JP7388029B2 - Ink set, printing method, and printing device - Google Patents

Description

The present invention relates to an ink set, a printing method, and a printing device.

Inkjet printers have advantages such as low noise, low running costs, and easy color printing, so they are widely used in general households as digital signal output devices.
In addition, in recent years, even in the commercial and industrial printing fields where analog printing such as offset printing and flexographic printing is mainstream, digital printing is being used as a plateless method that does not require a plate and can print a wide variety of designs in small quantities. , the need for inkjet printers is increasing.

Here, in commercial printing, for example, pamphlets, catalogs, posters, manuals, etc., and in industrial printing, for example, labels, packages, textiles, cardboard, etc. are listed as main printing items. Particularly in the field of industrial printing, designs that produce a wide variety of products in small quantities are preferred and are used to promote product sales.

In addition, for example, solvent-based inks and UV-curable inks are often used as inks used for printing with inkjet printers, but in recent years, demand for water-based inks has increased due to considerations for worker safety and the environment. ing.

However, printing with an inkjet printer using water-based ink has a problem in that productivity is inferior to analog printing because it is necessary to volatilize water in order to dry the ink. In view of this problem, for example, a technique has been proposed in which drying performance is improved by adding a certain amount of a low boiling point solvent (see, for example, Patent Document 1).
However, in such technology, when printing with ink that has high drying properties, the ink thickens quickly after landing on the media (printing material), so the ink cannot sufficiently wet and spread, causing the ink to touch the media. If the area cannot be filled in completely, the density of the image may become low.

An object of the present invention is to provide an ink set that has excellent drying properties and can provide high image density.

The ink set of the present invention as a means for solving this problem is an ink set having white ink and non-white ink,
The white ink contains an organic solvent, water, and a coloring material,
the non-white ink contains a surfactant;
The dynamic surface tension A of the non-white ink at 25°C and a surface life of 15 msec determined by the maximum bubble pressure method is 45.0 mN/m or less, and the dynamic surface tension A and the static surface tension at 25°C of the non-white ink are 45.0 mN/m or less. The surface tension B is given by the following formula,
2.0(%)≦[(AB)/(A+B)]×100(%)≦10.0(%).

According to the present invention, it is possible to provide an ink set that has excellent drying properties and provides high image density.

FIG. 1 is a diagram showing an example of a recording apparatus of the present invention. FIG. 2 is a perspective view of a main tank containing ink according to the present invention.

(ink set)
The ink set of the present invention includes a white ink and a non-white ink, and further includes other inks as necessary. The white ink contains an organic solvent, water, and a coloring material, and further contains other components as necessary. The non-white ink contains a surfactant and further contains other components as necessary. In addition, the non-white ink of the present invention has a dynamic surface tension A of 45.0 mN/m or less at 25° C. and a surface life of 15 msec by the maximum bubble pressure method, and the dynamic surface tension A is 45.0 mN/m or less. , the static surface tension B at 25°C of non-white ink is expressed by the following formula: [2.0(%)≦[(AB)/(A+B)]×100(%)≦10.0(% )], satisfies.

Furthermore, the ink set of the present invention is based on the knowledge that conventional ink sets may not be able to achieve both dryness after application and density of images formed using the ink set.
As mentioned above, when printing with an inkjet printer using water-based ink, it is necessary to dry the ink during printing. Improves ink drying.
However, in such conventional techniques, after the ink ejected onto the base material (printed material) lands, the ink may not spread sufficiently. In this way, if the ink does not spread sufficiently, in the image area where the image is formed, there will be white spots (no ink, exposed areas) may occur. When white spots occur in the image area, the density of the formed image becomes low, and the quality of the image may deteriorate.

Therefore, the present inventors have developed an ink set that can achieve both drying properties after application and high density of images formed using the ink set, in other words, an ink set that has excellent drying properties and can provide high image density. After extensive research, the present invention was conceived. That is, the present inventors have proposed an ink set having a white ink and a non-white ink, in which the white ink contains an organic solvent, water, and a coloring material, and the non-white ink contains a surfactant. The non-white ink has a dynamic surface tension A of 45.0 mN/m or less at 25°C and a surface life of 15 msec by the maximum bubble pressure method, and the dynamic surface tension A and the non-white ink at 25°C An ink set in which the static surface tension B at It has been found that this method provides excellent drying properties and high image density.

Here, in the ink set of the present invention, as described above, the dynamic surface tension A of the non-white ink at 25° C. and a surface life of 15 msec by the maximum bubble pressure method is 45.0 mN/m or less, and The dynamic surface tension A and the static surface tension B at 25°C in non-white ink are calculated by the following formula: [2.0(%)≦[(AB)/(A+B)]×100(%) ≦10.0(%)].
In the ink set of the present invention, for example, the dynamic surface tension A of the non-white ink is 45.0 mN/m or less, so that the ink ejected onto the base material (printed material) can be used for a short period of time immediately after landing. Instantly spreads wetness over a wide area. Therefore, in the ink set of the present invention, the surface area of the ink increases quickly, and the moisture evaporates efficiently, improving drying performance, suppressing the occurrence of white spots, and achieving high image density. Obtainable.
Further, in the ink set of the present invention, for example, the dynamic surface tension A and the static surface tension B of the non-white ink are expressed by the following formula: [2.0(%)≦[(AB)/(A+B)] ] × 100 (%) ≦ 10.0 (%)], the relative difference between dynamic surface tension A and static surface tension B becomes smaller, and the ink becomes uniformly wetted in a short time. spread. In other words, in the ink set of the present invention, for example, the dynamic surface tension A and the static surface tension B of the non-white ink satisfy the relationship of the above formula, so that the center of the ink droplet landing on the printing substrate is Since there is less difference in film thickness between the circumferential area and the circumferential area, and a smooth ink film can be obtained by uniformly wetting and spreading, high image density can be obtained.

In this manner, the ink set of the present invention can wet and spread uniformly over a wide area in a short time, for example, immediately after landing on the printing substrate. As a result, the ink set of the present invention has excellent drying properties and can obtain high image density. Further, since the ink set of the present invention has excellent drying properties, it is possible to improve the productivity of printed matter by using it in an inkjet printing method or printing apparatus.

<White ink>
The white ink contains an organic solvent, water, and a coloring material, and further contains other components as necessary.

<<Organic solvent>>
The organic solvent used in the present invention is not particularly limited, and water-soluble organic solvents can be used. Examples include polyhydric alcohols, ethers such as polyhydric alcohol alkyl ethers and polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds.
Specific examples of water-soluble organic solvents include ethylene glycol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, Diol, 2,3-butanediol, 3-methyl-1,3-butanediol, triethylene glycol, polyethylene glycol, polypropylene glycol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol , 2,4-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, 1,3-hexanediol, 2,5-hexanediol, 1,5-hexanediol, Glycerin, 1,2,6-hexanetriol, 2-ethyl-1,3-hexanediol, ethyl-1,2,4-butanetriol, 1,2,3-butanetriol, 2,2,4-trimethyl- Polyhydric alcohols such as 1,3-pentanediol and petriol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monoethyl Polyhydric alcohol alkyl ethers such as ether, polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone , 1,3-dimethyl-2-imidazolidinone, ε-caprolactam, nitrogen-containing heterocyclic compounds such as γ-butyrolactone, formamide, N-methylformamide, N,N-dimethylformamide, 3-methoxy-N,N- Amides such as dimethylpropionamide and 3-butoxy-N,N-dimethylpropionamide, amines such as monoethanolamine, diethanolamine, and triethylamine, sulfur-containing compounds such as dimethyl sulfoxide, sulfolane, and thiodiethanol, propylene carbonate, and ethylene carbonate. etc.
It is preferable to use an organic solvent with a boiling point of 250° C. or lower because it not only functions as a wetting agent but also provides good drying properties.

The content of the organic solvent in the ink is not particularly limited and can be appropriately selected depending on the purpose, but from the viewpoint of ink drying properties and ejection reliability, it is preferably 10% by mass or more and 60% by mass or less, More preferably 20% by mass or more and 60% by mass or less.

＜＜Water＞＞
As water, for example, pure water such as ion-exchanged water, ultrafiltrated water, reverse osmosis water, distilled water, or ultrapure water can be used.
The water content in the ink is not particularly limited and can be appropriately selected depending on the purpose, but from the viewpoint of ink drying properties and ejection reliability, it is preferably 10% by mass or more and 90% by mass or less, and 20% by mass or less. % to 60% by mass is more preferable.

＜＜Color material＞＞
The coloring material contained in the white ink is not particularly limited as long as it exhibits white color, and can be appropriately selected depending on the purpose. Examples include pigments and dyes that exhibit white color.
Note that the white color exhibited by the white ink in the ink set of the present invention means that when the white ink is in a dry coating state, L ^* is 50 or more and 100 or less in the L ^* a ^* b ^* color space, and a ^* means -5 or more and 5 or less, and b ^* means -5 or more and 5 or less. The color of the white ink in the L ^* a ^* b ^* color space can be measured using a known device, for example, based on the JIS Z 8781-4 standard. More specifically, for example, a solid image of white ink (uniform white image formed using white ink) is printed out with an inkjet printer, dried, and printed with X-Rite eXact (manufactured by X-Rite). By measuring, the color in the L ^* a ^* b ^* color space of the white ink can be measured.

Examples of the pigment in the coloring material contained in the white ink include metal oxides.
Examples of the metal oxide include titanium oxide, iron oxide, tin oxide, zirconium oxide, and iron titanate (a composite oxide of iron and titanium). These may be used alone or in combination of two or more.

The number average particle diameter of the pigment is not particularly limited and can be appropriately selected depending on the purpose, but the maximum frequency in terms of maximum number is preferably 50 nm or more and 600 nm or less. When the number average particle diameter is 50 nm or more, dispersion and classification operations become easy, and when it is 600 nm or less, not only the pigment dispersion stability as an ink is improved, but also the ejection stability is excellent, and the image quality is improved. Image quality such as density is also high, which is preferable.
The number average particle diameter can be measured, for example, using a particle size analyzer (Nanotrack MODEL UPA9340, manufactured by Nikkiso Co., Ltd.).

There are no particular restrictions on the method for dispersing the pigment in the ink, and it can be selected as appropriate depending on the purpose. Examples include a method of coating and dispersing with a resin, and a method of dispersing using a dispersant.
Examples of methods for creating self-dispersing pigments by introducing hydrophilic functional groups into pigments include self-dispersing pigments that are made dispersible in water by adding functional groups such as sulfone groups and carboxyl groups to pigments (e.g., carbon). can be used.
As a method for coating the surface of a pigment with a resin and dispersing it, a method can be used in which the pigment is encapsulated in microcapsules and can be dispersed in water. This can be referred to as a resin-coated pigment. In this case, all the pigments blended into the ink do not need to be coated with the resin, and uncoated pigments or partially coated pigments may be dispersed in the ink as long as the effects of the present invention are not impaired. You can leave it there.

Examples of the method for dispersing using a dispersant include methods for dispersing using known low-molecular-type dispersants and polymer-type dispersants, typified by surfactants.
As the dispersant, it is possible to use, for example, an anionic surfactant, a cationic surfactant, an amphoteric surfactant, a nonionic surfactant, etc. depending on the pigment.
RT-100 (nonionic surfactant) manufactured by Takemoto Yushi Co., Ltd. and a formalin condensate of naphthalene sulfonate can also be suitably used as the dispersant.
One type of dispersant may be used alone, or two or more types may be used in combination.

Ink can be obtained by mixing pigments with materials such as water and organic solvents. It is also possible to manufacture ink by mixing a pigment with other materials such as water and a dispersant to form a pigment dispersion, and then mixing materials such as water and an organic solvent.
The pigment dispersion is obtained by dispersing water, a pigment, a pigment dispersant, and other components as necessary, and adjusting the particle size. For dispersion, it is preferable to use a disperser.
There is no particular restriction on the particle size of the pigment in the pigment dispersion, but the maximum frequency in terms of the maximum number of particles is 20 nm because the dispersion stability of the pigment is good and the image quality such as ejection stability and image density is also high. The thickness is preferably 500 nm or more, more preferably 20 nm or more and 150 nm or less. The particle size of the pigment can be measured using, for example, a particle size analyzer (Nanotrac Wave-UT151, manufactured by Microtrac Bell Co., Ltd.).
The content of pigment in the pigment dispersion is not particularly limited and can be appropriately selected depending on the purpose, but from the viewpoint of obtaining good ejection stability and increasing image density, 0.1% by mass It is preferably 50% by mass or less, more preferably 0.1% by mass or more and 30% by mass or less.
The pigment dispersion is preferably degassed by filtering coarse particles using a filter, centrifugal separator, etc., as necessary.

The content of the coloring material in the white ink is preferably 0.1% by mass or more and 15% by mass or less, more preferably 1% by mass or more and 10% by mass from the viewpoint of improving image density, good fixing properties, and ejection stability. % or less.

The pigment content in the white ink is preferably 0.1% by mass or more and 15% by mass or less, more preferably 0.1% by mass or more and 10% by mass or less, and 1% by mass or more and 10% by mass or less, based on the total amount of the white ink. Particularly preferably less than % by mass. When the pigment content in the white ink is 0.1% by mass or more and 15% by mass or less, image density, fixing properties, and ejection stability can be improved.

<<Other ingredients>>
Other components that may be included in the white ink are not particularly limited and can be appropriately selected depending on the purpose, such as surfactants, additives, and the like.

<<<Surfactant>>>
As the surfactant, any of silicone surfactants, fluorine surfactants, amphoteric surfactants, nonionic surfactants, and anionic surfactants can be used.
The silicone surfactant is not particularly limited and can be appropriately selected depending on the purpose. Among these, those that do not decompose even at high pH are preferable, such as side chain-modified polydimethylsiloxane, double-end modified polydimethylsiloxane, single-end modified polydimethylsiloxane, and both side-chain ends modified polydimethylsiloxane. Those having an oxyethylene group or a polyoxyethylene polyoxypropylene group are particularly preferred since they exhibit good properties as a water-based surfactant. Further, as the silicone surfactant, a polyether-modified silicone surfactant can also be used, such as a compound in which a polyalkylene oxide structure is introduced into the side chain of the Si part of dimethylsiloxane.
Examples of fluorine-based surfactants include perfluoroalkyl sulfonic acid compounds, perfluoroalkyl carboxylic acid compounds, perfluoroalkyl phosphate ester compounds, perfluoroalkyl ethylene oxide adducts, and perfluoroalkyl ether groups in their side chains. Polyoxyalkylene ether polymer compounds are particularly preferred because they have low foaming properties. Examples of the perfluoroalkylsulfonic acid compound include perfluoroalkylsulfonic acid, perfluoroalkylsulfonic acid salts, and the like. Examples of the perfluoroalkylcarboxylic acid compound include perfluoroalkylcarboxylic acids, perfluoroalkylcarboxylic acid salts, and the like. The polyoxyalkylene ether polymer compound having a perfluoroalkyl ether group in its side chain includes a sulfate ester salt of a polyoxyalkylene ether polymer having a perfluoroalkyl ether group in its side chain, and a sulfate salt of a polyoxyalkylene ether polymer having a perfluoroalkyl ether group in its side chain. Examples include salts of polyoxyalkylene ether polymers. Counter ions of the salts in these fluorosurfactants include Li, Na, K, NH ₄ , NH ₃ CH ₂ CH ₂ OH, NH ₂ (CH ₂ CH ₂ OH) ₂ , NH (CH ₂ CH ₂ OH) _3rd prize is mentioned.
Examples of the amphoteric surfactant include lauryl aminopropionate, lauryl dimethyl betaine, stearyl dimethyl betaine, lauryl dihydroxyethyl betaine, and the like.
Examples of nonionic surfactants include polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl ester, polyoxyethylene alkylamine, polyoxyethylene alkylamide, polyoxyethylene propylene block polymer, sorbitan fatty acid ester, polyoxyethylene sorbitan Examples include fatty acid esters and ethylene oxide adducts of acetylene alcohol.
Examples of the anionic surfactant include polyoxyethylene alkyl ether acetate, dodecylbenzene sulfonate, laurate, polyoxyethylene alkyl ether sulfate salt, and the like.
These may be used alone or in combination of two or more.

Additives for the white ink are not particularly limited and can be appropriately selected depending on the purpose, and include, for example, antifoaming agents, antiseptic and antifungal agents, and rust preventives.

<<<Defoaming agent>>>
The antifoaming agent is not particularly limited and includes, for example, silicone antifoaming agents, polyether antifoaming agents, fatty acid ester antifoaming agents, and the like. These may be used alone or in combination of two or more. Among these, silicone antifoaming agents are preferred because they have excellent foam-breaking effects.

＜＜＜Preservative and fungicidal agent＞＞＞
The preservative and fungicide is not particularly limited and includes, for example, 1,2-benzisothiazolin-3-one.

<<<Rust preventive agent>>>
There are no particular limitations on the rust preventive, and examples thereof include acidic sulfites, sodium thiosulfate, and the like.

<Non-white ink>
The non-white ink preferably contains a surfactant and at least one of an organic solvent, water, and a coloring material, and further contains other components as necessary.
Here, the color of the non-white ink is not particularly limited as long as it is white, and can be appropriately selected depending on the purpose. In other words, when the non-white ink is in a dry coating state, in the L ^* a ^* b ^* color space, L ^* is 50 or more and 100 or less, a ^* is -5 or more and 5 or less, and b ^* is -5 or more. It may not be less than 5.

Examples of the non-white ink include colored inks such as color ink, black ink, gray ink, and metallic ink, and colorless inks such as clear ink. These may be used alone or in combination of two or more.
Furthermore, colored ink can be produced by appropriately combining pigments, dyes, etc., which will be described later. Note that the clear ink refers to an ink that does not contain a coloring material and mainly contains resin particles, an organic solvent, and water.
Examples of the color ink include cyan ink, magenta ink, yellow ink, light cyan ink, light magenta ink, red ink, green ink, blue ink, orange ink, and violet ink. It will be done.

<<Surfactant>>
As the surfactant contained in the non-white ink, surfactants similar to those that can be contained in the above-mentioned white ink can be selected, but at least one of a silicone surfactant and a nonionic surfactant may be selected. It is preferable to include. Since the surfactant contained in the non-white ink contains at least one of a silicone surfactant and a nonionic surfactant, the non-white ink wets and spreads uniformly immediately after landing on the printing substrate to obtain a smooth ink film. Therefore, high image density can be obtained.
Note that the silicone surfactant and the nonionic surfactant may be used in combination.

The silicone surfactant is not particularly limited and can be appropriately selected depending on the purpose. Among these, those that do not decompose even at high pH are preferable, such as side chain-modified polydimethylsiloxane, double-end modified polydimethylsiloxane, single-end modified polydimethylsiloxane, and both side-chain ends modified polydimethylsiloxane. Those having an oxyethylene group or a polyoxyethylene polyoxypropylene group are particularly preferred since they exhibit good properties as a water-based surfactant. Further, as the silicone surfactant, a polyether-modified silicone surfactant can also be used, such as a compound in which a polyalkylene oxide structure is introduced into the side chain of the Si part of dimethylsiloxane.
Examples of silicone surfactants include BYK-345, BYK-347, BYK-348, BYK-349 (manufactured by BYK Additives & Instruments), WET240, WET270, WET280 (manufactured by Evonik), SAG002, SAG013, SA G503A (manufactured by Nissin Chemical Industry Co., Ltd.).
The content of the silicone surfactant in the non-white ink is preferably 0.1% by mass or more and 3.0% by mass or less, and 0.1% by mass or more, from the viewpoint of wetting and spreading on the media and drying properties of the ink. It is more preferably 1.0% by mass or less.

In addition, there are no particular restrictions on the nonionic surfactant, and it can be selected as appropriate depending on the purpose, such as a compound that has a hydrophilic group and a hydrophobic group and does not have a group that dissociates into ions. can be used.
Examples of nonionic surfactants include polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl ester, polyoxyethylene alkylamine, polyoxyethylene alkylamide, polyoxyethylene propylene block polymer, sorbitan fatty acid ester, polyoxyethylene sorbitan Examples include fatty acid esters, glycerin fatty acid esters, and ethylene oxide adducts of acetylene alcohol. More specifically, but not limited to, Surfynol 104E, Surfynol 420, Surfynol 440, Surfynol SE-F, Surfynol PSA-336, Surfynol 465, Surfynol 485, Surfynol 2502, Envirogem AD01 (manufactured by Nissin Chemical Industry Co., Ltd.), Rheodol MO-60, Emazol L-10V, Rheodol AO-15V, and Emulgen 102KG (manufactured by Kao Corporation).
The content of the nonionic surfactant in the non-white ink is preferably 0.1% by mass or more and 3.0% by mass or less, and 0.1% by mass or more, from the viewpoint of wetting and spreading on the media and drying properties of the ink. It is more preferably 1.0% by mass or less.

As described above, the content of the surfactant relative to the total amount of white ink is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 1.0% by mass or less. Here, if the non-white ink contains multiple types of surfactants, such as when a silicone surfactant and a nonionic surfactant are used together as surfactants, It is preferable that the total content of the surfactant is 1.0% by mass or less.
By setting the surfactant content to 1.0% by mass or less based on the total amount of non-white ink, a more uniform film can be obtained and high image density can be obtained, and the surfactant can reduce the amount of solvent in the ink. Since drying proceeds without hindering evaporation, high drying performance (productivity) can be obtained.

<<Organic solvent>>
The organic solvent for the non-white ink is not particularly limited and can be appropriately selected depending on the purpose. For example, the same organic solvent as for the white ink can be used.

＜＜Water＞＞
The water in the non-white ink is not particularly limited and can be appropriately selected depending on the purpose. For example, the same water as in the white ink can be used.

＜＜Color material＞＞
The coloring material in the non-white ink is not particularly limited as long as it exhibits non-white color, and can be appropriately selected depending on the purpose, and examples include dyes and pigments. These may be used alone or in combination of two or more. Among these, pigments are preferred. Examples of the pigment include inorganic pigments and organic pigments.

Examples of inorganic pigments include titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, and chrome yellow, as well as pigments manufactured by known methods such as contact method, furnace method, and thermal method. Examples include carbon black. These may be used alone or in combination of two or more.

Examples of organic pigments include azo pigments (including, for example, azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments, etc.), polycyclic pigments (for example, phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, quinofularone pigments, etc.), dye chelates (e.g., basic dye type chelates, acidic dye type chelates, etc.), nitro pigments, nitroso pigments, aniline black, etc. Can be mentioned. These may be used alone or in combination of two or more. In addition, hollow resin particles and inorganic hollow particles can also be used. Among these pigments, those having good affinity with the solvent are preferably used.

Examples of pigments include carbon blacks (C.I. Pigment Black 7) such as furnace black, lamp black, acetylene black, and channel black, copper, iron (C.I. Pigment Black 11), and aniline black (C.I. Pigment Black 11). Examples include organic pigments such as I. Pigment Black 1). These may be used alone or in combination of two or more.

Further, as the pigment, for example, C.I. I. Pigment Yellow 1, 3, 12, 13, 14, 17, 24, 34, 35, 37, 42 (yellow iron oxide), 53, 55, 74, 81, 83, 95, 97, 98, 100, 101, 104 , 108, 109, 110, 117, 120, 138, 150, 153, 155; C. I. Pigment Orange 5, 13, 16, 17, 36, 43, 51; C.I. I. Pigment Red 1, 2, 3, 5, 17, 22, 23, 31, 38, 48:2, 48:2 (Permanent Red 2B (Ca)), 48:3, 48:4, 49:1, 52: 2, 53:1, 57:1 (Brilliant Carmine 6B), 60:1, 63:1, 63:2, 64:1, 81, 83, 88, 101 (Red), 104, 105, 106, 108 ( C.I. I. Pigment Violet 1 (Rhodamine Lake), 3, 5:1, 16, 19, 23, 38, C.I. I. Pigment Blue 1, 2, 15 (phthalocyanine blue), 15:1, 15:2, 15:3 (phthalocyanine blue), 16, 17:1, 56, 60, 63; C.I. I. Pigment Green 1, 4, 7, 8, 10, 17, 18, 36 and the like. These may be used alone or in combination of two or more.

Examples of dyes include C.I. I. Acid Yellow 17, 23, 42, 44, 79, 142; C. I. Acid Red 52, 80, 82, 249, 254, 289; C. I. Acid Blue 9, 45, 249; C. I. Acid Black 1, 2, 24, 94; C. I. Food black 1, 2; C. I. Direct Yellow 1, 12, 24, 33, 50, 55, 58, 86, 132, 142, 144, 173; C. I. Direct Red 1, 4, 9, 80, 81, 225, 227; C.I. I. Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, 202; C. I. Directed Black 19, 38, 51, 71, 154, 168, 171, 195; C. I. Reactive Red 14, 32, 55, 79, 249; C. I. Examples include Reactive Black 3, 4, and 35. These may be used alone or in combination of two or more.

The coloring material used in metallic ink is a fine powder made by finely pulverizing a single metal, an alloy, or a metal compound, and more specifically, it includes aluminum, silver, gold, nickel, chromium, tin, zinc, indium, Consisting of one or more metals selected from titanium, silicone, copper, and platinum, alloys obtained by combining a group of these metals, or oxides and nitrides of single metals or alloys of these groups It is obtained by finely pulverizing one or more of a substance, a sulfide, and a carbide.

As a method for dispersing the pigment in the non-white ink, a method similar to the method for dispersing the pigment in the white ink can be used.
Further, the pigment can be made into a pigment dispersion in the same manner as the pigment in white ink.

The content of the coloring material in the non-white ink is preferably 0.1% by mass or more and 15% by mass or less based on the total amount of the non-white ink, from the viewpoint of improving image density, good fixing properties, and ejection stability. , more preferably 1% by mass or more and 10% by mass or less.

The pigment content is preferably 0.1% by mass or more and 15% by mass or less, more preferably 0.1% by mass or more and 10% by mass or less, and 1% by mass or more and 10% by mass or less, based on the total amount of the non-white ink. The following are particularly preferred. When the pigment content is 0.1% by mass or more and 15% by mass or less, image density, fixing properties, and ejection stability can be improved.

<<Other ingredients>>
Other components that may be included in the non-white ink are not particularly limited and can be appropriately selected depending on the purpose, such as additives.
As the additive for the non-white ink, the same additives as those for the white ink can be appropriately selected and used.

<<Dynamic surface tension A, static surface tension B>>
Here, the non-white ink in the ink set of the present invention has a dynamic surface tension A of 45.0 mN/m or less at 25° C. and a surface life of 15 msec by the maximum bubble pressure method, and The surface tension A and the static surface tension B at 25°C in non-white ink are calculated by the following formula: [2.0(%)≦[(AB)/(A+B)]×100(%)≦10 .0 (%)].
The dynamic surface tension A and static surface tension B of the non-white ink can be adjusted, for example, by appropriately selecting the type and amount of surfactant contained in the non-white ink.

The dynamic surface tension A of a non-white ink at 25° C. and a surface life of 15 msec by the maximum bubble pressure method can be measured at 25° C. using, for example, SITA DynoTester (manufactured by SITA).
More specifically, the dynamic surface tension A of non-white ink can be measured, for example, as follows.
After putting 30 ml of non-white ink into a 30 ml beaker, place it in a water bath adjusted to 25°C and let it stand for 10 minutes. Adjust the temperature of the non-white ink to 25°C, and then run it for 15 msec using SITA DynoTester. Measure surface tension.

The static surface tension B at 25° C. of the non-white ink can be measured at 25° C. using, for example, a fully automatic surface tension meter (CBVP-Z, manufactured by Kyowa Interface Science Co., Ltd.).
More specifically, the static surface tension B of non-white ink can be measured, for example, as follows.
Pour the non-white ink into a petri dish with a diameter of 30 mm, let it stand for 5 minutes, and then measure it using an automatic surface tension meter DY-300 using the Wilhelmy method using a platinum plate.

Furthermore, in the present invention, the dynamic surface tension A of the non-white ink at 25° C. and a surface life of 15 msec by the maximum bubble pressure method is 35.0 mN/m or less, and the dynamic surface tension A and the non-white ink are The static surface tension B of the ink at 25°C is expressed by the following formula: [4.0(%)≦[(AB)/(A+B)]×100(%)≦8.0(%)] It is preferable to satisfy the following.
By doing so, in the present invention, for example, immediately after landing on the substrate, the ink spreads evenly over a wider area in a shorter time, and it is possible to obtain better drying properties and higher image density.

<Print material>
The printing substrate (substrate) to which each ink is applied in the ink set of the present invention can be used without any particular restriction, and plain paper, glossy paper, special paper, cloth, etc. can also be used, but non-permeable It can be particularly suitably used for plastic substrates.
The term "impermeable base material" in the present invention refers to a base material that has a surface with low water permeability, absorbency, and/or adsorption property, and is a material that has many cavities inside but is not open to the outside. Also included.
More quantitatively, it means a base material whose water absorption amount is 10 mL/m ² or less from the start of contact to 30 msec ^1/2 in the Bristow method.

Among non-permeable substrates, resin films are preferred, and particularly good adhesion can be obtained to polypropylene films, polyethylene terephthalate films, and nylon films.
Examples of polypropylene films include Toyobo's P-2002, P-2102, P-2161, P-4166, SUNTOX's PA-20, PA-30, PA-20W, Futamura Chemical's FOA, FOS, FOR, etc. It will be done.
Examples of polyethylene terephthalate films include E-5100 and E-5102 manufactured by Toyobo, P60 and P375 manufactured by Toray Industries, and G2, G2P2, K, and SL manufactured by Teijin DuPont Films.
Examples of nylon films include Harden Film N-1100, N-1102, and N-1200 manufactured by Toyobo, and ON, NX, MS, and NK manufactured by Unitika.
When the ink of the present invention is subjected to a heating step after printing, the amount of residual solvent in the ink coating is reduced, which further improves the adhesion to the substrate, which is desirable.

<Printing device, printing method>
The ink set of the present invention can be suitably used in various recording devices using an inkjet recording method, such as printers, facsimile machines, copying machines, printer/fax/copier multifunction devices, and three-dimensional modeling devices.
In the present invention, a printing (recording) device and a printing (recording) method are a device capable of ejecting ink, various processing liquids, etc. onto a recording medium, and a method of performing recording using the device. A recording medium means something to which ink or various processing liquids can be attached even temporarily.
This printing (recording) device includes not only a head part that discharges ink, but also means for feeding, transporting, and discharging the recording medium, and other devices called pre-processing devices and post-processing devices. be able to.
The printing (recording) device and the printing (recording) method may include a heating means used in the heating step and a drying means used in the drying step. The heating means and drying means include, for example, means for heating and drying the printed surface and back surface of the recording medium. The heating means and drying means are not particularly limited, but for example, a hot air heater or an infrared heater can be used. Heating and drying can be performed before, during, or after printing.
Further, the printing (recording) device and the printing (recording) method are not limited to those in which significant images such as characters and figures are visualized using ink. For example, it includes those that form patterns such as geometric patterns, and those that form three-dimensional images.
Further, the printing (recording) device includes both a serial type device in which the ejection head is moved and a line type device in which the ejection head is not moved, unless specifically limited.
Furthermore, this printing (recording) device includes not only a desktop type but also a wide recording device that can print on A0 size recording media, and a device that uses, for example, continuous paper wound into a roll as the recording medium. This also includes continuous paper printers that are capable of printing.

An example of a printing (recording) device will be described with reference to FIGS. 1 and 2. FIG. 1 is a perspective explanatory view of the device. FIG. 2 is a perspective explanatory view of the main tank. Image forming apparatus 400, which is an example of a printing (recording) apparatus, is a serial type image forming apparatus. A mechanism section 420 is provided within the exterior 401 of the image forming apparatus 400. Each ink storage section 411 of the main tank 410 (410k, 410c, 410m, 410y) for each color of black (K), cyan (C), magenta (M), and yellow (Y) is made of packaging such as aluminum laminated film. It is formed from members. The ink storage section 411 is housed in a container case 414 made of plastic, for example. Thereby, the main tank 410 is used as an ink cartridge for each color.
On the other hand, a cartridge holder 404 is provided on the back side of the opening when the cover 401c of the apparatus main body is opened. A main tank 410 is detachably attached to the cartridge holder 404. As a result, each ink discharge port 413 of the main tank 410 and the ejection head 434 for each color communicate with each other via the supply tube 436 for each color, and ink can be ejected from the ejection head 434 onto the recording medium.

That is, the printing device of the present invention has ink and a discharge means for discharging the ink, and the ink is the white ink and the non-white ink in the ink set of the present invention, and further includes other means as necessary. have The printing apparatus of the present invention can suitably perform the printing method of the present invention.

Further, the printing method of the present invention includes a step of applying the white ink in the ink set of the present invention to the substrate to be printed (white ink applying step), and a step of applying the non-white ink in the ink set of the present invention to the substrate to print. (non-white ink application step), preferably includes a step of surface modification of the printing substrate (surface modification step), a step of applying a pretreatment liquid to the printing substrate (pretreatment step), and further necessary Other steps may be included depending on the situation.

<Surface modification process>
In the surface modification step, any treatment method that can eliminate unevenness during ink application and improve adhesion may be used, such as corona treatment, atmospheric pressure plasma treatment, flame treatment, ultraviolet irradiation treatment, etc. can be mentioned.
These processing methods can be implemented using known equipment.
Note that the surface modification process can be said to be a process of modifying the surface condition of the printing substrate itself into a state suitable for applying ink, and the surface modification process is a process of modifying the surface condition of the printing substrate itself into a state suitable for applying ink. This is different from the step of applying (for example, a pretreatment step).

Among the above treatment methods, surface modification of the printing surface (recording surface) is preferably performed by a corona treatment step in which the printing surface (recording surface) is subjected to a corona discharge treatment or a streamer treatment (plasma treatment) in which the print surface (recording surface) is subjected to a streamer discharge treatment. Compared to atmospheric pressure plasma treatment, flame treatment, and ultraviolet irradiation treatment, these methods have superior corona discharge output stability and the ability to uniformly modify the surface of the printed surface (recording surface). Therefore, it is preferably used.

<Pre-treatment liquid application step>
In the pretreatment liquid application step, there is no particular restriction as long as the pretreatment liquid is applied to the printing substrate, and it can be selected as appropriate depending on the purpose. For example, blade coating method, gravure coating method, gravure offset method, etc. Coating method, bar coating method, roll coating method, knife coating method, air knife coating method, comma coating method, U comma coating method, AKKU coating method, smoothing coating method, microgravure coating method, reverse roll coating method, 4 to 5 Examples include the present roll coating method, dip coating method, curtain coating method, slide coating method, die coating method, and the like.

The amount of wet adhesion of the pretreatment liquid to the printing substrate in the pretreatment liquid application step (the amount of the liquid composition attached before drying the printing substrate) shall be 0.1 g/m ² to 10.0 g/m ² is preferable, and more preferably 1.0 g/m ² to 3.0 g/m ² . When the wet adhesion amount is 0.1 g/m ² or more, the image quality (density, saturation, color bleed, feathering) of the recorded material improves, and when it is 10.0 g/m ² or less, 10. The same agglomeration effect as in the case of exceeding 0 g/m ² is achieved, the feel of the recorded material is not impaired, the drying process does not take much time, and there are no problems in terms of cost.

It is preferable to dry the pretreatment liquid that has adhered to the printing material. In this case, the pretreatment liquid that has adhered to the substrate is transferred to the conveyance member that comes into contact with it from the pretreatment liquid application step to the printing by ejecting ink, causing failure of the conveyance member and deterioration of image quality due to dirt accumulation. It is sufficient to use an artificial drying method to the extent that this does not occur, and the drying temperature is preferably 40°C to 130°C, and more preferably 80°C to 100°C. Examples of the drying method include a heat drum method, an oven method, a hot air blowing method, a preheater method, and a heated roller method. Furthermore, a combination of these methods may be used. "Drying" here does not mean that the pretreatment liquid is absorbed by the printing substrate and it appears dry, but rather that the liquid in the liquid composition, such as water, evaporates and becomes liquid. This means that it will no longer be able to maintain its properties and will solidify.

The pretreatment liquid contains a polyvalent metal salt and an organic solvent, preferably contains water, and further contains other components as necessary.

-Polyvalent metal salt-
Polyvalent metal salts have the function of destabilizing the dispersion of the coloring material in the ink, causing the pigments in the ink to quickly aggregate after being deposited, suppressing color bleeding, and improving color development. be able to.
The cation in the polyvalent metal salt is not particularly limited and can be appropriately selected depending on the purpose, such as aluminum (Al(III)), calcium (Ca(II)), magnesium (Mg(II)), etc. ), copper (Cu(II)), iron (Fe(II) or Fe(III)), zinc (Zn(II)), tin (Sn(II) or Sn(IV)), strontium (Sr(II)) ), nickel (Ni(II)), cobalt (Co(II)), barium (Ba(II)), lead (Pb(II)), zirconium (Zr(IV)), titanium (Ti(IV)), Antimony (Sb(III)), bismuth (Bi(III)), tantalum (Ta(V)), arsenic (As(III)), cerium (Ce(III)), lanthanum (La(III)), yttrium ( Examples include ions such as Y(III)), mercury (Hg(II)), and beryllium (Be(II)). Among these, calcium (Ca(II)) and magnesium (Mg(II)) are preferred.

The anion in the polyvalent metal salt is not particularly limited and can be appropriately selected depending on the purpose, for example, halogens such as fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). Elemental ions; nitrate ions (NO3-), sulfate ions (SO42-); ions of organic carboxylic acids such as formic acid, acetic acid, lactic acid, malonic acid, oxalic acid, maleic acid, benzoic acid; benzenesulfonic acid, naphtholsulfonic acid , ions of organic sulfonic acids such as alkylbenzenesulfonic acids; thiocyanine ions (SCN-, thiosulfate ions S2O32-), phosphate ions (PO43-), nitrite ions (NO2-), and the like. Among these, chlorine ion (Cl-), sulfate ion (SO42-), acetate ion and nitrate ion (NO3-) are preferred from the viewpoint of cost and safety.

The polyvalent metal salt is not particularly limited and can be selected as appropriate depending on the purpose, for example, aluminum chloride, calcium chloride, nickel chloride, potassium acetate, sodium acetate, calcium acetate, magnesium acetate, aluminum nitrate, nitric acid. Examples include magnesium, magnesium chloride, calcium nitrate, magnesium hydroxide, aluminum sulfate, magnesium sulfate, ammonium alum, and the like. More specifically, calcium acetate monohydrate, calcium nitrate tetrahydrate, calcium chloride hexahydrate, magnesium acetate tetrahydrate, magnesium sulfate (anhydrous), aluminum nitrate nonahydrate, nickel chloride hexahydrate. Examples include hydrates. These may be used alone or in combination of two or more. Among these, calcium acetate monohydrate, calcium nitrate tetrahydrate, calcium chloride hexahydrate, magnesium acetate tetrahydrate, and magnesium sulfate (anhydrous) are preferred.

The content of the polyvalent metal salt is preferably 0.1% by mass or more and 5% by mass or less, more preferably 0.5% by mass or more and 3% by mass or less, based on the total amount of the pretreatment liquid.

The organic solvent in the pretreatment liquid is not particularly limited and can be appropriately selected depending on the purpose. For example, the same organic solvent as in the white ink can be used.

The water in the pretreatment liquid is not particularly limited and can be appropriately selected depending on the purpose. For example, the same water as in the white ink can be used.

<White ink application step, non-white ink application step>
The white ink application step and the non-white ink application step are not particularly limited as long as each ink can be applied to the printing substrate, and can be appropriately selected depending on the purpose, and preferably can be performed by an inkjet method. can.

Here, the white ink may be applied to the entire surface of the printing medium to form a background and a base, or may be applied to a part of the printing medium to form a base. In addition, when applying white ink to a part of the printing substrate, for example, it may be applied to the same area where non-white ink is used for printing, or it may be applied to a part that is partially common to the area where printing is performed. It may be given to a certain place. When printing with a non-white ink on a layer made of white ink, when a transparent base material is used as the printing substrate, compared to the case where the non-white ink is applied directly onto the transparent base material, Image visibility is improved.
When white ink is applied to areas where no image is to be formed, it is possible to form various images, such as forming a background.
The term "base" as used herein means that it is a base when viewed from the image surface to which non-white ink has been applied. Even when ink is applied to a substrate in the order of non-white ink and then white ink, the white ink becomes the base when viewed from the image surface to which the non-white ink is applied.

As described above, in the printing method of the present invention, the order in which the white ink applying step and the non-white ink applying step are performed is not particularly limited and can be appropriately selected depending on the purpose. In the present invention, for example, it is preferable to perform a white ink application step after the non-white ink application step to perform so-called back printing.

Note that the method of applying (using) ink is not limited to the inkjet recording method (system), and can be widely used. In addition to inkjet recording methods, examples include blade coating, gravure coating, bar coating, roll coating, dip coating, curtain coating, slide coating, die coating, and spray coating.

Further, in the terms of the present invention, image formation, recording, printing, printing, etc. are all synonymous.
Recording medium, media, and printing material are all synonyms.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. In addition, "parts" in the examples are "parts by mass", and "%" is "% by mass" except for those in the evaluation criteria.

(Preparation example 1 of pigment dispersion)
<Preparation of black pigment dispersion>
After premixing the following three materials, they were circulated and dispersed for 7 hours using a disc type bead mill (manufactured by Shinmaru Enterprises Co., Ltd., KDL type, media: using zirconia balls with a diameter of 0.3 mm) to produce black A pigment dispersion (pigment concentration: 15% by mass) was obtained.
・Carbon black pigment (product name: Monarch 800, manufactured by Cabot): 15 parts by mass ・Acrylic polymer dispersant (product name: Disperbyk-2010, manufactured by BYK Japan): 5 parts by mass ・Ion exchange water: 80 parts by mass

(Preparation example 2 of pigment dispersion)
<Preparation of cyan pigment dispersion>
Preparation example 1 of pigment dispersion liquid except that the carbon black pigment was changed to 15 parts by mass of Pigment Blue 15:3 (trade name: HELIOGEN BLUE K 7090, manufactured by BASF Japan Ltd.) In the same manner as above, a cyan pigment dispersion (pigment solid content concentration: 15% by mass) was obtained.

(Preparation example 3 of pigment dispersion)
<Preparation of magenta pigment dispersion>
Magenta pigment dispersion was carried out in the same manner as in Pigment Dispersion Preparation Example 1, except that the carbon black pigment was changed to 15 parts by mass of Pigment Red 269 (manufactured by Tokyo Shikizai Kogyo Co., Ltd.). A liquid (pigment solid content concentration: 15% by mass) was obtained.

(Preparation example 4 of pigment dispersion)
<Preparation of yellow pigment dispersion>
The same procedure as Preparation Example 1 of Pigment Dispersion Liquid was carried out, except that the carbon black pigment was changed to 15 parts by mass of Pigment Yellow 74 (trade name: Irgalite Yellow L 1254 HD, manufactured by BASF Japan Ltd.). Similarly, a yellow pigment dispersion (pigment solid content concentration: 15% by mass) was obtained.

(Preparation example 5 of pigment dispersion)
<Preparation of white pigment dispersion>
25 parts by mass of titanium oxide (trade name: STR-100W, manufactured by Sakai Chemical Industry Co., Ltd.), 5 parts by mass of a pigment dispersant (trade name: TEGO Dispers 651, manufactured by Evonik), and 70 parts by mass of water were mixed, and the mixture was milled in a bead mill ( Zirconia beads with a diameter of 0.3 mm were dispersed at a filling rate of 60% and a speed of 8 m/s for 5 minutes using a white pigment dispersion (pigment solid concentration: 25% by mass).

<Preparation of non-white ink 1>
Non-white ink 1 was prepared by mixing and stirring the following formulation and filtering with a polypropylene filter having an average pore size of 0.8 μm.

・Black pigment dispersion: 20 parts by mass ・FS-300 (manufactured by DuPont, fluorine-based surfactant): 0.5 parts by mass ・Proxel LV (manufactured by Avecia, preservative): 0.1 part by mass ・1, 2-propanediol: 5 parts by mass ・1,3-butanediol: 2 parts by mass ・1,3-propanediol: 2 parts by mass ・Propylene glycol monomethyl ether acetate: 10 parts by mass ・Ion exchange water: 60.4 parts by mass

<Example 1>
Ink set 1 was prepared by combining white ink 1 and non-white ink 1.

<Examples 2 to 13, Comparative Examples 1 to 3>
<Preparation of non-white inks 2 to 15>
Non-white inks 2 to 15 were prepared in the same manner as in the preparation of non-white ink 1, except that the formulations listed in Tables 1 to 3 were changed in the preparation of non-white ink 1.
White ink 1 and each of non-white inks 2 to 12 were combined to form a set, and ink sets 2 to 12 (Examples 2 to 12) were prepared. Similarly, white ink 1 and each of non-white inks 13 to 15 were combined to form a set, forming ink sets 13 to 15 (comparative examples 1 to 3).
Note that the numerical values in Tables 1 to 3 indicate parts by mass.

The manufacturers of each material in Tables 1 to 3 are as follows.
・WET-270 (manufactured by Evonik, silicone surfactant)
・Surfynol 465 (manufactured by Evonik, nonionic surfactant)
・Surfynol 465 (manufactured by Evonik, nonionic surfactant)
・Emazol L-10V (manufactured by Kao Corporation, nonionic surfactant)

<Preparation of white ink 1>
White Ink 1 was prepared by mixing and stirring the following formulation and filtering through a polypropylene filter with an average pore size of 0.8 μm.
・White pigment dispersion: 30 parts by mass ・WET-270 (silicone surfactant manufactured by Evonik): 0.3 parts by mass ・Surfynol 465 (nonionic surfactant manufactured by Evonik): 0.3 parts by mass ・Proxel LV (manufactured by Avecia, preservative): 0.1 parts by mass ・1,2-propanediol: 20 parts by mass ・1,3-butanediol: 2 parts by mass ・3-methoxy-3-methyl-1-butanol : 2 parts by mass ・Propylene glycol monomethyl ether acetate: 2 parts by mass ・Propylene glycol n propyl ether: 2 parts by mass ・Ion exchange water: 41.3 parts by mass

<Measurement of dynamic surface tension A and static surface tension B of non-white ink>
For the prepared non-white inks 1 to 15, the dynamic surface tension A at 25° C. and the surface life of 15 msec by the maximum bubble pressure method and the static surface tension B at 25° C. were measured by the following method. Then, using the measured results, [(AB)/(A+B)]×100(%)] was calculated for each non-white ink. The results are shown in Tables 4-6.

[Measurement of dynamic surface tension A]
After putting 30 ml of non-white ink into a 30 ml beaker, place it in a water bath adjusted to 25°C and let it stand for 10 minutes. Adjust the temperature of the non-white ink to 25°C, and then run it for 15 msec using SITA DynoTester. The surface tension was measured.

[Measurement of static surface tension B]
The non-white ink was poured into a Petri dish with a diameter of 30 mm, left to stand for 5 minutes, and then measured using an automatic surface tension meter DY-300 using the Wilhelmy method using a platinum plate.

<Image formation>
For white ink 1 and non-white inks 1 to 15, an image forming apparatus (IPSiO GXe-5500, manufactured by Ricoh Co., Ltd.) was used under environmental conditions adjusted to 23 ° C ± 0.5 ° C and 50 ± 5% RH. The driving voltage of the piezo element was varied so that the ejection amount of white ink and non-white ink was equalized, and the recording medium coated with pre-treatment liquid "OK Top Coat +" manufactured by Oji Paper Co., Ltd. (basis weight 104.7 g/ m ² ), the same amount of white ink and non-white ink were applied to form a solid image. Further, the white ink and the non-white ink were ejected by ejecting the white ink after ejecting the non-white ink.

<Evaluation of dryness>
Regarding the drying properties of the ink, immediately after forming the image, dry it in a dryer at 80°C for 30 seconds, then take out the printed matter and rub the solid image area with your finger. Judge by the condition of the image in the rubbed area. did. Evaluation was performed according to the following evaluation criteria, and cases where the evaluation was B or higher were judged to be practical. The results are shown in Tables 7-9.
-Evaluation criteria-
A: The image does not peel off. B: Less than 5% of the rubbed area peels off. C: 5% or more of the rubbed area peels off. D: 10% or more of the rubbed area peels off.

<Evaluation of image density>
The density of the formed image was measured using a colorimeter (product name: Spectrophotometric Densitometer (manufactured by X-Rite), the optical density was measured at five arbitrary locations in the printed image, and the average value was evaluated using the following criteria. A case where the evaluation was B or higher was determined to be practical. The results are shown in Tables 7-9.
-Evaluation criteria-
A: Black: 1.25 or more, Yellow: 0.8 or more, Magenta: 1.00 or more, Cyan: 1.05 or more B: Black: 1.20 or more and less than 1.25, Yellow: 0.75 or more, 0. Less than 8, Magenta: 0.95 or more and less than 1.00, Cyan: 1.00 or more and less than 1.05, C: Black: 1.15 or more and less than 1.20, Yellow: 0.70 or more and less than 0.75, Magenta: 0.90 or more and less than 0.95, Cyan: 0.95 or more and less than 1.00 D: Black: less than 1.15, Yellow: less than 0.70, Magenta: less than 0.90, Cyan less than 0.95

As described above, the ink set of the present invention is an ink set having a white ink and a non-white ink, wherein the white ink contains an organic solvent, water, and a coloring material, and the non-white ink contains a surfactant, and the dynamic surface tension A of the non-white ink at 25° C. and a surface life of 15 msec by the maximum bubble pressure method is 45.0 mN/m or less, and the dynamic surface tension A is 45.0 mN/m or less, and The static surface tension B at 25°C in non-white ink is expressed by the following formula: [2.0(%)≦[(AB)/(A+B)]×100(%)≦10.0(%) ], satisfies. As a result, the ink set of the present invention has excellent drying properties and can provide high image density.

Aspects of the present invention are, for example, as follows.
<1> An ink set including white ink and non-white ink,
The white ink contains an organic solvent, water, and a coloring material,
the non-white ink contains a surfactant,
The non-white ink has a dynamic surface tension A of 45.0 mN/m or less at 25°C and a surface life of 15 msec by the maximum bubble pressure method, and the dynamic surface tension A and the non-white ink at 25°C The static surface tension B at is given by the following formula,
2.0(%)≦[(A-B)/(A+B)]×100(%)≦10.0(%)
This is an ink set that satisfies the following.
<2> The dynamic surface tension A of the non-white ink at 25° C. and a surface life of 15 msec measured by the maximum bubble pressure method is 35.0 mN/m or less, and the dynamic surface tension A and the non-white ink are The static surface tension B at 25°C in white ink is expressed by the following formula:
4.0(%)≦[(A-B)/(A+B)]×100(%)≦8.0(%)
The ink set described in <1> above satisfies the above.
<3> The ink set according to any one of <1> to <2>, wherein the surfactant includes at least one of a silicone surfactant and a nonionic surfactant.
<4> The ink set according to any one of <1> to <3>, wherein the content of the surfactant based on the total amount of the non-white ink is 1.0% by mass or less.
<5> Applying the white ink in the ink set according to any one of <1> to <4> to a substrate;
applying the non-white ink in the ink set according to any one of <1> to <4> to the printing substrate;
This is a printing method characterized by including the following.
<6> The printing method according to <5>, further comprising the step of surface modifying the printing target.
<7> Comprising ink and ejection means for ejecting the ink,
The printing apparatus is characterized in that the ink is the white ink and the non-white ink in the ink set according to any one of <1> to <4>.

According to the ink set described in <1> to <4> above, the printing method described in <5> to <6> above, and the printing method apparatus described in <7> above, various conventional problems can be solved. , the object of the present invention can be achieved.

400 Image forming apparatus 401 Exterior of image forming apparatus 401c Cover of apparatus body 404 Cartridge holder 410 Main tank 410k, 410c, 410m, 410y For each color of black (K), cyan (C), magenta (M), yellow (Y) Main tank 411 Ink storage section 413 Ink discharge port 414 Storage container case 420 Mechanism section 434 Discharge head 436 Supply tube L Ink storage container

Patent No. 6424413

Claims (6)

A white ink containing an organic solvent (1), water, and a coloring material;
An ink set comprising a non-white ink containing water, a surfactant, and an organic solvent (2) , and used for printing the white ink and the non-white ink in an overlapping manner ,
The surfactant includes at least one of a silicone surfactant and a nonionic surfactant,
The content of the surfactant is 1.0% by mass or less based on the total amount of the non-white ink,
The organic solvent (2) includes 1,2-propanediol, 1,3-butanediol, 1,3-propanediol, 2-ethoxyethanol, 3-methoxy-3-methyl-1-butanol, and ethylene glycol monomethyl. At least one of ether acetate, propylene glycol monomethyl ether acetate, and propylene glycol n-propyl ether,
The non-white ink has a dynamic surface tension A of 45.0 mN/m or less at 25°C and a surface life of 15 msec by the maximum bubble pressure method, and the dynamic surface tension A and the non-white ink at 25°C The static surface tension B at is given by the following formula,
2.0(%)≦[(A-B)/(A+B)]×100(%)≦10.0(%)
An ink set that satisfies the following. The dynamic surface tension A of the non-white ink at 25° C. and a surface life of 15 msec measured by the maximum bubble pressure method is 35.0 mN/m or less, and the dynamic surface tension A and the non-white ink have a The static surface tension B at 25°C is expressed by the following formula,
4.0(%)≦[(A-B)/(A+B)]×100(%)≦8.0(%)
The ink set according to claim 1, which satisfies the following. applying the white ink in the ink set according to any one of claims 1 to 2 to a printing substrate;
applying the non-white ink in the ink set according to any one of claims 1 to 2 to the printing substrate;
A printing method characterized by comprising: The printing method according to claim 3, further comprising the step of surface modifying the printing substrate. 5. The printing method according to claim 3, wherein the non-white ink is applied onto the layer made of the white ink. comprising an ink and an ejection means for ejecting the ink,
3. A printing apparatus, wherein the ink is the white ink and the non-white ink in the ink set according to claim 1.