it is also effective to discharge a combination of different liquid appropriate amounts.

Further, the head A and the head B may each have a liquid repellent film on the surface on which the white ink is ejected (ink ejection surface).
Examples of the liquid repellent film include those described in paragraphs 0178 to 0184 of JP-A-2016-193980.

In the image recording step, the formed ink dots A and ink dots B may be heated and dried.
Examples of the means for performing heat drying include known heating means such as a heater, known blowing means such as a dryer, and means combining these.
As a method for heating and drying the ink dots A and the ink dots B, for example,
A method of applying heat with a heater or the like from the side opposite to the surface on which the ink dots A and ink dots B of the non-permeable substrate are formed.
A method of applying warm air or hot air to the surface on which ink dots A and ink dots B of a non-permeable substrate are formed.
A method of applying heat with an infrared heater, a method of combining a plurality of these, etc. Can be mentioned.

The heating temperature of the ink dots A and the ink dots B during heating and drying is preferably 55 ° C. or higher, more preferably 60 ° C. or higher, and particularly preferably 65 ° C. or higher.
The upper limit of the heating temperature of the ink dots A and the ink dots B is not particularly limited, but the upper limit is preferably 100 ° C., more preferably 90 ° C.
The time for heating and drying the ink dots A and B is not particularly limited, but is preferably 3 seconds to 60 seconds, more preferably 5 seconds to 60 seconds, and particularly preferably 10 seconds to 45 seconds.

(Preferable aspect of image recording device)
A preferred embodiment of the image recording step is a transport mechanism for transporting the impermeable base material, a head A, and a downstream side in the transport direction of the non-permeable base material with respect to the head A (hereinafter, also simply referred to as “downstream side”). The impermeable base material is conveyed by a conveying mechanism using an image recording device including the head B arranged in the head A, and white ink A is ejected from the head A onto the conveyed impermeable base material. This is an embodiment in which the white ink B is ejected from the head B and applied to the region to which the white ink A is applied on the impermeable substrate.
According to this aspect, the landing interval T can be easily adjusted by adjusting the transport speed of the impermeable base material.

As the image recording device used in the above-described preferred embodiment, an image recording device in which the head A and the head B are both fixedly arranged line heads is more preferable.
As the line head, the recording element and the nozzle are preferably arranged in a direction intersecting the transport direction of the non-permeable base material and parallel to the surface of the non-permeable base material). It is a line head.
In this case, the impermeable base material is conveyed, and the white ink A and the white ink B are transferred from the head A which is the line head and the head B which is the line head to the conveyed non-penetrating base material, respectively. The ink dots A and ink dots B described above can be formed by ejecting.

The degree of overlap of the ink dots A and the ink dots B can be adjusted by adjusting the degree of deviation between the arrangement of the nozzles in the head A and the arrangement of the nozzles in the head B.
For a technique for adjusting the degree of deviation between the nozzle arrangement in the head A and the nozzle arrangement in the head B, for example, Japanese Patent Application Laid-Open No. 2005-81642 can be referred to.

(Specific example of image recording device)
The image recording method of the present disclosure can be carried out using, for example, a known inkjet recording device.
Examples of the known inkjet recording device include the known inkjet recording devices described in JP-A-2010-83021A, JP-A-2009-234221, JP-A-10-175315, and the like.

Hereinafter, an example of an image recording device that can be used in the image recording method of the present disclosure will be described with reference to FIG.

FIG. 2 is a schematic configuration diagram showing an example of an image recording device that can be used in the image recording method of the present disclosure.
As shown in FIG. 2, the image recording apparatus according to this example includes a transport mechanism for transporting a non-permeable base material (hereinafter, also simply referred to as “base material”) in the direction of the arrow in the drawing, and an inkjet head A. The ink ejection head 30WA and the ink ejection head 30WB as the inkjet head B arranged downstream of the ink ejection head 30WA in the transport direction (arrow direction in the drawing) of the base material are provided.
More specifically, in the image recording apparatus according to this example, the ink ejection unit 14 (white) that ejects various inks sequentially from the substrate supply unit 11 toward the substrate transport direction (the direction of the arrow in the drawing). An ink ejection head 30WA for ejecting ink A and an ink ejection head 30WB for ejecting white ink B) and an ink drying zone 15 for drying the ejected ink (that is, an image) are arranged. There is.

The base material supply unit 11 in this image recording device may be a supply unit that supplies the base material from a case loaded with the base material, or the base material is rolled from a roll in which the base material is wound in a roll shape. It may be a supply unit that supplies.
The base material is sent from the supply unit 11 in the order of the ink ejection unit 14 and the ink drying zone 15 by the transfer rollers 41, 42, 43, 44, 45, 46 as the transfer mechanism, and is integrated in the accumulation unit 16. Ink.
In the integration unit 16, the base material may be wound into a roll.
In addition to the method using a transfer roller as shown in FIG. 2, the substrate may be conveyed by a drum transfer method using a drum-shaped member, a belt transfer method, a stage transfer method using a stage, or the like.

Of the plurality of transfer rollers 41, 42, 43, 44, 45, 46, at least one transfer roller can be a drive roller to which the power of a motor (not shown) is transmitted.
By rotating the drive roller rotated by the motor at a constant speed, the base material is conveyed in a predetermined direction at a predetermined transfer speed.

White ink A (WA), white ink B (WB), black ink (K), cyan ink (C), magenta ink (M), and yellow ink (Y) are stored in the ink ejection unit 14. Ink ejection heads 30WA, 30WB, 30K, 30C, 30M, and 30Y connected to each ink storage unit (not shown) are arranged. Ink of each color is stored in each ink storage unit (not shown), and the ink of each color is supplied to each ink ejection head as needed when recording an image.
In the example shown in FIG. 2, the ink ejection heads 30WA and 30WB are arranged on the downstream side with respect to the other ink ejection heads, but the ink ejection heads 30WA and 30WB are other ink ejection heads. It may be arranged on the upstream side with respect to.
In either case, the ink ejection heads 30WA and 30WB are arranged in this order with respect to the transport direction of the base material. As a result, the white ink A on the base material is imparted to the conveyed base material by ejecting the white ink A from the ink ejection head 30WA and ejecting the white ink B from the ink ejection head 30WB. White ink B can be applied to the region.

The arrangement order of the ink ejection heads 30K, 30C, 30M, and 30Y can be changed as appropriate.
Although not shown, the image recording device ejects special color inks (for example, inks of colors such as orange, green, purple, light cyan, and light magenta) in addition to the ink ejection heads described above. A discharge head may be provided.
Further, the image recording device may not include the ink ejection heads 30K, 30C, 30M, and 30Y. The image recording device in this case is an image recording device dedicated to white images.

The ink ejection heads 30WA, 30WB, 30K, 30C, 30M, and 30Y eject the corresponding inks from the ejection nozzles arranged to face the image recording surface of the base material.

In each of the ink ejection heads 30WA, 30WB, 30K, 30C, 30M, and 30Y, a large number of ejection ports (nozzles) are arranged over the maximum recording width (maximum recording width) of the image recorded on the surface of the base material. It is a full line head that has been made. As a result, images can be recorded on the base material at a higher speed than the serial type, which records while reciprocally scanning a short shuttle head in the width direction of the base material (direction orthogonal to the transport direction of the base material). Can be done.
In the present disclosure, either serial recording or a method capable of relatively high-speed recording, for example, recording in a single-pass method in which one line is formed by one scan may be adopted, but single When recording by the pass method is adopted, the effect of the image recording method of the present disclosure is more effectively exhibited.

In this example, the ink ejection heads 30WA, 30WB, 30K, 30C, 30M, and 30Y all have the same structure.

The ink drying zone 15 is arranged on the downstream side of the ink ejection unit 14 in the transport direction of the base material.
The ink drying zone 15 can be configured by using a known heating means such as a heater, a blowing means using a blowing air such as a dryer or an air knife, or a means combining these.
The heating means is a heating element such as a heater on the side opposite to the ink-applied surface (that is, the image recording surface) of the base material (for example, in the case of automatically transporting the base material, below the transport mechanism on which the base material is placed and transported). Examples thereof include a method of applying hot air or hot air to the ink-applied surface (that is, the image recording surface) of the base material, and a heating method using an infrared heater. Further, the heating means may be a combination of a plurality of the above methods.
In the ink drying zone 15, the solvent may be removed from the ink by using a solvent removing roller or the like.

The image recording apparatus may further include a heating means for heat-treating the base material in the transport path from the supply unit 11 to the integration unit 16.
For example, by arranging the heating means at a desired position such as on the upstream side of the ink ejection unit 14 or between the ink ejection unit 14 and the ink drying zone 15, the temperature of the base material can be raised to a desired temperature. It becomes possible to effectively dry the ink, fix the ink, and the like.

In addition, since the surface temperature of the base material changes depending on the type (material, thickness, etc.) of the base material, the environmental temperature, etc., the image recording device controls the measuring unit for measuring the surface temperature of the base material and the heating conditions. It is preferable to provide a heating control mechanism having a heating control unit and a control unit that feeds back the surface temperature value of the base material measured by the measurement unit to the heating control unit.
By providing the image recording device with a heating control mechanism, it is possible to apply ink while controlling the temperature of the base material.
A contact or non-contact thermometer is preferable as the measuring unit for measuring the surface temperature of the base material.

The image recording apparatus according to the above example is arranged on the downstream side in the transport direction of the base material with respect to the transport mechanism for transporting the impermeable base material, the ink ejection head 30WA as the inkjet head A, and the ink ejection head 30WA. Since the ink ejection head 30WB as the inkjet head B is provided, it is suitable for carrying out the image recording method of the present disclosure.
For example, the landing interval T can be adjusted by adjusting the transport speed of the impermeable substrate.

<Other processes>
The image recording method of the present disclosure may include the preparation step and other steps other than the image recording step.
For example, the image recording method of the present disclosure may include a step of curing the ink by irradiation with an active energy ray (ultraviolet rays or the like). However, in general, in image recording that does not include the step of curing the ink, the above-mentioned problems of landing interference and image roughness are likely to occur. Therefore, when the image recording method of the present disclosure does not include the step of curing the ink, the image recording method of the present disclosure is based on setting γ _A (10) -γ _B (10) to more than 0 mN / m. (The effect of suppressing the graininess of the image) is more effectively exhibited.
Further, the image recording method of the present disclosure is described in, for example, International Publication No. 2019/004485, which is a pretreatment liquid for a non-permeable base material (specifically, a coagulant such as a polyvalent metal compound or an organic acid). It may include a pretreatment step of imparting a pretreatment liquid containing the above. However, in general, in image recording that does not include the pretreatment liquid step, the above-mentioned problems of landing interference and image roughness are likely to occur. Therefore, when the image recording method of the present disclosure does not include the pretreatment step, the effect of the image recording method of the present disclosure by setting γ _A (10) -γ _B (10) to more than 0 mN / m. (The effect of suppressing the graininess of the image) is more effectively exhibited.

[Ink set]
The ink set of the present disclosure is
White ink A and
A white ink B having a smaller dynamic surface tension at 10 ms than the white ink A is provided.
The ink set of the present disclosure is suitable for the image recording method of the present disclosure described above.

Each of the white ink A and the white ink B is as described in the section of the preparation step of the image recording method described above, and the preferred embodiment is also the same.
For example, the white ink A does not contain an organic solvent having a boiling point of 270 ° C. or higher, or when it is contained, the content of the organic solvent having a boiling point of 270 ° C. or higher is 5% by mass or less based on the total amount of the white ink A. It is preferable that the white ink B does not contain an organic solvent having a boiling point of 270 ° C. or higher, or when it is contained, the organic solvent having a boiling point of 270 ° C. or higher is 5% by mass or less based on the total amount of the white ink B. Is preferable.

The ink set of the present disclosure may include other inks other than white ink A and white ink B.
Examples of other inks include at least one type of ink having a color other than white (for example, black ink, cyan ink, magenta ink, yellow ink, etc.).

Hereinafter, examples of the present disclosure will be shown, but the present disclosure is not limited to the following examples.
Hereinafter, unless otherwise specified, "parts" and "%" are based on mass.

<Preparation of base white ink>
As described below, a white ink as a base for the white ink A and the white ink B described later was prepared.

(Preparation of dispersion resin P-1)
As described below, a dispersion resin P-1 as a dispersant for white pigments in white ink was prepared.
Dipropylene glycol was added to a three-necked flask equipped with a stirrer and a cooling tube in the same mass as the total amount of the monomers described below, and heated to 85 ° C. under a nitrogen atmosphere.
Solution I which is a mixture of 9.1 molar equivalents of stearyl methacrylate, 34.0 molar equivalents of benzyl methacrylate, 31.9 molar equivalents of hydroxyethyl methacrylate, 25.0 molar equivalents of methacrylate, and 0.8 molar equivalents of 2-mercaptopropionic acid. And 1% by mass of t-butylperoxy-2-ethylhexanoate (perbutyl O manufactured by Nichiyu Co., Ltd.) based on the total mass of the monomer is dissolved in 20% by mass of dipropylene glycol based on the total mass of the monomer. The resulting solution II and the solution II were prepared respectively. Solution I was added dropwise to the three-necked flask over 5 hours, and solution II was added dropwise over 5 hours.
After completion of the dropping, the reaction was carried out for another 2 hours, the temperature was raised to 95 ° C., and the mixture was heated and stirred for 3 hours to react all the unreacted monomers. The disappearance of the monomer was confirmed by nuclear magnetic resonance ( ¹ H-NMR) method.
The obtained reaction solution is heated to 70 ° C., 20.0 molar equivalents of dimethylaminoethanol (dimethylethanolamine) is added as an amine compound, propylene glycol is added and stirred, and 30% by mass of the dispersed resin P-1 is added. A solution was obtained.
The constituent components of the obtained polymer were confirmed by ^{1 1} H-NMR. The weight average molecular weight (Mw) determined by GPC was 22,000.
The mass ratio of each structural unit in the dispersion resin P-1 is the structural unit derived from stearyl methacrylate / the structural unit derived from benzyl methacrylate / the structural unit derived from hydroxyethyl methacrylate / the structural unit derived from methacrylic acid = 20/39/27. It was / 14. However, the above mass ratio is a value that does not include dimethylaminoethanol.

(Preparation of resin particles A)
Resin particles A, which is one component in the white ink, were produced as follows.
293 g of methyl ethyl ketone was charged into a 2-liter three-necked flask (hereinafter, also referred to as “reaction vessel”) equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas introduction tube, and the temperature was raised to 80 ° C. Next, while maintaining the temperature inside the reaction vessel at 80 ° C., 165.7 g of methyl methacrylate (manufactured by Mitsubishi Gas Chemical Industries, Ltd.), 63.7 g of isobornyl methacrylate (manufactured by Kyoei Co., Ltd.), and methacrylic acid (Mitsubishi). A mixed solution consisting of 25.5 g (manufactured by Gas Chemical Co., Ltd.), 48 g of methyl ethyl ketone, and 1.25 g of "V-601" (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., polymerization initiator) so that the dropping can be completed in 2 hours, etc. Dropped at high speed. After the dropping was completed, a solution prepared by mixing 0.60 g of (1) "V-601" and 5.0 g of methyl ethyl ketone was added, and the mixture was further stirred for 2 hours. Then, the step (1) was repeated 4 times, a solution containing 0.60 g of "V-601" and 5.0 g of methyl ethyl ketone was added, and the mixture was stirred for 3 hours.
From the above, a polymer solution which is a solution of a methyl methacrylate / isobornyl methacrylate / methacrylic acid (= 65/25/10 [mass ratio]) copolymer was obtained.
The weight average molecular weight (Mw) of the copolymer in the polymer solution was 72,000, and the acid value was 62.9 mgKOH / g.
The acid value was measured according to the method described in Japanese Industrial Standards (JIS K0070: 1992). The weight average molecular weight was measured by GPC by the method described above.
The disappearance of the monomer was confirmed by nuclear magnetic resonance ( ¹ H-NMR) method.

Next, 588.2 g of the polymer solution was weighed into the reaction vessel, 165 g of isopropanol and 120.8 ml of a 1 mol / L sodium hydroxide (NaOH) aqueous solution were added, and the temperature inside the reaction vessel was raised to 80 ° C. Next, 718.0 g of distilled water was added dropwise to the reaction vessel at a rate of 20 ml / min to carry out water dispersion. Then, the temperature inside the reaction vessel was kept at 80 ° C. for 2 hours, 85 ° C. for 2 hours, and 90 ° C. for 2 hours under atmospheric pressure, and then the inside of the reaction vessel was depressurized to add isopropanol, methyl ethyl ketone, and distilled water. In an amount, 913.7 g was distilled off. In this way, an aqueous dispersion (emulsion) of the resin particles A having a solid content concentration of 23.2% by mass was obtained.
The resin constituting the resin particles A is a neutralized product of a methyl methacrylate / isobornyl methacrylate / methacrylic acid (= 65/25/10 [mass ratio]) copolymer.

(Preparation of TiO ₂ dispersion)
A dispersion of titanium dioxide (TiO ₂ ) (white pigment) was prepared as follows.
Using a ready-mill model LSG-4U-08 (manufactured by IMEX), a TiO ₂ dispersion was prepared as follows. That is,
Titanium dioxide as a white pigment (TiO ₂ ; average primary particle size: 210 nm, trade name: PF-690, manufactured by Ishihara Sangyo Co., Ltd .; white inorganic pigment) 45 parts by mass in a zirconia container, obtained in Synthesis Example 1. 15 parts by mass of a 30% by mass solution of the dispersed resin P-1 and 40 parts by mass of ultrapure water were added. Further, 40 parts by mass of 0.5 mmφ zirconia beads (manufactured by TORAY, Trecerum beads) were added, and the mixture was lightly mixed with a spatula. The mixture was placed in a zirconia container in a ball mill and dispersed at 1000 rpm (revolutions per minute) for 5 hours. After completion of the dispersion, the beads were removed by filtration through a filter cloth to prepare a TiO ₂ dispersion liquid which is an aqueous pigment dispersion having a TiO ₂ concentration of 45% by mass.

(White ink)
Each component shown in Table 1 was mixed to prepare a base white ink.

In Table 1, the "remaining amount", which is the content of water, means the remaining amount for the total of all the components to be 100% by mass.
The details of the components shown in Table 1 are as follows.
-PVP K15: Polyvinylpyrrolidone (manufactured by Tokyo Chemical Industry Co., Ltd.)
Orfin E1010: acetylene glycol-based surfactant (manufactured by Nissin Chemical Industry Co., Ltd.)
-Orphin E1020: Acetylene glycol-based surfactant (manufactured by Nissin Chemical Industry Co., Ltd.)
-Snowtex XS: Colloidal silica (manufactured by Nissan Chemical Industries, Ltd.); Solid content concentration 20.0% by mass)
BYK-024: Silicone defoamer (manufactured by Big Chemie Japan, solid content concentration 15.0% by mass)

[Examples 1 to 11, Comparative Examples 1 to 3]
<Preparation of white ink A and white ink B>
In the examples other than Example 3, Table 2 shows the same as the preparation of the base white ink except that the content of Orphine E1020 was changed in the range of 0.1% by mass to 2.0% by mass. White ink A and white ink B having dynamic surface tensions (γ _A (10) and γ _B (10)) at 10 ms were prepared, respectively. The higher the content of Orphine E1020, the smaller the dynamic surface tension at 10 ms.
In Example 3, by further adding BYK-3450 (manufactured by BYK) as a surfactant to the base white ink, white having γ _A (10) and γ _B (10) shown in Table 2 is added. Ink A and white ink B were prepared, respectively.
The base white ink is the white ink A in Example 1.

Each of the white ink A and the white ink B of Example 9 further contained 3% by mass of glycerin (GL) (organic solvent having a boiling point of 290 ° C.) with respect to the total amount of the ink (see Table 2).
In each of the white ink A and the white ink B of Example 10, the content of the white pigment with respect to the total amount of the ink was changed to 6% by mass (see Table 2).
In each of the white ink A and the white ink B of Example 11, the content of the white pigment with respect to the total amount of the ink was changed to 17% by mass (see Table 2).
The white ink A and the white ink B of Comparative Example 1 are the same white ink. That is, Comparative Example 1 is an example in which the same white ink is ejected from each of the inkjet head A and the inkjet head B.

<Preparation of impermeable base material>
A biaxially stretched polypropylene (OPP) film (thickness 40 μm, surface treatment: corona discharge treatment, manufactured by Futamura Chemical Co., Ltd., abbreviated as OPP) was prepared as a non-permeable substrate for recording an image described later.

<Preparation of image recording device>
An image recording device including a transport mechanism for transporting a non-permeable substrate, a fixedly arranged inkjet head A, and a fixedly arranged inkjet head B on the downstream side of the inkjet head A was prepared.
The inkjet head A and the inkjet head B were both 1200 dpi / 20 inch wide piezo full line heads. Here, dpi is an abbreviation for dot per inch.
In both of the arrangements of the inkjet head A and the inkjet head B, the nozzle arrangement direction is 75. In the direction orthogonal to the transport direction of the impermeable substrate (that is, the width direction of the impermeable substrate). It was arranged to be tilted by 7 °.
Further, the relative positional relationship between the nozzle of the inkjet head A and the nozzle of the inkjet head B is such that the ink dots A and the ink dots B formed by ejecting ink from each nozzle have a portion where they overlap each other. Adjusted so that they are arranged alternately.

<Image recording>
Using the above image recording device, white ink A is ejected from the inkjet head A onto the conveyed non-permeable base material (specifically, the corona discharge-treated surface of the OPP film) to apply the non-permeable group. Ink dots A and ink dots B having overlapping portions are formed by ejecting and applying the white ink B from the inkjet head B to the region to which the white ink A is applied on the material, and the formed ink dots. A and ink dot B were dried at 80 ° C. for 30 seconds to obtain a solid white image.
The ejection amount of the white ink A and the white ink B was set to 4.0 pL.
The transport speed of the impermeable substrate is in the range of 5 m / min to 300 m / min, and the landing interval T (ms) (that is, the time from the landing of the droplet A to the landing of the droplet B) is shown. The value was adjusted to the value shown in 2.
Hereinafter, the impermeable base material on which the white solid image is recorded is also referred to as a “base material with a white solid image”.

In the image recording of Comparative Example 2, a white image was recorded only with white ink A without using white ink B, and in the image recording of Comparative Example 3, a white image was recorded only with white ink B without using white ink A. Was recorded.

<Evaluation>
The following measurements and evaluations were carried out using a base material with a solid white image and each white ink.
The results are shown in Table 2.

(Concealment of solid white image)
The hiding property of the white solid image on the base material with the white solid image was evaluated as follows.
Separately from the base material with a white solid image, a commercially available black ink was used on the corona discharge-treated surface of the impermeable base material (the OPP film), and the sizes of 2 pt (points), 4 pt, 6 pt, and 8 pt were used. Black character images (4 in total) were recorded. The four black character images were all black character images shown in FIG. From the above, a base material with a black character image was obtained.
A base material with a white solid image and a base material with a black character image were laminated in a direction in which non-image recording surfaces (surfaces on which no image was recorded) were in contact with each other to form a laminate. Hold the obtained laminate over a 30 W fluorescent lamp so that the white solid image faces the evaluator's side, check whether the details of each black character image can be visually recognized through the white solid image, and follow the evaluation criteria below. , The hiding property of the white solid image was evaluated. At this time, the distance between the eyes of the evaluator and the laminate was 20 cm, and the distance from the laminate to the fluorescent lamp was 2 m.
In the following evaluation criteria, the rank with the best concealment of a solid white image is "5".

-Evaluation criteria for concealment of solid white images-
No details could be visually recognized for the 5: 2pt, 4pt, 6pt and 8pt black character images.
The details of the 4: 8 pt black character image could be visually recognized, but the details of the 2 pt, 4 pt, and 6 pt black character images could not be visually recognized.
The details of the 3: 6 pt and 8 pt black character images could be visually recognized, but the details of the 2 pt and 4 pt black character images could not be visually recognized.
The details of the 2: 4 pt, 6 pt, and 8 pt black character images could be visually recognized, but the details of the 2 pt black character images could not be visually recognized.
Details could be visually recognized for the 1: 2 pt, 4 pt, 6 pt and 8 pt black character images.

(Roughness of solid white image)
The white solid image on the substrate with the white solid image was visually observed, and the roughness of the white solid image was evaluated according to the following evaluation criteria.
In the following evaluation criteria, the rank in which the roughness of the white solid image is most suppressed is "5".

-Evaluation criteria for graininess of solid white images-
5: White solid image is uniform without any roughness.
4: The solid white image has a slight graininess, but it is almost uniform as a whole.
3: A slight graininess is observed in the solid white image, which is within a practically acceptable range.
2: Roughness is conspicuous in the solid white image, which is an unacceptable range for practical use.
1: A lot of "roughness" with strong shading occurs in a solid white image, and it cannot be said to be uniform, which is an unacceptable range for practical use.

(Dryness of solid white image)
The above-mentioned OPP film was overlapped and adhered to the white solid image 5 minutes after the recording of the white solid image in the above image recording (that is, drying at 80 ° C. for 30 seconds), and then the OPP film was peeled off. .. At this time, the transfer condition of the white solid image to the OPP film was visually observed, and the dryness of the white solid image was evaluated according to the following evaluation criteria.
In the following evaluation criteria, the rank with the best dryness of the white solid image is "5".

-Evaluation criteria for image dryness-
5: No transfer of solid white image is seen.
4: The transfer of the white solid image is less than 5% of the entire white solid image.
3: The transfer of the white solid image is 5% or more and less than 10% of the entire white solid image.
2: The transfer of the white solid image is 10% or more and less than 15% of the entire white solid image.
1: The transfer of the white solid image is 15% or more of the entire white solid image.

(Ejectability of white ink A (Ejectability A))
The recording paper 40 is under the same conditions as the image recording except that A2 size photographic paper (printing paper for inkjet, painting, manufactured by Fujifilm Co., Ltd.) is used and the ejection of white ink B from the inkjet B is omitted. White solid images were continuously recorded on the sheets. Hereinafter, the recording paper on which the white solid image is formed is referred to as “Ejectability Evaluation Sample A”.
Forty sheets of the sample A for evaluation of ejection property were visually observed, and the number of samples for evaluation of ejection property in which nozzle omission (that is, an image defect due to poor nozzle ejection) was confirmed was examined. Based on this result, the ejection property of the white ink A (hereinafter, also referred to as ejection property A) was evaluated according to the following evaluation criteria.
In the following evaluation criteria, the rank with the highest dischargeability A is "5".

-Evaluation criteria for ejection property (ejection property A) of white ink A-
5: There are 0 or 1 samples for which nozzle omission is confirmed.
4: There are two or three samples in which nozzle omission is confirmed.
3: There are 4 or 5 samples in which nozzle omission is confirmed.
2: There are 6 or 7 samples in which nozzle omission is confirmed.
1: There are 8 or more samples in which nozzle omission is confirmed.

(Ejectability of white ink B (Ejectability B))
In the same manner as the evaluation of the ejection property (ejection property A) of the white ink A, except that the ejection of the white ink A from the inkjet A was omitted instead of omitting the ejection of the white ink B from the inkjet B A solid white image is continuously recorded on the 40 sheets of the recording paper, and the sample B for evaluating the ejection property is used.
Using 40 sheets of sample B for evaluating the ejection property, the ejection property (ejection property B) of the white ink B was evaluated according to the same criteria as the evaluation criteria of the ejection property (ejection property A) of the white ink A.

-Explanation of Table 2-
The "amount (%)" is the content (mass%) of the corresponding component with respect to the entire white ink A or white ink B.
γ _A (10) is the dynamic surface tension of the white ink A at 10 ms (unit: mN / m), and γ _B (10) is the dynamic surface tension of the white ink B at 10 ms (unit: mN). / _M ), and γ _A (T) is the dynamic surface tension (unit: mN / m) of the white ink A at T (landing interval) ms. γ _A (10), γ _B (10) and γ _A (T) were measured by the methods described above, respectively.
The landing interval T (ms) is the time from the landing of the droplet A of the white ink A to the landing of the droplet B of the white ink B. The landing interval T (ms) was measured by the method described above.

As shown in Table 2, white ink A and white ink B having γ _A (10) -γ _B (10) of more than 0 mN / m were used, and the white ink A from the inkjet head A was used on the impermeable substrate. Is ejected and applied, and white ink B is ejected from the inkjet head B to the region on the impermeable substrate to which the white ink A is applied to form ink dots A and ink dots B having overlapping portions. In Examples 1 to 11 in which the time from the impact of the droplet A to the impact of the droplet B (landing interval T (ms)) was set to 20 ms to 10000 ms, the concealment property was excellent and the roughness was suppressed. It was possible to record a solid white image with excellent drying properties.

In Comparative Example 1 in which γ _A (10) −γ _B (10) was 0 mN / m (that is, the same white ink was ejected from each of the inkjet head A and the inkjet head B) for each embodiment, the image The roughness became noticeable.
Further, in Comparative Example 2 in which a white solid image was recorded using only white ink A without using white ink B, and Comparative Example 3 in which a white solid image was recorded using only white ink B without using white ink A. In both cases, the concealment of the image was reduced.

From the results of Examples 1 to 3 and 5, it can be seen that when γ _B (10) is 25.0 mN / m to 40.0 mN / m (Example 1), the graininess of the image is further suppressed.

From the results of Examples 1, 4 and 6, when | γ _A (T) -γ _B (10) | is 3.0 mN / m or less (Examples 1 and 6), the roughness of the image is further suppressed. You can see that.

IDA Ink Dot A
IDB Ink Dot B
XA1 Center of ink dot A XA2 Center of ink dot A XA Midpoint between centers of ink dot A D Distance between centers of ink dot A XB Center of ink dot B 11 Supply section 14 Ink ejection section 15 Ink drying zone 16 Accumulation Parts 30WA, 30WB, 30K, 30C, 30M, 30Y Ink ejection head 41, 42, 43, 44, 45, 46 Conveying rollers

Claims (11)

1. The dynamic surface tension at 10 ms measured by the maximum foam pressure method is smaller than that of the white ink A with respect to the region where the droplet A of the white ink A is landed on the non-permeable substrate from the inkjet head A. A step of recording an image by landing a droplet B of white ink B on the area from the inkjet head B so as to overlap a part thereof is included, and
   An image recording method in which the time T from the impact of the droplet A to the impact of the droplet B is 20 ms to 10000 ms.
2. When the dynamic surface tension at Tms measured by the maximum foam pressure method of the white ink A is γ _A (T) and the dynamic surface tension of the white ink B at 10 ms is γ _B (10), γ The image recording method according to claim 1, wherein the absolute value of the difference between _A (T) and γ _B (10) is 3.0 mN / m or less.
3. Claim 1 or claim 2 in which the value obtained by subtracting the γ _B (10) from the dynamic surface tension γ _A (10) of the white ink A at 10 ms is 1.0 mN / m to 7.0 mN / m. The image recording method described in.
4. The image recording method according to any one of claims 1 to 3, wherein the γ _B (10) is 25.0 mN / m to 40.0 mN / m.
5. In the step of recording the image, the transport mechanism for transporting the impermeable base material, the inkjet head A, and the non-permeable base material arranged on the downstream side in the transport direction with respect to the inkjet head A. Using an image recording device including an inkjet head B, the impermeable substrate is conveyed by the conveying mechanism, and the white ink A is transferred from the inkjet head A onto the conveyed impermeable substrate. Any of claims 1 to 4, wherein the white ink B is ejected and applied from the inkjet head B to the region of the impermeable substrate to which the white ink A is applied. The image recording method according to item 1.
6. The white ink A has a boiling point of 270 ° C. or higher and an organic solvent content of 5% by mass or less based on the total amount of the white ink A.
   The image recording method according to any one of claims 1 to 5, wherein the white ink B contains 5% by mass or less of an organic solvent having a boiling point of 270 ° C. or higher with respect to the total amount of the white ink B.
7. The white ink A contains a white pigment, and the content of the white pigment with respect to the total amount of the white ink A is 6% by mass to 20% by mass, and
   The image according to any one of claims 1 to 6, wherein the white ink B contains a white pigment, and the content of the white pigment with respect to the total amount of the white ink B is 6% by mass to 20% by mass. Recording method.
8. The white ink A contains water and
   The image recording method according to any one of claims 1 to 7, wherein the white ink B contains water.
9. The white ink A has a content of the polymerizable compound of less than 1% by mass based on the total amount of the white ink A, and
   The image recording method according to any one of claims 1 to 8, wherein the white ink B contains less than 1% by mass of the polymerizable compound with respect to the total amount of the white ink B.
10. White ink A and
    An ink set comprising white ink B having a smaller dynamic surface tension at 10 ms than the white ink A.
11. The white ink A has a boiling point of 270 ° C. or higher and an organic solvent content of 5% by mass or less based on the total amount of the white ink A.
    The ink set according to claim 10, wherein the white ink B contains 5% by mass or less of an organic solvent having a boiling point of 270 ° C. or higher with respect to the total amount of the white ink B.

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