JP2023101528A - Aqueous white ink, ink set, and printing method - Google Patents

Abstract

To provide aqueous white ink which can suppress occurrences of a printing streak phenomenon and a liquid gathering phenomenon.SOLUTION: Aqueous white ink for inkjet printing contains at least water, a pigment, a water-soluble organic solvent, and a resin, wherein a dynamic surface tension value of the aqueous white ink at 25°C at a surface age of 10 ms is 33 mN/m or more and 42 mN/m or less, a static surface tension value of the aqueous white ink at 25°C is 23 mN/m or more and 30 mN/m or less, and the water-soluble organic solvent contains at least one alkanediol-based solvent.SELECTED DRAWING: None

Description

The present invention relates to a water-based white ink, an ink set comprising the water-based white ink, and a printing method using the ink set, and more particularly to a water-based white ink capable of suppressing the occurrence of print streaks and liquid pooling.

Various inks have been developed as inks used for printing by inkjet printers, but water-based inks are widely used from the viewpoint of reducing environmental impact. However, since water-based ink contains water as a solvent, it tends to cause bleeding during printing. As a method for improving bleeding of a printed layer formed by printing, for example, a method of using a treatment liquid having an action of aggregating colored ink together is known (for example, JP-A-6-57192
Publication and Japanese Patent Application Laid-Open No. 2009-190379). A water-based ink set in which such treatment liquid and colored ink are combined is also called a two-liquid reaction type water-based ink set.

By the way, in the field of flexible food packaging and labels, printed matter is conventionally produced using flexographic printing and gravure printing. When performing the printing, there are two types of printing methods: "front printing" in which white ink is first printed on a transparent film, then color ink is printed and viewed from the printed surface side, and "reverse printing" in which white ink is printed after printing color ink and the printed matter is viewed from the opposite side of the printed surface (i.e., the printed matter is viewed through the transparent film). In recent years, the demand for high-mix low-volume printing has increased in these fields, and along with this, the demand for inkjet printing and other digital printing has begun to grow.

JP-A-6-57192 JP 2009-190379 A

Under these circumstances, when inkjet printing on a transparent film was investigated by further combining the two-liquid reaction type aqueous ink set described above with a water-based white ink, there were problems such as the occurrence of printing streaks peculiar to inkjet printing and uneven movement of the white ink during reverse printing, resulting in the phenomenon of liquid pooling.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a water-based white ink capable of solving the above-described problems of the prior art and suppressing the occurrence of the print streak phenomenon and the liquid side effect. Another object of the present invention is to provide an ink set comprising such a water-based white ink and a printing method using the ink set.

In inkjet printing using the above-described ink set, the print streak phenomenon and liquid pooling phenomenon were confirmed when performing reverse printing, but it could be applied without problems when performing surface printing. Therefore, the present inventors considered that the properties of the water-based white ink when it lands on the water-based colored ink layer are important, and focused on the surface tension of the ink and further studied. Thus, the present inventors have found that the occurrence of print streaks and liquid spillage can be suppressed not only in surface printing but also in reverse printing, and have completed the present invention.

That is, the water-based white ink of the present invention is a water-based white ink for inkjet printing containing at least water, a pigment, a water-soluble organic solvent and a resin, and the dynamic surface tension value of the water-based white ink at 25°C at a surface life of 10 ms is 33 mN/m or more and 42 mN/m or less,
The water-based white ink has a static surface tension value of 23 mN/m or more and 30 mN/m or less at 25° C., and the water-soluble organic solvent contains at least one alkanediol solvent.

In a preferred embodiment of the water-based white ink of the present invention, the water-soluble organic solvent contains at least one 1,2-alkanediol solvent.

In another preferred example of the water-based white ink of the present invention, the pigment has an average particle size (D50) of 150 nm or more and 500 nm or less.

In another preferred embodiment of the water-based white ink of the present invention, the resin is at least one polyether or polyester urethane resin particle.

Another preferred example of the water-based white ink of the present invention further contains a surface modifier.

In another preferred embodiment of the water-based white ink of the present invention, the surface conditioner has an HLB value of 3.0.
Contains at least one silicone-based surface control agent of ~16.0.

In another preferred embodiment of the water-based white ink of the present invention, the surface conditioner has an HLB value of 3.0.
At least one of the above acetylene glycol-based surface conditioners is included.

Further, the ink set of the present invention is an ink set containing the water-based white ink, the water-based coating liquid, and the water-based colored ink, wherein the water-based coating liquid contains at least water,
A water-soluble polymer having a cation and an organic solvent are included, and the water-based colored ink is characterized by including at least water, a resin, an organic solvent and a colorant.

Further, the printing method of the present invention is a printing method for forming a printed layer on a substrate by an inkjet printer equipped with the ink set described above, and is characterized by including a step of printing a water-based white ink, a water-based coating liquid and a water-based colored ink in this order to form a printed layer on the substrate, or a step of performing printing of a water-based coating liquid, a water-based colored ink and a water-based white ink in this order to form a printed layer on a substrate.

According to the water-based white ink of the present invention, it is possible to provide a water-based white ink capable of suppressing the occurrence of the print streak phenomenon and the liquid side effect. Further, according to the ink set of the present invention, it is possible to provide an ink set comprising such a water-based white ink, and according to the printing method of the present invention, it is possible to provide a printing method using such an ink set.

The water-based white ink of the present invention is described in detail below. The water-based white ink of the present invention is a water-based white ink for inkjet printing containing at least water, a pigment, a water-soluble organic solvent and a resin, wherein the water-based white ink has a dynamic surface tension value at 25°C of 33 mN/m or more and 42 mN/m or less at a surface life of 10 ms, a static surface tension value of the water-based white ink at 25°C of 23 mN/m or more and 30 mN/m or less, and the water-soluble organic solvent contains at least one alkanediol solvent. It is characterized by

As used herein, the term "aqueous ink" refers to ink containing water as a main solvent.
As used herein, the term “white ink” refers to ink that can color an object white. Further, in this specification, "white" refers to achromatic white, but it is not limited to this, and includes off-white with a slight tint such as beige and gray.
As used herein, the term “inkjet printing ink” refers to ink for use in printing by an inkjet printer (inkjet printing).

The water-based white ink of the present invention has a dynamic surface tension value of 33 at 25° C. with a surface life of 10 ms.
It is mN/m or more and 42 mN/m or less. By adjusting the dynamic surface tension value of the water-based white ink of the present invention to a relatively low range of 33 mN/m or more and 42 mN/m or less, it is possible to solve the problem that the white ink is difficult to wet and spread even during reverse printing, and it is possible to suppress the occurrence of print streaks in both surface printing and reverse printing. From the viewpoint of suppressing the occurrence of printing streaks, the dynamic surface tension value at 25°C at a surface life of 10 ms for water-based white ink is 40
. It is preferably 5 mN/m or less, more preferably 39.0 mN/m or less. In addition, when a surface conditioner or solvent with a high ability to lower the surface tension is used in the white ink, the movement of the white ink that has landed on the colored ink layer is biased during reverse printing, resulting in the phenomenon of liquid spillage. Therefore, the water-based white ink of the present invention has a dynamic surface tension value of 33 mN/m or more at 25°C at a surface life of 10 ms. From the viewpoint of suppressing the occurrence of the liquid crowding phenomenon, the dynamic surface tension value at 25 ° C. with a surface life of 10 ms for water-based white ink is 34.5 m
It is preferably N/m or more, more preferably 36.0 mN/m or more.

"Dynamic surface tension" refers to the surface tension that approaches equilibrium over time, using a dynamic surface tension meter (for example, BP2 manufactured by KRUSS), the maximum bubble pressure method (Maximum
bubble pressure method). Herein,
The surface tension is measured with a surface life of 10 ms for ink or coating liquid at 25°C.
In the maximum bubble pressure method, air is passed through a probe (tube) inserted in a liquid, and surface tension is calculated by measuring the maximum pressure (maximum bubble pressure) when bubbles are generated. By ejecting bubbles continuously from the tip of the probe in the liquid, the pressure inside the probe changes periodically, and the pressure reaches its maximum when the radius of curvature of the bubble and the tip of the probe become equal. The time when a new interface is generated in the probe is 0 ms, and the time until the maximum bubble pressure is reached is the surface life. From the maximum pressure (maximum bubble pressure) here, the surface tension at each surface life is obtained.

The reason why the surface life is set to 10 ms is that the timing is considered to be suitable for controlling the wetting and spreading behavior of the ink that occurs immediately after landing. In high-speed printing with an inkjet printer, it takes about 10 to 10 seconds from the landing of one dot to the completion of wetting and spreading.
It takes 0 ms, and the spread behavior itself immediately after impact develops on a very short time scale. 10
Since ms is the timing at which the ink begins to wet and spread immediately after landing on the base material,
By controlling the dynamic surface tension value at this time to an appropriate value, it is considered possible to control the wetting of the water-based white ink immediately after it comes into contact with the substrate.

In addition to adjusting the dynamic surface tension value as described above, by adjusting the static surface tension value, it is possible to control the behavior of the ink from the time the ink lands to the completion of wetting and spreading.
It is possible to suppress the occurrence of the print streak phenomenon and the liquid crowding phenomenon. "Static surface tension value" means
It refers to the surface tension value that has reached an equilibrium state, and is measured here based on the plate method.

The water-based white ink of the present invention has a static surface tension value of 23 mN/m or more and 30 mN/m at 25°C.
N/m or less. In addition, from the viewpoint of suppressing the occurrence of printing streaks, water-based white ink at 25 ° C.
is preferably 28.5 mN/m or less, more preferably 27.0 mN/m or less. Furthermore, from the viewpoint of suppressing the occurrence of the liquid crowding phenomenon, the static surface tension value of the water-based white ink at 25° C. is preferably 24.0 mN/m or more.
It is more preferably 0 mN/m or more.

Since the water-based white ink of the present invention is water-based and generally tends to have a high surface tension value, it is important to adjust the surface tension value by appropriately adjusting the type and content of the organic solvent and/or the type and content of the additive including the surface modifier. In particular, a silicone-based surface conditioner, an acetylene glycol-based surface conditioner, and an alkanediol-based solvent, which will be described later, are highly effective in reducing the dynamic surface tension and are effective in adjusting the dynamic surface tension value.

The water-based white ink of the present invention contains water, and preferred examples include pure water such as ion-exchanged water and distilled water, and ultrapure water. Further, when the ink is to be stored for a long period of time, water sterilized by ultraviolet irradiation or the like may be used in order to prevent the generation of mold or bacteria. In the water-based white ink of the present invention, the content of water can be exemplified to be in the range of 20 to 90% by mass, preferably 50 to 90% by mass, more preferably 60 to 80% by mass.
This makes it possible to provide a water-based white ink that is less harmful to the environment.

The water-based white ink of the present invention contains a pigment. As the pigment, a pigment commonly used for white ink can be used, but it is preferable to use a white pigment. Specific examples of white pigments include titanium dioxide and zinc oxide. In addition to color pigments, extender pigments such as silica, talc, mica, calcium carbonate, and barium sulfate, and antirust pigments such as zinc, zinc phosphate, aluminum phosphate, aluminum tripolyphosphate, zinc molybdate, barium metaborate, and hydrocalumite can also be used. The pigment content in the water-based white ink of the present invention is preferably 0.5 to 10% by mass. In addition, a pigment may be used individually by 1 type, and may be used in combination of 2 or more types.

In the water-based white ink of the present invention, the pigment has an average particle diameter (D50) of 150 nm or more.
It is preferably 00 nm or less, more preferably 180 nm or more and 400 nm or less. By setting the average particle diameter (D50) of the pigment to 150 nm or more, it is possible to improve the concealment rate of the back side of the printed layer (the side opposite to the viewing side, for example, the substrate side in the case of surface printing). Also, by setting the average particle diameter (D50) of the pigment to 500 nm or less, it is possible to suppress the pigment from settling in the ink.
In this specification, the average particle size (D50) is the 50% particle size of the volume-based particle size distribution ( _D5
. The particle diameter in the present invention is represented by the equivalent sphere diameter according to the laser diffraction/scattering method.

The water-based white ink of the present invention contains a water-soluble organic solvent, and the water-soluble organic solvent is
Contains at least one alkanediol solvent. The alkanediol-based solvent is preferable from the viewpoint of adjusting the surface tension value of the ink, particularly the dynamic surface tension value, and also has the effect of suppressing the phenomenon of liquid pooling that occurs during reverse printing. Further, from the viewpoint of suppressing the occurrence of the liquid crowding phenomenon, the water-soluble organic solvent more preferably contains at least one 1,2-alkanediol solvent. The content of the alkanediol-based solvent in the water-based white ink of the present invention is preferably 5.0 to 40.0% by mass.

In the water-based white ink of the present invention, the water-soluble organic solvent is an alkanediol-based solvent,
From the viewpoint of improving the ejection stability, wettability, and storage stability of the ink, it is preferable to include at least one solvent selected from the group consisting of glycol ether solvents, three- to five-membered ring lactone solvents, and amide solvents.

Alkanediol-based solvents are acyclic saturated hydrocarbons having two hydroxyl groups, such as ethylene glycol, propylene glycol, 2-methyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2
-pentanediol, 1,2-hexanediol, 1,6-hexanediol, 1,2-
heptanediol, 1,2-octanediol, 1,9-nonanediol, 1,10-decanediol and the like. Among these, ethylene glycol, 1,2-propylene glycol, 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,2-heptanediol and 1,2-octanediol are preferred.

Specific examples of glycol ether solvents include ethylene glycol methyl ether, ethylene glycol ethyl ether, ethylene glycol propyl ether, ethylene glycol butyl ether, ethylene glycol pentyl ether, ethylene glycol hexyl ether, ethylene glycol cyclohexyl ether, ethylene glycol phenyl ether, ethylene glycol benzyl ether, ethylene glycol isobutyl ether, ethylene glycol tertiary butyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol propyl ether,
Diethylene glycol butyl ether, diethylene glycol pentyl ether, diethylene glycol hexyl ether, diethylene glycol cyclohexyl ether, diethylene glycol phenyl ether, diethylene glycol benzyl ether, diethylene glycol monobutyl ether, diethylene glycol isobutyl ether, triethylene glycol methyl ether, triethylene glycol ethyl ether, triethylene glycol propyl ether, triethylene glycol butyl ether, triethylene glycol pentyl ether, triethylene glycol hexyl ether, triethylene glycol cyclohexyl ether, triethylene glycol phenyl ether, triethylene glycol benzyl ether and triethylene glycol monobutyl ether Ethylene glycol ethers such as propylene glycol methyl ether, propylene glycol ethyl ether, propylene glycol propyl ether, propylene glycol butyl ether, propylene glycol pentyl ether, propylene glycol hexyl ether, propylene glycol cyclohexyl ether, dipropylene glycol methyl ether, dipropylene glycol ethyl ether, dipropylene glycol propyl ether, dipropylene glycol butyl ether, dipropylene glycol pentyl ether, dipropylene glycol pentyl ether, dipropylene glycol cyclohexyl ether, tripropylene glycol methyl ether, tripropylene glycol ethyl ether, tripropylene glycol propyl ether, tripropylene glycol butyl ether, tripropylene glycol butyl ether and propylene glycol ethers such as glycol pentyl ether, tripropylene glycol hexyl ether and tripropylene glycol cyclohexyl ether. Among these, ethylene glycol monobutyl ether, ethylene glycol isobutyl ether, ethylene glycol tertiary butyl ether, diethylene glycol monobutyl ether, diethylene glycol isobutyl ether and triethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether and triethylene glycol monobutyl ether are preferred.

The three- to five-membered ring lactone-based solvent is a three-membered ring having 3 atoms, a four-membered ring having four atoms, or a five-membered ring having five atoms, among compounds having a lactone ring containing -C(=O)-O- as a part thereof. Specific examples include α-acetolactone, β-propionlactone, γ-butyrolactone, δ-valerolactone and the like. Among these, γ-butyrolactone is preferred.

The amide-based solvent is preferably an acyclic amide compound, such as dimethylacetamide,
dimethylformamide, sulfanilamide, toluenesulfonamide, benzenesulfonamide, N-dimethyl-β-methoxypropionamide, N,N-dimethyl-β-butoxypropionamide, N,N-dimethyl-β-pentoxypropionamide, N,N-
dimethyl-β-hexoxypropionamide, N,N-dimethyl-β-heptoxypropionamide, N,N-dimethyl-β-2-ethylhexoxypropionamide, N,N-
Dimethyl-β-octoxypropionamide, N,N-diethyl-β-methoxypropionamide, N,N-diethyl-β-butoxypropionamide, N,N-diethyl-β-
Pentoxypropionamide, N,N-diethyl-β-hexoxypropionamide, N
, N-diethyl-β-heptoxypropionamide, N,N-diethyl-β-octoxypropionamide and the like. Among these, dimethylacetamide, dimethylformamide, N,N-dimethyl-β-methoxypropionamide, N,N-dimethyl-β
-butoxypropionamide, N,N-diethyl-β-methoxypropionamide, N,
N-diethyl-β-butoxypropionamide is preferred.

In the water-based white ink of the present invention, the content of the water-soluble organic solvent can be exemplified as 5 to 49% by mass, preferably 5 to 35% by mass, more preferably 10 to 3%.
It can also be adjusted within a lower range of 5% by weight, particularly preferably 15-35% by weight. As a result, it is possible to provide a water-based white ink with less environmental load,
Since the organic solvent is less likely to remain in the printed layer, physical properties of the film such as abrasion resistance are likely to be improved.

The water-based white ink of the invention contains a resin. Resins that can be used for water-based white inks are not particularly limited, and resins commonly used in the ink industry can be used. Examples include acrylic resins, silicone resins, acrylic silicone resins, styrene-acrylic copolymer resins, polyester resins, rosin resins, petroleum resins, coumarone resins, phenolic resins, urethane resins, melamine resins, urea resins, epoxy resins, cellulose resins, xylene resins, alkyd resins, aliphatic hydrocarbon resins, butyral resins, maleic acid resins, fumaric acid resins, and vinyl resins. These resins may be used individually by 1 type, and may be used in combination of 2 or more types.

The resin that can be used in the water-based white ink can contain a self-dispersing resin. A self-dispersing resin is a resin that can maintain a dispersed state in an ink without using a surfactant or an emulsifier. Generally, a polymer having a hydrophilic group such as a sulfonic acid or its salt or a carboxylic acid or a salt thereof at its end or side chain, or a polymer having a hydrophilic group such as a polycarbonate group, a polyester group, or a polyether group in its main chain is preferably used. These self-dispersible resins may be used singly or in combination of two or more. In addition, self-dispersing resin may use a commercial item.

The self-dispersing resin preferably contains a self-dispersing urethane resin from the viewpoint of improving the performance of the printed layer such as scratch resistance and water resistance, and further preferably contains a self-dispersing urethane resin containing a polyester group or a polyether group from the viewpoint of imparting high adhesion to various substrates. The ratio of the self-dispersing urethane resin in the self-dispersing resin is 30 to 100
% by mass is preferred.

The self-dispersible urethane resin has a weight average molecular weight of 100,000 to 1,000,00
preferably 0, more preferably 150,000 to 750,000,
More preferably 200,000 to 500,000. If the weight average molecular weight of the self-dispersible urethane resin is within the specified range, the abrasion resistance can be further improved, and a strong printed layer can be formed.
In the present specification, the weight average molecular weight is determined by gel permeation chromatography (GPC)
Polystyrene is used as the standard and tetrahydrofuran is used as the mobile phase.

The self-dispersible urethane resin includes polyester polyol, polyether polyol,
It can be obtained by reacting a polyol component such as a polycarbonate polyol, a polyisocyanate component, and optionally a chain extender.

Polyester polyols are not particularly limited, and examples include polyethylene adipate, polyethylene propylene adipate, polybutylene adipate, polyhexamethylene adipate, polydiethylene adipate, polyethylene terephthalate, polyethylene isophthalate, polyhexamethylene isophthalate, polyethylene succinate, polybutylene succinate, polyethylene sebacate, polybutylene sebacate, poly-ε-caprolactamdiol and poly(3-methyl-1,5-pentylene adipate). etc. can be mentioned. A polyester group-containing self-dispersible urethane resin can be obtained by using a polyester polyol as the polyol component. Since such resins are dispersed in the ink in the form of particles, they are also referred to as polyester urethane resin particles in the present specification.
The polyether polyol is not particularly limited, and examples thereof include polyoxytetramethylene glycol, polyoxypropylene glycol, polyoxyethylene glycol and polyoxyethylene/propylene glycol. A polyether group-containing self-dispersible urethane resin can be obtained by using a polyether polyol as the polyol component. Since such resins are dispersed in the ink in the form of particles, they are also referred to as polyether urethane resin particles in the present specification.
The polycarbonate polyol is not particularly limited, and examples thereof include 1,6-hexanediol polycarbonate polyol, 1,4-butanediol polycarbonate polyol and poly-1,4-cyclohexanedimethylene carbonate diol. By using a polycarbonate polyol as the polyol component, a polycarbonate group-containing self-dispersible urethane resin can be obtained. Since such resins are dispersed in the ink in the form of particles, they are also referred to herein as polycarbonate urethane resin particles.
As the polyol component, acrylic polyol or the like may be used.
These polyol components can be used singly or in combination of two or more.

Examples of polyisocyanate components include tolylene diisocyanate, xylene diisocyanate, diphenylmethane diisocyanate, naphthylene diisocyanate, 1,
Polyisocyanate compounds such as 3-bis(isocyanatomethyl)cyclohexane, tetramethylxylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate and norbornane diisocyanate. Among these polyisocyanate components, xylene diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, hexamethylene diisocyanate, isophorone diisocyanate, 4,4′-methylenebis(cyclohexyl isocyanate) or norbornane diisocyanate are preferred. These polyisocyanate components can be used singly or in combination of two or more.

Examples of chain extenders include low molecular weight polyhydric alcohols and low molecular weight polyamines. Examples of low-molecular-weight polyhydric alcohols include ethylene glycol,
Diethylene glycol, 1,4-butanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, trimethylolpropane, pentaerythritol, 1,4-cyclohexanedimethanol, dimethylolalkanoic acids such as dimethylolbutanoic acid and dimethylolpropionic acid. Low molecular weight polyamines include, for example, ethylenediamine, trimethylenediamine, tetramethylenediamine, hexamethylenediamine, hydrazine, piperazine, isophoronediamine, norbornanediamine, diaminodiphenylmethane, diaminocyclohexylmethane, tolylenediamine, xylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine and iminobispropylamine. These chain extenders can be used singly or in combination of two or more.

The water-based white ink of the present invention preferably contains at least one polyether or polyester urethane resin particle (that is, polyether urethane resin particle or polyester urethane resin particle). Such an ink has good storage stability and can form a strong film having excellent adhesion to a wide range of substrates including non-absorbent substrates and non-absorbent substrates after drying.

The self-dispersing resin is dispersed in the ink and is in the form of particles. Here, the self-dispersing resin preferably has an average particle size (D50) of 10 nm to 90 nm.
It is more preferably 0 nm to 70 nm, even more preferably 30 nm to 60 nm. When the average particle size is within the specified range, an ink can be prepared in which the self-dispersing resin is well dispersed and the storage stability is excellent. In the present invention, the average particle size (D50) refers to the 50% particle size (D ₅₀ ) of the volume-based particle size distribution, and can be obtained from the particle size distribution measured using a laser diffraction/scattering particle size distribution analyzer (eg, SALD-7000: manufactured by Shimadzu Corporation). The particle diameter in the present invention is represented by the equivalent sphere diameter according to the laser diffraction/scattering method.

The self-dispersing resin preferably has an acid value of 5.0 to 60.0. If the acid value is within the range specified above, the dispersibility can be improved. As used herein, the acid value of a resin means mg of potassium hydroxide required to neutralize 1 g of resin.

The water-based white ink of the present invention preferably has a resin content of 1 to 10% by mass.
Moreover, the proportion of the self-dispersible resin in the resin is preferably 50% by mass or more.

From the viewpoint of adjusting the surface tension value, the water-based white ink of the present invention preferably contains a surface modifier. Examples of surface modifiers include silicone-based surface modifiers, acrylic surface modifiers, vinyl-based surface modifiers, fluorine-based surface modifiers, acetylene glycol-based surface modifiers, and the like. Especially from the viewpoint of adjusting the dynamic surface tension value of the water-based white ink of the invention, the water-based white ink of the invention contains at least one silicone-based surface modifier or at least one silicone-based surface modifier.
It preferably contains an acetylene glycol-based surface modifier, more preferably both a silicone-based surface modifier and an acetylene glycol-based surface modifier. Here, when both the silicone-based surface conditioner and the acetylene glycol-based surface conditioner are contained, the mass ratio (A:B) of the silicone-based surface conditioner (A) and the acetylene glycol-based surface conditioner (B) is preferably 5:1 to 1:5, more preferably 3:1 to 1:3. In addition, from the viewpoint of use in the water-based white ink of the present invention, the silicone-based surface conditioner has an HLB value of 3.
. It is preferably from 0 to 16.0, more preferably from 3.0 to 14.0. The acetylene glycol-based surface conditioner preferably has an HLB value of 3.0 or more.
It is more preferably 0 to 16.0. Various calculation methods are known for the HLB value, but in this specification, the HLB value of the surface conditioner (surfactant) is based on the Griffin method, which is calculated based on the formula weight and molecular weight of the hydrophilic group.

Specific examples of silicone-based surface conditioners include polyether-modified polysiloxane, polyester-modified polysiloxane, polyether-modified hydroxyl-containing polysiloxane, polyester-modified hydroxyl-containing polysiloxane, etc. Commercial products from BYK-Chemie, Shin-Etsu Chemical Co., etc. are readily available.

（式中、Ｒ¹及びＲ²は、それぞれ独立した炭化水素基を示す）で表されるような、アセチ
レン基を中心とした左右対称構造を有する非イオン性界面活性剤が好適である。また、本
明細書においては、界面活性剤の水酸基にアルキレンオキシド（エチレンオキシド、プロ
ピレンオキシド等）を付加してなるアルキレンオキシド付加物もアセチレングリコール系
表面調整剤に含まれる。アセチレングリコール系表面調整剤は、日信化学工業株式会社等
から市販される商品が容易に入手可能である。 The acetylene glycol-based surface conditioner is a surfactant having an acetylene group and two hydroxyl groups, and is represented by the following formula (1)

(In the formula, R ¹ and R ² each represent an independent hydrocarbon group). Preferred nonionic surfactants have a bilaterally symmetrical structure centered on an acetylene group. In the present specification, acetylene glycol-based surface conditioners also include alkylene oxide adducts obtained by adding alkylene oxides (ethylene oxide, propylene oxide, etc.) to hydroxyl groups of surfactants. Acetylene glycol-based surface conditioners are readily available as commercial products from Nissin Chemical Industry Co., Ltd. and the like.

In the water-based white ink of the present invention, it is preferable to use a surface modifier so that the dynamic surface tension value and the static surface tension value are within the ranges specified above.

If necessary, the water-based white ink of the present invention may contain pH adjusters, antifoaming agents, moisturizing agents, wetting and dispersing agents, preservatives/antifungal agents, dissolution aids, antioxidants, metal trapping agents, etc., as long as they do not impair the object of the present invention.

The water-based white ink of the present invention can be prepared by mixing various components appropriately selected as necessary.

The water-based white ink of the present invention is suitable for metal parts (especially print heads) of printing equipment such as printers.
From the viewpoint of suppressing the occurrence of corrosion in, it is preferably basic, and the pH is 7.01 to
It is preferably in the range of 10.0.
A pH adjuster can be used to adjust the pH, but an amine compound is preferably used.
More preferred is the use of amine compounds with a boiling point of 70-270°C. Specific examples of amine compounds having a boiling point of 70 to 270° C. include N-methyldiethanolamine, N-ethyldiethanolamine, N,N-dimethylethanolamine, N,N-diethylethanolamine and the like. These amine compounds may be used singly or in combination of two or more. In the water-based white ink of the present invention, the content of the amine compound is 0.
. 1 to 2.0% by mass is preferred.

The water-based white ink of the present invention preferably has a viscosity of 3.0 to 10.0 mPa·s at 25° C. independently from the viewpoint of use in an inkjet printer.
In this specification, the viscosities of inks and coating liquids are measured after adjusting the liquid temperature to 25° C. using a rheometer (for example, rheometer ARES manufactured by TA Instruments).

Next, the ink set of the present invention will be described in detail. The ink set of the present invention is an ink set containing the water-based white ink of the present invention described above, the water-based coating liquid, and the water-based colored ink. Here, the water-based coating liquid is a liquid for aggregating the colored ink, and usually contains water, a resin and an organic solvent, and is preferably a coating liquid for inkjet printing. Moreover, the water-based colored ink usually contains water, a resin, an organic solvent and a colorant, and is preferably an ink for inkjet printing.
In this specification, the term “colored ink” refers to ink that can be colored in a color different from white. In this specification, a composition containing more than 0.1% by mass of a coloring agent is referred to as "ink", and a composition containing no coloring agent or containing 0.1% by mass or less of coloring agent is simply referred to as "liquid". As used herein, the term "aqueous coating liquid" refers to a coating liquid containing water as a main solvent.

In the ink set of the present invention, the water-based colored inks may consist of a plurality of water-based colored inks that emit different colors, and examples include water-based colored inks containing at least four types of ink: cyan ink, magenta ink, yellow ink, and black ink.

In the ink set of the present invention, for example, the water-based coating liquid is printed on the water-based white ink layer in the case of surface printing, and is printed on the base material in the case of reverse printing. For this reason, the water-based coating liquid has a dynamic surface tension value of 26.0 at 25 ° C. with a surface life of 10 ms.
mN / m or more and 34.0 mN / m or less, and the static surface tension value at 25 ° C. is 19.0 m
It is preferably N/m or more and 23.0 mN/m or less.

In the ink set of the present invention, the water-based colored ink is usually printed on the water-based coating liquid layer. Therefore, the water-based colored ink preferably has a dynamic surface tension value of 38.0 mN/m or more and 48.0 mN/m or less at 25°C at a surface life of 10 ms, and a static surface tension value of 24.0 mN/m or more and 30.0 mN/m or less at 25°C.

Both the colored ink and the coating liquid used in the ink set of the present invention are water-based like the water-based white ink, and the surface tension value generally tends to be high. Therefore, it is important to adjust the surface tension value by appropriately adjusting the type and content of the organic solvent and/or the type and content of the additive including a surface conditioner (preferably a silicone-based surface conditioner, more preferably polyether-modified polysiloxane). In the case of colored inks and coating liquids, the use of alkanediol-based solvents and glycol ether-based solvents, which will be described later, is particularly effective in adjusting the dynamic surface tension value.

In the ink set of the present invention, the water-based colored ink and the water-based coating liquid contain water like the water-based white ink. Here, the content of water in the water-based colored ink and the water-based coating liquid can be exemplified as being in the range of 20 to 90% by mass, preferably 50 to 90% by mass, more preferably 60 to 80% by mass.

In the ink set of the present invention, the water-based coating liquid usually contains a resin, and preferably contains a water-soluble polymer having a cation as the resin. Since the water-soluble polymer has a cation, it can exhibit the ability to aggregate the colored ink. As a result, the adhesion of the printed layer to the base material can be improved while suppressing the bleeding of the printed layer, and high-speed printing becomes possible. Moreover, if it is a cation, it can exhibit the ability to coagulate the colored ink even if it is present in the aqueous coating liquid whose pH is in the basic range. However, the above water-soluble polymer has a high ability to aggregate the colored ink, and causes the occurrence of aggregation of the colored ink remarkably early, which may reduce the glossiness of the printed layer. Moreover, the water-based coating liquid prepared using a water-soluble polymer having a cation maintains its viscosity and pH even when stored for a long period of time, and exhibits excellent storage stability.
In this specification, a water-soluble polymer means a polymer that dissolves in water or an aqueous solution containing less than 50% by mass of a water-soluble organic solvent.

The water-soluble polymer having a cation is preferably a water-soluble polymer having a quaternary ammonium cation (cationized nitrogen atom). By using a water-soluble polymer having a quaternary ammonium cation, bleeding of the printed layer is further suppressed, and the abrasion resistance of the printed layer and the storage stability of the aqueous coating liquid are improved.

The water-soluble polymer having the above cation has a weight average molecular weight of 1,000 to 50,000
is preferably 2,500 to 45,000, more preferably 5,00
More preferably 0 to 40,000. The weight average molecular weight of the water-soluble polymer is 1
,000 or more, the ability of the water-soluble polymer having a cation to agglomerate the colored ink increases, and the effect of suppressing bleeding of the printed layer and the effect of improving adhesion can be improved. On the other hand, if the weight average molecular weight exceeds 50,000, the ejection stability may be lowered.

The water-soluble polymer having a cation preferably has a cation in its main chain. When a water-soluble polymer having such a structure is used, when the water-based colored ink lands on the water-based coating liquid, only the interface of the water-based colored ink instantly aggregates, and the water-based colored inks are fixed at the landing position without mixing with each other, which is more preferable when performing high-speed printing.

The water-soluble polymer having a cation is preferably two or more water-soluble polymers having different cationic degrees. By using multiple water-soluble polymers with different cationic degrees,
It becomes easy to adjust the size of the dot diameter and bleeding.
Specifically, the water-soluble polymer having the above cation has a cation degree of 5.0 at pH 7.1.
A water-soluble polymer that is 5-7.5 meq/g and a cationic degree at pH 7.1 of 2.0-5
. a water-soluble polymer having a cationic degree of 6.0 to 7.0 meq/g at pH 7.1 and a cationic degree of 2 at pH 7.1.
. and a water-soluble polymer that is between 5 and 4.5 meq/g. 2 above
As for the ratio of water-soluble polymers having different cationic degree ranges, the weight ratio of the water-soluble polymer having a high cationic degree range to the water-soluble polymer having a low cationic degree range is preferably in the range of 1:1 to 20:1, more preferably in the range of 7:3 to 10:1.
In this specification, the degree of cation can be obtained by colloidal titration using a polyvinyl potassium sulfate reagent. The detailed procedure is as follows.
90 mL of deionized water is placed in a conical beaker, 10 mL of a 500 ppm aqueous solution of the sample (on a dry basis) is added, the pH is adjusted to 7.1 with an aqueous amine solution, and the mixture is stirred for about 1 minute. Then add 2-3 drops of toluidine blue indicator, N/400 polyvinyl potassium sulfate reagent (N/400P
VSK). The titration rate is 2 mL/min, and the end point is when the color of the test water changes from blue to reddish purple and is maintained for 10 seconds or longer. The formula for calculating the degree of cation (meq/g) is as follows.
Cationic degree = (N/400 PVSK titer) x (N/400 PVSK titer)/2

A commercially available product can be used as the water-soluble polymer having the above cation. Among them, a water-soluble polymer having a quaternary ammonium cation is preferable.
WS4027, WS4052, CA6018 (manufactured by Seiko PMC), Hersize CP-
300, CP-800 (manufactured by Harima Chemicals), PAS-H-1L, PAS-H-5L,
PAS-2401, PAS-A-1 (manufactured by Nitbo Medical Co., Ltd.), Catiomaster PDT-2, PD-7, PD-30 (manufactured by Yokkaichi Gosei Co., Ltd.), reaction products of epichlorohydrin and alkylamine, polyamine resins, polyamide/epichlorohydrin resins, and the like. The water-soluble polymer having the cation may be used singly or in combination of two or more.

The proportion of the water-soluble polymer having the cation in the resin contained in the water-based coating liquid is preferably 50% by mass or more, and in particular, from the viewpoint of appropriately controlling the aggregation action, the proportion of the water-soluble polymer having the quaternary ammonium cation in the resin contained in the water-based coating liquid is preferably 50% by mass or more.

As other resins that can be used in the water-based coating liquid, resins commonly used in the ink industry other than the water-soluble polymer having a cation can be used. For example, acrylic resin, silicone resin, acrylic silicone resin, styrene acrylic copolymer resin, polyester resin, rosin resin, phenol resin, urethane resin, melamine resin, urea resin, epoxy resin, cellulose resin, butyral resin, maleic acid resin,
Examples include fumaric acid resins and vinyl resins. These resins may be used individually by 1 type, and may be used in combination of 2 or more types. As used herein, the term "resin" refers mainly to resins classified as binders, and excludes polymers classified as thickeners, which will be described later.

In the water-based coating liquid, the content of the resin can be exemplified to be 0.005 to 15% by mass, preferably 0.005 to 10% by mass, and 0.0
It is more preferably 05 to 5% by mass, even more preferably 0.005 to 3% by mass, and particularly preferably 0.005 to 2% by mass.

In the ink set of the present invention, the water-based colored ink contains a resin. Here, the resin that can be used for the water-based colored ink is not particularly limited, and for example, the description of the resin for the water-based white ink of the present invention can be applied. Therefore, the types and contents of the resins that can be used in the water-based colored ink are as described in the description of the resin that can be used in the water-based white ink of the present invention.

Further, in the ink set of the present invention, by adjusting the acid value of the self-dispersible resin contained in the water-based colored ink and the cation degree of the water-soluble polymer having a cation contained in the water-based coating liquid, it is possible to increase the dot diameter of the water-based colored ink and form a printed layer with excellent gloss that does not cause bleeding. Here, the ratio (C:D) of the acid value (C) of the self-dispersing resin to the cationic degree (meq/g) (D) of the cationic polymer at pH 7.1 is preferably in the range of 10:1 to 1:2, more preferably in the range of 6:1 to 1.2:3, and even more preferably in the range of 3:1 to 1:1.

In the ink set of the present invention, the water-based colored ink contains a colorant. Here, the colorant that can be used in the water-based colored ink is not particularly limited, and pigments such as organic pigments and inorganic pigments that are commonly used as colorants in the ink industry can be used, but it is preferable that the ink contains a self-dispersing pigment. A self-dispersing pigment is a pigment that can maintain a dispersed state in ink without using a pigment dispersant, and is usually obtained by imparting a highly hydrophilic functional group to the surface. The present inventors have found that a combination of a water-soluble polymer having the above-described cation, particularly a water-soluble polymer having a quaternary ammonium cation, and a self-dispersing pigment can prevent the formation of irregularities on the surface of the printed layer due to too early occurrence of aggregation, thereby preventing a decrease in the gloss of the printed layer.

In the present invention, the self-dispersible pigment is preferably a pigment having anions such as carboxyl ions, sulfate ions, nitrate ions, phosphate ions, and hydroxide ions directly bonded to the surface. By using such an anionic self-dispersing pigment, the pigment can be stably dispersed in the ink without adding a dispersant, and a clearer image can be printed. Commercially available products can be suitably used as these anionic self-dispersing pigments.

Examples of the pigment include Pigment Yellow 12, 13, 14, 17, 20, 24
, 31, 42, 53, 55, 74, 83, 86, 93, 109, 110, 117, 120
, 122, 125, 128, 129, 137, 138, 139, 147, 148, 150
, 151, 152, 153, 154, 155, 166, 168, 180, 181, 184
, 185, 213; Pigment Orange 16, 36, 38, 43, 51, 55, 59, 6
1, 64, 65, 71; Pigment Red 9, 48, 49, 52, 53, 57, 97, 1
01, 122, 123, 149, 168, 177, 180, 192, 202, 206, 2
15, 216, 217, 220, 223, 224, 226, 227, 228, 238, 2
40, 244, 254; pigment violet 19, 23, 29, 30, 32, 37,
40, 50; Pigment Blue 15, 15:1, 15:3, 15:4, 15:6, 22,
Pigment Green 7, 36; Pigment Brown 23, 25, 26; Pigment Black 1, 7, 26, 27, 28, Pigment White 6, and the like. In addition, these pigments may be used individually by 1 type, and may be used in combination of 2 or more types.
Examples of pigments that can be used in cyan ink include Pigment Blue 15, 15:1, 1
5:3, 15:4, 15:6, 22, 27, 28, 29, 30, 60, 64, 80 and the like,
Examples of pigments that can be used for magenta ink include Pigment Red 9, 48, 49,
52, 53, 57, 97, 101, 122, 123, 149, 168, 177, 180,
192, 202, 206, 215, 216, 217, 220, 223, 224, 226,
227, 228, 238, 240, 244, 254 and the like,
Examples of pigments that can be used in yellow ink include Pigment Yellow 12, 13, 1
4, 17, 20, 24, 31, 42, 53, 55, 74, 83, 86, 93, 109, 1
10, 117, 120, 122, 125, 128, 129, 137, 138, 139, 1
47, 148, 150, 151, 152, 153, 154, 155, 166, 168, 1
80, 181, 184, 185, 213 and the like,
Examples of pigments that can be used in black ink include Pigment Black 1, 7, 26,
27, 28 and the like.
In addition, Pigment Orange 16, 36, 38, 43, 51, 55, 59, 61, 64,
65, 71; Pigment Violet 19, 23, 29, 30, 32, 37, 40, 50
pigment green 7, 36; pigment brown 23, 25, 26;
It can also be used as special color ink such as violet ink, green ink and red ink.

The content of the pigment in the water-based colored ink can be arbitrarily determined depending on the type of pigment used, but is preferably 0.5 to 10% by mass.

In the ink set of the present invention, the water-based colored ink and the water-based coating liquid contain an organic solvent. Here, the organic solvent that can be used for the water-based colored ink and the water-based coating liquid is not particularly limited, and organic solvents commonly used in the ink industry can be used. In the water-based colored ink and the water-based coating liquid, the content of the organic solvent can be exemplified as 5 to 49% by mass, preferably 5 to 35% by mass, more preferably 10 to 35% by mass, and particularly preferably 15 to 35% by mass. It can also be adjusted within a low range. As a result, it is possible to provide a water-based colored ink and a water-based coating liquid with less environmental load, and since the organic solvent is less likely to remain in the printed layer, the physical properties of the film such as scratch resistance can be easily improved.

The organic solvent that can be used for the water-based colored ink and the water-based coating liquid is preferably a water-soluble organic solvent, and the water-soluble organic solvent preferably contains at least one selected from the group consisting of alkanediol solvents, glycol ether solvents, three- to five-membered ring lactone solvents, and amide solvents, from the viewpoint of improving the ejection stability, wettability, and storage stability of the ink and coating liquid. Specific examples of the alkanediol-based solvent, glycol ether-based solvent, three- to five-membered ring lactone-based solvent, and amide-based solvent are as described in the description of the water-soluble organic solvent that can be used in the water-based white ink of the present invention.

In addition, the ink set of the present invention preferably contains at least one (preferably at least two) selected from the group consisting of alkanediol solvents and glycol ether solvents from the viewpoint of adjusting the dynamic surface tension values of the coloring ink and the coating liquid, and particularly preferably contains both the alkanediol solvent and the glycol ether solvent from the viewpoint of adjusting the dynamic surface tension value of the coating liquid. Here, when both the alkanediol-based solvent and the glycol ether-based solvent are included, the alkanediol-based solvent (E)
and the glycol ether solvent (F) (E:F) is preferably in the range of 8:1 to 1:8, preferably in the range of 5:1 to 1:5.

In the ink set of the present invention, the water-based coating liquid preferably contains a thickening agent from the viewpoint of improving ejection stability. By using a thickener, it is possible to prepare a coating liquid that does not contain a pigment or contains 0.1% by mass or less of a pigment, or a coating liquid that has excellent ejection stability even with a coating liquid that has a low resin content. Since the amount of organic solvent can be reduced, it is possible to provide a water-based coating liquid that has a low environmental load. In the water-based coating liquid, the content of the thickener is 0.01% by mass to 2
% by mass is preferable, more preferably 0.10% by mass to 1% by mass, and 0
. More preferably, it ranges from 20% by mass to 0.80% by mass.

When the water-based coating liquid is used in an inkjet printer, the thickener preferably has a low thixotropic effect or no thixotropic effect. From this point of view, the thickener used in the water-based coating liquid preferably contains a nonionic water-soluble thickener, and the nonionic water-soluble thickener is preferably a urethane polymer, and more preferably a polyether polyol-based urethane polymer. The proportion of the nonionic water-soluble thickener in the thickener is preferably 50% by mass or more.
In the present invention, the water-soluble thickener means a thickener that dissolves in water or an aqueous solution containing less than 50% by mass of a water-soluble organic solvent.
Commercially available thickeners can be used, and examples of polyether polyol-based urethane polymers include Adekanol UH-530, UH-541VF, UH-438,
UH-450VF (manufactured by ADEKA Co., Ltd.), SN Thickener 612, 619, 6
12NC, 621N, 621TF, 623N, 625N (manufactured by San Nopco) and the like. In addition, a thickener may be used individually by 1 type, and may be used in combination of 2 or more types.

If necessary, the water-based colored ink and water-based coating liquid may further contain pH adjusters, surface conditioners, antifoaming agents, moisturizing agents, wetting and dispersing agents, preservatives/antifungal agents, solubilizers, antioxidants, metal trapping agents, and the like, which may be appropriately selected and blended within a range that does not impair the purpose of the present invention.

The water-based colored ink and the water-based coating liquid can be prepared by mixing various components appropriately selected as necessary.
The water-based coating liquid contains 50% by mass to 90% by mass of water and 5% by mass of an organic solvent.
to 35% by mass, and the resin is preferably contained in the range of 0.005% to 5% by mass. Such a water-based coating liquid with a small amount of resin dries quickly, and is therefore preferable from the viewpoint of suppressing the occurrence of printing streaks after aggregation.

For the same reason as the water-based white ink, the water-based colored ink and the water-based coating liquid are preferably basic, and preferably have a pH in the range of 7.01 to 10.0.
The adjustment of the pH of the water-based colored ink and the water-based coating liquid is as described in the description of the water-based white ink of the present invention.

In the ink set of the present invention, the water-based colored ink and the water-based coating liquid each independently have a viscosity of 3.0 to 1 at 25° C. from the viewpoint of use in inkjet printers.
It is preferably within the range of 0.0 mPa·s.

The ink set of the present invention can be used in various inkjet printers. Such an inkjet printer is equipped with a print head, and droplets of ink and coating liquid forming an ink set are ejected from the nozzles of the print head.

Next, the printing method of the present invention will be described in detail. The printing method of the present invention is characterized by forming a print layer on a base material by an inkjet printer equipped with the above ink set of the present invention. Further, the printing method of the present invention includes a step of printing a water-based white ink, a water-based coating liquid and a water-based colored ink in this order to form a printed layer on a substrate, or a step of printing a water-based coating liquid, a water-based colored ink and a water-based white ink in this order to form a printed layer on a substrate.

Here, the step of forming a printed layer on the base material by printing the water-based white ink, the water-based coating liquid and the water-based colored ink in this order (hereinafter also referred to as the first step) will be described in detail. In the printing method of the present invention, the first step includes a step of ejecting a water-based white ink from the print head and causing ink droplets to land on a substrate, a step of ejecting a water-based coating liquid from the print head and causing the coating droplets to land on the white ink layer that has landed on the substrate, and a step of ejecting water-based colored ink from the print head and causing the ink droplets to land on the coating liquid layer that has landed on the white ink, thereby forming a printed layer. This is the preferred printing process for printing.

Similarly, the step of forming a printed layer on the substrate by printing the water-based coating liquid, the water-based colored ink, and the water-based white ink in this order (hereinafter also referred to as the second step) will be described in detail. In the printing method of the present invention, the second step includes a step of ejecting a water-based coating liquid from a print head to cause coating droplets to land on a substrate, a step of ejecting water-based colored ink from the print head to land ink droplets on the coating liquid layer that has landed on the substrate, and a step of ejecting water-based white ink from the print head and causing the ink droplets to land on the colored ink layer that has landed on the coating liquid, thereby forming a printing layer. This is the preferred printing process for printing.

In the above printing method, the substrate is not particularly limited, and the printing method of the present invention is
For example, metal substrates such as iron and steel, galvanized steel (e.g. galvanized steel), tin-plated steel (e.g. tin plate), stainless steel, magnesium alloys, aluminum, aluminum alloys, inorganic substrates such as glass and ceramics, acrylic resins, polyvinyl chloride, polycarbonate, AB
Such as plastic base materials such as S resin, polyethylene terephthalate, polyolefin, etc.
It is also suitable for printing on substrates that do not absorb ink (non-absorbent substrates) and substrates that do not absorb ink or coating liquid easily (non-absorbent substrates) such as coated paper, art paper, cast paper, lightly coated paper, etc. Examples of other base materials include paper base materials such as fine paper, synthetic paper, and inkjet paper, wood, gypsum, calcium silicate, concrete, cement,
Examples include inorganic base materials such as mortar and slate. In addition, the base material may be subjected to a general surface treatment such as primer treatment or corona treatment in order to improve adhesion to the printed layer.

According to the printing method of the present invention, it is possible to suppress the occurrence of printing streaks and liquid dripping not only in surface printing but also in reverse printing, so it is preferably applied to transparent plastic films, especially plastic films for flexible packaging and labels.

In the printing method of the present invention, the substrate temperature is preferably 30 to 45°C. This allows the white ink or water-based coating liquid to spread evenly on the substrate. Note that the temperature of the substrate is the temperature of the surface of the substrate on which the white ink or coating droplets land.

In the above printing method, the next ink or coating liquid can be printed without waiting for drying of the ink or coating liquid (that is, without drying the ink or coating liquid). In the above printing method, the total thickness of the discharged liquid of the water-based coating liquid, the water-based colored ink, and the water-based white ink immediately after the first step and the second step (that is, before the water and the organic solvent evaporate) is preferably in the range of 1 to 20 μm.

In the printing method of the present invention, when the water-based colored ink is composed of a plurality of water-based colored inks, the water-based colored ink that first lands on the coating liquid layer preferably has the lowest dynamic surface tension at 25 ° C. with a surface life of 10 ms among the plurality of water-based colored inks. The water-based colored ink that first lands on the coating liquid layer is most strongly affected by the aggregation of the colored ink by the coating liquid. Therefore, by causing the water-based colored ink having the lowest dynamic surface tension to land on the coating liquid layer first, the aggregating action of the colored ink by the coating liquid can be effectively exhibited.

The printing method of the present invention preferably further includes a step of drying the printed layer formed on the substrate with hot air. The drying can be performed at any time. For example, the drying may be performed after the printing of the water-based white ink, the water-based coating liquid, and the water-based colored ink is completed, or may be performed each time. By applying hot air (usually using air) to the printed layer to dry it, the resin contained in the printed layer can be fused onto the base material to form a strong film, and as a result, it is possible to provide printed matter with excellent robustness.
The temperature of the hot air is preferably 70 to 130°C, more preferably 80 to 110°C, from the viewpoint of fusing the resin contained in the printed layer onto the substrate. The drying time is preferably 2 seconds or more and 20 seconds or less, more preferably 5 seconds or more and 15 seconds or less.
Although the drying means is not particularly limited, a dryer equipped with a blower function is preferable. The air volume is preferably 1.0 m ³ /min or more, more preferably 1.5 to 5.0 m ³ /min.

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

<Water-based white ink containing white pigment>
According to the formulation shown in Tables 1 and 2, a resin and a surface control agent are added to an aqueous coloring dispersion prepared by dispersing a white pigment, an antifoaming agent, a water-soluble solvent, a wetting dispersant, and ion-exchanged water by a known method,
Water-based white inks 1 to 23 containing white pigment (however, white ink 8 is clear ink)
was prepared. The static surface tension (25° C.), dynamic surface tension (25° C.) and viscosity (25° C.) at a surface life of 10 ms of each water-based white ink were measured, and the results obtained are shown in Tables 1 and 2.

The formulations listed in Tables 1 and 2 above are as follows.
*1 The following white pigments were used.
・ JR-600A (Al-treated rutile type titanium oxide pigment, manufactured by Tayca, average particle size (D50
) 250 nm)
・ A-220 (Al-treated rutile type titanium oxide pigment, manufactured by Ishihara Sangyo Co., Ltd., average particle size (D50)
160nm)
・JR-301 (Al-treated rutile-type titanium oxide pigment, manufactured by Tayca, average particle size (D50)
300 nm)
・ TTO-55 (A) (Al-treated rutile-type titanium oxide pigment, manufactured by Ishihara Sangyo Co., Ltd., average particle size (D
50) 55 nm)
* 2 Defoamer (SN Deformer 1312, manufactured by San Nopco)
*3 Wetting and dispersing agent (BYK190, dispersant content 40% by mass, manufactured by BYK)
*4 As the resin dispersion liquid A, the following was used.
NEOREZ R-9621 (manufactured by DSM Coating Resins, polyester group-containing self-dispersing urethane resin, average particle size (D50) 50 nm, acid value 18, resin content 38% by mass)
*5 As the resin dispersion liquid B, the following was used.
NEOREZ R-967 (manufactured by DSM Coating Resins, polyether group-containing self-dispersing urethane resin, average particle size (D50) 60 nm, acid value 15, resin content 40% by mass)
*6 As the resin dispersion liquid C, the following was used.
Neosticker HA-560 (manufactured by Nicca Chemical, polycarbonate group-containing self-dispersing urethane resin, average particle size (D50) 30 nm, acid value 14, resin content 35% by mass)
*7 As the resin dispersion liquid D, the following was used.
AE986B (manufactured by E-Tech Co., Ltd., self-dispersing acrylic resin, average particle size (D50) 60
nm, acid value 15, resin content 35% by mass)
* 8 SAG008 (manufactured by Nissin Chemical Industry Co., Ltd., polyether-modified silicone surfactant, surfactant content 100% by mass, HLB value 7.0, surface modifier)
* 9 WET280 (manufactured by EVONIK, polyether-modified silicone surfactant, surfactant content 100% by mass, HLB value 3.5, surface modifier)
* 10 SAG502A (manufactured by Nissin Chemical Industry Co., Ltd., polyether-modified silicone surfactant, surfactant content 100% by mass, HLB value 11.0, surface modifier)
*11 Olfine D-10PG (manufactured by Nissin Chemical Industry Co., Ltd., acetylene glycol-based surfactant, surfactant content 50% by mass, HLB value 4.0, surface modifier)
*12 Surfynol 107L (manufactured by Nissin Chemical Industry Co., Ltd., acetylene glycol-based surfactant, surfactant content 50% by mass, HLB value 4.0, surface modifier)

<Preparation example of water-based coating liquid>
Aqueous coating liquids 1 to 3 were prepared by mixing a resin, an amine compound, a water-soluble solvent, a surface conditioner and ion-exchanged water according to the formulation shown in Table 3 by a known method. The pH of each water-based coating liquid, static surface tension (25 ° C), dynamic surface tension at 10 ms surface life (
25° C.) and viscosity (25° C.) were measured, and the results obtained are shown in Table 3.

The formulations listed in Table 3 below are as follows.
*13 The following was used as the aqueous solution A of the water-soluble polymer having a quaternary ammonium cation.
Catiomaster PE-30 (manufactured by Yokkaichi Synthesis, dimethylamine/ethylenediamine/epichlorohydrin polymer resin, resin content 50% by mass, weight average molecular weight (Mw): 9
000, cation degree at pH 7.1 6.5 meq/g)
*14 The following was used as the aqueous solution B of the water-soluble polymer having a quaternary ammonium cation.
DK6851 (manufactured by Seiko PMC Co., Ltd., polyamine resin, resin content 70.0% by mass, pH
cation degree at 7.1 6.8 meq/g)
*15 The following was used as the aqueous solution C of the water-soluble polymer having a primary cation.
PAA-SA (manufactured by Nitbo Medical, allylamine amide sulfate polymer resin, resin content 20% by mass, Mw: 12,000, cation degree at pH 7.1 5.8 meq/g
)
*16 WET270 (manufactured by EVONIK, polyether-modified silicone oil, silicone oil content 100% by mass, surface conditioner)

<Preparation example of water-based colored ink containing self-dispersing pigment>
According to the formulation shown in Table 4, the self-dispersing pigment, resin, water-soluble solvent, surface conditioner and ion-exchanged water were mixed by a known method to prepare a water-based colored ink containing the self-dispersing pigment.
The static surface tension (25° C.), dynamic surface tension (25° C.) and viscosity (25° C.) at a surface life of 10 ms of each water-based colored ink were measured.

The formulations listed in Table 4 above are as follows. Already described compounding agents are omitted.
*17 The following was used as the self-dispersible pigment dispersion.
・CAB-O-JET 250C
(manufactured by Cabot Corporation, cyan self-dispersing pigment aqueous dispersion, pigment content 10% by mass)
・CAB-O-JET-465M
(manufactured by Cabot Corporation, magenta self-dispersible pigment aqueous dispersion, pigment content 15% by mass)
・CAB-O-JET 270Y
(manufactured by Cabot Corporation, yellow self-dispersing pigment aqueous dispersion, pigment content 10% by mass)
・CAB-O-JET 300K
(manufactured by Cabot Corporation, black self-dispersing pigment aqueous dispersion, pigment content 15% by mass)

<Water-based colored ink containing non-self-dispersing pigment>
According to the formulation shown in Table 5, a non-self-dispersing pigment, an antifoaming agent, a water-soluble solvent, a wetting dispersant, and an aqueous colored dispersion prepared by dispersing ion-exchanged water by a known method, a resin and a surface control agent were added to prepare an aqueous colored ink containing a non-self-dispersing pigment. The static surface tension (25° C.), dynamic surface tension (25° C.) and viscosity (25° C.) at a surface life of 10 ms of each water-based colored ink were measured, and Table 5 shows the obtained results.

The formulations listed in Table 5 above are as follows. Already described compounding agents are omitted.
*18 As the non-self-dispersing pigment, the following was used.
・FASTOGEN Blue FA5380 (phthalocyanine blue, cyan pigment manufactured by DIC)
・Shinkasha Magenta RT (dichloroquinacridone, magenta pigment manufactured by BASF)
・Hostaperm Yellow H5G (Quinoxaline dione, yellow pigment manufactured by Clariant)
・ Nerox-1000 (carbon black, manufactured by Orion Engineered Carbon Co., Ltd., black pigment)
* 19 Wetting and dispersing agent (Noigen EA-157, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.)

<Surface printing: print streaks and liquid streaks>
The ink sets shown in Examples 1 to 50 in Tables 6 to 7 and Comparative Examples 1 to 10 in Table 8 were prepared to evaluate surface printing.
Using Stage JET manufactured by Tritech, first, water-based white ink droplets of 12 pL,
Single-pass ejection from two heads at a conveying speed under high-speed printing conditions of 25 m/min,
Each 100% solid image was printed on the surface of the transparent PET sheet. After that, drying was performed at a temperature of 80° C. for 5 minutes. After that, 12 pL of water-based coating droplets are ejected in a single pass at a transport speed of 25 m / min under high-speed printing conditions to print a 70% solid image on the white ink layer, and then, without drying the water-based coating liquid, 12 pL of ink droplets of cyan ink, magenta ink, and yellow ink excluding black ink are applied onto the landed water-based coating liquid.
At a transport speed of 25 m / min under high-speed printing conditions, single-pass ejection is made to land according to the order of the colored ink sets in Tables 5 to 7, solid printing is performed with a printing density of 80% for each ink and a total printing density of 240%. Drying was performed at a temperature of 80 ° C. for 5 minutes. Evaluation was made by visual observation according to the following evaluation criteria. Here, the resolution of the water-based white ink, the water-based coating ink, and the water-based colored ink was set to vertical×horizontal=600×600 dpi. Evaluation criteria are as follows. Tables 6 to 8 show the composition of the ink set used and the evaluation results.
◯: No streaks or liquid leaks are observed on the printed surface.
Δ: Streaks are observed on the printed surface, but liquid dripping does not occur, and there is no problem as solid printing.
x: Streaks and liquid streaks are observed on the printed surface, and solid printing is not buried.
-: Printed, but the density of white is too thin, so it is difficult to visually confirm streaks and liquid.

<Reversing printing: streaks and liquid streaks>
Ink sets shown in Examples 1 to 50 in Tables 6 to 7 and Comparative Examples 1 to 10 in Table 8 were prepared to evaluate reverse printing.
First, using Stage JET manufactured by Tritech, 12p of water-based coating droplets
A 70% solid image is printed on the surface of a transparent PET sheet, and then, without drying the water-based coating liquid, ink droplets of cyan ink, magenta ink, and yellow ink excluding black ink are discharged on the water-based coating liquid that has landed at a conveying speed of 12 pL under high-speed printing conditions of 25 m / min. Solid printing was performed with a printing density of 80% and a total printing density of 240%. Then, after drying at a temperature of 80 ° C. for 5 minutes, water-based white ink droplets were discharged in a single pass from two heads at a transport speed of 12 pL and a high-speed printing condition of 25 m / min, and each 100% solid image was printed on the water-based coating liquid and water-based colored ink. After that, drying is performed for 5 minutes at a temperature of 80°C,
Evaluation was made by visual observation according to the following evaluation criteria. Here, water-based coating liquid and water-based colored ink,
The resolution of the water-based white ink was set to vertical×horizontal=600×600 dpi. Evaluation criteria are as follows. Tables 6 to 8 show the composition of the ink set used and the evaluation results.
◯: No streaks or liquid leaks are observed on the printed surface.
Δ: Streaks are observed on the printed surface, but liquid dripping does not occur, and there is no problem as solid printing.
x: Streaks and liquid streaks are observed on the printed surface, and solid printing is not buried.
-: Printed, but the density of white is too thin, so it is difficult to visually confirm streaks and liquid.

<Surface printing adhesion>
The ink sets shown in Examples 1 to 50 in Tables 6 to 7 and Comparative Examples 1 to 10 in Table 8 were prepared to evaluate surface printing.
Using Stage JET manufactured by Tritech, first, water-based white ink droplets of 12 pL,
Single-pass ejection from two heads at a conveying speed under high-speed printing conditions of 25 m/min,
Each 100% solid image was printed on the surface of the transparent PET sheet. After printing, after drying at 80 ° C. for 5 minutes, 12 pL of water-based coating droplets are discharged in a single pass at a transport speed of 25 m / min under high-speed printing conditions to print a 70% solid image on the white ink layer.
A single-pass ejection was made to land according to the order of the colored ink sets shown in Tables 5 to 7 at a conveying speed of min under high-speed printing conditions, and solid printing was performed with a print density of 80% for each ink and a total print density of 240%. After that, drying was performed at a temperature of 80° C. for 5 minutes. Cellotape (registered trademark, manufactured by NICHIBAN Co., Ltd.) having a width of 24 mm was adhered to the printed portion, and then the tape was peeled off, and the state of the peeled portion was visually evaluated according to the following evaluation criteria. Here, the resolution of the water-based white ink, the water-based coating ink, and the water-based colored ink was set to vertical×horizontal=600×600 dpi. Evaluation criteria are as follows. Tables 6 to 8 show the composition of the ink set used and the evaluation results.
◯: Not peeled △: Less than 50% of the taped portions were peeled off.
x: 50% or more of the portion where the tape was applied, or the entire surface was peeled off.

<Reverse printing adhesion>
Ink sets shown in Examples 1 to 50 in Tables 6 to 7 and Comparative Examples 1 to 10 in Table 8 were prepared to evaluate reverse printing.
First, using Stage JET manufactured by Tritech, 12p of water-based coating droplets
A 70% solid image is printed on the surface of a transparent PET sheet, and then, without drying the water-based coating liquid, ink droplets of cyan ink, magenta ink, and yellow ink excluding black ink are discharged on the water-based coating liquid that has landed at a conveying speed of 12 pL under high-speed printing conditions of 25 m / min. Solid printing was performed with a printing density of 80% and a total printing density of 240%. Then, after drying for 5 minutes at a temperature of 80 ° C., water-based white ink droplets were discharged in a single pass from two heads at a transport speed of 12 pL and 25 m / min under high-speed printing conditions. Width 2 for printed area
A 4 mm cellophane tape (registered trademark, manufactured by NICHIBAN) was adhered, and then the tape was peeled off. Here, the resolution of the water-based coating liquid, the water-based colored ink, and the water-based white ink was set to length×width=600×600 dpi. Evaluation criteria are as follows. Tables 6 to 8 show the composition of the ink set used and the evaluation results.
◯: Not peeled △: Less than 50% of the taped portions were peeled off.
x: 50% or more of the portion where the tape was applied, or the entire surface was peeled off.

<Scratch resistance>
Using Stage JET manufactured by Tritech, first, water-based white ink droplets of 12 pL,
Single-pass ejection from two heads at a conveying speed under high-speed printing conditions of 25 m/min,
Each 100% solid image was printed on the surface of the transparent PET sheet. After printing, the print was dried at 80° C. for 5 minutes, and the printed portion was rubbed back and forth with a cotton swab (registered trademark, manufactured by Hakujuji Co., Ltd.) five times, and visually evaluated according to the following evaluation criteria. The evaluation results are shown in Tables 6-8.
○: No ink adheres to the cotton swab △: Ink adheres to the cotton swab, but the ink does not peel off from the base material ×: Ink adheres to the cotton swab and the ink peels off from the base material

<Discharge rate>
Using Stage JET manufactured by Tritech, first, the printer was filled with water-based white ink, and then the ink was made to land on a transparent OHP sheet, and a check pattern read into the device was printed (process A). Next, water-based white ink droplets were ejected, and 12 pL1 equivalent to 25 m ²
00% solid printing was performed. After that, water-based white ink droplets are made to land on a transparent OHP sheet,
The same check pattern as in process A read into the device was printed (process B). Process A
Each OHP sheet on which the check pattern was printed in the process B was visually confirmed, and the ratio of pins missing from the check pattern was evaluated. Evaluation criteria are as follows. The evaluation results are shown in Tables 6-8.
○: There is no ejection failure in the check pattern printed in process A, and the ratio of pins missing from the check pattern printed in process B is less than 5%.
Δ . . . There is no ejection failure in the check pattern printed in the process A, and the percentage of pins missing from the check pattern printed in the process B is 5% or more and less than 30%.
×: There is no non-ejection in the check pattern printed in process A, and the percentage of pins missing from the check pattern printed in process B is 30% or more.

<Concealment rate>
Using Tritech's Stage JET, first, 12 pL of water-based white ink, 2
A 100% solid image was printed on the surface of a transparent PET sheet by single-pass ejection from two heads at a conveying speed of 5 m/min under high-speed printing conditions. After that, it is dried at a temperature of 80 ° C. for 5 minutes, and an opacity test paper (manufactured by Motofuji Co., Ltd.) and a color difference meter (CR-40 manufactured by Konica Minolta Co., Ltd.)
0) to measure the tristimulus value Y _B under black and the tristimulus value Y _W under white, respectively, Y _B /Y
_W was calculated as a percentage to calculate the concealment rate. Based on the value, evaluation was made according to the following evaluation criteria. Here, the resolution of the water-based white ink was set to vertical×horizontal=600×600 dpi. Evaluation criteria are as follows. The evaluation results are shown in Tables 6-8.
○: Concealment rate is 50.0% or more △: Concealment rate is over 40.0% and less than 50.0% ×: Concealment rate is 40.0% or less

<Storage stability>
Take 100 g of water-based white ink in a 110 cc glass bottle and store it at 60° C. for 4 weeks.
Viscosity, surface tension, specific gravity and pH were measured before and after storage. The results were compared. Evaluation criteria are as follows. The evaluation results are shown in Tables 6-8.
○: Rate of change within 10% for all items △: Rate of change of more than 10% and less than 20% in any one item ×: Rate of change of 20% or more in any one item

Claims (9)

A water-based white ink for inkjet printing containing at least water, a pigment, a water-soluble organic solvent and a resin,
The water-based white ink has a dynamic surface tension value of 33 mN/
m or more and 42 mN/m or less,
The water-based white ink has a static surface tension value of 23 mN/m or more and 30 mN/m at 25°C.
and
A water-based white ink, wherein the water-soluble organic solvent contains at least one alkanediol-based solvent. 2. The water-based white ink according to claim 1, wherein the water-soluble organic solvent contains at least one 1,2-alkanediol solvent. 3. The water-based white ink according to claim 1, wherein the pigment has an average particle diameter (D50) of 150 nm or more and 500 nm or less. The water-based white ink according to any one of claims 1 to 3, wherein the resin is at least one polyether or polyester urethane resin particle. 5. The water-based white ink according to any one of claims 1 to 4, further comprising a surface modifier. 6. The water-based white ink according to claim 5, wherein the surface modifier contains at least one silicone-based surface modifier having an HLB value of 3.0 to 16.0. 7. The water-based white ink according to claim 5, wherein the surface modifier contains at least one acetylene glycol-based surface modifier having an HLB value of 3.0 or more. An ink set comprising the water-based white ink according to any one of claims 1 to 7, a water-based coating liquid and a water-based colored ink,
The water-based coating liquid contains at least water, a water-soluble polymer having a cation and an organic solvent,
An ink set, wherein the water-based colored ink contains at least water, a resin, an organic solvent and a colorant. A printing method for forming a print layer on a substrate by an inkjet printer equipped with the ink set according to claim 8,
Water-based white ink, water-based coating liquid, and water-based colored ink are printed in this order,
A step of forming a printed layer on a base material, or printing with a water-based coating liquid, a water-based colored ink and a water-based white ink in this order,
A printing method, comprising the step of forming a printed layer on a substrate.